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| Morphologies of secondary austenite in 2507 duplex stainless steel after heat treatment |
| Xiao-han Wu1,2, Zhi-gang Song2, Bao-shun Wang3, Ming-hua Wu4, Qi-liang Nai5, Liang Yao4, Han Feng2, Wen-jie Zheng2 |
1 School of Material Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China
2 Special Steel Institute, Central Iron & Steel Research Institute, Beijing 100081, China
3 Engineering Research Center of High-Performance Nuclear Power Pipe Forming of Zhejiang Province, Huzhou 313028, Zhejiang, China
4 Yongxing Special Stainless-Steel Co., Ltd., Huzhou 313005, Zhejiang, China
5 Zhejiang Jiuli Hi-Tech Metals Co., Ltd., Huzhou 313028, Zhejiang, China |
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Abstract The microstructure evolution of secondary austenite in 2507 duplex stainless steel was investigated by means of optical metallography, scanning electron microscopy and confocal scanning laser microscopy. Four types of secondary austenite (γ2) morphologies including partially transformed austenite, grain boundary austenite, Widmannstätten austenite (WA) and intragranular austenite could be formed during cooling after solution treatment. It was concluded that secondary austenite morphology was mainly dependent on cooling rates. Two mechanisms of WA formation were proposed. WA nucleated at grain boundary of ferrite or at the formed phase boundary. Transmission electron microscopy (TEM) analysis displayed that WA grew in parallel to the ferrite. The effects of Cr2N on secondary austenite precipitation were discussed in detail. Once Cr2N was involved, a mechanism was proposed that secondary austenite formed by element diffusion, leading to the migration of the austenite–ferrite interface. Cr2N acted as the nucleation sites for γ2 and provided the nitrogen for the transformation; meanwhile, the precipitation of Cr2N during the rapid cooling was captured by TEM. A process of nucleation followed by diffusion was concluded to be the formation of secondary austenite with no Cr2N precipitated. The decomposition of secondary austenite was also studied, which was found to be a diffusion mechanism followed by displacement in connection with the element distribution.
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Received: 08 January 2021
Published: 25 June 2022
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| Cite this article: |
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Xiao-han Wu,Zhi-gang Song,Bao-shun Wang, et al. Morphologies of secondary austenite in 2507 duplex stainless steel after heat treatment[J]. Journal of Iron and Steel Research International, 2022, 29(6): 994-1003.
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2022, Vol. 29 
