Engineering materials

MATERIALS
By:
Nishant Khatod
Assistant Professor
STC, Latur

Why to study materials??
 Many an applied scientist or engineer, whether mechanical, civil, chemical, or
electrical, will at one time or another be exposed to a design problem involving
materials.
 Examples might include a transmission gear, the superstructure for a building, an
oil refinery component, or an integrated circuit chip.
 Selection criteria for materials:
 Required properties
 In-service conditions
 Cost

Mechanical properties of materials
 Strength: Ability of material that can resist or withstand mechanical load
 Ductility: Ability to material to form wires
 Malleability: Ability of material to form sheets
 Brittleness: Ability of a material to withstand mechanical load without plastic
deformation
 Hardness: Ability of a material that can offer resistance against mechanical
deformation
 Toughness: Ability of a material that can absorb energy at the time of failure
 Stiffness: Ability of a material that can resist mechanical deformation under
stress
 Resilience: Ability of a material that can absorb energy against failure, without
undergoing shape change

Classification of materials
Engineering
Materials
Metals
Polymers
(C-H-O chain;
Includes
rubber and
plastics)
Ceramics
(Mixture of
oxides,
carbides or
nitrides;
Includes glass,
concrete etc)
Composites
(Mixture of
two or more
individual
materials;
Includes FRP,
MMC etc)

Classification of materials
Familiar objects that are
made of metals and metal
alloys: (from left to right)
silverware (fork and
knife), scissors, coins, a
gear, a wedding ring, and
a nut and bolt
Common objects that are
made of ceramic
materials: scissors, a
china tea cup, a building
brick, a floor tile, and a
glass vase.
Several common objects
that are made of
polymeric materials:
plastic tableware (spoon,
fork, and knife), billiard
balls, a bicycle helmet,
two dice, a lawnmower
wheel (plastic hub and
rubber tire), and a
plastic milk carton

Classification of metals
Metals
Ferrous
Steels Cast Iron
Non-ferrous

STEELS
(Iron-carbon alloys containing appreciable concentration of other alloying
elements; contain ≤ 2% C)

Effect of alloying elements
 Solid solution strengthening/hardening:
 Dissolve in ferrite to form solid solutions which stronger and harder than pure
metals.
 Eg: P, Si, Mn, Ni, Mo, V, W, Cr etc
 Formation of carbides:
 Elements react with carbon to form carbides
 Increase in hardness, wear resistance, abrasion resistance, hot hardness
 Eg: Ti, Zr, V, Nb, W, Mo, Cr, Mn etc
 Formation of intermediate compounds:
 Form intermediate compounds which are hard and brittle
 Eg: Ni, Si, Al, Zr, V, Ti, W, Cr etc
 Formation of inclusions:
 Combine with oxygen and form oxides
 Eg: Si, Al, Mn, Cr, V, Ti etc

Effect of alloying elements
 Shifting of critical temperatures and eutectoid carbon:
 Ni and Mn lower A1
 Ti and Mo raise A1
 Cr shifts eutectoid carbon % to lower values
 Lowering of critical cooling rate:
 Except Co all alloying elements shift nose of TTT curve to the right
 Increases hardenability
 Changes in volume during transformation:
 Reduces distortions and quench cracks
 Eg: Si, Mn, Ni, Cr, Mo, Co etc
 Other effects:
 Transformation may become slow
 Corrosion resistance, creep strength, fatigue strength may increase
 NOTE:
 Creep: Permanent deformation at constant stress at elevated temperature

Classification of alloying elements
 With respect to the relation with carbon, all alloying elements can be classified as;
 Carbide forming elements:
 Form carbides
 Eg: Ti, Zr, V, Nb, W, Mo, Cr, Mn etc
 Neutral elements:
 Neither form carbide nor graphite
 Eg: Co
 Graphitizing elements:
 Carbide decompose into graphite
 Eg: Si, Ni, Cu and Al
 With respect to the effect on temperature intervals in which the allotropic forms of iron exist,
alloying elements can be classified as;
 Austenite stabilizers:
 Raise A4 lower A3
 Beyond certain % of alloying element, A3 may become less than room temperature and these
alloys show austenite from room temperature to melting point and such steels are called
austenitic steels
 Eg: Ni, Mn, Cu, C, N etc
 Ferrite stabilizers:
 Lower A4 raise A3
 At a certain composition, A4 and A3 merge such that ferrite exists from room temperature to
melting point and such steels are called ferritic steels
 Eg: Cr, W, Mo, V, Si, Al, B, Zr, Nb, P, Ti etc

Properties and uses of alloying elements
 Sulphur:
 Combines with iron and forms FeS (hard and brittle)
 FeS has low melting point and hence solidifies last; appears at grain boundaries
 During hot working, cracks develop during working (hot short)
 Thus amount of S to be restricted to 0.05% and more than 5 times of S, Mn to
be added
 MnS is not so hard and brittle as FeS
 MnS has higher melting point than FeS
 Thus Mn addition reduces brittleness and hot shortness
 Hence, some amount of Mn is always present in any steel
 FeS and MnS promote chip formation and hence improves machinabilty

 Phosphorous:
 Dissolves in ferrite and forms a solid solution
 Increase tensile strength and hardness
 If solubility is exceeded, Fe3P is formed which is hard and brittle
 Thus, amount of phosphorous is kept below 0.05%
 Phosphorous reduces solubility of carbon in ferrite and thus rejects carbon
adjacent areas forming banded structures (Alternate pearlite and ferrite layers);
easy crack propagations; hence banded structures are not desirable

 Silicon:
 Dissolves in ferrite and forms a solid solution
 Increases strength, hardness and toughness without loss of ductility
 Strong deoxidiser
 Upto 5% Si, produces magnetically soft materials for transformer, motor and
generator cores; Less eddy current losses due to high electrical resistivity
 Steels with 2% Si, 1%Mn and %C between 0.5 to 0.7 are suited for
manufacturing leaf springs, coiled springs, chisels, punches [Heating : 840-930ᵒ
C, holding and oil quenching followed by tempering @ 400-550ᵒ C]
 Higher amount of Si (say 8% or more) are never added, because cementite from
steel decompose into graphite and ferrite which spoil the properties of steel

 Manganese:
 Either less than 2% or more than 10% because Mn content between 2-10%
induces brittleness
 Dissolves in ferrite and increases yield strength, tensile strength, toughness and
hardness
 Least expensive and hence added to all structural steels for strengthening
 Enhances response to heat treatment
 Normalizing improves impact property of manganese steels
 Combines with S and forms MnS and reduces detrimental effects of FeS
 Improves machinability and hence added to free cutting steels upto maximum
1.6%
 Applications:
 Low carbon steels with Mn content 1.65-1.9%: Rails, gears, axles, connecting
rods, crankshafts, bolts, nuts, studs, steering levers, aircraft fittings and gun
barrels

 Hadfield steel:
 1-1.2 % C, 12-14% Mn
 Extremely tough, wear resistant and non-magnetic on suitable heat treatment
(Heating: 1000ᵒ C, holding and quenching in water)
 Mn is austenitic stabilizer and with high amount Mn, critical temperature is
sufficiently lower, so that by rapid cooling austenitic structure can be obtained at
room temperature
 Applications: Jaw plates for stone crusher, frogs in rail road tracks, dredge
bucket and power shovel teeth

 Nickel:
 Dissolves in ferrite and increases tensile strength, hardness and toughness
without decreasing ductility
 Added upto 5% to increase tensile strength and toughness
 Austenitic stabilizer: High addition of Ni makes steel austenitic at room
temperature. Such steels are soft, ductile, malleable and non-magnetic
 Increases corrosion and oxidation resistance if added in excess of 5%
 Increases impact resistance of steels at low temperature
 Increases hardenability of steels
 Reduces coefficient of thermal expansion:
 Invar:- 36% Ni, 0.2%C and 0.5%Mn; Elinvar:- 36%Ni, 12%Cr and W; Ni-
span:- 42%Ni, 5.5%Cr and 2.5%Ti. All these three alloys have zero coefficient
of thermal expansion in the temperature range of 0-100ᵒ C
 These three alloys can be used for surveyor’s tape, gauges, watch parts etc
 Applications: Steels with 2-3% Ni are used in large forgings, castings and
structural components which cannot conveniently quenched, locomotive boilers,
bolts, railway axles and bridge structures

 Chromium:
 Increases hardenability
 Forms carbides and increases hardness and wear resistance of
steels
 Increases corrosion and oxidation resistance when added in
substantial amount
 Increases service life and performance of steels
 May cause temper embrittlement
 Surface markings (Chrome lines) may be formed
 Applications:
 Composition and heat treatment for gears, jaws of wrenches,
machine gun barrels, axles and shafts: 0.35% C, 0.5% Cr;
Heating:870ᵒ C, holding and oil/water quenching followed by
low temperature tempering ]
 Composition and heat treatment for springs and compressed air
tools: 0.5% C, 1.5% Cr; Heating: 840ᵒ C, holding and oil
quenching followed by tempering @ 300ᵒ C
 Composition and heat treatment for twist drills, hacksaw blades,
knives, hammers: 0.9% C, 1% Cr; Heating: 810ᵒ C, holding and
oil quenching followed by tempering @ 250-300ᵒ C]
 Composition and heat treatment for ball bearing: 0.95-10% C,
1.3-1.6% Cr; Heating:840ᵒ C, holding and Oil quenching
followed by tempering @ 150-160ᵒ C [long time; spherodising to
improve machinability]
 Medium chromium and high chromium steels find applications in
cutting tools, dies, stainless steels, heat resisting steels

 Tungsten:
 Increases hardenability
 Forms carbides and increases hardness and wear resistance of steels
 Resistance to tempering (Secondary hardening)
 Refines grain size, and carbide prevents grain coarsening
 Reduces tendency of decarburisation
 Molybdenum:
 Reduces temper embrittlement (added upto 0.5%)
 Properties similar to W
 Resistance to grain coarsening and decarburization is less as compared to W

 Vanadium:
 Excellent resistance to grain coarsening
 Improves fatigue and creep resistance; hence used in leaf and coil springs,
heavy duty axles, gears, pinions, valves etc
 Strong deoxidiser
 Excellent wear resistance and resistance to tempering
 HSS : 1% V
 Super HSS: 5% V
 Titanium
 Strong carbide former
 High wear resistance with no loss of toughness
 Prevents grain coarsening
 Cobalt
 Neutral element
 Only element reducing hardenability of steels
 Resistance to tempering
 Applications: Permanent magnets, Cemented carbide cutting tools

 Aluminum:
 Powerful deoxidiser
 Prevents grain coarsening
 Boron:
 0.001-0.003% B increases hardenability of medium carbon steels
 Reduces grain size but does not prevent grain coarsening
 Improves machinability
 Boron diffused steels have high surface hardness, wear resistance and
corrosion resistance
 Boron diffused surfaces of hot forging dies considerably increase service life
 Used for control rods in nuclear reactors

Classification of steels
 Depending upon %C:
 Low carbon steel
 Medium carbon steel
 High carbon steel
 These 3types are further sub-classified as;
 Plain carbon steel: Contain only residual concentrations of impurities other
than carbon and a little manganese
 Alloy steel: More alloying elements are intentionally added in specific
concentrations

Low carbon steels
 % C = 0.008 – 0.3; very low amount of alloying elements like Mn
 Properties:
 Soft, ductile, malleable, tough, machinable, weldable and non-hardenable
 Least expensive
 Cold working is necessary to improve the strength
 Applications: Wires, nails, rivets, screws, panels, welding rods, ship plates,
boiler plates and tubes, fan blades, gears, valves, camshafts, crankshafts,
connecting rods, railway axles, cross-heads, etc

Mild steels
 % C = 0.15-0.25
 Microstructure consists of about 25% pearlite in a
ferrite matrix
 Properties:
 High strength, low ductility as compared to
conventional low carbon steels (0.1% C)
 Excellent weldability
 Y.S. = 300-350MPa, U.T.S = 400-450MPa,
%elongation = 26-30
 HAZ near the weld attains a temperature above A3 and
becomes austenite. When the welding is complete this
region cools more rapidly than in air cooling, due to
self-quenching
 If carbon content does not exceed 0.25% the
hardenability is low for non-martensitic products to
form in HAZ
 If martensite forms, its hardness is less that 45Rc
 Applications: Ship hulls, boilers, oil pipelines, I
beams, H beams, angles, channels, grills, building bars
etc
 Weathering steels: Adding phosphorous and copper to
mild steels to improve the resistance to atmospheric
corrosion

Free cutting steels
 Can be machined and cut with fast speeds, because of their high machinability
and hence named free cutting steels
 Also known as resulphurized grade steels
 Both extremely hard and extremely soft materials are difficult to machine
 Low carbon steels containing 0.6% S, 0.12% P, Mn: 5-8times amount S
 Mn + S = MnS Favors chip formation and breaking; Increases strength
and hardness
 P + Fe = Fe3P Favors chip formation
 High carbon steels containing 0.35% Pb
 Pb is insoluble and appears as microscopic globules in steel
 Favors chip formation with less resistance to tip of tool
 Pb improves machinability without affecting normal temperature ductility and
toughness

High strength low alloy (HLSA) OR Micro-
alloyed steels
 % C: 0.07-0.13% with small (< 0.5%) additions of Ti, V, Nb and Al
 Properties:
 High strength to weight ratio than conventional steels of identical carbon
content
 Good ductility, malleability, formability, toughness and weldability
 Y. S. = 400-700MPa, U. T. S. = 500-800MPa, % Elongation = 18-25
 Superior properties because of ultrafine grain size, solid solution strengthening
of ferrite, precipitation of carbides and nitrides and martensitic or bainitic
transformation which are likely to occur in these steels due to increased
hardenability
 Applications: Oil and gas pipelines, Automotive (pressed chassis and
reinforcement parts, beams or welded tubes), construction and farm machinery,
industrial equipment, storage tanks, mine and railroad cars, barges and
dredges, lawn mowers, and passenger car components, bridges, power
transmission towers, light poles, lifting and handling equipment (cranes, fork
lifts, platforms, warehouse shelves, lifts)

Maraging steels
 Composition: 0.03% C, 18-25% Ni, 3-5%Mo, 3-8% Co and 0.2-1.6% Ti, with
small amounts of Al
 Formed by martensite transformation (comparatively soft because of low
carbon content) + Cold working (as desired) + Aging @ 500ᵒ C
 During aging, strain induced precipiatation hardening occurs due to the
precipitation of Ni3TiAl and Ni3Mo phases
 Y. S. upto 1800 MPa with excellent fracture toughness
 Good weldability
 Expensive
 Applications: Rocket casing and other aerospace applications, pressure vessels,
injection moulds and dies

TRIP steels
 Stands for Transformation Induced Plasticity
 Composition: 0.25% C, 2% Mn, 2% Si, 8% Ni, 9% Cr and 4% Mo
 Composition is so adjusted that Ms temperature is below room temperature
and Md is above room temperature (Md = highest temperature upto which
deformation of austenite can induced martensite)
 Steel is first heavily deformed above Md, where no transformation occurs
 Deformation produces the right degree of metastability so that a small plastic
strain at the tip of the crack is sufficient to induce the austenite to transform to
martensite
 Plastic zone size is enlarged, so that more work is done during crack growth
 Y. S. = 1400MPa with excellent fracture toughness
 Expensive and hence used for specialized applications

Medium carbon steels
 Also known as machinery steels
 % C = 0.3 – 0.6
 Properties:
 Intermediate to low and high carbon steels
 Medium hard, Not so ductile and malleable, medium tough, slightly difficult to
machine, weld and harden
 Difficult to cold work and hence hot worked
 Least expensive
 Applications: Bolts, axles, springs, wires, wheel spokes, rods, hammers, lock
washers, crankpin, turbine rotors, railway rails, railway tyres, cylinder liners
etc

Rail steels
 Structural parts used by railways such as rails, wheels, axles, are either forged,
or hot rolled and have carbon of 0.5-0.65%
 Higher level of carbon combines with about 1% Mn shifts eutectoid
composition sufficiently to a yield a mostly pearlitic structure
 Lowering of transformation temperature by Mn results in fine pearlite
 Weight loss due to wear of rail steels decreases with increasing hardness of the
steel and decreasing interlamellar spacing of pearlite
 Hadfield steel:
 Used where there is exceptionally high rate of wear in rails
 0.75 – 0.9% C, 12-14% Mn
 Steel is austenitic in structure and high rate of work hardening

Spring steel
 Carbon content: 0.5-0.65%
 Spring properties: High resilience
 Quenched and tempered to get a yield strength of about 1500MPa
 Role of alloying elements in spring steels:
 Increase hardenability
 Presence of Si in 55Si2Mn90 spring steel serves the purpose of retarding the
softening during tempering, so that stresses are relieved are without much loss
in hardness and strength
 Vanadium in the 50Cr1V23 steel prevents grain coarsening during
austenitizing and improves the toughness of steel. A fine grain size and
prevention of decarburization during heat treatment ensure a good fatigue
strength

Ni-Cr-Mo low alloy steels
 Ni increases toughness of ferrite; Cr increases hardenability, strength and wear
resistance but at the expense of toughness. Thus for structural alloys Ni/Cr
should be about 2.5
 To reduce temper embrittleness induced due to Ni-Cr, 0.25% Mo is added
 Well known Ni-Cr-Mo low alloy steel is AISI 4340
 For same ductility and toughness, low alloy steel possess superior strength
 Conversely for same strength, the low alloy steel would have larger ductility
and toughness
 High hardenability implies slower cooling rates and hence less residual
stresses
 High hardenability makes welding difficult in case of AISI 4340

Ausformed steel
 Ausforming process:
 Heating the steel upto austenitic
region
 Rapidly cooling (avoiding nose)
slightly below nose of TTT curve
 Plastically deforming either by rolling
or forging
 Quenched in oil avoiding non-
martensitic products
 Finely dispersed austenite is obtained
 On tempering at 100ᵒ C,
 Y. S. = 2300MPa, T.S. = 2700MPa, %
elongation = 8
 A plain carbon steel component
hardened at same hardness level by
any other treatment will be brittle
with poor tensile strength
Ausforming [Source: V.D.
Kodgire, S.V. Kodgire, 2010]

High carbon steels
 Also called as tool steels
 % C = 0.6 – 2%
 Properties:
 Hard, wear resistant, brittle, difficult to machine, difficult to weld and can be
hardened by heat treatment
 Can be cold worked
 Applications: Knives, Chisels, cutting tools, forging dies, punches, hammers,
springs, clips, clutch discs, drills, leaf springs, razer blades, balls and races for
ball bearings, mandrels, cutters, reamers etc

Properties/Requirements
 Hardenability
 Rates the steel on the probability of hardening during cracking
 Depth of hardening: Higher the alloying elements, higher is the depth of hardening
 Resistance to decarburisation:
 Ability to resist loss of carbon at the surface during hardening
 Loss of carbon leads to softening and cracking
 Red hardness
 Capacity to withstand hardness at high temperatures
 HSS have high red hardness as compared to other tool steels
 Wear resistance
 Removal of surface area of a material by abrasion, erosion, adhesion and other processes can
cause wear and tear of the material
 Abrasion: Removal of material by action of hard, sharp particles or projections on sliding
surface
 Erosion: Progressive loss of material from surface by mechanical action of fluid on surface
 Adhesive wear: Wear caused by action of relatively smooth surfaces sliding together
 Toughness
 Must absorb sufficient energy and resist breaking
 Should be rigid and there should be no plastic deformation
 Machinability:
 Ease of machining
 Specific alloying elements to be added to improve machinability

Types of tool steels
Tool steels
Cold
work tool
steels
Water
hardening
(W-series)
Oil
hardening
(O-series)
Air
hardening
(A-series)
High
carbon
high
chromium
(D-series)
Hot work
tool steels
(H-series)
High
speed tool
steels
Special
purpose
tool steels

Water hardening tool steels
 Composition: % C = 0.6-1.4%
 Properties:
 Used when maintenance of sharp cutting edges and wear resistance are more
important that shock resistance
 Poor hardenability, thus hardened by water, and hence known as water
hardening steels
 Applications: Blanking dies, threading dies, tube drawing dies, drills, forming
tools, hammers, chisels, wood working tools, shear blades, knives and razors
 Drawbacks:
 Poor red hardness and strength
 More distortions
 Shallow hardening type
 More tendency of oxidation, decarburisation and grain coarsening
 To eliminate this drawbacks, small amount of Cr, V and Mo are added

Oil hardening tool steels
 Also known as oil hardening non-shrinkage (OHNS) steels
 Composition: 1% C, 0.95% Mn, 0.5% W, 0.75% Cr, 0.2% V and small
amounts of Mo
 Better hardenability than water hardened steels and can be hardened by oil
quenching
 Less expensive than other tool steels
 Distortion during hardening is less and hence called as oil hardening non-
shrinkage tool steels
 Applications: Blanking and forming dies, shear blades, master tools, cutting
tools and gauges

Air hardening tool steels
 Contain alloying elements like Mn, Cr, Mo and W.
 Total alloying elements is > 5%
 Properties:
 High hardenability
 Less distortions
 High wear resistance and good depth of hardening
 Applications: Thread rolling and slitting dies, drawing dies, intricate die
shapes, gauges and punches

High carbon high chromium (HCHC) steels
 High hardenability and hence can be hardened by oil or air quenching
 Less distortions
 Composition: % C > 1.5 and some grades contain % C > 2, % Cr = 12, with
some other alloying elements like W, Mo, and V
 Thus, amount of complex alloy carbides is more which increases hardness and
wear resistance of steels, but these are difficult to machine
 Maintain hardness upto 550ᵒ C due to presence of alloy carbides
 Applications: Drawing dies, blanking dies, forming dies, coining dies, thread
rolling dies, trimming dies, bushings, shear blades, punching, cold forming
rolls, cutting tools, gauges etc
 Oil hardening, air hardening and HCHC show less distortion during hardening
and hence are called as non-deforming or non-shrinkage tool steels

Hot work tool steels
 Composition: % C = 0.35-0.65 with alloying elements varying from low to
high content
 Properties:
 Good strength, toughness, hardness and wear resistance at elevated
temperatures
 Excellent resistance to tempering at elevated temperature
 Depending upon principal alloying elements, classified as;
 Chromium type tool steels:
 Composition: % C = 0.35-0.55, 3-7% Cr, with small amounts of W, Mo and V
 Properties: High ductility, toughness and resistance to splitting
 Applications: Aluminium and Magnesium die casting dies, extrusion dies,
forging dies, mandrels and hot sheers
 Tungsten type tool steels:
 Composition: % C = 0.3-0.5, 2-12% Cr, 9-18% W
 Properties: Excellent red hardness and resistance to wear at elevated
temperature
 Applications: Dummy blocks, hot extrusion dies for brass, nickel and steel,
forging dies and hot punches

Hot work tool steels
 Molybdenum type tool steels
 Composition: % C = 0.55-0.65, 14-20% alloying elements like Mo, Cr, V and
W
 Properties: Intermediate properties
 Applications: Used when compromise in resistance to high temperature and
toughness is required
Dummy block and its use

High speed steels (HSS)
 Properties:
 Maintain high hardness upto temperature of about of 550ᵒ C and hence cane be
used for cutting metals at high speeds
 High wear resistance and cutting ability.
 Classification depending upon principal alloying elements:
 T-type HSS [18:4:1 steels/ Tungsten steels]:
 Composition: 0.7% C, 18% W, 4% Cr, 1% V
 M-type HSS [Molybdenum steels]:
 Composition: 0.85% C, 6% W, 5% Mo, 4% Cr, 2% V
 Properties: Low cost compared to T-type; Difficult to heat treat because of
more tendency of oxidation, decarburization and grain growth as compared to
T-type steels
 W, Mo, Cr and V are carbide formers and hence increase red hardness, wear
resistance and cutting ability at high temperatures
 V increases resistance to grain coarsening. Super high speed steel contains 5%
V
 Applications: Drills, taps, milling cutters, saw blades, lathe tools, punches,
drawing dies and wood working tools etc

High speed steels (HSS)
M-series drill bits with titanium
coating
Drawing diesMilling cutter
Taps
Wood working tools

Stellites
 Composition: 30% Cr, 19% W, 2% C, 3.5% Ni and rest Co
 Properties:
 Excellent red hardness, wear resistance and corrosion resistance
 Difficult to machine hence cast to rough shape followed by grinding to final
shape
 Applications:
 Used in single point cutting tool where they brazed to mild steel shank
 Small milling cutters may be cast entirely from stellite while large ones are of
mild steels with brazed stellite inserts

Stainless steel
 Have high corrosion resistance and hence they do not corrode in most of the
usual environment conditions; hence called stainless steels
 Exhibits extraordinary corrosion resistance due to formation of a very thin
layer hydrous chromium oxide is formed on the surface
 Composition of the alloy varies from alloy to alloy and with treatment of alloy
such as rolling, pickling and heating; and thus corrosion resistance also varies
 For sufficient corrosion resistance, minimum Cr content in solid solution form
should be greater than 12%
 When Cr added to steel, it first combines with carbon and form complex
chromium carbides and remaining goes in solid solution form
 Since the Cr chromium going with carbon is 17times the amount of carbon, the
Cr is solid solution form will be:
Cr in solid solution form = Total Cr – 17 x %C
 Higher the Cr is solid solution form and lesser the amount of carbides, the
corrosion resistance is more
 In addition to Cr, many other elements like Ni, Mn, Mo, Ti, Nb, Ta etc are
added to improve the properties

Stainless steel
 Properties of stainless steel:
 Corrosion resistant
 High ductility and formability
 Good mechanical properties at low and high temperatures
 High resistance to scaling and oxidation at elevated temperatures
 Good weldability
 Good machinability
 Good creep resistance
 Excellent surface finish and appearance
 Types of stainless steel:
 Martensitic stainless steel
 Ferritic stainless steel
 Austenitic stainless steel
 Precipitation hardened stainless steel

Martensitic stainless steel (Group A)
 Amount of Cr in solid solution form is
less than 13% i.e.
% Cr – (17 x % C) < 13
 Shows austenitic phase at high
temperature and hence can be hardened
by martensitic transformation. Thus,
called as martensitic stainless steel
 Properties: Hard, wear resistant,
corrosion resistant and magnetic in
nature
 Typical mechanical properties in
hardened condition;
 Y. S. = 1200MPa, U. T. S. = 1300 MPa,
% elongation = 5
 Composition of AISI 410: 12-14% Cr,
< 0.15 %C
 Applications: Springs, ball bearings,
valves, razors and razor blades, surgical
instruments, cutting tools, cutlery items
etc
Surgical instruments

Ferritic stainless steel (Group B)
 Amount of Cr in solid solution form is greater than 13% i.e.
% Cr – (17 x % C) > 13
 Cr is ferrite stabiliser and at 12.5% Cr austenitic phase disappears, thus steels
containing more than 13% Cr show only ferrite from room temperature to high
temperature and are called ferritic stainless steel
 Cannot be hardened by martensitic transformation
 Properties: High corrosion and oxidation resistance as compared to group A,
soft, ductile, malleable and magnetic in nature, low cost (absence of Ni), good
formability
 Typical mechanical properties in annealed condition;
 Y. S. = 350MPa, U. T. S. = 550 MPa, % elongation = 30
 Composition of AISI 430: 14-18% Cr, < 0.12% C, with small amounts of Mo,
V
 Applications: Vessels in chemical and food industries, pressure vessels,
furnace parts, heaters, heat exchangers, juice carrying pipes in sugar industries,
restaurant equipments, pots and pans etc

Austenitic stainless steel (Group C)
 Includes at least 24% of total of Cr, Ni and Mn
 Ni and Mn are austenitic stabilizers and hence these steels contain austenite at
room temperature and called as austenitic stainless steel
 Composition of AISI 202: 17-19% Cr, 4-6% Ni, 7-10% Mn, < 0.15% C,
0.25% N
 Properties: Soft, ductile, malleable (more than group B), non-magnetic,
excellent cold forming strength, high temperature strength, high coefficient of
thermal expansion, low thermal conductivity, high corrosion resistance (more
than group A and B, because of high amount of nickel and chromium)
 Applications: Engine manifolds, food and chemical plants, tubular
exchangers, utensils, wrist watches, sanitary fittings etc

Precipitation hardened stainless steel
 Contains elements such as Mo, Co, Ti, N, Cu, Al in addition to basic elements
Cr and Ni
 Maintain high strength upto 550ᵒ C
 Applications: Aircraft and missile industries for skins, bulk heads and other
structural components

Super alloys (High temperature alloys)
 Properties: High strength, high hardness and wear resistance , high creep
resistance and high oxidation resistance at elevated temperatures
 Super alloys can be iron base alloys, nickel base alloys, cobalt base alloys or
refractory metals or alloys
 Iron base alloys:
 Contain W, Mo, V and Cr as alloying elements
 High speed steels and super high speed steels belong to this category
 Nickel base alloys:
 Contain Mo, Cr and Co
 Inconels, hastealloys, nimonics and waspalloy are some of the alloys
belonging to this category
 Composition of nimonic alloy: 0.2% C, 10% Cr, 20% Co, 5% Mo, 5% Al,
1.3% Ti and rest Ni
 Cobalt base alloys:
 Contain Mo, Cr, Ni and rest Co
 Stellites and Vitallium are some of the alloys belonging to this category

Super alloys (High temperature alloys)
 Refractory metals and alloys:
 Metals like W, Mo, Cr, Co and their alloys; ceramic materials like silicon
nitride; cermets (refractory ceramics) such as Al2O3 and TiC embedded in Ni-
Cr matrix are extensively used for high temperature applications
 Applications: Aircraft turbine components, petrochemical equipments,
nuclear reactors components etc

Introduction
 Alloys of iron and carbon in which % C varies between 2-6.67%
 Poor ductility and malleability; hence cannot be forged, rolled, drawn or
pressed into desired shape
 Named “CAST IRONS”, because the components are formed by melting and
casting with or without machining to the required final shape and size
 Properties:
 Cheap
 Lower melting temperatures (1150-1250ᵒ C) as compared to steels (1350-
1500ᵒC)
 Excellent castability
 Corrosion resistant
 Brittle
 Properties can be adjusted by suitable alloying elements and heat treatment

Classification of cast irons
Furnace
Cupola CI
Air
furnace
CI
Electric
furnace
CI
Duplex CI
Composition and purity
Low
carbon, low
silicon CI
High
carbon, low
sulphur CI
Nickel
alloy CI
Microstructure and appearance of fracture
White CI Malleable
CI
Gray CI
Nodular
CI
Mottled
CI
Chilled CI Alloy CI

White cast iron
 Carbon present in combined form (cementite)
and there is no free carbon (graphite)
 Composition: C: 2.3-3%, Si: 0.5-1.3%, S: 0.06-
0.1%, P: 0.1-0.2%, Mn: 0.5-1%
 Named after its white fractured surface
 No graphitisation and hence its solidification can
be represented on I-C diagram
 Properties: Strong in compression (1750MPa),
hard (350-500 BHN), resistant to abrasive wear,
brittle, difficult to machine hence finishing to
final size is done by grinding only
 Used to malleable CI
 Applications: Pump liners, Road roller surfaces,
mill liners, grinding balls, dies and extrusion
nozzles
Microstructures of white CI:
the light cementite regions
are surrounded by pearlite,
which has the ferrite
cementite layered structure.
200x [Source: William
Callister, 2007]

Malleable cast iron
 Heating white cast iron around 900ᵒ C and holding
for long time (24hrs to several days), followed by
very slow cooling to room temperature produces
malleable cast iron
 Contains 2.5% C and 1% Si
 Cementite decomposes during the heat treatment to
more stable form (graphite)
 The free carbon precipitates in the form of
spheroidal particles (temper carbon)
 Properties:
 Show ductility, toughness and are bendable
 Good capacity to absorb shock and vibrations
 NOT MALLEABLE; cannot be rolled, forged or
extruded
 T. S. = 700MPa, % elongation = 10-15%, Hardness
= 80-275 BHN
 More expensive than grey cast iron because of heat
treatment involved
 Applications: Automobile crankshaft, chain links
and brackets, brake pedals, tractor springs, universal
joint yoke
Microstructure of
malleable CI: dark
graphite rosettes (temper
carbon) in an α-ferrite
matrix. 150x [Source:
William Callister, 2007]

Malleable cast iron
 Types of malleable cast iron:
 Ferritic malleable
 Pearlitic malleable
 Pearlitic-ferritic malleable
 Black heart malleable
 White heart malleable

Pearlitic-ferritic malleable cast iron
 Produced due to intermediate cooling rate between
those to produce ferritic malleable and pearlitic
malleable cast irons
 Cooling rate is slow enough to graphitise all the
proeutectoid cementite and a part of eutectoid
cementite
 Since carbon itself is a graphitiser, the cementite
from pearlite adjacent to the existing rosettes of
temper carbon graphite decomposes rapidly without
graphitising cementite away from the rosettes
 Thus, microstructure at room temperature shows
rosettes of temper carbon graphite surrounded by an
envelope of ferrite
 Matrix is coarse pearlite or slightly spherodised due
to slow cooling
 Properties: Intermediate to ferritic and pearlitic
cast iron
 Applications: Machinery parts such as rolls,
pumps, nozzles, cams and rocker arms; axle and
differential housing, cam shaft and crankshaft
Microstructure of pearlitic
ferritic malleable cast iron
showing bull’s eye
structure. 100x [Source: V.
D. Kodgire, 2009]

Grey cast iron
 Show gray fracture and contain graphite flakes
 Flakes are curved plates, interconnected in three
dimensions
 Graphite formed during freezing
 Graphite flakes are sharp at their tips and act like internal
cracks or stresses
 Composition: 2.5-3.8% C, 1.1-2.8% Si, 0.4-1% Mn,
0.15%P and 0.1% S
 Properties: Depend upon morphology and size of
graphite flakes
 Brittle, weak in tension, strong in compression (as cracks
do not propagate under compressive load)
 High fluidity and hence it can be cast into complex shapes
and thin sections easily
 Low shrinkage during solidification
 Good wear resistance because graphite acts as lubricant
 Better damping capacity than steel
 Low notch sensitivity due to the presence of large number
of internal sharp notches (edges of graphite flakes) which
make the influence of external notch ineffective
 Easy to machine, as chip formation is promoted by
graphite flakes. Also flakes serve as lubricant for cutting
tool
 Good bearing properties
 Fairly good corrosion resistance
Microstructures of Gray iron:
the dark graphite flakes are
embedded in an –ferrite
matrix. 500x [Source: William
Callister, 2007]

Grey cast iron
 Low ductility and impact strength
 T. S. = 150-400MPa, Hardness = 150-300BHN, % elongation = < 1%
 Cheaper than steel (low temperatures involved in casting and low control on
impurities as compared to steel)
 Defects:
 Growth
 Firecracks or heat checks
 These defects can be reduced by adding Cr, Mo and Ni
 Applications: Manhole covers, M/c tool structures like bed, frames; Cylinder
block and head of IC engine, Gas or water pipes for underground purpose,
flywheels etc, elevators etc
Engine cylinder blockManhole covers

Nodular (Ductile or Spheroidal) cast iron
 Contains graphite in the form of spheroids
 Produced from grey cast iron by adding nodulising
elements like Mg, Ca, Ba, Li, Zr or Ce
 Composition: 3.2-4.2% C, 1.1-3.5% Si, 0.3-0.8% Mn,
0.08% P, 0.2% S
 Since nodulising elements have strong affinity for
sulphur and they scavenge sulphur from the molten bath
as an initial step in producing nodular graphite. These
elements are expensive and hence for effective
utilization of these elements, the original grey melt must
contain less amount of sulphur (< 0.03%). Sulphur
content is reduced by treating the melt with soda ash
 Properties:
 More tensile strength, ductility and toughness as
compared to grey cast iron
 Excellent machinability, castability and wear resistance
 Do not suffer from defects like growth and firecracks
 T. S. = 400-800MPa, % elongation = 10-18, Hardness =
100-300 BHN
 Defects:
 Blow holes
 Shrinkage
 Applications: Agricultural implements, industrial fan
hub, Crankshafts, gears, punch dies, sheet metal dies,
steel mill rolls and milling equipment, valves, pistons etc
Microstructure of nodular
CI: the dark graphite nodules
are surrounded by an -ferrite
matrix. 200x [Source:
William Callister, 2007]

Pistons Universal joint yoke
Tractor springs
Flywheel
Valve
Pump liner

Mottled cast iron
 Shows free cementite and graphite flakes
in its microstructure
 Composition: 93.5% iron, 1.75%
graphite, remaining impurities
 For a given composition, faster cooling
rates gives white structure and slow
cooling rates results in grey structure.
Intermediate cooling rates produces
mottled cast iron
 Mottled structures to be avoided because
of bad properties
 Can be avoided by increasing or
decreasing carbon and silicon content
 Increasing carbon and silicon content
yields grey cast iron
 Decreasing carbon and silicon content
yields white cast iron
Microstructure of mottled cast
iron. 500x [Source: V. D.
Kodgore, 2009]

Chilled cast iron
 Shows white structure at surface and grey
structure in centre
 Composition is adjusted in such a way that
rapid cooling gives white structure and usual
cooling gives grey structure
 Composition: % C: 3.3-3.5, %Si: 2-2.5
 Surface cooled rapidly by metal or graphite
chillers or chill plates
 Depth of chill can be controlled by
controlling the carbon and silicon contents
and by other alloying additions which are
either carbide formers or graphitisers
 Increase in % C, silicon and graphitizers
decreases chill depth and viceversa
 Properties:
 Hard and wear resistant
 Good machinability
 Good damping capacity
 Low notch sensitivity
 Applications: Railway freight car wheels,
crushing balls, road rollers, hammers, dies
etc
Chiller plates

Mechanite
 Also called as high duty cast iron OR inoculated grey cast iron
 Adding inoculants (ferro-silicon with 75% Si, calcium silicate etc) to the liquid
cast iron in the ladle before pouring into the moulds
 Additions of calcium silicate produces fine and uniform size graphite flakes
 Composition of the moulds melt is adjusted in such a way that it will give
either white or mottled structure, if cast without additions of inoculants
 Composition: 2.9-3.2% C, 1-1.5% Si, 0.8-1.2% Mn, < 0.3% P, <0.12% S
 Due to the additions of inoculants, which are predominantly graphitizers, the
structure obtained after solidification is grey with fine and random distribution
of flakes
 Properties:
 High strength and machinability as compared to ordinary CI
 Applications: Machine parts subjected to wear such as gears, brake drums,
steam engine cylinders etc

Effect of cooling rate microstructure of cast iron
 Rapid cooling: Suppresses graphitization – white
 Slow cooling: Favors graphitization – grey
 Thus, different structure in thin and thick sections of a
casting or in large casting in which cooling rate varies
for centre to surface
 Relative content of carbon and silicon determines
whether CI contains cementite, graphite or both
 Region I – Cementite is stable and structure is of white
cast iron
 Region II – Sufficient cementite to cause graphitization
of all cementite except eutectoid cementite (i.e.
cementite in pearlite) and structure is of grey cast iron
with pearlite matrix
 Region IIa – Structure is of mottled cast iron
 Region IIb – Matrix is pearlitic-ferritic
 Region III – Large amount of silicon promotes
decomposition of cementite and results in formation of
ferrite and graphite, giving grey cast iron with ferrite
matrix
 Amount of graphite can be controlled by controlling the
total carbon and silicon
 Shape, size and distribution of graphite can be
controlled by adding certain alloying elements
 Matrix can be controlled by controlling cooling rate or
suitable heat treatment
 Thus, it is easy to control the properties of cast iron over
a wider limit and its low cost makes it suitable for
general purpose applications
Effect of cooling rate on
microstructure of cast iron
[Source: V, D. Kodgire, 1991]

Introduction
 Steel and other ferrous alloys are consumed in exceedingly large quantities
because they have such a wide range of mechanical properties, may be
fabricated with relative ease, and are economical to produce.
 However, they have some distinct limitations, chiefly: (1) a relatively high
density, (2) a comparatively low electrical conductivity, and (3) an inherent
susceptibility to corrosion in some common environments.
 Thus, for many applications it is advantageous or even necessary to utilize other
alloys having more suitable property combinations.
 Alloys that are so brittle that forming or shaping by appreciable deformation is
not possible ordinarily are cast; these are classified as cast alloys.
 Alloys that are amenable to mechanical deformation are termed wrought alloys.

Properties of copper and its alloys
 FCC Structure
 Soft, Ductile, tough and difficult to machine
 Can be cold worked
 Good corrosion resistance in diverse environments including the ambient
atmosphere, seawater, and some industrial chemicals
 High electrical (second only to silver) and thermal conductivity
 Reddish in color and non-magnetic
 Antibacterial
 Easily joined by brazing and soldering
 Low strength to weight ratio than Al and Mg alloys
 Better resistance to fatigue, creep and wear than Al and Mg alloys
 Usual alloying elements added to copper are Zn, Al, Sn, P, Be, Si, Ni, Mn, Mg,
Fe and Pb
 Alloys of Cu:
 Brass: Alloy of Cu and Zn
 Bronze: Alloys of copper and several other elements, including tin, aluminum,
silicon, and nickel

Brasses
α-brass α-β brass
Contains Zn < 30% Contains Zn between 30-40%
Expensive (since Zn is cheaper than Cu) Cheap
Soft and ductile Hard and strong
Good corrosion resistance than α-β brass Poor corrosion resistance than α-β brass
Cold worked Hot worked
Eg: Cap copper, gliding metals, cartridge
brass, admiralty brass
Eg: Muntz metal, Naval brass, leaded brass,
High tensile brass, brazing brass
Classification of brasses

Brasses
Classification Sub-classification Composition Uses
α-brass
Cap copper Cu: 95-98%, Zn: 2-5%
Caps of detonators in
ammunition factories
Gliding metals Cu: 85-95%, Zn: 5-15%
Bullet envelopes, drawn
containers, condenser
tubes, coins, needles,
emblems, dress-jewelry
Cartridge brass
(70/30 brass)
Cu: 70%, Zn: 30%
Cartridge cases, radiator
fans, lamp fixtures,
rivets and springs
Admiralty brass
Zn: 22%, Al: 2% , Sn: 1%,
As: 0.04% , remaining Cu
Condenser tubes and
heat exchangers in
steam power plants,
marine applications

Brasses
Classification Sub-classification Composition Uses
α-β brass
Muntz metal
(60/40 brass)
Cu: 60%, Zn: 40%
Utensils, shafts, nuts and
bolts, pump parts,
condenser tubes and
similar applications
where corrosion is not so
severe
Naval brass
(Tobin bronze)
Cu: 60%, Zn: 39%, Sn:
1%
Marine hardware,
propeller shafts, piston
rods, nuts and bolts,
welding rods
Brazing brass Cu: 50%, Zn: 50% Brazing
High tensile brasses
(Alloying elements
like Al, Fe, Mn, Sn,
Ni added to 60/40
brass)
Eg: Manganese bronze =
Cu: 58%, Zn: 39%, Mn:
1%, Fe: 2% )
Marine engine pumps,
ship propellers, gears,
valve bodies

Bronzes
 Aluminum bronze:
 Alloy of Al and Cu in which Cu is base metal and Al is alloying element
 Commercial aluminum bronzes contain 4-11% aluminum
 Other alloying elements like Fe, Ni, Mn and Si may be added
 Properties:
 Good strength, ductility and toughness
 Good bearing properties
 Good corrosion resistance
 Good fatigue resistance
 These alloys are lustrous and their color is the finest of all the Cu alloys and hence
they are frequently named as imitation gold
 Alloys with 4-7% Al :
 Single phase alloys
 Can be fabricated by cold working processes such as drawing, pressing, rolling etc
because of their good ductility and malleability.
 Properties: In annealed state, they show tensile strength of 35MPa with elongation
of over 50% and hardness in the range of 80-90VPN
 Applications: Available in sheet, plate and tube forms and are used in jewelry,
cigarette cases, heat exchangers, chemical plants etc

Bronzes
 Alloys with 8-11% Al :
 Two phase alloys
 Can be cast, hot rolled, or forged
 Properties: Sand cast alloys show tensile strength of 45-55MPa with elongation
between 20-30%. Hot worked alloys show better mechanical properties not only
at room temperatures but also at elevated temperatures.
 Applications: Pump castings, valve fittings, propellers, cylinder heads, gears,
dies, bearings, spark plug bodies and electrical contacts

Bronzes
 Tin bronze:
Name Composition Uses
Coinage
bronze
Cu: 94% , Sn: 5%, Zn: 1% Coins
Gun metal Cu: 88% , Sn: 10%, Zn: 2%
Gun barrels and ordnance parts, marine
castings, gears, bearings, valve bodies
and similar applications
Phosphor
bronze
Wrought phosphor bronze:
Sn: 2.5-8%, P: 0.1-0.35%, rest
Cu
Springs, wire gauges, wire brushes and
electrical contacts
Cast phosphor bronze:
Sn: 5-13%, P: 0.3-1%, rest Cu
Gears, bushings, slide valves and similar
applications
Statuary
bronze
Cu: 86% , Sn: 10%, Zn: 2% ,
Pb: 2%
Statues
80-10-10
bronze
Sn: 9-11%, Pb: 8-11%, rest Cu
High speed heavy pressure bearings and
bushings
80-5-5-5
bronze (Ounce
metal)
Cu: 85% , Sn: 5%, Zn: 5%, Pb:
5%
Bearings, low pressure valves, taps and
pipe fittings, small gears

Bronzes
 Beryllium bronze:
 Beryllium bronze contain 1.5-2.25% Be, which is
responsible for precipitation hardening treatment
 Solid solubility of Be in Cu is 2.1% at 864ᵒ C and
decreases to less than 0.2% at room temperature
 Precipitation hardening treatment:
 Heating the alloy at around 800ᵒ C for half hour and
quenching in water (Solution treatment)
 Cold working to improve the tensile strength
 Heating the alloy at around 300-320ᵒ C for 1-2 hours
(Precipitation or aging treatment)
 By a combination of cold work and precipitation , the
alloy with about 2% Be shows a tensile strength of
1300MPa and hardness of 350BHN
 Properties: Good corrosion resistance, fatigue
resistance, high resilience, good bearing properties and
non-sparking characteristics
 High cost and hence used only when other alloys do not
fulfill the requirements
 Applications: Springs, Diaphragms, Flexible bellows,
gears, bearings, certain tools like hammers requiring
hardness and non-sparking characteristics, moulds for
forming of plastics
Flexible bellows

Bronzes
 Silicon bronze:
 Alloy of Cu and Si
 Solubility of Si in Cu is 5.3% at 845ᵒ C and decreases to less than 4% at room
temperature
 Si content in these alloys varies between 1-5.5%
 Elements like Mn, Fe, Zn, Sn and Pb are added to increase strength and
machinability
 Properties: High resistance to corrosion, high tensile strength, high toughness,
cheaper than tin bronzes, Can be cast, cold worked and hot worked
 Produced in the form of strips, plates, wires, rods, tubes, pipes and castings
 Applications: High strength bolts, rivets, springs, propeller shafts of marine
vehicles, bells, handrails, fountains, bells

Cu-Ni alloys
 Cu and Ni are completely soluble in each other
 Properties:
 Ductile and malleable
 Can be cold worked and hot worked
 Corrosion resistance increases with increase in Ni content
 Tensile strength, proof stress and fatigue strength increases rapidly with Ni
content and reach to maximum in the range of 60-70% Ni and decreases with
further increase in Ni content

Cu-Ni alloys
Name Composition Properties Uses
Constantan Cu: 55%, Ni: 45%
High electrical resistivity,
zero coefficient of thermal
expansion over a temperature
range of 20-350ᵒ C
Resistors,
Thermocouples
Cupro-
nickel
Ni: 15-30%, rest Cu
Excellent resistance to
corrosion
Marine condensers,
turbine blades, bullet
envelopes and coins
Ni: 40-60%, rest Cu
High resistance and small
temperature coefficient of
resistance
Resistance wires in
electrical instruments
Ni: 70%, Cu: 30%
Excellent corrosion
resistance in salt water, oils
containing brines and sodium
sulphide, alkaline solutions;
Retains high strength at
elevated temperatures
Turbine blades, valve
parts, impellors and
parts in chemical
industries
 Applications:

Cu-Ni alloys
German
silver
(Nickel
silver)
Single phase:
Cu: > 60%, Ni: 5-30%,
Zn: 5-40%
Ductile, Malleable, Can be
cold worked, Silver-blue
white color, Good resistance
to action of food chemicals,
water and atmosphere
Rivets, Screws,
custom jewelry,
name plates, radio
dials, camera and
optical parts
Two phase:
Cu: 50-60%, Ni: 5-
30%, Zn: 5-40%
Can be hot worked
Springs, Contacts in
electrical and
telephone equipment,
resistance wires,
surgical and dental
equipment
 Applications:

Applications of copper (Cu) and its alloys

Properties of aluminum and its alloys
 FCC Structure, Ductile and malleable
 Can be hot worked and cold worked
 Light in weight (Density = 2.7 g/cc)
 Good thermal and electrical conductivity (Carries more electricity than Cu)
 Excellent ability to get alloyed with other elements Cu, Si, Mg, Mn, Zn etc.
Some alloys respond to precipitation hardening, some have excellent castability
 Excellent corrosion and oxidation resistance due to the formation of Al2O3 film
on metal surface
 Al2O3 is non-toxic and hence makes it suitable for food packaging
 Remains ductile and tough upto -40ᵒ C and hence finds applications in
refrigeration and cryogenic services
 Non magnetic, non sparking in character
 High reflectivity for heat and radiant energy
 Powerful deoxidiser
 Powerful grain refiner, thus results in improved mechanical properties and
surface finish

Aluminum alloys
Magnalium
Al: 94.5% , Mg: 5%,
Mn: 0.5%
High corrosion resistance,
machinability, Surface
finish, good strength
Marine applications
Duralumin
Al: 94% , Cu: 4%,
Mg, Mn, Si, Fe:
0.5% each
High tensile strength after
precipitation hardening,
good electrical conductivity
Used in aircrafts
industries in the form
of sheets, tubes,
rivets, bolts, plates,
etc
Y-alloy
Al: 92.5%, Cu: 4%,
Ni: 2%, Mg: 1.5%
Excellent ability to retain
strength at elevated
temperatures, good
corrosion resistance, Can be
easily cast
Piston and cylinder
heads of diesel and
high duty petrol
engines
Hinduminium
Cu: 5%, Ni: 1.5%,
with small additions
of Mn, Ti, Sb, Co, Zr
and rest Al
Superior to Y alloy at
elevated tempearatures
Aero-engine
components

Precipitation (Age) hardening
 Types:
 Natural aging: Precipitation with time at room temperature
 Artificial aging: Precipitation at higher temperatures (120-300ᵒ C)
 It is observed in Al-4.5% Cu, Al-6% Zn-2.5% Mg, Cu-2%Be, Ni-17% Cu-8% Sn,
etc
 Conditions for age hardening to occur:
 Solubility of solute in the solvent must decrease with decrease in temperature
 Precipitate that separates out from the matrix should be coherent. (Coherent
precipitation means that the solute atoms concentrate to a degree sufficient to give
the composition of second phase)
 Coherent particles are powerful obstacles to the motion of dislocations and thus the
hardness increases
 Aging time varies between 2-24 hours
 Spontaneous decomposition of supersaturated solution takes place during aging
treatment
 Higher ageing temperature and higher the degree of saturation, more intensive will
be the aging
 High temperature aging is adopted when more stable phase is required with together
with dimensional stability. This process is also called stabilize aging
 Rise in temperature changes the atomic positions with corresponding changes in
forces associated with interatomic bonds. At the same time, distribution of second
phase particles also changes

Precipitation (Age) hardening
 Steps in precipitation hardening:
 Heating (Solutionizing):
 Alloy heated between the solvus and eutectic
temperature, say T, so that it forms a single phase
solid solution i.e. α + θ α
 Held at this temperature for homogenisation
 Quenching:
 Rapidly cooling in water to obtain supersaturated
solution (α’)
 Alloy is now solution treated condition and its
hardness is relatively low, but higher than annealed
component
 Alloy can easily cold worked in this condition to
increase the tensile strength
 Aging:
 Natural aging or artificial aging
 For artificial aging, aging temperature is roughly
between 15-25% of the temperature of difference
between room temperature and soutionizing
temperature
 Overaging decreases the hardness and hence is
stopped as soon as optimum hardness is obtained
Typical equillibrium diagram
showing decrease in solubility
with decrease in temperature
[Source: V. D. Kodgire, 2009]

Precipitation hardening of Al-4.5%Cu
system
 Equilibrium solubility of Cu in Al increases as
temperature rises
 At 250ᵒ C, the solid solubility of Cu in Al is about
0.2%
 Maximum solid solubility of Cu in Al is 5.65% at 548ᵒ
C
 Process:
 Alloy is first solutionized by heating into a single
phase region at about 490-500ᵒ C and soaking for
sufficient time for required diffusion. Cu goes in solid
solution completely
 Alloy is quenched in water to get a supersaturated
solid solution.
 If these alloy is kept for a long time at room
temperature, natural aging is said to occur. If it is
reheated slightly to higher temperatures, say 130ᵒ C,
artificial aging takes place
 Diffusion rates are very slow at these temperatures,
thus the solute atoms have limited mobility
 Thus, we obtain very finely distributed particles in a
matrix which in turn leads to increase in strength
Typical equilibrium diagram
showing decrease in solubility
with decrease in temperature
[Source: V. D. Kodgire, 2009]

Applications of aluminum (Al) and its alloys

Properties and applications of magnesium and
its alloys
 Properties:
 HCP structure
 Light in weight (Density = 1.7 g/cc)
 Difficult to deform at room temperatures and hence are difficult to cold work. Thus
are fabricated by casting and hot working at temperatures between 200-350ᵒ C
 Low melting point (650ᵒ C)
 High strength to weight ratio
 Good damping capacity
 Relatively high thermal and electrical conductivity
 Good dimensional stability upto 100ᵒ C
 Fine Mg powder ignites easily when heated in air
 Susceptible to corrosion in marine environments
 Good corrosion and oxidation resistance in normal environments
 Usual alloying elements added to magnesium are Al, Zn, Mn etc
 Solutionizing treatment improves the strength and gives very good toughness and
shock resistance to Mg alloys
 Precipitation hardening after solutionizing treatment of Mg alloys improves
hardness and strength , while the hardness decreases by a marginal amount

its alloys
 Applications: Wrought form of Mg alloys are used in aircraft fuel tanks, ducts,
wings and flaps in the form of sheets. The extrusions are used in the seat frames.
Cast form of Mg alloys are used in jet engine parts, landing wheels, helicopter
gearbox housing, cockpit canopies and missile bodies. Also used in hand-held
devices (e.g., chain saws, power tools, hedge clippers), in automobiles (e.g.,
steering wheels and columns, wheels seat frames, transmission cases), and in
audio-video-computer-communications equipment (e.g., camcorders, TV sets,
cellular telephones).

its alloys
Chain saws
Hedge clippers
Seat frameWheels

Properties and applications of titanium and
its alloys
 Properties:
 Density of titanium is midway between aluminum and steel (4.5g/cc)
 High melting point (1668ᵒ C)
 High elastic modulus (107 GPa)
 Excellent corrosion resistance at normal temperatures in wide range of
environments
 High tensile strength at room temperature (1400MPa)
 Highly ductile and can be easily forged and machined
 Titanium chemically reacts with other materials at elevated temperatures. This
property has necessitated the development of nonconventional refining, melting,
and casting techniques; consequently, titanium alloys are quite expensive
 Used as substitute for aluminum alloys in aircraft structure subjected to a
service in the temperature range of 200-500ᵒ C
 Applications: Airplane structures, space vehicles, surgical implants, and in the
petroleum and chemical industries, heat exchangers

Properties and applications of titanium and its
alloys
Heat exchangers of titanium alloys

Properties of nickel and its alloys
 FCC structure
 Ductile and malleable
 White in color
 Good resistance to corrosion and oxidation
 Good electrical conductivity (Not so good as Cu and Al)
 Good ability to get alloyed with other materials

Nickel alloys
Dura Nickel
Ni: 94%, Al: 4.5%
with elements like C,
Mn, Fe, S, Si, Cu and
Ti in small amounts
Age hardneable, Good
corrosion resistance
Laundry clips,
jewelry parts, optical
frames, diaphragms,
bellows, fish-hooks
Hastelloy D
Ni: 87%, Si: 10%,
Cu: 3%
Good strength and toughness,
high hardness, difficult to
machine, Excellent corrosion
resistance to sulphuric acid at
elevated temperatures
Evaporators,
Reaction vessels,
pipelines and fittings
in chemical industry
Invar
Ni: 36% , C: 0.2%
and Mn: 0.5%, rest
Fe
Zero coefficient of thermal
expansion in the range of 0-
100ᵒ C
Length standards,
measuring tapes,
instrument parts,
variable condensors,
tuning forks and
special springs

Nickel alloys
Elinvar
Ni: 36%, Cr : 12%
and rest Fe
Zero coefficient of thermal
expansion in the range of 0-
100ᵒ C
Hair springs, balance
wheels in watches
and for similar parts
in precision
instruments
Inconel
Ni: 77%, Cr: 15%,
Fe: 8%
Good corrosion and oxidation
resistance, Maintains good
strength at elevated
temperatures, Good ability to
withstand repeated heating
and cooling cycles in the
range of 0-875ᵒ C
Exhaust manifolds of
aero engines, furnace
parts, carburising
boxes, retorts,
thermocouple
protection tubes and
food processing
equipments
Inconel X
Cr: 15%, Fe: 8%, Ti:
2.25-2.75%, Al: 0.4-
1%, rest Ni
Precipitation hardened
inconel, Maintains good
strength upto 800ᵒ C
Springs used at
elevated temperature,
gas turbines and jet
propulsion parts

Nickel alloys
Monel metal
Ni: 66%, Cu: 29%,
Al: 2.75%, small
amounts of Fe, Si,
Mn, C
Good corrosion resistance and
good strength
Parts of water pumps,
propellers, valve
seatings in light alloy
cylinder heads,
components that are
in contact with some
acid and petroleum
solutions
Alnico
Ni: 14-28%, Al: 8-
12%, Co: 5-35%, rest
Fe
Excellent magnetic propeties
Used as permanent
magnets in motors,
generators, radio
speakers, telephones,
microphones and
galvanometer
Permalloys Ni: 78%, Fe: 22%
High magnetic permeability
under even very weak
magnetizing forces, Low
hysteresis losses and low
electrical resistivity
Loading coils in
electrical
communication
circuits

F. BEARING MATERIALS
(SLIDING BEARINGS)

Properties/ Requirements of bearing
material
 Less friction to reduce power loss in transmission
 Hard and wear resistant for longer life (Not harder than shaft)
 Sufficient load bearing ability at low and high temperatures
 Sufficient plasticity and deformability to take care of large deflection and
misalignment of shaft
 High fatigue resistance
 Good resistance to galling and seizing
 Good thermal conductivity
 Should not have very high or low melting point
 High oil retaining capacity
 Good corrosion resistance
 Cheap and readily available

Babbit bearing (White metal alloys)
%
Composition
Sn Pb Sb Cu Others
Pb- based 1-10 Balance 10-15 1.5-3.5 Cd: 1.25-1.75, As: 0-1
Sn-based Balance Upto 10 5-12 3-5 As: 0-0.1
Composition:
Tin based (Cu additions) Lead based

Babbit bearing (White metal alloys)
 Microstructure: Consists of hard cuboids of Sn-Sb in a soft matrix. In addition
to these hard needles of CuSn and hard star shaped crystals of Cu3Sn, if the
babbit contains Cu
 During solidification, Sn-Sb cuboids are formed first, and being lighter than the
melt, tend to float to the surface. Due to this, bearing becomes too hard at the
top and too soft at the bottom. This trouble is added by rapid cooling or addition
of Cu
 With both the methods, a more uniform distribution of cuboids is observed in a
matrix of binary or ternary eutectic with sharp increase in performance and life
of bearing
 Properties:
 Tin based bearings have better corrosion and wear resistance as compared to
lead based bearings
 Tin based bearings are more costly than lead based bearings
 Lead based bearings have low load bearing ability than tin based bearings
 Applications: Diesel engine crankshafts

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