PRODUCTION OF HOT ROLLED STEEL PLATE HAVING =60KGF/MM2 TENSILE STRENGTH AND EXCELLENT WORKABILITY AND WELDABILITY

摘要

PURPOSE:To provide a hot rolled steel plate having excellent tensile strength, workability and weldability as a steel plate for automobiles, by combining control of components consisting mainly of C, Si and Mn and specific conditions for hot rolling thereby forming fine composite structures of ferrite and pearlite. CONSTITUTION:In the stage of producing a steel plate having 1.6-4.0mm. thickness, =60kgf/mm.2 tensile strength and excellent workability and weldability as a steel plate for automobiles, the steel slab contg. 0.15-0.25% C, 1.5% Si, 0.7- 1.5% Mn, 0.01% P, 0.005% S and 0.01-0.10% Al, or further contg. =1 or =2 kinds among 0.0005-0.0050% Ca, 0.005-0.015% REM and 0.0005-0.010% Mg as granulating agents of sulfide inclusions is hot-rolled at =1,200 deg.C and after the finish rolling is finished at the Ar3 transformation point -930 deg.C, the steel plate is cooled at =15 deg.C/sec average cooling rate and is coiled at 350-560 deg.C, whereby the fine composite structures of ferrite and pearlite are obtained.