PSI - Issue 42

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ScienceDirect

Procedia Structural Integrity 42 (2022) 886–894 Structural Integrity Procedia 00 (2019) 000–000 Structural Integrity Procedia 00 (2019) 000–000

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

© 2022 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 scientific committee of the 23 European Conference on Fracture – ECF23 Abstract The e ff ect of heat treatment conditions on the tensile properties, impact toughness properties and the brittle fracture initiation mechanisms of a low-alloy steel were investigated. Only one type of location for the cleavage initiation sites, common to all cooling rates, was identified. Cleavage crack initiation always occurred in the very vicinity of a high angle boundary. MnS inclusions and Ti(CN) precipitates may play a role, but they did not seem to be necessary for cleavage initiation. The critical stress for cleavage increased with the cooling rate and decreased with the tempering parameter. This is consistent with the observed di ff erences in the ductile-to-brittle transition behavior with the heat treatment conditions. 2020 The Authors. Published by Elsevier B.V. is is an open access article under the CC BY-NC-ND license (http: // cr ativec mmons.org / licenses / by-nc-nd / 4.0 / ) r-review unde responsibility of 23 European Conference on F acture – ECF23 . Keywords: Low alloy steel; RPV steel; Cleavage; Fracture mechanisms; Microstructure; Impact toughness; Charpy Test 23 European Conference on Fracture – ECF23 E ff ect of heat treatment on the impact toughness and brittle fracture initiation mechanism of a quenched and tempered nuclear Pressure Vessel Steel Jean-Baptiste Delattre a,b, ∗ , Bernard Marini b , Pierre Joly c , Anne-Franc¸oise Gourgues b a CEA, DES-Service de Recherches Me´tallurgiques Applique´es, Universite´ Paris-Saclay, Gif-sur-Yvette, F-91191, France b Mines Paris, PSL University, Centre des Mate´riaux, UMR CNRS 7633, B.P. 87, 91003 Evry cedex, France c FRAMATOME, Direction Technique et Inge´nierie, Tour Areva, 92400 Courbevoie, France Abstract The e ff ect of heat treatment conditions on the tensile properties, impact toughness properties and the brittle fracture initiation mechanisms of a low-alloy steel were investigated. Only one type of location for the cleavage initiation sites, common to all cooling rates, was identified. Cleavage crack initiation always occurred in the very vicinity of a high angle boundary. MnS inclusions and Ti(CN) precipitates may play a role, but they did not seem to be necessary for cleavage initiation. The critical stress for cleavage increased with the cooling rate and decreased with the tempering parameter. This is consistent with the observed di ff erences in the ductile-to-brittle transition behavior with the heat treatment conditions. © 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 23 European Conference on Fracture – ECF23 . Keywords: Low alloy steel; RPV steel; Cleavage; Fracture mechanisms; Microstructure; Impact toughness; Charpy Test 23 European Conference on Fracture – ECF23 E ff ect of heat treatment on the impact toughness and brittle fracture initiation mechanism of a quenched and tempered nuclear Pressure Vessel Steel Jean-Baptiste Delattre a,b, ∗ , Bernard Marini b , Pierre Joly c , Anne-Franc¸oise Gourgues b a CEA, DES-Service de Recherches Me´tallurgiques Applique´es, Universite´ Paris-Saclay, Gif-sur-Yvette, F-91191, France b Mines Paris, PSL University, Centre des Mate´riaux, UMR CNRS 7633, B.P. 87, 91003 Evry cedex, France c FRAMATOME, Direction Technique et Inge´nierie, Tour Areva, 92400 Courbevoie, France

1. Introduction 1. Introduction

In pressurized water reactors, primary loop components such as steam generators and pressurizers are made of heavy forgings of low alloy steel grade (RCC-M 18 and 20MND5). The final heat treatment consists in an austen itization between 860 and 900°C, followed by a water quench and tempering at about 650°C. This heat treatment aims at obtaining a bainitic microstructure with as little proeutectoid ferrite content as possible, to ensure a suitable balance between strength and toughness. However, the large thickness of these components (typically, from 150 mm for some shells up to 700 mm for steam generator plates) induces a large range of microstructures after quenching, mostly bainitic with potentially some ferrite at mid-thickness. Even after tempering, such a range of microstructures may induce local variations in mechanical properties, especially in impact toughness. This involves a need of in In pressurized water reactors, primary loop components such as steam generators and pressurizers are made of heavy forgings of low alloy steel grade (RCC-M 18 and 20MND5). The final heat treatment consists in an austen itization between 860 and 900°C, followed by a water quench and tempering at about 650°C. This heat treatment aims at obtaining a bainitic microstructure with as little proeutectoid ferrite content as possible, to ensure a suitable balance between strength and toughness. However, the large thickness of these components (typically, from 150 mm for some shells up to 700 mm for steam generator plates) induces a large range of microstructures after quenching, mostly bainitic with potentially some ferrite at mid-thickness. Even after tempering, such a range of microstructures may induce local variations in mechanical properties, especially in impact toughness. This involves a need of in

∗ Corresponding author. E-mail address: jean-baptiste.delattre@cea.fr ∗ Corresponding author. E-mail address: jean-baptiste.delattre@cea.fr

2452-3216 © 2022 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 scientific committee of the 23 European Conference on Fracture – ECF23 10.1016/j.prostr.2022.12.112 2210-7843 © 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 23 European Conference on Fracture – ECF23 . 2210-7843 © 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 23 European Conference on Fracture – ECF23 .