M. Głowacki

The Physical and Computer Modeling of Plastic Deformation of Low Carbon Steel in Semisolid State

This paper reports the results of theoretical and experimental work leading to the construction of a dedicated finite element method (FEM) system allowing the computer simulation of physical phenomena accompanying the steel sample testing at temperatures that are characteristic for integrated casting and rolling of steel processes, which was equipped with graphical, database oriented pre- and postprocessing. The kernel of the system is a numerical FEM solver based on a coupled thermomechanical model with changing density and mass conservation condition given in analytical form. The system was also equipped with an inverse analysis module having crucial significance for interpretation of results of compression tests at temperatures close to the solidus level. One of the advantages of the solution is the negligible volume loss of the deformation zone due to the analytical form of mass conservation conditions. This prevents FEM variational solution from unintentional specimen volume loss caused by numerical errors, which is inevitable in cases where the condition is written in its numerical form. It is very important for the computer simulation of deformation processes to be running at temperatures characteristic of the last stage of solidification. The still existing density change in mushy steel causes volume changes comparable to those caused by numerical errors. This paper reports work concerning the adaptation of the model to simulation of plastic behavior of axial-symmetrical steel samples subjected to compression at temperature levels higher than 1400 ° C. The emphasis is placed on the computer aided testing procedure leading to the determination of mechanical properties of steels at temperatures that are very close to the solidus line. Example results of computer simulation using the developed system are presented as well.

Modelling of heat transfer, plastic flow and microstructural evolution during shape rolling

The paper describes investigations on the development of an integrated model allowing for the prediction of heat transfer, plastic flow, and microstructure evolution during shape rolling. Finite element method was adopted to describe the heat transfer and plastic flow phenomena. Generalized plane strain method is applied to modelling the 3D problem using 2D finite element formulation. In consequence, significant savings of the computing time and required memory can be obtained. A computer program in FORTRAN 77 was written according to the developed mathematical model. Data on temperature, strain and strain rate relevant to the rail rolling process were computed and employed to model microstructure evolution in austenite.

Modeling of Strain-Stress Relationship for Carbon Steel Deformed at Temperature Exceeding Hot Rolling Range

The subject of the presented paper is the modeling of strain-stress relationship, which is the main mechanical property characteristic of the behavior of steel subjected to plastic deformation. The major cliallenge of the research is the temperature of the deformation, which significantly exceeds the hot rolling temperature range. This paper presents the results of work leading to the development of a rheological model describing the phenomena accompanying the deformation of 18G2A grade steel at temperature 1420°C and higher. Such temperature is a characteristic of the central parts of steel strands subjected to latest, very high temperature rolling technologies such as integrated rolling and casting processes. Rheological models have crucial influence on the results of the computer simulation of the mentioned processes. The methodology of yield stress curves development requires high accuracy systems of tension and compression test simulation. Hence, the proposed testing procedure is related to dedicated hybrid finite element method system with variable density, which was developed by the authors. The experimental work has been done using the Gleeble ® 3800 thermomechanical simulator in the Institute for Ferrous Metallurgy in Gliwice, Poland. The testing machine allows the physical deformation of samples while solidification of their central part is still in progress. The essential goal of the simulation was the computer reconstruction of both temperature changes and strain evolution inside a specimen subjected to simultaneous deformation and solidification. In order to verify the predictive ability of the developed rheological model, a number of compression tests using Gleeble ® 3800 simulator have been done, as well. The comparison between the numerical and the experimental results is also a part of the presented paper.

Inverse analysis applied for determination of strain–stress curves for steel deformed in semi-solid state

The integrated casting and rolling of plates in processes such as ISP or AST is the latest and very efficient method of hot strip production. The subject of the presented article is the modelling of steel behaviour at temperatures characteristic for the mentioned rolling technologies, which exceed the standard hot rolling temperature range. Numerical modelling can be very helpful in developing ‘know how’ theory for the mentioned processes. One of the most important relationships having a crucial influence on the metal flow path is the strain–stress curve. It is not easy to construct isothermal curves for a selected temperature range. The inverse method, which is usually applied for calculation of the real strain-stress relationship, needs a good mathematical model describing the plastic behaviour of the material. The model presented in the current article fills the gap in the modelling of plastic deformation of semi-solid materials. The methodology of constructing strain–stress curves is presented, as well. On the other hand, the mathematical modelling should be closely related to experiments. The only well-known method allowing laboratory tests in the discussed temperature range (over 1400°C) is the deformation of cylindrical samples using GLEEBLE thermo-mechanical simulator. However, experiments of steel deformation in semi-solid state by using this machine are very expensive. Therefore, application of a dedicated computer simulation system with an inverse method makes the tests possible in the first place and it also results in lowering testing costs.

Modelling of plastic flow, heat transfer and microstructural evolution during rolling of eutectoid steel rods

Abstract A study was undertaken in an attempt to quantitatively describe the rolling process of eutectoid steel rods. Finite element method was employed to model plastic flow and heat transfer in the deformed material, and heat transfer during cooling to ambient temperature. The numerical calculation gave an assessment of the strain, strain rate and temperature distributions in the work piece. This allowed the prediction of the austenite microstructure evolution during the process. Finally, the relationships describing the microstructure-mechanical properties were used to quantitatively characterize the influence of processing parameters on strength of rods after rolling.

Prediction of mechanical properties of heavy forgings

Abstract This paper deals with the problem of forging of heavy parts. The stock material for this process has the microstructure of the casted material, which is characterised by strong inhomogeneity of grains and the presence of pores. This structure is altered during forging by subsequent processes of plastic deformation and recrystallization. Therefore, the problem of penetration of plastic deformation inside the forging becomes essential. The general objective of the work is an evaluation of the minimum reduction of the cross-section of the forging, which still allows the required mechanical properties to be obtained. The research included both experimental tests and finite-element simulation of the forging process. The tested material was middle carbon steel containing 0.4% C and 1.3% Mn. The experiments consisted of the measurement of yield stress, tensile strength and hardness for samples cut from various parts of the forging. The results were compared with the local values of strains and temperatures during the forging process predicted by the finite-element program. The microstructure evolution models were implemented into the finite-element code, which allowed the prediction of distributions of grain size in the volume of the forging. Analysis of all the results allowed conclusions to be drawn regarding a design of forging technology that will guarantee required properties of forging.

Simulation of metal flow, heat transfer and structure evolution during hot rolling in square-oval-square series

Abstract The objective of the paper is to develop the numerical model which describes metal flow, heat transfer and microstructure evolution in the hot shape rolling processes. The generalized plane strain program developed by authors is adapted to the simulation. The closed form equations describing microstructural events which were used in modelling of the strip rolling process are implemented into the program and calculations of the grain size distribution across the sample are performed. Independently, an additivity rule is applied in order to take into consideration the temperature variations after materials exit from the roll gap. The model is validated by a comparison of its predictions with the experimental results.

Finite element three-dimensional modelling of the solidification of a metal forming charge

Abstract The paper deals with the modelling of density changes during the solidification of the ingots and cast strands after casting. The finite element solution of the Navier-Stokes equations are implemented into the modelling of the process. The models for both steady-state and non steady-state solutions as well as the influence of the physical parameters distribution in the cooling zone on the solidification process are discussed. Some results of the density distribution in the cross sections of a hot-top ingot during solidification process after casting are presented. Some aspects of the numerical solution are discussed.

Mobile Monitoring System for Environment Parameters.

Problems related to the monitoring of environmental parameters, and in particular air-pollution in urban agglomerations, are some of the more publicly discussed public issues in recent times. This paper presents the concept, functionality, main hardware and software components, and test results of low-cost prototype of the system, enabling monitoring of environmental parameters such as air-pollution, temperature, humidity, pressure and UV radiation. The main features of this solution are its low cost, relatively high precision of measurement and the ability to operate in mobile version, without wired power supply and communication, including GPS coordinates as one of the measured parameters. The prototype can be an alternative to expensive professional solutions and a base for developing more advanced sensor networks. For home use it can be used as a home weather station with an air pollution sensor, being an extension of the of Personal Area Network of the recently popular Internet of Things solutions.

Fast parallel computation algorithm in application to simulation of semi-solid steel rolling and inverse analysis of its properties

The contribution deals with the problem of development of a fast computation system allowing for correct interpretation of results of experiments concerning mechanical properties of semi-solid steel. Accurate computer simulation of steel deformation at very high temperature requires information about plastic properties of the material. One of the most important properties of steel subjected to deformation is the stress-strain relationship - yield stress curve. Unlike low temperature tests, deformation of steel samples in temperatures over 1400°C causes strain, stress and temperature fields that are strongly inhomogeneous from the physical point of view. Correct interpretation of such experimental results requires inverse analysis based on numerical models providing accurate and fast computation. Similar requirements apply to simulation of the integrated casting and rolling process of semi-solid steel in a sequence of passes. This problem is the main subject of the current paper. Some globally unique examp...