Abstract
This work is focused on the evolution of the microstructure of Inconel 718 during multi-pass forging processes. During the forming process, the material is subjected to several physical phenomena such as work-hardening, recovery, recrystallization and grain growth. In this work, transformation kinetics are modeled in the δ-Supersolvus domain (T>Tsolvus) where the alloy is single-phase, all the alloying elements being dissolved into the FCC matrix. Torsion tests were used to simulate the forging process and recrystallization kinetics was modeled using a discontinuous dynamic recrystallization (DDRX) two-site mean field model. The microstructure evolution under hot forging conditions is predicted in both dynamic and post-dynamic regimes based on the initial distribution of grain size and the evolution of dislocation density distribution during each step of the process. The model predicts recrystallization kinetics, recrystallized grain size distribution and stress–strain curve for different thermo-mechanical conditions and makes the connection between dynamic and post-dynamic regimes.
Highlights
Inconel 718 is a nickel-based superalloy combining good mechanical properties and resistance to oxidation at high temperatures
The kinetics of recrystallization and stress– strain curves are predicted for different thermomechanical conditions and a connection is made between dynamic and post-dynamic regimes, which is usually difficult to do with more phenomenological approaches
The evolution of recrystallization kinetics, recrystallized grain size, and mechanical behavior during hot forging of Inconel 718 were investigated in this work
Summary
Inconel 718 is a nickel-based superalloy combining good mechanical properties and resistance to oxidation at high temperatures. This alloy is widely used for manufacturing hot parts of turbojet engines. During hot forging of these parts, the microstructure of the alloy changes with the different cycles of heating, holding at high temperature, forging and cooling. The properties of the final piece depend greatly on the microstructure obtained at the end of the forging process. Controlling the final grain size is a key element to improve the mechanical properties of the forged pieces and meet the tight specifications imposed by the aeronautic industry. The kinetics of recrystallization and stress– strain curves are predicted for different thermomechanical conditions and a connection is made between dynamic and post-dynamic regimes, which is usually difficult to do with more phenomenological approaches
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