Abstract
A series of tensile tests, Charpy impact tests, optical microscopy observations, and field emission-scanning electron microscopy examinations, were carried out to investigate the mechanical properties and microstructural evolution of 20Cr32Ni1Nb steel. Experimental results indicate that the as-cast microstructure of the steel typically consists of a supersaturated solid solution of austenite matrix with a network of interdendritic primary carbides (NbC and M 23C6). In the ex-service samples, large amounts of secondary carbides precipitate within austenite matrix. Besides the growth and coarsening of NbC and M 23C6 carbides during service condition, the Ni-Nb silicides known as G-phase (Ni16Nb6Si7) are formed at the interdendritic boundaries. The microstructural evolution results in the degradation of the mechanical properties of the ex-service steel. In addition, the precipitate rate of G-phase, depending in part on Si content, varies greatly for the 20Cr32Ni1Nb steel, which plays a key role in the long-term microstructural stability of the steel. Based on the X-ray diffraction data, time–temperature–transformation curve for the steel is obtained from the aged specimens.
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Acknowledgements
The work was financially supported by the National Natural Science Foundation of China (No. 50775107), the China Petrochemical Corporation (No. 315007) and the Innovation Program for Graduate Students in JiangSu Province of China (No. KYLX15_-0800).
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Guo, XF., Ni, YY., Gong, JM. et al. Formation of G-phase in 20Cr32Ni1Nb Stainless Steel and its Effect on Mechanical Properties. Acta Metall. Sin. (Engl. Lett.) 30, 829–839 (2017). https://doi.org/10.1007/s40195-017-0589-0
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DOI: https://doi.org/10.1007/s40195-017-0589-0