PURPOSE: To make the stable production of a cold rolled mild steel plate of superior deep drawability and uniformity in material quality by hot rolling a low carbon ingot contg. specific trace amts. of N and Al under specific conditions and heat treating the same after cold rolling.
CONSTITUTION: After the steel slab contg. 0.010W0.030% C, <0.30% Mn, 0.020W 0.100% sol.Al and <0.0040% N is subjected to hot finish rolling, water is sprayed to the steel plate at ≤830°C in the stage of travelling on runout tables or the steel plate is cooled at ≤30°C/sec cooling rates and is coiled at ≥650°C. After this is descaled, it is cold-rolled at 60W90% drafts, and in the stage of continuous annealing, it is heated and soaked for ≥10sec at recrystallization temp. WA3 transformation point and is cooled quickly at ≥50°C/sec cooling rates from 500W700°C down to room temp. or overaging treatment temp., following to which it is subjected to an overaging treatment.
NOZOE OSAMU
JITSUKAWA MASAHARU
