Abstract
The surface of high-speed steel M2 was treated by a 2.5-kW CW Nd:YAG laser with different power densities for achieving laser transformation hardening and laser surface melting. It was found that M2 cannot be hardened so effectively by laser transformation hardening, with the hardness increased to 415 Hv_<0.2> whereas for laser-melted M2, the hardness was increased to 612 Hv_<0.2>, which is at the same level as the conventionally hardened M2. Potentiodynamic polarization test shows that the laser-melted M2 possesses the highest corrosion resistance in 3.5% NaCl solution at 23℃. The enhancement in the surface hardness and the corrosion resistance of the laser-melted M2 is due to the combined effects of refinement and dissociation of large carbides and the dissolution of the alloying elements (Cr, Mo V and W) in the ultrafine martensitic and austenitic solid solution.
