Effect of copper precipitation on the development of recrystallization textures through continuous annealing of low-carb
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I.
INTRODUCTION
IT is over ten years since the technologies producing the highly ductile and deep drawable cold-rolled steel sheets by continuous annealing, not by conventional box annealing, were developed. ~'2'3 In order to improve deep drawability which depends mainly upon plastic anisotropy, i . e . , r-value, it is necessary to develop the textures with strong {l 11} and very weak {100} components parallel to the sheet plane at final annealing. 4 In the deep drawing quality or extra deep drawing quality Al-killed steel processed by box annealing, the desirable textures are developed by the proper control of AIN precipitation; that is, most of the aluminum and nitrogen in steel are held in a supersaturated solid solution by low temperature coiling in a hot strip mill and are then precipitated as AI-N pre-precipitation clusters and/or AIN during annealing after cold rolling. These clusters and/or precipitates give the preferred texture selection during nucleation and/or the growth stage of recrystallization, giving rise to a large texture component ratio of {111}/{100}. 5 However, in continuous annealing, the annealing time is too short to obtain a fine dispersion of precipitates effective for texture control during recrystallization and for further grain growth after recrystallization. To obtain the desirable texture through the continuous annealing process, careful control of the chemical compositions in steel and/or high temperature coiling in a hot strip mill have been applied as especially important conditions among other factors. Abe e t a[. 6 showed that high-purity iron sheets, when cold rolled, produced favorable microstructures inducing a highly deformed zone in the vicinity of the grain boundaries which gave preferential nucleation sites of (111} grain on subsequent recrystallization annealing, developing strong {lll}(uvw)-textures. Abe e t a l . 7 and Takahashi e t a l . s H. ERA, Research Associate, and M. SHIMIZU, Professor, are with the Department of Metallurgy, Faculty of Engineering, Kyushu University, Fukuoka, Japan. T. HIRUTA, formerly Graduate Student, Kyushu University, is now with Kawasaki Steel Corporation, Research Laboratories, Chiba, Japan. Manuscript submitted January 23, 1985.
METALLURGICALTRANSACTIONS A
pointed out the effectiveness of ferrite purification due to stabilizing impurity atoms such as carbon, nitrogen, oxygen, sulfur, etc. in steel by scavenging additions, for example titanium, to develop strong {Ill} type textures when steels were to be finally processed by continuous annealing. They showed that ferrite purification due to scavenging additions, in addition to forming a favorable cold rolling texture including fairly strong {112}(110) components which produced {554}(225) in the recrystallized state, gave rise to complete recrystallization and sufficient grain growth in a short annealing time. As reviewed by Mangonon, Jr. and Bramfitt9 and Hutchinson, ~~these "scavenging effects" seem to be widely accepted as a reasonable explanation for the mechanism of the favorable
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