MANUFACTURE OF SIICR SYSTEM HOT ROLLED HIGH TENSILE STEEL SHEET HAVING HIGH DUCTILITY AND LOW YIELD RATIO

摘要

PURPOSE:To manufacture steel sheet having low yield ratio, high strength, excellent ductility, by rolling steel having a specific composition contg. C, Si, Mn, Cr so that rolling may be completed in a specific temp. range. CONSTITUTION:Steel consisting by weight. of, 0.05-0.15% C, 1.01-2% Si, 0.5- 1.5% Mn, 0.05-0.8% Cr, the balance being Fe and inevitable impurities, and contg. at need =0.015% S, in addition, Zr in the ratio 2=Zr/S=10 or rare earth elements (REM) in the ratio 1.3=REM/S=5 or Ca in the ratio 0.5=Ca/S=1.5 is rolled. The rolling is completed at a temp. =Ar3-30 deg.C and =Ar3+60 deg.C. The steel may be rolled after heated in a heating furnace of slab, then it is wound at 250-480 deg.C temp. thereby manufacturing steel sheet having =60% yield ratio.