150 環境負荷の低い有機酸溶液による SUS304 鋼電解研磨面の不働態化処理 石見 清隆 a,* ，井田 義明 b ，津高 文幸 c ，杉本 克久 d a マルイ鍍金工業㈱ 千葉・柏工場 (〒 277-0805 千葉県柏市大青田 692-1) b マルイ鍍金工業㈱ 本社 (〒 672-8023 兵庫県姫路市白浜町甲 402) c マルイ鍍金工業㈱ 姫路工場 (〒 672-8022 兵庫県姫路市白浜町宇佐崎南 1-29) d 東北大学 名誉教授 (〒 982-0222 宮城県仙台市太白区人来田 2-11-18

To develop a safe and environmentally friendly passivation treatment, the pitting resistance of Type 304 stainless steels, which were finished with different polishing methods and then passivated in H 2 O 2 solutions under various conditions, were examined by measuring their pitting potentials in deaerated 3.5 %NaCl. Results show that pitting potentials were strongly dependent on the surface polishing conditions. A remarkable increase in pitting potential was attained on an electro-polished surface. The highest resistance to pitting was obtained on a surface treated in 3.5 %H 2 O 2 at 25 ℃ for 2 h. The steels treated under this condition showed extremely high pitting potential of 1075 mV （vs. Ag/AgCl （sat. KCl） ） in 3.5 %NaCl, but they showed no change in pitting potential after immersion in aerated 3.5 %NaCl for 100 d. Change in anodic polarization curves of electro-polished and passivation-treated Type 304 stainless steel in deaerated 3.5 %NaCl with immersion time in aerated 3.5 %NaCl. The electro-polished steel was passivated in 3.5 %H O for 2h and then immersed in aerated 3.5 %NaCl for 1-100d before the measurement of anodic polarization curves in deaerated 3.5 %NaCl.Contents of

To develop effects of surface polishing conditions on pitting resistance after passivation treatments, pitting potentials of Type 304 stainless steels finished using different polishing techniques and passivated with HNO 3 solutions of different types were measured in deaerated 3.5%NaCl. Steel finished with electropolishing and then passivated in 30%HNO 3 showed high pitting potential of 1010 mV (vs. Ag/AgCl (sat. KCl) ) , which is in a trans-passive potential region. Increased pitting potential of 1053 mV was obtained when 0.1 kmol･m -3 Na 2 MoO 4 -containing 30%HNO 3 was used for passivation. Steel finished with mechanical polishing never showed such high pitting potential. No decrease in pitting potential was observed on steel finished with electropolishing and 30%HNO 3 or 0.1 kmol･m -3 Na 2 MoO 4 -containing 30%HNO 3 passivation after accelerated corrosion tests such as long term immersion in aerated 3.5%NaCl, salt spraying with 5%NaCl or steaming at 121 ℃. To achieve high pitting resistance, combined surface treatment of electropolishing and 30%HNO 3 or 0.1 kmol･m

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