| 摘要 |
PROBLEM TO BE SOLVED: To improve the toughness of a steel product, and to improve the machinability by adding a deoxidizing agent in which the content of a deoxidizing element in the deoxidizing agent is regulated to a molten steel in which the oxygen content is regulated before deoxidization, and effecting the deoxidization by reducing the deoxidizing concentration product ratio in the molten steel within a specified range to surely grain refine and diffuse impurities during the deoxidization. SOLUTION: The deoxidization product ratio in the molten steel is 8×10<2> -8×10<5> , and the deoxidization product ratio is defined by the formula (S: deoxidization concentration product ratio, [M]: content (%) of the deoxidizing element in the deoxidizing agent, [O]: content (%) in molten steel before deoxidization, K: deoxidization constant, X: mol. number of oxygen to be reacted with the deoxidizing element of 1 mol. in the deoxidizing reaction). The deoxidizing agent sets the deoxidizing element in the vicinity of the deoxidizing agent to a low concentration area by alloying Fe, Ni, Cu, Mn, etc., as the not-deoxidizing element with the deoxidizing element such as Al, Ti, Mg and Ca, and suppresses the growth of impurities in a dissolving process in which the solubility of the deoxidizing agent is reduced, and grain-refines the impurities. The impurities are grain-refined as the deoxidizing concentration product ratio is lower, but the ratio is preferably >=8×10<2> .
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