利用背散射电子衍射技术研究了0.02C-5Mn低碳板条马氏体钢中大角度界面对冲击断口中解理裂纹扩展或断口附近二次解理裂纹扩展的影响, 以分析该钢韧性的组织控制单元; 依据马氏体变体中理想解理晶面{100}的取向差, 比较了板条束界和板条块界改变解理裂纹扩展方向的能力。结果表明: 解理裂纹或二次解理裂纹扩展时在原奥氏体晶界、板条束界和大部分的板条块界处都发生了大角度转折; 板条块界和板条束界阻碍解理裂纹扩展的能力相近, 板条块是控制板条马氏体钢解理断裂和韧脆转变温度的组织单元。

In order to analyze the microstructure unit controlling the toughness of 0.02C-5Mn low-carbon lath martensite steel, the effects of high angle boundaries on the propagation of impact fracture cleavage cracks or the propagation of secondary cleavage cracks near the impact fracture in the steel were studied by electron backscatter diffraction (EBSD). Further more, based on the misorientation of ideal cleavage planes {100} between martensitic variants, the ability of packet and block boundaries to change the propagation direction of cleavage cracks was compared. The results indicate that the cleavage cracks or secondary cleavage cracks were deflected through large angles when crossing through the prior austenite grain boundaries, packet boundaries and most of the block boundaries. The ability of packet and block boundaries to hinder cleavage crack propagation was close. Blocks are the microstructure unit controlling cleavage fracture and ductile to brittle transition temperature of lath martensite.