| 摘要 |
PURPOSE:A free cutting steel secured in good cut property by making sulfide impurities macro-spherical, obtained by compositely adding Te, Pb and Bi to S while reducing Al in oxide impurities by lowering Al-content. CONSTITUTION:A steel ingot containing 0.2% or less C, 0.2% or less Si, 2.0% or less Mn, 10% or less P, 0.02% or less N, 0.002% or less Al, 0.4-0.50% S, 0.02-0.50% Te, 0.01-0.40% Pb and 0.01-0.40% Bi so as to adjust Te+Pb+Bi to 0.20% or more and further containing 0.0040-0.030% O and comprising the remainder of substantially Fe is prepared. In the next step, this steel is melted and continuously cast to obtain free cutting steel with high quality wherein MnS impurities with a long diameter of 5mum or more, a short diameter of 2mum or more and a long diameter/short diameter ratio of 5 or less occupies 50% or more of total MnS impurities and the average Al2O3-content in oxide impurities is 15% or less.
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