The document classifies and describes different types of plain carbon and alloy steels. It discusses three types of plain carbon steels based on carbon content: low carbon steels containing less than 0.25% carbon, medium carbon steels containing 0.25-0.60% carbon, and high carbon steels containing more than 0.60% carbon. It then provides details on properties, applications and heat treatment of each type. The document also classifies alloy steels into low alloy steels containing 3-4% alloying elements and high alloy steels containing over 5% alloying elements. It discusses AISI, HSLA, tool/die and stainless varieties of alloy steels.

1. Classification of Plain carbon steels
1. Low carbon steels (Less than 0.25% carbon)
2. Medium carbon steels (Between 0.25 to 0.60%)
3. High carbon steels (More than 0.60% carbon)

2. Low carbon steels
1. Low carbon steels are relatively soft and weak.
2. They cannot be hardened appreciably by heat
treatment but it can be strengthening by cold
work.
3. They posses good formability and weldability.
Recrystalisation Temperature: The lowest level of heat at which the distorted grain structure of a metal is replaced by a strain-
free grain structure.

3. Application of Low carbon steels
Automobile body parts
Structural Applications (I – Beams, channel and angle iron

4. Application of Low carbon steels
Sheets for tin cans
Sheets for bridges

5. Medium carbon steels
They have high strength and
hardness properties with the absence of
ductility and toughness.

6. Application of Medium carbon steels
Railway wheels
Gears
Railway Tracks

7. Application of Medium carbon steels
Crank Shaft
Machine Parts

8. High carbon steels
1. They are the least ductile (more brittle)
of the carbon steels.
2. They have more wear resistant
3. They are capable of holding a sharp
cutting edge (It is the important property
of making tools)

9. Application of high carbon steels
Cutting tools
Hacksaw Blades
Dies

10. Application of high carbon steels
Springs Razor Blades
High strength wires

11. Alloy Steels
Any steel other than carbon steel is called alloy steels.
Alloying elements : chromium, nickel, molybdenum,
vanadium, tungsten, cobalt, boron, copper and others.

12. Classification of Alloy steels
1. Low alloy steels (Having 3 to 4% alloying element)
2. High alloy steels (Having more than 5% alloying element)

13. Low alloy steels
They have similar microstructure
and require similar heat treatments to
that of the plain carbon steels.

14. Classification of Low Alloy steels
1. AISI(American Iron and Steel Institute) steels
2. HSLA(High – strength Low- Alloy) steels

15. AISI(American Iron and Steel Institute) steels
These steels are generally used in machine construction.
It is also referred as constructional steels or structural steels.
They have less than about 5% total addition of elements such as
Cr, Ni, Cu, Mn, Mo, V, etc.
The major interest in this AISI steels group is hardebability

16. HSLA(High – strength Low- Alloy) steels
It is also referred as micro alloyed steels.
They have addition of elements such as Al, Nb(Niobium) and V
either singly or in combination.

17. High alloy steels
They have different microstructure and require heat
treatments than that of the plain carbon steels.
Classification of High Alloy steels
1. Tool and die steels
2. Stainless steels