Development of {111} transformation texture in interstitial-free steels
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I. INTRODUCTION
IT is well known that fully stabilized interstitial-free (IF) sheet steels exhibit high r values and nonaging properties, which make this kind of material a good choice for deepdrawing applications.[1] This drawability is normally attributable to the existence of the ND㥋{111} (where ND denotes the normal direction) gamma-fiber recrystallization texture found after continuous annealing. However, the origin of this and other texture components is still under debate. Hutchinson[2] indicated that adequate control of both the hot-band grain size and hot-band texture are fundamental to enhancing the formability properties of the final annealed material. It is, thus, very important to monitor the effect of the thermomechanical processing (TMP) parameters that affect the transformation texture and the hot-band grain size. Among them, it was thought that the chemical composition of the material was a key parameter. Recent developments[3–6] in IF steels have shown that the stabilization of carbon can occur by the formation of Ti4C2S2 (H phase), in addition to the traditional MCN precipitation. Whether C is stabilized by the formation of either MCN or H depends on the overall composition of the steel and may affect the final microstructure and texture of the hot-band material. For example, it has been indicated[7,8] that the presence of suitably dispersed NbCN precipitates in the hot-band material may lead to sharp {111}具uvw典 annealing textures. Also, some investigators have shown that texture development in IF steels is not as susceptible to variations in compositional and processing parameters as are aluminum-killed steels.[9,10] The aim of this article is, therefore, to analyze the interdependency between the carbon stabilization mechanism and various hot-rolling parameters in the formation of hot-band crystallographic texture in low-strength, fully stabilized IF steels.
L.J. RUIZ-APARICIO, Manager, Steel Development, is with Reference Metals Co., Inc., Bridgeville, PA, 15017. C.I. GARCIA and A.J. DeARDO, Professors, are with the Basic Metals Processing Research Institute, Department of Materials Science and Engineering, University of Pittsburgh, Pittsburgh, PA 15261. Manuscript submitted January 28, 2000.
METALLURGICAL AND MATERIALS TRANSACTIONS A
II. EXPERIMENTAL PROCEDURE A. Materials The steels used in this study were provided as typical commercial grades in the form of as-continuously cast slabs. Their chemical compositions, shown in Table I, suggest that C stabilization in both steels occurs primarily by the formation of H phase. Details concerning C stabilization by the H phase have been presented elsewhere.[3–6] B. Processing Parallelepiped sections (100 ⫻ 75 ⫻ 25 mm) obtained from the as-cast slabs were reheated at 1250 ⬚C in a controlled-atmosphere furnace for 1 hour. These blanks were then thermomechanically processed in a laboratory reversible rolling mill, in accordance with the deformation schedule shown in Table II. This schedule was designed based on the results published in a previous a
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