Development of 2500MPa-class ultra-high-performance hypereutectoid steel: elucidation of the origins for strength and ductility

2023 Fiscal Year Final Research Report

• Project/Area Number: 21H01652
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 26040:Structural materials and functional materials-related
• Research Institution: Nagoya Institute of Technology
• Principal Investigator: Hagihara Koji 名古屋工業大学, 工学(系)研究科(研究院), 教授 (10346182)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: 鉄鋼材料 / 高強度 / 高延性 / 高炭素鋼 / マルテンサイト

Outline of Final Research Achievements

In this study, we developed a strategy to improve ductility of hypereutectoid steel (high carbon steel) via microstructural control, which has received little attention in the past. Furthermore, we conducted studies aimed at elucidating the mechanisms by which high strength and high ductility are simultaneously achieved, which is essential for disseminating the use of developed new steel to society, and further improving its properties. As a result of this study, we have achieved the development of a new high-carbon steel that has a maximum strength of over 2500 MPa with having a plastic elongation of over 5%. The microstructural factors that control the strength of the developed steel were also revealed. Including the contribution of these results, in the spring of 2023, through the joint development with Komatsu Corporation and Sanyo Special Steel, we could commercialize the ultra-high strength carbon steel with maintaining ductility, named " TOUGHFIT ".

Free Research Field

材料強度学

Academic Significance and Societal Importance of the Research Achievements

本研究にて実験，解析の両観点から，引張，シャルピー衝撃値といった各種力学特性に対し各制御パラメータが及ぼす影響度を明らかにした．具体的に，炭化物の粒径，分布が非常に強い影響を及ぼすとともに，これに加えさらに焼き入れ前の旧オーステナイト粒径が力学特性に強い影響を及ぼすことが示された．実際の組織観察結果と突き合わせることにより，この解析結果の妥当性についても確認された．このように本研究の遂行により学問的，実用的両観点から非常に大きな進展を得ることができ，実用化にまでつなげることができた．本鋼材のさらに広範な普及に向け求められるのは使用時の「長期信頼性」であり，引き続きこの点について検討を進める．