Effect of Gradient Nanostructure on Plasma Sulfonitrocarburizing of 42MnCr52 Steel

Abstract

A nanocrystalline layer was fabricated on the surface of 42MnCr52 steel by ultrasonic surface rolling processing (USRP). Plasma sulfonitrocarburizing (PSNC) was performed on the untreated surface and nanostructure surface to obtain a composite layer composed of the solid lubrication layer (FeS) and nitrocarburized subsurface layer. The effect of the nanocrystalline layer on PSNC was investigated using phase analysis, microstructural analysis, element analysis, hardness analysis, and wear property analysis. The results are as follows: The average grain size of the gradient nanostructure surface was about 40 nm. A more compact and homogeneous sulfide composite layer was formed on the surface of the USRP + PSNC specimen, and the sulfide composite layer was mainly composed of an FeS phase with excellent solid lubrication properties. The thickness of the nitrocarburized layer was increased by 130% on average and its homogeneity also improved after USRP. The hardness value of the subsurface (nitrocarburized layer) of the USRP + PSNC specimen was higher than that of the PSNC specimen. The wear volume and frictional coefficient of the USRP + PSNC specimen were obviously lower than those of the PSNC specimen. The USRP + PSNC specimen exhibited strong wear resistance.