Elucidating electrochemical properties at the boundary between MnS and steel matrix: Towards the improvement of pitting corrosion resistance of stainless steels

Izumi Muto, Aya Chiba, Masayuki Tohjoh, Yu Sugawara, Nobuyoshi Hara

Research output: Contribution to journalArticlepeer-review

Abstract

Synopsis: This paper presents an introduction to the electrochemical properties at the boundary between MnS and steel matrix of Type 304 stainless steel. It starts with the information about the corrosion mechanism from trenching to pitting at the boundary. The proposed mechanism is as follows: 1) MnS dissolution leads to the deposition of elemental sulfur on and around the inclusions; 2) the coexistence of S and Cl - ions results in the dissolution of the steel matrix side of the boundary, forming the trenches along the periphery of the inclusions, 3) rapid active dissolution occurs locally at the bottom of the trenches, because of the decrease of pH due to the hydrolysis reaction of Cr 3+ and the electrode potential decrease at the bottom of the trench due to ohmic drop. The prevention of MnS dissolution is effective to inhibit the pit initiation. The oxide film was found to be generated on the MnS inclusions by the exposure to humidified air for 30 and 90 days, and it was confirmed that the oxide films effectively inhibit the inclusion dissolution and the trench formation at the boundaries, making the inclusions less active as the initiation sites for pitting. The suppression of the active dissolution of the steel matrix is also effective to prevent the pitting. No pit initiation occurred at the MnS inclusions in low-temperature carburized stainless steels. It was clarified that the interstitial carbon sufficiently inhibits the active dissolution rate of the steel matrix.

Original languageEnglish
Pages (from-to)85-92
Number of pages8
JournalTetsu-To-Hagane/Journal of the Iron and Steel Institute of Japan
Volume105
Issue number2
DOIs
Publication statusPublished - 2019 Feb

Keywords

  • Active dissolution
  • Carburizing
  • Elemental sulfur
  • Interstitial carbon
  • MnS inclusion
  • Oxide film
  • Pitting
  • Stainless steel

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Physical and Theoretical Chemistry
  • Metals and Alloys
  • Materials Chemistry

Fingerprint Dive into the research topics of 'Elucidating electrochemical properties at the boundary between MnS and steel matrix: Towards the improvement of pitting corrosion resistance of stainless steels'. Together they form a unique fingerprint.

Cite this