In heat treatment, tempering after quenching is performed to increase toughness while maintaining hardness. Which option best represents this description?

• A. Higher hardness at expense of toughness
• B. Reduces brittleness to improve toughness
• C. Increases brittleness
• D. No change in properties

Answer: (B)

Tempering after quenching reduces brittleness to improve toughness while keeping hardness high. After quenching, steel becomes very hard but also very brittle due to the martensitic structure and internal stresses. Reheating to a moderate tempering temperature allows some carbon to diffuse and internal stresses to relax, which smooths the microstructure and makes the metal more ductile. This trade-off lowers brittleness and crack sensitivity without a large drop in hardness, so toughness increases while hardness remains substantial. The other descriptions don’t capture this balance: tempering doesn’t increase brittleness or leave properties unchanged, and it doesn’t make hardness stay the same while sacrificing toughness.