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本文通过起裂源粒子的特征和尺寸分布、裂源处显微组织和残留裂纹的尺寸分布情况,研究了C-Mn钢和两种焊缝金属的Charpy V,COD和预制裂纹冲击试样的微观断裂行为。发现焊缝中的解理裂纹形核于夹杂物或第二相粒子,母材形核于珠光体团;对于同一材料用缺口试样和裂纹试样测得的微观解理断裂应力的不同值是由于断裂过程中临界事件发生了变化。在-45～-65℃范围内,Charpy V 缺口试样中的临界事件是铁素体晶粒尺寸的微裂纹扩展进入铁素体基体;而在-110℃的裂纹试样中,是第二相粒子尺寸的微裂纹扩展进入临近的铁素体晶粒。临界事件的变化认为与缺口根部和裂纹前端不同的有效剪应力有关。建立Charpy V 和COD实验结果之间关系的条件是有关材料铁素体晶粒和第二相粒子的尺寸应当是类似的。
In this paper, the characteristics and size distribution of the source particles, the size distribution of the microstructure and the residual cracks at the crack source were studied. The effects of Charpy V, COD and pre-cracked impact specimens on C-Mn steel and two weld metals Micro-fracture behavior. It was found that the cleavage crack nucleation in inclusions or inclusions in the second phase particles, the parent material nucleation in the pearlite group; for the same material with a notch sample and cracked specimens measured micro-cleavage fracture stress of different values It is due to the critical event in the fracture process has changed. The critical event in the Charpy V notched specimen extends from -45 ° C to -65 ° C into the ferrite matrix as a result of the formation of ferrite grain-size micro-cracks; in the cracked specimen at -110 ° C, it is the second Phase-cracked microcracks expand into adjacent ferrite grains. Changes in critical events are thought to be related to different effective shear stresses at the root of the notch and the crack tip. The condition for establishing the relationship between the Charpy V and COD experimental results is that the dimensions of the ferrite grains and the second phase particles of the relevant material should be similar.