Characterisation of inclusions in resulphurised microalloyed steel

Resulphurised steels, due to their good mechanical properties and machinability, are employed in the manufacture parts of trucks and high strength components. The microstructure control of these steels can improve their toughness without losing strength. In this sense, the chemical composition, morphology and distribution of MnS achieved with different thermomechanical processes affect the mechanical properties of the steel. In this work, the morphology and distribution of MnS inclusions in resulphurised steel 15V45 were analysed. Samples of the steel in its as cast condition and after hot rolling were examined using light and scanning electron (SEM) microscopies. Microhardness measurements and chemical composition of different MnS types were carried out to evaluate the plastic behaviour of each inclusion. The SEM images have provided information about the nucleation sites and size of the inclusions. Applying a Fe-Mn-S diagram under different thermomechanical conditions, this study could predict ductility problems and crack generation during hot rolling processes.