Operation of the technology of converter production of steel with different carbon content

Abstract

The ever growing requirements on the quality of coldrolled sheet used in the automobile and electrotechnical industries are satisfied to a great extent due to the production of new grades of steel with more complex chemical compositions. Most attention is paid to the carbon and nitrogen content. The usual carbon content in steels is: 1) not more than 0.04% (steels of the type Stl4, Stl5); 2) not more than 0.008% (steels of the IF type and electrotechnical steels). The nitrogen content in these steels should not exceed 0.004-0.006%.Production of the first group of steels was organized in converter shop No. 2 of Novolipetsk Metallurgical Works, equipped with 350-ton converters providing combined blowing: oxygen lancing from above through the water-cooled tuyere and neutral gas blow (nitrogen and argon) through blast devices located in the converter bottom. The devices are metal tubes with a diameter of 6 -8 mm pressed into periclase-carbon blocks. The consumption of neutral gas is 0.015 -0.15 m3/(ton 9 min).Numerous experiments established that a combined blow is the most effective for reduction of the carbon content without overoxidation of the metal and slag. If the supply of neutral gases through the converter bottom is organized correctly, such a blow does not influlence significantly the nitrogen TsNllchermet State Scientific Center, Novolipetsk Metallurgical Works, Russia content compared to upper oxygen lancing. The oxygen content in the metal for a combined blow is nearer to the equilibrium content than in standard melts (Fig. I). The actual oxygen content in the metal in melts with a combined blow occupies an intermediate position. The oxygen contents also differ significantly. For a similar content of carbon the oxygen content in the metal for a combined blow is 16% less (relative) or 0.013% less (absolute) on the average (Fig. 2.) An additional blow of metal with argon after oxygen lancing brings the state of oxidation of the metal to an equilibrium value but does not decrease it significantly. Apparently this is due to an insignificant change in the carbon content, determining the concentration of dissolved oxygen. An increase in the intensity of the argon blow after the end of oxygen lancing is not always possible to implement technically, raises the cost of treatment, and results in considerable heat losses. However, with an increase in the neutral gas consumption to 1 m3/(ton 9 min) the rate of decarbonization of the metal increases significantly. Figure 3 shows the dependence of decarbonization of the metal on the initial carbon content, with the increase of which the decarbonization proceeds more intensely but does not influence equivalently the state of oxidation of the slag.The most widespread is the technology of tapping the metal out of a converter without any ladle additions. Its main