WO2022215526A1

WO2022215526A1 - Surface hardening treatment apparatus and surface hardening treatment method

Info

Publication number: WO2022215526A1
Application number: PCT/JP2022/013509
Authority: WO
Inventors: 泰平岡
Original assignee: パーカー熱処理工業株式会社
Priority date: 2021-04-09
Filing date: 2022-03-23
Publication date: 2022-10-13
Also published as: TW202302886A

Abstract

The present invention is provided with: a furnace atmosphere gas concentration detection device for detecting a hydrogen concentration or an ammonia concentration in a treatment furnace; a furnace nitriding potential calculation device for calculating a nitriding potential in the treatment furnace on the basis of the hydrogen concentration or the ammonia concentration detected by the furnace atmosphere gas concentration detection device; and a gas introduction amount control device for varying the introduction amount of each of a plurality of furnace introduction gases excluding an ammonia decomposition gas in accordance with the calculated nitriding potential in the treatment furnace and a target nitriding potential while keeping the introduction amount of the ammonia decomposition gas at a constant value, thereby bringing the nitriding potential in the treatment furnace close to the target nitriding potential.

Description

Surface hardening treatment apparatus and surface hardening treatment method

The present invention relates to a surface hardening treatment apparatus and a surface hardening treatment method for performing surface hardening treatment, such as nitriding, nitrocarburizing, nitriding and quenching, on metal objects to be treated.

Among the surface hardening treatments for metal objects to be treated, such as steel, there are many needs for nitriding treatment, which is a low-strain treatment. Nitriding methods include a gas method, a salt bath method, a plasma method, and the like.

Among these methods, the gas method is comprehensively superior when considering quality, environmental friendliness, mass productivity, etc. Distortion caused by carburizing, carbonitriding, or induction hardening accompanied by quenching of mechanical parts can be improved by using gas nitriding (gas nitriding). Nitro-nitriding by gas method accompanied by carburizing (gas nitro-nitriding) is also known as a process similar to gas nitriding.

　Gas nitriding is a process in which only nitrogen penetrates and diffuses into the workpiece to harden the surface. In the gas nitriding process, ammonia gas alone, a mixed gas of ammonia gas and nitrogen gas, ammonia gas and ammonia decomposition gas (composed of 75% hydrogen and 25% nitrogen, also called AX gas), or ammonia gas and ammonia A mixed gas of decomposition gas and nitrogen gas is introduced into the processing furnace to perform surface hardening.

The basis of atmosphere control in gas nitriding treatment is to control the nitriding potential (K _N ) in the furnace. By controlling the nitriding potential (K _N ), the volume fraction of the γ' phase (Fe ₄ N) and the ε phase (Fe _2-3 N) in the compound layer generated on the surface of the steel material can be controlled, It is possible to obtain a wide range of nitridation quality, such as realizing a process that does not generate the compound layer. For example, according to Japanese Patent Application Laid-Open No. 2016-211069 (Patent Document 1), by selecting the γ' phase and increasing its thickness, the bending fatigue strength and wear resistance are improved, and further high functionality of mechanical parts is realized. .

In the gas nitriding process as described above, in order to control the atmosphere in the processing furnace in which the workpiece is placed, a furnace atmosphere gas concentration measuring sensor is installed to measure the hydrogen concentration or the ammonia concentration in the furnace. be done. Then, the in-furnace nitriding potential is calculated from the measured value of the in-furnace atmosphere gas concentration measuring sensor, compared with the target (set) nitriding potential, and the flow rate of each introduced gas is controlled ("Heat Treatment", Vol. 55, No. 1, pp. 7-11 (Tai Hiraoka, Yoichi Watanabe) (Non-Patent Document 2)). As for the control method of each introduced gas, a method of controlling the total introduced amount while keeping the flow ratio of the gas introduced into the furnace constant is well known (“Nitriding and Nitrocarburizing of Iron”, 2nd edition (2013), 158 163 (Dieteritke et al., Agne Technical Center) (Non-Patent Document 3)).

In Japanese Patent No. 5629436 (Patent Document 2), the control mode of controlling the total introduction amount while keeping the flow rate ratio of the gas introduced into the furnace constant is the first control, and the flow rate ratio of the gas introduced into the furnace is changed. The second control is a control mode in which the introduction amount of the gas introduced into the furnace is individually controlled, and an apparatus is disclosed in which both can be performed (only one of them is selectively performed at the same time). However, Japanese Patent No. 5629436 (Patent Document 2) discloses only one specific example of nitriding treatment in which the first control is effective (described in paragraphs 0096 and 0099 of Japanese Patent No. 5629436 (Patent Document 2): "By controlling the total amount of ammonia gas and nitrogen gas introduced into the treatment furnace while maintaining NH ₃ (ammonia gas):N ₂ (nitrogen gas) = 80:20", the nitriding potential was set to 3.3. Accurate control), there is no disclosure as to what kind of nitriding treatment is effective in adopting the second control, nor is there any disclosure of a specific example of an effective second control.

In addition, the method of controlling the total amount of gas introduced into the furnace while keeping the flow ratio of the gas introduced into the furnace constant has the advantage that the total amount of gas used can be expected to be suppressed, but it was also found that the control range of the nitriding potential is narrow. ing. As a measure to deal with this problem, the present inventor developed a control method for realizing a wide nitriding potential control range (for example, about 0.05 to 1.3 at 580 ° C.) on the low nitriding potential side, and patented No. 6345320 (Patent Document 3) has been obtained. In the control method of Japanese Patent No. 6345320 (Patent Document 3), the flow rate ratio of the plurality of types of furnace introduction gases is changed while maintaining the total introduction amount of the plurality of types of furnace introduction gases constant. In order to bring the nitriding potential closer to the target nitriding potential, the introduction amounts of the plurality of types of furnace introduced gases are individually controlled.

(Basic Matters of Gas Nitriding)
Chemically explaining the basics of gas nitriding, in gas nitriding, a nitriding reaction represented by the following formula (1) takes place in a processing furnace (gas nitriding furnace) in which an object to be treated is placed. Occur.
_NH3 →[N]+3/ _2H2 (1)

At this time, the nitriding potential K _N is defined by the following equation (2).
^KN = _PNH3 / _PH23 / ₂ (2)
where P _NH3 is the reactor ammonia partial pressure and _PH2 is the reactor hydrogen partial pressure. The nitriding potential K _N is well known as an index representing the nitriding ability of the atmosphere in the gas nitriding furnace.

On the other hand, in the furnace during the gas nitriding treatment, part of the ammonia gas introduced into the furnace is thermally decomposed into hydrogen gas and nitrogen gas according to the reaction of formula (3).
_NH3 →1/2N2 ₊ 3/ _2H2 (3)

Inside the furnace, the reaction of formula (3) mainly occurs, and the nitriding reaction of formula (1) can be almost ignored quantitatively. Therefore, if the concentration of in-furnace ammonia consumed in the reaction of formula (3) or the concentration of hydrogen gas generated in the reaction of formula (3) is known, the nitriding potential can be calculated. That is, since the hydrogen and nitrogen generated are 1.5 mol and 0.5 mol, respectively, from 1 mol of ammonia, the hydrogen concentration in the furnace can be obtained by measuring the ammonia concentration in the furnace, and the nitriding potential can be calculated. can be done. Alternatively, if the in-furnace hydrogen concentration is measured, the in-furnace ammonia concentration can be obtained, and the nitriding potential can also be calculated.

The ammonia gas flowed into the gas nitriding furnace is discharged outside the furnace after circulating inside the furnace. That is, in the gas nitriding treatment, fresh (new) ammonia gas is constantly flowed into the furnace with respect to the existing gas in the furnace, so that the existing gas continues to be discharged out of the furnace (pushed out by the supply pressure). .

Here, if the flow rate of ammonia gas introduced into the furnace is small, the gas residence time in the furnace will be long, so the amount of ammonia gas to be decomposed will increase, and the nitrogen gas generated by the decomposition reaction will be + The amount of hydrogen gas increases. On the other hand, if the flow rate of ammonia gas introduced into the furnace is large, the amount of ammonia gas discharged outside the furnace without being decomposed increases, and the amount of nitrogen gas + hydrogen gas generated in the furnace decreases. do.

(Basic matter of flow rate control)
Next, the basic matter of flow rate control will be described for the case where only ammonia gas is introduced into the furnace. When the degree of decomposition of the ammonia gas introduced into the furnace is s (0<s<1), the gas reaction within the furnace is expressed by the following equation (4).
_NH3 →(1−s)/(1+s) _NH3 +0.5s/(1+s) _N2 +1.5s/( ₁ +s)H2 (4)
Here, the left side is the gas introduced into the furnace (only ammonia gas), and the right side is the gas composition in the furnace. exist. Therefore, when measuring the hydrogen concentration in the furnace with a hydrogen sensor, 1.5s/(1+s) on the right side corresponds to the value measured by the hydrogen sensor, and the decomposition degree s can be calculated. As a result, the in-furnace ammonia concentration corresponding to (1-s)/(1+s) on the right side can also be calculated. That is, the in-furnace hydrogen concentration and the in-furnace ammonia concentration can be known only from the measured value of the hydrogen sensor. Therefore, the nitriding potential can be calculated.

Even when using a plurality of gases introduced into the furnace, the nitriding potential K _N can be controlled. For example, two types of gases, ammonia and nitrogen, are introduced into the furnace, and the introduction ratio is x: y (x and y are known and x + y = 1. For example, x = 0.5, y = 1- The gas reaction in the furnace when 0.5=0.5 (NH ₃ :N ₂ =1:1) is represented by the following equation (5).
_xNH3 +(1-x) _N2 →x(1-s)/(1+sx) _NH3 +(0.5sx+1-x)/(1+sx) _N2 +1.5sx/(1+sx) )H2 ( ₅ )

Here, the gas composition in the furnace on the right side is composed of undecomposed ammonia gas, nitrogen and hydrogen generated at a ratio of 1:3 by decomposition of ammonia gas, and nitrogen gas on the left side as introduced (not decomposed in the furnace). ) and At this time, since x is known (for example, x=0.5), the only unknown is the degree of decomposition s of ammonia at the in-furnace hydrogen concentration on the right side, that is, 1.5sx/(1+sx). Therefore, as in the case of equation (4), the degree of decomposition s of the ammonia gas introduced into the furnace can be calculated from the measured value of the hydrogen sensor, and the in-furnace ammonia concentration can also be calculated from this. Therefore, the nitriding potential can be calculated.

When the flow ratio of the gas introduced into the furnace is not fixed, the hydrogen concentration in the furnace and the ammonia concentration in the furnace are determined by using two variables: the degree of decomposition s of the ammonia gas introduced into the furnace and the introduction ratio x of the ammonia gas. Including as Since a mass flow controller (MFC) is generally used as a device for controlling the gas flow rate, the ammonia gas introduction ratio x can be continuously read as a digital signal based on the flow rate value. Therefore, the nitriding potential can be calculated by combining the introduction ratio x and the measured value of the hydrogen sensor based on the equation (5).

JP 2016-211069 Patent No. 5629436 Patent No. 6345320

The inventors of the present invention have extensively studied the case of gas nitriding treatment in which a plurality of types of furnace-introduced gases including ammonia gas, ammonia decomposition gas, and nitrogen gas are introduced into the treatment furnace, and aimed at the nitriding potential in the treatment furnace. During control to approach the nitriding potential, by changing the introduction amount of each of the plurality of types of furnace introduction gases other than the ammonia decomposition gas while maintaining the introduction amount of the ammonia decomposition gas constant, It was found that nitriding potential control sufficient for practical use can be realized.

In addition, the inventor of the present invention has extensively studied the case of gas nitriding treatment in which a plurality of types of furnace-introduced gases including ammonia gas, ammonia decomposition gas, and nitrogen gas are introduced into the treatment furnace, and found that the nitriding potential in the treatment furnace When controlling to approach the target nitriding potential, it was found that practically sufficient nitriding potential control can be realized by changing the introduction amount of ammonia gas and nitrogen gas while keeping the introduction amount of ammonia decomposition gas constant.

The present invention was invented based on the above findings. An object of the present invention is to provide a surface hardening treatment apparatus capable of realizing practical nitriding potential control in a gas nitriding treatment in which a plurality of types of furnace-introduced gases including ammonia gas, ammonia decomposition gas, and nitrogen gas are introduced into the treatment furnace. and to provide a surface hardening treatment method.

The present invention introduces a plurality of types of furnace-introduced gases including ammonia gas, ammonia decomposition gas, and nitrogen gas into a processing furnace, and performs gas nitriding as surface hardening treatment of an article to be processed placed in the processing furnace. A surface hardening apparatus for performing treatment, comprising: an in-furnace atmosphere gas concentration detection device for detecting a hydrogen concentration or an ammonia concentration in the treatment furnace; and a hydrogen concentration or ammonia concentration detected by the in-furnace atmosphere gas concentration detection device. and an in-furnace nitriding potential calculation device for calculating the nitriding potential in the processing furnace based on the nitriding potential in the processing furnace calculated by the in-furnace nitriding potential calculation device and the target nitriding potential, the ammonia The nitriding potential in the treatment furnace is set to the target nitriding potential by changing the introduction amount of each of the plurality of kinds of gases introduced into the furnace, other than the ammonia decomposition gas, while maintaining the introduction amount of the decomposition gas constant. A gas introduction amount control device that brings the gas introduction amount closer to the potential,
A surface hardening apparatus characterized by comprising:

According to the present invention, a relatively wide nitriding potential is obtained by changing the introduction amount of each furnace introduction gas other than the ammonia decomposition gas among a plurality of types of furnace introduction gases while keeping the introduction amount of the ammonia decomposition gas constant. It was confirmed that control (especially relatively low nitriding potential control) could be achieved.

It is desirable that the amount of ammonia decomposition gas to be introduced to be maintained constant is determined in advance by conducting a preliminary experiment before operation. This is because the degree of thermal decomposition of ammonia gas is actually affected by the environment inside the furnace used.

Further, the gas introduction amount control device sets the amount of ammonia gas introduced into the furnace as A, the amount of ammonia decomposition gas introduced into the furnace as B, and x as a predetermined constant. , CN (N is an integer equal to or greater than 1) of each of the gases introduced into the furnace other than the ammonia gas and the ammonia cracked gas is assigned to each of the gases introduced into the furnace. , using cN,
C1=c1×(A+x×B), CN=cN×(A+x×B)
It is preferable to control so as to be

An actual experiment by the inventor of the present invention confirmed that control of a relatively wide nitriding potential (in particular, control of a relatively low nitriding potential) can be realized when such control conditions are adopted.

The value of x is, for example, 0.5. This is because the amount of hydrogen generated in the furnace by thermal decomposition of 1 mol of ammonia gas is 1.5 mol, whereas the amount of hydrogen supplied into the furnace by 1 mol of ammonia decomposition gas is 0.5 mol. Since it is 75 mol (3/4 mol), the ratio of 1.5:0.75 = 1:0.5 is used to divide the amount of ammonia cracking gas introduced into the furnace with respect to the amount of hydrogen into the furnace of ammonia gas. It can be explained that it is a coefficient for conversion to the introduction amount A.

However, the value of x does not have to be strictly 0.5, and practically sufficient nitriding potential control can be realized as long as it is in the range of approximately 0.4 to 0.6.

The present invention can also be recognized as a surface hardening treatment method. That is, the present invention introduces a plurality of types of furnace-introduced gases including ammonia gas, ammonia decomposition gas, and nitrogen gas into a treatment furnace, and performs surface hardening treatment on an article to be treated placed in the treatment furnace. A surface hardening method for performing gas nitriding, comprising: a furnace atmosphere gas concentration detecting step of detecting a hydrogen concentration or an ammonia concentration in the treatment furnace; and a hydrogen concentration or hydrogen concentration detected by the furnace atmosphere gas concentration detecting step. According to the in-furnace nitriding potential calculation step of calculating the nitridation potential in the treatment furnace based on the ammonia concentration, and the nitridation potential in the treatment furnace and the target nitridation potential calculated by the in-furnace nitridation potential calculation step, The nitriding potential in the treatment furnace is changed by changing the introduction amount of each of the plurality of types of furnace introduction gases other than the ammonia decomposition gas while maintaining the introduction amount of the ammonia decomposition gas constant. and a step of controlling the amount of introduced gas to bring the potential closer to a target nitriding potential.

Further, according to the present invention, a plurality of types of furnace-introduced gases including ammonia gas, ammonia decomposition gas, and nitrogen gas are introduced into the processing furnace, and the surface hardening treatment of the article to be processed placed in the processing furnace is performed. A surface hardening apparatus for performing gas nitriding, comprising: a furnace atmosphere gas concentration detection device for detecting a hydrogen concentration or an ammonia concentration in the processing furnace; and a hydrogen concentration or hydrogen concentration detected by the furnace atmosphere gas concentration detection device. According to an in-furnace nitriding potential calculation device for calculating the nitriding potential in the processing furnace based on the ammonia concentration, and the nitriding potential in the processing furnace calculated by the in-furnace nitriding potential calculation device and the target nitriding potential, a gas introduction amount control device that brings the nitriding potential in the processing furnace closer to the target nitriding potential by changing the introduction amounts of the ammonia gas and the nitrogen gas while keeping the introduction amount of the ammonia decomposition gas constant. The surface hardening apparatus is characterized by:

This is characterized only by changing the introduction amounts of ammonia gas and nitrogen gas while keeping the introduction amount of ammonia decomposition gas constant, and does not care about the introduction amount control of other gases. According to this, it is possible to clearly include within the scope of right the aspect of introducing a certain amount of a very small amount of gas (approximately 1% or less in terms of flow rate) that does not substantially participate in the reaction. For example, relatively wide nitriding potential control (particularly, relatively low nitriding potential control) can be realized even in the mode of introducing a constant amount of other argon gas which is introduced in a small amount in the present invention. Furthermore, even in the mode of introducing a certain amount of carburizing gas (CO, CO ₂ , etc.) that is introduced in such a small amount that it cannot be called nitrocarburizing, relatively wide nitriding potential control (especially, relatively low nitriding potential control) ) can be realized.

In this case, when the amount of ammonia gas introduced into the furnace is A, the amount of ammonia decomposition gas introduced into the furnace is B, and x is a predetermined constant, the amount of nitrogen gas introduced is C1 using the proportionality coefficient c1 assigned to the nitrogen gas,
C1=c1×(A+x×B)
It is preferable to control so as to be

The present invention can also be recognized as a surface hardening treatment method. That is, the present invention introduces a plurality of types of furnace-introduced gases including ammonia gas, ammonia decomposition gas, and nitrogen gas into a treatment furnace, and performs surface hardening treatment on an article to be treated placed in the treatment furnace. A surface hardening treatment method for performing gas nitriding, comprising: a furnace atmosphere gas concentration detecting step of detecting hydrogen concentration or ammonia concentration in the treatment furnace; and hydrogen concentration or hydrogen concentration detected by the furnace atmosphere gas concentration detection device. In accordance with an in-furnace nitriding potential calculation step of calculating the nitriding potential in the processing furnace based on the ammonia concentration, and the nitriding potential in the processing furnace and the target nitriding potential calculated by the in-furnace nitriding potential calculation device, and a gas introduction amount control step of bringing the nitriding potential in the processing furnace closer to the target nitriding potential by changing the introduction amounts of the ammonia gas and the nitrogen gas while keeping the introduction amount of the ammonia decomposition gas constant. The surface hardening treatment method is characterized by:

According to one aspect of the present invention, by changing the introduction amount of each furnace introduction gas other than the ammonia decomposition gas among a plurality of types of furnace introduction gases while keeping the introduction amount of the ammonia decomposition gas constant, the comparison can be performed. It was confirmed that a wide range of nitriding potential control (especially relatively low nitriding potential control) can be realized.

Alternatively, according to another aspect of the present invention, relatively wide nitriding potential control (in particular, relatively low It was confirmed that nitriding potential control) can be realized.

1 is a schematic diagram showing a surface hardening apparatus according to an embodiment of the present invention; FIG. 4 is a graph showing the control of gas introduced into the furnace in Example 1-2. 4 is a graph showing nitriding potential control in Example 1-2. 1 is a table comparing Examples 1-1 to 1-3 with respective comparative examples. 10 is a graph showing the control of gas introduced into the furnace in Example 2-2. 10 is a graph showing nitriding potential control in Example 2-2. FIG. 10 is a table comparing Examples 2-1 to 2-3 with each comparative example; FIG. 10 is a graph showing the control of gas introduced into the furnace in Example 3-2. 10 is a graph showing nitriding potential control in Example 3-2. 3 is a table comparing Examples 3-1 to 3-3 with respective comparative examples.

Preferred embodiments of the present invention will be described below, but the present invention is not limited to the following embodiments.

(Constitution)
FIG. 1 is a schematic diagram showing a surface hardening apparatus according to one embodiment of the present invention. As shown in FIG. 1, the surface hardening treatment apparatus 1 of the present embodiment introduces ammonia gas, ammonia decomposition gas, and nitrogen gas into the treatment furnace 2, and treats an article S to be treated placed in the treatment furnace 2. It is a surface hardening apparatus that performs gas nitriding as the surface hardening treatment.

Ammonia decomposition gas is also called AX gas, and is a mixed gas consisting of nitrogen and hydrogen at a ratio of 1:3. The article S to be processed is made of metal, and is assumed to be, for example, a steel part or a mold.

As shown in FIG. 1, the processing furnace 2 of the surface hardening apparatus 1 of the present embodiment includes a stirring fan 8, a stirring fan drive motor 9, a furnace temperature measuring device 10, a furnace body heating device 11, An atmospheric gas concentration detector 3, a nitriding potential controller 4, a temperature controller 5, a programmable logic controller 31, a recorder 6, and an in-furnace introduction gas supply unit 20 are provided.

The stirring fan 8 is arranged inside the processing furnace 2 and rotates inside the processing furnace 2 to stir the atmosphere inside the processing furnace 2 . The stirring fan drive motor 9 is connected to the stirring fan 8 and rotates the stirring fan 8 at an arbitrary rotational speed.

The in-furnace temperature measuring device 10 has a thermocouple and is configured to measure the temperature of the in-furnace gas present in the processing furnace 2 . After measuring the temperature of the furnace gas, the furnace temperature measuring device 10 outputs an information signal (furnace temperature signal) including the measured temperature to the temperature controller 5 and the recorder 6. .

The atmospheric gas concentration detection device 3 is composed of a sensor capable of detecting the hydrogen concentration or ammonia concentration in the processing furnace 2 as the furnace atmospheric gas concentration. A detection main body of the sensor communicates with the interior of the processing furnace 2 through an atmospheric gas pipe 12 . In the present embodiment, the atmospheric gas pipe 12 is formed as a single line path that directly communicates the sensor body of the atmospheric gas concentration detection device 3 and the processing furnace 2 . An on-off valve 17 is provided in the middle of the atmosphere gas pipe 12 , and the on-off valve is controlled by an on-off valve control device 16 .

After detecting the concentration of the atmosphere gas in the furnace, the atmospheric gas concentration detection device 3 outputs an information signal including the detected concentration to the nitriding potential controller 4 and the recorder 6 .

The recorder 6 includes a storage medium such as a CPU and a memory, and measures the temperature in the processing furnace 2 and the concentration of the atmospheric gas in the furnace based on the output signals from the furnace temperature measuring device 10 and the atmospheric gas concentration detecting device 3. are stored in correspondence with the date and time when the surface hardening treatment was performed, for example.

The nitriding potential controller 4 has an in-furnace nitriding potential computing device 13 and a gas flow rate output adjusting device 30 . The programmable logic controller 31 also has a gas introduction control device 14 and a parameter setting device 15 .

The in-furnace nitriding potential computing device 13 computes the nitriding potential in the processing furnace 2 based on the hydrogen concentration or the ammonia concentration detected by the in-furnace atmospheric gas concentration detecting device 3 . Specifically, a calculation formula for the nitriding potential programmed based on the same idea as formula (5) is incorporated according to the actual gas introduced into the furnace, and the nitriding potential is calculated from the value of the gas concentration in the furnace atmosphere. It is designed to be calculated.

In the present embodiment, when the amount of ammonia gas introduced into the furnace is A, the amount of ammonia decomposition gas introduced into the furnace is B, and x is a predetermined constant, the furnace introduction gas other than ammonia gas and ammonia decomposition gas is Using a proportionality coefficient c1 assigned to the introduction amount C1 of a certain nitrogen gas to the gas introduced into the furnace,
C1=c1×(A+x×B)
is controlled so as to be

The parameter setting device 15 comprises, for example, a touch panel, and sets target nitriding potential, treatment temperature, treatment time, introduction amount of ammonia decomposition gas, predetermined constant x, proportionality coefficient c1, etc. for the same object to be treated. Settings can be entered. In addition, it is also possible to set and input setting parameter values for PID control for each different value of the target nitriding potential. Specifically, the "proportional gain", "integral gain or integral time", and "differential gain or derivative time" of PID control can be set and input for each different value of the target nitriding potential. Each setting parameter value that has been set and input is transmitted to the gas flow rate output adjusting means 30 .

Then, the gas flow rate output adjusting means 30 sets the nitriding potential calculated by the in-furnace nitriding potential calculation device 13 as an output value, sets the target nitriding potential (set nitriding potential) as a target value, and selects three types of in-furnace introduced gases. Of these, PID control is performed using the introduction amounts of each of ammonia gas and nitrogen gas as input values. More specifically, in the PID control, the nitriding potential in the processing furnace 2 is brought closer to the target nitriding potential by changing the introduction amounts of the ammonia gas and the nitrogen gas while keeping the introduction amount of the ammonia decomposition gas constant. . In addition, each setting parameter value transmitted from the parameter setting device 15 is used in the PID control.

Candidates for PID control setting parameter values for inputting settings to the parameter setting device 15 are preferably obtained in advance by performing a pilot process. In this embodiment, even if (1) the state of the processing furnace (the state of the furnace walls and jigs), (2) the temperature conditions of the processing furnace, and (3) the state of the workpiece (type and number) are the same, (4) Candidates for setting parameter values can be obtained for different values of the target nitriding potential by the auto-tuning function of the nitriding potential controller 4 itself. In order to configure the nitriding potential controller 4 having an auto-tuning function, UT75A (high-performance digital indicator controller manufactured by Yokogawa Electric Co., Ltd., http://www.yokogawa.co.jp/ns/cis/ utup/utadvanced/ns-ut75a-01-ja.htm) etc. are available.

Setting parameter values obtained as candidates (sets of "proportional gain", "integral gain or integral time", and "derivative gain or derivative time") are recorded in some form, and parameter settings are performed according to the desired processing content. It can be manually entered into device 15 . However, the setting parameter values acquired as candidates are stored in some storage device in a form linked with the target nitriding potential, and are automatically read by the parameter setting device 15 based on the input target nitriding potential value. It may be possible to

Prior to PID control, the gas flow rate output adjusting means 30 adjusts the initial values of the introduced amount of ammonia cracking gas to be maintained constant and the introduced amounts of ammonia gas and nitrogen gas to be varied based on the value of the target nitriding potential. is designed to determine These value candidates are preferably obtained in advance by performing a pilot process, and are automatically read out from a storage device or the like by the parameter setting device 15, or manually input from the parameter setting device 15. . After that, according to PID control, ammonia gas and nitrogen gas are mixed so that the nitriding potential in the processing furnace 2 approaches the target nitriding potential and the above-mentioned relationship of C1=c1×(A+xxB) is maintained. It is designed to determine the (varying) amount introduced (the amount of ammonia cracking gas introduced is kept constant). The output value of the gas flow rate output adjustment means 30 is transmitted to the gas introduction amount control means 14 .

The gas introduction amount control means 14 sends a control signal to the first supply amount control device 22 for ammonia gas.

The in-furnace introduction gas supply unit 20 of the present embodiment includes a first in-furnace introduction gas supply unit 21 for ammonia gas, a first supply amount control device 22, a first supply valve 23, and a first flow meter 24. ,have. Further, the in-furnace introduced gas supply unit 20 of the present embodiment includes a second in-furnace introduced gas supply unit 25 for ammonia decomposition gas (AX gas), a second supply amount control device 26, and a second supply valve 27. , and a second flow meter 28 . Further, the in-furnace introduced gas supply unit 20 of the present embodiment includes a third in-furnace introduced gas supply unit 71 for nitrogen gas, a third supply amount control device 72, a third supply valve 73, a third flow meter 74 and .

In this embodiment, the ammonia gas, the ammonia decomposition gas, and the nitrogen gas are mixed in the furnace introduction gas introduction pipe 29 before entering the processing furnace 2 .

The first in-furnace introduction gas supply unit 21 is formed by, for example, a tank filled with the first in-furnace introduction gas (ammonia gas in this example).

The first supply amount control device 22 is formed by a mass flow controller (capable of changing the flow rate in small increments within a short period of time), and the first in-furnace introduction gas supply section 21 and the first supply valve 23 interposed in between. The degree of opening of the first supply amount control device 22 changes according to the control signal output from the gas introduction amount control means 14 . Further, the first supply amount control device 22 detects the supply amount from the first in-furnace introduction gas supply unit 21 to the first supply valve 23, and transmits an information signal including the detected supply amount to the gas introduction control means 14. It is designed to output to the controller 6 . The control signal can be used for correction of control by the gas introduction amount control means 14 and the like.

The first supply valve 23 is formed by an electromagnetic valve that switches between open and closed states in accordance with a control signal output by the gas introduction amount control means 14 . intervened.

The first flowmeter 24 is, for example, a mechanical flowmeter such as a flow-type flowmeter, and is interposed between the first supply valve 23 and the in-furnace introduction gas introduction pipe 29 . Further, the first flow meter 24 detects the amount of gas supplied from the first supply valve 23 to the in-furnace introduction gas introduction pipe 29 . The amount of supply detected by the first flow meter 24 can be used for visual confirmation work by the operator.

The second in-furnace introduction gas supply unit 25 is formed, for example, by a tank filled with the second in-furnace introduction gas (ammonia decomposition gas in this example).

The second supply amount control device 26 is formed by a mass flow controller (which can change the flow rate in small increments within a short period of time), and the second in-furnace introduction gas supply section 25 and the second supply valve 27 interposed in between. The degree of opening of the second supply amount control device 26 changes according to the control signal output from the gas introduction amount control means 14 . Further, the second supply amount control device 26 detects the supply amount from the second in-furnace introduction gas supply unit 25 to the second supply valve 27, and transmits an information signal including the detected supply amount to the gas introduction control means 14. It is designed to output to the controller 6 . The control signal can be used for correction of control by the gas introduction amount control means 14 and the like.

The second supply valve 27 is formed by an electromagnetic valve that switches between open and closed states in response to a control signal output by the gas introduction amount control means 14. intervened.

The second flowmeter 28 is, for example, a mechanical flowmeter such as a flow-type flowmeter, and is interposed between the second supply valve 27 and the in-furnace introduction gas introduction pipe 29 . The second flow meter 28 detects the amount of gas supplied from the second supply valve 27 to the in-furnace introduction gas introduction pipe 29 . The amount of supply detected by the second flow meter 28 can be used for visual confirmation work by the operator.

However, in the present invention, since the introduction amount of the ammonia decomposition gas is not fluctuated in small increments, the second supply amount control device 26 is omitted, and the flow rate (opening degree) of the second flow meter 28 is controlled by the gas introduction amount control means. It may be manually adjusted to correspond to the control signal output from 14 .

The third in-furnace introduction gas supply unit 71 is formed by, for example, a tank filled with the third in-furnace introduction gas (nitrogen gas in this example).

The third supply amount control device 72 is formed by a mass flow controller (capable of changing the flow rate in small increments within a short period of time). interposed in between. The degree of opening of the third supply amount control device 72 changes according to the control signal output from the gas introduction amount control means 14 . Further, the third supply amount control device 72 detects the supply amount from the third in-furnace introduction gas supply unit 71 to the third supply valve 73, and transmits an information signal including the detected supply amount to the gas introduction control means 14. It is designed to output to the controller 6 . The control signal can be used for correction of control by the gas introduction amount control means 14 and the like.

The third supply valve 73 is formed by an electromagnetic valve that switches between open and closed states in accordance with a control signal output by the gas introduction amount control means 14 . intervened.

The third flowmeter 74 is formed of a mechanical flowmeter such as a flow-type flowmeter, and is interposed between the third supply valve 73 and the in-furnace introduction gas introduction pipe 29 . The third flow meter 74 detects the amount of gas supplied from the third supply valve 73 to the in-furnace introduction gas introduction pipe 29 . The amount of supply detected by the third flow meter 74 can be used for visual confirmation work by the operator.

(Action: Example 1-2 (Example 1-1 will be described later))
Next, the operation of the surface hardening apparatus 1 of this embodiment will be described with reference to FIGS. 2 and 3. FIG. First, the article S to be processed is put into the processing furnace 2, and the heating of the processing furnace 2 is started. In the example shown in FIGS. 2 and 3, a pit furnace with a size of φ700×1000 is used as the processing furnace 2, the heating temperature is 570° C., and a steel material having a surface area of 8 m ² is used as the work S to be processed. was taken.

During heating of the processing furnace 2, ammonia gas, ammonia decomposition gas, and nitrogen gas are introduced into the processing furnace 2 from the in-furnace introduction gas supply unit 20 at the set initial flow rates. Here, as shown in FIG. 2, the initial set flow rate of ammonia gas is set to 9.75 [l/min], the initial set flow rate of ammonia decomposition gas is set to 25 [l/min], and the set initial flow rate of nitrogen gas is set to 9.75 [l/min]. The flow rate was set to 14.8 [l/min], x=0.5, and c1=0.67. These set initial flow rates can be set and input in the parameter setting device 15 . Further, the stirring fan driving motor 9 is driven to rotate the stirring fan 8, thereby stirring the atmosphere in the processing furnace 2. As shown in FIG.

In the initial state, the on-off valve control device 16 keeps the on-off valve 17 closed. In general, as a pretreatment for gas nitriding treatment, a treatment for activating the steel material surface to make it easier for nitrogen to enter may be performed. In this case, hydrogen chloride gas, hydrogen cyanide gas, etc. are generated in the furnace. Since these gases can deteriorate the in-furnace atmosphere gas concentration detector (sensor) 3, it is effective to keep the on-off valve 17 closed.

Further, the furnace temperature measuring device 10 measures the temperature of the furnace gas and outputs an information signal including the measured temperature to the nitriding potential controller 4 and the recorder 6 . The nitriding potential controller 4 determines whether the state in the processing furnace 2 is in the middle of temperature rising or in a state (stable state) where the temperature rising has been completed.

Further, the in-furnace nitriding potential calculator 13 of the nitriding potential controller 4 calculates the nitriding potential in the furnace (which is initially a very high value (because there is no hydrogen in the furnace), but the decomposition of the ammonia gas (hydrogen occurrence), and it is determined whether or not the sum of the target nitriding potential (0.6 in this example: see FIG. 3) and the standard deviation value is exceeded. This standard deviation value can also be set and input in the parameter setting device 15, and is, for example, 0.1.

When it is determined that the temperature rise is completed and the calculated value of the in-furnace nitriding potential is lower than the sum of the target nitriding potential and the standard deviation value (0.7 in this example), the nitriding potential The controller 4 starts controlling the introduction amount of the gas introduced into the furnace through the gas introduction amount control means 14 . In response to this, the opening/closing control device 16 switches the opening/closing valve 17 to the open state.

When the on-off valve 17 is switched to the open state, the processing furnace 2 and the atmospheric gas concentration detection device 3 are communicated with each other, and the furnace atmospheric gas concentration detection device 3 detects the hydrogen concentration in the furnace or the ammonia concentration in the furnace. A detected hydrogen concentration signal or ammonia concentration signal is output to the nitriding potential controller 4 and the recorder 6 .

The in-furnace nitriding potential calculator 13 of the nitriding potential controller 4 calculates the in-furnace nitriding potential based on the input hydrogen concentration signal or ammonia concentration signal. Then, the gas flow rate output adjusting means 30 sets the nitriding potential calculated by the in-furnace nitriding potential calculation device 13 as an output value, sets the target nitriding potential (set nitriding potential) as a target value, and selects three types of in-furnace introduced gases. PID control is performed using the introduction amounts of ammonia gas and nitrogen gas as input values. Specifically, in the PID control, by changing the introduced amounts of the ammonia gas and the nitrogen gas while keeping the introduced amount of the ammonia decomposition gas constant, the nitriding potential in the processing furnace 2 approaches the target nitriding potential. , and control is carried out so that the relationship C1=c1.times.(A+x.times.B) described above is maintained. In the PID control, each setting parameter value set and input by the parameter setting device 15 is used. This setting parameter value may differ according to the value of the target nitriding potential.

Then, the gas introduction amount control means 14 controls the introduction amount of ammonia gas and the introduction amount of nitrogen gas as a result of PID control. The gas introduction amount control means 14 controls the first supply amount control device 22 for the ammonia gas and the second supply amount control device 26 for the ammonia decomposition gas (constant supply amount) in order to realize the determined introduction amount of each gas. , and the third feed rate controller 72 for nitrogen gas.

Through the above control, the in-furnace nitriding potential can be stably controlled near the target nitriding potential as shown in FIG. As a result, the surface hardening treatment of the workpiece S can be performed with extremely high quality. As a specific example, according to the example shown in FIG. 3, the amount of ammonia gas introduced is within a fluctuation range of about 3.0 l/min (±1.5 l/min) by feedback control with a sampling time of about several hundred milliseconds. It can be seen that the nitriding potential can be controlled to the target nitriding potential (0.6) with extremely high accuracy from about 5 minutes after the start of the treatment. (In the examples shown in FIGS. 2 and 3, the recording of each gas flow rate and nitriding potential is stopped about 100 minutes after the start of treatment.)

(Action: Example 1-1)
Next, a case where the target nitriding potential is set to 1.0 using the surface hardening apparatus 1 of the present embodiment (Example 1-1) will be described. Also in Example 1-1, a pit furnace having a size of φ700×1000 is used as the processing furnace 2, the heating temperature is set to 570° C., and a steel material having a surface area of 8 m ² is used as the work S to be processed. rice field.

During heating of the processing furnace 2, ammonia gas, ammonia decomposition gas, and nitrogen gas are introduced into the processing furnace 2 from the in-furnace introduction gas supply unit 20 at the set initial flow rates. Here, the set initial flow rate of the ammonia gas is set to 9 [l/min], the set initial flow rate of the ammonia decomposition gas is set to 20 [l/min], and the set initial flow rate of the nitrogen gas is set to 12.7 [l/min]. ], x=0.5, and c1=0.67. These set initial flow rates can be set and input in the parameter setting device 15 . Further, the stirring fan driving motor 9 is driven to rotate the stirring fan 8, thereby stirring the atmosphere in the processing furnace 2. As shown in FIG.

In the initial state, the on-off valve control device 16 keeps the on-off valve 17 closed.

Further, the in-furnace nitriding potential calculator 13 of the nitriding potential controller 4 calculates the nitriding potential in the furnace (which is initially a very high value (because there is no hydrogen in the furnace), but the decomposition of the ammonia gas (hydrogen It is determined whether or not the sum of the target nitriding potential (1.0 in this example) and the standard deviation value is exceeded. This standard deviation value can also be set and input in the parameter setting device 15, and is, for example, 0.1.

When it is determined that the temperature rise is completed and the calculated value of the in-furnace nitriding potential is lower than the sum of the target nitriding potential and the reference deviation value (1.1 in this example), the nitriding potential The controller 4 starts controlling the introduction amount of the gas introduced into the furnace through the gas introduction amount control means 14 . In response to this, the opening/closing control device 16 switches the opening/closing valve 17 to the open state.

The in-furnace nitriding potential calculator 13 of the nitriding potential controller 4 calculates the in-furnace nitriding potential based on the input hydrogen concentration signal or ammonia concentration signal. Then, the gas flow rate output adjusting means 30 sets the nitriding potential calculated by the in-furnace nitriding potential calculation device 13 as an output value, sets the target nitriding potential (set nitriding potential) as a target value, and selects three types of in-furnace introduced gases. Of these, PID control is performed using the introduction amounts of ammonia gas and nitrogen gas as input values. Specifically, in the PID control, the introduction amount of the ammonia decomposition gas is kept constant while the introduction amount of the ammonia gas and the nitrogen gas is changed so that the nitriding potential in the processing furnace 2 approaches the target nitriding potential. , and control is carried out so that the relationship C1=c1.times.(A+x.times.B) described above is maintained. In the PID control, each setting parameter value set and input by the parameter setting device 15 is used. This setting parameter value may differ according to the value of the target nitriding potential.

Then, the gas introduction amount control means 14 controls the introduction amount of ammonia gas and the introduction amount of nitrogen gas as a result of PID control. The gas introduction amount control means 14 controls the first supply amount control device 22 for the ammonia gas and the second supply amount control device 26 for the ammonia decomposition gas (constant supply amount) in order to realize the determined introduction amount of each gas. , the third feed rate controller 72 for nitrogen gas.

Through the above control, the in-furnace nitriding potential can be stably controlled near the target nitriding potential. As a result, the surface hardening treatment of the workpiece S can be performed with extremely high quality. Specifically, by feedback control with a sampling time of about several hundred milliseconds, the amount of ammonia gas introduced is increased or decreased within a fluctuation range of about 3.0 l/min (±1.5 l/min), and after the start of processing, about 5 The nitriding potential could be controlled to the target nitriding potential (1.0) with extremely high accuracy from the time point of 10 min (illustration of the graph is omitted).

(Action: Example 1-3)
Next, a case where the target nitriding potential is set to 0.2 using the surface hardening apparatus 1 of the present embodiment (Example 1-3) will be described. Also in Example 1-3, a pit furnace having a size of φ700×1000 is used as the processing furnace 2, the heating temperature is set to 570° C., and a steel material having a surface area of 8 m ² is used as the work S to be processed. rice field.

During heating of the processing furnace 2, ammonia gas, ammonia decomposition gas, and nitrogen gas are introduced into the processing furnace 2 from the in-furnace introduction gas supply unit 20 at the set initial flow rates. Here, the set initial flow rate of ammonia gas is 2 [l/min], the set initial flow rate of ammonia decomposition gas is 30 [l/min], and the set initial flow rate of nitrogen gas is 11.3 [l/min]. ], x=0.5, and c1=0.67. These set initial flow rates can be set and input in the parameter setting device 15 . Further, the stirring fan driving motor 9 is driven to rotate the stirring fan 8, thereby stirring the atmosphere in the processing furnace 2. As shown in FIG.

Further, the in-furnace nitriding potential calculator 13 of the nitriding potential controller 4 calculates the nitriding potential in the furnace (which is initially a very high value (because there is no hydrogen in the furnace), but the decomposition of the ammonia gas (hydrogen It is determined whether or not the sum of the target nitriding potential (0.2 in this example) and the reference deviation value is exceeded. This standard deviation value can also be set and input in the parameter setting device 15, and is, for example, 0.1.

When it is determined that the temperature rise is completed and the calculated value of the in-furnace nitriding potential is lower than the sum of the target nitriding potential and the reference deviation value (0.3 in this example), the nitriding potential The controller 4 starts controlling the introduction amount of the gas introduced into the furnace through the gas introduction amount control means 14 . In response to this, the opening/closing control device 16 switches the opening/closing valve 17 to the open state.

Through the above control, the in-furnace nitriding potential can be stably controlled near the target nitriding potential. As a result, the surface hardening treatment of the workpiece S can be performed with extremely high quality. Specifically, by feedback control with a sampling time of about several hundred milliseconds, the amount of ammonia gas introduced is increased or decreased within a fluctuation range of about 3.0 l/min (±1.5 l/min), and about 15 l/min after the start of processing. The nitriding potential could be controlled to the target nitriding potential (0.2) with extremely high accuracy from the time point of 10 min (illustration of the graph is omitted).

(Description of Comparative Example)
For comparison, nitriding potential control was performed in such a manner that no ammonia decomposition gas was introduced, the flow rate ratio of ammonia gas and nitrogen gas was always maintained at 60:40, and the total flow rate thereof was varied.

Specifically, the in-furnace nitriding potential calculator 13 of the nitriding potential controller 4 calculated the in-furnace nitriding potential based on the input hydrogen concentration signal or ammonia concentration signal. Then, the gas flow rate output adjusting means 30 sets the nitriding potential calculated by the in-furnace nitriding potential calculator 13 as an output value, sets the target nitriding potential (set nitriding potential) as a target value, and sets each of the ammonia gas and the nitrogen gas. PID control was performed using the amount of introduced as an input value. More specifically, in the PID control, by changing the total introduction amount of ammonia gas and nitrogen gas while keeping the flow rate ratio of ammonia gas and nitrogen gas constant, the nitriding potential in the processing furnace 2 is adjusted to the target. Control was performed to approach the nitriding potential.

However, it was not possible to stably control the nitriding potential with the control of the comparative example as described above.

(Comparison between Examples 1-1 to 1-3 and Comparative Example)
A table summarizing the above results is shown in FIG.

(Further modified example of Example 1-2)
In Example 1-2, a small amount (on the order of 0.1%) of argon gas may additionally be introduced. Specifically, let A be the amount of ammonia gas introduced into the furnace, B be the amount of ammonia decomposition gas introduced into the furnace, x be a predetermined constant (x=0.5 in this example), and the amount of argon gas introduced Using a proportionality coefficient c2 (for example, c2 = 0.002) assigned to the gas introduced into the furnace,
C2=c2×(A+x×B)
may be controlled to be

Also in this case, as in Example 1-2, the in-furnace nitriding potential can be stably controlled in the vicinity of the target nitriding potential. As a result, the surface hardening treatment of the workpiece S can be performed with extremely high quality. Specifically, by feedback control with a sampling time of about several hundred milliseconds, the amount of ammonia gas introduced is increased or decreased within a fluctuation range of about 3.0 l/min (±1.5 l/min), and about 15 l/min after the start of processing. The nitriding potential could be controlled to the target nitriding potential (0.6) with extremely high precision from the time point of 10 min.

Furthermore, in Example 1-2, a small amount (about 0.1%) of argon gas may be additionally introduced while keeping the introduction amount constant.

Alternatively, in Example 1-2, a very small amount (about 0.1%) of carburizing gas (CO, CO ₂ , etc.), which cannot be called nitrocarburizing, may be additionally introduced. Specifically, let A be the amount of ammonia gas introduced into the furnace, B be the amount of ammonia decomposition gas introduced into the furnace, x be a predetermined constant (in this example, x=0.5), and introduce carburizing gas. Using a proportionality coefficient c2 (for example, c2 = 0.002) assigned to the gas introduced into the furnace,
C2=c2×(A+x×B)
may be controlled to be

Furthermore, in Example 1-2, a small amount (about 0.1%) of carburizing gas may be additionally introduced while keeping the introduction amount constant.

(Further modification of Example 1-1)
Also in Example 1-1, a small amount (about 0.1%) of argon gas may be additionally introduced. Specifically, let A be the amount of ammonia gas introduced into the furnace, B be the amount of ammonia decomposition gas introduced into the furnace, x be a predetermined constant (x=0.5 in this example), and the amount of argon gas introduced Using a proportionality coefficient c2 (for example, c2 = 0.002) assigned to the gas introduced into the furnace,
C2=c2×(A+x×B)
may be controlled to be

Also in this case, as in Example 1-1, the in-furnace nitriding potential can be stably controlled in the vicinity of the target nitriding potential. As a result, the surface hardening treatment of the workpiece S can be performed with extremely high quality. Specifically, by feedback control with a sampling time of about several hundred milliseconds, the amount of ammonia gas introduced is increased or decreased within a fluctuation range of about 3.0 l/min (±1.5 l/min), and about 15 l/min after the start of processing. The nitriding potential could be controlled to the target nitriding potential (1.0) with extremely high precision from the time point of 10 min.

Furthermore, in Example 1-1, a small amount (about 0.1%) of argon gas may be additionally introduced while keeping the introduction amount constant.

Alternatively, in Example 1-1, a very small amount (about 0.1%) of carburizing gas (CO, CO ₂ , etc.), which cannot be called nitrocarburizing, may be additionally introduced. Specifically, let A be the amount of ammonia gas introduced into the furnace, B be the amount of ammonia decomposition gas introduced into the furnace, x be a predetermined constant (in this example, x=0.5), and introduce carburizing gas. Using a proportionality coefficient c2 (for example, c2 = 0.002) assigned to the gas introduced into the furnace,
C2=c2×(A+x×B)
may be controlled to be

Furthermore, in Example 1-1, a small amount (about 0.1%) of carburizing gas may be additionally introduced while keeping the introduction amount constant.

(Further modified example of Example 1-3)
Also in Examples 1-3, a small amount (about 0.1%) of argon gas may be additionally introduced. Specifically, let A be the amount of ammonia gas introduced into the furnace, B be the amount of ammonia decomposition gas introduced into the furnace, x be a predetermined constant (x=0.5 in this example), and the amount of argon gas introduced Using a proportionality coefficient c2 (for example, c2 = 0.002) assigned to the gas introduced into the furnace,
C2=c2×(A+x×B)
may be controlled to be

Also in this case, similarly to Example 1-3, the in-furnace nitriding potential can be stably controlled near the target nitriding potential. As a result, the surface hardening treatment of the workpiece S can be performed with extremely high quality. Specifically, by feedback control with a sampling time of about several hundred milliseconds, the amount of ammonia gas introduced is increased or decreased within a fluctuation range of about 3.0 l/min (±1.5 l/min), and about 15 l/min after the start of processing. The nitriding potential could be controlled to the target nitriding potential (0.2) with extremely high accuracy from the time point of 10 min.

Furthermore, in Examples 1-3, a small amount (about 0.1%) of argon gas may be additionally introduced while keeping the introduction amount constant.

Alternatively, in Examples 1-3, a very small amount (approximately 0.1%) of carburizing gas (CO, CO ₂ , etc.), which cannot be called nitrocarburizing, may be additionally introduced. Specifically, let A be the amount of ammonia gas introduced into the furnace, B be the amount of ammonia decomposition gas introduced into the furnace, x be a predetermined constant (in this example, x=0.5), and introduce carburizing gas. Using a proportionality coefficient c2 (for example, c2 = 0.002) assigned to the gas introduced into the furnace,
C2=c2×(A+x×B)
may be controlled to be

Furthermore, in Examples 1-3, a small amount (about 0.1%) of carburizing gas may be additionally introduced while keeping the introduction amount constant.

(Action: Example 2-2 (Example 2-1 will be described later))
Next, with reference to FIGS. 5 and 6, the operation of the surface hardening apparatus 1 of this embodiment when the introduction amount of nitrogen gas is reduced compared to Examples 1-1 to 1-3 will be described. do. Also in this case, the article S to be processed is put into the processing furnace 2, and the heating of the processing furnace 2 is started. 5 and 6, a pit furnace with a size of φ700×1000 is used as the processing furnace 2, the heating temperature is set at 570° C., and a steel material having a surface area of 8 m ² is used as the work S to be processed. was taken.

During heating of the processing furnace 2, ammonia gas, ammonia decomposition gas, and nitrogen gas are introduced into the processing furnace 2 from the in-furnace introduction gas supply unit 20 at the set initial flow rates. Here, as shown in FIG. 5, the set initial flow rate of ammonia gas is set to 10.3 [l/min], the set initial flow rate of ammonia decomposition gas is set to 32.5 [l/min], and the set initial flow rate of nitrogen gas is set to 10.3 [l/min]. The set initial flow rate was 6.6 [l/min], x=0.5, and c1=0.25. These set initial flow rates can be set and input in the parameter setting device 15 . Further, the stirring fan driving motor 9 is driven to rotate the stirring fan 8, thereby stirring the atmosphere in the processing furnace 2. As shown in FIG.

Further, the in-furnace nitriding potential calculator 13 of the nitriding potential controller 4 calculates the nitriding potential in the furnace (which is initially a very high value (because there is no hydrogen in the furnace), but the decomposition of the ammonia gas (hydrogen occurrence), it is determined whether or not the sum of the target nitriding potential (0.6 in this example: see FIG. 6) and the reference deviation value is exceeded. This standard deviation value can also be set and input in the parameter setting device 15, and is, for example, 0.1.

Through the above control, the in-furnace nitriding potential can be stably controlled near the target nitriding potential as shown in FIG. As a result, the surface hardening treatment of the workpiece S can be performed with extremely high quality. As a specific example, according to the example shown in FIG. 6, the amount of ammonia gas introduced is within a fluctuation range of about 3.0 l/min (±1.5 l/min) by feedback control with a sampling time of about several hundred milliseconds. It can be seen that the nitriding potential can be controlled to the target nitriding potential (0.6) with extremely high accuracy from about 10 minutes after the start of the treatment. (In the examples shown in FIGS. 5 and 6, the recording of each gas flow rate and nitriding potential is stopped about 100 minutes after the start of treatment.)

(Action: Example 2-1)
Next, a case where the target nitriding potential is set to 1.0 using the surface hardening apparatus 1 of the present embodiment (Example 2-1) will be described. Also in Example 2-1, a pit furnace with a size of φ700×1000 is used as the processing furnace 2, the heating temperature is set at 570° C., and a steel material having a surface area of 8 m ² is used as the work S to be processed. rice field.

During heating of the processing furnace 2, ammonia gas, ammonia decomposition gas, and nitrogen gas are introduced into the processing furnace 2 from the in-furnace introduction gas supply unit 20 at the set initial flow rates. Here, the set initial flow rate of ammonia gas is 12.0 [l/min], the set initial flow rate of ammonia decomposition gas is 24.0 [l/min], and the set initial flow rate of nitrogen gas is 6.0 [l/min]. [l/min], x=0.5 and c1=0.25. These set initial flow rates can be set and input in the parameter setting device 15 . Further, the stirring fan driving motor 9 is driven to rotate the stirring fan 8, thereby stirring the atmosphere in the processing furnace 2. As shown in FIG.

Through the above control, the in-furnace nitriding potential can be stably controlled near the target nitriding potential. As a result, the surface hardening treatment of the workpiece S can be performed with extremely high quality. Specifically, by feedback control with a sampling time of about several hundred milliseconds, the amount of ammonia gas introduced is increased or decreased within a fluctuation range of about 3.0 l/min (±1.5 l/min), and after the start of treatment, about 10 The nitriding potential could be controlled to the target nitriding potential (1.0) with extremely high accuracy from the time point of 10 min (illustration of the graph is omitted).

(Action: Example 2-3)
Next, a case where the target nitriding potential is set to 0.2 using the surface hardening apparatus 1 of the present embodiment (Example 2-3) will be described. Also in Example 2-3, a pit furnace with a size of φ700×1000 is used as the treatment furnace 2, the heating temperature is set at 570° C., and a steel material having a surface area of 8 m ² is used as the work S to be treated. rice field.

During heating of the processing furnace 2, ammonia gas, ammonia decomposition gas, and nitrogen gas are introduced into the processing furnace 2 from the in-furnace introduction gas supply unit 20 at the set initial flow rates. Here, the set initial flow rate of ammonia gas is 3.0 [l/min], the set initial flow rate of ammonia decomposition gas is 40.0 [l/min], and the set initial flow rate of nitrogen gas is 5.7 [l/min]. [l/min], x=0.5 and c1=0.25. These set initial flow rates can be set and input in the parameter setting device 15 . Further, the stirring fan driving motor 9 is driven to rotate the stirring fan 8, thereby stirring the atmosphere in the processing furnace 2. As shown in FIG.

Through the above control, the in-furnace nitriding potential can be stably controlled near the target nitriding potential. As a result, the surface hardening treatment of the workpiece S can be performed with extremely high quality. Specifically, by feedback control with a sampling time of about several hundred milliseconds, the amount of ammonia gas introduced is increased or decreased within a fluctuation range of about 3.0 l/min (±1.5 l/min), and after the start of treatment, about 10 The nitriding potential could be controlled to the target nitriding potential (0.2) with extremely high accuracy from the time point of 10 min (illustration of the graph is omitted).

(Description of Comparative Example)
For comparison, nitriding potential control was performed in such a manner that no ammonia decomposition gas was introduced, the flow rate ratio of ammonia gas and nitrogen gas was always maintained at 80:20, and the total flow rate thereof was varied.

(Comparison between Examples 2-1 to 2-3 and Comparative Examples)
A table summarizing the above results is shown in FIG.

(Further modified example of Example 2-2)
In Example 2-2, a small amount (on the order of 0.1%) of argon gas may additionally be introduced. Specifically, let A be the amount of ammonia gas introduced into the furnace, B be the amount of ammonia decomposition gas introduced into the furnace, x be a predetermined constant (x=0.5 in this example), and the amount of argon gas introduced Using a proportionality coefficient c2 (for example, c2 = 0.002) assigned to the gas introduced into the furnace,
C2=c2×(A+x×B)
may be controlled to be

Also in this case, as in Example 2-2, the in-furnace nitriding potential can be stably controlled in the vicinity of the target nitriding potential. As a result, the surface hardening treatment of the workpiece S can be performed with extremely high quality. Specifically, by feedback control with a sampling time of about several hundred milliseconds, the amount of ammonia gas introduced is increased or decreased within a fluctuation range of about 3.0 l/min (±1.5 l/min), and after the start of treatment, about 10 The nitriding potential could be controlled to the target nitriding potential (0.6) with extremely high precision from the time point of 10 min.

Furthermore, in Example 2-2, a small amount (about 0.1%) of argon gas may be additionally introduced while keeping the introduction amount constant.

Alternatively, in Example 2-2, a very small amount (about 0.1%) of carburizing gas (CO, CO ₂ , etc.), which cannot be called nitrocarburizing, may be additionally introduced. Specifically, let A be the amount of ammonia gas introduced into the furnace, B be the amount of ammonia decomposition gas introduced into the furnace, x be a predetermined constant (in this example, x=0.5), and introduce carburizing gas. Using a proportionality coefficient c2 (for example, c2 = 0.002) assigned to the gas introduced into the furnace,
C2=c2×(A+x×B)
may be controlled to be

Furthermore, in Example 2-2, a small amount (about 0.1%) of carburizing gas may be additionally introduced while keeping the introduction amount constant.

(Further modification of Example 2-1)
Also in Example 2-1, a small amount (about 0.1%) of argon gas may be additionally introduced. Specifically, let A be the amount of ammonia gas introduced into the furnace, B be the amount of ammonia decomposition gas introduced into the furnace, x be a predetermined constant (x=0.5 in this example), and the amount of argon gas introduced Using a proportionality coefficient c2 (for example, c2 = 0.002) assigned to the gas introduced into the furnace,
C2=c2×(A+x×B)
may be controlled to be

Also in this case, as in Example 2-1, the in-furnace nitriding potential can be stably controlled in the vicinity of the target nitriding potential. As a result, the surface hardening treatment of the workpiece S can be performed with extremely high quality. Specifically, by feedback control with a sampling time of about several hundred milliseconds, the amount of ammonia gas introduced is increased or decreased within a fluctuation range of about 3.0 l/min (±1.5 l/min), and after the start of treatment, about 10 The nitriding potential could be controlled to the target nitriding potential (1.0) with extremely high precision from the time point of 10 min.

Furthermore, in Example 2-1, a small amount (about 0.1%) of argon gas may be additionally introduced while keeping the introduction amount constant.

Alternatively, in Example 2-1, a very small amount (about 0.1%) of carburizing gas (CO, CO ₂ , etc.) that cannot be called nitrocarburizing may be additionally introduced. Specifically, let A be the amount of ammonia gas introduced into the furnace, B be the amount of ammonia decomposition gas introduced into the furnace, x be a predetermined constant (in this example, x=0.5), and introduce carburizing gas. Using a proportionality coefficient c2 (for example, c2 = 0.002) assigned to the gas introduced into the furnace,
C2=c2×(A+x×B)
may be controlled to be

Furthermore, in Example 2-1, a small amount (about 0.1%) of carburizing gas may be additionally introduced while keeping the introduction amount constant.

(Further modification of Example 2-3)
Also in Example 2-3, a small amount (approximately 0.1%) of argon gas may be additionally introduced. Specifically, let A be the amount of ammonia gas introduced into the furnace, B be the amount of ammonia decomposition gas introduced into the furnace, x be a predetermined constant (x=0.5 in this example), and the amount of argon gas introduced Using a proportionality coefficient c2 (for example, c2 = 0.002) assigned to the gas introduced into the furnace,
C2=c2×(A+x×B)
may be controlled to be

Also in this case, as in Example 2-3, the in-furnace nitriding potential can be stably controlled in the vicinity of the target nitriding potential. As a result, the surface hardening treatment of the workpiece S can be performed with extremely high quality. Specifically, by feedback control with a sampling time of about several hundred milliseconds, the amount of ammonia gas introduced is increased or decreased within a fluctuation range of about 3.0 l/min (±1.5 l/min), and after the start of treatment, about 10 The nitriding potential could be controlled to the target nitriding potential (0.2) with extremely high accuracy from the time point of 10 min.

Furthermore, in Example 2-3, a small amount (approximately 0.1%) of argon gas may be additionally introduced while keeping the introduction amount constant.

Alternatively, in Example 2-3, a very small amount (about 0.1%) of carburizing gas (CO, CO ₂ , etc.), which cannot be called nitrocarburizing, may be additionally introduced. Specifically, let A be the amount of ammonia gas introduced into the furnace, B be the amount of ammonia decomposition gas introduced into the furnace, x be a predetermined constant (in this example, x=0.5), and introduce carburizing gas. Using a proportionality coefficient c2 (for example, c2 = 0.002) that assigns the amount C2 to the gas introduced into the furnace,
C2=c2×(A+x×B)
may be controlled to be

Furthermore, in Example 2-3, a small amount (about 0.1%) of carburizing gas may be additionally introduced while keeping the introduction amount constant.

(Action: Example 3-2 (Example 3-1 will be described later))
Next, with reference to FIGS. 8 and 9, the operation of the surface hardening apparatus 1 of this embodiment when the introduction amount of nitrogen gas is increased compared to Examples 1-1 to 1-3 will be described. do. Also in this case, the article S to be processed is put into the processing furnace 2, and the heating of the processing furnace 2 is started. In the examples shown in FIGS. 8 and 9 as well, a pit furnace with a size of φ700×1000 is used as the processing furnace 2, the heating temperature is set at 570° C., and a steel material having a surface area of 8 m ² is used as the workpiece S. was taken.

During heating of the processing furnace 2, ammonia gas, ammonia decomposition gas, and nitrogen gas are introduced into the processing furnace 2 from the in-furnace introduction gas supply unit 20 at the set initial flow rates. Here, as shown in FIG. 8, the set initial flow rate of ammonia gas is set to 4.0 [l/min], the set initial flow rate of ammonia decomposition gas is set to 20.0 [l/min], and the set initial flow rate of nitrogen gas is set to 4.0 [l/min]. The set initial flow rate was set to 21.0 [l/min], x=0.5, and c1=1.5. These set initial flow rates can be set and input in the parameter setting device 15 . Further, the stirring fan driving motor 9 is driven to rotate the stirring fan 8, thereby stirring the atmosphere in the processing furnace 2. As shown in FIG.

Further, the in-furnace nitriding potential calculator 13 of the nitriding potential controller 4 calculates the nitriding potential in the furnace (which is initially a very high value (because there is no hydrogen in the furnace), but the decomposition of the ammonia gas (hydrogen occurrence), it is determined whether or not the sum of the target nitriding potential (0.6 in this example: see FIG. 9) and the standard deviation value is exceeded. This standard deviation value can also be set and input in the parameter setting device 15, and is, for example, 0.1.

Through the above control, the in-furnace nitriding potential can be stably controlled near the target nitriding potential as shown in FIG. As a result, the surface hardening treatment of the workpiece S can be performed with extremely high quality. As a specific example, according to the example shown in FIG. 9, the amount of ammonia gas introduced is within a fluctuation range of about 3.0 l/min (±1.5 l/min) by feedback control with a sampling time of about several hundred milliseconds. It can be seen that the nitriding potential can be controlled to the target nitriding potential (0.6) with extremely high accuracy from about 10 minutes after the start of the treatment. (In the examples shown in FIGS. 8 and 9, the recording of each gas flow rate and nitriding potential is stopped about 100 minutes after the start of treatment.)

(Action: Example 3-1)
Next, a case where the target nitriding potential is set to 1.0 using the surface hardening apparatus 1 of the present embodiment (Example 3-1) will be described. Also in Example 3-1, a pit furnace with a size of φ700×1000 is used as the processing furnace 2, the heating temperature is set at 570° C., and a steel material having a surface area of 8 m ² is used as the work S to be processed. rice field.

During heating of the processing furnace 2, ammonia gas, ammonia decomposition gas, and nitrogen gas are introduced into the processing furnace 2 from the in-furnace introduction gas supply unit 20 at the set initial flow rates. Here, the set initial flow rate of ammonia gas is 6.0 [l/min], the set initial flow rate of ammonia decomposition gas is 17.0 [l/min], and the set initial flow rate of nitrogen gas is 21.8 [l/min]. [l/min], x=0.5 and c1=1.5. These set initial flow rates can be set and input in the parameter setting device 15 . Further, the stirring fan driving motor 9 is driven to rotate the stirring fan 8, thereby stirring the atmosphere in the processing furnace 2. As shown in FIG.

(Action: Example 3-3)
Next, a case where the target nitriding potential is set to 0.2 using the surface hardening apparatus 1 of the present embodiment (Example 3-3) will be described. Also in Example 3-3, a pit furnace having a size of φ700×1000 is used as the processing furnace 2, the heating temperature is set to 570° C., and a steel material having a surface area of 8 m ² is used as the work S to be processed. rice field.

During heating of the processing furnace 2, ammonia gas, ammonia decomposition gas, and nitrogen gas are introduced into the processing furnace 2 from the in-furnace introduction gas supply unit 20 at the set initial flow rates. Here, the set initial flow rate of ammonia gas is 1.0 [l/min], the set initial flow rate of ammonia decomposition gas is 25.0 [l/min], and the set initial flow rate of nitrogen gas is 20.0 [l/min]. [l/min], x=0.5 and c1=1.5. These set initial flow rates can be set and input in the parameter setting device 15 . Further, the stirring fan driving motor 9 is driven to rotate the stirring fan 8, thereby stirring the atmosphere in the processing furnace 2. As shown in FIG.

(Description of Comparative Example)
For comparison, nitriding potential control was performed in such a manner that no ammonia cracking gas was introduced, the flow rate ratio of ammonia gas and nitrogen gas was always maintained at 40:60, and the total flow rate thereof was varied.

(Comparison between Examples 3-1 to 3-3 and Comparative Example)
A table summarizing the above results is shown in FIG.

(Further modification of Example 3-2)
In Example 3-2, a small amount (on the order of 0.1%) of argon gas may additionally be introduced. Specifically, let A be the amount of ammonia gas introduced into the furnace, B be the amount of ammonia decomposition gas introduced into the furnace, x be a predetermined constant (x=0.5 in this example), and the amount of argon gas introduced Using a proportionality coefficient c2 (for example, c2 = 0.002) assigned to the gas introduced into the furnace,
C2=c2×(A+x×B)
may be controlled to be

Also in this case, as in Example 3-2, the in-furnace nitriding potential can be stably controlled near the target nitriding potential. As a result, the surface hardening treatment of the workpiece S can be performed with extremely high quality. Specifically, by feedback control with a sampling time of about several hundred milliseconds, the amount of ammonia gas introduced is increased or decreased within a fluctuation range of about 3.0 l/min (±1.5 l/min), and after the start of treatment, about 10 The nitriding potential could be controlled to the target nitriding potential (0.6) with extremely high precision from the time point of 10 min.

Furthermore, in Example 3-2, a small amount (about 0.1%) of argon gas may be additionally introduced while keeping the introduction amount constant.

Alternatively, in Example 3-2, a very small amount (about 0.1%) of carburizing gas (CO, CO ₂ , etc.), which cannot be called nitrocarburizing, may be additionally introduced. Specifically, let A be the amount of ammonia gas introduced into the furnace, B be the amount of ammonia decomposition gas introduced into the furnace, x be a predetermined constant (in this example, x=0.5), and introduce carburizing gas. Using a proportionality coefficient c2 (for example, c2 = 0.002) assigned to the gas introduced into the furnace,
C2=c2×(A+x×B)
may be controlled to be

Furthermore, in Example 3-2, a small amount (about 0.1%) of carburizing gas may be additionally introduced while keeping the introduction amount constant.

(Further modification of Example 3-1)
Also in Example 3-1, a small amount (about 0.1%) of argon gas may be additionally introduced. Specifically, let A be the amount of ammonia gas introduced into the furnace, B be the amount of ammonia decomposition gas introduced into the furnace, x be a predetermined constant (x=0.5 in this example), and the amount of argon gas introduced Using a proportionality coefficient c2 (for example, c2 = 0.002) assigned to the gas introduced into the furnace,
C2=c2×(A+x×B)
may be controlled to be

Also in this case, as in Example 3-1, the in-furnace nitriding potential can be stably controlled near the target nitriding potential. As a result, the surface hardening treatment of the workpiece S can be performed with extremely high quality. Specifically, by feedback control with a sampling time of about several hundred milliseconds, the amount of ammonia gas introduced is increased or decreased within a fluctuation range of about 3.0 l/min (±1.5 l/min), and after the start of treatment, about 10 The nitriding potential could be controlled to the target nitriding potential (1.0) with extremely high precision from the time point of 10 min.

Furthermore, in Example 3-1, a small amount (approximately 0.1%) of argon gas may be additionally introduced while keeping the introduction amount constant.

Alternatively, in Example 3-1, a very small amount (about 0.1%) of carburizing gas (CO, CO ₂ , etc.), which cannot be called nitrocarburizing, may be additionally introduced. Specifically, let A be the amount of ammonia gas introduced into the furnace, B be the amount of ammonia decomposition gas introduced into the furnace, x be a predetermined constant (in this example, x=0.5), and introduce carburizing gas. Using a proportionality coefficient c2 (for example, c2 = 0.002) assigned to the gas introduced into the furnace,
C2=c2×(A+x×B)
may be controlled to be

Furthermore, in Example 3-1, a small amount (about 0.1%) of carburizing gas may be additionally introduced while keeping the introduction amount constant.

(Further modification of Example 3-3)
Also in Example 3-3, a small amount (about 0.1%) of argon gas may be additionally introduced. Specifically, let A be the amount of ammonia gas introduced into the furnace, B be the amount of ammonia decomposition gas introduced into the furnace, x be a predetermined constant (x=0.5 in this example), and the amount of argon gas introduced Using a proportionality coefficient c2 (for example, c2 = 0.002) assigned to the gas introduced into the furnace,
C2=c2×(A+x×B)
may be controlled to be

Also in this case, as in Example 3-3, the in-furnace nitriding potential can be stably controlled in the vicinity of the target nitriding potential. As a result, the surface hardening treatment of the workpiece S can be performed with extremely high quality. Specifically, by feedback control with a sampling time of about several hundred milliseconds, the amount of ammonia gas introduced is increased or decreased within a fluctuation range of about 3.0 l/min (±1.5 l/min), and after the start of treatment, about 10 The nitriding potential could be controlled to the target nitriding potential (0.2) with extremely high accuracy from the time point of 10 min.

Furthermore, in Example 3-3, a small amount (approximately 0.1%) of argon gas may be additionally introduced while keeping the introduction amount constant.

Alternatively, in Example 3-3, a very small amount (about 0.1%) of carburizing gas (CO, CO ₂ , etc.) that cannot be called nitrocarburizing may be additionally introduced. Specifically, let A be the amount of ammonia gas introduced into the furnace, B be the amount of ammonia decomposition gas introduced into the furnace, x be a predetermined constant (in this example, x=0.5), and introduce carburizing gas. Using a proportionality coefficient c2 (for example, c2 = 0.002) assigned to the gas introduced into the furnace,
C2=c2×(A+x×B)
may be controlled to be

Furthermore, in Example 3-3, a small amount (about 0.1%) of carburizing gas may be additionally introduced while keeping the introduction amount constant.

Reference Signs List 1 surface hardening treatment device 2 treatment furnace 3 atmosphere gas concentration detector 4 nitriding potential controller 5 temperature controller 6 recorder 8 stirring fan 9 stirring fan drive motor 10 furnace temperature measuring device 11 furnace heating device 13 nitriding potential arithmetic device 14 gas introduction amount control device 15 parameter setting device (touch panel)
16 On-off valve controller 17 On-off valve 20 Furnace gas supply unit 21 First in-furnace gas supply unit 22 First in-furnace gas supply controller 23 First supply valve 24 First flow meter 25 Second in-furnace gas supply Part 26 Second Furnace Gas Supply Control Device 27 Second Supply Valve 28 Second Flow Meter 29 Furnace Introduction Gas Introduction Pipe 30 Gas Flow Output Adjusting Device 31 Programmable Logic Controller 40 Furnace Gas Waste Pipe 41 Exhaust Gas Combustion Decomposition Device 71 3rd Furnace Introduction Gas Supply Unit 72 3rd Furnace Gas Supply Controller 73 3rd Supply Valve 74 3rd Flow Meter

Claims

A plurality of types of furnace-introduced gases including ammonia gas, ammonia-decomposed gas, and nitrogen gas are introduced into the processing furnace to perform gas nitriding treatment as surface hardening treatment of the article to be treated placed in the processing furnace. A curing treatment device,
an in-furnace atmosphere gas concentration detection device for detecting the hydrogen concentration or the ammonia concentration in the processing furnace;
an in-furnace nitriding potential computing device for computing a nitriding potential in the processing furnace based on the hydrogen concentration or the ammonia concentration detected by the in-furnace atmosphere gas concentration detecting device;
According to the nitriding potential and the target nitriding potential in the treatment furnace calculated by the in-furnace nitriding potential calculating device, while maintaining the introduction amount of the ammonia decomposition gas constant, a gas introduction amount control device for bringing the nitriding potential in the processing furnace closer to the target nitriding potential by changing the introduction amount of each of the gases introduced into the furnace other than the ammonia decomposition gas;
A surface hardening apparatus comprising:
In the gas introduction amount control device, when A is the amount of ammonia gas introduced into the furnace, B is the amount of ammonia decomposition gas introduced into the furnace, and x is a predetermined constant, Proportional coefficients c1, . using cN,
C1=c1×(A+x×B), CN=cN×(A+x×B)
2. The surface hardening apparatus according to claim 1, wherein the control is performed so that
3. The surface hardening apparatus according to claim 2, wherein said predetermined constant x is 0.4 to 0.6.
4. The surface hardening apparatus according to claim 3, wherein said predetermined constant x is 0.5.
A plurality of types of furnace-introduced gases including ammonia gas, ammonia-decomposed gas, and nitrogen gas are introduced into the processing furnace to perform gas nitriding treatment as surface hardening treatment of the article to be treated placed in the processing furnace. A curing treatment method,
a furnace atmosphere gas concentration detecting step of detecting the hydrogen concentration or the ammonia concentration in the processing furnace;
an in-furnace nitriding potential calculation step of calculating a nitriding potential in the processing furnace based on the hydrogen concentration or the ammonia concentration detected by the in-furnace atmosphere gas concentration detection device;
According to the nitriding potential and the target nitriding potential in the treatment furnace calculated by the in-furnace nitriding potential calculating device, while maintaining the introduction amount of the ammonia decomposition gas constant, a gas introduction amount control step for bringing the nitriding potential in the processing furnace closer to the target nitriding potential by changing the introduction amount of each of the gases introduced into the furnace other than the ammonia decomposition gas;
A surface hardening treatment method comprising:
A surface subjected to gas nitriding as a surface hardening treatment of an article to be treated placed in the treatment furnace by introducing a plurality of types of furnace introduced gases including ammonia gas, ammonia decomposition gas, and nitrogen gas into the treatment furnace. A curing treatment device,
an in-furnace atmosphere gas concentration detection device for detecting the hydrogen concentration or the ammonia concentration in the processing furnace;
an in-furnace nitriding potential computing device for computing a nitriding potential in the processing furnace based on the hydrogen concentration or the ammonia concentration detected by the in-furnace atmosphere gas concentration detecting device;
According to the nitriding potential and the target nitriding potential in the treatment furnace calculated by the in-furnace nitriding potential calculation device, the introduction amount of the ammonia gas and the nitrogen gas is adjusted while keeping the introduction amount of the ammonia decomposition gas constant. a gas introduction amount control device that changes the nitriding potential in the processing furnace to approach the target nitriding potential;
A surface hardening apparatus comprising:
When the amount of ammonia gas introduced into the furnace is A, the amount of ammonia decomposition gas introduced into the furnace is B, and x is a predetermined constant, the gas introduction amount control device sets the introduction amount C1 of the nitrogen gas to the relevant Using the proportionality coefficient c1 assigned to the carburizing gas,
C1=c1×(A+x×B)
7. The surface hardening apparatus according to claim 6, wherein the control is performed so that
A plurality of types of furnace-introduced gases including ammonia gas, ammonia-decomposed gas, and nitrogen gas are introduced into the processing furnace to perform gas nitriding treatment as surface hardening treatment of the article to be treated placed in the processing furnace. A curing treatment method,
a furnace atmosphere gas concentration detecting step of detecting the hydrogen concentration or the ammonia concentration in the processing furnace;
an in-furnace nitriding potential calculation step of calculating a nitriding potential in the processing furnace based on the hydrogen concentration or the ammonia concentration detected by the in-furnace atmosphere gas concentration detection device;
According to the nitriding potential and the target nitriding potential in the treatment furnace calculated by the in-furnace nitriding potential calculator, the introduced amounts of the ammonia gas and the nitrogen gas are adjusted while keeping the introduced amount of the ammonia decomposition gas constant. a gas introduction amount control step of changing the nitriding potential in the processing furnace to approach the target nitriding potential;
A surface hardening treatment method comprising: