Microstructure and properties of low temperature plasma carburized layer on precipitation hardening stainless steel

15-5PH and 17-4PH precipitation hardening stainless steels were plasma carburized at 460 ℃. Metallographic observation, X-ray diffraction analysis were used to characterize the microstructure and phase composition of the carburized layer. Hardness change of the carburized layer was tested by microhardness tester. The corrosion behavior of carburized layer was tested by electrochemical polarization method in 3.5wt%NaCl solution. The results show that after plasma carburizing, a “double” structure forms on the surface of stainless steels. The phases formed on stainless steel surfaces are mainly of carbon “expanded” martensite with a small amount of Fe₃C phase. The hardnesses of low temperature plasma carburized steels are all remarkablely improved. The corrosion test results show that, under the present test conditions, the corrosion resistance of stainless steel samples shows a little decrease after carburizing. For 15-5PH and 17-4PH stainless steels, as the carburized time increase, the corrosion resistances of the layer almost does not change; with increase of the carburized layer depth, for 15-5PH stainless steel, the corrosion resistance of the carburized layer decreases, while for 17-4PH stainless steel, the corrosion resistance of the carburized layer first increase and then decreases.