details about steel and steel alloys

1. Chapter No-02
Steels and Alloy of steels
(Iron-carbon alloys containing appreciable concentration of other alloying
elements; contain ≤ 2% C)
1Prof.Ghadage M.M.

2. 2
Ferrous Metals - Iron and Steel
Pure iron is soft and ductile to be of much practical use.
BUT when carbon is added, useful set of alloys are produced.
They are known as carbon steel.
The amount of carbon will determine the hardness of the steel.
The carbon amount ranges from 0.1% to 4%.
Prof.Ghadage M.M.

3. 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
3Prof.Ghadage M.M.

4. 4
Types of Steel
Steel
•Low carbon steel (mild steel)
•Medium carbon steel
•High carbon steel (tool steels)
Alloy Steels
•Stainless steel
•High speed steel
Prof.Ghadage M.M.

5. 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
5Prof.Ghadage M.M.

6. Low carbon steels
6Prof.Ghadage M.M.

7. 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 7Prof.Ghadage M.M.

8. 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
8Prof.Ghadage M.M.

9. 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
9Prof.Ghadage M.M.

10. 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
10Prof.Ghadage M.M.

11. Alloy Steels
Carbon content less than 1.2%
Alloying element of Steel :-
Mn-Manganese
Si-Silicon
Cu-Copper
Cr-Chromium
Ni-nickel
Molybdenum
Cobalt
vanadium
Example :-
•Stainless steel
•High speed steel
11Prof.Ghadage M.M.

12. Effect of alloying element on properties of alloy steel:-
1. The maximum ultimate tensile strength increased
2. Thick section are available with high hardness
3. More controlled quenching
4. Improve impact resistance
5. Improve corrosion resistance
6. Improve high temperature performance
7. Improve machinability
8. Improve high or low temperature stability
9. Better were resistance
12Prof.Ghadage M.M.

13. Effect of individual alloying element on
properties of alloy steel:-
13Prof.Ghadage M.M.

14. Properties and uses of alloying elements
 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
14Prof.Ghadage M.M.

15. Properties and uses of alloying elements
 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
15Prof.Ghadage M.M.

16. Properties and uses of alloying elements
 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
16Prof.Ghadage M.M.

17. Properties and uses of alloying elements
 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
17Prof.Ghadage M.M.

18. Properties and uses of alloying elements
 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 18Prof.Ghadage M.M.

19. Properties and uses of alloying elements
 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
19Prof.Ghadage M.M.

20. Properties and uses of alloying elements
 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
20Prof.Ghadage M.M.

21. Properties and uses of alloying elements
 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
21Prof.Ghadage M.M.

22. Properties and uses of alloying elements
 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
22Prof.Ghadage M.M.

23. Examples of alloy steels
23Prof.Ghadage M.M.

24. 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
24Prof.Ghadage M.M.

25. 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)
25Prof.Ghadage M.M.

26. 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
26Prof.Ghadage M.M.

27. 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
27Prof.Ghadage M.M.

28. 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
28Prof.Ghadage M.M.

29. 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
29Prof.Ghadage M.M.

30. 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
30Prof.Ghadage M.M.

31. TOOL STEELS
31Prof.Ghadage M.M.

32. 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
32Prof.Ghadage M.M.

33. 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
33Prof.Ghadage M.M.

34. 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
34Prof.Ghadage M.M.

35. 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
35Prof.Ghadage M.M.

36. 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
36Prof.Ghadage M.M.

37. 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
37Prof.Ghadage M.M.

38. 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
38Prof.Ghadage M.M.

39. 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 39Prof.Ghadage M.M.

40. 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
40Prof.Ghadage M.M.

41. High speed steels (HSS)
M-series drill bits with titanium
coating
Drawing diesMilling cutter
Taps
Wood working tools
41Prof.Ghadage M.M.

42. STAINLESS STEELS
42Prof.Ghadage M.M.

43. 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
43Prof.Ghadage M.M.

44. 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
44Prof.Ghadage M.M.

45. 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
45Prof.Ghadage M.M.

46. 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
46Prof.Ghadage M.M.

47. 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
47Prof.Ghadage M.M.