Case harden is a metal heat treatment process designed to increase the hardness and wear resistance of the steel surface while maintaining its internal toughness and strength. This process is usually applied to mild steel or alloy steel. The specific process includes the following steps:

1.Carburizing: The workpiece is placed in an environment containing carbon sources (such as carbides, gases or solids) for heating, so that carbon atoms penetrate into the surface of the steel.

2.Quenching: After carburizing, the workpiece is quickly cooled to form a hardened martensite structure, which significantly increases the surface hardness.

3.Tempering: In order to eliminate internal stress and improve toughness, tempering is then performed, usually at a lower temperature.

Through this method, the surface of the workpiece can obtain a hardness of up to 60 HRC (Rockwell Hardness), while the interior maintains a relatively low hardness to ensure that the workpiece is not easily broken when subjected to pressure and impact. Surface hardening is widely used in parts such as gears, bearings, and cutting tools that require high wear resistance.