图a、b、c和d分别为DZ2（0.04V0Nb）钢在20℃、-40℃、-120℃和-196℃下紧凑拉伸试样断口形貌，由图可知，不同温度下紧凑拉伸试样断口形貌差异较大，纤维区宽度随着温度的降低逐渐减小。在20℃、-40℃时断口呈韧性断裂，基本由大小尺寸韧窝组成；-120℃时开始出现解理或准解理裂纹扩展区，纤维区宽度变小；在-196℃时纤维区基本消失，只有解理区或准解理区。

Figure a, b, c and d show the fracture morphology of DZ2 (0.04V0Nb) steel at 20℃, -40℃, -120℃ and -196℃, respectively. It can be seen from the figure that the fracture morphology of compact tensile samples at different temperatures is quite different, and the fiber zone width gradually decreases with the decrease of temperature. At 20℃ and -40℃, the fracture is ductile fracture, basically composed of small and large dimples. Cleavage or quasi cleavage crack growth zone appeared at -120℃, and fiber width became smaller. At -196℃, the fiber region disappeared and only cleavage region or quasi cleavage region was found.