Saturday, July 27, 2019

MATERIALS OF CONSTRUCTION AND THEIR PROPERTIES - Draft

Chapter I

MATERIALS OF CONSTRUCTION AND THEIR

PROPERTIES

Introduction — General consideration — Structure of materials — Mechanical properties of materials of construction — Determination of mechanical properties — Fabrication characteristics and processes of fabrication — Non-ferrous metals and alloys — Available sizes —
Accuracy — Finishing processes — Non-metallic materials — Plastics

CHAPTER


MATERIALS OF CONSTRUCTION
AND THEIR PROPERTIES


1-1. Introduction:

A machine is a combination of resistant bodies, with successfully constrained relative motions, which is used for transforming other forms of energy into mechanical energy or transmitting and modifying available energy to do some particular kind of work. The machine is known as a heat engine when it receives heat energy and transforms it into mechanical energy. The majority of machines receive mechanical energy, and modify it so that the energy can be used for doing some specific task for which it is designed; common examples of such machines being hoist, lathe, screw Jack, etc.

The transmission and modification of energy within the machine require the inclusion of a number of elements, which are so designed that they carry with safety the forces to which they arc subjected; in addition the desired motion is produced so that the machine can perform its task successfully. The analysis of forces involved and the design of machine parts, so that they can perform their duties without failure or undue distortion, lie within the province of machine design. In study of this subject we are required to apply constantly our knowledge of mathematics, classical mechanics, strength of materials, mechanics of machines, metallography and technical drawing.

1-2. General considerations:

One of the first point to be decided when designing a certain machine part is the material of which the part is to be made. The choice of the material is governed by the following considerations:

(i) Suitability of the material of the component for working conditions during service

(ii) Amenability of the material to the fabrication processes required in making the component

(iii) Cost of the material in relation to selling price of the component.

The quantity required, delivery date, material availability and scrap utilisation are the other factors which determine the choice of the material.

Materials of construction are classified as metallic or non- metallic. Non-metallic materials include ceramics, glass, rubber, plastics, etc.

The metals in general use may be classified under two main headings: (a) ferrous metals (b) non-ferrous metals. Within these two main sections, there are several sub-divisions, which depend primarily upon the base metal and the alloying elements. A grouping under the various sub-divisions may be arranged in the order as given below:

Ferrous Metals:

Ferrous metals may be classified as follows:

Cast irons comprising grey cast iron, malleable cast iron, alloy cast iron, and chilled iron.

Wrought Iron & Steel comprising of wrought iron, carbon steel, alloy steel for engineering construction, high alloy steel and tool steel.

Non-ferrous Metals:

Non-ferrous group may be divided into three main sections ;

Light metal group comprising aluminium and aluminium alloys, and manganese and magnesium alloys.

Copper-based alloys comprising copper, copper-zinc alloys or brasses and gilding metals, copper-zinc-nickel alloys or nickel- silvers, bronzes, copper- aluminium group or aluminium bronzes,
copper-lead- tin group giving leaded bronzes, copper- zinc or copper-silver-zinc group giving hard solders.

White-metal group comprising nickel silver, white bearing metals, nickel alloys, tin, white metal solders (soft solders), lead, type metal, zinc.

1-3. Structure of Materials:

To study the various properties of materials it is necessary to understand the basic structures of them.

Structure of Metallic Materials:

The atoms of metals when they are brought together tend to arrange themselves in infinitesimal cubes, prisms and other symmetrical shapes. These geometrical units join to each other like perfectly fitted blocks and are embryos of the larger structure known as crystals. Crystals start forming when molten metal begins to solidify. As cooling continues, each tiny crystal grows by adding to itself other crystals in a pine-tree or dendritic fashion until each group of crystals touches every other group and the metal becomes solid. These groups of crystals are called grains. After abrasive polishing and etching the metal with an acid, these grains can be examined with a high powered microscope and they will appear as shown in fig. 1-1, when viewed through it.


Grains

Grain

boundaries

Minute

indioidual

crystais


Fig. 1-1


Each grain consists of millions of tiny unit cells made up of atoms arranged in a definite geometric pattern. Each unit cell may take the form of an imaginary cube, with an atom in each corner and one in the centre. This is called a body-centred cubic space lattice [fig. 1-2 (a)] and is the structure of iron at normal temperature.

If, however, the centre of the cube is vacant, and a single atom is contained in the centre of each face, [fig. 1-2(4)], it is called a face-centred cubic structure. This is the structure of copper, aluminium and nickel. It is *also the structure of iron at elevated temperatures.

When the unit cell takes the form of an imaginary hexagonal prism, having an atom in each corner, another at each of the top and bottom hexagons, and three atoms equally spaced in the centre
of the prism [fig. l-2(<:)] it is known as a close-packed hexagonal structure. This is the structure of magnesium, zinc and titanium.




The distance between the atoms is extremely small. These closely spaced atoms have a tremendous attraction for each other. This attraction constitutes the force that resists any attempt to tear the metal apart.

The metals used in practice are subjected to heavy stresses and strains. When the metal is deformed or cut certain rows of crystals slip or flow in fixed direction and in one or more parallel planes. Slippage occurs in those planes that have the greatest number of atoms. The ability of the slipping crystal to hold together makes the metal ductile.


Atoms of iron at Atoms of Aluminium, normal temperature Copper or Nickel


Atoms of Magnesium.
Zinc or Titanium

4 ^

Fio. 1-2


Body centred crystals have no planes of dense atomic concentration and so pure iron which has a body centered cubic structure is somewhat less ductile then pure aluminium, copper or nickel,
which have face centred cubic structure. In pure metals the force that must be exerted to cause slippage is much less than the force that holds the crystals together and this is the reason for
providing ductility to the material. The crystal structure of metals could be deformed by only a fraction of the stress needed to overcome the binding force between atoms in a crystal lattice. As
such the crystal structures could be very strong under perfect condition but tiny imperfections would cause some mis-alignment of the atoms called dislocations which tend to weaken the crystaline
structure which results into deformation of metals. There are two main types of dislocations — edge and screw. The edge dislocation occurs at the end of an extra half plane of atoms, while the screw dislocation corresponds to a partial tearing of the crystal planes. Most dislocations are combination of both types.






The effect of alloying in metals and heat treatment of metals can be more thoroughly understood if the crystaline structure of the metal is understood in detail. The addition of alloying element in the parent metal changes the properties by forming new phases and by heat treating the alloy the dispersion of the phases or new phases formed at the boundaries of crystals or at the grains
will give further changes in properties of the alloy.

Non-metallic materials are usually characterized by ionic, covalent and intermediate bonding. They may exist as crystals, glasses or gels (a colloidal suspension) e.g. silica may be found in either of these three forms. Non-metallic materials are mostly brittle. The effects of impurity, locking of dislocations and the limited number of independent slip systems cause the randomly oriented polycrystalline forms of these materials to be brittle. They may be formed from the melt or they may be fabricated by sintering or by cementing powder particles. Although non-metallic materials are generally weak in tension, their strength in compression is often appreciable.

The mechanical behaviour of polymers (plastics) is markedly influenced by their molecular structure. The degree of polymerization, branching and cross linking affect their strength. The strength and density of polymers can be increased by increasing their crystallinity. As polymers are heated they pass through five general states i.e. glassy, leathery, rubbery, viscous-rubbery and liquid. Polymeric materials are sometimes classified as thermoplastic or thermosetting, depending on their behaviour at elevated temperatures.


1-4. Mechanical properties of materials of construction: 


The proper and efficient use of materials of construction requires considerable knowledge of their mechanical properties. The mechanical properties of materials are those properties which
describe the behaviour of the material under mechanical usage. The most important mechanical properties are strength, elasticity, stiffness, ductility, hardness, malleability, resilience, toughness,
creep and machinability.

Strength is the ability of the material to resist stress without failure. Several materials such as structural steel, copper, aluminium, etc. have equal strength in tension or compression, but their strength in shear is about two-thirds of the strength in tension while in grey cast iron the strength in tension and shear is a fraction of the strength in compression. The measure of the strength is the ultimate stress. Ultimate strength refers to the force needed to fracture the material.

When materials are subjected to a pulling force they stretch as the stress increases. The stress-strain relationship can be graphed,  when test specimen is subjected to tensile load. The diagram is a graph between stress and % elongation. With the help of this diagram different-strengths of material can be defined.

When material is subjected to a pulling force the point where the stretch suddenly increases is known as the yield strength. In many design problems when the yield strength of materials is passed it is considered unsafe for further service. When mild steel is subjected to a pulling force it indicates a distinct point where the stretch suddenly increases. This is known as yield point. Some materials like high nickel alloys, monel metal and other similar non-ferrous materials do not show a definite break in the stress strain curve. In this case it is difficult to assign yield point for them. For such materials yield strength of material is defined at the point where 0.5% elongation takes place.

Proportional limit is the maximum stress under which a material will maintain a perfectly uniform rate of strain to stress. However, it is difficult to measure the exact proportional limit.

The maximum stress from which a material can recover is called the elastic limit. It is difficult to specify the elastic limit and so the idea of proof stress has been developed.

Proof stress is the maximum stress a material can withstand without taking more than small amount of set. The amount is usually specified as the smallest that can be measured by an extensometer.

The proportional limit is yield strength at 0.00% offset in the stress-strain relationship graph. Proof stress is yield strength at 0.01% offset and yield strength is yield strength at 0.2% offset on stress elongation curve under tensile load.

Elasticity is the property of regaining original shape after deformation. All materials of construction are elastic but the degree of elasticity varies with different materials. This property is exceedingly important in precision tools and machines. Steel is highly elastic material.

Plasticity is the property that enables the formation of permanent deformation in a material. Stiffness is the property by virtue of which a material can resist deformation. Measure of stiffness is the modulus of elasticity. This property is desirable in materials used in machines, columns, beams and machine tools.

Ductility is the property of material that enables it to be drawn out or elongated to an appreciable extent before rupture occurs. The percentage elongation and the percentage of reduction of area
before rupture of a test specimen are measures of ductility of the material.

Percentage elongation depends on gauge length and so gauge length is required to be stated when percentage elongation is given. Indian Standard Institution recommends gauge length of 
5.65 SQRT( A) where A is the cross sectional area of the test specimen.

Brittleness is opposite to ductility. It shows lack of ductility. Brittle materials show little deformation before rupturing.

Materials with more than 15% elongation are usually considered ductile. Those with less than 5% elongation are considered brittle. Those between 5 and 15% elongation are of intermediate ductility. Mild steel, wrought iron, copper and aluminium are ductile materials. Cast iron is a brittle material. Property of ductility is desirable in machine parts which may be subjected to sudden and severe loads.

For a variety of engineering uses a material requires good combination of strength and ductility. Usually if two materials having the same strength and hardness the one that has the higher ductility is more desirable in engineering practice.

Malleability is the property of a material that enables it to undergo great change in shape under compressive stress without rupture.Malleable materials may be hammered or rolled into any desired shape without rupture. Soft steel, wrought iron, copper and aluminium are malleable metals.

Hardness is that property of a material that enables it to resist penetration, indentation, abrasion or plastic deformation. In selecting a metal to withstand wear or erosion, mainly three properties are considered: ductility, toughness and hardness. However, the most important from wear resistance point is hardness Wear may be either due to friction or erosion by steam, oil, and water and it is resisted by materials having higher hardness. This property is decreased by heating.

Several methods have been developed for hardness testing. Those most often used are Brinell, Rockwell, Vickers, and Scleroscope. The first three are based on indentation tests and the fourth
on the rebound height of a diamond-tipped metallic hammer.

In order to relate one method of testing hardness with another, hardness conversion charts are available. However, these charts are only approximation, because most hardness testing is based on
indentation on a localised area.

Tensile strengths are often listed on hardness conversion charts. Although relationships exist between hardness, and tensile strength and yield strength, but there are chances for error. Therefore, use of tensile testing machine is preferred to determine strength.

Resilience is that property of a material which enables it to store energy and resist shock and impact. The measure of resilience is the amount of energy that can be stored per unit volume after being stressed to elastic limit. This property is desirable in materials for springs.

Toughness is the property which enables a material to be twisted, bent or stretched under a sudden impact or under a high stress before rupture. It is measured by the Izod test or Charpey test. The measure of toughness is the amount of energy that a unit volume of material has absorbed after being stressed up to the point of fracture. This property is decreased by heating.



Shear strength is the force per unit area produced to fracture a specimen when it is impressed along the cross section of material. The material may be subjected to single shear or double shear. The shear strength of steels compared to their ultimate tensile strength ranges from about 50 to 80 per cent, the lower values for the harder materials.

Creep is expressed as the plastic behaviour of the metals or plastics under constant load and at constant temperature. Under the above condition the material deforms slowly but progressively over a period of time. There are three stages of creep. In the first stage the material elongates rapidly but at a decreasing rate. In the second stage which is ordinarily of long duration the rate of elongation is constant. In the third stage the rate of elongation increases rapidly until the material fails.

Design engineer is most concerned with second stage of creep, where elongation takes place at a constant specific rate. The percentage of elongation and time required are decided by the requirements of the particular application, viz, 0.1 per cent elongation in 10,000 hours. In rapidly rotating structural members such as rotors and blading of steam and gas turbines, the clearances are extremely small and critical. The designer will be satisfied with nothing short of experimentally determined stress of 1 creep rate unit (CRU) or 1 per cent in 100,000 hours.



1-5. Determination of mechanical properties:

In order to determine the mechanical properties of the material, certain tests are carried out in mechanical testing laboratories. These tests are carried out according to various standard procedures laid down for the purpose. The simplest test that can be made on most materials is the static tensile test. The procedure to carry out this test is suggested by Indian Standards Institution. The following informations are obtained from this test:

(i) Ultimate tensile strength

(ii) Proportional limit

(iii) Elastic limit or Proof Stress

(iv) Yield point or Yield strength

(v) Percentage elongation

(vi) Percentage reduction in area.


Some details of this test are given in Art. 2-4. IS 1608 — 1960 is to be adhered to while carrying out the static tensile test. '

Other tests commonly employed are compression, torsion, flexure, cold bending, hardness, impact and fatigue. Data of these various tests are usually shown graphically by the stress strain diagrams. Indian Standards, relating to these tests are listed in Appendix I.





1-6. Fabrication Characteristics and Processes of Fabrication:

The fabrication characteristics of metals are discussed from the stand point of formability, castability machinability and weldability.

(a) Formability:

The ability of a metal to be formed is based on ductility of the metal, which is based on its crystal structures. The metal that has the face centred cubic crystal structure is most ductile because the crystal has the greatest opportunity for slip in four distinct nonparallel planes and three directions of slip in each plane.

The other factors which control ductility of the material are grain size, hot and cold working, alloying elements and softening heat treatments such as annealing and normalizing. The small grain sizes are recommended for shallow drawing of copper and relatively large grains for heavy drawing on the thicker gauges.

The high pressure applied in hot drawing distorts the grains which determine the ductility; cold working also results in distortion of crystals. Generally, cold worked crystals are more distorted and are usually less ductile than the hot worked crystals.

Alloying elements in a pure metal normally reduce its ductility, because if they replace the atoms of pure metal it reduces the number of slip planes as it occurs in steel, which is an alloy of carbon and iron and so steel is less ductile than iron. If the alloy finds its room in the spaces between the atoms of pure metal it offers increased resistance to slip, which happens in steel when iron carbide
precipitates in slip planes when steel solidifies. By softening heat treatment such as annealing which consists of heating the metal to the re-crystallisation temperature at which at first the grains may be very small but they grow in size as long as the metal is exposed to the high temperature, when the desired size is obtained the metal is allowed to cool. During recrystallization ductility of metal is
restored because distorted crystals are reformed in re-crystallisation.

The processes using the property of formability of' metal may be divided into two types: (i) Hot working and (ii) Cold working.





Hot working processes:

By hot working is meant processes such as rolling, forging, extrusion and hot pressing. In this working the metal is heated sufficiently to make it plastic and easily worked. The temperature
of the heated metal or alloy should be above the re-crystallisation temperature. This temperature is different for different metals.

Hot rolling is used to create a bar of material of particular shape and dimensions. The principal rolled steel sections arc plates, angles, tees, channels and joists; round, hexagonal and square bars for forging and machining operations; sheets, rails, etc. All of them are available in many different sizes and in different materials. The materials most available in the hot rolled bar sizes are steel,
aluminium and copper alloys. Tubes may be manufactured by hot rolling of strips or plates; the product may be butt welded or lap welded.

Forging is the hot working of metals by hammers, presses or forging machines. For small work forging is carried out with hand hammers but for large work hammers and forging machines are used. Forging alters the internal structure of metals which results in increased strength and ductility. Compared with castings, forgings have greater strength for the same weight. Forging should be
carried out within proper temperature range. If the temperature is too high the metal will be weak and brittle. If the temperature is too low, there will be internal stresses which may lead to distortion or cracking.

Many small parts are drop forged. In drop forging, solid lump with little or no previous treatment by hand is squeezed between dies to the shape required with one or more blows from a drop hammer. The component can be made to dimensions and with a good surface so that machining may be unnecessary. The limitations of this process are that the number of parts should be great and
complicated shapes cannot be produced as they can not be removed from dies.

Extrusion is a process where a heated blank is caused to flow through a restricted orifice under great pressure. Very complicated shapes may be produced by the extrusion process. The process is restricted to materials of low melting points such as brass, aluminium and certain alloys of tin, lead and other soft metals.

Hot pressing consists of forming metal to shape in a very rigid type of power press. A hot piece of metal is pressed and extruded in suitable dies into a smoothly finished piece to accurate dimensions. Automobile valves are formed by this process. •

Cold working processes:

By cold working is meant the forming of a metal usually at room temperature. Though this temperature is higher sometimes but always lower than re-crystallisation temperature. Gold
working may vary from a simple bend to great deformation produced by deep pressing and tube drawing. The result of cold work is to increase hardness and tensile strength but to
decrease ductility and shock resistance. Cold worked parts have a bright new finish, are more accurate and require less machining. Where cold work is considerable, the part may
be annealed at some intermediate stage or stages of work. In cold working the surface of a material is very important as scale may be worked into the finished article with serious results.
Some of cold working processes are drawing, heading, spinning, stamping, etc.

Drawing is a process by which the cross section of a metal is diminished by pulling it through an accurately formed hole in a drawing die. The operation is performed cold and only simpler forms can be produced without excessive resistance and tearing.

Heading is a cold working process in which the metal is gathered or upset . This  operation is commonly used to make screw and rivet heads. The blank is usually a piece of wire of suitable length and cross section; one end is cold forged in dies to form the desired shape of the head. Annealing may be required after
cold heading.

Spinning is the operation of working sheet material around a rotating form
into a ciicular shape. Pressure is applied to the sheet by means of a blunt nosed
tool which presses it against the former. This is an economical method of forming
parts if the quantities are small.

Stamping is the term used to describe punch press operations such as blanking, coining, forming and shallow drawing.

Powder metallurgy :

It is the art of making small components by heat treatment of compressed metallic powders, sometimes with inclusion of non-metallic material.

The powdered metals in desired proportions are compressed in moulds under a very high pressure varying from 700 to 14,000 kg/sq cm depending on the metal. The compacted part is heated
at a temperature which is less than melting point of the major ingredient. T'he disadvantages of this method are (i) low strength of the component (ii) higher cost of material and (iii) the limited
range of materials which can be used.

Filaments of refractory metals such as tungsten, self lubricating bearings, tungsten carbide tips for cutting tools and iron alloys for permanent magnets are examples of articles made from
powdered metal. By this process small components can be made out of some metals whose melting point is too high to allow use of die casting.

(b) Castability:

Castability of a metal is judged to a large extent on the following factors: solidification rate, shrinkage, segregation, gas porosity, and hot strength.

Solidification Rate:

The ease at which a metal will continue (o flow after it has been poured in the mold depends on its analysis and pouring temperature. Some metals such as grey iron are very fluid and can be poured into thin sections of complex castings.

Shrinkage :

Shrinkage refers to the reduction in volume of a metal when it goes from a molten to a solid state. For steel, the amount of contraction amounts to about 6*9 to 7-4% by volume, or 2 cm per metre; grey iron contracts half as much. This shrinkage factor has to be taken into account by the pattern maker and designer, not only to allow for the proper finished .size, but also to sec that undue strains
will not be encountered during shrinkage due to the mould design. Various elements can be added to the alloy to control fluidity and shrinkage as discussed later in this chapter.

Segregation :

As the metal starts to solidify tiny crystal structures resembling pine trees and leferiTd to as dendrites start to form at the mold edges. As they form, they tend to c'xcludc alloying elements. .Subsequent crystals that form are progressively richer in alloy content as the metal .solidifies. Thus the surface of the casting is not of the same quality as that in the centre. This is overcome in part at least
by subsequent heat treatment, or very slow cooling.

Gas Porosity:

Some metals in the molten state have a high affinity for oxygen and nitrogen. These gases become trapped as the metal solidifies creating voids or pinholes.

Hot Strength:

Metals are very low in strength right after .solidification. This is especially true of the non-ferrous metals. Precautions must b(‘ taken at the lime of casting to avoid stress concentration that causes flaws and hot tears to develop as the metal
solidifies .

Coasting is the oldest form of metal shaping and is still the basic engineering process since most metals are melted and cast from ores. Castings are made of iron, steel, various brasses and
bronzes, aluminium and its alloys and the various white metal alloys.

Patterns may be made of wood or metal and with its help the sand mould is formed in which molten metal is poured. The mould is dried before the metal is poured. Metal in cooling solidifies to the form outlined in the mould.


In die casting process the mould is usually made of steel and molten metal is poured or forced under pressure into the mould. This method is used for mass production only.

Non-ferrous alloys arc sometimes cast centrifugally. Molten metal is poured into a rapidly rotating cylindrical mould and is held against the mould by centrifugal force so that core is not required. On cooling the casting is complete. Such castings are generally denser and more homogeneous than ordinary sand castings. This process is limited to simple shapes and to fairly large quantities.

The following precautions should be observed in design of castings :

(i) All sections should be designed as far as possible with a uniform thickness.

(ii) All walls should be sufiiciently thick to allow the molten metal to flow freely into all corners.

(iii) Adjoining sections should be designed with generous fillets or radii.

(iv) Parts should be designed so that patterns may be drawn readily from the moulds.

(v) A complicated part should be designed in two or more castings. These castings are assembled by fasteners.

(vi) Where the section uniformity is not possible, light sections should be blended into heavy sections.

Thickness of casting determined by calculations is often too small to permit production of good castings. The following arc the minimum values of the thicknesses for various castings:


Material


Minimum thickness
in mm


Grey cast iron

Malleable cast iron

Steel casting

Brass

Bronze

Aluminium


6

(i

G

3

3

3



(c) Machinability :

Machinability is the ease with which metal can be removed in operations such as turning, drilling, reaming, etc. Ease of metal removal requires that the forces acting against the cutting tools should be relatively low and the chips will be broken up, a good finish should result and the tools should last a reasonable period of time before it has to be replaced or resharpened. Machinability is also expressed as a machinability rating for each material. [This rating is given for most ferrous metals using steels
13S25 in the cold drawn conditions as the basis of 100% machinability. This value involves turning at a cutting speed of 54-9 surface metre per minute for feeds upto 0-1778 mm per revolution
and depths cut upto 6-35 mm using appropriate cutting fluid with high speed steel T70W18Cr4Vl tools. Machinability of other metals will be judged with respect to this basis.] This property
plays a predominant role in deciding the selection of material when components manufactured from it are to be machined on automatic machine for mass production.

By adding alloying materials like sulphur and lead in steel its machinability can be increased, however, with some reduction in tensile strength.

(d) Weldability:

It may be said that all metals are weldable by one process or another. However, the real criterion in deciding on the weldability of a metal is weld quality and the ease with which it can be
obtained.

In deciding on weldability of a metal, the characteristics commonly considered are the heating and cooling effects on the metal, oxidation, and gas vaporization and solubility.

Heat and Cooling:

The effect of heat in determining the weldability of a material is related to the change in microstructure that results. For example, steels are sometimes considered weldable or not weldable on the basis of the hardness of the weld. The deposited weld metal may pick up carbon or other alloys and impurities from the parent metal that make it hard and brittle so that cracks result upon cooling.

The opposite effect may also be considered. A metal may have a certain hardness temper that will be changed by the heat of the weld. Although both of these conditions can be corrected by added precautions and heat treatment, they add to the cost and hinder the simplicity of the weld.





Hot shortness, a characteristic which is indicated by lack of strength at high temperature, may result in weld failures during cooling of certain metals.

Oxidation :

Oxidation of the base metal, particularly at elevated temperatures, is an important factor in rating weldability of a metal. Metals that oxidize rapidly, such as aluminium, interfere with the welding process. The oxide has a higher melting point than the base metal, thus preventing the metal from flowing. It also may become entrapped in the weld metal, resulting in porosity, reduced strength, and brittleness

Gas:

Large volumes of troublesome gases may bt! formed in the welding of some metals. These gases may become trapped in the weld because certain elements vaporize at temperatures below those needed for welding. Not only will this cause porosity, but some of the beneficial effects of these elements are lost.



1-7. Ferrous metals — Cast iron, Wrought iron and Steel:


All ferrous metals are made by refining pig iron and adding
to it other elements to produce a desired combination of mechaniral
properties. It is used in practice as casting or as wrought form.
Ferrous castings are cast iron castings and steel castings.

(A) Cast iron :

C^asl iron is an alloy of iron, carbon and silicon and is hard
and brittle. Carbon content is always more than 1*7% and
often around 3%. Clarbon may be present in two forms: as free
carbon or graphite and as combined carbon or iron carbide (FcaC) .

Clast iron castings are of following types:

Grey irem, malleable iron, spheroidal or nodular graphite
iron, austenitic iron and abrasion resistance casting.

Grey iron castings:

It is a cast iron in which the carbon is mainly in graphite form;
as it is grey in colour, it is called grey cast iron. They arc extensively
used for machine parts because they are inexpensive, can be
given almost any desired form and have high compressive strength.
Graphite is an excellent lubricant, and grey cast iron is easily
machined as the tool is lubricated and chips break off readily.
The freedom with which articles slide over a smooth surface of
cast iron is largely due to graphite in the surface. However,
brittleness and lack of ductility and shock resistance prohibit their






use in parts subject to high tensile stress or suddenly applied
loads. Its use above a temperature of 300®C is avoided.

Silicon is used as a softener in cast iron. Increasing the
silicon content of cast iron increases the free carbon and decreases
the combined carbon. Manganese tends to harden cast iron as it
promotes combined carbon. In a foundry balance has to be struck
between silicon and manganese contents so as to obtain a machine-
able but strong casting.

I'he speed of cooling has a considerable influence on the final
liardness of cast iron. Castings of light sections cool more rapidly
than heavy castings thus results in formation of more combined
carbon and less free carbon with a consequent increase in hardness.
For these reasons for light castings more silicon is required to
encourage formation of graphite.

The grey iron castings used for general engineering purposes
are designated by letters FG followed by ultimate tensile strength
in kg/sq mm viz. FG20, FG35.

The grey iron castings where chemical composition is more
important are indicated as FG35Sil5 where the important element
Si is also added in designation.

'Fhe details of grey cast iron are given in IS: 210 — 1965. In
this properties of standardised designated castings, according to IS,
FG15, FG20, FG25, FG3(), FG35 and FG40 are given. The
properties given are minimum ultimate tensile strength and results
of transverse test such as breaking load, rupture stress and deflection,
lor the above grey cast iron. The hardness value as Brinell
hardness number are also given for them.

Ferrous Castings in which carbon is in form of iron carbide
are referred to as white cast iron because they have a whitish
appearance. Iron carbide is a hard, brittle substance and its
presence increases hardness of cast iron. White cast iron is almost
immachinable and is used somewhat in* parts which require
abrasion resistance.

Malleable Cast iron:

Malleable cast iron is white cast iron which is rendered
malleable by proper annealing. Malleable iron is an inexpensive
material, tougher than grey cast iron and more resistant to bending
and twisting.





Malleable Cast iron is classified as black heart, pearlitic and
white heart and they are designated as follows:

(a) Black heart BM35, BM32, and BM30

(b) Pearlitic PM70, PM65, PM55, PM50 and PM45

(c) White heart WM42 and WM35

The number after letters indicates ultimate tensile strength in
kg/sq mm.

Malleable cast iron is useful for many purposes such as gear
housing, brake pedals, plough, tractor and various automobile
parts.

Method of designating some important ferrous castings are
given below:

Spheroidal or nodular graphite iron:

This cast iron has a graphite in form of spheres or nodules.
This type of cast iron possesses high tensile strength and has good
elongation. They are designated bv letter SG and a percentage
elongation is also specified alongwith. Spheroidal graphite irons
available and designated are SG80/2, SG70/2, SG60/2, SG50/7,
SG42/12 and SG38/17. The first number indicates the tensile
strength in kg/sq mm and the number after the oblique is percentage
elongation.

Austenitic flake graphite iron castings:

It is designated by the letters AFG followed by the important
elements of components in the casting, viz. AFGNil6Cu7Cr2.

Austenitic spheroidal or nodular graphite iron castings:

It is designated as ASGNi20Cr2. The important elements Ni
and Cr arc included in designation in percentages.

Abrasion resistance iron castings:

They are designated as ABR33Ni4Gr2, where 33 indicates
the minimum tensile strength in kg/sq mm and Ni and Cr, which are
important elements, have their amounts indicated in percentages.

Steel castings:

Five types of steel castings arc designated.

(i) Unalloyed steel castings are designated by letters CS
followed by minimum tensile strength in kg/sq mm.

Such standardised castings arc CS41, CS47, CS55,
GS71, CS85, GS105 and GS125.

(ii) Unalloyed special steel castings (high magnetic perme-
ability) are designated by letters GSM, viz OSM35,
GSM41, etc.

(iii) Alloy steel castings a^e designated by letter GS but
the important alloying contents have their amounts
indicated in percentages after the minimum tensile
strength value, viz CS50GrlV20.

(iv) Heat resistant steel castings are designated by letters
GSH, viz. GSH130Ni6Gr28.

(v) Gorrosion resistance steel castings are designated by
letters CSG, viz GSG16Grl3.

In order to have hard durable surface, the castings are
chilled. Such castings are produced by burying iron plates in
the mould; as a result, the metal coming in contact with these
plates will be cooled rapidly and will be harder than the rest of
the casting.

(B) Wrought iron:

Wrought iron is a mechanical mixture of pig iron and uni-
formly distributed silicate slag. It possesses the important
propoerties of ductility, malleability and toughness. It is suitable
for machine parts to be shaped by forging. It has also got excellent
welding properties. With the introduction of steel the use of
wrought iron has decreased although it is still used extensively for
chains and crane hooks, for bolts subjected to shock loads, for
pipes, pipe fittings and culvert plates. The ultimate strength is
about three quarters of that of structural steel while the price is
approximately three times that of mild steel. Several processes
are used in the production of wrought iron of which the puddling
process is most commonly used.

(C) Steel:

It is an alloy of iron and carbon in which the carbon content
is less than 1-7%. It is produced by oxidizing the impurities in
molten pig iron and then adding the amount of necessary carbon
which will give required combination of strength, ductility and
hardness. Since carbon is the controlling element, the steel is
known as plain carbon steel.






The processes commonly used for manufacture of steel are
(i) the open hearth process, (ii) the Bessemer process and (iii) the
electric furnace process. The particular process used depends on
the chemical analysis of pig iron to be refined and upon the desired
quality of the steel to be produced. The finished molten steel is
to be poured into ingots in sizes suitable for use by rolling mills.

Steel and its alloys are one of the widely used material for
engineering construction. The plain carbon and alloy steels
standardised in India have been covered in Indian Standards
IS: 1570-1961 under the following broad headings:

(a) Steels specified by tensile properties but without
detailed chemical composition; and

(b) Steels specified by chemical composition. These have
been further sub-divided into:

1 . Carbon steels

2. Carbon and carbon manganese free cutting steels

3. Alloy steels other than stainless and heat resisting
steels

4. High alloy steels: stainless and heat resisting
steels

5. Carbon and alloy tool steels.

IS: 1871-1965 is a commentary on Indian Standard Wrought
steels which are discussed in IS: 1570-1961. According to this
commentary the standard steels given in IS: 1570-1961 are
regrouped as follows:

(a) Steels specified by tensile properties but without detailed
chemical composition

(b) Carbon and low alloy steels with specified chemical
compo.sition and related mechanical properties

(c) , Carbon and carbon-manganese free cutting steels

(d) Hardened and tempered steels

(e) (^ase hardening steels (flame and induction hardening,
case carburizing, cyaniding, carbonitriding and
nitriding)

: (f) Creep resisting steels
(g) High alloy steels — stainless and heat resisting steels
including valve steels

(h) Carbon and alloy tool steels

In India many collaborations with different firms in different
countries of the world are made and as the standards adopted in
these countries are different, it is difficult to get equivalent
steels in Indian Standards. To help in searching the proper equi-
valent steels, IS: 1870-1965, which gives comparison of Indian
and Overseas standards for wrought steels for general engineering
purposes, is published. It gives comparison of wrought steels
available according to British stanadrds BS, American Standards
SAE (Society of Automotive Engineers), AISI (American Iron
and Steel Institute), ASM (American Society of Metals) and
ASTM (American Society of Testing Materials), German Standards
DIN, Japanese Standards JIS, Russian Standards GOST and
Indian Standards and their important properties.

It contains 17 tables and in these tables (excluding table
1 and 2) steels are arranged in ascending order of maximum
carbon content thereby bringing together, as far as possible,
similar composition.

Index to IS: 1870-1965 is also published by ISI and it helps by
providing the ready reference to each of standard steel compared
in IS : 1 870-1965. In this index 8 country wise sections are provided,
according to the standards of countries compared in IS 1870-1965. In
each section specification number, designation and reference number
as in IS: 1870-1965 are provided, thereby a ready reference in IS:
1870-1965 can be easily obtained and details of the specifications of
steels in other countries can be obtained. When standards number
with designation for the steel of any country is specified, then the
material designated in any of the other seven countries mentioned
above can be obtained by noting the reference number given in
the index and referring it in IS: 1870-1965.

r The Indian Standards Institution has adopted a standard IS : 1 762 — 1961
for uniform system of designation of steels. According to it a steel may be
designated by a group of symbols, indicating the important characteristics such
as tensile strength, carbon content, alloy content, sulphur and phosphorus
limits, weldability, surface finish, surface condition, steel quality and treatment.
The following prefixes may precede the designation of steel to avoid confusion
with designation of other materials:





S for wrought steel
CS for cast steel

If the steel is to be designated on the basis of its tensile strength without
detailed chemical composition, the symbol "St' is to be followed by the value of
minimum ultimate tensile strength in kg/mm®. *St 50’ designates steel whose
minimum ultimate tensile strength is 50 kg/mm®. For plain carbon steels, the
letter C is followed by the average carbon content in hundredths of a percent.
Plain carbon steel containing carbon from 0*10 to 0*18% will be designated by
*C 14’. For alloy steels the carbon content in hundredths of a percent shall be
used without the prefix ‘C*. For carbon and alloy tool steels the letter ‘T* is to
be followed by the average carbon content in hundredths of a percent. The
alloy index shall consist of chemical symbols of the significant elements arranged
in descending order of percentage contents. The nominal or average percentage
of each alloying elements shall be indicated by an index number following its
chemical symbol.

A nickel chromium molybdenum alloy steel with grain size controlled and
case carburised with composition

Carbon 0*12 to 0*18

Silicon 0*10 to 0*35

Manganese 0*6 to 1*00

Nickel 1*00 to 1*50

Chromium 0*75 to 1*25

Molybdenum 0*08 to 0*15

is designated as ISJVi 13CrlMol2Gc.

Here the first numbers indicate the average carbon content in hundredths
of a percent. The rest of the numbers indicate the average percentage of the
alloying elements designated by its chemical symbols which precedes the numbers.
The underlined number is number after the decimal points. Last letter
indicates steel quality while indicates treatment given to the steel. In this
manner the chemical composition of any alloy can be given.

Guaranteed weldability of steel shall be indicated by leticrs
W for fusion weldable,

WP for pressure weldable,

WP for weldable by resistance welding, and

WS for weldable by spot welding.

Weldable steel is designated as St 55 St 60 IVP, etc.

Surface C’ttnditions for sheets arc designated by letter F; however, this is
applicable to sheets only. For black sheets the varieties are F, F2, F3, and F4
with different surface hnishes. F5 is suitable for deep drawing, F6 for extra
deep drawing, and FI for cold finish sheets.

Surface conditions are designated by letter J.






The following surface finishes are designated:


Designation Surface condition

J 1 , Bright drawn or bright rolled

J 2 Precision ground skinned

J 3 Pickled or descaled

J 4 Shot blasted or sand blasted

J 5 Deseamed or scarfed

J 6 Reeled


Steel quality designated are as under:


A

E

L

D

D2

R

G

H

I

M


Non ageing quality

Stabilized against stress corrosion

Control cooled to ensure freedom from flaws

Fully killed (deoxidised)

Semi killed
Rimming quality
Grain size controlled
Hardenability controlled
Inclusion controlled
Structural quality guaranteed


Treatment designated are as follows:


a

c

d

h

ti

0

p

<7

X

t


Annealed or softened

Case carburized

Hard drawn, cold reduced

Hot rolled

Normalised

Spherodised

Patented

Hardened and tempered
Stress relieved
Tempered.


Steels specified by tensile properties:

The following steels specified by tensile properties are
standardised :

St 30, St 32, St 34, St 37, St 39, St 42, St 44, St 47,

St 50, St 52, St 55, St 58, St 63, St 66, St 78, St 88.

Schedule I of IS: 1570-1961 specifies the ultimate tensile
strength and corresponding minimum percentage elongation for
round and flat test pieces for the above steels.

St 30 to St 50 are general structural steels and are available
in the form of bar sections, tubes, plates and strips. St 55 to St 66
are medium tensile structural steels, while St 78 and St 88 are high
tensile steels.






Typical uses of structural steels are given in table 1-7-1.

Table 1-7.1

Typical uses of steels specified by tensile properties
but without detailed chemical composition

Steel Designation Typical Uses

St 30 Structural steel sheets for plain drawn parts, tubes for oil well casing,
steam, water and air passages, cycle, motorcycle and automobile tubes,
rivet bars and wire

St 32 1 Steels for locomotive carriage and car structures, screw stock
St 34)

St 37 Structural steel for chemical pressure vessels

St 39 Structural steel for ships, chemical vessels, aii receivers and fasteners

St 42 Structural steel for bridges and building construction, railway rolling

stock, screw spikes, and oil well casing
5"/ 44 Structural steel for railway rolling stock, pressure vessels, fasteners,
and valve fittings for compressed gas cylinders
St 47 Structural steel for railway rolling stock, pressure parts of marine and
land boilers, and rivets for air receivers
St 50 Structural steel for mines, forgings for marine engines, and machine
parts.

St 52 Steel for railway wheels, di.se wheel centres for railway and electric
tramway cars, and seamless tubes.

St 55 High tensile steel for locomotive, c.nriage wagon and tramway axles,
bolts, and seamless and welded lubjs.

St 58 High tensile steel for bridges and ;^encral construction, and bars and
wire for concrete reinforcement.

St 63 High tensile steel for tramway axles and seamless tubes.

St 66 1 High tensile steel for locomotive, carriage and wagon wheels and tyres,
St 78 [• and machine parts for heavy loading.

St S8J

Carbon steels with specified chemical composition:

The standard carbon steels specified in schedule II of IS:
1570-1961 and manufactured in practice are as follows:

C04, C05, C07, CIO, C14, G15, C15Mn75^ G20, G25,

, G25Mn7^, C30, G35,G35Mn75, G40, G45, G50, G50Mn 1 , G55, G55Mn75, G60,

G65, G70, G75, G80, G85, G98 and G113.

Steels having upto 0-7 percent carbon are generally employed
in hot worked or normalised condition and so the tensile properties
and the percentage elongation for this steel is specified under
above conditions.

Cold drawn bars of CIO, C15 Mr^5, C20, G30, C40, G50 and
C55Mn75 are standardised and their minimum ultimate tensile






Strength m kg/sq mm and percentage elongation for different sizes
are specified in schedule II of IS: 1570-1961.

Mechanical properties giving minimum values of ultimate
tensile strength, yield strength in kg/sq mm with corresponding
percentage elongation and minimum Izod impact value for bar
and forgings in hardened and tempered conditions are specified
in table V of schedule II for the following carbon steels:

C30, C35Mn^5, C40, C45, G50, and C55Mn75

I'he above values of mechanical properties for the core and
for the case hardened steels CIO and G14 are specified for the
refined and quenched conditions in the table VI of the schedule.

Tensile strength and elongation properties of mild steel sheets
and strips of G07, GIO, G15, G20 in cold rolled and annealed
conditions arc given in table VII of the schedule, while the tensile
properties in cold rolled condition for G15 in quarter hard, half
hard and full hard conditions are specified in the table VIII of the
schedule. When maximum ductility for very severe drawing
and pressing operation is required, steels G04, G05 and G07 are
used. For less cold working, steels GIO, G15 and G20 are used.

Minimum ultimate tensile strength and minimum yield
stress for tubes in cold drawn annealed conditions and in cold
drawn and tempered conditions and made of the following carbon
steels are given in table IX of the schedule:

G14, C15, G15Mn75, G20, G25, G25Mn75, G35, G35Mn75,

G45 and G50

Hot finished tubes depending on the size requirements arc
also further modified in dimensions by cold drawing or rolling.
These tubes provide smaller diameters and thinner wall thicknesses
and possess better surface and dimensional accuracy. Their
properties are specified in table X of the schedule.

Small flat section springs are made of steel strips of G50,
G50Mn25, G60, G65, C70, G80, G85, G98 and G113. The flat
sections are available in annealed or drawn conditions for the
purpose.





Table 1-7.2 gives typical uses of carbon steels.

Table 1-7.2

Typical uses of carbon steels of specified chemical composition

D^ation Typical Uses

CX)4 Dead soft steel generally used in electrical industry.

CX)5, C07 They are used as sheet, strip, rod and wire specially where

and CIO excellent surface finish or good drawing qualities are required,

such as automobile body and fender stock, hoods, lamps, oil
psms, and a multiple of deep drawn and formed products.
They arc also used for cold heading wire and rivets and low
carbon wire products.

CIO and Used for making camshaits, cams, light duty gears, worms,

G14 gudgeon pins, selector forks, spindles, pawls, ratchets, chain

wheels and tappets.

Cl 5 Used for lightly stressed parts.

G15Mn75, G20, General purpose steels for low stressed components.

G25 and'G25Mn75

G30 Used for making cold formed parts, such as shift and brake

levers. After suitable case hardening or hardening and
tempering, this steel is used for making parts, such as socket,
tie rod, adjustable control lever cable, shaft fork and rear hub,
2-wheeler and 3-wheclcr lambrctta parts such as sprocket,
lever, hubs, forks, cams, and bushes. Tubes for aircraft, auto-
mobile and bicycle are made of this steel.

C35 Used for low stressed parts, automobile tubes and fasteners.

G35Mn75 Used for making low stressed parts in machine structures,

cycle and motorcycle tubes, and fasteners.

C40 Used for crankshafts, shafts, spindles, automobile axle beams,

push rods, connecting rods, studs, bolts, lightly stressed gears.

G45 Used for spindles of machine tools, bigger gears, bolts and shafts.

G50 Used for making keys, shafts, cylinders, machine components

requiring moderate wear resistance. In surface hardened
condition it is also suitable for large-pitch worms and gears.

G50Mnl Used for bolts, gear shafts, rocking levers and cylinder liners

and as rail steel.

G55 and Used for making gears, cylinders, cams, keys, crank shafts,

G55Mn75 sprockets and machine parts requiring moderate wear resistance

for which toiighness is not of primary importance.

C60 Used for making spindles for machine tools, hardened screws

and nuts, couplings, crank shafts, axles and pinions.

G65 Used for making locomotive carriage and wagon tyres. Typical

uses of this steel in the spring industry include engine valve
springs, small washers and thin stamped parts.

070 Used for making buffer springs, shock absorbers, springs for

seat cushions for road vehicles. It is also used for making rail
tyres, unhardened gears and worm.s.






Steel 

Designation 

C75 


G80 and 
C85 

G98 and 
GU3 


Typical Uses 

Used for making light flat springs formed from annealed 
stock. When properly heat treated it is used for making plough 
shears, rake teeth scrappers and cultivators’ shovels. 

Used for making flat and coil springs for automobiles and 
railway vehicles. After suitable heat treatment these steels are also 
used for making scraper blades, discs and spring tooth harrows. 
In oil hardened and tempered condition used for coil or 
spiral springs. 


Carbon and carbon manganese free cutting steels: 

The standardised free cutting carbon and carbon manganese 
steels as per schedule III are as follows: 

lOSU, 14MnlSJl4, 25MnlS14, 40S^, 13S25, 40Mn2S12. 

All the above steels are available in hot rolled or normalised 
condition and cold drawn form. 

Machinability ratings for the above steels in the cold drawn 
condition are as under: 


Steel 

BHN 

Average machinability rating 

losn 

121 

80 

14MnlS14 

137 

90 

25MnlS14 

143 

80 

40S18 

197 

70 

13S25 

137 

100 

40Mn2Sl2 

212 

70 


These steels are used where high machinability is desirable in 
parts which are to be machined on automatic machines. The 
properties of these steels are given in schedule III of IS: 1570-1961 
and in sectional list it is given separately as 18:4431-1967. 

Following properties for the different shapes for free cutting 
steels are given in various tables of schedule III of 18:1570-1961. 

(i) The ultimate tensile strength and corresponding mini- 
mum elongation in percent for hot rolled or normalised 
bars and billets are given in table XVII and for cold 
drawn bars in table XVIII. 

(ii) Table XIX gives ultimate tensile strength, yield strength, 
elongation and Izod impact values for 408^, and 40Mn2 
812 for free cutting hardened and tempered bars and 
forgings in hardened and tempered conditions. 






Addition of lead, usually upto 0*3 per cent, improves machin- 
ability of steels which are not included in schedule III of IS: 1570- 
1961. 

Gold drawing of low carbon steel improves its surface finish 
on machining; however, the addition of sulphur enhances its 
machinability considerably ahd makes the steel free cutting. 
Addition of sulphur decrease the cold forming properties, and 
weldability and reduces forging characteristics. This steel is used 
where easy machining is primary requirement and its properties 
are similar to carbon and steek with similar carbon and man- 
ganese content. 

Steels lOSll, 14MnlS14 and 13S25 may be case hardened 
and steels 40S18, and 40Mn2S12 can be hardened and tempered. 
Steel 25MnlS14 is commonly used in the bright condition. 

Steels lOSn, l4MnlS14, 13S25 and 25MnlSM are used 
where combination of good machinability and uniform response 
to heat treatment is needed. The low carbon variety lOSll is 
used for small parts which arc to be cyanided or carbonitrided. 
Steels 14MnlS14 and 13S25 carry more manganese, permitting 
oil quenching during case hardening treatment. High carbon 
steel 25MnlS14 provides more core hardness when this is needed. 
It is used for the production of small parts by rapid machining, 
such as nuts. 

Steek 40S18 and 40Mn2S12 have characteristics comparable 
to carbon steels of the same carbon level and are preferred where 
large amount of machining is necessary, or where operations offer 
tooling problems. They may be obtained as hot rolled, normalized 
or cold drawn. These steels may be hardened and tempered 
to increase strength and are usually suitable for oil quenching. 
The high manganese variety steel 40Mn2S12 offers greater 
hardenability. 

Table 1-7*3 on page 29 gives typical uses of carbon and 
carbon manganese free cutting steek. 

Low alloy Steels: 

The properties of these alloy steels such as chemical composi- 
tion and mechanical properties are given in schedule IV of IS ; 
1570-1961. 





Table 1-7.3 

Typical use of carbon and carbon-manganese free cutting steels 


Sted 

Designati on 

lOSll 

14MnlS14 


2r)MnlS14 


40S18 

13S25 


40Mn2S12 


Typical Uses 

Used for small parts to be cyanided or carbonitrided. 

Used for parts where good machinability and finish arc impor- 
tant, and where disadvantages of the higher sulphur required 
to give full free cutting properties make the use of the more 
rapid machining steel 13S25 undesirable. 

Bolls, studs and other heat-treated parts of small section. 
Suitable in either cold drawn, normalized or heat treated 
condition for moderately stressed parts requiring more strength 
than that of mild steel. 

Heat treated bolts, engine shafts, connecting rods, 

Used for lightly stressed components not subjected to shock 
(nuts, studs, etc.) and suitable for production on automatic 
lathes. It should be used when ease of machining is the 
deciding factor. It is not intended for use where the hardened 
case is subjected to severe impact in service. 

Heat treated axles, shafts, small crankshafts and other vehicle 
parts. It is not recommended for forgings in which transverse 
properties arc important. 


According to IS: 1570-1961, 48 different low alloy steels are 
standardized and are designated as under: 


37Si2Mn90 

15CrG5 

1 5Gr90Mo55 

lGNilCr80 

55Si2Mn90 

17MnTCr95 

40GrlMo60 

13Ni3Gr80 

llMn2 

20MnCrl 

10Gr2Mol 

15Ni4Crl 

20Mn2 

55Cr70 

15Gr3Mo55 

35NilGr60 

27Mn2 

40Crl 

25Gr3Mo55 

30Ni4GrI 

37Mn2 

jOCrl 

10Gr5Mo55 

15NiGrlMol2 

47Mn2 

l05Grl 

20Gr5Mo55 

15Ni2GrlMol5 

35Mn2Mo28 

105GrlMn60 

35GrlMo65V25 

40NiGrlMol5 

35Mn2Mo45 

50GrlV23"" 

40Gr3MolV20 

40Ni2GrlMo28 

10Mo55 

21GrlMo28 

40Gr2AllMol8 

31Ni3Gr65Mo55 

20Mo55 

40GrlMo28 

40Ni3 

‘ 40Ni3Gr65Mo55 

33Mo55 

07Gr90Mo55 

l6Ni80Gr60 

^ 16NiGr2Mo20 


Schedule IV of IS: 1570-1961 gives properties for different 
types of low alloy steels in tabular form. The chemical composi- 
tion of above standardized low alloy steels are given in table 
XXI of the schedule. The list of tables giving the important 
mechanical properties of some of the above alloy steels given in 
the schedule are as follows: 






(i) Table XXII specifies the values of ultimate tensile 
strength, minimum yield stress and minimum percentage 
elongation for plates, sections, bars, billets and forgings 
in the hot rolled or normalised condition when made 
of the following low alloy steels: 

llMn2, 20Mn2, 27Mn2. 

(ii) Table XXIII specifies ultimate tensile strength and 
percentage elongation for limiting ' ruling sections for 
cold drawn 1*5% manganese steel bars made of 20Mn2. 

(iii) Table XXIV specifies the tensile strength, yield strength, 
0-2% proof stress, percentage elongation, Izod impact 
value and BHN for different limiting ruling section 
for bars and forgings in the hardened and the tempered 
conditions mostly for oil hardening of the following 
materials : 

20Mn2, 27Mn2, 37Mn2, 35Mn2Mo^, 35Mn2Mo45, 
40Crl, 40GrlMo28, ISCrMo^ and 25Gr3Mo55, 
40Cr3MolV20, 46Cr2AllMol8, 40Ni3, 35NilCr60, 
30Ni4Grl , 40NiCrlMol5, 40Ni2Grl Mo28, 31NiGr- 
65Mo55, 40Ni3Gr65Mo55. 

(iv) Table XXV specifies mechanical properties for wear 
resistance steels 55Gr70 in the hardened and tempered 
conditions. The properties specified are, for different 
limiting ruling sections, the ultimate tensile strength, 
percentage elongation, Izod impact value and BHN. 

(v) Table XXVI specifies mechanical properties of ultimate 
tensile strength, percentage elongation and minimum 
Izod impact value for the following case hardening 
steels in the refined and quenched condition: 
llMn2, 15Gr^, 16Ni80Gr60, 17MnlGr95, 16NilGr80, 
13NiGrM, 20MnGrl, 15NiGrlMol2, r5Ni2GrlMor5, 
15Ni4Grl, 16NiGr2Mo2a 

(vi) Table XXVII specifies ultimate tensile strength limits 
for steel sheet and strips made of 20Mn2, 47Mn2 and 
21GrlMo28. It is provided for soft, hot rolled or 
normalised or normalised and tempered conditions 
and also for hardened and tempered or cold rolled and 
tempered conditions. The properties specified are 
ultimate tensile strength, 0*1% proof stress and BHN. 

(vii) Table XXVIII specifies the ultimate tensile strength, 
yield stress or 0*2% proof stress and percentage elonga- 
tion for different heat treated conditions for the follow- 
ing low alloy steels; 

20Mn2, 27Mn2, 40Crl and 50Crl 21CrlMo28, 

40Cr 1 Mo28, 30Ni4Cr 1 , 3 1 Ni3Cr^5Mo55. 

(viii) Table XXIX specifies ultimate tensile strength, yield 
stress and percentage elongation for plates, sections and 
bars in normalised or annealed conditions made of 
following creep resisting steels: 

10Mo55, 20Mo55, 15Cr^ Mo55, lOCrSMo^. 

(ix) Table XXX specifies ultimate tensile strength, yield 
stress, percentage elongation, minimum Izod impact 
value for steel bars and forgings in the normalised or 
normalised and tempered conditions for the following 
creep resisting steels: 

10Mo55, 20Mo55, 15Cr90Mo55, 10C^r2Mol, 15Cr3- 
Mo55, '35CrlMo'65V^. 

(x) Table XXXI specifies ultimate tensile strength, yield 
stress, percentage elongation, Izod impact value for 
corresponding limiting ruling sections, for steel bars 
and forgings in the hardened and tempered conditions 
and made of the following creep resisting steels: 
33Mo^, 40GrlMo60, 20Cr5Mo55, 

(xi) Table XXXI I specifies ultimate tensile strength, yield 
stress and percentage elongation for tubes made of 
following creep resisting steels: 

10Mo55, 20Mo55, 07Cr90Mo^, 15Cr90Mo55, 
10Cr2Mol, l5Cr3Mo^5, 10Cr5Mo55. 

(xii) Table XXXIII specifies limiting ruling sections (in mm) 
of hardened and tempered steels lying in the range of 
tensile strength 60 to 135 kg/sq mm. 

Table 1-7.4 gives typical uses of low alloy steels. 

Some of the low alloy steels and few carbon steels show useful 
properties like hardening, case hardening and creep' resistance 
after suitable treatment. 





Table 1-7.4 

Typical uses of low alloy steels 
(other than stainless and heat resisting steels) 


Steel 

Designation 


Typical Uses 


37Si2Mn90 

55Si2MnW 

llMn2 


20Mn2 and 

27Mn2 

37Mn2 

47Mn2 

35Mn2Mo28 

and 

35Mn2Mo45 
lOMo^ and 
20Mo55 
33Mo55 

15Gr65 

17MnlGr95 

20MnCil 

55Gr70 

40Grl 


50Grl 

105Grl and 

105GrlMn60 

50GrlV23 


21CrlMo28 

40GrlMo28 

07Gr90Mo55 

15Gr90Mo55 


40Gr]Mo60 


Water-hardening spring steel for road and railway vehicles 
Oil-hardening spring steel for road and railway vehicles 
Notch ductile steel for general purposes. Also used in making 
filler rods, colliery cage suspension gear tube, mine car draw 
gear, couplings and rope sockets. 

Used for welded structures, crankshafts, slet'ring levers, 
shifting spindles, 

Used for making axles, shafts, crankshafts, connecting rods 
Used for tram rails 

Used for components such as crankshafts, bolls, wheel studs 
axles shafts, levers and connecting rods 
Used for making steam piping, boiler tubing, pipe fittings and 
plates for use in steam service 

Used for bolting material and miscellaneous fittings for steam 
service 

Used for roller bearings, measuring instruments, and piston pins 
Used for small gear wheels and shafts, cardan joints and 
steering regulators 

Used for medium size gear wheels and shafts of vehicles 
Used for making rollers, shaft*’, mandrels, cylinder liners, 
axles, gears, etc 

Used for making gears, connecting rods, stub axles, steering 

arms, wear-resistant plates for earth moving and concrete 

handling equipment 

Spring steel 

Roller bearing steels 

Used for making laminated, coil and volute springs. (This 
steel is not susceptible to decarburization as silico-manganese 
steels are.) 

Used for making axles, shafts, steering arms and other medium 
stressed components 

Used for making axle shafts, crankshafts, connecting rods, 
gears, high tensile bolts and studs, propeller shaft joint 
Used for boiler and superheater tubes, plates for pre^ssure 
vessels and welding electrodes. 

Used for boiler and superheater tubes, plates, pipe fittings, 
forgings and bolting material for petroleum and chemical 
industries 

Bolting material for steam service 





Steel 

Designation 


Typical uses 


10Gr2MoJ 

15Cr3MoW and 
25Cr3MoW 

lOCr5Mo55 

20Cr5Mo55 

35GrlMo65V25 

40Gr3MoiV20 


40Gr2AllMol8 

40Ni3 


IGNi^GrGO and 
IGNiiCrSb' 

13Ni3Gr80 

15Ni4Grl 

35NilGr60 

30Ni4Cri 

15NiGrlMol^ 

and 

15Ni2GrlMol5 

40NiCrlMol5' 

40Ni2GrlMo28 


31Ni3Gr^Mo^ 

and 

40N13Gr65Mo55 

16NiGr2Mo20 


Used for tubes, pipe fittings and forgings for high temperature 
service 

Used for crank-shafts, cylinder liners for aero and automobile 
engines, gears, and machine parts requiring high surface 
hardness, and wear resistance 

Steel for tubes, pipe fittings and plates for use in chemical and 
petroleum industries 

Bolting material for use in chemical and petroleum industries. 
Steel for high temperature bolts and nuts 
Used for components requiring high tensile properties and in 
the nitrided condition for components subjected to heavy 
stress and severe wear 

Used for components requiring the maximum surface hardness 
of a nitrided case combined with a fairly high core strength 
Used for parts requiring excessively high toughness, for 
components working at low temperatures in refrigerators, 
compressors, locomotives and aircrafts and for heavy forgings, 
and severely stressed screws, bolts and nuts 
Used in the automobile industry for lightly loaded gear box 
and transmission components; and in the aircraft industry 
for cams 

Used for heavy duty gears for aircraft, heavy vehicles and 
automobile transmission components 

Used for heavy duty components including aero engines, gears 

and supercharger gears and worms 

Used for aircrafts and heavy vehicles engine components 

Used for highly stressed gears and for components where 

minimum distortion in heat treatment is essential 

Used for heavy duty gears, and automobile transmission 

components 

Used for general machine parts, such as bolts, nuts, gears, 
axles, connecting rods, shafts, etc. 

Used for high strength machine parts, high tensile bolts and 
studs, gears, pinions, axle shafts, tappets, crankshafts, connecting 
rods 

Used for making higlily stressed* components for all types of 
aircraft power units, air frames and under carriages, and for 
low temperature service 

Used for heavy duty gears and heavy vehicles and automobile 
t ransmission components . 




These steels, therefore, are further classified as 

(i) Hardened and tempered steels 

(ii) Case hardening steels which are subclassified as : 

(a) flame and induction hardening steels 

(b) case carburizing steels 

(c) carbonitriding, cyaniding and nitriding steels 

(iii) Creep resisting steels. 

Hardened and tempered steels: 

Carbon steels (containing carbon from 0*25 to 0*60 percent and 
manganese 1 -0 percent maximum) are used in the form of general 
engineering forgings and drop forgings after simple normalizing 
treatment, but superior combinations of tensile strength, yield 
strength, ductility and shock resistance properties may be obtained 
from these steels after hardening and tempering. Hardening 
requires rapid cooling by quenching in a medium, such as oil or 
water. Oil hardening being more common because it is less liable 
to cause cracking and distortion. 

By addition of alloying elements, such as manganese, nickel, 
chromium and molybdenum, the minimum rate at which cooling 
should be carried out to obtain effective hardening is decreased 
depending on the amount of elements or the combination of ele- 
ments added. Thus, it becomes possible by the use of alloy steels 
to produce effective hardening in sizes larger than those could be 
hardened in carbon steels. The standardised carbon and alloy 
steels intended for hardening and tempering are given below: 

Steels for hardening and tempering 

(i) Carbon steels: C30, G35Mn75, C40, C45, G50, G55Mn75 

(ii) Carbon and carbon-manganese free cutting steels: 40S18, 40Mn2S12. 

(iii) Low Alloy steels 

20Mn2 35Mn2Mo45 40Ni2CrlMo28 40Gr3MolV20 

27Mn2 40GrlMo28 31Ni3Cr^Mo55 40Gr2AllMol8 

37Mn2 40Ni3 30Ni4Grl 55Gr70 

40Crl 35NilGr^ 15Gr3Mo55 105Grl 

35Mn2Mo28 40NiGrlMol5 25Cr3Mo55 105GrlMo60 

The tensile strength of th^e steels ranges from 60 kg/sq mm, 
to 150 kg/sq mm in ruling sections upto 150 mm. The yield 
strength for the different ruling sections for these steels are given 
in corresponding schedules of IS: 1570-1961, 






The main criterion for the selection of hardened and tempered 
steel is the ruling section and the mechanical properties of heat 
treated parts but the present day trend is also to select steels 
on the basis of hardenability. According to the degree of harde- 
nability, hardened and tempered steels are divided into four groups : 

(a) Poor hardenability steels which include carbon steels 

(b) Medium hardenability steels which include low alloy 
steels 

(c) Increased hardenability steels which include some 
complexly alloyed steels 

(d) High hardenability steels which include high alloy steels 
containing three or more alloying elements. 

The hardenability is decided for the steel by the hardening 
obtained on the cylindrical specimen of the corresponding steel of 
maximum specified diameter after quenching it in water. The 
maximum specified diameter for the above cases are (a) 15 mm, 
(b) 35 mm, (c) 75 mm and (d) 100 mm. 

Case Hardening Steels: 

It is classified as 

(i) Flame and induction hardening steels, 

(ii) Case carburizing steels, 

(iii) Carbonitriding, cyaniding and nitriding steels. 

The case hardening provides the surface called case, substantia- 
lly harder than the interior called core. This is achieved either 
by altering the structure at the surface by local hardening with 
flame or induction hardening or by altering both composition 
or structure at the surface by case carburizing, nitriding, cyaniding 
or carbonitriding. These types of case hardened steels are 
used fti number of engineering applications where the surface is 
heavily stressed compared to interior which is stressed to a much 
smaller extent. ^ 

In IS: 1570-1961 only case carburizing steels are classified as 
case hardening steels. The steels which can be hardened by other 
processes mentioned as above arc also grouped in this class in 
practice. 

Flame hardening and induction hardening: 

In flame hardening, case depth upto 6 mm is quite common. 
It is not possible to obtain case depth smaller than 1 mm with 





flame hardenings on account of the limitations in flame temperature 
and thermal conductivity of steel. Case depth as low as 0*1 mm 
may be achieved by induction hardening and there is no limit for 
the maximum case depth that can be obtained with it. For all 
practical purposes flame hardening and induction hardening 
processes may be considered identical except for the mode of heat- 
ing and minimum obtainable depth of case. 

Flame hardening is widely used where: 

(a) large work piece is to be case hardened, 

(b) small area of work piece is to be case hardened, and 

(c) higher dimensional accuracy is required. 

Surface hardness of above 59 G Rockwell hardness is desirable 
for wear resistance for which carbon content about 0*4% is 
normally employed. 

In induction hardening the heat is developed at the steel 
surface by electrical induction by the field of an alternating 
current. The heat produced depends upon the induced current 
and the electrical resistivity of the material, while the depth of 
heat penetration depends on the frequency power density and the 
time. 

Steels listed under hardened and tempered steels in table are 
usually used for flame hardening and induction hardening. 


Case carburizing: 

It consists of introducing carbon at the surface of steel to 
form high carbon layer and subsequently hardening to obtain a 
hard case and tough core. Case carburized steel should not have 
carbon content more than 0*22% to obtain an adequate core 
toughness in finished component. 

Case carburizing steels are used when high toughness, fatigue 
strength and resistance to wear are required than those obtained in 
steels hardened by flame or induction hardening. 

Steels which can be case carburized are as under: 


Case Carburizing Steels 


(i) 

(ii) 

(iii) 


Carbon steels: CIO, G14 

Free cutting steels: lOSll, 14MnlS14 


Alloy steels: 
liMn2 
15Gr^ 
17MnlCr^ 
20MnCrl 


16Ni80Gr^ 

IGNilGr^ 

13Ni3Cr80 

15Ni4Crl 


ISNiCrlMol^ 

15Ni2GrlMoJl5 

16NiCr2Mo20 





Case carburizing is recommended for case depth upto 2 mm. 
The tensile strengths expected in the core of case carburized 
components are given in tables VI and XXVI of IS; 1570-1961 for 
carbon steel and low alloy steel respectively. 

Nitriding: 

It is the process by which nitrogen is introduced in the surface 
of the steel. It is classified as: 

(i) carbonitriding, 

(ii) cyaniding, and 

(iii) nitriding. 

Garbonitriding : 

In this process carbon and nitrogen are simultaneously intro- 
duced in the surface of the steel by heating it between 650°C to 
950°C in an atmosphere obtained by the addition of anhydrous 
ammonia to carburizing gases and finally quenching it in a 
suitable medium. 

Nitrogen gets concentrated near the surface and is backed up 
by a carburized case. If enough nitrogen is present a very hard 
surface is obtained even without quenching. The surface hardness 
obtained by this method is higher than that obtained in carburizing 
process. 

Medium carbon steels are carbonitrided with case depth 
upto 0*6, mm for applications which do not involve heavy shock 
loads. Case depth upto 0*25 mm is usually used for light di^jty. 

Cyaniding : 

It is carried out in a molten salt bath containing upto 50% 
cyanide. The treatment is carried out at a temperature range of 
650°C to 950”C. This process is similar to carbonitriding except 
the medium used, which is liquid. For practical purposes results 
obtained by cyaniding and carbonitriding may be considered 
identical. 

Nitriding: 

It is carried out by exposing the component to the action 
of nascent nitrogen in either a gaseous medium of dry ammonia or 
liquid medium of a mixture of cyanide and cyanates in the 
temperature range of 490®C to 590®C. It is not necessary to use 





quenching at the end. The nitrided case obtained consists of 
two zones: 

(i) A white brittle zone next to the surface, consisting 
entirely of nitrides which is very hard and brittle 

(ii) A tougher diffused zone below the white zone. 

The white zone is usually restricted below 0-01 mm and is 
removed later by lapping to avoid flake failure. The hardness 
developed depends upon the amount of stable nitride forming 
elements like aluminium, chromium, vanadium and tungsten 
and the nitriding cycle. The hardness ranging between 900 to 
1,100 Vickers Hardness can be obtained. The distortion due to 
nitriding is low and, therefore, the components can be finished to 
final dimenion before this treatment. The treatment in gaseous 
medium will give less distortion. 

Nitriding steels are: 

15Cr3Mo^, 25Cr3Mo^, 40Cr3MolV20, 40Cr2AllMoJ^8.' 

The nitrided steels produce high surface hardness, low distor- 
tion, resistance to softening upto 500®C, anti-weld properties, 
improved fatigue properties and superior corrosion resistance. 
However, it cannot be produced to have case depth more than 
0*5 mm and it cannot take highly concentrated loads. 

Creep resisting steels: 

Steel behaves plastically at the stress level below its elastic 
limit when continuously subjected to temperatures above 300®C. 
The selection of steel for parts operating above 300°G should be 
made on the basis of creep. The creep resisting steels of low alloy 
content are specified as under: 

Creep resisting steels 

10Mo5^ 07Gr90Mo55 10Cr2Mol lOGrSMoM 

20Mo^ ISCrWMoW 15Cr3Mo55 20Gr5Mo5^ 

33Mo55 40GrlMo^ 25Gr3Mo55 35GrlMo65V2^ 

Addition of molybdenum to steel considerably improves 
the creep resistance and therefore, molybdenum is added more 
than 0*5% alone or with other elements in creep resisting steels. 
Chromium about 1 to 1*25% is used with 0*5% molybdenum with 
differing carbon contents in creep resisting steels. Steel with 
0*12% carbon is used for pipes and tubes, with higher carbon 




for forgings and 04% carbon for high temperature when heat 
treated. Steels with chromium contents of 3% and 6% with 
0*5% molybdenum are used for many parts of petroleum and 
chemical plants. Addition of 0*2% vanadium into later steels 
increases the endurance limit. 

High alloy steels ^stainless and heat resisting steels: 

Alloy steels containing more than 12% chromium are stainless 
and heat resisting steels. Corrosion and heat resisting properties 
of these steels are improved by addition of nickel and molybdenum. 
As the alloy content in these steels is more so it is known as high 
alloy steel. These steels are classified, according to the chemical 
composition and heat treatment, as follows: 

(a) Chromium steels containing 12 to 14 percent chromium, 
magnetic, hardenable by heat treatment and possessing 
martenistic structure 

(b) Chromium steels containing more than 16 percent 
chromium, magnetic, non-hardenablc and possessing 
ferritic structure and 

(c) Chromium-nickel and chromium-nickel-molybdenum 
steels, non-magnetic and possessing austenitic structure. 

Chromium steels containing 12 to 14 percent chromium are 
07Crl3, 15Crl3, 22Crl3, 30Crl3 and 22Crl3S28. 

These steels contain very low carbon to maximum^ about 
0*35%. They may be hardened and the hardness depends on the 
carbon content. These steels find many useful general applications 
where mild corrosion resistant is required. 

Chromium content to 16 percent with low carbon content 
provides better corrosion resistance and a standard steel 07Crl7 
is available. However, these steels have little capacity for hard- 
ening by heat treatment but in softened condition it possesses 
good ductility and is mainly used as sheet or strip for cold forming 
and pressing operations for purposes requiring moderate corrosion 
resistance. It develops brittleness after electric arc or gas welding. 
It possesses good machinability. 

The standard steel 20Crl8Ni2 is more resistant to corrosive 
action than steel with 12 to 14 percent chromium. It possesses 



40 MACHINE DESIGN [ CA. 1 

good resistant to electrolytic corrosion when in contact with non- 
ferrous metals and graphite packings. 

Austenitic stainless steels: 

These steels have high content of chromium and nickel. They 
possess very good properties of resistance to corrosion and scaling 
and also good mechanical properties at elevated temperatures. 
Standard austenitic stainless steels are as under: 

Austenitic stainless steels 

07Crl9Ni9Ti35 05Crl8Nil lMo3 

07Crl9Ni9Nb^ 05Crl8Nil lMo3Ti20 

0 7Cr 1 9Ni9Mo2 1 0Cr2 5Ni 1 8 

07Crl9Ni9Mo2Ti28 10Gr25Nil8Ti40 

10Gr25Nil8Nb8b 

These steels cannot be hardened by quenching; actually they 
get softened by rapid cooling from about 1,000®C. These steels 
possess high ductility in softened condition and can be used for 
production of pressing. When maximum ductility is required for 
deep drawing or for cold spinning low carbon is desired. It is also 
required when maximum corrosion resistance after welding is 
required because these steels though readily weldable but are 
suceptible to corrosive attack in an area adjacent to weld. This 
effect may be removed by heating to about 1,100°C and cooling 
rapidly. 

High tensile strength is obtained in these steels after cold 
drawing when high carbon percentage exists in these steels. Wire 
with tensile strength upto 200 kg/sq mm can be obtained by cold 
drawing and they can be used for manufacturing small springs. 

There are many variations in chemical composition of these 
steels but the general purpose stainless steel known as 18/8 steel 
contains about 18% chromium and 8% nickel. It provides 
excellent resistance to attack by many chemicals. These steels 
also possess good resistance to oxidation upto about 800°C tempera- 
ture and also have good creep resistance at this temperature. If 
superior strength and scaling resistance for higher temperature 
upto 1,150®C are required, steels containing 25% chromium and' 
18% nickel are often used. 

The mechanical properties of high alloy steels for different 
shapes and different treatment conditions are given in tables of 
schedule V of IS: 1570-1961. 


04Grl9Ni9 

07Grl9Ni9 

04Grl9Ni9Ti20 

04Grl9Ni9Nb40 



Art, ] MATERIALS OF CONSTRUCTION AND THEIR PROPERTIES 41 

Table XXXV gives ultimate tensile strength, yield stress, 
0*2% proof stress, percentage elongation, Izod impact value, BHN 
for different ruling sections for bars and forgings in the hardened 
and tempered conditions made of the following steels: 

07Crl3, 15Crl3, 22Crl3, 30Crl3, 22Grl35M and 20Crl8Ni2 
Table XXXVI gives ultimate tensile strength and percentage 
elongation for sheet and strip in the softened condition and made 
of following steels: 

07Crl3, 15Crl3, 22Grl3, 30Grl3 and 20Grl8Ni2 
Table XXXVII gives ultimate tensile strength, 0*2% proof stress 
and percentage elongation for strip and sheet in the hardened and 
the tempered conditions for the steels mentioned in table XXXVI. 

Table XXXVIII gives ultimate tensile strength, yield stress 
and percentage elongation for tubes made of 15Grl3 in annealed 
and also in hardened and tempered conditions. 

Table XXXIX gives ultimate tensile strength for wires in soft- 
ened and also in cold drawn conditions and made of following steels : 
07Grl3, 15Grl3, 22Grl3, 30Grl3, 20Grl8Ni2. 

Table XL gives the ultimate tensile strength for the wires in 
hardened and tempered conditions and made of steels given in 
table XXXIX. 

Table XLI gives ultimate tensile strength, yield stress, 0*2% 
proof stress, percentage elongation and Izod impact value for 
plates, sections, bars, billets and forgings in the softened conditions 
for the austenitic stainless steels made of b 

04Grl9Ni9, 07Grl9Ni9, 04Grl9Ni9TiM, 04Grl9Ni9Nb40, 
07Grl9Ni9Mo2, 07Grl9Ni9Mo2TiM, 05Grl8NillMo3, 
05Grl8NillMo3TiM 10Gr25Nil8Ti4q, 10Gr25Nil8Nb8q 
Table XLI I gives for the above mentioned steels the same 
properties for bars in cold drawn conditions with different ruling 
diameters. 

Table XLIII gives ultimate tensile strength, yield stress, 0*2% 
proof stress, and percentage elongation for sheet and strip steels 
made of all the materials given in table XLI and also for these two 
steels 07Grl9Ni9Ti35 and 07Grl9Ni9Nb7a 

Table XLIV gives ultimate tensile strength for tubes in softened 
condition, cold drawn or cold drawn and tempered conditions for 
the steels given in table XLIII. 






Table XLV gives ultimate tensile strength limit for the wire 
steels for hard drawn conditions and of different sizes maximum 
upto 10 mm size for the steels same as given in table XLIII. 

Table XL VI gives the hardness in BHN and Izod impact value 
for valve steels made of 40Cr9$i4 and 80Cr20Si2Nil both in 
hardened and tempered conditions and 40CrNil4W3Si2 in softened 
condition. 

Typical uses of high alloy steel are given in table 1-7*5. 

Table 1-7.5 

Typical uses of high alloy steels 


Snation typical use s 

Used for structural parts, armatures, etc. 

Used for turbine blades, plastic moulds, glass moulds, and 
surgical instruments 
Used for machine parts and springs 
Used for stioictural parts with high strength 
Used for bolts, nuts and screws, carburator parts, instrument 
parts 

Used for decorative trim, annealing boxes for brass, oil-burner 
rings, nitric acid storage tanks and tank cars, nitrogen fixation 
equipment 

Used for aircraft fittings, wind shield wiper arms, bolting 
materials, paper machinery 

Used for chemiceil handling equipment, recording wire, textile 
dyeing equipment, soda-fountain equipment, coffee urns, etc. 
Used for radar and micro-wave antennae, auto antennae, 
automotive wheel covers, refrigerator trays, railway passenger 
car bodies, ice-making equipment, tubular furniture, screen 
door and storm window frames, electric switch parts 
04Crl9Ni9Ti20 Used for aircraft engine exhaust manifolds, boiler shells, 

and expansion joints, high temperature chemical handling equip- 

04Crl9Ni9Nb^ ment 

07Crl9Ni9Ti^ Used for food processing equipment and welded structures 
and 

07Crl9Ni9Ti^ 

07C2rl9Ni9Mo2 Used for acid resistant parts and equipment for chemical 

and industries 

07Crl9Ni9Mo2Ti28 

05Crl8NillMo3 Used for high temperature chemical handling equipment 
and for rayon, rubber and marine industries, photographic devc- 

05GrI8Nil lMo3Ti20 loping equipment, pulp handling equipment, coke plant 
equipment, food processing'^equipment, edible oil- storage tanks 


07Grl3 

15Crl3 

22Crl3 

30Crl3 

22Grl3S28 

07Crl7 

20Crl8Ni2 

()4Crl9Ni9 

07Crl9Ni9 





E^gna tion Typical use,^ 

10Cr25Ni]8, Used for hydrogenation tubes and equipment, heat exchangers, 
10Cr25Nil8Ti40 retorts, furnace bolts, annealing boxes and tubes, gas turbine 
and and air-craft engine exhaust systems, furnace conveyor belts 

10Gr25Nil8Nb80 

45Cr9Si4 Used for heat resisting exhaust valves in automobile engines 

80Cr20Si2Nil Used for highly stressed exhaust valves in high speed petrol 
and heavy oil engines 

40CrNil4W3Si2 Used for inlet and exhaust valves of aero-engines 


Carbon and alloy tool steels: 

To produce carbon and alloy steels of very high grade they are 
made in the electric furnace in controlled conditions and with 
great care. By tool steels it is understood to refer to very high 
grade steels as produced above and this is included in schedule VI 
of IS: 1570-1961. The steel used in many ordinary tools such 
as hammers, screw drivers, spanners, files, axes, etc. which are 
subjected to less severe conditions of service and should be of low 
cost are made from good quality open hearth steels. They are 
included in the above schedule as well as in the appropriate 
schedules as general engineering steels. 

The selection of the steels is made on the basis of the charac- 
teristics of steel required for the given duty. The major factors in 
the choice of the tool steels are the temperature at which the tool 
operates, its size and shape and the type of operation such as 
cutting, shearing, forming, etc. Tool steels are classified as under: 

(i) Cutting tools used for drills, lathe, broaches, etc. 
requiring high hardness and high wear resistance 

(ii) Shearing tools used for blanking and trimming dies and 
shears, requiring high wear resistance and toughness 

(iii) Forming tools used in die casting dies, forging and cold 
heading dies requiring high toughness with high strength 

(iv) Battering tools used for chisels and shock resisting tools 
requiring high toughness 

(v) Extrusion dies requiring toughness and resistance to 
softening 

(vi) Drawing as used in wire drawing dies possessing wear 
resistance 

44 MACHINE DESIGN [ CA. I 

(vii) Rolling used in roughing and finishing rolls possessing 
wear resistance 

To help in selection of tool steels they are grouped as : 

(a) Cold work water hardening steels 

(b) Gold work oil/air hardening steels 

(c) Hot work steels 

(d) High speed steels 

(e) Low carbon mould steels. 

Cold work steels are used where the operating temperature 
is below 200°C. Above this temperature hot work steels and high 
speed steels are used. Water hardening steels are used when 
tool shapes are simple. 

Cold work water hardening steels: 

This group includes carbon tool steels, improved carbon steels 
with 0*25% vanadium and chromium and tungsten steels. Cold 
work water hardening steels are as under: 

Gold work water hardening steels 

T140W4Gr^ T118 T103V23 T80V2^ 

T133 T105Grl T90 T70 

T133Gr45 T118Gr45 T90V23 T55Si2Mn% 

T105W2Gr60V25 T103 T80 ~ . T55Si2Mn90Mo3^ 

Carbon tool steels : They have poor hardenability and have to be 
water quenched to get the desired properties. To improve tough- 
ness of carbon steels as small amount upto 0-25% of vanadium is 
added. These steels have shallow hardened depth but slightly 
better hardness than that of carbon steels with corresponding 
percentage of carbon. 

Addition of chromium upto 1*5% and tungsten upto 4% in 
steel increases wear resistance and decreases toughness of carbon 
tool steels. This tool steel is used in wear resistance tools. 

Silico-manganese steels are used where shock resistance at low 
cost is required. 

Cold work oil I air, hardening steels: 

In these steels alloy addition is mainly for increasing harden- 
ability. Chromium, molybdenum, tungsten, vanadium, nickel, 
manganese and silicon increase the hardenability and wear resis- 



tance at the same carbon level. Silicon and nickel also increase 
toughness. Some combinations of alloying elements chromium, 
chromium-manganese, manganese-tungsten-chromium impart non- 
deforming characteristics on heat treatfnent and so these steels arc 
called non-shrinking steels. 

These cold work oil /air hardening steels are as under: 


Gold work oil/air hardening steels 


T215Grl2 

T85 

T55 

r45GrlSi95 

T160Grl2 

T75 

T55Ni2Cr65Mo30 

T40W2GrlVI8 

T110W2Grl 

T65 

T55Si2Mn9b 

T40Ni2GrlMo28 

T105W2Gr60V25 

T60 

T55Si2Mn90Mo33 

T40Ni3Gr65Mo55 

T105GrlMn60“ 

T60Nil 

T50W2CrlV18 

T40Ni3 

TlOSGrl 

T55Gr70 

T50CrlV23 

T31Ni3Gr65Mo55 

T90Mn2W50Gr45 

T55Gr70V15 

T50 

T30Ni4GrI 


Hot work steels: 

Hot work steels are used where operating temperature is above 
200®C. It is used in all such applications except cutting tools. 
For cutting tools for temperature above 200®G high speed steels 
are used. Hot work steels should possess the desired combination 
of hardness, toughness and wear resistance at the operating tem- 
perature. For toughness the carbon content of the steels should 
be around 0-35%. These steels should be capable of resisting of 
heat cracking when suddenly heated and cooled. Tungsten, 
molybdenum and chromium increase red hardness. 

Hot work steels are as under: 

Hot work steels 

T33W9Cr3V38, T35Gr5MoVl , T35Gr5Mol V30, T35Gr5MoWl V30 


High speed steels: 

They are used for cutting operations aboye 200°C temperature. 
The minimum carbon content is 0-5% because these steels have to 
possess good hardness and wear resistance. For this purpose the 
percentages of alloying elements are higher than those for hot work 
steels. Tungsten, chromium and molybdenum are used to provide 
red hardness and hardenability. Cobalt increases red hardness 
but reduces toughness. Vanadium imparts wear resistance. On 
account of recent uses of carbide tips and cermets in cutting tools, 
the development of high speed steels is towards improving wear 






resistance by replacing cobalt steel by high vanadium-steels. The 
different combination of toughness, wear resistance and red 
hardness can be obtained within limit by varying the heat treatment. 

Standardised high speed steeb are as under: 

High speed steels 

r75W18ColOCr4V2Mo^ T83MoW6Gr4V2 

T75W18Co6Gr4VlMo75 T70W14Gr4V75 

T123W14Go5Gr4 T55W14Gr3V« 

T70W18Gr4Vl 

Low carbon mould steels: 

These steels are used in case carburized condition for plastic 
moulds. They possess high toughness and good machinability. 
The important property required from them is the case harden- 
ability. Low carbon mould steels available for plastic moulds 
are listed below: 


Low carbon mould steels 

TIO T16Ni80Cr^ 

T15Gi65 T15NiGrlMol2 

T10GrMo75V2^ T16NiGr2Mo2^b 

The typical applications of tool steels are given in table 1-7.6. 

Table 1-7.6 

Typical applications of tool steels 


Steel _ . , 

tn . .• Typical uses 

Designation 


T140W4Gr50 Finishing tools with light feeds, marking tools 


T133 

T118 

T103 

T90. 

T80 

T70 

T215Crl2 

T160Grl2 


Engraving tools, files, razors, shaping tools, wood working 
tools, drills, heading tools, punches, chisels, shear blades, 
vice jaws, press tools, swages, etc. 


High quality press tools, drawing and cutting dies, shear blades, 
thread rollers, cold rolk 


T110W2Grl Engraving tools, press tools, gauges, taps, dies, drills, hard 

T105W2Gr60V^ reamers, milling cutters, broaches, cold punches, knives 
T90Mn2W50Gr45 

T105GrlMn60 Gold forming rolls, lathe centres, knurling took, press took 
TlOSGrl 






SS^ation Typical uao 

T85 Die blocks, variety of hand tools, agricultural tools 

T80Mn^ 

T75 

T70Mn65 

T65 

T60 

T55 

T50 

T55Cr^ Chisels, shear blades, * scarfing tools, trimming dies, heavy 

T55Gr70V15 duty punches, pneumatic chisels 

T55Si2Mn90 

r55Si2Mn£SMoM 

T50W2CrlV^8 

T50CrlV23 

T45GrlSi^ 

T40W2CrlV18 

TGONil 

T55Ni2GrWMo^ 

T40Ni2CrlMo28 

T40Ni3Gr65Mo55 

T40Ni3 

T31Ni3Cr65Mo5_5 

T30Ni4Grl 

T33W9Gr3V38 Dies for extrusion, stamping dies, casting dies for light alloys, 

T35Cr5MoVl forging dies 

T35Cr5MolV30 

T35Gr5MoWlV30 

T75W18Gol0Cr4V2Mo75 Drills, reamers, broaches, form cutters, milling cutters, 

T75W18Co6Gr4VlMo75 deep hole drills, slitting saws, and other high speed 

T123W14Co6CrV4 and heavy cut tools 

T70W18Cr4Vl 

T83MoW6Gr4V2 

T70W14Cr4V75 

T55W14Cr3V45 

TIO Used after case hardening for moulds for plastic materials 

T15Cr65 

T10Gr5Mo75V23 

T16Ni80Cr^ 

T15NiCrlMol2 

T16NiGr2Mo26 


1-8. Non-ferrous Metals and Alloys: 


Important non-ferrons metals and alloys which are discussed 
here are as follows: 




(i) Aluminium and its alloys, their castings and wrought 
form 

(ii) Copper and copper zinc alloys called brasses 

(iii) Anti-friction bearing alloys made of tin with different 
alloying elements. 

(A) Aluminium and aluminium alloys: 

IS: 617-1959 gives specifications and the designation of alumi- 
nium and aluminium alloy ingots and castings for general engineering 
purposes. They are all designated by first letter as A followed by 
numbers from 0 to 24 depending on the variety for ingots while the 
castings of them are designated in the same way with a last letter 
like M, P, W and WP depending on the method of casting and 
treatments. In the above specifications the ultimate tensile 
strength in kg/sq mm for sand cast and chilled cast aluminium and 
its alloys are given for each variety. 

Aluminium ingots of 99% pure aluminium used for re-melting 
purpose are designated as A-0 while aluminium alloy ingots are 
designated as A-1. Aluminium alloy castings are designated as 
A-l-M, A-2-M, A-8-WP, etc. Aluminium alloy castings are 
normally designated by letter M sft the end. If the aluminium 
alloy casting materials are precipitation treated, they are designated 
by letter P instead of M. If they are solution treated letter W is 
used at the end and if they are fully heat treated letter WP is 
used at the end. 

A-l-M is the aluminium alloy casting material mainly used for 
gravity die casting and it has ultimate tensile strength of 12-6 
kg/sq mm when sand cast and 15*7 kg/sq mm when chilled cast. 
Aluminium alloy casting material mainly used for pressure die 
casting is designated as A-2-M. The aluminium alloy casting 
used for sand casting, gravity and special die casting and of 
increasing strength are designated as A-4-M, A-5-M, A-6-M, A-8-M. 

A-22-W is a gravity die cast aluminium alloy which gives 25-2 
kg/sq mm as chilled cast with 8% elongation, while A-24 is used 
for pressure die cast and gives 18 kg/sq mm with 1*5% elongation. 

In 18:617-1959, characteristics and uses of the aluminium 
and aluminium alloys ingots and castings are given in the appendix. 
With the help of these characteristics the suitability of the particular 
grade of aluminium casting can be determined for required 
properties and uses. 

Wrought aluminium: 

Wrought aluminium and its alloys, their designation, 
their characteristics and their typical uses are given in 18:736-1965. 
Aluminium in wrought form is designated by I and there are 
three grades Ay B and C. While aluminium alloys for normal duty are 
indicated by letter JV with number 2 to 8 and for medium strength 
by letter //followed by numbers 9, 11, 12, 14, 15, 18, 19, 20 and 30. 

The outstanding characteristics of aluminium and its alloys 
are their high strength-weight ratio, their resistance to corrosion 
and their high electrical and thermal conductivity. 

Pure aluminium is extremely light, ductile and highly 
resistant to corrosion. When used with other metals such as 
copper, magnesium and silicon, alloys of aluminium compare 
favourably in strength and hardness with alloy steels. 

Duralumin is an alloy of aluminium containing small percen- 
tages of copper, magnesium and manganese. It has a high 
tensile strength and is extensively used for structural forms for air 
planes and other machines where weight is a deciding factor. 

Some typical uses and the characteristics for the different 
grades of wrought aluminium, and aluminium alloys are given in 
table 1-8.1. 

Wrought aluminium and wrought aluminium-alloys are avail- 
able in sheets, plates, extrusions, tubes, wires, rolled rods and 
forgings, when shapes are not mentioned in the table. 


Table 1-8.1 

Uses and characteristics of different grades 
of wrought aluminium and aluminium alloys 

Designation Characteristics Typical uses 


IB High purity aluminium, it is more Corrosion-resistant cladding on 
resistant to corrosion than other stronger alloys, impact extruded 
grades. containers, food and chemical 

plant, compressor accessories, elec- 
tricsil conductors and reflectors 







[CA. 1 


Designation Characteristics 


Typical uses 


IC 




//30 


N5 



JV7 




H9 \ 


H\9 


H20 

HU 


Commercially pure aluminium, 
very ductile in annealed or 
extruded condition, shows ex- 
cellent resistance to corrosion and 
good conductivity for its density. 

Stronger and harder than IC 
but has good workability, welda- 
bility and corrosion resistance. 

Alloy in which magnesium is 
the main, or the only addition. 
They all have high resistance t6 
corrosive attack, especially in 
marine atmospheres 
A medium strength alloy with 
good mechanical properties, 
corrosion resistance and weld- 
ability 

They are available in all the 
above forms except plate forms. 
Their strength increases with 
the magnesium content. They 
all have high resistance to cor- 
rosive attack in marine atmo- 
spheres. They are stronger than 
JV4. N7 is available in extrusion 
form. 


It is available in sheet extrusion, 
tube and forgings. H9 is suitable 
for intricate extruded section. 
H19 is similar to H9 but stronger 
and slightly less ductile, while 

H2Q is of medium strength and 
have very good forming charac- 
teristics. 


Good machining alloy, may be 
extruded in complex section 


Panelling and mounting, lightly 
stressed and decorative assemblies, 
especially in architecture and 
transport, hollow-ware, equipment 
for chemical, food and brewing 
industries, packaging 
Building sheets, vehicle panelling 
and sheet metal work, packaging, 
hollow-ware, tanks 

Panelling and structures exposed 
to marine atmospheres, pressings, 
certain aircraft parts 


For structural applications of all 
kinds, such as road and rail tran- 
sport vehicles, bridges, cranes, roof 
trusses, rivets 

They are used for ship building, 
deep pressing and rivets. N6 is 
used for other applications de- 
manding moderately high strength 
with good corrosion 

Used as roof suppoers in mines 
and such other applications 
requiring high strength with large 
plastic deformation and good 
corrosion resistance. 

It is highly corrosion resistant so 
used for architectural members 
such as window frames, etc. where 
surface finish is important and 
strength required is not high. 

General structural and archi- 
tectural application where both 
surface finish and strength are 
important. 

It has good corrosion resistance 
and used for structural engineering, 
body work and pressings. 

Aircraft components and repeata- 
tion machine parts 





Art. ] MAtERlALS OF GONSTRUGTION AND THEIR PROPERTIES 51 


Designation Characteristics 


Typical uses 


HH 


//15 


.Y21 


It is a stronger alloy than /fll. 
It ages naturally at room tem- 
perature after solution treatment 
and is fairly ductile. 

It combines high strength with 
fair ductility. ‘Alclad* corrosion 
resistance sheet comprises H\b 
core with coating of high purity 
aluminium. 

It is available in sheet, wire and 
rolled rod form. In sheet form 
this alloy anodizes to a pleasing 
grey finish. It blends itself well 
to welding, brazing and soldering. 


Aircraft components, stressed to a 
higher value and components 
requiring high strength 

Aircraft and general engineering 
components requiring high strength 


Architectural applications of in- 
door type for decoration; used 
as welding wire 


(B) Copper and copper-zinc alloys: 

Designations of copper and its alloys are specified in IS:2378- 
1974. Copper is designated by letters Cu followed by group of 
symbols indicating important characteristics. The internationally 
accepted symbols for pure copper are as follow: 

Cathode copper CuCATH 

Electrolytic tough pitch copper CuETP 

Fine refined high conductivity copper CuFRHC 

Phosphorised high residual phosphorous non arsenical grade 

CuDPH. 

Copper-alloys are designated by symbol of copper followed by 
next most significant element after which other significant elements 
shall be stated in the order of decreasing percentage or when equal 
in alphabetical order, viz. CuZnSO, CuSnPb4Zn3. Amount of 
copper is given by the remainder. 

Distinct methods of castings are specified by symbols placed 
before the designation. Absence of symbols indicates that material 
is in wrought form. Surface finish are designated by letters at 
the end of designation, viz. GCuSn7Zn5Pb2 H. 

The designations for copper alloys are not yet completely 
accepted by Indian industries and IS standard also gives the 
available aUoys as alloy 1, alloy 2, etc. as manufactured by the 
industry. However, this is a temporary phase. 






[a. / 


Copper- Zi^ alloys: Brasses: 

The alloys of copper and zinc are known as brasses. These 
alloys are highly resistant to corrosion, machine easily and make 
good bearing materials. The properties of a brass vary \vith its 
zinc percentage. Zinc percentage varies from 5 to 45. By 
increasing the percentage of zinc the ductility of the alloy 
increases but after 37%, there is a fall in ductility. When the 
zinc percentage is less than 20%, the alloy is known as red brass, 
which, is used for plumbing of pipe and connections, rivets, hard 
ware, etc. When the percentage of zinc lies between 28 and 35, 
the alloy is known as cartridge brass which is the most ductile of 
all the brasses. It is used for stamping and deep drawing, cartridge 
shells, wires, tubes, etc. The composition of Admiralty brass is 
70% copper, 29% zinc and 1% tin. This alloy is highly corrosion 
resistant and is used for steam condenser tubes. A brass of greater 
tensile strength and less ductility is known as muntz metal and 
contains 40 to 45% zinc. It is suitable for hot working by rolling, 
stamping or extruding; it is used for certain marine fittings and 
for pump parts. It can be machined readily. 

The machining properties of the brass can be improved by 
including small amounts of lead. The tensile strength is almost 
unchanged, but the shock resistance is lowered. For automatic 
screw-machine work, leaded brass bars are used to produce lightly 
loaded components. 

Various other metals are added to improve the particular 
properties such as tensile strength, hardness, shock resistance, 
corrosion resistance, etc. Manganese and iron are added to 60/40 
brass to increase the tensile strength* and resistance to salt 
corrosion. The resulting alloy, known as manganese bronze, 
can be rolled, drawn and cast. It is used for under water shafts 
and heavy duty bearings and gears. 

Tobin bronze (brass) is extensively used for shafts on small 
boats and for feed pump shafts. 

The most well-known zinc base alloy, containing 4% alu- 
minium and 2*5% copper, is used for die castings. 

Bronze: It is an alloy of copper with tin. The use of tin 
in bronze results in a much harder and stronger alloy than brass. 
Bronze is formed by casting whereas brass is formed by work- 






ing. The tin content of simple bronzes oxidizes quickly, when 
the metal is hot, resulting in brittleness. Various deoxidisers are 
used, the most common being zinc or phosphorous. 

Gun metal: It contains zinc as a deoxidiser. The usual pro- 
portion is 88% copper, 10% tin and 2% zinc. As it is highly 
resistant to corrosion, it is used for small valves and fittings for 
water and general services. Owing to the high price of tin, 
gun metals of poorer casting qualities are available. 

Phosphor bronze: When phosphorous is used as a deoxidiser, 
we get a phosphor bronze, an alloy of improved hardness and 
resilience. Phosphor bronzes with 5 to 10% tin and not more 
than 0*5% phosphorous are suitable for rods for machining and 
valve castings. When tin percentage ranges from 10 to 12% 
and phosphorous is up to 1%, we get an alloy suitable for gear 
wheels and heavily loaded bearings. These bearing metals are 
very rigid and have no plasticity. Plastic bronze is a bearing 
metal which will work under less rigid conditions than forging. 
A typical composition is copper 65-70%, lead 30-25% and tin 
5%. Small quantities of nickel are added to ensure even spreading 
of lead globules. Copper tin alloy containing 75 to 80% tin is 
known as bell metal and is used for making bells and gongs. 

Monel metal: It consists of 68% nickel, 28% copper and 
balance small amounts of carbon, silicon, iron, cobalt and manga- 
nese. The metal has a remarkable resistance to corrosion in 
addition to capacity to retain tensile strength at elevated tenjpera- 
tures. A number of highly corrosive acids and alkaline sub- 
stances have little or no effect on monel metals. This is used 
for making valves, pump rods and fittings for use with high pressure 
steam and chemical plants. Nickel-copper alloy of the name 
constantan has high electrical resistance and low temperature 
coefficient. Nichrome or chromel has a high reistance and is 
used for heatirfjg coils for furnaces. 

Table 1-8.2 gives the composition and uses of various kinds 
of non-ferrous alloys: 

(G) Antifriction bearing alloys: 

They are psed as linings in journal bearings. The main 
component of these alloys is tin and are designated with letters Sn 
followed by the average percentage of it. If no number is being 






given after Sn, then the balance of the alloy gives the minimum 
amount of tin. The alloying elements are followed by the letter 
and percentage in the order of importance. The following grades 
of antifriction bearing alloys are designated in 18:25-1966: 

90, 84, 75, 69, 60, 20, 10, 6, 5, 1. 

Table 1-8.2 


Kind of alloy 


Standard brass 
Gu Zn 30 


Composition of 
mloy 


70% copper; 30% zinc 


Admiralty brass 
CuZn29Snl 
Muntz metal 
Gu Zn 40 
Ordinary bronze 
CuSn5 

Phosphor bronze 
CuSn97P3 


Manganese bronze! 

CuZn35Mn5 
Delta metal 
CuZn41FePb2 


70% copper; 29% zinc; 
1% tin 

60% copper; 40% zinc 

95% copper; 5% tin 

90% copper; 9*7% tin; 
0*3% phosphorus 
60% copper; 35% zinc; 
5% manganese 
55% copper; 41% zinc; 
2% lead; 2% iron 


Gun metal 
Gu Sn 10 
Engineer’s bronze 
GuSnl0Zn2 
Gupro nickel 
CuNi25 
Monel metal 
CuNi67 


90% copper; 10% tin 

88% copper; 10% tin; 
2% zinc 

75% copper; 25% nickel 

67% nickel; 28% copper 
and the rest iron, man- 
ganese and carbon 


Gonstantan 

CuNi50 

Msmganin 

GuMnl2Ni4 

Silveriod 

GuNi45 


50% copper; 50% nickel 

84% copper; 12% man- 
ganese; 4% nickel 

55% copper; 45% nickel 


German Silver 
GuNi20Zn30 


50% copper; 20% nickel 
30% zine 


Uses 


Rolling into sheets or drawing 
into tubes for locomotives, 
cartridge, pump liners 
Steam condenser tubes 

Suitable for hot working by 
rolling, stamping or extruding 
Worms, gean, pump bodies, 
bushes 

Bearings, worm wheels, rods, 
sheets 

Under water shafts and fittings 

Parts of marine engine, screw 
propellers, ordnance, chemical, 
hydraulic, mining plants, 
sanitary fittings 

Small valves, fittings for water 
services 

Engine parts, steam fittings, 
hy^aulic machineries 
Coinage, casing of rifle bullets, 
condenser tub^ 

Valve parts for superheated 
steam, turbine blades, pumps 
and condenser tubes, in che- 
mical industries for vats and 
coils exposed to corrosive in- 
fluences, dyeing plants, arti- 
ficial silk processes 
Standard resistance; thermo 
couple junction metal 


Decorative work in connection 
with shop fronts, hotel entran- 
ces, etc. 

Ornamental work of motor 
cars, shop and house fittings 





Typical uses of antifriction bearing are given in table 1-8.3. 
Table 1-8.3 

Typical use of antifriction bearing alloys 




Grade 

Alloy 

Typical Uses 

901 

SnSb7Gu3 

For lining of petrol and diesel engine bearings, cross- 

84 J 

SnSblOCu5 

heads in steam engines and other bearings used at high 
speeds (As the tin content drops in these alloys, their 
resistance to shock and heavy load increases.) 

75 

Sn75SbllPb 

Mostly used for repair jobs in mills and marine installa- 
tions. (Because of its long plastic range, it can be 
spread in as a wipe joint.) 

69 

Sn69Zn30 

For under water applications as a bearing alloy and 
gland packings. 

60 

Sn60SbllPb 

For lining of bearings required for medium speeds, such 
as centrifugal pumps, circular saws, convertors, dynamos 
and electrical motors 

201 

Sn20Sbl5Pb 

For low speed bearings, such as pulp crushers, concrete 

10/ 

SnlOSbHPb 

mixers and rope conveyors 


Sn6Sbl5Pb 

Heavy duty bearings, rolling mill bearings in sugar, 
rubber, paper, steel industries, etc., bearings for diesel 
engines, cross-heads in steam engines, turbines, etc. 


Sn5Sbl5Pb 

For mill shaftings, railway carriage and wagon bearings 


SnlSbl5Pb 

Used as a thin line overlay on steel strips where white 
metal lining material is 0*076 mm thick 


Grade indicates the minimiun amount of tin (Sn) in the alloy. Pb 
indicates that the remainder is Pb. 


1-9. Available sizes: 


In industries one encounters the terms, foil, sheet, strip and plate with the generally accepted meanings as follows: 

Foil is sheet metal of varying widths having thickness not exceeding 1*6 mm. 

Strip is a metal rolled in any thickness between 1*6 mm and 10 mm and its widths vary from 100 mm to 1,550 mm. It is designated with letters ISST followed by the dimensions in mm in order of length, width and thickness. 

Sheet is a term used for metals having thickness lying between 0*4 mm to 4 mm and having a 
width varying from 1,800 mm to 4,000 mm. It is designated by letter ISSH followed by the dimensions in mm in order of length, width and thickness. 

Plates denote all widths of metals where the minimum thickness exceeds 5 mm and maximum upto 63 mm and all widths of metal and length varying from 2,200 mm to 13,500 mm. It is designated by letters ISPL followed by dimension in mm in order of length, width and thickness. 

The manufacturing problems bring to the fore the need to have limiting dimensions on the width, thickness and length of strip and sheet metal. 18:1138-1958 gives sizes of metal strips, sheets, flats, 
plates, and bars round and square. Here the nominal sizes are given as well as the tolerances in the sizes kept in their manufacture arc also specified. 

18:1731-1961 gives dimensions for steel flats, and their tolerances for structural and general engineering purposes while 18: 1732-1961 gives dimensions for round and square steel bars for 
structural and general engineering purposes. 

Dimensions for steel plates, sheets and strips for structural and general engineering purposes are given in 18:1730-1961. The following 18 specifications also give the sizes of different structural 
sections made of steels for general purposes of engineering: 

18:808-1957 specification for rolled steel beams, channels and angle sections 

18 : 1173-1957 specification for rolled steel beams, channels and angle sections and for bars 

18:1250-1958 Specification for rolled steel beams, channels and angle sections, and bulb angles 

18:1863-1963 Dimensions for rolled steel bulb plates. 

All these structural steel sections are given combined in ISI standard handbook for structural engineers. 

18:6911-1972 gives dimensions of stainless steel plates, sheets and strips 

18:1079-1973 gives dimensions of hot rolled, carbon steel sheets and strip 

1^:6527-1972 gives dimensions of stainless steel wire rods 

18:6528-1972 gives dimensions of stainless steel wire 

18:6529-1972 gives dimensions of stainless blooms, billets and slabs for forgings. 

18:6603-1973 gives dimensions of stainless steel bars and fiats 

18:6911-1972 gives dimensions of stainless steel plates, sheets and strips. 






All sizes standardised and given in IS standards are not manufactured by industries. They manufacture only those sizes which are in large and continuous demands. So design engineers 
should refer to manufacturers' catalogues for the available sizes. 

1-10. Accuracy: 

When two parts have to fit together, one within the other, a definite difference in size is usually necessary depending upon the nature of the fit required. This difference in dimensions between two parts is called the allowance. As it is difficult to manufacture any part true to size, certain maximum permissible deviation from the given dimension is allowed. This variation which covers imperfection of workmanship is termed tolerance. This variation of dimension depends upon the kind of component.

Tolerances and allowances have been standardised in each country by Standards Association. In our country, the' recommended values for tolerances and allowances are given in specification IS: 
919-1959. 

If close tolerances are necessary for interchangeability of parts, jigs and fixtures may be carefully prepared so that hole locations and other dimensions may be duplicated on any number 
of parts. Jigs guide the tool as well as hold the work while fixtures only hold the work and simplify and regulate the set up. 

Except for drilling machines, all machine tools of cutting type give about the same degree of accuracy under ordinary conditions. 

1-11. Finishing processes: 

In many processes such as die casting, rolling, extruding, etc. accuracy and smoothness may be obtained so that components manufactured by these methods require no further finishing operations in order to use the component. However, castings, forgings and welded parts do not have the accuracy of dimensions or necessary smoothness. Therefore such parts may be subjected to further finishing operations. Finishing operations are necessary from many considerations such as lightness, attractive appearance, etc. 

Finishing may be accomplished by abrasives or by cutting tools, the former are finding more extended use. The finishing processes comprise turning, milling, shaping, planing, drilling, reaming, boring, broaching grinding, honing and lapping. Many times hand scraping is used to finish the product. 

1-12. Non-metallic materials: 

The commonly adopted non-metallic materials are leather, rubber, asbestos and plastics. 

Leather is used for belt drives and as a packing or as washers. It is very flexible and will stand considerable wear under suitable conditions. The modultus of elasticity varies according to load. 

Rubber is used as a packing, as a drive element and as an electric insulator. It has a high bulk modulus and must have lateral freedom if used as a packing ring. 

Asbestos is used for lagging round steam pipes and steam boilers. 

1-13. Plastics: 

These materials have come into extensive use now-a-days. The name plastic materials has been derived from the state of plasticity existing at a certain stage in their manufacture. This 
makes it possible to give plastic products any desired shape. 

They are classified into two main categories: Thermoplastics which soften under the application of heat and can be repeatedly moulded. Thermosetting plastics which, under pressure and heat 
are cured and polymerised so that the plastic assumes a different chemical combination, becomes hard and will not deform when again subjected to heat. 

The basic compounds in both categories are available mainly 
in powder, tablet, liquid and sheet forms, and are converted into 
the finished product by moulding, die casting under pressure and 
conventional casting, by pneumatic vacuum moulding, by machin- 
ing and by extrusion using screw presses. With thermosetting 
plastics the finished shape is usually obtained from powder by 
compression moulding in a die under heat and pressure. Thermo- 
plastic compounds may be formed by extrusion, compression or 
injection moulding. Sheets of thermoplastic materials may be 
re-shaped by heating. With some shapes additional machining 
operations, cutting, drilling, etc. are necessary. 

Plastics are produced on a synthetic or less frequently on a 
natural resin base. Apart from resins most plastics contain 
what is known as a filler, to provide particular properties such as 
colour, strength and impact and wear resistance. Fillers include 





paper, fabric, chipped-wood, moulding compound, graphite, wood 
veneer, textile, glass fibers, asbestos and more recently molyb- 
denum disulphide, which provides excellent lubricating and wear 
properties — particularly when introduced into nylon. 

The good features of plastic materials are 

(i) Low cost 

(ii) Light weight 

(iii) Good resistance to shock and vibration 

(iv) Self lubrication, which means low friction and high 
wear resistance 

(v) Heat and electric insulating properties 

(vi) Resistance to corrosion, and 

(vii) Ease of fabrication. 

The unfavourable features of plastics are 

(i) Low strength 

(ii) High thermal expansion 

(iii) Low heat resistance 

(iv) High creep and deformation under load, and 

(v) Embrittlement at low temperatures. 

Table 1-13.1 gives the list of some of the plastics most com- 
monly used in Mechanical Engineering: 

TABLE 1-13.1 

Name of plastic Uses 

Textolite (Laminated fabric) Gear wheels, machine tool slide ways, 

pulleys, and bearing liners k 

Wood laminate Shells of large sized bearings, pulleys 

and gears and as a substitute for non- 
ferrous metals 

Ck>mpressed-wood plastic Bearing material, and substitute for non-ferrous metab and for making 
pipes, hand rails, etc. 

Fibreglass Hulls of small ships, boats and yachts, and automobile bodies 

Fluorinated plastics (Ethylene Lining of friction surfaces, packings, polymers) electric and radio parts, pipes and pipe valves 

Polyamide resins (Gapron and High speed gears, compressor discs nylon) and blades, and parts with high impact strength and abrasion resistance 

Faolite Pipes to convey chemically aggressive fluids 
Pipes 


Polythylene 






EXAMPLES 1 

1. What are the important considerations that govern the choice of a material? 

2. Classify the materials of construction. 

3. Define the meaning of the term base metal as applied to engineering 
materials. 

4. What is meant by the term *^mechanical properties of material”? 

5. Define in general the properties of strength and elasticity. 

6. What is meant by ductility, malleability and plasticity? 

7. Explain the term resilience. 

8. What is meant by toughness and how is it measured ? 

9. Why is brittleness an undesirable property, especially for materials to \yt used as machine parts? 

10. Explain the terms creep and machinability. 

1 1 . What useful information is obtained from a static tensile test ? 

12. Name hot working process. 

13. What are the advantages of forged components? 

14. What are the advantages of using extruded parts? 

15. Name two articles which are shaped by cold working. 

16. Explain the terms: drawing, heading, spinning and stamping. 

17. Enumerate the precautions to be taken while designing castings. 

18. Define powder metallurgy. Outline the general process used. 

19. Discuss the advantages and the limitations of powder metallurgy. 

20. Name several examples of parts that can be made of powdered metals. 

21. Name finishing processes. 

22. Define tolerance and allowance. 

23. What characteristics of metal arc required to be considered in deciding 
Its weldability? 

24. How does the carbon content affect cast iron, wrought iron and steel 
with reference to hardness and toughness? 

25. What advantages has cast iron as construction material? 

26. For what particular parts is malleable iron used? 

27., What advantages malleable iron has over white or grey cast iron? 

28. What advantages are there in using alloy cast iron? 

29. Name the processes by which steel is commonly produced. 

30. Classify carbon steels. 

31. Explain the difference between carbon steel and alloy steel. 

32. How are alloying elements effective in changing the properties of steel? 

33. What alloy steel is suitable for springs? 

34. For what types of service are brasses and bronzes used? 

35. What are the constituents and physical properties of monel metal? 

36. What is the advantage of aluminium bronze over tin bronze? 

37. Why is duralumin said to be a successful steel substitute? 

38. Name the important non-metallic materials of construction. 

39. How is grey cast iron designated in Indian Standards? 

40. Select a grey iron casting which can withstand ultimate tensile strength 
of 32 kg/sq mm. 

41. A gear housing requires a malleable casting which should withstand an 
ultimate tensile strength of 50 kg/sq mm. Find a suitable material and designate 
it as per Indian Standards. 

42. A steel is to be selected for railway wheels such that it should have at 
least an ultimate tensile strength of 50 kg/sq mm. Explain the method of selecting 
such steels with the help of Indian Standards for wrought steels. Designate 
the steel selected. 

43. A free cutting steel having a machinability rating above 70% and capable 
of being hardened is required. Designate the steel and give its ultimate tensile 
strength and Izod impact value with the help of Indian standards for wrought 
steel. 

44. An alloy steel is required for roller bearing. Find out the suitable 
steel and designate it and also give its mechanical properties and method of heat 
treatment with the help of Indian Standards. 

45. For a highly stressed part of an aircraft power unit a suitable alloy steel 
is to be selected. Explain the method of choosing the material and designate it 
as per ISI and state its mechanical properties as available from the standards. 

46. A case carburized steel is required for a gear having a tough core with a 
case depth of 1 mm. Select the steel which can give a minimum hardness of 
60G Rockwell and can have a core of as high toughness as possible. Designate 
the steel available and state its mechanical properties. 

47. For a petroleum plant a steel tube of creep resistance is j^equired. 
Select the standard material available as per ISI and state its properties. Also 
write its designation. What composition you will prefer for higher endurance 
limit? 

48. An Indian firm has a collaboration with an American firm which has 
specified a steel in their design as AISl 304. Select the equivalent steel available 
according to Indian standards with the help of IS: 1870-1965 and the Index to IS: 
1870-1965. Designate it as per ISI and give its mechanical properties with the 
help of IS: 1570-1961. 


49. Give the Indian standards equivalent for the following wrought steels: 


(a) ASTM A41-30 ' 

(e) 

(b) SAE 1050 

(f) 

(c) SAE 6130 

- (American) (g) 

(d) AISI 321 

(h) 



(j) 


EN8 1 . . , , 

EN24j 

VCN45 (DIN-Gcrmanyj 
MCr6 (Gost.Russian) 
SKH9 (JlS-Japanese) 


50. Designate an aluminium alloy casting suitable for die casting and 
having an ultimate tensile strength of at least 16 kg/sq mm. 
51. (a) What are the chief physical characteristics of materials that are important in deciding on their choice as material for manufacture of different types of machine dements? 

(b) Discuss in detail the material used and the special property which makes it most suitable for use in manufacturing the following: 

(i) Cylinder block of an aero engine 
(ii) Boiler shell 
(iii) Pipes 
(iv) Pulleys 
(v) Gears 
(vi) Rim of locomotive wheels 
(vii) Pump bodies 
(viii) Worm wheels. 

52. Select suitable materials for the manufacture of the following : 

(i) Drop hammer dies 
(ii) Metal cutting saws 
(iii) Die castings 
(iv) Electrical switch boxes 
(v) Condenser tubes 
(vi) I.C, engine pistons 
(vii) Bearings
(viii) Heating coils for furnaces. 

Clearly give reasons for your choice of the material, give the composition 
and the properties of the same. 


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