Effect of Nb and V on the continuous cooling transformation of undercooled austenite in Cr–Mo–V steel for brake discs

Dan Wu; Fu-ming Wang; Jin Cheng; Chang-rong Li

doi:10.1007/s12613-018-1638-z

Volume 25 Issue 8

Aug. 2018

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Article Navigation > International Journal of Minerals, Metallurgy and Materials > 2018 > 25(8): 892-901

Dan Wu, Fu-ming Wang, Jin Cheng, and Chang-rong Li, Effect of Nb and V on the continuous cooling transformation of undercooled austenite in Cr–Mo–V steel for brake discs, Int. J. Miner. Metall. Mater., 25(2018), No. 8, pp. 892-901. https://doi.org/10.1007/s12613-018-1638-z

Cite this article as:

Dan Wu, Fu-ming Wang, Jin Cheng, and Chang-rong Li, Effect of Nb and V on the continuous cooling transformation of undercooled austenite in Cr–Mo–V steel for brake discs, Int. J. Miner. Metall. Mater., 25(2018), No. 8, pp. 892-901. https://doi.org/10.1007/s12613-018-1638-z

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Research Article

Effect of Nb and V on the continuous cooling transformation of undercooled austenite in Cr–Mo–V steel for brake discs

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Corresponding author:
Fu-ming Wang E-mail: wangfuming@metall.ustb.edu.cn
Received: 25 January 2018; Revised: 8 March 2018; Accepted: 15 March 2018

Abstract

Abstract

The increasing speed of trains necessitates the development of brake-disc materials that meet more stringent requirements. Therefore, Nb and V have been added to Cr–Mo–V steel to improve its thermal fatigue performance when used in brake discs. In this paper, the influences of Nb and V on the static continuous cooling transformation (CCT) behaviors of undercooled austenite were studied. The microstructures, hardness, and dislocation densities at different cooling rates and with the addition of different alloying elements were also investigated. The results show that the transformation products of ferrite, granular bainite, lower bainite, and martensite form under different cooling conditions. With increasing Nb and V contents, the CCT curves are shifted to the left, ferrite and bainite transformations are promoted, and the critical cooling rate of total martensite formation is increased. The added V mainly forms V-rich M₈C₇ precipitates and reduces the dissolved C content; therefore, the A_c1, A_c3, and M_s-point temperatures increase. Moreover, the stability of retained austenite is also reduced; its content therefore decreases. Compared with V, the effect of added Nb is weaker because of its smaller content. However, the addition of Nb improves the hardness at lower cooling rates because of the precipitation of fine NbC particles and refining of the microstructure.
- brake-disc steel;
- niobium;
- vanadium;
- microstructure;
- continuous cooling transformation

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