Masahiro Fujikura

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.

Three-Dimensional Magnetic Field Numerical Calculation by Equivalent

The 3-D magnetic field numerical analysis of a full-scale magnetic shielding room is advantageously performed by using the equivalent B-H method. In the proposed numerical method, the magnetic anisotropy and the nonlinearity due to material magnetic saturation are taken into account, by directly introducing the magnetization characteristics of the considered materials. An equivalent element, which substitutes the plural finite elements having different material properties for a homogeneous one, is introduced to reduce the number of unknowns. When the equivalent B-H method is applied to a full-scale magnetic shielding room (length 5.8 m, width 3.3 m, height 3.3 m), the measured leakage magnetic flux density distribution is found to be in good agreement with the calculated one, proving the reliability of the proposed approach, which can be adopted in many large-scale electromagnetic field problems.

B\hbox{–}H

An innovative image processing methodology is proposed to draw the magnetization curves of electrical steels. Our methodology enables to draw the continuous magnetization curve from a series of the distinct scanning electron microscope (SEM) images of magnetic domains. Our image processing methodology has two distinguished features. One is that the contrast of a domain image is regarded as an average of flux density. Another one is that domain motion observed in several domain images is represented by the image Helmholtz equation. Its solution generates any magnetized states of the magnetic domains. Moreover, computing averaged contrast of each image gives value of flux density on a magnetization curve. In this paper, we apply our methodology to the domain images of a grain-oriented electrical steel. This paper demonstrates the macroscopic- as well as microscopic-magnetization curves reflecting on their physical conditions.

Method for Magnetic Field Mitigation

We propose a new type of magnetic shield structure, in which some closed magnetic paths surround a defined space. Because there are some openings between paths, the freedom in designing and the ease of constructing a shield room are attained. This structure shows better magnetic shield performance than conventional shield structures when openings between magnetic paths, widths of magnetic paths, and weight distribution of magnetic materials are designed appropriately.

Magnetization curve plotting from the magnetic domain images

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.

Open-Type Magnetic Shield Structure and its Performance

The morphology of deformation twinning, which influences a brittle fracture at low temperatures, was investigated in Fe-8mass%Al. Tensile tests were performed at 129K and room temperature. The specimen tested at room temperature showed yielding and kept deformed by usual slip while the specimen tested at 129K fractured in a brittle manner in an elastic regime with a number of straight markings due to deformation twinning. Detail analysis of those deformation twins suggests that the collision of deformation twinning is the initiation site of the brittle fracture.

Effects of Cu Precipitates on Magnetic Properties of Nonoriented Electrical Steel

A two-layer open-type magnetic shield was constructed by using cubic open-type magnetic shield structures in a nested arrangement. Measurements were conducted in order to verify the performance of the magnetic shield in terms of preventing magnetic field leakage from the interior towards the exterior. Data regarding the distribution of leaked magnetic fields around the structure and the distribution of the magnetic flux density in the magnetic material is presented.

The brittle-to-ductile transition behaviour in Fe-Al single crystalline alloys

This paper proposes the image Helmholtz equation method to visualize iron loss distribution of magnetic materials. The Helmholtz-type equations carry out dynamic image analysis of a series of distinct magnetized domain images. The domain images derive the state transition matrices of which imaginary parts correspond to the phase lag components of magnetization. In the present paper, iron loss distribution of a grain-oriented electrical steel is studied by utilizing its scanning electron microscope (SEM) images. The result of analysis visualizes iron loss generating parts reflecting on the magnetic domains. Moreover, the solution of image Helmholtz equation demonstrates computing magnetization curves, which agree well with the experimental result.