Abstract
Hot deformation behavior of a high-titanium Nb-micro-alloyed steel was investigated by conducting hot compression tests at the temperature of 900–1100 °C and the strain rate of 0.005–10 s−1. Using a sinh type constitutive equation, the apparent activation energy of the examined steel was 373.16 kJ/mol and the stress exponent was 6.059. The relations between Zener–Hollomon parameters versus peak stress (strain) or steady-state stress (strain) were successfully established via the Avrami equation. The dynamic recrystallization kinetics model of the examined steel was constructed and the validity was confirmed based on the experimental results. The 3-D atomic distribution maps illustrated that strain can significantly affect the values of power dissipation efficiency and the area of instability domains. The 3-D processing maps based on a dynamic material model at the strains of 0.2, 0.4, 0.6 and 0.8 were established. Based on traditional and 3-D processing maps and microstructural evaluation, the optimum parameter of for a high-titanium Nb-micro-alloyed steel was determined to be 1000–1050 °C/0.1–1 s−1.
Highlights
Hot deformation behavior of high-strength low-alloy steels has become the focus of many researchers for many years because of higher yield strength, lower impact transition temperature and better cold formability
Temperature is higher than 950 ◦ C (Figure 1b), the flow stress decreases after reaching a peak stress value and (DRX)
The deformation behavior of materials at high temperature can be expressed by constitutive equation, which describes the relations among strain rate, deformation temperature and flow stress, and is represented by Equation (1) [6]
Summary
Hot deformation behavior of high-strength low-alloy steels has become the focus of many researchers for many years because of higher yield strength, lower impact transition temperature and better cold formability. Raj et al proposed to build a processing map on the basis of cavity nucleation mechanisms, dynamic recrystallization and adiabatic heating effects [8]. This processing map, has limitations that it can only be applied to pure metals and simple alloys, but not Materials 2020, 13, 1501; doi:10.3390/ma13071501 www.mdpi.com/journal/materials. Some studies have studied the hot deformation behavior of Nb–Ti micro-alloyed steel [24], few researchers have studied the effect of 3-D processing maps considering strain and high-titanium on the hot deformation behavior of Nb steel. The equations of flow models such as stress exponent, Zener-Hollomon, apparent activation energy, dynamic recrystallization fraction and 3-D processing maps of the material are established to optimize the hot processing parameters
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