JP3784622B2 - Ring manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a ring used for a continuously variable transmission belt or the like.
[0002]
[Prior art]
Conventionally, a ring used for a continuously variable transmission belt or the like is manufactured by the following manufacturing method. First, end portions of a thin plate of maraging steel, which is super strong steel, are welded together to form a cylindrical drum, and a first solution treatment is performed on the drum. Next, the solutionized drum is cut into a predetermined width to form a ring, and after the ring is rolled, a second solution treatment is performed on the rolled ring. Then, after correcting the melted ring to a predetermined circumferential length and improving the hardness by aging and nitriding treatment, a plurality of rings are laminated together to form a laminated ring, and a continuously variable transmission belt And
[0003]
In the manufacturing method, the first solution formation on the drum after welding is performed in order to homogenize the hardness that has been partially hardened by the heat during the welding, and by performing the solution formation, Rolling after forming a ring by cutting the drum into a predetermined width can be easily performed. The solution treatment is generally performed by heating at a temperature equal to or higher than the recrystallization temperature of the maraging steel. At this time, the maraging steel contains Ti, Mo, etc. as aging precipitation strengthening elements. When these elements, particularly Ti, are oxidized, the predetermined hardness may not be obtained by the subsequent aging treatment. Therefore, the solution treatment is performed in a vacuum furnace in order to avoid oxidation of the aging precipitation strengthening element.
[0004]
On the other hand, the rolled ring has a rolled structure in which metal crystals are crushed by the rolling. Nitrogen does not easily penetrate in the subsequent nitriding treatment, and nitriding may not be performed uniformly. Therefore, in order to restore the deformed metal crystal particle shape and facilitate the nitriding treatment on the rolled ring, a second solution treatment is performed.
[0005]
The second solution treatment is also generally performed by heating at a temperature higher than the recrystallization temperature of the maraging steel, and it is desirable that the aging precipitation strengthening element is not oxidized. However, since the vacuum furnace is expensive, the second solution treatment is performed using a heating furnace in which the inside of the furnace is a reducing atmosphere. As the reducing atmosphere, for example, a nitrogen atmosphere containing 1 to 10% hydrogen is used. The nitrogen atmosphere contains a small amount of oxygen. However, by reacting the hydrogen with oxygen, the oxygen can be removed and oxidation of the aging precipitation strengthening element can be prevented. According to the conventional manufacturing method, the number of vacuum furnaces can be reduced by reducing the number of vacuum furnaces by performing the second solution out of the two solutions in a reducing atmosphere using a heating furnace. it can.
[0006]
However, if separate furnaces are used for the first and second solution treatments, there is an inconvenience that the production cost cannot be sufficiently reduced.
[0007]
[Problems to be solved by the invention]
An object of the present invention is to provide a method of manufacturing a laminated ring that can eliminate such inconvenience and further reduce the manufacturing cost.
[0008]
[Means for Solving the Problems]
In order to eliminate the inconvenience, the present inventors have repeatedly studied the conditions for solution treatment between the drum after welding and the ring after rolling, and as a result, Ti, Mo contained as an aging precipitation strengthening element in the maraging steel. In order to prevent such oxidation, it has been found that a complete vacuum is not necessarily required, and a pressure of 10 ⁻³ Pa or less is sufficient, and the present invention has been completed.
[0009]
Therefore, in order to achieve the above object, the ring manufacturing method of the present invention includes a step of welding the ends of thin sheets of maraging steel containing Ti and Mo as aging precipitation elements to form a ring-shaped drum, and A first solution treatment for the drum after welding, a step of cutting the solution-formed drum into a predetermined width to form a ring, and rolling the ring; and a second solution for the rolled ring In a method for manufacturing a ring, comprising: a step of performing heat treatment; and a step of aging and nitriding after correcting the solutionized ring to a predetermined circumference, the first solution treatment on the drum after welding, and the rolling The second solution treatment for the subsequent ring is performed using the same heating furnace and under the same temperature condition under a pressure of 10 ⁻³ Pa or less.
[0010]
Under a pressure of 10 ⁻³ Pa or less, Fe that is the base material of the maraging steel and Mo that is one of the aging strengthening elements are substantially in the reduction region. Like Mo, Ti, which is one of the aging strengthening elements, is not reduced under a pressure of 10 ⁻³ Pa or less, but is not at least oxidized.
[0011]
Therefore, according to the manufacturing method of the present invention, by the atmosphere during the heating furnace and 10 ^-3 Pa or less pressure, the first solution for the previous SL drum after welding, the relative ring after the rolling Since the solution treatment of 2 can be performed under the same conditions using the same heating furnace, the manufacturing cost can be greatly reduced.
[0012]
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 diagram schematically showing the manufacturing method of the present embodiment, FIG. 2 is a graph showing hardness before and after solutionizing according to the manufacturing method of the present invention to a drum after welding, and FIG. 3 is a graph after welding. It is a graph which shows the hardness after performing solution treatment according to the manufacturing method of this invention with respect to the drum and the ring after rolling.
[0013]
In the production method of this embodiment, 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% or less. Steel, 18-19% Ni, 4.7-5.2% Mo, 0.05-0.15% Al, 0.50-0.70% Ti, 8.5-9. A laminated ring for a continuously variable transmission is manufactured in accordance with the process of FIG. 1 using maraging steel which is 18% Ni steel containing 5% Co. Of the maraging steel composition, Ti and Mo are aging precipitation strengthening elements. When Ti and Mo are oxidized, uniform aging hardness cannot be obtained in the subsequent aging treatment.
[0014]
In the manufacturing method of this embodiment, first, as shown in FIG. 1, a maraging steel thin plate 1 having the above composition is bent to form a loop, and then the ends are welded to form a cylindrical drum 2. . At this time, the maraging steel exhibits age hardening due to the heat of welding, and high hardness portions appear in portions around 1 mm on both sides from the welding center 2a of the drum 2.
[0015]
Then, next, the drum 2 is accommodated in the heating furnace 3, and the first solution treatment is performed at a temperature not lower than 10 ⁻³ Pa and not lower than the recrystallization temperature of the maraging steel and not higher than 850 ° C. . In the first solution heat treatment, the pressure of the heating furnace 3 may be 10 ⁻⁴ Pa or less, but it is difficult to achieve with normal vacuum evacuation, and the cost is increased.
[0016]
When the first solution is finished, the drum 2 is taken out of the heating furnace 3 and cut into a predetermined width to form a ring 4. Since the entire hardness of the drum 2 is homogenized as a result of the first solution treatment, the cutting can be easily performed and rolling is also facilitated. The ring 4 is then rolled at a rolling reduction of 40-50%.
[0017]
As a result of the rolling, a rolled structure in which metal crystals are crushed is formed in the ring 4, and in this state, nitrogen does not easily penetrate into the metal structure in the subsequent nitriding treatment. Then, next, the ring 4 is accommodated in the heating furnace 3 again, and the second solution treatment is performed under the same temperature condition as the first solution treatment under a pressure of 10 ⁻³ Pa or less.
[0018]
When the second solution treatment is completed, the ring 4 is taken out of the heating furnace 3 and corrected to a predetermined circumference. The circumference correction is performed, for example, by applying a load in a direction perpendicular to the traveling direction of the ring 4 while rotating the ring 4 around a driving roller and a driven roller (not shown).
[0019]
Next, an aging treatment and a nitriding treatment are performed on the ring whose circumference has been corrected. The aging treatment is performed, for example, by holding the ring in a heating furnace (not shown) at a temperature in the range of 450 to 530 ° C. for 90 to 240 minutes. The nitriding treatment is performed by a method such as gas nitriding, gas soft nitriding, or salt bath nitriding.
[0020]
A plurality of rings 4 having a predetermined hardness by the aging / nitriding treatment are laminated together to form a laminated ring suitable as a power transmission belt for a continuously variable transmission.
[0021]
In the drum 2, when the ends of the maraging steel thin plates 1 are welded to each other, as shown in FIG. A portion with high hardness appears. Therefore, in the present embodiment, such a drum 2 is accommodated in the heating furnace 3, and the first solution treatment is performed under the temperature condition under a pressure of 10 ⁻³ Pa or less. As a result, in the drum 2, Mo and Ti which are the aging strengthening elements and Fe which is the base material of the maraging steel are not oxidized, and the high hardness portion is eliminated, and the overall hardness is reduced as shown in FIG. It can be homogenized.
[0022]
On the other hand, the rolled ring 4 has a rolled structure in which metal crystals are crushed as a result of the rolling. Therefore, in this embodiment, such a drum 2 is accommodated in the heating furnace 3, and the second solution is formed under the same temperature condition as the first solution under a pressure of 10 ⁻³ Pa or less. As a result, in the ring 4, the shape of the metal crystals in the rolled structure is restored to the state before rolling without oxidizing the Mo and Ti as the aging strengthening elements and Fe as the base material of the maraging steel. can do.
[0023]
As shown in FIG. 3, the ring 4 after the second solution forming has a uniform overall hardness, and it is clear that the particle shape of the metal crystal is restored to the state before rolling. From FIG. 3, the hardness of the ring 4 after the second solution treatment is substantially equal to the hardness of the drum 2 after the first solution treatment, and both solution treatments are 10 ⁻³ Pa. It is clear that an equivalent effect can be obtained by carrying out under the same temperature conditions under the following pressure. The hardness of the drum 2 after the first solution treatment is the same as that shown in FIG. 2, but is reprinted for comparison.
[0024]
In the manufacturing method of the present embodiment, the second solution treatment with respect to the ring 4 may be performed independently of or simultaneously with the first solution treatment with respect to the drum 2 welded after the ring 4. When the second solution treatment for the ring 4 and the first solution treatment for the drum 2 are performed at the same time, the ring 4 takes time to restore the rolling structure, so the first solution treatment for the drum 2 is performed by the ring 4. For the same time as the second solution treatment. Further, a partition wall (not shown) is provided in the heating furnace 3 to divide the inside of the furnace into two sections, and in each section, the second solution for the ring 4 and the first solution for the drum 2 are performed independently. May be.
[0025]
According to the manufacturing method of the present embodiment, since the oxidation of the aging precipitation strengthening element is suppressed in the first and second solution treatments, it is possible to uniformly perform the aging treatment of the circumferentially corrected ring. it can. Further, in the second solution heat treatment, the metal crystal particle shape of the rolled structure is restored to the state before rolling, so that nitrogen easily penetrates into the metal structure and the nitriding treatment can be easily performed. .
[0026]
In this embodiment, equipment can be made common by performing the first solution heat treatment and the second solution heat treatment under the same temperature condition under the pressure of 10 ⁻³ Pa or less using the same heating furnace 3. Cost can be reduced.
[Brief description of the drawings]
FIG. 1 is a process chart schematically showing an embodiment of a production method of the present invention.
FIG. 2 is a graph showing the hardness before and after solution welding according to the manufacturing method of the present invention is applied to a drum after welding.
FIG. 3 is a graph showing hardness after solution welding according to the manufacturing method of the present invention is applied to a drum after welding and a ring after rolling.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Thin sheet of maraging steel, 2 ... Drum, 3 ... Heating furnace, 4 ... Ring.

Claims (1)

A process of forming a ring-shaped drum by welding ends of thin sheets of maraging steel containing Ti and Mo as aging precipitation elements , a process of performing a first solution treatment on the drum after welding, and a solution treatment. The drum was cut into a predetermined width to form a ring, the step of rolling the ring, the step of performing a second solution treatment on the rolled ring, and the solution-formed ring was corrected to a predetermined circumference. In the manufacturing method of the ring comprising the step of aging and nitriding afterwards,
The first solution treatment for the drum after welding and the second solution treatment for the ring after rolling are performed in the same temperature condition under the pressure of 10 ⁻³ Pa or less using the same heating furnace. A method for manufacturing a ring.

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