Abstract

Precipitation and related phase transformation during aging of a hot-rolled Mo-free lean duplex stainless steel (DSS) were investigated. This steel belongs to a class of newly developed TRIP-aided lean DSS. The hot-rolled plate of the present DSS was solutionized at 1100 °C for 5 min, aged in the temperature range of 600–1000 °C for up to 2 h and then water-quenched. The microstructure of the aged DSS was analyzed by electron backscattered diffraction, (scanning-)transmission electron microscopy, and electron probe micro analysis. The Cr₂N rapidly precipitated at the δ-ferrite/γ-austenite phase boundary and δ grain interior and boundary, but precipitation of the σ phase and carbides was suppressed due to the absence of Mo. A zone of Cr and N depletion related to Cr₂N precipitation formed on the primary austenite side rather than on the δ-ferrite side, resulting in formation of secondary austenite by consuming the primary austenite as aging proceeded. The secondary austenite formation of the present DSS is in contrast to that of conventional Mo-bearing DSS in which the σ phase and secondary austenite precipitate on the δ ferrite side. The fractions of Cr₂N and secondary austenite continuously increased during up to 2 h aging without σ phase precipitation. The similarities and differences of microstructural evolution of the present TRIP-aided lean DSS and conventional DSS during aging were addressed. The effects of such microstructural evolution on the room temperature tensile properties of the present DSS were also discussed.

Graphic Abstract

中文翻译：

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TRIP辅助无钼精益双相不锈钢热轧板时效过程中二次奥氏体的形成

摘要

研究了热轧无钼贫双相不锈钢 (DSS) 时效过程中的沉淀和相关相变。这种钢属于一类新开发的 TRIP 辅助精益 DSS。本 DSS 的热轧板在 1100°C 下固溶 5 分钟，在 600-1000°C 的温度范围内时效长达 2 小时，然后水淬。通过电子背散射衍射、（扫描-）透射电子显微镜和电子探针显微分析来分析老化的DSS的微观结构。Cr ₂ N 在 δ-铁素体/γ-奥氏体相界和 δ 晶粒内部和边界处快速析出，但由于没有 Mo，σ 相和碳化物的析出受到抑制。铬₂N 析出在初生奥氏体侧而不是在 δ-铁素体侧形成，导致随着时效进行消耗初生奥氏体而形成二次奥氏体。本 DSS 的二次奥氏体形成与常规含 Mo DSS 形成对比，其中 σ 相和二次奥氏体沉淀在 δ 铁素体侧。Cr ₂ N 和二次奥氏体的分数在长达 2 小时的时效期间不断增加，而没有 σ 相析出。解决了当前 TRIP 辅助精益 DSS 和传统 DSS 在老化过程中微观结构演变的异同。还讨论了这种微观结构演变对本 DSS 室温拉伸性能的影响。

图形摘要