AbstractThe continuous cooling transformation behaviour of a niobium microalloyed steel is studied by combining multipass deformation and continuous cooling torsion testing and by monitoring the variation of flow stress as afunction of temperature during cooling. Deformation above the non-recrystallisation temperature Tnrslightly increases the Ar3temperature and so encourages the austenite to ferrite transformation. Further deformation below Tnrboth enhances the Ar3temperature and promotes the transformation significantly. Decreasing the interpass time and increasing the pass strain below Tnrincreases the Ar3temperature. A method is proposed to estimate the stored deformation energy from pass to pass as the deformation proceeds below Tnrbased on the course of the mean flow stress curve and on the concept of shear deformation energy. The effect of the process variables, mainly the interpass time below Tnron the stored deformation energy and consequently on the Ar3temperature is discussed.MST/3198