NaCl溶液中20Cr9Ni5Co14不锈钢电化学腐蚀行为

采用电化学极化技术(动电位极化技术、线性极化技术和循环极化技术)和交流阻抗技术研究了不同条件下20Cr9Ni5Co14超高强度不锈钢的电化学腐蚀行为,并采用扫描电镜对极化后腐蚀形貌进行了表征.结果表明,20Cr9Ni5Co14钢在3.5%(质量分数)Na Cl溶液中出现钝化.随着Na Cl浓度的升高,钝化现象消失,而自腐蚀电流密度从8.223×10-7A/cm2减小至1.129×10-7A/cm2;随着p H值的降低,20Cr9Ni5Co14钢的致钝电位和过钝化电位增加.在p H值高于3时,腐蚀产物膜具有良好的耐腐蚀性能而导致反应步骤成为控制步骤.而当p H值降低到2时,腐蚀产物溶解速度很快,金属界面发生腐蚀速率很大,浓差极化成为了控制步骤.对腐蚀形貌研究表明,20Cr9Ni5Co14钢在极化过程中出现点腐蚀,导致了材料的耐腐蚀性能下降.

Electrochemical Corrosion Behaviors of 20Cr9Ni5Co14 Stainless Steels in NaCl Solution

The corrosion behaviors of 20Cr9Ni5Co14 ultra high strength steel (USS) were studied by the electrochemical polarization methods (potentiodynamic polarization， linear polarization and cyclic polarization technologies) and alternating current impedance spectrum methods in different corrosion conditions， and after polarization the corrosion morphologies were characterized by Scanning Electron Microscopy(SEM). The results showed that the passivation phenomenon of 20Cr9Ni5Co14 steels appeared in 3.5wt.% NaCl solution while disappeared with the increase of NaCl concentration. The corrosion current also reduced from 8.223×10^-7A/cm² to 1.129×10^-7A/cm² with the increase of NaCl concentration. The passivation and transpassivation potentials of 20Cr9Ni5Co14 steels increased with the increase of hydrogen ion concentrations. When the pH value was higher than 3， the corrosion product film had excellent corrosion resistancewhich led the electrochemical polarization step as a dominated step， while the pH value decreased to 2， the corrosion products dissolution rate was fast， the corrosion rate of the interface of the metal surface and the solution was also fast， thus the polarization caused by concentration differences became the dominated step. Corrosion morphology studies showed that the corrosion of 20Cr9Ni5Co14 steels in the polarization process oriented from pitting corrosion， which leads to the reduction of corrosion resistance.