Which statement about low carbon steel and heat treating is true?

• A. Steel with low carbon content can be hardened and tempered by heat treating.
• B. Steel with low carbon content cannot be hardened and tempered by heat treating.
• C. Low carbon steel is always harder than high carbon steel.
• D. Low carbon steel cannot be welded.

Answer: (B)

Hardening by heat treating depends on carbon content: enough carbon lets the steel form a hard martensitic structure when quenched, and then tempering adjusts that hardness. Low carbon steels have too little carbon to form significant martensite, so the typical austenitize-then-quench-hardening path won’t produce meaningful hardness. In practice, these steels are not heat-treatable for hardening in the same way higher-carbon steels are; they remain relatively soft, though they can be treated in other ways (like carburizing) for surface hardness.