Abstract
Two microalloyed steel heats have been produced to obtain sheets of different thicknesses by controlled rolling in one instance and conventional rolling followed by a normalising heat treatment in the other. The mechanical properties and microstructures of these materials have been evaluated and their fracture behaviour, from the ductile region to the brittle region, has been assessed by notched impact testing and elastoplastic fracture mechanics testing. The sheets submitted to thermomechanical treatment, having similar optical microstructures, show higher strength and lower ductility and toughness than the normalised sheets. In addition, both heats manifest the influence of the sheet thickness on these properties owing to its effect on the final cooling rate. Finally, although a linear correlation has been obtained between the results of notched impact and crack tip opening displacement or J interval, the dispersion of these data does not enable the prediction of fracture mechanics parameters from Charpy parameters.
MST/1998
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