Cold working die steel, SKD11, is commonly used for the fabrication of metal molds owing to its superior wear and corrosion resistance properties. Carbides containing coarse grains in a melted layer can be completely decomposed into their elements by the laser irradiation of SKD11. Crystalline structures also change in the melted layer. In this study, the creation of a functionally graded material based on hardness was carried out experimentally, by controlling the crystalline structure and grain size on the basis of the change in feed speed. The crystalline structures in the melted layer become fine-grained, columnar and coarse-grained at a power density of 3.1x10
5W/cm
2 and a feed speed of 300mm/min. The tensile residual stress on the laser-irradiated material can be removed by aging treatment for 5 minutes at 850°C. Under the above-mentioned conditions, the crystalline structures barely change before and after the aging treatment. Finally, the hardness changes linearly from 830
HV at the surface to 680
HV in the base metal. Thus, SKD11 with functionally graded structure was developed by combining laser irradiation and aging treatment.
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