Control Of Chemical Composition And Inclusions In IF Steel

Owing to its excellent deep stamping and no-aging performances, IF steel becomes a new generation of stamping steel following boiling steel and aluminium killed steel and represents the development level of steel sheets for automobiles in a country. Now, IF steel's manufacture is in an elementary development stage in China. And China's IF steel can meet the quality demands for trucks and low-grade automobiles. Large numbers of high quality steel sheets for the top grade automobiles must be imported. Expecially, for skin plates with very strict surface quality, there is much greater disparity between foreign and China's product quality.By means of industrial test and sampling, variation regulations of chemical composition and inclusions in IF steel from BOF smelting, RH refining to continuous casting are studied in this work. The control level of chemical composition and inclusions in IF steel is analyzed. Correspondingly, some measurements and study trends are put forward. By means of mathmatics and physical modeling, steel fluid's flow and slag entrapments in a mold for IF steel's are investigated, and the technological parameters for continuous casting and structural parameters of SEN are evaluated and optimized. The optimum parameters are applied to IF steel's industrial manufacture, and the good results are acquired.Some important results of this work are as follows.(1) Carbon content and nitrogen content of IF steel's slab are 22×10^-6 and 21×10^-6, respectively. Carbon pickup for IF steel after RH decarburizing is 11×10^-6. And nitrogen pickup for IF steel after BOF smelting is 9×10^-6.(2) Total oxygen content and inclusion content of IF steel's slab are 16×10^-6 and 0.92 mg·(10kg)^-1, respectively, being international advanced level.(3) There are 4 style of inclusions in IF steel's slab, which are the cluster inclusions of Al₂O₃ system, block inclusions of Al₂O₃ system, inclusions of Al₂O₃-CaO or Al₂O₃-CaO -SiO₂ system, and inclusions of Al₂O₃-Ti₂O₃ system. Big block inclusions of Al₂O₃ system and inclusions of Al₂O₃-CaO-SiO₂ system is the main factor causing the surface defects of IF steel's slab.(4) With increasing the gas flow of SEN, the surface flunctuation in a mold is enhanced,...