Nov način ocenjevanja kemijske mikroheterogenosti kontinuirno ulitih slabov

The paper deals with a new approach to measuring and evaluating the chemical micro-heterogeneity of the elements in solidified poly-component metallic systems. The original approach is based on experimental measurements made on the samples taken from characteristic places in a casting and the subsequent application of an original mathematical model for determining the element-distribution profile, characterizing the most probable distribution of an element concentration in the frame of a dendrite, and an original mathematical model for determining the effective partition coefficients of these elements in the structure of the analyzed alloy. The paper also describes an application of this method in the research of the chemical heterogeneity on a cross-section of a CC steel slab and presents the selected results (indices of the heterogeneity and effective partition coefficients of seven analyzed elements) characterizing the chemical micro-heterogeneity on one-half of the cross-section of this CC steel slab. The following main results were obtained: (i) the dendritic heterogeneity of the accompanying elements and impurities is comparatively high; (ii) all the analyzed elements segregate during the solidification into an inter-dendritic melt, and their partition coefficient is smaller than one; (iii) the effective partition coefficients calculated in this new way inherently include both the effect of segregation in the course of an alloy solidification, and the effect of the homogenization occurring during the solidification as well as during the cooling of an alloy.Web of Science471837

Effect of CaO/ SiO2 ratio on viscosity and structure of slag

The objective of this work is experimental determination of temperature dependences of viscosity of the molten CaO - Al2O3 - SiO2 system and assessment of impact of CaO/SiO2 ratio on viscosity and structure of this system. Experimental measurements of viscosity were performed with use of the high-temperature viscometer Anton Paar FRS 1 600. Viscosity was measured in a rotational mode during heating at the rate of 3,3 °C/min in the temperature interval from 1 673 to 1 873 K. Viscosity in the molten oxide system is determined by the internal structure. Exact clarification of the change of structure of the oxide system caused by the increased content of CaO was performed by Fourier transform infrared spectroscopy.Web of Science54345845

Interfacial tension at the interface of a system of molten oxide and molten steel

This paper is focused on a study of the interfacial tension between selected oxide and metal phases. The experimental research on the interfacial tension was performed in a horizontal resistive graphite Tamman furnace using an original method of measuring. This method consists of fixing both liquid phases in a horizontal position using a mandrel made of tungsten wire in a corundum cover. In this work the influence of the carbon content in the steel on the interfacial tension was studied. For this purpose a steel with 0.411 % of mass fraction of carbon and a steel with 2.64 % of carbon were used. Because of the wide variety of oxide systems used in industry, a characteristic system of casting powder was chosen for this study. This system contains dominant components, i.e., SiO2, CaO, Al2O3 and MgO, as well as a range of attendant mixtures, e.g., Fe2O3, TiO2 and Na2O. Simultaneously, the influence of SiO2 on the temperature dependence of the interfacial tension was observed. For this reason a concentration series with gradual additions of SiO2 was created. It was found that an increasing content of carbon in the steel significantly decreases the interfacial tension between the oxide system and the steel. The interfacial tension was found to decrease slightly with an increase in the content of SiO2 in the oxide system.Web of Science48341841

Hot ductility of TiNb IF steel slab after hot torsion testing

The aim of the work was to evaluate the hot ductility loss in TiNb stabilized IF steel directly from the continuously-cast slab using hot torsion testing (plastometry) in the temperature range 600-1250 degrees C according to the basic programme, and also after temperature cycling. A good match of the temperature dependences of number of turns to failure (N-f) and intensity of deformation Se was confirmed. In both cases, the existence of three temperature areas with decrease in plasticity to a minimum was confirmed. The two-stage temperature cycling according to the CT1150 and CT900 programmes mostly resulted in a decrease in plasticity compared to the basic programme. The most significant effect of cycling was related to the CT900 programme below the maximum plasticity in the base programme at 850 degrees C. A less pronounced decrease was observed for CT1150 cycling below the maximum plasticity in the base program at 1050 degrees C. In the case of CT1150 cycling, more complex particles were observed at the fractures compared with the basic programme, namely carbonitrides of Ti and Nb in combination with oxisulfides respectively, then Ti nitrides with oxisulfides or oxides and, in addition, complex (Fe,Nb)P-4, (Ti,Nb)(3)S-4 type particles. Their mean size determined statistically using TEM was much finer, only 20 nm versus 42 nm in the basic programme. Similarly, CT900 cycling revealed finer particles with an average size of 37 nm compared to 105 nm in the basic programme. The observed particles were Al oxides, Ti(N, C) and (Ti, Nb) 2S, in contrast to the particles probably of TiFe and FeMnS in the basic programme. The decrease in plasticity corresponded to the finer particles, newly created in the temperature cycling.Web of Science97art. no. 75

Comprehensive study of rheological and surface properties of the selected slag system in the context of its internal structure

Rheological (dynamic viscosity, flow curves) and surface properties (surface tension) of real slag system were experimentally investigated. Measurements of dynamic viscosity were performed with use of the high-temperature viscometer Anton Paar FRS 1 600. The method of sessile drop was used for measurement of surface tension. Surface tension and dynamic viscosity were measured in the temperature interval from 1 200 to 1 600 °C. The structural characteristics of the selected samples were determined by X-ray diffraction (XRD). The samples for given analysis were prepared by quench cooling. Experimentally determined values of dynamic viscosity and surface tension were compared with the results of X-ray diffraction phase analysis.Web of Science55470069

Uporaba teorije fizikalne podobnosti za opis filtriranja kovinske taline

The Bernoulli equation is the basis for the primary description of the flow of a real metallic melt through the pouring system for the filling of the casting mould with an inserted ceramic filter. In principle, a modified, dimensionless form of the Bernoulli equation can be used for the determination of the loss coefficient as a general function of the dimensionless criteria – the Reynolds, Froude and Euler numbers. It was verified by modelling the flow of the modelling liquid (in this case water) through ceramic filters. In the same interval of Reynolds numbers the loss coefficient was greater for foam filters than for filters with direct holes (strainers); however, the outlet coefficient μ of the foam filters was, in identical conditions, significantly lower than that of filters with direct holes.Bernoullijeva enačba je podlaga za opis pretoka taline skozi livni sistem z vstavljenim keramičnim filtrom. Načeloma je mogoče uporabiti modificirano brezdimenzijsko obliko Bernoullijeve enačbe za določitev koeficienta izgube kot funkcije brezdimenzijskega kriterija – Reynoldsovega, Froudovega ali Eulerjevega števila. S pretokom modelne tekočine (vode) je bilo preverjeno, da je pri enakem intervalu Reynoldsovih števil koeficient izgube večji pri penastem filtru kot pri filtru z direktnimi luknjicami, vendar pa je izhodni koeficient μ za penaste filtre pri enakih pogojih pomembno nižji kot pri filtrih z neposrednimi luknjicami

Effect of chemical composition and temperature on viscosity and structure of molten CaO-Al2O3-SiO2 system

The effects of the change of chemical composition and temperature on the viscosity of CaO-Al2O3-SiO2 oxide system with basicity from 0.78 to 1.63 were investigated in this paper. Experimental measurements of viscosity were performed with use of the high-temperature viscometer Anton Paar FRS 1600. Viscosity was measured in a rotational mode during heating at the rate of 2.2 K/min in the temperature interval from 1673 to 1873 K. Viscosity is often sensitive to the structural changes in molten oxide systems, which implies that the analysis of viscosity is an effective way to understand the structure of molten oxide systems. Exact clarification of the change of structure of the oxide system caused by increased content of CaO was performed by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and X-ray diffraction (XRD).Web of Science6042878287

Determination of the solidus and liquidus temperatures of the real-steel grades with dynamic thermal-analysis methods

The knowledge of the solidus and liquidus temperatures of the real-steel grades is one of the most important technological factors – especially when dealing with the processes of casting and solidification. These temperatures are critical parameters for proper settings of the models (physical or numerical) or in the final stage of an applied research of a real process. A correct setting of a production technology is significantly affecting the final quality of the as-cast steel (billets or ingots). Therefore, this paper is devoted to discussing the findings obtained during a utilization of dynamic thermal-analysis methods to identify the solidus and liquidus temperatures applicable to commercially produced steels. The results obtained with a differential thermal analysis (DTA) for three steel grades and with 3D differential scanning calorimetry (3D DSC) for two steel grades are compared with the results of the selected equations commonly used for liquidus and/or solidus temperature calculations. The calculations obtained with the Computherm SW for the discussed steels were also realized. It can be stated that the equilibrium liquidus and solidus temperatures obtained with the above-mentioned methods for each steel grade differ. The differences between the calculated results, the thermodynamic calculations and thermal-analysis results are very unpredictable and vary individually for different steels. These differences are not marginal (tens of Celsius degrees). So, it is sometimes suitable to combine several methods for a proper determination of the liquidus and solidus temperatures for a correct setting of a steel-making process or its modelling. The best solution for a technological process is to obtain the liquidus and solidus temperatures for a concrete-steel grade from a given steelmaking practice – a thermal analysis of a concrete-steel grade is a possible way.Web of Science47557556