对基体组织为 25%P +75%F 和 50%P +50%F 的后桥主减速器壳体轴承座材料 QT450 的显微组织进行比较，以研究组织与裂解性的内在联系． 首先，对不同金相组织的 QT450 试件进行拉伸试验，获取数值模拟所需的材料参数，并与模拟相结合，分别确定两 种基体组织的临界断裂韧度 J IC ，利用 ABAQUS 模拟获得不同显微组织的 QT450 的裂解 载荷及应力集中程度;然后建立回弹模型，分析两种组织的塑性变形及失圆;最后进行裂 解试验对数值分析的有效性进行验证． 结果表明:基体为 50% 珠光体 + 50% 铁素体的 QT450 相比基体为 25%珠光体 +75%铁素体的 QT450 更适于裂解;QT450 材料的强度和 刚度取决于珠光体的含量，随珠光体含量的上升，材料的脆硬性好，缺口敏感性好，其裂解 性能更佳;采用基体组织为 25%珠光体 +75%铁素体的 QT450 生产的轴承座的失圆度大 于 0． 2mm，无法完成后续精加工及装配，而采用基体组织为 50% 珠光体 +50% 铁素体的 QT450 材料生产的轴承座的失圆度小于 0． 2 mm，裂解产生的塑性变形小，更符合实际生 产的工艺要求．

The microstructure of rear axle main reducer shell bearing seat material QT450 with 25% P + 75% F and 50% P + 50% F was compared to study the internal relation between structure and fracture splitting perfor- mance． Firstly，tensile tests were performed on the QT450 specimens with different metallographic structure to ob- tain the material parameters required for numerical simulation． Combined with the simulation，the critical fracture toughness J IC of the two matrix tissues was determined respectively． The fracture-splitting force and the stress con- centration of QT450 with different microstructures were obtained by ABAQUS． Then a springback model was estab- lished to analyze the plastic deformation and out-of-roundness of the two tissues． Finally，the fracture splitting test was carried out to verify the validity of the numerical analysis． The results show that QT450 with 50% pearlite + 50% ferrite is more suitable for the fracture splitting than QT450 with 25% pearlite + 75% ferrite． The strength and stiffness of QT450 material depend on the content of pearlite． With the increase of pearlite content，the britt- leness of the material，the notch sensitivity increase and the fracture splitting performance are all improved． The shell bearing seat produced by QT450 with 25% pearlite + 75% ferrite matrix has an out-of-roundness of more than 0. 2 mm，which can not complete the subsequent finishing and assembly． While the shell bearing seat pro- duced by QT450 material with 50% pearlite + 50% ferrite has an out-of-roundness of less than 0. 2 mm，and the plastic deformation caused by fracture splitting is small，so it can well meet the requirement of the actual produc- tion process．