- Address
- 305-0047 1-2-1 Sengen Tsukuba Ibaraki JAPAN [Access]
Accepting Students
Research
- Keywords
発電プラント 耐熱鋼 クリープ 高温強度 弾性特性 材質劣化 組織解析 寿命予測 余寿命評価 クリープ構成式 電子顕微鏡
1. 高効率火力発電用高Cr鋼の長時間クリープ強度評価と材質劣化評価
2. 高効率火力発電用高Cr鋼溶接部の組織解析
3. 各種耐熱鋼の長時間クリープに伴う材質劣化と組織変化
4. 超長時間クリープ曲線解析
5. 高強度ステンレス鋼の組織特徴量に基づく部材温度推定
PublicationsNIMS affiliated publications since 2004.
Research papers
- Kota Sawada, Kaoru Sekido, Kazuhiro Kimura, Ko Arisue, Masaki Honda, Nobuyoshi Komai, Norihide Fukuzawa, Tomonori Ueno, Nobuaki Shimohata, Hitoshi Nakatomi, Kenji Takagi, Takahiro Kimura, Kyohei Nomura, Keiji Kubushiro. Effect of Initial Microstructure on Creep Strength of ASME Grade T91 Steel. ISIJ International. 60 [2] (2020) 382-391 10.2355/isijinternational.isijint-2019-358 Open Access
- Nobuaki Sekido, Haruka Nagai, Tomotaka Hatakeyama, Kyosuke Yoshimi, Kota Sawada. Microstructural Characteristics of Modified 9Cr-1Mo Steel with Low Creep Ductility. ISIJ International. 65 [8] (2025) ISIJINT-2025-049 10.2355/isijinternational.isijint-2025-049 Open Access
- Kota Sawada, Tomotaka Hatakeyama, Masahiro Kusano, Makoto Watanabe. Creep data of Hastelloy X fabricated by laser powder bed fusion. Science and Technology of Advanced Materials: Methods. 5 [1] (2025) 2582996 10.1080/27660400.2025.2582996 Open Access
Proceedings
- KIMURA, Kazuhiro, SAWADA, Kota. History of Allowable Stresses in Japan and Perspective on Improvement in Creep Strength Property of Grade 91 Steel. Proc. Joint 9th Int. Conf. on Advances in Materials Technology and 2nd Int. 123HiMAT Conf. on High Temperature Materials. (2019) 47-59
- SAWADA, Kota, SEKIDO, Kaoru, KIMURA, Kazuhiro. CREEP STRENGTH AND MICROSTRUCTURAL CHANGE OF 25CR-20NI-NB-N STEEL. Joint EPRI - 123HiMAT International Conference on Advances in High Temperature Materials. (2019) 665-672
- 澤田 浩太. 耐熱鋼の長時間クリープと組織変化. 西山記念技術講座. (2019) 29-51
Presentations
- SAWADA, Kota. Microstructure characterization of simulated HAZ in Mod.9Cr-1Mo steel. 123HiMAT-2015. 2015
- SAWADA, Kota. Creep property and microstructural changes of ASME T91 steels. 41st MPA-Seminar. 2015
- SAWADA, Kota. EFFECT OF STRESS AND STRAIN ON MICROSTRUCTURAL CHANGES DURING LONG-TERM CREEP IN T91 STEEL. 8th International Conference on Advances in Materials Technology. 2016
Misc
- KIMURA, Kazuhiro, SAWADA, Kota. Assessment of the earthquake impact on the creep rupture life of Grade 91 steels. ECCC 2026 Creep and Fracture, Aix-en Provence, 18-20 May 2026, Conference Proceedings. 7 (2026) P044
- 澤田 浩太. 構造材料データシートの現状と新展開－特集にあたって. 金属. (2021) 287
- 澤田 浩太. クリープデータシート. 金属. (2021) 288-293
Published patent applications
- クリープ破断寿命に対応する負荷応力推定装置及び方法、並びに耐熱金属材料の最適組成の予測装置及び方法 (2024)
- 歪み検出装置 (2020)
- 損傷状態判定装置、および損傷状態判定方法 (2019)
Society memberships
日本鉄鋼協会, 日本材料学会, 日本機械学会, 日本金属学会
Awards
- 日本鉄鋼協会学術貢献賞(三島賞) (2022)
- 日本機械学会標準事業コードエンジニア賞 (2021)
- 日本材料学会 高温強度部門委員会貢献賞 (2020)
- Acta Materialia, Outstanding reviewer (2017)
- 日本鉄鋼協会西山記念賞 (2016)
- 日本材料学会 高温強度部門委員会躍進賞 (2012)
- 日本鉄鋼協会研究奨励賞 (2007)
Research Center for Structural Materials
Effect of abnormal microstructure on creep strength of heat-resistant materials
heat-resistant steel, long-term creep strength, material degradation, abnormal grain, creep rupture ductility
Overview
There is heat-to-heat variation of long-term creep strength in commercial heat-resistant materials even in the same specification. The reason for the heat-to-heat variation should be clarified to determine the minimum creep strength. High Cr ferritic steels are widely used for high efficiency thermal power plants. However, the review of allowable stress has been performed for the steels due to presence of heat with low creep strength. It is difficult to predict the presence of abnormal microstructure by chemical compositions and heat treatment conditions. In this study, the effect of abnormal microstructure on creep properties were clarified. The investigation for weldment of steel with abnormal microstructure is ongoing.
Novelty and originality
● heat-to-heat variation of long-term creep properties for commercial heat-resistant materials
● abnormal microstructure due to manufacturing process and long-term creep property
● high-quality materials due to decrease in abnormal microstructure
Details
Abnormal prior austenite grains (PAG) were observed in ASME P91 steel. The grain size was about several millimeters. There was no difference in long-term creep strength between abnormal PAG steel and normal PAG steel. On the other hand, the creep rupture ductility of abnormal PAG steel was abruptly decreased in the long-term although the creep rupture ductility of normal PAG steel was good even in the long-term. The transgranular fracture occurred in normal PAG steel. In abnormal PAG steel, normal PAG was observed in between abnormal PAGs. Creep voids were formed in the abnormal PAG area after creep rupture. The KAM value of normal PAG area was higher than that of abnormal PAG area in EBSD analysis for the abnormal PAG steel. For the abnormal PAG steel, the concentration of deformation in local areas resulted in the low creep rupture ductility in the long-term.
Summary
● reason for presence of abnormal microstructure
● effect of abnormal microstructure in weldment
● material specification to retard abnormal microstructure
