图为DZ2（模铸）钢不同温度下的紧凑拉伸断口形貌。由图可知，其断口形貌与1#钢基本相似，主要是由纤维区与解理或准解理断面组成，但其在20℃、-40℃时出现了解理断面或准解理断面。这是由于DZ2（模铸）钢试样中合金渗碳体的尺寸较大(153nm)，在拉伸的过程更容易出现应力集中现象，因此在室温下就出现解理或准解理断裂。且随着温度的降低其纤维区的宽度也逐渐减小，对应的K_q或K_IC也逐渐减小。

The fracture morphology of DZ2 (die cast) steel under compact tension at different temperatures is shown. As can be seen from the figure, its fracture morphology is basically similar to that of 1# steel, mainly composed of fiber region and cleavage or quasi-cleavage section, but there are cleavage section or quasi-cleavage section at 20℃ and -40℃. This is due to the large size of alloy cementation in DZ2 (die cast) steel samples (153nm), which is more prone to stress concentration in the process of tensile, so cleavage or quasi cleavage fracture occurs at room temperature. With the decrease of temperature, the width of fiber area decreases gradually, and the corresponding Kq or KIC also decreases gradually.