电化学充氢条件下X70管线钢及其焊缝的氢致开裂行为

HYDROGEN INDUCED CRACKING BEHAVIORS OF X70 PIPELINE STEEL AND ITS WELDS UNDER ELECTROCHEMICAL CHARGING

采用电化学充氢的方法研究了X70管线钢在不同浓度硫酸溶液中的氢致开裂(HIC)行为．结果表明,增大充氢电流密度、延长充氢时间以及降低充氢溶液的pH值能够促进氢进入X70钢基体．微观观察表明,X70钢中的非金属夹杂物如氮化物和氧化物等对其氢致开裂行为有不同的影响,氮化物夹杂并不是充氢裂纹的必然形核位置,而Mg,Al,Ca等的氧化物是更为有害的氢致裂纹源．通过氢渗透实验测得室温下氢在X70钢中的有效扩散系数为3．34×10-9cm2／s．对XT0管线钢基体及焊缝试样电化学预充氢后拉伸,焊缝试样的拉伸塑性较差,各项塑性指标在充氢前、后均低于X70钢基体材料．

The hydrogen induced cracking （HIC） of X70 pipeline steel was studied in H2SO4 solutions with different concentrations by means of electrochemical charging. Larger current densities, longer charging time and lower pH values of solution would promote the hydrogen atoms to enter into X70 steel. Non-metallic inclusions such as nitrides and oxides play different roles in HIC of X70 steel. Microscopic observation showed that there is no dependent relation between cracks induced by hydrogen and the inclusions of nitrides. Otherwise, the oxides of magnesium, aluminum and calcium etc are more harmful as the sources of hydrogen induced cracks. According to the results of hydrogen permeation test, the effective diffusivity （Deft） of hydrogen at room temperature is 3.34×10^-9 cm^2/s. Tensile specimens of X70 steel and welds showed severe plasticity loss after hydrogen charging, while the welds have lower plasticity than that of X70 base metal.