Austenite Formation and Decomposition in a High-Strength Alloy Subjected to Heating and Cooling Cycles

This study investigates the critical transformation temperatures of a high-strength API-grade steel through thermal analysis and software simulations; the precise determination of these temperatures is essential for enhancing the efficacy of subsequent experimental trials. Utilizing the ‘Quench Properties’ module of JMatPro® V14, characteristic transformations were identified between 950 °C and 25 °C under stable conditions. Heating rates of 5, 10, and 30 °C/s were applied to determine critical temperatures, with Ac1 ranging from 700 °C to 750 °C and Ac3 from 850 °C to 900 °C. Niobium content may influence Ac1 and Ac3, promoting the ferritic phase and elevating transformation temperatures at a heating rate of 30 °C/s. Conversely, a rate of 10 °C/s significantly influenced austenite formation, impacting the development of microconstituents that enhance both strength and elongation post-quenching. Furthermore, slow cooling was found to favor the premature formation of allotriomorphic ferrite, which hinders the transformation of austenite into bainite and martensite during accelerated cooling. Finally, this study corroborates that JMatPro® is a reliable tool for predicting critical temperatures and designing optimized thermomechanical processing routes.