PSI - Issue 69

Zeynab Aalipour et al. / Procedia Structural Integrity 69 (2025) 105–112

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4. Conclusion In summary, this study demonstrates that silicon content, partitioning time, and partitioning temperature jointly govern phase transformations and retained austenite (RA) stability in medium-carbon steels undergoing a deformation quenching and partitioning (DQ&P) process. High-silicon (H-Si) steel, partitioned at 300 °C, accelerates RA stabilization and effectively suppresses both secondary martensite and bainitic transformations, achieving around 19% RA after 1000 s. In contrast, low-silicon (L-Si) steel, partitioned at 250 °C, shows a slower rise in RA content and retains higher fractions of secondary martensite and bainite; only after 10000 s does the L-Si steel reach approximately17% RA. Despite these differences, both steels exhibit progressive carbon enrichment in RA, underscoring the vital role of carbon partitioning. However, at lower partitioning temperatures, the smaller average diffusion distances in L-Si steel result in finer, more dispersed RA regions. EBSD and SEM analyses confirm that H Si steel favors extensive RA networks, whereas L-Si steel exhibits more tempered martensite. These microstructural distinctions significantly influence mechanical performance: higher RA fractions in H-Si steel typically enhance ductility and toughness via the TRIP effect, whereas L-Si steel, with its higher tempered martensite fraction, demonstrates greater strength. Overall, controlling silicon content and carefully selecting partitioning temperatures and times offers a powerful means of optimizing the phase balance and mechanical properties in advanced medium carbon steels. Acknowledgements The authorswould like to thank Jane and Aatos Erkko (J&AE), Tiina ja Antti Herlin (TAH) foundations and Kvantum Institute, University of Oulu for their financial supports on Advanced Steels for Green Planet (AS4G) and Green4GTech Projects. References [1] D.V. Edmonds, K. He, F.C. Rizzo, B.C. De Cooman, D.K. Matlock, J.G. 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