PSI - Issue 28

Sicong Ren et al. / Procedia Structural Integrity 28 (2020) 684–692 Ren et al. / Structural Integrity Procedia 00 (2020) 000–000

692

9

ture can change from upper bainite for low carbon content to lower bainite for the highest carbon content. So the γ f increase could be possibly seen as the consequence of the refinement of the microstructure which counterbalance the e ff ect of the increase of number and size of carbides.

4. Conclusions

Experimental and numerical studies were carried out on 3 model alloys containing 0.19, 0.29, and 0.38%C, the chemical compositions of which are representative of those encountered in macro-segregated areas of large size ingots. The carbide size distributions have been analysed based on SEM images. 3D FE simulations on CT12.5 specimens were carried out using Cast3M. The experimentally determined size distributions of carbides were introduced into the MIBF model to predict the fracture toughness of these materials. The main result of this work is the identification of a beneficial e ff ect of a micro-structural evolution that can counter balance the detrimental e ff ect of carbon increase.

Acknowledgements

The authors gratefully acknowledge A. Ganglo ff (CEA) for SEM observations of carbides, B. Tanguy (CEA) for fractographic analysis, E. Pons (CEA) for mechanical testing preparation and P. Forget (CEA) for the fruitful discussions on MIBF model.

References

Andrieu, A., Pineau, A., Besson, J., Ryckelynck, D., Bouaziz, O., 2012. Beremin model: Methodology and application to the prediction of the Euro toughness data set. Engineering Fracture Mechanics 95, 102-117 Brimbal, D., Private Communication, Framatome, August 1, 2017 Bridgman, P.W., 1964. Studies in large plastic flow and fracture. Harvard University Press. Beremin, F.M., 1983. A local criterion for cleavage fracture of a nuclear pressure vessel steel. Metallurgical Transactions A 14(11), 2277-2287. Curry, D. A., Knott, J. F., 1976. The relationship between fracture toughness and microstructure in the cleavage fracture of mild steel. Metal Science 10(1), 1-6. Forget, P., Marini, B., Vincent, L., 2016. Application of local approach to fracture of an RPV steel: e ff ect of the crystal plasticity on the critical carbide size. Procedia Structural Integrity 2, 1660-1667. Gerberich, W. W.,Kurman, E., 1985. New contributions to the e ff ective surface energy of cleavage. Scripta metallurgica 19(3), 295-298. Heerens, J. and Hellmann, D., 2002. Development of the Euro fracture toughness dataset. Engineering Fracture Mechanics 69(4), pp.421-449. Im, Y. R., Lee, B. J., Oh, Y. J., Hong, J. H., Lee, H. C., 2004. E ff ect of microstructure on the cleavage fracture strength of low carbon MnNiMo bainitic steels. Journal of nuclear materials 324(1), 33-40. Lefever B., Marie S., Berger T., Bobin-vastra I., 2018. Flamanville EPR RPVs heads carbon segregation: vessel heads manufacturing, ASME 2018 Pressure Vessel and Piping Conference. Prague, Czech Republic, paper #PVP 84492 Libert, M., Rey, C., Vincent, L., Marini, B., 2011. Temperature dependant polycrystal model application to bainitic steel behavior under tri-axial loading in the ductilebrittle transition. International Journal of Solids and Structures 48(14-15), 2196-2208. Lee, S., Kim, S., Hwang, B., Lee, B. S., Lee, C. G., 2002. E ff ect of carbide distribution on the fracture toughness in the transition temperature region of an SA 508 steel. Acta materialia 50(19), 4755-4762 Ortner, S. R., 2006. A microstructure-based probabilistic model for cleavage in RPV steels. ASME Pressure Vessels and Piping Conference. Vancouver, BC, Canada, paper #PVP47578 Vincent, L., Libert, M., Marini, B., Rey, C., 2010. Towards a modelling of RPV steel brittle fracture using crystal plasticity computations on polycrystalline aggregates. Journal of Nuclear Materials 406(1), 91-96. Vincent, L., Gelebart, L., Dakhlaoui, R., Marini, B., 2011. Stress localization in BCC polycrystals and its implications on the probability of brittle fracture. Materials Science and Engineering: A 528(18), 5861-5870. Wallin, K., 1984. The scatter in K IC -results. Engineering Fracture Mechanics 19(6), 1085-1093.