What effect does tempering have on steel after quenching?

• A. No change in properties
• B. Maximum hardness regardless of toughness
• C. Balanced hardness with improved toughness
• D. Reduced hardness and reduced toughness

Answer: (C)

Tempering after quenching changes the metal from very hard but brittle martensite into a form that’s still hard but much tougher. Heating to a moderate temperature relieves internal stresses from the rapid quench and allows some carbon to form small carbides, which reduces brittleness and makes the steel more able to deform without cracking. The trade-off is a slight drop in hardness, but a clear gain in toughness, giving a balanced combination that’s suitable for many applications. If tempered hotter, hardness drops further but toughness continues to improve; cooler tempering retains more hardness with less toughness gain. So the best description is a balance of hardness with improved toughness.