不同加工表面對304L不銹鋼間隙腐蝕速率的影響

Studying Crevice Corrosion Susceptibility of 304L Stainless Steel with Various Surface Conditions

本研究比較不同表面狀況下，不銹鋼的間隙腐蝕速率。不同加工表面的304L不銹鋼試片先於表面均勻噴上海鹽溶液並於攝氏60度的加熱板乾燥，之後試片鎖上耦接墊片，放置於設定為攝氏50度及相對溼度50%的環境溫濕度控制箱中，時間分別是100、400、700、及1000小時。取出的試片利用雷射共軛聚焦顯微鏡及掃描式電子顯微鏡來量測及觀察腐蝕面積及最大腐蝕深度，此外量測試片的重量變化。在腐蝕起始階段，機械加工表面較拋光表面有較快的全面腐蝕速率與間隙腐蝕速率。以EDS分析表面的成分來看，推測此處的腐蝕起始機制類似於孔蝕的起始機制，於MnS與母材界面發生並形成較深之蝕孔，而在耦接墊片覆蓋下的蝕孔周圍表面，氧化產物的表面並存有氯與微量的硫，在硫與鹽的共同作用下，產生較大的腐蝕面積。

This study focuses on the corrosion rate of 304L stainless steel with various surface conditions under crevice corrosion situation. 304L stainless steel specimens with both polished and machined surfaces were firstly covered with a crevice former; then they were keep in a relative humidity condition of 50% at a temperature of 50oC, of which were examined subsequently 100, 400, 700, and 1000 hours. Corrosion areas and maximum corrosion depth were measured and observed by confocal laser scanning microscope and scanning electron microscopy. Moreover, the weight loss and weight gain were measured. The results of EDX show the initiation of corrosion is similar to the mechanism of pitting, which initiated from the boundaries of MnS inclusions and steel. Below the cover of crevice former, the surface is covered by oxide products which contain chlorine and trace amounts of sulfur. It shows the metal matrix is dissolved by the synergistic effect of sulfur and chloride ions, which enlarge the corrosion areas.