Determination of Critical Temperatures of Dual-Phase Steel DP600 by Simulating a Real Hot Rolling Schedule Using Hot Torsion Test

Introduction and Objectives: Dual-phase steels, particularly DP600, are among the most widely used materials in the automotive industry due to their unique combination of high strength and good formability. Understanding the hot deformation behavior of these steels is crucial for designing optimal hot rolling schedules to produce steel sheets with desired mechanical properties. In this study, an investigation was conducted on the hot deformation behavior of DP600 steel with the aim of determining its critical temperatures.Materials and Methods: In this research, the hot torsion test, one of the most practical methods for simulating industrial hot rolling conditions, was employed to determine the critical temperatures (Tnr, Ar3, and Ar1) of the dual-phase steel by simulating two different rolling schedules, namely average and actual tests.Results: In the average test, the no-recrystallization temperature (Tnr), the starting temperature of austenite-to-ferrite transformation (Ar3), and finishing temperature of ferrite transformation (Ar1) were measured to be 910 °C, 790 °C, and 760 °C, respectively. In contrast, in the actual test, these temperatures were found to be 931 °C, 825 °C, and 765 °C, respectively. Microstructural analyses confirmed the reliability of the obtained results.Conclusion: The results indicated that the values of critical temperatures differ between the two tests due to non-equilibrium conditions. However, the values obtained from the actual test, which closely simulates real rolling conditions, can be effectively used to design an optimal rolling schedule for producing dual-phase steel with the desired tensile strength.