Which heat-treating operation would be performed when the surface of the metal is changed chemically by introducing a high carbide or nitride content?

Case-hardening

Explanation:

Case-hardening

It is the process of hardening the surface of the metal object and allowing the metal which is deep inside to remain soft, hence, making a thin hard outer layer on the surface.

In case of iron which have low carbon content, the case - hardening is done by introducing high carbide or nitride content.

The process of case - hardening is done, in the final shaping process.