Effect of low-temperature salt bath nitriding on the corrosion and wear resistance of Custom 465

To improve the wear resistance of maraging stainless steel Custom 465, the 580℃ aged steel was modified by salt bath nitriding at 440, 480 and 520℃ for 2 h, respectively. The surface phases and hardness, the microstructure of the nitrided layer, and the corrosion and wear resistance of the steel were characterized by microhardness testing, X-ray diffractometry, electrochemical corrosion workstation, ball-on-disc tribometry, surface profilometry, and scanning electron microscopy. With increasing nitriding temperature, the surface hardness increases but the corrosion resistance decreases. When the nitriding temperature is 520℃, the surface hardness is 1240 HV, much greater than 400 HV of the unnitrided specimen, and the case depth is 22 μm. The surface phase is nitrogen supersaturated solid solution in the martensite substrate at 440℃ and the pitting potential decreases by about 60 mV. A small quantity of CrN precipitates at 480℃, which decreases the pitting potential by about 180 mV and reduces the wear volume by 43%. The CrN content significantly increases at 520℃, the corrosion potential decreases by about 70 mV, and no passive region appears in the polarization region. The wear volume gets a significant reduction, about 82% less than that of the unnitrided sample. The 520℃ nitrided sample has a better wear resistance.