Materials Science Forum Vols. 702-703

Abstract: The phenomenon of secondary recrystallization in 3%Si-Fe under relatively high cold rolling reduction rate condition has been investigated. The texture of the secondary recrystallized sample under 97.2% cold rolling reduction rate condition consists of {110} orientation, which is quite different from Goss ({110}) orientation obtained under lower cold rolling reduction rate conditions. As a result of Grain Boundary Character Distribution (GBCD) analysis on primary recrystallized texture, {110} orientation has the highest frequency of High Energy (HE) boundary with misorientation angle between 20° and 45°. This result demonstrates that the orientation, which has the highest frequency of HE boundary in primary recrystallized texture, is selected during secondary recrystallization. However, as a result of GBCD analysis based on Coincidence Site Lattice (CSL) boundary, Goss orientation has the highest frequency of S9 (CSL) boundary in the primary recrystallized texture throughout all cold rolling conditions.

Abstract: Cold rolled grain oriented (CRGO) steel was deformed by uni-axial tensile loading in three different directions: Rolling Direction (RD) (110) , Transverse Direction (TD) (110) and 45° to RD (110) . Deformation behavior was found to be different for the different directions of loading. Such differences were biased by the heat flattening coating and could be captured, effectively, through discrete dislocation dynamics simulations. Results from texture and micro-texture studies, mechanical tests and magnetic measurements show a clear relationship between strain hardening exponent (n) and degradation in magnetic properties (watt loss and permeability). These were also related to misorientation developments, relative recovery and deviations from ideal Goss orientation.

Abstract: The texture evolution in the surface and center layer of hot rolled electrical steel containing initial columnar grains with their <100> nearly along ND, RD and TD of sheets were determined by EBSD technique. The transition from Goss to Brass or Copper orientation in surface was analyzed. The difference in texture of center layers in these samples was compared. In particular, orientation evolutions within grains and at grain boundaries of different types of orientations were explored. The results are discussed in terms of the special alignments of grain boundaries among columnar grains.

Abstract: The core loss and magnetic induction of electrical steels are dependent on the microstructure and texture of the material, which are produced by the thermo-mechanical processing. After a conventional rolling process, crystal orientations of the α-(//RD) and γ-(//ND) fibers are strongly present in the final texture. These fibers have a drastically negative effect on the magnetic properties of electrical steels. By applying asymmetric rolling, significant shear strains could be introduced across the thickness of the sheet and thus a deformation texture with more magnetically favorable components is expected. In this study, an electrical steel of 1.23 wt.% Si was subjected to asymmetric warm rolling in a rolling mill with different roll diameters. The evolutions of both deformed and annealed textures were investigated. The texture evolution during asymmetric warm rolling was analyzed by crystal plasticity simulations using the ALAMEL model. A good fit between measured and calculated textures was obtained. The annealing texture could be understood in terms of an oriented nucleation model that selects crystal orientations with a lower than average stored energy of plastic deformation.

Abstract: Through-thickness shear strain variation with speed/radius/friction ratio in cold rolled silicon steel under different asymmetric rolling modes was analyzed by finite element method (FEM). Cold rolling textures were also investigated quantitatively to correlate with the calculated shear strain. With increasing speed/radius/friction ratio, shear strain distribution under differential-speed and differential-radius rolling exhibits similar characteristic in contrast to differential-friction rolling. Unidirectional shear strain develops through sheet thickness when asymmetric speed and radius ratio exceeds 1.125, whereas it does not appear even at friction ratio of 1.5. Shear strain distribution dependent on asymmetric rolling modes can be well understood by forward and backward slip zones as well as roll pressure as a function of speed/radius/friction ratio.

Abstract: Charpy impact testing (over the transition temperature rage) on different samples of a Ti-microalloyed steel, having the same average-TiN particle size but different average-ferrite grain sizes, showed that in spite of the presence of large TiN cuboides, ferrite grain refinement can significantly improve the impact toughness, provided the meso-texture (i.e. the intensity of low-angle boundaries) and matrix strength can be restricted to low values.

Abstract: Low ductile crack arrestability in a full-scale burst test of 1420 mm-diameter X80 steel line pipes was accompanied by a high intensity of fracture surface separation. The texture of the steel plates was studied using different techniques in order to evaluate the influence of {001} planes oriented parallel to the rolling plane on the separation intensity during fracture. Though no clear correlation between the content of {001} planes parallel to the rolling plane and intensity of separation was found, the local distribution of the {001}<110> texture component among the microstructure components was different in different steels providing long areas suitable for cleavage fracture parallel to the rolling plane in steel with low arrestability.

Abstract: In this study, severe plastic deformation (SPD) of Ti-bearing interstitial-free steel was carried out by multi-axial forging (MAF) technique. The grain refinement achieved was comparable to that by other SPD techniques. A considerable heterogeneity was observed in the microstructure and texture. Texture of multi-axially forged steels has been evaluated and reported for the first time. The material exhibited a six-fold increase in the yield strength after four cycles of MAF.

Abstract: This paper investigates the bulk texture evolution during cold rolling and annealing of Dual Phase steels for different processing conditions, i.e. cold reduction within the reduction range of 45 to 73% and annealing at temperatures between 650 and 850°C, which includes the recovery, recrystallisation and partial phase transformation domains. Textures have been measured by X-ray diffraction. The results reveal that the rolling texture is strengthened during the recovery process or initial stage of recrystallisation while during recrystallisation a weak RD-ND type of texture appears. During subsequent phase transformation the RD-ND type of texture further weakens and later randomises as the second phase fraction increases beyond 75%.

Abstract: Ultra low carbon (ULC) steel samples were deformed in near plane-strain compression mode with different strains, strain rates and temperatures. Different aspects of microstructural developments, for deformed γ (ND//) and θ (ND//) fibre grains, were investigated using X-ray line profiles and high resolution electron diffraction. The study clearly showed increase in grain interior strain localizations and in-grain misorientation at the intermediate deformation temperature. This effect was more apparent in γ-fibre and can best be explained through orientation sensitive recovery. γ-fibre also demonstrated higher potential for increase in dislocation density. This was observed experimentally and simulated through discrete dislocation dynamic simulations. Higher textural softening with stronger increase in dislocation density and possible effects of orientation sensitive recovery appears to define the orientation dependent recovery in low carbon steels.