Papers by Keyword: Hot Working

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Authors: Matthew R. Barnett, Aiden G. Beer
Abstract: An analytical approximation for the steady state dynamic recrystallized grain size is combined with a simple nucleation criterion to assess the propensity for dynamic recrystallization. In line with observation, the criterion predicts dynamic recrystallization in 99.9995% pure Al but not in material 99.5% pure. It also agrees with the observation that zone refined ferrite can display dynamic recrystallization at high temperatures and low strain rates but not at lower hot working temperatures. The criterion is applied here to common wrought magnesium alloys to argue that conventional dynamic recrystallization is expected under "normal" hot working conditions.
369
Authors: Mohamad El Mehtedi, Samer El Mohtadi, Stefano Spigarelli
Abstract: A new constitutive relationship based on the combination of the Garofalo and Hensel-Spittel equations has been developed and successfully used to model the plastic flow of a AA6082 aluminum alloy. Two regimes of temperature and strain rate were identified: the constitutive analysis suggested that in the low strain rate/high temperature regime, deformation was controlled by viscous glide of dislocations in atmospheres of Mg solute atoms, while in the high strain rate/ low temperature regime, deformation was controlled by climb.
59
Authors: Fu Guo Li, Xiao Na Wang, Xiao Lu Yu
Abstract: This paper advances a new optimization method about material constitutive equation on the basis of physical simulation and numerical simulation results which basic thinking can be described as the following: through comparing the results of the material deformation process under actual experimental conditions and virtually simulated by the finite element numerical simulation method with the constitutive equation established on the basis of the physical simulation, the constitutive equation established by the experimental data is optimized in turn. Based on it, this paper advances a visco/plastic constitutive equation to depict the semi-solid thixo-forming and the constitutive equation is analyzed and optimized through coupling of the physical simulation and numerical simulation. It is observed that this method can effectively eliminate the influence of the factor outside material itself on the constitutive equation. So, it can exactly depict the deformation behavior of the materials and improve the accuracy and reliability of the numerical simulation.
402
Authors: D. Jorge-Badiola, J.L. Lanzagorta, Isabel Gutiérrez
Abstract: A reversion of the strain produces a modification of the static recrystallization kinetics. Initially, the reversion increases the recrystallization time, that reaches a maximum at a certain strain, and decreases again for increasing reverse strains. This transient on recrystallization kinetics develops over a strain interval similar to that of the microstructural and stress-strain transients. At strains beyond the transient, the reversion can be regarded as a shift on the strain axis. However, at the authors knowledge there is no formulation able to describe the material behaviour during the transient. The present work introduces an equivalent strain concept based on the substructural dissolution/build-up processes taking place as a result of the strain reversal. This formulation allows including the effect of the strain path on recrystallization models.
643
Authors: Bradley P. Wynne, R. Bhattacharya, Bruce Davis, W.M. Rainforth
Abstract: The dynamic recrystallisation (DRX) behaviour of magnesium AZ31 is investigated using a plane strain compression (PSC) testing machine at 450°C. The variables included strain rate, double hit including intermittent anneal and double hits with different strain rate at each hit. The alloy shows higher peak stress and strain with increasing strain rates. Predominant basal texture with different intensities are observed at different strain rates. The annealing treatment between double tests leads to strong basal texture. Reversal of strain rate during double hit results in similar flow curves. This shows that in AZ31 alloy, DRX mechanism is independent of the initial microstructure and only depends on the test condition viz. temperature, strain rate and total equivalent strain.
164
Authors: L. Sanz, B. Pereda, B. López
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.
1170
Authors: Fritz Appel, Michael Oehring, Jonathan H.D. Paul
Abstract: Intermetallic titanium aluminide alloys are multiphase assemblies with complex microstructure and constitution, involving the phases γ(TiAl), α2(Ti3Al), β, and B2. The earlier stages of phase transformation and dynamic recrystallization occurring upon hot-working of such an alloy were investigated at the atomic scale by high-resolution electron microscopy. Accordingly, the conversion of the microstructure is triggered by heterogeneities in the deformation state and non-equilibrium phase composition. The β/B2 phase is apparently unstable under tetragonal distortion, which gives rise to the formation of the B19 phase via distinct shuffle displacements. These processes lead to a modulated microstructure, which is comprised of several stable and metastable phases. The phase transformations are accomplished by the propagation and coalescence of ledges. Large and broad ledges can apparently easily be rearranged into intermediate metastable structures, which serve as precursor for the nucleation of new grains.
465
Authors: Werner Ecker, Thomas Antretter, R. Ebner
Abstract: Pressure casting dies are subjected to a large number of thermal as well as mechanical load cycles, which are leading to a characteristic thermally induced crack network on the die surface. As a typical representative for a die material the cyclic thermo-mechanical behavior of the hot work tool steel grade 1.2343 (X38CrMoV5-1) is investigated both experimentally as well as numerically. On the one hand the information from isothermal compression-tension tests is used in a subsequent analysis to calibrate a constitutive model that takes into account the characteristic combined isotropic-kinematic hardening/softening of the material. On the other hand the non-isothermal mechanical response of the material to thermal cycles is characterized by means of a periodic laser pulse applied to a small plate-like specimen which is cooled on the back. The residual stresses developing at the surface of the irradiated region of the specimen are determined ex-situ by means of X-ray diffraction. The obtained values agree well with the results of an accompanying finite-element study. This information is used to verify the calibrated constitutive model. The material law is finally used for the prediction of stresses and strains in a die.
685
Authors: Zhi Yu Chen, De Ning Zou, Huan Liu, Hong Bo Wang
Abstract: Elevated compression tests were conducted on 2205 duplex stainless steel using a Gleeble 3800 thermal simulator under constant strain rates ranging from 0.1 s−1 to 50 s−1 and at deformation temperatures ranging from 900°C to 1200°C for the sample. All tests were performed at a total true strain of 0.9. The elevated temperature deformation behavior of the 2205 duplex stainless steel was characterized based on an analysis of the stress–strain curves. A set of constitutive equations for 2205 duplex stainless steel was proposed by employing hyperbolic sine function. The equations revealed the dependence of flow stress on strain, strain rate and temperature. In order to evaluate the accuracy of the constitutive equations, the mean errors of flow stress between the experimental data and predicted results were calculated. The results showed that there was a good agreement between the prediction and experimental values.
381
Authors: Ran Xu Yu, Shi Yi Wang, Qiong Tang, Xiao Qin Zeng
Abstract: Gleeble 3500 thermo mechanical simulator was used to perform hot compression tests of GW103K (Mg-10Gd-3Y-0.6Zr) magnesium alloy at a temperature range of 573K-723K and strain rates of 0.001-1. The workability of the alloy can be evaluated by means of processing maps on the basis of dynamic materials model (DMM) and the superior processing condition is selected. Combining true compression stress-strain curves with the results of microstructure observation, it was found that the peak stress decreased observably as the decrease of strain rate and the increase of deformation temperature. Constitutive equation is built to reveal the accurate relationship among flow stress, temperature and strain rate.
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