饱和CO_(2)溶液中Cl^(-)浓度对马氏体不锈钢应力腐蚀敏感性的影响

Effect of Cl^(-) Concentration on the Stress Corrosion Sensitivity of Martensitic Stainless Steel in Saturated CO_(2) Solution

为了明确Cl-浓度的变化对超级13Cr马氏体不锈钢耐蚀性能的影响规律,利用电化学动电位测试技术对比分析了Cl-浓度对超级13Cr腐蚀电位的影响关系;采用慢应变速率拉伸(SSRT)应力腐蚀开裂(SCC)试验方法和应力-应变曲线(σ-ε)、扫描电镜(SEM)等分析手段,研究了饱和CO2环境下在一定慢应变速率条件下Cl-浓度的变化对超级13Cr马氏体不锈钢的抗拉强度、延伸率、应力腐蚀敏感指数(ISSRT)的影响,并结合断口形貌分析了材料的断裂特征。结果表明:在Cl-浓度≤60 g/L的饱和CO2溶液中,超级13Cr相对于空气中强韧性变化不大,属于韧性断裂模式;随着Cl-浓度的增大,材料的断裂寿命和伸长率均逐渐降低;材料断裂模式由韧性断裂逐渐转变为韧性-脆性混合断裂模式;当Cl-浓度增大到90 g/L时,断口侧面开始出现二次裂纹;当Cl-浓度≥120 g/L时,材料点蚀电位明显降低,点蚀敏感性增大,同时断口侧面出现点蚀现象,进一步促进了应力腐蚀开裂。

The purpose of this paper is to clarify the influence rule of Cl- concentration changes on the corrosion resistance of super 13 Cr Martensite stainless steel. The influence of Cl- concentration on the corrosion potential of super 13 Cr was compared and analyzed by electrochemical potentiometric test. In addition,the influence of Cl- concentration on the tensile strength,elongation and stress corrosion sensitivity index( ISSRT) of super 13 Cr martensitic stainless steel under a certain slow tensile rate in saturated CO2 solutions were studied by the means of slow strain rate tensile( SSRT) SCC test,stress-strain curve( σ-ε) and scanning electron microscope( SEM). Furthermore,the fracture characteristics of the materials were researched by the fracture morphology. Results showed that in the saturated CO2 solution with Cl- concentration lower than 60 g/L,super 13 Cr had little change in strength and toughness compared with that in the air,which belonged to the ductile fracture mode;with the increase of Cl-concentration,the fracture life and elongation of the material decreased gradually;the fracture mode of the material changed from the ductile fracture to the ductile brittle mixed fracture mode;when Cl- concentration increased to 90 g/L,the second crack began to appear at fracture side. When Cl-concentration was higher than 120 g/L,the pitting potential of the material decreased significantly,the pitting sensitivity increased,and the pitting phenomenon appeared on the side of the fracture,which further promoted the stress corrosion cracking.