Carbon Steel is steel in which main alloy is carbon, but only in the range of 0.12-2.0%. Above that percentage then the material is no longer considered Carbon Steel. Trace metals may be present but must be below a certain threshold for each.
Carbon Steel is broken down into four classes based on carbon content:
Low-carbon steel: .12 to 0.3% carbon content.
Medium-carbon: steel: Approximately 0.3-0.6%. Balances ductility and strength and has good wear resistance.
High-carbon steel: 0.6-1.0% carbon content. Very strong, used for springs, swords and high-strength wires.
Ultra-high-carbon steel: Approximately 1.25-2.0% carbon content. Steels that can be tempered to great hardness. Used for special purposes like knives, axles or punches.
As the carbon percentage content rises, steel has the ability to become harder and stronger through heat treating; however, it becomes less ductile. Regardless of the heat treatment, a higher carbon content reduces weldability. In carbon steels, the higher carbon content lowers the melting point.
Carbon Steel has a melting temperature of 1425 - 1540C (2600 - 2800F).