What is the typical carbon content range of steel, and what property does carbon primarily confer?

• A. 0.60% carbon; improves oxidation resistance
• B. 0.05-2.0% carbon; principal hardening agent
• C. 1.5-3.0% carbon; increases brittleness
• D. 0.01-0.05% carbon; exceptional weldability

Answer: (B)

Carbon content in steel and its role in hardening. Steel typically contains about 0.05 to 2.0 percent carbon by weight. This range is what makes steel capable of heat treatment to achieve higher hardness and strength. Carbon acts as the primary hardening agent because it enables the formation of harder microstructures and iron-carbide, which impede dislocation motion and raise hardness when the steel is properly quenched and tempered. There are trade-offs: higher carbon increases hardness but can reduce ductility and weldability, while very low carbon steel is more ductile and easier to weld. Oxidation resistance comes mainly from other alloying elements and coatings, not carbon. So the best description is the typical carbon range plus carbon as the principal hardening agent.