Combined Effects of Deformation and Undercooling on Isothermal Bainitic Transformation in an Fe-C-Mn-Si Alloy

Abstract

Both ausforming and transformation temperature affect the successive bainitic transformation and microstructure. The individual influence of each case is clear, whereas the combined effects are still unknown. Thermomechanical simulation and metallography were used to investigate the combined effects of ausforming and transformation temperature on bainitic transformation and microstructure. The kinetics of isothermal bainitic transformation in non-deformed and deformed materials was analyzed. A lower transformation temperature can lead to more bainite formation without deformation. However, ausforming with small strains can partially compensate for the decrease of bainite amount caused by the decreased undercooling. The larger the applied strain is, the smaller the difference between the final amounts of bainite with different undercooling. Ausforming at a relatively higher temperature is more favorable to the acceleration of subsequent isothermal bainitic transformation. The results in the present work provide reference for optimizing the fabrication technology of medium-carbon nanobainite steels.

Effect of Multi-Step Austempering Treatment on the Microstructure and Mechanical Properties of a High Silicon Carbide-Free Bainitic Steel with Bimodal Bainite Distribution

“…Furthermore, both for the isothermal treatment at 350 • C and 370 • C, the transformation is characterised by an incubation time (160 s and 300 s, respectively) as it is displayed in Figure 3B. Bainitic reaction at 350 • C is characterised by a shorter incubation period thanks to an increase in the driving force for bainitic transformation, in agreement with Khare et al [50] and Zhou and co-authors [51]. In addition, the kinetics of the transformation at 350 • C is faster than the transformation at a higher temperature, as indicated by the more rapid increase in change in length, in agreement with Xu and co-authors [49].…”