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Open AccessArticle

The Evolution of Complex Carbide Precipitates in a Low Alloy Cr–Mo–V Steel after Long-Term Aging Treatment

1
School of Materials Science and Engineering, Northeastern University, Shenyang 110819, China
2
Central Research Institute (R&D Center), Baoshan Iron & Steel Co. Ltd., Shanghai 201900, China
3
Steel Institute, RWTH Aachen University, 52072 Aachen, Germany
*
Authors to whom correspondence should be addressed.
Materials 2019, 12(10), 1724; https://doi.org/10.3390/ma12101724
Received: 30 April 2019 / Revised: 21 May 2019 / Accepted: 24 May 2019 / Published: 27 May 2019
(This article belongs to the Section Structure Analysis and Characterization)
Complex carbide precipitates in a quenched and tempered low alloy Cr–Mo–V steel after long-term aging at 650 °C for 13,000 h and 30,000 h were investigated in this study. The mass fraction and sizes of precipitates were quantified by electrolytical extraction technique. The types of precipitate were further studied by combined X-ray diffraction and transmission electron microscopy with selected area electron diffraction and energy dispersive spectrometry. A series of carbide precipitates, namely MC, M7C3, M6C, and M2C, were found existing in the near-equilibrium state. The precipitate sequence of these carbides was identified as MC + M7C3 + M2C → MC + M2C + M7C3 + M6C → MC + M7C3 + M6C. It was clarified that the stable phases for the investigated steel aged at 650 °C were composed of MC, M7C3, and M6C. For the first time, the in-situ transformations of M2C to M6C and M7C3 to M6C were directly observed. It was also observed that the nucleation site of the M6C was located at the interface of M7C3 carbides and the matrix. The orientation relationships between the secondary phases of the in-situ transforming carbides aged for 13,000 h and 30,000 h at 650 °C were established. The coherent interfaces between these secondary phases became incoherent with prolonged aging treatment due to the exerted strain field of the growing carbides. View Full-Text
Keywords: Cr–Mo–V steel; long-term aging; carbide evolution characterization; planar mismatch Cr–Mo–V steel; long-term aging; carbide evolution characterization; planar mismatch
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Liu, Z.; Liu, C.; Miao, L.; Guo, X.; Ding, J.; Zhang, H. The Evolution of Complex Carbide Precipitates in a Low Alloy Cr–Mo–V Steel after Long-Term Aging Treatment. Materials 2019, 12, 1724.

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