PSI - Issue 68

Julie Papin et al. / Procedia Structural Integrity 68 (2025) 727–733 Julie Papin et al. / Structural Integrity Procedia 00 (2025) 000–000

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Fig. 7. Initiation sites frequency for increasing T 0 values, (a) at tempering condition 640°C – 6h; (b) at quenching rate 2000°C/h.

5. Conclusions The investigation of fracture toughness properties of a low-alloyed reactor pressure vessel steel, as a function of quenching and tempering conditions, paired with detailed fractographic analysis at crack initiation sites led to the following conclusions. • The fracture toughness reference temperature T 0 (according to ASTM E1921 standard) decreased with increasing the quenching rate, in agreement with the evolution of impact toughness properties. • For all quenching rates, and especially for those higher than 150°C/h, the value of T 0 increased for a tempering parameter > 20.00. • Fracture initiation sites at grain boundary carbides were globally predominant. • The predominant crack initiator depended on the heat treatment conditions with a predominance of the tempering conditions: inclusions were more frequently observed at low tempering parameters (TP < 20.00) and low T 0 , for which the amount of coarser boundary carbides was assumed to be lower. Acknowledgements The authors thank Pierre Wident at CEA (SRMA/LC2M) for support in fracture toughness analysis. They also thank Amélie Gangloff at CEA (SRMA/LA2M) for support for fractographic study. References Beremin, F.M., 1983. A local criterion for cleavage fracture of a nuclear pressure vessel steel. Metallurgical Transactions A 14A, 2278–2287. Chekhonin, P., Das, A., Bergner, F., Altstadt, E., 2023. Microstructural characterisation of brittle fracture initiation sites in reactor pressure vessel steels. Nuclear Materials and Energy 37, 101511. https://doi.org/10.1016/j.nme.2023.101511 Delattre, J.-B., Marini, B., Gourgues, A.-F., 2024. A study of the link between heat treatment, mechanical properties, and brittle cleavage crack initiation in a quenched and tempered low-alloy steel. (PhD thesis). Université PSL - Mines Paris. Delattre, J.-B., Marini, B., Joly, P., Gourgues, A.-F., 2022a. Effect of heat treatment on the impact toughness and brittle fracture initiation mechanism of a quenched and tempered nuclear Pressure Vessel Steel. Procedia Structural Integrity, 23 European Conference on Fracture 42, 886–894. https://doi.org/10.1016/j.prostr.2022.12.112 Delattre, J.-B., Marini, B., Joly, P., Todeschini, P., Gourgues, A.-F., 2022b. Effect of cooling rate after austenitization on the ductile-to-brittle transition of a quenched and tempered nuclear component Pressure Vessel Steel. Fontevraud X. Druce, S.G., Gibson, G.P., Capel, M., 1992. Microstructural control of cleavage fracture in a A508 class 3 pressure vessel steel. Fracture Mechanics 682–706. Gibson, G.P., Capel, M., Druce, S.G., 1989. Effect of heat treatment on the fracture toughness transition properties of an A508 class 3 steel, Proceedings of the European Symposium on Elastic-Plastic Fracture Mechanics: Elements of Defect Assessment. Freiburg, Germany. Li, C., Han, L., Yan, G., Liu, Q., Luo, X., Gu, J., 2016. Time-dependent temper embrittlement of reactor pressure vessel steel: Correlation between microstructural evolution and mechanical properties during tempering at 650 °C. Journal of Nuclear Materials. Wallin, K., 1998. Master curve analysis of ductile to brittle transition region fracture toughness round robin data: The “EURO” fracture toughness curve, VTT-publications. Technical Research Centre of Finland, Espoo. Wallin, K., Saario, T., Törrönen, K., 1984. Statistical model for carbide induced brittle fracture in steel. Metal Science 18, 13–16. https://doi.org/10.1179/030634584790420384