Quenching and partitioning (Q&P) produces steel microstructures with martensite and austenite that exhibit promising property combinations for third generation advanced high strength steels. Understanding kinetics of reactions that compete for the available carbon, such as carbide formation, is critical for alloying and processing design and achieving austenite enrichment and retention during Q&P. Mössbauer effect spectroscopy (MES) was used to characterize Q&P microstructures in a 0.38C-1.54Mn-1.48Si wt. pct. steel after quenching to 225 °C and partitioning at 400 °C for 10 or 300 s, with an emphasis on transition carbides. The recoilless fraction for η-carbide was calculated and a correction for saturation of the MES absorption spectrum was applied, making quantitative measurements of small amounts of η-carbide, including non-stoichiometric η-carbide, possible in Q&P microstructures. Complementary transmission electron microscopy confirmed the presence of η-carbides, and MES and x-ray

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The influence of partitioning temperature on microstructural evolution during quenching and partitioning was investigated in a 0.38C-1.54Mn-1.48Si wt.% steel using Mössbauer spectroscopy and transmission electron microscopy. -carbide formation occurs in the martensite during the quenching, holding, and partitioning steps. More effective carbon partitioning from martensite to austenite was observed at 450 than 400 C, resulting in lower martensite carbon contents, less carbide formation, and greater retained austenite amounts for short partitioning times. Conversely, greater austenite decomposition occurs at 450 C for longer partitioning times. Cementite forms during austenite decomposition and in the martensite for longer partitioning times at 450 C. The quenching and partitioning (Q&P) steel heat treatment [1-3] produces microstructures containing primarily martensite (M) and retained austenite (RA) [4,5]. Q&P involves quenching to a quench temperature (QT) between the martensite start (M s) and finish temperatures, partitioning at a temperature (PT) the same or higher temperature than the QT, followed by a final quench (FQ) to room temperature (RT) [2,6]. The goal is to partition carbon (C) from martensite to austenite, thereby reducing the C supersaturation of the martensite and stabilizing the

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