The document discusses different types of alloy steels. It begins by explaining that alloy steels have other elements added to iron beyond just carbon in order to improve properties like strength, hardness, toughness, creep resistance, and corrosion resistance. It then classifies alloy steels into low, medium, and high alloy steels based on their composition. Low alloy steels are further broken down into low carbon, medium carbon, and high/ultra high carbon steels. High alloy steels include stainless steels and tool steels. Stainless steels are classified as austenitic, ferritic, martensitic, or precipitation hardening depending on their microstructure. Austenitic stainless steels

1. G H Patel College of Engineering and
Technology
Subject :- Material Science and Metallurgy
Topic:- ALLOY STEEL
BY:
UTTAM TRASADIYA
MECHANICAL ENGINEERING
GCET college
vvnagar.
GUIDE BY :-
Ms. ELA JHA.
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2. Alloy Steel - Introduction,
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Alloying
Changing chemical composition of steel by adding elements
with purpose to improve its properties as compared to the
plane Carbon steel.
Alloy Steels are irons where other elements (besides
carbon) can be added to iron to improve:
Mechanical property - Increase strength, hardness,
toughness (a given strength & hardness),
creep, and high temp resistance.
Increase wear resistance,
Environmental property [Eg: corrosion].

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Classification of metal
alloys
Ferrous Non - ferrous
Cast Iron Steels
Low Alloy High Alloy
Low
Carbon Med.
Carbon
High
Carbon Stainless
Steel
Tool
Steel
White
Grey

4. Classification of alloy steel
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5. Classification of alloy steel
Alloy steels grouped into low, medium and high alloy steels.
 High-alloy steels would be the stainless steel groups.
 Most alloy steels in use fall under the category of low alloy
Alloy steels are, in general, with elements as:
> 1.65%Mn, > 0.60% Si, or >0.60% Cu.
The most common alloy elements includes:
Chromium, nickel, molybdenum, vanadium,
tungsten, cobalt, boron, and copper
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6. Low Alloys: Low Carbon
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•Composition:
• less than ~ 0,25% C ( 0,30%)
•Microstructure:
•ferrite and pearlite
•Properties:
•relatively soft and weak, but possess high ductility and toughness
•Other features: machinable and weldable, not responsive to heat
treatment - Plain carbon steels
Applications: auto-body components, structural shapes, sheets etc.
• High-strength low alloy (HSLA) steels:
• up to 10 wt% of alloying elements, such as Mn, Cr, Cu, V, Ni, Mo –
can be strengthened by heat-treatment

7. Low Alloys: Medium Carbon Steels
 Composition:
 0.25< C <0.6 C wt.%
 Microstructure:
 typically tempered martensite
 Processing: Increasing the carbon content to approximately
0.5% with an accompanying increase in manganese allows
medium carbon steels to be used in the quenched and tempered
condition.
 Properties: stronger than low-carbon steels, but in expense of
ductility and toughness
 Applications: couplings, forgings, gears, crankshafts other
high-strength structural components. Steels in the 0.40 to
0.60% C range are also used for rails, railway wheels and rail
axles.
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8. Low Alloys: High&Ultra High - Carbon Steels
• High-carbon steels
0.60 to 1.00 % C with manganese contents ranging
from 0.30 to 0.90%.
Application: High-carbon steels are used for spring
materials, high-strength wires, cutting tools and etc.
Ultrahigh-carbon steels are experimental alloys
containing 1.25 to 2.0% C. These steels are thermo-
mechanically processed to produce microstructures
that consist of ultra-fine, equiaxed grains of spherical,
discontinuous proeutectoid carbide particles.
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9. High-Alloy Steels: Stainless Steels
(SS)
 The primarily-alloying element is Cr (≥11 wt.%)
 Highly resistance to corrosion;
 Nickel and molybdenum additions INCREASE
corrosion resistance
 A property of great importance is the ability of alloying
elements to promote the formation of a certain phase or
to stabilize it.
 These elements are grouped as four major classes:
1. austenite-forming,
2. ferrite-forming,
3. carbide-forming and
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10. Distribution of alloying elements in steels.
 Alloying elements can influence the equilibrium
diagram in two ways in ternary systems Fe-C-X.
1. Expanding the γ -field, and encouraging the
formation of austenite over wider compositional
limits. These elements are called γ -stabilizers.
2. Contracting the γ-field, and encouraging the
formation of ferrite over wider compositional limits.
These elements are called α-stabilizers.
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 Phase change- SS

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Classification of iron alloy phase diagrams: a. open γ -field; b. expanded γ -field;

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Classification of iron alloy phase diagrams: c. closed γ -
field d. Contract γ - field

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Nickel and manganese
depress the phase
transformation from γ to α to
lower temperatures
both Ac1 and Ac3 are lowered.
It is also easier to obtain
metastable austenite by
quenching from the γ-region to
room temperature
A. Open  - field: austenitic steels.

15. B. Expanded  -field : austenitic
steels
Carbon and nitrogen (Copper,
zinc and gold)
The γ-phase field is expanded
Heat treatment of steels,
 allowing formation of a
homogeneous solid solution
(austenite) containing up to
2.0 wt % of carbon or 2.8 wt %
of nitrogen
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16. C. Closed  -field : ferritic
steels
Silicon, aluminium, beryllium and
phosphorus (strong carbide forming
elements - titanium, vanadium,
molybdenum and chromium )
γ-area contract to a small area referred to
as the gamma loop
 encouraging the formation of BCC
iron (ferrite),
Not amenable to the normal heat
treatments involving cooling through the
γ/α-phase transformation
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17. D. Contracted  -field : ferritic steels
 Boron is the most significant element of this
group (carbide forming elements - tantalum,
niobium and zirconium.
 The γ-loop is strongly contracted
 Normally elements with opposing tendencies
will cancel each other out at the appropriate
combinations, but in some cases irregularity
occur. For example, chromium added to
nickel in a steel in concentrations around 18%
helps to stabilize the γ-phase, as shown by
18Cr8Ni austenitic steels.
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18. 18Cr8Ni austenitic steels.
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opposing tendencies

19. High-Alloy Steels: Stainless Steels
(SS)
(a) The austenitic SS:
• -Fe FCC microstructure at room temperature. Typical
alloy Fe-18Cr-8Ni-1Mn-0.1C
• Stabilizing austenite – increasing the temperature range,
in which austenite exists.
• Raise the A4 point (the temperature of formation of
austenite from liquid phase) and decrease the A3
temperature.
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20. Fe-Ni equilibrium
diagram
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A4 increase
A3 Decrease

21. High-Alloy Steels: Stainless Steels
(SS)
• Austenite-forming elements
 The elements Cu, Ni, Co and Mn
Disadvantage: work harden rapidly so more difficult to
shape and machine
 Advantages of ALL fcc metals and alloys
toughness;
ductility;
creep resistance
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22. High-Alloy Steels: Stainless Steels
(SS)
(b) The ferritic SS:
 α−Fe BCC structure.
 Not so corrosion resistant as austenitic SS, but less
expensive magnetic steel;
An alloy Fe-15Cr-0.6C, used in quench and tempered
condition
Used for: rust-free ball bearings, scalpels, knives
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23. Cr-Fe equilibrium
diagram
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Lower A4
Increase the A3

24. High-Alloy Steels: Stainless Steels
(SS)lower the A4 point and increase the A3 temperature.
Ferrite-forming elements
 The most important elements in this group are Cr, Si, Mo,
W, V and Al.
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25. High-Alloy Steels: Stainless Steels
(SS)
(c) The martensitic SS this fine magnetic bcc structure is produced by rapid quenching
and possesses high yield strength and low ductility.
Applications: springs.
(d) The precipitation hardening SS – producing multiple microstructure form a single-
phase one, leads to the increasing resistance for the dislocation motion.
 (a) and (b) are hardening and strengthening by cold work
 Microstructure - martensitic, ferritic or austenitic based on microstructure, and
precipitation hardening based on strengthening mechanism
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26. High-Alloy Steels: Tools steels
• Wear Resistant, High Strength and Tough BUT low ductility
 High Carbon steels modified by alloy additions
AISI-SAE Classification
Letter & Number Identification
Classification
Letters pertain to significant characteristic
W,O,A,D,S,T,M,H,P,L,F
– E.g. A is Air-Hardening medium alloy
Numbers pertain to material type
1 thru 7 (E.g. 2 is Cold-work )
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27. High-Alloy Steels: Tools steels
 Provide the necessary hardness with simpler heat-
treatment and retain this hardness at high
temperature.
 The primary alloying elements are:
 Mo, W and Cr
 Examples:
I. HSS – Turning machine tools
II. High carbon tool steels – Drill
bits/Milling tools/punches/saw
blade
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28. THANK YOU
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