Bainitic Ferrite Plate Thickness Evolution in Two Nanostructured Steels

Bainitic ferrite plate thickness evolution during isothermal transformation was followed at the same holding temperatures in two nanostructured steels containing (in wt.%) 1C-2Si and 0.4C-3Si. A dynamic picture of how the bainitic transformation evolves was obtained from the characterization of the microstructure present at room temperature after full and partial transformation at 300 and 350 degrees C. The continuous change during transformation of relevant parameters influencing the final scale of the microstructure, YS of austenite, driving force of the transformation and evolution of the transformation rate has been tracked, and these variations have been correlated to the evolution of the bainitic ferrite plate. Instead of the expected refinement of the plate predicted by existing theory and models, this study revealed a thickening of the bainitic ferrite plate thickness as the transformation progresses, which is partially explained by changes in the transformation rate through the whole decomposition of austenite into bainitic ferrite.

Automated summary

The evolution of bainitic ferrite plate thickness was studied in two nanostructured steels, showing an unexpected thickening of the plate during transformation contrary to existing predictions. This study tracked the changes in relevant parameters influencing microstructure scale, austenite YS, transformation driving force, and transformation rate evolution.