16Mn钢低温疲劳裂纹扩展速率的预测

PREDICTION OF FATIGUE CRACK GROWTH RATES IN 16Mn STEEL AT LOW TEMPERATURE

研究了１６Ｍｎ钢（热轧和高温正火状态）的低温疲劳裂纹扩展规律，建立了低温疲劳裂纹扩展速率通式。若室温疲劳极限和裂纹扩展门槛值已定，利用该式可根据拉伸性能预测材料的低温疲劳裂纹扩展速率而不需任何低温疲劳试验和经验修正。研究结果表明，可将断裂韧度的热激活分量为零时的上限温度定义为疲劳裂纹扩展机制脆转温度ＴＦＤＢＴ。当Ｔ＞ＴＦＤＢＴ，疲劳裂纹扩展速率随温度降低而下降；但当Ｔ＜ＴＦＤＢＴ，中区疲劳裂纹扩展机制由条带转变为解理，裂纹扩展速率随温度下降而升高。

Low temperature fatigue crack growth (FCG) behaviour of a low carbon low alloy steel ( 16Mn) is investigated under hot-rolled and high temperature-normalized conditions and a general expression for the low temperature FCG rates is offered. By means of this expression, much money will be saved because the FCG rates can be Predicted from the tensile Properties without additional empirical modification and low temperature fatigue test, if the endurance limit and FCG threshold at room temperature are predetermined.The results indicate that the upper bound temperature, below which the thermal component of fracture toughness equals to zero, may be defined as the ductile-brittle transition temperature of FCG mechanism, TFDBT. Above TFDBT the FCG rates decrease with decreasing temperature but blow TFDBT the trend is reversed due to the change of the FCG mechanism in the intermediate region (da/dN≈10-～10-6m·cycle-1) from the ductile striation into microcleavage.