| 摘要 |
PURPOSE:To produce a titled steel plate of superior surface characteristics, tensile strength, quenching hardenability and dent resistance by hot-rolling the steel material of the specified Mn, P, Al, Si and C components to unequal thickness then cold rolling the same and subjecting this to batch annealing under proper conditions. CONSTITUTION:The Al killed type steel material comprising essentially 0.2-0.6% Mn, 0.04-0.15% P, 0.02-0.08% Al, <=0.10% C, further contg. <=0.04 Si and comprising Fe for the remainder is hot-rolled at a finishing temperature of >=Ar3 and is then rolled with hourglass rolling rolls in such a manner that the thickness ratio between the central part and end part of the steel plate is made >=1.1 in rough rolling or finish rolling prestage process, after which this thickness ratio is maintained approximately. It is then coiled at <=600 deg.C, is pickled and is cold-rolled at a draft of >=40%. This steel plate is quickly heated at >=50 deg.C 1h in a batch type annealing furnace, is annealed for a predetermined time at recrystallization temperature-750 deg.C, is then cooled at an instantaneous cooling rate of >=0.15T deg.C 1h at a passage temperature T deg.C, whereby the unequal thickness steel plate of 35- 45kg f/mm.<2> tensile strength is produced. |
