Papers by Keyword: Static Recrystallization

Abstract: Understanding and predicting static recrystallization (SRX) behavior is crucial for controlling the microstructure and mechanical properties of metals during thermomechanical processing. Among various numerical modelling approaches that can be used to support experimental studies on this topic is the cellular automata (CA) method. This approach gained significant attention due to its ability to simulate microstructural evolution at the mesoscale with high spatial resolution. However, the main limitation of CA models is their significant simulation time, especially for the 3D computational domains. Therefore, the paper focuses on enhancing the efficiency of CA SRX simulations to deliver results within an acceptable time frame. The goal is to minimize computation time and memory usage through code-level optimization, without altering the hardware or compiler settings. Optimization is performed on the sequential version of the validated CA SRX code. Initially, the source code was analyzed using a profiler tool to identify performance bottlenecks. The most inefficient parts of the code were then reimplemented to eliminate these bottlenecks. Optimization methods included eliminating redundant functions, modifying neighbor assignments in the automata space, reducing class data structures, enabling direct access to attributes, simplifying mathematical formulas, and removing unused objects. The obtained results are also validated against the output from the sequential version to ensure the model's predictive capabilities. The work clearly demonstrates that the optimization improved simulation efficiency across all tested variants, with only minor increases in memory usage.

Abstract: High-entropy alloys (HEAs), owing to their exceptionally favourable strength–ductility balance, are regarded as promising candidates for applications in the energy, automotive, and aerospace industries. A defining characteristic of face-centered cubic (FCC) high-entropy alloys is their low stacking fault energy, which facilitates deformation via mechanical twinning and promotes the activation of transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP) mechanisms. The present study focuses on the development of a heterostructured material composed of CoNiFeMn and (CoNiFeMn)₉₅Mo₅ alloys. Furthermore, the Erichsen cupping test was performed to assess the formability of the produced material and to evaluate its suitability for deep drawing applications.

Abstract: Determination of the influence of grain boundary curvature model type on the cellular automata (CA) static recrystallization (SRX) simulation predictions is the primary goal of the research. The developed CA model is a full-field approach that captures local heterogeneities in grain morphology, crystallographic orientation, and distribution of stored deformation energy. The main driving force of the model is the value of the stored energy; however, the curvature of the grain boundary may also play a role during the recrystallization. Therefore, different variants of grain boundary curvature calculations within the discrete computational domain during recrystallization and additionally subsequent grain growth are compared within this work.

Abstract: The Co-20Cr-15W-10Ni (CCWN, mass%) alloy has excellent corrosion resistance and strength-ductility balance and is applied in almost all balloon-expandable stent platforms. To further reduce the invasiveness of stent placement, it is necessary to reduce the diameter of the stent. That is, both high strength and high ductility should be achieved while maintaining a low yield stress. In our previous studies, it was discovered that low-temperature heat-treatment (LTHT) at 873 K improves the elongation of the CCWN alloy. In this study, we focused on the grain refinement by swaging and static recrystallization to improve the strength of the alloy. The as-swaged alloy was recrystallized at 1373–1473 K for 100–300 s, followed by LTHT. A fine grain structure with an average grain size of 3–17 μm was obtained by static recrystallization. The η-phase (M₁₂X-M₆X type precipitates, M: metallic elements, X: C and/or N) formed during the recrystallization at 1373–1448 K. The alloys recrystallized at 1448 and 1473 K had a homogeneous structure with a small variation in the grain size. On the other hand, the alloys recrystallized at 1373 and 1423 K had an inhomogeneous structure in which fine and coarse grains were mixed. Both the strength and ductility of the CCWN alloy were improved by combining high-temperature short-time recrystallization and LTHT.

Abstract: Refinement and uniform austenite grains are essential to obtain excellent and homogenous properties for non-quenched and tempered steel, which is mainly affected by static recrystallization of the rolling process. Using the Gleeble-3500 thermal simulation test machine, 20% compression test was carried out for two passes at 850~1050 °C (interval of 50 °C) and different pass interval time conditions to study the static softening and recrystallization behavior of 38MnSiVS non-quenched and tempered steel during deformation process. The effects of strain rate, deformation temperature and interval time on static softening rate and austenite recrystallization fraction were analyzed. The results showed that the increase of deformation temperature and the increase of pass interval time had more significant impact on the static recrystallization volume fraction of 38MnSiVS steel, while the influence of strain rate was relatively smaller. When the deformation temperature was 950 °C or higher, the non-conditioning steel 38MnSiVS could undergo complete recrystallization, and partial recrystallization occurred in the temperature range of 850-950 °C. A static recrystallization volume fraction model of non-regulatory steel 38MnSiVS was established. The static recrystallization activation energy was 296.7 kJ·mol^-1, and the static recrystallization volume fraction model had a relative error of 2%.

Abstract: The understanding of the softening behaviour during the hot rolling process is required to optimize the hot rolling schedule. Therefore, the microstructural evolution in the hot rolling of austenitic stainless steel was simulated. In this work, kinetics of grain growth was investigated by means of compression tests using the Gleeble HDS V40 and described by appropriate kinetic equations based on the obtained experimental results. Moreover, numerical simulation was performed using the Simufact.forming software. The results of the numerical simulation were further validated by experimental data, which were obtained from the labour continuous hot rolling of the austenitic stainless steel.

Abstract: In a previous study, the damping capacity gradually increased with increasing annealing time and temperature in AZ31. Also, at damping capacity test under similar conditions, AZ61 with a higher solute content showed a more rapid microstructure change than AZ31. In this study, it was investigated damping capacity on various aluminum concentration conditions in order to damping capacity that was influenced by microstructure and solute content. Three types such as pure Mg, AZ31 and AZ61 alloy of specimens were rolled at 673K with a rolling reduction of 30%, respectively. The annealing were conducted at various temperature and time. In this study, static recrystallization was occurred under all annealing conditions. The hardness gradually decreased until 60 minutes after the heat treatment. All annealing conditions, the damping capacity gradually increased with increasing annealing time and temperature. Especially, damping capacity and C₁ value were increased with a decreasing of solute content.

Abstract: During hot rolling, austenite recrystallization determines the grain size evolution and the extent of strain accumulation, and therefore, it can be used to tailor the microstructure and mechanical properties of the final product. However, at the moment, models describing the recrystallization kinetics of high-Mn steels are scarce and they do not take into account the effect of the alloying elements present in these steels. The aim of this work is to provide a quantitative model for the determination of the static recrystallization kinetics valid for a wide range of high-Mn steel compositions. Softening data determined for steels with different Mn (20 to 30%), Al (0 to 1.5%) and C (0.2 to 1%) levels at different strain, strain-rate and temperature conditions were analyzed. Static recrystallization of the investigated high-Mn steels follow Avrami’s law, with n Avrami exponents which are temperature dependent and lower than those determined for low C steels. A dependence of the t0.5 (time for 50% fractional softening) on the carbon content has been also observed and it was incorporated into an equation for the calculation of this parameter.

Abstract: Semi-empirical models for predicting the austenite static recrystallization behavior are widely used in designing thermomechanical treatments to improve final mechanical properties. However, a problem with these models is that their utility can be limited to the range of deformation conditions and chemical compositions they were developed for. This work focuses on the study of the applicability of current recrystallization models to the range of low strain conditions and/or high Nb microalloying additions (≈0.1%). To do so, the recrystallization behavior of two low carbon Nb-Ti microalloyed steels (0.04 and 0.11% Nb and ≈0.01% Ti) has been investigated by torsion tests. Experimental results for recrystallization time and recrystallized grain size have been compared to previously developed equations. It has been observed that at low strains (ε = 0.1) the predictions fail. A dependence of the n Avrami exponent both on temperature and applied strain was also found.

Abstract: Recrystallization kinetics of aluminum with various purities from 99.5 to 99.999(5N) has been investigated in this study. Aluminum plates of 10 mm thickness with various purities were solution-treated at 400^oC for 24 hrs and then rolled into sheets of 50 μm thickness at room temperature. Cold rolling was conducted on samples with various purities from 99.9 to 99.999 including commercial AA 1050 Al alloy and high purity through about 20 passes to obtain thin foils of 50 μm thickness. Accumulative rolling was employed when sample thickness reached at 1 mm and thin foils were successfully obtained for all samples. Hardness was measured just after cold rolling at room temperature as a function of time up to 1hr to elucidated recrystallization behavior. For aluminum with 99.999% purity, recrystallization occurred after 200 s and finished at 360 s. Recrystallization kinetics of aluminum at high temperatures from 100 to 350^oC were investigated by measure hardness after annealing thin foils for various time intervals ranging from 1 s to 24 hrs. For high purity sample with 99.999% purity, recrystallization finished just after 1 s even at the relatively low temperature of 100^oC, while recrystallization of commercial AA 1050 (2N) alloy finished after 360 s at 350^oC.