Strain-rate dependent hot deformation behavior and mechanism of interphase- precipitated Ti-Mo-xNb steels: Physical modeling and characterization

The hot flow behaviors of interphase precipitated Ti-Mo-xNb (x = 0, 0.02) steels were investigated by conducting compression tests at higher strain rates of 0.1–10 s−1 and temperatures of 800–1150 °C using a Gleeble-2000 thermo-mechanical simulator. The hot deformation behavior was modeled through combining the dislocation density based Bergstrom and the diffusional transformation based KJMA models. The results show that even small amount of Nb addition can effectively increase the activation energy for hot deformation, thus delaying the occurrence of dynamic recrystallization. However, the ascend rates in flow stress σ, peak stress σp and dislocation density ρp with Nb appeared to be more significant at higher strain rates, implying that the effectiveness of Nb in Ti-Mo-xNb steels was sensitive to strain rate. The microstructual features demonstrated that the hardening effect caused by Nb addition was offset by the softening effect of DRX at 0.1 s−1, causing the weak strain-rate dependence; whereas, at the strain rate of 10 s−1, the softening mechanism was considered as DRV, giving rise to a relatively large discrepancy in flow behaviors with Nb addition.