Study On Hot Deformation Behavior And Dynamic Recrystallization Of GH4742Superalloy

GH4742superalloy is a high alloying niekel-based superalloy with excellent performance at high temperature, serving temperature range is750-800°. However, the hot workability becomes quite poor due to various reinforcement methods. Hot compression tests of GH4742superalloy are conducted on a Gleeble-1500thermal simulating tester in the range of temperature900～1150℃, strain rate10～5×10-4s-1and stain30%-60%. Constitutive equation is set up, Processing maps and deformation mechanism maps for GH4742superalloy are drawn, dynamical recrystallization model is set up based on the data of true stain-true stress curves and microstruetur ananlysising. The main results are summarized as following:(1)Obvious dynamic recrystallization behavior is observed in hot deformation for GH4742superalloy by the way of OM and TEM, etc. The experimental results indicate that the flow stress and peak stress corresponding strain decrease with increasing deformation temperature and decreaseing strain rate. At the same time, dynamic recrystallization behavior is more and more fully. The best hot deformation temperature1100℃for GH4742superalloy is obtained by calculation and analysis of the m and Q. Constitutive equation and flow stress model of GH4742superalloy are setup by linear-regression analysis.(2)Processing maps of GH4742superalloy are drawn based on the Dynamic Material Modeling(DDM). There are two instability regimes:(900～1020℃、10～10-2s-1)(1075～1150℃,10-1～10-2s-1) and three domains where the efficiency of power dissipation reaches a local maximum:(950～1050℃、10-2～5×10-4s-1)(1050～1150℃、10～0.5s-1)(1070～1150℃、10-2～10-3s-1). These processing maps can accurately forecast the feasibility of hot deformation for GH4742superalloy by comparing with the actual micro structure. The optimal hot deformation condition is at the temperature of1100℃,the strain rate of10-2～10-3s-1. The dislocation-incorporation R-W-S deformation mechanism maps for GH4742superalloy which are constructed at different temperature can predict results conforming to the law.(3)There dynamic reerystallization nucleationin methods (DDRX, CDRX, TDRX) are finded though TEM, etc. The dynamic reerystallization critical stress and critical strain model and the recrystallized volume fraction model and the size of reerystallized grains model are obtained based on the curves of the true stress-true strain.