Carbon steel is a steel with carbon content up to 2.1% by weight.

Carbon steel is broken down into four classes based on carbon content:

Low-carbon steel
0.05 to 0.30% carbon content..

Medium-carbon steel
Approximately 0.3–0.8% carbon content. Balances ductility and strength and has good wear resistance; used for large parts, forging and automotive components.

High-carbon steel
Approximately 0.8–2.0% carbon content. Very strong, used for springs, edged tools, and high-strength wires.

Ultra-high-carbon steel
Approximately 3.25–4.0% carbon content. Steels that can be tempered to great hardness. Used for special purposes like (non-industrial-purpose) knives, axles or punches. Most steels with more than 2.5% carbon content are made using powder metallurgy.