Abstract
In electrical discharge machining (EDM) of die steel, a hard white layer, which is different from the base metal, is formed on the metal mold surfaces caused by rapid heating and cooling. Cracks and micro-craters appear on the surface of the white layer depending on the machining conditions used. Such heat-affected zones (HAZ) can greatly shorten the life of metal molds. In this study, the method of laser surface modification with melting has been proposed as a new surface modification method. This method can eliminate defects, such as cracks and micro-craters, by melting and solidifying HAZ using a laser beam as the heat source. As a result, the laser-irradiated surface, in the absence of an absorbent, is converted into a flat surface with neither cracks nor micro-craters that are generated by EDM. It was found that tensile stress with values ranging from 550MPa to 850MPa is retained in the irradiated surface, and the residual stress can be removed by aging treatment at 580-600℃.
