Write short note on – Carbon steels.

Write short note on – Carbon steels.

Ans. A plain carbon steel is an alloy of pure Iron and carbon. Depending

upon the percentage of carbon content they may be classified as –

(i) Low carbon (or mild) steel

(ii) Medium carbon steel

( iii) High carbon steel.

(i) Low carbon (or mild) steel- mild steel contains 0.05 to 0.3 carbon. It is further classified into three types-

(a) Dead mild steel       –     0.05-0.15% c

(b) Mild steel                –     0.15 – 0.2% c

(c) Mild steel                –      0.2 _0 3%

Properties – Various properties of mild  steel are given as follow-

(a) It can be easily forged and welded.

(b) It can  magnetized permanently.

(c) It has fibrous structure .

(d) It cannot be hardened and tempered easily.

(e) It cannot be easily affected by hard water.

(f) It is ductile and malleable.

(g) It rusts readily.

(h) Its ultimate compressive strength is about 80 to 120 kN/cmsqr.

(i) Its specific gravity is 7.80

(j) It is tougher and more elastic than wrought iron.

(k) Its ultimate tensile and shear strengths are about 60 to 80 kN/cmsqr.

(l) Its melting point is about 1390C.

Uses – The uses of mild steel are as follows –

(a) Mild steel containing  0.5 to 0.15% carbon is used for

making stampings, wires, rivets, sheets, screws, pipes, thin plates, automobile

body, nails and chain.

(b) Mild steel containing 0.5 to 0.20% carbon has a tensile strength of 420 MPa, is used

For making camshafts, sheets, and strips for fan blades, universal beams, welded tubing, forgings, drag lines etc.

(c)mild steel containing 0.20 to 0.30% carbon has a tensile strength of 555 MPa and hardness of 140 BHN. It is used for making gears, valves, connecting rods, crankshafts, railway axles, fish plates, small forgings etc.

(ii) Medium carbon steel – Medium carbon steel contains carbon from 0.35 to 0.70%.

Steel containing 0.35-0.45% carbon has tensile strength of 750 N/mm .

They have good machinability and good deep hardening properties. They are used for making axels, heavy duty shafts, connecting rods, rails, turbine dices, rotor and gear shafts etc.

Steel containing 0.45-0.55 carbon has tensile strength of 1000 N/mmsqr. And are used for manufacturing parts which have to be subjected to shock and heavy reversal of stress, such as railways coach axles, large size forgings such as crank, shafts, gear axles, spline shafts etc.

Steel containing 0.6-0.7% carbon are used for making drop forging dies,

die blocks, plate punch, self tapping screws, value springs, cushion springs,

lock washers, thrust washers, etc.

(iii) High carbon steel-  steel containing 0.60 to 1.5% carbon is

known as high carbon steel. They possess wear resistance and high hardness after heat treatment.

Chemical composition of high carbon steel is given as follows-

Material percentage
Carbon

Silicon

Manganese

chromium

0.6- 1.5

0.15- 0.3

0.15- 0.35

0.2

 

Properties– various properties of high carbon steel are given as follows-

(a) Its ultimate tensile strength is about 80 to 110 kN/cm2 .

(b) Its ultimate shear strength is about 110 kN/cm2.

(c) Its ultimate compressive strength is about 140 to 200 kN/cm2.

(d) Its specific gravity is 7.90.

(e) It can be easily tempered and hardened.

(f) It can be magnetized permanently.

(g) It can be easily forged and welded.

(h) It rusts easily and rapidly.

(i) It is tougher and more elastic than mild steel.

(j) It has granular structure.

(k) It cannot be easily affected by salt water.

Uses – Uses of high carbon steel are given as follows –

(a) Steels containing ·0.6 to 0.8% carbon are used for making

cold chisels, wrenches, automatic clutch discs etc.

(b) Steels containing 0.8 to 0.9% carbon are used for making

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