Dynamic Recrystallization Microstructure Evolution Research Articles

Kinetics and microstructure evolution of dynamic recrystallization of medium-Mn steel during hot working

The dynamic recrystallization (DRX) behavior and microstructure evolution of medium-Mn (0.15C–10Mn) steel were investigated through isothermal hot compression tests. The flow stress–strain curves and microstructure analysis, in wide ranges of temperatures (900–1150 °C) and strain rates (10−3 - 1 s−1), were employed to establish constitutive equations and a grain size evolution model. Since the material constants were calculated based on polynomial function of strains, strain compensation was introduced into constitutive analysis. Comparison and verification showed that the constitutive equation had a high predictive ability. The correlation coefficient and average absolute relative error were 0.99 and 4.46%, respectively, which confirm the accuracy and guidance of the model. Metallographic observation was used to implement the grain size evolution analysis of the medium-Mn steel. Microstructure evolution was characterized with a gradual increase in average recrystallized grain size and an obvious expansion in the range of grain size distribution with both deformation temperature and strain rate, which were attributed to the competition between nucleation and grain boundary migration. Besides, a grain size evolution model was established to analyze the microstructure evolution.

Study on constitutive model and dynamic recrystallization softening behavior of AZ80A magnesium alloy

The microstructures of as-cast AZ80A magnesium alloy before and after homogenization treatment were studied. The flow behaviors of the homogenized alloy under different deformation conditions were studied by isothermal compression tests. Based on the flow stress-strain curves of the homogenized alloy, the constitutive model was established by the strain compensation method. The strain rate sensitivity index maps with different strains were constructed to quantify the dynamic recrystallization softening behavior of the homogenized alloy. Based on this, the influence of deformation temperature and strain rate on strain rate sensitivity index and dynamic recrystallization microstructure evolution were studied. The results show that both increasing homogenization temperature and holding time are beneficial for the β-phases to dissolve and alloying elements to diffuse. It is concluded that the proper homogenizing parameter of as-cast AZ80A magnesium alloy is 683 K for 20 h. Both the increase of deformation temperature and the decrease of strain rate are beneficial to the increase of strain rate sensitivity index. The region with an index greater than 0.22 corresponds to dynamic recrystallization softening zone and has good deformation properties.

Review on modeling and simulation of microstructure evolution during dynamic recrystallization using cellular automaton method

The macro-mechanical properties of metal and alloy are largely depended on their chemical composition and microstructures resulting from the complicated processing and heat treatment history in industrial production. During these thermoplastic processes, dynamic recovery, dynamic recrystallization, static recovery and static recrystallization are the key microstructural evolution mechanisms. Accurate prediction and precise control of the microstructural evolution are of great importance for designers to achieve excellent mechanical properties for metals and alloys through hot working. Up to date, dynamic recrystallization has been recognized as a powerful mechanism for grain refinement. In-depth understanding of the microstructural evolution of dynamic recrystallization and furthermore to accurately predict and control the microstructure evolution during dynamic recrystallization process has become a research focus in the field of plastic processing. Cellular automaton (CA) method has been commonly employed to simulate the microstructure evolution of dynamic recrystallization due to its unique advantages, for example, it is easier to represent topological features and more realistically reflect the grain boundary migration process. In this paper, the basic ideas and characteristics of the CA method are briefly introduced. The physical mechanisms of dynamic recrystallization are summarized. Meanwhile, the state-of-the-art overview of the CA method of simulating the DRX process is introduced. Furthermore, this paper points out several problems that need to be solved urgently and prospects the development trend of the CA method for simulating the microstructure evolution in dynamic recrystallization.

Microstructure Evolution Modeling and Simulation for Dynamic Recrystallization of Cr12MoV Die Steel During Hot Compression Based on Real Metallographic Image

In this work, microstructure evolution of dynamic recrystallization (DRX) behavior in Cr12MoV die steel was investigated via experiments and simulations systematically. Firstly, hot compression tests were performed to obtain the true stress–strain curves. Based on the experimental results, the flow stress model was established, and Avrami equation was developed to model the kinetics of DRX. Then, the cellular automaton (CA) model was established to describe DRX behavior. In order to obtain more accurate simulation results, a microstructure enhancement, extraction and conversion program based on fingerprint image enhancement algorithm was developed to generate real initial microstructure which could be directly used in CA simulation. With real initial microstructure generation, good agreement between simulated and experimental results was achieved, indicating the high accuracy of the established CA model. Finally, the CA model was employed to investigate the hot deformation behavior of Cr12MoV die steel under multiple thermomechanical conditions. It could be found that a lower strain rate was beneficial to the occurrence of DRX. When the strain rate was beyond 1.0 s−1, the DRX fraction was very small. This work would provide a significant guidance to optimize the hot working process of Cr12MoV die steel or some other similar steels.

Cellular automaton simulation of dynamic recrystallization behavior in V-10Cr-5Ti alloy under hot deformation conditions

Abstract The deformation behavior of V-10Cr-5Ti alloy was studied on the Gleeble-1500 thermomechanical simulator at the temperatures of 950-1350 °C, and the strain rates of 0.01-10 s−1. Based on the Arrhenius model, dislocation density model, nucleation model and grain growth model, a numerical cellular automaton (CA) model coupling simulation of hot deformation is established to simulate and characterize the microstructural evolution during DRX. The results show that the flow stress is fairly sensitive to the strain rate and deformation temperature. The error between the predicted stress by the Arrhenius model and the actual measured value is less than 8%. The initial average grain size calculated by the CA model is 86.25 μm, which is close to the experimental result (85.63 μm). The simulations show that the effect of initial grain size on the dynamic recrystallization microstructure evolution is not significant, while increasing the strain rate or reducing the temperature can refine the recrystallized grains.

Microstructure Evolution of Dynamic Recrystallization of 42CrMo Steel during Multi-Stage Forging by FEM

Different process steps of the workpiece have different effects on the microstructure in the multi-stage forging. In this study, the effect of four different process steps of steering arm on microstructure was studied by FEM. Results have showed that upsetting is beneficial to refine the microstructure as well as finish forging. Especially drawing can make the distribution of microstructure homogeneous while bending has less effect on it. The already-designed forging process for steering arm was reasonable based on the simulation. Eventually, the grain size level of the steering arm was tested as 6.5 based on the conventional standard.

A simulation of dynamic recrystallization by coupling a cellular automaton method with a topology deformation technique

A quasi-synchronous integration model is constructed in this paper by coupling a cellular automaton (CA) model with a topology deformation technique for simulating the microstructure evolution of dynamic recrystallization (DRX). The uniform topology deformation technique based on vector operation can track the change of grain topology effectively during DRX simulation. The effects of topology deformation on the kinetics of DRX, mean grain size and effective nucleation sites are discussed in detail. This flexible simulation technique provides a novel way for investigating the dynamic microstructure evolution accompanied with plastic deformation on a mesoscale.