Correct option is D
Cyaniding is a surface hardening process that involves the addition of nitrogen and carbon to the surface of steel. This is typically done by immersing the steel in a molten cyanide bath at temperatures ranging from 800°C to 900°C. The nitrogen from the cyanide compound diffuses into the steel's surface, resulting in a hard, wear-resistant surface layer. This process is commonly used to improve the wear resistance and fatigue strength of steel components.
