| 摘要 |
PROBLEM TO BE SOLVED: To provide a powder to suppress generation of bubble defects while keeping high lubrication between an internal wall of a mold and a solidification shell by containing CaO, Al2 O3 and F, and specifying the SiO2 concentration and the weight concentration ratio of CaO to SiO2 . SOLUTION: The concentration of SiO2 is <=15%, and the weight concentration ratio of T.CaO to SiO2 indicated by the formmla T.CaO=CaO+CaF×(56/78) is >=4.0. The F concentration is 5-30 wt.%, while the concentration of' Na2 O and K2 O is below 1.0 wt.% in total. The raw material to be used in the powder may be one generally used. That is, the raw material of CaO is quick lime and lime, the raw material of Al2 O3 is alumina, the raw material of F is fluorite, and the raw material of Si2 O3 is silica sand and diatomite. A cast slab excellent in surface quality can be obtained by the mold powder.
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