THE DEVELOPMENT OF ROLLING TEXTURES IN LOW-CARBON STEELS

The crystallite orientation distribution analysis was applied to the study of the development of the rolling textures in low-carbon steels. It was found that the constraining effect of the grain boundary remarkably influences the rolling textures of polycrystalline iron. This enhances the crystal rotations, which would not be expected to occur in single crystals; and grains having the {111 }(112) orientations are forced to rotate about the (111) axes lying in the sheet normal direction toward the {111}(110) orientations. This is the origin of the (111) fiber texture normally found in the rolling textures of low-carbon steels. The presence of the partial fiber texture having the (110) axes inclined 30 deg from the sheet normal toward the rolling direction could not be confirmed.


INTRODUCTION
The rolling textures of polycrystalline ironhave been described in various ways. [1][2][3][4][5][6][7][8][9] According to Barrett and Levenson, these consist of two continuous sets of end orientations. The first set is a partial fiber texture with the (110) fiber axes in the rolling direction, while the second set is a fiber texture having the (111) axes in the sheet normal direction. The presence of the first set has been confirmed by all investigators. As to the second set, there have been controversies in its description.
Based on the (110) pole figures of cold rolled carbonyl iron, Haessner and Weik 2 described this in terms of a (110) fiber texture having the (110) axes inclined 35 deg from the sheet normal toward the rolling direction. Bennewitz ' found, on the other hand, that the second set of orientations could better be described as a partial fiber texture with the (110) axes inclined 30 deg from the sheet normal toward the rolling direction. This was designated as a "(110) 60 deg RD fiber texture". On this basis, he divided the development of the rolling texture into three stages.
However, the presence of the "(110) 60 deg RD fiber axes" is theoretically difficult to explain. Direct experimental evidence, verifying that individual grains really rotate about these fiber axes, have not been obtained so far. The presence of these fiber axes was only indirectly inferred from the pole figures, above all from (110) pole figures. 129 Generally, pole figures describe only the distribution of particular crystallographic axes in the sample coordinate system. Two crystallites, whose orientations are related to each other by a rotation about one of these axes cannot be discriminated in the pole figure. In this respect, the precise distribution of the crystallite around the (110) fiber axes cannot adequately be described by the (110) pole figure alone. This uncertainty is completely eliminated in the method of the crystallite orientation distribution analysis developed by  and Bunge 4-8. It is the purpose of the present investigation, using this method of analysis, to study the formation of the rolling textures in low-carbon steels. For the detailed discussions on the formation of the fiber textures, it is necessary to clarify how individual grains reorient during cold rolling. To this end, several polycrystalline specimens with sharp initial textures were cold rolled, and from their orientation changes the behaviour of a grain having a specific initial orientation in a random polycrystal was indirectly deduced. The results were finally compared with the development of the rolling texture observed in a low-carbon steel having a weak initial texture.

METHOD OF ANALYSIS
Chemical compositions and hot rolling finishing and coiling temperatures of the starting hot bands Sharp initial textures were obtained from these steels in the following way.
(2) {110)(110) texture: The transverse direction of the {110)(001) specimen was chosen as the rolling direction.     To explain the increase of the {111}(110) orientations observed above 70 pct reduction, it would be necessary to assume that some part of the {111)(110) orientations were formed from the (111) fiber texture.
It is to be noted in Figure 2(c) that the exact position of the maximum on the 90 deg line is not at 0= 55deg, but at 0= 50deg. This  texture derived from the {111}(112) initial texture, Figure 3(a), is much stronger than that derived from the { 111 }(110) initial texture, Figure 2(b). As both the specimens were taken from the same original sheet and only the rolling directions were different, the sharpness of the initial textures must be the same in these two cases. In comparison with the {111}(110) initial orientations, the {111} (112) initial orientations seem to be, therefore, more probable sources of the (111) fiber texture. This fiber texture can be formed from the {111} (110) texture. 26 The crystal rotation about the sheet plane normal was observed only under restricted conditions.  (111)[112] initial orientation. 26 They ascribed this to the higher stress on the specimen surface due to friction between the rolls and the specimen.
Taking these results into account, it might be deduced that, in the present (111}(112) polycrystalline specimen, the crystal rotation about the sheet plane normal would be caused by the constraining effect of the grain boundary. Such possibility appears to be indicated by Figure 4, which shows (001) facet pits on the rolling plane of Steel 18 cold rolled 70 pct. It can readily be seen that, in a (111) grain, the pyramids rotate continuously about the sheet plane normal, as the grain boundary is approached.  Although single crystals having the (110) [110] orientations tend also to rotate slightly about the rolling direction, they retain their initial orientations up to 70 pct reduction. 27'29 Taking these results into account, it might be concluded that this The instability of the {001 } (110) initial texture was also confirmed by Richards  constraining effect of the grain boundary could be relaxed relatively easily, accompanying large orientation changes in the neighbourhood of the grain boundary. Aspden 31 studied the effect of constraints in decreased by using constraints during rolling. Thus, this effect seems to depend on the orientation of the grain in question. Furthermore, it may be influenced by the shape, grain size and orientation of neighbouring grains. At present, this problem is too difficult to be discussed theoretically. At 90 pct reduction, both the {335}(110) peak and the (111) fiber texture developed remarkably, Figure 8(f). In the latter, some preference for the {111}(110) orientations seems to be present. The {554}(225) orientations were no more at the center of the peak on the k 0 deg line.
Thus, the rolling textures of this specimen having a weak initial texture could be explained in terms of the crystal rotations which were observed in specimens having sharp initial textures. It can be constructed approximately by the superpositions of various components, which follow their predetermined rotation path to reach their stable end orientations. Figures 8(a)  From these observations it can be concluded that the whole features of the orientation changes occurring continuously during cold rolling cannot be properly described in terms of the (110) 60 deg RD fiber texture.

Dashed lines in
The description in terms of the (111 ) fiber texture having the (111) axes in the sheet normal direction seems to be a better one. The same conclusion was reached by Takechi, Kato and Nagashima, 8 Bunge 16 and Heckler and Granzow. 24 In the latter two investigations, the crystallite orientation distribution analysis was adopted. direction, mentioned above, would be caused by the constraining effect of the grain boundary.
Although instability might be also attributed to the constraining effect of the grain boundary. Thus, the rolling texture of ploycrystalline iron seems to be largely influenced by the constraining effect of the grain boundary. This may be due to the fact that, in a-Fe, slip can occur on any of the {110}, {112} and {123} planes, so that the constraining effect of the grain boundary would be relaxed relatively easily. In this case large orientation changes would be produced in the neighbourhood of the grain boundary.
The development of the rolling texture in low carbon steels could not adequately be described in terms of Bennewitz's (110) 60 deg RD fiber texture.