Papers by Keyword: Silicon Steel

Abstract: High silicon steel is used for electrical applications because its electrical resistivity is increased and the magnetostriction is reduced. A silicon content up to 6.5 wt.-% gives excellent magnetic properties. The improvement of the magnetic properties stays in contrast with the lack of ductility of these alloys, making their thermo-mechanical processing difficult. The optimum final microstructure and texture depends on the final application of the material: extremely big grains with a Goss orientation ({110} <001>) are desired in transformers and grains with an average size of 100 -m and cube component ({100} <001>) are used in electrical motors. A series of plane strain compression (PSC) tests were performed on 3 electrical steels, with a silicon content from 1.8 to 4.1 wt.-%, in a temperature range of 800 to 1100°C, strain rates between of 0.5 and 5 s-1. Reductions and time between deformation and quenching were also varied in order to study the recrystallisation progress. Apparent activation energies for hot working, calculated using the hyperbolic sine equation, was in good agreement with literature and higher than the activation energy for self diffusion in iron. These values increase with the silicon content. The high temperature texture evolution was investigated by means of electron back scattering Diffraction (EBSD) technique, which allows the quantification of important texture components in function of the thermo-mechanical parameters applied during hot rolling and the plane strain compression tests. The hot rolled microstructures have shown an average grain size of 140 -m and a texture with a maximum on the cube fibre ({001} <-1-10>). The conventional α (<110> // RD) / γ (<111> // ND) fibre texture was developed after plane strain compression and their intensities depend on the deformation temperature and reduction. A similar tendency was observed for the fraction of static recrystallised grains.

Abstract: Electrical steels, in particular Fe-Si alloys, are used as magnetic flux carrier in transformers and motors because of their excellent magnetic properties. They owe these magnetic properties in part to the presence of specific texture components such as the Goss ({110} <001>) or the cube components ({001} <010>), but also to the chemical composition which is optimum with 6.5 wt. % Si. This high silicon content provides a stable BCC lattice structure to the alloy over the entire solid state domain, but also renders the material more brittle. This embrittlement, which is induced by ordering phenomena, makes it impossible to produce the alloy in a conventional rolling process unless a specific thermomechanical route at high temperature is applied. In order to examine the working behaviour of high Si electrical steels, a series of room temperature plane strain compression tests was carried out on a Fe-3%Si alloy in hot band condition. The samples were compressed with a constant strain rate of 20 s-1 to a reduction of 10, 35 and 70% and subsequently annealed for different times at 800 and 900°C in an electrical furnace without protecting atmosphere. The hot rolled microstructure displayed an average grain size of 195 7m and the texture showed on the cube component ({001} <010>) of maximum 5x random levels. After plane strain compression the samples developed the conventional α (<110> // RD) / γ (<111> // ND) fibre texture by plastic shear which was also accommodated, in part, by mechanical twinning. With regard to the annealed material, it was observed that the recrystallisation started in grains with the higher stored energy and within the shear bands. After a reduction of 70% the samples that were annealed at 800°C for 4 hours displayed an average grain size of 27 7m and a relative maximum of 4x random on the cube component. Also other less intense components such as the rotated cube ({001} <110>) and the Goss ({110} <001>) were present in the annealing texture. The samples that were annealed at 900°C, after a reduction of 70%, were characterized by an average grain size of 36 7m and by the appearance of the {111} <121> γ fibre component with an intensity of 4.7.

Abstract: In order to develop an economical production method of high Si steel sheet, 6%Si (by weight percent, unless specified otherwise) steel was prepared by a combined process of conventional casting and hot- and cold-rolling. Tension and nano-hardness tests and TEM analysis were carried out to examine the effects of ordered phases, Si-content, and testing temperature on cold workability. By optimizing the successive processes of casting, hot-rolling, heat treatment, and cold-rolling, 0.5 mm thick 6%Si steel sheet was successfully produced without crack formation. As Si content increased from 3% to 6%, core loss (W10/50) of the 0.5 mm thick Si steel sheet decreased from 1.36 W/kg to 0.89 W/kg.

Abstract: High silicon steel (up to 6.5 wt.-%Si) is important for the electrical industry because of its magnetic properties. However, its production in low thickness by cold rolling is difficult due to extreme brittleness, mainly caused by ordering processes, making dislocation motion more complex. Nevertheless, these materials appear to be deformable at higher temperatures. The cooling rate after hot deformation, the temperature from which it is cooled and the time delay prior to cold deformation are important elements for the understanding of their workability. Hot torsion tests were performed on Fe-Si steel (4.2 and 5.6 wt.-%Si) under continuous cooling to study the influence of strain and interpass time on ordering and non-recrystallization temperatures. Compression tests at a constant strain rate were used to study the effect of continuous cooling to RT and the delay time between deformations for series of silicon alloys (from 3.3 to 6.3 wt.-% Si) with different thermomechanical treatments. An aging phenomenon due to an ordering reaction at RT was observed. Finally, extrapolating the hot torsion and compression tests parameters to the rolling mill a suitable schedule for hot rolling was found guaranteeing good conditions for further cold rolling.

Abstract: The influences of different rolling modes and speed ratios on cold rolling texture development, and the characteristics of recrystallization textures after ordinary annealing as well as magnetic annealing have been investigated for non-oriented silicon steel. Results show that the through-thickness deformation textures were effectively changed by asymmetric cold rolling even in the case of small speed ratios, and the recrystallization textures were modified with the enhanced favorable {100} and η (<100>//RD) texture components by magnetic annealing. Much improved magnetic properties can be obtained through optimization of asymmetric rolling and annealing parameters. Thus, application of asymmetric cold rolling and magnetic annealing might open up new possibilities for texture control in high-grade silicon steel production.

Abstract: The magnetic domain refinement was carried out by laser pulse scribing in order to reduce the core loss of SiFe. The laser pulses were generated by a Q-switched Nd:YAG laser, and the optical frequencies of the laser pulses were altered by using the SHG and the THG. The core losses were measured and analyzed to find optimal parameters of the laser treatment. The laser beam was focused with a spot size of 0.2 mm, and pulse energy of 10~30 mJ and the lines were scribed with a period of ~5 mm. The core loss was improved up to 19 % with the THG of Q-switched Nd:YAG laser in 3% SiFe.

Abstract: Steels with high amounts of silicon are used in electrical applications due to their low mangectoestriction, high electrical resistivity and reduced energy losses, but they exhibit poor formability. A fundamental study of the workability of such materials using torsion testing may help to understand and to optimise its production. Single deformation torsion tests were carried out on a steel containing 2 wt.-% Si in a temperature range of 800 to 1100°C and strain rates in the range of 0.01 to 2 s-1. A value of 299 kJ/mol was found for the apparent activation energy for hot working after applying the hyperbolic-sine equation to the mean flow stress (MFS) values computed from the test. Multiple deformation torsion tests under continuous cooling conditions were carried out in the same temperature range at strain rates from 0.2 to 1 s-1, the strain per pass and interpass time (determining the cooling rate) were varied. Different critical temperatures, which are of importance for processing this alloy, can be calculated from the dependence of MFS with the inverse absolute temperature; such a method was used to determine the temperature at which recrystallisation stops (Tnr). It was found that this temperature depends on strain rate, pass strain and interpass time. Results of the microstructure analysis of quenched samples are in good agreement with the values of Tnr.

Abstract: Magnetic annealing at five different magnitudes of field was conducted to evaluate the effect of the field on the recrystallized microstructure of Fe-0.75%Si samples. At higher fields the retardation during recrystallization is compensated by the magnetic filed driving force that causes an increase in the grain boundary mobility of grains that have a certain relationship with the direction of the field

Abstract: A silicon steel single crystal with initial Goss orientation, i.e. the {110}<001> orientation, was cold rolled up to 89 % thickness reduction. Most of the crystal volume rotates into the two symmetrical equivalent {111}<112> orientations. However, a weak Goss component is still present after high strain, although the Goss orientation is mechanically instable under plane strain loading. Two types of Goss-oriented crystal volumes are found in the highly deformed material. We suggest that their origin is different. The Goss-oriented regions that are observed within shear bands form during the cold rolling process. In contrast, those Goss-oriented crystal volumes that are found inside of microbands survive the cold rolling.

Abstract: Fe-3.10%Si thin strips were prepared by symmetric and asymmetric cold rolling from commercial grain oriented silicon steel sheets, then annealed with and without a magnetic field. Magnetic field of 12T was applied along the rolling direction. Magnetic annealing does not essentially change the texture development that recrystallization texture consists mainly of η fiber (RD//<001>), and the strongest component tends to transform from Goss ({110}<001>) to {210}<001> with the increase in speed ratio and annealing temperature. But magnetic annealing promotes Goss component in the strips rolled with small speed ratios, while decreases {210 <001> component in those rolled with large speed ratios. Possible effect mechanism of magnetic annealing was discussed.