Hitachi, Ltd.

Hitachi Astemo Ltd.

Hisamitsu Hatou

Matahiro Komuro

Yuichi Satsu

Seunghwan Park

Kotaro Shiino

Koji Numakura

Shintaro Tsujimi

A soft magnetic material that is sheet-shaped or foil-shaped and has a high saturation magnetic flux density, contains iron, carbon, and nitrogen, and includes a martensite containing carbon and nitrogen, and γ-Fe, wherein the γ-Fe includes a nitrogen-containing phase. The soft magnetic material is produced by steps of heating an iron-based material that is sheet-shaped or foil-shaped, carburizing the iron-based material with a carburizing gas, dispersing a granular carbide in α-Fe in the iron-based material at a temperature equal to or lower than a eutectoid temperature, transforming the α-Fe into γ-Fe at a temperature higher than the eutectoid temperature, diffusing nitrogen into the γ-Fe using a nitrogen supply gas to form γ-Fe—N—C, and rapidly heating and then rapidly cooling the γ-Fe—N—C to transform the γ-Fe—N—C into a martensite. The result is a thermally stable soft magnetic material having a saturation magnetic flux density higher than that of pure iron.

Soft magnetic material and method for producing the same, and electric motor containing soft magnetic material

An object of the present invention is to provide a ball screw having a structure in which a screw shaft and a nut satisfy required performance and having improved durability, a method for manufacturing the ball screw, a power steering device, and a method for manufacturing the power steering device. A ball screw according to the present invention includes: a nut made of a steel substrate having an inner peripheral surface on which a female screw is formed; a screw shaft that is combined with the nut and is made of a steel substrate having an outer peripheral surface on which a male screw facing the female screw is formed; and a plurality of balls arranged between the female screw and the male screw. A surface of the nut in contact with the ball and a surface of the screw shaft in contact with the ball each have carburized layers. A carbon concentration in the carburized layer of the nut is higher than a carbon concentration in the carburized layer of the screw shaft.

Ball screw, method for manufacturing ball screw, power steering device, and method for manufacturing power steering device

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Tokyo, Japan

Hisamitsu Hatou