| 摘要 |
PROBLEM TO BE SOLVED: To obtain a non refining steel excellent in machinability at a low cost by specifying the compsn. composed of C, Si, Mn, P, S, Cu, Ni, Cr, Mo, W, Ti, Zr, Nb, Al, N, Pb and Fe and specifying the diameter and quantity of Ti and Zr carbosulfides. SOLUTION: This steel is the one having a compsn. contg., by weight, 0.3 to 0.6% C, 0.5 to 2.0% Si, 1.0 to 2.0%, Mn, <=0.05% P, 0.002 to 0.2% S, 0.01 to 0.5% Cu, 0 to 0.2% Ni, 0 to 0.5% Cr, 0 to 0.2% Mo, 0 to 0.35% W, <=1.0% Ti and <=1.0% Zr so as to also satisfy Ti+Zr: 0.04 to 1.0%, 0 to 0.03% Nb, 0.01 to 0.10% Al, <=0.008% N and 0 to 0.30% Pb, also satisfying fn2 =C+0.1Si+0.2Mn+0.5Cu:0.75 to 1.0% and fn2 =Ti+Zr-1.25:>0%, and the balance Fe with inevitable impurities, in which the maximum diameter of Ti carbosulfides and Zr carbosulfides is regulated to <=10μm, and total content thereof is regulated to >=0.05% by cleanliness.
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