Mobile hardening method and mobile hardening device

Abstract

Provided is a mobile hardening method characterized in that a shaft body (10) is heated by a plurality of high-frequency coils (111), a cooling unit (120) is caused to follow the high-frequency coils (111) from behind in the relative moving direction of the high-frequency coils (111) along the axial direction of the shaft body (10), the part heated by the high-frequency coils (111) is cooled by the cooling unit (120), and mobile hardening is carried out while moving the high-frequency coils (111) toward the direction perpendicular to the axial direction of the shaft body (10) so that the distances from the surface of the shaft body (10) to the respective high-frequency coils (111) are constant, wherein the speed in the axial direction of the high-frequency coils (111) at the time when the high-frequency coils (111) pass through a step part (13) is slower than the speed in the axial direction of the high-frequency coils (111) at the time when the high-frequency coils (111) pass through a small diameter part (12) or a large diameter part (11).

Description

Moving hardening method and moving hardening device

[0001] The present invention relates to a moving hardening method and a moving hardening device.

[0002] Steel parts that are required to have a long life are often subjected to various surface treatments. In particular, induction hardening is widely used to improve the surface hardness, wear resistance, and fatigue resistance of the part surface. For this reason, various induction hardening devices have been proposed. For example, when induction hardening a long member such as a steel shaft-shaped body, so-called traverse hardening is performed. Traverse hardening is a hardening technique in which a high-frequency induction heating coil (also referred to as a high-frequency coil) and a cooling means are moved relative to the shaft-shaped body along the axial direction of the shaft-shaped body.

[0003] In traveling hardening, a shaft-shaped body is locally heated by a high-frequency coil until at least the surface layer of the shaft-shaped body becomes austenite phase. Next, a cooling means following the high-frequency coil sprays a cooling medium such as a coolant onto the surface of the heated shaft-shaped body to rapidly cool it in a short time, thereby turning the surface layer of the shaft-shaped body into a structure with the desired hardness, such as a martensite phase.

[0004] The outer diameter of a shaft-shaped body may not be constant along its axis (also referred to as the axial direction). That is, some shaft-shaped bodies have a small-diameter portion with a relatively small outer diameter and a large-diameter portion with a relatively large outer diameter along the axial direction of the body. Furthermore, these small-diameter and large-diameter portions are connected by a stepped portion whose outer diameter gradually changes along the axial direction. For example, in the technology disclosed in Patent Document 1 or Patent Document 2, a split coil is advanced and retreated in the radial direction of the shaft-shaped body, which is the heated body, to accommodate changes in the outer diameter of the shaft-shaped body.

[0005] However, while this variable-diameter coil method has the advantage of simplifying the equipment configuration, it is important to appropriately control the coil movement speed. The reason for this is as follows: To achieve uniform axial heating at the stepped portion of a shaft-shaped body, it is desirable to maintain a constant movement speed along the surface as much as possible when moving the coil along the radial direction of the axial cross section. If the axial movement speed of the coil is constant rather than along the surface, heating will concentrate at the corners of the step, and heating of the recessed portion of the step will be reduced. Attempting to suppress this drawback while maintaining a constant axial movement speed of the coil would require a larger current to heat the recessed portion of the step. This would result in insufficient heating due to limitations on the upper current limit, such as the cooling capacity of the coil. Specifically, the inventors discovered a problem with the conventional structure using a split coil, such as those disclosed in Patent Document 1 or Patent Document 2, in that the stepped portion connecting the small-diameter portion and the large-diameter portion and its vicinity, as described above, are not heated sufficiently to obtain the desired structure.

[0006] Japanese Patent Publication No. 2008-150640 Japanese Patent Publication No. 1983-10457

[0007] The present invention has been made in consideration of the above circumstances, and aims to provide a moving hardening method and a moving hardening device that can perform the desired hardening on a step portion and its vicinity in an axial body whose outer diameter is not constant in the axial direction.

[0008] (1) A traveling hardening method according to one aspect of the present invention is a traveling hardening method for hardening an axial body having a small diameter portion, a large diameter portion, and a step portion connecting the small diameter portion and the large diameter portion, using a traveling hardening device equipped with a plurality of high-frequency coils and a cooling unit, the method comprising the steps of: rotating the axial body inserted inside the plurality of high-frequency coils relative to the plurality of high-frequency coils and moving the plurality of high-frequency coils relative to the axial body in the axial direction, heating the axial body with the high-frequency coils; making the cooling unit follow the high-frequency coils from behind the relative movement direction of the high-frequency coils along the axial direction of the axial body, and cooling the areas heated by the high-frequency coils with the cooling unit; and performing traveling hardening while moving the high-frequency coils in a direction perpendicular to the axial direction of the axial body so that the distance from the surface of the axial body to each of the high-frequency coils is constant; (2) In the method for rolling hardening described in (1), the axial speed of the high frequency coil when it passes through the step portion is smaller than the axial speed of the high frequency coil when it passes through the small diameter portion or the large diameter portion. (2) In the rolling hardening method described in (1), the following formula 1 may be established, where V0 is the axial speed of the high frequency coil when it passes through the small diameter portion or the large diameter portion, Vs is the axial speed of the high frequency coil when it passes through the step portion, and Vc is the speed of the multiple high frequency coils in a direction perpendicular to the axial direction. V0 ２ ≦Vs ２ +Vc ２...Equation 1 (3) In the traveling hardening method described in (1) or (2), the distance between the high frequency coil and the cooling unit in the axial direction when the high frequency coil passes through the stepped portion may be smaller than the distance between the high frequency coil and the cooling unit in the axial direction when the high frequency coil passes through the small diameter portion or the large diameter portion. (4) In the traveling hardening method described in any one of (1) to (3), the cooling unit may inject a cooling medium, and the injection amount or injection pressure of the cooling medium when the high frequency coil passes through the stepped portion may be smaller than the injection amount or injection pressure of the cooling medium when the high frequency coil passes through the small diameter portion or the large diameter portion.

[0009] (5) A moving hardening device according to one aspect of the present invention is a moving hardening device for hardening an axial body having a small diameter portion, a large diameter portion, and a step portion connecting the small diameter portion and the large diameter portion in the axial direction, the moving hardening device comprising: a plurality of high frequency coils and a cooling portion in the axial direction; and a control portion capable of controlling movement of the plurality of high frequency coils and the cooling portion; each of the high frequency coils has a high frequency induction portion for heating the axial body and a conductive portion connected to the high frequency induction portion, and is movable relative to the axial body in the axial direction and relatively movable in a plane perpendicular to the axial direction; the cooling portion has an injection portion capable of injecting a cooling medium and is movable relative to the axial body in the axial direction; the control portion is capable of controlling movement of the high frequency coils in the plane so that a distance from the surface of the axial body to each of the high frequency coils is constant; (6) In the moving hardening device described in (5), the control unit may be capable of controlling the high frequency coil so that the axial speed of the high frequency coil when it passes through the step portion is V0, the axial speed of the high frequency coil when it passes through the small diameter portion or the large diameter portion is Vs, and the speed of the high frequency coils in a direction perpendicular to the axial direction is Vc. V0 ２ ≦Vs ２ +Vc ２...Equation 1 (7) In the traveling hardening device described in (5) or (6), the control unit may be capable of controlling the distance between the high frequency coil and the cooling unit in the axial direction when the high frequency coil passes through the stepped portion to be smaller than the distance between the high frequency coil and the cooling unit in the axial direction when the high frequency coil passes through the small diameter portion or the large diameter portion. (8) In the traveling hardening device described in any one of (5) to (7), the control unit may be capable of controlling the injection amount or the injection pressure of the cooling medium when the high frequency coil passes through the stepped portion to be smaller than the injection amount or the injection pressure of the cooling medium when the high frequency coil passes through the small diameter portion or the large diameter portion.

[0010] According to the traveling hardening method and traveling hardening device of the present invention, it is possible to perform desired hardening on a stepped portion and its vicinity in a shaft-shaped body whose outer diameter is not constant in the axial direction.

[0011] FIG. 1 is a partially cutaway side view of a moving hardening device according to an embodiment of the present invention; FIG. 2 is a cross-sectional view schematically showing a partial cross-section of a shaft-shaped body and two high-frequency coils when viewed from above in a direction along the axis of the shaft-shaped body, illustrating a state in which the high-frequency coil has been moved to match the outer diameter of a small-diameter portion; FIG. 3 is a cross-sectional view schematically showing a partial cross-section of a shaft-shaped body and two high-frequency coils when viewed from above in a direction along the axis of the shaft-shaped body, illustrating a state in which the high-frequency coil has been moved to match the outer diameter of a large-diameter portion; FIG. 4 is a cross-sectional view schematically showing a partial cross-section of a shaft-shaped body and three high-frequency coils when viewed from above in a direction along the axis of the shaft-shaped body, illustrating a state in which the high-frequency coil has been moved to match the outer diameter of a small-diameter portion; FIG. 5 is a cross-sectional view schematically showing a partial cross-section of a shaft-shaped body and three high-frequency coils when viewed from above in a direction along the axis of the shaft-shaped body, illustrating a state in which the high-frequency coil has been moved to match the outer diameter of a large-diameter portion; Fig. 1 is a schematic cross-sectional view of a shaft-shaped body and a high-frequency coil viewed in a plane passing through the axis of the shaft-shaped body; Fig. 2 is a cross-sectional view schematically showing a partial cross-section of the shaft-shaped body and one high-frequency coil when viewed in a plane along the axis of the shaft-shaped body, and is a view showing a state in which the high-frequency coil has moved to match the outer diameter of the small-diameter portion; Fig. 3 is a cross-sectional view schematically showing a partial cross-section of the shaft-shaped body and one high-frequency coil when viewed in a plane along the axis of the shaft-shaped body, and is a view showing a state in which the high-frequency coil has moved to match the outer diameter of the large-diameter portion; and Fig. 4 is a block diagram for explaining a moving hardening device of an embodiment of the present invention.

[0012] A moving hardening method and a moving hardening device according to an embodiment of the present invention will be described below with reference to Figures 1 to 10. It is obvious that the present invention is not limited to the following embodiment. It is also obvious that the elements of the following embodiment can be combined within the scope of the present invention.

[0013] As shown in Fig. 1, the traverse hardening apparatus 100 of this embodiment is an apparatus for performing traverse hardening on a shaft-shaped body 10 using a high-frequency current. Traverse hardening is a hardening technique in which a heating section equipped with a high-frequency induction heating coil (also referred to as a high-frequency coil) and a cooling section equipped with a cooling ring that follows the heating section are moved relative to the heated body. The heated body is, for example, a shaft-shaped body.

[0014] (Shaft-shaped body) The shaft-shaped body 10 includes a large diameter portion 11 (large diameter portions 11A and 11B) and a small diameter portion 12 provided between the large diameter portions 11A and 11B in the direction along the axis C. The large diameter portions 11A, 11B, and small diameter portions 12 are each formed in a cylindrical shape. The central axes of the large diameter portions 11A, 11B, and small diameter portions 12 are arranged to coincide with a common axis C. In this embodiment, the axis C is the central axis of the shaft-shaped body 10. Hereinafter, the portion arranged on one side D1 of the small diameter portion 12 in the direction along the axis C will also be referred to as the first large diameter portion 11A. The portion arranged on the other side D2 of the small diameter portion 12 in the direction along the axis C will also be referred to as the second large diameter portion 11B.

[0015] The first large diameter portion 11A, the small diameter portion 12, and the second large diameter portion 11B are each formed in a cylindrical shape and share a common central axis along the axis C. When viewed in a cross section perpendicular to the axis C of the large diameter portions 11A and 11B, the outer diameter of the small diameter portion 12 is smaller than the outer diameters of the large diameter portions 11A and 11B. In this embodiment, the outer diameters of the large diameter portions 11A and 11B are the same, but the outer diameters of the large diameter portions 11A and 11B may be different.

[0016] Between the large diameter portion 11A or 11B and the small diameter portion 12, there is a step portion 13 (step portion 13A and step portion 13B) that connects them. The step portion 13A and step portion 13B are inclined at a predetermined angle with respect to the axis C of the shaft-shaped body 10. The inclination angle is, for example, in the range of 15° to 90°. Note that, in a plane including the axis C of the shaft-shaped body 10, the outer diameter of the step portion 13 is not particularly limited, but may have a shape that smoothly connects the large diameter portion 11 and the small diameter portion 12, as exemplified in FIG. 1 . Within the moving hardening device 100 of this embodiment, the shaft-shaped body 10 is arranged so that the axis C is parallel to the up-down direction of the moving hardening device 100.

[0017] The shaft-shaped body 10 is formed of a conductive material, such as carbon steel or low-alloy steel containing 95% by weight or more of iron (Fe), which has a ferrite phase or pearlite phase. The shaft-shaped body may also be an axle for a railway vehicle. The number of large diameter portions 11, step portions 13, etc. provided on the shaft-shaped body 10 is not limited to the example shown in FIG. 1. The number of small diameter portions 12, large diameter portions 11, and step portions 13 may each be one, two, or three, or may be four or more. For example, the shaft-shaped body that is the target of the traveling hardening method and traveling hardening device of this embodiment may be a shaft-shaped body having one large diameter portion and one small diameter portion.

[0018] (Traveling Hardening Apparatus) The traveling hardening apparatus 100 includes a heating unit 110, a cooling unit 120, a support unit 130, a heating unit moving device 140, a cooling unit moving device 150, and a control unit 160. As shown in FIG. 1 , the heating unit 110 includes a plurality of high-frequency coils 111 (high-frequency coils 111A and 111B). The heating unit 110 is connected to the heating unit moving device 140, which serves as a moving means. The cooling unit 120 includes a cooling ring 121. The cooling unit 120 is connected to the cooling unit moving device 150, which serves as a moving means. The support unit 130 includes an upper center 131 and a lower center 132. The upper center 131 supports the first large diameter portion 11A of the shaft-shaped body 10 from above the first large diameter portion 11A. The lower center 132 supports the second large diameter portion 11B of the shaft-shaped body 10 from below the second large diameter portion 11B. The upper center 131 and the lower center 132 support the shaft-shaped body 10 so that one side D1 in the direction of the axis C is upward and the other side D2 is downward. The shaft-shaped body 10, while supported by the upper center 131 and the lower center 132, can rotate in the circumferential direction of the shaft-shaped body 10 about the axis C. The shaft-shaped body 10 can be rotated around its axis by a driving device (not shown) via the upper center 131 and the lower center 132 during moving hardening. Rotating the shaft-shaped body 10 around its axis means rotating the shaft-shaped body 10 in any direction circumferentially about the axis C of the shaft-shaped body 10. The line connecting the center of the upper center 131 and the center of the lower center 132 corresponds to the vertical direction (also referred to as the up-down direction) of the moving hardening device 100.

[0019] The heating unit moving device 140 supports the heating unit 110 and includes a support member 141 and a motor (not shown). The heating unit moving device 140 is attached to a rack member 180. The rack member 180 extends in the vertical direction. The support member 141 is provided with a pinion gear 141a, which meshes with a gear portion 180a of the rack member 180. When the motor is driven, the pinion gear 141a rotates, and the heating unit moving device 140 moves upward or downward relative to the rack member 180.

[0020] The cooling unit moving device 150 supports the cooling unit 120 and includes a support member 151 and a motor (not shown). The cooling unit moving device 150 is attached to a rack member 180. The support member 151 is provided with a pinion gear 151a, which meshes with a gear portion 180a of the rack member 180. When the motor is driven, the pinion gear 151a rotates, and the cooling unit moving device 150 moves upward or downward relative to the rack member 180.

[0021] The moving speeds of the heating unit moving device 140 and the cooling unit moving device 150 are independently controlled by the control unit 160. The heating unit moving device 140 supporting the heating unit 110 and the cooling unit moving device 150 supporting the cooling unit 120 move in the vertical direction, thereby performing moving hardening in the axial direction of the shaft-shaped body 10. In other words, the vertical direction of the moving hardening device 100 can be said to be the direction in which moving hardening is performed.

[0022] While Figure 1 shows an example in which a rack and pinion gear is used as the mechanism for moving the heating unit 110 and the cooling unit 120 in the vertical direction, the moving mechanism of the present invention is not limited to this and may be any mechanism that can move the heating unit 110 and the cooling unit 120 in the vertical direction relative to the shaft-shaped body 10. Also, while Figure 1 shows an example in which the heating unit 110 and the cooling unit 120 move relative to the fixed shaft-shaped body 10, the traveling hardening method and traveling hardening device of the present invention are not limited to this configuration and the heating unit 110 and the cooling unit 120 may be fixed and the shaft-shaped body 10 may move relative to the heating unit 110 and the cooling unit 120. Also, while Figure 1 assumes an example in which the axial direction of the shaft-shaped body 10 is oriented vertically, the traveling hardening method and traveling hardening device of the present invention are not limited to this configuration and the axial direction of the shaft-shaped body 10 may be oriented horizontally or inclined relative to the vertical direction.

[0023] (Heating Unit) The heating unit 110 of this embodiment includes multiple high-frequency coils. FIG. 2 shows a schematic plan view of the high-frequency coils 111A and 111B included in the heating unit 110 and the shaft-shaped body 10, as viewed from the A-A direction in FIG. 1 (a direction parallel to the axial direction) along the axis C. In FIG. 2, the shaft-shaped body 10 is shown broken away in the middle of the small-diameter portion 12. As shown in FIG. 2, the high-frequency coils 111A and 111B included in the heating unit 110 have high-frequency induction portions 112A and 112B that are C-shaped and partially surround the shaft-shaped body 10 in a plan view viewed along the axis C of the shaft-shaped body 10. The high-frequency induction portion 112A is connected at its end to conductive portions 113a and 113b. Similarly, the high-frequency induction portion 112B is connected at its end to conductive portions 113c and 113d.

[0024] The high-frequency coils 111A and 111B are arranged side by side and spaced apart from each other in the circumferential direction (also referred to as the circumferential direction) centered on the axis C of the shaft-shaped body 10. This circumferential direction is parallel to the direction in which the high-frequency induction portion 112A of the high-frequency coil 111A and the high-frequency induction portion 112B of the high-frequency coil 111B extend. In other words, the plane (also referred to as the horizontal plane) in which the high-frequency induction portion 112A and the high-frequency induction portion 112B extend is perpendicular to the up-down direction of the moving hardening device 100. In addition, the horizontal plane is perpendicular to the axial direction of the shaft-shaped body 10.

[0025] In the above-described horizontal plane, the high-frequency induction portion 112A of the high-frequency coil 111A and the high-frequency induction portion 112B of the high-frequency coil 111B may have an arc shape as shown in Fig. 2. The arc shape of the high-frequency induction portion 112A and the high-frequency induction portion 112B has the advantage that the high-frequency coil 111 and the shaft-shaped body 10 are generally uniformly close to each other in the circumferential direction.

[0026] When the high-frequency induction section 112A and the high-frequency induction section 112B have an arc-shaped shape, it is preferable that the diameter of the inscribed circle on the above-mentioned horizontal plane that contacts each inner surface (the surface on the axial body 10 side) of the high-frequency induction section 112A and the high-frequency induction section 112B facing the axis C is larger than the outer diameter of the small diameter section 12 of the axial body 10 and smaller than the outer diameter of the large diameter section 11.

[0027] Alternatively, one or both of the high-frequency induction portion 112A and the high-frequency induction portion 112B may form part of an ellipse in the horizontal plane, or may have a shape composed of a plurality of straight lines. Furthermore, the high-frequency coils 111A and 111B may be shaped such that a portion of the high-frequency coil 111A and a portion of the high-frequency coil 111B overlap in the axial direction of the shaft-shaped body 10. For example, the conductive portion 113a and the conductive portion 113b in FIG. 2 may be located closer to the high-frequency induction portion 112B than the conductive portion 113d and the conductive portion 113c, respectively. In this case, the high-frequency coils 111A and 111B are disposed at different positions in the axial direction.

[0028] Each of the conductive portions 113a, 113b, 113c, and 113d extends from each end of the high-frequency induction portion 112A or 112B in a direction away from the shaft-shaped body 10. It is more preferable that each of the conductive portions 113a, 113b, 113c, and 113d extends in a direction perpendicular to the axis C of the shaft-shaped body 10 at a position where the high-frequency coil 111A and the high-frequency coil 111B are closest to each other.

[0029] Each of the high-frequency coils 111A and 111B can be moved in a direction away from or toward the shaft-shaped body 10. Fig. 2 shows a state in which the high-frequency coils 111A and 111B are closest to the small diameter portion 12 of the shaft-shaped body 10. It is preferable to heat the small diameter portion 12 in this state.

[0030] On the other hand, Figure 3 shows a state in which high-frequency coils 111A and 111B move in a direction away from shaft-shaped body 10 (direction P in Figure 3) to match the outer diameter of large-diameter portion 11B and surround large-diameter portion 11B of shaft-shaped body 10. It is preferable to heat large-diameter portion 11 in this state. In the state of Figure 3, high-frequency coils 111A and 111B move in the direction of axis C of shaft-shaped body 10, and high-frequency coils 111A and 111B are at the position of large-diameter portion 11 in the axial direction.

[0031] The conductive portions 113a and 113b of the high frequency coil 111A are connected to a power source (not shown), and when a high frequency current is supplied from the power source to the high frequency induction portion 112A, an induced current is generated in the shaft-shaped body 10, and Joule heat is generated in the shaft-shaped body 10 due to the electrical resistance of the shaft-shaped body 10. The same applies to the high frequency coil 111B. For example, current flows in the high frequency coils 111A and 111B in the direction of arrow i shown in Figure 2, etc. In the multiple high frequency coils 111, current flows in the same direction in the circumferential direction.

[0032] Each of the high frequency coils 111A and 111B may be connected to the heating unit 110 via a coil moving unit (not shown). The coil moving unit includes a drive motor and a stage, and is configured to move each of the high frequency coils 111A and 111B in a direction perpendicular to the axis C of the shaft-shaped body 10, i.e., on a horizontal plane. The movement of the high frequency coils 111A and 111B on the horizontal plane is controlled by the control unit 160. The power source may be fixed to the heating unit 110, or may move together with the high frequency coil 111 by the coil moving unit.

[0033] The number of the multiple high-frequency coils 111 provided in the moving hardening device 100 is preferably two, from the viewpoint of enabling the continuous circumferential length of the adjacent portion between the high-frequency coil 111 and the shaft-shaped body 10 to be the longest. Furthermore, from the viewpoint of preventing the gap between the high-frequency coil 111 and the shaft-shaped body 10 from widening excessively even when the spacing between the multiple high-frequency coils 111 is narrowed or widened in response to changes in the diameter of the shaft-shaped body 10 while increasing the length of the adjacent portion, a number of three is preferred, as shown in FIGS. 4 and 5 . When three high-frequency coils 211 (high-frequency coils 211A, 211B, and 211C) as shown in FIGS. 4 and 5 are employed, a configuration similar to that using two high-frequency coils 111 and a heating unit 110 described above can be employed. The multiple high-frequency coils 111 are disposed spaced apart from each other in a horizontal plane. It is preferable that each of the multiple high-frequency coils 111 is movable in a direction perpendicular to the axis C of the shaft-shaped body 10 to be subjected to moving hardening.

[0034] The cross section of each part of the high-frequency coil 111 in the extension direction may be rectangular, elliptical, or circular, as shown in FIG. 1 . The interior of the high-frequency coil 111 may be hollow, through which a refrigerant for cooling flows. The high-frequency coil 111 is preferably formed of a material such as copper, because it is nonmagnetic, unlikely to cause eddy current loss, has low electrical resistance, and is unlikely to cause Joule loss. The surface of the high-frequency coil 111 may be covered with a heat-resistant, highly insulating material such as bakelite or silicon, to prevent short circuits between the high-frequency coils 111 or between the high-frequency coils 111 and the shaft-shaped body 10 when they come into contact with each other.

[0035] The high frequency coil 111 may be connected to the heating unit 110 via a support member (not shown) at each of the conductive portions 113a, 113b, 113c, and 113d, for example.

[0036] (Cooling section) The cooling section 120 is disposed behind the heating section 110 in the relative movement direction. The relative movement direction means the direction in which the heating section 110 moves axially relative to the shaft-shaped body 10 during moving hardening. In the case of this embodiment, the heating section 110 performs moving hardening while moving in the direction D1 in Fig. 1, so the cooling section 120 is disposed below the heating section 110, as shown in Fig. 1. Fig. 6 illustrates an example of the positional relationship between the heating section 110 and the cooling section 120 with respect to the shaft-shaped body 10 in this embodiment.

[0037] In this embodiment, the cooling section 120 is formed in an annular shape. The cooling section 120 has an internal space through which the shaft-shaped body 10 can be inserted. A plurality of injection nozzles 122 serving as injection sections are formed at intervals in the circumferential direction on an inner peripheral surface 121a of the cooling section 120 that faces the internal space of the cooling ring 121. The injection nozzles 122 are capable of injecting a cooling medium toward the internal space. The shape of the cooling section 120 is not limited to the annular shape shown in FIG. 6 , and may be circular, elliptical, rectangular, or the like in a horizontal plane perpendicular to the up-down direction.

[0038] A pump (not shown) is connected to the cooling unit 120. The pump supplies a cooling medium cl to the cooling unit 120. The cooling medium cl supplied to the cooling ring 121 of the cooling unit 120 is sprayed toward the shaft-shaped body 10 through a plurality of spray nozzles 122 to cool the shaft-shaped body 10. The cooling medium cl is, for example, water, oil, or an aqueous solution similar to oil. The amount of the cooling medium cl sprayed can be adjusted by controlling the pump using the control unit 160, for example.

[0039] Figure 7 shows a schematic cross-sectional view of the shaft-shaped body 10 and the high-frequency coil 111 taken along a plane passing through the axis of the shaft-shaped body 10. The X coordinate axis in Figure 7 is perpendicular to the axis C of the shaft-shaped body 10 and perpendicular to the Z and Y coordinate axes. The Y coordinate axis is oriented perpendicular to the plane of the paper in Figure 7 and is perpendicular to the X and Z coordinate axes. The Z coordinate axis is parallel to the axis C (the vertical direction of the moving hardening device 100), and the positive direction of the Z coordinate coincides with the direction D1.

[0040] If the coil is controlled to move at a constant speed along the surface of the stepped portion and the cooling ring is made to follow the coil, the speed of the cooling ring will decrease significantly as it moves along the curved portion of the stepped portion. This will result in uneven cooling in the axial direction of the heated object. In the moving hardening device 100 of this embodiment, control is performed to maintain a constant distance from the surface of the shaft-shaped body 10 to the high-frequency coils 111A and 111B. The distance from the surface of the shaft-shaped body 10 to the high-frequency coils 111A and 111B is defined as the shortest distance between the surface of the shaft-shaped body 10 and the surface of the high-frequency coil 111. Eddy currents generated in the shaft-shaped body 10, which is the heated object, due to the current flowing through the high-frequency coil 111 vary significantly depending on the distance between the high-frequency coil 111 and the heated object. However, by maintaining this distance constant to prevent this change, the magnitude of the eddy currents will remain constant, and heating will also be maintained constant. 7 is a line drawn in a plane passing through the axis of the shaft-shaped body 10 so that the distance from the surface of the shaft-shaped body 10 in a direction perpendicular to the surface of the shaft-shaped body 10 is constant. The part of the high-frequency coil 111 that is closest to the shaft-shaped body 10 moves on this imaginary line m.

[0041] Here, Vz represents the Z-coordinate component of the relative movement speed of the high frequency coil 111 with respect to the shaft-shaped body 10, and Vx represents the X-coordinate component of the relative movement speed of the high frequency coil 111 with respect to the shaft-shaped body 10. Vz corresponds to the relative movement speed of the high frequency coil 111 with respect to the shaft-shaped body 10 in the axial direction. Vx corresponds to the relative movement speed of the high frequency coil 111 with respect to the shaft-shaped body 10 in a direction perpendicular to the axis C of the shaft-shaped body 10.

[0042] In this case, in the moving hardening device of this embodiment, when the high frequency coil 111 passes through the large diameter portion 11 or the small diameter portion 12, the high frequency coil 111 moves in the axial direction and does not move in a direction perpendicular to the axis C, so Vx is 0. Therefore, the moving speed V0 of the high frequency coil 111 along the imaginary line m when the high frequency coil 111 passes through the large diameter portion 11 or the small diameter portion 12 is equal to the speed V0z of the Z coordinate component.

[0043] On the other hand, when the high frequency coil 111 passes through the step portion 13, the high frequency coil 111 moves in the axial direction and also in a direction perpendicular to the axis C. Therefore, the moving speed V1 of the high frequency coil 111 along the imaginary line m when the high frequency coil 111 passes through the step portion 13 satisfies the relationship of the following formula A. V1 ２ = V1x ２ +V1z ２ Here, V1x is the velocity of the X-coordinate component when the high-frequency coil 111 passes through the step portion 13, and V1z is the velocity of the Z-coordinate component when the high-frequency coil 111 passes through the step portion 13.

[0044] In the moving hardening device 100 of this embodiment, it is desirable that the moving speed of the high frequency coil 111 along the imaginary line m when the high frequency coil 111 passes through the large diameter portion 11, the small diameter portion 12, and the stepped portion 13 be as constant as possible. In other words, the high frequency coil 111 moves so as to satisfy the relationship V0 = V1. Here, the following formula B is derived from the relationships V0 = V0z and V0 ≦ V1 and formula A. V0z ２ ≦V1x ２ +V1z ２ ...Formula B

[0045] In controlling the moving hardening device 100, it is desirable to satisfy the relationship V0 = V1, but there are cases where V0 = V1 cannot be satisfied due to various constraints, such as the response performance of an actuator such as a motor for moving the moving device and the response performance when changing the flow rate of the cooling medium Cl sprayed by the cooling unit 120, and even under these constraints, it is desirable to get as close to V0 = V1 as possible. The surface of the heated body is heated by eddy currents generated in the shaft-shaped body 10, which is the heated body, due to the current flowing through the high-frequency coil 111, but by keeping the moving distance per unit time constant as described above, the heat generation energy per unit time on the surface unit length of the shaft-shaped body 10 is also constant.

[0046] As is clear from equation B, the moving speed V1z of the high frequency coil 111 in the axial direction when it passes through the step portion 13 is smaller than the moving speed V0z of the high frequency coil 111 in the axial direction when it passes through the large diameter portion 11 or the small diameter portion 12. With this configuration, the moving hardening device 100 of this embodiment can perform desired hardening on the step portion and its vicinity in a shaft-shaped body whose outer diameter is not constant in the axial direction.

[0047] That is, in the moving hardening device 100 of this embodiment, when the axial speed of the high frequency coil 111 when the high frequency coil 111 passes through the step portion 13 is Vs and the speed of the high frequency coil 111 in a direction perpendicular to the axial direction is Vc, it is more preferable that the moving speed of the high frequency coil 111 be controlled so that the following formula 1 is satisfied: V0 ２ ≦Vs ２ +Vc ２ ...Equation 1 Vs is the same as V1z above, and Vc is the same as V1x above.

[0048] As shown in FIG. 8 , the distance from the surface of the shaft-shaped body 10 to the high-frequency coil 111A and the high-frequency coil 111B is defined as the average distance from the surface of the shaft-shaped body 10 to the high-frequency induction portion 112 of the high-frequency coil 111 in a direction perpendicular to the surface of the shaft-shaped body 10 in a horizontal plane. For example, in the example of FIG. 8 , the distance d from the surface of the shaft-shaped body 10 at the small-diameter portion 12 to the high-frequency induction portion 112 of the high-frequency coil 111 is constant in the circumferential direction. On the other hand, in the example of FIG. 9 , the distance from the surface of the shaft-shaped body 10 at the large-diameter portion 11 to the high-frequency induction portion 112 of the high-frequency coil 111 is not constant in the circumferential direction. In this case, the arithmetic mean value of the shortest and longest points from the surface of the shaft-shaped body 10 to the high-frequency induction portion 112 of the high-frequency coil 111 is used. For the sake of explanation, only one high-frequency coil 111A is shown in FIG. 8 or 9 . It is preferable that the multiple high-frequency coils 111 move at the same speed in the horizontal plane.

[0049] Generally, if cooling after heating for hardening is delayed, a portion of the hardened portion may undergo pearlite transformation, resulting in insufficient hardening. Even if cooling after heating is performed quickly, the grain size of the crystals in the hardened portion or the volume fraction of retained austenite may change depending on the time from heating to cooling, resulting in changes in the hardness and mechanical properties of the hardened material. However, the traveling hardening device 100 of this embodiment can suppress such changes in the hardness and mechanical properties of the hardened material by adopting the following configuration.

[0050] In the traveling hardening device 100 of this embodiment, it is more preferable to control the axial distance between the high-frequency coil 111 and the cooling unit 120 when the high-frequency coil 111 passes through the stepped portion 13 so that it is smaller than the axial distance between the high-frequency coil 111 and the cooling unit 120 when the high-frequency coil 111 passes through the large-diameter portion 11 or the small-diameter portion 12. This configuration makes the time from heating to the start of cooling nearly constant, suppressing changes in grain size and volume fraction of retained austenite, thereby maintaining constant the hardness and mechanical properties of the material. Another advantage is that the traveling speed of the cooling unit 120 becomes nearly constant, and the cooling capacity also becomes nearly constant. Specifically, in this operation, it is preferable to control the axial position of the cooling unit 120 so that the end (the front end) of the cooling unit 120 passes the axial position where the end (the rear end) of the high-frequency coil 111 passed after a certain time. As a result of this operation, the axial distance between the high-frequency coil 111 and the cooling unit 120 is smaller when the axial movement speed of the high-frequency coil 111 is slow than when the axial movement speed of the high-frequency coil 111 is fast.

[0051] 1, the distance between the high frequency coil 111 and the cooling section 120 in the axial direction is the distance from the lower end of the high frequency coil 111 to the upper end of the cooling section 120 in the vertical direction of the moving hardening device 100. In other words, the lower end of the high frequency coil 111 is the end at the rear in the moving direction, and the upper end of the cooling section 120 is the end at the front in the moving direction.

[0052] In the moving quenching device 100 of this embodiment, it is more preferable to control the amount of cooling medium cl injected when the high-frequency coil 111 passes through the step portion 13 so that it is less than the amount of cooling medium Cl injected when the high-frequency coil 111 passes through the large-diameter portion 11 or the small-diameter portion 12. As a cooling mode, it is preferable to control the cooling capacity by adjusting the amount or pressure of the cooling medium Cl so that the cooling rate on the CCT curve is kept within a range in which no change in hardness occurs. More specifically, when the axial moving speed of the high-frequency coil 111 is fast, the amount of cooling medium Cl injected is increased or the pressure of the cooling medium Cl is increased, and when the axial moving speed of the heating coil is slow, the amount of cooling medium Cl injected is decreased or the pressure of the cooling medium Cl is decreased. The relationship between the heat transfer coefficient h and the amount of injected water (water volume density) W is shown to be proportional to the nth power of W (n is a constant determined by the water cooling conditions) (Mitsuzuka: Cooling Technology for High-Temperature Steel, Iron and Steel, Vol. 79, No. 6, pp. N405-N416 (1993)). Here, if the moving speed of the cooling part 120 is fast, the cooling capacity per unit time drops in inverse proportion to the speed. Therefore, W is set so that the heat transfer coefficient h increases by the rate of increase in speed. ｎ In this way, the cooling capacity can be kept constant regardless of the moving speed of the cooling unit 120, and the cooling speed of the object to be heated can be kept within a desired range.

[0053] FIG. 10 shows a block diagram of the moving hardening device 100 of this embodiment. In the example of this embodiment, the control unit 160 controls the axial movement of the heating unit moving device 140 and the cooling unit moving device 150, the movement of the high-frequency coil 111 in the horizontal plane, and the amount of cooling medium Cl injected by the pump provided in the cooling unit 120. However, the moving hardening device 100 may be configured to include multiple control units, each controlling the movement and the amount of cooling medium injected. For example, the moving hardening device 100 may be configured to include a coil position control unit that can independently change the axial movement speed Vz of the high-frequency coil 111 of the shaft-shaped body 10 and the direction Vx perpendicular to the axis C. Furthermore, the moving hardening device 100 may be configured to independently control the axial movement speed of the cooling unit 120 by the cooling unit moving device 150, independently of the movement speed of the heating unit 110 by the heating unit moving device 140.

[0054] Next, a method of performing rolling hardening on the shaft-shaped body 10 using the rolling hardening device 100 of this embodiment will be described.

[0055] First, as shown in FIG. 1 , the heating unit 110 and the cooling unit 120 are positioned at the lower end of the shaft-shaped body 10. Next, a high-frequency current is passed through the high-frequency coil 111. The pump is also driven to eject the cooling medium cl from the multiple injection nozzles 122 of the cooling unit 120. Next, the shaft-shaped body 10 is rotated by the support unit 130. Then, the motor is driven to move the heating unit moving device 140 and the cooling unit moving device 150 upward relative to the rack member 180. As a result, the heating unit 110 and the cooling unit 120 are extrapolated in order relative to the shaft-shaped body 10 and move upward.

[0056] In the heating section 110, a high-frequency current supplied to the high-frequency coil 111 generates an induced current on the surface of the shaft-shaped body 10, and Joule heat is generated due to the electrical resistance of the shaft-shaped body 10, heating the surface layer of the shaft-shaped body 10 to the austenite phase formation region.

[0057] Next, the cooling part 120 rises to the location heated by the heating part 110, and a cooling medium cl is sprayed onto the heated location of the shaft-shaped body 10. As a result, at least the surface layer of the shaft-shaped body 10 is rapidly cooled to generate a martensite structure. As the heating part 110 and the cooling part 120 rise from the lower end to the upper end of the shaft-shaped body 10, heating by the heating part 110 and cooling by the cooling part 120 are performed sequentially, and the surface of the shaft-shaped body 10 is induction hardened.

[0058] In the traveling hardening method of this embodiment, the high frequency coil 111 is moved in a direction perpendicular to the axial direction of the shaft-shaped body 10 so that the distance from the surface of the shaft-shaped body 10 to each high frequency coil 111 is constant, and the axial speed of the high frequency coil 111 when it passes through the step portion 13 is smaller than the axial speed of the high frequency coil 111 when it passes through the small diameter portion 12 or the large diameter portion 11. This makes it possible to perform the desired hardening on the step portion 13 and its vicinity in the shaft-shaped body 10, whose outer diameter is not constant in the axial direction.

[0059] The present invention includes the use of a traveling hardening device for hardening an axial body having a small diameter portion, a large diameter portion, and a step portion connecting the small diameter portion and the large diameter portion in the axial direction, the traveling hardening device comprising a plurality of high frequency coils and a cooling portion in the axial direction, and a control portion capable of controlling the movement of the plurality of high frequency coils and the cooling portion, each high frequency coil having a high frequency induction portion for heating the axial body and a conductive portion connected to the high frequency induction portion, and being movable relative to the axial direction with respect to the axial body and also movable relative to the axial direction in a plane perpendicular to the axial direction, the cooling portion having an injection portion capable of injecting a cooling medium and being movable relative to the axial direction with respect to the axial body, the control portion being capable of controlling the movement of the high frequency coil in the plane so that the distance from the surface of the axial body to each high frequency coil is constant, and being capable of controlling the axial speed of the high frequency coil when it passes through the step portion to be smaller than the axial speed of the high frequency coil when it passes through the small diameter portion or the large diameter portion.

[0060] In using the above-described moving hardening device, the control unit may be capable of controlling the high frequency coil so that the following formula 1 holds, where V0 is the axial speed of the high frequency coil when it passes through the small diameter portion or the large diameter portion, Vs is the axial speed of the high frequency coil when it passes through the step portion, and Vc is the speed of the multiple high frequency coils in a direction perpendicular to the axial direction. ２ ≦Vs ２ +Vc ２ ...Equation 1 When using the above-mentioned traveling hardening device, the control unit may be capable of controlling the distance in the axial direction between the high frequency coil and the cooling unit when the high frequency coil passes through the stepped portion to be smaller than the distance in the axial direction between the high frequency coil and the cooling unit when the high frequency coil passes through the small diameter portion or the large diameter portion. When using the above-mentioned traveling hardening device, the control unit may be capable of controlling the injection amount or injection pressure of the cooling medium when the high frequency coil passes through the stepped portion to be smaller than the injection amount or injection pressure of the cooling medium when the high frequency coil passes through the small diameter portion or the large diameter portion.

[0061] [Experimental Example 1] A numerical simulation analysis was performed to verify the heating state of a stepped portion when rolling hardening was performed on a shaft-shaped body having a small diameter portion, a large diameter portion, and a stepped portion connecting the small diameter portion and the large diameter portion in the axial direction using a rolling hardening device equipped with multiple high-frequency coils. In this experimental example, the shaft-shaped body was made of carbon steel, and the outer diameter of the small diameter portion was 170 mm and the outer diameter of the large diameter portion was 200 mm. The number of high-frequency coils was four.

[0062] In this experimental example, the moving speed of the high-frequency coil in the axial direction of the shaft-shaped body and in the direction perpendicular to the axial direction was controlled when the high-frequency coil was passed through the large-diameter section, the step section, and the small-diameter section in that order, thereby maintaining a constant distance from the surface of the shaft-shaped body. Furthermore, the moving speed of the high-frequency coil was controlled so that the axial speed of the high-frequency coil when passing through the step section was smaller than the axial speed of the high-frequency coil when passing through the large-diameter section or the small-diameter section. Specifically, as shown in Table 1 below, the moving speed (feed rate) of the high-frequency coil was constant. Therefore, the axial speed of the high-frequency coil was slower when passing through the step section than when passing through the large-diameter section or the small-diameter section. The times 59 to 74 seconds and 105 to 121 seconds represent the time it took to pass through the step section. The moving speed of the cooling section was the same as the axial speed of the high-frequency coil.

[0063]

[0064] The temperature of the surface of the shaft-shaped body at the boundary between the large diameter portion and the step portion was 1176° C. The depth from the surface of the region at this location that was heated to 800° C. or higher was 5 mm.

[0065] [Experimental Example 2] Analysis was performed using the same numerical simulation as in Experimental Example 1. In this experimental example, the same axial body and high-frequency coil as in Experimental Example 1 were used. As in Experimental Example 1, the distance of the high-frequency coil from the surface of the axial body was kept constant by controlling the moving speed of the high-frequency coil in the axial direction of the axial body and in a direction perpendicular to the axial direction.

[0066] In this experimental example, the high-frequency coil was controlled to move at a constant speed in the axial direction. Therefore, as shown in Table 2 below, the moving speed (feed speed) of the high-frequency coil varied between the large-diameter section or small-diameter section and the stepped section. The moving speed of the cooling section was the same as the axial speed of the high-frequency coil. The times from 36 seconds to 43.4 seconds and from 64.1 seconds to 71.95 seconds were the times for passing through the stepped section.

[0067]

[0068] The temperature of the surface of the shaft-shaped body at the boundary between the large diameter portion and the step portion was 1287° C. The depth from the surface of the region at this location that was heated to 800° C. or higher was 4 mm.

[0069] From the above results, in Experimental Example 1, an appropriate heating temperature was obtained on the surface of the stepped portion of the shaft-shaped body, and the hardening depth at which the specified temperature was reached was also sufficient. Furthermore, as can be seen from Tables 1 and 2, in Experimental Example 2, the current amplitude value applied to the high-frequency coil must be increased around the stepped portion in order to achieve the above heating temperature. On the other hand, in Experimental Example 1, the desired hardening temperature and hardening depth were obtained while suppressing the increase in the current amplitude value.

[0070] In this experimental example, a numerical simulation analysis was performed to verify the hardening state when a moving hardening process was performed on a cylindrical shaft-shaped body made of carbon steel and having a fixed outer diameter (170 mm) using a moving hardening device equipped with multiple high-frequency coils. The shape of the high-frequency induction part of the high-frequency coil was set to follow the outer diameter of the shaft-shaped body, and the number of high-frequency coils was three.

[0071] As shown below, the hardness distribution of the shaft-shaped body was calculated when the cooling capacity of the cooling unit, the distance between the high-frequency coil and the cooling unit, and the moving speed of the high-frequency coil and the cooling unit were changed, and the surface hardness and hardening depth were evaluated. The surface hardness and hardening depth were evaluated by determining the temperature distribution of the shaft-shaped body using magnetic field analysis and heat transfer analysis, estimating the phase transformation from the time-series transition of the temperature distribution at each part of the shaft-shaped body, and then calculating the hardness after cooling. Tables 3 and 4 show the surface hardness ratio when the hardness at a martensite fraction of 90% is set to 1, and Tables 5 and 6 show the thickness (mm, hardening depth) from the surface in the range where the hardness is 70% or more martensite fraction. The cooling capacity of the cooling unit in the tables refers to the convective heat transfer coefficient of the shaft-shaped body surface. The distance between the high-frequency coil and the cooling unit was as specified in the above embodiment. Furthermore, the high-frequency coil and the cooling unit moved in the axial direction of the shaft-shaped body at the same speed shown in the tables.

[0072]

[0073]

[0074]

[0075]

[0076] As can be seen from the results in Tables 3 and 4, the hardness due to quenching tends to decrease as the moving speed of the high-frequency coil and the cooling unit decreases. On the other hand, the decrease in hardness can be suppressed by shortening the distance between the high-frequency coil and the cooling unit. This shows that, when the shaft-shaped body has a step portion and the axial speed of the high-frequency coil when it passes through the step portion is smaller than the axial speed of the high-frequency coil when it passes through the small-diameter portion or the large-diameter portion, the quenching hardness can be ensured by shortening the distance between the high-frequency coil and the cooling unit in the axial direction of the shaft-shaped body when it passes through the step portion compared to the distance between the high-frequency coil and the cooling unit in the axial direction when it passes through the small-diameter portion or the large-diameter portion.

[0077] Furthermore, as can be seen from the results in Tables 3 and 4, the hardness due to quenching tends to decrease as the moving speed of the high-frequency coil and cooling unit decreases, but the decrease in hardness can also be suppressed by improving the cooling capacity of the cooling unit. This shows that the quenching hardness can be ensured by making the amount or pressure of the cooling medium injected when the high-frequency coil passes through the step portion smaller than the amount or pressure of the cooling medium injected when the high-frequency coil passes through the small-diameter portion or the large-diameter portion.

[0078] Furthermore, as can be seen from the results in Tables 5 and 6, the baking depth can be kept constant by adjusting the cooling capacity of the cooling section in accordance with the moving speed of the coil and cooling section. In Table 5, the convective heat transfer coefficient was adjusted to match a baking depth of 5 mm. In Table 6, the convective heat transfer coefficient was adjusted to match a baking depth of 3 mm.

[0079] The results of this experiment show that the desired quench hardness can be ensured by appropriately controlling the speed of the heating coil, as well as the moving speed and cooling capacity of the cooling section. This makes it possible to suppress changes in grain size and the volume fraction of retained austenite, thereby maintaining constant hardness and mechanical properties of the material.

[0080] The moving hardening method and moving hardening device of the present invention make it possible to perform the desired hardening on the step portion and its vicinity in an axial body whose outer diameter is not constant in the axial direction, and therefore have extremely high industrial value.

[0081] 100 Moving hardening device 110 Heating section 111A, 111B, 211A, 211B, 211C High frequency coil 112A, 112B, 212A, 212B, 212C High frequency induction section 113a, 113b, 113c, 113d, 213a, 213b, 213c, 213d, 213e, 213f Conductive section 120 Cooling section 130 Support section 140 Heating section moving device 150 Cooling section moving device 160 Control section 10 Shaft-shaped body 11A, 11B Large diameter section 12 Small diameter section 13A, 13B Step section

Claims

1. A moving quenching method for quenching a shaft-shaped body having a small-diameter portion, a large-diameter portion, and a stepped portion connecting the small-diameter portion and the large-diameter portion in the axial direction, using a moving quenching apparatus including a plurality of high-frequency coils and a cooling unit, while rotating the shaft-shaped body inserted inside the plurality of high-frequency coils relative to the plurality of high-frequency coils and moving the plurality of high-frequency coils relative to the shaft-shaped body in the axial direction, heating the shaft-shaped body by the high-frequency coils, causing the cooling unit to follow the high-frequency coils from behind in the relative moving direction of the high-frequency coils along the axial direction of the shaft-shaped body, and cooling the portion heated by the high-frequency coils by the cooling unit, performing moving quenching while moving the high-frequency coils in a direction orthogonal to the axial direction of the shaft-shaped body so that the distance from the surface of the shaft-shaped body to each of the high-frequency coils becomes constant, wherein the axial velocity of the high-frequency coils when the high-frequency coils pass through the stepped portion is smaller than the axial velocity of the high-frequency coils when the high-frequency coils pass through the small-diameter portion or the large-diameter portion. A moving quenching method characterized by the above.

2. When the axial velocity of the high-frequency coils when the high-frequency coils pass through the small-diameter portion or the large-diameter portion is V0, the axial velocity of the high-frequency coils when the high-frequency coils pass through the stepped portion is Vs, and the velocity of the plurality of high-frequency coils in a direction orthogonal to the axial direction is Vc, the following formula 1 holds. A moving quenching method according to claim 1, characterized by the above. V0 ２ ≤ Vs ２ + Vc ２ ... Equation 1

3. Making the distance between the high-frequency coils and the cooling unit in the axial direction when the high-frequency coils pass through the stepped portion smaller than the distance between the high-frequency coils and the cooling unit in the axial direction when the high-frequency coils pass through the small-diameter portion or the large-diameter portion. A moving quenching method according to claim 1 or 2, characterized by the above.

4. The cooling unit injects a cooling medium, and making the injection amount or ejection pressure of the cooling medium when the high-frequency coils pass through the stepped portion smaller than the injection amount or ejection pressure of the cooling medium when the high-frequency coils pass through the small-diameter portion or the large-diameter portion. A moving quenching method according to claim 1, characterized by the above.

5. A moving quenching device for quenching a shaft-shaped body having a small-diameter portion, a large-diameter portion, and a stepped portion connecting the small-diameter portion and the large-diameter portion in the axial direction, wherein the moving quenching device, in the axial direction, comprises a plurality of high-frequency coils and a cooling unit, and comprises a control unit capable of controlling the movement of the plurality of high-frequency coils and the cooling unit, each of the high-frequency coils has a high-frequency induction portion for heating the shaft-shaped body and a conductive portion connected to the high-frequency induction portion, and is movable relative to the shaft-shaped body in the axial direction and movable relative to the plane perpendicular to the axial direction, the cooling unit has an injection portion capable of injecting a cooling medium, and is movable relative to the shaft-shaped body in the axial direction, wherein the control unit, is capable of controlling the movement of the high-frequency coil in the plane so that the distance from the surface of the shaft-shaped body to each of the high-frequency coils becomes constant, and is capable of controlling so that the axial speed of the high-frequency coil when the high-frequency coil passes through the stepped portion is smaller than the axial speed of the high-frequency coil when the high-frequency coil passes through the small-diameter portion or the large-diameter portion A moving quenching device characterized by the above.

6. When the control unit sets the axial speed of the high-frequency coil when the high-frequency coil passes through the small-diameter portion or the large-diameter portion as V0, the axial speed of the high-frequency coil when the high-frequency coil passes through the stepped portion as Vs, and the speed of the plurality of high-frequency coils in the direction orthogonal to the axial direction as Vc, the control unit is capable of controlling the high-frequency coil so that the following formula 1 holds The moving quenching device according to claim 5, characterized by the above. V0 ２ ≤ Vs ２ + Vc ２ ... Equation 1

7. The control unit is capable of controlling so that the distance between the high-frequency coil and the cooling unit in the axial direction when the high-frequency coil passes through the stepped portion is smaller than the distance between the high-frequency coil and the cooling unit in the axial direction when the high-frequency coil passes through the small-diameter portion or the large-diameter portion The moving quenching device according to claim 5 or 6, characterized by the above.

8. The control unit is capable of controlling so that the injection amount or ejection pressure of the cooling medium when the high-frequency coil passes through the stepped portion is smaller than the injection amount or ejection pressure of the cooling medium when the high-frequency coil passes through the small-diameter portion or the large-diameter portion The moving quenching device according to claim 5, characterized in that...