JP2017082275A - Nitriding treatment apparatus and nitriding treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nitriding treatment apparatus capable of reducing furthermore a used amount of gas for heat treatment without lowering quality of a nitriding treatment, and to provide a nitriding treatment method.SOLUTION: A nitriding treatment apparatus 1 has a nitriding potential detector 18, an ammonia sensor 16 and a control part 5. The control part 5 controls supply of gas for heat treatment into a heat treatment furnace 6 based on both a nitriding potential P and a residual ammonia concentration C1.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a nitriding apparatus and a nitriding method.

  Nitriding treatment such as gas soft nitriding treatment may be performed on the surface of an object to be treated such as a steel part. In the gas soft nitriding treatment, a heat treatment gas (mixed gas) mainly composed of ammonia gas is supplied into a heat treatment furnace heated to about 550 ° C. to 600 ° C. Thereby, nitrogen atoms and carbon atoms are solid-dissolved while penetrating and diffusing from the surface of the workpiece in the heat treatment furnace toward the inside. As a result, a compound of nitrogen atoms and carbon atoms is formed as a nitride layer on the surface of the workpiece. Thereby, the wear resistance, fatigue strength, corrosion resistance, and the like of the workpiece can be improved.

A nitriding apparatus for performing nitriding is known (see, for example, Patent Documents 1 to 3). The nitriding apparatus described in Patent Document 1 detects the hydrogen concentration in the heat treatment furnace and calculates the nitriding potential from the hydrogen concentration in the gas soft nitriding process. The nitriding potential is a value defined by (residual ammonia concentration × 0.01) / {(hydrogen concentration × 0.01) ^1.5 }. The residual ammonia refers to ammonia that is not decomposed in the heat treatment furnace and remains without reacting with other gases. The residual ammonia concentration refers to the concentration of residual ammonia. The nitriding apparatus adjusts the flow rates of various gases introduced into the heat treatment furnace so that the nitriding potential is constant. This is intended to reduce the amount of gas used for the heat treatment.

  In the nitriding methods described in Patent Documents 2 and 3, the residual ammonia concentration in the heat treatment furnace is controlled in order to ensure the nitriding quality of the object to be processed. In this method, control is performed so that the residual ammonia concentration becomes the lower limit necessary for forming a desired nitrided layer in the workpiece. Thus, it is intended to reduce the amount of heat treatment gas used while ensuring the quality of nitriding in the object to be processed.

JP 2011-26627 A JP 2007-169723 A JP-A-8-134626

  By the way, in the soft nitriding treatment using the heat treatment gas, it is preferable to reduce the amount of the heat treatment gas used from the viewpoint of reducing the cost of the soft nitriding treatment. In particular, it is preferable from the viewpoint of protecting the global environment to further reduce the discharge amount of ammonia gas having a relatively large environmental load.

  In view of the above circumstances, an object of the present invention is to provide a nitriding apparatus and a nitriding method that can further reduce the amount of heat treatment gas used without degrading the quality of the nitriding process. .

  As a result of earnest research, the inventor of the present application has obtained the following knowledge. That is, the control for adjusting the flow rate of various gases introduced into the heat treatment furnace according to the set nitriding potential, and the various gases introduced into the heat treatment furnace according to the residual ammonia concentration remaining in the heat treatment furnace. By adjusting the flow rate of the gas, various gases introduced into the heat treatment furnace without deteriorating the quality of the object to be processed, especially ammonia that is several times the price of nitrogen. The amount of gas used can be reduced.

  Further, the nitriding potential can be arbitrarily controlled by adjusting the total flow rate of the heat treatment gas while keeping the flow rate ratio of various gases introduced into the heat treatment furnace constant. On the other hand, the residual ammonia concentration in the heat treatment furnace can be arbitrarily controlled by adjusting the flow ratio of various gases in the heat treatment gas while keeping the total flow rate of the heat treatment gas introduced into the heat treatment furnace constant. .

  (1) A nitriding apparatus according to an aspect of the present invention, which has been made based on the above knowledge, introduces a heat treatment gas containing ammonia gas into a heat treatment furnace, so that the substrate disposed in the heat treatment furnace. A nitriding apparatus for performing nitriding treatment on a workpiece, a nitriding potential detecting unit for detecting a nitriding potential in the heat treatment furnace, and a residual ammonia concentration for detecting a residual ammonia concentration in the heat treatment furnace A detection unit; and a control unit for controlling the supply of the heat treatment gas into the heat treatment furnace based on the nitriding potential and the residual ammonia concentration, and the control unit includes the residual ammonia concentration and When changing any one of the nitriding potentials, the residual ammonia concentration detected by the residual ammonia concentration detector and the nitriding Based on either one of the nitriding potentials detected by the temporal detector, the total flow rate of the heat treatment gas per unit time into the heat treatment furnace is constant, while the unit flow rate per unit time into the heat treatment furnace is constant. The flow rate ratio of the ammonia gas in the heat treatment gas is changed, and the control unit detects the residual ammonia concentration detection unit when changing either the residual ammonia concentration or the nitriding potential. Based on either the residual ammonia concentration or the nitriding potential detected by the nitriding potential detector, the flow rate ratio of each component gas in the heat treatment gas per unit time into the heat treatment furnace is constant, The total flow rate of the heat treatment gas per unit time into the heat treatment furnace It is configured to be of.

  According to this configuration, the control unit sets the supply mode of the heat treatment gas into the heat treatment furnace based on both the nitriding potential and the residual ammonia concentration. That is, in the nitriding process, the control unit sets the supply mode of the heat treatment gas into the heat treatment furnace in consideration of the residual ammonia concentration in addition to the nitriding potential. Thereby, the amount of heat treatment gas used can be further reduced while sufficiently satisfying the quality of the nitriding treatment of the workpiece (specifications required for the components of the nitrided layer, uniformity of thickness, etc.).

  Further, the control unit is configured to set the flow rate ratio of the heat treatment gas to the heat treatment furnace, particularly the ammonia gas, based on the concentration of the ammonia gas itself remaining in the heat treatment furnace. Thereby, the control unit can perform control to reduce the supply amount of ammonia gas into the heat treatment furnace while satisfying sufficient quality for nitriding more reliably.

  Furthermore, when changing any one of the residual ammonia concentration and the nitriding potential, the control unit keeps the total flow rate of the heat treatment gas per unit time into the heat treatment furnace, while keeping the total flow rate per unit time into the heat treatment furnace. The flow rate ratio of ammonia gas is changed. According to this configuration, even when either the residual ammonia concentration or the nitriding potential is changed, the total flow rate of the heat treatment gas per unit time into the heat treatment furnace does not change. As a result, quality variations related to nitriding can be more reliably suppressed.

  Further, the control unit can set the total heat treatment gas flow rate to the heat treatment furnace based on the nitriding potential, that is, the progress of the nitriding treatment. As a result, the control unit can perform control to reduce the supply amount of ammonia gas into the heat treatment furnace while satisfying sufficient quality for nitriding more reliably.

  Further, when changing either the residual ammonia concentration or the nitriding potential, the control unit keeps the flow rate ratio of each component gas in the heat treatment gas per unit time into the heat treatment furnace into the heat treatment furnace. The total flow rate of the heat treatment gas per unit time is changed. According to this configuration, when changing either the residual ammonia concentration or the nitriding potential, the flow rate ratio of each component gas in the heat treatment gas into the heat treatment furnace per unit time does not change. Therefore, it is possible to suppress the nitriding reaction mode from rapidly changing around the surface of the workpiece. As a result, quality variations related to nitriding can be more reliably suppressed. As described above, according to the present invention, it is possible to realize a nitriding apparatus capable of further reducing the amount of heat treatment gas used without degrading the quality of the nitriding process.

  (2) Preferably, when the controller changes either the residual ammonia concentration or the nitriding potential, the controller enters the heat treatment furnace based on the residual ammonia concentration detected by the residual ammonia concentration detector. The flow rate ratio of the ammonia gas in the heat treatment gas per unit time into the heat treatment furnace is changed while the total flow rate of the heat treatment gas per unit time is constant, and the control unit When changing any one of the residual ammonia concentration and the nitriding potential, each of the heat treatment gases in the heat treatment furnace per unit time based on the nitridation potential detected by the nitriding potential detector The flow rate ratio of the component gases is kept constant, while And it is configured to vary the total flow rate of the heat treatment gas.

  According to this configuration, the nitriding treatment can be completed more quickly, and the amount of heat treatment gas used can be further reduced.

  (3) Preferably, the control unit is configured to alternately perform control for changing the flow rate ratio of the ammonia gas and control for changing the total flow rate of the heat treatment gas.

  According to this configuration, the nitriding treatment can be completed more quickly, and the amount of heat treatment gas used can be further reduced.

  (4) More preferably, the control unit includes an initial value of a total flow rate of the heat treatment gas, an initial value of the flow rate ratio of the ammonia gas, a target value of the residual ammonia concentration, and a target value of the nitriding potential. The control for changing the flow rate ratio of the ammonia gas and the control for changing the total flow rate of the heat treatment gas are performed.

  According to this configuration, finer control for completing the nitriding process more quickly and reducing the amount of heat treatment gas used can be realized.

  (5) Preferably, the control unit is configured to be able to control a total flow rate of the heat treatment gas into the heat treatment furnace based on predetermined equal ammonia flow rate ratio characteristics in order to control the nitriding potential. The equi-ammonia flow rate ratio characteristic is a graph in which the residual ammonia concentration is on the horizontal axis and the nitriding potential is on the vertical axis, and the flow rate ratio of the ammonia gas in the heat treatment gas per unit time is shown in the graph. The characteristic when it is made constant is shown.

  According to this configuration, the control unit sets the supply mode of the heat treatment gas, particularly the ammonia gas, supplied into the heat treatment furnace based on the preset equal ammonia flow rate ratio characteristic. Thereby, the control unit can perform control to reduce the supply amount of ammonia gas into the heat treatment furnace while satisfying sufficient quality for nitriding more reliably.

  (6) Preferably, in order to control the residual ammonia concentration, the control unit sets a flow ratio of the ammonia gas in the heat treatment gas into the heat treatment furnace based on a predetermined equal total flow characteristic. The equal total flow rate characteristic is configured such that the total flow rate of the heat treatment gas per unit time is constant in the graph in which the horizontal axis is the residual ammonia concentration and the vertical axis is the nitriding potential. The characteristics when set to.

  According to this configuration, the control unit sets the supply mode of the heat treatment gas, particularly the ammonia gas, which is supplied into the heat treatment furnace based on the preset equal total flow characteristics. Thereby, the control unit can perform control to reduce the supply amount of ammonia gas into the heat treatment furnace while satisfying sufficient quality for nitriding more reliably.

  (7) Preferably, the control unit performs the heat treatment to the heat treatment furnace so that the residual ammonia concentration in the heat treatment furnace is 12% or more and the nitriding potential in the heat treatment furnace is 0.75 or more. It is configured to control supply of the working gas.

  According to this configuration, the residual ammonia concentration is set to a minimum of 12% and the nitriding potential is set to a minimum of 0.75, so that the quality related to the nitriding treatment is sufficiently secured, and the heat treatment gas, particularly ammonia gas is used. The amount can be further reduced.

  (8) In order to solve the above-mentioned problem, a nitriding apparatus according to an aspect of the present invention introduces a heat treatment gas containing ammonia gas into a heat treatment furnace, and thereby the object to be processed disposed in the heat treatment furnace. A nitriding apparatus for nitriding an object, for controlling the supply of the heat treatment gas to the heat treatment furnace based on a predetermined equal ammonia flow rate ratio characteristic and a predetermined equal total flow characteristic In the graph in which the horizontal ammonia axis is the residual ammonia concentration in the heat treatment furnace and the nitriding potential in the heat treatment furnace is the vertical axis, the equal ammonia flow rate ratio characteristic is the heat treatment per unit time. Shows the characteristics when the flow rate ratio of ammonia in the working gas is constant, and the equal total flow characteristics are the heat treatment per unit time in the graph Shows the characteristic when the total flow rate of the gas constant.

  According to this configuration, the control unit sets the supply amount of the heat treatment gas into the heat treatment furnace based on both the nitriding potential and the residual ammonia concentration. That is, in the nitriding treatment, the supply amount of the heat treatment gas into the heat treatment furnace is set in consideration of the residual ammonia concentration in addition to the nitriding potential. As a result, the amount of heat treatment gas used, particularly the amount of ammonia gas, can be satisfied while sufficiently satisfying the quality of the nitriding treatment of the workpiece (specifications required for the components of the nitrided layer, thickness uniformity, etc.) It can be further reduced.

  More specifically, the control unit sets the flow rate of the heat treatment gas, particularly ammonia gas, supplied into the heat treatment furnace based on the preset equal ammonia flow rate ratio characteristic and the equal total flow characteristic. As a result, the control unit can realize a state in which both the residual ammonia concentration and the nitriding potential are further reduced while sufficiently ensuring the quality related to the nitriding treatment. In other words, the control unit can further reduce the amount of heat treatment gas, particularly ammonia gas, used in the nitriding treatment. As described above, according to the present invention, it is possible to realize a nitriding apparatus capable of further reducing the amount of heat treatment gas used without degrading the quality of the nitriding process.

  (9) In order to solve the above-described problem, a nitriding method according to an aspect of the present invention is a treatment process disposed in the heat treatment furnace by introducing a heat treatment gas containing ammonia gas into the heat treatment furnace. A nitriding method for nitriding an object, wherein a nitriding potential detecting step for detecting a nitriding potential in the heat treatment furnace and a residual ammonia concentration detection for detecting a residual ammonia concentration in the heat treatment furnace And a control step of controlling supply of the heat treatment gas into the heat treatment furnace based on the nitridation potential and the residual ammonia concentration, wherein the control step includes the residual ammonia concentration and the nitridation potential. When changing either one of the residual ammonia concentration detected in the residual ammonia concentration detection step, Based on either the concentration or the nitriding potential detected by the nitriding potential detection step, the total flow rate of the heat treatment gas per unit time into the heat treatment furnace is made constant while the unit into the heat treatment furnace is kept constant. The flow rate ratio of the ammonia gas in the heat treatment gas per time is changed, and the control step detects the residual ammonia concentration when changing either the residual ammonia concentration or the nitriding potential. The flow ratio of each component gas in the heat treatment gas per unit time into the heat treatment furnace is based on either the residual ammonia concentration detected in step 1 or the nitriding potential detected in the nitriding potential detection step. Unit time into the heat treatment furnace while keeping constant It is configured to vary the total flow rate of the heat treatment gas in streams.

  According to this configuration, in the control step, the supply mode of the heat treatment gas into the heat treatment furnace is set based on both the nitriding potential and the residual ammonia concentration. That is, in the nitriding treatment, the supply mode of the heat treatment gas into the heat treatment furnace is set in consideration of the residual ammonia concentration in addition to the nitriding potential. Thereby, the amount of heat treatment gas used can be further reduced while sufficiently satisfying the quality of the nitriding treatment of the workpiece (specifications required for the components of the nitrided layer, uniformity of thickness, etc.).

  In the control step, the flow rate ratio of the heat treatment gas to the heat treatment furnace, particularly the ammonia gas, is set based on the concentration of ammonia gas remaining in the heat treatment furnace. Thus, in the control step, it is possible to perform control to reduce the supply amount of ammonia gas into the heat treatment furnace while satisfying sufficient quality for nitriding more reliably.

  Further, in the control step, when changing either the residual ammonia concentration or the nitriding potential, the total flow rate of the heat treatment gas per unit time into the heat treatment furnace is kept constant, while the unit flow rate per unit time into the heat treatment furnace is constant. The flow rate ratio of ammonia gas is changed. According to this configuration, even when either the residual ammonia concentration or the nitriding potential is changed, the total flow rate of the heat treatment gas per unit time into the heat treatment furnace does not change. As a result, quality variations related to nitriding can be more reliably suppressed.

  Further, in the control step, the total heat treatment gas flow rate to the heat treatment furnace can be set based on the nitriding potential in the heat treatment furnace, that is, the degree of progress of the nitriding treatment. As a result, in the control step, it is possible to perform control to reduce the supply amount of ammonia gas into the heat treatment furnace while satisfying sufficient quality for nitriding more reliably.

  Further, in the control step, when either the residual ammonia concentration or the nitriding potential is changed, the flow rate ratio of each component gas in the heat treatment gas per unit time into the heat treatment furnace is kept constant while the flow rate ratio of each component gas into the heat treatment furnace is kept constant. The total flow rate of the heat treatment gas per unit time is changed. According to this configuration, when changing either the residual ammonia concentration or the nitriding potential, the flow rate ratio of each component gas in the heat treatment gas into the heat treatment furnace per unit time does not change. Therefore, it is possible to suppress the nitriding reaction mode from rapidly changing around the surface of the workpiece. As a result, quality variations related to nitriding can be more reliably suppressed. As described above, according to the present invention, it is possible to realize a nitriding method that can further reduce the amount of heat treatment gas used without degrading the quality of the nitriding treatment.

  (10) In order to solve the above-described problem, a nitriding method according to an aspect of the present invention includes a heat treatment gas containing ammonia gas introduced into a heat treatment furnace, so that the treatment object disposed in the heat treatment furnace is provided. A control method for controlling supply of the heat treatment gas to the heat treatment furnace based on a predetermined equal ammonia flow rate ratio characteristic and a predetermined equal total flow characteristic. And the equi-ammonia flow rate ratio characteristic includes the heat treatment gas per unit time in a graph in which the horizontal axis is the residual ammonia concentration in the heat treatment furnace and the nitriding potential in the heat treatment furnace is the vertical axis. In the graph, the equal total flow rate characteristic is the heat treatment per unit time. The total flow rate of the use gas shows the characteristics when the constant.

  According to this configuration, in the control step, the supply amount of the heat treatment gas into the heat treatment furnace is set based on both the nitriding potential and the residual ammonia concentration. That is, in the nitriding treatment, the supply amount of the heat treatment gas into the heat treatment furnace is set in consideration of the residual ammonia concentration in addition to the nitriding potential. As a result, the amount of heat treatment gas used, particularly the amount of ammonia gas, can be satisfied while sufficiently satisfying the quality of the nitriding treatment of the workpiece (specifications required for the components of the nitrided layer, thickness uniformity, etc.) It can be further reduced.

  More specifically, in the control step, the flow rate of the heat treatment gas, particularly ammonia gas, supplied into the heat treatment furnace is set based on the preset equal ammonia flow rate ratio characteristic and equal total flow characteristic. As a result, in the control step, it is possible to realize a state where both the residual ammonia concentration and the nitriding potential are further reduced while sufficiently ensuring the quality related to the nitriding treatment. That is, in the control step, the amount of heat treatment gas, particularly ammonia gas, can be further reduced in the nitriding treatment. As described above, according to the present invention, it is possible to realize a nitriding method that can further reduce the amount of heat treatment gas used without degrading the quality of the nitriding treatment.

  According to the present invention, the amount of heat treatment gas used can be further reduced without degrading the quality of the nitriding treatment.

It is a schematic diagram of the nitriding apparatus which concerns on one Embodiment of this invention. It is a figure which shows the control map used for control in a control part. It is a flowchart for demonstrating an example of the heat processing operation | movement in a nitriding processing apparatus. It is a figure for demonstrating one specific example of the control action in control of a control part. It is a figure for demonstrating the example of the control pattern in embodiment and the modification of this invention. It is a graph which shows the relationship between the time after nitriding start, and nitriding potential, and the relationship between the time after nitriding start and residual ammonia concentration.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. The present invention can be widely applied as a nitriding apparatus and a nitriding method.

  FIG. 1 is a schematic view of a nitriding apparatus 1 according to an embodiment of the present invention. Referring to FIG. 1, the nitriding apparatus 1 introduces a heat treatment gas containing ammonia gas into the heat treatment furnace 6 so as to perform the nitriding treatment on the workpiece 100 arranged in the heat treatment furnace 6. It is configured.

  The material of the workpiece 100 is not particularly limited as long as the material can be nitrided on the surface. As an example of the workpiece 100, metal parts such as steel parts can be exemplified. The nitriding process is a process for supplying a heat treatment gas (mixed gas) mainly composed of ammonia gas into the heat treatment furnace 6 heated to about 550 ° C. to 600 ° C., for example.

  By this treatment, nitrogen atoms and carbon atoms penetrate and diffuse from the surface of the object to be processed 100 to the inside to be dissolved in the metal portion of the object to be processed 100. As a result, a compound of nitrogen atoms and carbon atoms (nitride layer) is formed in the vicinity of the surface of the workpiece 100. Thereby, the wear resistance, fatigue strength, and corrosion resistance of the workpiece 100 are improved.

The heat treatment gas used in the present embodiment includes nitrogen gas (N ₂ ), ammonia gas (NH ₃ ), and carbon dioxide gas (CO ₂ ). The heat treatment gas may contain ammonia gas and endothermic modified gas (CO, N ₂ , H ₂ ).

  The nitriding apparatus 1 includes a gas supply unit 2, a heat treatment unit 3, a gas sensor 4, and a control unit 5. The heat treatment unit 3 includes a heat treatment furnace 6, a fan 7, and a heater 8.

  The gas supply unit 2 is provided to supply the heat treatment gas including the above-described ammonia gas, nitrogen gas, and carbon dioxide gas to the heat treatment furnace 6. In the present embodiment, the gas supply unit 2 is configured to be able to individually set the flow rates (L / min) of ammonia gas, nitrogen gas, and carbon dioxide gas.

  The gas supply unit 2 includes an ammonia gas supply unit 11, a nitrogen gas supply unit 12, a carbon dioxide gas supply unit 13, and a collecting pipe 14.

  The ammonia gas supply unit 11 includes a supply pipe 11a, a mass flow sensor 11b, and an electromagnetic valve 11c.

  The supply pipe 11a is connected to an ammonia gas supply source such as a tank (not shown) filled with ammonia gas, and the ammonia gas flows from the ammonia gas supply source. A mass flow sensor 11b and an electromagnetic valve 11c are provided in the supply pipe 11a.

  The mass flow sensor 11b is provided to detect the flow rate of ammonia gas in the supply pipe 11a. The mass flow sensor 11b is disposed upstream of the electromagnetic valve 11c in the flow direction of the supply pipe 11a. The mass flow sensor 11b is, for example, a thermal flow sensor, and is configured to detect the flow rate of ammonia gas passing through the supply pipe 11a. The mass flow sensor 11 b outputs a signal indicating the detected flow rate of ammonia gas to the control unit 5. The electromagnetic valve 11c is provided to adjust the flow rate of ammonia gas in the supply pipe 11a. The electromagnetic valve 11c has, for example, an actuator such as a solenoid, and the opening degree of the electromagnetic valve 11c is set by the operation of this actuator. The electromagnetic valve 11 c is controlled by the control unit 5. More specifically, the solenoid valve 11c operates so that the difference between the ammonia gas flow rate detected by the mass flow sensor 11b and the ammonia gas target flow rate set by the control unit 5 becomes zero.

  The nitrogen gas supply unit 12 includes a supply pipe 12a, a mass flow sensor 12b, and an electromagnetic valve 12c.

  The supply pipe 12a is connected to a nitrogen gas supply source such as a tank (not shown) filled with nitrogen gas, and the nitrogen gas flows from the nitrogen gas supply source. The supply pipe 12a is provided with a mass flow sensor 12b and an electromagnetic valve 12c.

  The mass flow sensor 12b is provided to detect the flow rate of nitrogen gas in the supply pipe 12a. The mass flow sensor 12b is disposed on the upstream side in the flow direction of the supply pipe 12a with respect to the electromagnetic valve 12c. The mass flow sensor 12b is, for example, a thermal flow sensor, and is configured to detect the flow rate of nitrogen gas passing through the supply pipe 12a. The mass flow sensor 12 b outputs a signal indicating the detected flow rate of nitrogen gas to the control unit 5. The solenoid valve 12c is provided to adjust the flow rate of nitrogen gas in the supply pipe 12a. The electromagnetic valve 12c has, for example, an actuator such as a solenoid, and the opening degree of the electromagnetic valve 12c is set by the operation of this actuator. The electromagnetic valve 12 c is controlled by the control unit 5. More specifically, the solenoid valve 12c operates so that the difference between the flow rate of nitrogen gas detected by the mass flow sensor 12b and the target flow rate of nitrogen gas set by the control unit 5 becomes zero.

  The carbon dioxide supply unit 13 includes a supply pipe 13a, a mass flow sensor 13b, and an electromagnetic valve 13c.

  The supply pipe 13a is connected to a carbon dioxide supply source such as a tank (not shown) filled with carbon dioxide, and the carbon dioxide from the carbon dioxide supply source flows. The supply pipe 13a is provided with a mass flow sensor 13b and an electromagnetic valve 13c.

  The mass flow sensor 13b is provided to detect the flow rate of carbon dioxide gas in the supply pipe 13a. The mass flow sensor 13b is disposed upstream of the electromagnetic valve 13c in the flow direction in the supply pipe 13a. The mass flow sensor 13b is, for example, a thermal flow sensor, and is configured to detect the flow rate of carbon dioxide passing through the supply pipe 13a. The mass flow sensor 13 b outputs a signal indicating the detected flow rate of carbon dioxide gas to the control unit 5. The electromagnetic valve 13c is provided to adjust the flow rate of carbon dioxide gas in the supply pipe 13a. The electromagnetic valve 13c has, for example, an actuator such as a solenoid, and the opening degree of the electromagnetic valve 13c is set by the operation of this actuator. The electromagnetic valve 13 c is controlled by the control unit 5. More specifically, the solenoid valve 13c operates so that the difference between the flow rate of the carbon dioxide gas detected by the mass flow sensor 13b and the target flow rate of the carbon dioxide gas set by the control unit 5 becomes zero.

  The collecting pipe 14 is connected to each of the supply pipes 11 a to 13 a and is configured to introduce ammonia gas, nitrogen gas, and carbon dioxide gas from the supply pipes 11 a to 13 a into the heat treatment furnace 6. With the above configuration, the heat treatment gas including ammonia gas, nitrogen gas, and carbon dioxide gas is supplied to the heat treatment furnace 6 under the control of the control unit 5.

  The heat treatment furnace 6 is provided as a storage chamber for storing the workpiece 100. The heat treatment furnace 6 is formed in a box shape, and is configured such that the workpiece 100 can be taken in and out. A heat treatment gas is supplied from the gas supply unit 2 into the heat treatment furnace 6 in a state where the workpiece 100 is accommodated. The heat treatment gas in the heat treatment furnace 6 and the workpiece 100 are heated by the heater 8. The heater 8 is, for example, an electric heater or a gas burner, and is disposed in the heat treatment furnace 6.

  The heater 8 heats the workpiece 100 and the heating gas in the heat treatment furnace 6 to a temperature required for nitriding (for example, about 550 ° C. to about 600 ° C.). Further, the atmosphere in the heat treatment furnace 6 is stirred by the fan 7 to have a more uniform distribution. The fan 7 is a centrifugal fan, for example. The fan 7 is disposed on a ceiling portion or the like inside the heat treatment furnace 6 and is rotated by an electric motor (not shown) to stir the atmosphere (heat treatment gas) in the heat treatment furnace 6. The gas in the heat treatment furnace 6 is detected by the gas sensor 4.

  The gas sensor 4 is an ammonia sensor (residual ammonia concentration) for detecting the concentration of the residual ammonia gas as the ammonia gas remaining in the sampling tube 15 and the heat treatment furnace 6 without being decomposed and reacting with other substances. And a hydrogen sensor 17 for detecting the concentration of hydrogen in the heat treatment furnace 6.

  The residual ammonia concentration C1 refers to the ratio of the concentration of ammonia gas to the total concentration (100%) of all components of the gas in the heat treatment furnace 6. Similarly, the hydrogen concentration C2 refers to the ratio of the concentration of hydrogen gas to the total concentration (100%) of all gas components in the heat treatment furnace 6.

  The sampling tube 15 is provided for taking out the gas in the heat treatment furnace 6. One end of the sampling tube 15 is connected to the heat treatment furnace 6. The other end of the sampling tube 15 is open to the outside of the heat treatment furnace 6, and the gas introduced into the sampling tube 15 is discharged. An ammonia sensor 16 and a hydrogen sensor 17 are provided in the middle of the sampling tube 15.

  The ammonia sensor 16 is formed using, for example, an infrared absorption gas analyzer or the like, and is configured to output a signal corresponding to the concentration of ammonia gas in the heat treatment furnace 6. The hydrogen sensor 17 is formed by using, for example, a hot-wire semiconductor sensor, and is configured to output a signal corresponding to the concentration of hydrogen gas in the heat treatment furnace 6. The ammonia gas detection signal of the ammonia sensor 16 and the hydrogen gas detection signal of the hydrogen sensor 17 are output to the control unit 5.

  The control unit 5 uses the mass flow sensors 11b, 12b, 13b of the gas supply units 11, 12, 13 and at least one of the gas sensors 4, and uses the residual ammonia concentration C1 in the heat treatment furnace 6, the nitriding potential P, Is configured to detect. Then, the control unit 5 controls the supply mode of the heat treatment gas, particularly the ammonia gas, into the heat treatment furnace 6 based on the nitriding potential P and the residual ammonia concentration C1. In the present embodiment, the control unit 5 controls the operations of the gas supply units 11, 12, and 13 so that the nitriding potential P and the residual ammonia concentration C1 have predetermined values.

  More specifically, in the present embodiment, the control unit 5 is configured to set the flow rate ratio of ammonia gas to the heat treatment furnace 6 based on the residual ammonia concentration C1. Similarly, in the present embodiment, the control unit 5 is configured to set the flow rate of ammonia gas to the heat treatment furnace 6 (total flow rate of heat treatment gas per unit time) based on the nitriding potential P. .

  The control unit 5 is formed using a computer including a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory). The control unit 5 may be a PLC (Programmable Logic Controller) or the like.

  The control unit 5 includes a calculator 5a and an adjuster 5b. In the present embodiment, the calculator 5a and the adjuster 5b are realized by the CPU executing a program stored in the ROM.

  The calculator 5a is provided for performing calculation processing. This computing unit 5 a is connected to each mass flow sensor 11 b, 12 b, 13 b, ammonia sensor 16, and hydrogen sensor 17. The arithmetic unit 5a performs arithmetic processing using the flow rate of ammonia gas, the flow rate of nitrogen gas, the flow rate of carbon dioxide gas, the residual ammonia concentration C1 in the heat treatment furnace 6, and the hydrogen concentration C2 in the heat treatment furnace 6. The calculator 5a controls the adjuster 5b based on the calculation result.

  The adjuster 5 b is provided to adjust the supply mode of each component gas of the heat treatment gas to the heat treatment furnace 6. The regulator 5b is connected to each electromagnetic valve 11c, 12c, 13c, and is configured to set the opening degree of these electromagnetic valves 11c, 12c, 13c.

  In the present embodiment, mass flow sensors 11b, 12b, and 13b that measure the flow rate of each component gas (ammonia gas, nitrogen gas, and carbon dioxide gas) of the heat treatment gas, an ammonia sensor 16 that detects the residual ammonia concentration C1, and An example in which the hydrogen sensor 17 for detecting the hydrogen concentration C2 is provided will be described. However, this need not be the case, and it is sufficient that at least one of the following mechanisms (1) to (3) is provided.

  That is, (1) a mechanism (ammonia sensor 16 and hydrogen sensor 17) for detecting a residual ammonia concentration C1 and a hydrogen concentration C2 in the heat treatment furnace 6, and (2) a residual ammonia concentration C1 in the heat treatment furnace 6 and a heat treatment gas. Mechanism for measuring the flow rate of the component gas (ammonia sensor 16 and mass flow sensors 11b, 12b, 13b), (3) Mechanism for measuring the hydrogen concentration C2 in the heat treatment furnace 6 and the flow rate of each component gas of the heat treatment gas (hydrogen sensor) 17 and the mass flow sensors 11b, 12b, 13b) need only be provided. However, in the configuration of (3), the residual ammonia concentration C1 is calculated by the calculator 5a using the data obtained from the sensor. In the combination of any one of the configurations (1) to (3) and the calculator 5a, the calculator 5a can calculate the nitriding potential P.

  In the present embodiment, the mass flow sensors 11b, 12b, and 13b, the ammonia sensor 16 that detects the residual ammonia concentration C1, the hydrogen sensor 17 that detects the hydrogen gas concentration C2, and the control unit 5 include the nitriding potential detection unit 18. Forming. The computing unit 5a of the control unit 5 of the nitriding potential detecting unit 18 detects the residual ammonia concentration C1 and the nitriding potential P in the heat treatment furnace 6.

In the present embodiment, the calculator 5a calculates (calculates) the nitriding potential P using data obtained from the mass flow sensors 11b, 12b, 13b, the ammonia sensor 16, and the hydrogen sensor 17, respectively. The nitriding potential P is calculated by the following equation.
P = (residual ammonia concentration C1 × 0.01) / {(hydrogen concentration C2 × 0.01) ^1.5 }

  The control unit 5 stores a target nitriding potential PT as a preset target value of the nitriding potential P and a target residual ammonia concentration C1T as a preset target value of the residual ammonia concentration C1 as numerical data. Yes.

  The computing unit 5a and the adjustment meter 5b then connect the gas supply units 11, 12 to match the detected nitriding potential P and residual ammonia concentration C1 with the corresponding target nitriding potential PT and target residual ammonia concentration C1T. , 13, the corresponding gas flow rates are set individually. That is, the adjustment meter 5b is configured so that the difference between the detected nitriding potential P and residual ammonia concentration C1 and the corresponding target nitriding potential PT and target residual ammonia concentration C1T becomes zero. The opening degree of the thirteen electromagnetic valves 11c, 12c, 13c is set.

  The control unit 5 having the above-described configuration is configured to perform equal flow ratio control and equal total flow control stepwise (alternately) with respect to the supply of each component gas of the heat treatment gas in the heat treatment furnace 6. .

  The above equal flow ratio control is performed by changing (adjusting) the total flow rate of the heat treatment gas per unit time while keeping the flow rate ratio of each component gas in the heat treatment gas per unit time constant. This is control for changing (adjusting) one of C1 and nitriding potential P (in this embodiment, nitriding potential P). Note that the flow rate ratio of each component gas means the ratio of the flow rate of each component gas when the total flow rate of the heat treatment gas is 100%). The above-mentioned equal total flow control changes the residual ammonia concentration C1 by changing (adjusting) the flow ratio of each component gas in the heat treatment gas per unit time while keeping the total flow rate of the heat treatment gas per unit time constant. This is control for adjusting one of the nitriding potential P and the residual ammonia concentration C1 in this embodiment.

  That is, the control unit 5 is configured to alternately perform control for changing the flow rate ratio of ammonia gas and control for changing the total flow rate of the heat treatment gas. In the present embodiment, the controller 5 sets the initial value of the total flow rate of the heat treatment gas, the initial value of the flow rate ratio of ammonia gas, the target residual ammonia concentration C1T as the target value of the residual ammonia concentration C1, and the nitriding potential P. Based on the target nitridation potential PT as a target value, control for changing the flow rate ratio of ammonia gas and control for changing the total flow rate of the heat treatment gas are performed.

  FIG. 2 is a diagram showing a control map M used for control in the control unit 5. Referring to FIGS. 1 and 2, control unit 5 stores control map M as numerical data, and controls the supply of each component gas of the heat treatment gas based on control map M. This control map M is specified by a graph with the residual ammonia concentration C1 as the horizontal axis and the nitriding potential P as the vertical axis.

  In the control map M, an equal flow ratio line (equal ammonia flow rate ratio characteristic) R and an equal total flow line (equal total flow characteristic) V are defined.

  The equiflow ratio ratio line R represents the heat treatment gas when the flow rate ratio in the heat treatment gas is constant for each component gas (ammonia gas, nitrogen gas, and carbon dioxide gas, particularly ammonia gas) in the heat treatment gas. The relationship (characteristic) between the residual ammonia concentration C1 and the nitriding potential P when the total flow rate is changed is shown. In the equal flow ratio line R, the nitriding potential P increases (decreases) as the total flow rate of the heat treatment gas increases (decreases). When it is determined that the nitriding potential P is higher (or lower) than the desired value, the control unit 5 performs heat treatment while maintaining the flow ratio of each component gas in the heat treatment gas constant according to the equiflow ratio ratio line R. Reduce (or increase) the total gas flow. In the present embodiment, a plurality (seven) of equal flow ratio lines R1 to R7 are set as the equal flow ratio lines R. The equal flow ratio lines R1 to R7 are lines set in advance by, for example, experiments or calculations. Note that the equal flow ratio lines R1 to R7 are collectively referred to simply as “equal flow ratio lines R”.

  The constant flow ratio line R1 is set to have the largest change rate of the nitriding potential P with respect to the change in the residual ammonia concentration C1 among the equal flow ratio lines R1 to R7. Further, the equal flow ratio line R1 is set such that the lowest value of the residual ammonia concentration C1 is the smallest among the equal flow ratio lines R1 to R7.

  Similarly, the constant flow ratio line Rn (n is any one of 2 to 7) is set to the nth largest change rate of the nitriding potential P with respect to the change in the residual ammonia concentration C1 among the constant flow ratio lines R1 to R7. Has been. In addition, the equal flow ratio line Rn is set to the nth smallest value of the residual ammonia concentration C1 among the equal flow ratio lines R1 to R7.

  On the other hand, the equal total flow line V indicates the residual ammonia concentration when the total flow rate (total flow rate of the heat treatment gas) of each component gas (ammonia gas, nitrogen gas, and carbon dioxide gas) in the heat treatment gas is constant. The relationship (characteristic) between C1 and the nitriding potential P is shown. In the equal total flow line V, the residual ammonia concentration C1 increases (decreases) as the flow rate ratio of ammonia gas increases (decreases).

  In the present embodiment, when the control unit 5 determines that the residual ammonia concentration C1 is higher (or lower) than a desired value, according to the equal total flow line V, while maintaining the total flow rate of the heat treatment gas constant, Based on the residual ammonia concentration C1 detected by the ammonia sensor 16, the flow rate ratio of ammonia gas in the heat treatment gas is reduced (or increased). In the present embodiment, a plurality (five) of equal total flow lines V1 to V5 are set as the equal total flow lines V. The equal total flow lines V1 to V5 are graphs set in advance, for example, by experiments or calculations. When the equal total flow lines V1 to V5 are collectively referred to, they are simply referred to as “equal total flow lines V”.

  In the equal total flow line V1, the change rate of the nitriding potential P with respect to the change in the residual ammonia concentration C1 is set to be the largest among the equal total flow lines V1 to V5. In the equal total flow line V1, the lowest value of the nitriding potential P is set to be the largest among the equal total flow lines V1 to V5.

  Similarly, in the equal total flow line Vn (n is any one of 2 to 5), the rate of change of the nitriding potential P with respect to the change in the residual ammonia concentration C1 is set to the nth largest among the equal total flow lines V1 to V5. Has been. In the equal total flow line Vn, the lowest value of the nitriding potential P among the equal total flow lines V1 to V5 is set to the nth largest.

  As is clear from the above equal flow ratio line R and the equal total flow line V, generally, the change rate of the nitriding potential P with respect to the change in the residual ammonia concentration C1 in the equal flow ratio line R is equal to the equal total flow line V. Is set larger than the rate of change of the nitriding potential P with respect to the change of the residual ammonia concentration C1.

  More specifically, the rate of change of the nitriding potential P with respect to the change in the residual ammonia concentration C1 in the equal flow ratio lines R1 to R7 at the intersections of the equal flow ratio lines R1 to R7 and the equal total flow lines V1 to V5 is The change rate of the nitriding potential P with respect to the change of the residual ammonia concentration C1 in the equal total flow lines V1 to V5 is set to be larger.

  As described above, the controller 5 performs equal total flow control based on the equal total flow line V in the control map M when changing the residual ammonia concentration C1. In this case, the control unit 5 sets the flow rate ratio of each component gas (ammonia gas) of the heat treatment gas into the heat treatment furnace 6 while keeping the total flow rate of the heat treatment gas per unit time to the heat treatment furnace 6 constant. Change. In this case, as an example, in the equal total flow line V, as indicated by the line segment between the signs S3 and S4, the flow rate ratio of ammonia gas is increased or decreased without changing the total flow rate of the heat treatment gas. As a result, the residual ammonia concentration C1 is increased or decreased.

  On the other hand, as described above, when the nitriding potential P is changed, the control unit 5 performs the equal flow ratio control based on the equal flow ratio line R in the control map M. In this case, in the present embodiment, the control unit 5 makes the nitriding potential P detected by the nitriding potential detection unit 18 while keeping the flow rate ratio of each component gas of the heat treatment gas to the heat treatment furnace 6 per unit time constant. Based on the above, the total flow rate of the heat treatment gas into the heat treatment furnace 6 per unit time is changed. In this case, as an example, as indicated by the line segment between S1 and S2 in the equal flow rate ratio line R, the total flow rate of the heat treatment gas is increased or decreased without changing the flow rate ratio of ammonia gas. As a result, the nitriding potential P is increased or decreased.

  In this embodiment, the control unit 5 controls the ammonia gas to the heat treatment furnace 6 so that the residual ammonia concentration C1 in the heat treatment furnace 6 is 12% or more and the nitriding potential P in the heat treatment furnace 6 is 0.75 or more. Is configured to control the supply of. More specifically, the controller 5 sets the target residual ammonia concentration C1T so that the residual ammonia concentration C1 and the nitriding potential P become the corresponding target residual ammonia concentration C1T = 12% and the target nitriding potential PT = 0.75. The target nitriding potential PT is set, and the supply mode of the heat treatment gas to the heat treatment furnace 6 is controlled. If the residual ammonia concentration C1 in the heat treatment furnace 6 is less than 12%, the variation of the compound layer (nitriding layer) formed on the surface of the workpiece 100 becomes large, and the nitriding quality is deteriorated. . Similarly, when the nitriding potential P in the heat treatment furnace 6 is less than 0.75, the variation of the compound layer (nitriding layer) formed on the surface of the workpiece 100 becomes large, and the nitriding quality decreases. Resulting in. More preferably, the target residual ammonia concentration C1T = 18% and the target nitriding potential PT = 1.00. Thereby, the amount of expensive ammonia gas used can be further reduced while more reliably suppressing variation in nitriding treatment (decreasing nitriding treatment quality).

  Next, an example of heat treatment in the nitriding apparatus 1, particularly an example of a control operation by the control unit 5 will be described. FIG. 3 is a flowchart for explaining an example of the heat treatment operation in the nitriding apparatus 1. In addition, when it demonstrates with reference to a flowchart, it demonstrates, referring also to figures other than a flowchart suitably.

  1 to 3, the atmosphere in the heat treatment furnace 6 is heated by the heater 8 in a state where the workpiece 100 is disposed in the heat treatment furnace 6. In this state, the component gases of the heat treatment gas are supplied from the gas supply units 11, 12, and 13 into the heat treatment furnace 6. In this state, the ammonia sensor 16 measures the residual ammonia concentration C1 (step S1).

  Next, the computing unit 5a determines whether or not the residual ammonia concentration C1 is greater than or equal to a predetermined value a (step S2). When the calculator 5a determines that the residual ammonia concentration C1 is less than the predetermined value a (NO in step S2), the control unit 5 increases the flow rate ratio of ammonia gas in the heat treatment gas (step S3). .

  Specifically, the arithmetic unit 5a of the control unit 5 outputs a command signal for increasing the flow rate ratio of ammonia gas to the regulator 5b. The regulator 5b outputs a command to increase the flow rate of ammonia gas to the electromagnetic valve 11c of the ammonia gas supply unit 11, and outputs a command to decrease the flow rate of nitrogen gas to the electromagnetic valve 12c of the nitrogen gas supply unit 12. In addition, a command to reduce the flow rate of carbon dioxide gas is output to the electromagnetic valve 13 c of the carbon dioxide gas supply unit 13. Accordingly, the control unit 5 increases the flow rate ratio of the ammonia gas based on the equal total flow line V without changing the total flow rate of the heat treatment gas. Note that the flow rate of the carbon dioxide gas is a small value of about several percent of the total flow rate of the heat treatment gas, and may be a fixed value. Since carbon dioxide gas is a small value of, for example, about 5% of the total flow rate of the heat treatment gas, it does not affect the heat treatment atmosphere.

  On the other hand, when the calculator 5a determines that the residual ammonia concentration C1 is equal to or greater than the predetermined value a (YES in step S2), the calculator 5a determines whether the residual ammonia concentration C1 is equal to or less than the predetermined value b. Determine (step S4). The predetermined value b is a value obtained by adding, for example, a constant (0.5% in the present embodiment) to the predetermined value a. The predetermined value b can be regarded as an error range with respect to the predetermined value a. That is, in step S4, the control unit 5 determines whether or not the residual ammonia concentration C1 has substantially reached the predetermined value a.

  When the calculator 5a determines that the residual ammonia concentration C1 is greater than the predetermined value b (NO in step S4), the control unit 5 decreases the flow rate ratio of ammonia gas in the heat treatment gas (step S5). Specifically, the arithmetic unit 5a of the control unit 5 outputs a command signal for reducing the flow rate ratio of ammonia gas to the regulator 5b. The regulator 5b outputs a command to decrease the flow rate of ammonia gas to the electromagnetic valve 11c of the ammonia gas supply unit 11, and outputs a command to increase the flow rate of nitrogen gas to the electromagnetic valve 12c of the nitrogen gas supply unit 12. In addition, a command to increase the flow rate of carbon dioxide gas is output to the electromagnetic valve 13 c of the carbon dioxide gas supply unit 13. Note that the flow rate of the carbon dioxide gas is a small value of about several percent of the total flow rate of the heat treatment gas, and may be a fixed value. Accordingly, the control unit 5 reduces the flow rate ratio of the ammonia gas based on the equal total flow line V without changing the total flow rate of the heat treatment gas.

  With the above control, the control unit 5 increases the flow rate ratio of the ammonia gas in the heat treatment gas when the residual ammonia concentration C1 is less than the predetermined value a (step S3). Further, when the residual ammonia concentration C1 is not less than the predetermined value a and not more than b, the control unit 5 does not change the flow rate ratio of the ammonia gas in the heat treatment gas, assuming that the residual ammonia concentration C1 has substantially reached the predetermined value a. . On the other hand, when the residual ammonia concentration C1 is larger than the predetermined value b, the control unit 5 decreases the flow rate ratio of ammonia gas in the heat treatment gas (step S5).

  After the process for setting the flow rate ratio of the ammonia gas in the heat treatment gas (residual ammonia concentration adjustment process, steps S1 to S5), the control unit 5 performs the process (nitriding for setting the total flow rate of the heat treatment gas. A potential adjustment process, steps S6 to S10) is performed.

  Specifically, the computing unit 5a of the control unit 5 detects the nitriding potential P by calculating the nitriding potential P using the detection results of the residual ammonia concentration C1 and the hydrogen concentration C2 and the above-described equations. (Step S6).

  Next, the computing unit 5a determines whether or not the nitriding potential P is equal to or greater than a predetermined value c (step S7). When the computing unit 5a determines that the nitriding potential P is less than the predetermined value c (NO in step S7), the control unit 5 increases the total flow rate of the heat treatment gas (step S8). Specifically, the arithmetic unit 5a of the control unit 5 outputs a command signal for increasing the total flow rate of the heat treatment gas to the regulator 5b. The regulator 5b outputs a command for increasing the flow rate of the corresponding gas to the electromagnetic valves 11c, 12c, and 13c of the gas supply units 11, 12, and 13, respectively. Accordingly, the control unit 5 increases the total flow rate of the heat treatment gas without changing the ratio of each component gas in the heat treatment gas based on the equal flow ratio line R.

  On the other hand, when the computing unit 5a determines that the nitriding potential P is equal to or greater than the predetermined value c (YES in step S7), the computing unit 5a determines whether the nitriding potential P is equal to or less than the predetermined value d. (Step S9). The predetermined value d is a value obtained by adding, for example, a constant (0.05 in this embodiment) to the predetermined value c. The predetermined value d can be regarded as an error range with respect to the predetermined value c. That is, in step S9, the control unit 5 determines whether or not the nitriding potential P has substantially reached the predetermined value c.

  When the computing unit 5a determines that the nitriding potential P is greater than the predetermined value d (NO in step S9), the control unit 5 decreases the total flow rate of the heat treatment gas (step S10). Specifically, the arithmetic unit 5a of the control unit 5 outputs a command signal for reducing the total flow rate of the heat treatment gas to the regulator 5b. The regulator 5b outputs a command to reduce the flow rate of each corresponding gas to the electromagnetic valves 11c, 12c, and 13c of the gas supply units 11, 12, and 13. Thereby, based on the equal flow rate ratio line R, the total flow rate of the heat treatment gas is decreased without changing the flow rate ratio of each component gas of the heat treatment gas.

  With the above control, the control unit 5 increases the total flow rate of the heat treatment gas when the nitriding potential P is less than the predetermined value c (step S8). In addition, when the nitriding potential P is not less than the predetermined value c and not more than d, the control unit 5 does not change the total flow rate of the heat treatment gas, assuming that the nitriding potential P has substantially reached the predetermined value c. On the other hand, when the nitriding potential P is larger than the predetermined value d, the control unit 5 decreases the total flow rate of the heat treatment gas (step S10).

  After the nitriding potential adjustment process (steps S6 to S10), the controller 5 performs the residual ammonia gas concentration adjustment process (steps S1 to S5) again. That is, the control unit 5 repeatedly performs the residual ammonia gas concentration adjustment process and the nitriding potential adjustment process alternately. In steps S3, S5, S8, and S10, the controller 5 controls the supply of the heat treatment gas in the heat treatment furnace 6 based on the nitriding potential P and the residual ammonia concentration C1.

  Next, a more specific example in the process according to the above flowchart will be described. FIG. 4 is a diagram for explaining one specific example of the control operation in the control of the control unit 5. FIG. 4 shows control based on a map slightly different from the map M described above. However, the map M shown in FIG. 2 and the map M shown in FIG. 4 differ only in specific numerical values, and the nitriding apparatus 1 performs the same process regardless of the control using any map. Is called.

  Referring to FIGS. 1, 3, and 4, for example, prior to control by control unit 5, control unit 5 sets an initial value of the total flow rate of the heat treatment gas and an initial value of the flow rate ratio of ammonia gas. In the present embodiment, the initial value of the total flow rate of the heat treatment gas is set to 100 L / min, and the initial value of the ammonia gas flow rate ratio is set to 50% (point D1). The initial value of the total flow rate of the heat treatment gas and the initial value of the ammonia gas flow rate ratio may be set uniformly by the control unit 5, or the residual ammonia concentration C1 and the hydrogen concentration in the heat treatment furnace 6 immediately before the start of the heat treatment. It may be set based on C2.

  The computing unit 5a of the control unit 5 includes the initial value of the total flow rate of the heat treatment gas and the initial value of the ammonia gas flow rate ratio among the plurality of equal total flow lines V ′ (V1 ′ to V3 ′). Set the total flow line V1 ′.

  Next, in this case, the control unit 5 determines that the residual ammonia concentration C1 is greater than the allowable upper limit b (NO in step S4). Accordingly, the control unit 5 reduces the ammonia gas flow rate ratio from 50% to 40% (from point D1 to point D2) along the equal total flow line V1 '(step S5). As a result, the residual ammonia concentration C1 in the heat treatment furnace 6 is adjusted, and the residual ammonia concentration C1 decreases.

  Next, the computing unit 5a of the control unit 5 determines the detected nitriding potential P (steps S7 and S9). In this case, the nitriding potential P is larger than the predetermined value d and is not in the desired range c ≦ P ≦ d (NO in step S9). Therefore, the computing unit 5a sets the total flow rate of the heat treatment gas to 100 L / min along the equal flow rate ratio line R1 ′ that intersects the above-mentioned equal total flow rate line V1 ′ and is closest to the measured nitriding potential P. To 83 L / min (from point D2 to point D3) (step S10). As a result, the nitriding potential P is adjusted in the heat treatment furnace 6 and the nitriding potential P is lowered.

  Next, the computing unit 5a of the control unit 5 determines the residual ammonia concentration C1 again (steps S1 and S4). In this case, the residual ammonia concentration C1 is larger than the predetermined value b and is not in the desired range a ≦ C ≦ b (NO in step S4). Therefore, the computing unit 5a calculates the flow rate ratio of the ammonia gas of the heat treatment gas along the isototal flow line V2 ′ that intersects the above equal flow ratio line R1 ′ and is closest to the measured residual ammonia concentration C1. 40%, for example, 35% (from point D3 to point D4) (step S5). As a result, the residual ammonia concentration C1 in the heat treatment furnace 6 is adjusted, and the residual ammonia concentration C1 decreases.

  Next, the computing unit 5a of the control unit 5 determines the detected nitriding potential P again (steps S7 and S9). In this case, the nitriding potential P is larger than the predetermined value d and is not in the desired range c ≦ P ≦ d (NO in step S9). Therefore, the computing unit 5a sets the total flow rate of the heat treatment gas to 83 L / min along the equal flow rate ratio line R2 ′ that intersects the above-mentioned equal total flow rate line V2 ′ and is closest to the measured nitriding potential P. To, for example, 75 L / min (from point D4 to point D5) (step S10). As a result, the nitriding potential P is adjusted in the heat treatment furnace 6 and the nitriding potential P is lowered.

  Next, the computing unit 5a of the control unit 5 determines the residual ammonia concentration C1 again (steps S1 and S4). In this case, the residual ammonia concentration C1 is larger than the predetermined value b and is not in the desired range a ≦ C ≦ b (NO in step S4). Therefore, the computing unit 5a calculates the flow rate ratio of the ammonia gas of the heat treatment gas along the equal total flow line V3 ′ that intersects the above equal flow ratio line R2 ′ and is closest to the measured residual ammonia concentration C1. 35% to 32.5% (from point D5 to point D6) (step S5). As a result, the residual ammonia concentration C1 in the heat treatment furnace 6 is adjusted, and the residual ammonia concentration C1 decreases.

  Next, the computing unit 5a of the control unit 5 determines the nitriding potential P again (steps S7 and S9). In this case, the nitriding potential P is larger than the predetermined value d and is not in the desired range c ≦ P ≦ d (NO in step S9). Therefore, the computing unit 5a sets the total flow rate of the heat treatment gas to 75 L / min along the equal flow rate ratio line R3 ′ that intersects the above-mentioned equal total flow rate line V3 ′ and is closest to the measured nitriding potential P. To, for example, 67 L / min (from point D6 to point D7) (step S10). As a result, the nitriding potential P is adjusted in the heat treatment furnace 6 and the nitriding potential P is lowered.

  By the above control process, the residual ammonia concentration C1 was about 12%, and the nitriding potential P was about 0.75.

  As described above, according to the present embodiment, the control unit 5 sets the supply mode of the heat treatment gas into the heat treatment furnace 6 based on both the detected nitriding potential P and the residual ammonia concentration C1. That is, in the nitriding process, the control unit 5 sets the supply mode of the heat treatment gas into the heat treatment furnace 6 in consideration of the residual ammonia concentration C1 in addition to the nitriding potential P. Accordingly, the amount of heat treatment gas used, in particular, the amount of ammonia gas used, while sufficiently satisfying the quality of the nitriding treatment of the workpiece 100 (specifications required for the components of the nitrided layer, uniformity of thickness, etc.). Can be further reduced.

  Further, the control unit 5 is configured to set the flow rate ratio of the heat treatment gas to the heat treatment furnace 6, particularly the ammonia gas, based on the concentration of the ammonia gas itself remaining in the heat treatment furnace 6. Yes. Thereby, the control part 5 can perform control which decreases supply_amount | feed_rate of the ammonia gas in the heat processing furnace 6 more reliably satisfy | filling sufficient quality about a nitriding process.

  Further, according to this embodiment, when the controller 5 changes either the residual ammonia concentration C1 or the nitriding potential P, the total flow rate of the heat treatment gas per unit time into the heat treatment furnace 6 is kept constant. The flow rate ratio of ammonia gas per unit time into the heat treatment furnace 6 is changed. According to this configuration, even when either the residual ammonia concentration C1 or the nitriding potential P is changed, the total flow rate of the heat treatment gas into the heat treatment furnace 6 per unit time does not change. As a result, quality variations related to nitriding can be more reliably suppressed.

  Further, the controller 5 can set the total flow rate of the heat treatment gas to the heat treatment furnace 6 based on the nitriding potential P, that is, the degree of progress of the nitriding treatment. As a result, the control unit 5 can perform control to reduce the supply amount of ammonia gas into the heat treatment furnace 6 while satisfying sufficient quality for the nitriding treatment more reliably.

  Further, according to the present embodiment, when the controller 5 changes any one of the residual ammonia concentration C1 and the nitriding potential P, the flow rate of each component gas in the heat treatment gas into the heat treatment furnace 6 per unit time is changed. The total flow rate of the heat treatment gas per unit time into the heat treatment furnace 6 is changed while keeping the ratio constant. According to this configuration, when the control unit 5 changes any one of the residual ammonia concentration C1 and the nitriding potential P, the flow rate ratio of each component gas in the heat treatment gas into the heat treatment furnace 6 per unit time changes. do not do. Therefore, a rapid change in the mode of the nitriding reaction around the surface of the workpiece 100 is suppressed. As a result, quality variations related to nitriding can be more reliably suppressed. As described above, according to the present embodiment, the nitriding apparatus 1 that can further reduce the amount of the heat treatment gas used without degrading the quality of the nitriding process can be realized.

  Further, according to the present embodiment, when the controller 5 changes either the residual ammonia concentration C1 or the nitriding potential P, the control unit 5 enters the heat treatment furnace 6 based on the residual ammonia concentration C1 detected by the ammonia sensor 16. The flow rate ratio of ammonia gas in the heat treatment gas per unit time into the heat treatment furnace 6 is changed while the total flow rate of the heat treatment gas per unit time is constant. In addition, when changing either the residual ammonia concentration C1 or the nitriding potential P, the control unit 5 per unit time into the heat treatment furnace 6 based on the nitriding potential P detected by the nitriding potential detecting unit 18. The total flow rate of the heat treatment gas per unit time into the heat treatment furnace 6 is changed while the flow rate ratio of each component gas in the heat treatment gas is kept constant. According to this configuration, the nitriding treatment can be completed more quickly, and the amount of heat treatment gas used can be further reduced.

  According to the present embodiment, the control unit 5 is configured to alternately perform control for changing the flow rate ratio of ammonia gas and control for changing the total flow rate of the heat treatment gas. According to this configuration, the nitriding treatment can be completed more quickly, and the amount of heat treatment gas used can be further reduced.

  Further, according to the present embodiment, the controller 5 sets the initial value of the total flow rate of the heat treatment gas, the initial value of the flow rate ratio of the ammonia gas, the target value C1T of the residual ammonia concentration C1, and the target value PT of the nitriding potential P. On the basis of the above, the control for changing the flow rate ratio of the ammonia gas and the control for changing the total flow rate of the heat treatment gas are performed. According to this configuration, finer control for completing the nitriding process more quickly and reducing the amount of heat treatment gas used can be realized.

  Further, according to the present embodiment, the control unit 5 is configured to be able to set the total flow rate of the heat treatment gas into the heat treatment furnace 6 based on a predetermined equiflow rate ratio line R in order to control the nitriding potential P. Has been. The equiflow rate ratio line R is obtained when the flow rate ratio of ammonia gas in the heat treatment gas per unit time is constant in the graph when the residual ammonia concentration C1 is the horizontal axis and the nitriding potential P is the vertical axis. The characteristics of According to this configuration, the control unit 5 sets the supply mode of the heat treatment gas supplied to the heat treatment furnace 6, particularly the ammonia gas, based on the preset equal flow ratio line R. Thereby, the control part 5 can perform control which decreases supply_amount | feed_rate of the ammonia gas in the heat processing furnace 6 more reliably satisfy | filling sufficient quality about a nitriding process.

  Further, according to this embodiment, the control unit 5 controls the flow rate ratio of ammonia gas in the heat treatment gas into the heat treatment furnace 6 based on the equal total flow line V in order to control the residual ammonia concentration C1. The equal total flow line V indicates a characteristic when the total flow rate of the heat treatment gas per unit time is constant. According to this structure, the control part 5 sets the supply aspect of the gas for heat processing especially the ammonia gas supplied in the heat processing furnace 6 based on the equal total flow line V set beforehand. Thereby, the control part 5 can perform control which decreases supply_amount | feed_rate of the ammonia gas in the heat processing furnace 6 more reliably satisfy | filling sufficient quality about a nitriding process.

  Further, according to the present embodiment, the control unit 5 supplies the heat treatment furnace 6 with the residual ammonia concentration C1 in the heat treatment furnace 6 so that the residual ammonia concentration C1 is 12% or more and the nitriding potential P in the heat treatment furnace 6 is 0.75 or more. The supply of the heat treatment gas is controlled. According to this configuration, the residual ammonia concentration C1 is set to 12% at the minimum and the nitriding potential P is set to 0.75 at the minimum, so that the quality for the nitriding process is sufficiently ensured, and the heat treatment gas, particularly the ammonia gas. Can be used more

  In particular, in the present embodiment, the control unit 5 sets the supply amount of the heat treatment gas into the heat treatment furnace 6 based on both the nitriding potential P and the residual ammonia concentration C1. That is, in the nitriding process, in addition to the nitriding potential P, the residual ammonia concentration C1 is also considered, and the supply amount of the heat treatment gas into the heat treatment furnace 6 is set. Thus, the amount of heat treatment gas used, particularly the amount of ammonia gas, is sufficiently satisfied while sufficiently satisfying the quality of the nitriding treatment of the workpiece 100 (required specifications such as the composition of the nitrided layer and uniformity of thickness). Can be further reduced.

  More specifically, the control unit 5 sets the flow rate of the heat treatment gas, particularly ammonia gas, supplied into the heat treatment furnace 6 based on the preset equal flow ratio line R and the equal total flow line V. . As a result, the control unit 5 can realize a state in which both the residual ammonia concentration C1 and the nitriding potential P are further reduced while sufficiently ensuring the quality related to the nitriding treatment. That is, the control unit 5 can further reduce the amount of heat treatment gas, particularly ammonia gas, used in nitriding.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the above-mentioned embodiment. The present invention can be variously modified as long as it is described in the claims.

  (1) In the above-described embodiment, in particular, a control object (residual ammonia concentration C1 and nitriding potential P as objects to be changed) and a measurement object (object to be measured to change the control object, that is, an ammonia sensor). The residual ammonia concentration C1 detected in FIG. 16 and the nitriding potential P detected by the nitriding potential detector 18) and the control method (the method of changing the total flow rate and the method of changing the flow rate ratio) are shown in the pattern 1 shown in FIG. Explained an example. However, this need not be the case.

  For example, any of patterns 2, 3, and 4 shown in FIG. 5 may be employed. Hereinafter, the total flow rate of the heat treatment gas per unit time into the heat treatment furnace 6 may be simply referred to as “total flow rate”. Further, the flow rate ratio of ammonia gas in the heat treatment gas per unit time into the heat treatment furnace 6 may be simply referred to as “flow rate ratio”.

  In pattern 1, when changing the residual ammonia concentration C1, the control unit 5 changes the flow rate ratio (pattern A) while keeping the total flow rate constant based on the residual ammonia concentration C1 detected by the ammonia sensor 16. In this pattern 1, when changing the nitriding potential P, the control unit 5 changes the total flow rate (pattern B) while keeping the flow rate ratio constant based on the nitriding potential P detected by the nitriding potential detection unit 18. .

  In pattern 2, when changing the nitriding potential P, the control unit 5 changes the flow rate ratio while keeping the total flow rate constant based on the residual ammonia concentration C1 detected by the ammonia sensor 16. In this pattern 2, when changing the residual ammonia concentration C1, the control unit 5 changes the total flow rate while keeping the flow rate ratio constant based on the nitriding potential P detected by the nitriding potential detection unit 18.

  In pattern 3, when changing the residual ammonia concentration C1, the control unit 5 changes the flow rate ratio while keeping the total flow rate constant based on the nitriding potential P detected by the nitriding potential detection unit 18. In this pattern 3, when the nitriding potential P is changed, the control unit 5 changes the total flow rate while keeping the flow rate ratio constant based on the residual ammonia concentration C1 detected by the ammonia sensor 16.

  In pattern 4, when changing the nitriding potential P, the control unit 5 changes the flow rate ratio while keeping the total flow rate constant based on the nitriding potential P detected by the nitriding potential detection unit 18. In this pattern 4, when changing the residual ammonia concentration C1, the control unit 5 changes the total flow rate while keeping the flow rate ratio constant based on the residual ammonia concentration C1 detected by the ammonia sensor 16.

  When the patterns 1 to 4 are summarized, the control unit 5 detects the residual ammonia concentration P detected by the ammonia sensor 16 and the nitriding potential detection unit 18 when changing either the residual ammonia concentration C1 or the nitriding potential P. Based on one of the nitriding potentials P, the flow rate ratio is changed while the total flow rate is kept constant. Further, when the controller 5 changes any one of the residual ammonia concentration C1 and the nitriding potential P, the controller 5 determines which of the residual ammonia concentration C1 detected by the ammonia sensor 16 and the nitriding potential P detected by the nitriding potential detector 18. On the other hand, the total flow rate is changed while the flow rate ratio is kept constant.

  (2) In the above-described embodiment, the soft nitriding process using the heat treatment gas has been described. However, this need not be the case. For example, the nitriding apparatus 1 can be used for other nitriding processes such as a nitriding process, an oxynitriding process, and a carbonitriding process.

<Test 1>
The nitriding apparatus having the configuration described in the above embodiment was manufactured as an example. Further, a nitriding apparatus having the same configuration as that of the example was manufactured as a comparative example, except that neither the control of the nitriding potential nor the control of the residual ammonia concentration was performed by the control unit.

  And the nitriding process of the to-be-processed object was performed using each of an Example and a comparative example. At this time, the relationship between the time from the start of the nitriding treatment (treatment time) and the nitriding potential, and the relationship between the treatment time and the residual ammonia concentration were measured. The results are shown in FIG.

  In the graph of FIG. 6, the horizontal axis represents the processing time. The vertical axis shows the nitriding potential and the residual ammonia concentration. As is apparent from FIG. 6, the nitriding potential decreases as the processing time elapses. However, in the comparative example, the decrease rate of the nitriding potential at the initial stage of the nitriding treatment is moderate, whereas in the example, the decrease rate of the nitriding potential is remarkably large. When the treatment time is 90 minutes, the nitriding potential in the comparative example is a large value close to 1.5, whereas the nitriding potential in the example is about 1.0, which is a sufficiently small value. It has become.

  In the comparative example, the residual ammonia concentration gradually increases as the processing time elapses. In particular, in the comparative example, the rate of increase in the residual ammonia concentration is large when the elapsed time is up to 30 minutes, and the residual ammonia concentration is gradually increased even after the elapsed time is 30 minutes. Then, when the elapsed time is 90 minutes, the residual ammonia concentration reaches about 30%. On the other hand, in the examples, the increase rate of the residual ammonia concentration is small during the elapsed time of up to 30 minutes, and the increase rate of the residual ammonia concentration is remarkably small after the elapsed time of 30 minutes. . Then, when the elapsed time is 90 minutes, the residual ammonia concentration almost converges to a constant value of less than 20%.

  As described above, it has been proved that the embodiment can further reduce the amount of the heat treatment gas, in particular, the amount of ammonia gas, by reducing the nitriding potential and the residual ammonia concentration in the nitriding treatment.

<Test 2>
Next, Comparative Reference Examples 1 to 8 were produced by performing nitriding treatment on the workpiece using the comparative example. Moreover, the reference examples 1-16 were produced by performing a nitriding process to a to-be-processed object using an Example.

  The conditions for producing Comparative Reference Examples 1 to 8 satisfy at least one of the condition that the nitriding potential is less than 0.75 and the condition that the residual ammonia concentration is less than 12%. On the other hand, the conditions for producing Examples Reference Examples 1 to 16 satisfy the conditions that the nitriding potential is 0.75 or more and the residual ammonia concentration is 12% or more.

For Comparative Reference Examples 1 to 8 and Example Reference Examples 1 to 16, the nitriding potential and the residual ammonia concentration are as follows.
Nitriding potential; residual ammonia concentration Comparative Reference Example 1 0.50; 12%
Comparative Reference Example 2 0.50; 18%
Comparative Reference Example 3 0.50; 24%
Comparative Reference Example 4 0.50; 30%
Comparative Reference Example 5 0.75; 6%
Comparative Reference Example 6 1.00; 6%
Comparative Reference Example 7 1.25; 6%
Comparative Reference Example 8 1.50; 6%
Implementation Reference Example 1 0.75; 12%
Implementation Reference Example 2 0.75; 18%
Implementation Example 3 0.75; 24%
Implementation Reference Example 4 0.75; 30%
Example of Reference Example 5 1.00; 12%
Example of Reference Example 6 1.00; 18%
Example of Reference Example 7 1.00; 24%
Example of Reference Example 8 1.00; 30%
Example of Reference Example 9 1.25; 12%
Example of Reference Example 10 1.25; 18%
Implementation Reference Example 11 1.25; 24%
Working Example 12 1.25; 30%
Implementation Reference Example 13 1.50; 12%
Reference Example 14 1.50; 18%
Reference Example 15 1.50; 24%
Working Example 16 1.50; 30%

For each of Comparative Reference Examples 1 to 8 and Example Reference Examples 1 to 16, the thickness variation R of the compound layer (nitride layer) was measured. The evaluation when R ≦ 2 μm was given as ◎, the evaluation when 2 μm <R <4 μm was given as ◯, and the evaluation when 4 μm ≦ R was given as x. The results are shown in Table 1.

  As is clear from Table 1, Comparative Reference Examples 1 to 8 are all results of x, the variation amount R of the nitride layer thickness is large, and the treatment quality of the nitride layer surface is not good. On the other hand, Examples 1 to 16 are the results of ◯ or ◎, and it was proved that the variation amount R of the thickness of the nitride layer was small and the treatment quality on the surface of the nitride layer was good. In particular, Examples 6 to 8, 10 to 12, and 14 to 16 were evaluated as ◎, and the variation amount R of the nitride layer thickness R was extremely small, and it was proved that the treatment quality of the nitride layer surface was extremely good. . That is, a nitriding potential of 0.75 or more and a residual ammonia concentration of 12% are effective for improving the quality of nitriding treatment, and in particular, a nitriding potential of 1.00 or more and a residual ammonia concentration of It was demonstrated that 18% or more is extremely effective for increasing the quality of the nitriding treatment.

  Table 2 shows the cost of the heat treatment gas for the nitriding treatment.

  Table 2 shows Examples 6 to 8, 10 to 12, and 14 to 16 that have been evaluated as ◎ in the quality of nitriding treatment.

  The numerical values shown in Table 2 are for the reference example when the cost of the heat treatment gas necessary for preparing the comparative reference example (any one of comparative reference examples 1 to 8) is 100. It shows the cost of the heat treatment gas required to do. Here, the ratio of the amount of ammonia gas: nitrogen gas is 6: 1. As is clear from Table 2, the heat treatment gas cost required for the production of Examples other than Example Reference Example 16 out of Example Reference Examples 6-8, 10-12, and 14-16 is more than the production cost of Comparative Reference Example. cheap. In particular, the cost of the heat treatment gas necessary for producing Example Reference Example 6 was half of the cost of the heat treatment gas necessary for producing the Comparative Reference Example. Further, even in Example Reference Example 16, the cost of the heat treatment gas necessary for production is the same as the cost of the heat treatment gas necessary for production of the comparative reference example. From the above, it was proved that, in the examples, since the variation in the thickness of the nitride layer is small, a high-quality nitriding treatment can be performed and the nitriding treatment can be realized at a low cost.

  The present invention can be widely applied as a nitriding apparatus and a nitriding method.

DESCRIPTION OF SYMBOLS 1 Nitriding apparatus 5 Control part 6 Heat treatment furnace 16 Ammonia sensor (residual ammonia concentration detection part)
18 Nitriding potential detector 100 Object C1 Residual ammonia concentration C1T Target value P of residual ammonia concentration P Nitriding potential PT Target value R of nitriding potential Equivalent flow ratio line (equal ammonia flow rate ratio characteristic)
V equal total flow line (equal total flow characteristics)

Claims (10)

A nitriding apparatus for performing nitriding treatment on an object to be processed disposed in the heat treatment furnace by introducing a heat treatment gas containing ammonia gas into the heat treatment furnace,
A nitriding potential detector for detecting the nitriding potential in the heat treatment furnace;
A residual ammonia concentration detector for detecting a residual ammonia concentration in the heat treatment furnace;
A control unit for controlling the supply of the heat treatment gas into the heat treatment furnace based on the nitriding potential and the residual ammonia concentration;
With
When the control unit changes any one of the residual ammonia concentration and the nitriding potential, either the residual ammonia concentration detected by the residual ammonia concentration detecting unit or the nitriding potential detected by the nitriding potential detecting unit Based on one, the flow rate ratio of the ammonia gas in the heat treatment gas per unit time into the heat treatment furnace is changed while the total flow rate of the heat treatment gas into the heat treatment furnace is constant. Configured to let
When the control unit changes either the residual ammonia concentration or the nitriding potential, the control unit selects either the residual ammonia concentration detected by the residual ammonia concentration detecting unit or the nitriding potential detected by the nitriding potential detecting unit. Based on the other, the total flow rate of the heat treatment gas per unit time into the heat treatment furnace while the flow rate ratio of each component gas in the heat treatment gas per unit time into the heat treatment furnace is constant. The nitriding apparatus is configured to change the temperature. The nitriding apparatus according to claim 1, wherein
The controller, when changing either the residual ammonia concentration or the nitriding potential, based on the residual ammonia concentration detected by the residual ammonia concentration detector, the unit per unit time into the heat treatment furnace The flow rate ratio of the ammonia gas in the heat treatment gas per unit time into the heat treatment furnace is changed while keeping the total flow rate of the heat treatment gas constant,
The controller controls the heat treatment per unit time into the heat treatment furnace based on the nitriding potential detected by the nitriding potential detector when changing either the residual ammonia concentration or the nitriding potential. A nitriding apparatus configured to change the total flow rate of the heat treatment gas per unit time into the heat treatment furnace while keeping a flow rate ratio of each component gas in the gas constant . The nitriding apparatus according to claim 1 or 2, wherein
The nitriding apparatus, wherein the control unit is configured to alternately perform control for changing the flow rate ratio of the ammonia gas and control for changing the total flow rate of the heat treatment gas. The nitriding apparatus according to claim 3, wherein
The control unit is configured to determine the ammonia gas based on an initial value of a total flow rate of the heat treatment gas, an initial value of the flow rate ratio of the ammonia gas, a target value of the residual ammonia concentration, and a target value of the nitriding potential. A nitriding apparatus configured to perform control for changing a flow rate ratio of the gas and control for changing a total flow rate of the heat treatment gas. The nitriding apparatus according to any one of claims 1 to 4, wherein
The control unit is configured to control the total flow rate of the heat treatment gas into the heat treatment furnace based on a predetermined equal ammonia flow rate ratio characteristic in order to control the nitriding potential,
The equiammonia flow rate ratio characteristic is a graph in which the residual ammonia concentration is on the horizontal axis and the nitriding potential is on the vertical axis, and the flow rate ratio of the ammonia gas in the heat treatment gas per unit time is made constant. A nitriding apparatus characterized by exhibiting characteristics at the time. The nitriding apparatus according to any one of claims 1 to 5,
The control unit is configured to control a flow rate ratio of the ammonia gas in the heat treatment gas into the heat treatment furnace based on a predetermined equal total flow characteristic in order to control the residual ammonia concentration. And
The equal total flow rate characteristic indicates a characteristic when the total flow rate of the heat treatment gas per unit time is constant in a graph when the residual ammonia concentration is on the horizontal axis and the nitriding potential is on the vertical axis. A nitriding apparatus characterized by the above. The nitriding apparatus according to any one of claims 1 to 6, wherein
The controller controls the supply of the heat treatment gas to the heat treatment furnace so that the residual ammonia concentration in the heat treatment furnace is 12% or more and the nitriding potential in the heat treatment furnace is 0.75 or more. It is comprised so that it may carry out. The nitriding apparatus characterized by the above-mentioned. A nitriding apparatus for performing nitriding treatment on an object to be processed disposed in the heat treatment furnace by introducing a heat treatment gas containing ammonia gas into the heat treatment furnace,
A control unit for controlling the supply of the heat treatment gas to the heat treatment furnace based on a predetermined equal ammonia flow rate ratio characteristic and a predetermined equal total flow characteristic;
The equiammonia flow rate ratio characteristic is a graph in which the horizontal axis represents the residual ammonia concentration in the heat treatment furnace and the vertical axis represents the nitriding potential in the heat treatment furnace, and the ammonia in the heat treatment gas per unit time. Shows the characteristics when the flow rate ratio is constant,
The equal total flow rate characteristic indicates a characteristic when the total flow rate of the heat treatment gas per unit time is constant in the graph. A nitriding method for nitriding a workpiece disposed in the heat treatment furnace by introducing a gas for heat treatment containing ammonia gas into the heat treatment furnace,
A nitriding potential detecting step for detecting a nitriding potential in the heat treatment furnace;
A residual ammonia concentration detection step for detecting a residual ammonia concentration in the heat treatment furnace;
A control step of controlling supply of the heat treatment gas into the heat treatment furnace based on the nitriding potential and the residual ammonia concentration;
Including
In the control step, when changing either the residual ammonia concentration or the nitriding potential, either the residual ammonia concentration detected in the residual ammonia concentration detecting step or the nitriding potential detected in the nitriding potential detecting step is selected. Based on one, the flow rate ratio of the ammonia gas in the heat treatment gas per unit time into the heat treatment furnace is changed while the total flow rate of the heat treatment gas into the heat treatment furnace is constant. Configured to let
In the control step, when changing either the residual ammonia concentration or the nitriding potential, either the residual ammonia concentration detected in the residual ammonia concentration detecting step or the nitriding potential detected in the nitriding potential detecting step is selected. Based on the other, the total flow rate of the heat treatment gas per unit time into the heat treatment furnace is set while the flow ratio of each component gas in the heat treatment gas per unit time into the heat treatment furnace is constant. It is comprised so that it may change, The nitriding method characterized by the above-mentioned. A nitriding method for nitriding a workpiece disposed in the heat treatment furnace by introducing a gas for heat treatment containing ammonia gas into the heat treatment furnace,
A control step of controlling supply of the heat treatment gas to the heat treatment furnace based on a predetermined equal ammonia flow rate ratio characteristic and a predetermined equal total flow characteristic;
The equiammonia flow rate ratio characteristic is a graph in which the horizontal axis represents the residual ammonia concentration in the heat treatment furnace and the vertical axis represents the nitriding potential in the heat treatment furnace, and the ammonia in the heat treatment gas per unit time. Shows the characteristics when the flow rate ratio is constant,
In the graph, the equal total flow rate characteristic indicates a characteristic when the total flow rate of the heat treatment gas per unit time is constant.

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