Papers by Author: János Ginsztler

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: The most promising process for metal matrix syntactic foam (MMSF) production is pressure infiltration. In case if it can be advanced to die casting the cost of the MMSFs will drop significantly. The first step on this road is to characterize the kinetics of the pressure infiltration with respect to infiltration pressure and time. Experimental infiltration equipment was built and many preliminary tests were performed on the AlSi12 + SLG system. The load bearing capacity is also important, therefore the compressive behaviour of MMSFs were investigated. According to the results engineering factors (matrix material, size of the microballoons, applied heat treatment, temperature of the tests) have significant effects on the compressive properties.

Abstract: In the development of modern drug eluting implants it is crucial to be able to measure the long term desorption processes which determine the drug elusion. In this article we set up a simple model for these measurements, which consists of stainless steel stent-model samples with polyurethane coatings incubated in heparin, and a label-free OWLS (Optical Waveguide Lightmode Spectroscopy) biosensor to measure the elusion of heparin from these samples. We found that porous coatings bind heparin better than smooth coatings, and that the PUR materials tested by us all have different binding properties. We also constructed a dual-flow set-up for the instrument, which enabled us to do real-time elusion measurements instead of sample injection, which would make the monitoring of desorption processes much clearer, although this measurement method is yet to be fully developed.

Abstract: This paper deals with the investigation of grain boundary engineering processes in case of AISI 304 type austenitic stainless steel. The effects of the thermo-mechanical treatments for the modification of the grain boundary structure are demonstrated on the special grain boundaries. The proper thermo-mechanical treatments can increase the fraction of the CSL-boundaries. Since the CSL-boundaries are resistant against intergranular degradation processes, materials owning enhanced properties can be developed due to these treatments. The investigation of the grain boundary character distribution is carried out by automated electron back scattered diffraction (EBSD) measurements after different thermo-mechanical treatment processes. The effect of the heat treatment duration on the grain boundary structure is examined; the optimal treatment is represented. It is shown by experimental results, that the parameter settings of the evaluation method strongly influence the obtained results.

Abstract: The high-carbon steel strips are one of the most widely used base materials of bandsaw blade manufacturing. These materials have sufficient strength and ductility to cope with the high fatigue load of the bandsaw blades. These endless strips are produced by welding, and therefore the weld and the heat affected zone have different mechanical properties, like tensile strength and fatigue resistance, than the base material. These properties of the weld can be influenced by preheat and post weld heat treatment. Regarding to the latest industrial requirements, the application of laserbeam welding was examined to produce higher standard bandsaw blade. The laserbeam welded joints has lower heat input and narrower heat affected zone compared to metal inert gas (MIG) welding, which is currently used in bandsaw blade manufacturing. To assure the proper mechanical properties and sufficient resistance to fatigue, an examination was carried out to determine the effect of preheat temperature and post weld heat treatment time on the mechanical properties and fatigue behaviour of the laserbeam welded joint.

Abstract: AISI 304 type austenitic stainless steel samples were subjected to different thermomechanical treatments in order to investigate the effect of thermo-mechanical treatment on the grain boundary structure of the material. Electron back scatter diffraction measurements have been carried out in order to obtain information about the boundaries of the treated specimen. The measurements showed that achieving the same deformation with the same number of deformation cycles and same heat treatment temperature, the application of shorter heat treatment holding time was advantageous in aspect of grain boundary structure comparing to the thermo-mechanical treatments with longer holding time. The frequency of the special Σ3n type CSL-boundaries excluding coherent twin boundaries was significantly decreased by increasing the heat treatment holding time of the samples from the very short heat treatment periods. Extending the holding time further, the frequency of the special Σ3n type CSL-boundaries excluding coherent twin boundaries increased and reached the results applying the shorter heat treatment periods.

Abstract: Welding experiences are demonstrated, which were developed on 2205 type duplex and 2509 type superduplex stainless steels (DSS and SDSS). The welded joints were produced by activated TIG welding and laser beam welding. For the ATIG process, which is a special kind of the TIG-welding, silica powder was used as activating flux. Microstructural characterizations were applied for the measurement of ferrite/austenite phase ratio in the weldments. The welded joints were thermally aged at temperature of 400 °C. The phase transformations produced during thermal ageing were investigated by optical and scanning electron microscopy and thermoelectric power measurement. Investigations show that the thermal ageing induced phase transformations are similar at ATIG-welded weldment and DSS base material, but the incubation time is significantly shorter in the weldment than in the base material when laser welding is applied.

Abstract: In the present paper we summarize some of our results obtained in the field of magnetic testing of thermal shock fatigue testing of power plant steels. In this work 15Mo3 type ferritic heat resistant steel was investigated. This steel and several similar grades are commonly used in power plants boilers as the material of reheating steam pipelines and pressure vessels. Their typical application temperature is about 500-550 °C. It is commonly accepted that a combined form of mechanical, thermal fatigue and the creep processes causes the long term deterioration of this structural steels. The applied thermal shock fatigue test can model the material degradation due to long term service in high temperature environment. A parallel motion vibrating sample magnetometer, an AC permeameter and a magnetic Barkhausen noise measuring device was used for testing the magnetic properties of the samples and several different magnetic properties were measured to characterize the microstructural processes of the deterioration.

Abstract: The reinforcement of high voltage electric power cables is a promising application field of the composite wires. The temperature of the power cables can reach 200-300 °C due to an over-loaded electrical grid. The composite wires have to stand these high temperatures for a long time in the power cables. Long term heat treatments have been done to examine the eligibility of the composite wires. After heat treatment impact test was applied to measure the changes of the mechanical properties of composite wires. With the instrumented impact tester the process of the failure was examined. In this paper the continuous production method of ceramic fibre reinforced metal matrix composite wires and their properties are shown.

Abstract: Stents are special metallic or polymer endoprostheses of meshed structure and tube shape. Their function is to prevent restenosis in the arteries. Stents can be coated or uncoated. In the expanded part of the artery the chance of restenosis is bigger even without a stent so it is practical to coat the stents. The aim of this work is to present the results of the coating experiments made on the coronary stents. Three types of commercially available polyurethanes were used for these experiments. The coatings were produced by a dipping method. Electro-polished and non-electro-polished metallic sheets and stents were used for these experiments. Contact angle measurements were done to examine the wetting properties of the three different polyurethane coatings. The quality and the changing of the coatings were examined by different methods (stereomicroscope, scanning electron microscope and energy dispersive spectrometry).