Microstructural studies of QPQ complex salt bath heat-treated steels

Abstract QPQ salt bath surface treatment has been developed successfully in China, introducing a new salt to the bath and offering superior surface properties such as high hardness, good wear-resistance, improved fatigue resistance and very good corrosion resistance for the treated components. In recent years the method has been used widely: for tools and moulds to increase their strength and to extend their life; for gears to increase their strength, wear-resistance and fatigue strength and to secure less distortion; for automobile parts to increase their wear-resistance and corrosion resistance; also for PCB parts to increase their hardness, wear resistance and corrosion resistance and to reduce their distortion. This article emphasizes the microstructural and compositional analysis, and also the effects of temperature and process duration on the depth of the nitrided layer.