Takehide Senuma1, Hajime Saitoh1, Kousaku Ushioda1, Naoki Yoshinaga1 and Hiroshi Yada1
1Sheets & Coil Laboratory, Nippon Steel Corp., Kita-Kyushu
Recent development in the automobile industry requires higher and higher formability of steel sheets. With an aim of improving the deep drawability, the influence of α-region hot rolling on the texture and r-values of cold rolled Ti-bearing extra low carbon steel sheets has been investigated and the following results were obtained.
(1) As for steel sheets hot rolled in the α-region, recrystallization textures in the midlayer of the cold rolled and annealed sheets show, regardless of the recrystallized or the non-recrystallized state before cold rolling, higher ND//<111> intensity, whose development is favorable for deep drawability, than that of conventional cold rolled sheets.
(2) If hot rolled sheets have a deformed microstructure, ND//<111> in the surface texture after final annealing does not develop and the main orientation is near 113<110>±15, while ND//<111> in the surface recrystallization texture of the cold rolled and annealed sheets increases with increasing cold rolling reduction if a recrystallization treatment is carried out after α-region hot rolling, though the scale of the increase is less than conventional cold rolled sheets.
(3) In consideration of the nucleation and growth mechanism and employing a crystal rotation model, the formation of the recrystallization textures was discussed from a viewpoint of the stored energy and crystal rotation relationship around certain axis between the orientation of the recrystallized grain and that of the surrounded deformed matrix.
(4) In the case of steel sheets hot rolled in the α-region, cold rolled and annealed, the averall r-value is positively influenced by the midlayer texture and negatively by the surface texture.
The detrimental effect of the surface texture was reduced through the α-region hot rolling in a lubricated condition and a great increase in r-value was achieved. In this case, if the microstructure of the sheet before cold rolling is recrystallized, the average r-value is 0.5-0.8 higher than that of the conventional cold rolled sheets.
texture, recrystallization, low carbon steel, deep drawability, warm rolling, cold rolled sheet
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