JP3452238B2 - Rolling element for high surface pressure and manufacturing method thereof - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used as a continuously variable transmission such as a toroidal type (rolling type) or belt type (variable groove width pulley type) in vehicles such as automobiles and other rotary power sources. The present invention relates to a high surface pressure rolling element which is suitable for a continuously variable transmission that can be used, and can be used as a rolling element that constitutes a toroidal type continuously variable transmission or a belt type continuously variable transmission, and a manufacturing method thereof. .

[0002]

2. Description of the Related Art Continuously variable transmissions are roughly classified into a belt drive system in which a belt and a variable groove width pulley are combined, and a traction drive system in which rolling elements are used. Of these, the former is already used when the transmitted power is small.

On the other hand, the toroidal type (rolling type) is one of the latter and has a mechanism capable of coping with high horsepower.
As shown in FIG. 4, the toroidal type continuously variable transmission 1 has a structure using metal rolling elements that come into contact with each other through lubricating oil. The toroidal type continuously variable transmission 1 includes a loading cam 3 connected to an input shaft 2 and a coupling. The input disks 5 and 5 that rotate integrally via the shaft 4 are provided, and the output disks 9 and 9 that rotate the output shaft 8 via the gears 6 and 7 are provided. , 9 are provided with power rollers 10, 10, 10, 10, and each power roller 10 is supported by a support 12 via a ball bearing 11.

In the toroidal type continuously variable transmission 1, the inclination of the power roller 10 sandwiched between the input disk 5 and the output disk 9 is changed to change the relative rotational speed of the input / output disks 5, 9. The mechanism is such that power is transmitted from the input shaft 2 to the output shaft 8 while shifting gears (Japanese Patent Laid-Open No. 1-229158, etc.).

In such a continuously variable transmission, in order to transmit a large amount of power, the rolling elements (input / output disks 5, 9, power roller 10) of the toroidal type continuously variable transmission 1 are transmitted.
Is a material and manufacturing capable of obtaining high surface hardness with excellent rolling contact fatigue life under high surface pressure (for example, about 3 to 4 GPa) and deep hardened layer depth (for example, ECD = 2 to 3 mm). A method is required.

FIG. 5 shows an example of a belt (drive) type continuously variable transmission. This belt type continuously variable transmission 21 has a variable groove width pulley 22 on the driving side and a groove width on the driven side. In the low state shown in FIG. 5A, the groove width variable pulley 22 on the driving side has a large groove width W _L and a structure in which a belt 24 is wound around the variable pulley 23. it is assumed that the groove width variable pulley 23 of the driven side is a small groove width W _S, 5 driving-side groove width varying pulley 2 in the overdrive state shown in (B)
2 has a small groove width W _S and the driven side groove width variable pulley 23 has a large groove width W _L , so that the gear ratio can be continuously changed between them. , Rolling elements in this case (variable groove width pulleys 22, 2
Also in 3), it is required that the rolling fatigue life is excellent.

Among these, when manufacturing the rolling elements (disks 5, 9 and power roller 10) for the toroidal type continuously variable transmission, for example, the manufacturing process of the disk (5, 9) is shown in FIG. ) And power rollers (10)
As is apparent from FIG. 6B showing the manufacturing process, first, the bar material purchased is cut into predetermined dimensions to form the forging materials 5a, 9a, and 10a, and then the metal mold prepared in advance. After hot forging into the shape of the die forgings 5b, 9b, 10b using, and slowly cooling it, the normalized material is used as the forged rough material, and the forged rough material is machined. Disc materials 5c and 9c having predetermined drawing dimensions
The power roller material 10c is finished and generally carburized or carbonitrided.

The belt type continuously variable transmission rolling elements (pulleys 22 and 23) are manufactured by forming the pulley materials 22c and 23c as shown in FIG. 7 and then carburizing or carbonitriding them in substantially the same process. Has been done.

[0009]

However, in such a conventional rolling element, the rolling element material is carburized or carbonitrided to leave the matrix in the martensite structure or the martensite structure. Since minute carbides (having a particle size of 0.2 to 0.3 μm) or carbonitrides are deposited in an area ratio of about 2 to 10%, a surface pressure of up to 3.5 GPa can be practically used. However, since reduction in size and weight of the unit is emphasized from the viewpoint of improving fuel efficiency, it is necessary to set the surface pressure to about 5 GPa in order to reduce the size and weight of the unit.

However, when the surface pressure increases, the maximum shear stress generation position also becomes deep with a depth of about 0.9 mm, and the amount of heat generation also increases. Therefore, there is a possibility that the tissue change will occur at the maximum shear stress generation position at an early stage. When a microstructure change occurs, surface fatigue damage may occur from this microstructure change point as a starting point, and peeling of the surface starting point occurs due to the inclusion of wear debris generated during use in the rolling surface. However, there is a problem that bending fatigue strength may be insufficient due to high surface pressure.

[0011]

SUMMARY OF THE INVENTION The present invention has been made by paying attention to such a conventional problem and has a depth of about 0.9 m from the surface.
m to a maximum shear stress generation position of 1.5 to 3.0 mm, which is not less than the stress-affected depth, and in some cases 1.5 to 2.
0 mm or 2.0 to 3.0 mm has a chill structure that does not change and decomposes (that is, a cementite (Fe ₃ C) structure that is an iron compound) to prevent peeling from the internal origin and to improve the hardness of cementite. Is Hv1100-
Since it is 1300, surface damage due to foreign matter such as abrasion powder can be prevented, and the decomposition temperature of cementite can be increased to improve the fatigue strength and wear resistance of martensite, bainite and / or sorbite other than cementite. By subjecting the compound layer to nitriding treatment at a temperature below and further applying a compressive residual stress stronger than the compressive residual stress generated in nitriding to the nitrided portion by shot peening treatment, it is possible to solve the above problems. Has an aim.

[0012]

A rolling element for high surface pressure according to the present invention is, as described in claim 1, in a rolling element subjected to a high surface pressure, a martensite structure or bainite in a cast and cooled state. An air-quenched (cast) steel having a microstructure or a mixed microstructure of both (a martensitic microstructure, a bainite microstructure, a sorbite microstructure, or a mixed microstructure of two or three of these may be obtained by controlling the cooling rate after casting). Is used as a material, and 1.5 to 3.0 mm from the surface of the rolling surface of the rolling element has a chill structure (cementite structure), and the core has a martensite structure or bainite structure or a mixture of both. The feature is that it is organized.

In an embodiment of the rolling element for high surface pressure according to the present invention, as described in claim 2,
The matrix hardness may be a sorbite structure having an HRC of 30 to 35.

Similarly, in an embodiment of the rolling element for high surface pressure according to the present invention, as described in claim 3,
A part of the rolling element may be hollow to reduce the weight.

Similarly, in an embodiment of the rolling element for high surface pressure according to the present invention, as described in claim 4,
The nitriding treatment may be performed to improve the fatigue strength.

Similarly, in an embodiment of the rolling element for high surface pressure according to the present invention, as described in claim 5,
A compressive residual stress due to shot peening is applied to a portion other than the chill structure to improve fatigue strength.

Similarly, in an embodiment of the rolling element for high surface pressure according to the present invention, as described in claim 6,
The surface of the rolling surface may have a chill structure (cementite (Fe ₃ C) structure) having a hardness of Hv1100 to 1300 to improve the foreign matter biting resistance.

According to the method for producing a rolling element for high surface pressure according to the present invention, as described in claim 7, when a rolling element having excellent resistance to high surface pressure is produced, the martensite structure is left as it is in the casting cooling state. Or an air-quenched (cast) steel having a bainite structure or a mixed structure of both (in the case where a cooling rate after casting is controlled to form a martensite structure, a bainite structure, a sorbite structure, or a mixed structure of two or three of these) Is also prepared to prepare a cast steel melt thereof, and when the cast steel melt comes into contact with a portion corresponding to the rolling surface of the rolling element inside the mold, heat is taken to form a chill structure. With the chiller set, the molten cast steel is poured into the mold and cast to form a chill structure of 1.5 to 3.0 mm from the surface of the rolling surface, and the core is martensa in a cooled state. It is characterized in that as a preparative tissue or bainite structure or both mixed structure of.

In an embodiment of the method for producing a rolling element for high surface pressure according to the present invention, as described in claim 8, the matrix hardness is controlled by cooling after casting to reduce the matrix hardness to HR.
It can be made to have a solvite structure of C30 to 35.

Similarly, in the embodiment of the method for manufacturing a rolling element for high surface pressure according to the present invention, as described in claim 9, by using a precision casting mold as a mold, the machining step of the next step is performed. It can be shortened.

Similarly, in an embodiment of the method for manufacturing a rolling element for high surface pressure according to the present invention, as described in claim 10, a part of the rolling element is made hollow so as to reduce the weight. be able to.

Similarly, in an embodiment of the method for manufacturing a rolling element for high surface pressure according to the present invention, as described in claim 11, the cementite decomposition start temperature 600 after cooling is set.
Nitriding treatment may be performed at a temperature of ℃ or less to improve fatigue strength. In this case, as described in claim 12, the compound layer (white layer) is not generated in the nitriding treatment. It is more desirable to

Similarly, in an embodiment of the method for manufacturing a rolling element for high surface pressure according to the present invention, as described in claim 13, a portion other than the chill structure is subjected to shot peening to impart a compressive residual stress. By doing so, the fatigue strength can be improved.

Similarly, in an embodiment of the method for manufacturing a rolling element for high surface pressure according to the present invention, as described in claim 14, the surface of the rolling element has a hardness Hv1100 to 130.
By setting the chill structure to be 0 (cementite (Fe ₃ C) structure), it is possible to improve the foreign matter biting resistance.

[0025]

For example, rolling elements for the toroidal type continuously variable transmission (discs 5, 9, power roller 10) and rolling elements for belt type continuously variable transmission (variable groove width pulleys 22, 23).
As the material of, the clean steel (low oxygen / low sulfur steel) developed as a bearing steel is used. This is because the rolling elements are exposed to almost the same operating conditions as the rolling bearing.

That is, there is almost no rolling contact between the disk and the power roller in the rolling element for a toroidal type continuously variable transmission, and the contact force of Hertz operates at a surface pressure of 3 to 3.5 GPa. There is.

The failure mode in this case is delamination due to surface fatigue, and the starting point is inside the material where the maximum shearing stress generated by the contact stress of Hertz is generated, and at the contact stress of 3 to 3.5 GPa. The lower position is 0.6 to 0.8 mm.

The reason why clean steel is used for this type of rolling element is as follows.
This is because unless the steel has a small amount of non-metallic inclusions, especially oxide-based inclusions, when oxide-based inclusions are present at the position where the maximum shear stress occurs, there is a risk of early delamination starting from this.

However, even when such clean steel is used, peeling may occur with a life of, for example, about 2 × 10 ⁷ times. Then, it was found that the cause of this peeling was a microstructural change due to heat generation in the vicinity of the maximum shear stress generation depth.

The disk, which is a rolling element, and the power roller are in contact with each other through the traction oil and have a mechanism for transmitting torque without direct contact. However, as the surface pressure increases, the amount of heat generated increases, Contact stress 3-3.5
With GPa level, it can be put to practical use without any particular problems.
It has been found that when the surface pressure is higher than that, a structural change occurs early and it is difficult to put it into practical use as a rolling element for a large capacity toroidal type continuously variable transmission.

The temperature of the rolling element portion used at a contact pressure of 3.5 GPa is about 180 ° C., but when it reaches 5 GPa it rises to about 250 ° C. Therefore, at this temperature the structure does not change or decompose, and The compound will be suitable.

Bending fatigue strength and impact strength are characteristics that must be provided as rolling elements, and their design values are about 1000 M at Ono-type rotating bending fatigue limit.
Pa, Charpy absorbed energy is about 10 to 20 J.

As a rolling element having such surface and core characteristics, the surface portion is made of cementite, and the core portion is made of martensite or bainite or a mixed structure of the two. These include alloy components having a martensite, bainite, or a mixed structure of both, which are obtained only by subsequent cooling, and alloy components having the above structure or a sorbite structure by controlling the cooling rate after casting.

As for the nitriding, it is easily conceivable that all the nitriding known at present such as gas nitriding using NH ₃ gas, gas soft nitriding and ion nitriding can be applied.

The present invention has been made based on the above findings, and will be described in more detail below.

In producing the rolling element excellent in high surface pressure resistance according to the present invention, a martensite structure, a bainite structure, a mixed structure of the two, or a sorbite structure obtained by controlling the cooling rate after casting, while being cast and cooled. Alternatively, air-quenched steel having a mixed structure of two or three kinds including this sorbite structure is used. Examples of such steels include SKD materials established by JIS G 4404 and air-hardened steels to which appropriate property improving elements are added.

Then, this steel is smelted to prepare its cast steel melt, and heat is generated when the cast steel melt comes into contact with a portion inside the mold (for example, a sand mold) corresponding to the rolling surface of the rolling element. A chiller (chilling plate, etc.) that quickly takes away and forms a chill structure is set in consideration of the thermal expansion and contraction of each member.

Then, the molten cast steel is poured into the casting mold and cast, so that 1. from the surface of the rolling surface.
The portion of 5 to 3.0 mm has a chill structure, and the core portion has a martensite structure or bainite structure or a mixed structure of both in a cooled state.

In this case, by performing controlled cooling after casting, the matrix hardness can be made to be a sorbite structure of HRC 30 to 35 together with the martensite structure or bainite structure or without these structures. .

In this way, the depth from the surface is about 0.9 mm.
Above the maximum shear stress generation position of 1.
5 to 3.0 mm, 1.5 to 2.0 m in some cases
It is possible to prevent exfoliation from the internal origin by making the chill structure (that is, the cementite (Fe ₃ C) structure which is an iron compound) up to m or 2.0 to 3.0 mm into which the structure does not change and decompose. As a result, the rolling element can withstand use even at a contact pressure of 5 GPa.

Here, the depth of the chill structure will be further described. For example, in the case of rolling elements (disks 5, 9 and power roller 10) used in a toroidal type continuously variable transmission, the maximum pressure at a surface pressure of 5 GPa is obtained. Shear stress generation depth is 0.9
~ 1.2 mm, the depth of influence of the stress is about 1.8 m
Since the depth is up to m, the chill structure needs to have a depth greater than this. Therefore, the depth is preferably 2.0 mm or more. Regarding the upper limit, when the rolling element has a wall thickness of about 10 mm, the impact strength significantly decreases when the ratio of the hardened layer (chill layer: cementite layer) to the base material exceeds 0.3. Therefore, it is desirable to set it to 3.0 mm or less.

On the other hand, in the case of the rolling elements (variable groove width pulleys 22 and 23) used in the belt type continuously variable transmission, the surface pressure is 2
Since it is ~ 3 GPa, the maximum shear stress generation depth is 0.3.
~ 0.6mm, the depth of influence of the stress is about 1.3m
Since it is about m, the thickness of the chill structure (cementite layer) may be 1.5 to 2.0 mm.

By using a precision casting mold (for example, a lost wax mold) as a mold, it is possible to make a near net shape casting product and shorten the finishing process such as the machining process in the next step. is there.

In some cases, it is possible to further reduce the weight by hollowing a part of the rolling element by using an appropriate core together with the mold.

Furthermore, in some cases, after cooling, a nitriding treatment is performed at a temperature of 600 ° C. or less (ie, a temperature at which cementite does not decompose) at which cementite decomposition starts, so that a nitriding treatment that does not leave a compound layer is performed, and martensite, bainite, and Further, the fatigue strength and wear resistance of the sorbite part can be further improved. In this case, it is more desirable not to expose the compound layer (white layer) in the nitriding treatment.

Furthermore, a portion other than the chill structure is subjected to shot peening to compressive residual stress (for example, -800).
(MPa or less), and also by adding a compressive residual stress stronger than the compressive residual stress generated by nitriding to the nitrided portion in the case of nitriding treatment, further improve fatigue strength and wear resistance. It can also be designed as intended.

Furthermore, the surface has a hardness of Hv 1100 to 1
A 300 chill structure (cementite (Fe ₃ C)) structure can be used to further improve the foreign matter entrapment resistance, and the surface damage due to the entrapment of foreign matter such as abrasion powder is also sufficient. Will be blocked.

[0048]

According to the rolling element for high surface pressure according to the present invention,
According to a first aspect of the present invention, in a rolling element subjected to a high surface pressure, air-quenched steel that becomes a martensitic structure, a bainite structure or a mixed structure of both in a cast and cooled state is used as a material, 1.5 to 3.0 mm from the surface of the rolling surface is a chill structure (cementite structure)
In addition, since the core has a martensite structure, a bainite structure, or a mixed structure of both, it is possible to prevent structural change due to heat generation during rolling, and peeling from the internal origin Can be prevented, the mechanical strength is large, and the contact pressure is 5 GP.
Even at the a level, it is possible to provide a rolling element for high surface pressure with good durability that can sufficiently withstand use, which is a remarkably excellent effect.

Then, as described in claim 2,
By having a sorbite structure having a matrix hardness of HRC 30 to 35, a remarkably excellent effect that it is possible to provide a rolling element for high surface pressure with further improved durability is brought about.

Further, as described in claim 3, by making a part of the rolling element hollow so as to reduce the weight, it is possible to contribute to the improvement of fuel consumption even a little. The outstanding effect that it is possible to provide a rolling element for surface pressure is brought about.

Further, as described in claim 4, the nitriding treatment is performed to improve the fatigue strength, so that the rolling element for high surface pressure has further improved durability. It is possible to provide a significantly superior effect.

Further, as described in claim 5, the compressive residual stress by shot peening is applied to the portion other than the chill structure to improve the fatigue strength. The remarkably excellent effect that it is possible to provide a rolling element for high surface pressure having further improved properties is brought about.

Furthermore, as described in claim 6, the surface of the rolling surface has a chill structure (cementite (Fe ₃ C) structure) having a hardness of Hv1100 to 1300, and the foreign matter biting resistance is improved. It is possible to provide a rolling element for high surface pressure capable of further improving durability by preventing separation of the starting point of the surface due to the inclusion of abrasion powder or the like in the rolling surface. It has the remarkable advantage of being possible.

According to the method for producing a rolling element for high surface pressure according to the present invention, as described in claim 7, in producing a rolling element excellent in resistance to high surface pressure, martensite is used while being cast and cooled. While preparing an air-quenched steel to be a structure or a bainite structure or a mixed structure of both, and preparing the cast steel molten metal, the molten cast steel comes into contact with a portion corresponding to the rolling surface of the rolling element inside the mold. Sometimes a chiller that takes heat to form a chill structure is set, and the molten cast steel is poured and cast into the mold to form a chill structure 1.5 to 3.0 mm from the surface of the rolling surface, and then cooled. Since the core is made to have a martensite structure, a bainite structure, or a mixed structure of both in this state, it is possible to prevent a structural change due to heat generation during rolling and prevent peeling from the internal origin. Can be, mechanical strength results in markedly excellent effect that it is possible to produce a good high surface pressure rolling elements durability to withstand sufficiently used even in a large contact pressure 5GPa level.

Then, as described in claim 8,
Controlled cooling after casting to reduce the matrix hardness to HRC30-3
By adopting the sorbite structure of No. 5, the rolling bearing for high surface pressure with further improved durability can be produced, which is a remarkably excellent effect.

Further, as described in claim 9, by using a precision casting mold as a mold so as to shorten the machining process of the next process, the material yield at the time of manufacturing the rolling element is remarkably increased. It is possible to improve not only the productivity but also the productivity, and it is also possible to make it hollow easily by using a core, and it is extremely easy to achieve weight reduction. The remarkably excellent effect of

Furthermore, as described in claim 10, by rolling a part of the rolling element so as to reduce the weight thereof, a rolling element for high surface pressure which can contribute to the improvement of fuel consumption as much as possible can be obtained. The remarkable advantage is that it is possible to manufacture.

Furthermore, as described in claim 11, the durability is further improved by nitriding at a temperature of 600 ° C. or less after the start of decomposition of cementite to improve fatigue strength after cooling. The extremely excellent effect that it is possible to manufacture the rolling element for high surface pressure described above is brought about.

Furthermore, as described in claim 12, by preventing the compound layer (white layer) from being exposed in the nitriding treatment, it is possible to make full use of the effect of improving the fatigue strength by the nitriding treatment. The remarkable advantage is that it is possible to produce pressure rolling elements.

Further, as described in claim 13, durability is improved by improving the fatigue strength by subjecting a portion other than the chill structure to shot peening to impart compressive residual stress. It is possible to produce a rolling element for high surface pressure, which is further improved.

Further, as described in claim 14, the chill structure (cementite (Fe ₃ C) structure) having a hardness of Hv1100 to 1300 is used for the surface of the rolling element to improve the foreign matter entrapment resistance. By doing so, it is possible to produce a rolling element for high surface pressure, which can prevent the occurrence of surface damage due to the inclusion of abrasion powder or the like on the rolling surface and the separation of the surface starting point, and further improve the durability. It has the remarkable advantage of being possible.

[0062]

EXAMPLES Examples of the present invention will be described below.
Needless to say, the present invention is not limited to such embodiments.

(Example 1) In Example 1, JIS G 4 was used as the cast steel material for the rolling elements (toroidal type continuously variable transmission disks 5, 9 and power roller 10).
SKD61 established in 404 (C: 0.36% by weight, S
i: 1.01% by weight, Mn: 0.25% by weight, Cr:
5.01% by weight, Mo: 1.24% by weight, V: 0.98
% By weight, Fe and impurities: balance), and a sand mold for precision casting was used as a mold.

Then, a chiller (chiller) is provided inside the sand mold in a state corresponding to the rolling surface of the rolling elements (5, 9, 10) in consideration of thermal expansion and contraction of each member.
The SK is placed in the casting space of the sand mold for precision casting in which
By injecting and casting a cast steel melt having a composition of D61, the rolling surface as shown in FIG.
Chill layer of 3 to 2.8 mm (hardness is Hv1150 to 125
0) C formed rolling elements (disks 5, 9) and rolling surfaces as shown in FIG. 2 from the surface to a depth of 2.3-2.
8mm chill layer (hardness is Hv1150 ~ 1250)
A rolling element (power roller 10) having C formed thereon was obtained.
The structure of the core of the rolling element (5, 9, 10) obtained here was composed of a martensite structure, a bainite structure or a mixed structure thereof.

Further, a chill layer C is formed on the rolling surface to form a cementite (Fe ₃ C) structure rolling element (5, 9, 1).
Part of 0) other than the cementite structure,
That is, in order to improve the fatigue strength of a portion composed of a martensite structure, a bainite structure, or a mixed structure thereof, the decomposition start temperature of cementite (about 6
The nitriding treatment was performed for 5 hours at a temperature of 570 ° C. or lower than 00 ° C.). In this case, the nitriding treatment was performed in an atmosphere in which 5 Vol% air was added to NH ₃ gas, and the oxynitriding treatment was performed so that the compound layer (white layer) did not appear.

The nitride layer thus obtained had a surface hardness Hv of about 1000, a total nitride layer depth of about 0.5 mm, and a surface residual stress of about -500 MPa.

Further, a portion other than the chill structure is shot peened (shot grain size: 0.6 mm, arc height: 0.8 mmA) to obtain about -900 MP.
It is possible to apply the compressive residual stress of a, and has a high bending fatigue strength of about 1100 MPa at the Ono-type rotating bending fatigue limit and a high impact strength of about 18 J at Charpy absorbed energy (disk 5, 9. Roller 10)
I was able to get

(Embodiment 2) In this Embodiment 2, as a cast steel material for rolling elements (belt 22 and 23 for belt type continuously variable transmission), SKD61 established in JIS G 4404.
(C: 0.36% by weight, Si: 1.01% by weight, Mn:
0.25% by weight, Cr: 5.01% by weight, Mo: 1.2
4% by weight, V: 0.98% by weight, Fe and impurities: balance), and a sand mold for precision casting was used as a mold.

Then, the rolling element (2
2,23) thermal expansion of each member at the site corresponding to the rolling surface
The SKD61 is placed in the casting space of the precision casting sand mold in which a chiller (chiller) is set in consideration of heat shrinkage.
By injecting and casting a molten cast steel having a composition of No. 1, the depth of the rolling surface as shown in FIG.
Rolling elements (pulleys 22 and 23) having a chill layer of 1.8 mm (hardness: Hv 1150 to 1250) C were obtained. The structure of the core of the rolling elements (22, 23) obtained here is
It had a martensite structure, a bainite structure, or a mixed structure thereof.

Further, a chill layer C is formed on the rolling surface to form a cementite (Fe ₃ C) structure rolling element (22, 23).
In order to improve the fatigue strength of the portion other than the cementite structure, that is, the portion having the martensite structure, the bainite structure, or a mixed structure thereof, the decomposition start temperature of the cementite (about 600
Nitriding treatment was performed for 5 hours at a temperature of 570 ° C. or lower. In this case, the nitriding treatment was performed in an atmosphere in which 5 Vol% air was added to NH ₃ gas, and the oxynitriding treatment was performed so that the compound layer (white layer) did not appear.

The nitride layer thus obtained had a surface hardness Hv of about 1000, a total nitride layer depth of about 0.5 mm, and a surface residual stress of about -500 MPa.

Further, it is possible to give a compressive residual stress of about -900 MPa by performing shot peening treatment on a portion other than the chill structure, and a high bending fatigue strength and Charpy of about 1100 MPa at the Ono type rotary bending fatigue limit. It was possible to obtain rolling elements (pulleys 22 and 23) having a high impact strength of about 18 J with absorbed energy.

[Brief description of drawings]

FIG. 1 is a cross-sectional explanatory view of a rolling element (disk) for a toroidal type continuously variable transmission manufactured in a first embodiment of the present invention.

FIG. 2 is a cross-sectional explanatory view of a rolling element (power roller) for a toroidal type continuously variable transmission manufactured in Example 1 of the present invention.

FIG. 3 is a cross-sectional explanatory view of a rolling element (pulley) for a belt type continuously variable transmission manufactured in Example 2 of the present invention.

FIG. 4 is a sectional explanatory view showing a structural example of a toroidal type continuously variable transmission.

FIG. 5 is a slope explanatory view showing a structural example of a belt type continuously variable transmission.

FIG. 6 is an explanatory view showing a manufacturing process of rolling elements (disk and power roller) of a toroidal type continuously variable transmission according to a conventional example.

FIG. 7 is a cross-sectional explanatory view of a rolling element (pulley) of a belt type continuously variable transmission according to a conventional example.

[Explanation of symbols]

5, 9 Disc (rolling element of toroidal type continuously variable transmission) 10 Power roller (rolling element of toroidal type continuously variable transmission) 22, 23 Pulley (rolling element of belt type continuously variable transmission) C Chill layer (cementite structure) )

Continuation of the front page (56) Reference JP-A-10-103440 (JP, A) JP-A-7-71555 (JP, A) JP-A-6-159463 (JP, A) JP-A-7-286649 (JP , A) (58) Fields investigated (Int.Cl. ⁷ , DB name) F16H 15/38 B22D 11/22 C23C 8/26 F16H 55/56

Claims (14)

(57) [Claims] 1. A rolling element that is subjected to high surface pressure is made of air-quenched steel that has a martensitic structure, a bainite structure, or a mixed structure of the two when cast and cooled, and is formed from the surface of the rolling surface of the rolling element. 1.5-3.0
mm has a chill structure, and the core has a martensite structure, a bainite structure, or a mixed structure of both, and a rolling element for high surface pressure. 2. A matrix hardness having a sorbite structure of HRC 30 to 35.
The rolling element for high surface pressure described in. 3. The high surface pressure rolling element according to claim 1, wherein a part of the rolling element is hollow to reduce the weight. 4. The rolling element for high surface pressure according to claim 1, wherein a nitriding treatment is performed to improve fatigue strength. 5. The high surface pressure use according to claim 1, wherein a compressive residual stress by shot peening is applied to a portion other than the chill structure to improve fatigue strength. Rolling body. 6. The surface of the rolling surface has a hardness of Hv1100 to Hv1300.
6. The rolling element for high surface pressure according to any one of claims 1 to 5, which has a chill structure of 00 (cementite (Fe ₃ C) structure) to improve foreign matter biting resistance. . 7. When manufacturing a rolling element having excellent high surface pressure resistance, an air-quenched steel having a martensite structure, a bainite structure, or a mixed structure of the two is melted while being cast and cooled, and the cast steel melt is obtained. With the preparation, a state in which a chiller that takes away heat and forms a chill structure when the molten molten steel comes into contact with a portion corresponding to the rolling surface of the rolling element in the mold is set, and the molten molten steel is in the mold Inject
For high surface pressure, which is cast to have a chill structure 1.5 to 3.0 mm from the surface of the rolling surface, and the core has a martensite structure or bainite structure or a mixed structure of both in a cooled state. Manufacturing method of rolling element. 8. The method of manufacturing a rolling element for high surface pressure according to claim 7, wherein the matrix hardness is controlled to be a sorbite structure having a hardness of HRC 30 to 35 after casting. 9. The method for manufacturing a rolling element for high surface pressure according to claim 7, wherein a precision casting mold is used as the mold to shorten the machining process in the next step. 10. The method for manufacturing a rolling element for high surface pressure according to claim 7, wherein a part of the rolling element is hollow to reduce the weight. 11. Cementite decomposition start temperature 6 after cooling
The method for manufacturing a rolling element for high surface pressure according to any one of claims 7 to 10, wherein nitriding is performed at a temperature of 00 ° C or lower to improve fatigue strength. 12. The method for producing a rolling element for high surface pressure according to claim 11, wherein the compound layer (white layer) is not exposed in the nitriding treatment. 13. The high surface pressure rolling according to claim 7, wherein the portion other than the chill structure is subjected to shot peening to give a compressive residual stress to improve fatigue strength. Manufacturing method of moving body. 14. The surface of the rolling element has a hardness Hv1100 to 1
The method for manufacturing a rolling element for high surface pressure according to any one of claims 7 to 13, wherein the chill structure of 300 (cementite (Fe ₃ C) structure) is used to improve the foreign matter biting resistance.