Contents

Abstract

During the elaboration of band strips due to ambient atmosphere at high temperature a compound Fe-oxide scale will be formed on the steel surface. The primordial aim of the steelmakers is that the Fe-loss ratio caused by oxidation should be the minimum at possible. Contemporaneously it is important that the properties of scales make possible an efficient descaling.The alloying elements of the steel materials which diffuse into the scale affect extremely the mechanical properties and the adhesion of scales.In the case of industrial samples examined first we have investigated by thermogravimetric method the influence of Ni and Si on the kinetic of scaling process. After that we examined the morphology of scale using scanning electron microscope, and energy dispersive X-ray spectrometer (EDS).The Si-content of the samples was between 0.18 and 0.35 mass%, while the Ni-content was between 0.002 and 0.25 mass%. The influence of these elements was more semnificative on the morphology of scale, while the effect on scaling mechanism was less traceable because the complexity of the mechanisms.

The Niobium-Sapphire interface was investigated in atomic level. The Sapphire crystal was taken to be rigid and the interaction was represented by pair potential in Niobium and non-pair potential between the Niobium and Sappier. Changing the strength of bonding the dislocation network was also changing. The simulation of the electronmicroscopic images helped the determination of the real structure.

The model of an ideally associated mixture has been applied to describe equilibria in the Fe-rich corner of the ternary Fe-B-N system. It has been found that when the nitrogen content of the melt reaches the value 80 ppm, then 37 % of B is complexed into BN molecules (associates) at a temperature of 1823 K. The phase boundaries between liquid iron and N₂ gas on the one hand, and between liquid iron and solid BN on the other hand have been determined. The solubility of N₂ gas increases with increasing the concentration of boron in the liquid. The concentration dependence of the BN solubility considerably differs from that predicted by the concept of the "solubility product", due to the strong complex (BN) formation in the system.

The most important things are - beyond that the good chemistry compound and suitable parameter selection of formation technology - the desired cross-section and steel strip of quality of material. That you know, mechanical and geometrical property of strip, which made from steel that the chemistry compounds have adjusted by steelmakers, are determined by degree-, speed- and quality of form. The fastest method of formation parameters can be determined by computer software.