Papers by Author: Tibor Berecz

Abstract: Lath martensitic microstructures were produced in steels containing 0.15% of carbon and various amounts of molybdenum and nickel. The behavior of the lath martensitic microstructure was studied during cold rolling in steels with six different chemical compositions. All materials have endured 75% deformation without damage. In addition, the effects of heat treatments on microstructures and hardness were investigated as well.

Abstract: The aim of this work was to analyze the performance of joints made by TIG (Tungsten Inert Gas) welding process in austenitic and duplex stainless steels with special regards to their corrosion resistance. Three different types of stainless steel were butt welded with TIG method. Ferric-chloride test and electrochemical treatments revealed how does the TIG process affects the corrosion resistance depending upon the alloy used for welding the joint. This work focuses on the weldability of the 2304, 2404 and 304 type stainless steel heterogeneous welds.

Abstract: Surface preparation for electron backscatter diffraction (EBSD) measurements requires a lot of time and experience. We chose a lath martensitic iron based alloy to demonstrate the efficiency of ion polishing techniques. The average image quality (IQ) values from the EBSD measurements were assigned to be the characteristic parameter for surface goodness. The ideal ion sputtering time and the angle of incidence were determined, and the corresponding inverse pole figure (IPF) and IQ maps were compared to the mechanical polishing treatment.

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: 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 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 micro hardness tests, optical microscopy, scanning electron microscopy (SEM) and X-ray line profile analysis.

Abstract: Duplex stainless steels constitute a famous group of the stainless steels. They consist of mainly ferritic and austenitic phases. The ratio between these phases is regulated by numerous alloying elements and low content of carbon. Because of this strong alloying a lot of metallurgical processes can take place at high temperature, e.g. the decomposition of ferritic phase into σ-phase and secondary austenite. In this paper the changes of amounts of these three phases are studied by automated EBSD, saturation magnetization measurement, XRD-analysis and micro-hardness test. Similar results were obtained by the different applied measurements for the change of phase ratios due to the isothermal heat treatment.

Abstract: Duplex stainless steels are a famous group of the stainless steels. Duplex stainless steels consist of mainly austenitic and ferritic phases, which is resulted by high content of different alloying elements and low content of carbon. These alloying elements can effect a number of precipitations at high temperatures. The most important phase of these precipitation is the σ-phase, what cause rigidity and reduced resistance aganist the corrosion. Several orientation relationships have been determined between the austenitic, ferritic and σ-phase in duplex stainless steels. In this paper we tried to verify them by EBSD (electron backscatter diffraction).