The influence of microstructure on the hot ductility of four low carbon steels with respect to transverse crack formation in continuously cast slabs /

The influence of Al, Mn and Ti on the hot ductility of four low C steels has been examined.Ductility troughs were exhibited by all the steels. These could be related to the austenite-to-ferrite phase transformation and grain boundary precipitation behavior. When no precipitation took place at the austenite grain boundaries, the trough occurred by intergranular failure. Fracture surfaces revealed microvoid coalescence, with voids associated with MnS inclusions.Increasing the Mn in the steels lowers the $ gamma to alpha$ transformation temperature, causing the trough to be moved to lower temperatures. It also decreases the volume fraction of MnS inclusions within the ferrite film. Increasing the Al level caused AlN to be precipitated at the austenite grain boundaries, extending the trough to higher temperatures into the single phase austenite region.The addition of Ti results in a fine austenite grain size after the solution treatment and impedes AlN precipitation. This leads to improved ductility in the austenite region.When austenite recrystallization occurs during deformation, any voids which have initiated at the boundaries are trapped within the newly recrystallized grains. Intergranular failure cannot progress and the ductility is high