| 摘要 |
PURPOSE:To prepare a cold rolled steel plate good in ageing resistance and ductility, by applying heat treatment after annealing to steel strip having a specific composition containing C, Mn, N, Al or the like and obtained through hot rolling, pickling and cold rolling under a specific condition. CONSTITUTION:A hot rolled steel strip containing, on the basis of a wt%, 0.008-0.04% C, 0.10-0.30% Mn, 0.008% or less N and 0.010% or more Al and wound up at 650 deg.C or more is subjected to pickling and cold rolling according to a usual method. In this next step, the steel plate is rapidly heating to 750- 950 deg.C and, after held at said temp. for 10sec or more, the heated steel plate is continuously annealed to adjust the crystal particle size of the cold rolled steel plate to 7.5-8.8 in G.S. No. Subsequently, the heated steel plate is gradually cooled to 640-720 deg.C over 30sec or more and quenching (a cooling speed; VCR), overageing treatment for holding a temp. TCR fo 320-440 deg.C over 60-210sec and final cooling (a cooling speed; VL) are advanced under a condition shown by the oblique line regions of the figures A, B to obtain a cold rolled steel plate good in ageing resistance and ductility. |
