Innovative Short Process of Preparation and Nitriding of Porous 316L Stainless Steel

Porous 316L stainless steel has a low density and high specific surface area, and is easy to process due to the large number of pores within it, making it ideal for applications such as piping in the chemical and food industries, as a medical tool, or as a fuel cell pole plate material. Nitriding treatment can further improve the hardness and strength of porous stainless steel. In this paper, a method combining vacuum sintering and nitriding treatment was proposed, i.e., 316L stainless steel powder was used as the raw material, and porous 316L was sintered in a vacuum tube furnace, in which the porous stainless steel was nitrided with nitrogen gas during the cooling process. In the research process, thermodynamic calculation and differential thermal analysis were used to determine the optimum nitriding temperature range of 700 °C~850 °C and nitriding pressure of 0.4 MPa~0.8 MPa. With the increase in nitriding temperature and pressure, the nitrogen content in the sample increased, and the nitrogen content of porous 316L stainless steel after nitriding was 0.03%~0.86%. The results show that nitrogen exists exclusively in solid solution at nitriding temperatures of 700 °C and 750 °C. At nitriding temperatures of 800 °C and 850 °C, the nitrogen existed in both solid solution and chromium nitride (CrN), and the Vickers hardness at 0.08 MPa and 850 °C was 135 HV, which was 2.82 times higher than that before nitriding. The compressive strength of the specimens was maximum at a nitriding pressure of 0.04 MPa and 850 °C. The corrosion resistance of the specimens is optimized when the nitriding pressure is 0.04 MPa and the temperature is 800 °C.