Hydrogen embrittlement characteristics of ultrafine-grained iron and ferritic stainless steels

2018 Fiscal Year Final Research Report

• Project/Area Number: 16K18268
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Material processing/Microstructural control engineering
• Research Institution: Yokohama National University
• Principal Investigator: IWAOKA Hideaki 横浜国立大学, 大学院工学研究院, 助教 (90751496)
• Project Period (FY): 2016-04-01 – 2019-03-31
• Keywords: 水素脆化 / HPT加工 / 結晶粒界

Outline of Final Research Achievements

In present study, the tensile tests while hydrogen charging were performed for the ultrafine-grained pure iron obtained by High-Pressure Torsion (HPT) processing. The effect of grain boundaries on hydrogen embrittlement was investigated by using a specimen whose grain size was changed by heat treatment at several temperatures. The deterioration in elongation by hydrogen embrittlement was confirmed in all specimens. Especially, when the volume fraction of grain boundaries is large, the fracture type changes from void coalescence type to shear type by charging hydrogen. The hydrogen embrittlement index increases with the volume fraction of grain boundary when shear-type fracture occurs, indicating that the grain boundary has a strong influence on hydrogen embrittlement.

Free Research Field

金属組織学

Academic Significance and Societal Importance of the Research Achievements

金属材料は強度が高いほど水素脆化を起こしやすいことが知られており、強度が求められる構造物において水素脆化は深刻な問題である。結晶粒微細化は高強度を得るための代表的な手法ではあるが、高密度に導入された結晶粒界が水素脆化に及ぼす影響についてはこれまで十分に調査は行われていない。本研究では破壊形態によって結晶粒界の水素脆化への影響が異なることを明らかにし、結晶粒径をせん断型破壊が起こらないサイズに制御することで高強度かつ水素脆化が起こりにくい材料が得られる可能性を示した。