| 摘要 |
PURPOSE:To prepare high tensile steel excellent in strength and tenacity, by applying rolling treatment and heat treatment to steel containing C, Si, Mn, S, Al in a specific ratio under a specific condition. CONSTITUTION:In subjecting steel consisting of 0.05-0.25% C, 0.7% or less Si, 0.5-2.0% Mn, 0.020% or less S, 0.005-0.10% Al and the remainder Fe and inevitable impurities to heat rolling at the transformation point while the cast structure thereof at the machine end of a continuous casting apparatus is held, said steel is rolled in a draft ratio of 30% or more at Ar3-Ar3+80 deg.C in a gamma region. In the next step, transformation is advanced by lowering the temp. thereof or by elapsing a definite time or the combination action therof and rolling is further carried out at a draft ratio of 10-65% in a gamma alpha transformation ratio of 5-60%. The resulting rolled steel is wound up at a room temp.-Ar1 or subjected to heat treatment for 30min or more or to heat treatment for 30min at a room temp.-Ar1 after once cooled by air to obtain a composite structure consisting of fine ferrite-perlite and restored ferrite. |
