The austenite to polygonal ferrite transformation in low-alloy steel: multi-phase-field simulation

The austenite to ferrite phase transformation is a critical structural transformation in steel production, where the morphology and grain size of ferrite substantially influence the mechanical properties of steel materials. In this work, the influences of cooling rate, prior austenite grain size (PAGS), and Mn content on the microstructure evolution and component distribution of austenite-to-polygonal ferrite phase transformation are investigated by a multi-phase-field model. It is found that higher cooling rates intensify the driving force for austenite to polygonal ferrite phase transformations and delay the phase transformation process. As PAGS decrease, the increased proportion of austenite grain boundary offers more nucleation sites for polygonal ferrite and thus refines the polygonal ferrite grain. Additionally, increased Mn content results in significant grain refinement due to a reduction in the transformation temperature of austenite to polygonal ferrite. This work provides valuable insights into adjusting and designing desired microstructures of polygonal ferrite for enhancing the mechanical performance of steel. & COPY; 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

The austenite to ferrite phase transformation is a crucial structural change in steel production, with the ferrite morphology and grain size significantly impacting the mechanical properties of steel materials. This study investigates the effects of cooling rate, prior austenite grain size (PAGS), and Mn content on the microstructure evolution of the austenite-to-polygonal ferrite phase transformation using a multi-phase-field model. The findings reveal that higher cooling rates enhance the driving force for the phase transformation and delay the process. Decreasing PAGS increases the proportion of austenite grain boundaries, providing more nucleation sites for polygonal ferrite and resulting in refined grain size. Furthermore, increased Mn content leads to significant grain refinement by reducing the transformation temperature. This work provides valuable insights for adjusting and designing desired microstructures of polygonal ferrite to enhance the mechanical performance of steel.