Layer growth kinetics and wear resistance of martensitic precipitation hardening stainless steel plasma nitrocarburized at 460 C with rare earth addition

To study the effect of rare earth (RE) addition on low temperature plasma nitrocarburizing of martensitic precipitation hardening stainless steel, 17-4PH stainless steel was plasma nitrocarburized at 460 C for different times with RE addition. The modified layers were tested by optical microscope, scanning electron microscope, X-ray diffraction, microhardness tester and pin-on-disc tribometer. The experimental results show that the layer depth of plasma RE nitrocarburized layer can be increased up to 56% compared with plasma nitrocarburizing without RE addition. Incorporation of RE element is beneficial to the formation of nitrogen and carbon expanded martensite (α′ _N). The surface microhardness of plasma RE nitrocarburized layer can be increased to 1286 HV and higher up to 80 HV than that obtained from the conventional treated one. The friction coefficient of martensitic stainless steel can be dramatically decreased by low temperature plasma nitrocarburizing with RE addition, and the friction coefficient of the modified specimens decrease gradually with increasing process time in the present test condition.