JP3986995B2 - Metal ring nitriding equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for nitriding a metal ring made of maraging steel used for a continuously variable transmission belt or the like.
[0002]
[Prior art]
Conventionally, for transmission of power of a continuously variable transmission (CVT) such as an automobile, a CVT belt in which a plurality of metal rings are laminated to form a laminated ring, and the laminated ring is assembled and held in an element having a predetermined shape. Are known.
[0003]
The metal ring forming the laminated ring is made of low carbon steel containing Ni and Mo such as maraging steel. For example, the low carbon steel thin plate is cut into a rectangle, the thin plate is rounded along the long side, After the end portions on the side are welded to form a cylindrical drum, the drum is cut into a predetermined width to form an endless metal ring. And after rolling the said metal ring and making it the thickness of about 0.1-0.3 mm, it is manufactured by further correcting the circumference to a predetermined circumference.
[0004]
The maraging steel is a super-strength steel that can have both high strength and high toughness by heating at an appropriate temperature to cause age hardening in the martensite state, and is therefore used for the metal ring. However, when a CVT belt composed of a laminated ring in which the metal rings are laminated is used for power transmission of the CVT, the CVT belt is stretched between a pair of pulleys whose V-groove interval can be freely changed. Used. Therefore, the metal ring is in a straight state when the CVT belt travels between the pulleys, is in a curved state when traveling along the pulley, and is severely deformed by repeating the linear state and the curved state. Added.
[0005]
Therefore, the metal ring is required to further have wear resistance and fatigue resistance, and for this purpose, surface hardening treatment is performed on the metal ring after age hardening. The surface hardening treatment is generally performed by nitriding the metal ring and forming a nitride layer on the metal ring surface. Examples of the nitriding treatment include gas nitriding treatment and gas soft nitriding treatment.
[0006]
According to the gas nitriding treatment or the gas soft nitriding treatment, nitrogen generated by the decomposition of ammonia penetrates into the metal structure of maraging steel and forms a nitride layer on the surface of the metal ring to be hardened. As a result, the wear resistance and fatigue strength of the metal ring can be improved.
[0007]
In order to promote the decomposition of ammonia during the gas nitriding treatment or gas soft nitriding treatment to form a nitrided layer having excellent hardness, for example, a steel material is made of ammonia 40 to 90% by volume, oxygen 0.2%. There is known a technique of holding at a temperature of 500 to 600 ° C. for 120 to 360 hours in an atmosphere containing ˜3% by volume and the balance being nitrogen. The technique is used for nitriding of a steel material such as a plastic molding die. By performing nitriding under the above conditions, the nitride layer is formed to a depth of 0.25 mm from the surface, and the hardness is increased. It can be improved (see, for example, Patent Document 1).
[0008]
On the other hand, since the metal ring is desired to have excellent hardness on the surface and to retain high toughness even after forming the nitride layer, the metal ring includes a portion that is not nitrided inside the nitride layer. Need to be. However, according to the above-described technology for promoting the decomposition of ammonia and forming a nitride layer having excellent hardness, the nitride layer is formed to a depth of 0.25 mm from the surface. When applied to the metal ring having a thickness, the nitride layer is formed over the entire thickness of the metal ring, and it is difficult to maintain high toughness after the nitride layer is formed.
[0009]
In order to solve the above problem, the present applicant has determined that the thickness of the nitride layer formed on the surface of the metal ring by the gas nitriding process or the gas soft nitriding process is 20 to 20% of the total thickness of the metal belt. A patent application has already been filed for a technique for achieving 40% (see Patent Document 2). In the technique, the metal ring is held at a temperature in the range of 450 to 500 ° C. for 60 to 90 minutes under an atmosphere of ammonia and nitrogen or an atmosphere of ammonia and RX gas. According to the above technique, a portion that is not nitrided remains in the metal ring, so that a high toughness can be obtained in this portion. However, it is desired to further improve the toughness of the metal ring.
[0010]
[Patent Document 1]
JP-A-62-270761
[Patent Document 2]
JP 2000-337453 A
[0011]
[Problems to be solved by the invention]
An object of the present invention is to provide a nitriding apparatus capable of eliminating such inconvenience and imparting excellent hardness and toughness to a metal ring made of maraging steel.
[0012]
[Means for Solving the Problems]
In order to achieve such an object, the metal ring nitriding apparatus of the present invention is a metal ring made of maraging steel and treated at a treatment temperature in the range of 450 to 500 ° C. for 30 to 120 minutes in an atmosphere containing at least ammonia. In a nitriding apparatus for holding and nitriding until a processing time in a range elapses, the apparatus includes a preheating chamber and a nitriding chamber, and the preheating chamber heats the preheating chamber when the metal ring is accommodated. A first heating unit that raises the temperature, and the nitriding chamber introduces nitrogen gas into the nitriding chamber, and a second heating unit that heats the nitriding chamber to maintain the processing temperature. Nitrogen gas introducing means, ammonia gas introducing means for introducing ammonia gas into the nitriding chamber, oxygen gas introducing means for introducing oxygen gas into the nitriding chamber, and the atmosphere in the nitriding chamber are discharged 50 to 90 volumes of ammonia by nitrogen gas introduced by the nitrogen gas introduction means, ammonia gas introduced by the ammonia gas introduction means, and oxygen introduced by the oxygen gas introduction means % And oxygen of 0.1 to 0.9% by volume, and the balance is substantially composed of nitrogen, and is transferred from the preheating chamber to the nitriding chamber in a first mixed gas atmosphere. The metal ring is accommodated, a nitride layer is formed on the surface of the metal ring, and when 1/3 to 1/2 of the processing time has elapsed, the first mixed gas is discharged by the exhaust means On the other hand, the nitrogen gas introduced by the nitrogen gas introducing means and the ammonia gas introduced by the ammonia gas introducing means produce a second mixed gas containing 0 to 25% by volume of ammonia and the balance being nitrogen. Holding Te, replacing the atmosphere in the nitride processing chamber to the second gas mixture, under the second mixed gas atmosphere of, the metal ring nitride processing chamber until the remaining time of the processing time has elapsed Then, a part of the nitrogen contained in the nitride layer is vaporized in the atmosphere to be desorbed from the metal ring, and a part is diffused further into the metal ring. It is characterized by that.
[0013]
In the metal ring nitriding apparatus of the present invention, first, the metal ring is accommodated in the preheating chamber. Then, the said preheating chamber is heated by the 1st heating means, and it heats up to the processing temperature of the range of 450-500 degreeC.
[0014]
On the other hand, nitrogen gas, ammonia gas, and oxygen gas are introduced into the nitriding chamber by the nitrogen gas introducing means, the ammonia gas introducing means, and the oxygen gas introducing means, respectively. As a result, a first mixed gas containing 50 to 90% by volume of ammonia and 0.1 to 0.9% by volume of oxygen with the balance being substantially nitrogen is contained inside the nitriding chamber. It is generated.
[0015]
The nitriding chamber is heated by the second heating means and is maintained at a processing temperature in the range of 450 to 500 ° C. If the temperature in the nitriding chamber is less than 450 ° C., nitriding cannot be performed, and if it exceeds 500 ° C., aging is further advanced due to heating of the nitriding treatment, and overaging occurs, martensite precipitates and the metal ring Hardness decreases.
[0016]
Therefore, when the metal ring is transferred from the preheating chamber to the nitriding chamber, the metal ring is maintained at a processing temperature in the above range under a first mixed gas atmosphere. If it does in this way, the nitrogen produced | generated by decomposition | disassembly of the said ammonia will diffuse in the said metal ring, and a nitride layer will be formed in the surface layer of this metal ring. At this time, hydrogen is generated simultaneously with nitrogen by the decomposition of ammonia. However, when the partial pressure of hydrogen is increased, the decomposition of ammonia is suppressed or hydrogen is recombined with nitrogen, so that nitridation is inhibited. Is done.
[0017]
However, since the first mixed gas contains oxygen in the above range, the hydrogen is combined with the oxygen and removed out of the system in the water state. As a result, the decomposition of the ammonia can be promoted.
[0018]
If the amount of ammonia contained in the first mixed gas is less than 50% by volume, a nitride layer cannot be sufficiently formed, and a desired hardness cannot be imparted to the surface of the metal ring. On the other hand, if the amount of ammonia exceeds 90% by volume, the amount of nitrogen to be produced becomes excessive, and a compound such as iron nitride is formed in the metal structure of the metal ring, which is not preferable.
[0019]
Further, if the amount of oxygen contained in the first mixed gas is less than 0.1% by volume, the effect of removing the hydrogen by combining the oxygen with hydrogen cannot be obtained sufficiently. On the other hand, if the amount of oxygen exceeds 0.9%, an oxide is formed in the metal structure of the metal ring, or the decomposition of ammonia is excessively promoted, so that the amount of nitrogen produced is excessive. Absent.
[0020]
The oxygen gas introduction means may introduce pure oxygen gas as long as it can generate the first mixed gas, or introduces a gas containing oxygen such as air. It may be.
[0021]
Next, in the nitriding chamber, a nitride layer is formed on the surface of the metal ring, and when 1/3 to 1/2 of the processing time has elapsed, the first mixed gas is discharged by the exhausting means. . Then, nitrogen gas and ammonia gas are newly introduced by the nitrogen gas introduction means and the ammonia gas introduction means, respectively. The inside of the nitriding treatment chamber contains 0 to 25% by volume of ammonia, and the balance is made of nitrogen. A second mixed gas is generated. As a result, the atmosphere in the nitriding chamber is replaced with the second mixed gas.
[0022]
Next, the metal ring is held in the nitriding chamber until the remaining processing time elapses in the second mixed gas atmosphere.
[0023]
When the atmosphere in the nitriding chamber is replaced with the second mixed gas, part of the nitrogen contained in the nitride layer formed on the surface of the metal ring is evaporated into the atmosphere and desorbed from the metal ring. , Some diffuse further into the metal ring. As a result, on the surface of the metal ring, a nitride layer having a structure in which the hardness is reduced by the same degree according to the depth from the surface, and having excellent hardness and excellent toughness is formed.
[0024]
If the atmosphere in the nitriding chamber is replaced with the second mixed gas before う ち or more of the processing time has elapsed, the formation of the nitride layer becomes insufficient, and the surface of the metal ring The desired hardness may not be obtained. On the other hand, if the replacement is performed at a time exceeding 1/2 of the processing time, the nitride layer is excessively formed to the inside of the metal ring, and sufficient toughness may not be obtained.
[0025]
When the amount of ammonia contained in the second mixed gas exceeds 25% by volume, an effect of detaching a part of nitrogen contained in the nitride layer from the metal ring, and another part of the metal ring. Furthermore, neither of the effects of diffusing inside can be obtained.
[0026]
Further, if the treatment time is less than 30 minutes, the nitriding treatment cannot be performed, and if it exceeds 120 minutes, the aging is further advanced due to heating of the nitriding treatment, and overaging occurs, and martensite precipitates, and the hardness of the metal ring Decreases.
[0027]
As a result, according to the nitriding apparatus of the present invention, in addition to the toughness held by the non-nitrided portion inside the metal ring, the toughness can be obtained also by the nitride layer having the above configuration. Further improved, it is possible to impart excellent hardness and toughness to the metal ring.
[0028]
In the nitriding apparatus of the present invention, it is preferable that the preheating chamber includes a halide gas introduction means for introducing a halide gas into the preheating chamber. The preheating chamber heats the preheating chamber by the first heating means in a halide gas atmosphere introduced by the halide gas introducing means, thereby allowing the surface of the metal ring to be in contact with the surface of the metal ring prior to the nitriding treatment. Activation by a halide gas can facilitate the formation of the nitride layer. As the halide, chloride, fluoride and the like can be used.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. FIG. 1 is a process explanatory diagram schematically showing a manufacturing process of a metal ring used as a belt for CVT, FIG. 2 is a system configuration diagram showing a configuration of a nitriding apparatus of this embodiment, and FIG. 3 is a diagram of this embodiment. FIG. 4 is a graph showing the relationship between the depth from the surface of the metal ring and the hardness.
[0030]
When manufacturing the metal ring, first, as shown in FIG. 1, the maraging steel thin plate 1 is bent to form a loop, and then the end portions are welded to form a cylindrical drum 2. At this time, since the maraging steel exhibits age hardening by the heat of welding, high hardness portions appear on both sides of the welded portion 2 a of the drum 2.
[0031]
Therefore, next, the drum 2 is accommodated in the vacuum furnace 3 and held at a temperature of 820 to 830 ° C. for 20 to 60 minutes to perform a first solution treatment to remove hardness unevenness. When the first solution treatment is completed, the drum 2 is unloaded from the vacuum furnace 3 and cut into a predetermined width to form a metal ring W.
[0032]
The metal ring W formed as described above is then rolled at a rolling reduction of 40 to 50%. The metal ring W has a thickness of 0.2 mm by the rolling, and a rolled structure is formed with a thickness of about 30 μm from the surface. Therefore, the rolled metal ring W is accommodated in the heating furnace 4 and subjected to the second solution treatment, thereby eliminating the rolled structure and forming uniform metal crystal grains.
[0033]
The solution-treated metal ring W is next subjected to circumference correction, and then accommodated in the heating furnace 5 and held at a temperature in the range of 440 to 480 ° C. for 60 to 120 minutes for aging treatment. When the aging treatment is completed, the metal ring W is cooled in the heating furnace 5 and transferred to the nitriding apparatus 6 to perform nitriding treatment.
[0034]
As shown in FIG. 2, the nitriding apparatus 6 of this embodiment includes a first replacement chamber 11, a preheating chamber 12, a nitriding chamber 13, a cooling chamber 14, and a second nitriding chamber 15. Each of the chambers is provided with a door (not shown) that can move up and down at the boundary of each other, and can communicate with each other by opening and closing the door. The first replacement chamber 11 includes a carry-in door (not shown) that is movable up and down on the side opposite to the preheating chamber 12, and the second replacement chamber 15 is a carry-out door that is movable up and down on the side opposite to the cooling chamber 14 (see FIG. Not shown). Each door is closed in a normal state.
[0035]
Further, the nitriding apparatus 6 is provided with transport means (not shown) for intermittently transporting the metal ring W from the first replacement chamber 11 toward the second replacement chamber 15 while performing processing in each of the chambers. The chamber 12 and the nitriding chamber 13 are each provided with heating means (not shown) for heating the chamber.
[0036]
The nitriding apparatus 6 further includes a nitrogen gas supply source 16, a halide gas supply source 17, an ammonia gas supply source 18, and an air (oxygen gas) supply source 19. The nitrogen gas supply source 16 is connected to a nitrogen gas conduit 20. A nitrogen gas branch pipe 20 a branched from the nitrogen gas pipe 20 is provided in the first replacement chamber 11, a nitrogen gas branch pipe 20 b is provided in the preheating chamber 12, and a nitrogen gas branch pipe 20 c. Are connected to the nitriding chamber 13, the nitrogen gas branch pipe 20 d is connected to the cooling chamber 14, and the nitrogen gas branch pipe 20 e is connected to the second replacement chamber 15.
[0037]
The halide gas supply source 17 is connected to the preheating chamber 12 via a halide gas conduit 21, and the ammonia gas supply source 18 is connected to the nitriding treatment chamber 13 via an ammonia gas conduit 22. Further, the air supply source 19 is connected to an air conduit 23, an air branch 23 a branched from the air conduit 23 is connected to the nitriding treatment chamber 13, and an air branch 23 b is connected to the cooling chamber 14.
[0038]
The first replacement chamber 11 includes an exhaust pipe 25 connected to the atmospheric discharge unit 24. A high vacuum pump 26 that exhausts the atmosphere in the first replacement chamber 11 and an oxygen sensor 27 that measures the oxygen concentration in the exhaust are provided in the middle of the exhaust pipe 24.
[0039]
The preheating chamber 12 includes an exhaust pipe 29 connected to the exhaust gas combustion device 28, and a low vacuum pump 30 that exhausts the atmosphere in the preheating chamber 12 in the middle of the exhaust pipe 29, and oxygen that measures the oxygen concentration in the exhaust A sensor 31 is provided. The exhaust gas combustion device 28 is connected to the atmospheric discharge unit 24 via the combustion gas conduit 32.
[0040]
The nitriding chamber 13 includes an exhaust pipe 33 connected to the exhaust gas combustion device 28, and a low vacuum pump 34 that exhausts the atmosphere in the nitriding chamber 13 in the middle of the exhaust pipe 33, and measures the oxygen concentration in the exhaust gas An oxygen sensor 35 is provided. The exhaust pipe 33 includes an exhaust branch pipe 33a branched from the exhaust pipe 33 and connected to the exhaust gas combustion device 28, and an ammonia analyzer 36 for measuring the ammonia concentration in the exhaust gas is provided in the middle of the exhaust branch pipe 33a. .
[0041]
The cooling chamber 14 includes an exhaust pipe 37 connected to the atmospheric discharge section 24, and the second replacement chamber 15 includes an exhaust pipe 38 connected to the atmospheric discharge section 24. A high vacuum pump 39 that exhausts the atmosphere in the second replacement chamber 15 and an oxygen sensor 40 that measures the oxygen concentration in the exhaust are provided in the middle of the exhaust pipe 38.
[0042]
Next, the operation of the nitriding apparatus 6 of this embodiment will be described.
[0043]
In the nitriding apparatus 6, first, a carry-in door (not shown) of the first replacement chamber 11 is opened, and the metal ring W is carried into the first replacement chamber 11 by a transfer means (not shown). Next, the carry-in door is closed, the high vacuum pump 26 is operated, and the atmosphere in the first replacement chamber 11 is exhausted to the air discharge unit 24 via the exhaust pipe 25. At the same time, nitrogen is introduced into the first replacement chamber 11 from the nitrogen supply source 16 through the nitrogen conduit 20 and the nitrogen branch 20a. When the oxygen concentration detected by the oxygen sensor 27 becomes less than a predetermined value, it is determined that the atmosphere in the first replacement chamber 11 has been replaced with nitrogen gas, and the high vacuum pump 26 is stopped.
[0044]
Next, a door (not shown) between the first replacement chamber 11 and the preheating chamber 12 is opened, and the metal ring W is transferred to the preheating chamber 12 by the transfer means. If the metal ring W is accommodated in the preheating chamber 12, the door between the first replacement chamber 11 and the preheating chamber 12 is closed, and the inside of the preheating chamber 12 is heated by a heating means (not shown) to The temperature is raised to a temperature in the range of 500 ° C.
[0045]
At this time, the atmosphere in the preheating chamber 12 includes nitrogen gas introduced from the nitrogen supply source 16 through the nitrogen conduit 20 and the nitrogen branch 20b, and from the halide gas supply source 17 through the halide gas conduit 21. The introduced halide gas is replaced with a mixed gas atmosphere containing 1.0 to 20.0% by volume of the halide gas and the balance being nitrogen. Therefore, the surface of the metal ring W is activated by the halide gas, and the nitriding process in the nitriding chamber 13 becomes easy.
[0046]
The atmosphere in the preheating chamber 12 is replaced by first operating the low vacuum pump 30 to change the atmosphere in the preheating chamber 12 to the atmospheric discharge section 24 through the exhaust pipe 29, the exhaust gas combustion device 28, and the combustion gas conduit 32. discharge. When the oxygen concentration detected by the oxygen sensor 31 becomes less than a predetermined value, the low vacuum pump 30 is stopped and the nitrogen gas and halogenated gas are respectively supplied from the nitrogen supply source 16 and the halide gas supply source 17. Gas is introduced into the preheating chamber 12.
[0047]
When the temperature in the preheating chamber 12 is raised to a temperature in the range of 450 to 500 ° C., a door (not shown) between the preheating chamber 12 and the nitriding chamber 13 is opened, and the metal ring W is nitrided by the transfer means. Transfer to the processing chamber 13. If the metal ring W is accommodated in the nitriding chamber 13, the door between the preheating chamber 12 and the nitriding chamber 13 is closed and the metal ring W is processed for 30 to 120 minutes. Until this occurs, the nitriding treatment is performed while being held in the nitriding treatment chamber 13.
[0048]
At this time, the atmosphere in the nitriding chamber 13 is introduced from the nitrogen supply source 16 through the nitrogen conduit 20 and the nitrogen branch 20 c and from the ammonia gas supply source 18 through the ammonia gas conduit 22. The ammonia gas and the air introduced from the air supply source 19 through the air conduit 23 and the air branch pipe 23a contain 50 to 90% by volume of ammonia gas and 0.1 to 0.9% by volume of oxygen. Is replaced with a first mixed gas atmosphere made of nitrogen, and is heated to a temperature in the range of 450 to 500 ° C. by a heating means (not shown).
[0049]
To replace the atmosphere in the nitriding chamber 13, first, the low vacuum pump 34 is operated to change the atmosphere in the nitriding chamber 13 through the exhaust pipe 33, the exhaust branch pipe 33 a, the exhaust gas combustion device 28, and the combustion gas conduit 32. To the atmospheric discharge part 24. At the same time, nitrogen gas, ammonia gas, and air are introduced into the nitriding treatment chamber 13 from the nitrogen supply source 16, the ammonia gas supply source 18, and the air supply source 19, respectively. When the oxygen concentration detected by the oxygen sensor 35 and the ammonia concentration detected by the ammonia analyzer 36 are within the range constituting the first mixed gas, the low vacuum pump 34 is stopped.
[0050]
In the nitriding treatment, first, a nitriding layer is formed on the surface of the metal ring W by maintaining the inside of the nitriding treatment chamber 13 at a temperature in the range of 450 to 500 ° C. in the first mixed gas atmosphere. When 1/3 to 1/2 of the processing time has elapsed, the low vacuum pump 34 is operated again, so that the first mixed gas in the nitriding chamber 13 is discharged into the exhaust pipe 33, the exhaust branch pipe 33a, The exhaust gas is discharged to the atmospheric discharge section 24 through the exhaust gas combustion device 28 and the combustion gas conduit 32. At the same time, nitrogen gas and ammonia gas are introduced into the nitriding treatment chamber 13 from the nitrogen supply source 16 and the ammonia gas supply source 18, respectively. When the ammonia concentration detected by the ammonia analyzer 36 falls within the range of 0 to 25% by volume, the low vacuum pump 34 is stopped. As a result, the atmosphere in the nitriding chamber 13 is replaced with a second mixed gas atmosphere containing ammonia gas in an amount of 0 to 25% by volume and the balance being nitrogen.
[0051]
Next, the nitriding treatment is performed by holding the inside of the nitriding treatment chamber 13 at the temperature in the range of 450 to 500 ° C. in the second mixed gas atmosphere until the treatment time elapses. Complete nitriding.
[0052]
Next, when the nitriding process is completed after the predetermined time has elapsed, a door (not shown) between the nitriding chamber 13 and the cooling chamber 14 is opened, and the metal ring W is moved into the cooling chamber 14 by the transfer means. Transport to. And if the said metal ring W is accommodated in the cooling chamber 14, the door between the nitriding processing chamber 13 and the cooling chamber 14 will be closed, and cooling processing will be performed.
[0053]
The cooling process is performed by nitrogen gas introduced from the nitrogen supply source 16 through the nitrogen conduit 20 and the nitrogen branch pipe 20d, and air introduced from the air supply source 19 through the air conduit 23 and the air branch pipe 23b. This is performed until the inside of the cooling chamber 14 is cooled to room temperature. The nitrogen gas and air are exhausted to the atmospheric discharge part 24 through the exhaust pipe 37.
[0054]
Next, when the inside of the cooling chamber 14 is cooled to room temperature, a door (not shown) between the cooling chamber 14 and the second replacement chamber 15 is opened, and the metal ring W is moved into the second replacement chamber 15 by the transfer means. Transport to. And if the said metal ring W was accommodated in the 2nd substitution chamber 15, the door between the cooling chamber 14 and the 2nd substitution chamber 15 will be closed, and the atmosphere in the 2nd substitution chamber 15 will be nitrogen atmosphere. Replace with.
[0055]
The replacement of the atmosphere in the second replacement chamber 15 is performed by operating the high vacuum pump 39 and exhausting the atmosphere in the second replacement chamber 15 to the air discharge unit 24 via the exhaust pipe 38 and at the same time from the nitrogen supply source 16. This is performed by introducing nitrogen into the second replacement chamber 15 through the nitrogen conduit 20 and the nitrogen branch 20e. When the oxygen concentration detected by the oxygen sensor 40 becomes less than a predetermined value, it is determined that the atmosphere in the second replacement chamber 15 has been replaced with nitrogen gas, and the high vacuum pump 39 is stopped.
[0056]
When the atmosphere in the second replacement chamber 15 is replaced with a nitrogen atmosphere, the unloading door (not shown) is opened, and the metal ring W is unloaded from the nitriding apparatus 6 by the transfer means.
[0057]
As a result, a metal ring W is obtained in which a nitrided layer is formed on the surface and the hardness is improved, and the toughness is maintained by the portion that is not nitrided inside. In addition, the metal ring W has a configuration in which the hardness of the nitrided layer is reduced by the same degree according to the depth from the surface, and further excellent toughness can be obtained by the nitrided layer.
[0058]
Next, the relationship between the depth from the surface of the metal ring W obtained by the nitriding apparatus 6 of this embodiment and the hardness is shown in FIG.
[0059]
As shown in FIG. 3, the metal ring W obtained by the nitriding apparatus 6 of this embodiment has a Vickers hardness (Hv) at the outermost surface. _0.3 ) Excellent hardness of 800 or more. Further, a portion having a constant hardness and not nitrided is provided in the interior of 40 μm or less from the surface, and a nitride layer whose hardness is reduced by the same degree is formed at a depth of 40 μm from the surface. Therefore, the metal ring W obtained by the nitriding apparatus 6 of the present embodiment has excellent toughness by adding the toughness of the nitride layer having the above structure to the toughness of the inner non-nitrided portion. it is obvious.
[0060]
In the nitriding apparatus 6 of this embodiment, the transfer means, doors, vacuum pumps 26, 30, 34, 39, nitrogen gas supply source 16, halide gas supply source 17, ammonia gas supply source 18, air The operation of the supply source 19 or the like may be manually controlled, or may be controlled by a control unit such as a computer having a CPU, ROM, RAM, or the like. When the computer is used, the operation can be controlled by the detection values of the oxygen sensors 27, 31, 35, 40 and the ammonia analyzer 36.
[0061]
In this embodiment, the halide gas supply source 17 is provided and the halide gas is introduced into the preheating chamber 12. However, the halide gas may not be introduced into the preheating chamber 12.
[0062]
In the present embodiment, the air supply source 19 is provided and air is introduced into the nitriding chamber 13 to form the first mixed gas. However, another oxygen-containing gas is introduced instead of air. Alternatively, pure oxygen gas may be introduced.
[0063]
Further, the atmosphere in the preheating chamber 12 contains a halide, and the atmosphere in the nitriding chamber 13 contains ammonia gas. If discharged as it is, there is a concern that it may cause air pollution. However, in the nitriding apparatus 6 of the present embodiment, the atmosphere in the preheating chamber 12 and the atmosphere in the nitriding chamber 13 are both burned and detoxified by the exhaust gas combustion device 28, and are then sent to the atmospheric discharge unit 24. Since it is released, it can be prevented from causing air pollution.
[Brief description of the drawings]
FIG. 1 is a process explanatory view schematically showing a manufacturing process of a metal ring used as a CVT belt.
FIG. 2 is a system configuration diagram showing the configuration of the nitriding apparatus of the present invention.
FIG. 3 is a graph showing the relationship between the depth from the surface of the metal ring and the hardness.
[Explanation of symbols]
6 ... Nitriding treatment apparatus, 12 ... Preheating chamber, 13 ... Nitriding treatment chamber, 20c ... Nitrogen gas introduction means, 21 ... Halide gas introduction means, 22 ... Ammonia gas introduction means, 23a ... Oxygen gas introduction means, 33, 34 ... Exhaust means, W ... Metal ring.

Claims (2)

In a nitriding apparatus for nitriding by holding a metal ring made of maraging steel in an atmosphere containing at least ammonia at a processing temperature in the range of 450 to 500 ° C. until a processing time in the range of 30 to 120 minutes elapses.
A preheating chamber and a nitriding chamber;
The preheating chamber comprises first heating means for heating the preheating chamber to raise the processing temperature when the metal ring is accommodated,
The nitriding chamber includes a second heating unit that heats the nitriding chamber to maintain the processing temperature, a nitrogen gas introducing unit that introduces nitrogen gas into the nitriding chamber, and ammonia gas that flows into the nitriding chamber. An ammonia gas introducing means for introducing into the nitriding chamber, oxygen gas introducing means for introducing oxygen gas into the nitriding chamber, and an exhaust means for discharging the atmosphere in the nitriding chamber,
The nitrogen gas introduced by the nitrogen gas introduction means, the ammonia gas introduced by the ammonia gas introduction means, and the oxygen introduced by the oxygen gas introduction means, ammonia 50-90 vol% and oxygen 0.1 A first mixed gas containing approximately 0.9% by volume and the balance being substantially nitrogen, and the metal ring transferred from the preheating chamber to the nitriding chamber in a first mixed gas atmosphere Containing a nitride layer on the surface of the metal ring;
When 1/3 to 1/2 of the treatment time has elapsed, the first mixed gas is discharged by the exhaust means, while the nitrogen introduced by the nitrogen gas introduction means and the ammonia gas introduction means are introduced. To produce a second mixed gas containing 0 to 25% by volume of ammonia and the balance being nitrogen, and replacing the atmosphere in the nitriding chamber with the second mixed gas,
Under the second mixed gas atmosphere, the metal ring is held in the nitriding chamber until the remaining time of the processing time elapses , and part of the nitrogen contained in the nitrided layer is vaporized in the atmosphere. An apparatus for nitriding a metal ring, wherein the metal ring is detached from the metal ring, and part of the metal ring is further diffused into the metal ring.   2. The metal ring nitriding apparatus according to claim 1, wherein the preheating chamber includes a halide gas introduction means for introducing a halide gas into the preheating chamber.

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