Influence of laser surface engineering of AISI P20-improved mold steel on wear and corrosion behaviors

The wear and corrosion characteristics of a mold steel (AISI P20-improved, KP4M) were investigated before and after the laser surface engineering. The laser surface engineering of AISI P20-improved steel was conducted at different laser energy densities by a high-power diode laser. The microstructure of the base metal changed from tempered martensite to lath-type martensite. In addition, the surface hardness was enhanced from 307 HV to 545, 657, and 610 HV when the laser energy density was 220, 315, and 420 J/mm², respectively. An electron probe micro-analyzer revealed that microstructural homogenization was introduced by the laser surface engineering at 220 and 315 J/mm², whereas an elemental segregation of chromium and manganese was observed with the laser surface engineering at 420 J/mm² due to partial melting and solidification process. The laser surface-engineered samples showed an enhancement in the wear resistance in both the fretting and block-on-ring tests as compared to that of the base metal, and the highest wear resistance was detected for the laser surface-engineered at 315 J/mm² owing to the largest increment in the hardness. In terms of corrosion resistance, the laser surface-engineered AISI P20-improved steel at 315 J/mm² showed a marginal improvement in the corrosion resistance as compared to that of the base metal because of the microstructural homogenization. Contrastingly, a marginal deterioration of the corrosion resistance was examined for the laser surface-engineered AISI P20-improved steel at 420 J/mm² because of the elemental segregation.