Abstract
In the present work, we have used unconventional short-term secondary recrystallization heat treatment employing extraordinary high heating rate to develop coarse-grained microstructure with enhanced intensity of rotating cube texture {100}<011> in semi-finish vacuum degassed non-oriented electrical steels. The soft magnetic properties were improved through the increase of grains size with favourable cube crystallographic orientation. The appropriate final textural state of the treated experimental steels was achieved by strain-induced grain boundary migration mechanism, activated by gradient of accumulated stored deformation energy between neighbouring grains after the application of soft cold work, combined with steep temperature gradient during subsequent heat treatment under dynamic heating conditions. The materials in our experimentally prepared material states were mounted on the stator and rotor segments of electrical motors and examined for their efficiency in real operational conditions. Moreover, conventionally long-term heat treated materials, prepared in industrial conditions, were also tested for reference. The results show that the electrical motor containing the segments treated by our innovative approach, exhibits more than 1.2% higher efficiency, compared to the motor containing conventionally heat treated materials. The obtained efficiency enhancement can be directly related to the improved microstructural and textural characteristics of our unconventionally heat treated materials, specifically the homogenous coarse grained microstructure and the high intensity of cube and Goss crystallographic texture.
Highlights
IntroductionThe non-oriented (NO) electrical steels belong to the group of soft magnetic materials
The non-oriented (NO) electrical steels belong to the group of soft magnetic materials.They represent important materials used for core laminations in the majority of electrical devices, and they are contributing to the efficiency improvement of the equipment [1]
In schemes (e.g., direction) and and subsequent subsequent conventional conventional heat heat schemes treatment with low heating rate, we have proposed a combination of a conventional temper rolling treatment with low heating rate, we have proposed a combination of a conventional temper rolling process for for the the steel steel after after primary primary recrystallization recrystallization with with aa subsequent subsequent final, final, unconventional unconventional second second process annealing treatment at dynamic heating conditions, i.e., using extraordinary high heating rate
Summary
The non-oriented (NO) electrical steels belong to the group of soft magnetic materials. The fully-finished grade is a final product of conventionally processed NO steel It has the microstructure, magneto-crystalline texture, and specific magnetic properties which have been adjusted through hot band annealing, cold rolling and final annealing of thin steel strip. The final heat treatment of semi-finished NO electrical steels is carried out according to EN 10 341 standard [20] In this case, the conventional long-term annealing process of steel laminations is used for the grain size increase by the mechanism of deformation-induced grain growth and the elimination of residual punching stresses, thereby eliminating all the deleterious effects affecting final magnetic properties.
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