An extensive investigation has been carried out on the sensitivity parameters determination describing the fracture behaviour of body with crack with respect to the character change of true stress-strain curve with dominant region of Lueders deformation. The attention is paid on the influence of hardening exponent of deformation to the history of the idealised true stress-strain material curve described by the Ramberg-Osgood relation. Above mentioned tests are used for the correct Weibull stress determination, which is as a measure of the failure probability of cracked body. The Weibull stress model for cleavage fracture of cast steel requires calibration of two micromechanics parameters (m, σ{sub}u). Local material parameters have been calculated arising from Beremin approach and calibration is based on the Gao and Ruggieri approach. The aim of the paper can be seen in fracture toughness transfer and correction from pre-cracked specimens to small scale yielding (SSY) represented by 1T (SENB) specimens and their precise computation using FEM. The fracture resistance has been assessed using data from static tests of the three point bend specimens.
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