PRODUCTION OF LOW YIELDING RATIO HIGH-TENSILE STEEL PLATE BY DIRECT HARDENING AND TEMPERING METHOD

摘要

PURPOSE:To produce a steel plate suitable for welded structures having a low yielding ratio and high tensile strength by working a specifically composed steel in an unrecrystallized austenite region at a specific draft, then forcibly cooling thereof, then subjecting the worked steel to direct hardening and tempering treatments. CONSTITUTION:The steel consisting of 0.05-0.2wt% C, 0.03-0.5% Si, 0.5-2.3% Mn, 0.01-0.1% Al, 0.1-0.5% Mo, 0.01-0.05% Nb, and the balance Fe and inevitable impurities is worked in the unrecrystallized austenite region at =30% draft. The steel is then quickly cooled at =10 deg.C/sec cooling rate and in succession thereof, the steel is quickly cooled by a direct hardening method and is subjected to the tempering treatment in a 300-700 deg.C range. The low yielding ratio high tensile steel plate having 80-90% yielding ratio and =70kgf/mm2 tensile strength is obtd. by the above-mentioned method. =1 kinds among 0.3-1.5% Ni, 0.3-1.5% Cu and 0.3-1.5% Cr and further 0.01-0.05% Ti and 0.005-0.003% B are incorporated at need into such steel compsn.