Gh625 Alloy Hot Deformation Behavior And Dynamic Recrystallization

The GH625 alloy has been deformed by Gleeble-3800 thermal simulation machine in the range of temperature 950～1050℃at 0.001～5s-1 strain rate. The plastic deformation behaviors have been investigated and a constitutive model is developed. Optimal deformation parameters and instability regions are determined according to the processing map theory and microstructure. How strain, deformation temperature and strain rate influence DRX and microstructure, which are analyzed by OM and TEM. Meanwhile, DRX dynamic equation and recrystallized grain size model are set up. The following conclusions have been drawn from this investigation:1. There is obvious peak on the flow stress curve of GH625 alloy during hot compression, so the curve belongs to the type of dynamic recrystallization. Meanwhile, peak stress and peak strain of GH625 alloy increase with the decrease of deformation temperature and decreases with the decrease of strain rate during. So relationship between flow stress and deformation condition can be described by hyperbolic sine function. Constitutive equation and steady-state stress model of GH625 alloy are set up by multiple linear regression analysis.2. According to the data of hot compression test, processing maps of GH625 alloy are drawn. In the steady flow state, the map exhibits three domains where the efficiency of power dissipation reaches a local maximum:domainⅠ(0.001～0.006s-1,970～1015℃)—low temperature and low strain rate region; domainⅡ(0.005～0.13s-1,1027～1100℃)—medium temperature and low strain rate region; domainⅢ(0.001～0.005s-1,1114～1143℃)—high temperature and low strain rate region. The optimal metalworking condition is at the temperature of 1050℃, the strain rate of 0.013s-1.3. According to instability maps of GH625 alloy, in the steady flow state there are two instability regimes:regimeⅠ(1～5s-1,950～965℃)—low temperature and high strain rate region; regimeⅡ(0.1～5s-1, 982～1135℃)—medium temperature and high strain rate region. In the regions, the efficiency of power dissipation decreases significantly which may be due to flow localization.4. The results of TEM analysis shows that it is easy to occur for DRX in the high deformation temperature, and recrystallized grains sizes increases with increase of temperature and decrease of strain rate. There is the phenomenon of second phase particles precipitating and dislocation pileup around the particles. In addition, volume fraction of DRX decreases with increase of strain rate. By using the data of flow stress curves, relationship between critical strain and Z parameters is founded. The size of recrystallized grains has a linear ship with Z parameter, and the recrystallized volume fraction can be expressed by Avrami equation.