NKK Marketing New High-Silicon Magnetic Steel Sheets

Keihin's magnetic steel sheet production facility

NKK has succeeded in the commercial production of two new series of high-silicon magnetic steel sheets. The company has added these products to its already-commercialized high-performance 6.5%-silicon magnetic steel sheet, "NK Super E-Core," which has won acceptance in the market since its introduction in 1993.

NKK's 6.5%-silicon steel sheet features excellent magnetic properties, including greatly reduced iron core loss (energy loss) at both commercial frequencies of 50/60Hz and high frequencies, and extremely low magnetostriction (de formation resulting from magnetization). Because of these characteristics, use of the product has increased in various electric devices and shielding materials, including cores for transformers and motors, offering the advantages of weight, vibration and noise reductions, as well as power savings.

To meet steadily growing and diversifying market needs, NKK has now expanded its product line with two higher-value-added magnetic steel sheets, which were developed by adjusting the distribution range of silicon content over the thickness of the sheet. Dubbed gradient high-silicon magnetic steel sheets,NKK recently began commercial production at its Keihin Works.

The first of the two products, marketed as "NK Super HF-Core," is a high-silicon steel sheet with ultralow iron loss under high-frequency conditions. By siliconizing the cold-rolled sheet to 6.5% at the surface and 3% at the core, magnetic flow has been increased at the sheet surface, thereby effectively reducing eddy current losses as a result of the skin effect created by the compositional difference. When magnetized at very high frequencies, above 10kHz, for example, this sheet has only half the iron loss of the highest-grade conventional magnetic steel sheet. With certain modifications in its thickness, the sheet exhibits excellent magnetic characteristics superior to those of amorphous metals. The new sheet will find promising application in high-speed motors for electric and hybrid vehicles and reactors for sub-power system for trains, enabling weight reductions of 30-50%.

The second new product, marketed as "NK Super Br-Core," is a high-silicon steel sheet with low residual magnetic flux density. By raising the silicon content at the surface and lowering it at the core for an optimal distribution effect, the sheet exhibits only a quarter to one-fifth the residual magnetic flux density of conventional magnetic steel sheet, although maximum magnetic flux density remains the same. The sheet will prove to be effective in such areas as high-frequency transformers and power supply systems for computers where the overflow of initial excess current, a cause of damage and failure in computers and other high-tech equipment, is effectively avoided. Such merits will lead to a 30-50% cost savings for users.

NKK's three magnetic steel sheets are currently manufactured at the Keihin Works with a continuous chemical vapor deposition (CVD) process. The 200 tons-per-month CVD furnace, originally installed in 1993, is effective in depositing and dispersing the silicon onto the steel in a high-temperature continuous heat treatment line. Sheets are available in a thickness of 0.05-0.3mm and a maximum width of 600mm. To date, NKK has filed more than 200 patents for its magnetic steel sheet production process and application technology, including nearly 50 patents related to the new gradient high-silicon steel sheets.

As the world's first manufacturer of a variety of silicon magnetic steel sheets, NKK intends to step up its marketing efforts while positively responding to wide-ranging customer needs.