Papers by Author: Éva Dénes

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Authors: Éva Dénes, Anna Fauszt, László Kopasz, Péter Török, Balázs Verő
Abstract: The coated product market is a highly quality exigent market which has been developing for decades. The technological process of galvanizing starts with a thermal cleaning in a continuous annealing furnace. Therefore the understanding of the processes which take place before dipping requires laboratory experiments modelling the oxidation and reduction of the base metal. Some of the presented experiments are thermogravimetric oxidation and reduction tests, others are laboratory trials carried out in special experimental furnace.
Authors: Szilvia Kőszegi, Éva Dénes
Abstract: Continuous hot dip galvanized steel samples have been treated with traditional chromium(VI)-containing passivator and environment friendly rare-earth metal containing ceriumsalt and lanthanum-salt based solutions using different immersion times. The treated surfaces have been examined by scanning electron microscope equipped with an energy dispersive X-ray analyser. After the pre-treatment the samples have been spray-painted with epoxy-based organic paint. The adhesion was tested with bending and cross-cut test. Thereafter salt spray test was performed on duplex systems. After 48 hours samples have been taken out from the corrosion chamber in order to perform electrochemical impedance measurements for 24 hours. Based on the results the most promising passivation among the chromium(VI)-free solutions has been found to be the cerium-salt based treatment. The adhesion of the organic coating was better on cerium-chloride treated substrate than on chromated one, while the anti corrosion properties of the two duplex systems were comparable.
Authors: Éva Dénes, Attila Lajos Tóth, Fábián Enikő-Réka
Abstract: The effect of the boron in steels is widely known as an element enhancing hardenability, but its role can also be related to the enamelability of steels. While the improvement of the hardenability is due to the solute boron, in the case of enameling grade steels the boron should be kept in form of precipitates 1. The hydrogen accumulated during processing and enameling diffuses to the metal/enamel interface and lead to the formation of the so called fish-scale failure. To prevent this it is needed an adequate type, number and dimension of precipitates which act as hydrogen traps hinder the free diffusion of the hydrogen in steel. The paper deals with the possibilities of investigation by scanning electron microscopy of the boron containing precipitates in the low carbon Al-killed steels apt for two side enamelling.
Authors: Éva Dénes, Piroska Fülöp, Judit Gergely, Ferenc Menyhárt, Sándor Tóth, Gábor Buza, Balázs Verő
Abstract: Diverse technologies in domestic enamelling production for machining, cutting and joining process are applied. The experiments presented in this paper focused on the opportunities of replacement of the drawn tubes built in heat exchangers longitudinal seam pipes produced by DUNAFERR Co. Ltd. The steel grade which satisfies the requirement of two-side enamelling, formability and after-fire sag resistance has been investigated. It has been shown that the coldrolled DC 04 EK-B steel grades stand all demands needed and therefore are able to replace the imported drawn tubes presently used.
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