The middle shelf (MS) exhibits medium absorbed energy during a two-step ductile to brittle transition and appears clearly in a ferrite + pearlite steel sheet. The analysis involved using the electron backscattered diffraction technique and indicated that the traces of fracture surface and secondary cracks at MS and lower shelf (LS) correspond to low index crystallographic planes in bcc iron. Although the {001} cleavage plane in the ferrite grain is dominant for the fracture propagation path at LS, the traces at MS correspond to {001}, {112}, and {011} planes. The potential of fracture in the {001} plane at MS (i.e., the number of traces normalized by the number of equivalent planes) exceeds that in the {112} plane. However, the difference between the same is significantly lower than that at LS. Furthermore, the{112} and {011} planes are typical slip planes in bcc iron. This suggests that the fracture at MS propagates on the {001} plane with cleavage fracture as well as on the {112} and {011} planes with a slipping-off mechanism.

中间层架（MS）在两步韧性至脆性转变过程中表现出中等的吸收能量，并且清楚地显示在铁素体+珠光体钢板中。该分析涉及使用电子背散射衍射技术，并表明在MS和下层架子（LS）处的断裂表面和二次裂纹的痕迹与bcc铁中的低折射率晶体学平面相对应。尽管铁素体晶粒中的{001}分裂平面是LS处裂纹扩展路径的主导，但MS处的迹线对应于{001}，{112}和{011}平面。在MS处，{001}平面中的破裂可能性（即，通过等效平面数归一化的迹线数）超过了{112}平面中的破裂数。但是，两者之间的差异明显低于LS处的差异。此外，{112}和{011}平面是bcc铁中的典型滑移平面。这表明MS处的裂缝在具有分裂裂缝的{001}面上以及具有滑脱机制的{112}和{011}面上传播。