Mesoscale modeling and simulation of microstructure evolution during dynamic recrystallization of a Ni-based superalloy

Microstructural evolution and plastic flow characteristics of a Ni-based superalloy were investigated using a simulative model that couples the basic metallurgical principle of dynamic recrystallization (DRX) with the twodimensional (2D) cellular automaton (CA). Variation of dislocation density with local strain of deformation is considered for accurate determination of the microstructural evolution during DRX. The grain topography, the grain size and the recrystallized fraction can be well predicted by using the developed CA model, which enables to the establishment of the relationship between the flow stress, dislocation density, recrystallized fraction volume, recrystallized grain size and the thermomechanical parameters

The coarsening effect of SA508-3 steel used as heavy forgings material

SA508Gr.3 steel is popularly used to produce core unit of nuclear power reactors due to its outstanding ability of anti-neutron irradiation and good fracture toughness. The forging process takes important role in manufacturing to refine the grain size and improve the material properties. But due to their huge size, heavy forgings cannot be cooled down quickly, and the refined grains usually have long time to grow in high temperature conditions. If the forging process is not adequately scheduled or implemented, very large grains up to millimetres in size may be found in this steel and cannot be eliminated in the subsequent heat treatment. To fix the condition which may causes the coarsening of the steel, hot upsetting experiments in the industrial production environment were performed under different working conditions and the corresponding grain sizes were measured and analysed. The observation showed that the grain will abnormally grow if the deformation is less than a critical value. The strain energy takes a critical role in the grain evolution. If dynamic recrystallization consumes the strain energy as much as possible, the normal grains will be obtained. While if not, the stored strain energy will promote abnormal growth of the grains

The coarsening effect of SA508-3 steel used as heavy forgings material

SA508Gr.3 steel is popularly used to produce core unit of nuclear power reactors due to its outstanding ability of anti-neutron irradiation and good fracture toughness. The forging process takes important role in manufacturing to refine the grain size and improve the material properties. But due to their huge size, heavy forgings cannot be cooled down quickly, and the refined grains usually have long time to grow in high temperature conditions. If the forging process is not adequately scheduled or implemented, very large grains up to millimetres in size may be found in this steel and cannot be eliminated in the subsequent heat treatment. To fix the condition which may causes the coarsening of the steel, hot upsetting experiments in the industrial production environment were performed under different working conditions and the corresponding grain sizes were measured and analysed. The observation showed that the grain will abnormally grow if the deformation is less than a critical value. The strain energy takes a critical role in the grain evolution. If dynamic recrystallization consumes the strain energy as much as possible, the normal grains will be obtained. While if not, the stored strain energy will promote abnormal growth of the grains

High Temperature Deformation Behavior and Constitutive Modelling for 05Cr17Ni4Cu4Nb Stainless Steel

AbstractThe high temperature deformation behavior of 05Cr17Ni4Cu4Nb stainless steel was investigated at the temperatures from 1000 to 1200°C and strain rates from 0.01 to 10s-1 on Gleeble-3500 thermo-simulation machine. The stress-strain curves at lower strain rate (0.01-0.5 s-1) exhibit a single peak stress, indicating a typical dynamic recrystallization (DRX) behavior of the steel, but at higher strain rates (10 s-1), the temperature rise due to the heat liberated from severe plastic deformation leads to the final drop of flow stress. Further microstructural observation confirmed the occurrence of DRX behavior, the average grain sizes decreased with the increasing strain rate and the decreasing deformation temperature, and the higher the deformation temperature, the larger the DRX degree. A new constitutive equation incorporating the effect of the strain on the deformation behavior was proposed based on the Arrhenius-type equation, in which the material constants α, n, Q and A were found to be polynomial functions of strain. The stress-strain relations of 05Cr17Ni4Cu4Nb steel predicted by the proposed constitutive equation agreed well with experimental results

Multiscale modeling of discontinuous dynamic recrystallization during hot working by coupling multilevel cellular automaton and finite element method

Discontinuous dynamic recrystallization (dDRX) is considered an effective way to obtain fine grain microstructures during hot working of materials with low-to-medium stacking fault energy (SFE). However, to date, investigation and modeling of dDRX in complex hot working processes are not appropriately performed, which hinders further control of the microstructure and forming quality of products during hot working. In this study, a multiscale modeling framework, namely the MCAFE-dDRX model, was constructed by coupling the multilevel cellular automaton (MCA) and finite element (FE) method. The data acquired via the FE method was used as an input for MCA simulation by discretizing the increment in FE time to consider the deformation history of materials. Compared to previous studies where only the effects of constant strain rate and temperature on the deformation of materials are analysed, the MCAFE-dDRX model can evaluate the dDRX microstructure evolution at different Zener-Hollomon levels, which has been validated by hot extrusion in this study. The developed simulation framework facilitates the prediction of microstructure evolution during heterogeneous and non-isothermal deformation of materials