Synergistic effect of austenite grain refinement and below-Ms isothermal quenching on microstructure and properties of a medium carbon bainitic steel

doi:10.13251/j.issn.0254-6051.2025.04.020

Abstract

Abstract: A medium carbon silicon-rich alloy steel was pre-treated by water cooling and furnace cooling respectively from 1100 ℃, reheated to 930 ℃ and then austempered at 260 ℃ (below Ms) and 320 ℃ (above Ms) respectively, by which the effects of austenite grain refinement and isothermal quenching temperature on the microstructure and mechanical properties of the medium carbon carbide-free bainitic steel were studied by means of scanning electron microscope, X-ray diffractometer, tensile and impact tests. The results show that the grain size of the water quenching pre-treated tested steel after re-austenitizing is about 55 μm, which is much smaller than that of the furnace cooling pre-treated tested steel (about 155 μm). Due to refinement of the prior austenite grains, compared with the furnace cooled tested steel, the bainite lath of the water cooled tested steel is refined after isothermal quenching, and the size of blocky M/A islands becomes smaller but the number increases. For both the water cooled and furnace cooled tested steels, below-Ms isothermal quenching can significantly refine the M/A islands size, and thus obtaining a higher strength-elongation product and impact properties.

Key words: carbide-free bainitic steel, grain refinement, isothermal quenching, microstructure, mechanical properties

CLC Number:

TG142.3

Liu Hao, Zhao Leijie, Wang Yanhui, Zhang Zi, Zhou Qian, Zeng Hongtao, Yang Guoqiang, Yue Yun. Synergistic effect of austenite grain refinement and below-Ms isothermal quenching on microstructure and properties of a medium carbon bainitic steel[J]. Heat Treatment of Metals, 2025, 50(4): 143-148.

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