不同组织的316L不锈钢在NH_(4)Cl环境下应力腐蚀行为与机理

Stress Corrosion Cracking Behavior of 316L Stainless Steel with Varying Microstructure in Ammonium Chloride Environment

采用动电位极化曲线、电化学阻抗谱以及U形弯试样浸泡实验研究了不同组织(原始组织、固溶组织与敏化组织)的316L不锈钢在NH_(4)Cl环境下的应力腐蚀开裂(SCC)行为与机理,分析了NH_(4)Cl浓度对不同热处理状态的316L不锈钢应力腐蚀行为和机理的影响。结果表明:不同组织的316L不锈钢在NH_(4)Cl环境中均具有明显的SCC敏感性,原始组织、固溶组织、敏化组织的SCC敏感性依次升高;随着NH_(4)Cl溶液浓度升高,316L不锈钢不同组织的钝化膜稳定性降低,原始组织、固溶组织及敏化组织在NH_(4)Cl环境下,破钝电位依次降低,维钝电流密度依次升高,阻抗值依次减小,钝化膜更加活泼易破坏,饱和NH_(4)Cl浓度下极易发生点蚀导致SCC的萌生。316L不锈钢在NH_(4)Cl环境中的SCC裂纹扩展机制主要为穿晶型阳极溶解机制。

The stress corrosion cracking(SCC) behavior in NH_(4)Cl solutions was studied by means of potentiodynamic polarization measurement, electrochemical impedance spectra(EIS) measurement for 316 L stainless steel with microstructures corresponding with different status of the steel, including asreceived, solid solution-and sensitization-treatment. The results show that 316 L stainless steels exert high SCC susceptibility in NH_(4)Cl containing environment, which increases in the order of as-received, solid solution-and sensitization-treatment. With the rising NH_(4)Cl concentration, the stability of passive film degrades, the passive current density increases, the breakdown potential and polarization resistance decline. In particular, in the saturated NH_(4)Cl solution, pits are prone to initiate, which leads to the occurrence of SCC. In NH_(4)Cl solution, SCC of 316 L stainless steel is dominated by anodic dissolution(AD) process, and the SCC cracks propagate transgranularly.