关键词: 前驱组织, 高强钢, 终轧, 淬火, 低温韧性

Abstract: Effect of the original microstructure on the microstructure and properties of Q690 high-strength steel after quenching was investigated using experimental methods such as metallographic microscopy, scanning electron microscopy, electron backscatter diffraction, tensile testing, and impact testing. The results show that when the finished rolling temperatures are 1050, 950, 850 and 750 ℃, the original microstructure are all granular bainite, with average grain sizes of 40.8, 13.2, 7.1 and 1.1 μm respectively, and the microstructure after quenching at 910 ℃ for 30 min are all martensite, with average grain sizes of 10.91, 10.17, 7.11 and 7.87 μm respectively, meanwhile, the proportions of high-angle grain boundaries are 15.1%, 25.8%, 26.3% and 20.9% respectively, which partially inherit the grain size of the original microstructure. The original microstructure has little effect on the strength of the quenched high-strength steel but has a significant effect on the low-temperature toughness. When the finished rolling temperatures are 1050, 950, 850, and 750 ℃, the ductile-brittle transition temperatures are -18, -58, -68 and -42 ℃, respectively. When finish rolling temperature is 850 ℃, the quenched high-strength steel shows the best low-temperature toughness, having the highest proportion of high-angle grain boundaries and the lowest dislocation density.

Key words: original microstructure, high strength steel, finish rolling, quenching, low temperature toughness