環境対応Ｐｂレス焼結電磁ステンレス材の開発

Abstract

In recent years, melted electromagnetic stainless steels containing a small amount of lead (Pb) have been used in the majority of magnetic parts in which corrosion resistance is required, beginning with solenoid valves and also including injectors for fuel injection systems and various other types of actuators. In these fields, the development of various types of sintered magnetic cores using the powder metallurgy method has been attempted in the past. But because it was not, however, possible to solve problems such as low magnetic flux density and excessive core loss, etc., these products have not reached application. This is attributable to the low density at 7.0 Mg/m3 of the conventional sintered electromagnetic stainless steel, SUS410, which made it impossible to obtain high magnetic flux density and satisfactory suction. Therefore, the authors developed a new sintered electromagnetic stainless steel with greatly improved compactibility and sinterability by optimizing the powder composition and annealing treatment. The developed sintered electromagnetic stainless steel has an Fe-6.5Cr-3Si composition with no Pb, considering the environment. Satisfactory compactibility is maintained in spite of the high content of Si at 3 mass%, and a high density ratio of more than 95% (7.4 Mg/m3) can be obtained after sintering. As a result, the developed material realized a sintered electromagnetic stainless steel with both a high magnetic flux density of B2500A/m: 1.4 T and satisfactory permeability of μm: 5000, which are necessary in actuators, as well as airtightness, which is important as a functional property in injectors. The mass production of the injectors core for LPG engines began in September 2005.