| 简介 |
PROBLEM TO BE SOLVED : To provide a method for producing a high tensile strength steel sheet having excellent SSC (Sulfide Stress Corrosion) resistance, and having a tensile strength in a class of ≥550 MPa. SOLUTION : A steel sheet having a composition containing, by mass, 0.03 to 0.09% C, 0.01 to 0.55% Si, 0.5 to 2.0% Mn, 0.005 to 0.06% Nb, 0.005 to 0.1% Al, 0.0005 to 0.006% N and ≤0.17% Pcm, and, if required, further comprising one or more kinds selected from Cu, Ni, Cr, Mo, V, Ti, B, Ca and rare earth metals, and the balance Fe with inevitable impurities is heated at 1, 000 to 1, 350°C, is thereafter hot-rolled, is subjected to accelerated cooling from an Ar3transformation point to 650°C, is subsequently heated in such a manner that the maximum arrival temperature of the surface in the steel sheet is controlled to an Ac1transformation point or above, the temperature at the inside of the steel sheet is controlled to less than an Ac1transformation point, and also, the difference in the maximum arrival temperature between the surface of the steel sheet and the central position of the sheet thickness is controlled to ≥50°C, and is thereafter air-cooled, thus the maximum hardness and the weld zone hardness in the sheet thickness direction of the steel sheet are controlled to ≤248 Hv. COPYRIGHT : (C)2007, JPO&INPIT |
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