以雙環動電位再活化技術評估鎳基800H合金敏化程度

Evaluation Degree of Sensitization of Incoloy 800H by Double-loop Electrochemical Potentiokinetic Reactivation Technique

雙環動電位再活化（double-loop electrochemical potentiokinetic reactivation, DL-EPR）技術為評估沃斯田鐵系不銹鋼敏化程度之測試法。本研究嘗試利用H2SO4 + KSCN濃度之調整，藉由比對ASTM G28浸泡試驗之結果，開發用於鎳基800H合金之DL-EPR方法。與不銹鋼不同的是，鎳基合金經DL-EPR試驗後，試片除沿晶腐蝕外，會有其他腐蝕形貌的出現，藉由適當試驗參數的調整，可降低非沿晶腐蝕的腐蝕量，而達成快速評估鎳基800H合金敏化（sensitization）程度之試驗方法。由DL-EPR之試驗結果顯示，鎳基800H合金經700℃、不同恆溫時間之熱處理，其Ir/Ia值隨著700℃恆溫熱處理時間的增加，呈現先增加、後下降的現象，而硫酸鐵-硫酸120小時沸騰浸泡試驗後，亦呈現相似的結果，意謂材料之敏化程度出現不同程度之差異，此乃晶界因熱履歷造成之敏化現象，於長時間後造成自癒（self healing）的結果。觀察經DL-EPR試驗後之試片，除了晶界腐蝕之外，另可觀察到基材內部腐蝕的現象發生，上述兩區域之再活化程度與溶液中之KSCN濃度有關，藉由適當的濃度調整，可降低再活化反應中之基材腐蝕比例。當溶液為0.5 M H2SO4 + 0.001 M KSCN時，為以DL-EPR評估鎳基800H合金敏化程度的較佳化溶液配比。

The degree of sensitization (DOS) of austenitic stainless steel is evaluated by double-loop electrochemical potentiokinetic reactivation (DL-EPR) test. In this study, a number of solutions based on H2SO4 + KSCN compositions have been evaluated a reliable DL-EPR test parameter for Incoloy 800H. Different with stainless steel, an extra matrix corrosion exception intergranular corrosion (IGC) is occurred for Incoloy 800H after DL-EPR test. With a proper parameter, such as solution concentration adjustment, the matrix corrosion might be eliminated mostly. The DOS of Incoloy 800H after sensitization at 700 ℃ for different time is quantified by the corrosion rate after a ASTM G28 method A test. It demonstrates that the DOS increased then decreased with increasing thermal treatment time, which showed a self-healing occurred after a long sensitization time. The DL-EPR tests in 0.5 M H2SO4 with various KSCN concentration gave the Ir/Ia values that all matched with the tendency of the DOS indicated by ASTM G28-A. The optimal sensitization sensitivity, however, was occurred in the solution with 0.001 M KSCN additions, because of its lowest ratio of matrix corrosion.