A series of experiments were carried out to study the influence of low temperature plasma nitriding on the mechanical properties of AISI 420 martensitic stainless steel. Plasma nitriding experiments were carried out for 15 hours at 350℃ by means of DC-pulsed plasma with 25%N2+75%H2 gas. The microstructure, phase composition and residual stresses profiles of the nitriding layers were determined by optical microscopy and X-ray diffraction. The microhardness profiles of the nitriding surfaces were also studied. The fatigue life, sliding wear and erosion wear loss of the untreated specimens and plasma nitriding specimens were determined on the basis of a rotating bending fatigue tester, a ball-disk wear tester and a solid particle erosion tester. The results show that the 350℃ nitriding surface is dominated by -Fe3N and , which is supersaturated nitrogen solid solution. They have high hardness and chemical stabilities. So the low temperature plasma nitriding not only increases the surface hardness values but also improves the wear and erosion resistance. In addition, The fatigue limit of AISI 420 steel can also be improved by plasma nitriding at 350℃， because plasma nitriding produces residual compressive stress inside the modified layer.
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