Abstract: The precipitation behavior of precipitates in S32750 super duplex stainless steel was studied by aging treatment at 850 ℃. Thermo-Calc software was used to predict the precipitates and phase composition in tested steel. OM， SEM and EDS were used to analysis the microstructure and precipitates of S32750 super duplex stainless steel after different aging treatment. K-J-M-A model was used to analysis the kinetic of precipitation of σ phase. The results showed that the σ phase was preferred to precipitate at ferrite/austenite boundaries during the aging process at 850 °C. There were two main steps to control the precipitation of σ phase： nucleation control and element diffusion control. In addition， χ phase and Cr₂N phase also precipitated during aging treatment. χ was the sub-stable phase， precipitated in the early aging period， and finally transformed into σ phase with the prolongation of aging time.

Key words: Duplex Stainless Steel, Precipitates, Kinetic, Aging Treatment

摘要： 通过在850 ℃时效处理研究了S32750超级双相不锈钢析出相的析出行为。采用Thermo-Calc热力学软件预测析出相及相组成，采用OM，FE-SEM和EDS对S32750超级双相不锈钢铸坯不同时效状态下的样品进行全面分析，利用K-J-M-A模型进行σ相析出动力学拟合。实验结果表明：850 ℃时效过程中，σ相优先在铁素体内部和双相晶界处析出，直至铁素体相耗尽；σ相的析出动力学控速环节主要是：初始阶段形核控速和时效40 min后的元素扩散控速；除σ相外，时效过程中还会析出χ相和Cr₂N相。其中χ相属于亚稳定相，主要在时效前期析出，随着时效时间的延长最终转化成σ相。

关键词: 双相不锈钢, 析出相, 析出动力学, 时效