Stepping motor, timepiece movement, timepiece, and manufacturing method of stepping motor

1. A stepping motor comprising:

a rotor configured to rotate an indicating hand; and

a stator configured to form a magnetic path, the stator being configured to be made of an alloy containing Fe, Ni, and Cr, and the stator comprising a Cr-diffusion region whose Cr-concentration is 14 mass % or greater is disposed in a portion whose cross-sectional area in the magnetic path is smaller than a cross-sectional area of other portions in the magnetic path.

2. The stepping motor according to claim 1 ,

the Cr-diffusion region is disposed in a portion which does not interfere with a positioning portion disposed in a rotor accommodating hole in order to secure a stable position for steadying the rotor.

3. The stepping motor according to claim 2 ,

a surface of the Cr-diffusion region is formed using a plane which is continuous with a surface of other portions.

4. The stepping motor according to claim 1 ,

a surface of the Cr-diffusion region is formed using a plane which is continuous with a surface of other portions.

5. The stepping motor according to claim 1 ,

the Cr-concentration of the Cr-diffusion region is 40 mass % or smaller.

6. The stepping motor according to claim 5 ,

the Cr-diffusion region includes a region having a distribution in which the Cr-concentration varies from 40 mass % to 14 mass %.

7. The stepping motor according to claim 1 ,

the Cr-concentration of the Cr-diffusion region is 16 mass % or smaller.

8. The stepping motor according to claim 7 ,

the Cr-diffusion region includes a region having a distribution in which the Cr-concentration varies from 40 mass % to 14 mass %.

9. The stepping motor according to claim 1 ,

the Cr-diffusion region includes a region having a distribution in which the Cr-concentration varies from 40 mass % to 14 mass %.

10. The stepping motor according to claim 1 ,

the stator is made of the alloy containing Fe, Ni, and Cr, in which a nickel component is 37.5% to 38.5%, a chromium component is 7.5% to 8.5%, and an iron component is 52.5% to 54.5%.

11. A timepiece movement comprising:

the stepping motor according to claim 1 .

12. A timepiece comprising:

the timepiece movement according to claim 11 .

13. A stepping motor comprising:

a rotor that configured to rotate an indicating hand; and

a stator configured to form a magnetic path, the stator being configured to be made of an alloy containing Fe, Ni, and Cr, the stator comprising a Cr-diffusion region disposed in a portion whose cross-sectional area in the magnetic path is smaller than a cross-sectional area of other portions in the magnetic path, and in which when Cr-concentration of the Cr-diffusion region is set to X % and Cr-concentration of the other portions is set to Y %, a difference between X and Y is 6% or greater.

14. A manufacturing method of a stepping motor, the step motor comprising:

a rotor configured to rotate an indicating hand; and

a stator configured to form a magnetic path, the stator being configured to be made of an alloy containing Fe, Ni, and Cr, and the stator comprising a Cr-diffusion region whose Cr-concentration is 14 mass % or greater is disposed in a portion whose cross-sectional area in the magnetic path is smaller than a cross-sectional area of other portions in the magnetic path;

wherein the method comprises:

machining a Fe—Ni alloy plate so as to form a stator material which has a rotor accommodating hole and a magnetic path arranged around the rotor accommodating hole;

arranging a Cr-material for diffusion in at least a portion of the stator material; and

placing the stator material having the Cr-material arranged therein at a temperature which is equal to or lower than a melting temperature of the Cr-material and diffusing the Cr-material into the magnetic path so as to form a Cr-diffusion region.

15. The manufacturing method of a stepping motor according to claim 14 ,

wherein the temperature for placing the stator material having the Cr-material arranged therein is set to 900° C. to 1,200° C., and a time for placing the stator material is set to one hour to 24 hours.

16. The manufacturing method of a stepping motor according to claim 15 ,

arranging the Cr-material is nickel plating performed for coating at least a portion of the magnetic path on a surface of the stator material, and arranging the Cr-material together with Cr powder and other compounding material powder in an inert gas atmosphere after removing a coated portion.

17. The manufacturing method of a stepping motor according to claim 15 ,

arranging the Cr-material is forming a chromium plating layer on a portion of a surface of the magnetic path of the stator material so as to arrange the Cr-material in an inert gas atmosphere.

18. The manufacturing method of a stepping motor according to claim 14 ,

arranging the Cr-material is nickel plating performed for coating at least a portion of the magnetic path on a surface of the stator material, and arranging the Cr-material together with Cr powder and other compounding material powder in an inert gas atmosphere after removing a coated portion.

19. The manufacturing method of a stepping motor according to claim 14 ,

arranging the Cr-material is forming a chromium plating layer on a portion of a surface of the magnetic path of the stator material so as to arrange the Cr-material in an inert gas atmosphere.

20. The manufacturing method of a stepping motor according to claim 14 ,

wherein in forming the stator material, a narrow portion in which a cross-sectional area of the magnetic path is narrower than a cross-sectional area of other portions is disposed in the stator material, and

wherein in arranging the Cr-material, the Cr-material is arranged in a region including at least the narrow portion.