TESTING MAGNESIA-CARBON BRICKS FOR OXIDATION RESISTANCE

<p> </p><p><span style="font-family: Times New Roman; font-size: small;">MgO-C based refractory materials are used in steel metallurgy to a large extent. Magnesia-carbon bricks are tested for basic physical-mechanical parameters in as supplied state, for carbon content, and chemical analysis of magnesium component. According to the type of their usage, they are subjected to tests at higher temperatures, carbonization firing, and after firing, the physical-mechanical parameters are determined at specified temperatures. One of the most tested properties of these materials is their resistance to oxidation. The methodology for such testing is not yet defined in ISO, EN and ASTM test procedures, therefore the methodology used in other countries is being applied. In conditions of U. S. Steel, Košice, s.r.o., the MgO-C bricks intended for the working lining of slag zones of steel ladles are tested by oxidation resistance test (oxidizing area procedure). </span><span style="font-family: Times New Roman; font-size: small;">The described test method was developed at U. S. Steel Research and Technology Center in Munhall and has been used for more than 15 years to evaluate various carbon containing bricks. Test specimens in the shape of a cube are heated in an oxidizing atmosphere to a temperature of 1482</span><span style="font-family: Times New Roman; font-size: small;">°C with holding time of 5 hours. After cutting of the test specimens, the percentage of oxidized area is calculated. This test is used for selecting the appropriate type of lining material for the working lining of slag zone of the steel ladle in the steelmaking secondary metallurgy process and for the building of database of different types of MgO-C bricks.</span></p><p> </p>

Effect of Premelted Calcium-Magnesium-Aluminate Flux on Magnesia Carbon Brick

The novel Calcium-Magnesium-Aluminate (CMA) based premelted fluxes with different concentrations of MgO are developed and their corrosion to MgO/C brick is compared with traditional fluxing practice based on CaF2 addition. Results show that the corrosion of the MgO/C brick can be reduced obviously with initial high content of MgO employed in CMA. Additionally, the corrosion could be decreased correspondingly with the increase of MgO content in CMA fluxes, and the working lifetime of ladle slag zone can be extended by adding CMA flux.

Effect of Wolastonite Mineral (CaO SiO2) Content in Continuous Casting Powder to SEN Erosion

The basic idea of the work was to analyze the effect of the wollastonite mineral CaO SiO2 content in the continuous casting powder related to the SEN erosion. In order to realize the research, experiments were conducted in the laboratory conditions. The research, experiment, was realized in the Magnohrom Kraljevo laboratory, and cryptonym furnace EV16 was used for refractory material behavior. Cut SEN pieces from the slag zone in the reduction atmosphere were treated in the furnace with three types of casting powder of different mixtures ratio of SRD1 (without wollastonite) and SRD2 (with wollastonite): Casting powder 1 - SRD1/SRD2 = 50/50 %, Casting powder 2 - SRD1/SRD2 = 25/75 % and Casting powder 3 - SRD1/SRD2 = 75/25 %. Temperature of the experiment was in the range of 15200C – 15400C, and treatment time was changed simulating the average casting time of the heat; one heat (45 min), two heats (90 min), and three heats (135 min). The experiment pointed out that the erosion of the SEN was reduced with the increased ratio of wollastonite in the casting powder. The erosion rate of the SEN exposed to the casting powder 2 in the laboratory conditions was 0.0055 mm/min, whilst the erosion rate of the SEN exposed to the casting powder 3 (with the least wollastonite content) was 0.0075 mm/min. Erosion rate of SEN exposed to the casting powder 2 was lower for the 26.27 % related to the casting powder 3, and 17.90% lower than the erosion rate of the casting powder 1 (the erosion rate of the casting powder 1 was 0.0067 mm/min). These laboratory experiments are very consistent with results obtained in the plant conditions [1,2,3]. At that time, results indicated that SRD1 casting powder without wollastonite has the erosion rate 46 % higher than SRD2 casting powder with wollastonite. On the basis of the laboratory researches and earlier plant conditions researches it could be concluded that wollastonite mineral content in the casting powders has significant effect on the SEN erosion, in the way that the SEN erosion rate was decreased with the increased wollastonite content in the casting powders.