Effect of Initial Microstructure on Creep Strength of ASME Grade T91 Steel

Sawada, Kota; Sekido, Kaoru; Kimura, Kazuhiro; Arisue, Ko; Honda, Masaki; Komai, Nobuyoshi; Fukuzawa, Norihide; Ueno, Takashi; Shimohata, Nobuaki; Nakatomi, Hitoshi; Takagi, Kenji; Kimura, Tsuyoshi; Nomura, Kayo; Kubushiro, Keiji

doi:10.2355/isijinternational.isijint-2019-358

Cited by 10 publications

(3 citation statements)

References 7 publications

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“…The heat-to-heat variation of creep rupture strength is of concern in relation to reviewing the allowable stress for ASME Gr.91 steel. The effects of the chemical composition, such as the Ni content, and of the initial microstructure, such as Cr segregation, on the creep rupture strength are presently under discussion [85,86].…”

Section: Methods For Evaluating the Long-term Creep Strengthmentioning

confidence: 99%

Catalog of NIMS creep data sheets

Sawada

Kimura

Abe

et al. 2019

Science and Technology of Advanced Materials

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The background of the NIMS Creep Data Sheet Project, together with the preliminary study and facilities, material selection, and testing method, is summarized. The outcomes from the project are explained, focusing on the long-term creep strength of ferritic and austenitic heat-resistant steels. In some cases, the slope of the stress versus time-to-rupture curve in the long term differed from that in the short term in a manner that was markedly dependent on the type of material. Heat-to-heat variations in creep strength were recognized for ferritic and austenitic steels, even when the chemical compositions of the steels examined were within the range of specifications. The reasons for the heat-to-heat variations were differences in the chemical composition, in the amounts of minor elements, and in the grain size, among others. The existence of inherent creep strength was discovered in the very long term for ferritic heatresistant steels. The amounts of minor solute elements affect the inherent creep strength, independently of precipitation strengthening or the dislocation structure. An inflection point was observed in the tertiary creep stage for a low-alloy steel and for austenitic stainless steels when precipitation occurred during creep. A region-splitting analysis method was proposed for long-term creep strength evaluation for high-chromium ferritic steels. This method was used to review the allowable stress of high-chromium ferritic steels in Japan. A metallographic atlas, time-temperature-precipitation diagram, and fracture-mode map were proposed for ferritic and austenitic steels on the basis of creep-ruptured specimens.

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Section: Methods For Evaluating the Long-term Creep Strengthmentioning

confidence: 99%

Catalog of NIMS creep data sheets

Sawada

Kimura

Abe

et al. 2019

Science and Technology of Advanced Materials

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“…Additionally, in heats containing the δ-ferrite phase, they noted a consistent trend of lower creep strength from the short-term to long-term regions compared to other heats [2]. Furthermore, Sawada et al [11] pointed out the influence of chromium layer segregation on the heat dependence of creep strength in Grade T91 tube materials from multiple heats. Maruyama et al [6,12] analyzed creep rupture data from Grade 91 steel with multiple heats and pointed out that the causes of heat dependence vary depending on the creep test conditions.…”

Section: Introductionmentioning

confidence: 91%

“…It is important to accurately evaluate the creep life of high-temperature components to properly maintain and manage the plants. However, recent research has highlighted significant variations in the creep rupture life and creep rupture ductility among different heats of Grade 91 steel [1][2][3][4][5][6][7][8][9][10][11][12]. Kimura et al [1,2] and Sawada et al [5] extensively investigated long-term creep rupture specimens of Grade 91 steel from multiple heats and pointed out that the creep strength in the long-term region at 600 • C is related to the Ni content.…”

Section: Introductionmentioning

confidence: 99%

Creep-Fatigue Life Evaluation for Grade 91 Steels with Various Origins and Service Histories

Shigeyama,

Takahashi,

Siefert

et al. 2024

Metals

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Grade 91 steel is widely used in the boilers and piping of thermal power plants. There has been significant research interest in understanding the variations in creep characteristics among different heats of this steel for effective plant management. In recent years, thermal power plants have been subjected to frequent load changes and startup/shutdown to adjust power supply and demand and stabilize frequencies. These operational shifts have raised concerns regarding the potential for creep-fatigue damage in high-temperature components. Therefore, this research focuses on creep-fatigue properties of Grade 91 steel and their predictability. Tensile, creep, strain-controlled fatigue, and strain-controlled creep-fatigue tests were performed on six Grade 91 steels with different heats and/or histories, and the characteristics in each test were compared. As a result, the variations in creep-fatigue life among the materials were found to be correlated with the difference in creep characteristics and stress level during stress relaxation. Furthermore, the study involved a comparative assessment of the predictive performance of creep-fatigue life using five different approaches: time fraction, classical ductility exhaustion, modified ductility exhaustion, energy-based, and hybrid approaches. Among these approaches, the hybrid approach, based on inelastic strain energy density at fracture formulated as a function of inelastic strain rate, exhibited the most accurate predictive performance.

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