Cast iron has been widely used for the parts of sliding wear such as cylinder bores of motor engines. High wear resistance of the cast iron is mainly due to the fine pearlite structure and the existence of graphite, which yield hardness and lubricity, respectively. These features are derived from the rich carbon content (3-4 %). However, under more severe sliding conditions such as those in high-power motor engines or exhaust-gas recycle (EGR) engines, cast iron without any treatment is not sufficient for wear resistance. In this study, the surface modification of cast iron by laser melting was carried out to obtain a higher wear-resistant surface. The surfaces of cast iron samples were melted by a pulsed Nd:YAG laser or a CW Nd:YAG laser. The thermal changing of the laser-processed substrates was analyzed numerically to estimate the cooling rate in solidification. It was showed analytically that cooling rate in solidification is varied by laser condition and that high cooling rate is obtained by pulsed laser. A fine martensite-ledeburite microstructure with hardness of about Hv 1000 was obtained by a pulsed laser. In the pulsed laser melting, not only the cooling rates, but also the differences of the peak temperatures in the cooling phase are important parameters that have effect on the formation of the chilled mirostructure.
