利用SEM、TEM、EBSD等技术手段研究了回火温度(450~650℃)对NiCrMoV低碳合金钢显微组织的影响，并通过拉伸和冲击实验测试其力学性能，同时利用相变仪和DICTRA模拟方法分别分析了两相区回火过程中奥氏体逆相变过程和合金元素的配分行为。结果表明，NiCrMoV低碳合金钢经热轧-在线淬火后的显微组织由板条马氏体和自回火马氏体组成。回火温度从450℃升高到550℃，马氏体板条发生回复，马氏体-奥氏体(M-A)组元逐渐分解；经两相区600℃回火后，在回火马氏体边界处形成了4.8% (体积分数)的残余奥氏体；提高两相区回火温度到650℃，显微组织由层状分布的新鲜马氏体和临界铁素体组成。随着回火温度升高，NiCrMoV低碳合金钢在-80℃的冲击功呈现先增加后降低的趋势，在600℃回火时达到峰值160 J；同时，NiCrMoV低碳合金钢在600℃回火时获得了最佳的强塑性匹配，屈服强度1030 MPa，抗拉强度1104 MPa，延伸率18%。相变仪分析结果表明NiCrMoV低碳合金钢经600℃回火后逆转变奥氏体全部保留到室温，而在650℃回火后逆转变奥氏体发生相变并转变成新鲜马氏体。DICTRA模拟结果证明奥氏体稳定化元素C、Ni和Mn在600℃等温回火过程中的富集程度要显著高于650℃等温回火。

The low carbon alloyed steel has been widely used in the shipbuilding and offshore structures owing to its high strength and toughness at low temperatures. To optimize the microstructure and mechanical properties of low carbon alloyed steel as well as investigate the relationship between them, this study focuses on the microstructure evolution and corresponding mechanical properties of a 1000 MPa grade NiCrMoV low carbon alloyed steel during tempering in the range of 450-650^oC. Microstructures of lath martensite and autotempered martensite were obtained after hot rolling followed by direct water cooling to room temperature. The evolution of lath martensite and retained austenite on tempering was characterized using SEM and TEM. The distribution of the retained austenite was investigated using EBSD. The result shows that when the tempering temperature of the NiCrMoV low carbon alloyed steel is increased from 450^oC to 550^oC, the lath martensite recovers and the martensite-austenite component gradually decomposes. The retained austenite with 4.8% volume fraction was obtained after tempering at 600^oC. The NiCrMoV low carbon alloyed steel obtained intercritical ferrite and fresh martensite when tempered at 650^oC. The reverse transformation process of austenite was analyzed through a dilatometer curve. The partition behavior of alloying elements C, Ni, and Mn during intercritical tempering was analyzed kinetically through DICTRA simulation. An appropriate fraction of thermally stable retained austenite obtained at 600^oC was attributed to the extent of partitioning of C, Ni, and Mn into the reversed austenite, which contributed to the best balance of strength-ductility-toughness properties. After direct quenching and tempering at 600^oC, high yield strength of 1030 MPa with a high ductility of 18%, low yield to tensile ratio of 0.93, and excellent low-temperature toughness of 160 J at -80^oC were obtained.