This study describes laser heat treatment of die steels using YAG laser on-the-machine tool. An optical fiber has been used in order to transmit the laser light from a source to workpieces at this system. At first, the temperatures based on a theoretical model during laser irradiation were estimated in order to predict the hardened range of workpieces. Second, experiments of laser heat treatment were carried out for various die steels in order to grasp the relationship between the hardened depth and irradiation conditions. Finally, a method to repeat laser irradiation at the same area was proposed to increase the hardened depth. As a result, the detail of the hardened depth for various die steels becomes clear under various laser irradiation conditions. It is found that this heat treatment of die steels with YAG laser on-the-machine tool is an effective method.
