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J J Jonas - One of the best experts on this subject based on the ideXlab platform.
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flow softening twinning and dynamic recrystallization in az31 magnesium
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2013Co-Authors: J J Jonas, Xiao Liu, B W ZhuAbstract:Abstract The compression tests were carried out on AZ31 magnesium alloy samples at temperatures from 300 to 450 °C and Strain rates of 0.03–0.3 s−1. The evolution of the microstructure and texture was followed and the volume fractions recrystallized were determined as a function of Strain and temperature. The flow curves were analyzed using the double differentiation method and double minima were detected on all the curves. The first set of minima is shown to identify the Critical Strain for twinning, while the second set indicates the Critical Strain for the initiation of dynamic recrystallization. The texture analysis and EBSD results indicate that flow softening is mainly caused by the grain reorientations brought about by twinning. The remainder of the flow softening is associated with the volume fraction recrystallized. The microstructure analysis shows that the volume fraction recrystallized does not approach its asymptotic value of one even during steady state flow.
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determination of the Critical Strains for the initiation of dynamic transformation and dynamic recrystallization in four steels of increasing carbon contents
Steel Research International, 2013Co-Authors: Chiradeep Ghosh, Vladimir V Basabe, J J JonasAbstract:Hot torsion tests are carried on three plain carbon steels and a Nb microalloyed steel of increasing C concentrations. The tests are performed at Strain rates up to 4 s−1 and over the temperature range 743–917°C. The onsets of dynamic transformation (DT) and dynamic recrystallization (DRX) are detected using the double-differentiation method. Both mechanisms are initiated under all testing conditions but one. The Critical Strain for DT increases with temperature while the reverse dependency is exhibited by the Critical Strain for DRX.
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Critical Strain for dynamic recrystallization in variable Strain rate hot deformation
Isij International, 2003Co-Authors: Evgueni I Poliak, J J JonasAbstract:In rolling, the Strain rate in a rolling pass is not constant but depends on pass reduction r p , decreasing or increasing along the arc of contact. In the present work, high temperature compression tests were performed with the rate varying according to Strain rate profiles pertaining to various flat rolling pass reductions. Due to the high rate sensitivity of the stress at elevated temperatures, the stress follows such variations in Strain rate. This can lead to peaks in the flow curves without regard to dynamic recrystallization (DRX). Nevertheless, Critical Strains for the onset of DRX can still be defined if the stresses and Strains in variable Strain rate deformation are normalized by the peak stresses and Strains that would be observed if the deformation were being performed at a series of constant Strain rates equal to that of successive points along the roll bite. Using plain carbon and Nb-bearing steels, it is demonstrated that the DRX Critical Strains are lower when r p 30% than in constant e deformation at the same initial Strain rate. The present method permits the more accurate extrapolation of laboratory test results to industrial conditions and enables rolling loads to be analyzed with greater precision.
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design of dynamic recrystallisation controlled rolling schedules for seamless tube rolling
Materials Science and Technology, 1992Co-Authors: L N Pussegoda, Peter Hodgson, J J JonasAbstract:AbstractA model developed by Sellars and Dutta, for Strain induced carbonitride precipitation under isothermal conditions, is extended to precipitation under continuous cooling conditions. It is applied here to laboratory simulations of the stretch reducing stage of a seamless tube mill. The model predictions are compared with experimental observations of the contrasting rolling behaviours of Ti–V and Nb–V steels and excellent agreement is obtained. It is shown that in order to design dynamic recrystallisation controlled rolling (DRCR) stretch reducing mill schedules, the Critical Strain for dynamic recrystallisation must be achieved well before the onset of Strain induced precipitation. If, however, precipitation begins before the Critical Strain is reached, then ‘pancaking’ occurs. Thus, Ti–V steels are more suitable for DRCR processing, because Strain induced precipitation takes place only at very low temperatures in these materials. As a result, rolling can be carried out at relatively low temperature...
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design of dynamic recrystallisation controlled rolling schedules for seamless tube rolling
Materials Science and Technology, 1992Co-Authors: L N Pussegoda, Peter Hodgson, J J JonasAbstract:Abstract A model developed by Sellars and Dutta, for Strain induced carbonitride precipitation under isothermal conditions, is extended to precipitation under continuous cooling conditions. It is applied here to laboratory simulations of the stretch reducing stage of a seamless tube mill. The model predictions are compared with experimental observations of the contrasting rolling behaviours of Ti–V and Nb–V steels and excellent agreement is obtained. It is shown that in order to design dynamic recrystallisation controlled rolling (DRCR) stretch reducing mill schedules, the Critical Strain for dynamic recrystallisation must be achieved well before the onset of Strain induced precipitation. If, however, precipitation begins before the Critical Strain is reached, then ‘pancaking’ occurs. Thus, Ti–V steels are more suitable for DRCR processing, because Strain induced precipitation takes place only at very low temperatures in these materials. As a result, rolling can be carried out at relatively low temperatur...
Peter Hodgson - One of the best experts on this subject based on the ideXlab platform.
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predicting the Critical Strain for dynamic recrystallization using the kinetics of static recrystallization
Scripta Materialia, 2000Co-Authors: Matthew Barnett, Georgina Kelly, Peter HodgsonAbstract:School of Engineering and Technology, Deakin University, Pigdons Rd, Geelong, VIC 3217,Australia(Received November 12, 1999)(Accepted March 9, 2000)Keywords: Steels-austenite; Dynamic recrystallization; Recrystallization1. IntroductionOne view of dynamic recrystallization is that it comprises static recrystallization occurring in the timescale of deformation. While this is clearly not true for geometric dynamic recrystallization [1] orcontinuous dynamic recrystallization [1], there is some metallographic support for it with respect to thebeginning of conventional dynamic recrystallization. The microstructure after a few volume percent ofrecrystallization by this mechanism appears very similar to that seen after a small degree of staticrecrystallization [2,3].A number of workers have constructed mathematical equations for the beginning of conventionaldynamic recrystallization (DRX) using a formulation based on the nucleation mechanisms of staticrecrystallization (SRX) [2,4,5]. These models fit the observed trends in DRX quite well. However, theydo not allow any firm conclusions to be drawn with respect to the relative kinetics of the two processes.In the present work, conventional equations for the kinetics of SRX are modified to allow “SRX” tobegin prior to the end of deformation. In this manner a Critical Strain for the beginning of “SRX” duringdeformation is derived. This value is then compared with observations of the Critical Strain required forthe initiation of DRX in steel.2. BackgroundThe static recrystallization kinetics following the hot deformation of steel are often expressed in termsof the time taken after deformation for 50% recrystallization (t
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design of dynamic recrystallisation controlled rolling schedules for seamless tube rolling
Materials Science and Technology, 1992Co-Authors: L N Pussegoda, Peter Hodgson, J J JonasAbstract:AbstractA model developed by Sellars and Dutta, for Strain induced carbonitride precipitation under isothermal conditions, is extended to precipitation under continuous cooling conditions. It is applied here to laboratory simulations of the stretch reducing stage of a seamless tube mill. The model predictions are compared with experimental observations of the contrasting rolling behaviours of Ti–V and Nb–V steels and excellent agreement is obtained. It is shown that in order to design dynamic recrystallisation controlled rolling (DRCR) stretch reducing mill schedules, the Critical Strain for dynamic recrystallisation must be achieved well before the onset of Strain induced precipitation. If, however, precipitation begins before the Critical Strain is reached, then ‘pancaking’ occurs. Thus, Ti–V steels are more suitable for DRCR processing, because Strain induced precipitation takes place only at very low temperatures in these materials. As a result, rolling can be carried out at relatively low temperature...
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design of dynamic recrystallisation controlled rolling schedules for seamless tube rolling
Materials Science and Technology, 1992Co-Authors: L N Pussegoda, Peter Hodgson, J J JonasAbstract:Abstract A model developed by Sellars and Dutta, for Strain induced carbonitride precipitation under isothermal conditions, is extended to precipitation under continuous cooling conditions. It is applied here to laboratory simulations of the stretch reducing stage of a seamless tube mill. The model predictions are compared with experimental observations of the contrasting rolling behaviours of Ti–V and Nb–V steels and excellent agreement is obtained. It is shown that in order to design dynamic recrystallisation controlled rolling (DRCR) stretch reducing mill schedules, the Critical Strain for dynamic recrystallisation must be achieved well before the onset of Strain induced precipitation. If, however, precipitation begins before the Critical Strain is reached, then ‘pancaking’ occurs. Thus, Ti–V steels are more suitable for DRCR processing, because Strain induced precipitation takes place only at very low temperatures in these materials. As a result, rolling can be carried out at relatively low temperatur...
Soheil Solhjoo - One of the best experts on this subject based on the ideXlab platform.
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determination of flow stress and the Critical Strain for the onset of dynamic recrystallization using a sine function
arXiv: Materials Science, 2014Co-Authors: Soheil SolhjooAbstract:A new model has been developed to estimate the flow stress under hot deformation conditions up to the peak of the stress-Strain curves. The model is constructed on the basis of the general form of sine functions by introducing an additional exponent. Besides, an equation is derived from the model, which could be used to predict the Critical Strain for the onset of dynamic recrystallization. The model has been examined for a 304 austenitic stainless steel. The estimated flow stress had an average percentage error of %1.66.
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determination of flow stress and the Critical Strain for the onset of dynamic recrystallization using a hyperbolic tangent function
Materials & Design, 2014Co-Authors: Soheil SolhjooAbstract:A new model has been developed to estimate the flow stress under hot deformation conditions up to the peak of the stress–Strain curves. This model is derived from the general form of hyperbolic function by introducing an additional parameter to bring the results to a more acceptable level. Stress–Strain curves and the Critical Strain of a ‘304 austenitic stainless steel’ are determined with an average percentage error of 1.24. The model is also used to obtain an equation which has the ability of predicting the Critical Strain for the onset of dynamic recrystallization.
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determination of Critical Strain for initiation of dynamic recrystallization
Materials & Design, 2010Co-Authors: Soheil SolhjooAbstract:Abstract Using the work hardening rate–Strain curves, an effective mathematical model has been developed to predict the stress–Strain curves of alloy steel during hot deformation up to the peak stress regardless of the level of the Strain, weather smaller or larger than the Critical Strain. This model is expressed in terms of peak stress, peak Strain and one temperature-sensitive parameter, S . In addition, one new model, which is a function of peak Strain, was proposed to predict the Critical Strain for the initiation of dynamic recrystallization using the second derivative of work hardening rate with respect to stress. Besides the theoretical study, the analysis is used to determine the stress–Strain curves and Critical Strain of 304 austenitic stainless steel. The predicted results were found to be in accord with the experimental data.
Gregory G Deierlein - One of the best experts on this subject based on the ideXlab platform.
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void growth model and stress modified Critical Strain model to predict ductile fracture in structural steels
Journal of Structural Engineering-asce, 2006Co-Authors: Amit Kanvinde, Gregory G DeierleinAbstract:Material tests and analyses are presented to investigate the accuracy of two micromechanics-based continuum criteria for predicting ductile crack initiation in low-carbon steels, which are representative of mild steels used in civil engineering construction. Referred to as the stress modified Critical Strain (SMCS) model and the void growth model (VGM), both criteria integrate plastic Strains and triaxial stresses to predict crack initiation associated with the mechanisms of void initiation, growth and coalescence. The models are suitable for implementation through finite-element analyses to simulate fracture initiation in steel structures. Material tests and finite-element analyses of seven varieties of structural steels, including two new high-performance steels, are conducted to validate and calibrate the model parameters for practical structural engineering applications. Both models are shown to predict fracture accurately across the spectrum of steel samples and geometric configurations. However, application of the models to situations with high stress and Strain gradients is shown to be quite sensitive to the characteristic length parameter of the models, which leads to large model variability in such cases. A strong empirical relationship between Charpy V-notch upper-shelf energy and the SMCS and VGM parameters is observed, which can be utilized to estimate the model parameters.
Guodong Wang - One of the best experts on this subject based on the ideXlab platform.
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comparison of cracking sensitivity between high permeability 1 5 wt si steel and 6 5 wt si steel in mushy zone
Journal of Magnetism and Magnetic Materials, 2020Co-Authors: Yuanxiang Zhang, G. Yuan, Xiaoming Zhang, J.h. Zhao, Guodong WangAbstract:Abstract Twin-roll thin strip casting process (SC) has been utilized in laboratory to fabricate typical high-permeability electrical steel (HPES) such as 1.5 wt% Si and 6.5 wt% Si steel with ideal crystallographic orientation and excellent permeability after a series of heat treatments. Whereas, there exists a problem associated to the cracking sensitivity in high temperature mushy zone, which further restricts the industrial application of SC to produce HPES. Mechanical behavior of 1.5 wt% Si and 6.5 wt% Si steels in high temperature mushy zone were comparatively studied by Gleeble-3800 physical simulation system under Strain rate 3 s−1, systematically. The high temperature brittle region composed of zero strength temperature (ZST) and zero ductility temperature (ZDT) in the mushy zone were quantitatively determined, and the Critical Strain threshold associated to hot crack initiation in the brittle region were further evaluated following empirical model proposed by Y Won. Results show that the tensile strength and fracture ductility in the mushy zone are both closely associated with the varying volume fraction of network-shaped structure during solidification, and are decreased with decreasing solid fraction concerning studied 1.5 wt% Si and 6.5 wt% Si steels. The high temperature brittle region corresponding to the studied 1.5 wt% Si and 6.5 wt% Si steels in mushy zone are separately confirmed to be 1459 ~ 1465℃ and 1390 ~ 1427℃, and the thresholds of Critical Strain for hot cracks initiation in high temperature brittle region are calculated to be ~ 1.18% and ~ 0.24%, respectively. Considering from perspective of width of high temperature brittle region and Critical Strain threshold for hot crack initiation, the cracking sensitivity of 6.5 wt% Si steel in the mushy zone is more serious compared to 1.5 wt% Si steel.