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采用阶梯能量夏氏V型缺口冲击试验法研究了P91钢在冲击弯曲破断时,裂纹的萌生、亚临界生长、失稳扩展三个阶段与力-位移曲线及断口的对应关系,研究了裂纹的亚临界生长与失稳扩展速率。结果表明,裂纹萌生于屈服后的第2个力-位移曲线峰值。裂纹亚临界生长的临界尺寸对应于力-位移曲线平台后的第2个下跌槛。裂纹亚临界生长对应于断口上的启裂区。裂纹失稳扩展对应于断口上的扩展区。在启裂前区裂纹以较低速率波动亚临界生长,启裂后区裂纹的亚临界生长速率更趋减缓。裂纹失稳扩展的前期扩展速率很高,后期则迅速下降。P91钢裂纹的缓慢亚临界生长和占总冲击能量66%的裂纹亚临界生长能量,保证了钢的强韧性优良,抗过载能力优良,工程服役的安全性高。
The stepwise energy Charpy V-notch impact test was used to study the corresponding relationship between P91 steel and the force-displacement curve and fracture at the time of impact bending fracture, the crack initiation, subcritical growth and instability propagation. Subcritical growth and instability expansion rate. The results show that the crack initiation occurs at the second peak of force-displacement curve after yielding. The critical size of crack subcritical growth corresponds to the second threshold after the force-displacement curve platform. The subcritical crack growth corresponds to the zone of cracking on the fracture. The crack instability expansion corresponds to the expansion zone on the fracture. In the area before cracking, the crack growth at a lower rate of subcritical growth, crack initiation zone after the subcritical growth rate more slowly. The early expansion rate of crack instability is very high and the latter is rapidly decreased. The slow subcritical growth of P91 steel crack and the subcritical crack growth energy of 66% of the total impact energy ensure excellent toughness of steel, excellent anti-overload capability and high safety of engineering service.