Q. 9 What is composition of Carbon steel? Give its applications.
Carbon steel किन तत्वों से बना होता है। इसका उपयोग भी बताइए।
Ans. Composition of Mild Steel –
Carbon steels are alloy of pure iron and carbon. Depending upon the percentage of carbon, they can be classified as –
(i) Low carbon (or mild) steel - 0.05-0.3% C
(a) Dead mild steel -0.05-0.15% C
(b) Mild steel - 0.15-0.2% C
(c) Mild steel - 0.2-0.3% C
(ii) Medium carbon steel - 0.3-0.6% C
(iii) High carbon steel - 0.6-1.5% C
A special type of high carbon steel containing 0.9-1.5% C is known as tool steel, used for making tools of various machines.
Properties of Mild Steel – Various properties of mild steel are given as follows -
(i) It can be easily forged and welded.
(ii) It can be magnetized permanently.
(iii) It has fibrous structure.
(iv) It cannot be hardened and tempered easily.
(v) It cannot be easily affected by hard water.
(vi) It is ductile and malleable.
(vii) It rusts readily.
(viii) Its ultimate compressive strength is about 80 to 120 kN/cm2.
(ix) Its specific gravity is 7.80.
(x) It is tougher and more elastic than wrought iron.
(xi) Its ultimate tensile and shear strengths are about 60 to 80 kN/cm2.
(xii) Its melting point is about 1390°C.
Uses of Mild Steel – The uses of mild steel are as follows –
(i) Mild steel containing 0.05 to 0.15% carbon is used for making stampings, wires, rivets, sheets, screws, pipes, thin plates, automobile body, nails and chain.
(ii) Mild steel containing 0.15 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.
(iii) 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.
Medium carbon steel contains carbon from 0.3 to 0.60%.
Steel containing 0.3-0.45% carbon has tensile strength of 750 N/mm2. They have good machinability and good deep hardening properties. They are used for making axles, heavy duty shafts, connecting rods, rails, turbine discs, rotor and gear shafts, etc.
Steel containing 0.45-0.55% carbon has tensile strength of 1000 N/mm2 and are used for manufacturing parts which have to be subjected to shock and heavy reversal of stress, such as railway coach axles, large size forgings such as crankshafts, gear axles, spline shafts, etc.
Steel containing 0.55-0.60% carbon are used for making drop forging dies, die blocks, plate punch, self tapping screws, valve springs, cushion springs, lock washers, thrust washers, etc.
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 –