Effect of Q&P process on microstructure and properties of 1000 MPa grade high strength steel

doi:10.13251/j.issn.0254-6051.2024.08.011

Abstract

Abstract: Microstructure transformation of two 1000 MPa grade high strength steels with different chemical compositions during salt bath Q&P treatment was analyzed through microstructure observation by scanning electron microscope and Gleeble thermal simulation test. The effect of microstructure transformation on mechanical properties was further analyzed by combining mechanical properties and XRD dislocation density calculation. The results show that two-stage phase transformation occurs during the salt bath Q&P treatment, where the salt-bath partitioning process has a tempering effect on the lath martensite formed in the first phase transformation stage to form a multi-phase tempered lath martensite with different strengths, making the yield ratio of both the tested steels not higher than 0.87. As the salt bath quenching temperature increases, the yield strength and yield ratio decrease, while as the partitioning temperature increases, the strength and yield ratio do not change much. When salt bath partitioned at 450 ℃, the lath martensite structure is partially decomposed and the dislocation density decreases, leading to a significant reduction in the strength.

Key words: high strength steel, Q&P treatment, microstructure, yield ratio, strength

CLC Number:

TG156.31

Guo Chengyu, Zhang Zhe, Zhang Chi, Dai Chunduo, Hou Huaxing, Li Jiangwen. Effect of Q&P process on microstructure and properties of 1000 MPa grade high strength steel[J]. Heat Treatment of Metals, 2024, 49(8): 67-73.

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