采用电化学测试、氢渗透电流检测、慢应变速率拉伸实验和断口分析等方法研究了X80管线钢在模拟深海条件下的氢脆敏感性,并对阴极极化电位的影响进行了考察. 结果表明,阴极极化电位对材料的氢渗透和氢致开裂行为影响明显.渗氢电流与阴极极化电位呈现良好的线性关系,X80管线钢在自腐蚀状态下没有氢脆敏感性, 在－900 mV以上的阴极电位范围内,渗氢电流密度不超过0.1157 μA/cm², 且力学性能也无明显下降,是较适合的阴极保护电位区间, 而负于该电位时, 渗氢电流增大,慢应变速率拉伸试样断口由韧窝形貌转变为准解理形貌, 材料脆断现象明显.

Pipeline steels utilized in deep seawater are usually protected cathodically. However, inappropriate operations of cathodic protection systems cause hydrogen embrittlement failures to these high strength steels in seawater which result from the application of excessive negative potentials, leading to massive generation of hydrogen at the protected pipelines' surface. With high strength steels increasingly widely used in the deep sea environment, the basic research to the cathodic protection and susceptibility to hydrogen embrittlement of high strength steels under such a circumstance is still unfortunately relatively lack and urgently needed to supplement. Electrochemical measurement, hydrogen permeation current detection, slow strain rate tensile test (SSRT) and fracture morphology analysis, therefore, were employed to investigate effect of cathodic polarization level on the susceptibility of API X80 pipeline steels to hydrogen embrittlement in simulated deep seawater in the present work. The results showed that the applied cathodic polarization potentials significantly affected hydrogen permeation and hydrogen--induced cracking behavior of X80 steels immersed in deep seawater. A linear relationship was found between the hydrogen permeation current densities and cathodic polarization potentials applied according to the findings of the potential dynamic polarization and hydrogen permeation current measurements. SSRT tests suggested that X80 pipeline steels immersed in simulated deep seawater didn't show susceptibility to hydrogen embrittlement at open circuit potential, and thus the optimum cathodic protection potential range was supposed to be above －900 mV (vs saturated calomel electrode). Under such a cathodic polarization potential, the hydrogen permeation current densities of X80 pipeline steel specimens were less than 0.1157 μA/cm² andtheir mechanical properties didn't decrease remarkably. Once the cathodic polarization potentials lower than －900 mV, however, hydrogen permeation current densities and calculated hydrogen embrittlement coefficients ψ of X80 pipeline steels increased significantly, exhibiting higher susceptibility to hydrogen embrittlement in simulated deep seawater. Furthermore, macro－and micro－morphologies of fracture surface of X80 pipeline steels after SSRT test indicated that the fracture morphology transformed from a dimpled pattern with ductile fracture to a quasi—cleavage pattern when cathodically polarized to lower than －900 mV, i.e. showing obvious brittle failure characteristics.