熱處理對2205雙相不銹鋼之晶界腐蝕影響研究

Effect of Heat Treatment on the Intergranular Corrosion of 2205 Duplex Stainless Steel

本研究是探討經熱處理後之2205雙相不銹鋼，σ相析出對晶界腐蝕的影響。研究結果發現：2205雙相不銹鋼經熱處理後，σ相在α/γ及α/α晶界析出；當溫度及時間增加時，α相中亦會析出σ相。σ相在α/γ晶界析出時，其界面附近之α相中有明顯的鉻缺乏現象。有關2205 雙相不銹鋼對晶界腐蝕的敏感性，可以ASTM A262 Practice A草酸電解試驗法作定性評估；而雙環電化學動電位再活化試驗法則可以進行定量分析。經熱處理之2205雙相不銹鋼，在25℃、pH=3、濃度1M之NaCl水溶液中進行極化曲線測試時，其孔蝕起始電位及孔蝕保護電位，隨σ相析出量的增加而下降。

In this study, effect of σ phase precipitates on the intergranular corrosion and pitting corrosion of 02205 duplex stainless steels after heat treatment were investigated. It's found that precipitation of σ phase were found along the α/γ and α/α grain boundaries after heat treatment; σ phase precipitates were found in α phase when time and temperature were high enough. Chromium depletion on the aside of the α/γ interface was more pronounced than that on the γ side. ASTM A262 Practice A oxalic acid etch test and double loop electrochemical potentiokinetic reactivation (DL-EPR) were used to evaluate the degree of intergranular corrosion in qualitative and quantitative manners, respectively. Cyclic potentiodynamic polarization measurements, in 1M NaCl solution of pH=3 at 25℃, revealed that Enp and Epp of 2205 duplex stainless steel decreased if σ phase precipitation occurred as compared with those of the solution annealed specimens and intergranular corrosion was observed after electrochemical testing.