Hot Deformation Behaviour of Q690 High-Strength Steel

This study systematically investigated the thermal deformation characteristics of industrial-grade Q690 HSLA steel under different temperatures and strain rates through isothermal compression tests conducted on the Gleeble-3500 simulator. The flow stress of Q690 steel exhibits significant sensitivity to deformation parameters (850–1150 °C and 0.001–10 s−1), characterized by a pronounced thermal softening effect at higher temperatures and strain-rate hardening as the strain rate increases. Through the construction of processing maps, we identified an optimal processing window within the temperature range of 1000–1100 °C and strain rates of 0.01–0.1 s−1, where the power dissipation efficiency (η) reaches a peak of 0.34, indicating superior hot workability. Conversely, flow instability zones were predominantly observed at lower temperatures and higher strain rates, with these regions expanding as strain increased. By integrating flow curve analysis, instability criteria, and microstructural characterization, we determined that complete dynamic recrystallization (DRX) is achieved at 1050 °C and 0.1 s−1. Under these conditions, the material exhibits a refined, homogeneous equiaxed grain structure with uniform martensitic laths and an average prior austenite grain size of approximately 9.88 µm.