Hot Deformation Behavior Of GH4742Superalloy

GH4742is a kind of hard deformation high performance Nicke-based superalloy since it is contained with many alloy elements such Cr, Co, W, Al, Ti and so on, the hot workability of the alloy becomes quite poor, which limits the further development of the alloy. In this dissertation, homogenization treatment and homogenization effect on the ductility of as-cast GH4742were studied, the hot deformation behavior and dynamic recrystallization of the alloy after1160℃×6h(QC) treatment were also investigated, in order to find a basic data for the forging process of the alloy.The GH4742alloy was fabricated by VIM+VAR. The dendritic segregation exists in GH4742ingot clearly, and it can be reduced by one step homogenization treatment at1160℃for6h(QC). After the one step homogenization treatment, when the alloy was homogenization treated at1200℃for4h(AC), the dendritic segregation in the original ingot will almost disappear and obtain homogeneous austenite. Meanwhile, the two step homogenization treatment can also increase the plastic, reduce the deformation resistance and was favorable for recrystallization.In the thermal simulation research, single-pass hot compression tests were performed for the GH4742alloy. The influence of deformation parameters, such as deformation temperature (1050℃,1075℃,1100℃,1125℃,1150℃), deformation amount (10%,30%,50%) and strain rate (0.001s-1,0.01s-1,0.1s-1,1s-1,10s-1) on the deformation behavior and recrystallization behaviors were investigated, based on the strain-stress curves. Then, the deformation activation energies for dynamic recrystallization and constitutive equation can be calculated, the energies of dynamic recrystallization is1496.9kJ/mol, and the constitutive equation is as follows:Z=3.0×1055[sinh(0.004185σ)]5.237. Combined with micristructure and fracture surface of sample after deformation, it can be found that:(1) The flow stress of the as-cast GH4742alloy can be reduced with increasing of deforming temperature and increased with increasing strain rate, while the elongation can be reduced with increasing of strain rate. The higher temperature and lower strain rate are suitable for hot deformation, it leads fewer cracking.(2) During the deformation, the deformation degree of the as-cast GH4742alloy can not be homogeneous, the degree in the edge part is quite different with that in the center part of sample.(3) The existence of γ’ particles significantly increases the flow stress, at the same time, the grain boundaries can be pinned by the γ’ particles, so that it restrain the dynamic recrystallization.