Mechanical behaviour and microstructural evolution of a microalloyed C-Mn steel during hot forming process

Abstract : The mechanical behaviour of a C-Mn steel is investigated under different thermomechanical paths, in order to determine its constitutive equation in industrial hot rolling conditions. Compression tests were performed and the maximum admissible strain level so that friction remains negligible was determined by numerical simulation. The limited maximum total strain requires selecting the key features of the thermomechanical path. It is shown that the austenitising temperature has a great influence on the mechanical and microstructural evolution of the steel. The influence of recrystallization in the roughing mill on the mechanical behaviour has been investigated by double compression tests, and seems not to be very important. The influence of strain and austenitising temperature on the phase transformation has also been studied. The austenitising temperature strongly affects the grain size, and the kinetics of phase transformation can be well understood using this parameter. But the strain raises the transformation start temperature up to a point at which the grain size is not a relevant parameter.