Describe the process of case hardening. Give an example of the application of case hardeningand state why it is suitable for that application.

Case hardening is a heat treatment process that is used to increase the hardness of the outer surface of a material, while maintaining a softer and ductile core. This process is typically used on low carbon steels to provide a harder exterior. Here are the steps involved in case hardening:

1. Carburizing: The steel piece is heated in a furnace in the presence of a carbon-rich environment. The carbon atoms diffuse into the surface of the steel, increasing its carbon content.

2. Quenching: The steel piece is then rapidly cooled, usually in water or oil. This rapid cooling causes the high carbon surface layer to harden, while the core remains relatively soft and tough.

3. Tempering: The steel is then reheated to a lower temperature and slowly cooled. This reduces the brittleness of the steel and improves its toughness.

An example of the application of case hardening is in the manufacturing of gears. Gears need to have hard surfaces to resist wear and tear, but they also need to be tough enough to resist breaking under the high loads they are subjected to. Case hardening is suitable for this application because it provides the necessary hard surface, while maintaining a tough interior.