冲击载荷下P91钢的裂纹萌生与扩展行为研究

Study on crack initiation and propagation behavior of P91 steel under impact loading

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 behavior of initiation,and propagation of cracks in P91 steel under impact loading was investigated by means of instrumented Charpy V-notch impact testing with stepped increasing impact loading.The crack growth rate in the stages of crack initiation,stable and instable growth was studied by analyzing the load-displacement curves and observation of fracture surface.The results show that the cracks initiate at the second peak on load-displacement curve after yielding,the critical size of stable crack growth is corresponding to the second decreasing point on load-displacement curve, and the crack propagation is corresponding to the fracture initiation area and the crack propagation is corresponding to the fracture propagation area. The cracks grow at a low speed in front part of initiation zone and even lower at the rear of initiation zone. The crack propagation rate is very high at the beginning, then decreases quickly as cracks propagate. That cracks grow at low speed and crack growth energy is 66% of fracture energy ensures this steel with good strength and toughness, good ability to resist overload and service safety.