Carburizing is a process that adds carbon to the surface of low-carbon steels at high temperatures, forming a high-carbon martensitic case. This case provides good wear and fatigue resistance while the core remains tough. The carbon content of the carburized layer is typically 0.8-1.0% carbon. Nitriding introduces nitrogen into steel surfaces using ammonia gas between 495-565°C, resulting in a hard nitride case that improves wear resistance, fatigue life, and corrosion resistance without quenching. Carbonitriding involves diffusing both carbon and nitrogen into steel surfaces to form a case with hardness up to HRC 65 using propane or methane mixed with ammonia.