| 摘要 |
PURPOSE:To manufacture the high tension steel sheet of the yield ratio of 0.8 or less with excellent ductility, in the hot strip mill, by rolling under a specified hot rolling condition the steel material containing the precipitation hardening element like as Nb, V, etc. CONSTITUTION:The steel material provided for the next process is specified to contain 0.15- 0.25% C, Si-0.7%, Mn-1.5%, 0.005-0.080% Al and one of 0.005-0.03% Nb or 0.01- 0.04% V, or otherwise, in case of containing both of Nb and V, total amount of Nb and V is specified to 0.005-0.05%. Or additionally, one or more than two kinds of Cr, Ni, Mo, Cu, respectively under 0.5%, REM and Zr respectively under 0.10% and Ca <=0.02%, are contained. The slab of this steel material is heated to above 1200 deg.C, in order to thoroughly transform the carbide and nitride of Nb and V into the solid solution; after that, the slab at about 1000 deg.C is rough rolled by the hot strip mill. Next, the slab is finish rolled at 830-900 deg.C, and is cooled at the cooling rate 5-20 deg.C/sec, and then, is wound into a coil at 550-700 deg.C. Or otherwise, the coiled strip is uncoiled for giving the bending deformation at the maximum surface strain 0.6-2.0% to the strip for producing the finished strip. Hereby, the hot rolled steel sheet with the yield strength above 30kg/mm<2> can be manufactured. |
