Power transfer member and impact tool

Abstract

The present invention improves the durability of a power transfer member. A power transfer member (10) comprises iron and 0.25 mass% or more carbon and has a content of retained austenite in the surface of 18.5-80 vol%.

Description

Power transmission member and impact tool

[0001] The technology disclosed in this specification relates to a power transmission member and an impact tool.

[0002] 2. Description of the Related Art Power transmission members are known. For example, Patent Document 1 discloses an impact wrench that includes an anvil as a power transmission member.

[0003] JP 2018-187700 A

[0004] If the durability of the power transmission member such as the anvil is low, there is a risk of it being damaged.

[0005] The technology disclosed in this specification aims to improve the durability of power transmission members.

[0006] The present specification discloses a power transmission member, which contains 0.25 mass % or more of carbon and iron, and has a surface with a retained austenite content of 18.5 volume % or more and 80 volume % or less.

[0007] The present specification discloses an impact tool, which includes a motor, a hammer rotated by the motor, and the power transmission member serving as an anvil struck by the hammer in the rotational direction.

[0008] According to the technology disclosed in this specification, the durability of the power transmission member can be improved.

[0009] Fig. 1 is a perspective view from the right front showing the impact tool according to the embodiment. Fig. 2 is a side view showing the impact tool according to the embodiment. Fig. 3 is a vertical cross-sectional view showing the upper part of the impact tool according to the embodiment. Fig. 4 is a horizontal cross-sectional view showing the upper part of the impact tool according to the embodiment. Fig. 5 is a vertical cross-sectional view showing an enlarged view of a portion of the impact tool according to the embodiment. Fig. 6 is an exploded perspective view from the right front showing the impact tool according to the embodiment. Fig. 7 is a graph showing the evaluation results of each example.

[0010] In one or more embodiments, the power transmission component may include 0.25 mass % or more carbon and iron, and the amount of retained austenite on the surface may be 18.5 vol % or more and 80 vol % or less.

[0011] With the above configuration, the durability of the power transmission member can be improved.

[0012] In one or more embodiments, the power transmission member may have an amount of retained austenite at a depth of 200 μm from the surface of the power transmission member of 20% by volume or more and 50% by volume or less.

[0013] With the above configuration, the durability of the power transmission member can be improved.

[0014] In one or more embodiments, in a unit area of ​​0.112 mm x 0.084 mm at a depth of 15 μm from the surface of the power transmission member, the ratio of the total area occupied by carbides to the entire area of ​​the unit area may be 0.05% or more and 6.50% or less.

[0015] With the above configuration, the durability of the power transmission member can be improved.

[0016] In one or more embodiments, the power transmission member may have an average grain size of prior austenite grain boundaries in a field that includes a point at a depth of 0.02 mm of 8 μm or more and 100 μm or less.

[0017] With the above configuration, the durability of the power transmission member can be improved.

[0018] In one or more embodiments, the power transmission member may have a Vickers hardness of 600 HV or more and 850 HV or less at a point 0.1 mm deep from the surface, and a Vickers hardness of 600 HV or more and 800 HV or less at a point 0.5 mm deep from the surface.

[0019] With the above configuration, the durability of the power transmission member can be improved.

[0020] In one or more embodiments, the power transmission member may have an initial residual stress at the surface of −300 MPa or more and 200 MPa or less.

[0021] With the above configuration, the durability of the power transmission member can be improved.

[0022] In one or more embodiments, the power transmission component may further include, by weight, 2.5% to 4.5% nickel, 1.0% to 4.0% chromium, and greater than 0% to 1.2% molybdenum.

[0023] With the above configuration, the durability of the power transmission member can be improved.

[0024] In one or more embodiments, the power transmission member may be used in an environment where it is subjected to torsional shock.

[0025] With the above configuration, the durability of the power transmission member can be improved.

[0026] In one or more embodiments, the power transmission member may be used as an anvil for an impact tool.

[0027] With the above configuration, the durability of the power transmission member can be improved.

[0028] In one or more embodiments, an impact tool may include a motor, a hammer rotated by the motor, and the power transmission member as an anvil that is struck in a rotational direction by the hammer.

[0029] With the above configuration, the durability of the power transmission member can be improved.

[0030] Hereinafter, embodiments will be described with reference to the drawings. However, the present invention is not limited to these embodiments. Furthermore, the components in the following embodiments include those that are easily replaceable by those skilled in the art, or those that are substantially the same.

[0031] (Power Transmission Member) The power transmission member 10 according to this embodiment is a member that transmits power received from one member to another member. For example, the power transmission member 10 is attached to one member and another member to transmit the motion of the one member to the other member. More specifically, the power transmission member 10 is used in an environment where it is subject to torsional impact (twisting and impact). That is, in this embodiment, the power transmission member 10 rotates in response to torsional impact associated with the rotation of one member, and rotates the other member in response to its own rotation, thereby transmitting power in the rotational direction to the other member. The power transmission member 10 is also a shaft-shaped member, in other words, a power transmission shaft. However, the power transmission member 10 is not limited to being used in an environment where it is subject to torsional impact, and may be used for any purpose. The power transmission member 10 is also not limited to being a shaft-shaped member, and may have any shape and size.

[0032] (Impact Tool) For example, the power transmission member 10 may be used as an anvil of an impact tool 1. The configuration of the impact tool according to this embodiment will be described below. In this embodiment, the positional relationship of each part will be described using the terms left, right, front, rear, top, and bottom. These terms indicate relative positions or directions with respect to the center of the impact tool 1.

[0033] The impact tool 1 has a motor 6 as a power source. In the embodiment, a direction parallel to a rotation axis AX of the motor 6 is referred to as an axial direction, a direction circumferentially around the rotation axis AX is referred to as a circumferential direction or a rotation direction, and a radial direction of the rotation axis AX is referred to as a radial direction.

[0034] The rotation axis AX extends in the front-to-rear direction. One axial side is the front, and the other axial side is the rear. In addition, in the radial direction, a position closer to or approaching the rotation axis AX will be referred to as the radially inner side, and a position farther from or away from the rotation axis AX will be referred to as the radially outer side.

[0035] Fig. 1 is a perspective view of the impact tool according to the embodiment, seen from the front right. Fig. 2 is a side view of the impact tool according to the embodiment. Fig. 3 is a vertical cross-sectional view of the upper part of the impact tool according to the embodiment. Fig. 4 is a horizontal cross-sectional view of the upper part of the impact tool according to the embodiment. Fig. 5 is a vertical cross-sectional view of an enlarged portion of the impact tool according to the embodiment. Fig. 6 is an exploded perspective view of the impact tool according to the embodiment, seen from the front right.

[0036] In the embodiment, the impact tool 1 is an impact wrench and includes a housing 2, a hammer case 4, a cover 3, a motor 6, a speed reducer 7, a spindle 8, a striking mechanism 9, a power transmission member 10 serving as an anvil, a fan 12, a battery mounting portion 13, a trigger lever 14, a forward / reverse rotation switch lever 15, an operation display 16, a light 17, a seal member 70, and a support member 80.

[0037] The housing 2 is made of synthetic resin. In this embodiment, the housing 2 is made of nylon. The housing 2 includes a left housing 2L and a right housing 2R located to the right of the left housing 2L. The left housing 2L and the right housing 2R are fixed together with a plurality of screws 2S. The housing 2 is made up of a pair of split housing halves.

[0038] The housing 2 has a motor accommodating portion 21 , a grip portion 22 , and a battery holding portion 23 .

[0039] The motor housing 21 houses the motor 6. The motor housing 21 and the hammer case 4 are fixed together by a plurality of screws 2T.

[0040] The grip portion 22 is held by an operator and extends downward from the motor housing portion 21. The trigger lever 14 is provided on the upper portion of the grip portion 22.

[0041] The battery holding portion 23 holds the battery pack 25 via the battery attachment portion 13. The battery holding portion 23 is connected to the lower end of the grip portion 22. The external dimensions of the battery holding portion 23 are larger than the external dimensions of the grip portion 22 in both the front-rear and left-right directions.

[0042] The motor accommodating section 21 has an intake port 19 and an exhaust port 20. The exhaust port 20 is provided forward of the intake port 19. Air in the external space of the housing 2 flows into the internal space of the housing 2 through the intake port 19. Air in the internal space of the housing 2 flows out to the external space of the housing 2 through the exhaust port 20.

[0043] The hammer case 4 accommodates at least a portion of the speed reduction mechanism 7, the spindle 8, the impact mechanism 9, and the power transmission member 10. At least a portion of the speed reduction mechanism 7 is disposed inside the bearing box 24. The speed reduction mechanism 7 includes a plurality of gears.

[0044] The hammer case 4 is made of metal. In this embodiment, the hammer case 4 is made of aluminum. The hammer case 4 is cylindrical. The hammer case 4 is connected to the front part of the motor accommodating portion 21. A bearing box 24 is fixed to the rear part of the hammer case 4. The front part of the bearing box 24 is fitted into the rear part of the hammer case 4, thereby fixing the bearing box 24 and the hammer case 4 together.

[0045] The cover 3 is arranged to cover at least a portion of the outer surface of the hammer case 4 .

[0046] The motor 6 is a power source of the impact tool 1. The motor 6 is an inner rotor type brushless motor. The motor 6 has a stator 26 and a rotor 27. The stator 26 is supported by the motor housing portion 21. At least a portion of the rotor 27 is disposed inside the stator 26. The rotor 27 rotates relative to the stator 26. The rotor 27 rotates around a rotation axis AX extending in the front-rear direction.

[0047] The reduction mechanism 7 connects the rotor 27 and the spindle 8. The reduction mechanism 7 transmits the rotation of the rotor 27 to the spindle 8. The reduction mechanism 7 rotates the spindle 8 at a rotational speed lower than the rotational speed of the rotor 27. The reduction mechanism 7 is disposed forward of the motor 6. The reduction mechanism 7 includes a planetary gear mechanism. The reduction mechanism 7 has a plurality of gears. The gears of the reduction mechanism 7 are driven by the rotor 27.

[0048] The spindle 8 rotates by the rotational force of the rotor 27 transmitted by the reduction mechanism 7. The spindle 8 is disposed forward of at least a portion of the motor 6. The spindle 8 is disposed forward of the stator 26. At least a portion of the spindle 8 is disposed forward of the rotor 27. At least a portion of the spindle 8 is disposed forward of the reduction mechanism 7. The spindle 8 is disposed rearward of the power transmission member 10.

[0049] The impact mechanism 9 impacts the power transmission member 10 in the rotational direction based on the rotational force of the spindle 8 rotated by the motor 6. The rotational force of the motor 6 is transmitted to the impact mechanism 9 via the speed reducer 7 and the spindle 8.

[0050] The power transmission member 10 is an output shaft of the impact tool 1 that rotates based on the rotational force of the rotor 27. The power transmission member 10 is struck in the rotational direction by the striking mechanism 9. The power transmission member 10 is disposed forward of the motor 6. A socket, which is a type of tool tip, is attached to the front end of the power transmission member 10. The power transmission member 10 is disposed forward of at least a portion of the spindle 8.

[0051] The fan 12 generates an airflow for cooling the motor 6. The fan 12 is disposed forward of the stator 26 of the motor 6. The fan 12 is fixed to at least a portion of the rotor 27. As the fan 12 rotates, air from the external space of the housing 2 flows into the internal space of the housing 2 through the air intake 19. The air that has flowed into the internal space of the housing 2 cools the motor 6 by circulating through the internal space of the housing 2. As the fan 12 rotates, the air that has circulated through the internal space of the housing 2 flows out into the external space of the housing 2 through the air exhaust 20.

[0052] The battery attachment section 13 is connected to the battery pack 25. The battery pack 25 is attached to the battery attachment section 13. The battery pack 25 is detachable from the battery attachment section 13. The battery attachment section 13 is disposed below the battery holding section 23. The battery pack 25 is attached to the battery attachment section 13 by being inserted into the battery attachment section 13 from the front of the battery holding section 23. The battery pack 25 is removed from the battery attachment section 13 by being removed forward from the battery attachment section 13. The battery pack 25 includes a secondary battery. In this embodiment, the battery pack 25 includes a rechargeable lithium-ion battery. When attached to the battery attachment section 13, the battery pack 25 can supply power to the impact tool 1. The motor 6 is driven by the power supplied from the battery pack 25.

[0053] The trigger lever 14 is operated by an operator to start the motor 6. Operating the trigger lever 14 switches between driving and stopping the motor 6. The trigger lever 14 is provided on the grip portion 22.

[0054] The forward / reverse switching lever 15 is operated by an operator. By operating the forward / reverse switching lever 15, the rotation direction of the motor 6 is switched from one of the forward direction and the reverse direction to the other. By switching the rotation direction of the motor 6, the rotation direction of the spindle 8 is switched. The forward / reverse switching lever 15 is provided on the upper part of the grip portion 22.

[0055] The operation display unit 16 has a plurality of operation buttons 16A and an indicator display 16B. The operation mode of the motor 6 is switched when the operator operates the operation button 16A. The indicator display 16B has a plurality of light-emitting elements. The indicator display 16B displays the operation mode of the motor 6 by changing the lighting pattern of the plurality of light-emitting elements. The operation display unit 16 is provided in the battery holding unit 23. The operation display unit 16 is provided on the top surface of the battery holding unit 23, further forward than the grip unit 22.

[0056] The light 17 emits illumination light. The light 17 illuminates the power transmission member 10 and the area around the power transmission member 10 with the illumination light. The light 17 illuminates the area in front of the power transmission member 10 with the illumination light. The light 17 also illuminates the tool accessory attached to the power transmission member 10 and the area around the tool accessory with the illumination light. The light 17 is disposed above the trigger lever 14.

[0057] The hammer case 4 has a first cylindrical portion 401, a second cylindrical portion 402, a case connecting portion 403, a third cylindrical portion 404, and a fourth cylindrical portion 405. The first cylindrical portion 401 is arranged around the striking mechanism portion 9. The second cylindrical portion 402 is arranged forward of the first cylindrical portion 401. The outer diameter of the second cylindrical portion 402 is smaller than the outer diameter of the first cylindrical portion 401. The case connecting portion 403 is arranged to connect the front portion of the first cylindrical portion 401 and the rear portion of the second cylindrical portion 402. The third cylindrical portion 404 is arranged forward of the second cylindrical portion 402. The fourth cylindrical portion 405 is arranged forward of the third cylindrical portion 404. The inner diameter of the second cylindrical portion 402 is smaller than the inner diameter of the first cylindrical portion 401. The inner diameter of the third cylindrical portion 404 is smaller than the inner diameter of the second cylindrical portion 402. The inner diameter of the fourth cylindrical portion 405 is smaller than the inner diameter of the third cylindrical portion 404 .

[0058] As shown in FIG. 5 , the second cylindrical portion 402 has a rear surface 402R facing rearward and an inner circumferential surface 402S facing radially inward. The third cylindrical portion 404 has a rear surface 404R facing rearward and an inner circumferential surface 404S facing radially inward. The fourth cylindrical portion 405 has a rear surface 405R facing rearward and an inner circumferential surface 405S facing radially inward. The front end of the inner circumferential surface 402S is connected to the radial outer end of the rear surface 404R. The front end of the inner circumferential surface 404S is connected to the radial outer end of the rear surface 405R. The inner circumferential surface 405S defines an opening of the hammer case 4 provided at the front end of the hammer case 4.

[0059] The motor 6 has a stator 26 and a rotor 27. The stator 26 has a stator core 28, a front insulator 29, a rear insulator 30, and a coil 31. The rotor 27 rotates about a rotation axis AX. The rotor 27 has a rotor core 32, a rotor shaft 33, and a rotor magnet 34.

[0060] The stator core 28 is disposed radially outward of the rotor 27. The stator core 28 includes a plurality of stacked steel plates. The steel plates are metal plates whose main component is iron. The stator core 28 is cylindrical. The stator core 28 has a plurality of teeth that support the coils 31.

[0061] The front insulator 29 is provided in the front portion of the stator core 28. The rear insulator 30 is provided in the rear portion of the stator core 28. The front insulator 29 and the rear insulator 30 are each an electrical insulating member made of synthetic resin. The front insulator 29 is arranged to cover a portion of the surface of the teeth. The rear insulator 30 is arranged to cover a portion of the surface of the teeth.

[0062] The coil 31 is attached to the stator core 28 via the front insulator 29 and the rear insulator 30. A plurality of coils 31 are arranged. The coils 31 are arranged around the teeth of the stator core 28 via the front insulator 29 and the rear insulator 30. The coils 31 and the stator core 28 are electrically insulated by the front insulator 29 and the rear insulator 30. The plurality of coils 31 are connected via a bus bar unit 38.

[0063] The rotor core 32 and the rotor shaft 33 are both made of steel. The rotor shaft 33 is disposed inside the rotor core 32. The rotor core 32 and the rotor shaft 33 are fixed together. The front end of the rotor shaft 33 protrudes forward from the front end surface of the rotor core 32, and the rear end of the rotor shaft 33 protrudes rearward from the rear end surface of the rotor core 32.

[0064] The rotor magnet 34 is fixed to the rotor core 32. The rotor magnet 34 is disposed inside the rotor core 32.

[0065] A sensor board 37 is attached to the rear insulator 30. The sensor board 37 has a disk-shaped circuit board with a hole in the center and a rotation detection element supported by the circuit board. At least a portion of the sensor board 37 faces the rotor magnet 34. The rotation detection element detects the position of the rotor magnet 34 of the rotor 27, thereby detecting the position of the rotor 27 in the rotational direction.

[0066] The rotor shaft 33 is rotatably supported by rotor bearings 39. The rotor bearings 39 include a front rotor bearing 39F that rotatably supports the front end of the rotor shaft 33, and a rear rotor bearing 39R that rotatably supports the rear end of the rotor shaft 33.

[0067] The front rotor bearing 39F is held in the bearing box 24. The bearing box 24 has a recess 241 recessed forward from the rear surface of the bearing box 24. The front rotor bearing 39F is disposed in the recess 241. The rear rotor bearing 39R is held in the rear part of the motor accommodating portion 21. The front end of the rotor shaft 33 is disposed in the internal space of the hammer case 4 through the opening of the bearing box 24.

[0068] The fan 12 is fixed to the front portion of the rotor shaft 33. The fan 12 is disposed between the front rotor bearing 39F and the stator 26. The fan 12 rotates due to the rotation of the rotor shaft 33. As the rotor shaft 33 rotates, the fan 12 rotates together with the rotor shaft 33.

[0069] A pinion gear 41 is formed on the front end of the rotor shaft 33. The pinion gear 41 is connected to at least a part of the speed reduction mechanism 7. The rotor shaft 33 is connected to the speed reduction mechanism 7 via the pinion gear 41.

[0070] The reduction mechanism 7 has a plurality of planetary gears 42 arranged around the pinion gear 41, and an internal gear 43 arranged around the plurality of planetary gears 42. The pinion gear 41, the planetary gear 42, and the internal gear 43 are each housed in the hammer case 4. Each of the plurality of planetary gears 42 meshes with the pinion gear 41. The planetary gear 42 is rotatably supported on the spindle 8 via a pin 42P. The spindle 8 is rotated by the planetary gear 42. The internal gear 43 has internal teeth that mesh with the planetary gear 42. The internal gear 43 is fixed to the hammer case 4. The internal gear 43 is always non-rotatable relative to the hammer case 4.

[0071] When the rotor shaft 33 is rotated by the drive of the motor 6, the pinion gear 41 rotates, and the planetary gear 42 revolves around the pinion gear 41. The planetary gear 42 revolves while meshing with the internal teeth of the internal gear 43. Due to the revolution of the planetary gear 42, the spindle 8 connected to the planetary gear 42 via the pin 42P rotates at a rotational speed lower than the rotational speed of the rotor shaft 33.

[0072] The spindle 8 rotates due to the rotational force of the motor 6. The spindle 8 transmits the rotational force of the motor 6 to the power transmission member 10 via the impact mechanism 9. The impact mechanism 9 rotates due to the rotational force of the rotor 27. The spindle 8 has a spindle shaft 801 and a flange 802 provided at the rear of the spindle shaft 801. The planetary gear 42 is rotatably supported on the flange 802 via a pin 42P. The rotation axis of the spindle 8 coincides with the rotation axis AX of the motor 6. The spindle 8 rotates around the rotation axis AX. The spindle 8 is rotatably supported by a spindle bearing 44. A protrusion 803 is provided at the rear end of the spindle 8. The protrusion 803 protrudes rearward from the flange 802. The spindle bearing 44 is disposed to surround the protrusion 803.

[0073] The bearing box 24 is disposed around at least a portion of the periphery of the spindle 8. The spindle bearing 44 is held in the bearing box 24. The bearing box 24 has a recess 242 recessed rearward from the front surface of the bearing box 24. The spindle bearing 44 is disposed in the recess 242.

[0074] The striking mechanism 9 has a hammer 47, a hammer ball 48, a coil spring 50, and a washer 61. The striking mechanism 9 including the hammer 47, the hammer ball 48, the coil spring 50, and the washer 61 is housed in a first cylindrical portion 401 of the hammer case 4. The first cylindrical portion 401 is disposed around the hammer 47.

[0075] The hammer 47 is disposed forward of the speed reduction mechanism 7. The hammer 47 is disposed around the spindle shaft 801. The hammer 47 is supported by the spindle shaft 801.

[0076] The hammer 47 is rotated by the motor 6. The rotational force of the motor 6 is transmitted to the hammer 47 via the reduction mechanism 7 and the spindle 8. The hammer 47 can rotate together with the spindle 8 based on the rotational force of the spindle 8 rotated by the motor 6. The rotation axis of the hammer 47, the rotation axis of the spindle 8, and the rotation axis AX of the motor 6 coincide with each other. The hammer 47 rotates around the rotation axis AX.

[0077] The hammer 47 has a base portion 471 , a rear ring portion 473 , a support ring portion 474 , and a hammer protrusion portion 475 .

[0078] The base portion 471 is disposed around the spindle shaft portion 801. The base portion 471 is annular. The spindle shaft portion 801 is disposed inside the base portion 471.

[0079] The rear ring portion 473 protrudes rearward from the outer periphery of the base portion 471. The rear ring portion 473 is cylindrical. A rear end portion of the rear ring portion 473 is located rearward of a rear end portion of the support ring portion 474.

[0080] The support ring portion 474 protrudes rearward from the inner periphery of the base portion 471. The support ring portion 474 is cylindrical. The support ring portion 474 is disposed around the spindle shaft portion 801. The support ring portion 474 is supported by the spindle shaft portion 801 via the hammer ball 48. The support ring portion 474 has a large diameter portion 474A and a small diameter portion 474B disposed rearward of the large diameter portion 474A. The outer diameter of the large diameter portion 474A is larger than the outer diameter of the small diameter portion 474B. A step portion 474C is provided at the boundary between the large diameter portion 474A and the small diameter portion 474B.

[0081] The hammer protrusions 475 protrude forward from the front surface of the base portion 471. The front surface of the hammer protrusions 475 is disposed forward of the front surface of the base portion 471. Two hammer protrusions 475 are disposed in the circumferential direction.

[0082] A recess 476 is formed by the rear surface of the base portion 471, the inner peripheral surface of the rear ring portion 473, and the outer peripheral surface of the support ring portion 474. The recess 476 is provided in the rear portion of the hammer 47. The recess 476 is formed so as to be recessed forward from the rear surface of the hammer 47.

[0083] The hammer ball 48 is made of metal such as steel. The hammer ball 48 is disposed between the spindle shaft portion 801 and the hammer 47. The spindle 801 has a spindle groove 804 in which at least a portion of the hammer ball 48 is disposed. The spindle groove 804 is provided on a portion of the outer circumferential surface of the spindle shaft portion 801. The hammer 47 has a hammer groove 477 in which at least a portion of the hammer ball 48 is disposed. The hammer groove 477 is provided on a portion of the inner circumferential surface of the support ring portion 474. The hammer ball 48 is disposed between the spindle groove 804 and the hammer groove 477. The hammer ball 48 can roll inside the spindle groove 804 and inside the hammer groove 477. The hammer 47 can move along with the hammer ball 48. The spindle 8 and the hammer 47 can move relative to each other in the axial direction and the rotational direction within a movable range defined by the spindle groove 804 and the hammer groove 477 .

[0084] The coil spring 50 is arranged around the spindle shaft portion 801. In this embodiment, the coil spring 50 includes a first coil spring 51 and a second coil spring 52 arranged in parallel to each other. The second coil spring 52 is arranged radially inward of the first coil spring 51. In this embodiment, the spring constant of the first coil spring 51 is greater than the spring constant of the second coil spring 52. The wire diameter of the first coil spring 51 is greater than the wire diameter of the second coil spring 52.

[0085] The rear ends of the first coil springs 51 and the second coil springs 52 are supported on the front surface of the flange portion 802. The rear ends of the first coil springs 51 contact the front surface of the flange portion 802. The rear ends of the second coil springs 52 are supported on the front surface of the flange portion 802 via washers 62.

[0086] The front end of the first coil spring 51 and the front end of the second coil spring 52 are disposed inside the recess 476. A washer 61 is disposed inside the recess 476. The front end of the first coil spring 51 and the front end of the second coil spring 52 are supported by the washer 61. The washer 61 is a ring-shaped member. The first coil spring 51 and the second coil spring 52 each constantly generate an elastic force that moves the hammer 47 forward.

[0087] The washer 61 is disposed rearward of the base portion 471. The washer 61 supports the front ends of the first coil spring 51 and the second coil spring 52. In the radial direction, the washer 61 is disposed between the rear ring portion 473 and the support ring portion 474. The washer 61 is disposed inside the recess 476. The washer 61 is supported by the hammer 47 via a plurality of support balls 54. When the hammer 47 is disposed at the frontmost position within the movable range of the hammer 47 in the front-to-rear direction, the support balls 54 are disposed forward of the rear end of the hammer ball 48.

[0088] The support ball 54 is disposed in a support groove 478 provided in the hammer 47 inside the recess 476. In the present embodiment, the support groove 478 is provided on the rear surface of the base portion 471. The support groove 478 is provided in a ring shape so as to surround the rotation axis AX. The support ball 54 supports the washer 61.

[0089] The washer 61 is sandwiched between the coil spring 50 and the support ball 54 in the front-rear direction. The washer 61 is spaced apart from the hammer 47 and the spindle 8.

[0090] The power transmission member 10 has an anvil shaft portion 101 , an anvil protrusion portion 102 , and a recess portion 103 .

[0091] The anvil shaft portion 101 extends in the axial direction (front-to-back direction). The anvil shaft portion 101 has a rotation axis AX. The anvil shaft portion 101 is disposed forward of the spindle 8 and the hammer 47. At least a portion of the anvil shaft portion 101 is disposed in an opening provided at the front end of the hammer case 4. As described above, the opening at the front end of the hammer case 4 is defined by the inner circumferential surface 405S of the fourth cylindrical portion 405. The front end of the anvil shaft portion 101 protrudes forward from the opening of the hammer case 4. A socket, which is a type of tip tool, is attached to the front end of the anvil shaft portion 101.

[0092] The anvil protrusion 102 protrudes radially outward from the rear end of the anvil shaft portion 101. The anvil protrusion 102 is struck in the rotational direction by the hammer protrusion 475. A washer 53 is disposed between the front surface of the anvil protrusion 102 and the rear surface 402R of the second cylindrical portion 402. The washer 53 prevents contact between the anvil protrusion 102 and the second cylindrical portion 402. The rear end of the second cylindrical portion 402 receives the load of the anvil protrusion 102 via the washer 53.

[0093] The recess 103 is recessed forward from the center of the rear surface of the power transmission member 10. The front end of the spindle 8 is disposed in the recess 103.

[0094] The base portion 471 is disposed rearward of the anvil protrusion 102. The rear surface of the anvil protrusion 102 and the front surface of the base portion 471 are spaced apart from each other.

[0095] The power transmission member 10 is rotatably supported by the anvil bearing 46. The rotation axis of the power transmission member 10, the rotation axis of the hammer 47, the rotation axis of the spindle 8, and the rotation axis AX of the motor 6 are aligned. The power transmission member 10 rotates around the rotation axis AX. The anvil bearing 46 is disposed around the anvil shaft portion 101. A portion of the anvil bearing 46 is disposed inside the second cylindrical portion 402 of the hammer case 4. A portion of the anvil bearing 46 is disposed inside the third cylindrical portion 404 of the hammer case 4. The anvil bearing 46 is held in the second cylindrical portion 402 of the hammer case 4. The anvil bearing 46 is press-fitted into the second cylindrical portion 402. The anvil bearing 46 is fixed to the hammer case 4 inside the hammer case 4. The anvil bearing 46 rotatably supports the anvil shaft portion 101.

[0096] As shown in FIG. 5 , the anvil bearing 46 has an outer annular portion 461, a rear support portion 462, a front support portion 463, a rear convex portion 464, and a front convex portion 465. The rear support portion 462 protrudes radially inward from a rear portion of the outer annular portion 461. The front support portion 463 protrudes radially inward from a front portion of the outer annular portion 461. The rear convex portion 464 protrudes rearward from the rear support portion 462. The front convex portion 465 protrudes forward from the front support portion 463. A recess 466 of the anvil bearing 46 is defined by the outer annular portion 461, the rear support portion 462, and the front support portion 463.

[0097] The outer annular portion 461 has a front surface 461F facing forward, a rear surface 461R facing rearward, an inner peripheral surface 461S facing radially inward, and an outer peripheral surface 461T facing radially outward.

[0098] The rear support portion 462 has a front surface 462F facing forward, a rear surface 462R facing rearward, and an inner circumferential surface 462S facing radially inward.

[0099] The front support portion 463 has a front surface 463F facing forward, a rear surface 463R facing rearward, and an inner circumferential surface 463S facing radially inward.

[0100] The rear convex portion 464 has a rear surface 464R facing rearward and an outer circumferential surface 464T facing radially outward.

[0101] The front convex portion 465 has a front surface 465F facing forward, an inner circumferential surface 465S facing radially inward, and an outer circumferential surface 465T facing radially outward.

[0102] An outer peripheral surface 461T of the outer ring portion 461 contacts an inner peripheral surface 402S of the second cylindrical portion 402. The inner peripheral surface 461S of the outer ring portion 461 is spaced apart from the outer peripheral surface of the anvil shaft portion 101. The recess 466 is defined by the inner peripheral surface 461S of the outer ring portion 461, a front surface 462F of the rear support portion 462, and a rear surface 463R of the front support portion 463.

[0103] The anvil shaft portion 101 has a rear cylindrical portion 112, a front cylindrical portion 114, and a recess 113. An inner peripheral surface 461S of the outer annular portion 461 faces the outer peripheral surface of the recess 113. An inner peripheral surface 462S of the rear support portion 462 contacts the outer peripheral surface of the rear cylindrical portion 112. An inner peripheral surface 463S of the front support portion 463 contacts the outer peripheral surface of the front cylindrical portion 114. The rear cylindrical portion 112 is supported by the rear support portion 462 of the anvil bearing 46. The outer peripheral surface of the rear cylindrical portion 112 and the inner peripheral surface 462S of the rear support portion 462 contact each other. The recess 113 is located forward of the rear cylindrical portion 112. The outer diameter of the recess 113 is smaller than the outer diameter of the rear cylindrical portion 112. The front cylindrical portion 114 is disposed forward of the recess 113. The outer diameter of the front cylindrical portion 114 is substantially equal to the outer diameter of the rear cylindrical portion 112. As shown in FIG. 5 , the front cylindrical portion 114 is supported by the front support portion 463 of the anvil bearing 46. The outer peripheral surface of the front cylindrical portion 114 and the inner peripheral surface 463S of the front support portion 463 are in contact with each other.

[0104] The radially outer outer edge of the front surface of the washer 53 faces the rear surface 402R of the second cylindrical portion 402. The radially inner inner edge of the front surface of the washer 53 faces the rear surface 461R of the outer ring portion 461. The radially inner inner circumferential surface of the washer 53 faces the outer circumferential surface 464T of the rear convex portion 464. The rear surface 464R of the rear convex portion 464 faces the front surface of the anvil protrusion 102 via a gap. The front surface 461F of the outer ring portion 461 faces the rear surface 404R of the third cylindrical portion 404. The outer circumferential surface 465T of the front convex portion 465 contacts the inner circumferential surface 404S of the third cylindrical portion 404.

[0105] The hammer protrusion 475 can come into contact with the anvil protrusion 102. When the motor 6 is driven while the hammer 47 and the anvil protrusion 102 are in contact with each other, the power transmission member 10 rotates together with the hammer 47 and the spindle 8.

[0106] The power transmission member 10 is struck in the rotational direction by the hammer 47. For example, during a bolt tightening operation, if the load acting on the power transmission member 10 becomes too high, a situation may arise in which the power transmission member 10 cannot be rotated by the load of the coil spring 50 alone. When the load of the coil spring 50 alone is no longer sufficient to rotate the power transmission member 10, the rotation of the power transmission member 10 and the hammer 47 stops. The spindle 8 and the hammer 47 are capable of relative movement in the axial and circumferential directions via the hammer ball 48. Even when the rotation of the hammer 47 stops, the rotation of the spindle 8 continues due to the power generated by the motor 6. When the spindle 8 rotates while the rotation of the hammer 47 is stopped, the hammer ball 48 moves rearward while being guided by the spindle groove 804 and the hammer groove 477. The hammer 47 receives force from the hammer ball 48 and moves rearward along with the hammer ball 48. That is, the hammer 47 moves rearward when the spindle 8 rotates while the rotation of the power transmission member 10 is stopped. When the hammer 47 moves rearward, the contact between the hammer 47 and the anvil protrusion 102 is released.

[0107] When the hammer 47 moves rearward, the hammer 47 rotates relative to the spindle shaft portion 801. The washer 61 is spaced apart from the hammer 47 and the spindle 8. Therefore, the rotation of the hammer 47 is not hindered by the washer 61. In addition, the support ball 54 is disposed between the washer 61 and the hammer 47. The rotation of the support ball 54 allows the hammer 47 to rotate smoothly.

[0108] As described above, the coil spring 50 constantly generates an elastic force that moves the hammer 47 forward. After moving backward, the hammer 47 moves forward due to the elastic force of the coil spring 50. When the hammer 47 moves forward, it receives a rotational force from the hammer ball 48. That is, the hammer 47 moves forward while rotating. When the hammer 47 moves forward while rotating, the hammer protrusion 475 comes into contact with the anvil protrusion 102 while rotating. As a result, the anvil protrusion 102 is struck in the rotational direction by the hammer protrusion 475. Both the power of the motor 6 and the inertial force of the hammer 47 act on the power transmission member 10. Therefore, the power transmission member 10 can rotate about the rotation axis AX with high torque.

[0109] <Sealing Member and Supporting Member> The sealing member 70 is disposed inside the hammer case 4. The sealing member 70 is disposed radially inward of the third cylindrical portion 404 of the hammer case 4. The sealing member 70 is disposed inside the hammer case 4 at the boundary between the anvil bearing 46 and the anvil shaft portion 101. At least a portion of the sealing member 70 contacts the outer peripheral surface of the anvil shaft portion 101. The sealing member 70 is supported by the anvil bearing 46. The sealing member 70 is disposed radially inward of the front convex portion 465 of the anvil bearing 46. In the embodiment, the sealing member 70 is a lip seal.

[0110] The seal member 70 seals the boundary between the anvil bearing 46 and the anvil shaft portion 101. The seal member 70 prevents lubricant (grease) present inside the hammer case 4 from leaking out of the hammer case 4 through the opening at the front end of the hammer case 4. The seal member 70 also prevents foreign matter from outside the hammer case 4 from entering the inside of the hammer case 4.

[0111] As shown in FIG. 5 , the seal member 70 has an outer annular portion 71, a rear lip portion 72, and a front lip portion 73. The outer peripheral surface of the outer annular portion 71, which faces radially outward, contacts the inner peripheral surface 465S of the front convex portion 465. The rear surface of the outer annular portion 71, which faces rearward, contacts the front surface 463F of the front support portion 463. The rear lip portion 72 and the front lip portion 73 are each positioned radially inward from the outer annular portion 71. The rear lip portion 72 is positioned rearward from the front lip portion 73. The rear lip portion 72 and the front lip portion 73 each contact the outer peripheral surface of the anvil shaft portion 101. The rear lip portion 72 and the front lip portion 73 each contact the outer peripheral surface of the front cylindrical portion 114.

[0112] The support member 80 is disposed inside the hammer case 4. The support member 80 is disposed forward of the seal member 70. The support member 80 faces the seal member 70. The support member 80 is capable of supporting the seal member 70 from the front. As described above, an opening in which the anvil shaft portion 101 is disposed is provided at the front end of the hammer case 4. The opening of the hammer case 4 is defined by the inner circumferential surface 405S of the fourth cylindrical portion 405. The support member 80 is disposed so as to face the opening of the hammer case 4. The support member 80 prevents the seal member 70 from slipping forward through the opening of the hammer case 4.

[0113] The support member 80 is ring-shaped. The support member 80 is a washer that is disposed around the anvil shaft portion 101. The support member 80 is spaced apart from the anvil shaft portion 101.

[0114] The support member 80 is fixed to at least one of the hammer case 4 and the anvil bearing 46. In the embodiment, the support member 80 is sandwiched in the front-rear direction between the anvil bearing 46 and a part of the hammer case 4. In the embodiment, the outer edge portion on the radially outer side of the support member 80 is sandwiched between the front surface 465F of the front convex portion 465 and the rear surface 405R of the fourth cylindrical portion 405.

[0115] The support member 80 is inserted into the hammer case 4 through an opening provided at the rear end of the hammer case 4. After the support member 80 is inserted into the hammer case 4 so that the front surface of the support member 80 contacts the rear surface 405R of the fourth cylindrical portion 405, the seal member 70 and the anvil bearing 46 are each inserted into the hammer case 4 through openings provided at the rear end of the hammer case 4. The anvil bearing 46 is fixed to the hammer case 4 by being press-fitted into the second cylindrical portion 402. The front surface 461F of the outer ring portion 461 contacts the rear surface 404R of the third cylindrical portion 404, thereby positioning the hammer case 4 and the anvil bearing 46 in the front-to-rear direction.

[0116] The support member 80 may be disposed on a portion of the periphery of the anvil shaft portion 101. A cutout may be provided in a portion of the support member 80. The support member 80 may be a circlip. When the support member 80 is a circlip, it may be disposed inside the hammer case 4 via an opening provided in the front end portion of the hammer case 4.

[0117] (Material Properties of Power Transmission Member) The material properties of the power transmission member 10 according to the embodiment will be described below.

[0118] (Composition) The power transmission member 10 is made of a steel-based material containing carbon and iron. More specifically, the power transmission member 10 is preferably a carburized member that has been subjected to a carburizing treatment.

[0119] The carbon content in the uncarburized portion of the power transmission member 10 is 0.25% by mass or more, preferably 0.25% by mass to 0.50% by mass, and more preferably 0.25% by mass to 0.35% by mass. Having the carbon content within this range can improve the durability of the power transmission member 10. Furthermore, having the carbon content within this range can prevent the amount of carbide from precipitating excessively, thereby appropriately preventing breakage.

[0120] The power transmission member 10 preferably has a nickel content of 2.5% by mass to 4.5% by mass, more preferably 3.0% by mass to 4.5% by mass, and even more preferably 3.5% by mass to 4.5% by mass. When the nickel content is within this range, the durability of the power transmission member 10 can be improved.

[0121] The power transmission member 10 preferably has a chromium content of 1.0% by mass to 4.0% by mass, more preferably 1.0% by mass to 3.5% by mass, even more preferably 1.5% by mass to 3.0% by mass, and even more preferably 2.0% by mass to 3.5% by mass. Having a chromium content within this range can improve the durability of the power transmission member 10.

[0122] The power transmission member 10 preferably has a molybdenum content of greater than 0 mass% and not more than 1.2 mass%, more preferably 0.1 mass% to 1.2 mass%, even more preferably 0.2 mass% to 1.0 mass%, even more preferably 0.2 mass% to 0.7 mass%, and even more preferably 0.5 mass% to 0.7 mass%. Having the molybdenum content within this range can improve the durability of the power transmission member 10.

[0123] The power transmission member 10 preferably has a total chromium and molybdenum content of 1.5% by mass to 5.5% by mass, more preferably 2.0% by mass to 5.0% by mass, even more preferably 2.7% by mass to 4.5% by mass, and even more preferably 3.0% by mass to 4.2% by mass. Having the total chromium and molybdenum content within this range can improve the durability of the power transmission member 10.

[0124] The silicon content of the power transmission member 10 is preferably 0.1 mass % or more and 0.4 mass % or less. When the silicon content is in this range, the durability of the power transmission member 10 can be improved.

[0125] The manganese content of the power transmission member 10 is preferably 0.3 mass % or more and 0.7 mass % or less. When the manganese content is in this range, the durability of the power transmission member 10 can be improved.

[0126] The remainder of the power transmission member 10, excluding the above components, is preferably iron.

[0127] The content of the above components contained in the power transmission member 10 can be measured by a method conforming to the provisions of JIS G 1201 (2022).

[0128] (Amount of retained austenite on the surface) The amount of retained austenite on the surface of the power transmission member 10 is preferably 18.5 vol% to 80 vol%, more preferably 19.5 vol% to 70 vol%, even more preferably 20 vol% to 65 vol%, and even more preferably 20 vol% to 60 vol%. Having the amount of retained austenite in this range can improve the durability of the power transmission member 10.

[0129] The amount of retained austenite on the surface is the larger of the amount of retained austenite measured on an unprocessed surface and the amount of retained austenite measured on a surface obtained by polishing to 40 μm using a polishing method that does not impart processing stress, such as electropolishing. The amount of retained austenite can also be measured by X-ray diffraction. The measurement device for the X-ray diffraction method may be the AutoMATE II micro-area X-ray stress measurement device manufactured by Rigaku Corporation. The measurement conditions may be a Cr tube, a tube voltage of 40 kV, a tube current of 40 mA, a collimator diameter of 2 mm, and an R value of 0.25371. Specifically, the amount of retained austenite can be measured based on the ratio of the integrated intensity of the X-ray diffraction peak of austenite at the measurement point to the integrated intensity of the X-ray diffraction peaks of other phases at the measurement point. For example, the amount of retained austenite may be determined as the ratio of the integrated intensity of the X-ray diffraction peak of austenite at the measurement point to the integrated intensity of the X-ray diffraction peaks of all iron phases at the measurement point. The measurement range for the amount of retained austenite may be within a diameter of 2 mm.

[0130] When the power transmission member 10 has a nickel content of 3% by mass or more and 5.5% by mass or less, a chromium content of 1% by mass or more and 3.5% by mass or less, and a molybdenum content of 0% by mass or more and 1.0% by mass or less, it is particularly preferable that the amount of retained austenite on the surface be 20% by volume or more and 80% by volume or less. By using such a composition, the amount of retained austenite on the surface can be appropriately increased, thereby improving the durability of the power transmission member 10. In this case, the contents of the components other than nickel, chromium, and molybdenum in the composition may be within the ranges described above, but it is more preferable that the vanadium content be 0% by mass or more and 0.3% by mass or less.

[0131] (Amount of retained austenite in the interior) The amount of retained austenite at a location 200 μm deep from the surface of the power transmission member 10 is preferably 20 vol% to 50 vol%, more preferably 22 vol% to 45 vol%, even more preferably 23 vol% to 40 vol%, and even more preferably 24 vol% to 35 vol%. Having the amount of retained austenite in this range can improve the durability of the power transmission member 10. The amount of retained austenite at a depth of 200 μm refers to the amount of retained austenite measured on a surface obtained by polishing the surface of the power transmission member 10 to a depth of 40 μm using a polishing method that does not apply processing stress by electropolishing. Other measurement conditions are the same as those for the method for measuring the amount of retained austenite on the surface.

[0132] The ratio of the amount of retained austenite on the surface to the amount of retained austenite at a depth of 200 μm from the surface of the power transmission member 10 is preferably 55% to 450%, more preferably 60% to 400%, even more preferably 65% ​​to 300%, and still more preferably 65% ​​to 250%. When the ratio of the amount of retained austenite on the surface to the interior is within this range, durability on the surface can be sufficiently ensured.

[0133] The amount of retained austenite described above is preferably a value in a state before the power transmission member 10 is used (i.e., the initial state after shipping from a factory, for example). In this example, the state before the power transmission member 10 is used may refer to a state before it is subjected to a torsional impact.

[0134] (Carbide) The power transmission member 10 contains carbide. The carbide here refers to a compound of carbon and metal, and examples thereof include iron carbide such as cementite, and chromium carbide.

[0135] (Location at a depth of 15 μm) In a unit area of ​​0.112 mm × 0.084 mm at a location 15 μm deep from the surface of the power transmission member 10, the ratio of the total area occupied by carbides in the unit area to the entire area of ​​the unit area is defined as the carbide distribution at the location at a depth of 15 μm. In this case, the carbide distribution at the location at a depth of 15 μm is preferably 0.05% to 6.50%, more preferably 0.05% to 1.0%, even more preferably 0.05% to 0.5%, still more preferably 0.05% to 0.3%, and even more preferably 0.19% to 0.21%. The total area occupied by carbides refers to the area occupied by one carbide when the unit area contains one carbide, and refers to the sum of the areas occupied by each carbide when the unit area contains multiple carbides. By setting the upper limit of the carbide distribution on the surface within this range, the amount of carbide can be reduced, thereby suppressing fracture originating from the carbides and improving the durability of the power transmission member 10. Furthermore, by setting the lower limit of the carbide distribution on the surface within this range, increasing brittleness can be suppressed, thereby suppressing brittle fracture of the power transmission member 10. The carbide distribution at a depth of 15 μm here may be the average value of the carbide distribution measured in a unit area at any four positions on a cross section at a depth of 15 μm. The measurement positions here are preferably, for example, positions 15 μm deep from the surface excluding hollow portions that are at angles of 80 degrees or more about a single axis in a cross section including a portion that receives at least one of a tensile load, a compressive load, a shear load, a bending load, and a torsional load associated with power transmission during power transmission. The measurement positions are preferably positions at a depth of 15 μm from the surface excluding hollow portions that are at angles of 80 degrees or more from each other about a single axis. The measurement positions are preferably positions at least 5 mm apart from each other, for example. Alternatively, the measurement positions may be, for example, the center of a surface that is a flat square area with a side of at least 5 mm or more, or the center position of a surface with the smallest curvature. The same applies to the following preferable measurement positions at a depth of 15 μm.

[0136] The area occupied by the carbides can be measured, for example, from an image of a unit area of ​​a target location (in this example, a location 15 μm deep from the surface) observed with a microscope. Furthermore, the area can be measured from an image of the etched cross section taken at a magnification of 1000 times with an optical microscope after selectively etching only the carbides in the cross section at a depth of 15 μm of the power transmission member 10. For example, the area occupied by the carbides can be measured by analyzing the captured image with image analysis software (ImageJ).

[0137] In a unit area of ​​0.112 mm x 0.084 mm at a depth of 15 μm from the surface of the power transmission member 10, the average grain size of carbides is preferably 0.1 μm to 1.2 μm, more preferably 0.1 μm to 1.0 μm, even more preferably 0.15 μm to 0.7 μm, even more preferably 0.2 μm to 0.55 μm, and even more preferably 0.4 μm to 0.45 μm. Having the average grain size of carbides on the surface within this range prevents the inclusion of carbides with large grain sizes, thereby suppressing fractures originating from carbides and improving the durability of the power transmission member 10. The average grain size of carbides at a depth of 15 μm may be the average value of the average grain sizes of carbides measured in a unit area at any four positions on a cross section at a depth of 15 μm.

[0138] The average grain size of the carbides can be measured, for example, from an image of a unit area of ​​a target location (in this example, a location 15 μm deep from the surface) observed with a microscope. Furthermore, the carbides alone are selectively etched in a cross section of the power transmission member 10 at a depth of 15 μm, and the etched cross section can be measured from an image captured at 1000x magnification with an optical microscope. For example, the average grain size of the carbides can be measured by analyzing the captured image with image analysis software (ImageJ). In this case, the diameter of a circle with the same area as the area of ​​the carbide shown in the image (i.e., the diameter equivalent to the projected area circle) is defined as the grain size of the carbide, and the average value of the grain sizes of the carbides shown in the image is defined as the average grain size.

[0139] In a unit area of ​​0.112 mm × 0.084 mm at a location 15 μm deep from the surface of the power transmission member 10, the number of carbides having a grain size of 0.1 μm or more is preferably 1,000 or less, more preferably 10 to 500, even more preferably 30 to 300, even more preferably 50 to 250, and even more preferably 120 to 150. By keeping the number of carbides of this size on the surface within this range, the inclusion of many carbides having a large grain size can be suppressed, thereby suppressing fracture originating from the carbides and improving the durability of the power transmission member 10. Note that the number of carbides having a grain size of 0.1 μm or more at a location 15 μm deep may be the average number of carbides having a grain size of 0.1 μm or more measured in a unit area at any four positions on a cross section 15 μm deep.

[0140] The carbide particles having a particle size of 0.1 μm or more are those having a particle size of 0.1 μm or more measured by the same method as the method for measuring the particle size of carbide described above in the description of the method for measuring the average particle size of carbide.

[0141] (Location at a depth of 6.25 mm) In a unit area of ​​0.112 mm × 0.084 mm at a location 6.25 mm deep from the surface of the power transmission member 10 (or, if there is no location 6.25 mm deep from the surface, at a location in the uncarburized portion 1 mm or deeper from the surface of the power transmission member 10), the ratio of the total area occupied by carbides in the unit area to the entire area of ​​the unit area is defined as the distribution of carbides within the power transmission member 10. In this case, the distribution of carbides within the power transmission member 10 is preferably 0.05% or more and 1.0% or less, more preferably 0.05% or more and 0.5% or less, even more preferably 0.05% or more and 0.2% or less, and even more preferably 0.10% or more and 0.13% or less. By setting the upper limit of the distribution of carbides within this range, the amount of carbides can be reduced, which can suppress fracture originating from carbides and improve the durability of the power transmission member 10. Furthermore, by setting the lower limit of the carbide distribution on the surface within this range, it is possible to suppress an increase in brittleness and thereby suppress brittle fracture of the power transmission member 10. The carbide distribution at a depth of 6.25 mm may be the average value of the carbide distribution measured in a unit area at any four positions on a cross section at a depth of 6.25 mm. The measurement positions are preferably, for example, positions at a depth of 6.25 mm from the surface excluding hollow portions that are at angles of 80 degrees or more about a common axis in a cross section including a portion subjected to at least one of tensile load, compressive load, shear load, bending load, and torsional load associated with power transmission (if no 6.25 mm deep position exists, positions at a depth of 1 mm or more of an uncarburized portion), and are preferably, for example, positions spaced apart by at least 5 mm. The preferred measurement positions at a depth of 6.25 mm may be the same as those described below.

[0142] In a unit area of ​​0.112 mm × 0.084 mm at a depth of 6.25 mm from the surface of the power transmission member 10, the average grain size of carbides is preferably 0.1 μm or more and 1.2 μm or less, more preferably 0.1 μm or more and 1.0 μm or less, even more preferably 0.15 μm or more and 0.7 μm or less, even more preferably 0.2 μm or more and 0.52 μm or less, and even more preferably 0.49 μm or more and 0.51 μm or less. By having the average grain size of carbides in the interior fall within this range, the inclusion of carbides with large grain sizes can be suppressed, thereby suppressing fracture originating from carbides and improving the durability of the power transmission member 10. Note that the average grain size of carbides at the 6.25 mm depth may be the average value of the average grain sizes of carbides measured in unit areas at any four positions on the cross section at a depth of 6.25 mm.

[0143] In a unit area of ​​0.112 mm × 0.084 mm at a location 6.25 mm deep from the surface of the power transmission member 10, the number of carbides having a grain size of 0.1 μm or more is preferably 300 or less, more preferably 10 to 200, even more preferably 20 to 100, even more preferably 30 to 70, and even more preferably 50 to 60. By keeping the number of carbides of this size within this range, the inclusion of many carbides having a large grain size can be suppressed, thereby suppressing fracture originating from the carbides and improving the durability of the power transmission member 10. Note that the number of carbides having a grain size of 0.1 μm or more at a location 6.25 mm deep may be the average number of carbides having a grain size of 0.1 μm or more measured in a unit area at any four positions on the cross section at a depth of 6.25 mm.

[0144] Furthermore, the ratio of the carbide distribution on the surface (unit area of ​​15 μm depth) of the power transmission member 10 is preferably greater than the ratio of the carbide distribution inside (unit area of ​​6.25 mm depth). The ratio of the carbide distribution on the surface (unit area of ​​15 μm depth) to the carbide distribution inside (unit area of ​​6.25 mm depth) of the power transmission member 10 is preferably 100% or more and 1000% or less, more preferably 130% or more and 600% or less, and even more preferably 150% or more and 400% or less. When the ratio of the carbide distribution on the surface to the inside is within this range, the amount of carbide on the surface can be reduced, thereby improving the durability of the power transmission member 10.

[0145] Furthermore, the average grain size of carbide on the surface (unit area of ​​15 μm depth) of the power transmission member 10 is preferably smaller than the average grain size of carbide inside (unit area of ​​6.25 mm depth). Furthermore, the ratio of the average grain size of carbide on the surface (unit area of ​​15 μm depth) to the average grain size of carbide inside (unit area of ​​6.25 mm depth) of the power transmission member 10 is preferably 40% or more and 150% or less, more preferably 50% or more and 100% or less, and even more preferably 60% or more and 90% or less. When the ratio of the average grain size of carbide on the surface to the interior is within this range, the inclusion of large carbide on the surface can be suppressed, thereby improving the durability of the power transmission member 10.

[0146] Furthermore, the number of carbides having a grain size of 0.1 μm or more on the surface (unit area at a depth of 15 μm) of the power transmission member 10 is preferably greater than the number of carbides having a grain size of 0.1 μm or more inside (unit area at a depth of 6.25 mm). The ratio of the number of carbides having a grain size of 0.1 μm or more on the surface (unit area at a depth of 15 μm) to the number of carbides having a grain size of 0.1 μm or more inside (unit area at a depth of 6.25 mm) of the power transmission member 10 is preferably 100% to 1000%, more preferably 150% to 600%, and even more preferably 200% to 400%. By ensuring that the ratio of the distribution of carbides on the surface to the inside falls within this range, the amount of carbides on the surface is prevented from becoming excessive, thereby improving the durability of the power transmission member 10.

[0147] (Prior Austenite Grain Boundary) The average grain size of the prior austenite grain boundary in a field of view that includes a location at a depth of 0.02 mm from the surface of the power transmission member 10 is preferably 8 μm or more and 100 μm or less, more preferably 9 μm or more and 70 μm or less, even more preferably 10 μm or more and 50 μm or less, and even more preferably 11 μm or more and 30 μm or less. Note that the field of view here conforms to the description of the counting method in JIS G 0551 (2013).

[0148] The unit grain area is the area of ​​the prior austenite grain boundary for each grain size in a unit region of 0.112 mm × 0.084 mm in a field of view that includes a location 0.02 mm deep from the surface of the power transmission member 10. That is, the prior austenite grain boundaries in the unit region are divided into grain sizes, and the total area of ​​the prior austenite grain boundaries divided into one grain size is defined as the unit grain area for that grain size, and the unit grain area is calculated for each grain size. Then, the unit grain area values ​​are arranged in order of grain size, and the grain size with the largest unit grain area is defined as the average grain size. Of three consecutive grain sizes including the average grain size, the three grain sizes with the largest total value of the unit grain area are defined as the average grain size group. That is, for example, if the average grain size (the grain size with the largest unit grain area) is 3, the three consecutive grain sizes are 1 to 3, 2 to 4, and 3 to 5. Of these, if the total unit grain area of ​​grain sizes 3 to 5 is the largest, the average grain size group is 3 to 5. In this case, the ratio of the total area (reference area) of the prior austenite grain boundaries assigned to the average grain size group to the entire area of ​​the prior austenite grain boundaries in that unit region is preferably 50% to 100%, more preferably 60% to 90%, even more preferably 65% ​​to 85%, and still more preferably 74% to 80%. Thus, the small variation in grain size of the prior austenite grain boundaries in the surface layer can improve the durability of the power transmission member 10. Here, the reference area may be the average value of the total area of ​​the prior austenite grain boundaries assigned to the average grain size group measured in a unit region at any four positions in a field of view including a point at a depth of 0.02 mm.

[0149] The grain size (grain size number) can be calculated based on JIS G 0551 (2013) and is an integer rounded off to one decimal place. The grain size of the prior austenite grain boundary can be measured using a coefficient method after revealing the austenite grain boundary using the Bechet-Beaujard method, which involves etching with a saturated aqueous solution of picric acid, based on JIS G 0551 (2013).

[0150] (Residual Stress) The initial residual stress on the surface of the power transmission member 10 is preferably −300 MPa or more and 200 MPa or less, more preferably −250 MPa or more and 100 MPa or less, even more preferably −200 MPa or more and 50 MPa or less, and even more preferably −180 MPa or more and 20 MPa or less. When the residual stress on the surface is within this range, compressive residual stress is imparted by operation without shot peening, thereby improving the durability of the power transmission member 10. Note that the initial residual stress refers to the residual stress in the state before the power transmission member 10 is used (i.e., for example, the state when it is first shipped from the factory), and in this example, it can also be said to be the residual stress in the state before it is subjected to a torsional impact. Note that the residual strain can be measured using an X-ray diffraction device.

[0151] (Hardness) The Vickers hardness at a depth of 0.1 mm from the surface of the power transmission member 10 is preferably 600 HV or more and 850 HV or less, more preferably 650 HV or more and 800 HV or less, and even more preferably 650 HV or more and 750 HV or less. Having a hardness within this range can improve the durability of the power transmission member 10. The Vickers hardness can be measured in accordance with JIS Z 2244, using a measurement load of 0.3 HV.

[0152] The Vickers hardness at a depth of 0.5 mm from the surface of the power transmission member 10 is preferably 600 HV to 800 HV, more preferably 620 HV to 750 HV, and even more preferably 630 HV to 720 HV. Having the hardness in this range can improve the durability of the power transmission member 10.

[0153] The ratio of the Vickers hardness at a location 0.5 mm deep from the surface of the power transmission member 10 to the Vickers hardness at a location 0.1 mm deep from the surface of the power transmission member 10 is preferably 79% to 110%, more preferably 80% to 105%, even more preferably 85% to 105%, still more preferably 90% to 100%, and even more preferably 92% to 100%. In this way, by preventing the internal hardness from becoming too small relative to the surface, the durability of the power transmission member 10 can be improved.

[0154] (Method of Manufacturing Power Transmission Member) The power transmission member 10 may be manufactured by any method. For example, in this embodiment, a base material for the power transmission member 10 is prepared. The base material is then carburized, quenched, and tempered to obtain the power transmission member 10. The type of base material and the heat treatment conditions, such as carburizing, quenching, or tempering, may be set appropriately so that the material properties of the power transmission member 10 satisfy the above description.

[0155] (Effect) After extensive research, the inventors have found that in a power transmission component containing 0.25 mass % or more of carbon and iron, durability can be appropriately improved by adjusting the amount of retained austenite to the above range. Furthermore, the inventors have found that sufficient retained austenite within the above range appropriately induces martensitic transformation when a load is applied to the power transmission component 10, thereby improving durability. Furthermore, the inventors have found that components used in power transmission components are prone to fracture originating from carbides. In contrast, by providing the power transmission component 10 according to the present embodiment with 0.25 mass % or more of carbon and iron and adjusting the carbide distribution at a depth of 15 μm to the above range, the amount of carbides can be reduced, suppressing fracture originating from carbides and more appropriately improving the durability of the power transmission component 10.

[0156] Examples Next, examples will be described. Table 1 shows the material properties and evaluation results of the power transmission members of each example. Tables 2 and 3 show the hardness measurement results of the power transmission members of each example. Fig. 7 is a graph showing the evaluation results of each example.

[0157]

[0158] Comparative Example 1 In Comparative Example 1, a cylindrical shaft member having a diameter of 18 mm and a length of 50 mm was prepared as a power transmission member. The power transmission member of Comparative Example 1 was an alloy steel containing carbon, nickel, chromium, molybdenum, and iron, and the carbon, nickel, chromium, molybdenum, and iron contents were as shown in Table 1. The contents of each component were measured using the method described in the above embodiment. For the power transmission member of Comparative Example 1, the amount of retained austenite was measured on the surface and in the interior (at a depth of 200 μm from the surface) using the method described in the above embodiment. The measurement results are shown in Table 1. For the power transmission member of Comparative Example 1, the carbide distribution, average grain size, and number of carbides with a grain size of 0.1 μm or more were measured at a depth of 15 μm from the surface and at a depth of 6.25 mm from the surface (interior) using the method described in the above embodiment. The measurement results are shown in Table 1. For the power transmission member of Comparative Example 1, the residual stress on the surface was measured using the method described in the above embodiment. The measurement results are shown in Table 1. For the power transmission member of Comparative Example 1, the average grain size and the reference area ratio of the prior austenite grain boundaries in a field of view including a location 0.02 mm deep from the surface were measured using the method described in the above embodiment. The measurement results are shown in Table 1. The hardness of the power transmission member of Comparative Example 1 was measured using the method described in the above embodiment. In addition, the ratio of the hardness at each depth from the surface to the hardness at a depth of 0.1 mm was calculated. The measurement results and calculation results are shown in Tables 2 and 3.

[0159] (Examples 1 and 2, Comparative Example 2) In Examples 1 and 2 and Comparative Example 2, power transmission members similar to those in Comparative Example 1 were prepared, except that the component contents, amount of retained austenite, average grain size and distribution of carbides, residual stress, average grain size of prior austenite grain boundaries, and hardness were set as shown in Table 1.

[0160] (Evaluation) A durability test was conducted on the power transmission members of each example. The number of times when damage was observed in the durability test is shown in Figure 7. In Figure 7, point P0 indicates the results of the durability test for Comparative Example 1, point P1 for Example 1, point P2 for Comparative Example 2, and point P3 for Example 2.

[0161] 7, the number of times breakage occurred was greater in each example than in the comparative example. Therefore, it is clear that durability can be appropriately improved by setting the amount of retained austenite on the surface to 18.5% by volume or more and 80% by volume or less, as in each example.

[0162] The technical scope of the present invention is not limited to the above-described embodiments, and appropriate modifications can be made without departing from the spirit of the present invention.

[0163] 1...impact tool, 2...housing, 3...cover, 4...hammer case, 6...motor, 7...reduction mechanism, 8...spindle, 9...impact mechanism, 10...power transmission member, 47...hammer, AX...rotating shaft

Claims

1. A power transmission component containing 0.25 mass% or more of carbon and iron, and having a surface with a retained austenite content of 18.5 volume% or more and 80 volume% or less.

2. A power transmission component according to claim 1, wherein the amount of retained austenite at a location 200 μm deep from the surface is 20% by volume or more and 50% by volume or less.

3. A power transmission component according to claim 1, wherein in a unit area of ​​0.112 mm x 0.084 mm at a depth of 15 μm from the surface, the ratio of the total area occupied by carbides to the entire area of ​​the unit area is 0.05% or more and 6.50% or less.

4. A power transmission component according to claim 1, wherein the average grain size of the prior austenite grain boundaries in a field of view including a point 0.02 mm deep from the surface is 8 μm or more and 100 μm or less.

5. A power transmission component according to claim 1, wherein the Vickers hardness at a location 0.1 mm deep from the surface is 600 HV or more and 850 HV or less, and the Vickers hardness at a location 0.5 mm deep from the surface is 600 HV or more and 800 HV or less.

6. The power transmission member according to claim 1, wherein the initial residual stress on the surface is -300 MPa or more and 200 MPa or less.

7. A power transmission component according to claim 1, further comprising 2.5% by mass or more and 4.5% by mass or less of nickel, 1.0% by mass or more and 4.0% by mass or less of chromium, and more than 0% by mass or more and 1.2% by mass or less of molybdenum.

8. The power transmission member according to claim 1, which is used in an environment where it is subjected to torsional impact.

9. A power transmission member according to any one of claims 1 to 8, which is used as an anvil for an impact tool.

10. An impact tool comprising: a motor; a hammer rotated by the motor; and a power transmission member according to any one of claims 1 to 8 serving as an anvil struck in the rotational direction by the hammer.

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