This document provides information on phase diagrams and the iron-carbon equilibrium diagram. It discusses key terminology related to phase diagrams including system, phase, equilibrium, component, and degree of freedom. It describes different types of reactions that can occur on a phase diagram including eutectic, eutectoid, peritectic, and peritectoid reactions. The document then focuses on the iron-carbon equilibrium diagram, outlining the different phases that can form (ferrite, austenite, cementite) and how their presence relates to classifications of ferrous alloys like cast iron, carbon steel, alloy steel, tool steel, and stainless steel. Microstructures and applications of these alloy classifications are also summarized.

1. 19UMEPC305 –
ENGINEERING METALLURGY
UNIT-II EQUILIBRIUM
DIAGRAM
1

2. Syllabus:
• Phase diagram- isomorphous, eutectic,
eutectoid, peritectic and peritectoid reactions,
Iron-carbon equilibrium diagram.
Classification of cast iron and steel- cast iron-
properties and classifications, Grey, white,
metastable, spheroidals. Microstructures- tool
steels- HSLA- Maraging steels.
2

3. PHASE DIAGRAM
• A phase diagram in physical chemistry, engineering,
mineralogy, and materials science is a type of chart used to
show conditions (pressure, temperature, volume, etc.) at
which thermodynamically distinct phases (such as solid, liquid
or gaseous states) occur and coexist at equilibrium.
• Phase diagram is a graphical representation of the physical
states of a substance under different conditions of
temperature and pressure.
3

4. PHASE DIAGRAM OF WATER
4

5. IMPORTANT TERMINOLOGIES
• SYSTEM- Any portion of the universe which is of interest
and can be studied experimentally.
• PHASE- A phase is one of the forms in which matter can
exist, such as solid, liquid, or a gas.
• EQUILIBRIUM - The condition of minimum energy for the
system such that the state of a reaction will not change
with time provided that pressure and temperature are
kept constant.
• COMPONENT - The smallest number of independent
variable chemical constituents necessary to define any
phase in the system.
5

6. • DEGREE OF FREEDOM:
State variables which can be changed
continuously and independently, e.g., pressure, temperature,
composition.
• CONSTITUENT:
The association of phases in a recognizably distinct fashion with a distinct
melting point, e.g., eutectic.
• COMPOSITION:
Fraction of one component to all the components. May be in terms of
weight or atoms.
6

7. GIBBS PHASE RULE
• The Phase Rule describes the possible number of degrees of
freedom in a (closed) system at equilibrium, in terms of the
number of separate phases and the number of chemical
constituents in the system.
• F = C - P + 2.
Where,
• F is the number of degrees of freedom
• C is the number of chemical components
• P is the number of phases in the system.
7

8. Isomorphous system
• An isomorphous system is one in which the solid has the same structure for all
compositions. In isomorphous systems the two components have unlimited
solubility, which means that they are like water and alcohol when they mix -
they always form a solid solution regardless of the ratio of atoms/molecules.
8

9. 9

10. EUTECTIC REACTION
• A eutectic reaction is a special type of phase reaction a three phase
reaction process in which a liquid solution that is cooled to the eutectic
temperature results in two solid phases occurring at the same time.
• For example, a liquid alloy becomes a solid mixture of alpha and beta at a
specific temperature, rather than existing over a temperature range
• A eutectic reaction is expressed as follows:
10
 A eutectic reaction is a special type of phase reaction a three phase reaction process in
which a liquid solution that is cooled to the eutectic temperature results in two solid
phases occurring at the same time.
 For example, a liquid alloy becomes a solid mixture of alpha and beta at a specific
temperature, rather than existing over a temperature range
 A eutectic reaction is expressed as follows:

11. 11

12. EUTECTOID REACTION:
• A eutectoid reaction is a three phase reaction by which, on cooling, a
solid transforms into two other solid phases at the same time.
• If the bottom of a single-phase solid field closes (and provided the
adjacent two phase fields are solid also), it does so with a
eutectoid point. The eutectoid reaction describes the phase
transformation of one solid into two different solids. In the FeC system,
there is a eutectoid point at approximately 0.8wt% C, 723°C.
• The phase just above the eutectoid temperature for plain carbon
steels is known as austenite or gamma.
• The general eutectoid reaction is therefore:
Solid γ → solid α + solid β
• or using the names given to these phases:
Austenite → ferrite + cementite (Fe3C)
12

13. EUTECTOID REACTION:
13

14. 14

15. PERITECTIC REACTION
• A peritectic reaction is a reaction where a solid phase and liquid phase will
together form a second solid phase at a particular temperature and
composition.
• These reactions are rather sluggish as the product phase will form at the
boundary between the two reacting phases thus separating them, and
slowing down any further reaction.
• Peritectics are not as common as eutectics and eutectiods, but do occur in
some alloy systems. There's one in the FeC system.
15
• The peritectic reaction also involves
three solid in equilibrium, the
transition is from a solid + liquid
phase to a different solid phase when
cooling. The inverse reaction occurs
when heating.
Solid Phase 1 + liquid → Solid Phase 2.
Peritectic reaction

16. PERITECIOID REACTION
16

17. All reactions
17

18. IRON CARBON EQUILIBRIUM DIAGRAM:
• Carbon is the most important alloying element in iron which significantly
affects the allotropy, structure and properties of iron.
• The study of Fe-C system is thus, important, more so as it forms the basis of
commercial steels and cast irons, and many of the basic features of this
system influence the behaviour of even the most complex alloy steels.
• Steels may have incidental elements, or intentionally added alloying
elements, which modify this diagram, but if modifications are interpreted
cautiously, then this diagram acts as a guide.
• The ability to interpret this diagram is important for proper appreciation of
phase changes. Fe-C diagram actually provides a valuable foundation on
which to build knowledge of large variety of both plain carbon and alloy
steels.
• Conventionally, the complete Fe-C diagram should extend from 100% Fe to
100% carbon, but it is normally studied up to around 6.67% carbon as is also
illustrated because iron alloys of practical industrial importance contain no
more than 5% carbon. Thus, this diagram is only just a part of the complete
Fe-C equilibrium diagram.
18

19. 19

20. 20

21. Micro constituents in iron-iron
carbide equilibrium diagram
–α Ferrite
–γ Austenite
–δ Ferrite
–Cementite
21

22. α Ferrite
22

23. γ Austenite
23

24. δ Ferrite
24

25. Cementite
25

26. Classification of ferrous alloys
26

27. Classification of steels
27

28. CARBON STEELS:
• Carbon steels are iron-carbon alloys containing up to 2.06% of
carbon, up to 1.65% of manganese, up to 0.5% of silicon and
sulphur and phosphorus as impurities.
• Carbon content in carbon steel determines its strength and
ductility. The higher carbon content, the higher steel strength
and the lower its ductility.
28

29. Low carbon steels (C < 0.25%):
• Low carbon steels generally contain less than 0.25% carbon and cannot be
strengthened by heat-treating (strengthening can only be accomplished
through cold working).
• The low carbon material is relatively soft and weak, but has outstanding
ductility and toughness. In addition, it is machineable, weld- able, and is
relatively inexpensive to produce.
• Low carbon steel is a type of steel that has small carbon content, typically
in the range of 0.05% to 0.3%. Its reduced carbon content makes it more
malleable and ductile than other steel types.
• Properties: good formability and weldability, low strength, low cost.
29

30. Applications:
• Used for applications such as cold headed fasteners and bolts.
• Low carbon steel is one of the most common types of steel.
• Low carbon steel is ideal for applications in which precision is
paramount due to its heightened flexibility.
• It is less prone to corrosion than other types of steel due to its reduced
carbon content and also in deep drawing parts, chain, pipe, wire, nails,
some machine parts.
• Used for simple structural applications such as cold formed fasteners
and bolts. It is often used in the case hardened condition.
30

31. Medium carbon steels (C =0.25% to 0.55%):
• Medium carbon steels have carbon
concentrations between 0.25% and 0.60%.
• An enormous variety of distinct properties
can be created for the steel by substituting
these elements in the recipe to increase
hardness, strength, or chemical resistance.
Properties: good toughness and ductility,
relatively good strength, may be hardened by
quenching
Applications:
• Generally used in the quenched and
31

32. High carbon steels (C > 0.55%):
• High carbon steels contain from 0.60 to 1.00%
C with manganese contents ranging from 0.30
to 0.90%.
• The pearlite has a very fine structure, which
makes the steel very hard.
• Unfortunately this also makes the steel quite
brittle and much less ductile than mild steel.
Properties: high strength, hardness and wear
resistance, moderate ductility.
Applications:
• This type of steel is excellent for making cutting
32

33. ALLOY STEEL
Low alloy steels (alloying elements < 8%):
• A special low carbon steel, containing specific small amounts of alloying elements,
that is quenched and tempered to get a yield strength of greater than 50,000 psi
and tensile strengths of 70,000 to 120,000 psi.
• Structural members made from these high-strength steels may have smaller
cross- sectional areas than common structural steels and still have equal or
greater strength. Additionally, these steels are normally more corrosion- and
abrasion resistant.
High alloy steels (alloying elements > 8%):
• Steel in these classes responds well to heat treatment and can be welded.
• When welding, special electrodes must be used along with preheating and stress-
relieving procedures to prevent cracks in the weld areas.
• These steels are used for dies, cutting tools, milltools, railroad car wheels, chisels,
knives, and so on.
33

34. NICKEL STEELS:
• These steels contain from 3.5% nickel to 5% nickel. The nickel increases the strength
and toughness of these steels.
• Nickel steel containing more than 5% nickel has an increased resistance to corrosion
and scale.
• Nickel steel is used in the manufacture of aircraft parts, such as propellers and
airframe support members.
CHROMIUM STEELS:
• These steels have chromium added to improve hardening ability, wear resistance,
and strength.
• These steels contain between 0.20% to 0.75% chromium and 0.45% carbon or
more.
• Some of these steels are so highly resistant to wear that they are used for the races
and balls in antifriction bearings. Chromium steels are highly resistant to corrosion
and to scale.
34

35. TUNGSTEN STEEL:
• This is a special alloy that has the property of red hardness. This is the ability to
continue to cut after it becomes red hot.
• A good grade of this steel contains from 13% to 19% tungsten, 1% to 2% vanadium,
3% to 5% chromium, and 0.6% to 0.8% carbon.
• Because this alloy is expensive to produce, its use is largely restricted to the
manufacture of drills, lathe tools, milling cutters, and similar cutting tools.
MOLYBDENUM STEEL
• This is often used as an alloying agent for steel in combination with chromium and
nickel.
• The molybdenum adds toughness to the steel.
• It can be used in place of tungsten to make the cheaper grades of high speed steel
and in carbon molybdenum high pressure tubing.
35

36. STAINLESS STEELS:
• Stainless steels are steels possessing high
corrosion resistance due to the presence of
substantial amount of chromium.
• Chromium forms a thin film of chromium oxide
on the steel surface. This film protects the steel
from further oxidation, making it stainless.
Most of them stainless steels contain 12% - 18%
of chromium.
• Other alloying elements of the stainless steels
are nickel, molybdenum, Nitrogen, titanium and
manganese. Stainless steels are divided onto
36

37. 37

38. Ferritic stainless steel
• Ferritic stainless steels (400 series) contain chromium only as alloying
element.
• The crystallographic structure of the steels is ferritic (BCC crystal lattice)
at all temperatures. The steels from this group are low cost and have the
best machinability.
• The steels are ferromagnetic. Ductility and formability of ferritic steels
are low. Corrosion resistance and weldability are moderate.
• Resistance to the stress corrosion cracking is high. Ferritic steels are not
heat treatable because of low carbon concentration and they are
commonly used in annealed state.
• Applications of ferritic steels: decorative and architectural parts,
automotive trims and exhausting systems, computer floppy disc hubs,
hot water tanks.
38

39. Microstructure
39

40. Austenitic stainless steel
• Austenitic stainless steels (200 and 300 series) contain chromium and
nickel (7% or more) as major alloying elements.
• The crystallographic structure of the steels is austenitic with FCC crystal
lattice. The steels from this group have the highest corrosion resistance,
weldability and ductility. Austenitic stainless steels retain their
properties at elevated temperatures.
• At the temperatures 900-1400ºF (482-760ºC) chromium carbides form
along the austenite grains.
• This causes depletion of chromium from the grains resulting in
decreasing the corrosion protective passive film.
• Applications of austenitic stainless steels: chemical equipment, food
equipment, kitchen sinks, medical devices, heat exchangers, parts of
furnaces and ovens.
40

41. Martensitic stainless steel
• Martensitic stainless steels (400 and 500 series) contain chromium as
alloying element and increased (as compared to ferritic grade) amount of
carbon.
• Due to increased concentration of carbon the steels from this group are
heat treatable. The steels have austenitic structure (FCC) at high
temperature, which transforms to martensitic structure (BCC) as
a result of quenching. Martensitic steels have poor weldability and
ductility.
• Corrosion resistance of these steels is moderate (slightly better than in
ferritic steels).
• Applications of martensitic stainless steels: turbine blades, knife blades,
surgical instruments, shafts, pins, and springs.
41

42. Duplex stainless steel
• Austenitic-ferritic (Duplex) stainless steels contain increased amount of
chromium (18% -28%) and decreased (as compared to austenitic steels)
amount of nickel (4.5% - 8%) as major alloying elements.
• As additional alloying element molybdenum is used in some of Duplex
steels. Since the quantity of nickel is insufficient for formation of fully
austenitic structure, the structure of Duplex steels is mixed: austenitic-
ferritic. The properties of Duplex steels are somewhere between the
properties of austenitic and ferritic steels.
• Duplex steels have high resistance to the stress corrosion cracking and to
chloride ions attack. These steels are weldable and formable and possess
high strength.
• Applications of austenitic-ferritic stainless steels: desalination equipment,
marine equipment, petrochemical plants, heat exchangers.
42

43. Precipitation hardened stainless steel
• Precipitation hardening stainless steels contain chromium, nickel as major
alloying elements. Precipitation hardening steels are supplied in solution
treated condition.
• These steels may be either austenitic or martensitic and they are
hardened by heat treatment (aging).
• The heat treatment is conducted after machining, however low
temperature of the treatment does not cause distortions. Precipitation
hardening steels have very high strength, good weldability and fair
corrosion resistance. They are magnetic.
• Applications of precipitation hardening stainless steels: pump shafts and
valves, turbine blades, paper industry equipment, aerospace equipment.
43

44. CAST IRON:
• An alloy of iron that contains 2 to 4 percent carbon, along with varying amounts of
silicon and manganese and traces of impurities such as sulphur and phosphorus.
• It is made by reducing iron ore in a blast furnace. The liquid iron is cast, or poured
and hardened, into crude ingots called pigs, and the pigs are subsequently remelted
along with scrap and alloying elements in cupola furnaces and recast into molds for
producing a variety of products.
• Most cast iron is either so called gray iron or white iron, the colours shown by
fracture. Gray iron contains more silicon and is less hard and more machinable than
is white iron.
• Cast iron is a ferrous alloy that is made by remelting pig iron in a cupola furnace
until it liquefies.
• The molten iron is poured into molds or casts to produce casting iron products of
the required dimensions. Based on the application of cast iron, the alloying
elements added to the furnace differ.
• The commonly added alloy elements are carbon followed by silicon. The other
alloying elements added are chromium, molybdenum, copper, titanium, vanadium,
etc.
44

45. CAST IRON:
• Iron with 1.7 to 4.5% carbon and 0.5 to 3% silicon
• Lower melting point and more fluid than steel (better castability)
• Low cost material usually produced by sand casting
• A wide range of properties, depending on composition & cooling
rate
– Strength
– Hardness
– Ductility
– Thermal conductivity
– Damping capacity
45

46. A few common mechanical properties for cast iron
• Hardness – material’s resistance to abrasion and indentation
• Toughness – material’s ability to absorb energy
• Ductility – material’s ability to deform without fracture
• Elasticity – material’s ability to return to its original dimensions
after it has been deformed
• Malleability – material’s ability to deform under compression
without rupturing
• Tensile strength – the greatest longitudinal stress a material can
bear without tearing apart
• Fatigue strength – the highest stress that a material can withstand
for a given number of cycles without breaking
46

47. Production of CI
• Pig iron, scrap steel, limestone and carbon (coke)
• Cupola
• Electric arc furnace
• Electric induction furnace
• Usually sand cast, but can be gravity die cast in reusable graphite moulds
• Not formed, finished by machining
47

48. Types of ci
• Grey cast iron - carbon as graphite
• White cast iron - carbides, often alloyed
• Ductile cast iron
– nodular, spheroidal graphite
• Malleable cast iron
• Compacted graphite cast iron
– CG or Vermicular Iron
48

49. Classification of cast iron
49

50. Effect of cooling rate
• Slow cooling favours the formation of graphite & low
hardness
• Rapid cooling promotes carbides with high hardness
• Thick sections cool slowly, while thin sections cool quickly
• Sand moulds cool slowly, but metal chills can be used to
increase cooling rate & promote white iron
50

51. Effect of composition
3
equivalent
Carbon
P
S
C
CE



• A CE over 4.3 (hypereutectic) leads to carbide or graphite
solidifying first & promotes grey cast iron
• A CE less than 4.3 (hypoeutectic) leads to austenite solidifying
first & promotes white iron
51

52. Grey cast iron
• Flake graphite in a matrix of pearlite, ferrite or martensite
• Wide range of applications
• Low ductility - elongation 0.6%
• Grey cast iron forms when
– Cooling is slow, as in heavy sections
– High silicon or carbon
52

53. Typical properties
• Depend strongly on casting shape & thickness
• AS1830 & ASTM A48 specifies properties
• Low strength, A48 Class 20, Rm 120 MPa
– High carbon, 3.6 to 3.8%
– Kish graphite (hypereutectic)
– High conductivity, high damping
• High strength, A48 Class 60, Rm 410 MPa
– Low carbon, (eutectic composition)
53

54. Graphite form
• Uniform
• Rosette
• Superimposed (Kish and
normal)
• Interdendritic random
• Interdendritic preferred
orientation
• See AS5094 “designation of
microstructure of graphite”
54

55. Matrix structure
• Pearlite or ferrite
• Transformation is to ferrite when
– Cooling rate is slow
– High silicon content
– High carbon equivalence
– Presence of fine undercooled graphite
55

56. Properties of grey cast iron
• Machineability is excellent
• Ductility is low (0.6%), impact resistance
low
• Damping capacity high
• Thermal conductivity high
• Dry and normal wear properties excellent
56

57. Applications of grey cast iron
• Engines
– Cylinder blocks, liners,
• Brake drums, clutch plates
• Pressure pipe fittings (AS2544)
• Machinery beds
• Furnace parts, ingot and glass moulds
57

58. Ductile cast iron
• Inoculation with Cerium or Magnesium or both causes
graphite to form as spherulites, rather than flakes.
• Also known as spheroidal graphite (SG), and nodular
graphite iron
• Far better ductility than grey cast iron
58

59. Microstructure
• Graphite spheres
surrounded by ferrite
• Usually some pearlite
• May be some cementite
• Can be hardened to
martensite by heat
treatment
59

60. Production
• Composition similar to grey cast iron except for
higher purity.
• Melt is added to inoculant in ladle.
• Magnesium as wire, ingots or pellets is added to
ladle before adding hot iron.
• Mg vapour rises through melt, removing sulphur.
60

61. Verification
• Testing is required to ensure nodularisation is
complete.
• Microstructural examination
• Mechanical testing on standard test bars
(ductility)
• Ultrasonic testing
61

62. Properties
• Strength higher than grey cast iron
• Ductility up to 6% as cast or 20% annealed
• Low cost
–Simple manufacturing process makes
complex shapes
• Machineability better than steel
62

63. Applications
• Automotive industry 55% of ductile iron in
USA
–Crankshafts, front wheel spindle
supports, steering knuckles, disc brake
callipers
• Pipe and pipe fittings (joined by welding)
see AS2280
63

64. White cast iron
64
► Shows a “white” crystalline fractured surface
► Low ductility, high hardness, high wear resistance  low
machinability
► Raw material for malleable cast iron
► High compressive stress
► Applications : engine bed, drawing dies, ball mill, extrusion
nozzle

65. CLASSIFICATION OF WHITE CAST
IRON
• HYPO-EUTECTIC WHITE C.I :- Alloy having carbon equivalent
between 2.11% to 4.3%
• EUTECTIC WHITE C.I:- Alloy having carbon equivalent 4.3%
• HYPER-EUTECTICWHITE C.I:- Alloy having carbon equivalent
between 4.3% to 6.67%.
65

66. Effects of alloy elements
• Promote graphite (Si, Ni)
• Promote carbides (Cr)
• Affect matrix microstructure
– Ferrite, pearlite, martensite or austenite
• Corrosion resistance (Cr)
• Specific effects
66

67. Microstructures
• Pearlite and ferrite in Fe3C matrix
• Austenite / martensite in Fe3C matrix
• M7C3 in a martensite matrix
67

68. Properties of white ci
• Hard but brittle and almost impossible to
machine
• Excellent wear resistance
• High compressive strength
68

69. Applications of white ci
• The wear surfaces (impeller and volute) of slurry
pumps,
• shell liner,
• lifter bars in ball mills,
• autogenous grinding mills,
• balls and rings in coal pulverisers, and
• teeth of a backhoe's digging bucket
69

70. Malleable iron
• Graphite in nodular form
• Produced by heat treatment of white cast
iron
• Graphite nodules are irregular clusters
• Similar properties to ductile iron
70

71. Microstructure
• Uniformly dispersed graphite
• Ferrite, pearlite or tempered martensite matrix
• Ferritic castings require 2 stage anneal.
• Pearlitic castings - 1st stage only
71

72. Annealing treatments
• Ferritic malleable iron
– Depends on C and Si
– 1st stage 2 to 36 hours at 940˚C in a controlled atmosphere
– Cool rapidly to 750˚C & hold for 1 to 6 hours
• For pearlitic malleable iron
– Similar 1st stage above (2 - 36 h at 940˚C)
– Cool to 870˚C slowly, then air cool & temper to specification
• Harden and temper pearlitic iron for martensitic castings
72

73. Properties
• Similar to ductile iron
• Good shock resistance
• Good ductility
• Good machineability
73

74. Applications
• Similar applications to ductile iron
• Malleable iron is better for thinner castings
• Ductile iron better for thicker castings >40mm
• Vehicle components
– Power trains, frames, suspensions and wheels
– Steering components, transmission and differential parts,
connecting rods
• Railway components
• Pipe fittings AS3673
74

75. 75
Irregular
shape
nodule
/rosette

76. 76

77. High Alloy Cast Iron
• Abrasion-resistant alloy cast iron
– Chilled Cast Iron  mottled cast iron
– White Cast Iron
– Chromium White Cast Iron
– Nickel-Chromium Cast Iron
77

78. High Alloy Cast Iron
• Heat-Resistant Alloy Cast Iron
– Chromium Iron
– High Silicon Iron
– High Nickel Iron
• Corrosion-Resistant Alloy Cast Iron
– High Silicon Iron
– High Chromium Iron
– High Nickel Iron
78

79. TOOL STEEL:
Tool steel is defined as special steel used for cutting or forming purpose.
Classification: According to quenching media
• Water hardening steel.
• Oil hardening steel.
• Air hardening steel.
According to alloy content
• Carbon tool steel.
• Low alloy tool steel.
• Medium alloy tool steel.
According to application
• Hot work steel.
• Shock resisting steel.
• High speed steel.
• Cold work steel.
79

80. Application of tool steel:
– Cutting tool like drill, tape reamer etc. (multi cutting tool).
– Shearing tool use for shear, punch and blanking die.
– Drawing and extrusion die.
– Thread rolling die.
– Single cutting tool in lathe and planning machine.
80

81. HIGH SPEED TOOL STEEL:
• These steels are the most highly alloyed of the tool steel usually contain large
amount of tungsten or molybdenum along with chromium, vanadium and
sometimes cobalt. Carbon content varies from 0.7 – 1.0% and sometimes up to
1.5%.
• Application of high speed steel is for cutting tools also they are used for making
extrusion dies, burnishing tools and blanking punches and dies.
Properties:
– Excellent red hardness (tool can operate at high temperature).
– Good shock resistance.
– Good non deforming properties.
– Good wear resistance.
– Fair machinability.
– Fair to poor resistance to decarburization.
81

82. Types:
• Molybdenum base (Group M).
• Tungsten base (Group T).
– Tungsten base is known as 18 – 4 – 1
– 18% tungsten, 4% chromium, 1% vanadium.
– Molybdenum base is known as 6 – 6 – 4 – 2
– 6% molybdenum, 6% tungsten, 4% chromium, 2% vanadium.
– Molybdenum steel is lower in price, so over 80% of H.S.S. is produced of
molybdenum type steel.
– When better than average red hardness is required, steel containing cobalt is
recommended.
– Higher vanadium content is desirable when the material cut is highly abrasive.
– In T-15 steel, a combination of cobalt and vanadium provides red hardness and
abrasion resistance.
• Application: cutting tools such as tool bits, drills, reamers, broaches, milling cutters,
hobs, saws, wood working tools etc.
82

83. HIGH-STRENGTH LOW-ALLOY
STEEL:
• Another group of low-carbon alloys are the high-strength low-
alloy (HSLA) steels.
• They contain other alloying elements such as copper,
vanadium, nickel, and molybdenum in combined
concentrations as high as 10 wt%, and possess higher
strengths than the plain low-carbon steels.
• Most may be strengthened by heat treatment, giving tensile
strengths in excess of 480 MPa (70,000 psi); in addition, they
are ductile, formable, and machinable. In normal
atmospheres, the HSLA steels are more resistant to corrosion
than the plain carbon steels, which they have replaced in many
applications where structural strength is critical (e.g., bridges,
towers, support columns in high-rise buildings, and pressure
vessels).
83

84. MARAGING STEELS:
• Maraging steels find applications as aluminium die-casting dies, inserts,
cores, extrusion dies, forging dies, punches, cold heading dies, die holders
etc.
• Maraging steels are low carbon, high nickel alloy steels capable of
attaining yield strengths in excess of 185 MN/m2 in combination with good
fracture toughness.
• These alloys contain carbon about 0.02%, Ni 18%, Co 8% and molybdenum
5% along with small amounts of titanium and aluminium as hardening
agents.
• This alloy is martensitic in the annealed condition and acquires ultra high
strength by an aging treatment.
84