Shaft component, method for manufacturing shaft component, method for manufacturing bearing raceway component, and bearing raceway component

Abstract

Provided is a shaft component for manufacturing a bearing raceway component having a power transmission portion with teeth by performing carburizing or carbonitriding. The shaft component is made of a columnar or cylindrical shaft member. The shaft member has a central axis, a first portion on a first side in the axial direction, and a second portion on a second side of the first portion in the axial direction. The first portion is integrated with the second portion. The first portion is made of a first steel material, and the second portion is made of a second steel material. The first portion has a portion that becomes a raceway, and the second portion has a portion that becomes teeth. An alloy composition of the first steel material is different from an alloy composition of the second steel material. A third portion includes a joint surface that is connected to the second portion on the second side of the first portion in the axial direction, and a fourth portion includes a joint surface that is connected to the first portion on the first side of the second portion in the axial direction. A fifth portion is located on the first side of the third portion in the axial direction in the first portion, and a sixth portion is located on the second side of the fourth portion in the axial direction in the second portion. The hardness of the third portion is greater than the hardness of the fifth portion, and the hardness of the fourth portion is greater than the hardness of the sixth portion. The portion that becomes the raceway is located in the fifth portion and is not located in the third portion.

Description

Shaft component, shaft component manufacturing method, bearing raceway component manufacturing method, and bearing raceway component

[0001] This application claims priority to International Patent Application Nos. PCT / JP2023 / 027685 filed on July 28, 2023, and PCT / JP2024 / 006361 filed on February 21, 2024, and incorporates the entire contents of these international patent applications by reference.

[0002] A bearing raceway component in which an inner ring of a bearing and a gear shaft are integrated is known. Patent Document 1 (JP-A-2005-102666) discloses a transmission including a first shaft unit connected to a drive shaft of a drive unit, the first shaft unit including a first shaft connected to the drive shaft and having a first shaft raceway on its outer circumferential surface, a first output gear mounted on the first shaft and rotating integrally with the first shaft, a first outer ring attached to a first support part supporting the first shaft and surrounding the first shaft raceway, the first outer ring having a first outer ring raceway on its inner circumferential surface, and a plurality of first rolling elements disposed between the first shaft raceway surface and the first outer ring raceway surface. The first shaft of the transmission includes a raceway and an output gear on its outer circumferential surface.

[0003] JP 2023-020380 A

[0004] When a single shaft member is provided with a raceway of a bearing portion having a raceway and teeth of a power transmission portion having teeth, such as the teeth of a gear or a toothed pulley, it has been difficult to simultaneously satisfy the strength required for the raceway of the bearing portion having a raceway and the strength required for the teeth of the power transmission portion having teeth. In other words, when a single shaft member is provided with a raceway of a bearing portion having a raceway and teeth of a power transmission portion having teeth, it has been found that if the shaft member is subjected to heat treatment to optimize one of the strength required for the raceway of the bearing portion having a raceway and the strength required for the teeth of the power transmission portion having teeth, the other strength must be compromised. Therefore, there is a need for a shaft member that can simultaneously satisfy the strength required for the raceway of the bearing portion having a raceway and the strength required for the teeth of the power transmission portion having teeth.

[0005] The shaft part of the present disclosure is a shaft part for manufacturing a bearing raceway part having a power transmission portion with teeth by carburizing or carbonitriding, and is made of a columnar or cylindrical shaft member, the shaft member having a central axis, the shaft member having a first portion on a first axial side and a second portion on a second axial side of the first portion, the first portion being integrated with the second portion, the first portion being made of a first steel material, and the second portion being made of a second steel material, the first portion comprising a portion that will become a raceway, and the second portion comprising a portion that will become teeth, the alloy composition of the first steel material being different from the alloy composition of the second steel material, the third portion comprising a joining surface of the first portion that is connected to the second portion on the second axial side, the fourth portion comprising a joining surface of the second portion that is connected to the first portion on the first axial side, and the fifth portion of the first portion being located on the first axial side of the third portion, The sixth portion is located on the second axial side of the fourth portion of the second portion, the hardness of the third portion is greater than that of the fifth portion, the hardness of the fourth portion is greater than that of the sixth portion, and the portion that becomes the track is located in the fifth portion and not in the third portion.

[0006] One method for manufacturing a shaft part according to the present disclosure is a method for manufacturing a shaft part for manufacturing a bearing raceway part according to the present disclosure, which comprises friction welding a first portion of a workpiece in a first state and a second portion of a workpiece in a first state to form an integrated first workpiece, and performing one of the following steps first and second: forming a portion of the first portion of the first workpiece that will become a bearing portion having a raceway by first machining; and forming a portion of the second portion of the first workpiece that will become a power transmission portion having teeth by second machining.

[0007] Another method for manufacturing a shaft part according to the present disclosure is a method for manufacturing a shaft part for manufacturing a bearing raceway part according to the present disclosure, in which one of the following is performed first: forming a portion that will become a bearing part having a raceway on a first portion of a workpiece in a first state by a first machining process; and forming a portion that will become a power transmission part having teeth on a second portion of a workpiece in the first state by a second machining process; to produce a first portion of a workpiece in a second state and a second portion of a workpiece in a second state; and to integrate the first portion of a workpiece in the second state and the second portion of a workpiece in the second state by friction welding.

[0008] The method for manufacturing a bearing raceway part according to the present disclosure is a method for manufacturing a bearing raceway part having a power transmission portion with teeth, including the method for manufacturing a shaft part according to the present disclosure, wherein the shaft part obtained by the method for manufacturing a shaft part according to the present disclosure is used as a second workpiece, and the portion of the second workpiece that will become the bearing portion with the raceway and the portion that will become the power transmission portion with teeth are simultaneously carburized or carbonitrided, followed by quenching and tempering, to form an integral carburized or carbonitrided layer on the outer peripheral surface of the portion on the second axial side of the fifth part, the outer peripheral surface of the third part, the outer peripheral surface of the fourth part, and the outer peripheral surface of the portion on the first axial side of the sixth part, and / or to form an integral carburized or carbonitrided layer on the inner peripheral surface of the portion on the second axial side of the fifth part, the inner peripheral surface of the third part, the inner peripheral surface of the fourth part, and the inner peripheral surface of the portion on the first axial side of the sixth part.

[0009] A bearing race component according to the present disclosure is a bearing race component comprising a power transmission portion having teeth, the bearing race component comprising a columnar or cylindrical shaft member, the bearing race component having a central axis, the bearing race component having a seventh portion on a first axial side and an eighth portion on a second axial side of the seventh portion, the seventh portion being integrated with the eighth portion, the seventh portion being made from a first steel material, and the eighth portion being made from a second steel material, the first steel material having an alloy composition different from the alloy composition of the second steel material, the seventh portion comprising a raceway, the eighth portion comprising teeth, a carburized layer or a carbonitrided layer being formed integrally on surfaces of the seventh portion and the eighth portion, the seventh portion including a joining surface connected to the eighth portion on the second axial side of the seventh portion, all of the raceways being in the seventh portion, and all of the teeth being in the eighth portion. All of the raceways are located at an axial distance of 5 mm or more from the joint surface.

[0010] According to the present disclosure, it is possible to provide a bearing raceway component with a power transmission part having teeth, which has both strength suitable for the raceway of a bearing part having a raceway and strength suitable for the teeth of a power transmission part having teeth, and which has good durability. It is also possible to provide a shaft part for manufacturing this bearing raceway component.

[0011] FIG. 1 is a cross-sectional schematic view of a bearing raceway component according to a first embodiment. FIG. 2 is a cross-sectional schematic view of a shaft component according to the first embodiment. FIG. 3 is a cross-sectional schematic view of a bearing device having the bearing raceway component of FIG. 2. FIG. 4 is a partially enlarged view of FIG. 1. FIG. 5 is a graph showing the Vickers hardness of the shaft component according to the first embodiment. FIG. 6 is a graph showing the Vickers hardness of the bearing raceway component according to the first embodiment. FIG. 7 is a graph showing the Vickers hardness of the bearing raceway component according to the first embodiment. FIG. 8 is a graph showing the Vickers hardness of the bearing raceway component according to the first embodiment. FIG. 9 is a diagram showing heat treatment conditions for obtaining the bearing raceway components whose Vickers hardness is shown in FIGS. 6 to 8. FIG. 10 is a diagram for explaining a first manufacturing method of a bearing raceway component. FIG. 11 is a diagram for explaining a second manufacturing method of a bearing raceway component. FIG. 12 is a cross-sectional schematic view of a bearing raceway component according to a second embodiment. FIG. 13 is a cross-sectional schematic view of a bearing raceway component according to the second embodiment.

[0012] <Outline of Embodiments of the Invention of the Present Disclosure> Below, outlines of embodiments of the invention of the present disclosure will be listed and described.

[0013] (1) A shaft part of the present disclosure is a shaft part for manufacturing a bearing raceway part including a power transmission portion having teeth by carburizing or carbonitriding, the shaft part comprising a columnar or cylindrical shaft member, the shaft member having a central axis, the shaft member having a first portion on a first axial side and a second portion on a second axial side of the first portion, the first portion being integrated with the second portion, the first portion being made of a first steel material, the second portion being made of a second steel material, the first portion comprising a portion that will become a raceway, the second portion comprising a portion that will become teeth, the alloy composition of the first steel material being different from the alloy composition of the second steel material, the third portion comprising a joining surface of the first portion that is connected to the second portion on the second axial side, the fourth portion comprising a joining surface of the second portion that is connected to the first portion on the first axial side, and the fifth portion of the first portion being located on the first axial side of the third portion, The sixth portion is located on the second axial side of the fourth portion of the second portion, the hardness of the third portion is greater than that of the fifth portion, the hardness of the fourth portion is greater than that of the sixth portion, and the portion that becomes the track is located in the fifth portion and not in the third portion.

[0014] The shaft part is a shaft part for manufacturing a bearing raceway part having a power transmission part with teeth. This shaft part has a first part and a second part integrated together, with the first part comprising a raceway and the second part comprising teeth. The first part and the second part are joined by, for example, friction welding. Therefore, a third part of the first part, including the joining surface, has a higher Vickers hardness than before friction welding. On the other hand, a fifth part of the first part, remote from the joining surface, has no change in Vickers hardness than before friction welding. The same is true for the fourth and sixth parts included in the second part. The fourth part of the second part, including the joining surface, has a higher Vickers hardness than before friction welding, while the sixth part of the second part, remote from the joining surface, has no change in Vickers hardness than before friction welding. Thus, the shaft part has portions at the joining surface and in the vicinity thereof that have been hardened by joining by friction welding. The residual stress and metal structure of the portion hardened by friction welding may differ from those of other portions (portions where hardness did not change). Therefore, if a raceway is provided in a bearing raceway component manufactured using the shaft component in a portion hardened by welding, the change in residual stress over time may cause structural deterioration or non-uniform deformation of the structure, resulting in a decrease in the durability of the raceway. In contrast, the shaft component can avoid this problem of decreased raceway durability by providing the raceway portion in the fifth portion, which is not hardened by welding and is less likely to develop a unique structure or non-uniform deformation. The shaft component may be manufactured by forming the raceway portion in the first portion and then joining the first and second portions by friction welding. The shaft component is then carburized or carbonitrided to form a surface-hardened layer on the surface and harden the interior, thereby producing a bearing raceway component. When carburized or carbonitrided, the deformation dimensions of the third portion and the fifth portion may differ. This difference in deformation dimensions may cause deformation in the portion that will become the raceway. Providing the portion that will become the raceway across the third and fifth portions is uneconomical because it requires additional post-processing.

[0015] (2) In the shaft part of (1) above, it is preferable that the portion that becomes the teeth is located in the sixth portion and not in the fourth portion.

[0016] As described above, the shaft part includes a joining surface and a portion (the fourth portion of the second portion including the joining surface) hardened by friction welding in its vicinity. If teeth were formed in the portion hardened by joining, the durability of the teeth would be reduced due to changes in residual stress over time and uneven deformation of the structure. In contrast, the shaft part can be formed with teeth in the sixth portion, which is not hardened by joining and is less likely to develop a unique structure or uneven deformation, thereby avoiding the problem of reduced durability of the teeth. The shaft part may be manufactured by forming teeth in the second portion and then joining the first and second portions by friction welding. In this case, when the shaft part is carburized or carbonitrided, the deformation dimensions of the fourth portion and the sixth portion may differ. This difference in deformation dimensions may cause deformation in the teeth. Providing teeth across the fourth and sixth portions is uneconomical because it requires additional post-processing.

[0017] (3) In the shaft component of (1) or (2), the portion that becomes the raceway is preferably a portion that becomes a raceway groove along which balls roll. The raceway groove is an arc in a cross section including the central axis, and the shape of the grinding stone used to form the raceway groove is an arc in cross section that conforms to the shape of the raceway groove after grinding. Therefore, if the portion that becomes the raceway groove is deformed by carburizing or carbonitriding, a difference in grinding allowance occurs depending on the axial position of the raceway groove during subsequent grinding, which changes the processing load and is likely to cause grinding burns or deteriorate shape accuracy. Therefore, if the portion that becomes the raceway provided in the fifth section of the shaft component is a portion that becomes a raceway groove along which balls roll, the above problem can be solved.

[0018] (4) In any of the shaft parts (1) to (3), the raceway portion is preferably a conical or cylindrical raceway portion along which rollers roll, and the shaft part further includes a flange portion axially adjacent to the raceway portion. This shaft part includes a conical or cylindrical raceway portion and a flange portion axially adjacent to the raceway portion. In this case, the shape of the grinding stone for forming the raceway portion and the flange portion conforms to the shape of the raceway and the flange. Therefore, if the raceway portion or the flange portion is deformed by carburizing or carbonitriding, the grinding allowance will vary depending on the axial position of the raceway during subsequent grinding, which will likely result in grinding burns and deterioration of shape accuracy due to changes in processing load. Therefore, if the conical or cylindrical raceway portion provided in the fifth portion of the shaft part is the portion along which rollers roll, this raceway can solve the above problem. Furthermore, in the shaft part, the flange portion is preferably also provided in the fifth portion of the first portion.

[0019] (5) In any of the shaft parts (1) to (4) above, the portion that will become the teeth is preferably a portion that will become the teeth of a gear, a spline, or a toothed pulley.

[0020] (6) It is preferable that any of the shaft parts (1) to (5) above is made of a columnar or cylindrical shaft member, the central axis of the first part coincides with the central axis of the second part, and the outer peripheral surface of the part on the second axial side of the fifth part, the outer peripheral surface of the third part, the outer peripheral surface of the fourth part, and the outer peripheral surface of the part on the first axial side of the sixth part form a single cylindrical surface.

[0021] If the dimensional changes of the fifth, third, fourth, and sixth portions are not uniform after carburizing or carbonitriding, tensile stress is likely to occur at the corners if there are any (concave) corners. In the above case, there are no corners at the boundaries of the outer peripheral surfaces of the fifth, third, fourth, and sixth portions of the shaft part, so damage to the shaft part is suppressed.

[0022] (7) It is preferable that any one of the shaft parts (1) to (5) above is made of a cylindrical shaft member, the central axis of the first part coincides with the central axis of the second part, and the inner peripheral surface of the part on the second axial side of the fifth part, the inner peripheral surface of the third part, the inner peripheral surface of the fourth part, and the inner peripheral surface of the part on the first axial side of the sixth part form a single cylindrical surface.

[0023] If the dimensional changes of the fifth, third, fourth, and sixth portions are not uniform after carburizing or carbonitriding, tensile stress is likely to occur at the corners (recessed corners). In the above case, there are no corners at the boundaries of the inner peripheral surfaces of the fifth, third, fourth, and sixth portions of the shaft part, so damage to the shaft part is suppressed.

[0024] (8) In the shaft part of any one of (1) to (7), a first combination of the first steel material and the second steel material is a combination in which: the first steel material contains at least one of manganese, nickel, chromium, and molybdenum as an alloy component; the second steel material contains at least one of manganese, nickel, chromium, and molybdenum as an alloy component; and the total content (mass%) of manganese, nickel, chromium, and molybdenum of the first steel material is more than 1.5 times the total content (mass%) of manganese, nickel, chromium, and molybdenum of the second steel material; and a second combination of the first steel material and the second steel material is a combination in which: the first steel material contains silicon as an alloy component; the second steel material contains silicon as an alloy component; and the silicon content (mass%) of the first steel material is less than the silicon content (mass%) of the second steel material. A third combination of the first steel material and the second steel material is a combination in which the first steel material contains, as alloy components, zero or 1.6% by mass or less of chromium, and zero or 0.01% by mass or less of niobium, and the second steel material contains, as alloy components, 1.0% by mass or more and 2.5% by mass or less of chromium, and 0.02% by mass or more and 0.10% by mass or less of niobium, and a fourth combination of the first steel material and the second steel material is a combination in which the first steel material contains, as alloy components, zero or 0.001% by mass or more and 0.050% by mass or less of nitrogen, zero or 0.001% by mass or less of boron, and zero or 0.003% by mass or less of titanium, and The second steel material is a combination of alloy components including nitrogen in an amount of 0.001% by mass or more and 0.050% by mass or less, boron in an amount of 0.001% by mass or more and 0.005% by mass or less, and titanium in an amount of 0.01% by mass or more and 0.08% by mass or less, and it is preferable that the combination of the first steel material and the second steel material satisfies at least one of the first combination, the second combination, the third combination, and the fourth combination.

[0025] (9) In the shaft part of any one of (1) to (8) above, it is preferable that the first steel material contains carbon as an alloy component, the second steel material contains carbon as an alloy component, and the carbon content (mass %) of the first steel material is greater than the carbon content (mass %) of the second steel material.

[0026] The combination of the first steel material and the second steel material in (8) and (9) above is suitable for making the first part have a strength suitable for the raceway of a bearing part having a raceway, and for making the second part have a strength suitable for the teeth of a power transmission part having teeth.

[0027] (10) A manufacturing method of a shaft part according to the present disclosure is a method for manufacturing a shaft part according to any one of (1) to (9) above, comprising: friction welding a first portion of a workpiece in a first state and a second portion of a workpiece in a first state to form an integrated first workpiece; forming a portion that will become a bearing portion having a raceway in the first portion of the first workpiece by a first machining process; and forming a portion that will become a power transmission portion having teeth in the second portion of the first workpiece by a second machining process. One of these processes is carried out first, and the other is carried out later.

[0028] (11) A method for manufacturing a shaft part according to the present disclosure is a method for manufacturing a shaft part according to any one of (1) to (9) above, comprising: forming a portion to become a bearing portion having a raceway in a first portion of a workpiece in a first state by a first machining process; and forming a portion to become a power transmission portion having teeth in a second portion of a workpiece in a first state by a second machining process; performing one of these processes first and the other later to produce a first portion of a workpiece in a second state and a second portion of a workpiece in a second state; and integrating the first portion of a workpiece in the second state and the second portion of a workpiece in the second state by friction welding.

[0029] According to the manufacturing method (10) and the manufacturing method (11), the shaft component of the present disclosure can be manufactured.

[0030] (12) A manufacturing method for a bearing raceway part according to the present disclosure is a method for manufacturing a bearing raceway part having a power transmission part with teeth, including the manufacturing method of (10) or (11) above, wherein the shaft part obtained by the manufacturing method of (10) or (11) above is used as a second workpiece, and the part of the second workpiece that will become the bearing part with the raceway and the part that will become the power transmission part with teeth are simultaneously carburized or carbonitrided, followed by quenching and tempering, to form an integral carburized or carbonitrided layer on the outer peripheral surface of the part on the second axial side of the fifth part, the outer peripheral surface of the third part, the outer peripheral surface of the fourth part, and the outer peripheral surface of the part on the first axial side of the sixth part, and / or to form an integral carburized or carbonitrided layer on the inner peripheral surface of the part on the second axial side of the fifth part, the inner peripheral surface of the third part, the inner peripheral surface of the fourth part, and the inner peripheral surface of the part on the first axial side of the sixth part.

[0031] (13) In the method for manufacturing the bearing raceway part described in (12) above, it is preferable to use the tempered work as a third workpiece, and perform a third machining process on the part of the third workpiece that will become the bearing part having the raceway, and perform a fourth machining process on the part of the third workpiece that will become the power transmission part having the teeth, and perform one of these processes first and the other second.

[0032] According to the manufacturing method of (12) and the manufacturing method of (13), a bearing raceway part can be manufactured.

[0033] (14) A bearing race part according to the present disclosure is a bearing race part comprising a power transmission portion having teeth, the bearing race part being made of a columnar or cylindrical shaft member, the bearing race part having a central axis, the bearing race part having a seventh portion on a first axial side and an eighth portion on a second axial side of the seventh portion, the seventh portion being integrated with the eighth portion, the seventh portion being made of a first steel material, and the eighth portion being made of a second steel material, the alloy composition of the first steel material being different from the alloy composition of the second steel material, the seventh portion comprising a raceway, the eighth portion comprising teeth, a carburized layer or a carbonitrided layer being formed integrally on surfaces of the seventh portion and the eighth portion, the seventh portion including a joining surface connected to the eighth portion on the second axial side of the seventh portion, all of the raceways being in the seventh portion, and all of the teeth being in the eighth portion. All of the raceways are located at an axial distance of 5 mm or more from the joint surface.

[0034] The bearing raceway component has a seventh portion having a raceway and an eighth portion having a power transmission portion having teeth, the seventh portion and the eighth portion being made of different steel materials and being integrated together, with a carburized or carbonitrided layer. Therefore, the bearing raceway component can achieve both strength suitable for the raceway of the bearing portion having a raceway and strength suitable for the teeth of the power transmission portion having teeth. Furthermore, all of the raceways of the bearing raceway component are located in the seventh portion, and all of the raceways are located at an axial length of 5 mm or more from the joining surface. This means that the raceways are not located in areas that would become hard when the seventh portion and the eighth portion are integrated by friction welding. Therefore, the bearing raceway component has good durability.

[0035] (15) In the bearing raceway part described in (14) above, it is preferable that the eighth portion includes a joint surface that connects to the seventh portion on a first axial side of the eighth portion, and that all of the teeth are located at an axial length of 5 mm or more from the joint surface.

[0036] All of the teeth of the bearing raceway part are located on the eighth part, and all of the teeth are located at a distance of 5 mm or more in the axial direction from the joining surface. This means that no teeth are provided in the part that would become hard when the seventh and eighth parts are integrated by friction welding. Therefore, the bearing raceway part has even better durability.

[0037] <Details of the Embodiments of the Invention of the Present Disclosure> Hereinafter, embodiments of the present disclosure will be described. Note that in this disclosure, the embodiments of the invention are to be considered as illustrative in all respects and not restrictive. The scope of the rights of the present invention is defined by the claims, and it is intended to include all modifications within the meaning and scope equivalent to the claims.

[0038] [First embodiment] Fig. 1 is a cross-sectional schematic view of a bearing raceway component according to this embodiment. Fig. 2 is a cross-sectional schematic view of a shaft component according to this embodiment. Fig. 3 is a cross-sectional schematic view of a bearing device having the bearing raceway component of Fig. 2. Fig. 4 is a partially enlarged view of Fig. 1. Fig. 4 shows the area A in Fig. 1. The shaft component according to this embodiment is a shaft component for manufacturing the bearing raceway component according to this embodiment by carburizing or carbonitriding. First, a bearing device 1 according to this embodiment will be described. Then, a bearing raceway component 2 and a shaft component 2' will be described in detail.

[0039] As shown in Figure 3, the bearing device 1 comprises a bearing raceway component 2, an outer ring 3, a cage 8, and a plurality of balls (rolling elements) 4. The bearing raceway component 2 has a central axis C. One axial side of the central axis C is defined as the first axial side, and the other axial side is defined as the second axial side. In the following description, the direction perpendicular to the central axis C is referred to as the radial direction. Furthermore, the direction circumferentially around the central axis C is referred to as the circumferential direction. Figures 1 to 3 show cross sections cut along an imaginary plane passing through the central axis C.

[0040] The outer ring 3 has an outer ring raceway 3c. The bearing raceway component 2 has an inner ring raceway 2c (raceway groove 11, described later). A plurality of balls 4 are held by a cage 8 and arranged between the outer ring raceway 3c and the inner ring raceway 2c.

[0041] As shown in Fig. 1, the bearing raceway component 2 is a cylindrical shaft member. The bearing raceway component 2 has a bearing portion 10 having a raceway and a power transmission portion 20 having teeth for transmitting power. The bearing portion 10 having the raceway is on a first axial side of the power transmission portion 20 having teeth. The power transmission portion 20 having teeth is on a second axial side of the bearing portion 10 having the raceway. The bearing portion 10 having the raceway and the power transmission portion 20 having teeth are joined at a joining surface 5 by friction welding. The bearing raceway component 2 is a member in which two portions are integrated.

[0042] The bearing raceway component 2 is a component that has an inner ring raceway of a bearing and teeth of an external gear on the outer peripheral surface of an integrated shaft member. Therefore, the bearing raceway component 2 can be more easily miniaturized than components that have the same function as the bearing raceway component 2 by press-fitting the inner ring and / or external gear of the bearing onto the shaft.

[0043] In the bearing raceway component 2, the diameter of the outer peripheral surface 12 of the bearing portion 10 having the raceway is smaller than the root diameter of the power transmission portion 20 having teeth. In this case, it is easy to mesh the teeth 21 of the external gear with the teeth 7 of the gear that is paired with the external gear. The portion of the power transmission portion 20 having teeth whose diameter is equal to or smaller than the root diameter is the root cylindrical portion 26, and the portion of the power transmission portion 20 having teeth whose diameter is larger than the root diameter is the tooth 21.

[0044] The bearing portion 10 having a raceway has a raceway groove 11, which becomes the inner ring raceway 2c, on part of its outer peripheral surface. The raceway groove 11 is located at a position axially 5 mm or more away from the joining surface 5. This provides good durability. As described above, the bearing portion 10 having a raceway is combined with the outer ring 3, cage 8, and multiple balls 4 to form a ball bearing, which is a rolling bearing 6.

[0045] The toothed power transmission portion 20 serves to transmit power between the bearing raceway component 2 and elements other than the bearing raceway component 2 via the teeth. The toothed power transmission portion 20 has gear teeth 21 for transmitting power on a portion of its outer circumferential surface. The teeth 21 are helical gear teeth. These teeth 21 mesh with the teeth 7, 7 of other gears (see FIG. 3 ), thereby transmitting power from elements other than the bearing raceway component 2 and transmitting power to elements other than the bearing raceway component 2. The teeth 21 are located at an axial length of 5 mm or more from the joining surface 5. This provides good durability. The toothed power transmission portion 20 also has a corner (recessed corner) E (see FIG. 3 ). This corner E is difficult to harden during heat treatment. Furthermore, this corner E is prone to stress concentration. From this perspective, it is preferable that the corner E not be located in an axial length from the joining surface 5 of less than 5 mm.

[0046] The bearing raceway component 2 is manufactured by carburizing or carbonitriding a shaft component 2'. As shown in Fig. 2, the shaft component 2' is a cylindrical shaft member. The shaft component 2' has a first portion 10' that is carburized or carbonitrided to become a bearing portion 10 having a raceway, and a second portion 20' that is carburized or carbonitrided to become a power transmission portion 20 having teeth for transmitting power.

[0047] The first portion 10' is on a first side of the second portion 20' in the axial direction. The second portion 20' is on a second side of the first portion 10' in the axial direction. The first portion 10' and the second portion 20' are joined at a joining surface 5' by friction welding. The shaft part 2' is a member in which two portions are integrated.

[0048] The first portion 10' is made of a first steel material. The preferred first steel material is a steel material suitable for raceway components of rolling bearings. None of the surfaces of the first portion 10' have been subjected to carburizing or carbonitriding treatment. The second portion 20' is made of a second steel material. The preferred second steel material is a steel material suitable for gears, splines, toothed pulleys, etc. None of the surfaces of the second portion 20' have been subjected to carburizing or carbonitriding treatment. The alloy composition of the first steel material is different from the alloy composition of the second steel material.

[0049] When a first portion 10' made of steel and a second portion 20' made of steel are joined by friction welding, the hardness of the portion near the joining surface 5' becomes harder than the hardness of the raw materials. Therefore, the first portion 10' has a third portion 19 having a predetermined hardness and a fifth portion 18 located on a first axial side (away from the joining surface) of the third portion 19. The third portion 19 has a joining surface 5' on a second axial side. The second portion 20' has a fourth portion 27 having a predetermined hardness and a sixth portion 28 located on a second axial side (away from the joining surface) of the fourth portion 27. The fourth portion 27 has a joining surface 5' on the first axial side.

[0050] The division of the first portion 10' into the third portion 19 and the fifth portion 18, and the division of the second portion 20' into the fourth portion 27 and the sixth portion 28, will be described in more detail. FIG. 5 is a graph showing Vickers hardness measured on a cross section including the central axis C of the shaft member 2'. In FIG. 5, the vertical axis represents Vickers hardness, and the horizontal axis represents the axial distance from the joining surface. In FIG. 5, the position at an axial distance of 0 mm is the position of the joining surface 5'. In FIG. 5, the region to the left of the axial distance of 0 mm represents the Vickers hardness measured on the cross section of the first portion 10', and the region to the right of the axial distance of 0 mm represents the Vickers hardness measured on the cross section of the second portion 20'. Note that the Vickers hardness shown in FIG. 5 is the Vickers hardness measured at a depth of 2 mm from the surface on a cross section including the central axis C of the shaft member 2', measured along the axial direction.

[0051] The measurement results shown in Figure 5 are for an example in which the first steel material is SCM440 and the second steel material is SCM420. The compositions (mass%) of the first steel material (SCM440) and the second steel material (SCM420) are shown in Table 1.

[0052]

[0053] In Table 1, carbon is represented by C, manganese by Mn, nickel by Ni, chromium by Cr, molybdenum by Mo, and silicon by Si.

[0054] 5, in the shaft component 2' in which a first portion 10' made of steel and a second portion 20' made of steel are joined by friction welding, the hardness of the portions near the joining surface 5' is greater than the hardness of the respective materials. On the other hand, in each region whose axial length from the joining surface 5' exceeds 5 mm, the Vickers hardness is almost constant, and this hardness is the hardness of the respective materials.

[0055] In a shaft part according to an embodiment of the present invention, the third portion 19 and the fifth portion 18, and the fourth portion 27 and the sixth portion 28 are determined based on the results of measuring Vickers hardness in a cross section including the central axis C. The joining surface 5' is at an axial distance of 0.0 mm. The third portion 19 and the fifth portion 18 in the first portion 10' are determined by the following method. The Vickers hardness is measured at five positions in the first portion 10', each of which is axially spaced from the joining surface 5' by 10.0 mm, 11.0 mm, 12.0 mm, 13.0 mm, and 14.0 mm, and the average value is calculated. Furthermore, the obtained average value is multiplied by 1.2 to calculate the reference hardness. The Vickers hardness is measured at positions 0.2 mm, 0.4 mm, 0.6 mm, 0.8 mm, 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, 3.0 mm, 3.5 mm, 4.0 mm, 4.5 mm, 5.0 mm, 5.5 mm, 6.0 mm, 6.5 mm, 7.0 mm, 8.0 mm, and 9.0 mm from the joining surface 5' toward the first side in the axial direction. The portion from the joining surface 5' to where the measured value is less than the standard hardness is the third portion 19 of the first portion 10'. Furthermore, the portion of the first portion 10' that is farther from the joining surface 5' than the third portion 19 is the fifth portion 18.

[0056] The Vickers hardness of the fourth portion 27 and the sixth portion 28 of the second portion 20' is determined by the following method. The Vickers hardness is measured at five positions in the second portion 20', axial lengths of which are 10.0 mm, 11.0 mm, 12.0 mm, 13.0 mm, and 14.0 mm from the joining surface 5', and the average value is calculated. Furthermore, the obtained average value is multiplied by 1.2 to calculate a value. This calculated value is the reference hardness. The Vickers hardness is then measured at positions 0.2 mm, 0.4 mm, 0.6 mm, 0.8 mm, 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, 3.0 mm, 3.5 mm, 4.0 mm, 4.5 mm, 5.0 mm, 5.5 mm, 6.0 mm, 6.5 mm, 7.0 mm, 8.0 mm, and 9.0 mm from the joining surface 5' toward the second axial side. The portion of the second portion 20' extending from the joining surface 5' to where the measured value is less than the reference hardness is the fourth portion 27. Furthermore, the portion of the second portion 20' that is farther away from the joining surface 5' than the fourth portion 27 is the sixth portion 28. Note that Fig. 5 only plots a portion of the measured values.

[0057] In the first portion 10' of the shaft part 2', the hardness of the third portion 19 is greater than the hardness of the fifth portion 18. In the second portion 20' of the shaft part 2', the hardness of the fourth portion 27 is greater than the hardness of the sixth portion 28.

[0058] The shaft part 2' includes a first portion 10' and a portion 11' that will become the raceway 11 after subsequent processing. The entire portion 11' that will become the raceway 11 is located in the fifth portion 18 of the first portion 10', and is not located in the third portion 19. This makes it possible to avoid the inconvenience that would occur if the portion 11' that will become the raceway 11 were provided in a portion that has been hardened by friction welding as described above.

[0059] The shaft part 2' includes a portion 21' in the second portion 20' that will become the teeth 21 after a subsequent process. The entire portion 21' that will become the teeth 21 is located in the sixth portion 28 of the second portion 20', and is not located in the fourth portion 27. This makes it possible to avoid the inconvenience that would occur if the portion 21' that will become the teeth 21 were provided in a portion that has been hardened by friction welding as described above.

[0060] In the shaft part 2', the outer peripheral surface 18s of the second axial side portion of the fifth portion 18, the outer peripheral surface 19s of the third portion 19, the outer peripheral surface 27s of the fourth portion 27, and the outer peripheral surface 28s of the first axial side portion of the sixth portion 28 preferably form a single cylindrical surface. In this way, when the outer peripheral surfaces of the four portions are formed as a single cylindrical surface, steps (corners) are unlikely to occur in each portion even after carburizing or carbonitriding. This makes it possible to avoid an increased risk of breakage due to the occurrence of steps (corners).

[0061] In the shaft part 2', it is preferable that the inner peripheral surface 18u of the portion on the second axial side of the fifth portion 18, the inner peripheral surface 19u of the third portion 19, the inner peripheral surface 27u of the fourth portion 27, and the inner peripheral surface 28u of the portion on the first axial side of the sixth portion 28 are a single cylindrical surface. In this way, when the inner peripheral surfaces of the four portions are configured as a single cylindrical surface, steps (corners) are unlikely to occur in each portion even after carburizing or carbonitriding. This makes it possible to avoid an increased risk of breakage due to the occurrence of steps (corners).

[0062] As described above, the alloy composition of the first steel material is different from the alloy composition of the second steel material. The bearing raceway component 2 manufactured by carburizing or carbonitriding the shaft component 2' has both strength suitable for the raceway in the bearing portion having the raceway and strength suitable for the teeth in the power transmission portion having the teeth.

[0063] The first steel material contains, for example, carbon as an alloy component. Examples of the first steel material include alloy steel materials for machine structures such as chromium steel, chromium-molybdenum steel, and nickel-chromium-molybdenum steel. Specific examples of the first steel material include SCr420, SCM420, SNCM420, SCM440, and SNCM439.

[0064] The second steel material contains, for example, carbon as an alloy component. Examples of the second steel material include alloy steel materials for machine structures such as chromium steel, chromium-molybdenum steel, and nickel-chromium-molybdenum steel. Specific examples of the second steel material include SCr420, SCM420, and SNCM420.

[0065] The first steel material and the second steel material preferably satisfy at least one of the first to fourth combinations described below. The first steel material and the second steel material may satisfy two or more of the first to fourth combinations described below.

[0066] (First Combination) The first steel material contains at least one of manganese, nickel, chromium, and molybdenum as an alloy component, the second steel material contains at least one of manganese, nickel, chromium, and molybdenum as an alloy component, and the total content (mass %) of manganese, nickel, chromium, and molybdenum in the first steel material is more than 1.5 times the total content (mass %) of manganese, nickel, chromium, and molybdenum in the second steel material.

[0067] In this case, when the shaft component 2' having the first portion 10' made of the first steel material and the second portion 20' made of the second steel material is hardened, the hardenability of the first portion 10' having the portion that will become the raceway tends to be superior to the hardenability of the second portion 20' having the portion that will become the teeth. Therefore, in the manufactured bearing raceway component 2, the depth of the range having a hardness of 700 HV or more in the inner ring raceway 2c of the bearing portion 10 having the raceway tends to be deeper than the depth of the range having a hardness of 700 HV or more in the tooth bottom between two adjacent teeth of the power transmission portion 20 having the teeth.

[0068] When the first combination is satisfied, the preferred total content of manganese, nickel, chromium, and molybdenum in the first steel material is 2.5 mass% or more and 6.5 mass% or less, and the preferred total content of manganese, nickel, chromium, and molybdenum in the second steel material is 1.5 mass% or more and 2.5 mass% or less.

[0069] (Second combination) The first steel contains silicon as an alloying component, the second steel contains silicon as an alloying component, and the silicon content (mass %) of the first steel is less than the silicon content (mass %) of the second steel. In this case, when carburizing or carbonitriding is performed, penetration of carbon into the first steel, which is the material for the first portion 10' having the portion that will become the raceway, is less inhibited than penetration of carbon into the second steel, which is the material for the second portion 20' having the portion that will become the teeth.

[0070] When the second combination is satisfied, the preferred silicon content in the first steel material is 0.10 mass% or more and 0.34 mass% or less, and the preferred silicon content in the second steel material is 0.35 mass% or more and 1.00 mass% or less.

[0071] (Third Combination) The first steel material contains zero or 1.6 mass% or less of chromium as alloying components, and zero or 0.01 mass% or less of niobium. The second steel material contains 1.0 mass% to 2.5 mass% of chromium and 0.02 mass% to 0.10 mass% of niobium as alloying components. When a steel material containing niobium and chromium is subjected to carburizing or carbonitriding after cutting, carbon is less likely to penetrate into the steel material. In other words, when a machined steel material containing niobium and chromium is subjected to carburizing or carbonitriding, the surface carbon content does not increase. This is because a chromium oxide film is formed on the surface of the steel material during carburizing or carbonitriding, which inhibits carbon penetration into the steel material. Therefore, the spalling life of a steel material containing niobium and chromium as a bearing cannot be improved even when carburized or carbonitrided. From this viewpoint, in the third combination, the first steel material does not contain niobium, or if it does contain niobium, the content is set to 0.01 mass % or less.

[0072] Furthermore, it is preferable that the steel material used in the power transmission part having teeth does not have an excessively high surface carbon content, from the viewpoint of improving the bending fatigue strength of the tooth root and improving the toughness of the tooth tip. Therefore, it is preferable that the second steel material is such that carbon does not easily penetrate into the steel material even when carburized or carbonitrided. From this viewpoint, in the third combination, the second steel material has a niobium content in the above range.

[0073] Furthermore, when the third combination is satisfied, the first steel material may contain 1.6 mass% or less of chromium, or may contain no chromium. Chromium is contained for the purpose of forming chromium carbide, which improves spalling life, and for improving hardenability. On the other hand, the second steel material contains chromium, and its preferred content is 1.0 mass% or more and 2.5 mass% or less. Chromium is contained for improving hardenability. In this case, when the second steel material is carburized or carbonitrided, a chromium oxide film suitable for suppressing carbon penetration is formed.

[0074] (Fourth Combination) The first steel material contains, as alloying components, 0.001% to 0.050% by mass of nitrogen, zero or 0.001% or less by mass of boron, and zero or 0.003% or less by mass of titanium. The second steel material contains, as alloying components, 0.001% to 0.050% by mass of nitrogen, 0.001% to 0.005% by mass of boron, and 0.01% to 0.08% by mass of titanium. With this combination, in the completed bearing raceway component, the bearing portion 10 having the raceway can be prevented from shortening its lifespan. Furthermore, the power transmission portion 20 having teeth can ensure appropriate bending fatigue strength.

[0075] When a steel material contains nitrogen and boron, BN (boron nitride) is likely to precipitate. The precipitation of boron nitride causes a shortened service life of the bearing portion. Furthermore, when a steel material contains nitrogen and titanium, TiN (titanium nitride) is likely to precipitate, and the precipitation of titanium nitride also causes a shortened service life of the bearing portion. Therefore, in the fourth combination, the first steel material contains nitrogen, does not contain boron or contains 0.001 mass % or less, and does not contain titanium or contains 0.003 mass % or less.

[0076] When boron is contained in a steel material, boron concentrates at grain boundaries, strengthening the grain boundaries and improving bending fatigue strength. However, simply adding boron to a nitrogen-containing steel material results in the precipitation of BN (boron nitride), preventing boron from concentrating at grain boundaries. Therefore, by including Ti (titanium) together with boron, TiN (titanium nitride) is precipitated, reducing the amount of nitrogen that bonds with boron, thereby achieving boron concentration at grain boundaries. Therefore, in the fourth combination, the second steel material contains nitrogen, 0.001% by mass or more and 0.005% by mass or less of boron, and 0.01% by mass or more and 0.08% by mass or less of titanium as alloying components.

[0077] In the combination of the first steel material and the second steel material, it is preferable that the carbon content (mass%) of the first steel material is greater than the carbon content (mass%) of the second steel material (hereinafter, this combination is also referred to as a fifth combination). In this case, with regard to the penetration depth of carbon into the steel materials by carburizing or carbonitriding, the penetration depth of the bearing portion 10 having the raceway is likely to be deeper than the penetration depth of the power transmission portion 20 having the teeth. Therefore, the depth of the range in which the bearing portion 10 having the raceway has a hardness of 700 HV or more is likely to be deeper than the depth of the range in which the power transmission portion 20 having the teeth has a hardness of 700 HV or more.

[0078] The carbon content of the first steel material is preferably 0.25% by mass or more and 1.10% by mass or less, and the carbon content of the second steel material is preferably 0.15% by mass or more and 0.25% by mass or less.

[0079] It is preferable that the number of non-metallic inclusions having a width of 30 μm or more contained in the first steel material be smaller than the number of non-metallic inclusions having a width of 30 μm or more contained in the second steel material. In this case, the inner ring raceway 2 c of the bearing portion 10 having a raceway in the bearing device 1 becomes a raceway that is easy to improve the bearing life.

[0080] The bearing raceway component 2 is manufactured by carburizing or carbonitriding a shaft component 2'. As shown in FIG. 1 , in the bearing raceway component 2, the bearing portion 10 having a raceway has a first surface-hardened layer 13 and a first interior portion 14. The first surface-hardened layer 13 is provided along the surface, including the outer peripheral surface 12, of the bearing portion 10 having a raceway. The first interior portion 14 is provided on the opposite side of the surface, including the outer peripheral surface 12, of the bearing portion 10 having a raceway, from the first surface-hardened layer 13. The first surface-hardened layer 13 is a carburized layer or a carbonitrided layer. Therefore, the first surface-hardened layer 13 refers to a region having a higher carbon content than the first steel material before the carburizing or carbonitriding treatment. When the carbon content of the bearing portion 10 having a raceway is measured in the depth direction (direction perpendicular to the outer peripheral surface) from the outer peripheral surface, the carbon content of the bearing portion 10 having a raceway gradually decreases and stops changing at a certain depth (referred to as a first depth D1 in this disclosure). The range from the surface, including the outer peripheral surface 12, of the bearing portion 10 having the raceway to a first depth D1 corresponds to the first surface-hardened layer 13. The average hardness of the first surface-hardened layer 13 is higher than the average hardness of the first interior 14. Therefore, the first surface-hardened layer 13 in the bearing portion 10 having the raceway contributes to extending the life of the bearing.

[0081] In the bearing raceway component 2, the toothed power transmission portion 20 has a second surface-hardened layer 23 and a second interior portion 24. The second surface-hardened layer 23 is provided along the surface, including the outer peripheral surface 22, of the toothed power transmission portion 20. The second interior portion 24 is provided on the opposite side of the surface, including the outer peripheral surface 22, of the toothed power transmission portion 20 from the second surface-hardened layer 23. The second surface-hardened layer 23 is a carburized layer or a carbonitrided layer. Therefore, the second surface-hardened layer 23 refers to a region having a higher carbon content than the second steel material before the carburizing or carbonitriding treatment. When the carbon content of the toothed power transmission portion 20 is measured in the depth direction (direction perpendicular to the outer peripheral surface) from the outer peripheral surface, the carbon content of the toothed power transmission portion 20 gradually decreases and stops changing at a certain depth (referred to as the second depth D2 in this disclosure). The range from the surface, including the outer peripheral surface 22, of the toothed power transmission portion 20 to a second depth D2 corresponds to the second surface-hardened layer 23. The average hardness of the second surface-hardened layer 23 is higher than the average hardness of the second interior portion 24. Therefore, the second surface-hardened layer 23 in the toothed power transmission portion 20 contributes to extending the life of the toothed power transmission portion 20.

[0082] The first surface-hardened layer 13 and the second surface-hardened layer 23 are connected. The first interior 14 and the second interior 24 are connected. The bearing raceway component 2 has the entire surface, including the outer peripheral surfaces 12 and 22 of the cylindrical shaft member, formed of the surface-hardened layers 13 and 23. The first surface-hardened layer 13 and the second surface-hardened layer 23 are formed through a carburizing treatment or a carbonitriding treatment. The carburizing treatment and the carbonitriding treatment will be described in detail later.

[0083] The depth D10 from the surface of the inner ring raceway 2c (raceway groove 11) of the bearing portion 10 having a raceway of the bearing raceway component 2 in the range having a hardness of 700 HV or more is deeper than the depth D20 from the surface of the tooth bottom 25 between two adjacent teeth 21 in the range having a hardness of 700 HV or more of the tooth bottom 25 between two adjacent teeth 21 of the toothed power transmission portion 20. In this case, the bearing life of the inner ring raceway 2c of the bearing raceway component 2 is likely to be good, and the strength of the tooth bottom 25 of the bearing raceway component 2 and the pitting strength of the usable tooth surface are also likely to be good due to the compressive stress applied to the teeth.

[0084] The depth D10 from the surface of the inner ring raceway 2c in the bearing part 10 having a raceway is the depth in a direction perpendicular to the surface of the inner ring raceway 2c. The depth D20 from the surface of the teeth 21 in the power transmission part 20 having teeth is the depth from the surface of the tooth bottom 25 between two adjacent teeth 21. Furthermore, the depth from the surface of the tooth bottom 25 is the depth in a direction perpendicular to the surface of the tooth bottom 25. When measuring the hardness of the teeth 21 of the power transmission part 20 having teeth in the depth direction, the tooth bottom 25 between two adjacent teeth 21 is measured. This is because the tooth bottom cylindrical portion 26 exists in the depth direction perpendicular to the surface of the tooth bottom 25 between two adjacent teeth 21, and therefore a position deeper than the depth D20 from the surface in the range having a hardness of 700 HV or more will always remain.

[0085] In the inner ring raceway 2c of the bearing part 10 having a raceway, a depth D10 from the surface of the inner ring raceway 2c, which is preferably in the range of hardness of 700 HV or more, is 0.2 mm or more and 2.0 mm or less. In the power transmission part 20 having teeth, a depth D20 from the surface of the tooth bottom 25 between two adjacent teeth 21, which is preferably in the range of hardness of 700 HV or more, is 0.1 mm or more and 1.0 mm or less.

[0086] The concept required for the depth from the surface of the raceway of a bearing part having a raceway in a hardness range of 700 HV (hard portion) or more is as follows: It is required that the rolling fatigue life of the raceway of a bearing part having a raceway be extended until internally initiated flaking occurs, which is initiated by non-metallic inclusions inside the raceway. When the depth from the surface of the raceway of a bearing part having a raceway in a hardness range of 700 HV (hard portion) or more is deep, the rolling fatigue life is longer than when this depth is shallow. It is also required that the formation of Brinell indentations in the raceway of a bearing part having a raceway, which is caused by the rolling elements being statically pressed against the raceway, is suppressed. When the depth from the surface of the raceway of a bearing part having a raceway in a hardness range of 700 HV (hard portion) or more is deep, the formation of Brinell indentations is suppressed compared to when this depth is shallow. For this reason, it is desirable that the range having a hardness of 700 HV (hard portion) or more exists from the surface of the raceway to a deep position in the bearing portion having the raceway.

[0087] On the other hand, the depth from the surface of the tooth root between two adjacent teeth in a power transmission part having a range of hardness of 700 HV (hard portion) or more is considered as follows: It is required to suppress pitting damage to the tooth surface of the teeth of a power transmission part having teeth, which occurs on the outermost surface of the usable tooth surface. Therefore, the teeth of the power transmission part having teeth must have a hardness of 700 HV (hard portion) or more on the tooth surface. Furthermore, the teeth of the power transmission part having teeth must have an uneven shape, and must have a core structure (non-carburized structure) inside the convex teeth of the power transmission part having teeth, and a hard portion (carburized structure) on the surface of the teeth of the power transmission part having teeth. If the inside of the teeth of the power transmission part having teeth has a hard portion (carburized structure), the toughness of the teeth of the power transmission part having teeth will decrease, making the teeth more susceptible to fracture. Therefore, it is desirable that the range of hardness of 700 HV (hard portion) or more remain shallow from the surface of the teeth of the power transmission part having teeth. The above description relates to the teeth (convex portions) of the toothed power transmission part. The depth from the surface of the teeth of the toothed power transmission part 20 where the hardness is 700 HV or more can be substituted by the depth from the surface of the tooth bottom between two adjacent teeth of the toothed power transmission part 20 where the hardness is 700 HV or more. Therefore, it is desirable that the range where the hardness is 700 HV or more at the tooth bottom between two adjacent teeth of the toothed power transmission part 20 remains shallow from the surface of the tooth bottom, similar to the tooth (convex portion).

[0088] The depth D10 in the inner ring raceway 2c of the bearing part 10 having a raceway is measured by the following method. First, the bearing raceway component 2 is cut along a plane including the central axis and passing through the inner ring raceway 2c. Next, a Vickers indenter is applied to the resulting cut surface from the surface (outer peripheral surface) toward the interior in the depth direction (a direction perpendicular to a tangent to the outer peripheral surface in the cross section) at positions 50 μm, 100 μm, 150 μm, 200 μm, 300 μm, 400 μm, 600 μm, 800 μm, 1000 μm, 1200 μm, 1400 μm, 1600 μm, 1800 μm, 2000 μm, 2500 μm, and 3000 μm from the surface to measure the Vickers hardness at each position. The change in Vickers hardness is plotted, and the depth of the range having a hardness of 700 HV or higher is calculated by interpolation. The measurement of the depth D20 at the tooth 21 of the toothed power transmission part 20 is performed in the same manner as the measurement of the depth D10, except that the cutting point is changed. In measuring the depth D20, the toothed power transmission part 20 is cut through the bearing raceway part 2 in a plane perpendicular to the central axis so as to pass through the tooth 21.

[0089] Figures 6 to 8 show the results of measuring the Vickers hardness of the interior of the bearing raceway component 2 and the surface-hardened layers 13, 23. The results shown in Figures 6 to 8 are for a bearing raceway component 2 manufactured by heat treating a shaft component 2' whose first steel material is SCM440 and whose second steel material is SCM420, the results of which are shown in Figure 5. In Figure 6, the position of 0 mm in axial distance is the position of the joining surface 5. The compositions (mass %) of the first steel material (SCM440) and the second steel material (SCM420) have already been shown in Table 1.

[0090] The heat treatment conditions for the shaft component 2', in which the first steel material was SCM440 and the second steel material was SCM420, were as shown in Figure 9. Specifically, the shaft component 2' was held in a carburizing atmosphere at a temperature of 930°C and a carbon potential of 1.2 for three hours. The carbon potential was then changed to 1.0 and held for two hours. Subsequently, the shaft component 2' was held at 850°C for 30 minutes, and then oil-cooled. The oil-cooled shaft component 2' was then tempered at 180°C for two hours and then air-cooled. This heat treatment formed a carburized layer on the outer peripheral surface of the shaft component 2'. The shaft component 2' with the carburized layer then underwent polishing, and the inner ring raceway and gear teeth were finished to form the bearing raceway component 2.

[0091] Fig. 6 is a graph showing Vickers hardness in a cross section including the central axis C of the bearing raceway component 2. In Fig. 6, the vertical axis shows Vickers hardness, and the horizontal axis shows axial distance from the joining surface 5. The region to the left of the axial distance of 0.0 mm in Fig. 6 shows the Vickers hardness inside the bearing part 10 having the raceway. The Vickers hardness is measured at positions 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, 3.0 mm, 3.5 mm, 4.0 mm, 4.5 mm, 5.0 mm, 5.5 mm, 6.0 mm, 6.5 mm, 7.0 mm, 8.0 mm, 9.0 mm, 10.0 mm, 11.0 mm, 12.0 mm, 13.0 mm, and 14.0 mm from the joining surface 5 toward the first axial side. The Vickers hardness of the interior of the toothed power transmission portion 20 is shown in the region to the right of the axial distance of 0.0 mm in Figure 6. Vickers hardness was measured at positions 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, 3.0 mm, 3.5 mm, 4.0 mm, 4.5 mm, 5.0 mm, 5.5 mm, 6.0 mm, 6.5 mm, 7.0 mm, 8.0 mm, 9.0 mm, 10.0 mm, 11.0 mm, 12.0 mm, 13.0 mm, and 14.0 mm from the joining surface 5 toward the second axial side. The Vickers hardness values ​​shown in FIG. 6 are measured at a depth of 2 mm from the surface of the bearing raceway component 2 in a cross section including the central axis C, along the axial direction. As shown in FIG. 6, the bearing raceway component 2 is harder than the material.

[0092] 7 and 8 are graphs showing the change in Vickers hardness from the surface toward the inside of the bearing raceway component 2. Figure 7 shows the Vickers hardness of the bearing part 10 having the raceway, and Figure 8 shows the Vickers hardness of the power transmission part 20 having the teeth.

[0093] The Vickers hardness values ​​were measured by the following method. First, the bearing raceway component 2 was cut at two locations. One of the cut locations was the portion where the inner ring raceway was provided. The other cut location was the portion where the gear teeth were provided. First, the portion where the gear teeth were provided was cut on a plane perpendicular to the central axis, and then the portion where the inner ring raceway was provided was cut on a plane including the central axis. The Vickers hardness values ​​of the bearing part 10 having a raceway were measured by applying a Vickers indenter to positions of 50 μm, 100 μm, 150 μm, 200 μm, 300 μm, 400 μm, 600 μm, 800 μm, 1000 μm, 1200 μm, 1400 μm, 1600 μm, 1800 μm, 2000 μm, 2500 μm, and 3000 μm in the depth direction from the surface of the inner ring raceway (see FIG. 7 ). The Vickers hardness of each toothed power transmission part 20 was measured by applying a Vickers indenter to each of the following positions in the depth direction from the surface of the tooth bottom between two adjacent gears: 50 μm, 100 μm, 150 μm, 200 μm, 300 μm, 400 μm, 600 μm, 800 μm, 1000 μm, 1200 μm, 1400 μm, 1600 μm, 1800 μm, 2000 μm, 2500 μm, and 3000 μm (see FIG. 8 ).

[0094] As shown in Figures 7 and 8, it has been confirmed that this bearing raceway part 2 has a preferable Vickers hardness in the interior and surface hardened layers 13, 23 of the bearing portion 10 having the raceway and the power transmission portion 20 having the teeth.

[0095] In a preferred bearing raceway component 2, the carbon content (mass %) within a range of 50 μm deep from the surface of the inner ring raceway 2c of the bearing portion 10 having a raceway is greater than the carbon content (mass %) within a range of 50 μm deep from the surface of the tooth root 25 between two adjacent teeth 21 of the toothed power transmission portion 20. In this case, the bearing life of the inner ring raceway 2C of the bearing raceway component 2 is likely to be good, the amount of coarse carbides in the teeth 21 of the bearing raceway component 2 is likely to be small, and tooth tip strength is likely to be good. The position at which the depth of the carbon content within the range from the surface of the teeth 21 of the toothed power transmission portion 20 is measured is the tooth root 25 between two adjacent teeth 21. The reason for measuring the tooth root 25 between two adjacent teeth 21 is that a tooth root cylindrical portion 26 exists in the depth direction perpendicular to the surface of the tooth root 25 between two adjacent teeth 21, so a position deeper than 50 μm deep from the surface will always remain.

[0096] The carbon content within a range of 50 μm deep from the surface of the inner ring raceway 2 c of the bearing part 10 having a raceway is preferably 0.75% by mass or more and 0.95% by mass or less. The carbon content within a range of 50 μm deep from the surface of the tooth bottom 25 between two adjacent teeth 21 of the power transmission part 20 having teeth is preferably 0.55% by mass or more and 0.75% by mass or less.

[0097] The considerations required for the surface carbon amount (carbon contained within a range of 50 μm deep from the surface) of the raceway of the bearing part 10 having a raceway are as follows: When the rolling elements repeatedly roll on the raceway of the bearing part 10 having a raceway, stress is repeatedly applied to the raceway 11 (2C) of the bearing part 10 having a raceway, resulting in internally initiated flaking or surface initiated flaking in the raceway 11 (2C) of the bearing part 10 having a raceway. It is required to extend the rolling fatigue life until internally initiated flaking or surface initiated flaking occurs. When the surface carbon amount is high, the rolling fatigue life is longer than when the surface carbon amount is low. For this reason, it is desirable for the surface carbon amount of the raceway 11 (2C) of the bearing part 10 having a raceway to be high.

[0098] On the other hand, the consideration required for the surface carbon amount at the tooth bottom between two adjacent teeth of the toothed power transmission part 20 is as follows: When the surface carbon amount is high, the bending fatigue strength of the tooth bottom of the toothed power transmission part 20 is lower than the bending fatigue strength of the tooth bottom of the toothed power transmission part 20 when the surface carbon amount is low. Furthermore, when the surface carbon amount is high, the toughness of the tooth tip is lower than the toughness of the tooth tip when the surface carbon amount is low due to the precipitation of coarse carbides at the tooth tip of the tooth of the toothed power transmission part 20. For this reason, it is desirable that the surface carbon amount of the teeth of the toothed power transmission part 20 is low.

[0099] The carbon content within a range of 50 μm deep from the surface of the inner ring raceway 2 c of the bearing part 10 having a raceway is determined by cutting the bearing raceway component 2 along a plane including the central axis so as to pass through the inner ring raceway 2 c, and measuring the carbon content within a range of 50 μm deep from the outer circumferential surface of the obtained cut surface using an electron probe microanalyzer (EPMA). The carbon content within a range of 50 μm deep from the tooth bottom 25 between two adjacent teeth 21 of the toothed power transmission part 20 is determined by cutting the bearing raceway component 2 along a plane perpendicular to the central axis so as to pass through the teeth 21, and measuring the carbon content within a range of 50 μm deep from the tooth bottom 25 between two adjacent teeth 21 of the toothed power transmission part 20 of the obtained cut surface using an electron probe microanalyzer (EPMA).

[0100] Appropriate combinations of the first and second steel materials, including the first to fifth combinations described above, and desirable qualities are obtained when the dimensional relationship between the raceway of the bearing part having a raceway (which may be an inner raceway or an outer raceway instead of the inner raceway) and the teeth of the power transmission part having teeth is such that the outer diameter of the teeth is about 0.5 to 5 times the smallest outer diameter of the inner raceway or the largest inner diameter of the outer raceway. Such combinations, qualities, and dimensional relationships ensure a balance between the performance of the raceway and the performance of the teeth.

[0101] Next, a method for manufacturing the bearing raceway component 2 will be described. The method for manufacturing the bearing raceway component 2 includes a method for manufacturing the shaft component 2'. The bearing raceway component 2 can be manufactured by, for example, a first manufacturing method or a second manufacturing method. These manufacturing methods involve manufacturing the shaft component 2' and then subjecting the shaft component 2' to carburizing or carbonitriding to manufacture the bearing raceway component 2.

[0102] (First Manufacturing Method) Figure 10 is a diagram illustrating a first manufacturing method for a bearing raceway component. (1) A cylindrical workpiece 51 made of a first steel material and a cylindrical workpiece 52 made of a second steel material are prepared, and these workpieces are joined to produce a cylindrical joined workpiece (first workpiece) 53 in which the two workpieces are integrated. The first steel material and the second steel material are steel materials with different alloy compositions, and their combination is as described above. The workpieces 51 and 52 are joined by friction welding. The workpiece 51 is a workpiece prior to first machining, which will result in a bearing portion having a raceway after subsequent processing. The workpiece 52 is a workpiece prior to second machining, which will result in a power transmission portion having teeth after subsequent processing. Friction welding is performed using a known technique, and the processing conditions are appropriately selected depending on the type and size of the steel material, etc.

[0103] In the friction-welded joined workpieces (first workpiece) 53, burrs 31 are usually generated near the joining surface of workpiece 51 with workpiece 52, and burrs 42 are generated near the joining surface of workpiece 52 with workpiece 51. These burrs 31, 42 are removed later in the first machining process or the second machining process, or are removed by a cutting process separate from the first machining process or the second machining process. These burrs 31, 42 may also be left without being removed.

[0104] When a joined workpiece (first workpiece) 53 is produced, the Vickers hardness of the workpiece 51 near the joining surface with the workpiece 52 becomes harder than that of the raw material (first steel) due to friction welding. The workpiece 51 constituting the joined workpiece 53 includes a portion 35 that will become a third portion after a later first machining process, and a portion 34 that is located further away from the joining surface with the workpiece 52 than the portion 35 and will become a fifth portion after a later first machining process. Furthermore, the Vickers hardness of the workpiece 52 near the joining surface with the workpiece 51 becomes harder than that of the raw material (second steel) due to friction welding. The workpiece 52 constituting the joined workpiece 53 includes a portion 43 that will become a fourth portion after a later second machining process, and a portion 44 that is located further away from the joining surface with the workpiece 52 than the portion 43 and will become a sixth portion after a later second machining process.

[0105] (2) A portion 55 that will become the inner ring raceway 2c is formed in a part of the workpiece 51 included in the joined workpiece 53 by cutting as a first machining process. The portion 55 that will become the inner ring raceway 2c is formed in a part 34 of the workpiece 51. A portion 56 that will become the gear teeth 21 is formed in a part of the workpiece 52 included in the joined workpiece 53 by cutting as a second machining process. The portion 56 that will become the gear teeth 21 is formed in a part 44 of the workpiece 52. Either the formation of the portion 55 that will become the inner ring raceway or the formation of the portion 56 that will become the gear teeth is performed first, and the other is performed later.

[0106] In this process, a second workpiece 57 is obtained, which has a portion 55 that will become the inner ring raceway and a portion 56 that will become the gear teeth. The second workpiece 57 is a workpiece formed by friction welding the workpiece 51 and the workpiece 52. The friction-welded workpiece 51 includes a joint surface with the workpiece 52 and is composed of a third portion 39 having a Vickers hardness harder than that of the first steel material, and a fifth portion 38 located on a first axial side of the third portion 39 and including a portion 55 that will become the inner ring raceway 2c. The friction-welded workpiece 52 includes a joint surface with the workpiece 51 and is composed of a third portion 47 having a Vickers hardness harder than that of the second steel material, and a fifth portion 48 located on a second axial side of the third portion 47 and including a portion 56 that will become the gear teeth 21. The second workpiece 57 is the shaft component 2' of this embodiment.

[0107] (3) The second workpiece 57 is subjected to heat treatment. Specifically, the second workpiece 57 is carburized or carbonitrided, followed by quenching, and then tempering. The entire second workpiece 57 is subjected to heat treatment. In other words, the portion 55 that will become the inner ring raceway and the portion 56 that will become the gear teeth are simultaneously heat-treated. The carburizing treatment is performed under conditions, for example, a carbon potential of 0.9 to 1.4, a carburizing atmosphere at a temperature of 900 to 1000°C, and a holding time of 1 to 15 hours. The carbonitriding treatment is performed under conditions, for example, a carbon potential of 0.9 to 1.4, an ammonia gas flow rate relative to the carburizing gas flow rate of 1 to 5 mass%, and a carbonitriding atmosphere at a temperature of 830 to 900°C, and a holding time of 1 to 15 hours. During the carburizing and carbonitriding treatments, the carbon potential, ammonia gas flow rate, and temperature may be changed during the process.

[0108] The conditions for the quenching treatment are, for example, that the workpiece after carburizing or carbonitriding is held at 820 to 870°C for 0.5 to 2 hours, followed by oil cooling.The conditions for the tempering treatment are, for example, that the workpiece after quenching is held at 150 to 200°C for 1 to 5 hours, followed by air cooling.

[0109] This step yields a third workpiece 58 having a carburized layer or a carbonitrided layer formed on its outer peripheral surface. Because the carburized layer or the carbonitrided layer formed on the third workpiece 58 is formed by the method described above, the carburized layer or the carbonitrided layer formed on the workpiece 51 made of the first steel material is connected to the carburized layer or the carbonitrided layer formed on the workpiece 52 made of the second steel material. Furthermore, the interior of the workpiece 51 made of the first steel material is connected to the interior of the workpiece 52 made of the second steel material. Furthermore, the carburized layer or the carbonitrided layer is a surface-hardened layer whose hardness has been increased through carburizing or carbonitriding, quenching, and tempering.

[0110] (4) The third workpiece 58 is subjected to polishing as the third machining process and polishing as the fourth machining process. The third workpiece 58 is finished to a predetermined precision by polishing as the third machining process to form the inner ring raceway 2c, and by polishing as the fourth machining process to form the gear teeth 21. At this time, one of the polishing as the third machining process performed on the portion that will become the inner ring raceway and the polishing as the fourth machining process performed on the portion that will become the gear teeth is performed first, and the other is performed later. Note that in step (4), one or both of the third machining process and the fourth machining process may be omitted. The bearing raceway component 2 is manufactured by performing steps (1) to (4) as described above.

[0111] (Second Manufacturing Method) Figure 11 is a diagram illustrating a second manufacturing method for a bearing raceway component. (1) A cylindrical workpiece 61 made of a first steel material is prepared. A portion 65 that will become the inner ring raceway 2c is formed in a portion of the workpiece 61 made of this first steel material by cutting as a first machining process. This results in a first portion of the workpiece 63 formed with the portion 65 that will become the inner ring raceway. A cylindrical workpiece 62 made of a second steel material is prepared. A portion 66 that will become the gear teeth 21 is formed in a portion of the workpiece 62 made of this second steel material by cutting as a second machining process. This results in a second portion of the workpiece 64 formed with the portion 66 that will become the gear teeth.

[0112] The first steel material and the second steel material are steel materials with different alloy compositions, and the combination is as described above. Either the first portion of the workpiece 63 or the second portion of the workpiece 64 is produced first, and the other is produced later. The workpiece 61 is an unmachined workpiece that will become a bearing part having a raceway after subsequent processes. The workpiece 63 is a workpiece that has been subjected to cutting as a first machining process and will become a bearing part having a raceway 65 after subsequent processes. The workpiece 62 is an unmachined workpiece that will become a power transmission part having teeth after subsequent processes. The workpiece 64 is a workpiece that has been subjected to cutting as a second machining process and will become a power transmission part having teeth 66 after subsequent processes.

[0113] (2) The first workpiece 63 and the second workpiece 64 are joined together to produce a cylindrical second workpiece 67, which is an integrated combination of the two workpieces. The first workpiece 63 and the second workpiece 64 are joined by friction welding. Friction welding is performed using a known technique, and processing conditions are appropriately selected depending on the type and size of the steel material, etc.

[0114] In the second workpiece 67 produced through friction welding, burrs 71 are usually generated near the joining surface of workpiece 63 with workpiece 65, and burrs 82 are generated near the joining surface of workpiece 64 with workpiece 63. These burrs 71 and 82 are removed by cutting the second workpiece 67 after friction welding. However, these burrs 71 and 82 may also be left behind without being removed.

[0115] Furthermore, the Vickers hardness of the workpiece 63 in the vicinity of the joining surface with the workpiece 64 becomes harder than that of the raw material (first steel material) due to friction welding. The Vickers hardness of the workpiece 64 in the vicinity of the joining surface with the workpiece 63 becomes harder than that of the raw material (second steel material) due to friction welding.

[0116] The second workpiece 67 obtained after this process is a workpiece in which the workpieces 63 and 64 are joined by friction welding. The friction-welded workpiece 63 includes a joining surface with the workpiece 64 and is composed of a third portion 79 having a Vickers hardness harder than that of the first steel material, and a fifth portion 78 located further away from the joining surface than the third portion 79 and including a portion 65 that will become the inner ring raceway 2c. The friction-welded workpiece 64 includes a joining surface with the workpiece 63 and is composed of a third portion 87 having a Vickers hardness harder than that of the second steel material, and a fifth portion 88 located further away from the joining surface than the third portion 87 and including a portion 66 that will become the teeth 21. The second workpiece 67 is the shaft component 2' of this embodiment.

[0117] (3) The second workpiece 67 is subjected to heat treatment. Specifically, the second workpiece 67 is carburized or carbonitrided, then quenched, and then tempered. This step is performed in the same manner as step (3) in the first manufacturing method. In this case, the bearing portion 65 having the raceway that will become the inner ring raceway and the power transmission portion 66 having the teeth that will become the gear teeth are simultaneously subjected to heat treatment.

[0118] This step yields a third workpiece 68 having a carburized layer or a carbonitrided layer formed on its outer peripheral surface. Because the carburized layer or the carbonitrided layer formed on the third workpiece 68 is formed by the method described above, the carburized layer or the carbonitrided layer formed on the workpiece 63 made of the first steel material is connected to the carburized layer or the carbonitrided layer formed on the workpiece 64 made of the second steel material. Furthermore, the interior of the workpiece 63 made of the first steel material is connected to the interior of the workpiece 64 made of the second steel material. Furthermore, the carburized layer or the carbonitrided layer is a surface-hardened layer whose hardness has been increased through carburizing or carbonitriding, quenching, and tempering.

[0119] (4) The third workpiece 68 is subjected to polishing as the third machining step and polishing as the fourth machining step. This step is performed in the same manner as step (4) of the first manufacturing method. In step (4), one or both of the third machining step and the fourth machining step may be omitted. The bearing raceway component 2 is also manufactured by the second manufacturing method, which performs steps (1) to (4) as described above.

[0120] Second Embodiment A bearing raceway component according to an embodiment of the present disclosure may have a bearing portion having two or more raceways and a power transmission portion having one or more teeth, or may have a bearing portion having one or more raceways and a power transmission portion having two or more teeth. Figure 12 is a cross-sectional view of a bearing raceway component according to the second embodiment. As shown in Figure 12, a bearing raceway component 102 according to this embodiment is a cylindrical shaft member. The bearing raceway component 102 has two bearing portions 110A, 110B having raceways and two power transmission portions 120A, 120B having teeth.

[0121] As shown in Figure 12, the bearing raceway part 102 comprises, in the axial direction, a power transmission part with teeth 120B, a bearing part with raceway 110A, a power transmission part with teeth 120A, and a bearing part with raceway 110B. The power transmission part with teeth 120B and the bearing part with raceway 110A are joined by friction welding at a joining surface 105B. The bearing part with raceway 110A and the power transmission part with teeth 120A are joined by friction welding at a joining surface 105A. The power transmission part with teeth 120A and the bearing part with raceway 110B are joined by friction welding at a joining surface 105C. The bearing raceway part 102 is a member in which four parts are integrated.

[0122] The configuration of the bearing portion 110A with a raceway is similar to that of the bearing portion 10 with a raceway of the first embodiment. The bearing portion 110A with a raceway 111A is combined with an outer ring 3, a cage 8, and a plurality of balls to form a ball bearing, which is a rolling bearing. The configuration of the toothed power transmission portion 120A is similar to that of the toothed power transmission portion 20 of the first embodiment. The toothed power transmission portion 120A has external gear teeth 121A on a portion of its outer circumferential surface as the toothed power transmission portion 120A. The power transmission portion 120A with teeth 121A has tooth roots 125A between two adjacent teeth 121A. The portion of the toothed power transmission portion 120A with a diameter equal to or smaller than the tooth root diameter is a tooth root cylindrical portion 126A, and the portion of the toothed power transmission portion 120A with a diameter larger than the tooth root diameter is the tooth 121A. The teeth 121A are helical gear teeth. The teeth 121A can mesh with the teeth of another gear to transmit power to an element other than the bearing raceway component 102. The first hardened surface layer 113A of the bearing portion 110A with raceways is connected to the second hardened surface layer 123A of the power transmission portion 120A with teeth. The first inner portion 114A of the bearing portion 110A with raceways is connected to the second inner portion 124A of the power transmission portion 120A with teeth.

[0123] The bearing part 110B having a raceway has a raceway groove 111B that forms an inner ring raceway on part of its outer periphery. The bearing part 110B having a raceway is combined with an outer ring, a cage, and a plurality of balls to form a ball bearing, which is a rolling bearing. The material of the bearing part 110B having a raceway is the first steel material described above. The material of the bearing part 110B having a raceway may be the same as or different from the material of the bearing part 110A having a raceway.

[0124] Similar to the raceway bearing portion 10, the raceway bearing portion 110B has a first hardened surface layer 113B and a first inner portion 114B. The first hardened surface layer 113B is provided along the surface, including the outer peripheral surface 112B, of the raceway bearing portion 110B. The first inner portion 114B is provided on the opposite side of the surface, including the outer peripheral surface 112B, of the raceway bearing portion 110B from the first hardened surface layer 113B. The average hardness of the first hardened surface layer 113B is higher than the average hardness of the first inner portion 114B. The first hardened surface layer 113B is a carburized layer or a carbonitrided layer. The first hardened surface layer 113B connects to the second hardened surface layer 123A of the adjacent toothed power transmission portion 120A. The first inner portion 114B of the raceway bearing portion 110B connects to the second inner portion 124A of the toothed power transmission portion 120A. The preferred configuration of the bearing portion 110B with raceway is similar to the bearing portion 10 with raceway.

[0125] The toothed power transmission portion 120B serves to transmit power between the bearing raceway component 102 and an element other than the bearing raceway component 102. The toothed power transmission portion 120B has spline teeth 121B on a portion of its outer periphery. These spline teeth 121B can be connected to a motor shaft, for example, to transmit power to and from the motor. The toothed power transmission portion 120B is made of the second steel material described above. The material of the toothed power transmission portion 120B may be the same as or different from the material of the power transmission portion 120A. The toothed power transmission portion 120B has a tooth root 125B between two adjacent teeth 121B. The portion of the toothed power transmission portion 120B having a diameter equal to or smaller than the tooth root diameter is a tooth root cylindrical portion 126B, and the portion of the toothed power transmission portion 120B having a diameter larger than the tooth root diameter is a tooth 121B.

[0126] Similar to the toothed power transmission portion 20, the toothed power transmission portion 120B has a second hardened surface layer 123B and a second inner portion 124B. The second hardened surface layer 123B is provided along the surface, including the outer peripheral surface 122B, of the power transmission portion 120B. The second inner portion 124B is provided on the opposite side of the surface, including the outer peripheral surface 122B, of the toothed power transmission portion 120B from the second hardened surface layer 123B. The average hardness of the second hardened surface layer 123B is higher than the average hardness of the second inner portion 124B. The second hardened surface layer 123B is a carburized layer or a carbonitrided layer. The second hardened surface layer 123B is connected to the first hardened surface layer 113A of the bearing portion 110A having the adjacent raceway. The second inner portion 124B of the toothed power transmission portion 120B is connected to the first inner portion 114A of the bearing portion 110A having the raceway. The preferred configuration of toothed power transmission portion 120B is similar to toothed power transmission portion 20.

[0127] In the bearing raceway component 102, the entire outer peripheral surfaces 112A, 112B, 122A, and 122B of the cylindrical shaft member are formed with surface-hardened layers 113A, 113B, 123A, and 123B. Both end surfaces and the inner peripheral surface of the bearing raceway component 102 are also formed with surface-hardened layers. The surface-hardened layers 123B and 113A, the surface-hardened layers 113A and 123A, and the surface-hardened layers 123A and 113B are all connected. The surface-hardened layers 113A, 113B, 123A, and 123B are either all carburized layers or all carbonitrided layers. Furthermore, the interiors 124B and 114A, the interiors 114A and 124A, and the interiors 124A and 114B are all connected.

[0128] In the bearing raceway component 102, the preferred combination of materials for the bearing portion having a raceway and the power transmission portion having teeth is the same as the combination of materials for the adjacent bearing portion having a raceway and the power transmission portion having teeth, which satisfies at least one of the first to fourth combinations described in the first embodiment. Therefore, in the preferred bearing raceway component 102, the bearing portion having a raceway 110A and the power transmission portion having teeth 120A, the bearing portion having a raceway 110A and the power transmission portion having teeth 120B, and the bearing portion having a raceway 110B and the power transmission portion having teeth 120A each independently satisfies at least one of the first to fourth combinations.

[0129] In the bearing raceway part 102, all of the raceways are located at an axial length of 5 mm or more from the joining surface, and all of the teeth are located at an axial length of 5 mm or more from the joining surface. In the bearing raceway part 102, the bearing portion having the raceways and the power transmission portion having the teeth also have preferred relationships with respect to the range of hardness of 700 HV or more, the relationship between the alloy composition of the first steel material and the alloy composition of the second steel material, and the carbon content contained within a range 50 μm deep from the outer circumferential surface. The preferred relationship between the bearing portion having the raceways and the power transmission portion having the teeth may be the same as that between the bearing portion having the raceways and the power transmission portion having the teeth that are adjacent to each other.

[0130] The bearing raceway component 102 can be manufactured in the same manner as in the first embodiment, except for the number of workpieces to be joined by friction welding. That is, the bearing raceway component 102 can be manufactured by preparing a workpiece made of steel for manufacturing the bearing portion 110A having a raceway, a workpiece made of steel for manufacturing the bearing portion 110B having a raceway, a workpiece made of steel for manufacturing the power transmission portion 120A having teeth, and a workpiece made of steel for manufacturing the power transmission portion 120B having teeth, and then performing cutting on each workpiece and friction welding to join the workpieces together under predetermined conditions to manufacture the shaft component, and then subjecting this shaft component to carburizing or carbonitriding.

[0131] In Fig. 12, 117A and 119A are portions of the workpiece for producing bearing portion 110A with a raceway that have been friction-welded to a hardness equal to or greater than the standard hardness, and 118A is the remaining portion of the workpiece. In Fig. 12, 117B is a portion of the workpiece for producing bearing portion 110B with a raceway that have been friction-welded to a hardness equal to or greater than the standard hardness, and 118B is the remaining portion of the workpiece. In Fig. 12, 127A and 129A are portions of the workpiece for producing power transmission portion 120A with teeth that have been friction-welded to a hardness equal to or greater than the standard hardness, and 128A is the remaining portion of the workpiece. In Fig. 12, 129B is a portion of the workpiece for producing power transmission portion 120B with teeth that have been friction-welded to a hardness equal to or greater than the standard hardness, and 128B is the remaining portion of the workpiece.

[0132] In the bearing raceway component 102 according to this embodiment, the raceways 111A, 111B, the external gear teeth 121A, and the pline teeth 121B are all positioned so as not to overlap with any portions that have become harder than the standard hardness due to friction welding.

[0133] (Third embodiment) Figure 13 is a cross-sectional view of a bearing raceway component according to a third embodiment. As shown in Figure 13, the bearing raceway component 202 according to this embodiment is a cylindrical shaft member. The bearing raceway component 202 has two bearing portions 210A, 210B having raceways, and one power transmission portion 220A having teeth.

[0134] As shown in Figure 13, the bearing raceway part 202 comprises, in the axial direction, a bearing portion 210A having a raceway, a power transmission portion 220A having teeth, and a bearing portion 210B having a raceway. The bearing portion 210A having a raceway and the power transmission portion 220A having teeth are joined at a joining surface 205A by friction welding. The power transmission portion 220A having teeth and the bearing portion 210B having a raceway are joined at a joining surface 205B by friction welding. The bearing raceway part 202 is a member in which the three portions are integrated.

[0135] The configuration of the bearing portion with raceway 210A is similar to that of the bearing portion with raceway 10 of the first embodiment, except that the raceway is a conical raceway 211A and has a flange 215A axially adjacent to the raceway 211A. The bearing portion with raceway 210A, in combination with the outer ring 3, the cage 8, and a plurality of rollers, constitutes a roller bearing (tapered roller bearing), which is a rolling bearing. The configuration of the toothed power transmission portion 220A is similar to that of the toothed power transmission portion 20 of the first embodiment. The toothed power transmission portion 220A has external gear teeth 221A on part of its outer circumferential surface as the toothed power transmission portion 220A. The power transmission portion with teeth 221A has tooth roots 225A between two adjacent teeth 221A. The portion of the toothed power transmission portion 220A having a diameter equal to or smaller than the root diameter is the root cylindrical portion 226A, and the portion of the toothed power transmission portion 220A having a diameter larger than the root diameter is the tooth 221A. The tooth 221A is a tooth of a helical gear. The tooth 221A can transmit power to elements other than the bearing raceway component 202 by meshing with the teeth of another gear. The first surface-hardened layer 213A of the bearing portion 210A having a raceway is connected to the second surface-hardened layer 223A of the toothed power transmission portion 220A. The first interior portion 214A of the bearing portion 210A having a raceway is connected to the second interior portion 224A of the toothed power transmission portion 220A.

[0136] The bearing portion 210B having a raceway has a tapered raceway 211B on part of its outer periphery and a flange 215B adjacent to the raceway 211B in the axial direction. The bearing portion 210B having a raceway is combined with an outer ring, a cage, and multiple rollers to form a roller bearing (tapered roller bearing), which is a rolling bearing. The tapered roller bearing formed by the bearing portion 210A having a raceway and the tapered roller bearing formed by the bearing portion 210B having a raceway are face-to-face. The material of the bearing portion 210B having a raceway is the first steel material described above. The material of the bearing portion 210B having a raceway may be the same as or different from the material of the bearing portion 210A having a raceway.

[0137] Similar to the raceway bearing portion 10, the raceway bearing portion 210B has a first hardened surface layer 213B and a first inner portion 214B. The first hardened surface layer 213B is provided along the surface, including the outer peripheral surface 212B, of the raceway bearing portion 210B. The first inner portion 214B is provided on the opposite side of the surface, including the outer peripheral surface 212B, of the raceway bearing portion 210B from the first hardened surface layer 213B. The average hardness of the first hardened surface layer 213B is higher than the average hardness of the first inner portion 214B. The first hardened surface layer 213B is a carburized layer or a carbonitrided layer. The first hardened surface layer 213B connects to the second hardened surface layer 223A of the adjacent toothed power transmission portion 220A. The first inner portion 214B of the raceway bearing portion 210B connects to the second inner portion 224A of the toothed power transmission portion 220A. The preferred configuration of the bearing portion with raceway 210B is similar to the bearing portion with raceway 10.

[0138] In the bearing raceway component 202, the entire outer peripheral surfaces 212A, 212B, 222A of the cylindrical shaft member are formed of surface-hardened layers 213A, 213B, 223A. Both end surfaces and the inner peripheral surface of the bearing raceway component 202 are also formed of surface-hardened layers. The surface-hardened layers 213A and 223A, and the surface-hardened layers 223A and 213B are all connected. The surface-hardened layers 213A, 213B, and 223A are either all carburized layers or all carbonitrided layers. Furthermore, the interiors 214A and 224A, and the interiors 224A and 214B are all connected.

[0139] In the bearing raceway component 202, the preferred combination of materials for the bearing portion having a raceway and the power transmission portion having teeth is the same as the combination of materials for the adjacent bearing portion having a raceway and the power transmission portion having teeth, which satisfies at least one of the first to fourth combinations described in the first embodiment. Therefore, in the preferred bearing raceway component 202, the bearing portion having a raceway 210A and the power transmission portion having teeth 220A, and the bearing portion having a raceway 210B and the power transmission portion having teeth 220A each independently satisfies at least one of the first to fourth combinations.

[0140] In the bearing raceway part 202, all of the raceways are located at an axial length of 5 mm or more from the joining surface, and all of the teeth are located at an axial length of 5 mm or more from the joining surface. In the bearing raceway part 202, the bearing part having the raceways and the power transmission part having the teeth also have preferred relationships with respect to the range of hardness of 700 HV or more, the relationship between the alloy composition of the first steel material and the alloy composition of the second steel material, and the carbon content included in the range to a depth of 50 μm from the outer peripheral surface. The preferred relationship between the bearing part having the raceways and the power transmission part having the teeth may be the same as that between the bearing part having the raceways and the power transmission part having the teeth that are adjacent to each other.

[0141] The bearing raceway component 202 can be manufactured in the same manner as in the first embodiment, except for the number of workpieces joined by friction welding. That is, the shaft component can be manufactured through friction welding, and then carburized or carbonitrided. That is, the shaft component can be manufactured by preparing a workpiece made of steel for manufacturing the bearing portion 210A having a raceway, a workpiece made of steel for manufacturing the bearing portion 210B having a raceway, and a workpiece made of steel for manufacturing the power transmission portion 220A having teeth, and then performing cutting on each workpiece and friction welding to join the workpieces together under predetermined conditions to manufacture the shaft component, and then carburizing or carbonitriding the shaft component.

[0142] In Fig. 13, 219A is a portion of the workpiece for manufacturing bearing portion 210A having a raceway that has been made hardness equal to or greater than the standard hardness through friction welding, and 218A is the remaining portion of this workpiece. In Fig. 13, 217B is a portion of the workpiece for manufacturing bearing portion 210B having a raceway that has been made hardness equal to or greater than the standard hardness through friction welding, and 218B is the remaining portion of this workpiece. In Fig. 13, 227A and 229A are portions of the workpiece for manufacturing power transmission portion 220A having teeth that have been made hardness equal to or greater than the standard hardness through friction welding, and 228A is the remaining portion of this workpiece.

[0143] In the bearing raceway component 202 according to this embodiment, the conical raceway 211A, the conical raceway 211B, and the external gear teeth 221A are all positioned so as not to overlap with any part that has become harder than the reference hardness due to friction welding.

[0144] (Other Embodiments) The bearing race component 2 according to the first embodiment is a cylindrical shaft member. On the other hand, the bearing race component according to the embodiment of the present disclosure may be a cylindrical shaft member that does not have the hole that the bearing race component 2 according to the first embodiment has. In this case, the bearing race component is manufactured by preparing a cylindrical workpiece made of a first steel material and a cylindrical workpiece made of a second steel material, and friction-welding these workpieces. Alternatively, the bearing race component according to the embodiment of the present disclosure may be manufactured by preparing a cylindrical workpiece made of a first steel material and a cylindrical workpiece made of a second steel material, and friction-welding these workpieces. Alternatively, the bearing race component according to the embodiment of the present disclosure may be manufactured by preparing a cylindrical workpiece made of a first steel material and a cylindrical workpiece made of a second steel material, and friction-welding these workpieces.

[0145] Furthermore, the bearing raceway part according to an embodiment of the present disclosure may be a hollow shaft member having a sealed hollow hole, in which a position on the first axial side of the joint surface 5 of the hole of the bearing raceway part 2 according to the first embodiment is sealed, and a position on the second axial side of the joint surface 5 of the hole of the bearing raceway part 2 according to the first embodiment is sealed.

[0146] The bearing raceway component according to the embodiment of the present disclosure may have teeth of a power transmission part having teeth, such as gear teeth, spline teeth, or toothed pulley teeth.

[0147] In the bearing raceway component according to the embodiment of the present disclosure, as long as the bearing portion having a raceway and the power transmission portion having teeth are joined, the number of bearing portions having a raceway and the power transmission portion having teeth is not limited. There may be a total of three, with one bearing portion having a raceway and two power transmission portions having teeth, or the total may be five or more. However, if the total number is too large, the central axes of the bearing portions and the power transmission portions may be misaligned, or distortion may occur in the bearing raceway component, so the total is preferably four or less.

[0148] In the bearing raceway component according to the embodiment of the present disclosure, the bearing portion having a raceway may have a plurality of raceways. In the bearing raceway component according to the embodiment of the present disclosure, the bearing portion having a raceway is not limited to a bearing portion having an inner ring raceway, but may be a bearing portion having an outer ring raceway. The raceway may be provided on the inner peripheral surface. In the bearing raceway component according to the embodiment of the present disclosure, the bearing portion having the raceway may be one of a shaft washer and a housing washer. The raceway may be provided on the end surface.

[0149] In the bearing raceway component according to the embodiment of the present disclosure, the power transmission portion having teeth may have multiple types of teeth as the teeth that make up the power transmission portion. In the bearing raceway component according to the embodiment of the present disclosure, the power transmission portion having teeth is not limited to a power transmission portion having an external gear, but may be a power transmission portion having an internal gear, or a power transmission portion that is a bevel gear, hypoid gear, or face spline. The gear may be provided on the inner peripheral surface or end surface.

[0150] The application of the bearing raceway component according to the embodiment of the present disclosure is not particularly limited, and it can be used in various applications. Specifically, it can be used in, for example, a drive reducer for an automobile.

[0151] 1: Bearing device 2, 102, 202: Bearing raceway component 2': Shaft component 2c: Inner ring raceway 3: Outer ring 3c: Outer ring raceway 4: Balls 5, 5', 105A, 105B, 105C, 205A, 205B: Joint surface 6: Bearing 7: Teeth 8: Cage 10, 110A, 110B, 210A, 210B: Bearing part having raceway 11, 111A, 111B, 211A, 211B: Raceway groove 12, 22, 112A, 112B, 122A, 122B, 211A, 211B, 222A: Outer circumferential surface 13, 23, 113A, 113B, 123A, 123B, 213A, 213B, 221A: Surface hardened layer 14, 24, 114A, 114B, 124A, 124B, 214A, 214B, 221A: Inside 20, 120A, 120B, 220A, 220B: Power transmission part having teeth 21, 121A, 121B, 221A: Teeth 25, 125A, 125B, 225A: Tooth root 26, 126A, 126B, 226A: Tooth root cylindrical part 51, 52, 57, 58, 61, 62, 63, 64, 67, 68: Workpiece 53: Joined workpiece 55, 65: Part that becomes the inner ring raceway 56, 66: Part that becomes the gear teeth

Claims

1. A shaft component for manufacturing a bearing raceway component having a toothed power transmission portion by carburizing or carbonitriding, It consists of a cylindrical or cylindrical shaft member, The aforementioned shaft member has a central axis, The shaft member has a first portion on the axial first side, and a second portion on the axial second side of the first portion. The first part is integrated with the second part, The first part is made of a first steel material, The second part is made of a second steel material, The first part comprises a track portion, The second part comprises a portion that will become a tooth, The alloy composition of the first steel material differs from that of the second steel material. The third part includes a joint surface that connects with the second part on the axial second side of the first part, The fourth part includes a joint surface that connects with the first part on the first axial side of the second part, The fifth part is located on the first axial side of the third part of the first part, The sixth part is located on the second axial side of the fourth part of the second part, The hardness of the third part is harder than the hardness of the fifth part. The hardness of the fourth part is harder than the hardness of the sixth part. The aforementioned track portion is a shaft component located in the fifth portion but not in the third portion.

2. The shaft component according to claim 1, wherein the tooth portion is located in the sixth portion but not in the fourth portion.

3. The shaft component according to claim 1 or 2, wherein the aforementioned track portion is a track groove for the ball to roll.

4. The shaft component according to claim 1 or 2, wherein the portion forming the raceway is a conical or cylindrical raceway for the roller to roll, and further comprises a flange portion adjacent to the raceway portion in the axial direction.

5. The shaft component according to claim 1 or 2, wherein the portion that becomes the tooth is a tooth of a gear, a tooth of a spline, or a tooth of a toothed pulley.

6. It consists of a cylindrical or cylindrical shaft member, The central axis of the first part coincides with the central axis of the second part. The shaft component according to claim 1 or 2, wherein the outer circumferential surface of the second axial side portion of the fifth portion, the outer circumferential surface of the third portion, the outer circumferential surface of the fourth portion, and the outer circumferential surface of the first axial side portion of the sixth portion are a single cylindrical surface.

7. It consists of a cylindrical shaft member, The central axis of the first part coincides with the central axis of the second part. The shaft component according to claim 1 or 2, wherein the inner circumferential surface of the second axial side portion of the fifth portion, the inner circumferential surface of the third portion, the inner circumferential surface of the fourth portion, and the inner circumferential surface of the first axial side portion of the sixth portion are a single cylindrical surface.

8. The first combination of the first steel material and the second steel material is The first steel material contains at least one of manganese, nickel, chromium, and molybdenum as an alloying component. The second steel material contains at least one of manganese, nickel, chromium, and molybdenum as an alloying component. The first steel material has a total content (mass%) of manganese, nickel, chromium, and molybdenum that is greater than 1.5 times the total content (mass%) of manganese, nickel, chromium, and molybdenum that is greater than the second steel material. The second combination of the first steel material and the second steel material is The first steel material contains silicon as an alloying component, The second steel material contains silicon as an alloying component, The silicon content (mass%) of the first steel material is less than the silicon content (mass%) of the second steel material, and this is the combination. The third combination of the first steel material and the second steel material is The first steel material contains no chromium or 1.6% by mass or less as an alloy component, and does not contain niobium or contains 0.01% by mass or less. The second steel material is a combination in which chromium is contained in an alloy component of 1.0% to 2.5% by mass and niobium is contained in an alloy component of 0.02% to 0.10% by mass. The fourth combination of the first steel material and the second steel material is, The first steel material contains 0.001% by mass or more and 0.050% by mass or less of nitrogen as an alloy component, does not contain boron or contains 0.001% by mass or less, and does not contain titanium or contains 0.003% by mass or less. The second steel material is a combination of alloy components containing 0.001% by mass or more and 0.050% by mass or less of nitrogen, 0.001% by mass or more and 0.005% by mass or less of boron, and 0.01% by mass or more and 0.08% by mass or less of titanium. The combination of the first steel material and the second steel material satisfies at least one combination from the first combination, the second combination, the third combination, and the fourth combination. The shaft component according to claim 1 or 2.

9. The first steel material contains carbon as an alloying component, The second steel material contains carbon as an alloying component, The shaft component according to claim 1 or 2, wherein the carbon content (mass%) of the first steel material is greater than the carbon content (mass%) of the second steel material.

10. A method for manufacturing the shaft component described in claim 1, The first part of the workpiece in the first state and the second part of the workpiece in the first state are joined together as a single first workpiece by friction welding. A method for manufacturing a shaft component, comprising first forming a bearing portion having a raceway on a first part of the first workpiece by first machining, and second forming a power transmission portion having teeth on a second part of the first workpiece by second machining, with the other being performed later.

11. A method for manufacturing the shaft component described in claim 1, Either first, then second, either first, forming a bearing portion with a raceway on the first part of the workpiece in the first state by first machining, or forming a power transmission portion with teeth on the second part of the workpiece in the first state by second machining, thereby obtaining the first part of the workpiece in the second state and the second part of the workpiece in the second state. A method for manufacturing a shaft component, comprising integrating the first part of the workpiece in the second state and the second part of the workpiece in the second state by frictional pressure welding.

12. A method for manufacturing a bearing raceway component having a toothed power transmission portion, comprising a method for manufacturing a shaft component according to claim 10 or 11, The shaft component obtained by the manufacturing method of claim 10 or 11 is used as a second workpiece. The portion of the second workpiece that will become the bearing portion having the raceway and the portion that will become the power transmission portion having the teeth are simultaneously subjected to carburizing or carbonitriding, followed by quenching, followed by tempering. A method for manufacturing a bearing raceway component, comprising forming an integral carburized or carbonitriding layer on the outer circumferential surface of the second axial side portion of the fifth portion, the outer circumferential surface of the third portion, the outer circumferential surface of the fourth portion, and the outer circumferential surface of the first axial side portion of the sixth portion, and / or forming an integral carburized or carbonitriding layer on the inner circumferential surface of the second axial side portion of the fifth portion, the inner circumferential surface of the third portion, the inner circumferential surface of the fourth portion, and the inner circumferential surface of the first axial side portion of the sixth portion.

13. The tempered material is designated as the third workpiece. A method for manufacturing a bearing raceway component according to claim 12, wherein one of the following is performed first and the other after: a third machining operation is performed on the portion of the third workpiece that will become the bearing portion having the raceway, and a fourth machining operation is performed on the portion of the third workpiece that will become the power transmission portion having the teeth.

14. A bearing raceway component having a power transmission portion with teeth, The bearing raceway component consists of a cylindrical or cylindrical shaft member. The bearing raceway component has a central axis, The bearing raceway component has a seventh portion on the first axial side, and an eighth portion on the second axial side of the seventh portion. The seventh part is integrated with the eighth part, The seventh part is made of the first steel material, The eighth part is made of the second steel material, The alloy composition of the first steel material differs from that of the second steel material. The seventh part is equipped with a track, The eighth part is equipped with teeth, The surfaces of the seventh portion and the eighth portion are integrally provided with a carburized layer or a carbonitrided layer, The seventh portion includes a joint surface that connects to the eighth portion on the second axial side of the seventh portion, The eighth portion includes a joint surface that connects with the seventh portion on the first axial side of the eighth portion, All of the aforementioned orbits are located in the seventh section. All of the aforementioned teeth are located in the eighth portion, All of the aforementioned tracks are located at a position where the axial length from the joint surface is 5 mm or more. Bearing raceway components.

15. The bearing raceway component according to claim 14, wherein all of the teeth are located at a position with an axial length of 5 mm or more from the joint surface.

16. The bearing raceway component according to claim 14 or 15, wherein the joining surface is a joining surface formed by friction welding.