Improving the Erosion and Erosion–Corrosion Properties of Precipitation Hardening Mold Steel by Plasma Nitriding

Abstract

In this study plasma nitriding of precipitation hardening mold steel has been carried out at 470, 500 and 530°C for 12 h in order to achieve good erosion and erosion–corrosion resistance. The microstructure, phase present and microhardness profiles of unnitrided and nitrided layers were examined. The influence of plasma nitriding on the erosion and erosion–corrosion resistance of the tested steel was investigated using a jet solid particle erosion tester and a rotated slurry erosion–corrosion tester.The results indicate that the surface properties of the plasma nitrided layers in terms of hardness, erosion wear, and erosion–corrosion resistance are highly dependent on nitriding temperature, and all three plasma surface treatments can significantly improve the surface hardness and effective enhance their erosion resistance under dry erosion. The erosion–corrosion resistance in 20 mass% SiC particles/3.5% NaCl slurry can be effectively improved 48, 65 and 68% by plasma nitrided at 470, 500 and 530°C, respectively. The erosion rate decreases with increasing surface hardness and obeys a power function (\skew4\dotE ∝ H - n) with exponent of 1.047. However, the correlation between erosion–corrosion rate and hardness does not obey any power functions of the exponent in the range of 1–1.5 due to the complexity of the interaction between erosion and corrosion.