本文研究了双相钢的断裂特性。用缺口试棒四点弯曲试验法测定了双相钢的解理断裂应力σ_f;根据解理断裂温度下断口形貌、微裂纹萌生和扩展以及显微组织的观察结果,得出了双相钢的裂纹扩展途径;根据σ_f与开裂单元的测定结果,并考虑到微裂纹的形状对解理断裂应力的影响,计算了双相钢的有效表面能。提出了双相钢解理断裂的应力扩展控制模型,并得出了σ_f=(0.33+19.33-c~(·1/2))kgf/mm~2的回归关系式。提高双相钢解理断裂应力的途径是:降低铁素体的晶粒尺寸,尽可能使马氏体岛细化,分布均匀和增加马氏体岛中板条马氏体的比例。
The cleavage fracture stress of the dual phase steels has been evaluated with slow-bend test of blunt V-notched specimens. Their crack propagation path and fracture mode were indicated by the observations of the fracture morphology, the mieroeraek initiation and propagation of fracture surfaces under the cleavage temperature and the mierostrueture. According to the measurements of the cleavage fracture stress and the crack unit, the effective surface energy of the dual phase steels was also calculated by Griffith's equation. It was proposed that the cleavage fracture of the dual phase steels seems to be controlled by stress propagation and its regressive equation may be σ_f =0.33+19.33c~(-1/2) kgf/mm~2. Thus, the cleavage fracture stress may be increased by reducing the grain size of ferrite and martensite islands and by increasing the amount of evenly distributed lath martensite in the islands.
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