Papers by Author: Péter János Szabó

Abstract: As a novel procedure for determining dislocation density, a software was improved with which data obtained by Scanning Electron Microscope (SEM) measurements can be collected and the value of superficial dislocation density can be calculated. Applying this method we investigated cold rolled lath martensitic steel samples. Besides dislocation density values, microstructure mapped by Electron Backscatter Diffraction (EBSD) will be discussed.

Abstract: Corrosion degradation was observed in a nuclear power plant spent fuel cooling system. A systematic and comprehensive investigation program was developed which was negatively influenced by the limit of sampling (contaminated material). Corrosion tests, mechanical and microstructural investigations were carried out and also microbiological effect was examined. Major contributors to the degradation were identified.

Abstract: Case hardened, double-walled train wheel, produced in the foundry of Abraham Ganz in 1867 and used for long time on the railroad tracks, was studied and evaluated by modern methods of materials sciences. The investigations indicated the presence of 0.059m% antimony (Sb), distributed uniformly in the material of the wheel. This quantity is several times higher than the average Sb amounts (<0.01m%) of the other components get into the castings. Sb was detected even in the several mm thick crust; except in the outermost surface layer with < 1 µm thickness. Based on the 20th century comprehensive studies, the antimony content, detected in the wheel, was found to be ideal. In grey iron it is a powerful pearlite stabilizer which has favourable effects on its mechanical properties and serviceability.The investigation of the surface structure proved that the excellent hardness (~600 HV) at the crust surface was due to the “nano-composite” structure formed from the pearlite as a consequence of severe plastic deformation during service. This was also promoted by the high amount (4.09m%) of carbon present in the casting. The microstructure refinement during operation most probably contributes to the long service lifetime of the wheels.The secret of the Abraham Ganz’s train wheels is inherently present – besides the novel construction and production technology (case hardening) – in the above mentioned composition and the structure of the material.

Abstract: From the lattice orientation of a sample, elements of the Nye-tensor can be determined. With the help of Nye’s tensor, dislocation density can be calculated for the certain sample. Since the measures were carried out with scanning electronmicroscope (SEM), just superficial orientations can be measured. Hence the Nye-tensor is an incomplete matrix, with five elements. Because of the absence of the other four elements just a quasi-dislocation density can be obtained. The algorithm of the calculation was programmed on the language C#.

Abstract: The aim of our investigation was to study the effect of deformation on the start temperature of the austenite-ferrite transformation. The deformation was carried out during cooling before the beginning of the transformation. The transformation start temperature was determined by dilatometric measurement with a Gleeble 3800 thermomechanical simulator. A novel method was developed to study the deformation induced ferrite transformation (DIFT) effect and successful experiments were carried out on S460MC grade steel specimens to determine the effect of the deformation stored energy on the transformation temperature of the austenite. Evaluating the dilatograms a strong relationship was observed between the temperature of the deformation and the austenite transformation start and finish temperatures. Lower deformation temperature resulted finer microstructure after austenite transformation.

Abstract: Commercial Cu-ETP drawn copper bar was both mechanically and thermally treated. Repeated cycles of cold rolling and heat treatment with altered parameters were applied on the specimens. Grain boundary character distribution (GBCD) was calculated from the orientation microscopy data. As regards the processing of the orientation data the coincidence site lattice theory was applied. The evolution of the GBCD is discussed in terms of the parameters of cold rolling and heat treatment processes.

Abstract: During brazing of austenitic stainless steel with copper based brazing material a common failure occurs, namely that the brazing material solutes along grain boundaries, which look like cracks. This unfortunate effect occurred when AISI 304 steel is brazed. To avoid this unwanted effect since the cracks propagate mainly on high angle grain boundaries our goal was to enhance the number of special coincident site lattice type grain boundaries with thermomechanical treatment. Experiments were performed for 1, 48 and 72 hour heat treatments at different level of cold rolled materials. After the thermomechanical treatment significant decrease in the crack size was found in depth and width, respectively. The grain boundaries were investigated on electro polished samples in an electron microscope with electron backscattered diffraction technique. The brazing was made with Boehler SG-CuSi3 brazing material.

Abstract: The relative fraction of the special grain boundaries can be increased by thermo-mechanical treatments. During this work, AISI 304-type austenitic stainless steels were plastically deformed and heat treated under different conditions, and then the grain boundary network, which developed during the treatments was investigated. Results showed that cyclic application of large cold rolling (30% reduction of thickness) and quick heat treatment at high temperature (800 °C, 2 minutes) gave the best grain boundary network. A possible reason of this behaviour is that grains which did not recrystallize after the first cycle, stored a high elastic energy, which helped the grain boundary motions in the next cycles. To characterize the developed grain boundary network, different parameters are also suggested in this paper.

Abstract: The environmental and polluting materials emission standards in Europe are going to be always stricter, so in order to keep up with them, one of the largest European automotive manufacturer performs a laser treatment on the cylinder bores of their internal combustion engines. Due to the laser treatment, the near surface area of the cylinder bore becomes harder and more wear resistant, furthermore, due to the inhomogenity of the pearlitic matrix and graphite lamellae, oil reserving holes are formed. In our present work we investigated the laser treated layer of cast iron cylinder bores with lamellar graphite. Samples prepared with two different lasertypes and different energies were investigated on behalf of metallographic and functional aspects.

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.