The effect of a Nb-addition on the transformation behaviour of CSiMn TRIP steels was investigated: the dilatometer curves showing the typical transformation behaviour and the CCT-diagrams of the steels investigated are presented. It is well known that the processing of hot rolled TRIP steels requires a particular attention as to their chemical composition and still more to the thermomechanical cycle to be applied. In particular, the kinetics of the austenite/ferrite transformation are of interest. It is shown that the austenite/ferrite transformation, under laboratory simulation conditions, is rather sluggish. Furthermore, the influence of niobium on the hot deformation behaviour of TRIP steels is studied. It was demonstrated that the Nb-addition leads to a significant change of the kinetics of the ferrite formation under continuous cooling conditions as well as after hot deformation and cooling. On the other hand, the formation kinetics of the lower temperature transformation products (bainite,...) are less affected. The results are compared with equilibrium Thermocalc calculations. Suggestions regarding the practical processing parameters are introduced. Based on the dilatometer results, some additional tests were carried out by means of a high strain rate MTS hot forging simulator.