Papers by Keyword: Zener-Hollomon Parameter

Abstract: The behavior of a 13% chromium steel subjected to hot deformation has been studied by performing hot compression tests in the temperature range of 850 to 12000C and at strain rates from 0.01 to 10 s^-1. The uniaxial hot compression tests were performed on a Gleeble thermo-mechanical simulator. The best function that fits the peak stress for the material and its relation to the Zener-Hollomon parameter (Z) is derived. The average activation energy of this alloy in the entire test domain was found to be about 557 [kJmol^-1] and the dynamic recrystallization (DRX) kinetics was studied to find the fraction DRX during deformation.

Abstract: Numerical estimation of rolling load and torque often showed large discrepancies when compared with experimental values. This was attributed to difficulty in estimating the mean rolling temperature from the available data. This work is thus directed at obtaining a good estimate for the mean rolling temperature which can effectively be used for load and torque estimates. Hot flat rolling stimulation by use of the Bland and Ford’s cold rolling (HRBF) theory confirmed the reverse sandwich effect in selected carbon steels at low strain rates. In this work, the effect of pass reduction on rolling temperature distribution, yield stress and rolling load were studied for AISI Type 316 stainless steel (HSCSS316). For this new simulation, at low and high strain rates, results showed that the ratio of experimental to calculated rolling load and torque were higher at lower reduction than at higher reduction. These results confirmed excess load and torque in the hot rolling of HSCSS316 low reductions. The results obtained from Hot Rolling Bland and Ford’s Theory based on Root Mean Square rolling temperature were in good agreement with values obtained using Reverse Sandwich Model and the Reverse Sandwich- Hot Rolling Bland and Ford’s Program under the same rolling conditions.

Abstract: Friction stir processing (FSP) is one of the severe plastic deformation (SPD) processes. It has been reported that SPD-processed Al with various purities attained a minimum grain size when Zener-Hollomon parameter is larger than 10¹⁶ s^-1. The minimum grain size is different by purity level and alloying elements. We investigated the influence of Fe solute atoms on grain refinement of high-purity Al on the condition that Zener-Hollomon parameter was larger than 10¹⁶ s^-1. FSP was conducted on Al-0.01%Fe, which was fabricated by using 5N Al (99.999% purity). FSP-ed Al-0.01%Fe exhibits the minimum grain size of 1.4 μm, although high-purity aluminums with more than 99.998% exhibits much larger minimum grain sizes of 30-40 μm. Only 101 at.ppm Fe played a critical role in the grain refinement of pure aluminums.

Abstract: In this work, plastic flow behavior of an as-cast manganese aluminum bronze was investigated under various compressive deformation conditions. The forming temperatures of 1023, 1073, 1123 and 1173 K and strain rates of 0.01, 0.1, 1.0 and 10 s^-1 were considered. It was found that all obtained stress-strain responses of manganese aluminum bronze showed a single peak stress that afterwards approached a steady flow stress. Additionally, constitutive equations based on the Arrhenius model were applied for describing the determined flow stresses, in which Zener-Hollomon parameter in a hyperbolic-sine function was taken into account. By the flow stress modeling, the activation energy of about 194 kJ/mol was calculated for the examined manganese aluminum bronze.

Abstract: The paper presents the results of a complex study of the Ti-6Al-4V alloy, conducted with the application of the dynamic material modelling (DMM) method, in a wide range of temperatures, strain rates and strains. A compression test was carried out in a wide range of temperatures (800 – 1100°C) and strain rates (0.01 – 100 s^-1), up to the constant final true strain value of 0.9. The obtained stress-strain curves were a basis for determining deformation activation energy with the use of an Arrhenius plot and a correlation between the Zener-Hollomon parameter and flow stress, for which the constitutive equation proposed by Sellars was used. The power dissipation efficiency parameter was calculated. The maps of power dissipation as the function of temperature and strain rate were plotted in the form of the isoclines of the power dissipation efficiency parameter expressed in %. The processing maps exhibited the range of occurrence and recrystallization of the primary α phase, the degree of the β phase recrystallization progress against the background of the process deformation windows and instability flow domain. An analysis of the influence of process parameters up on the microstructure and hardness changes was conducted.

Abstract: Axisymmetric compression tests using Gleeble 3800 simulator were carried out to investigate hot deformation behaviors of an AA5083 alloy under high strain rate conditions. Sharp temperature rise and load cell ringing characterized by severely vibrational load responses were encountered at strain rates higher than 20 s^-1 and sample buckling occurred at low temperatures. The load cell ringing was corrected using a moving average method with a two-way filtering operation to correct phase distortion. Isothermal flow curves were obtained by fitting the instantaneous temperatures into a binomial function, while buckling was correlated with sample height and Young’s modulus. After the corrections, hyperbolic sine equation was successfully used to extend from the hot tensile data having strain rates lower than 3 s^-1 to 100 s^-1. Quantitative analyses were accordingly made over the effects of temperature, strain rate and work hardening behavior on the flow curves. The previous constitutive equation in form of temperature, strain and strain rate was modified to predict the hot deformation resistance of the AA5083 alloy at temperatures of 250-450^oC under the high strain rate operations.

Abstract: Calculation of the critical condition for the initiation of DRX is of considerable interest for the modeling of industrial processes but it strongly depends on the chemical composition of the material, the grain size prior to deformation, and the deformation conditions ( T and ε ). This paper was therefore to show an approach that allows for accurate but convenient identification of the occurrence of DRX. For a Fe-Cr-Ni super stainless steel, the results show that there is a linear relationship between σc and lnZ ( σc=457.26-12.52lnZ). In addition, within the entire range of temperature and strain rate studied, it can be found that the values of both σc and σp or εc and εp keep similar variation trends, respectively. Finally, it was found that the critical ratios of both σc/σp and εc/εp remain fairly constant (≈0.92 and ≈0.47, respectively).

Abstract: The hot compressive deformation behavior of SWRCH 35K was studied with uniaxial hot compression simulation tests at 923 ~ 1223 K and strain rate of 0.01 ~ 20 /s. The results show that the hot compressive deformation activation energy was 408 kJ/mol and the rang of deformation stored energy was 10 ~ 50 J/mol. The quadratic fitting expression between deformation stored energy and Zener-Hollomon parameter (Z) was established and the deformation stored energy was considered to increased with increasing Z or with lower deformation temperature and increasing deformation rate.

Abstract: This paper presents an investigation about the occurrence of the dynamic recrystallization (DRX) during hot forming. Two 7075 aluminum alloy samples in different initial states were examined by compression tests at temperatures between 573 K and 723 K and constant strain rates ranging from 0.002 to 2 (s-1) with the maximum strain of 0.5 mm/mm. The activation energies of the examined aluminium were calculated, being 137.7 kJ/mol and 142.4 kJ/mol. The critical stresses and strains for the initiation of the dynamic recrystallization were determined using a numerical method based on the changes of the work hardening rate (θ) as a function of the flow stress (σ) or a strain (ε), respectively. Based on the micrographs taken after the deformations it was revealed that in some cases only dinamyc recovery (DRV) whereas in others DRX occurred under the applied examination conditions. The critical stress which belongs to the onset of the DRX or the DRV depend on the temperature, the strain rate, and the initial grain size. The critical and maximal stresses and the corresponding strain values at different conditions were determined. In the examined range of deformation, temperature and strain rate, the critical rations are σ_c/σ_p= (0.93-0.99) and εc/ εp = (0.3-0.74), respectively.

Abstract: Tensile experiments were carried out on advanced high strength steel (AHSS) by the test machine Gleeble3500, under the temperature ranging from 650 to 850 and the strain rate of 0.1/s~5/s, and the corresponding stress-strain curves were obtained. The peak stress level decreases with the increasing of deformation temperature or the decreasing of strain rate, which can be represented by a ZenerHollomon parameter in a linear equation. A revised model describing the relationships between the peak stress, strain rate and temperature of advanced high strength steel at elevated temperatures was proposed by compensation of strain and strain rate. The comparison of the predicted and experimental results of stressstrain curve can prove the good predictive power of the model, the Adj. R-Square between the peak stress and the linear equation was reached to 0.97.