Heat Treatment of Metals ›› 2023, Vol. 48 ›› Issue (1): 29-34.DOI: 10.13251/j.issn.0254-6051.2023.01.006

• MICROSTRUCTURE AND PROPERTIES • Previous Articles     Next Articles

Effect of Nb microalloying on microstructure and mechanical properties of Cr-Ni-Mo-V high-strength steels

Zhang Weifeng1,2, He Xiaofei2, Yu Wenchao2, Li Li1, Wang Maoqiu2   

  1. 1. Faculty of Material Science and Engineering, Kunming University of Science and Technology, Kunming Yunnan 654199, China;
    2. Research Institute of Special Steel, Central Iron and Steel Research Institute Co., Ltd., Beijing 100081, China
  • Received:2022-08-10 Revised:2022-10-25 Online:2023-01-25 Published:2023-02-03

Abstract: After quenching at 880 ℃ for 1 h and tempering at 300 ℃ for 3 h, the microstructure and precipitated phases of the tested Cr-Ni-Mo-V high-strength steels with and without Nb were observed and analyzed by means of SEM, EBSD, TEM and physicochemical phase analysis. The results show that with the addition of 0.035%Nb, the microstructure of the tested steel is refined, the martensite lath block size decreases from 3.1 μm to 2.9 μm, and the content of MC-type precipitated phase increases, the size distribution of the precipitated phases is optimized, and the content of the precipitated phases with the size ranging from 18 to 200 nm is significantly increased. Due to the increase in precipitated phase content, the decrease of C content in solid solution, and the slightly lower total C content in the Nb-containing steel, so that the strength of the steel decreases slightly, but still reaching the level of 2000 MPa. The toughness of the Nb-containing tested steels is improved by the refinement of the martensite microstructure and the optimization of the size distribution of the precipitated phases, the room temperature and -40 ℃ low temperature impact absorbed energy (KU2) are both increased to 44 J.

Key words: high-strength steel, Nb microalloying, precipitated phase, microstructure, mechanical properties

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