PREPARATION OF SUPER 70KG GRADE HIGH STRENGTH HOT ROLLED STEEL PLATE EXCELLENT IN ELONGATION FLANGE PROPERTY

摘要

PURPOSE:To economically prepare a high strength hot rolled steel plate excellent in an elongation flange property, by continuously casting steel with a specific composition which contains C, Si, Mn and Al and reduced in the content of S, P and Ca, and rolling and cooling the cast steel under a specific condition. CONSTITUTION:Steel containing, on a wt. basis, 0.12-0.30% C, Si1.5%, 1.0- 2.0% Mn, 0.01-0.10% Al, S0.005% and, if necessary one or more of P0.008% and Ca0.005% and comprising the remainder of Fe and inevitable impurities is continuously cast and heated at 1,200 deg.C or less to be rolled under such a condition that a total draft at 1,000 deg.C or less is set to 90% or more and finish rolling is completed in a temp. region of Ar3+50 deg.C-Ar3+150 deg.C. After the completion of finish rolling, the cooling of the steel plate is started within 2sec and the cooling speed in this case is set so as to satisfy formula logCR( deg.C/sec)=31/10(1- Ceq) (wherein Ceq=C+Mn/5). Subsequently, the steel plate is wound up at 500 deg.C or less and a super 70kg grade high strength hot rolled steel plate having 50% or more of a bainite structure and excellent in an elongation flange property is obtained.