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An extensive investigation has been carried out on the sensitivity parametersdetermination describing the fracture behaviour of body with crack with respect to thecharacter 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 historyof the idealised true stress-strain material curve described by the Ramberg-Osgoodrelation. 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 modelfor cleavage fracture of cast steel requires calibration of two micromechanics parameters(m, su). Local material parameters have been calculated arising from Beremin approachand calibration is based on the Gao and Ruggieri approach. The aim of the paper can beseen in fracture toughness transfer and correction from pre-cracked specimens to smallscale yielding (SSY) represented by 1T (SENB) specimens and their precise computationusing FEM. The fracture resistance has been assessed using data from static tests of thethree point bend specimens.