JP2001049347A - Production of endless metallic belt and heat treating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an endless metallic belt capable of reducing the treating time of aging treatment and nitriding treatment and capable of executing the nitriding treatment in a stable atmosphere and to provide a heat treating device. SOLUTION: A drum formed by welding the edge parts in a steel sheet of maraging steel is cut to a prescribed width to form a ring W, the ring W is rolled, and the circumferential length thereof is corrected. After the correction of the circumferential length, the ring W is stored into an aging treatment chamber 1, the inside of the aging treating chamber 1 is heated to a prescribed aging treating temp., the ring W is held for a prescribed time, and aging treatment is executed. After the aging treatment, the ring W is held to the aging treatment temp., is moved to a nitriding treatment chamber 2 previously heated to a prescribed nitriding treatment temp., is held to the nitriding treatment temp. for a prescribed time in an atmosphere at least contg. gaseous ammonia, is subjected to nitriding treatment and is subsequently cooled. After the nitriding treatment, a plurality of rings W are laminated to produce an endless metallic belt. In the heat treating device, the space between the aging treatment chamber 1 and the nitriding treatment chamber 2 is provided with an intermediate chamber 3. The heat treating device is provided with a cooling chamber 8 adjacently to the nitriding treatment chamber 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an endless metal belt used for a belt for a continuously variable transmission and a heat treatment apparatus used for the method.

[0002]

2. Description of the Related Art In a continuously variable transmission having a power transmission belt stretched between a pair of pulleys, an endless metal belt holding a plurality of rings in a stacked state is used as the power transmission belt. .

[0003] The endless metal belt exhibits a linear state when traveling between the pulleys, and exhibits a curved state when traveling along the pulleys, and severe bending deformation due to repetition of the linear state and the curved state. Is added. Therefore, the endless metal belt is required to have strength enough to withstand the severe bending deformation.

[0004] Maraging steel is known as a material having the strength to withstand the severe bending deformation. The maraging steel is composed of 17-19% Ni, Co, M
The endless metal belt is a low-carbon steel containing o, Ti, etc., which is an ultra-strength steel having a high strength and a high toughness due to age hardening in a martensitic state by being heated to an appropriate temperature after solution treatment. To be awarded.

The ring constituting the endless metal belt is formed by cutting a drum formed by welding the ends of the thin maraging steel sheet to a predetermined width and then rolling the drum to a predetermined length. ing. However, when used for the endless metal belt for a power transmission belt, it is desired to further provide wear resistance and fatigue resistance. Therefore, a surface hardening treatment is performed on the maraging steel. .

[0006] The surface hardening treatment is generally performed by subjecting the ring to a nitriding treatment to form a nitrided layer on a surface portion thereof. When performing the surface hardening treatment, first, the ring that has been rolled to a predetermined length is subjected to a solution treatment so that the surface thereof is in a state suitable for the nitriding treatment. When the solution treatment is performed, the dimensions of the ring change due to the heat distortion. Therefore, after the circumference is corrected for the ring, an aging treatment is performed.

The aging treatment is for imparting high strength by expressing the aging hardness to the maraging steel. The ring is housed in an aging treatment chamber, and the aging treatment chamber is heated to a predetermined aging treatment temperature. For example, after heating to 480 to 520 ° C., the aging treatment temperature is maintained for a predetermined time. The aging treatment is performed in an atmosphere of an inert gas such as nitrogen to avoid formation of an oxide layer on the surface of the ring.

[0008] When the aging treatment is completed, the ring is cooled in the aging treatment chamber and then subjected to a nitriding treatment. The nitriding treatment includes gas nitriding treatment, gas nitrocarburizing treatment, and salt bath nitriding treatment. Here, the gas nitriding treatment and gas nitrocarburizing treatment will be described.

[0009] After the aging treatment is completed, the ring cooled in the aging treatment chamber is transferred to the nitriding treatment chamber.

In the gas nitriding, the ring is housed in the nitriding chamber, and the nitriding chamber is heated to a predetermined nitriding temperature, for example, 500 to 550 ° C., and then the ring is heated in an ammonia gas atmosphere. This is performed by maintaining the temperature of the nitriding treatment for a predetermined time. The atmosphere containing the ammonia gas may contain other inert gas in addition to pure ammonia. Then, when the gas nitriding is completed, the ring is cooled in the nitriding chamber.

In the gas nitrocarburizing process, the ring is accommodated in the nitriding chamber, and ammonia gas and RX are replaced with an ammonia gas atmosphere in the gas nitriding process.
Except that a mixed gas atmosphere with a gas is used, the gas nitriding treatment is performed in the same manner as described above.

According to the gas nitriding treatment or the gas nitrocarburizing treatment, nitrogen generated by decomposition of ammonia penetrates into the metal structure of the maraging steel, thereby forming a nitride layer on the surface of the ring and hardening the ring. Abrasion resistance and fatigue resistance can be improved.

However, when performing the gas nitriding treatment or the gas nitrocarburizing treatment, the aging treatment chamber and the nitriding treatment chamber are each heated to a predetermined temperature, maintained at the temperature for a predetermined time, and then cooled. The operation is repeated. For this reason, there is a problem that the time required for the aging treatment and the nitriding treatment becomes long, and the manufacturing cost increases.

In order to solve the above problem, it has been proposed to sequentially perform both the aging treatment and the nitriding treatment in one treatment chamber. This is because the ring is housed in a processing chamber, the processing chamber is heated to a predetermined aging temperature, the aging is performed while the ring is kept at the aging temperature for a predetermined time, and then the cooling is performed without cooling. The atmosphere in the room is switched to an ammonia gas atmosphere or a mixed gas atmosphere of ammonia gas and RX gas, and the nitriding treatment is performed by maintaining the temperature at a predetermined nitriding temperature for a predetermined time.

As described above, by performing both the aging treatment and the nitriding treatment in one processing chamber, the cooling operation after the aging treatment and the ring subjected to the aging treatment can be performed. After being housed in the nitriding chamber, the operation of heating the nitriding chamber to the nitriding temperature can be omitted, and the time required can be shortened. However, in this case, there is a disadvantage that the atmosphere is hardly stabilized after the atmosphere is switched between the aging treatment and the nitriding treatment.

In order to solve the above-mentioned problem, it has been proposed to simultaneously perform both the aging treatment and the nitriding treatment in one treatment chamber. This is because the heating for the nitriding treatment also serves as the heating for the aging treatment.

However, when doing this,
There is an inconvenience that it is difficult to adjust the atmosphere so as to obtain a proper aging hardness and a proper depth of the nitrided layer.

[0018]

SUMMARY OF THE INVENTION According to the present invention, it is possible to eliminate such inconveniences, shorten the processing time required for the aging treatment and the nitriding treatment, and perform the nitriding treatment in a stable atmosphere. It is an object of the present invention to provide a method for manufacturing an endless metal belt that can be manufactured.

Another object of the present invention is to provide a heat treatment apparatus suitable for the manufacturing method.

[0020]

In order to achieve this object, a method of manufacturing an endless metal belt according to the present invention is to cut a drum formed by welding ends of a maraging steel steel plate to a predetermined width. Forming a ring, rolling the ring to a predetermined length, correcting the circumference, performing aging treatment and nitriding treatment, and then laminating a plurality of rings to form a power transmission belt for a continuously variable transmission. In the method for producing an endless metal belt used in (1), a ring rolled to a predetermined length is accommodated in an aging treatment chamber, and the aging treatment chamber is heated to a predetermined aging treatment temperature to cool the ring to the aging treatment. A step of performing aging by holding at a processing temperature for a predetermined time; and, after the aging, maintaining the ring at the aging temperature and being provided independently of the aging chamber and heating to a predetermined nitriding temperature in advance. Moved to the nitriding chamber It was subjected to a nitriding treatment by a predetermined time retained in the nitride treatment temperature in an atmosphere containing ammonia gas with, characterized in that it comprises a step of cooling.

According to the manufacturing method of the present invention, the ring subjected to the aging treatment in the aging treatment chamber is not cooled after the aging treatment, and is kept at the aging treatment temperature without being cooled. Moved to The nitriding chamber,
Since the ring is heated to a predetermined nitriding temperature in advance, the moved ring is maintained at the nitriding temperature for a predetermined time, so that the ring is subjected to nitriding in an atmosphere containing at least ammonia gas.

Therefore, it is possible to omit the operation of cooling after the aging treatment and the operation of subsequently heating to the nitriding treatment temperature for the nitriding treatment as in the prior art, thereby shortening the treatment time. Moreover, in the manufacturing method of the present invention, since the nitriding chamber is provided independently of the aging chamber, it is not necessary to switch the atmosphere between the aging process and the nitriding process, and in a stable atmosphere. A nitriding treatment can be performed.

In the nitriding treatment performed in an atmosphere containing at least ammonia gas, the ring is maintained at the nitriding treatment temperature for a predetermined time in an ammonia gas atmosphere that may contain other inert gas in addition to pure ammonia. It is selected from either gas nitriding or gas soft nitriding in which the ring is kept at the nitriding temperature for a predetermined time in a mixed gas atmosphere of ammonia gas and RX gas.

In the manufacturing method of the present invention, in order to smoothly and continuously perform the aging treatment and the nitriding treatment, the nitriding treatment is performed at a nitriding treatment temperature equal to or higher than the aging treatment temperature. It is preferred to do so.

[0025] In the manufacturing method of the present invention, the ring may be cooled in the nitriding chamber after nitriding, or may be cooled outside the nitriding chamber. When performing cooling after the nitriding treatment outside the nitriding treatment chamber,
For example, after performing the nitriding treatment, the ring is moved to a cooling chamber provided so as to be able to communicate with the nitriding chamber through a door that can be freely opened and closed, and cools in the cooling chamber.

[0026] The ring exhibits aging hardness and high strength by the aging treatment. However, if the nitriding treatment is performed after the aging treatment, the aging proceeds further by heating for the nitriding treatment. The strength may decrease. Therefore, in the manufacturing method of the present invention, the aging treatment is performed in a range where the aging hardness is less than the maximum value, and the aging hardness is caused to reach the maximum value by the nitriding treatment. In the present specification, aging in the range where the aging hardness is less than the maximum value is described as `` sub-aging '', and after the aging hardness reaches the maximum value, further aging proceeds, and the state in which the strength is reduced is referred to as Overage ”.

According to the production method of the present invention, the aging in the aging treatment chamber is performed so as to be sub-aged, and the aging hardness reaches the maximum value by heating accompanying the subsequent nitriding treatment, whereby an appropriate aging is achieved. Hardness can be obtained.

The manufacturing method of the present invention comprises an aging chamber for accommodating the ring and heating the ring to a predetermined aging temperature to hold the ring at the aging temperature for a predetermined time; A nitriding chamber for accommodating the ring and holding the ring at a nitriding temperature for a predetermined time in an atmosphere containing at least ammonia gas, wherein the nitriding chamber is openable and closable with the aging chamber. The present invention can be advantageously implemented by a heat treatment apparatus characterized in that the heat treatment apparatus is provided so as to be freely communicable through the heat treatment apparatus.

According to the heat treatment apparatus of the present invention, the aging chamber and the nitriding chamber are separated by an openable / closable door. Therefore, the atmosphere containing at least ammonia gas in the nitriding chamber, that is, pure ammonia In addition, it is possible to maintain a stable state of an ammonia gas atmosphere or a mixed gas atmosphere of ammonia gas and RX gas which may contain other inert gas or the like. When the aging process in the aging chamber is completed, the ring is moved from the aging chamber to the nitriding chamber by opening the door and communicating the nitriding chamber with the aging chamber. be able to.

The heat treatment apparatus of the present invention further includes an intermediate chamber between the nitriding chamber and the aging chamber, the intermediate chamber being previously heated to an intermediate temperature between the aging temperature and the nitriding temperature. The chambers are provided so as to be able to communicate with each other via a door which can be freely opened and closed, and the ring is moved from the aging treatment chamber to the nitriding treatment chamber via the intermediate chamber.

In the heat treatment apparatus, the ring rolled to the predetermined length is accommodated in the aging chamber, the aging chamber is heated to a predetermined aging temperature, and the ring is heated to the aging temperature. After performing the aging treatment by holding for a predetermined time, the ring is moved to the nitriding treatment chamber heated to a predetermined nitriding treatment temperature via the first door, the intermediate chamber, and the second door,
After performing the nitriding treatment while maintaining the nitriding treatment temperature for at least a predetermined time in an atmosphere containing at least ammonia gas, cooling is performed.

In the intermediate chamber, when the nitriding temperature is the same as the aging temperature, the intermediate chamber has the same temperature as the aging chamber and the gas nitriding chamber or the gas nitrocarburizing chamber. I have. Further, when the nitriding temperature is higher than the aging temperature, the intermediate chamber is at an intermediate temperature between the aging chamber and the nitriding chamber.

As a result, when the intermediate chamber moves the ring from the aging chamber to the nitriding chamber,
By temporarily storing, it is possible to reduce the influence of the temperature difference on the ring during the movement.

The heat treatment apparatus includes the intermediate chamber, and when the ring is moved from the aging treatment chamber to the nitriding treatment chamber after the aging treatment, the atmosphere of the aging treatment chamber is transferred to the nitriding treatment chamber. It is possible to prevent inflow and destabilization of the atmosphere.

Further, the heat treatment apparatus of the present invention includes a cooling chamber which is communicated with the nitriding chamber through a door which can be freely opened and closed. From the cooling chamber to be cooled in the cooling chamber.

The heat treatment apparatus of the present invention is provided with the independent cooling chamber as described above, whereby the atmosphere in the nitriding chamber can be stabilized. Further, by quickly moving the ring subjected to the nitriding treatment to the cooling chamber, the transfer efficiency is improved, which can contribute to automation.

[0037]

Next, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. FIG. 1 is an explanatory cross-sectional view showing the configuration of the heat treatment apparatus according to the present embodiment, FIG. 2 is a graph showing a heating pattern of the aging treatment and the gas nitrocarburizing treatment, and FIG. FIG. 4 is a graph showing the relationship between the depth from the surface of the endless metal belt and the hardness.

The maraging steel used in the present embodiment is:
C is 0.03% or less, Si is 0.10% or less, Mn is 0.10% or less, P is 0.01% or less, and S is 0.01%.
The following low carbon steels, 18-19% Ni, 4.7-
5.2% Mo, 0.05-0.15% Al, 0.5
18% Ni steel with 0-0.70% Ti, 8.5-9.5% Co.

In the manufacturing method of this embodiment, first, a thin sheet of maraging steel having the above composition is bent and looped, and then the ends are welded to form a cylindrical drum. Next, this was heated to 820-830 ° C. in a vacuum furnace for 2 hours.
The solution treatment is performed by holding for 0 to 60 minutes. By the solution treatment, the crystals can be rearranged and welding distortion can be removed.

Next, the cylindrical drum is cut into a predetermined width to form a ring. Since the edge of the ring-shaped body is raised by the cutting, the ring-shaped body is chamfered by barrel polishing, and then cold-rolled at a rolling reduction of 40 to 50% to form a ring.

Next, as shown in FIG. 1 (a), the ring W is housed in a heat treatment apparatus and subjected to aging treatment and nitriding treatment. In the heat treatment apparatus shown in FIG. 1A, an aging treatment chamber 1 and a nitriding treatment chamber 2 and an intermediate chamber 3 between both chambers 1 and 2 are linearly arranged. Doors 4 and 5 provided between room 2 and intermediate room 3 and which can be opened and closed by vertical movement.
Is to be communicated through. The aging treatment chamber 1 has an openable / closable carry-in port 6 on the side opposite to the intermediate chamber 3, and the nitriding treatment chamber 2 has an openable / closable carry-out port 7 on the opposite side to the intermediate chamber 3.

In the heat treatment apparatus shown in FIG. 1A, first, the ring W is carried into the aging treatment chamber 1 from the carry-in port 6. When the ring W is carried in, the aging treatment chamber 1 is heated by a heating means (not shown) and heated to a predetermined aging treatment temperature, and the aging treatment is performed by maintaining the ring W at the aging treatment temperature for a predetermined time. Do. The aging treatment is performed in a nitrogen atmosphere introduced into the aging treatment chamber 1 by an introduction means (not shown), thereby preventing an oxide layer from being formed on the surface of the ring W, and advantageously performing a subsequent nitriding treatment. It can be carried out.

When the aging process is completed, the door 4 is opened, and the ring W is moved from the aging chamber 1 to the intermediate chamber 3. When the door 4 is closed, the door 5 is opened, and the ring W is moved from the intermediate chamber 3 to the nitriding chamber 2.

At this time, an atmosphere containing at least ammonia gas is introduced into the nitriding chamber 2 by introducing means (not shown), and the nitriding chamber 2 is heated to a temperature equal to or higher than the aging temperature in the aging chamber 1. .
The intermediate chamber 3 is heated to the same temperature as the aging temperature in the aging chamber 1 or to an intermediate temperature between the aging temperature in the aging chamber 1 and the higher temperature in the nitriding chamber 2. The atmosphere introduced into the nitriding chamber 2 is an ammonia gas atmosphere containing other inert gas in addition to pure ammonia or a mixed gas atmosphere of ammonia gas and RX gas.

In this embodiment, the ring W is moved from the aging chamber 1 to the nitriding chamber 2 via the intermediate chamber 3 as described above, so that the ring W is affected by the temperature difference during the movement. Can be reduced. Opening doors 4, 5
Are movable up and down, the atmosphere in the aging chamber 1 and the nitriding chamber 2 can be stably maintained without disturbing the atmosphere.

Next, the ring W is mixed with the ammonia gas atmosphere or the ammonia gas in the nitriding chamber 2 previously heated to the same temperature as the aging temperature or higher than the aging temperature as described above. The nitriding treatment is performed by maintaining the mixed gas atmosphere with the RX gas for a predetermined time. When the nitriding is completed, the ring W is cooled in the nitriding chamber 2 and is unloaded from the outlet 7.

Further, as shown in FIG. 1B, the heat treatment apparatus may further include a cooling chamber 8 adjacent to the nitriding chamber 2 on the opposite side of the intermediate chamber 3. The cooling chamber 8 communicates with the nitriding chamber 2 through a door 7 that can be opened and closed by vertical movement, and has a carry-out port 9 that can be opened and closed by vertical movement on the side opposite to the nitriding chamber 2.

In the heat treatment apparatus shown in FIG.
After being treated in the aging treatment chamber 1 and the nitriding treatment chamber 2 in exactly the same manner as the heat treatment apparatus shown in FIG. 1 (a), it is moved to the cooling chamber 8 through the door 7 and cooled in the cooling chamber 8. After a while
It is carried out from the carry-out port 9.

Next, FIG. 2A shows a heating pattern in the heat treatment apparatus when the intermediate chamber 3 and the gas nitrocarburizing chamber 2 are previously heated to the same temperature as the aging temperature in the aging chamber 1. Show. For comparison, FIG. 2B shows a heating pattern when the conventional aging treatment chamber and the conventional soft gas treatment chamber are completely independent.

From FIG. 2 (a), according to the heat treatment apparatus of this embodiment, the aging treatment A is followed by the nitriding treatment B without cooling, as in the conventional case shown in FIG. 2 (b). Time C for cooling in aging chamber 1 after aging treatment A
And the time D for heating to the nitriding temperature in the nitriding chamber 2.
It is clear that the processing time can be reduced by a time corresponding to (C + D).

In the conventional case shown in FIG. 2B, even if the set temperature rises in the nitriding chamber 2, the actual ambient temperature (shown by a phantom line in FIG. 2B) does not increase. And it takes time until the ambient temperature in the nitriding chamber 2 becomes uniform. For this reason, in the case of the prior art shown in FIG. However, in the present embodiment, as shown in FIG. 2A, the nitriding temperature in the nitriding treatment B is previously heated to the same temperature as the aging treatment temperature in the aging treatment chamber 1, and the atmosphere temperature in the nitriding treatment chamber 2 is uniform. Therefore, the nitriding treatment can be performed uniformly.

Next, the relationship between the heating time in the aging treatment A and the aging hardness will be described with reference to FIG.
From FIG. 3, when the aging temperature is 480 ° C., 60
The aging hardness does not reach the maximum value even after heating for minutes, indicating that the aging hardness is in the sub-aging range. However, the aging temperature is 500 ℃
In this case, it is apparent that the aging hardness reaches the maximum value after heating for 60 minutes, and that the aging hardness starts to decrease when the heating time exceeds 60 minutes due to overaging. Also, when the aging temperature is 520 ° C., it is clear that if the heating time exceeds 20 minutes, overaging occurs and the aging hardness starts to decrease.

Therefore, in this embodiment, in order to avoid a decrease in aging hardness due to the overaging, the heating time in the aging treatment A is limited to the sub-aging region, and the subsequent nitriding treatment B is performed.
The aging hardness reaches the maximum value by heating.
Therefore, for example, when the aging temperature is 500 ° C.,
The heating time in the aging treatment A is preferably less than 60 minutes.

Next, the relationship between the nitriding temperature and the heating time in the nitriding B will be described. According to the nitriding treatment, the ring W is formed with a nitrided layer by infiltration of nitrogen from its surface, and the nitrided layer develops hardness. Therefore, in the ring W, a hardness gradient is formed from the surface to the inside, where the hardness decreases as the nitrogen penetration depth increases.

In an endless metal belt used for a power transmission belt of a continuously variable transmission, a plurality of rings W are used in a superposed state, and when an engine brake is applied, the surfaces of the rings W are relative to each other. Sliding occurs. In view of this, the surface of the ring W is, of course, large in terms of fatigue resistance against the slip, but it is desired that an appropriate hardness gradient is formed from the surface to the inside.

Next, as shown in FIG. 2 (a), the state of the hardness gradient formed when the ring W subjected to the aging treatment A within the sub-aging range is subjected to the nitriding treatment B as shown in FIG. Shown in
In Table 1, aa is the optimum hardness gradient for the power transmission belt of the continuously variable transmission, bb is the applicable hardness gradient, cc is the low gradient and inappropriate hardness gradient, and dd is the high gradient and inappropriate hardness gradient. Shown respectively.

[0057]

[Table 1]

From Table 1, it can be seen that the aging treatment A is within the range of sub-aging.
When the nitriding treatment B is performed on the ring W to which the nitriding treatment is performed, the nitriding treatment temperature is set in a range of 480 to 520 ° C., and the heating time is set to 4 hours.
It is clear that by setting the range to 5 to 60 minutes, it is possible to obtain an optimum hardness gradient for the power transmission belt of the continuously variable transmission.

Next, according to the heating pattern shown in FIG. 2A, the aging treatment A is performed at 500 ° C. for 40 minutes within the range of sub-aging, and the ring W when the nitriding treatment B is performed at 500 ° C. for 50 minutes. Between hardness from surface depth and hardness (hardness gradient)
Is shown by a solid line in FIG. Also, for comparison, FIG.
According to the heating pattern shown, aging treatment A was performed at 500 ° C for 6 hours.
The hardness gradient when the peak aging hardness is obtained for 0 minute and the nitriding treatment B is performed at 500 ° C. for 50 minutes is shown by a broken line in FIG.

FIG. 4 shows that the hardness on the surface of the ring W is larger in the case of the manufacturing method of the present embodiment (shown by a solid line in FIG. 4) than in the case of the comparative embodiment (shown by a broken line in FIG. 4). It is apparent that the hardness gradient in the range from the surface of the ring W to a depth of 30 μm is higher than that in the comparative example.

[Brief description of the drawings]

FIG. 1 is an explanatory sectional view showing one configuration example of a heat treatment apparatus of the present invention.

FIG. 2 is a graph showing heating patterns of an aging treatment and a gas nitrocarburizing treatment.

FIG. 3 is a graph showing the relationship between the heating time and the aging hardness in the aging treatment.

FIG. 4 is a graph showing the relationship between the depth from the surface of the endless metal belt and the hardness.

[Explanation of symbols] 1 ... Aging chamber, 2 ... Nitriding chamber, 3 ... Intermediate chamber,
4, 5, 7 ... opening and closing door, 8 ... cooling room.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) C21D 9/50 102 C21D 9/50 102Z C23C 8/26 C23C 8/26 F16G 1/26 F16G 1/26 5 / 16 5/16 B

Claims (9)

[Claims] 1. A ring formed by cutting a drum formed by welding the ends of a maraging steel plate to a predetermined width to form a ring, rolling the ring to a predetermined length, and correcting the circumferential length. In a method of manufacturing an endless metal belt used for a power transmission belt of a continuously variable transmission by laminating a plurality of rings after performing an aging treatment and a nitriding treatment, a ring rolled to a predetermined length is used. Housed in an aging treatment room,
Heating the aging chamber to a predetermined aging temperature, maintaining the ring at the aging temperature for a predetermined time to perform aging, and after the aging, maintaining the ring at the aging temperature. The nitriding treatment is provided independently of the aging treatment chamber, moved to a nitriding treatment chamber heated to a predetermined nitriding treatment temperature in advance, and held at the nitriding treatment temperature for at least a predetermined time under an atmosphere containing ammonia gas to perform the nitriding treatment. After the application, a step of cooling the endless metal belt. 2. The nitriding treatment includes a gas nitriding treatment in which the ring is kept at the nitriding treatment temperature for a predetermined time in an ammonia gas atmosphere, or the ring is treated with an ammonia gas and an RX gas.
The method for producing an endless metal belt according to claim 1, wherein the method is selected from gas nitrocarburizing treatment in which the nitriding temperature is maintained for a predetermined time in a mixed gas atmosphere with a gas. 3. The method for producing an endless metal belt according to claim 1, wherein the nitriding treatment is performed at a nitriding treatment temperature equal to or higher than the aging treatment temperature. 4. The method for producing an endless metal belt according to claim 1, wherein said ring is subjected to a nitriding treatment and then cooled in said nitriding treatment chamber. 5. The method according to claim 1, wherein the ring is subjected to a nitriding treatment, and then moved to a cooling chamber provided so as to be able to communicate with the nitriding chamber through an openable / closable door, and cooled in the cooling chamber. The method for producing an endless metal belt according to any one of claims 1 to 3. 6. The method according to claim 1, wherein the aging treatment is performed within a range where the aging hardness is less than a maximum value, and the aging hardness is made to reach the maximum value by the nitriding treatment. The method for producing an endless metal belt according to the above item. 7. A ring formed by cutting a drum formed by welding the ends of a maraging steel plate to a predetermined width to form a ring, rolling the ring to a predetermined length, and correcting the circumferential length. ,
A heat treatment apparatus for performing an aging treatment and a nitriding treatment on the ring, wherein the aging treatment chamber holds the ring and is heated to a predetermined aging treatment temperature to hold the ring at the aging treatment temperature for a predetermined time, A nitriding chamber heated to a predetermined nitriding temperature, accommodating the ring, and holding the ring at the nitriding temperature for at least a predetermined time in an atmosphere containing at least ammonia gas; A heat treatment apparatus, which is provided so as to be able to communicate with a treatment chamber via a door that can be freely opened and closed. 8. An intermediate chamber preheated to an intermediate temperature between the aging temperature and the nitriding temperature between the nitriding chamber and the aging chamber, wherein each chamber is openable and closable. While being provided so as to be able to communicate through a door, the ring is
The heat treatment apparatus according to claim 7, wherein the heat treatment apparatus is moved from the aging treatment chamber to the nitriding treatment chamber via the intermediate chamber. 9. A cooling chamber communicated with the nitriding chamber through a door that can be opened and closed, and a ring subjected to nitriding in the nitriding chamber is moved from the nitriding chamber to the cooling chamber. ,
The heat treatment apparatus according to claim 7, wherein the heat treatment apparatus is cooled in the cooling chamber.