316不銹鋼於600及900℃含氯氣氛之高氯化腐蝕機構

Chlorination Mechanism of 316 Stainless Steel in Chlorine Containing Atmospheres at 600 and 900℃

選用316不銹鋼於0℃和900℃之20%O2-Ar、1% Cl2-Ar及1% Cl2-20%O2-Ar等三式氣氛進行氧化、氯化及混合氯氧化實驗，探討其高溫腐蝕反應機構。在含氯之氣氛中，液態的氯化物提供高溫腐蝕反應離子之快速傳輪路徑，並於合金基材造成蝕孔，揮發性的氯化物則會破壞保護性氧化皮膜的生成，加速合金的高溫腐蝕。較高的氧分壓，生成外側以氧化鐵內側以氧化鉻為主的外部多孔質雙層氧化皮膜；肥厚的外部氧化物可分隔氯化物與氣氛之交流，減緩合金持續之初次氯化反應或因氯化揮發而流失，但氯化物二次氧化所釋出的氯會形成更深入合金的侵蝕孔洞。

316 stainless steel was selected to investigate the high temperature chlorine corrosion behavior in 20%O2-Ar, 1%Cl2-Ar and 1%Cl2-20%O2-Ar environments at 600 and 900℃. In chlorine containing environments, liquid chloride products provided the easy transporting path for the reactant ions, and induced internal pores on alloy substrate. The volatile chloride products inhibited the formation of protective oxide, and accelerated the metal oxidation. The higher oxygen partial pressure, an external two-layered oxides scales could be form. Iron oxide was concentrated in the outer layer and the chromium oxide was in the inner side. The external bulky oxides separated the interactions of chloride products from atmospheres, and retarded the alloy depletion caused by chlorination and sublimation. However, the chlorine released from the reoxidation of metal chlorides attacked alloy matrix and resulted in a deeper internal attacked pores structure.