PRODUCTION OF COLD ROLLED HIGH TENSILE STEEL SHEET FOR DRAWING BY CONTINUOUS ANNEALING

摘要

PURPOSE:To produce inexpensively a cold-rolled high tensile steel sheet having excellent drawability by hot rolling a slab of a low carbon Al-killed steel contg. P then coiling the rolled sheet at a high temp., allowing the coil to cool after quick rolling in a specific temp. range then subjecting the sheet to cold rolling followed by continuous annealing. CONSTITUTION:A slab contg., by weight %, 0.018-0.06% C, 0.10-0.40% Mn, 0.03-0.08% P, 0.02-0.10% Al, and =0.005% N and consisting of the balance substantially Fe is hot-rolled and the hot rolling is finished at the Ar3 point or above. The hot-rolled sheet is then coiled at 620-750 deg.C and in succession, the coil is cooled at the average cooling rate controlled to =150 deg.C/hr in a 600- 350 deg.C region; further, the sheet is allowed to cool in the state of the coil in a 350 deg.C- ordinary temp. region. Such hot-rolled sheet is cold-rolled at =60% draft after pickling and descaling. The cold-rolled sheet is subjected to the continuous annealing consisting of soaking and holding for 10-180sec in the temp. region of the recrystallization tem. - the A3 transformation point and an overaging treatment for 40-240sec in a 450-300 deg.C temp. region.