Yoshiyuki Ushigami

Recent progress and future trend on grain-oriented silicon steel

Secondary recrystallization mechanism has rapidly progressed together with the advance in manufacturing process for grain-oriented silicon steel. The acquired inhibitor method was developed to avoid the metallurgical problem for controlling secondary recrystallization. As magnetic domain structure is affected largely by core loss, pinning of domain wall movement and surface closure domains must be removed to reduce core loss further.

Production of very low core loss grain-oriented silicon steel

The present paper is concerned with the production of very low core loss grain-oriented silicon steel. Domain refining techniques and their mechanisms have been studied. A quantitative interpretation for the domain refining phenomena is not sufficient. However, it is anticipated that these results will be based on the same principle, that is, an interaction between tensile stress and subdomains which consists mainly of transverse domains resulted from magnetic free poles and/or internal stress. An attempt to develop grain-oriented silicon steel with almost perfect

Secondary Recrystallization in Grain-Oriented Silicon Steel

Mechanism of Goss secondary recrystallization in grain-oriented silicon steel has been investigated by temperature gradient annealing and by in situ observation utilizing synchrotron x-ray topography. The results support the selective growth theory. Migration of Goss grains is controlled by second phase particles (inhibitor) and sharper Goss grains, which have higher frequency of CSL boundaries to the matrix, start to grow preferentially while the other matrix grains are stagnated by inhibitor. CSL boundaries are supposed to have lower grain boundary energy, thus suffer lower pinning force from the inhibitor and start to migrate at higher inhibition level. Based on this model, we have made a computer simulation and have found that this model successfully depicts the important features of secondary recrystallization; grain growth behavior of secondary grains, secondary grain size and sharpness of Goss texture.

Production of single-crystal 3% silicon-iron sheet with orientation near (110) [001]

Abstract The production of single-crystal 3% silicon iron sheet with a near (110) [001] orientation was studied. This study presented the possibility of the industrial production of grain-oriented 3% silicon steel with very high induction. This production is characterized by a unique grain-growth inhibition system for promoting secondary recrystallization. The system is composed of final annealing in a temperature gradient. Final annealing in a temperature gradient above 3°C/cm enables production of grain-oriented 3% silicon steel with a very high induction of 2.0 T.

Effects of Cu Precipitates on Magnetic Properties of Nonoriented Electrical Steel

Tests to measure the effects of the precipitating size of Cu on the magnetic properties of nongrain-oriented (NGO) electrical steel were carried out. The hysteresis loss had a maximum value when the diameter of the precipitates was around the thickness of the domain wall and decreased rapidly with decreasing size of the precipitates. Alternatively, yield point (YP) rose steeply with reduction in the size of Cu precipitates. It can be confirmed that the precipitating Cu has an ability of rising over 100 MPa in YP without deteriorating core loss. Regarding the effects of Cu precipitates on the hysteresis loss, the surface tension effect might be dominant for the case in which precipitates are smaller than the domain wall thickness, and internal magnetic poles are effective for the larger precipitates.

Characteristic Microstructure and Grain Boundary Motion in Secondary Recrystallization of Fe-3%Si Alloys

The microstructure of Fe-3 mass% Si alloys before secondary recrystallization has been characterized by analyzing precipitates and grain boundary segregated elements. The samples used were mainly sheets of Fe-3%Si alloys containing manganese, sulfur, aluminum, nitrogen and tin, which were decarburized and annealed up to secondary recrystallization. Grain boundary segregation in primarily recrystallized samples was studied using Auger electron spectroscopy (AES), and precipitates were analyzed using transmission electron microscopy (TEM) with an energy dispersive X-ray spectrometer (EDX). AES spectra showed that tin and nitrogen were enriched on grain boundaries in the Fe-3 mass% Si alloys. TEM/EDX analysis showed that the morphology and distribution of the fine precipitates such as manganese sulfide and aluminum nitride were influenced by addition of tin. The characteristic structure formed by secondary recrystallization of grain oriented silicon steel is considered to be influenced by the fine precipitates and segregation of a small amount of elements, as the abnormal motion of grain boundaries of the silicon steel was correlated with the precipitation and segregation of the alloying elements.

Effect of Aluminum and Titanium Content on Grain Growth, Texture and Magnetic Properties in 3%Si Non-Oriented Electrical Steel

The effect of annealing temperature on grain growth, texture development and magnetic properties of Al-free and Al-1% added non-oriented electrical steel were investigated. Normal grain growth occurred in Al-free steel. On the other hand, abnormal grain growth occurred in Al-added steel which was annealed at 800°C for 24h. Precipitates in these two steels were different. TiN precipitated in Alfree steel, but in the case of Al-added steel, AlN and TiC precipitated. The TiC in Al-added steel was so fine that it inhibited the normal grain growth and finally caused the abnormal grain growth. Main textures of both steels were near {111}<112>, but the intensity of near {111}<112> in the abnormal grain growth was higher than that in the normal grain growth. Magnetic flux density (B50/Bs) was decreased by the grain growth. Especially B50/Bs in the abnormal grain growth was lower than that in normal grain growth. B50/Bs in these steels can be estimated by their three-dimensional textures in vector method.

Orientation Selectivity of Secondary Recrystallization in Grain-Oriented Silicon Steel

It has been observed that grain size of Goss secondary grain has a strong correlation with deviation angle from the exact Goss orientation and sharper Goss grain has larger grain diameter. This orientation selectivity of secondary recrystallization has been investigated with the statistical model of grain growth in which inhibitor and texture are taken into account. The model assumes that sharper Goss grain has a higher frequency of CSL boundaries to the matrix grains and thus has lower statistical grain boundary energy and suffers lower pinning force from the inhibitor. The analysis showed that this model successfully explains orientation selectivity and depicts the effect of inhibitor and texture.

Texture Change during Grain Growth in Non-Oriented Electrical Steel

Texture change during grain growth in Fe-3%Si non-oriented electrical steel was investigated. Cold rolled steel, 0.35mm in thickness, was annealed and recrystallized as an initial structure. Normal grain growth and abnormal grain growth occurred by additional annealing. {111} was dominant in the initial texture. However {100} component, which was not in majority in the initial structure, became stronger after normal grain growth. It was revealed that an average grain size of {100} in the initial structure was bigger than those of other components by analysis of the EBSD data,. Therefore, it is concluded that {100} strengthened after normal grain growth due to its size advantage. On the other hand, {111} components became more stronger after abnormal grain growth. It is inferred that another mechanism of the texture change worked in abnormal grain growth.

Mechanism of Secondary Recrystallization in Grain-Oriented Si Steel

On the basis of Hillerts model of grain growth, a new model of Goss secondary recrystallization in silicon steel has been developed in which inhibitor and grain boundary energy are taken into account. An analysis shows that these two parameters synergistically affect secondary recrystallization and Goss grain evolves to a coarse grain as inhibitor intensity increases and statistical grain boundary energy decreases. This model successfully explains Goss secondary recrystallization.