超厚高强钢心部组织对断裂机制的影响

摘要：为了研究超厚钢板心部显微组织与微观断裂机制的关系，利用扫描电子显微镜（SEM）、透射电子显微镜（TEM）和电子背散射衍射（EBSD）等技术手段对试验钢板1/4厚度、1/2厚度（心部）显微组织及裂纹形貌进行表征和分析。结果表明，心部处低温冲击韧性较1/4厚度处有明显的降低，这是由于心部组织为回火板条贝氏体和回火粒状贝氏体，其中粒状贝氏体的比例较高，粒状贝氏体中M-A岛的存在促进了微孔或微裂纹的启裂；1/4厚度处为回火板条马氏体与回火板条贝氏体二者的混合组织，板条间的位错运动释放局部应力集中，而舒缓裂纹尖端区域所受应力，产生裂纹钝化、阻碍裂纹扩展，提高低温冲击韧性。

Effect of center microstructure on fracture mechanism of ultra-thick high strength steel

Abstract： In order to study the relationship between microstructure and fracture mechanism of ultra-thick steel plate, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) were used to characterize and analyze the microstructure and crack morphology of 1/4 and 1/2 thickness (center) of the test plate. The results show that the low temperature impact toughness at the center is significantly lower than that at the 1/4 thickness, which is due to the microstructure of the center is tempered lath bainite and tempered granular bainite, and the proportion of granular bainite is higher. The presence of M-A island in granular bainite promotes the initiation of micro pores or micro cracks. The 1/4 thickness is a mixed microstructure of tempered lath martensite and tempered lath bainite. The dislocation movement between laths releases local stress concentration, and relieves the stress at the crack tip region, resulting in crack passivation, hindering crack propagation and improving low temperature impact toughness.