It is known that the load level, the way deformation is applied and the level of plastic strain, all can ‘aid’ or ‘hinder’ the occurrence of brittle fracture, but the question is - to what extent? These influential factors are analysed by testing of C(T)50 specimens made of ferritic steel 20MnMoNi 55 at two temperatures within the transition temperature range. The effect of displacement rates is analysed by testing C(T) specimens at -60 °C, while the effect of plastic strain is analysed by introducing an initial fatigue crack with low and high stress intensity factor threshold values of ΔK, by testing the C(T) specimens at -90 °C, in accordance with ASTM 1820 standard. The analysis of these influences involves interpretation of test results for parameters Jc, CMOD, and rc. Conclusions based on this analysis can be used in further studies which involve understanding of ductile to brittle transition region, as well as the general fracture behaviour of ferritic steels.
Keywords: transition region, 20MnMoNi 55 ferritic steel, brittle fracture, displacement rate