types of steels and their composition

1. STEEL
PLAIN CARBON
STEEL
(UNALLOYED
STEEL)
ALLOY STEEL

2. Plain Carbon Steel
 Only C is present.
 No other alloying element (metal) present (non-metal may be present).
 No final heat treatment is required.
PLAIN
CARBON
STEEL
Low C Medium C
High C
(used where resistance
to WEAR is essential)
Tool steel
(High C)

3. Effect of % of C
Hardness
Strength
Brittleness.
Ductility
Machinability
Weld ability
Thermal & electrical
conductivity
Magnetic
permeability
Corrosion resistance
IncreasewithincreaseinC
DecreasewithincreaseinC

4. Elements in Plain Carbon Steel
ELEMENT MERITS DEMERITS
C Strength, elasticity (yield point), hardness Ductility, impact strength
Si Prevents porosity, good deoxidizer, removes
gases & oxides, prevents blow-holes, increase
toughness & hardness
Mn Deoxidizer, decrease harmful effects of S
(forms manganese sulphide), increase ductility
S Improves surface finish when used in TOOL
STEEL
Brittleness, tensile strength,
yield point, fatigue limit,
corrosion resistance
P Improves surface finish when used in TOOL
STEEL, tensile strength
Brittleness, impact strength,
ductility
Note:- % of S & P are kept very low

5. ALLOY STEELS
Alloy steel
Chemical composition
Ex: 3-component, 4-
copmponent etc
Structure
1) Pearlitic
2) Martensitic
3) Austenitic
4) Ferritic
5) Carbidic
Application
1) Structural
2) Tool steel
3) Special physical property

6. Elements in alloy steels
ELEMENTS EFFECT
Ni Provides toughness, corrosion resistance, deep hardening
Cr Improves corrosion resistance, toughness, hardenability
Mn Deoxidizes, contributes to strength & hardness, decrease critical cooling rate
Si Deoxidizes, promotes resistance to high temp. oxidation, raises the critical temp. for
heat treatment
Mo Promotes hardenability, increase tensile & creep strength at high temp.
V Deoxidizes & promotes fine-grained structure
Al Deoxidizes & promotes fine-grained structure, aids nitriding
Cu Improves corrosion resistance, acts as strengthening agent
B Increase hardenability

7. Structural alloy steel
Chief alloying elements :- Ni, Cr, Mn

8. • High Co %, low W
• Used in permanent magnets of magnetos, loud speakers
etc.
Magnet steel
• Cr (major)
• Ni, WHeat resisting steel
• W, Cr, V or
• Si, Mn, MoShock resisting steel
• Name because these are used as cutting tools for very high speeds
at wich plain carbon steels fail
• Major-> W, Cr, V Variable-> V, Co, Mo
High speed steel (HSS)
• ( next slide)Stainless steel
• Applied on the tip of cutting tool
• 2 types:- cemented carbides -> W & Ti carbides + Co binder
stellites:- hig W, Co
Cutting alloys
Special physical property alloyed steel

9. Stainless steel
 Cr (major), Ni
Austenitic Ferritic Martensitic
• Major-> Cr, Ni
• Can’t be hardened by heat
treatment
• Major-> Cr
• Can’t be hardened by heat
treatment
• Major-> Cr
• Can be hardened by heat
treatment