Refractory for VOD furnace
VOD stands for vacuum oxygen decarburization. The equipment is vacuum degassing, oxygen blowing and decarburization of molten steel. Since oxygen blowing makes the temperature in the furnace rise above 1700℃ and desulfurization and reduction is needed at last, the alkalinity of slag changes greatly, the steelmaking temperature is high, and the vacuum condition damages the refractory lining greatly. Such harsh service conditions decided VOD lining to use high quality refractory materials, and decided to lower lining service life, generally only about 20 furnace times.
VOD slag lines are generally recombined or pre-reacted magnesia-chrome bricks, while cladding walls are made of low-grade magnesia-chrome bricks. Although magnesia-Chrome brick makes the service life of VOD furnace higher, but its price is higher, resulting in a ton of steel refractory cost higher. Therefore, resource-rich dolomite refractories are commonly used in Europe. Ultra-high temperature magnesia dolomite bricks are used for slag lines, and low-grade magnesia dolomite bricks or non-magnesia dolomite bricks combined with asphalt are used for cladding. Although the service life of this furnace lining is a little lower than that of magnesia-Chrome brick lining, the cost of steelmaking is reduced a lot and the social and economic benefits are obvious. With the development of magnesium carbon bricks, the use of low carbon magnesium carbon bricks or magnesium dolomite carbon bricks below the slag line has become a very reasonable choice, which can make the service life of VOD molten pool reach more than 40 times, if the maintenance or repair is well done, the service life can reach more than 60 times. Another trend in the development of refractories for molten pools is the use of aluminum-magnesium castable or prefabricated parts, which completely eliminates the adverse effects of carbon in the lining.
Magnesia-chrome brick in alkaline slag and oxidation atmosphere, namely in the process of use, trivalent chromium is oxidized to hexavalent chromium, it can cause human cancer, harm human health, so the use of magnesia-chrome brick by environmental protection laws and regulations and policies restrictions and influence. Therefore, people step up the study of magnesia-chrome brick substitutes, currently more recognized substitutes are ultra-high temperature fired magnesia dolomite bricks for slag line, and low carbon magnesia carbon bricks or low carbon magnesia dolomite bricks for molten pool, if further consideration of the impact on carbon, can be used aluminum-magnesia castable or prefabricated parts. However, the service life and cost are still lower than those of low carbon magnesia or magnesia dolomite bricks.
In addition to the choice of high quality refractory as lining, the best way to improve the service life of VOD furnace is :(1) improve the operating conditions. Making slag with dolomite and reducing steel temperature are very effective measures to improve service life. Of course, faster turnover and ladle insulation can also significantly improve the service life of the lining. Through the improvement of these operating conditions, the lining service life can be more than doubled; (2) Strengthen furnace protection or furnace repair. Any metallurgical equipment must be carefully maintained and reheated. If this is not done well, its service life will be greatly reduced. This aspect has done the service life to increase more than one time is without any problem. At present, VOD furnace repair work is not strong enough, should be strengthened, now is generally the lining of the furnace spray, the material used and the composition of the lining material is equivalent, such as magnesia-chrome brick lining, repair with magnesia-chrome quality spray material; If magnesium dolomite brick lining is used, magnesium calcium shotcrete is used for shotcrete maintenance. As for magnesia dolomite brick lining, the spraying and replenishment time will cause the temperature drop and the hydration of calcium oxide, which will lead to the destruction of furnace lining. Therefore, the spraying effect of magnesia dolomite brick lining is not significant, so it is necessary to study this aspect of the problem and find out the solution.