SLAB EXCELLENT IN WORKING CHARACTERISTIC AND STEEL OBTAINED BY WORKING THE SAME

PROBLEM TO BE SOLVED: To improve the working characteristics of the slab by controlling the maxi mum value of the crystal grain size in the depth equal from the surface of the cast slab to the one equal to or below the specified times of the average crystal grain size in the depth. SOLUTION: The maximum value of the crystal grain size is controlled to the one equal to or below the three times the average crystal grain size in the depth thereof, where >=60% of the cross-section in the thickness direction of the slab can be formed of equi-axed crystals. Moreover, the whole cross section in the thickness direction of the slab can be formed of crystal grains composed of equi-axed crystals. The slab may be incorporated with the oxide of Mg formed by adding Mg or an Mg alloy to molten steel. The slab, in which the maximum value of the crystal grain size in the depth equal from the surface has been controlled to the one equal to or below the three times the average crystal grain size in the depth, is heated at 1100 to 1350 deg.C and is thereafter subjected to working such as rolling. Since the slab having a structure of uniform crystal grains is used in this way, the cracking resistance at the time of working such as rolling is high, and (r) value expressing drawing characteristics, or the like, can be improved.