| 摘要 |
PURPOSE:To produce a free-cutting steel having the better machinability than by an ingot making method by subjecting a steel which contains specified ratios of C, Mn, P, Sn, N, and O2, has the specific value of the average sizes of an MnS inclusion and satisfies the specific formula to continuous casting. CONSTITUTION:The steel which contains, by weight %, 0.04-0.2% Cr, 0.6-1.5% Mn, 0.05-0.2% P, 0.16-0.5% S, 0.003-0.03% N, and <=300ppm O2, has <=50mum<2> average size of the MnS inclusion, consists of the balance Fe and unavoidable impurities and satisfies the formula is continuously cast. In the formula, Rz(cc): the machinability (finish surface roughness) of the continuously cast free-cutting steel, R2(ic): the machinability (finish surface roughness) of the ingot making free-cutting steel, DELTAP: the difference in the content of P between the continuously cast free-cutting steel and the ingot making free-cutting steel, DELTAS: the difference in the content of S between both free-cutting steels, DELTAN: the difference in the content of N between both free-cutting steels, DELTAPb: the difference in the content of Pb between both free-cutting steels, DELTABi: the difference in the content of Bi between both free-cutting steels, DELTATe: the difference in the content of Te between both free-cutting steels, DELTAMnS: the difference in average size (mum<2>) between both free-cutting steels.
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