Assessing the scale contributing factors of three carbide-free bainitic steels: A complementary theoretical and experimental approach

The bainitic ferrite plate thickness is the main parameter that controls the strength of this type of microstructures. Such thickness has been proved to mainly depend on the austenite yield strength, the driving force for the transformation and the transformation temperature. However, no research has focused on how these parameters evolve throughout the transformation and how this evolution can affect the outcome. In this study, thermal and thermomechanical treatments have been performed in three selected steels. The treatments have been designed in such a way that all the mentioned parameters are comparable, aiming to obtain similar microstructures in terms of bainitic ferrite plate thickness. However, significant differences have been found among the microstructures, with variations in plate thickness larger than 100 nm. These results indicate that there might be other factors that take part in the scale of bainitic microstructures. To explain these differences and based on the kinetics of the transformation and on the carbon content of austenite at the end of the transformation, a possible explanation has been proposed.Richard Huizenga at the Department of Materials Science and Engineering of the Delft University of Technology is acknowledged for the X-ray analysis. The authors gratefully acknowledge the support for this work by the European Research Fund for Coal and Steel under the Contracts RFCS-2015-709607 & RFCS-2019-899482 and by the Program Atracción de talento investigador (Consejería de Educación, Juventud y Deporte, Comunidad de Madrid), under the fellowship 2016-T2/IND-1693. They also acknowledge the support provided by the subsequent laboratories belonging to CENIM: X-Ray Diffraction, Metallography and Phase Transformations. The financial and equipment support from National Science and Engineering Research Council (NSERC) Canada is acknowledged by M. Jahazi and M. Zorgani acknowledges the scholarship provided by the Lybian government for his PhD studies