Development of pit initiation mechanism from MnS inclusions in stainless steel and new principles for improving pitting resistance

2014 Fiscal Year Final Research Report

• Project/Area Number: 24246118
• Research Category: Grant-in-Aid for Scientific Research (A)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Material processing/treatments
• Research Institution: Tohoku University
• Principal Investigator: HARA NOBUYOSHI 東北大学, 工学(系)研究科(研究院), 教授 (40111257)
• Co-Investigator(Kenkyū-buntansha): MUTO Izumi 東北大学, 大学院工学研究科, 教授 (20400278) ; SUGAWARA Yu 東北大学, 大学院工学研究科, 助教 (40599057) ; AKAO Noboru 東北大学, 大学院工学研究科, 助手 (80222503)
• Project Period (FY): 2012-04-01 – 2015-03-31
• Keywords: ステンレス鋼 / 孔食発生機構 / 硫化物介在物 / 耐孔食性 / コンビナトリアルアプローチ / 低温浸炭処理

Outline of Final Research Achievements

In order to improve the pitting corrosion resistance of stainless steels without the addition of a large amount of rare metals such as Cr and Mo, the mechanism of pit initiation at MnS inclusions has been examined and an new method for improving pitting resistance has been developed. While the inclusions dissolve under anodic polarization, elemental sulfur is deposited at the boundaries between the inclusions and steel matrix. The synergistic effect of the elemental sulfur and chloride ions causes the breakdown of passivity at the boundaries to form trenches, in which pit is initiated when pH and potential satisfy a critical condition of pit growth. Based on this pit initiation mechanism, the inhibition of the active dissolution of steel matrix in acidic chloride solutions seems to be beneficial. By using the combinatorial approach, it was proposed that the addition of a small amount of Sn (<1%) was effective to improve pitting resistance.

Free Research Field

材料電子化学