在扫描电子显微镜下观察分析了B级船板钢试样在原位拉伸过程中的断裂行为以及低温脆性断口中二次裂纹的扩展。结果表明：在拉伸变形过程中，微裂纹首先在试样缺口处形成，然后沿铁素体+珠光体界面扩展。加载过程中，多边形铁素体发生塑性变形，裂纹在基体内以“Z”字型扩展。在低温脆性断裂区，二次裂纹以穿晶方式通过铁素体基体，在扩展到珠光体区域时有时沿铁素体和珠光体的界面扩展，有时穿过珠光体区域扩展。
The microprocesses of crack initiation and propagation in a B hull structural steel have been investigated by using an scanning electron microscope with a microtensile holder, and the secondary crack propagation at low temperature has also been studied by SEM.It was found that the microcracks were initiated at the notch, then the microcracks propagated along the pearliteferrite interface, shear ligament formation occurred in the ferrite in the process of loading, and internal fracture of the matrix showed “Z” morphology. When the cracks propagated in the matrix under low temperature condition,they often showed transgranular crack in the ferrite matrix; intragranular crack and transgranular crack occurred in the pearlite during the connection of main cracks with microcracks.
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