PSI - Issue 69

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ScienceDirect

Procedia Structural Integrity 69 (2025) 105–112

13th European Symposium on Martensitic Transformation 2024 (ESOMAT 2024) Effect of Partitioning Time and Silicon Content on Retained Austenite Stability in Medium-Carbon Advanced High-Strength Steels Zeynab Aalipour a* , Sumit Ghosh a , Jukka Kömi a , Vahid Javaheri a a Materials and Mechanical Engineering, Centre for Advanced Steels Research, University of Oulu, 90014, Finland Abstract This study investigates the effects of silicon content and partitioning time on the phase transformations and microstructural evolution of medium-carbon steels. Two compositions—a high-silicon (H-Si) alloy and a low-silicon (L-Si) alloy—were subjected to varying holding times during deformation quenching and partitioning. Their retained austenite (RA) fraction, secondary martensite and bainite content were quantified using X-ray diffraction. Microstructural observations were carried out via electron backscatter diffraction (EBSD) and scanning electron microscopy (SEM). The results revealed that the H-Si steel achieves a stable RA fraction at shorter partitioning times (around 19% at 1000 s), with secondary martensite formation effectively prevented. In contrast, the L-Si steel exhibits a slower RA stabilization process; after 10000 seconds in the final quench, around 17% RA was stabilized, allowing some secondary martensite to persist. Similarly, while the L-Si steel shows a progressive and sustained increase in the bainite fraction, the H-Si steel remains largely resistant to bainitic transformation under the investigated conditions. Lattice parameter-based calculations confirm that both steels experience progressive carbon enrichment in RA, although the L-Si steel undergoes a faster initial rise in carbon content. EBSD and SEM analyses illustrate how these phase evolutions are reflected at the microstructural level. H-Si micrographs show larger, more continuous RA regions forming over time, whereas L-Si steel displays finer RA grains and a higher tendency toward martensite tempering. These findings emphasize the critical role of silicon in modulating phase stability, carbon partitioning, and, ultimately, the balance of mechanical properties. © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of Guest Editors

Keywords: Deformation Quenching and partitioning; Carbon partitioning; Retained austenite; Alloy design

* Corresponding author. Tel.: +35-850-568-6437; fax: +0-000-000-0000 . E-mail address: Zeynab.Aalipourhafshejani@oulu.fi

2452-3216 © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of Guest Editors 10.1016/j.prostr.2025.07.015