Abstract
It is discussed in the article the concept proposed for the production of ultra-low carbon steel, which involves the production of crude steel in basic oxygen furnace followed by oxidative blowing with an oxygen-argon mixture in a teeming ladle to decrease a carbon content in steel to less than 0.03%. High efficiency of the proposed technology is possible only under the intensive process of metal decarburization, which consists of the three stages: supply of reagents to the gas bubble, chemical interaction of reagents on the interfacial surface and removal of reaction products. At low carbon concentrations in the metal, the limiting link of the process is carbon mass transfer to the interfacial surface, which can be intensified by melt stirring. The objective of this article is to study the influence of design of the blowing devices, namely, the position and shape of the pores, on the efficiency of metal homogenization in the teeming ladle. Blowing devices with a circular hole, a slit and undirectional porosity were considered. To perform physical simulation by Buckingham's theorem, similarity numbers were chosen to describe the considered process. In particular, it is proposed to use dimensionless volume flow and a modified homochronicity number. Based on the physical simulation on the “water” model, it was found that the best results of homogenization of the chemical composition of the liquid metal in the teeming ladle show blowing devices with undirected porosity. They are ideal for oxidative purging in a crowded ladle with a mixture of argon and oxygen required for the production of ultra-low carbon steel with an oxygen content of less than 0.03%. The purpose of further research is to develop the design of the mixing chamber of the purge device, in which oxygen and argon are pre-mixed before injection into the liquid metal.
Highlights
Ultra Low Carbon (ULC) steels have good formability and a superior surface quality. These advantages provide their use as automobile panels since the latter half of the 1980s. This automobile panel material is normally produced by cold rolling and annealing after hot rolling, in which hot rolling is usually finished in the austenite region at the elevated temperature [1]
Niobium and/or titanium were added to these steels to stabilize the interstitial carbon and nitrogen atoms [1]
Liquid steel is processed through a vacuum degasser to reduce carbon and nitrogen to levels low enough that the remainder can be “stabilized” by small additions of titanium and niobium [1]
Summary
Ultra Low Carbon (ULC) steels have good formability and a superior surface quality. These advantages provide their use as automobile panels since the latter half of the 1980s. Conventional IF steels which following the introduction of vacuum degassing technology contained carbon in the range of 40-70 ppm and nitrogen in the range of 30-50 ppm. Niobium and/or titanium were added to these steels to stabilize the interstitial carbon and nitrogen atoms [1]. Liquid steel is processed through a vacuum degasser to reduce carbon and nitrogen to levels low enough that the remainder can be “stabilized” by small additions of titanium and niobium [1]. Non-ageing IF steel has no yield point elongation, which means fluting and stretcher strains are never a problem [1]
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