Effect Of Laser Surface Re-melting On The Microstructure And Properties Of Electro-metallurgic WC/steel Composites

The electro-metallurgic WC/steel composites of DGW40 and DGW50 were re-melted by CO₂ laser. The primary purpose was to find a better method to improve the surface properties of the composites. The research was focused on the analysis of microstructure transformation, the properties performing and the relationship between the solidified microstructure and the property.The result showed that the melted zone had a high homogenous and fine microstructure with the various laser processing parameters as far as the heat-treated substrate was concerned. The uniform phases were obtained in the melted zone of DGW40 and DGW50 as well. The laser affected zone could be separated into the melted zone, transient zone and heat-affected zone. As for the as-cast substrate, the matrix microstructure of the surface also could be refined as well as the carbides.Three parts including the steel matrix, WC dendrite and fine-isolated carbides, were involved into the microstructure transformation of electro-metallurgic WC/steel composites. The steel matrix went through re-solidification. Some of them reacted with the WC dendrite, forming the eutectic. The WC dendrites couldn't be dissolved completely, so-called partial dissolution. And the degree of dissolution was related to the thermal absorption. The fine and isolated carbides were dissolved into the steel matrix during the melting. The phases of melted zone was composed of WC, Fe₃W₃C, (Cr,Fe)₇C₃, martensite and retained austenite. After the melting, the phases changed a little such as the complex carbides of M₇C₃ precipitated and retained austenite.The microhardness and wear resistance of the composites could be improved by laser surface re-melting. The hardened depth increased with the increase of the melt depth, which increases with the increase of laser power and decreases with the increase of laser scanning rate. Different melted zone had approximately the same wear resistance with the same content of WC. However, the content of WC increased from 40wt% to 50wt%, the wear resistance of melted zone increased. The high microhardness and wear resistance possessed for the laser melted zone were attributed to the structure refinement, carbides precipitation and the solid solution of elements etc.