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The aim of this paper is the determination of the fracture toughness fromthe Charpy impact test results in the ductile to brittle transition temperature range via thelocal approach to fracture.Fractographic analyses showed that cleavage crack initiation is preceded by ductile crackgrowth. Furthermore, there is an evolution of cleavage fracture micromechanisms when thetesting temperature increases: at low temperature, cleavage is triggered by second phaseparticle cracking, whereas at higher temperature another micromechanism induced byplastic deformation takes place.Ductile fracture is modeled by the “Gurson Tvergaard Needleman” model, and brittlefracture is accounted for with Weibull type model. Finite element method was used toprovide the local mechanical field needed for the local approach. Weibull parameters werefound to vary with increasing temperature, which is consistent with fractographicobservation. However, taking into account the evolution of cleavage micromechanisms in aphenomenological way, i.e. evolution of Weibull parameters with temperature is notsufficient to predict the fracture toughness from the Charpy impact tests. The influence ofstrain rate on the fracture criterion is discussed.