A new alloy design concept for high-corrosion resistant steels based on micro-electrochemistry of local dissolution and repassivation

2019 Fiscal Year Final Research Report

• Project/Area Number: 17H01331
• Research Category: Grant-in-Aid for Scientific Research (A)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Material processing/Microstructural control engineering
• Research Institution: Tohoku University
• Principal Investigator: Muto Izumi 東北大学, 工学研究科, 教授 (20400278)
• Co-Investigator(Kenkyū-buntansha): 菅原 優 東北大学, 工学研究科, 准教授 (40599057)
• Project Period (FY): 2017-04-01 – 2020-03-31
• Keywords: 耐食材料 / 腐食防食 / 炭素鋼 / ステンレス鋼 / 孔食

Outline of Final Research Achievements

The initiation sites and morphology during the early stage of pitting on pearlite strucure were investigated. Pits were initiated in the ferrite lamellae and proceeded along the ferrite lamellae. Cementite acts as a barrier against the pit growth. In as-quenched and tempered martensitie, interstitial carbon was found to improve pitting corrosion resistance. Short-time tempering of martensite was suggested to be a feasible approach to striking an optimal balance between facilitating corrosion resistance and achieving the desired mechanical properties . For stainless steels, the addition of inhibitor to sulfide inclusions was determined to improve pitting corrosion resistance at sulfide inclusions. It was demonstrated that Ce3+ ions are likely to be produced by the dissolution of Ce-containing inclusions, and the Ce3+ ions inhibit trench formation at the sulfide/steel matrix boundary, resulting in improved pitting corrosion resistance at sulfide inclusions.

Free Research Field

腐食防食学

Academic Significance and Societal Importance of the Research Achievements

耐孔食性に優れる鋼を開発するためには、材料表面に点在する腐食起点を特定し、そのうえでミクロな視点から高耐食化のための知見を見出すことができる新技術の開発に成功した。さらに、孔食が自発的に成長を開始する前に、溶解を停止させる技術を見出した。高合金化に代わる新しい原理であり、省資源高耐食鋼を開発する基盤技術になるものと期待される。特に、固溶炭素と鉄炭化物が鋼の高耐食化に寄与することを、マイクロメートルオーダー視点から解明したことは意義深い。輸送用機器などの軽量化に不可避な高強度鋼の高耐食化に応用可能である。