Abstract: A cast slab comprising fine particles of oxides and MnS, said oxide comprising an Mn silicate, with Mn oxide occupying 50 to 80% by weight of the sum of Mn oxide and Si oxide, unavoidably included oxides, and an optionally added oxide of at least one member selected from Zr, Ti, Ce, Hf, Y, and Al, said oxide having a size of 0.1 to 10 .mu.m being dispersed in an amount of 30 to 2000 pieces per mm.sup.2 of section of said cast slab. The dispersion of many oxide particles, which are likely to serve as nucli for the precipitation of MnS, in said cast slab can provide a plate steel having good toughness in a HAZ and a steel sheet product having excellent deep drawability.

Abstract: MnS is finely dispersed and precipitated in a steel, and the steel obtained has highly improved characteristics such as HAZ toughness, cold cracking resistance, and corrosion resistance. This steel is obtained by continuously casting a component-adjusted molten steel having a dissolved oxygen concentration of 20 to 60 ppm and containing 0.01 to 0.05% by weight of a deoxidizing element, at a specific cooling rate.

Abstract: In a method for controlling solidification segregation in casting of carbon steel containing 0.53 wt. % or less of carbon, .alpha.-phase stabilizing elements and .gamma.-phase stabilizing elements of the carbon steel are separated from each other at inter-dendritic portions by adding 2 wt. % or less of at least one element selected from the group consisting of Be, Cr, Nb, Sn, Ti, Mo, and V into the molten steel.

Abstract: The .alpha.-stabilizing element, e.g. P, and the .gamma.-stabilizing element, e.g. Mn, do not segregate at an identical site of a casting. Castings are cooled at a rate of 40.degree. C./min or less in a temperature range of the peritectic reaction and/or the Ar.sub.4 transformation, thereby condensing P and Mn into .delta. and .gamma. phases, respectively.

Abstract: In a method for continuous casting of steel, an improvement which is constituted by carrying out the continuous casting process while the thickness of a molten mold powder pool adjacent to the molten steel melt within a continuous casting mold is maintained at a desired preset value, and whenever the actual value deviates from the preset value, the continuous casting can still be continued by adjusting the casting conditions or by selecting a powder appropriate for the casting conditions. The method produces a casting requiring no subsequent processing to remove defects.