1. Xinxing Ductile Iron Pipes Co., Ltd., Handan 056000, Hebei, China; 2. Institute for Special Steels, Central Iron and Steel Research Institute, Beijing 100081, China
Abstract:The equilibrium precipitates of S31254 super austenitic stainless steel in the temperature range of 500-1 200 ℃ were calculated by thermodynamics. The precipitating behavior of different precipitates were characterized and analyzed by thermal simulation test, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and other methods. The results show that the second phases in the austenitic matrix of S31254 stainless steel include intermetallic phases such as σ, χ and Laves, Cr2N, π-type nitride phases and M23C6 type carbide phases. The high Mo, high N and high Cr contents are the main reasons for the complexity of precipitates. The experimental steel has a high tendency to precipitate the second phase. The initial precipitation temperature of σ phase is about 1 150 ℃, and the conversion of χ phase and σ phase can be found in the range of 900-800 ℃. The χ phase is more likely to exist as a stable phase. The location and morphology of precipitates are different. The grain boundary precipitates are mainly σ phase, χ phase and Laves phase, while the intergrain precipitates are mainly acicular and massive χ phase and rod-shaped Cr2N phase.
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