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Achieving high tensile properties and impact toughness in ultrahigh strength lean alloy steel by quenching and partitioning treatment

Wang Lirong, Liang Yilong, Zhao Fei, Xu Fahong, Lei Lei, Long Shaolei, Yang Ming, Jiang Yun

Archives of Civil and Mechanical Engineering

2024

Vol. 24, no. 1

art. no. e32, 2024

In this study, a desirable combination of strength, ductility, and toughness in low-carbon 30CrMnSiA steel is achieved by a hierarchical multiphase microstructural architecture subjected to one- and two-step quenching and partitioning (Q&P) processes. The microstructural constituents are studied by EBSD, x-ray diffraction, dilatometry, and TEM. Experimental results show that microstructural refinement occurs in the martensite and bainite at a lower quenching temperature, where more Bain groups form in one close-packed plane group. This causes random distribution between martensite and bainite blocks, enlarging the volume of high-angle grain boundaries. Such refined microstructure, particularly for the increased martensite with higher-density dislocations, causes an increased strength at a decreased quenching temperature. By comparison, increased quenching and partitioning temperature produces more stable film-like retained austenite (RA) and a low dislocation density in martensite/bainite (M/B); thus, it provides better deformation by accommodating with M/B laths and absorbing substantial energy due to the transformation-induced plasticity effect. The lower dislocation density, the higher volume fraction of RA, and the higher HAGBs improve the impact toughness and tensile properties of lean alloy steel through a moderate Q&P process.