PSI - Issue 68

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Procedia Structural Integrity 68 (2025) 425–431 Structural Integrity Procedia 00 (2024) 000–000 Structural Integrity Procedia 00 (2024) 000–000

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European Conference on Fracture 2024 Evaluation of the C ∗ Parameter in Welded Joints of 9%Cr Steels Under Consideration of the Heat A ff ectedZone Josef Arthur Scho¨nherr a, ∗ , Falk Mueller a , Christian Kontermann a , Matthias Oechsner a a Technical University of Darmstadt, Chair and Institute for Materials Technology (IfW), Grafenstr. 2, 64283 Darmstadt, Germany Abstract In fracture mechanics based component assessment of parts containing microstructural defects subjected to elevated temperatures, the C ∗ parameter is a common choice for describing the crack tip loading under steady-state creep conditions. Welded joints of ferritic-martensitic 9%Cr steels, commonly used in applications of up to 650 °C operation temperature, comprise a rather complex and inhomogeneous microstructure in the heat a ff ected zone, with wildly di ff ering creep properties in comparison to the base materials. Therefore, the influence of the inhomogeneous material must be considered carefully when calculating C ∗ . This paper is subjected to the evaluation of the C ∗ parameter in compact tension fracture mechanics specimens for a welded joint made from two di ff erent 9%Cr steels with an additional buttering. Based on finite element simulations, di ff erent methods for calculating C ∗ are assessed. It is shown that the application of methods disregarding the properties of the heat a ff ecting zone leads to erroneous results. © 2025 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of ECF24 organizers. Keywords: creep crack growth; C* parameter; welded joint; heat a ff ected zone; compact tension specimen European Conference on Fracture 2024 Evaluation of the C ∗ Parameter in Welded Joints of 9%Cr Steels Under Consideration of the Heat A ff ectedZone Josef Arthur Scho¨nherr a, ∗ , Falk Mueller a , Christian Kontermann a , Matthias Oechsner a a Technical University of Darmstadt, Chair and Institute for Materials Technology (IfW), Grafenstr. 2, 64283 Darmstadt, Germany Abstract In fracture mechanics based component assessment of parts containing microstructural defects subjected to elevated temperatures, the C ∗ parameter is a common choice for describing the crack tip loading under steady-state creep conditions. Welded joints of ferritic-martensitic 9%Cr steels, commonly used in applications of up to 650 °C operation temperature, comprise a rather complex and inhomogeneous microstructure in the heat a ff ected zone, with wildly di ff ering creep properties in comparison to the base materials. Therefore, the influence of the inhomogeneous material must be considered carefully when calculating C ∗ . This paper is subjected to the evaluation of the C ∗ parameter in compact tension fracture mechanics specimens for a welded joint made from two di ff erent 9%Cr steels with an additional buttering. Based on finite element simulations, di ff erent methods for calculating C ∗ are assessed. It is shown that the application of methods disregarding the properties of the heat a ff ecting zone leads to erroneous results. © 2025 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of ECF24 organizers. Keywords: creep crack growth; C* parameter; welded joint; heat a ff ected zone; compact tension specimen © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of ECF24 organizers Due to their function, thermal power plant components have complex part geometries. These often utilize ferritic martensitic 9%Cr steels, which are suitable for operation temperatures up to 650 °C. Welded joints play a critical role in both the manufacturability and repairability of these components. A number of factors, including varying peak temperatures and cooling conditions, contribute to the formation of a rather complex inhomogeneous heat a ff ected zone (HAZ) during welding. Next to the fusion line, the formation of a coarse-grained zone (CGHAZ) is promoted by a high peak temperature combined with a relatively low cooling rate. This zone is followed by a region where the temperature is insu ffi cient for complete dissolution of all precipitates, resulting in a fine-grained structure (FGHAZ). In the transition region to the pristine base material, the former martensitic-ferritic microstructure is only partially transformed and an over-tempered martensitic microstructure follows, also referred to as the intercritical heat a ff ected zone (ICHAZ), Mayr (2007). In the latter two zones, the rate of creep void formation is increased compared to the base Due to their function, thermal power plant components have complex part geometries. These often utilize ferritic martensitic 9%Cr steels, which are suitable for operation temperatures up to 650 °C. Welded joints play a critical role in both the manufacturability and repairability of these components. A number of factors, including varying peak temperatures and cooling conditions, contribute to the formation of a rather complex inhomogeneous heat a ff ected zone (HAZ) during welding. Next to the fusion line, the formation of a coarse-grained zone (CGHAZ) is promoted by a high peak temperature combined with a relatively low cooling rate. This zone is followed by a region where the temperature is insu ffi cient for complete dissolution of all precipitates, resulting in a fine-grained structure (FGHAZ). In the transition region to the pristine base material, the former martensitic-ferritic microstructure is only partially transformed and an over-tempered martensitic microstructure follows, also referred to as the intercritical heat a ff ected zone (ICHAZ), Mayr (2007). In the latter two zones, the rate of creep void formation is increased compared to the base 1. Introduction 1. Introduction

2452-3216 © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of ECF24 organizers 10.1016/j.prostr.2025.06.077 ∗ Corresponding author. Tel.: + 49-6151-16-20348. E-mail address: josef.schoenherr@tu-darmstadt.de 2210-7843 © 2025 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of ECF24 organizers. ∗ Corresponding author. Tel.: + 49-6151-16-20348. E-mail address: josef.schoenherr@tu-darmstadt.de 2210-7843 © 2025 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of ECF24 organizers.