PSI - Issue 68

Atef Hamada et al. / Procedia Structural Integrity 68 (2025) 581–587

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Atef Hamada et al./ Structural Integrity Procedia 00 (2025) 000–000

1. Introduction Fast heating treatment (FHT) is a novel approach in materials engineering, characterized by rapid heating rates (approximately 300 °C/s), followed by quenching (Liu et al. 2016). The key principle behind FHT is the rapid heating of the material to elevated temperatures, followed by controlled cooling (Tan et al., 2022). This technique can potentially replace traditional annealing methods due to its short heating cycles, which help maintain fine-grained microstructures through thermomechanical processing (Gaggiotti et al., 2023; Lolla et al., 2011). FHT holds significant economic benefits, as it reduces energy consumption and processing time compared to conventional heat treatment methods (Kisku and Kisku, 2020). This makes FHT an attractive option for industries looking to enhance performance without increasing production costs (Hamada et al., 2023). Its efficiency is particularly relevant for large-scale manufacturing of advanced high-strength steels (AHSS) (Jovičević-Klug et al., 2022), offering a cost-effective alternative while delivering superior material performance. This innovative technique has been explored across various steel types, including carbon steels, ferritic, and austenitic stainless steels (Gaggiotti et al., 2022; Tajmiri et al., 2024). One of the key advantages of FHT is the promotion of fine-grained microstructures, which are desirable for improving the tensile strength and ductility of steels (Banis et al., 2019). The rapid heating rates accelerate phase transformations and grain refinement, as observed in cold-rolled quenching and partitioning (Q&P) steels [1, 9]. This grain refinement leads to improved mechanical properties, such as increased strength and elongation, which are crucial for demanding applications in the automotive and aerospace industries (Raabe et al., 2020). The FHT process is particularly relevant for optimizing steels that undergo cold-rolling, where the rapid thermal cycles can promote full recrystallization, resulting in ultrafine-grained microstructures (Fabrègue et al., 2018). Thermomechanical treatments, such as those applied to high-Mn twinning-induced plasticity (TWIP) steels, have been explored to control grain growth and phase composition (Dobrzański and Borek, 2012). Recent studies have shown that flash annealing of austenitic TWIP steels can optimize microstructural features, such as the thickness and volume fraction of twin plates, achieved through cold rolling (Khedr et al., 2019). The concept of flash annealing is the short annealing period at an elevated temperature, which efficiently allows to obtain large amount of retained austenite and fast carbon partitioning (Wan et al., 2021). However, the application of FHT in this context has not yet been fully explored, motivating the present study to investigate the effects of FHT on cold-rolled austenitic TWIP steel. (Liu et al., 2022) explored the use of ultra-flash annealing (UFA) to improve the mechanical properties of 316L austenitic stainless steel, which is typically limited by low yield strength. The research focused on how UFA can create a heterostructured microstructure that combines both strength and ductility, which are often difficult to achieve simultaneously in stainless steels (Hamada et al., 2022b; Järvenpää et al., 2021). The study utilized cold rolling with 90% thickness reduction followed by UFA through extremely high heating rates (>1000°C/s), aiming to create a hybrid microstructure consisting of recrystallized and non-recrystallized zones. These zones contribute to both strength (via grain boundary strengthening) and ductility (via back-stress hardening). After cold rolling, yield strength significantly increased (from 248 MPa to 1430 MPa), but with a dramatic reduction in ductility (from 60% to 1.6%). UFA restored ductility while retaining improved yield strength, displaying yield strength of 602 MPa and elongation% of 36%. Microstructural analysis revealed that the non-recrystallized zones in the UFA-treated samples played a crucial role in maintaining high strength, while dislocation and back-stress hardening improved the ductility. In the present work, the mechanical properties of high-Mn TWIP steels were fine-tuned through FHT by manipulating parameters such as heating rate, peak temperature, and dwell time. The study focuses on FH at 1000 °C and 1200 °C, followed by microstructural characterization via electron backscattered diffraction (EBSD) to optimize grain size and mechanical properties of the investigated TWIP steel. 2. Experimental procedures Fig. 1 shows schematically the cycle of time vs temperature for the applied FH treatment. The time of heating up to the peak temperature is extremely short. A cycle of conventional thermal processing was included for comparison in Figure 1. Conventional heat treatment involves prolonged times during heating, i.e., low heating rates ≤ 20 °C, and at peak temperatures that are extremely long, i.e., on the order of hours.