用扫描电子显微镜及微拉伸台对奥氏体 -贝氏体球墨铸铁裂纹萌生、扩展的微观过程进行了跟踪观察。结果发现 :受拉时微裂纹首先在石墨 -基体界面上萌生 ,并沿界面扩展 ;基体中的裂纹多数是沿贝氏体铁素体 -奥氏体界面扩展 ,不同取向的基体组织可使裂纹偏转或分叉 ;主裂纹扩展过程中前方始终存在石墨 -基体界面的开裂。此外 ,还根据实验结果进一步分析了奥氏体 -贝氏体球墨铸铁的强韧化机理 The microscopic observation of the initiation and propagation of crack in austenite-bainitic ductile iron with scanning electron microscope and microtensile was carried out. The results show that the microcracks first initiated at the graphite-matrix interface and extended along the interface when subjected to tension. Most of the cracks in the matrix broaden along the bainitic ferrite-austenite interface. Different orientations of the matrix structure can cause cracks Deflection or bifurcation; the main cracks in the expansion process there is always graphite - substrate interface cracking. In addition, based on the experimental results, the strengthening and toughening mechanism of austenite-bainitic ductile iron