How and why case hardening is done?

Case hardening is a heat treatment process used to harden the surface of a metal while maintaining a softer, ductile interior. This is typically achieved through methods like carburizing, nitriding, or carbonitriding, where carbon or nitrogen is introduced into the surface layer of the metal at high temperatures. The primary purpose is to enhance wear resistance and fatigue strength, making components more durable in high-stress applications, such as gears and bearings. By hardening the surface, the underlying material retains its toughness, preventing brittleness and failure.