This document discusses the classification of steels based on their carbon content and alloying elements. It describes low carbon steels as containing less than 0.25% carbon, being tough, malleable, and ductile. Medium carbon steels range from 0.25 to 0.6% carbon and can be heat treated to increase strength. High carbon steels contain more than 0.6% carbon. Alloying elements like manganese, chromium, nickel, and molybdenum are discussed and their effects on properties such as strength, hardness, toughness, and corrosion resistance. Common applications of different steel types are also mentioned.

1. MATERIAL SCIENCE AND ENGINEERING
Classification
Of
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2. R
E
F
E
R
E
N
C
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S
 Materials Science and Engineering, V
.Raghavan,
Fifth Edition, Prentice Hall of India Pvt. Ltd., New
Delhi, 2004.
 Materials Science and Engineering: An Introduction,
William D. Callister
John Wiley & Sons, 2010.
ONLINE - Nptel

3. Ferrous Materials
Ferrous
Steels Cast iron
Low Alloy HighAlloy
Tool steel Stainless steel

4. CLASSIFICATION OF STEELS

5. FERROUS MATERIAL - STEELS
• Steels - alloys of iron-carbon.
- May contain other alloying elements.
• Several grades are available
• Low Alloy (<10 wt%)
.
–Low Carbon (<0.25 wt% C)
–Medium Carbon (0.25 to 0.60 wt% C)
–High Carbon (0.6 to 1.4 wt% C)
•High Alloy
– Stainless Steel (>11 wt% Cr)
- Tool Steel

6. EFFECT OF CARBON ON PROPERTIES OF STEELS

7. Low Carbon Steel
- Also known as Mild Steel
- Tensile strength of 555 N/mm
- Hardness of 140 BHN
- Bright fibrous structure
-Tough , malleable , ductile and more elastic than
wrought iron
- Melting point 1410

8. Low Carbon Steel
Plain carbon steels - very low content of alloying elements
and small amounts of Mn.
Most abundant grade of steel is low carbon steel –
greatest quantity produced; least expensive.
Not responsive to heat treatment; cold working needed to
improve the strength.
Good Weldability and machinability
High Strength, Low Alloy (HSLA) steels - alloying elements
(like Cu, V, Ni and Mo) up to 10 wt %; have higher strengths
and may be heat treated.

9. LOW CARBON STEEL
Compositions of some low carbon and low alloy steels

10. AISI - SAE CLASSIFICATION SYSTEM
AISI XXXX
American Iron and Steel Institute (AISI)
 classifies alloys by chemistry
 4 digit number
1st number is the major alloyingelement
2nd number designates the subgroup alloying
element OR the relative percent of primary
alloying element.
last two numbers approximate amount of
carbon (expresses in 0.01%)

11. AISI - SAE CLASSIFICATION
SYSTEM
 letter prefix to designate the process used to produce the
steel
E = electric furnace
X = indicates permissible variations
 If a letter is inserted between the 2nd and 3rd number
B = boron has been added
L = lead has been added
 Letter suffix
H = when hardenability is a major requirement
 Other designation organizations
ASTM and MIL

14. MEDIUM CARBON STEEL
Carbon content in the range of 0.3 – 0.6%.
Can be heat treated - austenitizing, quenching and then
tempering.
Most often used in tempered condition – tempered
martensite
Medium carbon steels have low hardenability
Addition of Cr, Ni, Mo improves the heat treating capacity
Heat treated alloys are stronger but have lower ductility
Typical applications – Railway wheels and tracks, gears,
crankshafts.

15. MEDIUM CARBON STEEL
- Bright fibrous structure when fractured
- Tough and more elastic in comparison to wrought iron
- Eaisly forged , welded , elongated due to ductility
- Good malleability
- Its tensile strength is better than cast iron and wrought iron
- Compressive strength is better than wrought iron but lesser
than cast iron

18. HIGH CARBON STEEL

19. APPLICATIONS -

21. STRUCTURAL STEELS
- Possess high strength and toughness
- resistance to softening at elevated temperatures
- resistance to corrosion
-possess weldability , workability & high
hardenability
-principle alloying elements chromium , nickel ,
manganese

23. STAINLESS STEELS

26. EFFECTS OF ALLOYING ELEMENTS ON STEEL
 Manganese contributes to strength and hardness; dependent upon the carbon
content. Increasing the manganese content decreases ductility and weldability.
Manganese has a significant effect on the hardenability of steel.
 Phosphorus increases strength and hardness and decreases ductility and notch
impact toughness of steel. The adverse effects on ductility and toughness are
greater in quenched and tempered higher-carbon steels.
 Sulfur decreases ductility and notch impact toughness especially in the transverse
direction. Weldability decreases with increasing sulfur content. Sulfur is found
primarily in the form of sulfide inclusions.
 Silicon is one of the principal deoxidizers used in steelmaking. Silicon is less
effective than manganese in increasing as-rolled strength and hardness. In low-
carbon steels, silicon is generally detrimental to surface quality.
 Copper in significant amounts is detrimental to hot-working steels. Copper can be
detrimental to surface quality. Copper is beneficial to atmospheric corrosion
resistance when present in amounts exceeding 0.20%.
 Nickel is a ferrite strengthener. Nickel does not form carbides in steel. It remains
in solution in ferrite, strengthening and toughening the ferrite phase. Nickel
increases the hardenability and impact strength of steels.
 Molybdenum increases the hardenability of steel. It enhances the creep strength
of low-alloy steels at elevated temperatures.