A508/IN-182/316L異質銲接件之加凡尼腐蝕

Galvanic Corrosion of A508/IN-182/316L Dissimilar Weldments

本研究使用鎳基IN-82/IN-182合金作為GTAW及SMAW銲接填料，製作A508/IN-182/316L異質銲接件。透過耐蝕能力評估，探討稀釋率及各區域金屬於加速腐蝕環境中的材料損失，建立實驗系統、評估材料減薄量的方法。
實驗結果顯示，異質銲接件中之三種材料中，因A508低合金鋼為相對活性較高之金屬，含有最多的鐵元素且具最低的腐蝕電位，在浸泡試驗中發生最嚴重的腐蝕。雖然316L不銹鋼也具有較多的鐵含量，但與IN-182有相近的鉻含量，使其與IN -182有相近的腐蝕電位及耐腐蝕性能。在局部動電位極化之數據結果顯示，愈靠近IN-182緩衝層時有愈大的腐蝕電流密度，亦即產生較嚴重的腐蝕程度，且在浸泡試驗之腐蝕深度結果顯示，愈靠近IN-182緩衝層之A508母材有愈大的腐蝕深度。另外，A508/IN-182/316L組合較A508/IN-182組合的陽極與陰極比例小，前者受到較嚴重的加凡尼腐蝕，提早出現微裂縫。綜合以上試驗的結果，顯示當陽極金屬發生嚴重的加凡尼腐蝕時，因距離效應有愈靠近陰極金屬產生愈嚴重的腐蝕，並呈現陽極金屬所占的面積比率愈小，加凡尼腐蝕愈嚴重。

In this study, nickel-based IN-82/IN-182 alloy was used as GTAW and SMAW welding filler to produce A508/IN-182/316L dissimilar weldments. In this study, the effect of microstructure and resistance on crevice corrosion and galvanic corrosion was thoroughly studied. Also, the effect of dilution rate and different weld zone on the thinning rate was investigated and the most proper way for specimen preparation and the corrosion rate evaluation were carried out.
The results show that the low alloy carbon steel, A508, has the lowest corrosion potential among the dissimilar weld. Due to high iron content, the fusion boundary reveals that the A508 side was suffered by galvanic corrosion. The other reason is inferred to the low chromium and nickel content of A508. Although the fusion boundary also was observed at the IN-182/316L interface, the corrosion rates of both metals are similar. This phenomenon could be attributed to the similarity of chromium content. In the comparison of the anodic polarization test and immersion test, the A508-side fusion boundary shows the tendency having a higher corrosion current density and the depth of corrosion attack. The A508/IN-182/316L couples has a smaller anode to cathode ratio than that of the A508/IN-182 couples. The former suffers from more serious galvanic corrosion and microcracks formation. In summary, it is shown that when the anode metal undergoes severe galvanic corrosion, the more severe corrosion occurs on the closer cathode due to the distance effect. Also the greater galvanic corrosion happened when the anode metal possessing the smaller area ratio.