Abstract: A nitrided part having excellent fatigue strength which has predetermined constituents, has structures comprised of ferrite and pearlite, has ferrite grains with an aspect ratio of a ratio of a long axis direction and short axis direction of 4.5 or more present in the entire region at a depth from the surface of the part where stress is expected to concentrate of (?×0.09+0.05) mm or less, and has an average concentration of N of 5000 ppm or more at a surface layer part from the surface down to 200 ?m in the depth direction.

Abstract: A gear keeping the bending stress at the dedendum from becoming locally high at the time of power transmission and thereby raising the dedendum bending strength. The radius of curvature is maximum at a critical section position determined by the Hofer's 30° tangent method. Both radii of curvature from the critical section position to the first and second connecting points X1 and Y1 are constant or decreasing. In dedendum line segment 23, there are points A1 and B1 where radius of curvature is smaller than the critical section position. In the dedendum line segment 23, the maximum radius of curvature is 3 times or less the minimum radius of curvature. By a cross-sectional view, the critical section position is part of an arc, and the arc extends to the two sides of the critical section position. Thus, the maximum bending stress becomes smaller and dedendum bending strength is improved.

Abstract: A nitrided part having excellent fatigue strength which has predetermined constituents, has structures comprised of ferrite and pearlite, has ferrite grains with an aspect ratio of a ratio of a long axis direction and short axis direction of 4.5 or more present in the entire region at a depth from the surface of the part where stress is expected to concentrate of (?×0.09+0.05) mm or less, and has an average concentration of N of 5000 ppm or more at a surface layer part from the surface down to 200 ?m in the depth direction.

Abstract: A ball bearing not allowing locations where the surface pressure becomes locally higher at a race at the time of a high load and thereby keeping cracking from occurring and in turn realizing a longer lifespan is provided. A pair of races (12, 14) and at least one rolling element (16) movably clamped between the pair of races move are provided. A cross-sectional profile line (14a) of a part of each of the pair of races contacting the rolling element has the smallest radius of curvature at a position (P) sticking out the most in the first direction (D1) over which the pair of races face. The cross-sectional profile line becomes larger in radius of curvature the further from the position (P) in a second direction (D2) vertical to the first direction (D1) in the cross-section. The cross-sectional profile line is comprised of a single function.

Abstract: A gear keeping the bending stress at the dedendum from becoming locally high at the time of power transmission and thereby raising the dedendum bending strength is provided. The radius of curvature is maximum at a critical section position determined by the Hofer's 30° tangent method. Both of the radii of curvature from the critical section position to the first and second connecting points X1 and Y1 are constant or decreasing. In the dedendum line segment 23, there are the points A1 and B1 where the radius of curvature is smaller than the critical section position. In the dedendum line segment 23, the maximum radius of curvature is 3 times or less the minimum radius of curvature. By a cross-sectional view, the critical section position is part of an arc, and the arc extends to the two sides of the critical section position. Due to this, the maximum bending stress becomes smaller and improvement of the dedendum bending strength can be realized.

Abstract: A ball bearing not allowing locations where the surface pressure becomes locally higher at a race at the time of a high load and thereby keeping cracking from occurring and in turn realizing a longer lifespan is provided. A pair of races (12, 14) and at least one rolling element (16) movably clamped between the pair of races move are provided. A cross-sectional profile line (14a) of a part of each of the pair of races contacting the rolling element has the smallest radius of curvature at a position (P) sticking out the most in the first direction (D1) over which the pair of races face. The cross-sectional profile line becomes larger in radius of curvature the further from the position (P) in a second direction (D2) vertical to the first direction (D1) in the cross-section. The cross-sectional profile line is comprised of a single function.