Continuous-cast slab, method and apparatus of manufacturing the same, and method and apparatus of manufacturing thick steel plate

A method of manufacturing a continuous-cast slab, the method comprising:

• a first step of forming a first reduction dent at least in one long side surface of the continuous-cast slab by carrying out reduction with first reduction rolls on the continuous-cast slab, the continuous-cast slab being 0.1 to 0.3 in ratio D/W, the ratio D/W being a ratio of casting thickness D to casting width W, and 230 to 380 mm in casting thickness D, the continuous-cast slab having a horizontally symmetrical granular equiaxed crystals at least in a center in a thickness direction;
• and
• a second step of forming a second reduction dent that is narrower than the first reduction dent by carrying out further reduction on a bottom surface of the first reduction dent with second reduction rolls that are narrower than the first reduction rolls,
• wherein in the first step, the reduction is carried out on the continuous-cast slab so that a dent amount d1 of the first reduction dent from an end surface of the continuous-cast slab is 0.08 to 1.1 mm, and
• in the second step, the reduction is carried out on the continuous-cast slab so that a dent amount d2 of the second reduction dent from the bottom surface of the first reduction dent is 1.2 to 12 mm, and/or
• wherein in the first step, the reduction is carried out on the continuous-cast slab so that a dent rate of the first reduction dent from an end surface of the continuous-cast slab, to the casting thickness D is 0.03 to 0.36%, and
• in the second step, the reduction is carried out on the continuous-cast slab so that a dent rate of the second reduction dent from the bottom surface of the first reduction dent, to the casting thickness D is 0.6 to 4%.

An apparatus of manufacturing a continuous-cast slab, the apparatus comprising:

• first reduction rolls that shape an intermediate shaped product having a first reduction dent at least on one long side surface of the continuous-cast slab, the continuous-cast slab being 0.1 to 0.3 in ratio D/W, the ratio D/W being a ratio of casting thickness D to casting width W, the continuous-cast slab being 230 to 380 mm in casting thickness D, and having horizontally symmetrical granular equiaxed crystals at least in a center in a thickness direction;
• and
• second reduction rolls that shape a second reduction dent denting further from a bottom surface of the first reduction dent of the intermediate shaped product and being narrower than the first reduction dent, the second reduction rolls having shapes narrower than the first reduction rolls and being arranged downstream from the first reduction rolls,
• wherein the first reduction rolls are provided so that a dent amount d1 of the first reduction dent from an end surface of the continuous-cast slab is 0.08 to 1.1 mm, and the second reduction rolls are provided so that a dent amount d2 of the second reduction dent from the bottom surface of the first reduction dent is 1.2 to 12 mm, and/or the first reduction rolls are provided so that a dent rate of the first reduction dent from an end surface of the continuous-cast slab, to the casting thickness D is 0.03 to 0.36%, and the second reduction rolls are provided so that a dent rate of the second reduction dent from the bottom surface of the first reduction dent, to the casting thickness D is 0.6 to 4%.