The present work concentrates on the application of orientation imaging microscopy (OIM) based on the electron backscattered diffraction (EBSD) technique to the investigation of the microstructural evolution of an extra-low carbon (ELC) steel and a Ti-Nb-bearing interstitial-free (IF) steel, during continuous annealing. Aspects like the nucleation, the evolution of the recrystallized volume fraction and grain size of grains with different orientations, the interface area limiting recrystallized {111} regions, and the apparent growth rates have been considered. Different criteria have been applied in order to identify crystallites produced during annealing. During the first stages of annealing, a network of grain boundaries with misorientations higher than 10 deg is produced, mainly inside the deformed g-fiber grains. The crystallites formed within this network, free from cells or subgrains at their interiors, can be considered as potential nuclei. However, among all, only some of them become effective due to an important selection. The {111} recrystallized grains have a significant size and number advantage as compared with other texture components, and a hard impingement between clusters of {111} grains is produced during grain growth. The effect of grain growth behind the recrystallization front seems to be negligible as compared with the grain coarsening produced by the migration of this front, driven by the cold-work stored energy.

Nb is added to C-Mn steels in order to use the solute drag and/or strain induced precipitation as a useful tool to condition the austenite in the hot rolling mill and produce during the subsequent cooling a refined ferrite grain size. The highest degree of refinement is obtained in conventional rolling mills by accumulating the deformation in austenite during the last passes, followed by early cooling in the run out table to produce a high density of nucleated ferrite grains. However, the maximum refinement is to a certain extent attenuated due to the ferrite grain coarsening taking place during the transformation. The present work analyses the different aspects limiting the final achievable ferrite grain refinement.

Recrystallization texture and microtexture in a cold-rolled ultra-low carbon steel were investigated using X-ray diffraction and electron backscattered diffraction based orientation imaging microscopy (EBSD/OIM). Aspects such as nucleation, evolution of the volume fraction, and grain size were considered. Special emphasis was put on the grain coarsening of various texture components during recrystallization: an important grain selection associated with a significant advantage in size and number of the {111} recrystallized grains is observed. This grain selection gives rise to the development, in the last stages of recrystallization, of a strong c fiber associated with good drawing properties.Recrystallization and texture evolution during continuous annealing of cold-rolled low-carbon steel have been studied by many authors. [1±3] A strong c-fiber texture appears to be responsible for the high formability in low-carbon steels. Two main theories based on oriented nucleation [4,5] and selective growth [6,7] have competed for an interpretation of texture development and some attempts have also been made to find complementary approaches based on advantage in frequency or size. [8,9] EBSD techniques have been used to analyze the evolution of the grain size and volume fraction of certain texture components during the recrystallization process.The material used was an ultra-low carbon steel whose composition is shown in Table 1. This steel was industrially produced and processed by casting to about 85 % cold reduction.After cold rolling, the material was laboratory annealed to obtain different amounts of recrystallization ( Table 2). The annealing cycles were performed on a laboratory CA simulator. The samples were heated in a protective atmosphere up to the soaking temperature, in the 580±700 C range, at a rate of about 17 C/s. Soaking time was 60 s, followed by gas cooling to the over-aging temperature (400 C) at a rate close to 40 C/s. The samples were then over-aged for 100 s and finally cooled to room temperature.Texture measurements were carried out using a Philips X'pert-MRD X-ray diffractometer with Co Ka radiation and the resulting data were analyzed with the MTM-HFM program to determine the orientation distribution function (ODF).Orientation imaging microscopy was carried out in a Philips XL30cp scanning electron microscope (SEM), using TSL (TexSEM Laboratories) MSC 2200 equipment.Quantitative metallography was carried out on the EBSD orientation images for different texture components. The components considered are the c-fiber grains having a {111} plane perpendicular to the normal direction (ND), the cube grains having a {100} plane perpendicular to ND, and finally the grains with a {110} plane perpendicular to ND. The orientation tolerance, for the definition of the texture components, is 15 in all cases. The rest of the grains that cannot be identified within these categories are hereafter called ¹othersª.Partially and fully recrystallized samples were analyzed and the criterion for grain definition in a p...

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