Corrosion Behavior of SUS⁽¹⁾ 329J1 Stainless Steel in Formic Acid Solution

The corrosion behavior of SUS 329J1 stainless steel in formic acid solution was investigated by corrosion weight loss, polarization curves, and natural electrode potential (NEP) variation with time. The surfaces of specimens after corrosion weight loss tests were analyzed by electron spectroscopy for chemical analysis (ESCA). The corrosion weight loss of the steel at room temperature was very small, indicating that the steel had good corrosion resistance. At the boiling point, the corrosion of the steels was severe, with the maximum corrosion rate in 80% formic acid solution. From the analysis of the steel surface by ESCA, it was considered that the corrosion of the steel in 20% formic acid solution was inhibited by Cr-oxide (Cr₂O₃) as a protective film, and in 80% formic acid, the corrosion of the steel progressed because the passive film was not sufficiently stabilized by oxide of Cr or Mo. In nonaqueous formic acid solution (containing 1000 to 3000 ppm of water), the corrosion rate was presumed to decrease because the oxide of Mo and Cu were formed.