An ultra-low carbon steel plate with the yield strength of 690 MPa was produced in the laboratory. The coarse-grain heat-affected zone (CGHAZ) was simulated on a thermal simulator based on the welding heat inputs of 25 kJ/cm and 100 kJ/cm, under which the microstructure and impact toughness were characterized compared with the base metal (BM). The results showed that the investigated steel exhibited a favorable low-temperature impact toughness at the heat input of 25 kJ/cm. Although high heat input was not conducive to the impact toughness, the average impact energy can still reach ⁓40 J at − 20℃ at the heat input of 100 kJ/cm. The welding thermal cycle led to the formation of more low-angle boundaries in the prior austenite grains, which was not conducive to the crack arrest behavior, resulting in a significant decrease of toughness in CGHAZ. Obvious decrease of high-angle boundaries in CGHAZ was mainly responsible for the deterioration of total impact absorbed energy. Besides, the martensite-austenite (M-A) constituents provided favorable conditions for crack initiation. In general, the mechanism of impact toughness deterioration of CGHAZ under high heat input condition was discussed in detail. The microstructure and low-temperature impact toughness of CGHAZ under different heat inputs can provide a theoretical basis for the research in 690 MPa ultra-low carbon high-strength microalloyed steels.
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This work is strongly supported by the fundamental research funds for the central universities of China (No. N2007009) and the major industrial projects of science and technology plan of Liaoning Province, China (No. 2019JH1/10100014).
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Recommended for publication by Commission X - Structural Performances of Welded Joints - Fracture Avoidance
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Yang, Y., Jia, X., Ma, Y. et al. Microstructure and Impact Toughness of the Coarse-Grain HAZ Physically Simulated with Different Heat Inputs in a 690 MPa Ultra-low Carbon High-Strength Microalloyed Steel. Weld World 66, 1213–1227 (2022). https://doi.org/10.1007/s40194-022-01296-3