PURPOSE: To obtain a slab from which a cold rolled sheet having decreased internal defects and good surface characteristics is obtainable by incorporating MgO and alumina clusters under specific conditions into inclusions of the cast slab for producing the cold rolled sheet.
CONSTITUTION: MgO blowing is executed at the end period of blowing in a converter to uniformly raise the content of the MgO in converter slag to ≥4% and the outflow slag of the converter is solidified by controlling its compsn. to a high melting point side to prevent outflow of the slag during tapping. In addition, Al is charged into the converter to lower FeO% in the slag, by which the amt. of the Al formed by reaction of the charged Al with the FeO in the slag is suppressed. Further, Ar is blown from the bottom of a ladle to deoxidize the steel under an inert gas. As a result, the slab for production of the cold rolled sheet which contains at least ≥4% of the MgO of a grain size ≤200μ in the inclusions of the steel, is dispersed with the aluminum clusters of a grain size ≤200μ at ≥103 pieces per 1kg slab, is free from the internal defects and has the good surface characteristics is formed.
KANEKO TOSHIYUKI
KASAMA AKIO
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