Microelectrochemical investigation on pit initiation at sulfide and oxide inclusions in type 304 stainless steel

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Abstract

MnS and MnO inclusions with a small amount of chromium were obtained by heat-treatments of Type 304 stainless steel at 1353, 1573, and 1673 K, and the anodic dissolution behavior of the inclusions was investigated using a microelectrochemical technique. In the case of the sulfide inclusions, those with a high dissolution potential were found to provide high pitting potentials in the macroscopic measurements in 0.1 M NaCl. The initiation sites of metastable and stable pits were at the boundaries of the inclusions and the matrix in 3 M NaCl, 3 M Mg Cl2, and 8 M LiCl. The dissolution current densities on the inclusion surface at the moment of the initiation of a stable pit decreased with increasing chloride-ion concentration. The synergistic effect of chloride ions and sulfur-containing species released from the inclusions was thought to play an important role in the pit-initiation process. The oxide inclusions did not dissolve in the passive region of Type 304 stainless steel. In the solutions with chloride-ion concentrations of up to 6 M, pitting did not occur at the oxide inclusions in microscopic polarization measurements. The oxide inclusions exhibited a comparatively inert characteristic as pit-initiation sites.

Original languageEnglish
Pages (from-to)C55-C61
JournalJournal of the Electrochemical Society
Volume156
Issue number2
DOIs
Publication statusPublished - 2009 Jan 1

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Renewable Energy, Sustainability and the Environment
  • Surfaces, Coatings and Films
  • Electrochemistry
  • Materials Chemistry

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