Effect of QT Treatment on Microstructure and Obdurability of a B-Nb Low Carbon Bainite Steel

doi:10.12068/j.issn.1005-3026.2019.11.008

Abstract

Abstract: Effects of QT (quenching+tempering) treatment on the proportion of grain boundary， grain size， carbide precipitation， strength and toughness of the tested steels were studied by room-temperature tensile test， pendulum impact test， optical and scanning electron microscopy， and the distribution and combination of the variants were also analyzed. The results show that when the tempering temperature increases， the strength of the tested steels gradually decreases with an increase of plasticity. The fracture modes of 450T and 500T steels are quasi-cleavage fracture， where the impact toughness becomes worse due to the carbides precipitated from bainite laths and the smaller proportion of high-angle grain boundary. The fracture modes of 600T and 650T steels are dimple fracture， where the increased proportion of the high-angle grain boundary hinders the crack propagation more effectively. The variant analysis shows that the variant combination mode of 450T steel is between Bain group and CP (close-packed) group， while that of 600T one tends to be a CP combination mode. The larger misorientation between the variants in the same CP group can deflect the path of crack propagation， which improves the low-temperature toughness.

Key words: B-Nb steel, hot rolling, tempering, strength and toughness, variant

CLC Number:

TG115.5

REN Jia-kuan， YAN Dong， CHEN Jun， LIU Zhen-yu. Effect of QT Treatment on Microstructure and Obdurability of a B-Nb Low Carbon Bainite Steel[J]. Journal of Northeastern University Natural Science, 2019, 40(11): 1561-1567.

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