JP6103279B2 - Heat treatment method - Google Patents

Description

  The present invention relates to a heat treatment method, and more particularly, to a heat treatment method in which a gas for heat treatment is supplied to a furnace in which the work is housed and the work is degreased by heating the furnace.

  An example of this type of heat treatment method is disclosed in Patent Document 1. According to Patent Document 1, in the degreasing step, the inside of the furnace is maintained at a predetermined degreasing temperature, and organic matter (for example, binder) contained in the workpiece is removed by evaporation. In the sintering process subsequent to the degreasing process, the temperature in the furnace is raised to a predetermined sintering temperature, and the workpiece is sintered.

  In the degreasing step, the supply amount of a carrier gas such as an inert gas is adjusted so that the inside of the furnace exhibits a predetermined pressure. Moreover, the gas concentration of the exhaust gas containing the organic substance evaporated in the degreasing process is measured by a sensor attached in the middle of the exhaust pipe. Furthermore, the timing for shifting from the degreasing process to the sintering process is determined based on the gas concentration measured by the sensor. Specifically, the gas concentration of the exhaust gas is high at the beginning of the degreasing process, and gradually decreases due to exhaust in the furnace. When the gas concentration decreases to a predetermined value, the degreasing process shifts to the sintering process.

JP-A 62-250103

  Although the change in the gas concentration of the exhaust gas indicates the progress of degreasing, in Patent Document 1, the supply amount of the carrier gas is not adjusted in accordance with the progress of degreasing (as described above, the supply of the carrier gas) The amount is adjusted so that the inside of the furnace shows a predetermined pressure regardless of the gas concentration). Therefore, in patent document 1, there exists a possibility that the quality of a to-be-processed object, ie, a workpiece | work, may deteriorate by degreasing.

  Therefore, a main object of the present invention is to provide a heat treatment method capable of avoiding deterioration of work quality.

A heat treatment method according to the present invention includes a supply / exhaust process for supplying a supply gas for heat treatment to a furnace chamber (RM1) in which a workpiece (WK1) is housed, and exhausting an exhaust gas used for the heat treatment from the furnace chamber, A heat treatment method comprising: heating with a heater (20) to degrease and sinter the workpiece, wherein the supply / exhaust step refers to the concentration of carbon in the exhaust gas and / or the temperature of the workpiece Thus, the heating process includes a supply gas control process (S7 to S19, S41 to S47) for controlling the concentration of oxygen in the supply gas, and the heating process includes carbon that accounts for the threshold (THo). A degreasing end step ( S21 to S25, S31 to S33) for ending degreasing when the concentration and / or the workpiece temperature satisfy predetermined conditions.

  Preferably, the supply gas control step includes a workpiece temperature measurement step (S7) for repeatedly measuring the workpiece temperature, and a concentration of oxygen in the supply gas so that the workpiece temperature measured by the workpiece temperature measurement step falls within a predetermined range. An oxygen concentration adjusting step (S9 to S19) for adjusting

  Preferably, the supply gas control step includes a carbon concentration measurement step (S41) for repeatedly measuring the concentration of carbon in the exhaust gas, and the supply gas so that the carbon concentration measured by the carbon concentration measurement step falls within a predetermined range. An oxygen concentration adjusting step (S43 to S47, S15 to S19) for adjusting the concentration of oxygen to be occupied is included.

  More preferably, the carbon concentration measurement step includes a gas decomposition step of decomposing the exhaust gas into water and carbon dioxide, and a carbon concentration detection step of detecting the carbon concentration by paying attention to the carbon dioxide decomposed by the gas decomposition step. .

  In one aspect, the oxygen concentration adjustment step stops the adjustment when the adjusted oxygen concentration reaches the upper limit (THo).

  Preferably, the predetermined condition in the heating step includes a concentration condition that a concentration of carbon in the exhaust gas is lower than a threshold value (THc).

  Preferably, the predetermined condition in the heating step includes a temperature condition that the temperature of the workpiece is lower than a threshold value (THw).

  The furnace chamber containing the workpiece was supplied with a heat treatment supply gas, and the workpiece was heated for degreasing and sintering. The oxygen concentration in the supply gas was exhausted from the furnace chamber along with the degreasing. It is controlled with reference to the concentration of carbon in the exhaust gas and / or the temperature of the workpiece. This avoids deterioration of work quality due to insufficient supply or excessive supply of oxygen. The degreasing step is terminated when the concentration of carbon in the exhaust gas discharged from the furnace chamber and / or the temperature of the workpiece satisfy the predetermined conditions. Thereby, deterioration of the quality of the work resulting from insufficient degreasing or excessive degreasing is avoided.

  The above object, other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

It is a block diagram which shows the structure of the batch type heat processing apparatus of this Example. It is sectional drawing which shows the AA cross section of the heating furnace shown in FIG. It is an illustration figure which shows an example of the workpiece holder stored in the heating furnace shown in FIG. It is a flowchart which shows a part of operation | movement of the control apparatus shown in FIG. It is a flowchart which shows a part of other operation | movement of the control apparatus shown in FIG. (A) is a graph which shows an example of the change of the furnace temperature, (B) is a graph which shows an example of the change of the density | concentration of the carbon dioxide which occupies for the waste gas processed by the waste gas processing apparatus, (C) is a furnace It is a graph which shows an example of the change of the density | concentration of oxygen which occupies for the mixed gas supplied to a chamber. It is a block diagram which shows the structure of the batch type heat processing apparatus of another Example. It is a flowchart which shows a part of operation | movement of the control apparatus shown in FIG. It is a flowchart which shows a part of other operation | movement of the control apparatus shown in FIG. It is a block diagram which shows the structure of the batch type heat processing apparatus of another Example. It is a flowchart which shows a part of operation | movement of the control apparatus shown in FIG. It is a flowchart which shows a part of other operation | movement of the control apparatus shown in FIG. It is a block diagram which shows the structure of the batch type heat processing apparatus of another Example. It is a flowchart which shows a part of operation | movement of the control apparatus shown in FIG. It is a flowchart which shows a part of other operation | movement of the control apparatus shown in FIG.

  Referring to FIGS. 1 and 2, a batch heat treatment apparatus 10 of this embodiment includes a cylindrical heating furnace 16 extending in the vertical direction. A cylindrical furnace chamber RM1 smaller than the cylinder forming the outer shape of the heating furnace 16 is formed inside the heating furnace 16. A plurality of supply pipes 18, 18,... Each extending in the vertical direction are provided on the inner wall of the furnace chamber RM1, and a plurality of heaters 20, 20,.

  Each of the supply pipes 18, 18,... Is a pipe for supplying a heat treatment mixed gas (supply gas) mixed with air and nitrogen to the furnace chamber RM1. The supply amount of air per unit time is controlled to a constant amount by the mass flow controller 34, and the supply amount of nitrogen per unit time is controlled to a constant amount by the mass flow controller 36. Each of the air supply pipes 18, 18,... Is formed with a plurality of air supply holes (not shown) along the length direction thereof. The mixed gas is supplied to the furnace chamber RM1 through these air supply holes.

  Each of the heaters 20, 20,... Is provided for heating the furnace chamber RM1. The heating temperature differs between degreasing and sintering (details will be described later), and the temperature setting of the heaters 20, 20,... Is switched according to the process.

  As can be seen from FIG. 2, the supply pipes 18 and the heaters 20 are alternately arranged at equal intervals in the circumferential direction of the inner wall of the heating furnace 16. Therefore, the density of the mixed gas is made uniform in the furnace chamber RM1, and the temperature is also made uniform in the furnace chamber RM1.

  A circular opening OP1 is formed below the furnace chamber RM1. A support device 12 that supports the rotating shaft 14 is provided below the heating furnace 16. The outer diameter of the rotating shaft 14 is slightly less than the inner diameter of the opening OP1. A seal member (not shown) is provided in the opening OP1 so as to fill a gap between the rotating shaft 14 and the opening OP1. The rotary shaft 14 is supported by the support device 12 so that the axis of the rotary shaft 14 overlaps the center of the opening OP1 and extends in the vertical direction.

  The support device 12 rotates the rotating shaft 14 in the direction around the axis and moves the rotating shaft 14 up and down in the vertical direction. At that time, the uppermost mortar 24a, which will be described later, appears so as to appear outside the heating furnace 16 when the rotating shaft 14 is moved down most, and is stored in the furnace chamber RM1 when the rotating shaft 14 is moved up most. Is raised and lowered.

  A base 22 is provided on the upper end surface of the rotating shaft 14. The upper end surface of the rotating shaft 14 is horizontal, and the upper surface of the base 22 is also horizontal. A work holder 24 is placed on the upper surface of the base 22. The base 22 and the work holder 24 are placed on the upper end surface of the rotary shaft 14 after the rotary shaft 14 is lowered, and then the rotary shaft 14 is raised to be housed in the furnace chamber RM1.

  As shown in FIG. 3, the workpiece holder 24 is formed by a plurality of bowls 24a, 24a,... And a plurality of spacers 24b, 24b,. Here, the distance between the pots 24a, 24a,... (The height of each spacer 24b) is preferably matched with the distance between the air supply holes provided in the air supply pipe 18.

  The bowl 24a is formed in a disc shape, and a plurality of workpieces WK1, WK1,. However, nothing is placed on the uppermost pot 24a, and the uppermost pot 24a functions as a lid that covers the second pot 24a. When the rotary shaft 14 rotates in the direction around the axis, the work holder 24 also rotates in the direction around the axis. Thereby, the workpieces WK1, WK,... Are heated evenly.

  As the work WK1, a multilayer electronic component such as a multilayer capacitor or a multilayer inductor is assumed. Further, in a stage before being heated in the heating furnace 16, a binder such as benzene is mixed in the work WK1. Therefore, when the workpiece WK1 is heated for degreasing, exhaust gas containing carbon is generated from the workpiece WK1.

  An exhaust pipe 26 is provided above the furnace chamber RM 1, and an exhaust gas treatment device 28 is provided above the heating furnace 16. The exhaust gas generated in the furnace chamber RM1 enters the exhaust gas treatment device 28 through the exhaust pipe 26, and is decomposed into water and carbon dioxide by the exhaust gas treatment device 28. The concentration of the decomposed carbon dioxide is measured by the CO2 concentration meter 30. As a result, the concentration of carbon in the exhaust gas discharged from the furnace chamber RM1 is detected.

  Further, thermocouples 28 are inserted into the peaks of the workpieces WK1, WK1,. A thermometer 40 is connected to the thermocouple 38, and the temperatures of the workpieces WK1, WK1,.

  The controller 32 heats the furnace chamber RM1 with the heater 20 to degrease the workpieces WK1, WK1,..., And refers to the temperature of the workpieces WK1, WK1,. , 36 are controlled. Further, the timing for shifting from the degreasing process to the sintering process is determined with reference to the concentration of carbon dioxide measured by the CO2 concentration meter 30. Specifically, the control device 32 performs degreasing according to the flowcharts shown in FIGS. 4 and 5.

  In step S1, various variables (= P, I, D, Δt, SV1 (n)) referred to in the calculation in step S9 described later, and thresholds THo and THc referred in steps S17 and S25 described later, respectively. Set initially.

  In step S3, the mass flow controllers 34 and 36 are activated to supply a heat treatment gas mixture to the furnace chamber RM1. At this time, the supply amount of the mixed gas per unit time is kept constant. In step S5, the heater 20 is activated to heat the furnace chamber RM1. The temperature of the furnace chamber RM1 is set to 280 ° which is a temperature suitable for degreasing.

In step S7, the temperatures of the workpieces WK, WK,... Measured by the thermometer 40 are acquired as “PV1 (n)”. In step S9, the difference ΔMV1 (n) is calculated according to Equation 1 and Equation 2.

  In Equation 1, the variable SV1 (n) is a target temperature, and is set to “297 ° C.”, for example. As a result of the calculation according to Equation 1, the difference between the temperature PV1 (n) acquired in step S7 and the target temperature SV1 (n) is calculated as a deviation e (n). In Equation 2, variables P, I, and D are a proportional parameter, an integral parameter, and a differential parameter, respectively, and variable Δt is a sampling period (= acquisition period of temperature PV1 (n), “n”, “n + 1”, and “ time difference from each of n−1 ″).

  Therefore, the difference ΔMV1 (n) obtained by Equation 1 and Equation 2 includes deviations e (n−1) and e (n−2) calculated in the past two times in addition to the latest deviation e (n). Is reflected.

  In step S11, it is determined whether or not the calculated difference ΔMV1 (n) is “0”. In step S13, it is determined whether or not the calculated difference ΔMV1 (n) exceeds “0”. If the determination result of step S11 is YES, it will return to step S7. If the determination result of step S11 is NO and the determination result of step S13 is NO, it will consider that acquisition temperature PV1 (n) is too high, and will progress to step S15.

  In step S15, the mass flow controllers 34 and 36 are controlled so that the concentration of oxygen in the mixed gas supplied to the furnace chamber RM1 decreases. When the process of step S15 is completed, the process returns to step S7.

  If the determination result of step S11 is NO and the determination result of step S13 is YES, it will consider that acquisition temperature PV1 (n) is too low, and will progress to step S17. In step S17, it is determined whether or not the concentration of oxygen in the mixed gas supplied to the furnace chamber RM1 is lower than the threshold value THo. If the determination result is YES, the process proceeds to step S19, while if the determination result is NO. Proceed to step S21.

  In step S19, the mass flow controllers 34 and 36 are controlled so that the concentration of oxygen in the mixed gas supplied to the furnace chamber RM1 increases. When the process of step S19 is completed, the process returns to step S7.

  Therefore, the oxygen concentration is adjusted so that the acquisition temperature PV1 (n) falls within the range of “297 ° C. ± α”. In step S15 or S19, the mass flow controllers 34 and 36 are controlled so that the supply amount of the mixed gas per unit time does not vary.

  In step S21, the mass flow controllers 34 and 36 are controlled so that the concentration of oxygen in the mixed gas supplied to the furnace chamber RM1 indicates the threshold value THo. In step S23, the carbon dioxide concentration measured by the CO2 concentration meter 30 is acquired. In step S25, it is determined whether or not the acquired carbon dioxide concentration is lower than a threshold value THc. If a determination result is NO, it will return to step S7, and if a determination result is YES, it will transfer to a sintering process.

  The threshold value THo is set to “9.8%”, and the threshold value THc is set to “1.0%”. For this reason, the degreasing is terminated when the oxygen concentration reaches 9.8% and the carbon dioxide concentration decreases to 1.0%. When the process proceeds to the sintering process, the furnace chamber RM1 is further heated by the heater 20, and the temperature of the furnace chamber RM1 is raised to a temperature suitable for the sintering process.

  As a result of the control device 32 executing the process as described above, the temperature of the furnace chamber RM1 changes as shown in FIG. 6A, and the carbon dioxide concentration measured by the CO2 concentration meter 30 is shown in FIG. 6B. The oxygen concentration in the mixed gas supplied to the furnace chamber RM1 changes as shown in FIG. 6C.

  That is, the oxygen concentration is in the range of 3.5% to 4.0% so that the temperature of the workpieces WK, WK,... It is adjusted with. When 300 minutes elapses, degreasing approaches the end, and the carbon dioxide concentration begins to decrease. The oxygen concentration gradually increases to compensate for the decrease in the carbon dioxide concentration and reaches the upper limit of 9.8%. The carbon dioxide concentration gradually decreases after the oxygen concentration reaches the upper limit, and decreases to 1.0% when about 355 minutes have elapsed. Degreasing is terminated here and the temperature of the heater 20 rises due to the sintering process.

  As can be seen from the above description, the supply gas for heat treatment is supplied to the furnace chamber RM1 in which the workpieces WK1, WK1,... Are housed, and the exhaust gas used for the heat treatment is discharged from the furnace chamber RM1 (supply / exhaust process). ). The furnace chamber RM1 is heated in order to degrease and sinter the workpieces WK1, WK1,... (Heating process). In part of the supply / exhaust process, the concentration of oxygen in the supply gas is controlled by referring to the temperatures of the workpieces WK, WK,... (Supply gas control process: S7 to S19). In a part of the heating process, degreasing is performed when the concentration of carbon in the exhaust gas (actually, the carbon dioxide concentration) satisfies a predetermined condition (specifically, the condition that the carbon dioxide concentration is equal to or lower than the threshold value THc). Finished (Degreasing end step: S23 to S25).

  Supply gas for heat treatment is supplied to the furnace chamber RM1 containing the workpieces WK, WK,... And the workpieces WK, WK,... Are heated for degreasing and sintering. The temperature is controlled with reference to the temperatures of the workpieces WK, WK,. This avoids deterioration of the quality of the workpieces WK, WK,... Due to insufficient supply of oxygen or excessive supply. Further, the degreasing step is terminated when the concentration of carbon in the exhaust gas discharged from the furnace chamber RM1 satisfies a predetermined condition. This avoids deterioration of the quality of the workpieces WK, WK,... Due to insufficient degreasing or excessive degreasing.

  This embodiment also has the following significance. That is, since the structure is simple and can be externally attached, it can be used not only in a small experimental furnace but also in a large experimental furnace, and can be used not only in an experimental furnace but also in a mass production furnace. Further, if a profile until the end of degreasing is automatically created, any charge can be automatically operated without changing the setting. Moreover, it is not necessary to acquire conditions for every charge, and degreasing can be performed even for parts whose degreasing time is unknown.

  Furthermore, even if there is a difference in work quality between batches or individual differences in the quality of the heating furnace, lack of degreasing does not occur. Moreover, since it does not move to the next process (sintering process) until the remaining carbon is fully discharged | emitted, the fall of the quality resulting from residual carbon can be suppressed. Furthermore, by using the logical product condition of the oxygen concentration and the carbon dioxide concentration as the determination condition (S17, S25), it is possible to avoid an erroneous determination of the timing for ending the degreasing process.

  Referring to FIG. 7, the batch type heat treatment apparatus 10 of another embodiment is the same as the batch type heat treatment apparatus 10 shown in FIG. 1 except that the CO 2 concentration meter 30 is omitted. Also, the flowcharts of FIGS. 8 to 9 representing the processing of the control device 32 are the same as the flowcharts of FIGS. 4 to 5 except that steps S31 to S33 are provided instead of steps S23 to S25. Therefore, the redundant description regarding the same configuration or processing is omitted.

  The control device 32 acquires the temperatures of the workpieces WK1, WK1,... From the thermometer 40 in step S31 shown in FIG. In step S33, it is determined whether or not the acquired temperature is equal to or lower than a threshold value THwk. The threshold value THwk is set to “292 °. If the determination result is NO, the process returns to step S7. If the determination result is YES, the degreasing is completed and the process proceeds to the sintering process. The threshold value THo is“ 9.8. Therefore, the degreasing process is terminated when the oxygen concentration reaches 9.8% and the temperature of the workpieces WK1 and WK1 is reduced to 292 °.

  According to this embodiment, the degreasing step is terminated when the temperature of the workpieces WK1, WK1, satisfies a predetermined condition (specifically, a condition that the workpiece temperature is equal to or lower than the threshold value THw) (end step: S31 ~ S33). This avoids deterioration of the quality of the workpieces WK1, WK1,... Due to insufficient degreasing or excessive degreasing.

  Referring to FIG. 10, the batch heat treatment apparatus 10 of the other embodiments is the same as the batch heat treatment apparatus 10 shown in FIG. 1 except that the thermocouple 38 and the thermometer 40 are omitted. Moreover, the flowchart of FIGS. 11-12 showing the process of the control apparatus 32 is the same as that of FIGS. 4-5 except the point provided with step S41-S47 instead of step S7-S13. Therefore, the redundant description regarding the same configuration or processing is omitted.

In step S41, the carbon dioxide concentration measured by the CO2 concentration meter 30 is acquired as “PV2 (n)”. In step S43, the difference ΔMV2 (n) is calculated according to Equation 3 and Equation 4.

  In Equation 3, the variable SV2 (n) is the target concentration, and is set to “1.3%”, for example. As a result of the calculation according to Equation 3, the difference between the carbon dioxide concentration PV2 (n) acquired in step S41 and the target concentration SV2 (n) is calculated as a deviation e (n). In Equation 4, variables P, I, and D are a proportional parameter, an integral parameter, and a differential parameter, respectively, and variable Δt is a sampling period (= an acquisition period of carbon dioxide concentration PV2 (n), “n” and “n + 1”. And a time difference from each of “n−1”).

  Therefore, the difference ΔMV2 (n) obtained by Equation 3 and Equation 4 includes the deviations e (n−1) and e (n−2) calculated in the past two times in addition to the latest deviation e (n). Is reflected.

  In step S45, it is determined whether or not the calculated difference ΔMV2 (n) is “0”. In step S47, it is determined whether or not the calculated difference ΔMV2 (n) exceeds “0”. If the determination result of step S45 is YES, it will return to step S41. If the determination result of step S45 is NO and the determination result of step S47 is NO, it is considered that the carbon dioxide concentration PV2 (n) is too high, and the process proceeds to step S15. If the determination result in step S45 is NO and the determination result in step S47 is YES, it is considered that the carbon dioxide concentration PV2 (n) is too low, and the process proceeds to step S17.

  According to this embodiment, the concentration of oxygen in the supply gas is controlled with reference to the carbon dioxide concentration (S41 to S47). This avoids deterioration of the quality of the workpieces WK, WK,... Due to insufficient supply of oxygen or excessive supply.

  Referring to FIG. 13, the batch heat treatment apparatus 10 of still another embodiment is the same as the batch heat treatment apparatus 10 shown in FIG. 14 to 15 representing the processing of the control device 32 are the same as the flowcharts of FIGS. 11 to 12 except that steps S31 to S37 are provided instead of steps S23 to S25. Therefore, the redundant description regarding the same configuration or processing is omitted.

  The control device 32 acquires the temperatures of the workpieces WK1, WK1,... From the thermometer 40 in step S31 shown in FIG. In step S33, it is determined whether or not the acquired temperature is equal to or lower than a threshold value THwk. The threshold value THwk is set to “292 °. If the determination result is NO, the process returns to step S7. If the determination result is YES, the degreasing is completed and the process proceeds to the sintering process. The threshold value THo is“ 9.8. Therefore, the degreasing process is terminated when the oxygen concentration reaches 9.8% and the temperature of the workpieces WK1 and WK1 is reduced to 292 °.

  According to this embodiment, in the supply gas control step, the concentration of oxygen in the supply gas is controlled by referring to the carbon dioxide concentration (S41 to S47, S15 to S19). Further, in the degreasing end step, the degreasing is completed when the temperature of the workpieces WK, WK,... Satisfies a predetermined condition (specifically, a condition that the temperature is equal to or lower than the threshold value THw) (S31 to S33).

  By controlling the concentration of oxygen in the supply gas with reference to the concentration of carbon dioxide, deterioration of the quality of the workpieces WK, WK,... Due to insufficient supply of oxygen or excessive supply is avoided. Moreover, when the temperature of the workpieces WK, WK,... Satisfies a predetermined condition, the degreasing is terminated, so that deterioration of the quality of the workpieces WK, WK,.

DESCRIPTION OF SYMBOLS 10 ... Batch type heat processing apparatus 16 ... Heating furnace 18 ... Supply pipe 20 ... Heater 24 ... Work holding tool 26 ... Exhaust pipe 28 ... Exhaust gas treatment apparatus 30 ... CO2 concentration meter 32 ... Control apparatus 34, 36 ... Mass flow controller 38 ... Thermocouple 40 ... thermometer WK1 ... work RM1 ... furnace chamber

Claims (7)

A supply / exhaust step of supplying a supply gas for heat treatment to the furnace chamber in which the workpiece is housed, and exhausting an exhaust gas used for the heat treatment from the furnace chamber;
A heating step of heating the furnace chamber with a heater to degrease and sinter the workpiece;
A heat treatment method comprising:
The supply / exhaust step includes a supply gas control step of controlling the concentration of oxygen in the supply gas by referring to the concentration of carbon in the exhaust gas and / or the temperature of the workpiece,
The heating step includes a degreasing end step of ending degreasing when the oxygen concentration reaches a threshold value and the concentration of carbon in the exhaust gas and / or the temperature of the workpiece satisfies predetermined conditions.   The supply gas control step includes a workpiece temperature measurement step of repeatedly measuring the workpiece temperature, and a concentration of the oxygen in the supply gas so that the workpiece temperature measured by the workpiece temperature measurement step falls within a predetermined range. The heat treatment method according to claim 1, further comprising an oxygen concentration adjusting step of adjusting.   The supply gas control step includes a carbon concentration measurement step for repeatedly measuring the concentration of the carbon in the exhaust gas, and the supply gas so that the carbon concentration measured by the carbon concentration measurement step is within a predetermined range. The heat processing method of Claim 1 including the oxygen concentration adjustment process of adjusting the density | concentration of the said occupying oxygen.   The carbon concentration measurement step includes a gas decomposition step of decomposing the exhaust gas into water and carbon dioxide, and a carbon concentration detection step of detecting the carbon concentration by paying attention to the carbon dioxide decomposed by the gas decomposition step. The heat treatment method according to claim 3.   5. The heat treatment method according to claim 2, wherein the oxygen concentration adjusting step stops the adjustment when the adjusted oxygen concentration reaches an upper limit value. 6.   The heat treatment method according to claim 1, wherein the predetermined condition in the heating step includes a concentration condition that a concentration of the carbon in the exhaust gas is lower than a threshold value.   The heat treatment method according to claim 1, wherein the predetermined condition in the heating step includes a temperature condition that a temperature of the workpiece is lower than a threshold value.

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