18Cr-8Niステンレス鋼の孔食および間隙腐食におよぼすハロゲンイオンおよび温度の影響

Abstract

In this paper, the effects of halogen ions and temperature were investigated on the pitting and crevice corrosion of 18Cr-8Ni stainless steel. The results obtained were summarized as follows. (1) In the anodic polarization curves of 18Cr-8Ni stainless steels in 0.1 M NaCl solution below 10°C, stable repassivation was observed at the potentials above 1.1 V (Eh), whereas in those of specimens in the crevice, no similar phenomenon was observed. (2) Apparent activation energies obtained for the onset of pitting and crevice corrosion were about 98.6 and 86.4 kcal/mol, respectively, and those for stationary state were about 4 kcal/mol for both. (3) The critical pitting potentials of 18Cr-8Ni stainless steel in the halide solutions were in the following order: Cl−≥Br−>I−, and the crevice corrosion potentials were, on the contrary, in the order: Cl−<Br−<I−. (4) From the results mentioned above, it is considered that the major cause for the crevice corrosion is the restricted supply of H2O and OH− ions in the narrow crevice, and that the higher EX0 of the hologen ions in the solution, the higher becomes the critical pitting potential because of the easy supply of H2O and OH− ions on the open surface which contributes to the repair of the surface film.