Laser transformation hardening of AISI 440C martensitic stainless steel for higher cavitation erosion resistance

摘要

Surface hardening of AISI 440C martensitic stainless steel was achieved by laser transformation hardening (LTH) using a high-power CW Nd:YAG laser. A hardened layer of a few 100 μm thick, composed of martensite, retained austenite and fine carbides was formed. The microstructure and hardness of the laser-treated layer were dependent on the laser processing parameters, with the hardness values reaching the range 600-800 HV. Compared with conventionally heat-treated samples, the laser-treated samples contained more retained austenite and finer carbides due to a higher degree of carbide dissolution. The cavitation erosion resistance of AISI 440C was significantly improved after laser treatment, and was approximately three-fold higher compared with that achieved by conventional heat treatment. The high erosion resistance was attributable to a desirable microstructure, which exhibited a favorable combination of hardness and toughness, and contained fewer weak sites for erosion attack.