Question

How are plain carbon steels and alloy steel important for engineering applications? Select any four plain carbon steel and alloy steel each and justify your answer with respect to their composition, mechanical properties and application

Answer 1

Plain carbon Steel:

Steel is an alloy of carbon and iron. Steels having carbon content less than 2.1% by weight are called Plain carbon steel. They are further classified into four types based on carbon content. They are as follows.

1. Low carbon steel

2. Medium carbon steel

3. High carbon steel

4.Very high carbon steel

Composition :

Low carbon steel - 0.05%-0.25% Carbon and up to 0.4% Manganese.

Medium carbon steel - 0.29% - 0.54% of carbon with 0.60% - 1.65% Mangenese

High carbon steel – 0.55% - 0.95% of carbon with 0.30% - 0.90% Manganese

Very high carbon steel – 0.96% - 2.1% Carbon

Mechanical properties :

Low carbon steel  

1.They have fair strength with high ductility.

2. Very good fabrication properties. Can be rolled, drawed, welded and pressed.

3. These have at strength of 350 -370 MPa , yield strength of 200 – 300 MPa and ductility of 28 to 40%

4. These have very high ductility because of its low carbon content. So it can be cold worked easily.

Medium carbon steel :

1. Tensile strength about 750 – 1230 MPa

2. Hardness ranging from 400 – 450 BHN depending on carbon content

3.Low hardenability

4.Can be heat treated

5.Mostlyt used in temperate state

High carbon steel

1.Can be heat treated to improve strength

2. Less ductile than mild steel

3.Quite brittle

4.Good wear resistance

Very high carbon steel:

These are experimental alloys used to produce specific microstructures.

Hardness of 500 – 600 BHN

It is a very brittle metal.

Application :

Low carbon steel :

Nuts, bolts,screws, nail, chain, rivets, pipes, tubes, and components that does not require high strength, welded tubing,

Medium carbon steels :

Connecting rods, spring clips, gear shafts, shift and brake levers, axles, key stock, railway coach axles, spline shafts, crankshaft, crank pin, drop forging dies, self tapping screws, set screws, valve springs, cushion rings, thrust washers, clutch plates.

High carbon steels:

Cold chisels, wrenches, jaws for vices, pneumatic drill bits, wire for structural works, shear blades, hacksaws, railway rails, circular saws, leaf springs, music wires, keys, knives, gear wheels,

Very high carbon steels :

Mandrels, taps, twist drills, reamers, files, metal cutting tools,

Alloy steels :

Types :

1.Chromium Molybdenum Steel

2. Nickel-Chromium-Molybdenum Steel

3.Chromium Vanadium Steel

4. HSLA -Nickel-Chromium-Molybdenum Steel

Chromium Molybdenum Steel

Composition :

C – 0..38 - 0.43 %

Mn – 0.75% - 1.00 %

P – 0..035%

S – 0.04%

Si – 0.15% - 0..35%

Cr – 0.80% - 1.10 %

Mo – 0.15% - 0.25%

Properties :

1. Good strength and Wear resistance

2. Ability to resist stress and creep at high temperature

3. Good machinability

Applications :

Drill collars, high temperature bolts, sprockets, kelly bars, reamer bodies, stay bolts,, couplings, , winch shafts, piston rods, rams, hydraulic machinery shafts, precision lead screws,

Nickel-Chromium-Molybdenum Steel :

Composition :

C – 0.38% - 0.43%

Mn – 0.60% - 0.90%

P – 0.035%

S – 0.04%

Si – 0.15% - 0.35%

Cr - 0.70% -0.90%

Mo – 0.20% - 0.30%

Ni - 1.65% - 2.00%

Properties :

Tensile Strength - 110,000 psi
Yield Point -   66,000 psi
Elongation -  23%
Brinell Hardness 197 BHN

Applications :

Crank shafts, axle shafts, dies, mine drilling parts, oil well fishing tools

Chromium Vanadium Steel

Composition :

C – 0.48% - 0.53%

Mn – 0.70% -0.90%

P – 0.035%

S – 0.04%

Si – 0.15% - 0.35%

Cr – 0.80% - 1.10%

V – 0.15%

Properties :

1.Higher strength and hardness.

2.Excellent toughness,

3.Water/abrasion resistance.

Applications :

shafting, heavy duty pins and hand tools

HSLA -Nickel-Chromium-Molybdenum Steel :

Composition :

C - 0.18% - 0 .23%

Mn – 0.70% - 0.90

P – 0.035%

S – 0.04%

Si – 0.15% - 0.35%

Cr – 0.40% - 0.60%

Mo – 0.15% - 0.25%

Ni – 0.40% - 0.70%

Properties :

1. Good toughness and ductility

2. Increased hardness penetration.

3. Tough core.

Applications :

jigs, plastic moulds,  oil tool slips, jaws, gauges, piston rods