Abstract Phase separation in ferrite of a duplex stainless steel during aging at 400 °C for up to 20,000 h has been found to be non-uniform in nature by using atom probe tomography. Aging-induced segregation of Ni takes place strongly at the austenite/ferrite interfaces accompanied by the formation of Ni depletion zones (NDZs) in the ferrite in the vicinity of the interfaces. Consequently, the phase separation in the NDZs is microscopically and kinetically different from that in the inner ferrite. The nucleation and growth of G-phase in the NDZs are suppressed, and the growth of α′-phase is decelerated. In contrast, the G-phase at the austenite/ferrite interfaces exhibits a delayed heterogeneous nucleation and thereafter accelerated growth. The phase-separation difference between the NDZ and the inner ferrite results in a gradient microstructure (from outer to inner) developing in each ferrite grain during the prolonged aging. The strong segregation of Ni and the high decoration of G-phase at the ferrite/austenite interface are responsible for degradation in impact toughness of the steel.

中文翻译：

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双相不锈钢铁素体的非均匀相分离

摘要 使用原子探针断层扫描发现双相不锈钢在 400 °C 时效长达 20,000 小时期间铁素体中的相分离在性质上是不均匀的。时效诱导的 Ni 偏析发生在奥氏体/铁素体界面，伴随着界面附近铁素体中 Ni 耗尽区 (NDZ) 的形成。因此，NDZ 中的相分离在微观和动力学上与内部铁氧体中的相分离不同。NDZs中G相的成核和生长受到抑制，α'相的生长减速。相比之下，奥氏体/铁素体界面处的 G 相表现出延迟的异质成核，然后加速生长。NDZ 和内部铁素体之间的相分离差异导致在长时间时效期间在每个铁素体晶粒中形成梯度微观结构（从外到内）。Ni 的强烈偏析和铁素体/奥氏体界面处 G 相的高度装饰是钢的冲击韧性下降的原因。