High strength alloy thick plates for cryogenic structural use and their microstructure control for high cracking resistance

2023 Fiscal Year Final Research Report

• Project/Area Number: 21K03748
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 18010:Mechanics of materials and materials-related
• Research Institution: Yokohama National University
• Principal Investigator: Umezawa Osamu 横浜国立大学, 大学院工学研究院, 教授 (20343171)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: 極低温構造材料 / 微小き裂形成 / ひずみ不整合

Outline of Final Research Achievements

Microstructure and strength of extra-thick plates with different thermomechanical conditions were examined. We experimentally determined how the strain incompatibility and local deformation concentration were developed at a specific interface and generates microcracks. Namely, the effect of N solid solution strengthening on SUS316LN based steels was numerically evaluated. Then austenitic steels and titanium alloys with different chemical compositions (segregation) and heat treatment conditions (plastic strain) were characterized to determine their strength and toughness. The factors of strain incompatibility were identified through high-cycle fatigue tests, and it was clarified that the grain refinement is dominant to improve the fatigue strength.

Free Research Field

金属組織学

Academic Significance and Societal Importance of the Research Achievements

高強度・高靱性な極低温構造材料の開発では、極厚材中心部の金属組織制御を如何に行って耐き裂形成能を高めるかがその鍵を握っている。すなわち、溶質元素や析出物などの偏析や混粒組織（軟質領域と硬質領域）の形成が、内部き裂破壊現象を加速したり現出させる。本研究では、局所的な塑性変形集中が微小ボイドなどの応力集中源を形成して微視割れを引き起こし、微視組織を反映した微小き裂形成に至るき裂発生モデルについて実験的検証による新たな進展を与えた。十分な鍛圧比が得られない極厚材料における変形・破壊機構の理解と高強度材料における微小き裂形成問題に対する新たな材料組織設計指針を与え、極低温構造材料の材料開発に資する。