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
M
//30
N5
M
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
1
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
6
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.
5
Sn5Sbl5Pb
For mill shaftings, railway carriage and wagon bearings
1
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)
4
(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.
