Laser hardening is a surface hardening technique. It is used exclusively on ferrous materials that are suitable for hardening. These comprise steels and cast iron that have a carbon content of more than 0.2%.
To harden the workpiece, the laser beam usually heats the surface to just below the melting temperature, which is around 900 to 1400 °C. Once the setpoint temperature is reached, the laser beam starts to move, thereby steadily heating the surface area in the direction of feed. The high temperature causes the carbon atoms in the metal lattice to rearrange (austenitization). As the laser beam moves on, the surrounding material cools down the hot surface very quickly in a process known as self-quenching. As a result of the rapid cooling, the metal lattice is unable to return to its original form, producing martensite. Martensite is a very hard metal structure. The transformation into martensite increases the hardness of the metal.