JP2019157272A - Work tempering process, and machine part obtained by said process - Google Patents

Abstract

To provide a tempering process in which a machine part suitable for use in high-temperature environment can be obtained, and having an excellent productivity.SOLUTION: The work tempering process according to the present invention comprises a heating step S21 for heating a workpiece W, and a cooling step S22 for cooling the workpiece W heated in the heating step S21, and the heating step S21 includes a temperature increasing step S211 of targeting workpiece W by induction heating to heat to a temperature r1, and a temperature maintaining step S213 in which the heating of workpiece W by atmospheric heating is controlled so that the temperature of workpiece W after the temperature increasing is maintained for a predetermined time within the range of a temperature range R having a predetermined width.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a work tempering method and a machine part obtained by this method, and more particularly to a tempering technique suitable for a machine part used in a high temperature environment.

  For example, in the manufacturing process of mechanical parts made of steel such as SUJ2 such as rolling bearing races, heat treatment (quenching hardening) is performed to give the mechanical strength required for the mechanical parts. After that, for example, tempering is generally performed for the purpose of relaxing residual stress or reducing residual austenite.

  Here, the tempering treatment includes, for example, a method of heating a work by induction heating for the purpose of heating in a short time in addition to a method of heating a work placed in the furnace by atmospheric heating using an electric furnace or the like ( For example, see Patent Document 1).

JP 2011-144448 A

  By the way, in a bearing used in a high temperature environment, when exposed to a high temperature during use, residual austenite contained in the bearing is transformed, and an excessive dimensional change tends to occur. Therefore, it is necessary to further reduce the amount of retained austenite as compared with a normal product for a product (bearing) used for this type of application. Specifically, it is necessary to set the temperature (for example, the maximum temperature) during the tempering process to a higher temperature range than in the normal tempering process.

  An atmosphere heating apparatus such as an electric furnace is relatively easy to control the temperature, but has a limited heating rate, and thus it takes a long time to raise the temperature. Therefore, if the tempering condition (heating condition) is set in the high temperature range for the above-mentioned reason, the processing time becomes longer than before, and deterioration of productivity is inevitable.

  Since induction heating has high energy efficiency when raising the temperature of metal parts, the workpiece can be heated to a high temperature range in a short time compared to atmospheric heating. However, when the workpiece is heated to a higher temperature range (for example, 250 ° C. or higher) than the conventional one, not only the amount of retained austenite is reduced, but also the hardness of the workpiece may be greatly reduced. Therefore, it is difficult to obtain a machine part suitable for use in a high temperature environment simply by heating the workpiece to a high temperature range by induction heating and cooling it.

  In addition, when applying induction heating to a machine part with an uneven thickness distribution in the axial direction, such as an outer joint member of a constant velocity universal joint, a portion in which magnetic flux is relatively dense and easily heated, The magnetic flux is relatively sparse and a portion that is difficult to be heated is generated. Therefore, the temperature difference in one work becomes large and soaking is difficult. In order to achieve soaking required for tempering only by induction heating, it is necessary to prepare an induction heating device (for example, an induction heating coil) in a form suitable for the size and shape of the workpiece. As the number of types of coils to be prepared increases as the model number (type of workpiece to be processed) increases, a decrease in productivity cannot be avoided.

  In view of the above circumstances, in this specification, it is a technical problem to be solved to provide a tempering method capable of obtaining a machine part suitable for use in a high temperature environment and having excellent productivity. .

  The solution to the above problem is achieved by the work tempering method according to the present invention. That is, this method includes a heating step for heating the workpiece and a cooling step for cooling the workpiece heated in the heating step, and the temperature history in the heating step and the cooling step is controlled, so that the workpiece is tempered. In the work tempering method to be applied, the heating step includes a heating step of heating the workpiece to a target temperature by induction heating, and the workpiece after the temperature rising within a temperature range of a predetermined width is kept warm for a predetermined time. Thus, it is characterized by having a heat-retaining step for controlling heating of the workpiece by atmospheric heating.

  The inventors of the present invention reduce the amount of retained austenite contained in the work after tempering treatment to a required level or less by keeping the work after being heated in a temperature range of a predetermined width for a predetermined time. It has been found that it may be possible to keep the hardness within a predetermined range. The present invention has been made on the basis of this finding. By heating the workpiece to a target temperature by induction heating (temperature raising step), the workpiece can be heated to a predetermined high temperature range in a shorter time than conventional. Further, by keeping the workpiece after the temperature rise within a predetermined temperature range for a predetermined time as described above, both the amount of retained austenite and the hardness after the tempering process can be within the allowable range. it can. In addition, since the heating control for keeping the work within the above temperature range is performed by atmospheric heating, the work can be kept warm while heating the work evenly. Therefore, it is possible to perform a uniform tempering process while suppressing variations in the temperature inside the workpiece. Even in the case of mechanical parts with an uneven thickness dimension distribution in the axial direction, such as the outer joint member of a constant velocity universal joint, the temperature variation in the workpiece caused by induction heating can be leveled by atmospheric heating. it can. Therefore, a uniform tempering process can be performed without preparing a plurality of coils and the like. Further, if the atmosphere is heated, the temperature of the workpiece is less likely to be lower than that of induction heating or the like. Therefore, it is possible to relatively easily perform heating control during the heat retaining step. Of course, if the atmosphere is heated, a large amount of workpieces can be processed at a time. As described above, according to the present invention, the amount of retained austenite contained in the workpiece can be reduced to a required level or less, and the hardness of the workpiece can be kept within a predetermined range, so that it can be used in a high temperature environment. Suitable machine parts can be obtained. In addition, the time required for the temperature increase is short, and a uniform process can be performed on a large number of workpieces in a relatively short time, so that the productivity is excellent.

  In the work tempering method according to the present invention, the temperature of the workpiece is recovered to the target temperature at the time of temperature increase by heating the workpiece after the temperature increase after the temperature increase step and before the heat retention step. A reheating step may be further provided.

  When the temperature of the workpiece is increased by induction heating, the temperature of the workpiece is reduced by a short time immediately after the workpiece is taken out from the apparatus for induction heating. If the target temperature is set higher in advance in anticipation of this temperature drop, the hardness of the workpiece will be reduced more than necessary as described above. Therefore, by providing a reheating step for recovering the temperature of the workpiece to the target temperature at the time of the temperature increase after the temperature increasing step, it is possible to shift to the heat retaining step in a state where the temperature of the workpiece is returned to the target temperature. Moreover, the temperature fall at the time of transfer to a heat retention process from a heat recovery process can be suppressed by heating a workpiece | work by atmospheric heating in both a heat recovery process and a heat retention process. As described above, by providing the rewarming process, the work can be efficiently transferred to the heat retaining process.

  In this case, in the work tempering method according to the present invention, the set temperature of the atmosphere heating may be set higher than the target temperature at the time of temperature increase in the reheating process.

  If a rewarming step is provided before the heat retaining step, the atmospheric temperature in the device (atmosphere heating furnace) used in the heat regenerating step is easier than the atmospheric temperature in the device (atmosphere heating furnace) used in the heat retaining step. Can be high. As a result, the time required for the rewarming can be shortened, so that a workpiece having a target temperature can be introduced into the heat retaining process more efficiently.

  In the work tempering method according to the present invention, the set temperature of the atmosphere heating may be set to the same temperature as the target temperature at the time of temperature increase in the heat retaining step.

  If it is atmosphere heating, it is easier to keep temperature constant than an induction heating device. Therefore, the tempering quality (residual austenite amount, hardness) as intended can be obtained by setting the set temperature of the atmospheric heating in the heat retaining step to the same temperature as the target temperature at the time of temperature increase.

  Further, in the work tempering method according to the present invention, an allowable temperature range as a temperature range of a predetermined width is set according to the amount of retained austenite and hardness required for the work, and within the range of the allowable temperature range. The heating of the workpiece by induction heating may be controlled so that the workpiece is kept warm for a predetermined time.

  In this way, by setting the allowable temperature range according to the amount of retained austenite and hardness required for the workpiece, it is possible to keep both the amount of retained austenite and the hardness within the allowable range with a shorter heat retention time. It becomes. Therefore, the productivity can be further improved.

  In this case, in the work tempering method according to the present invention, the first temperature lower limit value at which the retained austenite amount falls within the allowable range is set based on the relationship between the target temperature at the time of raising the workpiece temperature and the retained austenite amount. In addition to setting, based on the relationship between the target temperature and hardness at the time of workpiece temperature rise, set the second temperature upper limit value and second temperature lower limit value where the hardness falls within the allowable range, and from these first temperature lower limit values The allowable temperature range may be set within a range in which the larger region overlaps the region between the second temperature upper limit value and the second temperature lower limit value.

  The amount of retained austenite decreases as the heating temperature (more precisely, the target temperature during the temperature raising step) increases, and the hardness also decreases as the heating temperature increases. Therefore, based on these tendencies, according to the amount of retained austenite and hardness required for the workpiece, as described above, the first temperature lower limit value is set, and the second temperature upper limit value and the second temperature lower limit value are set. Set. And by setting the allowable temperature range within the range where the region larger than the first temperature lower limit value and the region between the second temperature upper limit value and the second temperature lower limit value overlap, the kind of workpiece It is possible to accurately set an optimum allowable temperature range for each (particularly material).

  In the work tempering method according to the present invention, when the work material is high carbon chromium bearing steel, the allowable temperature range may be set within a range of 290 ° C. or higher and 340 ° C. or lower.

  Moreover, when the material of the workpiece is high carbon chrome bearing steel, the heat retention time of the workpiece may be set to 3 minutes or more and 7 minutes or less.

  Thus, when the material of the workpiece is high-carbon chromium bearing steel, an appropriate allowable temperature range is specifically derived by using, for example, the setting method described above. Therefore, it is possible to keep the workpiece warm within an appropriate allowable temperature range, and thereby it is possible to stably impart an appropriate amount of retained austenite and hardness to the workpiece after tempering.

  Alternatively, in the work tempering method according to the present invention, when the material of the work is carbon steel for machine structure, the allowable temperature range may be set within a range of 130 ° C. or higher and 220 ° C. or lower.

  Moreover, when the material of the workpiece is carbon steel for machine structure, the heat retention time of the workpiece may be set to 10 seconds or more and 70 minutes or less.

  Thus, even when the material of the workpiece is carbon steel for machine structure, an appropriate allowable temperature range is specifically derived by using the setting method described above. Therefore, it is possible to keep the workpiece warm within an appropriate allowable temperature range, and thereby it is possible to stably impart an appropriate amount of retained austenite and hardness to the workpiece after tempering.

  In the work tempering method according to the present invention, the work may be heated in the heat retaining step using an atmosphere heating furnace having an electric heater.

  For example, in the case of an infrared heater, the temperature rise may change depending on the color (gloss) of the surface of the metal workpiece, but if the atmosphere is heated by an electric heater, the surrounding atmosphere (gas) is not the workpiece. Since heating is performed, the above-described problems do not occur. Therefore, stable heating is possible without being affected by individual differences in the workpiece.

  Further, as described above, the work tempering method according to the present invention can provide a machine part suitable for use in a high temperature environment and has excellent productivity. It is suitable as a method for heat-treating mass-produced products of machine parts such as rings (outer rings, inner rings) and outer joint members of constant velocity universal joints.

  As described above, according to the present invention, a mechanical part suitable for use in a high temperature environment can be obtained, and a tempering method excellent in productivity can be provided.

It is a flowchart which shows the whole flow of the heat processing process which concerns on 1st embodiment of this invention. (A) (b) is a flowchart which shows the flow of the tempering process shown in FIG. It is sectional drawing which shows the whole outline | summary of the tempering apparatus which concerns on 1st embodiment of this invention. It is sectional drawing of a heating apparatus. It is sectional drawing of an induction heating apparatus. It is a graph which shows the temperature history during the tempering process shown in FIG. (A) a graph conceptually showing the relationship between the heating temperature and the amount of retained austenite during the tempering process, (b) a graph conceptually showing the relationship between the heating temperature and hardness, and (c) an allowable temperature range. It is a graph which shows a range notionally. When a workpiece | work is a bearing ring of a rolling bearing, it is an example of sectional drawing which shows the position of the several temperature measurement point provided in the surface of the workpiece | work. It is sectional drawing of the temperature rising apparatus which concerns on 2nd embodiment of this invention. When a workpiece | work is an outer joint member of a constant velocity universal joint, it is an example of sectional drawing which shows the position of the some hardness measurement point provided in the surface of a workpiece | work.

  Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a flowchart showing the overall flow of the heat treatment process according to the first embodiment of the present invention. As shown in FIG. 1, the heat treatment process according to the present embodiment includes a quenching process S <b> 1 in which a target workpiece W (see FIG. 3) is quenched and a tempering process in which the workpiece W after quenching is tempered. Step S2. Moreover, after hardening process S1 and tempering process S2, washing | cleaning process S3, S5 and inspection process S4, S6 are provided, respectively. The cleaning steps S3 and S5 and the inspection steps S4 and S6 can be partially or entirely omitted as necessary. Or although illustration is abbreviate | omitted, you may add a grinding | polishing process etc. after hardening process S1 or tempering process S2 as needed.

  Here, as shown in FIG. 2A, the tempering step S2 includes a heating step S21 for heating the workpiece W after quenching, and a cooling step S22 for cooling the heated workpiece W. In addition, as shown in FIG. 2B, the heating step S21 includes a heating step S211 for heating the workpiece W to the target temperature r1 by induction heating, and heating the workpiece W after the heating to the atmosphere W The temperature recovery step S212 recovers the target temperature to the target temperature r1, and the heat retention step S213 maintains the temperature of the workpiece W recovered to the target temperature r1 by atmospheric heating.

  FIG. 3 is a front view of the heat treatment apparatus (tempering apparatus 10) used in the tempering step S2 shown in FIG. The tempering device 10 is configured to continuously perform a tempering process on a plurality of workpieces W conveyed in a predetermined direction on the conveyance path 11, and is arranged on the upstream side of the conveyance path 11. A heating device 12 is provided, and a cooling device 13 is provided downstream of the heating device 12 in the conveyance path 11. Hereinafter, the configuration of the tempering apparatus 10 will be described with a focus on the heating apparatus 12, and then an example of a tempering method (tempering step S2) using the tempering apparatus 10 will be described.

  Here, the shape of the target workpiece W is arbitrary in principle, and may be, for example, an annular shape. The material of the workpiece W is also arbitrary in principle, and examples thereof include high carbon chrome bearing steel such as SUJ2. In addition, the type of workpiece W from the viewpoint of application is also arbitrary. For example, outer and inner rings of rolling bearings, sliding bearings, outer joint members constituting constant velocity universal joints, rolling joint bearings, rolling bearings, A cage (base material) incorporated in a constant velocity universal joint can be a target. In the present embodiment, for example, the bearing ring (outer ring or inner ring) of the rolling bearing is the target of the tempering step S2.

  The heating device 12 includes a temperature raising device 14, a reheating device 15, and a heat retaining device 16 in order from the upstream side of the conveyance path 11. Here, the temperature raising device 14 is for heating, for example, the workpieces W one by one. In the present embodiment, as shown in FIG. 4, the temperature raising device 14 is conveyed on the conveyance path 11 in a predetermined direction. The support part 17 which can support the several workpiece | work W carried out one by one, the raising / lowering part 18 which drives the support part 17 up and down, and the induction heating apparatus 19 located above the support part 17 are mainly provided. The induction heating device 19 includes, for example, a heating coil 20 formed in an annular shape with a conductive metal such as a copper tube (in FIG. 5, the two heating coils 20 and 20 are illustrated), and power to the heating coil 20. The power supply 21 is supplied, and the support part 17 is raised by the elevating part 18 so that the workpiece W placed on the support part 17 can be introduced into the inner periphery of the heating coil 20. In this case, it is desirable that the center line of the elevating unit 18 and the center line of the heating coil 20 coincide. In addition, although not shown in the drawings, the support portion 17 and a part of the elevating portion 18 connected to the support portion 17 may be configured to rotate around the center line. Similarly, although not shown in the figure, a pin that can be projected and retracted with respect to the transport path 11 or its upper surface so that the work W transported on the transport path 11 can be stopped at a predetermined position on the support portion 17. A positioning part such as may be provided.

  For example, as shown in FIG. 4, the temperature raising device 14 having the above configuration may further include a wall portion 22 that surrounds the periphery of the induction heating device 19 or the like. In this case, the atmospheric temperature inside the temperature raising device 14 can be adjusted by a predetermined temperature adjusting device (not shown). In FIG. 4, a member denoted by reference numeral 23 is first opening / closing means for opening and closing the inlet side opening 14 a of the temperature raising device 14 on the upstream side of the conveyance path 11, and a member denoted by reference numeral 24 is on the downstream side of the conveyance path 11. This is a second opening / closing means for opening / closing the outlet side opening 14b of the temperature raising device 14. Of course, when special atmosphere temperature control is not necessary (for example, as in the present embodiment, the reheating step S212 is provided after the temperature raising step S211, and the process can smoothly shift to the heat retaining step S213), the wall The part 22 is not necessary.

  The temperature raising device 14 having the above configuration is connected to the reheating device 15 via the first passage chamber 25 on the conveyance path 11 (see FIG. 3). As a result, the workpiece W that has been subjected to the temperature raising process in the temperature raising device 14 is carried into the reheating device 15 through the first passage chamber 25.

  The recuperator 15 is for heating the heated workpiece W to the atmosphere, and includes a first furnace chamber 26 and a first heater 27 disposed in the first furnace chamber 26. The first heater 27 is an electric heater, for example, and heats the atmosphere (gas) in the first furnace chamber 26. Thereby, the atmosphere heating with respect to the workpiece | work W in the 1st furnace chamber 26 is enabled.

  The heat retaining device 16 is for heating the work W heated by the rewarming device 15 to the atmosphere, and includes a second furnace chamber 28 and a second heater 29 disposed in the second furnace chamber 28. The second heater 29 is, for example, an electric heater, and heats the atmosphere (gas) in the second furnace chamber 28. Thereby, the atmosphere heating with respect to the workpiece | work W in the 2nd furnace chamber 28 is enabled.

  The inlet side opening 15a of the recuperator 15 is provided with means (third opening / closing means 30) for opening and closing the inlet side opening 15a, and the outlet side opening 15b of the recuperator 15 is provided in the outlet side opening 15a. A means (fourth opening / closing means 31) for opening and closing the outlet side opening 15b is provided. Thereby, the airtightness in the recuperator 15 is ensured. Of course, although not shown in the drawings, opening / closing means are also provided in the inlet side opening of the heat retaining device 16 (that is, the outlet side opening 15b of the rewarming device 15) and the outlet side opening. Moreover, since the inlet side opening part of the heat retention apparatus 16 becomes the outlet side opening part 15b of the heat recovery apparatus 15 (refer FIG. 4), the airtightness in the heat insulation apparatus 16 is ensured.

  The heating device 12 having the above configuration is connected to the cooling path 13 via the second passage chamber 32 on the transport path 11 (see FIG. 3). As a result, the workpiece W that has been subjected to a predetermined heat treatment in the heating device 12 is carried into the cooling device 13 through the second passage chamber 32.

  Moreover, as a means for conveying the workpiece | work W along the conveyance path 11, it is arbitrary, for example although illustration is abbreviate | omitted, the conveyance conveyor arrange | positioned straddling the bottom part of the heating apparatus 12 and the cooling device 13, Alternatively, a power cylinder (hydraulic cylinder, air cylinder, electric cylinder) or the like can be employed.

  The cooling device 13 is a device for performing a cooling process for cooling the workpiece W heated by the heating device 12 with a predetermined temperature history, and has a device configuration corresponding to the cooling method. For example, in the case of air cooling, the internal space of the cooling device 13 is managed at a predetermined atmospheric temperature by a temperature adjusting device (not shown), and the work W carried into the cooling device 13 is cooled to a predetermined temperature at a predetermined cooling rate. The Or if it is water cooling, the cooling device 13 has the liquid tank of the cooling fluid which is not shown in figure, and immersing the workpiece | work W carried in in the cooling device 13 in a cooling fluid, and predetermined temperature with a predetermined cooling rate. Until cooled.

  Next, the temperature condition (temperature history) of the tempering process will be described with reference to FIG. 6 and FIG.

  In the tempering method (tempering step S2) according to the present invention, as shown in FIG. 6, the temperature of the workpiece W is increased by induction heating from the temperature rising start temperature r0 to the target temperature r1 (temperature rising step S211). At this time, the rate of temperature increase is, for example, constant, and the workpiece W is continuously heated so that the temperature rises as time elapses from the start of heating. Such a temperature history is, for example, output during the temperature raising step S211 of the induction heating device 19 until the workpiece W reaches the target temperature r1 (between the temperature raising start time t0 and the temperature raising end time t1) ( This can be achieved by maintaining the output during heating at a constant value.

  Next, atmosphere heating is performed on the workpiece W that has been heated (heated up) to the target temperature r1, and the temperature of the workpiece W is recovered from the temperature r2 at the start of recovery to the target temperature r1 (reheating step S212). ). Since the temperature raising step S211 and the heat retaining step S213 are performed by different heating devices (induction heating device 19, second furnace chamber 28 and second heater 29 as the atmosphere heating device), the temperature raising step S211 to the heat retaining step are performed. Until the process proceeds to S213, the temperature of the workpiece W decreases with the passage of time from the target temperature r1. Therefore, the workpiece W that has completed the temperature raising step S211 is carried into the recuperator 15 (see FIG. 4), and the temperature of the workpiece W is recovered to the target temperature r1 by atmospheric heating. Such a temperature history is, for example, until the workpiece W reaches the target temperature r1 from the temperature r2 at the start of recuperation (between the time t2 from the start of recuperation and the time t3 at the end of recuperation). This can be achieved by heating the atmosphere in the first furnace chamber 26 so that the temperature in the first furnace chamber 26 is slightly higher than the target temperature r1 (for example, the target temperature r1 + 20 to the target temperature r1 + 30 ° C.) with one heater 27 (see FIG. 4).

  After the temperature of the workpiece W is recovered to the target temperature r1 in this way, the workpiece W is subjected to atmospheric heating, and a temperature range of a predetermined width including the target temperature r1, specifically, the residual required for the workpiece W. The workpiece W after rewarming is kept warm for a predetermined time within the allowable temperature range R set according to the austenite amount and hardness (heat keeping step S213). In the present embodiment, the atmosphere heating of the workpiece W is controlled so that the workpiece W is maintained at a temperature substantially equal to the target temperature r1 from the heat retention start time t3 to the heat retention end time t4. Such a temperature history is obtained, for example, by the second heater 29 of the heat retaining device 16 (see FIG. 4) from the heat retention start time t3 to the heat retention end time t4, so that the ambient temperature in the second furnace chamber 28 becomes the target temperature r1. This can be realized by heating the atmosphere so as to maintain a substantially equal state.

  Here, the allowable temperature range R is set as follows, for example. First, the amount of retained austenite after heat treatment (after tempering) of the workpiece W when the target temperature r1 at the time of raising the workpiece W is changed is measured. Then, based on the relationship between the measured amount of retained austenite and the target temperature r1, a first temperature lower limit value at which the amount of retained austenite falls within the allowable range is set. In the present embodiment, as shown in FIG. 7A, approximate curves C1 and C2 indicating the relationship between the target temperature r1 and the retained austenite amount are derived based on the measured values of the retained austenite amount. In FIG. 7 (a), C1 represents an approximate curve on the upper limit side of the variation when the variation in the measured value of the retained austenite amount is taken into account, and C2 represents the lower limit side of the variation in the measured value of the retained austenite amount. An approximate curve is shown. Here, for example, when the allowable upper limit value of the retained austenite amount is Q1, the target temperature ra1 corresponding to the allowable upper limit value Q1 is calculated based on the upper limit side approximate curve C1. The temperature range R1 higher than the target temperature ra1 is a temperature range (first allowable temperature range) where the amount of retained austenite falls within the allowable range, and the target temperature ra1 at that time is the first temperature lower limit value referred to in the present invention. Become.

  Next, the hardness after heat treatment (after tempering) of the workpiece W when the target temperature r1 at the time of raising the workpiece W is changed is measured. The type of hardness is not particularly limited, but for example, Rockwell hardness is measured. Then, based on the relationship between the measured hardness and the target temperature r1, a second temperature upper limit value and a second temperature lower limit value at which the hardness falls within an allowable range are set. In the present embodiment, as shown in FIG. 7B, approximate curves C3 and C4 indicating the relationship between the target temperature r1 and the hardness are derived based on a plurality of measured hardness values. In FIG. 7B, C3 represents an approximate curve on the upper limit side of the variation when the variation in the measured value of hardness is taken into account, and C4 represents an approximate curve on the lower limit side of the variation in the measured value of hardness. Is shown. Here, for example, when the allowable upper limit value of hardness is H1 and the allowable lower limit value is H2, the target temperature rb1 corresponding to the allowable upper limit value H1 is calculated based on the upper limit side approximate curve C3. Further, a target temperature rb2 corresponding to the allowable lower limit value H2 is calculated based on the lower limit side approximate curve C4. The temperature range R2 between these target temperatures rb1 and rb2 is a temperature range (second allowable temperature range) in which the hardness falls within the allowable range, and the target temperatures rb1 and rb2 at that time are referred to in the present invention. It becomes a two temperature upper limit and a second temperature lower limit.

  As described above, after obtaining the first allowable temperature range R1 in which the retained austenite amount falls within the allowable range and the second allowable temperature range R2 in which the hardness falls within the allowable range, the first allowable temperature range R1 and the second allowable temperature range R1 are calculated. The allowable temperature range R (see FIG. 6) is set within a range where the allowable temperature range R2 overlaps. In the case of the present embodiment, as shown in FIG. 7C, the entire range where the first allowable temperature range R1 and the second allowable temperature range R2 overlap is set as the allowable temperature range R. Thus, the allowable temperature range R at the time of heat retention can be set. In this case, the target temperature r1 is set within the allowable temperature range R.

  Finally, the workpiece W kept warm for a predetermined time within the allowable temperature range R is cooled. In the present embodiment, the workpiece W is unloaded from the second furnace chamber 28 of the atmosphere heating device (the heat retaining device 16), and conveyed to the cooling device 13 through the second passage chamber 32 (see FIG. 3). Thereby, the workpiece | work W is cooled to the predetermined | prescribed temperature r5 with a predetermined | prescribed cooling rate, and the tempering process is performed to the workpiece | work W (cooling process S22).

  In the present embodiment, for example, the output pattern of the induction heating device 19 and the output patterns of the first and second heaters 27 and 29 are stored in the control unit 33 (see FIG. 4) so as to follow the above-described temperature history. Then, in the heating step S21 (temperature raising step S211, reheating step S212, heat retention step S213) and cooling step S22, the control unit 33 sends a command to the power source 21 based on the stored output pattern. Thus, a predetermined pattern of electric power is applied to the heating coil 20 (see FIGS. 4 and 5) of the induction heating device 19 connected to the power source 21 and the first and second heaters 27 and 29 also connected to the power source 21. The temperature history shown in FIG. 6 can be applied to the workpiece W.

  Next, an example of the tempering step S2 of the workpiece W using the tempering apparatus 10 having the above configuration will be described.

(S21) Heating step (S211) Temperature raising step In this step, first, the first opening / closing means 23 shown in FIG. The workpiece W conveyed to the inside is carried into the temperature raising device 14. At this time, the upper surface of the support portion 17 is at the same level as the transport path 11. The output of the induction heating device 19 is at or near zero. And if the workpiece | work W arrives on the support part 17, the support part 17 will be raised by the raising / lowering part 18 with the horizontal positioning with respect to the support part 17 of the workpiece | work W as needed. Thus, the workpiece W placed on the support portion 17 is introduced and held at a predetermined position of the induction heating device 19, in this embodiment, at a predetermined position on the inner circumference of the heating coil 20 of the induction heating device 19 ( (See FIG. 4). In this state, the control unit 33 sends a command to the power source 21 and supplies a predetermined pattern of power to the heating coil 20 to start heating the workpiece W, and heats the workpiece W to a target temperature r1 with a constant gradient. (See FIG. 6). The induction heating described above is preferably performed in a so-called low frequency range (up to several kHz). Thereby, not only the surface layer part of the workpiece W but also the core part can be heated to a high temperature. During this period (between the temperature raising start time t0 and the temperature raising end time t1), the control unit 33 controls the work W so that the temperature of the work W does not exceed the upper limit of the allowable temperature range R (allowable temperature upper limit value r3). It is better to control the heating. In this case, the target temperature r1 is set within the range of the allowable temperature range R (the allowable temperature lower limit value r4 or more and the allowable temperature upper limit value r3 or less). Further, the temperature of the support unit 17 may be increased by rotating the shaft of the support unit 17 by the control unit 33 while heating. By rotating the support portion 17, the entire workpiece W on the support portion 17 is heated uniformly.

(S212) Reheating Step After the workpiece W is heated up to the target temperature r1 in this way, the workpiece W is detached from the heating processing position of the induction heating device 19 (a predetermined position on the inner periphery of the heating coil 20), and is brought into an open state. It is carried out of the temperature raising device 14 through a certain outlet side opening 14b. Specifically, the control unit 33 sends a command to the power source 21 to stop the heating of the workpiece W by the induction heating device 19, and lowers the support unit 17 by the elevating unit 18 to move the workpiece W on the support unit 17. Return to the conveyance path 11. Then, with the second opening / closing means 24 opening the outlet side opening 14b of the temperature raising device 14, it is conveyed in a predetermined direction on the conveyance path 11 by an appropriate means (not shown), and the workpiece W Unload. Then, the unloaded work W is carried into the first furnace chamber 26 of the recuperator 15 through the first passage chamber 25, and the work W is subjected to predetermined atmosphere heating. As a result, after the temperature rise, the temperature of the workpiece W (see FIG. 6) that has fallen to the temperature r2 between the temperature rise end time t1 and the temperature recovery start time t2 is recovered to the target temperature r1. At this time, the inlet-side opening 15 a of the recuperator 15 is temporarily opened and then closed after the work W is carried into the recuperator 15. During this period (between the reheating start time t2 and the rewarming end time t3), the control unit 33 controls the work piece 33 so that the temperature of the work W does not exceed the upper limit of the allowable temperature range R (allowable temperature upper limit value r3). It is good to control the heating of W.

(S213) Heat retention step After the workpiece W is heated again to the target temperature r1 in this way, the outlet side opening 15b is opened, the workpiece W is carried out of the recuperator 15 and carried into the adjacent heat retainer 16. To do. At this time, the inlet-side opening of the heat retaining device 16 (that is, the outlet-side opening 15b of the recuperating device 15) is temporarily opened and then closed after the work W is carried into the heat retaining device 16. Then, the workpiece W is heated in the atmosphere, and the workpiece W is kept warm for a predetermined time within the allowable temperature range R. During this period (between the heat retention start time t3 and the heat retention end time t4), the temperature of the workpiece W is maintained within the allowable temperature range R (the allowable temperature upper limit value r3 or less and the allowable temperature lower limit value r4). As described above, it is preferable to control the heating of the workpiece W by the control unit 33. However, since the heating during this time is performed by atmospheric heating by the electric heater (second heater 29), the above temperature control is relatively Easy. As an example, when the material of the workpiece W is high carbon chrome bearing steel, the allowable temperature range R is set within a range of 290 ° C. or higher and 340 ° C. or lower, preferably 303 ° C. or higher and 315 ° C. or lower. Set within the range. The warming time of the workpiece W (between the warming start time t3 and the warming end time t4) is set within a range of 3 minutes or more and 7 minutes or less, preferably 4 minutes or more and 6 minutes or less. Set by.

(S22) Cooling step After the workpiece W is kept warm for a predetermined time in this way, an unshown outlet side opening is opened and the workpiece W is carried out of the heat retaining device 16. The unloaded work W is carried into the cooling device 13 through the second passage chamber 32 (see FIG. 3), and at a predetermined cooling rate, for example, a temperature lower than a predetermined temperature r5, for example, a temperature rising start temperature r0. (At the end of cooling t5). Thereby, the tempering process for the workpiece W is completed. The subsequent workpiece W is also subjected to a tempering process following the same path, and is discharged to the outside of the tempering apparatus 10. The discharged work W is conveyed to the next process such as a cleaning process S5 or a polishing process (not shown). As described above, the tempering process is continuously and automatically performed on the plurality of workpieces W.

  As described above, according to the tempering method according to the present invention, the workpiece W is heated to the target temperature r1 by induction heating (temperature raising step S211). Heating to a necessary temperature range (for example, 250 ° C. or higher) is possible. Further, in the present invention, the allowable temperature range R is set according to the amount of retained austenite and hardness required for the work W, and the temperature of the work W after the temperature rise is kept within the allowable temperature range R. While raising the temperature in a short time, the amount of retained austenite contained in the work W after tempering can be reduced to a required level or less, and the hardness of the work W can be kept within a predetermined range. In addition, since the heating control for keeping the workpiece W within the temperature range R is performed by atmospheric heating, the workpiece W can be kept warm while heating the workpiece W evenly. Therefore, variation in temperature inside the workpiece W can be suppressed and uniform tempering processing can be performed. Moreover, if it is atmosphere heating, compared with induction heating etc., the temperature of the workpiece | work W is hard to fall. Therefore, the heating control during the heat retaining step S213 can be performed relatively easily. Of course, if the atmosphere is heated, a large amount of workpieces W can be processed at one time. As described above, according to the present invention, the amount of retained austenite contained in the workpiece W can be reduced to a required level or less, and the hardness of the workpiece W can be kept within a predetermined range. Also suitable machine parts can be obtained. In addition, the time required for the temperature increase is short, and a uniform process can be performed on many workpieces W in a relatively short time, so that the productivity is excellent. Of course, the equipment can be reduced in size as compared with the case where all the heat treatments from the temperature raising step S211 to the heat retaining step S213 are performed in the atmosphere heating furnace.

  Further, in the present embodiment, after the temperature raising step S211, and before the heat retention step S213, the workpiece W after the temperature rise is heated in the atmosphere to recover the temperature of the workpiece W to the target temperature r1 at the time of the temperature rise. Since the temperature step S212 is further provided, the temperature of the workpiece W can be shifted to the heat retention step S213 in a state in which the temperature is returned from the temperature r2 when the reheating device 15 is carried to the target temperature r1 (see FIG. 6). . In addition, by heating the workpiece W by atmospheric heating in both the warming step S212 and the warming step S213, it is possible to suppress a decrease in temperature when shifting from the warming step S212 to the warming step S213. Therefore, by providing the rewarming step S212, the work W can be efficiently transferred to the heat retaining step S213.

  In this case, in the rewarming step S212, the set temperature of the atmosphere heating is set slightly higher than the target temperature r1 at the time of temperature rise (for example, the target temperature + 20 to the target temperature + 30 ° C.). The time required can be shortened. Moreover, since the internal temperature of the recuperator 15 and the heat retaining device 16 is sealed separately, it is easy to make individual atmosphere temperatures different.

  Although the tempering method and the tempering apparatus 10 according to the first embodiment of the present invention have been described above, the tempering apparatus 10 can be appropriately modified without departing from the gist of the present invention. .

  For example, as shown in FIG. 8, a plurality of temperature measurement points w1 to w6 are provided on the surface of the workpiece W, and an easy temperature rise point that is most likely to rise among the plurality of temperature measurement points w1 to w6 by induction heating. The heating of the workpiece W may be controlled in advance so that the temperature at the easy temperature rising point does not exceed the upper limit (allowable temperature upper limit value r3) of the allowable temperature range R, particularly in the temperature raising step S211. As a result, it is possible to avoid a situation in which the workpiece W is partially heated excessively, so that the hardness after the heat treatment of the workpiece W is homogenized over the entire region and is within an allowable range, so that more accurate baking can be performed. Return processing can be performed.

  Moreover, in the said embodiment, the output part of the induction heating which can heat the said workpiece | work W to the target temperature r1 is made to memorize | store in the control part 33 beforehand, without the workpiece | work W exceeding the upper limit of the allowable temperature range R by temperature rising process S211. The case where the heating of the workpiece W is controlled based on the output pattern stored in the temperature raising step S211 is exemplified, but a control method different from this may be adopted. For example, although illustration is omitted, the temperature of the workpiece W is raised while measuring the surface temperature of the workpiece W with a temperature measuring device (such as a thermocouple) provided in the heating device 12, and the control unit is based on the measured temperature each time. 33 may control the temperature rise of the workpiece W by sending an appropriate output command to the power source 21. According to this, more precise heating control reflecting the variation for each workpiece W is possible. At this time, the temperature rise of the workpiece W may be controlled while measuring the temperature at the easy temperature rise point of the workpiece W described above.

  Of course, the above-described control method can also be applied to the reheating step S212 and the heat retaining step S213. That is, although illustration is similarly omitted, the workpiece W is heated and kept warm while measuring the surface temperature of the workpiece W with a temperature measuring device provided in the heating device 12, and the control unit 33 is based on the measured temperature each time. The heating and heat retention of the workpiece W may be controlled by sending an appropriate output command to the power source 21.

  Moreover, although the case where the workpiece | work W was heated one by one with the induction heating apparatus 19 (temperature rising and heat retention) was illustrated in the said embodiment, it is also possible to take methods other than this. For example, although illustration is omitted, two or more workpieces W in a vertically stacked state are raised at a time, for example, a predetermined position of an induction heating device having three or more heating coils (the inner circumference of three or more heating coils) ) Introduce two or more works together. And by starting the induction heating apparatus of the said structure, temperature rising process S211 is implemented with respect to the 2 or more workpiece | work W at once. By performing the heat treatment in this way, it becomes possible to further improve productivity. When different output patterns are required depending on the position in the vertical stacking direction of the workpieces W, some of the heating coils may be heated and controlled separately from the remaining heating coils.

  In the above embodiment, the case where the workpiece W is a raceway ring (outer ring or inner ring) of a rolling bearing is illustrated as an object of the tempering method according to the present invention. It is applicable to. FIG. 9 shows a longitudinal sectional view of a temperature raising device 101 constituting a tempering device according to an example (second embodiment of the present invention). As shown in FIG. 9, the temperature raising device 101 is for performing a predetermined heat treatment by induction heating on an outer joint member of a constant velocity universal joint as a work Wa. It mainly includes a support unit 102 that can support a plurality of workpieces Wa conveyed in the direction one by one, a lifting unit 103 that drives the support unit 102 to move up and down, and an induction heating device 104 that is positioned above the support unit 102. The induction heating device 104 includes, for example, a heating coil 105 formed in an annular shape with a conductive metal such as a copper tube, and a power source 21 that supplies power to the heating coil 105. In this embodiment, the heating coil 105 is a general-purpose multi-winding heating coil such as a solenoid coil, and the workpiece is placed on the support unit 102 by raising the support unit 102 by the elevating unit 103. When W is introduced into the inner periphery of the heating coil 105, the number of turns (axial dimension) of the heating coil 105 is set so that the entire area in the axial direction of the workpiece Wa is covered with the heating coil 105 as shown in FIG. .

  Further, when the workpiece Wa is an outer joint member, it is desirable to place the workpiece Wa on the support portion 102 with the cup portion Wb of the outer joint member facing downward and the stem portion Wc of the outer joint member facing upward, and the workpiece Wa. It is desirable to match the center line of the (outer joint member) with the center line of the heating coil 105. Therefore, in this case, it is desirable to provide a positioning device on or around the transport path 11 so that the workpiece Wa is positioned and fixed on the support portion 102 at a position that satisfies the above-described relationship. Although not shown, it is desirable that the support unit 102 and a part of the elevating unit 103 connected to the support unit 102 be rotatable around the center line, as in the first embodiment.

  In addition, you may comprise similarly to 1st embodiment about structures other than the temperature rising apparatus 101 mentioned above among tempering apparatuses. That is, for the reheating device, the heat retaining device, and the cooling device that constitute the heating device 12 together with the temperature raising device 101, the reheating device 15, the heat retaining device 16, and the cooling device 13 shown in FIGS. Is possible.

  Moreover, it is possible to set about the temperature conditions (temperature history) of a tempering process based on the same idea as 1st embodiment. That is, in the temperature raising step S211 of the tempering step S2, as shown in FIG. 6, the workpiece Wa is heated to the target temperature r1 at a constant temperature raising rate. When the heating coil 105 having the form shown in FIG. 9 is used, the cup portion Wb and the stem portion Wc of the outer joint member have different easiness in raising the temperature. Is desirably controlled so as not to exceed the target temperature r1. As in the first embodiment, the temperature history in the reheating step S212 and the heat retaining step S213 may be controlled as shown in FIG. Moreover, you may set similarly to 1st embodiment also about the allowable temperature range R at the time of heat retention process S213. In this case, the target temperature r1 is set within the allowable temperature range R.

  In the present embodiment, for example, the output pattern of the induction heating device 104 and the output patterns of the first and second heaters 27 and 29 are stored in the control unit 33 (see FIG. 4) so as to follow the above-described temperature history. Then, in the heating step S21 (temperature raising step S211, reheating step S212, heat retention step S213) and cooling step S22, the control unit 33 sends a command to the power source 21 based on the stored output pattern. Thereby, electric power of a predetermined pattern is supplied to the heating coil 105 (see FIG. 9) of the induction heating device 104 connected to the power source 21 and the first and second heaters 27 and 29 that are also connected to the power source 21. The temperature history shown in FIG. 6 can be given to the workpiece Wa.

  Next, an example of the tempering step S2 of the workpiece Wa using the tempering apparatus having the above configuration will be described.

(S21) Heating step (S211) Temperature raising step In this step, first, the first opening / closing means 23 shown in FIG. 4 opens the inlet side opening 14a of the temperature raising device 101 (FIG. 9) on the conveying path 11. Is carried into the temperature raising device 14. When the workpiece W reaches the support portion 102 (FIG. 9), the support portion 104 is raised by the elevating portion 103 with the horizontal positioning of the workpiece Wa with respect to the support portion 102 as necessary. Thereby, the whole area in the axial direction of the workpiece Wa placed on the support portion 102 is introduced to a predetermined position of the induction heating device 104, in this embodiment, to a predetermined position on the inner periphery of the heating coil 105 of the induction heating device 104, Held (see FIG. 9). In this state, the control unit 33 sends a command to the power source 21 and supplies a predetermined pattern of power to the heating coil 105 to start heating the workpiece Wa, and heats the workpiece Wa to a temperature r1 with a constant gradient. (See FIG. 6). The induction heating described above is preferably performed in an appropriate frequency range in accordance with the material, shape, size, and the like of the workpiece Wa. For example, in the present embodiment, it is preferably performed in a low frequency range (up to several kHz). Thereby, not only the surface layer part of the workpiece Wa but also the core part can be heated to a high temperature. During this period (between the temperature raising start time t0 and the temperature raising end time t1), the temperature of the cup portion Wb that is relatively easy to raise the temperature of the workpiece Wa is the upper limit of the allowable temperature range R (allowable temperature upper limit value r3). The heating of the workpiece Wa is preferably controlled by the control unit 33 so as not to exceed. In this case, the target temperature r1 is set within the range of the allowable temperature range R (the allowable temperature lower limit value r4 or more and the allowable temperature upper limit value r3 or less). Further, while heating, the temperature of the entire workpiece Wa on the support portion 102 is raised uniformly by raising the temperature while rotating the support portion 102 by the control portion 33.

(S212) Reheating step After the workpiece Wa is heated to the target temperature r1 in this way, the workpiece Wa is detached from the heating processing position of the induction heating device 104 (a predetermined position on the inner periphery of the heating coil 105), and the workpiece Wa is opened. It is carried out of the temperature raising device 101 through a certain outlet side opening 14b. Specifically, the control unit 33 sends a command to the power source 21 to stop the heating of the work Wa by the induction heating device 104 and lower the support unit 102 by the elevating unit 103 to move the work Wa on the support unit 102. Return to the conveyance path 11. Then, the outlet side opening 14b of the temperature raising device 101 is opened by the second opening / closing means 24, and is conveyed in a predetermined direction on the conveyance path 11 by an appropriate means (not shown). Unload. Then, the unloaded workpiece Wa is loaded into the first furnace chamber 26 of the recuperator 15 through the first passage chamber 25, and the workpiece Wa is subjected to predetermined atmosphere heating. As a result, after the temperature rise, the temperature of the workpiece Wa (see FIG. 6) that has fallen to the temperature r2 between the temperature rise end time t1 and the temperature recovery start time t2 is recovered to the target temperature r1. During this period (between the reheating start time t2 and the rewarming end time t3), control is performed so that the temperature of the cup portion Wb of the workpiece Wa does not exceed the upper limit (allowable temperature upper limit value r3) of the allowable temperature range R. The heating of the workpiece Wa may be controlled by the unit 33.

(S213) Thermal insulation process After heating the workpiece Wa to the target temperature r1 in this way, the outlet side opening 15b is opened, the workpiece Wa is carried out of the reheating device 15, and carried into the adjacent thermal insulation device 16. To do. Then, the workpiece Wa is heated in the atmosphere, and the workpiece Wa is kept warm for a predetermined time within the allowable temperature range R. During this period (from the heat retention start time t3 to the heat retention end time t4), the temperature of the cup portion Wb of the workpiece Wa is maintained within the allowable temperature range R (allowable temperature upper limit r3 or less and allowable) The heating of the work Wa is preferably controlled by the control unit 33 so that the temperature is lower than the lower temperature limit r4. As an example, when the material of the workpiece Wa is carbon steel for machine structure, the allowable temperature range R is set within a range of 130 ° C. or higher and 220 ° C. or lower, preferably 150 ° C. or higher and 200 ° C. or lower. Set within the range. In addition, the warming time of the workpiece Wa (between the warming start time t3 and the warming end time t4) is set in the range of 10 seconds or more and 70 minutes or less, preferably in the range of 30 seconds or more and 60 minutes or less. Set by.

(S22) Cooling Step After the workpiece Wa is kept warm for a predetermined time in this way, an unshown outlet side opening is opened and the workpiece Wa is carried out of the heat retaining device 16. The unloaded work Wa is carried into the cooling device 13 through the second passage chamber 32 (see FIG. 3), and at a predetermined cooling rate, for example, a temperature lower than a predetermined temperature r5, for example, a temperature rising start temperature r0. (At the end of cooling t5). Thereby, the tempering process for the workpiece Wa is completed. The subsequent workpiece Wa also follows the same path, is tempered, and is discharged to the outside of the tempering device. The discharged work Wa is conveyed to the next process such as a cleaning process S5 or a polishing process (not shown). As described above, the tempering process is continuously and automatically performed on the plurality of workpieces Wa.

  As described above, according to the tempering method according to the present embodiment, since the workpiece Wa is heated to the target temperature r1 by induction heating (temperature raising step S211), the workpiece Wa is shortened in a shorter time than conventional. Can be heated to the required temperature range. Further, in the present embodiment, the allowable temperature range R is set according to the amount of retained austenite and hardness required for the workpiece Wa, and the workpiece Wa after the temperature rise is kept warm within the allowable temperature range R. While increasing the temperature in a short time, the amount of retained austenite contained in the work Wa after tempering can be reduced to a required level or less, and the hardness of the work Wa can be kept within a predetermined range. Further, since the heating control for keeping the workpiece Wa within the temperature range R is performed by atmospheric heating, the workpiece Wa can be kept warm while heating the workpiece Wa uniformly. Therefore, it is possible to perform a uniform tempering process while suppressing variations in temperature inside the workpiece Wa. In particular, even in the case where the workpiece Wa is a mechanical part having an uneven thickness dimension distribution in the axial direction like the outer joint member of the constant velocity universal joint as in the present embodiment, the temperature in the workpiece Wa generated during induction heating. Can be leveled by atmospheric heating. Therefore, a uniform tempering process can be performed without preparing a plurality of heating coils or the like according to the type of the workpiece Wa or without preparing a heating coil in a dedicated form according to the workpiece Wa. Accordingly, it is possible to avoid the increase in the replacement cost of the heating coil and the setup time associated with the replacement work, and to perform a uniform tempering process at a low cost and in a short time.

  Of course, it is possible to make it difficult to lower the temperature of the workpiece Wa as compared with induction heating or the like by keeping the workpiece Wa warm by atmospheric heating. Therefore, the heating control during the heat retaining step S213 can be performed relatively easily. Of course, if the atmosphere is heated, a large amount of workpieces Wa can be processed at a time. From the above, according to the tempering method according to the present embodiment, the amount of retained austenite contained in the workpiece Wa can be reduced to a required level or less, and the hardness of the workpiece Wa can be kept within a predetermined range. A machine part suitable for use in a high temperature environment can be obtained. Further, the time required for the temperature increase is short, and a uniform treatment can be performed on a large number of workpieces Wa in a relatively short time, so that the productivity is excellent. Specifically, the processing lead time is shortened, which leads to improvement in productivity and reduction of in-process inventory. Of course, the equipment can be reduced in size as compared with the case where all the heat treatments from the temperature raising step S211 to the heat retaining step S213 are performed in the atmosphere heating furnace.

  The present invention is not limited to the embodiment described above, and can be implemented in various forms without departing from the gist of the present invention. That is, the scope of the present invention is defined by the terms of the claims, and includes the equivalent meanings recited in the claims and all modifications within the scope.

  Hereinafter, the details of the experiment demonstrating the usefulness of the tempering method according to the present invention will be described.

  In this experiment, a predetermined tempering treatment was performed using the outer joint member of the constant velocity universal joint as a workpiece. Here, the outer joint member is S53C, which is carbon steel for machine structure, and the outer diameter of the cup portion Wb (see FIG. 10) is 60.85 mm, and the outer diameter of the large-diameter side region of the stem portion Wc is 30 mm. The outer diameter of the small-diameter side region was formed to be 24 mm and subjected to quenching treatment by high-frequency heating.

In addition, the tempering process was performed under the conditions shown in Table 1 while using, for example, the tempering apparatus shown in FIGS. 3, 4, and 9.

And as shown in FIG. 10, with respect to the workpiece | work after a tempering process, the some hardness measurement points W7-W11 were provided, and the hardness [HV] of the workpiece | work in each measurement point W7-W11 was measured. Precisely, the hardness [HV] at a position 0.25 mm deep from each measurement point W7 to W11 set on the surface of the workpiece Wa was measured. The measurement results are shown in Table 2. From Table 2, it was found that the same level of hardness as that of the conventional tempering treatment only by atmospheric heating can be obtained. Further, it has been found that the variation in hardness (for example, the variation in hardness between the cup portion Wb and the stem portion Wc) can be kept small.

DESCRIPTION OF SYMBOLS 10 Tempering apparatus 11 Conveyance path 12 Heating apparatus 13 Cooling apparatus 14,101 Temperature raising apparatus 15 Reheating apparatus 16 Heat retention apparatus 17,102 Supporting part 18,103 Lifting part 19,104 Induction heating apparatus 20,105 Heating coil 21 Power supply 22 Wall portions 23, 24, 30, 31 Opening / closing means 25, 32 Passage chamber 26, 28 Furnace chamber 27, 29 Heater 33 Control unit H1 Allowable upper limit (hardness)
H2 allowable lower limit (hardness)
Q1 allowable upper limit (residual austenite amount)
R allowable temperature range R1 first allowable temperature range (residual austenite amount)
R2 Second allowable temperature range (hardness)
r0 Temperature rising start temperature r1 Target temperature r2 Recovery temperature starting temperature r3 Allowable temperature upper limit r4 Allowable temperature lower limit r5 Cooling end temperature S21 Heating step S211 Heating step S212 Heating step S213 Heat retaining step S22 Cooling step t0 Temperature rising Start time t1 Temperature rise end t2 Heat recovery start time t3 Heat recovery end (at the start of heat retention)
t4 At the end of heat insulation t5 At the end of cooling W, Wa Work

Claims (14)

A heating step of heating the workpiece; and a cooling step of cooling the workpiece heated in the heating step, and controlling the temperature history of the workpiece in the heating step and the cooling step, thereby baking the workpiece. In the method of tempering the workpiece,
The heating step is a heating step of heating the workpiece to a target temperature by induction heating,
Tempering the workpiece, characterized by having a heat retaining step for controlling the heating of the workpiece by atmospheric heating so that the workpiece after the temperature rise is kept warm for a predetermined time within a temperature range of a predetermined width. Method.   A reheating step that is provided after the temperature raising step and before the heat retaining step, recovers the temperature of the workpiece to the target temperature during the temperature elevation by heating the workpiece after the temperature elevation to the atmosphere The work tempering method according to claim 1.   The work tempering method according to claim 2, wherein, in the reheating step, a set temperature of the atmosphere heating is set higher than a target temperature at the time of the temperature rise.   The tempering method for a workpiece according to any one of claims 1 to 3, wherein, in the heat retaining step, the set temperature of the atmosphere heating is set to the same temperature as a target temperature at the time of the temperature rise.   An allowable temperature range as the temperature range of the predetermined width is set according to the amount of retained austenite and hardness required for the workpiece, and the workpiece after the temperature rise is kept warm for a predetermined time within the range of the allowable temperature range. The work tempering method according to claim 1, wherein heating of the work by atmospheric heating is controlled. Based on the relationship between the target temperature when the workpiece is heated and the amount of retained austenite, a first temperature lower limit value is set so that the amount of retained austenite falls within an allowable range, and the target temperature and hardness when the workpiece is heated are increased. Based on the relationship between the second temperature upper limit value and the second temperature lower limit value, the hardness falls within an allowable range,
The allowable temperature range is set in a range in which the region larger than the first temperature lower limit value and the region between the second temperature upper limit value and the second temperature lower limit value overlap each other. The work tempering method described.   The work tempering method according to claim 5 or 6, wherein when the work material is high carbon chromium bearing steel, the allowable temperature range is set within a range of 290 ° C or higher and 340 ° C or lower.   The workpiece according to any one of claims 5 to 7, wherein when the material of the workpiece is high carbon chrome bearing steel, the heat retention time of the workpiece in the heat retention step is set to 3 minutes or more and 7 minutes or less. Tempering method.   The work tempering method according to claim 5 or 6, wherein when the material of the work is carbon steel for machine structure, the allowable temperature range is set within a range of 130 ° C or higher and 220 ° C or lower.   10. The work baking according to claim 5, 6, or 9, wherein when the material of the work is carbon steel for machine structure, the heat keeping time of the work in the heat keeping step is set to 10 seconds or more and 70 minutes or less. Return method.   The method for tempering a workpiece according to any one of claims 1 to 10, wherein the workpiece is heated in the heat retaining step using an atmosphere heating furnace having an electric heater.   A machine part that is tempered by the method according to any one of claims 1 to 11.   The machine part according to claim 12, wherein the machine part is an annular ring of a rolling bearing.   The machine part according to claim 12, wherein the machine part is an outer joint member of a constant velocity universal joint.

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