PSI - Issue 28

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ScienceDirect

Procedia Structural Integrity 28 (2020) 684–692 Structural Integrity Procedia 00 (2020) 000–000 Structural Integrity Procedia 00 ( 20) 000–000

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© 2020 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 the European Structural Integrity Society (ESIS) ExCo Abstract The macro-segregation of carbon and alloying elements in heavy forged nuclear components can lead to significant variations in mechanical properties, and especially in fracture toughness. In the current work, the prediction of fracture toughness was addressed for three model alloys chemically representative of the compositions encountered in macro-segregated zones. Characterisations of the microstructure and of the fracture toughness properties, measured by compact tension (CT) specimens, were performed. Tensile properties were measured around the reference temperature for each material for the calibration of elasto-plastic parameters. Carbide size distributions were determined thanks to scanning electron microscopy (SEM) image analysis. The microstructure informed brittle fracture (MIBF) local approach model was applied here to predict the scatter of brittle fracture toughness. This model involves two sources of scatter: the stress distribution inside a representative volume of the bainitic microstructure and the size distribution of carbides, which are assumed to be the brittle facture initiators. The simulation results demonstrated the capabilities of the MIBF model for predicting the fracture toughness scatter and the shift towards higher temperature of the brittle to-ductile transition with the increase of carbon and alloying elements. The only parameter of the MIBF model to be calibrated is the e ff ective surface energy γ f which was found very close to estimated values for ferrite. The observed variation of γ f in these three model alloys also suggests a possible e ff ect of microstructural evolution on fracture toughness, in addition to the constitutive law and carbide distributions. c he Authors. Published by Elsevier B.V. T is is an open a cess article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) nde respons bility of the European St uctural Integrity Society (ESIS) ExCo. Keywords: Fracture toughness ; Carbon segregation ; Brittle fracture; Local approach; MIBF model Abstract The macro-segregation of carbon and alloying elements in heavy forged nuclear components can lead to significant variations in mechanical properties, and especially in fracture toughness. In the current work, the prediction of fracture toughness was addressed for three model alloys chemically representative of the compositions encountered in macro-segregated zones. Characterisations of the microstructure and of the fracture toughness properties, measured by compact tension (CT) specimens, were performed. Tensile properties were measured around the reference temperature for each material for the calibration of elasto-plastic parameters. Carbide size distributions were determined thanks to scanning electron microscopy (SEM) image analysis. The microstructure informed brittle fracture (MIBF) local approach model was applied here to predict the scatter of brittle fracture toughness. This model involves two sources of scatter: the stress distribution inside a representative volume of the bainitic microstructure and the size distribution of carbides, which are assumed to be the brittle facture initiators. The simulation results demonstrated the capabilities of the MIBF model for predicting the fracture toughness scatter and the shift towards higher temperature of the brittle to-ductile transition with the increase of carbon and alloying elements. The only parameter of the MIBF model to be calibrated is the e ff ective surface energy γ f which was found very close to estimated values for ferrite. The observed variation of γ f in these three model alloys also suggests a possible e ff ect of microstructural evolution on fracture toughness, in addition to the constitutive law and carbide distributions. c 2020 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 the European Structural Integrity Society (ESIS) ExCo. Keywords: Fracture toughness ; Carbon segregation ; Brittle fracture; Local approach; MIBF model 1st Virtual European Conference on Fracture Microstructure-informed modelling of the fracture toughness of alloys representing macro-segregated zones in heavy forgings Sicong Ren a, ∗ , Bernard Marini a , Pierre Joly b , Patrick Todeschini c a Universite´ Paris-Saclay, CEA, Service de Recherches Me´tallurgiques Applique´es, 91191, Gif-sur-Yvette, France b Framatome, Technical Direction and Engineering (DTI), 1 Place Jean Millier, 92084, Paris La De´fense, France c EDF R & D, Avenue des Renardie`res, 77250, Moret-sur-Loing, France 1st Virtual European Conference on Fracture icrostructure-infor ed odelling of the fracture toughness of alloys representing acro-segregated zones in heavy forgings Sicong Ren a, ∗ , Bernard Marini a , Pierre Joly b , Patrick Todeschini c a Universite´ Paris-Saclay, CEA, Service de Recherches Me´tallurgiques Applique´es, 91191, Gif-sur-Yvette, France b Framatome, Technical Direction and Engineering (DTI), 1 Place Jean Millier, 92084, Paris La De´fense, France c EDF R & D, Avenue des Renardie`res, 77250, Moret-sur-Loing, France

1. Introduction 1. Introduction

Evaluating the embrittlement of materials is an important issue for the integrity assessment of components in pressurized water reactor (PWR). Parts of PWR are manufactured by forging of heavy-ingots. Macro-segregation of Evaluating the embrittlement of materials is an important issue for the integrity assessment of components in pressurized water reactor (PWR). Parts of PWR are manufactured by forging of heavy-ingots. Macro-segregation of

2452-3216 © 2020 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 the European Structural Integrity Society (ESIS) ExCo 10.1016/j.prostr.2020.10.079 ∗ Corresponding author. Tel.: + 33-169088599 ; fax: + 33-169087167. E-mail address: sicong.ren@cea.fr 2210-7843 c 2020 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 r ponsibility of the European Structural Integrity Society (ESIS) ExCo. ∗ Corresponding author. Tel.: + 33-169088599 ; fax: + 33-169087167. E-mail address: sicong.ren@cea.fr 2210-7843 c 2020 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 the European Structural Integrity Society (ESIS) ExCo.