What process is used to increase the hardness of mild steels by adding carbon?

The process used to increase the hardness of mild steels by adding carbon is case hardening. This technique involves hardening the surface layer of the steel while maintaining a relatively softer, ductile core. By introducing carbon into the outer surface, the steel can undergo a transformation into a harder phase, such as martensite, upon subsequent heat treatment.

Case hardening is particularly beneficial in applications where wear resistance is crucial while still retaining toughness in the core of the material. The process often involves heating the steel in a carbon-rich environment and then quenching it to lock in the hardness achieved through this superficial interaction.

Other processes mentioned, such as hardening, nitriding, and normalising, serve different purposes. Hardening generally refers to increasing hardness through various heat treatments without specifically adding carbon. Nitriding introduces nitrogen, which alters the properties differently than carbon. Normalising is a heat treatment aimed at refining the grain structure to improve toughness rather than directly increasing hardness. Each process has its specific applications based on the desired properties of the steel.