The hot deformation behavior of a medium-Mn steel was studied in terms of hot compression flow curves in the temperature range of 850–1050 ℃ and strain rates of 0.05–10 s-1.The thermo-mechanical analysis was carrie...The hot deformation behavior of a medium-Mn steel was studied in terms of hot compression flow curves in the temperature range of 850–1050 ℃ and strain rates of 0.05–10 s-1.The thermo-mechanical analysis was carried out and suggested that the microstructure during deformation was completely austenite which had high tendency for dynamic recrystallization(DRX).The flow behavior was characterized by significant flow softening at deformation temperatures of 950–1050 ℃ and lower strain rates of 0.05–5 s-1, which was attributed to heating during deformation, DRX and flow instability.A step-by-step calculating procedure for constitutive equations is proposed.The verification of the modified equations indicated that the developed constitutive models could accurately describe the flow softening behavior of studied steel.Additionally, according to the processing maps and microstructure analysis, it suggested that hot working of medium Mn steel should be carried out at 1050 ℃, and the strain rate of 0.05–10 s-1 resulted in significantly recrystallized microstructures in the in steel.The flow localization is mainly flow instability mechanism for experimental steel.展开更多
Grain shape of the hot deforming alloy is an important of material. The fractal theory was applied to analyze index to character the microstructure and performance the recrystallized microstructure of Ti-15-3 alloy af...Grain shape of the hot deforming alloy is an important of material. The fractal theory was applied to analyze index to character the microstructure and performance the recrystallized microstructure of Ti-15-3 alloy after hot deformation and solution treatment. The fractal dimensions of recrystallized grains were calculated by slit island method. The influence of processing parameters on fractal dimension and grain size was studied, It has been shown that the shapes of recrystallized grain boundaries are self-similar, and the fractal dimension varies from 1 to 2. With increasing deformation degree and strain rate or decreasing deformation temperature, the fractal dimension of grain boundaries increased and the grain size decreased. So the fractal dimension could characterize the grain shape and size. A neural network model was trained to predict the fractal dimension of recrystallized microstructure and the result is in excellent agreement with the experimental data.展开更多
Hot compression tests of Mg-8Al-1.5Ca-0.2Sr magnesium alloy were performed on the Gleeble-1500 machine at temperatures of 300,350,400,and 450℃and strain rates of 0.01,0.1 and 1 s^(−1).The flow stress behavior and mic...Hot compression tests of Mg-8Al-1.5Ca-0.2Sr magnesium alloy were performed on the Gleeble-1500 machine at temperatures of 300,350,400,and 450℃and strain rates of 0.01,0.1 and 1 s^(−1).The flow stress behavior and microstructural evolution were followed.The work hardening was derived according to the Laasraoui-Jonas model.An improved approach,which considered the influence of yield stress on flow stress and the effect of grain boundary(GB)migration on the evolution of dislocation density during compression,was used to simulate the microstructural evolution,the flow stress and the volume fraction recrystallized of Mg-8Al-1.5Ca-0.2Sr magnesium alloy.The simulated results are in good agreement with experimental results.展开更多
基金financially supported by the National Natural Science Foundation of China (No.51775102)the National key research and development plan (2017YF0703001)
文摘The hot deformation behavior of a medium-Mn steel was studied in terms of hot compression flow curves in the temperature range of 850–1050 ℃ and strain rates of 0.05–10 s-1.The thermo-mechanical analysis was carried out and suggested that the microstructure during deformation was completely austenite which had high tendency for dynamic recrystallization(DRX).The flow behavior was characterized by significant flow softening at deformation temperatures of 950–1050 ℃ and lower strain rates of 0.05–5 s-1, which was attributed to heating during deformation, DRX and flow instability.A step-by-step calculating procedure for constitutive equations is proposed.The verification of the modified equations indicated that the developed constitutive models could accurately describe the flow softening behavior of studied steel.Additionally, according to the processing maps and microstructure analysis, it suggested that hot working of medium Mn steel should be carried out at 1050 ℃, and the strain rate of 0.05–10 s-1 resulted in significantly recrystallized microstructures in the in steel.The flow localization is mainly flow instability mechanism for experimental steel.
基金supported by the National Natural Science Foundation of China under grant No.50405020.
文摘Grain shape of the hot deforming alloy is an important of material. The fractal theory was applied to analyze index to character the microstructure and performance the recrystallized microstructure of Ti-15-3 alloy after hot deformation and solution treatment. The fractal dimensions of recrystallized grains were calculated by slit island method. The influence of processing parameters on fractal dimension and grain size was studied, It has been shown that the shapes of recrystallized grain boundaries are self-similar, and the fractal dimension varies from 1 to 2. With increasing deformation degree and strain rate or decreasing deformation temperature, the fractal dimension of grain boundaries increased and the grain size decreased. So the fractal dimension could characterize the grain shape and size. A neural network model was trained to predict the fractal dimension of recrystallized microstructure and the result is in excellent agreement with the experimental data.
基金The authors gratefully acknowledge research support from the National Key Project Of Science and Technology“Highgrade CNC machine tools and basic manufacturing equipment”(No:2014ZX04002071)the Changsha Science and Technology Project(No.K1112067-11)and the Supporting Program of the“Twelfth Five-year Plan”for Sci&Tech Research of China(No.2011BAG03B02).
文摘Hot compression tests of Mg-8Al-1.5Ca-0.2Sr magnesium alloy were performed on the Gleeble-1500 machine at temperatures of 300,350,400,and 450℃and strain rates of 0.01,0.1 and 1 s^(−1).The flow stress behavior and microstructural evolution were followed.The work hardening was derived according to the Laasraoui-Jonas model.An improved approach,which considered the influence of yield stress on flow stress and the effect of grain boundary(GB)migration on the evolution of dislocation density during compression,was used to simulate the microstructural evolution,the flow stress and the volume fraction recrystallized of Mg-8Al-1.5Ca-0.2Sr magnesium alloy.The simulated results are in good agreement with experimental results.
