JP3850659B2 - Manufacturing method of laminated ring - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a laminated ring constituting a continuously variable transmission belt used for power transmission of a continuously variable transmission.
[0002]
[Prior art]
A continuously variable transmission belt used for power transmission of a continuously variable transmission is configured by a stacked ring in which a plurality of metal rings are stacked and a number of metal elements assembled to the stacked rings.
[0003]
Conventionally, the laminated ring is manufactured by the following method. First, the ends of the maraging steel thin plates, which are super-extreme steels, are welded together to form a cylindrical drum, and the hardness unevenness that is partially hardened by the heat during the welding to the drum is homogenized. In order to do so, the first solution treatment is performed. Next, the solution-treated drum is cut into a predetermined width to form a ring, and the ring is rolled. Next, in order to recrystallize the rolled structure on the rolled ring and restore the shape of the metal structure deformed by rolling, a second solution treatment is performed. Then, the ring after the solution treatment is corrected to a predetermined circumference, subjected to aging and nitriding treatment to improve the hardness, and then a plurality of rings having different circumferences are laminated to form a laminated ring. To do.
[0004]
In order to use the laminated ring for the continuously variable transmission belt, it is desirable that the laminated ring has excellent surface hardness as well as excellent wear resistance and fatigue resistance. In Japanese Patent Publication No. 5-82452, the ring is stretched between a pair of rollers and rotated, and the ring is stretched to correct the circumferential length. A production method is described which imparts a compressive residual stress of 60 kg / mm ² . According to the description in the above publication, the ring to which the compressive residual stress is applied is maintained at a temperature of 400 to 480 ° C. for a predetermined time in a pure ammonia atmosphere immediately after the circumference correction without performing other processing. It is said that a ring excellent in wear resistance and fatigue strength can be obtained by performing aging treatment and nitriding treatment simultaneously.
[0005]
However, according to the manufacturing method described in the above publication, there is a disadvantage in that in the nitriding treatment after the circumference correction, nitrogen is difficult to diffuse into the metal structure and sufficient surface hardness may not be obtained. Moreover, when the manufacturing method described in the above publication is used, the nitriding treatment is performed in a pure ammonia atmosphere, which disadvantageously increases the manufacturing cost.
[0006]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for manufacturing a laminated ring that can eliminate such disadvantages and obtain a ring having excellent surface hardness at low cost.
[0007]
[Means for Solving the Problems]
The present inventors have made various studies on the reason why sufficient surface hardness may not be obtained in the production method described in JP-B-5-82452. As a result, when the nitriding treatment is performed immediately after the circumference correction without performing other treatments, Al, Ti, etc., which are solid-solutioned as an aging strengthening element, are present in the maraging steel near the surface of the ring. Therefore, while nitrogen is reacted and consumed with Al and Ti, it has been found that nitrides such as AlN and TiN formed by the reaction prevent diffusion of nitrogen into the metal structure. As a result of further investigation based on the above findings, the present inventors have performed aging treatment prior to nitriding treatment after circumference correction, and the aging strengthening elements such as Al and Ti are made of a metal such as Ni ₃ AlTi. It was found that by precipitating and fixing as an intercalation compound, nitrogen was sufficiently diffused into the metal structure in the subsequent nitriding treatment, and excellent surface hardness was obtained, and the present invention was completed.
[0008]
Therefore, the method for manufacturing a laminated ring according to the present invention comprises a cylindrical drum formed by welding ends of thin sheets of maraging steel containing Ni and containing Al and Ti as aging strengthening elements. Forming a ring by cutting into a ring, a step of rolling the ring, a step of forming a solution on the rolled ring, and a step of correcting the circumference of the ring subjected to the solution formation to a predetermined circumference And aging treatment and nitriding treatment on the ring whose circumference has been corrected, in the method of manufacturing a laminated ring, the ring whose calibration is corrected is subjected to aging treatment , and Al and Ti are intermetallic compounds. ₃ and fixing to precipitate as AlTi, after aging treatment completion, nitride and cooling the ring, then in a mixed atmosphere of an inert gas and ammonia to the ring to which the aging process has been performed And a step of performing management, the aging treatment is kept to a sub Aging aging hardness of the ring is less than the maximum value, the aging hardness of the ring by the nitriding treatment, characterized in that to reach the maximum value.
[0009]
In the manufacturing method of the present invention, after the circumference of the solution-treated ring is corrected to a predetermined circumference, an aging treatment is first performed. In the maraging steel, Al, Ti and the like are dissolved as aging strengthening elements, but the Al, Ti and the like are precipitated and fixed as an intermetallic compound such as Ni ₃ AlTi by the aging treatment.
[0010]
Therefore, when the ring subjected to the aging treatment is subjected to nitriding treatment, nitrogen does not react with Al, Ti, etc., and nitrides such as AlN, TiN are not formed, so that the nitrogen is hindered by the nitride. It can penetrate deeply into the metal structure without forming iron and nitride, which are base materials of maraging steel.
[0011]
As a result, excellent surface hardness can be obtained by the effects of the aging treatment and nitriding treatment.
[0012]
Further, according to the production method of the present invention, in the nitriding treatment, nitrogen can penetrate deeply into the metal structure without being consumed in the reaction with Al, Ti or the like. Therefore, in the production method of the present invention, after performing the aging treatment, the nitriding treatment may be performed in a mixed atmosphere of an inert gas and ammonia, and the production cost can be reduced by reducing the required amount of ammonia. Can do.
[0013]
Further, in the production method of the present invention, in order to provide excellent wear resistance and fatigue strength resistance, the circumference correction is performed in an amount of 0.2 to 0.9% with respect to the solution-treated ring. It is preferable to carry out with a circumference correction factor in the range. The circumference correction factor is expressed by the following equation (1).
[0014]
Perimeter correction ratio (%) = (perimeter after correction−perimeter before correction) / perimeter before correction × 100 (1) When the perimeter correction ratio is less than 0.2%, compression residual Although a stress is generated, the permanent length cannot be obtained, and the circumference cannot be corrected. Moreover, if the circumference correction rate exceeds 0.9%, the ring may be broken, which is not preferable.
[0015]
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 a method for manufacturing a laminated ring of the present embodiment, and FIG. 2 is a diagram showing a relationship between a ring circumference correction factor and a compressive residual stress applied to the ring surface. is there.
[0016]
In the manufacturing method of this embodiment, first, as shown in FIG. 1, the maraging steel thin plate 1 is bent to form a loop, and then the ends are welded to form a cylindrical drum 2. The maraging steel is a low carbon steel having C of 0.03% or less, Si of 0.10% or less, Mn of 0.10% or less, P of 0.01% or less, and S of 0.01% or less. Yes, 18-19% Ni, 4.7-5.2% Mo, 0.05-0.15% Al, 0.50-0.70% Ti, 8.5-9.5% 18% Ni steel containing Co. 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 of the drum 2.
[0017]
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 the ring 4.
[0018]
The ring 4 formed as described above is then rolled at a rolling reduction of 40 to 50%. A rolled structure is formed on the rolled ring 4 with a thickness of about 30 μm from the surface. Therefore, the rolled ring 4 is accommodated in the heating furnace 5 and subjected to the second solution, thereby eliminating the rolled structure and forming uniform metal crystal grains.
[0019]
In the present embodiment, next, the circumference of the solution-formed ring 4 is corrected with a circumference correction factor in the range of 0.2 to 0.9%. The circumference correction factor is expressed by the above equation (1). FIG. 2 shows the relationship between the strain rate and the compressive residual stress when the ring 4 is expanded.
[0020]
In FIG. 2, the thick solid line P shows the relationship between the strain rate when the ring 4 is stretched and the nominal tensile stress (MPa), and the solid line Q shows the strain rate and the tensile stress (MPa at the center of the thickness of the ring 4). The solid line R indicates the relationship between the strain rate and the tensile stress (MPa) of the outermost layer of the ring 4. The solid lines P, Q, and R become one straight line OS in the range where the distortion rate is small, and the straight line OS indicates the Young's modulus of the ring 4. The end T of the thick solid line P indicates the breaking limit point of the ring 4, and the ring 4 breaks when the strain rate exceeds T (%).
[0021]
In the range in which the tensile stress when the ring 4 is stretched under a load is in the straight line portion between the OSs in FIG. 2, when the load is released, the ring 4 contracts along the straight line OS and returns to the original length. Cannot be obtained. However, the ring 4 is parallel to the straight line OS from the point B ₁ when the load is released after extending the straight line OS to the range where the straight line OS branches to the solid lines P, Q, R, for example, to the point B ₁ on the thick solid line P. When shrinking along the straight line and the tensile stress becomes zero, an elongation corresponding to the point A ₁ on the horizontal axis is obtained. Therefore, the distortion rate (elongation rate) is equal to the circumference correction rate in the ring 4 subjected to circumference correction.
[0022]
Conversely, in order to obtain the elongation corresponding to the point A ₁ on the horizontal axis, a straight line parallel to the straight line OS is drawn from the point A ₁ , and the point B ₁ where the straight line intersects the thick solid line P This indicates that it is necessary to apply a load corresponding to the tensile stress.
[0023]
Further, when releasing the load after stretching the ring 4 to the point B ₁ on the thick solid line P, and parallel straight lines OS from the point B ₁ 'on the straight line Q corresponding to the point B ₁ and the same strain rate When pulled, a residual tensile stress corresponding to the point A ₁ ′ corresponding to the same strain rate as the point A ₁ on the straight line is generated inside the ring 4. In this case, the outermost layer of the ring 4, when drawn parallel straight lines OS from the point B ₁ on the straight line R corresponding to the point B ₁ and the same strain rate '', points with straight lines A residual compressive stress corresponding to _one same a ₁ point corresponding to the distortion rate 'and' occurs.
[0024]
In FIG. 2, the point A ₁ has a distortion rate of 0.2%. Therefore, in order to correct the circumference of the ring 4 with a circumference correction rate of 0.2% corresponding to the point A ₁ , the ring 4 is a thick solid line. It can be seen that it is necessary to extend to point B ₁ on P. Further, when the load is released after the ring 4 is extended to the point B ₁ on the thick solid line P, it is clear that a compressive stress of about −150 MPa corresponding to the point A ₁ ″ is generated in the outermost layer portion of the ring 4. is there.
[0025]
Similarly, in order to correct the circumference of ring 4 with a circumference correction factor of 0.4% corresponding to point A ₂ , it is necessary to extend ring 4 to point B ₂ on thick solid line P, and thereafter When the load is released, it is apparent that a compressive stress of about −200 MPa corresponding to the point A ₂ ″ is generated in the outermost layer portion of the ring 4. Further, in order to correct the circumference of the ring 4 with the circumference correction factor of 0.9% corresponding to the point A ₃ , it is necessary to extend the ring 4 to the point B ₃ on the thick solid line P, and then the load When is released, it is apparent that a compressive stress of about −300 MPa corresponding to the point A ₃ ″ is generated in the outermost layer portion of the ring 4.
[0026]
Further, from FIG. 2, when the circumference of the ring 4 is corrected with a circumference correction factor exceeding 0.9%, it is parallel to the straight line OS from a point on the horizontal axis corresponding to such an elongation rate (distortion rate). When a straight line is drawn, it is clear that the intersection of the straight line and the thick solid line P approaches the breaking limit point T of the ring 4 and the ring 4 may be broken. Further, when trying to correct the circumference of the ring 4 with a circumference correction factor of less than 0.2%, a straight line parallel to the straight line OS was drawn from a point on the horizontal axis corresponding to such an elongation rate (distortion rate). Sometimes, the straight line approximates the straight line OS, and no permanent distortion occurs, so it is clear that the circumference of the ring 4 cannot be corrected.
[0027]
Therefore, in the manufacturing method of the present embodiment, the circumferential length is corrected with the circumferential length correction rate in the range of 0.2 to 0.9%, thereby applying a compressive residual stress of about 150 to 300 MPa to the surface of the ring 4. The ring 4 can be provided with excellent wear resistance and fatigue resistance due to the compressive residual stress.
[0028]
In this embodiment, next, as shown in FIG. 1, the ring 4 subjected to the circumference correction is accommodated in a heating furnace (not shown), and is kept at a predetermined temperature for a predetermined time to perform an aging treatment.
[0029]
Next, when the predetermined time has elapsed and the aging treatment is completed, the ring 4 is cooled in a heating furnace and transferred to a nitriding apparatus. Then, in a mixed atmosphere of an inert gas such as nitrogen and ammonia gas, the gas nitriding process is performed by holding the ring 4 at a predetermined temperature for a predetermined time in the nitriding apparatus. When the predetermined time has elapsed and the gas nitriding process is completed, the ring 4 is cooled in the nitriding apparatus.
[0030]
According to the gas nitriding treatment, a compressive residual stress of −800 MPa can be applied to the outermost layer of the ring 4 even for the ring 4 that has not been subjected to the circumference correction. However, in the method of the present embodiment, since the compressive residual stress is applied to the outermost layer of the ring 4 even by the circumference correction, a larger compressive stress is applied together with the compressive stress applied by the gas nitriding treatment. Can be granted.
[0031]
The compressive stress applied to the outermost layer of the ring 4 after the gas nitriding treatment is −1000 MPa in the ring 4 whose circumference is corrected with a circumference correction factor of 0.4%, and with a circumference correction factor of 0.9%. In the ring 4 whose circumference is corrected, it reaches −1100 MPa. Therefore, in the method of the present embodiment, the ring 4 can be provided with further superior wear resistance and fatigue resistance due to the compressive residual stress.
[0032]
In the method of this embodiment, the aging strengthening element such as Al and Ti contained in the ring 4 is precipitated and fixed as an intermetallic compound such as Ni ₃ AlTi by the aging treatment. Is not consumed in the reaction with Al, Ti or the like. Accordingly, the ammonia gas may be used in an amount required for nitriding the ring 4, and need not be used excessively.
[0033]
Next, the ring 4 subjected to the nitriding treatment is formed by laminating a plurality of rings 4 having different circumferential lengths little by little to form a laminated ring (not shown).
[0034]
In the nitriding treatment, the aging of the ring 4 proceeds by heating. Therefore, in the aging treatment, only the sub-aging where the aging hardness of the ring 4 is less than the maximum value is limited, and the aging hardness of the ring 4 reaches the maximum value by the nitriding treatment .
[0035]
Further, in the manufacturing method of the present embodiment, after the pre-Symbol aging treatment ended, once can better to cool the ring 4 to obtain a ring 4 which is excellent in surface hardness.
[Brief description of the drawings]
FIG. 1 is a process chart schematically showing an embodiment of a method for producing a laminated ring of the present invention.
FIG. 2 is a diagram showing a relationship between a ring circumference correction factor and a compressive residual stress applied to the ring surface.
[Explanation of symbols]
1 ... thin plate of maraging steel, 2 ... drum, 4 ... ring.

Claims (1)

A step of cutting a cylindrical drum formed by welding ends of thin sheets of maraging steel containing Ni and Al and Ti as aging strengthening elements to form a ring; and A step of rolling the ring, a step of performing solution treatment on the rolled ring, a step of correcting the circumference of the ring subjected to the solution treatment to a predetermined circumferential length, an aging treatment on the ring having the corrected circumferential length, and In a method for manufacturing a laminated ring comprising a step of performing nitriding
Aging treatment of the circumference-corrected ring to precipitate and fix Al and Ti as Ni ₃ AlTi , which is an intermetallic compound, a step of cooling the ring after completion of the aging treatment, and then the aging treatment And a step of performing nitriding treatment in a mixed atmosphere of an inert gas and ammonia on the ring subjected to
The aging treatment is limited to sub-aging where the aging hardness of the ring is less than the maximum value, and the aging hardness of the ring reaches the maximum value by the nitriding treatment .

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