Laminar plasma jet surface hardening of P20 mold steel: Analysis on the wear and corrosion behaviors

Insight into the effects of the laminar plasma jet (LPJ) surface hardening on the wear and corrosion behaviors of P20 mold steel is critical for seeking an effective way to improve the service life of the injection mold. In this study, the LPJ treatment was conducted on the surface of commercial P20 mold steel. Numerical simulation for the temperature field of the workpiece surface was employed to analyze the transformation mechanism of the microstructure. According to the numerical simulation results, the formation of a hardened layer with the lath-martensite microstructure was attributed to the ultra-fast cooling rate. Alteration in the wear and corrosion behaviors were investigated in detail by a series of ball-on-disk tribological tests and electrochemical corrosion tests. The results showed that the average coefficient of friction for the treated sample decreased from 0.314 to 0.186, and the wear rate decreased from 0.323 × 10−4 to 0.141 × 10−4 mm3/N·m. In addition, the wear mechanism of the surface of the P20 mold steel changed from abrasive wear combined with adhesive wear to mild oxidative wear after LPJ treatment. Improvement of the wear resistance was mainly attributed to the formation of lath-martensite with high hardness. Besides, it was found that the corrosion rate for the treated sample decreased from 0.2427 to 0.0680 mm/year. This was mainly attributed to the generation of the compact lath-martensite structure and the homogeneously distributed Cr element after LPJ treatment. These findings provide the theoretical feasibility for applying the LPJ surface hardening to the P20 mold steel to elevate the service life of the injection mold.