CN114829668A

CN114829668A - Surface hardening treatment device and surface hardening treatment method

Info

Publication number: CN114829668A
Application number: CN202080069395.4A
Authority: CN
Inventors: 平冈泰
Original assignee: Parker Netsushori Kogyo KK
Current assignee: Parker Netsushori Kogyo KK
Priority date: 2019-10-11
Filing date: 2020-10-09
Publication date: 2022-07-29
Also published as: US20220341021A1; KR20220057601A; JPWO2021070938A1; WO2021070938A1; TW202124731A; EP4043606A4; EP4043606A1; MX2022002518A

Abstract

The present invention is provided with: a furnace atmosphere gas concentration detection device for detecting the hydrogen concentration or ammonia concentration in the treatment furnace; a furnace nitriding potential calculating device for calculating the nitriding potential in the treatment furnace based on the hydrogen concentration or the ammonia concentration detected by the furnace atmosphere gas concentration detecting device; and a gas introduction amount control device for changing the introduction amount of each of the furnace introduction gases other than the ammonia decomposition gas among the two or more kinds of furnace introduction gases while keeping the introduction amount of the ammonia decomposition gas constant, based on the calculated nitriding potential in the processing furnace and the target nitriding potential, thereby bringing the nitriding potential in the processing furnace close to the target nitriding potential.

Description

Surface hardening treatment device and surface hardening treatment method

Technical Field

The present invention relates to a surface hardening treatment apparatus and a surface hardening treatment method for performing a surface hardening treatment on a metal workpiece, such as nitriding, tufftriding, nitriding quenching, and the like.

Background

In case hardening treatment of a workpiece made of metal such as steel, nitriding treatment as low strain treatment is in great demand. Examples of the nitriding method include a gas method, a salt bath method, and a plasma method.

Among these methods, the gas method is superior in overall quality, environmental performance, mass productivity, and the like. By using a nitriding treatment (gas nitriding treatment) by a gas method, strain caused by carburizing, carbonitriding treatment, or induction quenching accompanying quenching of a machine part can be improved. As a process of the same kind as the gas nitriding process, a soft nitriding process (gas soft nitriding process) by a gas method involving carburizing is also known.

The gas nitriding treatment comprises the following processes: only the treated article is permeated with diffused nitrogen to harden the surface. In the gas nitriding treatment, ammonia gas alone, a mixed gas of ammonia gas and nitrogen gas, ammonia gas and an ammonia decomposition gas (composed of 75% of hydrogen and 25% of nitrogen, also referred to as AX gas), or a mixed gas of ammonia gas, an ammonia decomposition gas, and nitrogen gas is introduced into a treatment furnace, and a surface hardening treatment is performed.

On the other hand, the gas soft nitriding is a process of: the surface of the article to be treated is hardened by additionally diffusing and permeating carbon together with nitrogen. For example, in a gas nitrocarburizing treatment, ammonia, nitrogen and carbon dioxide (CO) are introduced ₂ ) Or a mixed gas of two or more kinds of introduced gases such as ammonia gas, nitrogen gas, carbon dioxide gas and carbon monoxide gas (CO), is introduced into the treatment furnace to perform a surface hardening treatment.

The basis of the atmosphere control in the gas nitriding and soft nitriding is to control the nitriding potential (K) in the furnace _N ). By controlling the nitriding potential (K) _N ) Can control the gamma' phase (Fe) in the compound layer formed on the surface of the steel material ₄ N) and epsilon phase (Fe) _2-3 N) bodyThe nitride film can have a wide range of nitriding qualities, such as a product ratio and a treatment for preventing the formation of the compound layer. For example, according to japanese patent laid-open publication No. 2016-.

On the other hand, the soft-nitriding treatment is used to positively utilize a hard epsilon phase, for example, to improve wear resistance ("nitriding and soft-nitriding of iron", 2 nd edition (2013), pages 81 to 86 (Dieter Liedtke et al, Agune center of technology: non-patent document 1).

In the above-described gas nitriding treatment and gas soft nitriding treatment, a furnace atmosphere gas concentration measuring sensor for measuring a hydrogen concentration or an ammonia concentration in a furnace is provided in order to control an atmosphere in the treatment furnace in which the object to be treated is disposed. Then, the in-furnace nitriding potential is calculated from the measurement value of the in-furnace atmosphere gas concentration measurement sensor, and the flow rate of each introduced gas is controlled by comparison with a target (set) nitriding potential ("heat treatment", 55 vol, No. 1, pages 7 to 11 (platacol, biantenna): non-patent document 2). As a method for controlling each introduced gas, a method of controlling the total introduced amount while keeping the flow rate ratio of the introduced gas in the furnace constant is known ("nitriding and soft nitriding of iron", 2 nd edition (2013), pages 158 to 163 (Dieter Liedtke et al, Agune center of technology): non-patent document 3).

Japanese patent No. 5629436 (patent document 2) discloses an apparatus capable of performing two kinds of control (selectively performing only one kind of control simultaneously) by using, as a first control, a control method of controlling the total introduction amount while keeping the flow rate ratio of the furnace interior introduction gas constant, and using, as a second control, a control method of individually controlling the introduction amount of the furnace interior introduction gas so that the flow rate ratio of the furnace interior introduction gas changes (japanese patent No. 5629436: patent document 2). However, Japanese patent No. 5629436 (patent document 2) discloses only 1 specific example of nitriding treatment for which the first control is effective (paragraphs 0096 and 0099 described in Japanese patent No. 5629436 (patent document 2): "holding NH ₃ (ammonia gas): n is a radical of ₂ (nitrogen) 80: 20 shapeIn this state, the

nitriding potentials

3, 3 are controlled with good accuracy by controlling the total introduction amounts of the ammonia gas and the nitrogen gas into the treatment furnace), and it is not disclosed at all that the second control is effective in what kind of nitriding treatment or soft-nitriding treatment, and that specific examples of the effective second control are not disclosed at all.

Further, the method of controlling the total introduction amount while keeping the flow rate ratio of the gas introduced into the furnace constant has an advantage that the total amount of the gas used can be expected to be suppressed, and it is also found that the control range of the nitriding potential is narrow. As a countermeasure against this problem, the present inventors have developed a control method for realizing a wide control range of the nitriding potential (for example, about 0.05 to 1.3 at 580 ℃) on the low nitriding potential side, and have obtained japanese patent No. 6345320 (patent document 3). In the control method of japanese patent No. 6345320 (patent document 3), the introduction amounts of two or more kinds of furnace-introduced gases are individually controlled so that the nitriding potential in the processing furnace approaches the target nitriding potential by changing the flow rate ratio of the two or more kinds of furnace-introduced gases while keeping the total introduction amount of the two or more kinds of furnace-introduced gases constant.

(fundamental items of gas nitriding treatment)

When the basic matters of the gas nitriding treatment are chemically described, in the gas nitriding treatment, a nitriding reaction represented by the following formula (1) occurs in a treatment furnace (gas nitriding furnace) in which a workpiece is disposed.

NH ₃ →[N]+3/2H ₂ ……(1)

At this time, the nitriding potential K _N Is defined by the following formula (2).

K _N ＝P _NH3 /P _H2 ^3/2 ……(2)

Here, P _NH3 Is the partial pressure of ammonia in the furnace, P _H2 Is the furnace hydrogen partial pressure. Nitriding potential K _N Known as an index indicating the nitriding ability of the atmosphere in the gas nitriding furnace.

On the other hand, in the furnace in the gas nitriding treatment, a part of the ammonia gas introduced into the furnace is thermally decomposed into hydrogen gas and nitrogen gas by the reaction of formula (3).

NH ₃ →1/2N ₂ +3/2H ₂ ……(3)

In the furnace, the reaction of formula (3) mainly occurs, and the nitriding reaction of formula (1) is almost negligible in amount. Therefore, if the concentration of ammonia consumed in the reaction of formula (3) or the concentration of hydrogen generated in the reaction of formula (3) is known, the nitriding potential can be calculated. That is, since 1 mole of ammonia generates 1.5 moles of hydrogen and 0.5 moles of nitrogen, the nitrogen potential can be calculated by determining the hydrogen concentration in the furnace and also the hydrogen concentration in the furnace. Alternatively, when the hydrogen concentration in the furnace is measured, the ammonia concentration in the furnace can be known, and the nitriding potential can also be calculated.

The ammonia gas flowing into the gas nitriding furnace is circulated in the furnace and then discharged to the outside of the furnace. That is, in the gas nitriding treatment, fresh (new) ammonia gas is continuously introduced into the furnace with respect to the existing gas in the furnace, and the existing gas is continuously discharged to the outside of the furnace (pushed out at the supply pressure).

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

(fundamental items of flow control)

Next, basic matters regarding the flow rate control will be described first, in which the furnace introduction gas is only ammonia gas. When the decomposition degree of ammonia gas introduced into the furnace is s (0< s <1), the gas reaction in the furnace is represented by the following formula (4).

NH ₃ →(1-s)/(1+s)NH ₃ +0.5s/(1+s)N ₂ +1.5s/(1+s)H ₂ ……(4)

Here, the furnace gas (ammonia gas only) is introduced on the left, the furnace gas composition is on the right, and the presence of undecomposed ammonia gas and the decomposition by ammonia gas are represented by a ratio of 1: 3 to produce nitrogen and hydrogen. Therefore, when the hydrogen concentration in the furnace is measured by the hydrogen sensor, the right 1.5s/(1+ s) corresponds to the measurement value by the hydrogen sensor, and the decomposition degree s of the ammonia gas introduced into the furnace can be calculated from the measurement value. From this, the 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 measurement value of the hydrogen sensor. Therefore, the nitride potential can be calculated.

Even when two or more kinds of gases are introduced into the furnace, the nitriding potential K can be controlled _N . For example, two gases, ammonia and nitrogen, are introduced into the furnace at an introduction ratio of x: y (x, y are known and x + y is 1. for example, x is 0.5, y is 1-0.5 is 0.5 (NH) ₃ ：N ₂ 1: 1) the gas reaction in the furnace is represented by the following formula (5).

xNH ₃ +(1-x)N ₂ →x(1-s)/(1+sx)NH ₃ +(0.5sx+1-x)/(1+sx)N ₂ +1.5sx/(1+sx)H ₂ ……(5)

Here, the right furnace gas composition was ammonia gas which was not decomposed, and the ratio of 1: 3, nitrogen and hydrogen, introduced left nitrogen gas (not decomposed in the furnace). At this time, since x is known (for example, x is 0.5), the unknown number is only the decomposition degree s of ammonia in the furnace hydrogen concentration on the right, i.e., 1.5sx/(1+ sx). Therefore, similarly to the case of the equation (4), the decomposition degree s of the ammonia gas introduced into the furnace can be calculated from the measurement value of the hydrogen sensor, and the in-furnace ammonia concentration can also be calculated. Therefore, the nitride potential can be calculated.

In the case where the flow rate ratio of the introduced gas in the furnace is not fixed, the furnace hydrogen concentration and the furnace ammonia concentration include two variables, i.e., the decomposition degree s of the ammonia gas introduced into the furnace and the introduction ratio x of the ammonia gas. Generally, as a device for controlling the flow rate of the gas, a Mass Flow Controller (MFC) is used, and therefore, the introduction ratio x of the ammonia gas can be read continuously as a digital signal based on the flow rate value thereof. Therefore, the nitridation potential can be calculated by combining the introduction ratio x and the measurement value of the hydrogen sensor based on the formula (5).

On the other hand, when the basic matters of the gas nitrocarburizing treatment are described chemically, in the gas nitrocarburizing treatment, a carbon supply reaction (carbon supply to the steel surface) represented by the following formulas (6) and (7) occurs in a treatment furnace (gas nitrocarburizing furnace) in which the workpiece is disposed.

2CO→[C]+CO ₂ ……(6)

CO+H ₂ →[C]+H ₂ O……(7)

As is clear from the expressions (6) and (7), the carbon supply source is carbon monoxide gas. The carbon monoxide gas may be introduced directly into the treatment furnace, or may be generated from carbon dioxide (carbon dioxide) in the treatment furnace. On the other hand, in the treatment furnace, an equilibrium reaction represented by the following formula (8) is established.

Further, in the treatment furnace, regarding H ₂ O, an equilibrium reaction represented by the following formula (9) is established.

Thus, the amount of hydrogen consumed by the reaction of the formulae (8) and (9) (which is assumed as the molar ratio w) is correlated with the amount of oxygen in the treatment furnace. Therefore, it is preferable to calculate w based on the measured value of the oxygen sensor after the measured value of the hydrogen sensor is associated with (1.5sx-w)/(1+ sx) and then calculate the degree of decomposition s of ammonia, instead of directly applying the measured value of the hydrogen sensor to 1.5sx/(1+ sx) in formula (5).

The equilibrium constant of formula (9) is K ═ pH ₂ O/(pH ₂ ·pO ₂ ^1.5 )，pH ₂ O、pH ₂ 、pO ₂ Respectively, H in the furnace ₂ O、H ₂ 、O ₂ Partial pressure of (c). Therefore, corresponding to the temperature conditions in the furnace, the equilibrium constant K and the values of both the oxygen sensor and the hydrogen sensor (═ pH) can be determined from the known equilibrium constant K and the values of both the oxygen sensor and the hydrogen sensor ₂ 、pO ₂ ) To calculate the pH ₂ The value of O. Further, as is clear from the formulae (8) and (9), the amount w of hydrogen consumed by these reactions is equal to pH ₂ The value of O. Thus, canSince w can be obtained, the decomposition degree s of ammonia can be obtained.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication 2016 No. 211069

Patent document 2: japanese patent No. 5629436

Patent document 3: japanese patent No. 6345320

Non-patent document

Non-patent document 1: "nitriding and soft nitriding of iron", 2 nd edition (2013), pages 81 to 86 (Dieter Liedtke et al, Agune center of technology)

Non-patent document 2: "Heat treatment", volume 55, No. 1, pages 7-11 (Pinggangtai, Dubianyang one)

Non-patent document 3: "nitriding and soft nitriding of iron", 2 nd edition (2013), pages 158 to 163 (Dieter Liedtke et al, Agune center of technology)

Non-patent document 4: "Effect of composite Layer Thickness of γ '-Fe 4N on Rotated-bonding Fatitue Strength in Gas-Nitred JIS-SCM435 Steel (the Effect of the Thickness of the composite Layer made of γ' -Fe4N on the rotating Bending Fatigue Strength of Gas nitriding JIS-SCM435 Steel)", Materials transformations, volume 58, No.7(2017), pages 993 to 999 (Y. Hiraoka and A. Ishida)

Non-patent document 5: "Special Steel", 61 vol, No. 3, 17 ~ 19 pp ( ze yu)

Disclosure of Invention

Problems to be solved by the invention

The present inventors have made extensive studies on the gas nitrocarburizing treatment in which two or more kinds of furnace introduction gases including ammonia gas and ammonia decomposition gas are introduced into a treatment furnace, and have found that: when controlling the nitriding potential in the treatment furnace to approach the target nitriding potential, the amount of introduction of each of the furnace introduction gases other than the ammonia decomposition gas in the two or more kinds of furnace introduction gases is changed while keeping the amount of introduction of the ammonia decomposition gas constant, thereby achieving a practical nitriding potential control.

The present invention has been made based on the above findings. The purpose of the present invention is to provide a surface hardening treatment apparatus and a surface hardening treatment method that can achieve nitriding potential control that is practical in gas nitrocarburizing treatment in which two or more kinds of furnace introduction gases including ammonia gas and ammonia decomposition gas are introduced into a treatment furnace.

Means for solving the problems

The present invention relates to a surface hardening treatment apparatus for performing a gas nitrocarburizing treatment as a surface hardening treatment of a treatment target object disposed in a treatment furnace by introducing two or more kinds of furnace introduction gases including ammonia gas and ammonia decomposition gas into the treatment furnace, the surface hardening treatment apparatus comprising: a furnace atmosphere gas concentration detection device for detecting the hydrogen concentration or ammonia concentration in the treatment furnace; a furnace nitriding potential calculation device for calculating a nitriding potential in the processing furnace based on the hydrogen concentration or the ammonia concentration detected by the furnace atmosphere gas concentration detection device; and a gas introduction amount control device for changing the introduction amount of each of the furnace introduction gases other than the ammonia decomposition gas among the two or more kinds of furnace introduction gases while keeping the introduction amount of the ammonia decomposition gas constant, based on the target nitriding potential and the nitriding potential in the processing furnace calculated by the furnace nitriding potential calculation device, thereby bringing the nitriding potential in the processing furnace close to the target nitriding potential.

According to the present invention, it was confirmed that: by changing the introduction amount of each of the furnace introduction gases other than the ammonia decomposition gas among the two or more kinds of furnace introduction gases while keeping the introduction amount of the ammonia decomposition gas constant, it is possible to realize a relatively wide nitriding potential control (particularly a relatively low nitriding potential control).

It is desirable to perform preliminary experiments before the operation to determine in advance the amount of the ammonia decomposition gas to be introduced so as to maintain a constant amount. This is because the thermal decomposition degree of ammonia is also actually affected by the furnace environment of the furnace used.

The surface hardening treatment apparatus of the present invention preferably further comprises a furnace oxygen concentration detection device that detects an oxygen concentration in the treatment furnace, and the furnace nitriding potential calculation device calculates the nitriding potential in the treatment furnace based on the hydrogen concentration or the ammonia concentration detected by the furnace atmosphere gas concentration detection device and the oxygen concentration detected by the furnace oxygen concentration detection device.

As described above, in the soft nitriding treatment, hydrogen is consumed in the carbon supply reaction to become water (H) ₂ O), the water (H) ₂ O) is in a state of equilibrium with respect to the amount of oxygen in the furnace, and therefore, by detecting the oxygen concentration in the furnace by the in-furnace oxygen concentration detection means and using the oxygen concentration for the calculation of the nitriding potential, a nitriding potential with higher accuracy can be realized.

When the furnace introduction amount of ammonia gas is a and the furnace introduction amount of ammonia decomposition gas is B, x, the gas introduction amount control device preferably controls the introduction amounts of the furnace introduction gases other than ammonia gas and ammonia decomposition gas, C1, … …, and cN (N is an integer of 1 or more), among the two or more kinds of furnace introduction gases, to C1 × (a + x × B), … …, and cN ═ cN × (a + x × B), by using the proportionality coefficients C1, … …, and cN assigned to the respective furnace introduction gases.

It has been confirmed through practical experiments by the present inventors that when such control conditions are adopted, control of a relatively wide nitridation potential (particularly control of a relatively low nitridation potential) can be achieved.

The value of x is for example 0.5. This can be interpreted as: 1 mol of ammonia gas causes thermal decomposition and the amount of hydrogen generated in the furnace is 1.5 mol, whereas the amount of hydrogen supplied to the furnace is 0.75 mol (3/4 mol) for 1 mol of ammonia decomposition gas, and therefore, 1.5: 0.75 ═ 1: the ratio of 0.5 is a coefficient obtained by converting the furnace introduction amount B of the ammonia decomposition gas into the furnace introduction amount a of ammonia gas.

However, the value of x is not strictly 0.5, but is substantially in the range of 0.4 to 0.6, and the practical control of the nitriding potential can be achieved.

The two or more kinds of furnace introduction gases include carbon dioxide as a carburizing gas. Alternatively, the two or more kinds of furnace-introducing gases include carbon monoxide gas as a carburizing gas.

Alternatively, the two or more kinds of furnace introduction gases include carbon dioxide and nitrogen gas, or carbon monoxide gas and nitrogen gas.

The present invention can also be considered as a surface hardening treatment method. That is, the present invention relates to a surface hardening treatment method for performing a gas nitrocarburizing treatment as a surface hardening treatment of a workpiece disposed in a treatment furnace by introducing two or more kinds of furnace introduction gases including ammonia gas and an ammonia decomposition gas into the treatment furnace, the surface hardening treatment method including: a furnace atmosphere gas concentration detection step of detecting a hydrogen concentration or an ammonia concentration in the treatment furnace; a furnace nitriding potential calculating step of calculating a nitriding potential in the treatment furnace based on the hydrogen concentration or the ammonia concentration detected in the furnace atmosphere gas concentration detecting step; and a gas introduction amount control step of changing the introduction amount of each of the furnace introduction gases other than the ammonia decomposition gas among the two or more kinds of furnace introduction gases while keeping the introduction amount of the ammonia decomposition gas constant, based on the target nitriding potential and the nitriding potential in the processing furnace calculated by the furnace nitriding potential calculation step, thereby bringing the nitriding potential in the processing furnace close to the target nitriding potential.

The present invention also relates to a surface hardening treatment apparatus for performing a gas nitrocarburizing treatment as a surface hardening treatment of a workpiece disposed in a treatment furnace by introducing two or more kinds of in-furnace introduction gases including ammonia gas, an ammonia decomposition gas, and a carburizing gas (for example, carbon dioxide gas or carbon monoxide gas) into the treatment furnace, the surface hardening treatment apparatus comprising: a furnace atmosphere gas concentration detection device for detecting the hydrogen concentration or ammonia concentration in the treatment furnace; a furnace nitriding potential calculation device for calculating a nitriding potential in the processing furnace based on the hydrogen concentration or the ammonia concentration detected by the furnace atmosphere gas concentration detection device; and a gas introduction amount control device for changing the introduction amounts of the ammonia gas and the carburizing gas while keeping the introduction amount of the ammonia decomposition gas constant, based on the nitriding potential in the processing furnace calculated by the furnace nitriding potential calculation device and a target nitriding potential, thereby bringing the nitriding potential in the processing furnace close to the target nitriding potential.

The method is characterized in that the amount of ammonia gas and carburizing gas to be introduced is changed while the amount of ammonia decomposition gas to be introduced is kept constant, and the amount of other gases to be introduced is not limited. Thus, the scope of the claims clearly includes a mode of introducing a certain amount of a trace amount of gas (about 1% or less in terms of flow rate ratio) to the extent of not substantially participating in the reaction. For example, the present invention is applied to the case where two or more types of carburizing gas are introduced, and even in the case where only the introduction amount of the main carburizing gas is changed and a certain amount of other carburizing gas introduced in a slight amount is introduced, relatively wide nitriding potential control (particularly relatively low nitriding potential control) can be achieved.

In this case, when the furnace introduction amount of ammonia gas is a and the furnace introduction amount of ammonia decomposition gas is B, x, the gas introduction amount control device preferably controls the introduction amount of carburizing gas C1 to C1 × (C1 × (a + x × B) by using the proportionality coefficient C1 allocated to the carburizing gas.

The present invention also relates to a surface hardening apparatus for performing a surface hardening treatment of a workpiece disposed in a treatment furnace by introducing a furnace introduction gas containing at least two kinds of ammonia gas, an ammonia decomposition gas, a carburizing gas, and a nitrogen gas into the treatment furnace and performing a gas nitrocarburizing treatment, the surface hardening apparatus comprising: a furnace atmosphere gas concentration detection device for detecting the hydrogen concentration or ammonia concentration in the treatment furnace; a furnace nitriding potential calculation device for calculating a nitriding potential in the processing furnace based on the hydrogen concentration or the ammonia concentration detected by the furnace atmosphere gas concentration detection device; and a gas introduction amount control device for changing the introduction amounts of the ammonia gas, the carburizing gas, and the nitrogen gas while keeping the introduction amount of the ammonia decomposition gas constant, based on the nitriding potential in the processing furnace calculated by the furnace nitriding potential calculation device and a target nitriding potential, thereby bringing the nitriding potential in the processing furnace close to the target nitriding potential.

The method is characterized in that the introduction amounts of ammonia gas, carburizing gas and nitrogen gas are changed while keeping the introduction amount of the ammonia decomposition gas constant, and the introduction amount of the other gas is not limited. Thus, the scope of the claims clearly includes a mode of introducing a certain amount of a trace amount of gas (about 1% or less in terms of flow rate ratio) to the extent of not substantially participating in the reaction. For example, the present invention is applied to the case where two or more types of carburizing gas are introduced, and even in the case where only the introduction amount of the main carburizing gas is changed and a certain amount of other carburizing gas introduced in a slight amount is introduced, relatively wide nitriding potential control (particularly relatively low nitriding potential control) can be achieved.

In this case, when the furnace introduction amount of the ammonia gas is a and the furnace introduction amount of the ammonia decomposition gas is B, x, the gas introduction amount control device preferably controls the introduction amount of the carburizing gas C1 and the introduction amount of the nitrogen gas C2 to C1 ═ C1 × (a + x × B) and C2 ═ C2 × (a + x × B) by using the proportionality coefficient C1 assigned to the carburizing gas and the proportionality coefficient C2 assigned to the nitrogen gas.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, it was confirmed that: by changing the introduction amount of each of the furnace introduction gases other than the ammonia decomposition gas in the two or more kinds of furnace introduction gases while keeping the introduction amount of the ammonia decomposition gas constant, it is possible to realize a relatively wide nitriding potential control (particularly a relatively low nitriding potential control).

Drawings

Fig. 1 is a schematic view showing a surface hardening treatment apparatus according to embodiment 1 of the present invention.

FIG. 2 is a graph showing the control of the introduced gas into the furnace in example 1-1.

FIG. 3 is a graph showing the control of the nitridation potential in example 1-1.

FIG. 4 is a graph showing the control of the introduced gas into the furnace in examples 1 to 3.

FIG. 5 is a graph showing the control of the nitridation potential of examples 1 to 3.

FIG. 6 is a table comparing example 1-1 to example 1-3 with each comparative example.

Fig. 7 is a schematic view showing a surface hardening treatment apparatus according to embodiment 2 of the present invention.

FIG. 8 is a graph showing the control of the furnace-introduced gas in example 2-2.

FIG. 9 is a graph showing the control of the nitridation potential of example 2-2.

FIG. 10 is a table comparing example 2-1 to example 2-3 with each comparative example.

Fig. 11 is a schematic view showing a surface hardening treatment apparatus according to embodiment 3 of the present invention.

FIG. 12 is a graph showing the control of the furnace-introduced gas in example 3-2.

FIG. 13 is a graph showing the control of the nitridation potential of example 3-2.

FIG. 14 is a table comparing example 3-1 to example 3-3 with each comparative example.

Fig. 15 is a schematic view showing a surface hardening treatment apparatus according to embodiment 4 of the present invention.

FIG. 16 is a table comparing example 4-1 to example 4-3 with each comparative example.

Fig. 17 is a schematic view showing a surface hardening treatment apparatus according to embodiment 5 of the present invention.

FIG. 18 is a table comparing example 5-1 to example 5-3 with each comparative example.

Detailed Description

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 view showing a surface hardening treatment apparatus according to an embodiment of the present invention. As shown in fig. 1, a surface hardening apparatus 1 of the present embodiment is a surface hardening apparatus that introduces ammonia gas, ammonia decomposition gas, and carbon dioxide gas into a treatment furnace 2, and performs a gas nitrocarburizing treatment as a surface hardening treatment of a workpiece S disposed in the treatment furnace 2.

Ammonia-decomposed gas is a gas also called AX gas, which is a gas composed of gases in the ratio of 1: 3 nitrogen and hydrogen. The workpiece S is made of metal, and is assumed to be a steel member, a mold, or the like, for example.

As shown in fig. 1, the treatment furnace 2 of the surface hardening treatment apparatus 1 of the present embodiment is provided with a stirring blade 8, a stirring blade drive motor 9, a furnace temperature measuring device 10, a furnace heating device 11, an atmosphere gas concentration detecting device 3, a nitriding potential adjuster 4, a temperature adjuster 5, a programmable logic controller 31, a recorder 6, and a furnace introduction gas supply unit 20.

The stirring blade 8 is disposed in the treatment furnace 2, rotates in the treatment furnace 2, and stirs the atmosphere in the treatment furnace 2. The stirring blade driving motor 9 is connected to the stirring blade 8, and rotates the stirring blade 8 at an arbitrary rotation speed.

The furnace temperature measuring device 10 includes a thermocouple configured to measure the temperature of the furnace gas present in the processing furnace 2. Further, the furnace temperature measuring device 10 measures the temperature of the furnace gas, and then outputs an information signal (furnace temperature signal) including the measured temperature to the temperature regulator 5 and the recorder 6.

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

After detecting the furnace atmosphere gas concentration and the oxygen concentration, the atmosphere gas concentration detection device 3 outputs an information signal including the detected concentrations to the nitriding potential adjuster 4 and the recorder 6.

The recorder 6 includes a storage medium such as a CPU and a memory, and stores the temperature in the processing furnace 2, the furnace atmosphere gas concentration, and the oxygen concentration in association with, for example, the date and time when the surface hardening process was performed, based on the output signals from the furnace temperature measuring device 10 and the atmosphere gas concentration detecting device 3.

The nitriding potential adjusting meter 4 has a furnace nitriding potential calculating device 13 and a gas flow output adjusting device 30. The programmable logic controller 31 includes a gas introduction control device 14 and a parameter setting device 15.

The in-furnace nitriding potential calculation device 13 calculates the nitriding potential in the treatment furnace 2 based on the hydrogen concentration or the ammonia concentration and the oxygen concentration detected by the in-furnace atmosphere gas concentration detection device 3. Specifically, a calculation formula of the nitriding potential programmed based on the same idea as that of the formulas (5) to (9) from the actual furnace-introduced gas is introduced, and the nitriding potential is calculated from the value of the furnace-atmosphere gas concentration and the value of the oxygen concentration.

In the present embodiment, when the furnace introduction amount of ammonia gas is a and the furnace introduction amount of ammonia decomposition gas is B, x are predetermined constants, the furnace introduction amount of carbon dioxide C1, which is a furnace introduction gas other than ammonia gas and ammonia decomposition gas, is controlled to C1 × (C1 × (a + x × B) by the proportional coefficient C1 allocated to the furnace introduction gas.

The parameter setting device 15 is constituted by, for example, a touch panel, and can set an input target nitriding potential, a processing temperature, a processing time, an introduction amount of the ammonia decomposition gas, a predetermined constant x, a proportionality coefficient c1, and the like for the same workpiece. In addition, the set parameter value to be input to the PID control can be set for each different value of the target nitride potential. Specifically, the "proportional gain", "integral gain or integral time", and "differential gain or differential time" of the input PID control can be set for each different value of the target nitride potential. The respective setting parameter values inputted for setting are transmitted to the gas flow output adjusting unit 30.

Then, the gas flow output adjusting means 30 performs PID control in which the nitriding potential calculated by the in-furnace nitriding potential calculating means 13 is set as an output value, the target nitriding potential (set nitriding potential) is set as a target value, and the respective introduction amounts of ammonia and carbon dioxide in the three kinds of in-furnace introduction gases are set as input values. More specifically, in the PID control, the nitriding potential in the treatment furnace 2 can be brought close to the target nitriding potential by changing the introduction amounts of ammonia gas and carbon dioxide while keeping the introduction amount of the ammonia decomposition gas constant. In the PID control, the setting parameter values transmitted from the parameter setting device 15 are used.

It is preferable that candidates of the setting parameter values for PID control for setting the input job to the parameter setting device 15 are obtained in advance by performing a tentative process. In the present embodiment, (4) candidates of the set parameter values can be obtained in advance by the automatic adjustment function of the nitride potential adjustment meter 4 itself for each different value of the target nitride potential, even if (1) the state of the treatment furnace (the state of the furnace wall or the jig), (2) the temperature condition of the treatment furnace, and (3) the state (type and number) of the workpiece are the same. For the nitride potential adjusting meter 4 having an automatic adjusting function, UT75A (high function type digital indicating adjusting meter, http:// www.yokogawa.co.jp/ns/cis/utup/utadvanced/ns-UT75a-01-ja. htm) manufactured by Yokogawa electric corporation, etc. can be used.

The set parameter values ("set of a proportional gain", "an integral gain or an integral time" and "a derivative gain or a derivative time") obtained as candidates are recorded in some form and can be manually input to the parameter setting device 15 in accordance with the target processing content. However, the setting parameter values obtained as candidates may be stored in a certain storage device so as to be associated with the target nitride potential, and the values of the target nitride potential based on the setting input may be automatically read by the parameter setting device 15.

The gas flow output adjusting unit 30 determines initial values of the introduction amount of the ammonia decomposition gas to be maintained constant and the introduction amounts of the ammonia gas and the carbon dioxide to be varied based on the value of the target nitriding potential before the PID control. These value candidates are preferably obtained in advance by performing a tentative process, and are automatically read out from a storage device or the like by the parameter setting device 15, or are manually input from the parameter setting device 15. Then, the amounts of ammonia gas and carbon dioxide gas introduced are determined (varied) by PID control so that the nitriding potential in the treatment furnace 2 approaches the target nitriding potential, and the relationship of C1 ═ C1 × (a + x × B) is maintained (the amount of ammonia decomposition gas introduced is maintained constant). The output value of the gas flow output adjustment unit 30 is transmitted to the gas introduction amount control unit 14.

The gas introduction amount control unit 14 sends a control signal to the 1 st supply amount control device 22 for ammonia gas.

The furnace introduced gas supply unit 20 of the present embodiment includes a 1 st furnace introduced gas supply unit 21 for ammonia gas, a 1 st supply amount control device 22, a 1 st supply valve 23, and a 1 st flow meter 24. The furnace introduced gas supply unit 20 of the present embodiment includes a 2 nd furnace introduced gas supply unit 25 for ammonia decomposition gas (AX gas), a 2 nd supply amount control device 26, a 2 nd supply valve 27, and a 2 nd flow meter 28. The furnace introduced gas supply unit 20 of the present embodiment includes a 3 rd furnace introduced gas supply unit 61 for carbon dioxide, a 3 rd supply amount control device 62, a 3 rd supply valve 63, and a 3 rd flow meter 64.

In the present embodiment, ammonia gas, ammonia decomposition gas, and carbon dioxide gas are mixed in the furnace introducing gas introducing pipe 29 before entering the treatment furnace 2.

The 1 st furnace introduction gas supply unit 21 is formed of, for example, a tank filled with the 1 st furnace introduction gas (ammonia gas in this example).

The 1 st supply amount control device 22 is formed of a mass flow controller (capable of changing the flow rate little by little in a short time), and is interposed between the 1 st furnace introduction gas supply portion 21 and the 1 st supply valve 23. The opening degree of the 1 st supply amount control device 22 is changed in accordance with the control signal output from the gas introduction amount control unit 14. The 1 st supply amount control device 22 detects the supply amount from the 1 st in-furnace introduced gas supply unit 21 to the 1 st supply valve 23, and outputs an information signal including the detected supply amount to the gas introduction control unit 14 and the adjustment meter 6. This control signal can be used for correction of control by the gas introduction amount control unit 14, and the like.

The 1 st supply valve 23 is formed of an electromagnetic valve that switches its open/closed state in accordance with a control signal output from the gas introduction amount control unit 14, and the 1 st supply valve 23 is interposed between the 1 st supply amount control device 22 and the 1 st flow meter 24.

The 1 st flow meter 24 is formed of a mechanical flow meter such as a flow meter, and is interposed between the 1 st supply valve 23 and the furnace introduced gas introduction pipe 29. The 1 st flow meter 24 detects the supply amount of the gas introduced into the furnace from the 1 st supply valve 23 through the gas introduction pipe 29. The supply amount detected by the 1 st flow meter 24 can be used for a confirmation operation by visual observation of the operator.

The 2 nd furnace introduction gas supply unit 25 is formed of, for example, a tank filled with the 2 nd furnace introduction gas (ammonia decomposition gas in this example).

The 2 nd supply amount control device 26 is formed of a mass flow controller (capable of changing the flow rate little by little in a short time), and is interposed between the 2 nd furnace introduction gas supply portion 25 and the 2 nd supply valve 27. The opening degree of the 2 nd supply amount control device 26 is changed in accordance with the control signal output from the gas introduction amount control unit 14. The 2 nd supply amount control device 26 detects the supply amount from the 2 nd furnace introduction gas supply unit 25 to the 2 nd supply valve 27, and outputs an information signal including the detected supply amount to the gas introduction control unit 14 and the regulator 6. This control signal can be used for correction of control by the gas introduction amount control unit 14, and the like.

The 2 nd supply valve 27 is formed by an electromagnetic valve that switches the open/close state in accordance with a control signal output from the gas introduction amount control unit 14, and the 2 nd supply valve 27 is interposed between the 2 nd supply amount control device 26 and the 2 nd flow meter 28.

The 2 nd flow meter 28 is formed of a mechanical flow meter such as a flow meter, for example, and is interposed between the 2 nd supply valve 27 and the furnace introduced gas introduction pipe 29. The 2 nd flow meter 28 detects the supply amount of the gas introduced into the furnace from the 2 nd supply valve 27 through the gas introduction pipe 29. The supply amount detected by the 2 nd flow meter 28 can be used for confirmation operation by visual observation of the operator.

However, in the present invention, the amount of ammonia decomposition gas introduced does not vary little by little, and therefore the 2 nd supply amount control device 26 is omitted, and the flow rate (opening degree) of the 2 nd flow meter 28 can be manually adjusted in accordance with the control signal output from the gas introduction amount control unit 14.

The 3 rd furnace introduced gas supply part 61 is formed of, for example, a tank filled with the 3 rd furnace introduced gas (carbon dioxide in this example).

The 3 rd supply amount control device 62 is formed of a mass flow controller (capable of changing the flow rate little by little in a short time), and is interposed between the 3 rd furnace introduction gas supply portion 61 and the 3 rd supply valve 63. The opening degree of the 3 rd supply amount control device 62 changes in accordance with the control signal output from the gas introduction amount control unit 14. The 3 rd supply amount control device 62 detects the supply amount from the 3 rd furnace introduction gas supply portion 61 to the 3 rd supply valve 63, and outputs an information signal including the detected supply amount to the gas introduction control unit 14 and the adjustment meter 6. This control signal can be used for correction of control by the gas introduction amount control unit 14, and the like.

The 3 rd supply valve 63 is formed of an electromagnetic valve that switches its open/closed state in accordance with a control signal output from the gas introduction amount control unit 14, and the 3 rd supply valve 63 is interposed between the 3 rd supply amount control device 62 and the 3 rd flow meter 64.

The 3 rd flow meter 64 is formed of a mechanical flow meter such as a flow meter, for example, and is interposed between the 3 rd supply valve 63 and the furnace introduced gas introduction pipe 29. The 3 rd flow meter 64 detects the supply amount of the gas introduced into the furnace from the 3 rd supply valve 63 to the furnace gas introduction pipe 29. The supply amount detected by the 3 rd flow meter 64 can be used for confirmation operation by visual observation of the operator.

(action: example 1)

Next, the operation of the surface hardening treatment apparatus 1 according to the present embodiment will be described with reference to fig. 2 and 3. First, the treatment target S is put into the treatment furnace 2, and heating of the treatment furnace 2 is started. In the example shown in fig. 2 and 3, as the processing furnace 2, a size is used

The heating temperature of the shaft furnace is 570 ℃, and the shaft furnace is used with a heating device of 4m ² The surface area of the steel material of (3) is defined as the workpiece S.

During heating in the treatment furnace 2, ammonia gas, ammonia decomposition gas, and carbon dioxide gas are introduced into the treatment furnace 2 from the furnace introduction gas supply unit 20 at a set initial flow rate. Here, as shown in fig. 2, the set initial flow rate of ammonia gas is 13 l/min, the set initial flow rate of ammonia decomposition gas is 19 l/min, the set initial flow rate of carbon dioxide is 1.03 l/min, x is 0.5, and c1 is 0.053. These set initial flow rates may be set as inputs in the parameter setting device 15. The stirring blade drive motor 9 is driven to rotate the stirring blade 8, thereby stirring the atmosphere in the processing furnace 2.

In the initial state, the open/close valve control device 16 closes the open/close valve 17. In general, as a pretreatment for gas nitriding treatment, a treatment for activating the surface of a steel material to allow nitrogen to easily enter therein may be performed. In this case, hydrogen chloride gas, hydrogen cyanide gas, or the like is generated in the furnace. Since these gases can deteriorate the in-furnace atmosphere gas concentration detection device (sensor) 3, it is effective to close the on-off valve 17 in advance.

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 regulator 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 rise or in a state in which temperature rise is completed (steady state).

The in-furnace nitriding potential calculating device 13 of the nitriding potential adjusting gauge 4 calculates the nitriding potential in the furnace (which is initially an extremely high value (due to the absence of hydrogen in the furnace), but gradually decreases as the ammonia gas is decomposed (hydrogen is generated)), and determines whether or not the value is lower than the sum of the target nitriding potential (0.6 in this example, see fig. 3) and the reference deviation value. The reference deviation value can also be set as an input in the parameter setting means 15, for example 0.1.

When it is determined that the temperature rise is completed and it is determined that the calculated value of the in-furnace nitriding potential is lower than the sum of the target nitriding potential and the reference deviation value (0.7 in this example), the nitriding potential adjusting gauge 4 starts the control of the amount of the in-furnace introduced gas by 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 communicates with the atmosphere gas concentration detection device 3, and the furnace atmosphere gas concentration detection device 3 detects the furnace hydrogen concentration or the furnace ammonia concentration and also detects the oxygen concentration. The detected hydrogen concentration signal or ammonia concentration signal and oxygen concentration signal are output to the nitriding potential regulator 4 and the recorder 6.

The in-furnace nitriding potential calculation device 13 of the nitriding potential adjustment meter 4 calculates the in-furnace nitriding potential based on the input hydrogen concentration signal or ammonia concentration signal and oxygen concentration signal. The gas flow output adjusting means 30 performs PID control in which the nitriding potential calculated by the in-furnace nitriding potential calculating means 13 is set as an output value, the target nitriding potential (set nitriding potential) is set as a target value, and the respective introduction amounts of ammonia and carbon dioxide in the three kinds of in-furnace introduction gases are set as input values. Specifically, in the PID control, the amount of ammonia gas and the amount of carbon dioxide gas introduced are changed while keeping the amount of ammonia decomposition gas introduced constant, thereby controlling the nitriding potential in the treatment furnace 2 to approach the target nitriding potential while maintaining the relationship of C1 ═ C1 × (a + x × B). In the PID control, each setting parameter value set and inputted by the parameter setting device 15 is used. The set parameter value may be different depending on the value of the target nitride potential.

Further, as a result of the PID control, the gas introduction amount control unit 14 controls the introduction amount of ammonia gas and the introduction amount of carbon dioxide gas. In order to realize the determined introduction amount of each gas, the gas introduction amount control unit 14 sends control signals to the 1 st supply amount control device 22 for ammonia gas, the 2 nd supply amount control device 26 (constant supply amount) for ammonia decomposition gas, and the 3 rd supply amount control device 62 for carbon dioxide.

By the above control, as shown in fig. 3, the in-furnace nitriding potential can be stably controlled to be in the vicinity of the target nitriding potential. This enables the surface hardening treatment of the workpiece S to be performed with extremely high quality. As a specific example, it is known from the example shown in fig. 3 that the introduction amount of ammonia gas is increased or decreased within a fluctuation range of about 3ml (± 1.5ml) by the feedback control with the sampling time of about several hundred milliseconds, and the nitriding potential can be controlled to the target nitriding potential (0.6) with extremely high accuracy from the time of about 30 minutes after the start of the treatment. (in the example shown in FIG. 2, the recording of the gas flow rates and the nitriding potentials was stopped at about 190 minutes after the start of the treatment.)

(action: example 1-2)

Next, as example 1-2, a case where the target nitriding potential is set to 0.4 by using the surface hardening treatment apparatus 1 of the present embodiment will be described. In this example 1-2, the dimensions were also used

The shaft furnace 2 used was a furnace having a heating temperature of 570 ℃ and a diameter of 4m ² The surface area of the steel material of (3) is defined as the workpiece S.

During heating in the treatment furnace 2, ammonia gas, ammonia decomposition gas, and carbon dioxide gas are introduced into the treatment furnace 2 from the furnace introduction gas supply unit 20 at a set initial flow rate. Here, the set initial flow rate of ammonia gas was 5.5 l/min, the set initial flow rate of ammonia decomposition gas was 25 l/min, the set initial flow rate of carbon dioxide was 0.95 l/min, x was 0.5, and c1 was 0.053. These set initial flow rates can be set and inputted in the parameter setting device 15. The stirring blade drive motor 9 is driven to rotate the stirring blade 8, thereby stirring the atmosphere in the processing furnace 2.

In the initial state, the open/close valve control device 16 closes the open/close valve 17.

The in-furnace nitriding potential calculating device 13 of the nitriding potential adjusting gauge 4 calculates the nitriding potential in the furnace (which is initially an extremely high value (due to the absence of hydrogen in the furnace), but gradually decreases as the ammonia gas is decomposed (hydrogen is generated)), and determines whether or not the value is lower than the sum of the target nitriding potential (0.4 in this example) and the reference deviation value. The reference deviation value can also be set as an input in the parameter setting means 15, 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 (0.5 in this example), the nitriding potential adjusting gauge 4 starts the control of the amount of the in-furnace introduced gas by 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 calculation device 13 of the nitriding potential adjustment meter 4 calculates the in-furnace nitriding potential based on the input hydrogen concentration signal or ammonia concentration signal and oxygen concentration signal. The gas flow output adjusting means 30 performs PID control in which the nitriding potential calculated by the in-furnace nitriding potential calculating means 13 is set as an output value, the target nitriding potential (set nitriding potential) is set as a target value, and the respective introduction amounts of ammonia and carbon dioxide in the three kinds of in-furnace introduction gases are set as input values. Specifically, in the PID control, the amount of ammonia gas and the amount of carbon dioxide gas introduced are changed while keeping the amount of ammonia decomposition gas introduced constant, thereby controlling the nitriding potential in the treatment furnace 2 to approach the target nitriding potential while maintaining the relationship of C1 ═ C1 × (a + x × B). In the PID control, each setting parameter value set and input by the parameter setting device 15 is used. The set parameter value may be different depending on the value of the target nitride potential.

By the above control, the in-furnace nitriding potential can be stably controlled to be in the vicinity of the target nitriding potential. This enables the surface hardening treatment of the workpiece S to be performed with extremely high quality. Specifically, the nitrogen potential can be controlled to the target nitrogen potential (0.4) with extremely high accuracy from about 30 minutes after the start of the treatment by increasing or decreasing the amount of ammonia gas introduced within a range of about 3ml (± 1.5ml) by feedback control with a sampling time of about several hundred milliseconds.

(action: examples 1 to 3)

Next, as examples 1 to 3, a case where the target nitriding potential is set to 0.2 by using the surface hardening treatment apparatus 1 of the present embodiment will be described. In examples 1 to 3, the dimensions were also used

During heating in the treatment furnace 2, ammonia gas, ammonia decomposition gas, and carbon dioxide gas are introduced into the treatment furnace 2 from the furnace introduction gas supply unit 20 at a set initial flow rate. Here, as shown in fig. 4, the set initial flow rate of ammonia gas is 2 l/min, the set initial flow rate of ammonia decomposition gas is 29 l/min, the set initial flow rate of carbon dioxide is 0.87 l/min, x is 0.5, and c1 is 0.053. These set initial flow rates can be set and inputted in the parameter setting device 15. The stirring blade drive motor 9 is driven to rotate the stirring blade 8, thereby stirring the atmosphere in the processing furnace 2.

The in-furnace nitriding potential calculating device 13 of the nitriding potential adjusting gauge 4 calculates the nitriding potential in the furnace (which is initially an extremely high value (due to the absence of hydrogen in the furnace), but gradually decreases as the ammonia gas is decomposed (hydrogen is generated)), and determines whether or not the value is lower than the sum of the target nitriding potential (0.2 in this example, see fig. 5) and the reference deviation value. The reference deviation value can also be set as an input in the parameter setting means 15, for example 0.1.

When it is determined that the temperature rise is completed and it is determined that 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 adjusting gauge 4 starts the control of the amount of the in-furnace introduced gas by 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.

By the above control, as shown in fig. 5, the in-furnace nitriding potential can be stably controlled to be in the vicinity of the target nitriding potential. This enables the surface hardening treatment of the workpiece S to be performed with extremely high quality. As a specific example, it is understood from the example shown in fig. 5 that the introduction amount of ammonia gas is increased or decreased within a fluctuation range of about 3ml (± 1.5ml) by the feedback control with the sampling time of about several hundred milliseconds, and the nitriding potential can be controlled to the target nitriding potential (0.2) with extremely high accuracy from the time of about 30 minutes after the start of the treatment. (in the example shown in FIG. 4, the recording of the gas flow rates and the nitriding potentials was stopped at a time of about 160 minutes after the start of the treatment.)

(description of comparative example)

For comparison, the following control of the nitridation potential was performed: the flow ratio of ammonia gas to carbon dioxide was always maintained at 95: 5, changing their total flow rate.

Specifically, the in-furnace nitriding potential calculation device 13 of the nitriding potential adjustment meter 4 calculates the in-furnace nitriding potential based on the input hydrogen concentration signal or ammonia concentration signal and oxygen concentration signal. The gas flow output adjusting means 30 performs PID control in which the nitriding potential calculated by the in-furnace nitriding potential calculating means 13 is set as an output value, the target nitriding potential (set nitriding potential) is set as a target value, and the respective introduction amounts of ammonia and carbon dioxide are set as input values. More specifically, in the PID control, the total introduction amount of ammonia gas and carbon dioxide is changed while keeping the flow ratio of ammonia gas and carbon dioxide constant, thereby performing control for bringing the nitriding potential in the processing furnace 2 close to the target nitriding potential.

However, in the control of the comparative example, the nitride potential cannot be stably controlled.

(example 1-1 to example 1-3 comparison with comparative example)

Fig. 6 shows the above results in a summary.

(constitution of embodiment 2)

As shown in fig. 7, in embodiment 2, the 3 rd furnace introduction gas supply portion 61' is formed by a tank filled with carbon monoxide gas instead of carbon dioxide.

In embodiment 2, when the amount of ammonia gas introduced into the furnace is a and the amount of ammonia decomposition gas introduced into the furnace is B, x, the amount of carbon monoxide gas introduced into the furnace, which is a gas introduced into the furnace other than ammonia gas and ammonia decomposition gas, C1 is controlled to C1 × (C1 × (a + x × B) by the proportionality coefficient C1 allocated to the gas introduced into the furnace.

The other structure of the present embodiment is substantially the same as that of embodiment 1 described with reference to fig. 1. In fig. 7, the same reference numerals are given to the same portions as those in embodiment 1. In this embodiment, the same portions as those in embodiment 1 will not be described in detail.

(action: example 2-1)

Next, as example 2-1, a case where the target nitriding potential is set to 0.6 by using the surface hardening treatment apparatus according to embodiment 2 will be described. In this example 2-1, the dimensions were also used

In the heating of the processing furnace 2, ammonia gas, ammonia decomposition gas, and carbon monoxide gas are introduced into the processing furnace 2 from the furnace introduction gas supply portion 20 at a set initial flow rate. Here, the set initial flow rate of ammonia gas was set to 5.5[ l/min ], the set initial flow rate of ammonia decomposition gas was set to 19[ l/min ], the set initial flow rate of carbon monoxide gas was set to 0.2[ l/min ], x was 0.5, and c1 was 0.01. These set initial flow rates can be set and inputted in the parameter setting device 15. The stirring blade drive motor 9 is driven to rotate the stirring blade 8, thereby stirring the atmosphere in the processing furnace 2.

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 adjuster 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 rise or in a state in which temperature rise is completed (steady state).

The in-furnace nitriding potential calculating device 13 of the nitriding potential adjusting gauge 4 calculates the nitriding potential in the furnace (which is initially an extremely high value (due to the absence of hydrogen in the furnace), but gradually decreases as the ammonia gas is decomposed (hydrogen is generated)), and determines whether or not the value is lower than the sum of the target nitriding potential (0.6 in this example) and the reference deviation value. The reference deviation value can also be set as an input in the parameter setting means 15, for example 0.1.

The in-furnace nitriding potential calculation device 13 of the nitriding potential adjustment meter 4 calculates the in-furnace nitriding potential based on the input hydrogen concentration signal or ammonia concentration signal and oxygen concentration signal. The gas flow output adjusting means 30 performs PID control in which the nitriding potential calculated by the in-furnace nitriding potential calculating means 13 is set as an output value, the target nitriding potential (set nitriding potential) is set as a target value, and the introduction amounts of the ammonia gas and the carbon monoxide gas in the three kinds of in-furnace introduction gases are set as input values. Specifically, in the PID control, the amount of ammonia gas and carbon monoxide gas introduced is changed while keeping the amount of ammonia decomposition gas introduced constant, thereby controlling the nitriding potential in the processing furnace 2 to approach the target nitriding potential and maintaining the relationship of C1 ═ C1 × (a + x × B). In the PID control, each setting parameter value set and inputted by the parameter setting device 15 is used. The set parameter value may be different depending on the value of the target nitride potential.

Further, as a result of the PID control, the gas introduction amount control unit 14 controls the introduction amount of the ammonia gas and the introduction amount of the carbon monoxide gas. In order to realize the determined introduction amount of each gas, the gas introduction amount control unit 14 sends control signals to the 1 st supply amount control device 22 for ammonia gas, the 2 nd supply amount control device 26 (constant supply amount) for ammonia decomposition gas, and the 3 rd supply amount control device 62 for carbon monoxide gas.

By the above control, the in-furnace nitriding potential can be stably controlled to be in the vicinity of the target nitriding potential. This enables the surface hardening treatment of the workpiece S to be performed with extremely high quality. Specifically, the nitrogen potential can be controlled to the target nitrogen potential (0.6) with extremely high accuracy from the time point of about 20 minutes after the start of the treatment by increasing or decreasing the amount of ammonia gas introduced within a fluctuation range of about 3ml (± 1.5ml) by feedback control with a sampling time of about several hundred milliseconds.

(action: example 2-2)

Next, as example 2-2, a case where the target nitriding potential is set to 0.4 by using the surface hardening treatment apparatus according to embodiment 2 will be described. In this example 2-2, the dimensions were also used

In the heating of the processing furnace 2, ammonia gas, ammonia decomposition gas, and carbon monoxide gas are introduced into the processing furnace 2 from the furnace introduction gas supply portion 20 at a set initial flow rate. Here, as shown in fig. 8, the set initial flow rate of ammonia gas is 3 l/min, the set initial flow rate of ammonia decomposition gas is 25 l/min, the set initial flow rate of carbon monoxide gas is 0.15 l/min, x is 0.5, and c1 is 0.01. These set initial flow rates can be set and inputted in the parameter setting device 15. The stirring blade drive motor 9 is driven to rotate the stirring blade 8, thereby stirring the atmosphere in the processing furnace 2.

When it is determined that the temperature rise is completed and it is determined that the calculated value of the in-furnace nitriding potential is lower than the sum of the target nitriding potential and the reference deviation value (0.5 in this example), the nitriding potential adjuster 4 starts the control of the amount of the in-furnace introduced gas by 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.

By the above control, as shown in fig. 9, the in-furnace nitriding potential can be stably controlled to be in the vicinity of the target nitriding potential. This enables the surface hardening treatment of the workpiece S to be performed with extremely high quality. Specifically, the nitrogen potential can be controlled to the target nitrogen potential (0.4) with extremely high accuracy from the time point of about 20 minutes after the start of the treatment by increasing or decreasing the amount of ammonia gas introduced within a fluctuation range of about 3ml (± 1.5ml) by feedback control with a sampling time of about several hundred milliseconds.

(action: examples 2 to 3)

Next, as example 2-3, a case where the target nitriding potential is set to 0.2 by using the surface hardening treatment apparatus according to embodiment 2 will be described. In examples 2 to 3, the dimensions were also used

In the heating of the processing furnace 2, ammonia gas, ammonia decomposition gas, and carbon monoxide gas are introduced into the processing furnace 2 from the furnace introduction gas supply portion 20 at a set initial flow rate. Here, the set initial flow rate of ammonia gas is 1[ liter/minute ], the set initial flow rate of ammonia decomposition gas is 29[ liter/minute ], the set initial flow rate of carbon monoxide gas is 0.15[ liter/minute ], x is 0.5, and c1 is 0.01. These set initial flow rates can be set and inputted in the parameter setting device 15. The stirring blade drive motor 9 is driven to rotate the stirring blade 8, thereby stirring the atmosphere in the processing furnace 2.

The in-furnace nitriding potential calculating device 13 of the nitriding potential adjusting meter 4 calculates the nitriding potential in the furnace (which is initially an extremely high value (due to the absence of hydrogen in the furnace), but gradually decreases as the decomposition of ammonia gas proceeds (hydrogen is generated)), and determines whether or not the value is lower than the sum of the target nitriding potential (0.3 in this example) and the reference deviation value. The reference deviation value can also be set as an input in the parameter setting means 15, for example 0.1.

When it is determined that the temperature rise is completed and it is determined that the calculated value of the in-furnace nitriding potential is lower than the sum of the target nitriding potential and the reference deviation value (0.4 in this example), the nitriding potential adjusting gauge 4 starts the control of the amount of the in-furnace introduced gas by 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.

A furnace nitriding potential calculating device 13 of the nitriding potential adjusting meter 4 calculates the furnace nitriding potential based on the input hydrogen concentration signal or ammonia concentration signal and oxygen concentration signal. The gas flow output adjusting means 30 performs PID control in which the nitriding potential calculated by the in-furnace nitriding potential calculating means 13 is set as an output value, the target nitriding potential (set nitriding potential) is set as a target value, and the introduction amounts of the ammonia gas and the carbon monoxide gas in the three kinds of in-furnace introduction gases are set as input values. Specifically, in the PID control, the amount of ammonia gas and carbon monoxide gas introduced is changed while keeping the amount of ammonia decomposition gas introduced constant, thereby controlling the nitriding potential in the processing furnace 2 to approach the target nitriding potential and maintaining the relationship of C1 ═ C1 × (a + x × B). In the PID control, each setting parameter value set and inputted by the parameter setting device 15 is used. The set parameter value may be different depending on the value of the target nitride potential.

By the above control, the in-furnace nitriding potential can be stably controlled to be in the vicinity of the target nitriding potential. This enables the surface hardening treatment of the workpiece S to be performed with extremely high quality. Specifically, the nitrogen potential can be controlled to the target nitrogen potential (0.2) with extremely high accuracy from about 30 minutes after the start of the treatment by increasing or decreasing the amount of ammonia gas introduced within a range of about 3ml (± 1.5ml) by feedback control with a sampling time of about several hundred milliseconds.

(description of comparative examples)

For comparison, the following control of the nitridation potential was performed: the flow ratio of ammonia gas to carbon monoxide gas was always maintained at 99: 1, changing their total flow rate.

Specifically, the in-furnace nitriding potential calculation device 13 of the nitriding potential adjustment meter 4 calculates the in-furnace nitriding potential based on the input hydrogen concentration signal or ammonia concentration signal and oxygen concentration signal. The gas flow rate output adjusting means 30 performs PID control in which the nitriding potential calculated by the in-furnace nitriding potential calculating means 13 is set as an output value, the target nitriding potential (set nitriding potential) is set as a target value, and the introduction amounts of the ammonia gas and the carbon monoxide gas are set as input values. More specifically, in the PID control, the total introduction amount of the ammonia gas and the carbon monoxide gas is changed while keeping the flow ratio of the ammonia gas to the carbon dioxide constant, thereby performing control for bringing the nitriding potential in the processing furnace 2 close to the target nitriding potential.

(example 2-1 to example 2-3 comparison with comparative example)

Fig. 10 shows the above results in a summary.

(constitution of embodiment 3)

As shown in fig. 11, the furnace introduced gas supply unit 20' of embodiment 3 further includes a 4 th furnace introduced gas supply unit 71 for nitrogen gas, a 4 th supply amount control device 72, a 4 th supply valve 73, and a 4 th flow meter 74.

The 4 th furnace introduction gas supply portion 71 is formed of, for example, a tank filled with the 4 th furnace introduction gas (nitrogen gas).

The 4 th supply amount control device 72 is formed of a mass flow controller (capable of changing the flow rate little by little in a short time), and is interposed between the 4 th furnace introduction gas supply portion 71 and the 4 th supply valve 73. The opening degree of the 4 th supply amount control device 72 is changed in accordance with the control signal output from the gas introduction amount control unit 14. The 4 th supply amount control device 72 detects the supply amount from the 4 th furnace introduction gas supply portion 71 to the 4 th supply valve 73, and outputs an information signal including the detected supply amount to the gas introduction control unit 14 and the adjustment meter 6. This control signal can be used for correction of control by the gas introduction amount control unit 14, and the like.

The 4 th supply valve 73 is formed by an electromagnetic valve that switches its open/closed state in accordance with a control signal output from the gas introduction amount control unit 14, and the 4 th supply valve 73 is interposed between the 4 th supply amount control device 72 and the 4 th flow meter 74.

The 4 th flow meter 74 is formed of a mechanical flow meter such as a flow meter, and is interposed between the 4 th supply valve 73 and the furnace introduction gas introduction pipe 29. The 4 th flow meter 74 detects the supply amount of the gas introduced into the furnace from the 4 th supply valve 73 to the gas introduction pipe 29. The supply amount detected by the 4 th flow meter 74 can be used for confirmation operation by visual observation of the operator.

In embodiment 3, when the furnace introduction amount of ammonia gas a and the furnace introduction amount of ammonia decomposition gas B, x are defined as constants, the furnace introduction amount of carbon dioxide C1 and the furnace introduction amount of nitrogen gas C2, which are furnace introduction gases other than ammonia gas and ammonia decomposition gas, are controlled by the proportional coefficients C1 and C2, respectively allocated to the furnace introduction amounts of ammonia gas a and ammonia decomposition gas a and B, x

C1＝c1×(A+x×B)

C2＝c2×(A+x×B)。

The other structure of the present embodiment is substantially the same as that of embodiment 1 described with reference to fig. 1. In fig. 11, the same portions as those in embodiment 1 are denoted by the same reference numerals. In this embodiment, the same portions as those in embodiment 1 will not be described in detail.

(action: example 3-1)

Next, as example 3-1, a case where the target nitriding potential is set to 1.0 by using the surface hardening treatment apparatus according to embodiment 3 will be described. In this example 3-1, the dimensions were also used

During heating in the treatment furnace 2, ammonia gas, ammonia decomposition gas, carbon dioxide gas and nitrogen gas are introduced into the treatment furnace 2 from the furnace introduction gas supply part 20' at a set initial flow rate. Here, the set initial flow rate of ammonia gas is set to 13[ l/min ], the set initial flow rate of ammonia decomposition gas is set to 19[ l/min ], the set initial flow rate of carbon dioxide is set to 2.2[ l/min ], the set initial flow rate of nitrogen gas is set to 20[ l/min ], x is 0.5, c1 is 0.1, and c2 is 0.9. These set initial flow rates can be set and inputted in the parameter setting device 15. The stirring blade drive motor 9 is driven to rotate the stirring blade 8, thereby stirring the atmosphere in the processing furnace 2.

The in-furnace nitriding potential calculating device 13 of the nitriding potential adjusting gauge 4 calculates the nitriding potential in the furnace (which is initially an extremely high value (due to the absence of hydrogen in the furnace), but gradually decreases as the ammonia gas is decomposed (hydrogen is generated)), and determines whether or not the value is lower than the sum of the target nitriding potential (1.0 in the present example) and the reference deviation value. The reference deviation value can also be set as an input in the parameter setting means 15, for example 0.1.

When it is determined that the temperature rise is completed and it is determined that 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 adjusting gauge 4 starts the control of the amount of the in-furnace introduced gas by 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 calculation device 13 of the nitriding potential adjustment meter 4 calculates the in-furnace nitriding potential based on the input hydrogen concentration signal or ammonia concentration signal and oxygen concentration signal. The gas flow output adjusting means 30 performs PID control in which the nitriding potential calculated by the in-furnace nitriding potential calculating means 13 is set as an output value, the target nitriding potential (set nitriding potential) is set as a target value, and the respective introduction amounts of ammonia, carbon dioxide, and nitrogen in the four kinds of in-furnace introduction gases are set as input values. Specifically, in the PID control, the amount of ammonia gas, carbon dioxide gas, and nitrogen gas introduced is changed while keeping the amount of ammonia decomposition gas introduced constant, thereby controlling the nitriding potential in the treatment furnace 2 to approach the target nitriding potential while maintaining the relationship between C1 ═ C1 × (a + x × B) and C2 ═ C2 × (a + x × B). In the PID control, each setting parameter value set and inputted by the parameter setting device 15 is used. The set parameter value may be different depending on the value of the target nitride potential.

Further, as a result of the PID control, the gas introduction amount control unit 14 controls the introduction amount of ammonia, the introduction amount of carbon dioxide, and the introduction amount of nitrogen. In order to realize the determined introduction amount of each gas, the gas introduction amount control unit 14 sends control signals to the 1 st supply amount control device 22 for ammonia gas, the 2 nd supply amount control device 26 for ammonia decomposition gas (constant supply amount), the 3 rd supply amount control device 62 for carbon dioxide gas, and the 4 th supply amount control device 72 for nitrogen gas.

By the above control, the in-furnace nitriding potential can be stably controlled to be in the vicinity of the target nitriding potential. This enables the surface hardening treatment of the workpiece S to be performed with extremely high quality. Specifically, the nitrogen potential can be controlled to the target nitrogen potential (1.0) with extremely high accuracy from the time point of about 20 minutes after the start of the treatment by increasing or decreasing the amount of ammonia gas introduced within a fluctuation range of about 3ml (± 1.5ml) by feedback control with a sampling time of about several hundred milliseconds.

(action: example 3-2)

Next, as example 3-2, a case where the target nitriding potential is set to 0.6 by using the surface hardening treatment apparatus according to embodiment 3 will be described. In this example 3-2, the dimensions were also used

The shaft furnace as the treatment furnace 2 is heated to a temperatureSet at 570 ℃, using a temperature of 4m ² The surface area of the steel material of (3) is defined as the workpiece S.

During heating in the treatment furnace 2, ammonia gas, ammonia decomposition gas, carbon dioxide gas and nitrogen gas are introduced into the treatment furnace 2 from the furnace introduction gas supply part 20' at a set initial flow rate. Here, as shown in fig. 12, the set initial flow rate of ammonia gas is set to 8 l/min, the set initial flow rate of ammonia decomposition gas is set to 25 l/min, the set initial flow rate of carbon dioxide is set to 2 l/min, the set initial flow rate of nitrogen gas is set to 18.5 l/min, x is 0.5, c1 is 0.1, and c2 is 0.9. These set initial flow rates can be set and inputted in the parameter setting device 15. The stirring blade drive motor 9 is driven to rotate the stirring blade 8, thereby stirring the atmosphere in the processing furnace 2.

By the above control, as shown in fig. 13, the in-furnace nitriding potential can be stably controlled to be in the vicinity of the target nitriding potential. This enables the surface hardening treatment of the workpiece S to be performed with extremely high quality. Specifically, the nitrogen potential can be controlled to the target nitrogen potential (0.6) with extremely high accuracy from about 30 minutes after the start of the treatment by increasing or decreasing the amount of ammonia gas introduced within a range of about 3ml (± 1.5ml) by feedback control with a sampling time of about several hundred milliseconds.

(action: example 3-3)

Next, as example 3-3, a case where the target nitriding potential is set to 0.2 by using the surface hardening treatment apparatus according to embodiment 3 will be described. In this example 3-3, the dimensions were also used

During heating in the treatment furnace 2, ammonia gas, ammonia decomposition gas, carbon dioxide gas and nitrogen gas are introduced into the treatment furnace 2 from the furnace introduction gas supply part 20' at a set initial flow rate. Here, the set initial flow rate of ammonia gas is 3 l/min, the set initial flow rate of ammonia decomposition gas is 29 l/min, the set initial flow rate of carbon dioxide is 1.8 l/min, the set initial flow rate of nitrogen gas is 15.8 l/min, x is 0.5, c1 is 0.1, and c2 is 0.9. These set initial flow rates can be set and inputted in the parameter setting device 15. The stirring blade drive motor 9 is driven to rotate the stirring blade 8, thereby stirring the atmosphere in the processing furnace 2.

The in-furnace nitriding potential calculating device 13 of the nitriding potential adjusting gauge 4 calculates the nitriding potential in the furnace (which is initially an extremely high value (due to the absence of hydrogen in the furnace), but gradually decreases as the ammonia gas is decomposed (hydrogen is generated)), and determines whether or not the value is lower than the sum of the target nitriding potential (0.2 in this example) and the reference deviation value. The reference deviation value can also be set as an input in the parameter setting device 15, for example, 0.1.

When it is determined that the temperature rise is completed and it is determined that 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 adjuster 4 starts the control of the amount of the in-furnace introduced gas by 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.

By the above control, the in-furnace nitriding potential can be stably controlled to be in the vicinity of the target nitriding potential. This enables the surface hardening treatment of the workpiece S to be performed with extremely high quality. Specifically, the nitrogen potential can be controlled to the target nitrogen potential (0.2) with extremely high accuracy from about 40 minutes after the start of the treatment by increasing or decreasing the amount of ammonia gas introduced within a range of about 3ml (± 1.5ml) by feedback control with a sampling time of about several hundred milliseconds.

(description of comparative example)

For comparison, the following control of the nitridation potential was performed: the flow ratio of ammonia gas, nitrogen gas and carbon dioxide was always maintained at 50: 45: 5, changing their total flow rate.

Specifically, the in-furnace nitriding potential calculation device 13 of the nitriding potential adjustment meter 4 calculates the in-furnace nitriding potential based on the input hydrogen concentration signal or ammonia concentration signal and oxygen concentration signal. The gas flow output adjusting means 30 performs PID control in which the nitriding potential calculated by the in-furnace nitriding potential calculating means 13 is set as an output value, the target nitriding potential (set nitriding potential) is set as a target value, and the respective introduction amounts of ammonia, nitrogen, and carbon dioxide are set as input values. More specifically, in the PID control, the total introduction amount of ammonia, nitrogen and carbon dioxide is changed while keeping the flow ratio of ammonia, nitrogen and carbon dioxide constant, thereby performing control for bringing the nitriding potential in the processing furnace 2 close to the target nitriding potential.

(example 3-1 to example 3-3 comparison with comparative example)

Fig. 14 shows the above results in a summary.

(constitution of embodiment 4)

As shown in fig. 15, in embodiment 4, the 3 rd furnace introduction gas supply portion 61' is formed by a tank filled with carbon monoxide gas instead of carbon dioxide.

In embodiment 4, when the furnace introduction amount of ammonia gas a and the furnace introduction amount of ammonia decomposition gas B, x are defined as constants, the introduction amount of carbon monoxide gas C1 and the introduction amount of nitrogen gas C2, which are furnace introduction gases other than ammonia gas and ammonia decomposition gas, are controlled to C1 ═ C1 × (a + x × B) by using the proportional coefficients C1 and C2 respectively allocated to the furnace introduction amounts

C2＝c2×(A+x×B)。

The other structure of the present embodiment is substantially the same as that of embodiment 1 described with reference to fig. 1. In fig. 15, the same portions as those in embodiment 3 are denoted by the same reference numerals. In this embodiment, the same portions as those in embodiment 3 are not described in detail.

(action: example 4-1)

Next, as example 4-1, a case where the target nitriding potential is set to 1.0 by using the surface hardening treatment apparatus according to embodiment 4 will be described. In this example 4-1, the dimensions were also used

In the heating of the processing furnace 2, ammonia gas, ammonia decomposition gas, carbon monoxide gas and nitrogen gas are introduced into the processing furnace 2 from the furnace introduction gas supply part 20' at a set initial flow rate. Here, the set initial flow rate of ammonia gas was set to 13 l/min, the set initial flow rate of ammonia decomposition gas was set to 19 l/min, the set initial flow rate of carbon monoxide gas was set to 0.9 l/min, the set initial flow rate of nitrogen gas was set to 20 l/min, x was 0.5, c1 was 0.04, and c2 was 0.96. These set initial flow rates can be set and inputted in the parameter setting device 15. The stirring blade driving motor 9 is driven to rotate the stirring blade 8, thereby stirring the atmosphere in the processing furnace 2.

The in-furnace nitriding potential calculation device 13 of the nitriding potential adjustment meter 4 calculates the in-furnace nitriding potential based on the input hydrogen concentration signal or ammonia concentration signal and oxygen concentration signal. The gas flow output adjusting means 30 performs PID control in which the nitriding potential calculated by the in-furnace nitriding potential calculating means 13 is set as an output value, the target nitriding potential (set nitriding potential) is set as a target value, and the respective introduction amounts of the ammonia gas, the carbon monoxide gas, and the nitrogen gas in the four kinds of in-furnace introduction gases are set as input values. Specifically, in the PID control, the amount of ammonia gas, carbon monoxide gas, and nitrogen gas introduced is changed while keeping the amount of ammonia decomposition gas constant, thereby controlling the nitriding potential in the processing furnace 2 to approach the target nitriding potential while maintaining the relationship between C1 ═ C1 × (a + x × B) and C2 ═ C2 × (a + x × B). In the PID control, each setting parameter value set and input by the parameter setting device 15 is used. The set parameter value may be different depending on the value of the target nitride potential.

Further, as a result of the PID control, the gas introduction amount control unit 14 controls the introduction amount of ammonia gas, the introduction amount of carbon monoxide gas, and the introduction amount of nitrogen gas. In order to realize the determined introduction amount of each gas, the gas introduction amount control unit 14 sends control signals to the 1 st supply amount control device 22 for ammonia gas, the 2 nd supply amount control device 26 for ammonia decomposition gas (constant supply amount), the 3 rd supply amount control device 62 for carbon monoxide gas, and the 4 th supply amount control device 72 for nitrogen gas.

By the above control, the in-furnace nitriding potential can be stably controlled to be in the vicinity of the target nitriding potential. This enables the surface hardening treatment of the workpiece S to be performed with extremely high quality. Specifically, the nitrogen potential can be controlled to the target nitrogen potential (1.0) with extremely high accuracy from about 30 minutes after the start of the treatment by increasing or decreasing the amount of ammonia gas introduced within a range of about 3ml (± 1.5ml) by feedback control with a sampling time of about several hundred milliseconds.

(action: example 4-2)

Next, as example 4-2, a case where the target nitriding potential is set to 0.6 by using the surface hardening treatment apparatus according to embodiment 4 will be described. In this example 4-2, the dimensions were also used

In the heating of the processing furnace 2, ammonia gas, ammonia decomposition gas, carbon monoxide gas and nitrogen gas are introduced into the processing furnace 2 from the furnace introduction gas supply part 20' at a set initial flow rate. Here, as shown in fig. 12, the set initial flow rate of ammonia gas is set to 8 l/min, the set initial flow rate of ammonia decomposition gas is set to 25 l/min, the set initial flow rate of carbon monoxide gas is set to 0.8 l/min, the set initial flow rate of nitrogen gas is set to 19.7 l/min, x is 0.5, c1 is 0.04, and c2 is 0.96. These set initial flow rates can be set and inputted in the parameter setting device 15. The stirring blade driving motor 9 is driven to rotate the stirring blade 8, thereby stirring the atmosphere in the processing furnace 2.

The in-furnace nitriding potential calculation device 13 of the nitriding potential adjustment meter 4 calculates the in-furnace nitriding potential based on the input hydrogen concentration signal or ammonia concentration signal and oxygen concentration signal. The gas flow output adjusting means 30 performs PID control in which the nitriding potential calculated by the in-furnace nitriding potential calculating means 13 is set as an output value, the target nitriding potential (set nitriding potential) is set as a target value, and the respective introduction amounts of the ammonia gas, the carbon monoxide gas, and the nitrogen gas in the four kinds of in-furnace introduction gases are set as input values. Specifically, in the PID control, the amount of ammonia gas, carbon monoxide gas, and nitrogen gas introduced is changed while keeping the amount of ammonia decomposition gas constant, thereby controlling the nitriding potential in the processing furnace 2 to approach the target nitriding potential while maintaining the relationship between C1 ═ C1 × (a + x × B) and C2 ═ C2 × (a + x × B). In the PID control, each setting parameter value set and input by the parameter setting device 15 is used. The set parameter value may vary depending on the value of the target nitridation potential.

By the above control, as shown in fig. 13, the in-furnace nitriding potential can be stably controlled to be in the vicinity of the target nitriding potential. This enables the surface hardening treatment of the workpiece S to be performed with extremely high quality. Specifically, the nitrogen potential can be controlled to the target nitrogen potential (0.6) with extremely high accuracy from about 40 minutes after the start of the treatment by increasing or decreasing the amount of ammonia gas introduced within a range of about 3ml (± 1.5ml) by feedback control with a sampling time of about several hundred milliseconds.

(action: example 4-3)

Next, as example 4-3, a case where the target nitriding potential is set to 0.2 by using the surface hardening treatment apparatus according to embodiment 4 will be described. In this example 4-3, the dimensions were also used

In the heating of the processing furnace 2, ammonia gas, ammonia decomposition gas, carbon monoxide gas and nitrogen gas are introduced into the processing furnace 2 from the furnace introduction gas supply part 20' at a set initial flow rate. Here, the set initial flow rate of ammonia gas was 3 l/min, the set initial flow rate of ammonia decomposition gas was 29 l/min, the set initial flow rate of carbon monoxide gas was 0.7 l/min, the set initial flow rate of nitrogen gas was 16 l/min, x was 0.5, c1 was 0.04, and c2 was 0.96. These set initial flow rates can be set and inputted in the parameter setting device 15. The stirring blade drive motor 9 is driven to rotate the stirring blade 8, thereby stirring the atmosphere in the processing furnace 2.

The in-furnace nitriding potential calculating device 13 of the nitriding potential adjusting gauge 4 calculates the nitriding potential in the furnace (which is initially an extremely high value (due to the absence of hydrogen in the furnace), but gradually decreases as the ammonia gas is decomposed (hydrogen is generated)), and determines whether or not the value is lower than the sum of the target nitriding potential (0.2 in this example) and the reference deviation value. The reference deviation value can also be set as an input in the parameter setting means 15, for example 0.1.

The in-furnace nitriding potential calculation device 13 of the nitriding potential adjustment meter 4 calculates the in-furnace nitriding potential based on the input hydrogen concentration signal or ammonia concentration signal and oxygen concentration signal. The gas flow output adjusting means 30 performs PID control in which the nitriding potential calculated by the in-furnace nitriding potential calculating means 13 is set as an output value, the target nitriding potential (set nitriding potential) is set as a target value, and the respective introduction amounts of the ammonia gas, the carbon monoxide gas, and the nitrogen gas in the four kinds of in-furnace introduction gases are set as input values. Specifically, in the PID control, the amount of ammonia gas, carbon monoxide gas, and nitrogen gas introduced is changed while keeping the amount of ammonia decomposition gas constant, thereby controlling the nitriding potential in the processing furnace 2 to approach the target nitriding potential while maintaining the relationship between C1 ═ C1 × (a + x × B) and C2 ═ C2 × (a + x × B). In the PID control, each setting parameter value set and inputted by the parameter setting device 15 is used. The set parameter value may be different depending on the value of the target nitride potential.

(description of comparative example)

For comparison, the following control of the nitridation potential was performed: the flow ratio of ammonia gas, nitrogen gas and carbon monoxide gas was always maintained at 50: 48: 2, varying their total flow rate.

Specifically, the in-furnace nitriding potential calculation device 13 of the nitriding potential adjustment meter 4 calculates the in-furnace nitriding potential based on the input hydrogen concentration signal or ammonia concentration signal and oxygen concentration signal. The gas flow rate output adjusting means 30 performs PID control in which the nitriding potential calculated by the in-furnace nitriding potential calculating means 13 is set as an output value, the target nitriding potential (set nitriding potential) is set as a target value, and the respective introduction amounts of the ammonia gas, the nitrogen gas, and the carbon monoxide gas are set as input values. More specifically, in the PID control, the total introduction amount of the ammonia gas, the nitrogen gas, and the carbon monoxide gas is changed while keeping the flow ratio of the ammonia gas, the nitrogen gas, and the carbon monoxide gas constant, thereby performing control for bringing the nitriding potential in the processing furnace 2 close to the target nitriding potential.

(example 4-1 to example 4-3 comparison with comparative example)

Fig. 16 shows the above results in a summary.

(constitution of embodiment 5)

As shown in fig. 17, the furnace introduced gas supply unit 20 ″ of embodiment 5 further includes a 5 th furnace introduced gas supply unit 81 for carbon dioxide, a 5 th supply amount control device 82, a 5 th supply valve 83, and a 5 th flow meter 84 in addition to the furnace introduced gas supply unit 20' of embodiment 4.

The 5 th furnace introduction gas supply part 81 is formed of, for example, a tank filled with a 5 th furnace introduction gas (carbon dioxide).

The 5 th supply amount control device 82 is formed of a mass flow controller (capable of changing the flow rate little by little in a short time), and is interposed between the 5 th furnace introduction gas supply portion 81 and the 5 th supply valve 83. The opening degree of the 5 th supply amount control device 82 is changed in accordance with the control signal output from the gas introduction amount control unit 14. The 5 th supply amount control device 82 detects the supply amount from the 5 th furnace introduction gas supply unit 81 to the 5 th supply valve 83, and outputs an information signal including the detected supply amount to the gas introduction control unit 14 and the regulator 6. This control signal can be used for correction of control by the gas introduction amount control unit 14, and the like.

The 5 th supply valve 83 is formed by an electromagnetic valve that switches its open and closed states in accordance with a control signal output from the gas introduction amount control unit 14, and the 5 th supply valve 83 is interposed between the 5 th supply amount control device 82 and the 5 th flow meter 84.

The 5 th flow meter 84 is formed of, for example, a mechanical flow meter such as a flow meter, and is interposed between the 5 th supply valve 83 and the furnace introduced gas introduction pipe 29. The 5 th flow meter 84 detects the supply amount of the introduced gas into the furnace 29 from the 5 th supply valve 83. The supply amount detected by the 5 th flow meter 84 can be used for confirmation operation by visual observation of the operator.

In embodiment 5, when the furnace introduction amount of ammonia gas a and the furnace introduction amount of ammonia decomposition gas B, x are predetermined constants, the introduction amount of carbon monoxide gas C1, the introduction amount of nitrogen gas C2, and the introduction amount of carbon dioxide C3, which are furnace introduction gases other than ammonia gas and ammonia decomposition gas, are controlled by the proportional coefficients C1, C2, and C3, which are distributed respectively, so that the introduction amounts of ammonia gas, and ammonia decomposition gas are controlled to be equal to each other

C1＝c1×(A+x×B)

C2＝c2×(A+x×B)

C3＝c3×(A+x×B)。

The other structure of the present embodiment is substantially the same as that of embodiment 4 described with reference to fig. 15. In fig. 17, the same portions as those in embodiment 4 are denoted by the same reference numerals. In this embodiment, the same portions as those in embodiment 4 will not be described in detail.

(action: example 5-1)

Next, as example 5-1, a case where the target nitriding potential is set to 1.0 by using the surface hardening treatment apparatus according to embodiment 5 will be described. In this example 5-1, the dimensions were also used

In the heating of the processing furnace 2, ammonia gas, ammonia decomposition gas, carbon monoxide gas, nitrogen gas, and carbon dioxide gas are introduced into the processing furnace 2 from the furnace introduction gas supply portion 20 ″ at a set initial flow rate. Here, the set initial flow rate of ammonia gas was set to 13[ l/min ], the set initial flow rate of ammonia decomposition gas was set to 19[ l/min ], the set initial flow rate of carbon monoxide gas was set to 0.45[ l/min ], the set initial flow rate of nitrogen gas was set to 21[ l/min ], the set initial flow rate of carbon dioxide was set to 0.9[ l/min ], x was 0.5, c1 was 0.02, c2 was 0.94, and c3 was 0.04. These set initial flow rates can be set and inputted in the parameter setting device 15. The stirring blade drive motor 9 is driven to rotate the stirring blade 8, thereby stirring the atmosphere in the processing furnace 2.

The in-furnace nitriding potential calculation device 13 of the nitriding potential adjustment meter 4 calculates the in-furnace nitriding potential based on the input hydrogen concentration signal or ammonia concentration signal and oxygen concentration signal. The gas flow output adjusting means 30 performs PID control in which the nitriding potential calculated by the in-furnace nitriding potential calculating means 13 is set as an output value, the target nitriding potential (set nitriding potential) is set as a target value, and the introduction amounts of the ammonia gas, the carbon monoxide gas, the nitrogen gas, and the carbon dioxide gas in the five kinds of in-furnace introduction gases are set as input values. Specifically, in the PID control, the amount of ammonia gas, carbon monoxide gas, nitrogen gas, and carbon dioxide gas introduced is changed while keeping the amount of ammonia decomposition gas introduced constant, thereby controlling the nitriding potential in the processing furnace 2 to approach the target nitriding potential while maintaining the relationships of C1 ═ C1 × (a + x × B), C2 ═ C2 × (a + x × B), and C3 ═ C3 × (a + x × B). In the PID control, each setting parameter value set and inputted by the parameter setting device 15 is used. The set parameter value may be different depending on the value of the target nitride potential.

Further, as a result of the PID control, the gas introduction amount control unit 14 controls the introduction amount of ammonia gas, the introduction amount of carbon monoxide gas, the introduction amount of nitrogen gas, and the introduction amount of carbon dioxide gas. In order to realize the determined introduction amount of each gas, the gas introduction amount control unit 14 sends control signals to the 1 st supply amount control device 22 for ammonia gas, the 2 nd supply amount control device 26 for ammonia decomposition gas (constant supply amount), the 3 rd supply amount control device 62 for carbon monoxide gas, the 4 th supply amount control device 72 for nitrogen gas, and the 5 th supply amount control device 82 for carbon dioxide gas.

(action: example 5-2)

Next, as example 5-2, a case where the target nitriding potential is set to 0.6 by using the surface hardening treatment apparatus according to embodiment 5 will be described. In this example 5-2, the dimensions were also used

In the heating of the processing furnace 2, ammonia gas, ammonia decomposition gas, carbon monoxide gas, nitrogen gas, and carbon dioxide gas are introduced into the processing furnace 2 from the furnace introduction gas supply portion 20 ″ at a set initial flow rate. Here, the set initial flow rate of ammonia gas is 12[ l/min ], the set initial flow rate of ammonia decomposition gas is 25[ l/min ], the set initial flow rate of carbon monoxide gas is 0.5[ l/min ], the set initial flow rate of nitrogen gas is 23[ l/min ], the set initial flow rate of carbon dioxide is 1.0[ l/min ], x is 0.5, c1 is 0.02, c2 is 0.94, and c3 is 0.04. These set initial flow rates can be set and inputted in the parameter setting device 15. The stirring blade drive motor 9 is driven to rotate the stirring blade 8, thereby stirring the atmosphere in the processing furnace 2.

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

By the above control, the in-furnace nitriding potential can be stably controlled to be in the vicinity of the target nitriding potential. This enables the surface hardening treatment of the workpiece S to be performed with extremely high quality. Specifically, the nitrogen potential can be controlled to the target nitrogen potential (0.6) with extremely high accuracy from about 40 minutes after the start of the treatment by increasing or decreasing the amount of ammonia gas introduced within a range of about 3ml (± 1.5ml) by feedback control with a sampling time of about several hundred milliseconds.

(action: example 5-3)

Next, as example 5-3, a case where the target nitriding potential is set to 0.2 by using the surface hardening treatment apparatus according to embodiment 5 will be described. In this example 5-3, the dimensions were also used

In the heating of the processing furnace 2, ammonia gas, ammonia decomposition gas, carbon monoxide gas, nitrogen gas, and carbon dioxide gas are introduced into the processing furnace 2 from the furnace introduction gas supply part 20 ″ at a set initial flow rate. Here, the set initial flow rate of ammonia gas is 3 l/min, the set initial flow rate of ammonia decomposition gas is 29 l/min, the set initial flow rate of carbon monoxide gas is 0.3 l/min, the set initial flow rate of nitrogen gas is 16 l/min, the set initial flow rate of carbon dioxide is 0.6 l/min, x is 0.5, c1 is 0.02, c2 is 0.94, and c3 is 0.04. These set initial flow rates can be set and inputted in the parameter setting device 15. The stirring blade drive motor 9 is driven to rotate the stirring blade 8, thereby stirring the atmosphere in the processing furnace 2.

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 regulator 4 and the recorder 6. The nitriding potential controller 4 determines whether the temperature inside the processing furnace 2 is in the process of increasing the temperature or in a state in which the temperature is completely increased (a stable state).

When the opening/closing valve 17 is switched to the open state, the processing furnace 2 communicates with the atmosphere gas concentration detection device 3, and the furnace atmosphere gas concentration detection device 3 detects the furnace hydrogen concentration or the furnace ammonia concentration and also detects the oxygen concentration. The detected hydrogen concentration signal or ammonia concentration signal and oxygen concentration signal are output to the nitriding potential regulator 4 and the recorder 6.

(description of comparative example)

For comparison, the following control of the nitridation potential was performed: the flow ratio of ammonia gas, nitrogen gas, carbon monoxide gas and carbon dioxide was always maintained at 50: 47: 1: 2, varying their total flow rate.

Specifically, the in-furnace nitriding potential calculation device 13 of the nitriding potential adjustment meter 4 calculates the in-furnace nitriding potential based on the input hydrogen concentration signal or ammonia concentration signal and oxygen concentration signal. The gas flow output adjusting means 30 performs PID control in which the nitriding potential calculated by the in-furnace nitriding potential calculating means 13 is set as an output value, the target nitriding potential (set nitriding potential) is set as a target value, and the respective introduction amounts of ammonia gas, nitrogen gas, carbon monoxide gas, and carbon dioxide are set as input values. More specifically, in the PID control, the total introduction amount of ammonia gas, nitrogen gas, carbon monoxide gas, and carbon dioxide is changed while keeping the flow rate ratio of ammonia gas, nitrogen gas, and carbon monoxide gas to carbon dioxide constant, thereby performing control to bring the nitriding potential in the processing furnace 2 close to the target nitriding potential.

(example 5-1 to example 5-3 comparison with comparative example)

Fig. 18 shows the above results in a summary.

Description of the symbols

1 surface hardening treatment device

2 treatment furnace

3 atmosphere gas concentration detection device

4 nitriding potential regulator

5 temperature regulator

6 recorder

8 stirring blade

9 stirring blade driving motor

10 furnace temperature measuring device

11 furnace heating device

13 nitriding potential calculating device

14 gas introduction amount control device

15 parameter setting device (touch control panel)

16 open/close valve control device

17 opening and closing valve

20. 20' gas supply part in furnace

21 st furnace introduced gas supply part

22 st 1 furnace gas supply control device

23 st supply valve

24 st flowmeter

25 nd 2 nd furnace introduction gas supply part

27 nd 2 supply valve

28 nd 2 flowmeter

29 furnace inlet gas introduction pipe

30 gas flow output adjusting device

31 programmable logic controller

40 furnace gas waste piping

41 waste gas combustion decomposition device

61. 61' 3 rd furnace introduction gas supply part

62 rd 3 furnace gas supply control device

63 rd 3 supply valve

64 rd flow meter

71 No. 4 furnace-introduced gas supply part

72 th furnace gas supply control device

73 th 4 supply valve

74 th flowmeter

81 th 5 furnace introduced gas supply part

82 th 5 furnace gas supply control device

83 th 5 supply valve

84 th flowmeter

Claims

1. A surface hardening treatment apparatus for performing a surface hardening treatment of a workpiece disposed in a treatment furnace by introducing two or more kinds of furnace introduction gases including ammonia gas and an ammonia decomposition gas into the treatment furnace and performing a gas nitrocarburizing treatment,

it is provided with:

a furnace atmosphere gas concentration detection device for detecting a hydrogen concentration or an ammonia concentration in the processing furnace;

a furnace nitriding potential calculation device for calculating a nitriding potential in the processing furnace based on the hydrogen concentration or the ammonia concentration detected by the furnace atmosphere gas concentration detection device; and

and a gas introduction amount control device for changing an introduction amount of each of the at least two kinds of furnace introduction gases other than the ammonia decomposition gas, based on the target nitriding potential and the nitriding potential in the processing furnace calculated by the furnace nitriding potential calculation device, while keeping the introduction amount of the ammonia decomposition gas constant, thereby bringing the nitriding potential in the processing furnace close to the target nitriding potential.

2. The surface hardening treatment apparatus according to claim 1, further comprising a furnace oxygen concentration detection device for detecting an oxygen concentration in the treatment furnace,

the in-furnace nitriding potential calculation device calculates the nitriding potential in the treatment furnace based on the hydrogen concentration or the ammonia concentration detected by the in-furnace atmosphere gas concentration detection device and the oxygen concentration detected by the in-furnace oxygen concentration detection device.

3. The surface hardening treatment apparatus according to claim 1 or 2, wherein when the furnace introduction amount of ammonia gas is a and the furnace introduction amount of ammonia decomposition gas is B, x, the gas introduction amount control means controls the introduction amounts of the respective furnace introduction gases other than ammonia gas and ammonia decomposition gas, C1, … …, and cN, among the two or more kinds of furnace introduction gases, to C1 ═ C1 × (a + x × B), … …, and cN ═ cN × (a + x × B), where N is an integer of 1 or more, by using the proportionality coefficients C1, … …, and cN allocated to the respective furnace introduction gases.

4. The surface hardening apparatus according to claim 3, wherein the predetermined constant x is 0.4 to 0.6.

5. A surface hardening apparatus according to claim 4, wherein the prescribed constant x is 0.5.

6. The surface hardening apparatus according to any one of claims 1 to 5, wherein the two or more kinds of furnace-introduced gases include carbon dioxide.

7. The surface hardening apparatus according to any one of claims 1 to 5, wherein the two or more kinds of furnace-introduced gases include carbon monoxide gas.

8. The surface hardening apparatus according to any one of claims 1 to 5, wherein the two or more kinds of furnace-introduced gases include carbon dioxide and nitrogen.

9. The surface hardening apparatus according to any one of claims 1 to 5, wherein the two or more kinds of furnace-introduced gases include carbon monoxide gas and nitrogen gas.

10. A surface hardening treatment method for conducting a surface hardening treatment of a workpiece disposed in a treatment furnace by introducing a gas into the treatment furnace, the gas including at least two kinds of furnace introduction gases including ammonia gas and an ammonia decomposition gas, and conducting a gas nitrocarburizing treatment,

it is provided with:

a furnace atmosphere gas concentration detection step of detecting a hydrogen concentration or an ammonia concentration in the treatment furnace;

a 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 furnace atmosphere gas concentration detection device; and

and a gas introduction amount control step of changing an introduction amount of each of the furnace introduction gases other than the ammonia decomposition gas among the two or more kinds of furnace introduction gases while keeping the introduction amount of the ammonia decomposition gas constant, based on the target nitriding potential and the nitriding potential in the processing furnace calculated by the furnace nitriding potential calculation means, thereby bringing the nitriding potential in the processing furnace close to the target nitriding potential.

11. A surface hardening treatment apparatus for performing a surface hardening treatment of a workpiece disposed in a treatment furnace by introducing into the treatment furnace a furnace introduction gas containing at least two of ammonia gas, an ammonia decomposition gas and a carburizing gas, and performing a gas nitrocarburizing treatment,

it is provided with:

and a gas introduction amount control device for changing the introduction amounts of the ammonia gas and the carburizing gas while keeping the introduction amount of the ammonia decomposition gas constant, based on the nitriding potential in the processing furnace calculated by the furnace nitriding potential calculation device and a target nitriding potential, thereby bringing the nitriding potential in the processing furnace close to the target nitriding potential.

12. The surface hardening apparatus according to claim 11, wherein the gas introduction amount control means controls the introduction amount of the carburizing gas C1 to C1 ═ C1 × (a + x × B) by using a proportionality coefficient C1 assigned to the carburizing gas, when the furnace introduction amount of the ammonia gas a and the furnace introduction amount of the ammonia decomposition gas B, x are predetermined constants.

13. A surface hardening treatment apparatus for performing a surface hardening treatment of a workpiece disposed in a treatment furnace by introducing into the treatment furnace a furnace introduction gas containing at least two of ammonia gas, an ammonia decomposition gas, a carburizing gas, and a nitrogen gas, and performing a gas nitrocarburizing treatment,

it is provided with:

a furnace nitriding potential calculation device for calculating a nitriding potential in the treatment furnace based on the hydrogen concentration or the ammonia concentration detected by the furnace atmosphere gas concentration detection device; and

and a gas introduction amount control device for changing the introduction amounts of the ammonia gas, the carburizing gas, and the nitrogen gas while keeping the introduction amount of the ammonia decomposition gas constant, based on the nitriding potential in the processing furnace calculated by the furnace nitriding potential calculation device and a target nitriding potential, thereby bringing the nitriding potential in the processing furnace close to the target nitriding potential.

14. The surface hardening apparatus according to claim 13, wherein when the amount of ammonia gas introduced into the furnace is a and the amount of ammonia decomposition gas introduced into the furnace is B, x are predetermined constants, the gas introduction amount control means controls the amount of carburizing gas introduced, C1 and the amount of nitrogen gas introduced, C2, to C1 ═ C1 × (a + x × B) and C2 ═ C2 × (a + x × B) using the proportionality coefficient C1 assigned to the carburizing gas and the proportionality coefficient C2 assigned to the nitrogen gas.