Strain Rate Dependence on the Dynamic Recrystallization Phenomena and Processing Map of Low Carbon Q690 V‐N and V‐N‐Cr Microalloyed High‐Strength Steels

Abstract

Strain rate dependence on the dynamic recrystallization phenomena of low carbon Q690 V‐N and V‐N‐Cr microalloyed high‐strength steels is studied through thermo‐simulation in terms of the flow stress changes of the steels at the temperatures from 850 to 1100 °C and strain rate from 0.01 to 10 s−1. The experimental results show that low carbon Q690 V‐N and V‐N‐Cr microalloyed high‐strength steels are deformation temperature and strain rate sensitive. With the decrease of temperature and increase of strain rate, the value of flow stress increases and remains constant. Flow stress constitutive equations are developed with average deformation activation energy Q of 377 and 325.58 kJ mol−1, respectively. The addition of Cr promotes the dynamic recrystallization of V‐N microalloyed steel; meanwhile, the stress index n(V‐N) = 6.23, n(V‐N‐Cr) = 4.59, power dissipation efficiency value ηmax(V‐N) is 44.5% and ηmax(V‐N‐Cr) is 50.6%. According to the obtained processing map by material dynamic model, the thermal processing safety region occurred in the high temperature and low strain rate region (T = 917–1100 °C, = 0.01–0.38 s−1); flow instability region occurred in the low temperature (T = 850–866 °C) low strain rate ( = 0.01–0.024 s−1) region and 880–970 °C high strain rate ( = 0.65–10 s−1) region. DRX behavior of V‐N and V‐N‐Cr microalloyed steels is sensitive to the strain rate and deformation temperature, the lower the strain rate and the higher temperature, the more likely is the dynamic recrystallization. The grain size increases with the increase of temperature and decrease of strain rate in the experimental steels, and the precipitates and/or inclusions play an essential role of the hot compressive deformation behavior in steel.