What heat-treating operation chemically changes the surface of the metal by introducing a high carbide or nitride content?

Case hardening is the process that chemically alters the surface of a metal by increasing its hardness through the introduction of carbon or nitrogen compounds. This specific treatment creates a hard outer layer while maintaining a tougher inner core, which enhances the overall durability and wear resistance of the component.

During the case hardening process, materials like steel are exposed to carbon or nitrogen-rich environments at elevated temperatures. This leads to the diffusion of these elements into the surface of the metal, resulting in a high concentration of carbides or nitrides. The new surface structure, which is significantly harder than the underlying material, is especially beneficial for components that face significant wear or stress during operation.

While tempering helps to relieve stresses post-hardening and normalizing aims to refine grain structure and improve mechanical properties, neither of these processes specifically involves the chemical transformation of the surface layer through the introduction of carbides or nitrides. Carburizing is a technique closely related to case hardening but focuses exclusively on carbon content. Case hardening, therefore, encapsulates both carburizing and nitriding methods, allowing for a more comprehensive treatment strategy for enhancing surface properties.