Steel is the intermediate product between wrought iron and cast iron. It contains 0.2-2.5% carbon and other impurities. The hardness of steel vary with the amount of carbon content in it. Steel is malleable and ductile. Steel has wide ranges of application in the modern world.
Steels are categorized in few types according to the carbon composition and presence of impurities.
1. Mild Steel (carbon steel): It contains low percentage of carbon. The hardness and elasticity of mild iron are similar to that of wrought iron. It is the most common form of steel.
2. Hard steel: It contains relatively higher percentage of carbon. It is hard and brittle.
3. Special steel: When steel is mixed with small amount of nickel, cobalt, chromium, Molybdenum etc according to the application for special purposes, it is said to be special steel. Some of the alloy steels and their uses are:
- Nickel steel: Computer cables, propeller, automobile and airplanes etc.
- Invar: Pendulums, survey tapes etc.
- Chrome steel: Ball bearing, cutting tools etc.
- Tungsten steel: High speed cutting tools and drilling tools.
- Chrom-vandadium steel: Axels, motorcar frames. gears, springs etc.
4. Stainless steel: It is an alloy of steel containing 18% of chromium and 16% nickel. Stainless steel can resist corrosion. The chemical composition of stainless steel is: Iron 75%, Chromium 18%, Nickel 6% and other elements in trace quantities. It is used in bicycle, automobile parts, bulbs, blades etc.