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

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