Heat Treatment of Metals ›› 2025, Vol. 50 ›› Issue (5): 40-45.DOI: 10.13251/j.issn.0254-6051.2025.05.007

• BEARING STEEL • Previous Articles     Next Articles

Effect of nanostructured bainite on M/Bn composite microstructure and mechanical properties of GCr15 bearing steel

Zhou Lina1, Yang Xiaofeng2, Ma Jianpeng1, Wei Yinghua3, Yu Xingfu3   

  1. 1. AECC Harbin Bearing Co., Ltd., Harbin Heilongjiang 150025, China;
    2. Unit 93156 of PLA, Harbin Heilongjiang 150025, China;
    3. School of Mechanical Engineering, Shenyang University of Technology, Shenyang Liaoning 110870, China
  • Received:2024-11-08 Revised:2025-03-28 Published:2025-06-25

Abstract: By oil quenching and 200 ℃ isothermal salt quenching for GCr15 bearing steel, composite structures (M/Bn) with martensite (M) and different contents of nano bainite (Bn) were obtained. The microstructure, hardness, and impact properties of the GCr15 bearing steel were characterized by means of scanning electron microscope, Rockwell hardness tester and impact testing machine to investigate the effect of nano bainite content in M/Bn composite microstructure on the microstructure and properties of the GCr15 bearing steel. The results show that the microstructure of oil quenched GCr15 bearing steel is mainly composed of spherical particle carbides, tempered martensite, and retained austenite. After isothermal salt quenching, the microstructure of bearing steel is mainly composed of spherical carbides, tempered martensite, bainite, retained austenite, and secondary precipitated fine carbides. The hardness of GCr15 steel gradually decreases with the increase of content of nano bainite. After austenitizing at 860 ℃, salt bath at 200 ℃ for 2 h, and then tempering at 200 ℃, the hardness of the M/Bn composite structure is equivalent to that of the fully martensitic microstructure obtained by austenitizing at 845 ℃, oil quenching and then tempering at 155 ℃. At this time, the content of nano bainite in the steel with M/Bn composite structure is 47%, with a hardness of 61.5 HRC, while that of the steel with fully martensitic microstructure is 61.1 HRC. Compared with the impact absorbed energy (7.67 J) of the steel with fully martensitic microstructure, the impact absorbed energy (9.92 J) of the steel with M/Bn composite structure is increased by 29.34%, indicating that under similar hardness, the M/Bn composite structure achieves better comprehensive mechanical properties.

Key words: GCr15 bearing steel, nano bainite, M/Bn composite structure, hardness, impact property

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