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Quenching and partitioning processing of plate steels for toughness and hardness applications
Bell, Miranda D.
Bell, Miranda D.
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2024
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2026-04-04
Abstract
The quenching and partitioning (Q&P) process has garnered much interest from the automotive industry for its ability to be implemented into current designs, produce excellent combinations of strength and formability, and lightweighting applications. While extensive research exists on Q&P processing of sheet steels, there is limited knowledge when Q&P processing plate steels for toughness and hardness applications. This work sought to investigate the Q&P processing of low-alloy steel plates to obtain microstructures containing martensite and retained austenite (RA) and produce favorable combinations of hardness and impact toughness compared to as-quenched and quenched and tempered (Q&T) heat-treated plates.
A combination of modeling, dilatometry, and Gleeble® thermal simulations were used to design and develop microstructures with a targeted hardness between 500-560 HV and above a minimum impact toughness of 16 J at -40°C. Dilatometry Q&P heat treatments that were within the targeted hardness range were then applied to bulk Charpy V-notch samples using a Gleeble® simulator. A systematic study was used for the development of the Q&P processing parameters by adjusting the Q&P temperature and partitioning time. The quenching step design employed dilatometry experiments and modeling to predict the “optimal” quenching temperature and martensite start and finish temperatures. The partitioning step design utilized literature to predict a range of partitioning times and temperatures that generated microstructures with mechanical properties in line with the objective of this project. A study into the effect of varying quenching times at the quenching temperature was performed to understand the extent of austenite decomposition that might occur during thermal equilibration at the quenching temperature.
Microstructure characterization of the heat-treated dilatometry specimens indicated that both one and two-step Q&P microstructures contained mixed amounts of tempered, partitioned, and fresh martensite, RA, and bainitic ferrite. The one-step Q&P treatments stabilized a smaller fraction of austenite compared to the two-step Q&P treatments. Comparisons between Q&P and Q&T conditions demonstrated that the Q&P heat treatments generally produced microstructures with better toughness than Q&T conditions. As such, the results of this work suggest that Q&P may be a viable option to achieve plate steel microstructures with enhanced property combinations for similar chemical compositions.
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