图为DZ2（连铸）钢不同部位冲击试样断口剖面图，由图可知，边部试样裂纹在扩展过程中沿着马氏体发生了多次转折，而在1/2半径和心部裂纹沿原始奥氏体界面或贝氏体以直线扩展，很少发生转折。这是由于发生马氏体相变时，马氏体通常是与奥氏体保持K-S取向关系，使得钢中具有由不同结构单元组成的分级亚结构，如原始奥氏体晶粒、板条束（packet）、板条块（block）、和亚板条块（sub-block）。这些亚结构之间的界面能够有效地阻碍裂纹的扩展，导致裂纹在马氏体中扩展时发生偏转。

The fracture sections of impact samples in different parts of DZ2 (continuous casting) steel are shown in the figure. It can be seen from the figure that the cracks in the edge samples take several turns along the martensite in the process of propagation, while the cracks in the 1/2 radius and center extend in a straight line along the original austenite interface or bainite, with few turns. This is because martensite usually maintains k-S orientation relationship with austenite during martensitic transformation, resulting in hierarchical substructures composed of different structural units in steel, such as primitive austenite grains, packet, block and sub-block. The interface between these substructures can effectively inhibit the crack propagation, resulting in deflection of the crack as it expands in martensite.