| 摘要 |
PURPOSE:To produce a non-heattreated hot rolled steel sheet having excellent hydrogen induced cracking resistance and stress corrosion cracking resistance by subjecting an ingot having a compsn. consisting of C, Si, Mn, Al, Nb, P, S and Fe to hot rolling and coiling at specific temps. CONSTITUTION:The ingot contg. 0.01-0.4wt.% C, 0.01-0.5% Si, 0.01-2.0% Mn, 0.01-0.1% Al, 0.01-0.1% Nb, <=0.1% P, <=0.03% S, contg., if necessary, at least one kind among 0.001-0.01% Ca, 0.01-0.1% V, 0.01-0.1% Ti, and 0.01-1.0% Cr, and consisting of the balance Fe and inevitable impurities is hot rolled. The rolled steel is subjected to finish rolling at >=850 deg.C. The steel sheet is thereafter cooled from a 950-700 deg.C temp. range at 5-40 deg.C/sec cooling rate and is coiled at 650-350 deg.C. The mixed grain structure of 10-50% area rate occupied by ferrite particles having >=5mum grain size is then formed. The non-heattreated hot rolled steel sheet which withstands severe NACE corrosion conditions is thereby obtd.
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