Nitriding:
Nitriding is a surface hardening process in which nitrogen is diffused into the surface of the steel to create a hardened layer. While nitriding can be a suitable method for hardening certain types of steel components, it is not typically used for surface hardening cast steel crankshafts.

Normalizing:
Normalizing is a heat treatment process that involves heating the steel to a specific temperature, holding it at that temperature for a period of time, and then cooling it in air. Normalizing is primarily used to refine the grain structure of the steel and improve its mechanical properties, but it does not provide surface hardening.

Induction Heating:
Induction heating is a process that uses electromagnetic induction to heat a metal object. In the case of a cast steel crankshaft, induction heating can be used to selectively heat the surface of the crankshaft to a high temperature, allowing for rapid quenching and subsequent hardening of the surface.

Carburizing:
Carburizing is a surface hardening process in which carbon is diffused into the surface of the steel to create a hardened layer. This process is commonly used for hardening steel components such as crankshafts, gears, and bearings. In the case of a cast steel crankshaft, carburizing can be an effective method for achieving the desired surface hardness.