STEEL SHEET AND SLAB SUPERIOR IN SURFACE QUALITY AND INNER QUALITY, AND MANUFACTURING METHOD THEREF

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PROBLEM TO BE SOLVED : To provide a steel sheet and a slab each with adequate surface quality and inner quality, which hardly causes the clogging of a nozzle in a continuous casting process, a surface defect due to cluster-shaped inclusions, and pressed cracks due to large-sized inclusions, and to provide a manufacturing method therefor. SOLUTION : The steel sheet or the slab includes, by mass, 0.05% or less S, 0.001% or more REM (rare earth elements) and 0.0004% or less Ca, in the steel; and contains non-metallic inclusions existing in the inner part, which have an average composition in the following range : a mass ratio (REM oxides/Ti oxide) of REM oxides to Ti oxide is 0.1 to 5.0, while satisfying the condition that Ti oxide is 10% to 95%, REM oxides are 5% to 90% (among them, La2O3 is less than 40%), Al2O3 is less than 50%, CaO is less than 5%, and S is less than 5%. COPYRIGHT : (C)2006, JPO&NCIPI