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)

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.

Application of Low carbon steels

Automobile body parts

Structural Applications (I – Beams, channel and angle iron

Application of Low carbon steels

Sheets for tin cans

Sheets for bridges

Medium carbon steels

They have high strength and hardness properties with the absence of ductility and toughness.

Application of Medium carbon steels

Railway wheelsGears

Railway Tracks

Application of Medium carbon steels

Crank ShaftMachine Parts

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)

Application of high carbon steels

Cutting toolsHacksaw Blades

Dies

Application of high carbon steels

Springs Razor BladesHigh strength wires

Alloy Steels

Any steel other than carbon steel is called alloy steels.

Alloying elements : chromium, nickel, molybdenum, vanadium, tungsten, cobalt, boron, copper and others.

Classification of Alloy steels

1. Low alloy steels (Having 3 to 4% alloying element)

2. High alloy steels (Having more than 5% alloying

element)

Low alloy steels

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

Classification of Low Alloy steels

1. AISI(American Iron and Steel Institute) steels

2. HSLA(High – strength Low- Alloy) steels

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

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.

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