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转变和准解理断裂面积比的增加。加载频率影响相变行为和QC面积比。在氮气环境和氢气环境中，存在韧性断裂占断裂面比例高和疲劳裂纹扩展速率加速率低的条件。疲劳裂纹扩展试验表明，即使在QC断裂的初期，也出现了韧性断裂和沿晶断裂。试图定义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