【正文】 C) is 100–500 ppm [11]. . Nucleation on shear bands The view that the presence of ingrain shear bands, such as those of Fig. 1b, stimulates the formation of {1 1 1} ponents during the annealing of warmrolled steels is supported by the results obtained recently by Bart [7]. In this study, progressively annealed samples of the warmrolled IF steel of Refs. [4, 5 and 6] were analysed by means of backscattered electron (BSE) imaging. An example of the observations made is reproduced here as Fig. 7. It can be seen that {1 1 1}oriented nuclei have formed within ingrain shear band structures. 19 Fullsize image (11K) Fig. 7. An example of {1 1 1} recrystallization nuclei forming in ingrain shear band structures in an IF steel (50 ppm C, % Mn, % Al, % Ti, 30 ppm N) [7]. The samples were deformed at 700176。C [8]. This phenomenon is at its peak when the diffusivity of the interstitial atom matches the velocity of the dislocations. For DSA to take place under rolling conditions, . at , the temperature range must be increased to 470–635176。 3. that the nearabsence of shear bands evident in the structure of warmrolled LC steels is responsible for the nearabsence of the Goss and ND fibre in these materials after annealing. . rValues of the experimental materials ravValues were calculated from the measured textures, as described in more detail in Ref. [4], and some representative predictions are presented in Fig. 4. Here it can be seen that the coldrolled and annealed steels all had estimated ravvalues in the range –。 2. that the ND fibre observed in the LC annealing textures after rolling at 70176。C rolling), the ND fibre is almost totally absent. This is why warmrolled and annealed LC steels have low ravvalues and are thus less suitable than similarly processed IF steels for deepdrawing purposes. . Nucleation of the Goss and ND fibre ponents The differences in the annealing textures will now be linked to the differences in shear band density and nature described above. Such an interpretation is based on the following hypotheses: 1. that the strong Goss ponent observed in the LC annealing textures after rolling at 70176。C) texture in the LC steels. This was shown in Ref. [5] to be attributable to the relative absence of shear bands in these samples. The absence of shear bands in turn has two practical consequences. One is that there is less grain splitup, with its attendant randomizing effect on the texture. The second is that there is more matrix grain rotation in the absence of bands because the occurrence of banding transfers flow (and therefore rotation) away from the matrix. Conversely, the presence of bands reduces the extent to which the “end texture” (. the ND fibre) is developed in the matrix and therefore reduces the intensity of the overall texture [5]. 16 The sharpness of the rolling texture has an important influence on the nucleation of new grains during annealing, and in particular on the orientations of the grains that form. In this way, it has a significant effect on the annealing texture. . Annealing textures As indicated above for the deformation textures, the influence of rolling temperature on the annealing textures is far greater for the LC grades than for the IF material. In the latter, the desirable ND fibre (1 1 1 ND) is dominant for all rolling temperatures (see Fig. 3). The LC textures, on the other hand, differ in two ways from the IF ones of Fig. 3: (i) under cold rolling conditions (. 70176。C, the degree of banding was far greater (about 50% as opposed to 25%) in the LC steels than in the IF material. As discussed in more detail below, this can be considered to arise from the DSA characteristics of the former materials, through the effects of this phenomenon on the work hardened state and on the rate sensitivity. By contrast, in the warm rolling range, . above 500176。C and annealed at 700176。C are displayed in Fig. 3. It is clear that the influence of rolling temperature is greater here than it was directly after rolling [6]. It is of particular note that the ND fibre ( 1 1 1 ND) is dominant after both warm and cold rolling in the IF steel, while in the LC grade, the situation is more plex. After cold rolling, the recrystallization texture is posed of the ND fibre together with a Goss ({0 1 1} 1 0 0 ) ponent. By contrast, after warm rolling, the entire texture changes to a partial RD fibre running from {0 0 1} 1 1 0 to {1 1 2} 1 1 0 , with negligible Goss and ND fibre intensities. The transition away from an ND fibre texture in the lattermost case is of particular importance and will be considered in more detail below. 15 Fullsize image (14K) Fig. 3. φ2=45176。C, this relationship was reversed. Fullsize image (5K) Fig. 2. Influence of rolling temperature on ingrain shear band frequency [5]. . Texture . Rolling textures The deformation textures determined in the investigation described above are illustrated in the form of orientation distribution functions (ODFs) in Ref. [5]. (This type of presentation is described and explained in more detail in the above reference.) All of the textures were typical of ferrite rolling, in that they were characterized by a partial rolling direction (RD) fibre (containing grains with their 1 1 0 axes parallel to the RD) as well as a plete normal direction (ND) fibre (with grains having a 1 1 1direction parallel to the ND). Although the rolling textures were qualitatively similar, the higher intensities (or maxima) evident in the 700176。C. Thus, at temperatures above 450176。 (b) IF steel. The above behaviour contrasted sharply with that of the IF material. Here the nature of the bands was unaffected by the rolling temperature, so that the example of banding illustrated in Fig. 1b for 700176。C. Fullsize image (15K) Fig. 1. E