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通过断裂试样断口的宏观和显微分析、显微组织表征、拉伸和冲击试验以及解理断裂应力条件,讨论分析了锌锅用低强度级别钢板弯曲成形断裂的微观解理断裂行为。结果表明,钢板发生解理断裂的微观机制与冲击试样断裂相同,即晶粒尺寸控制的穿过晶界的裂纹扩展是解理断裂的临界事件。粗大的铁素体晶粒的面积分数过高显著降低了裂纹扩展阶段所需的局部解理断裂应力σf。断口宏观分析判断在钢板边部应存在导致应力集中的初始裂纹源,这极大降低了启动解理断裂的断裂应力并同时提高裂纹源前端的正应力σyy,扩大了解理断裂活跃区至初始裂纹前端,从而不可避免地发生脆性解理断裂。
The microscopic cleavage fracture behavior of the low strength steel plate for zinc pot with bending deformation was analyzed by macroscopical and microscopic analysis, microstructure characterization, tensile and impact test and cleavage fracture stress condition of fracture specimen fracture. The results show that the microscopic mechanism of the cleavage fracture of the steel plate is the same as that of the impact specimen, ie, the grain size controlled crack propagation across the grain boundary is the critical event of cleavage fracture. The large area fraction of coarse ferrite grains significantly reduces the local cleavage fracture stress σf required for the crack propagation phase. The macroscopical analysis of the fracture shows that there should be the source of the initial cracks in the edge of the steel sheet, which leads to the stress concentration. This greatly reduces the fracture stress at the start of the cleavage fracture and at the same time increases the normal stress σyy of the crack source front and enlarges the active crack zone to the initial crack Front-end, brittle cleavage fracture inevitably occurs.