Clarification of crack initiation mechanism under irradiation and fatigue and development of method for detecting and lengthening initiation life by nano-level analysis of surface morphology

本研究的目的是阐明低活性铁素体钢及其焊缝在辐照和疲劳损伤下的裂纹萌生机理，提出裂纹萌生的检测指标和延长裂纹萌生寿命的方法。裂纹萌生主要发生在基体中。辐照损伤导致了起爆寿命的缩短。辐照损伤对裂纹萌生部位及其比例没有影响，说明了无论辐照损伤程度如何，原始奥氏体晶界对裂纹扩展的抑制作用都是不同的。在此基础上，通过优化晶界尺寸和晶界存在概率来抑制辐照损伤下疲劳裂纹的萌生。

The objective of this study is to clarify the crack initiation mechanism under irradiation and fatigue damages in the reduced activation ferritic steel and its weld, and to develop the index for detecting the crack initiation and the method for lengthening the initiation life.It was clarified that the crack initiation occurred at the prior austenitic grain boundary, the packet boundary, the block boundary, and the inside of the block structure. Most of the crack initiation was observed in the matrix. The irradiation damage induced the shortening of the initiation life. No change of the initiation sites and their ratio occurred due to the irradiation damage.The suppression of the crack growth by the prior austenitic grain boundary was clarified regardless of the irradiation damage. Based on this result, the fatigue crack initiation under the irradiation damage would be suppressed by the optimization of the grain size and the probability of the existence of the grain boundary.