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对低合金高强钢分别进行淬火+回火(QT)热处理和淬火+两相区的亚温淬火+回火(QLT)三段式热处理,采用光学显微镜(OM)、扫描电镜(SEM)、电子背散射衍射(EBSD)方法等观察分析其显微组织形貌、组成相和大角度晶界的密度分布,并测试其力学性能。结果表明:相比于QT工艺,低合金高强钢在QLT工艺后,强度虽稍有下降,但低温冲击韧性显著提高,而且屈强比降低,表现出良好的综合力学性能。在发生奥氏体逆转变以及两相区等温过程中,亚温淬火工艺细化新生成的奥氏体晶粒尺寸、增加大角度晶界密度,使有效晶粒尺寸明显减小,残留奥氏体的含量明显增加。
The low alloy high strength steel was quenched and tempered (QT), quenched and tempered quenched and tempered (QLT) three-stage heat-treated. The microstructures of the low alloy high strength steel were characterized by optical microscope (OM), scanning electron microscope Backscattering diffraction (EBSD) method to observe the distribution of the microstructure, compositional phase and large-angle grain boundary, and to test its mechanical properties. The results show that the strength of low alloyed high strength steel decreases slightly after QLT process compared with that of QT process, but the impact toughness at low temperature increases remarkably and the yield ratio decreases, showing good mechanical properties. In the event of austenite retrogradation and the two-phase isothermal process, the sub-temperature quenching process can refine the newly formed austenite grain size and increase the large-angle grain boundary density so as to reduce the effective grain size. The residual austenite Body content increased significantly.