Which crankshaft hardening technique achieves the deepest hardening effect?

Induction hardening is considered the technique that achieves the deepest hardening effect among the options provided. This method involves using an induction coil to generate a strong electromagnetic field, which heats the surface of the crankshaft rapidly to austenitizing temperatures. The depth of hardening achieved through induction hardening can vary based on several factors, such as the frequency of the current and the duration of exposure. As the heated surface cools, it transforms into a hard martensitic structure, leading to a significant increase in hardness over a relatively deep area compared to other techniques.

Flame hardening, while effective, typically hardens a shallower section of the material due to the nature of the heat source and the cooling method employed. Surface hardening refers to techniques that improve surface wear resistance but do not penetrate deeply into the material. Case hardening combines hardening the surface with a protective layer, but again, it does not provide the same depth of hardness that induction hardening can achieve.

Understanding the nuances of these processes is crucial for optimal crankshaft performance, particularly in applications that demand high wear resistance in deeper sections of the material.