氢气含量与加载频率对X80钢管接头疲劳裂纹扩展速率的影响

Effect of Hydrogen Content and Loading Frequency on Fatigue Crack Growth Rate of X80 Steel Pipe Joint

在氮气,体积分数均为2%的H_(2)+CO_(2)以及体积分数分别为5%,2%的H_(2)+CO_(2)环境中,对X80钢管接头试样进行不同加载频率(0.1,1.0,10.0 Hz)的疲劳裂纹扩展试验,研究了氢气含量和加载频率对疲劳裂纹扩展速率的影响。结果表明:当加载频率为1.0 Hz时,氢气含量越高,接头母材、热影响区和焊缝裂纹扩展速率越大,且焊缝中的裂纹扩展速率增大程度最大;含氢环境中焊缝的疲劳裂纹扩展速率小于母材和热影响区;当氢气体积分数为5%时,母材和热影响区均发生韧性断裂,但疲劳断口上存在微小的二次裂纹和少量平台状结构等脆性断裂特征,焊缝疲劳断口出现长度近80μm的二次裂纹,但断口形貌仍主要呈韧性断裂特征;氢气体积分数为5%时,随着加载频率增加,母材的疲劳裂纹扩展速率先增大后减小,加载频率为1.0 Hz时的疲劳裂纹扩展速率最大。

Fatigue crack growth tests were carried out on X80 steel pipe joint samples at different loading frequencies(0.1,1.0,10.0 Hz)under nitrogen atmosphere,H_(2)+CO_(2)atmospheres with the volume fraction of 2%and H_(2)+CO_(2)atmospheres with the volume fraction of 5%and 2%,respectively.The effect of hydrogen content and loading frequency on fatigue crack growth rate was studied.The results show that when the loading frequency was 1.0 Hz,the higher the hydrogen content,the larger the crack growth rate of the joint base metal,heat affected zone and weld,and the increase degree of the crack growth rate of the weld was the largest.The fatigue crack growth rate of the weld was smaller than that of the base metal and heat affected zone under hydrogen atmosphere.When the hydrogen volume fraction was 5%,ductile fracture occurred in both the base metal and the heat affected zone,but there were small secondary cracks and a small number of platform structures on the fatigue fracture.The weld fatigue fracture had secondary cracks nearly 80μm in length,but the fracture morphology was still mainly ductile fracture characteristics.When the hydrogen volume fraction was 5%,the fatigue crack growth rate of the base metal increased first and then decreased with the increase of loading frequency,and reached the maximum when the loading frequency was 1.0 Hz.