PRODUCTION OF HIGH-STRENGTH STEEL PLATE HAVING GOOD DUCTILITY AND PROCESSABILITY

摘要

PURPOSE:To produce a high-tension steel plate having excellent ductility and processability by subjecting a steel plate to a soaking treatment under a specific condition and the succeeding cooling treatment. CONSTITUTION:The heating of a steel plate contg. <0.15% C, 0.2-3.5% Mn, 0.01-0.15% P, and <0.10% Al, or a steel plate further contg. 1 or >=2 kinds selected from a group A consisting of 0.1-1.5% Si, 0.1-1.0% Cr, 0.1-1.0% Mo, 5-100ppm B and a group B consisting of 0.01-0.1% Nb, 0.01-0.2% Ti and 0.01 0.2% V up to a soaking temp. of the Ac3 transformation point or above is accomplished at a heating rate of >=5 deg.C/sec at least from 600 deg.C up to the Ac3 transformation point and the steel plate is held for 10sec- 10min at said temp., whereby the steel plate is subjected to a soaking treatment. The average cooling rate between 600-300 deg.C in the succeeding cooling is made to the critical cooling rate CR( deg.C/sec) calculated by the equation ( I ) or above in the case of the steel having the former compsn. and said rate calculated by the equation (II) or above in the case of the steel having the latter compsn.