A unified evaluation of fatigue crack growth rate in different gas environments and its application limits

碳钢在氢环境中疲劳裂纹扩展速率的高加速是由于韧性断裂向准解理断裂过渡以及准解理断口面积比的增加。加载频率影响过渡特性和QC面积比。在氮气环境和氢气环境中，均存在韧性断裂占断面比例高、疲劳裂纹扩展速率加速度低的条件。常规疲劳裂纹扩展试验显示，即使在QC断裂开始时，也有韧性断面和沿晶断面。试图确定与裂纹扩展速率直接相关的滑移行为是不成功的

High acceleration of the fatigue crack growth rate of carbon steel in hydrogen environment is due to transition from ductile fracture to quasi-cleavage(QC) fracture and to increase in area ratio of QC fracture surface. Loading frequency influences the transition behavior and QC area ratio. There exist conditions where ductile fracture has high proportion of the fracture surface and low acceleration of fatigue crack growth rate in nitrogen environment as well as in hydrogen. Usual fatigue crack growth test reveals not only ductile fracture surface but intergranular fracture surface even at the beginning of QC fracture. It was not successful to attempt to define the slip behaviordirectly related to the crack growth rate