Thermomechanical Processing Map in Retaining {100}//ND texture via Strain-Induced Boundary Migration Recrystallization M
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TEXTURE significantly affects the final magnetic properties of electrical steel. {100}//ND texture is desirable for non-grain oriented (NGO) electrical steels. Humphreys and Hatherly summarized that the {100}// ND texture is a minor recrystallization texture attributed to its low nucleation rate and growth rate during recrystallization with subgrain growth (SGG) recrystallization mechanism.[1] Strain-induced boundary recrystallization migration (SIBM) occurs when pre-existing grain boundaries are bulging into a neighboring grain with a higher dislocation density. Dislocations will be swept up during boundary movement. Rosenberg et al. reported that {100}//ND fiber texture components have the lowest Taylor factors, whereas grains with {111}// ND texture have relatively high Taylor factors.[2] That is, grains with {100}//ND fiber texture carry less stored energy compared to grains with {111}//ND texture after
MO JI is with the University of Warwick, Coventry CV4 7AL, UK and also with the Brunel University London, Kingston Lane, Uxbridge UB8 3PH, UK. Contact e-mail: [email protected] CARL SLATER and CLAIRE DAVIS are with the University of Warwick. Manuscript submitted May 26, 2020; accepted September 25, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS A
deformation, for similar grain sizes. As a result, {100}// ND textured grains are expected to be promoted during SIBM recrystallization. Warm deformation has been studied extensively as a feasible processing route for Fe-6 wt pct Si steel. Mo et al. reported that the warm rolling temperature range varies from 400 °C to 700 °C to overcome poor plasticity during cold rolling as well as to minimize oxidation and dimensional distortion during hot deformation.[3] Humphreys et al. commented that SIBM is known to occur particularly at low strains and after high-temperature deformation, i.e., low stored energy conditions.[4] Takashima et al. reported that f001g h210i textured grains bulged into the adjacent grains via SIBM recrystallization after cold rolling (12 pct reduction) in the central region of a partially recrystallized NGO electrical steel sheet.[5] Stojakovic et al. also observed that SIBM recrystallization occurred in electrical steels after warm rolling at 350 °C by 12 pct with intermediate annealing at 760 °C, and the {100}//ND textured grains were promoted after recrystallization.[6] Although these studies have been carried out to retain {100}//ND texture via SIBM recrystallization in electrical steels, no thermomechanical mapping relating the strain and deformation temperatures to the different softening mechanisms, i.e., recovery, SIBM, and subgrain growth (SGG) mechanism have been established.
In this paper, the recovery and recrystallization behavior in Fe-6 wt pct Si steel with a starting columnar {100}//ND texture at various strains and deformation temperatures have been considered, and the concept of a processing map to promote SIBM mechanism has also been established. Other processing parameters, i.e., reheating rate and annealing temperature have a
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