Microstructure Evolution of a Cold-rolled 25Cr-7Ni-3Mo-0.2N Duplex Stainless Steel during Two-step Aging Treatments

doi:10.1007/s40195-013-0210-0

Abstract

Abstract:

A cold-orlled 25Cr-7Ni-3Mo-0.2N duplex stainless steel (DSS) has been aged in two steps. Firstly, the aging treatment at interval of 50℃ in a temperature range from 900 to 1050℃ was carried out in order to obtain fine grains. Secondly, another aging treatment at 850℃ was performed to reveal the σ-phase precipitation behavior. A detailed microstructure evolution during those two aging steps was observed by the optical microscope (OM), the scanning electron microscope (SEM), the electron backscatter diffraction (EBSD) and the transmission electron microscope (TEM). The results revealed that the micro-duplex structure with grain size of lower than 10 μm appeared after the first aging step. However, their grain size was rapidly increased with increasing aging temperature. Meanwhile, the δ→γ and /or δ→γ+σ transformations took place in association with the occurrence of the extensive recovery or a little recrystallization inδ-grains. During the second aging treatment, σ-phase mainly nucleated atδ/γinterfaces and further grew along those interfaces into various morphologies (e.g., butterfly and granule). A novelprecipitation behavior was found in this study that theγ-grain boundaries bulged not only into the δ-grains as usual, but abnormally into theσ-phase precipitates without the prior precipitation of the isolated secondary austeniteγ₂ or another phases.

Key words: Duplex stainless steel, Microstructure evolution, Sigma phase, Aging Treatment, Micro-duplex structure

Tian LIANG, Xiaoqiang HU, Xiuhong KANG, Dianzhong LI. Microstructure Evolution of a Cold-rolled 25Cr-7Ni-3Mo-0.2N Duplex Stainless Steel during Two-step Aging Treatments[J]. Acta Metallurgica Sinica (English Letters), DOI: 10.1007/s40195-013-0210-0.

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