Comparative study on tribological properties of ion sulfurized layers on different steel under oil lubrication

High speed steel, die steel and plain carbon steel were sulfurized by means of the low temperature ion sulfurization process, allowing the formation of sulfide layers mainly composed of FeS with a thickness of 10 μm. The tribological properties of the sulfide layers under oil lubrication were investigated on a ball-on-disc friction and wear tester. The morphologies of the cross-section and wear scars, and the phase structure of the sulfide layers were analyzed by means of scanning electron microscopy equipped with energy dispersive spectrometry and X-ray diffraction. The chemical states of the worn surfaces of the sulfide layers were examined by means of X-ray photoelectron spectrometry. It was found that the sulfide layers were of porous and non-uniform structure and composed of randomly distributed nano-scale sulfide grains. The tribological properties of all the tested steel were improved remarkably after sulfurization. The differences in the tribological properties of the different steel were mainly attributed to the differences in the hardness, microstructure and corrosion resistance. 5CrNiMo, 45 steel and W6Mo5Cr4V2 are used in the test.