Wear and corrosion behavior of P20 steel surface modified by gas nitriding with laser surface engineering

Abstract

Gas nitriding and laser surface engineering are popular technologies to improve the surface performance of steels. This study evaluates the effect of duplex treatment of gas nitriding and laser surface engineering on surface hardness, wear and corrosion resistance of P20 plastic mold steel. It is found that gas nitriding at 550 °C for 20 h with nitrogen potential of 0.18 generates a nitrided layer without nitrides, which drastically improves the wear resistance. Simultaneously, the corrosion resistance is also marginal improved by the gas nitriding. Laser surface hardening further elevates the surface hardness and wear resistance of the nitrided layer due to the formation of martensite. Besides, a small amount of austenite retains in surface layer after laser surface hardening, which may lead to the galvanic attack at the phase interface between martensite and retained austenite and deteriorate the surface corrosion resistance. Laser surface melting results in the denitrification of nitrided layer and the formation of holes at the bottom of melted layer, thus reducing the surface hardness and wear resistance. Meanwhile, the denitrified surface layer also exhibits a degraded corrosion resistance owe to the decreasing nitrogen content and the formation of mixed structure of martensite and retained austenite.