Search for: dynamic-strain-aging
Total 25 records
Article ISIJ International ; Volume 44, Issue 11 , 2004 , Pages 1867-1873 ; 09151559 (ISSN) ; Sharif University of Technology
Iron and Steel Institute of Japan 2004
In this work, the effects of dynamic strain aging and dynamic recovery on metal flow during warm working are studied. Compression experiments are utilized to assess the flow behavior of a low carbon steel under warm deformation conditions. Then, a two dimensional finite element routine is coupled with dynamic recovery and dynamic strain aging models. In this way, the temperature and the velocity fields are predicted during warm working operations with regard to the effects of dynamic recovery and dynamic strain aging. Warm rolling tests are performed in order to verify the modelling results. Comparison between the predicted and measured roll forces shows reliability of the employed model
M.Sc. Thesis Sharif University of Technology ; Kazeminezhad, Mohsen
Al-6wt%Mg alloy has been enormously exploited in aerospace industry. Since for production of this alloy in the form of sheets of different thickness, the cold rolling process is used, thus to understand the final mechanical properties of the rolled alloy products, their work hardening should be examined. Also, one of the important phenomena that occurs in cold state of the alloy is dynamic strain-aging (DSA), which can cause serrations in realistic stress-strain curve. The aforementioned issue is discussed in the current study. Therefore, the work-hardening values for the mentioned alloy during and after rolling is determined, and then compared with the experimental studies. The results of...
Article Materials Science and Engineering A ; Volume 371, Issue 1-2 , 2004 , Pages 318-323 ; 09215093 (ISSN) ; Sharif University of Technology
Dynamic strain ageing may occur during warm working of low carbon steels and causes significant changes in flow behaviour and microstructure of the deformed material. Therefore, for a proper designing of an industrial forming process performing under warm deformation conditions, the effect of dynamic strain aging should be taken into account. The aim of this investigation is to predict the velocity and the temperature fields within the rolling metal with regard to the dynamic strain aging. For this purpose, compression tests at various temperatures and strain rates have been conducted to evaluate dynamic strain aging in a low carbon steel. Then, by coupling the experimental results with a...
Article Materials Letters ; Volume 61, Issue 4-5 , 2007 , Pages 1023-1026 ; 0167577X (ISSN) ; Sharif University of Technology
A 0.15% C-1.2% Si-1.7% Mn steel was intercritically annealed at 780 °C for 5 min and then isothermally held at 400 °C for 4 min followed by oil quenching to room temperature and the annealed microstructure consist of 75% ferrite, 15% bainite and 10% retained austenite was produced. Samples of this steel with triple phase structure were tensile tested at temperature range of 25-450 °C. Stress-strain curves showed serration flow at temperature range of 120-400 °C and smooth flow at the other temperatures. All of the stress-strain curves showed discontinuous yielding at all testing temperatures. Both yield and ultimate tensile strength decreased with increasing temperature, but there exists a...
Flow behavior and mechanical properties of a high silicon steel associated with dynamic strain aging, Article Journal of Materials Engineering and Performance ; Volume 21, Issue 9 , September , 2012 , Pages 1919-1923 ; 10599495 (ISSN) ; Serajzadeh, S ; Sharif University of Technology
Flow behavior of two grades of steel including a high silicon (HS) steel and a plain low carbon steel as the reference were considered in this work. Tensile testing at temperatures varying between 25 and 550 °C and different strain rates in the range of 4×10-5 to 0.1 s-1 were conducted and the mechanical properties, such as elongation at fracture point and strain rate sensitivity were then determined. It is observed that for both steels, dynamic strain aging occurs in the employed deformation conditions, however, the region of serrated flow and the type of the serration were somehow different. For the case of the HS steel, the serrated flow region is shifted to the higher temperatures and...
Article Materials Letters ; Volume 59, Issue 16 , 2005 , Pages 2070-2074 ; 0167577X (ISSN) ; Sharif University of Technology
Dual phase steels with different martensite volume fraction and morphology were tensile tested at temperature range of 25-550 °C. Stress-strain curves of all steels showed serration flow at temperature range of 250-450 °C and smooth flow at the other temperatures. Both yield and ultimate tensile strengths increased with increasing testing temperature up to about 450 °C and then decreased at higher temperatures. At a given temperature, yield stress, tensile strength, and work hardening increased with increasing volume fraction of martensite. Similar behavior was observed by changing martensite morphology from network to fibrous martensite. The change in mechanical properties was related to...
Ph.D. Dissertation Sharif University of Technology ; Karimi Taheri, Ali
The manufacture of ultra high strength materials has always been a target for aerospace and transportation industries. Currently, the limitation of energy resources even makes this goal more serious. Nowadays, more than 50% of total extrusion products are made from Al alloys and around 90% of them are the 6000 series alloys. Therefore, regarding to high strength, low weight, and hardening aluminum AA6000 alloys capabilities can play a major role in fulfilling this task. Over the last decade, a number of techniques collectively referred to as severe plastic deformation (SPD), have emerged as a promising approach for the production of bulk ultrafine-grained (UFG) nano-structured materials....
M.Sc. Thesis Sharif University of Technology ; Serajzadeh, Siamak
A mathematical model has been proposed to estimate the deformation pattern and the required power in cold plate rolling using the stream function method and upper bound theorem. In the first place admissible velocity distributions as well as the geometry of deformation zone were derived from the proposed stream functions. Then, the optimum velocity field was obtained by minimization of the power function computed based on the upper bound theorem. Then a steady state heat transfer equation has been solved in whole model using finite element method. In order to verify the predictions, rolling experiments on aluminum plates were conducted and also, a finite element analysis performed employing...
Simulation and experimental analyses of dynamic strain aging of a supersaturated age hardenable aluminum alloy, Article Materials Science and Engineering A ; Volume 585 , 2013 , Pages 165-173 ; 09215093 (ISSN) ; Karimi Taheri, A ; Kim, H. S ; Sharif University of Technology
In this paper, dynamic strain aging (DSA) behavior in a temperature range of (25-235°C) and strain rate range of (10-4-5×10-2s-1) was investigated using a supersaturated age hardenable aluminum alloy. It was found that two mechanisms consisted of pinning of solute atoms to mobile dislocations and dynamic precipitation, were responsible for DSA in the testing conditions. The effects of both mechanisms on the macroscopic flow curve were studied using experimental and improved physically based material modeling approaches. It was shown that both phenomena lead to a negative strain rate hardening in the alloy. Dynamic precipitation acting at high temperature results in considerable work...
Article Materials and Design ; Volume 67 , February , 2015 , Pages 318-323 ; 02613069 (ISSN) ; Ranjbar Motlagh, S ; Mirbagheri, S. M. H ; Akhgar, J. M ; Sharif University of Technology
Elsevier Ltd 2015
In this work, the flow stress behavior of a metal matrix composite AA2017-10% SiCp was studied by means of the uni-axial compression test. The composite was first produced by stir casting technique and then, hot extrusion with the ratio of 18:1 was carried out to achieve a microstructure with a homogeneous distribution of SiC particles. In the next stage, the isothermal compression tests were conducted on the cylindrical specimens up to the true strain of 0.6. The experiments were performed at temperatures between room temperature to 400°C and strain rates of 0.003, 0.03 and 0.3s-1. Negative strain rate sensitivity was observed in the temperatures less than 250°C indicating the occurrence of...
Dynamic strain aging of a commercial Al-Mg-Si-Cu alloy during equal channel angular extrusion process, Article Journal of Alloys and Compounds ; Volume 502, Issue 1 , July , 2010 , Pages 59-62 ; 09258388 (ISSN) ; Karimi Taheri, A ; Vaseghi, M ; Sharif University of Technology
In this research, the occurrence of dynamic strain aging (DSA) phenomenon during equal channel angular extrusion (ECAE) of a commercial air cooled Al-Mg-Si-Cu alloy is investigated. In order to detect the negative strain rate sensitivity behaviour associated with DSA, samples were ECAE-ed at various temperatures and strain rates. Subsequently, the extruded billets were subjected to mechanical and physical tests and it was found that at a certain ECAE temperature range there is a critical strain rate above which DSA occurs. The implication of the results to strengthening of dilute solid solutions is discussed
Effect of rolling speed on the occurrence of strain aging during and after warm rolling of a low-carbon steel, Article Journal of Materials Science ; Volume 45, Issue 13 , July , 2010 , Pages 3405-3412 ; 00222461 (ISSN) ; Ohadi, D ; Serajzadeh, S ; Akhgar, J. M ; Sharif University of Technology
In this study, effect of rolling speed on strain aging phenomena in warm rolling of a carbon steel has been investigated. For this purpose, by using a mathematical model and predicting temperature and strain rate fields, the possibility of occurrence of dynamic strain aging during the warm rolling was first evaluated. In the next stage, warm-rolled samples were aged up to 11 months at room temperature for studying the kinetics of static strain aging, while mechanical tests as well as microstructural evolutions have been performed to determine the effect of strain aging on material behavior. The results indicate that dynamic strain aging may not occur for the employed rolling program;...
Article Ironmaking and Steelmaking ; Volume 37, Issue 2 , Jul , 2010 , Pages 155-160 ; 03019233 (ISSN) ; Sadeghi, A. R ; Akhgar, J. M ; Serajzadeh, S ; Sharif University of Technology
In this work, the phenomenon of dynamic strain aging in a high carbon steel is studied and different initial microstructures including fine and coarse pearlite structures are considered. Tensile tests at different temperatures and strain rates are performed to evaluate the occurrence of dynamic strain aging and mechanical properties as well as to calculate apparent activation energies for onset and termination of dynamic strain aging. The results show that dynamic strain aging occurs for both microstructures while the initial microstructures alters the activation energies for appearance and termination of this phenomenon. The microstructural studies illustrate that a combination of cementite...
Effect of two steps annealing on the microstructure and dynamic strain aging behavior of Al-6Mg alloy, Article Materials Science and Engineering A ; Volume 798 , 2020 ; Khani Moghanaki, S ; Kazeminezhad, M ; Goodarzi, M ; Ghiasi Afjeh, S. M. B ; Sharif University of Technology
Elsevier Ltd 2020
The microstructure of cold rolled Al–6Mg alloy is investigated after two steps annealing at different coupled temperatures of 250–320 °C and 320–400 °C for various times. Dynamic strain aging behavior in terms of serrated flow and strain rate sensitivity is investigated. The effect of three microstructural features, cell structure, recovered and recrystallized microstructures, on the strain rate sensitivity is elucidated. Two steps annealing process is utilized to capture the effect of recovery and precipitation phenomena on recrystallization and dynamic strain aging behaviors. The results show that the negative strain rate sensitivity of cold rolled specimen increases to positive values in...
Article Materials Science and Engineering A ; Volume 475, Issue 1-2 , 2008 , Pages 293-298 ; 09215093 (ISSN) ; Ekrami, A ; Sharif University of Technology
High bainite dual phase steel has been subjected to tension test at different temperatures from 25 to 500 °C with strain rate of 4.6 × 10-4 s-1 to investigate the effect of temperature on its mechanical properties. Stress-strain curves of steels showed serration flow at temperature range of 200-350 °C and smooth flow at the other temperatures. In agreement with previous studies on some steels, peaks in the variations of yield strength (YS) and ultimate tensile strength (UTS) and minima in ductility were observed at temperature range of 200-350 °C which are various manifestations of dynamic strain aging (DSA). It has been also found that ferrite volume fraction has no effect on the...
Flow stress optimization for 304 stainless steel under cold and warm compression by artificial neural network and genetic algorithm, Article Materials and Design ; Volume 28, Issue 2 , 2007 , Pages 609-615 ; 02613069 (ISSN) ; Madaah Hosseini, H. R ; Bahrami, A ; Sharif University of Technology
Elsevier Ltd 2007
Artificial neural network (ANN) and genetic algorithm were used in this study to obtain a relatively high flow stress in compression tests for 304 stainless steel. Cold and warm compression were carried out in a temperature range from 20 to 600 °C, strain-rate from 0.001 to 100 S-1 and a strain range from 0.1 to 0.5. Optimum conditions for each case were obtained experimentally and were evaluated by the ANN model. The ANN model was used as fitness function for genetic algorithm. The results indicated that this combined algorithm offers an effective condition for 304 stainless steel, which avoids flow localization, dynamic strain aging, adiabatic shear deformation and void generation. © 2005...
A model for prediction of flow behavior and temperature distribution during warm rolling of a low carbon steel, Article Materials and Design ; Volume 27, Issue 7 , 2006 , Pages 529-534 ; 02641275 (ISSN) ; Sharif University of Technology
A two-dimensional finite element analysis is coupled with dynamic recovery and dynamic strain aging models to achieve metal flow during warm deformation of a low carbon steel. In order to assess metal behavior, compression experiments are utilized under warm deformation conditions and the results are used in the model and temperature and velocity fields are predicted with regard to the effects of dynamic recovery and dynamic strain aging. In addition, warm rolling tests are performed to verify the modelling results. Comparison between the predicted and measured roll forces shows reliability of the employed model. © 2005 Elsevier Ltd. All rights reserved
The effect of dynamic strain aging on room temperature mechanical properties of high martensite dual phase (HMDP) steel, Article Materials Science and Engineering A ; Volume 550 , 2012 , Pages 325-332 ; 09215093 (ISSN) ; Koohbor, B ; Ahadi, K ; Ekrami, A ; Khakian Qomi, M ; Izadyar, T ; Sharif University of Technology
AISI 4340 steel bars were heated at 900 °C for one hour, annealed at 738 °C for different durations and oil-quenched in order to obtain dual phase steels with different ferrite volume fractions. A 3% prestrain at the temperature range of 150-450 °C was then imposed to the samples, and room temperature tensile tests were carried out, afterwards. Results indicate that the maximum values for both yield and ultimate tensile strength would exist for the samples pre-strained at the temperature range of 250-300 °C. Also, a sudden drop of the ductility was observed at the mentioned temperature range. The observed behavior might be attributed to the occurrence of dynamic strain aging taken place at...
The effect of pre-straining at intermediate temperatures on the mechanical behavior of high-bainite dual phase (HBDP) steels, Article Materials Science and Engineering A ; Volume 543 , May , 2012 , Pages 224-230 ; 09215093 (ISSN) ; Haghshenas Fatmehsari, D ; Ekrami, A ; Sharif University of Technology
High-bainite dual phase (HBDP) steels with 34. vol.% ferrite were subjected to tensile strains of 1%, 3%, and 5% at intermediate temperatures (150-450. °C). Mechanical behavior of pre-deformed steels was then investigated at room temperature. A maximum value for both yield stress and ultimate tensile strength was observed for pre-deformed steels. A minimum elongation was also found in the same pre-deformed specimens at the range of 250-350. °C. It was found that dynamic strain aging (DSA) plays the major role in mechanical properties of pre-strained HBDP steels. The DSA indicator parameter (DSAP) was introduced to evaluate DSA mechanism. Maxima of DSAP were likewise observed at the range of...
Article Journal of Materials Engineering and Performance ; Volume 19, Issue 9 , 2010 , Pages 1264-1267 ; 10599495 (ISSN) ; Sharif University of Technology
In this study, the plastic instabilities associated with the Portevin-Le Chatelier (PLC) and their effects on the mechanical properties and the fracture surfaces have been investigated for AA 5083. Tensile tests were performed at various temperatures and strain rates in order to do so. Then, serrated and smooth yielding domains were determined in Ln ε̇-1/T diagram. The stress-strain curves related to the serrated domain show the values of flow stress decreases by increasing the strain rate at a constant temperature. In addition, the plot of critical strain versus imposed strain rate indicates an inverse manner at very low strain rates. It is confirmed that the type of PLC bands alters the...