Sensitiveness of Magnetic Inductive Parameters for the Characterization of Recovery and Recrystallization in Cold-Rolled
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THE cold-rolled steel substructure experiences recovery and recrystallization processes during an annealing treatment. Recovery involves the rearrangement of dislocations into low energy configurations and the annihilation of dislocations at a substructure level, while recrystallization implies the nucleation and growth of new defect-free grains and migration of high-angle grain boundaries, which results in a new grain microstructure with a low dislocation density.[1] Microstructural features, such as dislocation density, grain size, secondphase precipitates, or even applied or residual stresses, act as local pinning sites that strongly influence the overall magnetization processes and, hence, the magnetic properties of steels. The deterioration of magnetic properties with plastic deformation has been extensively analyzed in different types of steels and related to domain wall pinning by dislocation network and residual stresses generated by deformation.[2] Although most studies concentrate on the effect of deformation on coercive field[2–4] and energy losses (e.g., Reference 3), few of them also report and discuss the effect on induction values (e.g., Reference 2 in pearlitic steel and References 3 and 4 in electrical steels). Overall, deformation significantly decreases Br,[2–4] and although it tends to diminish high induction values, these changes have been found not to be strong K. GURRUCHAGA and A. MARTI´NEZ-DE-GUERENU, Researchers, and I. GUTIE´RREZ, Principal Researcher, Materials Department, and Head of Thermomechanical Treatments Group, are with the CEIT and Tecnun (University of Navarra), Manuel de Lardiza´bal 15, 20018 San Sebastia´n, Basque Country, Spain. Contact e-mail: [email protected] Manuscript submitted April 7, 2009. Article published online February 3, 2010 METALLURGICAL AND MATERIALS TRANSACTIONS A
enough to overshadow the anisotropy.[3] Additionally, a lower sensitivity to dislocation density variations after plastic deformation, as the measured magnetic field value rises, has been found in electrical steel.[5] The reduction of Br has been attributed to the increase in individual pinning site energies as dislocation tangles form very effective barriers that strongly hinder the movement of domain walls;[2] therefore, the coercive field[2–4] and hysteresis losses[3] increase. The annealing of plastically deformed electrical steels[3,6] and of iron[7] has received less attention in the literature. In general terms, annealing tends to turn back the magnetic properties of the material previous to deformation, which has also been attributed to the elimination of macroscopic residual stresses.[3] However, it should be noted that each magnetic property recuperates to a different degree.[3] Additionally, in a polycrystalline material, if the constituent crystals have a preferred orientation (or texture), then the polycrystalline aggregate itself will have a magnetic anisotropy (magnetocrystalline energy) dictated by the individual crystals;[8] therefore, the energy necessary to magnetize the material will depen
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