| 摘要 |
PURPOSE:To obtain a machine structural steel having >=145kgf/mm<2> tensile strength and superior delayed fracture resistance by providing a steel compsn. contg. prescribed amts. of C, Si, Mn, P, S, Ni, Cr, Zr, Nb and Al and a hardened and tempered structure. CONSTITUTION:This machine structural steel has a compsn. consisting of, by weight, 0.20-0.45% C, >0.50-2.0% Si, <0.50% Mn, <=0.01% P, <=0.01% S, >0.10-4.0% Ni, 0.5-5.0% Cr, 0.01-0.15% Zr, 0.005-0.20% Nb, 0.01-0.10% Al and the balance Fe with inevitable impurities and a hardened and tempered structure. The steel has >=145kgf/mm<2> tensile strength and does not cause delayed fracture over >=2,000hr, so the steel is suitable for use as the material of shoe bolts, etc., of a large-sized bulldozer.
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