静水压力对X70钢在海洋环境中腐蚀行为影响研究

Effect of Hydrostatic Pressure on Corrosion Behavior of X70 Steel in Simulated Sea Water

利用高温高压反应釜,采用失重、电化学实验和慢应变拉伸方法,结合X射线衍射(XRD)、扫描电子显微镜(SEM)和能量散射X射线谱(EDS)等手段研究了0~3 MPa静水压力对X70钢在模拟海洋环境中的腐蚀行为的影响。结果表明:静水压力在0~2 MPa范围内,X70钢的腐蚀形态表现为局部腐蚀,腐蚀产物主要成分为FeOOH。静水压力为3 MPa时,腐蚀形态倾向于均匀腐蚀,腐蚀产物除FeOOH外,还出现少量的Fe_(3)O_(4)。随着静水压力的增加,X70钢的腐蚀速率先增加后减小,在2 MPa时达到最大。静水压力在0~2 MPa范围内,X70钢SCC敏感性随着压力增加而增加;继续增加到3 MPa时,SCC敏感性有降低的趋势。X70钢在模拟海洋环境溶液中应力腐蚀开裂敏感性取决于金属表面点蚀的状况,而不一定正相关于静水压力。随静水压力的增加,X70钢表面的阳极溶解被促进,同时也促进更多的氢原子进入钢中,其应力腐蚀开裂机制是由阳极溶解和氢致开裂共同控制的混合机制。

The influence of hydrostatic pressure on the corrosion behavior of X70 steel in simulated sea water was studied in the pressure range of 0~3 MPa by means of high temperature and high pressure reaction kettle, mass loss measurement, electrochemical means and slow strain tensile method, as well as XRD, SEM and EDS. The results showed that X70 steel suffered from localized corrosion and the main component of the corrosion product was FeOOH in the pressure range of 0~2 MPa. When the hydrostatic pressure was 3 MPa, the corrosion morphology turned to be general corrosion, and a small amount of Fe_(3)O_(4) appeared in addition to FeOOH in the corrosion product. With the increase of hydrostatic pressure, the corrosion rate of X70 steel increased first and then decreased, and reached the maximum by 2 MPa. When the hydrostatic pressure was in the range of 0~2 MPa, the stress corrosion cracking(SCC) sensitivity of X70 steel increased with the increasing pressure, whereas, as the pressure increase up to 3 MPa, the SCC sensitivity decreased. The SCC sensitivity of X70 steel in the simulated sea water depended on the pitting degree on the steel surface, but not necessarily have a positive correlation to the hydrostatic pressure. With the increase of hydrostatic pressure, the anodic dissolution of X70 steel surface was promoted, and more hydrogen atoms were promoted to enter the steel. The SCC process of X70 steel in the simulated sea water could be ascribed to a mixed mechanism controlled by both anodic dissolution and hydrogen induced cracking.