In Situ Synchrotron XRD Analysis of Phase Evolution and its Impact on Mechanical Properties in Quenched and Partitioned Medium-Carbon AHSS

Abstract:

In-situ high-energy synchrotron X-ray diffraction was employed to track phase evolution in a medium-carbon (0.4 wt.% C) advanced high-strength steel processed via quench-and-partitioning (Q&P). Real-time diffraction data, captured during quench stop temperatures of 200 °C (QT200) and 240 °C (QT240), followed by a 1000 s holding time at the partitioning temperature of 300 °C, revealed precise phase fractions during the Q&P. However, the retained austenite in both process routes produced comparable retained-austenite fractions at room temperature —23% for QT200 and 21% for QT240—the higher quench-stop temperature generated three times more fresh martensite (15% vs. 5%). The mechanical properties were examined by tensile tests, showing that the lower fresh-martensite content in QT200 promotes progressive, strain-induced austenite transformation, delays necking, and yields a uniform elongation of 6.9%. By contrast, QT240 reaches a higher ultimate tensile strength (around 2023 MPa vs. 1984 MPa) and yield strength (about 983 MPa vs. 938 MPa) at the expense of ductility (around 4.7% uniform elongation). In both conditions, the TRIP effect is active, but its contribution is curtailed by the presence of fresh martensite. The present study thus establishes a quantitative link between in-situ phase evolution pathways and the resulting strength–ductility balance, providing guidance for tailoring Q&P processing route in medium-carbon advanced high-strength steel for crash-critical automotive applications.

• Periodical: Materials Science Forum (Volume 1174)
• Pages: 21-26
• DOI: https://doi.org/10.4028/p-IFqR6Z
• Online since: January 2026
• Authors: Zeynab Aalipour Hafshejani*, Rafael Fillus Chuproski, Sumit Ghosh, Andreas Stark, Marko Huttula, Samuli Urpelainen, Jukka I. Kömi, Vahid Javaheri
• Keywords: Advanced High Strength Steel, In Situ Synchrotron Xrd, Medium Carbon Steel, Partitioning, Quench

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