在备有拉伸装置的扫描电镜下,连续观察了双相钢的微观断裂过程,并讨论了裂纹扩展条件及其影响因素,认为裂纹扩展是拉应力和塑性切应变综合作用的结果.采用位错塞积模型能较好地解释马氏体含量,马氏体含碳量及低温回火对裂纹萌生方式的影响.最后,从断裂特征角度分析了影响双相钢延性的因素. Under the scanning electron microscope equipped with a stretching device, the microscopic fracture process of the dual phase steel was continuously observed and the conditions of crack propagation and its influencing factors were discussed. It is considered that the crack propagation is the result of the combined action of tensile stress and plastic shear strain. The fault-plugging model can explain the influence of martensite content, carbon content of martensite and tempering at low temperature on the crack initiation mode.Finally, the factors influencing ductility of dual-phase steel are analyzed from the fracture characteristics.