Which process involves heating a steel and quenching it with water or oil to achieve a suitable hardness and toughness ratio?

Which process involves heating a steel and quenching it with water or oil to achieve a suitable hardness and toughness ratio?

• A. Heat treatment
• B. Hardening and tempering
• C. Annealing
• D. Nitriding

Answer: (B)

This question is about a heat treatment sequence used to increase hardness while keeping toughness workable. When steel is heated into its austenite range and then quenched in water or oil, it forms a very hard martensite. That hardness, however, can make the material brittle. To regain toughness without losing too much hardness, the steel is tempered—heated to a lower temperature after quenching—to relieve internal stresses and adjust the hardness-toughness balance. Doing both steps—hardening by quenching and tempering afterward—gives the best combination of hardness and toughness for many applications. The other processes don’t fit this specific balance: annealing softens steel and reduces hardness; nitriding hardens only the surface through diffusion and doesn’t focus on balancing hardness with toughness via tempering; a general heat treatment term is too broad to capture the two-step hardening-plus-tempering sequence.

This question is about a heat treatment sequence used to increase hardness while keeping toughness workable. When steel is heated into its austenite range and then quenched in water or oil, it forms a very hard martensite. That hardness, however, can make the material brittle. To regain toughness without losing too much hardness, the steel is tempered—heated to a lower temperature after quenching—to relieve internal stresses and adjust the hardness-toughness balance. Doing both steps—hardening by quenching and tempering afterward—gives the best combination of hardness and toughness for many applications.

The other processes don’t fit this specific balance: annealing softens steel and reduces hardness; nitriding hardens only the surface through diffusion and doesn’t focus on balancing hardness with toughness via tempering; a general heat treatment term is too broad to capture the two-step hardening-plus-tempering sequence.