Austenitic Heat-resistant Steel Deformation Mechanism Three-dimensional Mapping Relationship Construction And Key Parameters Of Electric Upsetting Nonlinear Loading Paths Design

In this paper, isothermal compression tests were conducted on Gleeble-1500 thermal simulator, then, elevated temperature flow stress curves of 3Cr20Ni10W2 austenitic heat-resistant steel were obtained, based on which elevated temperature deformation behaviors were studied. Strain rate sensitivity coefficient(m), power dissipation efficiency(η) and instability coefficient(ζ) were calculated, and the 3-D power dissipation maps, 3-D instability maps and the processing maps were plotted, on the basis of which temperature and strain rate parameters range for steady deformation have been obtained. Finally, the 3-D deformation mechanism map wad established. According to the fine grain parameter domain identified by processing map, the nonlinear current-speed loading mode for the electric upsetting process is initially set up. Furthermore, a series of numerical simulations were carried out for upsetting process, then, the optimal nonlinear current-speed loading mode was gained. And the main contents and conclusions are as follows:①Isothermal compression tests were conducted at temperature range 1203~1403 K, strain rate range 0.01~10 s-1, and the true stress-strain curves of 3Cr20Ni10W2 austenitic heat-resistant steel were obtained. Through the analyses of stress-strain curves, it can be found that with the increase of the strain, when dynamic recovery is the main softening mechanism, the curves first show a rapid growth trend, and after reaching the peak gradually tend to a steady state. When dynamic recrystallization is the main softening mechanism, the curves first show the trend of rapid growth, and then a certain degree of decline arises after reaching the peak, and finally they tend to be steady.②Based on the true stress, strain data from hot compression tests, 3-D power dissipation maps, 3-D instability maps, 3-D processing map and 3-D deformation mechanism map were plotted, on the basis of which the optimal parameter range for hot forming and the deformation mechanisms were identified. The optimal parameter range of 3Cr20Ni10W2 austenitic heat-resistant steel is temperatures of 1333~1403 K, and strain rates of 0.01~0.66 s-1.③Subroutine of recrystallization and grain size of 3Cr20Ni10W2 austenitic heat-resistant steel was developed by using Fortran. Moreover, the numerical simulation of hot compressions and microstructural observation verify the reliability of the subroutine.④The finite element model of electric upsetting is established based on the nonlinear finite element software Marc. Through the optimum deformation strain rate range identified by using processing map, a series of numerical simulations were conducted for electric upsetting process under different nonlinear current-speeds. Through the analysis of the simulation results under different loading conditions, it can be found that with the decrease of loading current, the temperature of workpiece and the grain size decreases and the recrystallization volume fraction increases slightly. With the decrease of the back speed, the temperature, recrystallization volume fraction and grain size will be reduced.⑤Considering the electric upsetting shape, grain size and recrystallization volume fraction, the optimal nonlinear current-speed loading scheme was selected, which can provide theoretical guidance for the practical electric upsetting production.