Development of Mold Powder for High Grade Sheet Steel

摘要

In the production of cast slab for high grade sheetsteel, the powder in continuous casting mold is entrained intothe molten steel and caused the surface defects in the products.The typical example is the white spot defect for tin plate steel.For preventing the white spot defect, new continuous castingpowders are developed. Those powders are consist of CaO-SiO_2-Al_2O_3-MgO-CaF_2-AlF_3 system and less Na content.The results of study in laboratory and casting in plant aresummarized as follows.(1) By replacing Na materials with the fluoridesof alkali-earth metal, the improved powder can be produced.(2) When Na in powder is less than 1 masspercent, the occurrence of white spot defect ofthe tin plate steel produced by high-speed casting is remarkably decreased.(3) Characteristics of the improved powder are as follows.? The powder is designed of higher viscosity and surface tension.? The crystallization temperature is lower.? The variation in viscosity due to Al_2O_3 pick up during casting is less.