Refractories for an argon-oxygen steel refining unit

Abstract

In recent decades such processes of outside-the-furnace refining of very low carbon steels as vacuum--oxygen decarburization, argon--oxygen decarburization, and steam--oxygen decarburization have obtained wide use. Vacuum-oxygen decarburization is done in the ladle and argon--oxygen decarburization and steam--oxygen decarburization in special converter-type units.In the USA, Japan, and the countries of Western Europe the most common are argon--oxygen decarburization converters, in which in recent years more than 70% of corrosionresistant steel has been made [i, 2].In the argon--oxygen deoxidation converter the semifinished product, melted in an electric furnace or other steel melting equipment, is treated by purging it with an argon--oxygen mixture supplied through several side or bottom tuyeres.During purging the temperature of the molten metal increases to 1700-1800~ and the slag is high chromium with a low basicity (~1.2). At the end of treatment of the semifinished product the chemical composition of the molten metal is adjusted by addition of ferroalloys and production of a highly basic slag. The average treatment time in an argon--oxygen decarburization converter is 90 min [3,4].The combination of high temperatures, the strong erosion action of the molten metal and slag, acid slags, and variable temperature loads presents very high requirements for the quality of refractories for the lining of argon--oxygen decarburization converters.In a number of countries the problem of refractories for the lining of argon--oxygen decarburization converters has been solved as a result of development of special magnesite--chromite parts from clinkers and melted powders with the use of pure SiO2 raw material and high firing temperatures (1750-1825~ [3-6].The average life of argon--oxygen decarburization converters of these refractories is 45 heats with a maximum life of about i00 heats [5]. Refractories with a high magnesium oxide content must be avoided since their life in contact with an acid slag was low (14 heats) [3]. In the parts of the lining which are most eroded (tuyere zone, slag area) cast periclase refractories possessed higher wear resistance than refractories from melted powders but as a result of their high cost and low heat resistance they have not found quite wide use in argon--oxygen converters [7,8].Substantial changes in the technology of the argon--oxygen decarburization process (a reduction in temperature, an increase in slag basicity, etc.) had made it possible to use dolomite refractories for argon--oxygen decarburization converter linings.The average life of a dolomite lining is about 60 heats [9, I0] and with the organization of intermediate repairs up to i00 heats [ii]. In Japan magnesite--chromite refractories with a weight content of 64-74% MgO and 15-18% Cr203 are used in the slag zone and magnesite--dolomite in a ceramic binder (78)(79)(80)(81)(82)(83)(84)(85)(86) in other portions of the lining [12].The authors of this article have made investigations of refractories for the lining of an a...