Abstract: Based on Cr₁₈Mn₁₄Mo₃ steel, four high-nitrogen austenitic stainless steels with 0.004%-0.850% N were designed, and smelted into electroslag remelting ingots with measured nitrogen content of 0.008%-0.770% N. The thermodynamic calculation of equilibrium phase transformations of the steels was carried out, and the microstructure morphologies were observed. The results show that for 0.40%-0.85%N steels, there is a wide single-phase austenite region in 900-1200 ℃. The four calculated equilibrium phase transformation diagrams for the tested steels show that, the maximum precipitation amount of δ-ferrite is decreased with the increase of nitrogen content. When the nitrogen content is 0.77%, the maximum precipitation amount of δ-ferrite is about 30%, the relationship between the precipitation temperature T_δ of δ-ferrite and the nitrogen content (N) during the heating process is obtained as T_δ=876+433w(N). With the increase of nitrogen content, the precipitation temperature of Cr₂N increases gradually in cooling of the tested steels, and its quantitative relationship is obtained as T_Cr2N=711+350w(N).

Key words: nitrogen content, high nitrogen austenitic stainless steel, δ-ferrite, Cr₂N, microstructure