PSI - Issue 68

ScienceDirect Structural Integrity Procedia 00 (2025) 000–000 Available online at www.sciencedirect.com Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2025) 000–000 Available online at www.sciencedirect.com ScienceDirect

www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia

Procedia Structural Integrity 68 (2025) 1188–1195

European Conference on Fracture 2024 Modelling the effect of carbide population and bainitic grain size on the fracture toughness of three forged low alloy steels Cainã Bemfica a , Ludovic Vincent a *, Bernard Marini a , Jean-Philippe Mathieu b , Pierre Joly c a Université Paris-Saclay, CEA, Service de Recherche en Matériaux et procédés Avancés, 91191, Gif-sur-Yvette, France b EDF, R&D, Renardières Ecuelles, Département MMC, 77250, Orvanne, France c Framatome SAS, Direction Technique et Ingénierie, Tour AREVA, 1 place Jean Millier, 92400 Courbevoie, France Abstract Fracture toughness of three low alloy quenched and tempered bainitic steels with similar chemical compositions but different manufacturing routes have been characterized in the Ductile to Brittle Transition (DBT) domain. One of these materials exhibits a much larger DBT temperature than the two other materials. The essential microstructural particularity of this material is its grain size, twice larger than the one of the two other materials. The Microstructure Informed Brittle Fracture model (MIBF) is modified to integrate grain size effects into the definition of the critical size of carbides used to compute cleavage initiation probability. The modified model predicts fairly well the different DBT temperatures of the three materials. © 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 Keywords: low alloy bainitic steels; cleavage fracture; grain size; carbide size distributions; microstructure informed brittle fracture modeling 1. Introduction The heavy forged components of the primary circuit of French pressurized water reactors are made of quenched and tempered low alloy steels. This leads to a bainitic microstructure that exhibits a Ductile to Brittle Transition (DBT) which reference Temperature (DBTT) tends to shift towards higher values after temperature and irradiation ageing European Conference on Fracture 2024 Modelling the effect of carbide population and bainitic grain size on the fracture toughness of three forged low alloy steels Cainã Bemfica a , Ludovic Vincent a *, Bernard Marini a , Jean-Philippe Mathieu b , Pierre Joly c a Université Paris-Saclay, CEA, Service de Recherche en Matériaux et procédés Avancés, 91191, Gif-sur-Yvette, France b EDF, R&D, Renardières Ecuelles, Département MMC, 77250, Orvanne, France c Framatome SAS, Direction Technique et Ingénierie, Tour AREVA, 1 place Jean Millier, 92400 Courbevoie, France Abstract Fracture toughness of three low alloy quenched and tempered bainitic steels with similar chemical compositions but different manufacturing routes have been characterized in the Ductile to Brittle Transition (DBT) domain. One of these materials exhibits a much larger DBT temperature than the two other materials. The essential microstructural particularity of this material is its grain size, twice larger than the one of the two other materials. The Microstructure Informed Brittle Fracture model (MIBF) is modified to integrate grain size effects into the definition of the critical size of carbides used to compute cleavage initiation probability. The modified model predicts fairly well the different DBT temperatures of the three materials. © 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 Keywords: low alloy bainitic steels; cleavage fracture; grain size; carbide size distributions; microstructure informed brittle fracture modeling 1. Introduction The heavy forged components of the primary circuit of French pressurized water reactors are made of quenched and tempered low alloy steels. This leads to a bainitic microstructure that exhibits a Ductile to Brittle Transition (DBT) which reference Temperature (DBTT) tends to shift towards higher values after temperature and irradiation ageing © 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

* Corresponding author. Tel.: E-mail address: ludovic.vincent@cea.fr * Corresponding author. Tel.: E-mail address: ludovic.vincent@cea.fr

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 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

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.2025.06.186