Abstract:
This study investigates the phase transformations and microstructural development of SAE 9254 steel subjected to various heat treatments aimed at achieving a combination of bainitic, martensitic, and retained austenitic phases. The critical austenitization and quenching temperatures, along with the holding times, were determined using a dilatometer to observe the steel’s phase transformation behavior. An austenitization temperature of 850°C with a holding time of 180 seconds and a quenching temperature of 220°C were established. Two isothermal holding temperatures at 325°C and 375°C, with holding times of 30 and 15 minutes respectively, were chosen for the partitioning process after quenching. The phase transformations during heat treatments were observed through dilatometry, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results showed that the quenched samples contained approximately 50% martensite and 50% untransformed austenite, with small amounts of ferrite. The partitioning process facilitated bainitic transformation and resulted in lower amounts of retained austenite compared to quenched samples. Unexpectedly, fine carbides were also observed, likely influenced by alloy composition and cooling rates. Microhardness tests using the Vickers scale revealed that the hardness increased with increasing partitioning temperature. The highest hardness was observed in the water-quenched sample due to its predominantly martensitic microstructure. The study provides insights into the microstructural evolution and phase transformations in SAE 9254 steel and demonstrates the impact of heat treatment parameters on mechanical properties, offering guidance for optimizing processing parameters.
Referência:
CENTENO, Dany; Michell Andrade TRESSIA, Gustavo; CARVALHO, Felipe Moreno; CEZARIO, Fabiano Eduardo Marques; MASOUMI, Mohammad. Tailoring phase transformations in SAE 9254 steel: a dilatometry-based study on austenitization quenching, and carbon partitioning processes. In: ANNUAL CONGRESS ABM, 76., 2023, São Paulo. Proceedings… 21 p.
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