Abstract: With the improvement of the quality and performance requirements of duplex stainless steel （DSS） in the industry， secondary austenite （γ₂） has become one of the key factors affecting the application of S32750 DSS. Secondary austenite is considered as the joint product of temperature and cooling rates， which performed near K-S or N-W orientation relationship with the ferrite phase and an enrichment for N elements .Secondary austenite can be divided into needle-shaped austenite （NA） and isolated austenite （IA） by morphology. In this paper， the effect of N mass fraction on the precipitation behavior of secondary austenite was studied by preparing test steels with N content of 0.02%， 0.09% and 0.17%. Thermal-Calc simulation and EBSD detection proved that with the increase of N， γ₂ evolved from curved feather-shape to needled-shape with the total proportion of austenite phase increased. The precipitation mode of austenite related to the Gibbs free energy， which was namely affected by elements composition and temperature.

Key words: Duplex Stainless Steel, Secondary Austenite, Nitrogen Mass Fraction, Precipitation Behavior, Nuclear Driving Forces

摘要： 随着行业对双相不锈钢品质及性能要求的提升，二次奥氏体已经成为影响S32750双相不锈钢应用的关键因素之一。二次奥氏体是“温度-冷却速率”共同作用的一种亚稳态产物，与铁素体相呈近K-S或N-W位向关系，且对N有富集作用，可按形貌将其分为针状二次奥氏体和孤岛状二次奥氏体。研究了N含量对二次奥氏体析出行为的影响。通过制备w［N］为0.02%、0.09%和0.17%的试验钢，并借助热模拟及EBSD检测可知，随着N含量增加，二次奥氏体由弯曲羽毛状向板条形针状转变，且奥氏体相的整体比例增加。经计算可知，奥氏体相的析出方式与本征吉布斯自由能相关，即受到成分与试验温度的影响。

关键词: 双相不锈钢, 二次奥氏体, N含量, 析出行为, 形核驱动力