Which heat-treatment process produces a hard, wear-resistant surface over a strong, tough core?

Which heat-treatment process produces a hard, wear-resistant surface over a strong, tough core?

• A. Case hardening
• B. Annealing
• C. Tempering
• D. Normalizing

Answer: (C)

The idea being tested is producing a hard, wear-resistant outer layer while keeping a strong, tough interior. Case hardening does exactly that by increasing the carbon content at the surface (through carburizing or similar methods) and then hardening the surface, typically by quenching. The inner core stays comparatively low in carbon, so it remains ductile and capable of absorbing shocks. This combination gives a surface that resists wear and a core that stays tough. Other processes don’t create that distinct contrast. Annealing softens the metal to improve ductility and reduce hardness. Normalizing refines the grain and yields a more uniform hardness throughout, not a specifically hardened surface over a tough core. Tempering, done after quenching, lowers brittleness but doesn’t establish a hard wear-resistant surface with a resilient core on its own; it’s used to adjust properties after the surface has already been hardened.

The idea being tested is producing a hard, wear-resistant outer layer while keeping a strong, tough interior. Case hardening does exactly that by increasing the carbon content at the surface (through carburizing or similar methods) and then hardening the surface, typically by quenching. The inner core stays comparatively low in carbon, so it remains ductile and capable of absorbing shocks. This combination gives a surface that resists wear and a core that stays tough.

Other processes don’t create that distinct contrast. Annealing softens the metal to improve ductility and reduce hardness. Normalizing refines the grain and yields a more uniform hardness throughout, not a specifically hardened surface over a tough core. Tempering, done after quenching, lowers brittleness but doesn’t establish a hard wear-resistant surface with a resilient core on its own; it’s used to adjust properties after the surface has already been hardened.