201不銹鋼與444不銹鋼中介在物對孔蝕敏感性之影響

Effect of Inclusions on Pitting Corrosion Susceptibility of 201 and 444 Stainless Steels

本研究旨在探討201與444不銹鋼中介在物對其發生孔蝕敏感性的影響。由於合金成分上的差異，201與444不銹鋼含有不同的介在物。201不銹鋼含錳較多，其介在物主要為硫化錳及氧化物；444不銹鋼含有鈦和鈮，其介在物則主要為氮化鈦、氧化鋁等。介在物密度的分析結果顯示，444不銹鋼之介在物密度略高於201不銹鋼。在NaCl水溶液中量測動電位極化曲線，結果顯示444不銹鋼之孔蝕成核電位明顯高於201不銹鋼。在施加略高於孔蝕成核電位的定電位實驗，觀察孔蝕的起始位置與孔蝕的潛伏時間，結果發現201不銹鋼之孔蝕起始於硫化介在物上，而444不銹鋼則起始於氧化鋁和氮化鈦之複合介在物上。從電化學試驗結果顯示，444不銹鋼之耐孔蝕性能優於201不銹鋼。

The effect of inclusions on pitting corrosion susceptibility of 201 and 444 stainless steels (SSs) were explored. Due to the difference in their chemical compositions, both SSs contains different types of inclusions. In 201 SS which had relative high manganese content, the main inclusions were manganese sulfide and oxides. In the titanium-containing 444 steels, the main inclusions are titanium nitride and aluminum oxide. The potentiodynamic polarization curves measured in NaCl aqueous solution showed that 444 SS exhibited a higher pitting nucleation potential than that of 201 SS. Potentiostatic tests at a potential slightly higher than their respective pitting nucleation potentials followed by scanning electron microscopical observation were conducted. The experimental results showed that sulfide inclusions were the pitting corrosion initiation sites in 201 SS, while pitting corrosion occurred mainly around titanium nitride and/or aluminum oxide inclusions in 444 SS. The results demonstrated that 444 SS was more resistant to pitting corrosion than 201 SS.