Mechanism of delayed fracture in fail-safe steel with an ultrafine elongated grain structure

2023 Fiscal Year Final Research Report

• Project/Area Number: 19H02468
• 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: National Institute for Materials Science
• Principal Investigator: KIMURA Yuuji 国立研究開発法人物質・材料研究機構, 構造材料研究センター, 主席研究員 (80253483)
• Project Period (FY): 2019-04-01 – 2024-03-31
• Keywords: 構造材料 / 鉄鋼 / 加工熱処理 / 水素脆化 / 遅れ破壊

Outline of Final Research Achievements

In this study, 1800-2000 MPa-class ultra-high strength low-alloy steels with ultrafine elongated grain structures were created by a thermomechanical treatment. The notched round-bar specimens and ultra-high strength bolts that were fabricated from the ultra-high strength low-alloy steels were fastened and subjected to outdoor exposure tests at the exposure site in National Institute for Materials Science, and at the in Miyako Island test site of Japan Weathering Test Center, respectively. Delayed fracture behavior of the ultra-high strength low-alloy steels was clarified in association with the ultrafine elongated grain structures, hydrogen uptake and the data obtained by accelerated delayed fracture tests.

Free Research Field

鉄鋼材料

Academic Significance and Societal Importance of the Research Achievements

次世代の新鋼構造物の実現や自動車等のさらなる軽量化で必要とされる超高強度鋼の社会実装では、材料および部材がその使用中に突然、破断するという遅れ破壊の克服が大きな課題となっている。本研究では、超高強度鋼が遅れ破壊しやすいことに着目して、つくば市のマイルドな大気腐食環境下でも応力負荷条件等の制御により数か月程度の短期間で遅れ破壊を発生させ、その挙動を観察したことは学術的意義が高い。さらに様々な金属組織を有する超高強度鋼材に今回開発した手法を展開してデータを収集することで遅れ破壊を克服した超高強度鋼材開発への貢献が期待できる。