Sharif Digital Repository

In this work, a model based on the finite element method and assumption of second order phase transformation has been developed to predict temperature history and austenite decomposition kinetics during continuous cooling of a low carbon steel. In order to accurately assess the temperature field and transformation rate the effects of various factors such as work hardening role on the kinetics of transformation, interconnection between austenite phase change and thermo-physical properties of the steel, and initial austenite grain size have been considered in the model. To verify the results of the modelling, time-temperature histories during cooling of a low carbon steel has been determined... 

In the present paper, employing compression experiments for three grades of low carbon steel, the effects of deformation condition and chemical composition on the occurrence of dynamic strain ageing are studied. Also, based on the achieved results, the flow behavior of steels under warm deformation conditions is predicted for the employed steels. The results show that both chromium and niobium postpone the happening of serrated flow and shifts the serrated flow region to lower temperatures in comparison with low carbon steel, while the activation energy for commencing dynamic strain ageing increases. © 2003 Elsevier Science B.V. All rights reserved  

This paper presents a mathematical model for predicting the temperature distribution and austenite microstructural changes during hot rolling of steel bars and rod. The model is based on the finite element method for evaluating the temperature distribution and Wusatowski approach to determine the strain field within the deformation zone. Also, by employing double and single hit hot compression experiments, the kinetics of dynamic and static recrystallization of a low carbon steel are determined to predict the flow stress as well as the phase changes in austenite range during and after the hot rolling process. To deal with the correlation between the metal flow and thermal behaviour and... 

In this study, strain ageing during and after warm rolling of a carbon steel has been investigated. At the first step, the occurrence of serrated flow was studied by means of tensile tests at different temperatures and strain rates. In the next stage, warm rolling experiments were performed under different rolling conditions and then the samples were aged at the room temperature for a period of 3 months. For both aged and non-aged samples, tensile tests were employed to evaluate their mechanical properties. The results show that static strain ageing is possible to happen in the utilized ageing period and increases the yield stress of the aged steel. However, the samples that experience both... 

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... 

In this study, a multistage strain aging method that used rolling pre-strain (compression) was developed to study the effects of temperature, and inter-pass time on static strain aging behavior of low carbon steel. An increase in hardness and strength caused by work hardening due to the forming process and aging at every stage of aging that is calculated separately. To comparing the effects of multistage aging against typical strain aging, the samples were rolled and subjected to the aging process both exist in typical one-stage aging that setting a 20% rolling pre-strain and in multiple stages pre-strain by setting a 5% rolling ratio in four stages. The mechanical properties of aged samples... 

An investigation was performed on the static strain aging behavior of warm-rolled low carbon steel during a nearly 1-year aging period, from the view point concerning with influence of changing the deformation speed and cooling media. Mechanical response of the examined material during aging period was evaluated through variations occurred in strength and hardness of the warm-deformed steel. It was shown that changing the rolling speed as well as cooling rate, may result in the occurrence of different metallurgical phenomena, consequently altering the aging kinetics of the material. It was also found that by increasing rolling speed, an increase in the value of hardness and UTS takes place,... 

In this research, constrained groove pressing (CGP) technique is used for imposing severe plastic deformation (SPD) on the low carbon steel sheets. Using transmission electron microscopy (TEM), X-ray diffraction (XRD) and optical microscopy, the microstructural characteristics of produced sheets are investigated. The results show that CGP process can effectively refine the coarse-grained structure to an ultrafine grain range. Dislocation densities of the ultrafine grained low carbon steel sheets are quantitatively calculated and it is found that the CGP can effectively enhance the dislocation density of the sheets. Measurements of their electrical resistivity values show that microstructure... 

Transformation of austenite to ferrite under continuous cooling condition was investigated. The heat conduction problem was managed by finite element method while two-dimensional cellular automata modeling was simultaneously performed to predict the progress of austenite decomposition using a two-step algorithm to reduce surface-to-volume ratio. Continuous cooling experiments on low carbon steel were made and the ferrite structure was determined and compared with the simulation data. The predicted and the experimental results demonstrated an acceptable consistency and the activation energy for ferrite growth was determined as 171 kJ/mole. The rate of ferrite transformation increased under... 

Transformation of austenite to ferrite under continuous cooling condition was investigated. The heat conduction problem was managed by finite element method while two-dimensional cellular automata modeling was simultaneously performed to predict the progress of austenite decomposition using a two-step algorithm to reduce surface-to-volume ratio. Continuous cooling experiments on low carbon steel were made and the ferrite structure was determined and compared with the simulation data. The predicted and the experimental results demonstrated an acceptable consistency and the activation energy for ferrite growth was determined as 171 kJ/mole. The rate of ferrite transformation increased under... 

α-Fe with low carbon content is a base material which is commonly used in manufacturing of Reactor Pressure Vessel (RPV) of commercial nuclear power plants. Carbon is generally diffused to α-Fe matrix to improve some of its mechanical properties. The presence of carbon may alter the irradiation response of the steel. In the current study, using molecular dynamics simulations, we have investigated the influence of carbon (∼in either dispersed form or carbon-rich region as chain) in the primary damage states of α-Fe low carbon steels. It is found that carbons in dispersed form have no significant effect on the self-interstitial atoms (SIAs) in α-Fe. While, carbon-rich (C-rich as...