Microstructure Evolution and Precipitation Behavior of a High Nitrogen 15Cr Martensitic Stainless Steel during Tempering

The microstructure evolution and precipitation behavior of a low carbon high nitrogen martensitic stainless steel containing 15%Cr-5%Ni-1%Mo-0.16%N (in mass percentage) after tempering at temperatures ranged from 300 °C~700 °C were investigated by hardness test, X-ray diffraction (XRD) and Transmission electron microscopy (TEM). The steel exhibits second hardening behavior after tempering at temperatures below 500 °C. Tempering at temperatures above 500 °C promotes the formation of reversed austenite and the precipitation of Cr2N. The coherent orientation relationship of Cr2N with martensite was revealed as , . Retained austenite originated from reversed austenite at room temperature results in the softening of the steel, and the retransformation of reversed austenite to untempered martensite after tempering at temperatures above 600 °C restores the hardness of the steel. σ phase was also found in specimens tempered at temperatures ranged from 500 °C to 700 °C.