Isothermal transition characteristics of bainitic spring steels with segregation

doi:10.13251/j.issn.0254-6051.2024.01.008

Abstract

Abstract: Microstructure evolution of bainitic steels with segregation during isothermal process was studied by means of ultra high temperature laser confocal microscope, OM, SEM and XRD. The results show that the segregation results in mixed crystals, and the grain size gradually decreases from the diluted zone to the enriched region of alloying elements. The higher the alloying element content, the longer the incubation period of bainite and the slower the transformation rate is. Therefore, the bainite structure nucleates and grows rapidly in the alloying element diluted zone, and expands to the untransformed zone layer by layer with the extension of isothermal time. During the isothermal process, the content of retained austenite increases first and then decreases under the control of bainite transformation rate and carbide precipitation rate. At different stages of bainite transformation, the effects of segregation are different. When bainite transformation is not completed, the hardness difference between bainite and martensite microstructure is large and the banded structures are formed. When the bainite transformation is completed, the banded structures are eliminated, and the segregation results in differences in alloying elements, grain size and bainite morphology at different segregation sites.

Key words: segregation, bainite transformation, in situ observation, retained austenite, microstructure evolution

CLC Number:

TG124.12

Yu Jinrui, Wu Kangjun, Yu Xinhong, Feng Yisheng, Zhao Ertuan. Isothermal transition characteristics of bainitic spring steels with segregation[J]. Heat Treatment of Metals, 2024, 49(1): 53-60.

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