Correct option is A
Case hardening is a heat treatment process used to increase the surface hardness of mild steel while maintaining a ductile and tough core.
Among the given options, Nitriding is a case hardening process where nitrogen is diffused into the surface of steel at a temperature of 500°C – 600°C to form hard nitrides, improving wear resistance and surface hardness.
Mild steel, due to its low carbon content, cannot be hardened by conventional quenching and tempering. However, case hardening processes like nitriding, carburizing, cyaniding, and carbonitriding can be used to create a hard surface layer while keeping the core soft and tough.
