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A model for predicting fracture toughness and scatter in thermally embrittled steels

Abstract : Temper embrittlement in a thick plate of a Mn-Ni-Mo pressure vessel steel was investigated using fracture toughness tests on Charpy and CT type specimens. A shift of the ductile-to-brittle transition temperature (~30–40 °C) was measured when the material was aged at 450 °C for 5000 h. Moreover an unusual scatter in fracture toughness tests was determined on aged material, such as KIC(PR=90%)/KIC(PR=10%)∼5, where P R is the probability of failure. Scanning electron micrographs (SEM) indicated that the fracture surface was partly intergranular along micro-segregated zones (MSZ). This observation was made both on the initial and the aged conditions. Intergranular facets were largely covered by phosphorus segregation. A fully predictive model involving a combination of a local approach to fracture based on Beremin theory and accounting for MSZ distribution, and on the modelling of segregation kinetics in ternary (Fe-C-P) systems is developed to analyze these results. This model predicts the scatter in fracture toughness measurements and the shift in DBT. Moreover the statistical distribution of MSZ leads to a size effect in fracture toughness measurements which is different from the K4B law inferred from the Beremin model applied to a homogeneous material.
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Submitted on : Wednesday, March 16, 2016 - 4:52:44 PM
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André Pineau, Antoine Andrieu. A model for predicting fracture toughness and scatter in thermally embrittled steels. ed. G. Hutter, L. Zybell. Recent trends in fracture and damage mechanics, Springer, pp.337-352, 2016, 978-3-319-21466-5. ⟨10.1007/978-3-319-21467-2_15⟩. ⟨hal-01289442⟩



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