真空度对2205双相钢在热浓缩海水中点蚀行为的影响

目的研究真空度对2205双相不锈钢在海水淡化环境中耐点蚀性能的影响。方法在1.5倍人工浓缩海水中,采用循环阳极极化曲线与电化学阻抗谱等电化学方法,研究了2205双相不锈钢的点蚀和再钝化行为,并通过扫描电子显微镜对极化后试样的腐蚀形貌进行分析。结果测试了七种不同真空状态下2205双相不锈钢的循环阳极极化曲线和电化学阻抗谱,发现随着真空度的升高,试样的自腐蚀电位和点蚀电位均不断降低,分别约从-256 m V和605 m V下降到-485 m V和363 m V(均vs.SCE),点蚀倾向明显增大。同时,Nyquist曲线中的半圆弧逐渐变得扁平,Bode图中的相位角约从80°下降到77°,但是点蚀电位与再钝化电位之差逐渐升高。不同真空度下循环阳极极化后,试样表面的点蚀坑形貌不完全相同,蚀坑数量随着真空度的升高而明显减少,当真空度升高为0.72时,点蚀坑尺寸明显减小。结论随着真空度的逐渐升高,不锈钢钝化膜的致密性和保护性降低,电化学阻抗值逐渐减小,耐点蚀性能变差,但是再钝化性能却有所增强。循环阳极极化后试样的腐蚀程度减小。

Effects of Vacuum Degree on Pitting Behavior of 2205 Duplex Stainless Steels in Hot Concentrated Seawater

The work aims to investigate the effects of vacuum degree on pitting of 2205 duplex stainless steels in seawater desalination environment. Pitting and repassivation behavior of the 2205 duplex stainless steels was studied in electrochemical methods including cyclic anodic polarization curve and electrochemical impedance spectroscopy (EIS) in 1.5× artificial concentrated seawater, corrosion morphology of polarized testpieces was analyzed with scanning electron microscope. Cyclic anodic polarization curves and electrochemical impedance spectra of the 2205 duplex stainless steels were tested in seven different vacuum states. It was found that self-corrosion potential(vs.SCE) of the testpieces decreased from -256 mV to -485 mV, pitting potential(vs. SCE) decreased from 605 mV down to 363 mV, and pitting tendency increased significantly as vacuum degree increased. Semicircle in Nyquist curve gradually became flat and phase angle in Bode plot decreased from 80° to 77°, while difference between the pitting potential and passivation potential gradually increased. Morphology of pits on the surface of testpieces was not exactly same after cyclic anodic polarization in different vacuum degree, and number of pits increased obviously with the vacuum degree increased. When the vacuum increased to 0.72, size of pits decreased significantly. As the vacuum degree increases gradually, compactness and protectiveness of passive film on stainless steel decrease, electrochemical impedance value decreases gradually, pitting corrosion resistance became worse, while repassivation performance increases and corrosion degree of the testpieces decreases after cyclic anodic polarization.