采用仪器化冲击试验方法对两种承压设备用钢Q245R钢和13MnNiMoR钢进行系列温度下的夏比V型冲击试验，对比研究了两种钢裂纹形成能量W_i与裂纹扩展能量W_p之间的关系。结果表明：两种钢在韧脆转变K_V2-t曲线的上平台以及紧邻转变区的温度范围内，裂纹形成能量W_i不随温度变化而变化，基本恒定，但13MnNiMoR钢的值高于Q245R钢的；材料的韧脆转变，始于裂纹扩展能量W_p转变，其是主导材料由韧向脆的关键。

The Charpy V-notch impact test of Q245R steel and 13MnNiMoR steel were carried out at a series of temperatures by using instrumented impact test method. The relationship between the crack formation energy W_i and the crack propagation energy W_p of two steels was studied comparatively. The results show that the crack formation energy W_i of two steels not changed along with the change of temperature at the upper platform and temperature range adjacent to the transition zone on ductile-brittle transition K_V2-t curve, but the value of 13MnNiMoR steel was higher than that of Q245R steel. The ductile-brittle transition of material originated from the transition of crack propagation energy W_p, which was the key factor determining the transition from toughness to brittleness of material.