Abstract: 16Cr25N ferritic stainless steel was nitrided by a high-temperature solution nitriding process in a self-designed high-temperature and high vacuum nitriding furnace, and then the microstructure and properties of the nitrided layer were analyzed by means of X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, metallographic microscopy, microhardness tester, and oxygen nitrogen analyzer. The results show that an austenitic nitrided layer with a thickness of more than 1 mm is formed on the surface of the tested steel, with the maximum single-side thickness of the nitrided layer being more than 2 mm and the maximum nitrogen content reaching 1.502%, and the original ferrite microstructure transforms into austenite, which is equivalent to obtaining a high-nitrogen and nickel-free stainless steel. and its hardness after the nitriding treatment is greatly increased to 320 HV0.5. The activation energy of nitrogen diffusion during solid solution nitriding of the 16Cr25N stainless steel is calculated by the depth of the infiltration layer, which is 176 kJ/mol under the condition of nitrogen pressure of 0.3 MPa, insulation time of 24 h, and nitriding temperature of 1200 ℃. The nitrogen content model for high temperature solution nitrided layer of the 16Cr25N ferrite stainless steel is established by using the infiltration layer hardness and diffusion theory, which has certain guiding impact.

Key words: solution nitriding, nickel-free stainless steel, high nitrogen steel, microstructure, diffusion activation energy