| 摘要 |
PURPOSE:To prepare a cold rolled steel good in ageing resistance used in processing, by a method wherein a continuously cast aluminum killed steel slab is rolled to be continuously annealed at a specific temp. and the rolled slab is subsequently subjected to quenching including short-time holding and sectional gradual cooling to be further subjected to over ageing treatment. CONSTITUTION:Aluminum killed steel is formed into a slab by continuous casting and the formed slab is subjected to hot rolling and cold rolling to be continuously annealed. Annealing is carried out under a temp. range of a recrystallizing temp.- a Ac3 transformation point and the rolled slab is held at this temp. for 10sec or more. Thereafter or occasionally, the heat treated slab is gradually cooled to 580-700 deg.C at a cooling speed of 20 deg.C/sec or less and thereafter quenched to an over ageing treatment temp. of 300-500 deg.C. On the way of this quenching, at least one of operations holding for 0.3- 3sec and gradually cooling at a speed of 10 deg.C/sec or less is applied one time - ten times and cooling is carried out at a speed of 100-300 deg.C/sec in an actual cooling speed (the holding or the gradual cooling time is not included). After over ageing treatment is applied at the above mentioned temp. for 60-300sec, the temp. is lowered to a room temp. to obtain a cold rolled steel plate excellent in ageing resistance used in processing. |
