CASTING SLAB FOR SHADOW MASK, METHOD FOR HEAT TREATMENT THEROF AND MATERIAL FOR SHADOW MASK

The present invention aims at providing a sophisticated segregation reducing technique which a conventional technique cannot achieve by finding the relationship between the casting structure and the segregation of components at the time of solidification and the heat treatment conditions. That is, the present invention aims at providing material for shadow masks which exhibits excellent quality with respect to streaks. A material for a shadow mask of the present invention is formed of a casting slab for preparing the shadow mask which comprises an Ni-Fe alloy containing 30 to 45 % of Ni. The casting slab has a cast structure comprising a columnar crystal and/or a chill crystal in an amount of 99 % or more. In particular, it is preferred that the casting slab contains no equiaxed crystal. To this end, such casting slab is prepared by a continuous casting method in which casting operation is carried out with no electromagnetic stirring and with maintaining a melt temperature of the non-solidificated part in the slab at a temperature equal to or more than the liquidus thereof. Further, the resultant slab is subjected to a heat treatment at a temperature for a time such that the K value becomes 150 mu m or more, to thereby diffuse the segregation of Ni.