Materials Science Forum Vols. 495-497

Abstract: Titanium alloyed interstitial free steel was processed by means of accumulative roll bonding (ARB) in order to obtain an ultrafine grained structure. Ten consecutive rolling passes were applied at 480°C with a nominal reduction of 50% per pass and an intermediate annealing treatment of 5 min. at 500°C. A total true strain was obtained of evM = 8.0 which corresponds to an accumulated reduction of 99.9%. Orientation imaging microscopy was used to evaluate textures and microstructures. A pronounced lamellar structure was observed until the 5th pass with an incidence of high angle grain boundaries predominantly parallel to the rolling direction. After the 6th pass (evM = 4.8) an increased fragmentation perpendicular to the rolling direction starts to develop in spite of the lamellar microstructure with an average spacing of approximately 1 µm. From the 7th pass onwards (evM ≥ 5.6) a random high angle grain boundary distribution develops which results in a more equi-axed ultrafine microstructure after the 9th pass (evM = 7.2) with an average grain width of 200 nm. As the rolling is carried out without lubrication, the surface areas display a slightly more fragmented structure than the midlayer sections and typical shear texture components are present in these surface zones (<110>//ND and <211>//ND fibre). Although the sheets are stacked upon each other after each subsequent pass, the shear strain microstructural and textural features are rapidly decomposed in the midlayer in each subsequent rolling pass which is clearly revealed by the cross sectional orientation scan on the composite sample. Hence it cannot be concluded that the surface shear strain significantly contributes to the grain fragmentation in the bulk volume of the composite sample.

Abstract: By applying a double cold rolling and annealing treatment, the evolution of the α and γ fiber components differed from the ones observed in conventional processing. This is attributed to the difference of the initial texture. An increased reduction of stored energy of the {111}<112> component was found by monitoring the change of the stored energy during annealing, indicating that the onset of the nucleation stage of recrystallization by relaxation and annihilation of dislocations occurred mainly on the {111}<112> component with its higher stored energy. The detailed texture evolution of the double cold rolled specimen during 2nd annealing is described by coupling the theory of oriented nucleation and orientation pinning, which is experimentally confirmed by OIM scan.

Abstract: In order to investigate the effect of the reduction degree per rolling pass on the evolution of recrystallization textures and microstructures, the hot band of 17.5 Cr-1.1 Mo ferritic stainless steel sheets were cold rolled with lubrication according to two processing routes, by which different reduction degrees per pass were introduced. Rolling with a large number of passes led to the formation of fairly homogeneous rolling textures at all through-thickness positions. In contrast, cold rolling with large draughts resulted in pronounced texture gradients along the thickness direction. After recrystallization annealing, the texture maximum was obtained at {334}<483> in all samples regardless of the rolling routes and thickness layers. During subsequent annealing, recrystallization was observed to be faster in those grains with {111} orientations, while it was retarded in grains having orientations close to {001}<110>.

Abstract: This paper presents simulations of the texture development during cold rolling of fully pearlitic steel. In order to investigate the importance of including microstructural aspects into texture simulations the calculations were carried out with the FC Taylor Pearlite model which takes the lamellar microstructure into account and with the FC Taylor and LAMEL model which are dedicated for one phase materials. The results are compared with those for ULC steel. For both materials the LAMEL model results are in good agreement with experimental data, while for the pearlitic steel, the FC Taylor Pearlite model improves the predictions only slightly with respect to the FC Taylor model.

Abstract: A development of deformation textures was examined in ferritic-austenitic duplex type steel subjected to cold-rolling within the range up to 90% of reduction by applying different rolling schedules. The investigations included X-ray phase analysis, texture measurements and microstructure observations by means of light microscopy. The experimental results indicate at the occurrence of strong initial textures in both component phases after preliminary thermo-mechanical treatment. Formation of the ferrite-austenite banded structure in the course of rolling along with the stability of major texture components, related by Bain orientation relationship, exert considerable effect on the development of the ferrite and austenite rolling textures.

Abstract: The orientation relationships operating during the austenite (FCC) to BCC phase transformation were investigated in a high performance steel using X-ray and electron diffraction techniques and employing several length scales. These steels contain some retained austenite that permits the direct comparison of the textures of the parent (austenite) and product (ferrite, bainite, martensite) phases. X-ray diffraction allowed the global texture of the rolled parent austenite phase to be determined as well as that of its transformation product. EBSD techniques permitted study of the orientation relationships on a local scale. The observed correspondence relations are expressed in Rodrigues-Frank space. The exact Kurdjumov-Sachs relation was never found. The local spread of orientation in the parent austenite (due to deformation) is seen to be inherited by the bainite. This is attributed to the displacive mode of transformation to bainite. The influence of prior deformation of the austenite on the occurrence of variant selection was also studied. It appears that a critical strain is necessary to produce a significant amount of variant selection.

Abstract: Cube texture ({001}<100>) influences extensively the plastic anisotropy and physical properties of materials. Researches on cube texture have been concentrated in f.c.c structured metals only since the scarce observation of the texture in b.c.c. metals. In the present work, the cube texture was found to be developed in low-carbon steel under the biaxial rolling mode (ND and TD rolling alternatively). Cube texture and {112}-{111}<110> partially concentrated a-fiber texture were observed in biaxially rolled samples instead of the typical a-fiber and g-fiber texture formed in the normal flat-rolling. At 923K rolling where recrystallization occurred, highly developed {001}<110> recrystallization texture with some g-fiber texture was observed in the flat rolled sample. In contrast a quite intensified cube texture and {hkl}<110> texture were observed in the biaxially rolled sample. EBSD measurement showed the fraction of grains belonging to the two orientations was 0.35 and 0.55, respectively. Elongated along RD, grains in cube texture showed both the near-equiaxial and diagonally elongated shapes when observed from RD in the 923K rolled samples. Those grains containing lighter plastic strain had an average grain size (~1.5µm) which was 2 times larger than the grains in the RD//<110> texture. Meanwhile, the cube oriented grains were characteristic of only low-angle grain boundaries (<15o), but showed a specific misorientation (S17b, <110> 86.6o) with the grains in the RD//<110> texture. Besides rolling deformation produced cube oriented grains, preferential growth of cube oriented recrystallization nuclei, and the transformation of the {001}<110> recrystallization grains were considered to cause the development of cube texture during the 923K biaxial rolling.

Abstract: We report the results of the microstructural characterization of a Ti-bearing IF-steel deformed at high strain rates (» 6.104 s-1) in a split Hopkinson bar. The shock-loading tests were performed in hat-shaped specimens to induce the formation of adiabatic shear bands (ASB). The samples were deformed at 223 K and 298 K. High-resolution electron backscatter diffraction (EBSD) reveals the development of an ultrafine-grained structure within the ASB. A closer inspection reveals the presence of deformation twins in grains adjacent to the shear band. These twins bend towards the ASB suggesting that mechanical twinning occurs before the flow associated to shear banding. The results of microtexture have indicated the presence of a sharp <111> g-fiber texture in the ASB for both temperatures.

Abstract: Low silicon carbon steel has been oxidised at varying temperatures in free flowing air using a thermomechanical simulator to control heating and cooling rates. The resultant oxide scales have been studies using Electron Backscatter Diffraction (EBSD) and the phases identified by the differences in the diffraction patterns. The crystallographic textures were calculated from the EBSD data. There is a correlation between the textures of the different phase layers within the scale, which depends on the formation mechanism of the individual phases.