Method for manufacturing a soft magnetic powder material
The invention provides a method for manufacturing a soft magnetic powder material covered by oxide layers at surfaces of the powder, by using a soft magnetic alloy powder containing a soft magnetic powder material and a second element such as Si having an oxidizing reactivity higher than iron, and heating the soft magnetic alloy powder in an atmosphere of a weak oxidizing gas by mixing a weak oxidizing gas in an inert gas, and oxidizing selectively the second element at surface layers of the powder while restraining an oxidation of iron to form thin oxide layers with high electrical resistance.
1. A method for manufacturing a soft magnetic powder material covered by oxide layers at the surfaces of the powder, comprising a step of forming said oxide layers, by heating a soft magnetic alloy powder containing iron as a major component and a second element, which is at least one element selected from a group consisting of Si, Ti, Al and Cr with higher oxidation reactivity than iron in an atmosphere consisting of a weak oxidizing gas and an inert gas to oxidize mostly said second element at surface layers of the powder, wherein the weak oxidizing gas mixed into said inert gas is steam, and the oxidation is carried out under a condition of a temperature of 400-700° Celsius.
2. The method for manufacturing the soft magnetic powder material according to claim 1 , wherein said second element is at least one element selected from a group consisting of Ti and Cr.
3. The method for manufacturing the soft magnetic powder material according to claim 1 , wherein the oxidation is carried out under a condition of a temperature of 500-600° Celsius.
4. The method for manufacturing the soft magnetic powder material according to claim 1 , wherein said soft magnetic alloy powder is an atomized alloy powder with an average particle diameter of 0.01-500 micrometers.
5. A method for manufacturing a soft magnetic powder material covered by oxide layers at the surfaces of the powder, comprising a step of forming said oxide layers, by carrying out alternately an oxidizing step of heating in an atmosphere of a weak oxidizing gas by mixing a weak oxidizing gas in an inert gas, and a reducing step of heating in a reducing atmosphere, a soft magnetic alloy powder containing iron as a major component and a second element with higher oxidation reactivity than iron, to oxidize mostly said second element at surface layers of the powder.
6. The method for manufacturing the soft magnetic powder material according to claim 5 , wherein said second element comprises at least one element selected from a group consisting of Si, Ti, Al and Cr.
7. The method for manufacturing the soft magnetic powder material according to claim 5 , wherein said weak oxidizing gas is steam or dinitrogen monoxide gas.
8. The method for manufacturing the soft magnetic powder material according to claim 5 , wherein said weak oxidizing gas is steam,
9. The method for manufacturing the soft magnetic powder material according to claim 5 , wherein the oxidation is carried out under a condition of a temperature of 400-900° Celsius.
10. The method for manufacturing the soft magnetic powder material according to claim 5 , wherein said soft magnetic alloy powder is an atomized alloy powder with an average particle diameter of 0.01-500 micrometers.