| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To provide a high-tensile thick steel plate showing little deterioration in material quality after warm molding at 400-600°C. <P>SOLUTION: The thick steel plate includes a composition containing, in mass%, 0.06-0.10% C, 0.03-0.35% Si, 1.0-1.6% Mn, 0.005-0.060% Al,≤0.0040% N, 0.20-0.50% Mo, 0.005-0.030% Nb and 0.015-0.080% V, provided that Mo, V and Nb satisfy the relations: 0.40≤(Mo+4.9V+5.8Nb)≤0.80 and 4.0≤Mo/V≤16.0. Also, the thick steel plate has a structure in which a region excluding surface layers within 5 mm from front and rear surfaces of the steel sheet essentially is composed of a bainite phase, which accounts for 80% of the area, and the nominal grain size in a region surrounded by high-angle boundaries with orientation differences of≥15°in the bainite phase is 4-40μm. The thick steel plate has a tensile strength of≥570 MPa and vTrs of≤-25°C and shows little deterioration in material quality, even after warm molding at 400-600°C. The thick steel plate can be tubulated by warm molding to readily form into a circular steel pipe having a yield strength of 500-620 MPa, a tensile strength of≥570 MPa, a yield ratio of≤90% and vTrs of≤-20°C. <P>COPYRIGHT: (C)2012,JPO&INPIT</p> |
