Abstract: Samples of a 1Cr13 martensitic stainless steel were plasma nitrided at different atmosphere proportions. Effects of different atmosphere proportions on performance of plasma nitrided layer of martensitic stainless steel were studied. The results showed that 1Cr13 stainless steel obtained the best microstructure and properties of nitrided layer after low temperature plasma nitriding when the atmosphere proportion of ammonia and argon was 8 ∶1. The surface hardness was 1 100HV 1 which was four times of the untreated samples and had a good gradient. Besides， its thickness was 85. 7μm. When the atmosphere proportion changed from 4∶1 to 8∶1，the hardness and thickness of nitrided layer were improved. The thickness almost remained the same when the proportions were 12 ∶1 and 16 ∶1，but the black substance formed on the surface of stainless steel made the hardness of surface and nitrided layer perform inhomogeneity. When the proportion was 16 ∶1，the central hardness declined to 625. 0HV 1 ，that was 450HV 1 lower than the hardness of the edge.

Key words: 1Cr13, stainless steel, low temperature, plasma nitriding, microstructure and property