| 摘要 |
PURPOSE:To obtain a cold rolled steel sheet with high drawability by adopting a staged heating cycle combining an ultra rapid heating zone and a slow heating zone as the heating zone of continuous annealing. CONSTITUTION:A cold rolled strip is ultra rapidly heated from room temp. To to recrystallization temp. Rs at a rate over 40 deg.C/sec, pref. over 100 deg.C/sec, slowly heated from Rs to A3 transformation point at a rate of 5-40 deg.C/sec, and soaked in a short time or slowly cooled. Thus, by carrying out ultra rapid heating in the temp. range below Rs and decreasing the heating rate in the temp. range above Rs, selective growth of[111]grains proceeds, so, collision of fine recrystallized grains of an orientation harmful to drawability and coarse grains of an advantageous orientation occurs at a temp. just above Rs in the early stage and using the collision as driving force the advantageous orientation erodes the harmful one to grow the coarse grains. The short-time slow heating process above Rs results in grain size condition and an aggregate structure advantageous to drawability is developed, enhancing the average plastic strain ratio. |
