Elucidation of strengthening mechanims by interstitial-subsitutional atomo cluster towards development of cluster-strengthened steel

2022 Fiscal Year Final Research Report

• Project/Area Number: 21K18803
• Research Category: Grant-in-Aid for Challenging Research (Exploratory)
• Allocation Type: Multi-year Fund
• Review Section: Medium-sized Section 26:Materials engineering and related fields
• Research Institution: Tohoku University
• Principal Investigator: Miyamoto Goro 東北大学, 金属材料研究所, 准教授 (60451621)
• Project Period (FY): 2021-07-09 – 2023-03-31
• Keywords: 鉄鋼材料 / 表面硬化 / 析出強化 / 強化機構

Outline of Final Research Achievements

The purpose of this study was to elucidate the strengthening mechanism by solute clusters consisting of interstitial and substitutional elements in steel. Tensile properties and microstructures of nitrided and hydrogen annealed Fe-Ti alloys were investigated. The results showed that monoatomic layered clusters were dominant in the specimen nitrided at below 650°C and they becomes larger in size and higher in number density at higher temperatures. On the other hand, when the nitriding temperature increases to 700°C, multi-atomic layer-thickness TiN is formed and the number density decreases. The amount of strengthening follows the interparticle spacing on the slip plane evaluated from the cluster-TiN distribution. The particle resistance force was much lower than predicted by the Orowan model, suggesting that the Ti-N clusters contribute to strengthening by a cutting mechanism.

Free Research Field

金属材料組織学

Academic Significance and Societal Importance of the Research Achievements

鉄鋼をはじめとする構造材料を高強度化することにより、自動車などの輸送機器に使われる材料を減らすことができるため、軽量化による燃費向上が実現できる。鉄鋼材料中にナノサイズの添加元素の濃化領域（クラスター）が形成されると、強度が著しく向上するがその機構は不明であった。本研究では、先端組織解析技術を駆使してクラスターが強度に及ぼす影響を調査し、変形を担う転位が高密度に生成するクラスターを切断しながら運動することで、転位運動が阻害されることが高強度化機構であることを明らかにしたものである。