Cl–对冷变形316L奥氏体不锈钢在H2S环境下应力腐蚀的影响

目的研究H2S环境下不同Cl^-浓度对冷变形316L奥氏体不锈钢应力腐蚀行为的影响,探究Cl^-造成影响的原因,为不锈钢安全服役提供理论数据。方法采用力学方法研究了冷变形316L奥氏体不锈钢的力学行为,通过计算延伸率损失表征材料的应力腐蚀敏感性,通过电化学手段表征了点蚀电位。最后为了研究点蚀与基体中氢含量的关系,进行了扩散氢含量的测试,通过测量试样的扩散氢含量,进一步理解应力腐蚀行为。结果随着Cl^-浓度的增加,316L奥氏体不锈钢的延伸率损失逐渐增大,应力腐蚀敏感性增强。断口形貌从杯状的等轴韧窝转变为解理型脆性断裂。动电位极化测试表明,Cl^-浓度的增加,点蚀电位逐渐降低,直至–0.0228V,试样更容易发生点蚀。扩散氢含量的测量进一步显示了点蚀坑的存在促进了氢进入到金属内部。结论 Cl^-对316L奥氏体不锈钢在H2S环境中的应力腐蚀行为有重要影响,随着Cl^-浓度的增加,应力腐蚀敏感性增强,结合点蚀电位的测量结果,可能是由于Cl^-破坏金属表面的钝化膜,产生点蚀坑,裂纹形核并扩展,同时点蚀坑还促进了氢进入金属内部,应力腐蚀敏感性增强。

Effect of Cl^- on Stress Corrosion of Cold Deformed 316L Austenitic Stainless Steel in H2S Environment

Austenitic stainless steel is widely used in oil exploitation, however, it is faced with severe corrosion because of S and Cl^- in the environment. So, its service safely has been widely concerned. In this paper, the influence of Cl^- concentrations on the stress corrosion behavior of cold deformation 316L austenitic stainless steel under H2S environment was studied, and the influence of Cl^- was discussion. The mechanical behavior of 316L was studied by mechanical method and the elongation loss was used to represent the stress corrosion susceptibility. The pitting potential was characterized by electrochemical method. The diffusion hydrogen content was measured to study the relationship between pitting corrosion and hydrogen. The result show the elongation loss and SCC susceptibility increased with Cl^- content. Fracture morphologies changed from cup-shaped equiaxed dimple to cleavage-type brittle fracture. Kinetic potential polarization experiment showed that the pitting potential gradually decreased to 0.0228 V and the sample was more prone to pitting as the increasing of Cl^- concentration. Hydrogen content showed that pitting increased hydrogen content in the metal matrix. Cl^- has an important influence on the stress corrosion behavior of 316L austenitic stainless steel in H2S environment. SCC susceptibility increases with Cl^- concentration. It may be due that Cl^- damaged the passivation film on the metal surface and resulted in pitting pits, where the crack nucleates and expands. At the same time, pitting also increased hydrogen content in the metal matrix and then improved the stress corrosion cracking susceptibility.