Papers by Author: István Mészáros

Abstract: The aim of this study was to investigate the effect of the previously applied cold rolling and the latter heat treatment for the eutectoidal decomposition of δ-ferrite in 2507 type superduplex stainless steel (SDSS). The samples were cold rolled at seven different deformation rates which was followed by heat treatment at were 20, 700, 750, 800 and 850 °C temperatures. The rolled and heat treated samples were investigated by hardness tester, AC magnetometer and thermoelectric power measurement. The activation energy of the decomposition was determined by the Arrhenius equation through the results of the AC magnetometer measurement.

Abstract: Nowadays, there is increasing importance of the remaining life time estimation of engineering structures. In this work the thermal fatigue process induced deterioration of the three different power plant steels was investigated. The tested steels are widely used as steam pipeline base material of power plants. The applied thermal fatigue test can model the material degradation due to long term service in high temperature environment. In this paper a new high sensitivity magnetic measuring technique is presented called Adaptive Nonlinear Harmonic (ANLH) method. The sensitivity of this measurement is optimized for controlling the thermal fatigue deterioration. The presented novel measurement was developed for non-destructive testing of pipelines and pressure vessels of power plants.

Abstract: This work demonstrates particularly the basic properties of shape memory alloys and gives a brief review about their basic crystallographic processes. The attributes of shape memory alloys will be presented through the NiTi alloys. The crystallographic principles of three unique properties were investigated and the functional mechanism described. One of the three essential mechanisms, the one-way effect was demonstrated through an experiment. The change of length depending temperature was tested and documented. The hysteresis behavior of shape memory alloys was recorded.

Abstract: Nowadays, there is increasing importance of the remaining life time estimation of engineering structures. In this work the thermal shock fatigue process induced deterioration of the three different power plant steels was investigated. The tested steels are widely used as steam pipeline base material of power plants. The applied thermal shock fatigue test can model the material degradation due to long term service in high temperature environment. A special AC magnetometer was designed and used for the magnetic measurements at the Department of Materials Science and Engineering of BUTE. In this paper a new high sensitivity magnetic measurement is presented for controlling the thermal shock fatigue deterioration. This measurement technique was developed for non-destructive testing of pipelines and pressure vessels of steam power plants.

Abstract: Surface rolling is a cold-working technology for hardening the surface of components made from steel or ductile cast iron. This process is able to increase the hardness of surfaces and to improve fatigue properties, so it is usually used on the axles (shafts) of railway-car wheels. In this paper the influence of surface strengthening technology on the microstructure of the material of railway car wheel axles is studied by Vickers microindentation hardness test, optical microscopy, scanning electron microscopy (SEM) automated EBSD (Electron Backscatter Diffraction) and non-destructive magnetic evaluation.

Abstract: The aim of this work is to study the microstructural changes in 2507 type superduplex stainless steel due to heat treatments. Two series of specimens were studied. The first series were heat treated isothermally at 800 °C for different times up to 42 minutes. The second ones were heat treated isochronically for 20 minutes in the temperature range of 720-900 °C. The microstuctural changes were investigated by metallography and by magnetic tests. The first magnetization curves and the saturation magnetization loops were measured by a double yoke DC magnetometer.

Abstract: In the present work the microstructure and the strain induced phase transformation of a Lean Duplex Stainless Steel (LDSS) were studied. Sheet samples were cold rolled, the number of samples was nine; the applied deformation was up to 80%. The magnetization curves were measured by a single sheet tester-type magnetic property analyzer. The series of symmetrical minor hysteresis loops and the saturation loop were measured. Our novel data evaluation technique was applied for data evaluation of the magnetic measurements. This method is based on the multiphase-hyperbolic model of magnetization and it is called model based data evaluation (MBDE) technique. This method allowed us to separate the magnetic contribution of ferrite and martensite phases in the tested LDSS. Several new details of the kinetics of austenite→martensite strain induced phase transformation were clarified.

Abstract: In this paper, we present an application of the so-called hyperbolic model of magnetization. The model was modified and it was applied for nine different soft magnetic alloys. The tested samples were electro-technical steels (FeSi alloys) and a permalloy (FeNi alloy) with strongly different magnetic properties. Among them, there are top, medium and definitely poor quality soft magnetic materials as well. Their minor hysteresis loops and normal magnetization curves were measured by alternating current measurement. The hyperbolic model of magnetization was applied for the experimental normal magnetization curves. It was proved that the applied model is excellent for describing mathematically the experimental magnetization curves.

Abstract: In this work a new magnetometer setup and a novel model based data evaluation technique was used to determine the creep damage in ferritic power plant steel. The tested material was 1Cr-0.5Mo-0.25V ferritic steel which is commonly used as pipeline base material of steam generators in power plants. It is commonly accepted that a combined form of fatigue and the creep processes cause the deterioration of this structural parts due to long time elevated temperature service. Nowadays, there is increasing need for remaining lifetime estimation of these engineering structures. In this paper, the variation of magnetization curves of Cr-Mo-V ferritic steel due to creep measured and the relation between creep damage and the magnetic property changes is discussed. A new data evaluation technique is presented which is based on the hyperbolic model of magnetization. A magnetic descriptor was derived from the hyperbolic model which can be determined from the initial part of the normal magnetization curve. The introduced parameter and evaluation technique seems to be especially useful for magnetic nondestuctive remanent lifetime evaluation.

Abstract: In this paper a new data evaluation technique is presented for non-destructive magnetic measurements. This method is based on the multiphase hyperbolic model of magnetization and it is called model based data evaluation (MBDE) technique. The MBDE method allows us to separate the magnetic contribution of the magnetizing yoke from the measured magnetization curves. Therefore the determined magnetic properties of the tested sample are independent of the parameters of the applied magnetic yoke and the lift-off. The proposed method could become a useful tool in magnetic non-destructive evaluation (NDE).