E690高强钢在SO_2污染海洋大气环境中的应力腐蚀行为研究

STRESS CORROSION BEHAVIORS OF E690 HIGH-STRENGTH STEEL IN SO_2-POLLUTED MARINE ATMOSPHERE

采用U形弯试样干湿交替腐蚀的实验方法,结合电化学测试、裂纹形貌观察和锈层分析,研究了E690钢在模拟SO_2污染海洋大气环境中的应力腐蚀行为及机理.结果表明,E690钢在SO_2污染海洋大气环境中具有较高的应力腐蚀开裂(SCC)敏感性,其SCC机理为阳极溶解和氢脆(AD+HE)的混合机制.大气环境中的SO_2可通过促进a-Fe OOH的形成以及Ni和Cr在内锈层中的富集促进内锈层的致密化,促进Cl-在锈层底部的浓聚和酸化,进而大大促进SCC裂纹的萌生与扩展,提高了E690钢的SCC敏感性.

With the development of industry, the atmosphere in many cities along the coastal lines such as Qingdao in China has been polluted with SO_2, and has been changed to coastal-industrial atmosphere with the coexistence of SO_2 and Cl-. The corrosion and stress corrosion cracking（SCC） behavior and mechanism of steel in this environment is different from that in the coastal atmosphere containing only Cl-or the industrial atmosphere containing only SO_2. Previous study have indicated that SO_2 in the marine atmosphere can greatly promote the stress corrosion cracking of high-strength steel due to acidification of thin electrolyte layer and reproduction of H＋through Fe SO4. E690 steel, as a newly- developed high strength steel, is very promising to be widely used in offshore platform in the near future for its excellent performance. However, there is few research about its SCC behav-ior in marine atmosphere, especially in SO_2-polluted atmosphere. Therefore, it＇s of great importance to investigate the SCC behavior and mechanism of E690 steel in this environment. In this work, U-bend specimen corrosion test under dry/wet cyclic condition, electrochemical measurements, crack morphology observation and rust layer analysis, were conducted to investigate the effect of SO_2 on SCC behavior of E690 steel in simulated SO_2-polluted marine atmosphere. The results indicated that E690 steel has a high SCC susceptibility in SO_2-polluted marine atmosphere with a combined mechanism of anodic dissolution（AD） and hydrogen embrittlement（HE）. SO_2 in the atmosphere can facilitate the densification of inner rust layer by promoting the formation of a-Fe OOH and enrichment of Ni and Cr in the inner rust layer, leading to the concentration of Cl-under the rust layer, which may result in the initiation and propagation of SCC cracks significantly and therefore enhance the SCC susceptibility.