What is Carbon Steel?

Carbon steel is a steel alloy composed of carbon (generally 0.30% or less), and iron. It is one of the most widely used types of steel because of its wide availability and low cost compared to other materials. It is used in applications such as automotive frames and engines, machine tools, valves, pipes, railway tracks, gun barrels, bicycle frames, and ship hulls.

Composition and Properties
The carbon presence in it allows it to be heat-treated to affect its hardness and strength. Increasing the carbon concentration to a maximum of around 2.1% makes the material significantly stronger but less ductile. The inclusion of carbon also lowers the melting point of steel and allows it to be cast. It contains fewer residual elements than other steels so it offers more consistency and reliability in machining and welding applications.

Common Grades
There are many standard grades of it based on variations in their composition and intended uses:

- Plain Carbon Steel: Contains 0.15-0.29% carbon. Used for applications requiring good formability like automobile bodies and domestic appliances.

- Low Carbon Steel: Contains 0.05-0.15% carbon. Used for applications requiring ductility and strength such as drilling pipes and structural steel.

- Medium Carbon Steel: Contains 0.3-0.60% carbon. Provides excellent machinability and hardness suitable for gears, shafts, small metal parts.

- High Carbon Steel: Contains 0.60-1.50% carbon. Very hard and used for knife blades, springs, rock drill bits and metal-cutting tools.

- Alloy Steel: Its composition with small alloying additions such as chromium, nickel, molybdenum. Used for applications needing high strength and temperature resistance like ball bearings and cutting tools.

Heat Treatment
The mechanical and physical properties of its products can be further improved through heat treatment processes:

- Annealing: Heating above critical temperature and gradual cooling. Softens the steel making it more ductile and machinable.

- Hardening: Heating to critical temperature, quenching in oil or water. Increases hardness significantly but reduces ductility. Used for cutting tools and springs.

- Tempering: Reheating hardened steel to a lower temperature, air cooling. Restores some ductility lost during hardening without reducing hardness.

- Normalizing: Heating above critical temperature, air cooling. Refines grain structure and relieves internal stresses without hardening. Improves machinability.

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