Which method uses localized heating followed by immediate quenching for steel hardening?

The method that uses localized heating followed by immediate quenching for steel hardening is flame hardening. In this process, a high-temperature flame is applied to a specific area of the steel component, causing that localized region to heat up rapidly. After reaching the desired temperature, the area is then quenched, commonly in water or oil, which rapidly cools the metal and increases its hardness due to the transformation of the microstructure.

Flame hardening is particularly effective for components that require hard surfaces but can maintain toughness in other areas, making it ideal for applications where wear resistance is crucial, such as in gears and crankshafts. The ability to control which parts of the steel are heated and hardened also provides flexibility in engineering designs.

Other methods mentioned, such as induction hardening, utilize electromagnetic induction to heat the steel, while nitriding involves diffusing nitrogen into the surface of the steel at lower temperatures to harden it without quenching. Case hardening, on the other hand, refers to processes that harden only the surface layer while leaving the inner material tougher and is not characterized by localized heating followed by quenching. Thus, flame hardening stands out as the correct answer in relation to the heating and quenching process described in the