Textures of Warm Rolled Low Carbon and Titanium Bearing Extra Low Carbon Steel Sheets

In this work, the formation of textures of low carbon and Ti-bearing extra low carbon steel sheets warm rolled in the temperature range between 900K and 1050K have been investigated through microscopic and microtextural studies using the ECC-ECP (electron chanelling contrast electron channeling pattern) techniques and selected area diffraction patterns to explain the different features of texture formation in the two steels and the effect ofcarbon in solution on the texture formation is discussed.

In this work, the formation of textures of low carbon and Ti-bearing extra low carbon steel sheets warm rolled in the temperature range between 900K and 1050K have been investigated through microscopic and microtextural studies using the ECC-ECP (electron chanelling contrast electron channeling pattern) techniques and selected area diffraction patterns to explain the different features of texture formation in the two steels and the effect ofcarbon in solution on the texture formation is discussed.

2.EXPERIMENTAL PROCEDURE
The chemical compositions of the Ti bearing extra low carbon steel (Steel A) and the low carbon steel (Steel B) used here are given in Table 1. structure. Subsequently, they were air cooled to a temperature of 1023K and then warm rolled at a reduction of 80% to 1ram thick sheet. The recrystallization texture was measured from specimens annealed for 1 hour at 1023K while the warm rolling texture was determined from specimens quenched just after rolling.
The measurement of texture was carried out on an automatic goniometer with a Mo tube. Detailed studies of the texture have been performed by means of the three dimensional analysis based on the vector method/I,2/.
For the microtextural studies, the SEM-ECP technique was employed to determine the orientation of each grain observed at the initial stages of recrystallization.
Both ECP as well as selected area diffraction patterns were used to determine the changes in crystal orientation taking place in the deformed grains, especially in the vicinity of grain boundaries.

EXPERIMENTAL RESULTS
The onset temperature of recrystallization of Steel A at a constant heating rate of 10 C/s.was about 80K higher than that of Steel B.
The carbon in Steel A was almost completely precipitated in the form of Ti compounds before the warm rolling. On the other hand, Steel B contained carbon in solution during warm rolling to approximately its total Content of 100 ppm. Fig.1 shows the rolling and recrystallization textures at the midplanes of Steels A and B warm rolled to 80% reduction at 1023K. Steel A developed a rather strong < 111 >//ND fiber in the rolling texture and these orientations became the main orientations ofthe recrystallization texture. On the other hand, the development of the <III >//ND fiber was in some measure hindered in the rolling texture of Steel B. The main orientation of the recrystallization texture was near {114) < 110 > and the < 111 >//ND fiber was negligibly weak.
To clarify the mechanism of formation of the different textures in the two steels, a detailed microstructural and microtextural study was carried out with specimens recrystallized about 5% using the ECC and ECP techniques.  To investigate the Table2: Classification of recrystallized grains.

Mark
Definition ofreerystallized grai XI Nucleated within X grains XX Nucleated at grain boundaries between X grains ZI Nucleated within Z grains ZZ Nucleated at grain boundaries between Z grains XZ-X Recrystallized from X grains at the grain boundary between X and Z grains XZ-Z Recrystallied from Z grains at the grain boundary between X and Z grains P Nucleation site could not be identified. relationship between the orientations of recrystallized grains and their nucleation sites, the latter were categorized as shown in Table 2. Fig.3

Effect of carbonin solution on the formation of texture
Selected area electron diffraction was employed to determine the orientation changes in the vicinity of the grain boundaries in the X grains. In Steel A, in which little carbon in solution was present, a rotation around < 111 >//ND was frequently observed in the vicinity of the grain boundaries between the X grains. This local rotation was also observed in a cold rolled low carbon steel sheet/3/and the occurrence of this rotation was explained by the selection of active slip systems of the {110} < 111 > type, which is influenced by the stresses produced by slips in the neighbouring grains/4/.
On the other hand, other crystal rotations forming {112}<110>-{115}<110> orientations were frequently found in the vicinity of the grain boundaries between the X grains in Steel B but seldom in Steel A. The probability of C-atoms lying in {110} planes is 1.73 times higher than that of lying in {112} planes, both of which are considered as the main slip planes in bcc crystals. It is therefore possible that dislocations pile up during deformation in the vicinity of grain boundaries and that the interaction between dislocations and carbon in solution leads to more work hardening of the {110 < 111 > slip systems so that further deformation takes place mainly on the {112< 111 > slip systems. Fig.6 shows an orientation distribution diagram predicted by a crystal rotation model/5,6/on the assumption that the first 60% rolling deformation occurs by means of pencil glide and the subsequent 50% only involves glide on the {112)<111> slip systems. The initial texture consists of 648 orientations representing the 36 planes given in the figure and 18 directions with an interval of 10 As shown in the figure, the main orientations of the rolling texture are near {114) < 110 >-{335) < 110 >, which are orientations frequently observed in subgrains in the vicinity of the grain boundaries between the X grains in Steel B. The fact that the main orientations of the XX grains of Steel B coincided approximately with the orientations mentioned above strongly indicates that the recrystallization occurred from these subgrains.

5.Conclusion
The textures of warm rolled low carbon and Ti-bearing extra low carbon steel sheets have been investigated. The study led to the following 3. To suppress the recrystallization of deformed grains of near < 100 >//ND, the addition of recrystallization retarding elements such as Ti is effective. 4. The differences in the recrystallization textures formed in low carbon and Ti-bearing extra low carbon steel sheets can be explained by the differences in the local crystal rotations in the vicinity of grain boundaries and in the preferred nucleation sites. 5. To obtain recrystallization textures with near < 111 >//ND as the main orientation through warm rolling, which is good for the deep drawability, it is necessary to employ steels containing Ti, Nb etc. which retard recrystallization and eliminate carbon in solution by the formation of precipitates.