Recrystallization–precipitation interaction during austenite hot deformation of a Nb microalloyed steel

The role of Nb during austenite processing of High Strength Low Alloy (HSLA) steels has been the subject of considerable interest and discussion over the past decades. In this work, the precipitation state of a Nb microalloyed steel is studied extensively during the different stages of the process, i.e. after reheating, during cooling, during deformation and during recrystallization. To do so, a combination of experimental methods was applied: Transmission Electron Microscopy in combination with Energy Dispersive X-ray Spectroscopy (TEM-EDX), Inductively Coupled Plasma-Mass Spectroscopy (ICP-MS) and X-ray Diffraction (XRD). To obtain the best accuracy for these precipitation measurements, a model alloy was designed that showed extensive precipitation. From this experimental study, a correlation between the precipitate pinning and the recrystallization driving force could be made and the precipitation state during recrystallization could be linked to the recrystallization kinetics by comparison of the recrystallization driving force to the Zener pinning force. It was confirmed that recrystallization occurred during the precipitate nucleation and coarsening stage, while it was halted completely during the precipitation growth stage.