JP2009203498A - High frequency-induction heating method, heating apparatus and bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide heat-treatment with which a hardened layer to the optional hardened layer depth is precisely formed by utilizing a high frequency-induction heating. <P>SOLUTION: This high frequency-induction heating method is performed, by which an article to be heat-treated composed of an axial symmetrical iron is heated with the high frequency-induction heating and after adjusting the hardening layer depth on the surface, the quenching is performed. After exceeding the A1 point in the length x1[mm] depth needed to the hardened layer with the heating, and further, after heating until the time satisfying formula (1), Σ(from t=0 to t1) (T-log<SB>B</SB>t+A)>200000, becomes the time t1, and then, the heating is completed to perform the quenching. Wherein, in above formula (1): T is the absolute temperature [K] at the position x1 of the article to be heat-treated; t is the time [sec] after exceeding the A1 point at the position x1 of the article to be heat-treated; and A is a correcting constant (10-20). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a heat treatment method using high-frequency induction heating suitable for steel parts, particularly bearing parts, a heating apparatus usable for the heat treatment method, and a bearing subjected to the heat treatment.

Heat treatment by induction heating is applied to machine parts made of many steels such as gears and shafts, because low-cost, low-heat treatment deformation and clean heat treatment are possible in a short time.
However, in the field of bearings, heat treatment by induction heating has been used only for limited applications such as axle support bearings. The reason for the limitation was that some quantity had to be produced in the same format. This is because one induction heating coil is designed and manufactured exclusively for a heat-treated product with a specific shape, and the position, output, and heating time of the induction heating coil and the heat-treated product are fixed and heat-treated. is there.

Also, in large and super large bearings currently used in windmill reducers and steel rolling mills, when toughness and especially long life are required, carburized steel is used instead of bearing steel, Carburizing or carbonitriding is performed to form a hardened layer.
Such a carburized bearing has an advantage that the core hardness is low and the toughness can be increased. However, in order to obtain the necessary hardened layer depth on the surface by carburizing or carbonitriding, a very long heat treatment is required, so that the heat treatment strain is also very large. In this regard, a method for improving both productivity and cost is required.

On the other hand, a method for heat-treating a large machine part by induction heating has been sought. Patent Document 1 discloses a technique for quenching the surface of a ring that becomes larger as the diameter and thickness of the ring are suppressed by heat treatment. In addition, as described in Patent Document 2 and Patent Document 3, there is a method of heating a ring-shaped heat-treated product with a coil having a U-shaped or horseshoe-shaped shape. In this case, the whole is heated uniformly and is baked. Moreover, in the method described in Patent Document 4, a technique is shown in which the temperature is measured at a plurality of points and the quenching is performed when the temperature difference becomes small in order to improve the quality of the soaking. Further, in the method of Patent Document 5, the diffusion length of carbon is calculated from the temperature at a position away from the heating part in order to further enhance the quality of the soaking, and it is quenched when the carbon is sufficiently dissolved in the matrix. Taking the way.
JP-A-11-140543 JP 2005-325409 A JP 2006-179359 A JP 2005-310645 A JP 2006-152429 A

Productivity can be greatly improved if a large-thickness material to be heat-treated can be quenched to a depth that can withstand heavy loads using induction heating. Moreover, the most excellent balance between strength and toughness can be realized by quenching to an arbitrary depth.
However, the above prior art does not disclose a heat treatment method for accurately forming a hardened layer up to an arbitrary hardened layer depth using high-frequency induction heating.
The present invention has been made paying attention to such points, and an object of the present invention is to provide a heat treatment for accurately forming a hardened layer up to an arbitrary hardened layer depth using high-frequency induction heating.

In order to solve the above-mentioned problems, the invention described in claim 1 of the present invention is a high-frequency method in which a heat-treated product made of steel is heated by high-frequency induction heating to adjust the depth of the hardened layer on the surface and then quenched. In the induction heating method,
After heating, when the cured layer exceeds the point A1 at the required depth x1 [mm] and further reaches the time t1 that satisfies the following expression (1), the heating is finished and quenching is performed. It is characterized by this.

However,
T: Absolute temperature [K] at position x1 of the heat-treated product
t: Time after exceeding the point A1 at the position x1 of the heat-treated product [sec]
A: Correction constant Next, in the invention described in claim 2, the heat-treated product is an axially symmetric heat-treated product with respect to the configuration described in claim 1, and the induction heating coil is replaced with the heat-treated product. A plurality of coils are arranged in the axial direction and the circumferential direction, and the output of each coil is set to be individually adjustable. The heat-treated product is heated while rotating the shaft, and the heat treatment is performed from the temperature distribution predicted from the surface during the heat treatment. At the required depth x1 [mm] inside the product, the minimum heating time t1 after exceeding the point A1 that satisfies the equation (1) is obtained, and the point A1 at the required depth x1 [mm]. When it is determined that the heating time t1 has passed since the time exceeded, the heating is terminated, and then the coolant is jet-cooled onto the heat-treated product for quenching.
Next, the invention described in claim 3 is the structure described in claim 2, wherein the heating is performed after the surface to form the cured layer of the heat-treated product is heated to a target quenching temperature. The output of each induction heating coil is adjusted so as to keep the temperature at the quenching temperature.

Next, the invention described in claim 4 is a heating device that heats a heat-treated product made of axisymmetric steel by high-frequency induction heating,
A support device that supports the heat-treated product so as to be axially rotatable, and each of the support devices are arranged to face the surface of the heat-treated product on which a hardened layer is formed, and a plurality of the devices are arranged along the axial direction and the circumferential direction of the heat-treated product A plurality of induction heating coils, a power supply device that individually outputs high-frequency power to the induction heating coils, temperature detection means for detecting temperatures at a plurality of locations of the heat-treated product, and coolant can be injected toward the heat-treated product A cooling means, and a controller for controlling induction heating by individually adjusting the high frequency power supplied to each induction heating coil based on the detection value of the temperature detection means,
The heating is performed while rotating the article to be heat-treated, and the controller needs the inside of the article to be heat-treated based on the temperature distribution predicted from the surface temperature during the heat treatment based on the detection value of the temperature detecting means. The minimum heating time t1 after exceeding the point A1 satisfying the expression (1) at the depth x1 [mm] to be calculated,
If it is determined that the required depth x1 [mm] exceeds the A1 point based on the detected value of the temperature detecting means, the heating is finished after the heating time t1 after the determination, and the refrigerant by the cooling means is quenched by injection. The present invention provides a heating device characterized in that it is shifted to the above.

However,
T: Absolute temperature [K] at position x1 of the heat-treated product
t: Time after exceeding the point A1 at the position x1 of the heat-treated product [sec]
A: Correction constant Next, the invention described in claim 5 is described in any one of claims 1 to 3, in which at least one bearing component of an outer ring, an inner ring, and a rolling element is the heat-treated product. The present invention provides a bearing that is heat-treated by a high-frequency induction heating method.

  For example, the heating is first performed until the surface of the heat-treated product reaches a predetermined temperature. After reaching the predetermined quenching temperature T1, heat is applied to keep the temperature on the surface, and the heat is transferred to the core. It is considered that sufficient heat treatment quality can be obtained when carbon migration occurs sufficiently in the γ matrix. It is assumed that the moving distance of carbon at the target quenching depth x1 [mm] is expressed by equation (1). That is, when Equation 1 is satisfied at the target quenching depth, sufficient quenching quality can be obtained at any depth by starting quenching (see examples described later).

Further, the temperature from the start of heating to the end of heating is obtained by calculation at a required position x1 in the depth direction from the surface to be heated by induction. That is, the temperature at the target depth position x1 can be estimated from the amount of heat applied to the heat-treated product, the measured value of the surface temperature, and the like by heat transfer calculation.
The correction constant A is a constant for correcting the difference in the rate of change in hardening due to heating due to the structural state of the steel. For example, it is set according to the structure state of steel (spheroidized state, pearlite, tempered), and takes a value of 10-20. For example, this value is specified by experience values or experiments.

ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the heat processing which forms a hardened layer to arbitrary hardened layer depth accurately in a short time using a high frequency induction heating.
In particular, the depth of the hardened layer is adjusted appropriately, leaving a portion with low hardness and toughness in the core, and a balance between surface hardness and toughness is required, such as a bearing ring. It is effective for application to parts.

Next, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic view seen from the axial direction of a heat-treated product showing an example of the arrangement configuration of the heating device according to the present embodiment. 2 is a cross-sectional view taken along the line AA in FIG.
In the present embodiment, the inner ring, which is a bearing component, is used as a heat-treated product (work 1), and a hardened layer is formed by quenching to a depth x1 required for the outer surface of the outer diameter surface. Illustrate.

  As shown in FIG. 1, a supporting device 2 that fixes and supports a work 1 composed of an inner ring, a plurality of induction heating coils 3 that are arranged to face the outer diameter surface of the work 1, and a plurality of induction heating coils 3 that are individually high frequency. Power supply device 4 for supplying electric power, temperature detection means 5 for measuring the temperature of the outer diameter surface of the work 1, cooling means 7 for injecting a refrigerant toward the outer diameter surface of the work 1, and detection by the temperature detection means 5 A controller 6 for controlling the heating process such as controlling the induction heating by individually adjusting the high frequency power supplied to each induction heating coil 3 based on the value.

  As shown in FIG. 1, a plurality of the induction heating coils 3 are arranged in a distributed manner along the circumferential direction. In FIG. 1, two sets of induction heating coils 3 are arranged across the axis of the workpiece 1. As shown in FIG. 2, a plurality of induction heating coils 3 in each group are arranged side by side in parallel with the axis of the workpiece 1. FIG. 2 illustrates the case where three are arranged, and the heating range is set so that there is no gap. By configuring each set of coils 3 with a plurality of coils 3 arranged in the axial direction of the workpiece 1, the temperature distribution can be controlled by adjusting the input power according to the respective locations along the axial direction. is there. As a result, it is possible to cope with the heat treatment of the heat-treated products having different lengths in the axial direction and the heat-treated products having different bowl-shaped or tapered shapes. Further, by dividing the induction heating coil 3 in the axial direction, a huge high frequency power source is not required.

Here, it is preferable that each set of induction heating coils 3 includes three or more. That is, the coil 3 that heats the axial end position of the workpiece 1 and the coil 3 that heats the central portion of the workpiece 1 are preferably separate coils 3. This is because it is possible to more appropriately cope with the fact that the heat radiation on the end portion side is larger than the central portion side in the axial direction.
The coil 3 is variable in position and angle in the tangential direction and radial direction. The output of each coil 3 can be controlled separately for each coil 3 having the same axial position and angle. Alternatively, it can be controlled completely separately. And the some coil 3 is arrange | positioned so that the whole workpiece | work 1 surface may be heated.

The temperature detection means 5 is composed of, for example, a radiation thermometer, and outputs the detected temperature signal to the controller 6. As shown in FIG. 2, a plurality of the temperature detecting means 5 are arranged along the axial direction (width direction) of the workpiece 1, and temperature distribution control along the axial direction of the surface of the workpiece 1 can be performed with higher accuracy. It has become.
The cooling means 7 is a device that ejects a coolant such as cooling air toward the surface of the work 1. For example, the cooling means 7 is constituted by a cooling jacket that can cover as much area as possible so that the entire surface of the workpiece 1 can be cooled at once.
The support device 2 includes a chuck portion 2a that is inserted into the inner diameter surface of the workpiece 1 and contacts the inner diameter surface of the workpiece 1, and a drive portion 2b that rotates the workpiece 1 supported by the chuck portion 2a.

Next, the process of the controller 6 will be described with reference to FIG.
When the processing start signal is input, the controller 6 first operates the support device 2 to fix the workpiece 1 to the support device 2 and rotates the workpiece 1 about its axis (step S10).
In this state, the power supply device 4 is operated, high frequency power is individually output to each induction heating coil 3, and induction heating is started (step S20). At this time, based on the detection signal from the temperature detection means 5, the output of each coil 3 is controlled so that the heating of the surface of the workpiece 1 is uniform.

  The temperature of the surface of the workpiece 1 increases as the heating is performed. Then, it is determined whether or not the surface temperature of the workpiece 1 has reached the target quenching temperature T1 (step S30), and when it is determined that the surface temperature has reached the target quenching temperature T1, On the surface, the output of each induction heating coil 3 is controlled with reference to the detection signal of the temperature detection means 5 so as to continue to apply the amount of heat sufficient to maintain the temperature to the workpiece 1 (step S40). As a result, heat is transferred toward the core of the work 1.

In the heat treatment, the output of each coil 3 is adjusted so that a large difference of several tens of degrees does not occur in the detection value of each temperature detection means 5. Further, the output is increased at the end face where heat easily escapes, and when the temperature is high at the overlapping portion of the coil 3, the entire input power itself is reduced.
In synchronization, the absolute temperature T at the depth x1 required for forming the hardened layer is estimated by estimating the temperature gradient inside the workpiece 1 based on the history of the surface temperature for each time. From the temperature distribution predicted from the surface temperature during such heat treatment, a time exceeding the A1 point at the required depth x1 and a minimum heating time t1 satisfying the following expression (1) are obtained (step S50). ).

However,
T: Absolute temperature [K] at position x1 of the heat-treated product
t: Time after exceeding the point A1 at the position x1 of the heat-treated product [sec]
A: Correction constant The correction constant A is selected according to the structure state of the steel (spheroidized state, pearlite, tempered), and takes a value of 10-20.
Then, when it is determined that the point A1 has been exceeded at the required depth x1 from the surface, it is further determined whether or not only the heating time t1 has elapsed after the determination (step S60), and it is determined that only the heating time t1 has elapsed. If so, the output to the coil 3 is stopped and the heating is terminated (step S70). After that, the operation command is output to the cooling device, the refrigerant is output to the work 1, and quenching is performed (step S80).

Next, the effect is demonstrated.
By inductively heating the axially symmetric workpiece 1 while rotating the shaft, the workpiece 1 can be heated uniformly along the circumferential direction. In addition, by dividing and arranging the plurality of coils 3 along the axial direction, even if the heat-treated product having a different length in the axial direction or the heat-treated product having a bowl-like shape or a tapered shape has a shaft It becomes possible to heat evenly in the direction.
At this time, by detecting the temperature of the workpiece 1 and adjusting the output of each coil 3, it becomes possible to perform heating control with higher accuracy.
Moreover, the cured layer is heated to the required depth position with high accuracy by calculating the heating time t1 after exceeding the A1 point at the required required depth position based on the above equation (1). Is possible.

Further, by dividing the induction heating coil 3 into a plurality along the axial direction, it is possible to avoid increasing the size of the power supply device 4 that generates high-frequency power.
From the above, quenching of an axially symmetric shape such as a ring shape and a thick member is possible in a short time, leading to an improvement in productivity.
Specifically, carbon is sufficiently dissolved to an arbitrary depth x1 of the workpiece 1 made of an annular member, and as a result, uniform quenching heat treatment quality can be obtained.
In addition, a portion that does not need to be deeply quenched, for example, an outer ring outer diameter and an inner ring inner diameter in the case of a bearing member, can have any hardened layer depth.

  That is, in the heating method of the present embodiment, a large-thickness material to be heat-treated can be quenched to a necessary depth that can withstand heavy loads, so that productivity can be greatly improved. Moreover, the most excellent balance between strength and toughness can be realized by quenching with high precision to any desired depth. In general, in the case of bearing parts, it is necessary to give a predetermined toughness without quenching the core part and to harden the surface in sliding contact with other rolling parts such as rolling elements, but this embodiment is adopted. As a result, the balance between strength and toughness can be realized with high accuracy.

By adopting the heat treatment method of the present embodiment, it is possible to carry out a hardening process uniformly and to an arbitrary depth by using the same heating device for heat-treated products having different thicknesses or various shapes of steel members.
Here, in the said embodiment, although the inner ring | wheel was illustrated as a to-be-heat-processed goods, this is not limited. It may be an outer ring or a rolling element (roller or the like) which is a bearing component having an axially symmetric shape. Further, the present invention is not limited to bearing parts, and may be mechanical parts such as shaft parts.
Further, the heat-treated product may not have an axisymmetric shape.

(Modification)
For a raceway ring that is an inner ring or an outer ring as a heat-treated product, the raceway surface that is in sliding contact with the rolling element is induction-heated for a time based on the above formula (1), and then the surface opposite to the raceway side is also on the raceway side The depth is set shallower than that, induction heating is performed for a time based on the above formula (1), and then cooling is performed for quenching.
In this case, a deep hardened layer is formed on the track surface side, a shallow hardened layer is formed on the tracked surface side, and a non-hardened layer is formed at the core between the two hardened layers.

As a heat-treated product that is a heat-treated product, a ring-shaped part having a rectangular cross-sectional shape and a wall thickness of 40 [mm] made of high-carbon chromium bearing steel is subjected to quenching treatment by the heating device described in the above embodiment. went.
It is assumed that the quenching heat treatment is performed up to a predetermined quenching depth x1 = 20 [mm], which is a necessary depth. The constant A was set to 20 for tempering.

  FIG. 4 shows changes in temperature distribution in the depth direction. The horizontal axis indicates the position in the depth direction from the outer diameter surface of the heat-treated product, and the vertical axis indicates the temperature calculated from the surface layer temperature. And it shows that it changes with (a)-> (b)-> (c)-> (d) with progress of heat processing. That is, FIG. 4A shows a state in which heating is started and only the heat generating portion near the surface is rising in temperature. In FIG. 4B, the surface has almost reached the temperature at the time of quenching, and from here the output of each induction heating coil 3 is adjusted to an output that is necessary for the surface to maintain this temperature. FIG. 4 (c) shows a state where the depth x1 where the hardened layer is to be applied exceeds the austenite transformation point and carbon diffusion begins in the matrix. FIG. 4D shows a state where the thermal diffusion further proceeds and exceeds the austenite transformation point.

In addition, when the left side of the equation (1) is referred to as a diffusion parameter D, the distribution of the diffusion parameter D viewed in the depth direction at each time point of the temperature gradient from (a) to (d) in FIG. As shown in FIG. In FIG. 5, the horizontal axis represents the depth position from the surface, and the vertical axis represents the diffusion parameter D.
In FIG. 5A, since no point exceeds the transformation point A1, the diffusion parameter D is zero in the entire area. At the time shown in FIG. 5B, the diffusion parameter D starts to increase in the region beyond the point A1 on the surface. At the time of FIG. 5 (c), the transformation point A1 is exceeded at the position of x1 [mm] where the hardened layer is to be applied, but the diffusion parameter D is about to start increasing. It is not possible to obtain sufficient hardness at the position. In FIG. 5D, the threshold of D> 200000 is exceeded even at the x1 position, and quenching is started at this point.
Next, the description will be made by paying attention to the required depth x1 position.
Table 1 shows the temperature change at the X1 position and the value of D.

今回の出力履歴における必要とされる深さｘ１での温度上昇は、図６に示されたパターンであった。すなわち、Ａ１変態点を越える２１秒後から拡散パラメータＤの増加が始まる。そして、このとき、必要とされる深さｘ１において、変態点Ａ１を越えたあとの時間と拡散パラメータＤとの関係は、図５に示すパターンとなっていた。図７によれば、Ａ１変態点を超えてから９秒後に拡散パラメータＤ＝２０００００を越えることが分かる。
以上から、上記加熱パターンにおいては、加熱開始から３０秒後にＤ＞２０００００を満たす。
以上のことに基づき、外径面からの必要とする深さｘ１＝２０［ｍｍ］とし、その深さｘ１での拡散パラメータＤ＝２０３３７２（＞２０００００）となった時点で焼入れを行った場合を実施例１とする。

The temperature rise at the required depth x1 in the current output history was the pattern shown in FIG. That is, the increase of the diffusion parameter D starts from 21 seconds after the A1 transformation point. At this time, the relationship between the time after the transformation point A1 and the diffusion parameter D at the required depth x1 is the pattern shown in FIG. According to FIG. 7, it can be seen that the diffusion parameter D = 200000 is exceeded 9 seconds after the A1 transformation point is exceeded.
From the above, in the heating pattern, D> 200000 is satisfied 30 seconds after the start of heating.
Based on the above, the case where the required depth x1 from the outer diameter surface is set to 20 [mm], and quenching is performed when the diffusion parameter D = 203372 (> 200000) at the depth x1. It is assumed Example 1.

The result of the hardness distribution in the depth direction of the surface in this case is shown in FIG.
Further, as Example 2, a case where the inner surface side is also shallowed (to form a hardened layer of 2 mm) following the heating of Example 1 and then subjected to a quenching treatment is shown.
The result of the hardness distribution in the depth direction of the surface in this case is shown in FIG.
On the other hand, the required depth x1 = 20 [mm] from the outer diameter surface is set as Comparative Example 1 when quenching is performed when the diffusion parameter D <200000 at the depth x1.

The result of the hardness distribution in the depth direction of the surface in this case is shown in FIG.
Here, low-temperature tempering is performed at 453 K in both the two examples and the comparative example.
From the above, it is possible to reliably form a hardened layer to the required depth x1 by heating until the diffusion parameter D> 200000 at the target required depth x1. I understand. On the other hand, in the comparative example quenched at D <200000, the target cured layer depth was not obtained.

  Here, the heating method of Example 2 is suitable for application to the bearing ring of the bearing. For example, in a radial bearing, since a large shear stress is applied to the inner ring outer diameter and the outer ring inner diameter, a large hardened layer depth is required. On the contrary, the inner ring inner diameter and the outer ring outer diameter do not suffer from rolling fatigue, so that a deep hardened layer is not required. However, when considering the aspect of toughness, it is better to have more low hardness structure in the center part of the bearing. Therefore, as in Example 2, it is possible to form a bearing having the maximum toughness by applying a deep hardened layer from the front surface to the vicinity of the center and then applying a shallow hardened layer on the back surface.

It is a schematic diagram which shows the apparatus structure which concerns on embodiment based on this invention. It is AA sectional drawing in FIG. It is a figure which shows the process example of the controller which concerns on 1st Embodiment based on this invention. It is a figure which shows the change of the temperature gradient from the surface. It is a figure which shows the gradient change of the diffusion parameter D. FIG. It is a figure which shows the temperature change after the voltage application in the depth x1. It is a figure which shows the change of the diffusion parameter after transformation in depth x1. It is a figure which shows the relationship between the depth in Example 1, and hardness. It is a figure which shows the relationship between the depth in Example 1, and hardness. It is a figure which shows the relationship between the depth and hardness in a prior art example.

Explanation of symbols

1 Workpiece (heated part)
2 Supporting device 3 Induction heating coil 4 Power supply device 5 Temperature detection means 6 Controller 7 Cooling means A Correction constant D Diffusion parameter t1 Heating time after transformation x1 Required depth position

Claims (5)

In the high frequency induction heating method of performing quenching after heating the heat-treated product made of steel by high frequency induction heating and adjusting the depth of the hardened layer on the surface,
After heating, when the cured layer exceeds the point A1 at the required depth x1 [mm] and further reaches the time t1 that satisfies the following expression (1), the heating is finished and quenching is performed. A high frequency induction heating method characterized by that.

However,
T: Absolute temperature [K] at position x1 of the heat-treated product
t: Time after exceeding the point A1 at the position x1 of the heat-treated product [sec]
A: Correction constant The heat-treated product is an axisymmetric shaped heat-treated product,
A plurality of induction heating coils are arranged in the axial direction and circumferential direction of the heat-treated product and the output of each coil is set to be individually adjustable, and the heat-treated product is heated while rotating the shaft, from the surface during the heat treatment. From the predicted temperature distribution, in the required depth x1 [mm] inside the heat-treated product, the minimum heating time t1 after exceeding the point A1 satisfying the expression (1) is obtained,
When it is determined that the heating time t1 has passed after exceeding the A1 point at the required depth x1 [mm], the heating is terminated, and then the coolant is injected and cooled to the heat-treated product for quenching. The high frequency induction heating method according to claim 1.   The heating is characterized by adjusting the output of each induction heating coil so that the surface temperature is maintained at the quenching temperature after the surface on which the cured layer of the heat-treated product is heated to the target quenching temperature. The high frequency induction heating method according to claim 2. A heating device that heats a heat-treated product made of axisymmetric steel by high-frequency induction heating,
A support device for supporting the heat-treated product so as to be axially rotatable;
A plurality of induction heating coils each disposed opposite to the surface of the article to be heat-treated to form a hardened layer, and arranged in a plurality along the axial direction and the circumferential direction of the article to be heat-treated;
A power supply device that individually outputs high-frequency power to the induction heating coil;
Temperature detecting means for detecting temperatures at a plurality of locations of the heat-treated product;
A cooling means capable of injecting a refrigerant toward the heat-treated product;
A controller for controlling induction heating by individually adjusting high-frequency power supplied to each induction heating coil based on the detection value of the temperature detection means,
The above heating is performed while rotating the product to be heat-treated,
The controller satisfies the expression (1) at a required depth x1 [mm] inside the heat-treated product from the temperature distribution predicted from the surface temperature during the heat treatment based on the detection value of the temperature detecting means. Calculate the minimum heating time t1 after exceeding the A1 point,
If it is determined that the required depth x1 [mm] exceeds the A1 point based on the detected value of the temperature detecting means, the heating is finished after the heating time t1 after the determination, and the refrigerant by the cooling means is quenched by injection. A heating device characterized by being transferred to.

However,
T: Absolute temperature [K] at position x1 of the heat-treated product
t: Time after exceeding the point A1 at the position x1 of the heat-treated product [sec]
A: Correction constant   A bearing that is heat-treated by the high-frequency induction heating method according to any one of claims 1 to 3, wherein at least one bearing component of an outer ring, an inner ring, and a rolling element is the heat-treated product.

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