レーザビームを用いた冷間ダイス鋼放電加工面の改質

残留応力解放機構の解明

抄録

The method of laser surface modification with melting has been proposed for surface modification of electrical discharge machined surfaces. This method can eliminate defects, such as cracks and micro-craters, by melting and solidifying heat-affected zones using a laser beam. However, the tensile stress, which ranges from 550MPa to 850MPa, is retained in the laser-irradiated surface, and residual stress can be removed by aging treatment. In this study, the residual stress relief mechanism was experimentally examined, and the following results were obtained. The tensile residual stress on the laser-treated material is removed due to the reason that the retained austenite structure is transformed into a martensite one. This transformation is achieved by precipitating the carbides at the grain boundaries. The relationship between the aging temperature and aging time was experimentally determined when the residual stress on the laser-treated material was removed by aging treatment. It was found that the residual stress on the laser-treated material can be removed after a short time of 5 minutes by performing aging treatment at 600°C.