M. P. Tonkovič, L. Kosec, J. Lamut, V. Gontarev, Z. Samardžija - Mechanism of the Oxidation of the Fe-C-Si-Al-Zr Alloys

     Mechanism of the oxidation of the thermal-resistant Fe-C-Si-Al-Zr alloys was investigated at high temperatures. For the analysis three series samples: L1, L2 and L3, had been annealed at 1100 °C, were cast. After annealing the samples were investigated on the oxide thickness increase. They were observed and analysed by optical and electron microscopes. In case of the small zirconium content in the L1 sample, the graphite lamellae and only a significant amount of zirconium carbide in the ferrite matrix have been observed. At higher zirconium content (the L2 and L3 samples) graphite lamellae and particles of ZrC have been observed. During annealing an oxidation of graphite and ZrC took place. The oxidation of ZrC into ZrO₂ is direct and progressive. Evolving CO gas formed the pores around ZrO₂. Under sufficient amount of the dissolved oxygen the oxidation of aluminium was taking place too. Al₂O₃ was precipitating in the CO-ferrite interface filling up the formed pores. Finally the interaction between ZrO₂ and Al₂O₃ were taking place and formation the compound of ZrO₂·Al₂O₃ retarded further oxidation.

R. Turk, I. Peruš, M. Knap - Modeling and the Reliability of Calculated Flow Curves

     Flow curves are very important input data for numerical modelling of industrial processes and for direct industrial applications. Precise thermal and mechanical testing of low carbon silicon steel showed obvious differences in yield stresses according to permissible oscillations of chemical composition. Since conventional Hajduk, Elfmark and Spittel equations for flow curve calculation are very rigid and cannot describe the local changes of yield stresses caused by phase transformations, a new neural network aproach for modelling the physical phenomena in materials science has been developed. The obtained results showed that neural-network method is a powerful tool, and it can be applied directly in solving problems of materials science (e.g. materials testing support, mathematical simulation of materials forming process).

M. Kundak, Đ. Nikolić - Analysis of the State of Production of Seamless Steel Tubes at the Sisak Steel Works

     The paper deals with the production of seamless steel tubes at the Sisak Steel Works in Sisak, Croatia since 1992, i.e. during the war and the postwar years. Due to operation at a greatly reduced capacity the steel mill and the rolling mill have faced major financial losses. Based on those negative experiences a way of overcoming the current state of affairs in steel production has been sought. The cost of specific energy consumption is analysed in respect to its share in the selling price of the product for the purpose of predicting the terms of operational profitability and reducing the financial losses caused by occasional drops in the production rate below the profit-making level.

R. Turk, P. Fajfar, R. Robič, I. Peruš - Prediction of Hot Strip Mill Roll Wear

     Wear of work rolls has significant influence on the flatness of hot rolled strip and therefore it is a technological parameter, which should be considered in planning and realization of the rolling technology. The relationship between the rolling program, pass schedule, and the work roll wear profile will be presented with the CAE neural network. The same method is applied in the program for prediction of the optimal shape and prediction of wear progress during the rolling process on one pair of work rolls. This study of the wear of work rolls refers to the Steckel rolling strip technology.

A. A. Milenin, A. N. Golovko, I. Mamuzić - The Application of Three-Dimensional Computer Simulation when Developing Dies for Extrusion of Aluminium Shapes

     The automated system of three-dimensional computer simulation with use of FEM is developed. The model is based on the Euler approach. The function of Markov variation principle is used for derivating. The connected task of thermo-viscous-plasticity is solved. The flat die is designed for extrusion of the thin-walled shape from a soft aluminium alloy 6060.