Papers by Keyword: Dynamic Recovery

Abstract: The microstructure evolution and the dynamic processes of grain refinement in a 304-type austenitic stainless steel during multiple calibre hot rolling at temperatures of 700-1000°C were studied. The structural changes are characterized by the elongation of original grains towards the rolling axis and the development of new fine grains, the mean size of which decreases with decreasing the deformation temperature. During multiple rolling at 1000°C, the new grains resulted from the development of discontinuous dynamic recrystallization involving a bulging of frequently corrugated grain boundaries. On the other hand, the new grain boundaries leading to remarkable refinement of original microstructure were developed at temperatures below 800°C as a result of continuous strain-induced reactions.

Abstract: Based on the warm tension test and metallurgical microstructure observations, the change of the microstructure of B340/590DP dual-phase steel, especially the change of grain size in different strain rates and temperatures, was studied in this paper. The results of the experiment show that: in the warm tension tests of the dual-phase steel, both the dynamic recovery and dynamic recrystallization affect the grain size, and the influence of dynamic recrystallization is stronger. In different rates of extension, the microstructure all has the minimum grain sizes in the medium term of the dynamic recrystallization. In the medium term of the dynamic recrystallization under different rates of extension, the minimum grain sizes increase as strain rate drops. The temperature in which the minimum grain size forms decreases as strain rates drops.

Abstract: The flow behavior and associated structural changes of an Inconel 600 superalloy were analyzed by using hot compression tests in the temperature and strain rate ranges of 850–1200 °C and 0.001 to 10 s^–1, respectively. The stress–strain curves exhibited the trend typical of materials in which deformation is recovery-controlled at high strain rates and low temperatures, while at low strain rates and high temperatures, the flow curves exhibited a softening typical of recrystallization phenomena. Constitutive analysis was carried out to investigate the hot deformation mechanism using the hyperbolic sine law.

Abstract: Soften behavior of 7050 aluminum alloy was investigated by high temperature compression tests conducted at 460 °C with different strain rates of 0.1, 1, 10 and 100 s-1. The results show that all the volume fractions of recrystallized grain and substructed grain of the 7050 aluminum alloy deformed at 460 °C with different strain rates are higher than 35% and 20%, respectively. Dynamic recovery and dynamic recrystallization are primary soften mechanism of the 7050 aluminum alloy deformation at 460 °C, which is not sensitive to strain rate. The recryatallization nucleation mechanisms of the 7050 aluminum alloy deformed at 460 °C include in grain boundary arch, subgrain growth and subgrain merging.

Abstract: Hot deformation tests were carried out on Al5083 – 2 %(vol) TiC nanocomposite in a temperature range of 250 – 450°C at varying strain rate of 0.01 – 1.0 sec^-1. Constitutive models were developed for the prediction of peak flow stress relating strain rate, true stress, temperature and activation energy. The percentage error between measured flow stress and constitutive model values were calculated to analyse the efficacy of the model in the prediction of peak stress. Finally, a window of working of the selected nanocomposite is established for finding out the safer region of working.

Abstract: Two 5Mn-1.5Al TRIP steels with and without Nb microaddition were developed in the present study. The steels contain bainite, martensite, interlath retained austenite and martensite- austenite islands. The paper presents the results of the compression tests carried out at various temperatures using the Gleeble simulator. To analyze the kinetics of static recrystallization in these steels, a softening kinetics were determined in a double-hit compression test. It was found that the dynamic recovery is a main thermally activated process occurring during hot deformation. The Nb microalloyed steel has higher flow stresses and peak strains than the Nb-free steel. A solute drag effect of Nb results in a slower softening kinetics of Nb containing steel. The effects of Mn on the retardation of Nb(C,N) precipitation and hot deformation characteristics are also discussed.

Abstract: The flow behavior and associated structural changes of an AZ61 Mg alloy were analyzed by using hot compression tests in the temperature and strain rate ranges of 250–400 °C and 0.001 to 1 s^–1, respectively. The stress–strain curves exhibited the trend typical of materials in which deformation is recovery-controlled in the high Z regime (Z is the Zener–Hollomon parameter), while at low strain rates and high T, the flow curves exhibited a softening typical of recrystallization phenomena. Microstructure analysis has been performed to correlate the microstructure changes to the flow behaviors.

Abstract: Based on the characteristics of the flow stress curves for one new kind of metastable Ti2448 titanium alloy from isothermal hot compression tests, the constitutive model was developed to describe the relation between flow stress and strain, strain rate, deformation temperature completely. During this process, the flow behavior of alloy at high temperature undergo flow softening caused by dynamic recovery (DRV) was modeled by the adopted hyperbolic sine function based on the unified viscoplasticity theory, the further drop in flow stress after the peak value in stress-strain curves was assumed to be caused by temperature rise and the constitutive model was modified accordingly. Additionally, the material constants were determined by optimization strategies, which is a new method to solve the nonlinear constitutive equation. The stress-strain curves predicted by the developed constitutive model well agree with experimental results, which confirms that the developed constitutive model gives an accurate estimate of the flow stress of Ti2448 titanium alloy and can provide an effect method to model the flow behavior of metastable titanium alloy at high temperature.

Abstract: The flow behaviour of material is strongly influenced by the microstructure evolution during hot deformation processes. In this work, a comprehensive mathematical modelling of heat transfer and plastic deformation was carried out employing finite element analysis based on rigidviscoplastic formulation. Semi-empirical models of dynamic recovery and recrystallization were utilized to develop the microstructure dependent constitutive equations. They were then integrated into the finite element code to simulate stress-strain curve of API-X70 steel during hot deformation process. Hot torsion tests were carried out at various deformation conditions for characterization of microstructure equations and model validation. The good agreement between experimental data and simulation results were achieved. The model predicts work hardening, dynamic recovery and recrystallization simultaneously and it considers their effects on the flow stress of the material during hot deformation.

Abstract: In this work, the hot deformation behavior of Fe₈₃Ga₁₇ alloy with 1.0 at.% B addition was investigated by plane strain compression tests on a Gleeble-1500 hot simulation test machine in the deformation temperature range of 350 to 900 °C. The effects of strain rate range 0.1-10 s^-1 on flow stress and microstructure were also studied. It was indicated that as the temperature increases, significant softening of the material occurred, and significant dynamic recovery at low strain rate (0.1 s^-1) and recrystallization at high strain rate (10 s^-1) occurred during deformation at 900 °C. The results also suggested that deformation mechanism under low temperature (~500°C) was twinning. The hot deformation activation energy (Q) of the Fe₈₃Ga₁₇ with 1.0 at.%B alloy was calculated to be 295.3 kJ/mol.