Method for manufacturing soft magnetic material

Abstract

The invention provides a method for manufacturing a soft magnetic material, wherein an Fe-Si alloy powder is heated in a weakly oxidizing atmosphere to form a SiO2 oxide film on the surface, and the powder is then press-molded and fired in a weakly oxidizing atmosphere to obtain a sintered product. By performing the surface oxidizing step in a weakly oxidizing atmosphere such as water vapor, Si is selectively oxidized to form a thin oxide film with high electrical resistance. Furthermore, by firing the molded product in a weakly oxidizing atmosphere, the sintering can be performed while the oxide film, in which cracks and the like are generated at the press-molding, is repaired.

Description

technical field [0001] The present invention relates to a method for the production of a soft magnetic material that can be applied, for example, as core material for solenoid actuators and converters. More specifically, the present invention relates to a method of producing a soft magnetic material by firing iron-based soft magnetic powder whose surface is covered with an oxide film having high electrical resistance. Background technique [0002] In order to increase the response speed of a solenoid valve used in an internal combustion engine fuel injection system or the like, a soft magnetic material as a core material of a converter is required to have a high saturation magnetic flux density and a high magnetic permeability. Soft magnetic materials for such applications are usually produced by sintering powders, and the raw material powders used are usually cheap iron-based soft magnetic powders with high saturation magnetic flux densities. At this ...

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Problems solved by technology

[0005] However, in the above-mentioned conventional production method, the surface of the pulverized alloy powder must be covered with various substances. In addition, since the pulverized alloy powder is repeatedly soaked in a solution and thereby oxidized to form a Ni-Zn ferrite thin layer or the step of sputtering Al in a nitrogen atmosphere to form an insulating film takes extra effort, so the production cost is high

In addition, in a method of forming an insulating film by covering the surface of a raw material powder with a different substance, such as sputtering Al, the thickness of the insulating film tends to become large, and it is difficult to uniformly form a nano-scale film

As a result, the density of the magnetic material of the soft magnetic element decreases, thereby reducing the saturation magnetic flux density, causing deterioration of the magnetic properties

[0006] On the other hand, when the insulating film is formed in a thin film to enhance magnetic properties, cracks may occur on the insulating film of the soft magnetic powder due to the pressing pressure during compression molding of the soft magnetic powder

When the insulating film is damaged, the insulating property between the soft magnetic powder particles decreases, and the iron loss (loss caused by eddy current) in the sintered soft magnetic material unfavorably increases

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