| 摘要 |
PROBLEM TO BE SOLVED: To provide steel combining high toughness and free cuttability and capable of contributing to the reduction of the production cost of machine parts and the miniaturizing and lightening of the parts in bainite type non- heattreated steel. SOLUTION: This high toughness non-heattreated steel has a composition containing, by weight, 0.01 to 0.50% C, 0.05 to 2.50% Si, 1.30 to 3.50% Mn, 0.50 to 2.50% Cr, 0.05 to 0.20% S, 0.003 to 0.060% Al, 0.003 to 0.025% N, and the balance Fe with inevitable impurities and contains sulfide inclusions with a cross-sectional area of 3μm2 or more by 200 pieces/mm2 or more in the case of being observed in the cross-section parallel to the rolling direction.
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