| 摘要 |
PURPOSE:To provide excellent resistance to hydrogen induced cracking and sulfide stress corrosion cracking to a steel sheet by heating a billet which is considerably decreased in the contents of P, S, O and N and is subjected to a morphology control treatment of MnS by addition of Ca, than rolling and cooling the same under specific conditions. CONSTITUTION:The compsn. consisting, by wt%, of <0.15 C, <0.6 Si, 0.6-1.5 Mn, <0.007 P, <0.001 S, 0.005-0.1 Al, 0.003-0.03 Ti, 0.0005-0.004 Ca, <0.0025 O, and 0.0035 N, contg. the components satisfying formulas I, II, III and consisting of the balance Fe and inevitable impurities is used for the billet. Such billet is heated to 950-1,250 deg.C and is then rolled at >=60% rolling reduction at <=900 deg.C and the Ar3 transformation point finishing temp. or above. The rolled sheet is cooled from the Ar3 transformation point or above down to 350-550 deg.C at 10-40 deg.C/sec cooling rate upon ending of the rolling and is then allowed to cool.
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