Laser hardening is a surface hardening process. It is used exclusively on ferrous materials suitable for hardening including, steels and cast iron with a carbon content of more than 0.2 percent.
To harden the workpiece, the laser beam usually warms the outer layer to just under the melting temperature (about 900 to 1400 degrees Celsius). Once the desired temperature is reached, the laser beam starts moving. As the laser beam moves, it continuously warms the surface in the processing direction. The high temperature causes the iron atoms to change their position within the metal lattice (austenization). As soon as the laser beam moves away, the hot layer is cooled very rapidly by the surrounding material in a process known as self-quenching. Rapid cooling prevents the metal lattice from returning to its original structure, producing martensite. Martensite is a very hard metal structure. The transformation into martensite yields greater hardness.