2 GPa级超高强度钢已成为扭力轴的候选材料之一。然而，关于其显微组织与力学性能之间关系的研究相对较少。本工作采用SEM、EBSD、AES、TEM、单轴拉伸和静态扭转等方法研究了奥氏体化温度对扭力轴用2 GPa超高强钢的显微组织、拉伸力学性能和静态扭转性能的影响。结果表明，在奥氏体化过程中，初始组织(珠光体和少量铁素体组成)中片层状合金渗碳体先球化后溶解，其球化机制主要以非连续辅助机制为主，包含少量的边缘迁移机制。随着奥氏体化温度的升高，渗碳体逐渐由(Fe, Cr, V)₃C合金渗碳体转变为Fe₃C渗碳体，直至渗碳体完全溶解(奥氏体化温度为950 ℃时)，并且VC的析出温度区间与渗碳体未溶解的温度区间相一致。奥氏体化温度为850 ℃时实验用钢获得了较优的拉伸力学性能，屈服强度、抗拉强度、均匀延伸率和总延伸率分别为1580 MPa、2062 MPa、8.4%和12.7%，这源于显微组织中渗碳体和VC提供的析出强化，以及细小的马氏体板条提供的细晶强化。静态扭转实验结果表明，当奥氏体化温度为800和850 ℃时，由于含有更多渗碳体和VC以及细小的马氏体板条，试样表现出更高的剪切模量和扭转屈服强度。随奥氏体化温度升高，剪切塑性变形区增加，断裂主导机制由剪切断裂转变为剪切韧性断裂，从而表现出更高的抗扭强度。

Recently, 2 GPa grade ultra-high strength steel has emerged as a potential candidate material for torsional axles. Nevertheless, studies focusing on the correlation between the microstructure and mechanical properties are scarce. To address this, the current study investigates the impact of austenitizing temperature on the microstructure, tensile mechanical properties, and static torsional properties of 2 GPa grade ultra-high strength steel used in torsion axles. Various techniques including SEM, EBSD, AES, TEM, uniaxial tension, and static torsion are employed. During the austenitizing process, the lamellar cementite in the initial microstructure (composed of pearlite and a minimal amount of ferrite) first spheroidized and then dissolved. This spheroidization process is primarily dominated by discontinuity-assisted spheroidization, with minimal contributions from termination-migration-assisted spheroidization. With increasing austenitizing temperature, the cementite gradually transforms from (Fe, Cr, V)₃C to Fe₃C, eventually completely dissolving (at the austenitizing temperature of 950 ^oC). Moreover, the precipitation temperature range of vanadium carbide is consistent with the temperature range of undissolved cementite. Additionally, austenitizing at 850 ^oC and tempering at 220 ^oC results in better tensile properties, including a yield strength of 1580 MPa, tensile strength of 2062 MPa, uniform elongation of 8.4%, and total elongation of approximately 12.7%. These improvements are attributed to the precipitation strengthening enabled by cementite and vanadium carbide and the fine grain strengthening provided by fine martensite block sizes. The static torsion test results show that when the austenitizing temperature is 800 and 850 ^oC, the sample shows the best shear moduli and torsional yield strength due to the increased cementite and vanadium carbide contents, along with fine martensite block sizes. With increasing austenitizing temperature, the shear plastic deformation zone expands, and the predominant fracture mechanism changes from shear fracture to shear ductile fracture, resulting in higher torsional strengths.