Papers by Keyword: Recrystallization

Abstract: The microstructure, texture, and tensile properties of hot extruded Mg-6Zn-1Y-1Ce alloy obtained at a temperature range of 300 °C to 400 °C were studied. Electron back-scatter diffraction (EBSD) results revealed that strong basal plane texture was found along extrusion direction in the sample extruded below 340 °C due to discontinuous dynamic recrystallization (DRX) mechanism. In the sample extruded at 340 °C the average value of Schmid factor (SF) of {0001}〈11-20〉 slip system was 0.09. However, the sample extruded above 370 °C had weak basal texture under the control of continuous DRX mechanism, and the SF was well-distributed with an average value of about 0.32. The strengths of as-extruded samples decreased with increase of extrusion temperatures. In addition to fine grain strengthening, texture strengthening had a significant contribution to the high strength for the sample extruded at low temperature.

Abstract: Corten steel is a type of weathering steel possessing high strength with low alloying elements content. The uniqueness of Corten steel lies in its excellent corrosion resistance to elements of nature, and having high strength to weight ratio among the carbon steels. The Corten steel is widely used in fabricating railway coaches, structures like bridges, etc. Even though the Corten steel is weldable, its inherent properties are lost during welding and other thermal processes. The behavior is due to the change in metallurgical and mechanical properties of Corten steel when undergoing processes exceeding the recrystallization temperature. Hence, necessitating the need for this research work. In this research work, the micro hardness, microstructure and grain size of Corten ASTM A242 Grade Steel was evaluated in as received normal condition and at recrystallization temperature. When the material is heated up to recrystallization temperature the formation of new grains is observed. Recrystallization had a positive impact on the microstructure and micro hardness of the Corten steel.

Abstract: Zirconium alloys are used in the nuclear industry due to their low neutron capture cross-section and resistance to corrosion, irradiation and creep. The microstructure of the nuclear fuel components evolves during the manufacturing route and can impact the subsequent processes or the final properties. Thus, numerical modeling of thermo-mechanical manufacturing processes is of interest to understand and master these microstructure evolutions.Numerical modeling of thermo-mechanical manufacturing processes with FORGE^® NxT software is applied. These models provide the thermo-mechanical history of the material at each integration point of the finite element (FE) mesh, which can be used to assess locally the continuous dynamic and post-dynamic recrystallization during hot extrusion.Mean-field models were developed in Python and integrated into FORGE^® NxT software, to quantify the microstructure evolution at the macro-scale of the component. Full-field models (DIGIMU^® software¹) were also developed for considering microstructural heterogeneities and the influence of initial microstructure at the mesoscopic scale while improving the mean-field equations by homogenization.After validation based on experimental results, these two recrystallization models provide complementary information to optimize the process parameters at the macro-scale and to better understand mesoscopic scale phenomena, such as:• At the macro-scale: influence of hot extrusion parameters on the continuous dynamic and post-dynamic recrystallization of Zircaloy-4.• At the meso-scale: influence of the initial microstructure on the recrystallization phenomena with improved precision. Indeed, the topology of the microstructure is predicted and not only the mean values/distributions of the state variables.

Abstract: Two schemes of thermomechanical processing of F420W cold-resistant steel to produce sheets with thickness of 5 and 15 mm for manufacture of wind turbine towers, were developed and tested in laboratory conditions. The first scheme simulated hot rolling on a continuous mill, including reductions with minimal inter-deformation pauses and subsequent slow cooling. The second one corresponded to hot rolling on a reverse mill with accelerated cooling. Mechanical properties were analyzed taking into account the related structural features. Technological recommendations for hot rolling of a thin sheet made of high-strength cold-resistant steel were proposed.

Abstract: The article investigates the effect of the strain rate on the driving force of recrystallization during hot working of the as-cast structure. For the study, we applied previously obtained experimental data of recrystallization kinetics during this stage of thermomechanical treatment. In addition, hot laboratory rolling, followed by saltpeter bath soaking, were performed in order to obtain supplemental data on grain structure size and orientations. Grain structure size was examined by optical microscopy, and its orientation was examined by X-ray texture analysis. The studies demonstrated, that overestimated recrystallization driving force not only results in erroneous kinetics estimation, but also gives excessive number of recrystallization centers and undersized grain structure. Besides, unaccounted effect of recrystallization driving force on grain size leads to distorted predictions of texture composition. In order to avoid this, it was recommended to apply an special exponential accumulated strain dependent coefficient.

Abstract: In the conditions of development of rates of the modern production the role of a heat treatment as a main way of receiving steels with the given structure and mechanical characteristics increases. The details applied on production have to have a long endurance not only at an ambient temperature, but also have high strength characteristics at low and high temperatures. In this regard, special attention is paid to the steel applied to manufacturing of such details. 13Mn6 steel concerns one of them. The definition of an influence of a heat treatment of steel - training at various temperatures, steel 13Mn6 on its rust resistance was the purpose of this work. For achievement of a goal such problems as a research of an influence of the various temperature of annealing of steel 13Mn6 on a value of hardness on Rockwell's method were solved; gravimetric researches after a heat treatment for identification of a temperature schedule of the annealing having the maximum indicators of corrosion were held. It is shown that, after spending vacation hardness of exemplars decreases with an increase in temperature. For assessment of corrosion aggression of the environment on the studied exemplars mass and deep indicators of corrosion were paid off. The maximum corrosion rate is observed when training, and the subsequent annealing at a temperature of 300°C, minimum at a temperature of annealing of 500°C.

Abstract: We investigate the effect of the cold reduction rate on ferrite recrystallization behavior during the annealing of low-carbon steel with different initial microstructures. Three types of hot-rolled sheet specimens are prepared: specimens P, B, and M, which consist of ferrite and pearlite, bainite, and martensite, respectively. To evaluate the effect of the cold reduction rate on ferrite recrystallization behavior, hot-rolled sheet specimens are cold-rolled at cold reduction rates of 40% and 67%. The cold-rolled sheet specimens are heated to the target temperature, and then water-quenched to room temperature. Irrespective of the initial microstructures, the ferrite recrystallization is accelerated by increasing the cold reduction rate. In addition, the dislocation densities of specimens P and B increase at the larger cold reduction rate, which accelerates ferrite recrystallization in these specimens. In the case of specimen M, the dislocation arrangement parameter remarkably decreases at the larger cold reduction rate, whereas the dislocation density hardly changes. Thus, we conclude that the accelerated ferrite recrystallization at the larger cold reduction rate for specimen M can be mainly attributed to an increase in the amount of interactions between dislocations in the specimen.

Abstract: The evolution of microstructural features such as local grain size and local grain size distribution are essential in view of the final physical and mechanical properties of the nickel base alloy 718 for aircraft parts forged in a multi-step production route. Due to increasing standards and the need of the prediction of fracture mechanical properties, a multi-class grain size model for a more detailed microstructure prediction is necessary. Therefore, a multi-class model considers the real initial non-uniform grain size distribution and structure of the pre-material at the beginning of the forging process, which affects the evolution of grain sizes during thermo-mechanical treatment and leads to different results than commonly used uniform grain structures. The initial distribution is defined by grain classes according the ASTM standard. It is shown that the presence of different classes and distributions of grains are as import as the applied strain, strain rate and temperature on dynamic, meta-dynamic and static recrystallization. Additionally, dissolution processes of delta phase and grain growth kinetics are included in the model to properly indicate the recrystallized fractions and represent the resulting multi-class microstructure. A series of simulations with different initial distributions is discussed and compared with examined forged samples in terms of the resulting microstructure for typical forging parameters. Based on these results the microstructure model can be used in combination with collected process data to predict the resulting properties and for the design of new aircraft parts.

Abstract: High-pressure torsion (HPT) was conducted under 6.0 GPa on commercial purity titanium up to 10 turns. An ultrafine-grained (UFG) pure Ti with an average grain size of ~96 nm was obtained. The thermal properties of these samples were studied by using differential scanning calorimeter (DSC) which allowed the quantitative determination of the evolution of stored energy, the recrystallization temperatures, the activation energy involved in the recrystallization of the material and the evolution of the recrystallized fraction with temperature. The results show that the stored energy increases, beyond which the stored energy seems to level off to a saturated value with increase of HPT up to 5 turns. An average activation energy of about 101 kJ/mol for the recrystallization of 5 turns samples was determined. Also, the thermal stability of the grains of the 5 turns samples with subsequent heat treatments were investigated by microstructural analysis and Vickers microhardness measurements. It is shown that the average grain size remains below 246 nm when the annealing temperature is below 500 °C, and the size of the grains increases significantly for samples at the annealing temperature of 600 °C.

Abstract: The aim of this work was to analyze the recrystallization behavior of cold rolled Aluminum/graphene composites during annealing. The Aluminum/graphene composite was cold rolled firstly, and then annealed at different temperature (250°C, 300°C, 350°C, 400°C) and for various time (1 h, 2 h, 8 h, 32 h). Full recrystallization did not occur until the annealing temperature was above 300 °C. With annealing temperature increasing from 250 to 300°C, the hardness of the composites decreased from 49.6 to 27.6 HV. Grain growth were not observed at high annealing temperature and longer annealing time, which suggested that Graphene has strong pinning effect on the grain boundary of Aluminum.