Abstract: The present invention provides a process for efficiently dephosphorizing, dephosphorizing and decarbonizing, or desulfurizing, dephosphorizing and decarbonizing a hot metal in a converter. The amount of flux to be charged and the amount of bottom-blown gas are adjusted so that the bottom-blowing agitation power and the CaO/SiO.sub.2 ratio subsequent to the treatment become at least 0.1 kW/ton and from 0.7 to 2.5, respectively and the hot metal temperature at the treatment end point becomes from 1,200.degree. to 1,450.degree. C. Furthermore, the operation of the process is controlled so that the sum of a T.Fe concentration and a MnO concentration in the slag subsequent to the treatment becomes from 10 to 35% by weight by adjusting the top-blown oxygen feed rate, the flow rate of bottom-blown gas or the top-blowing lance height.

Abstract: A carbon steel containing super-finely dispersed oxide system inclusions, comprising, by weight, not more than 1.2% carbon, 0.01 to 0.10% Al, total oxygen of not more than 0.0050%, Mg which fulfills the relationship of the following formula:(total oxygen wt %.times.0.5).ltoreq.total Mg wt %<(total oxygen wt %.times.7.0)and Mg oxides comprising MgO.multidot.Al.sub.2 O.sub.3 and free MgO.