JPH0979338A - Material of rolling body for toroidal type continuously variable transmission having excellent rolling factigue strength and rolling body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide excellent pitching resistance and rolling fatigue strength and to provide an increased life by using a rolling body material of a specified component for a toroidal type continuously variable transmission and applying cabonitruding treatment. SOLUTION: The steel material for an input disc 5, an output disc 9, and a power roller 10 is used containing C: 0.1-0.6wt.%, Si: 0.05-1.5wt.%, Mn: 0.2-2.0wt.%, V: 0.03-1.0wt.%, P: 0.02wt.% or less, Al: 0.005-0.10wt.%, Ti: 0.005wt.% or less, N: 0.004-0.03wt.%, O: 0.002wt.% or less, and a rest consisting of Fe and inevitable impurities, and Veq being Veq<=0.2 in Veq=(V)+1.2(Si)-1.1(Mn) 0.1+0.3(Cr)+0.4(Mo)+0.2(W) and R being O<=R*<=4.5 in R*=-(Si)+1.5(Mn)+0.5(Ni)+1.5(Cr)+(Mo)-0.5(V)-0.2(W) on which carbonitriding treatment is applied. This constitution provides excellent pitching resistance and rolling fatigue strength and provides an increased life.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a toroidal type (rolling type) continuously variable transmission that can be used as a continuously variable transmission in vehicles such as automobiles and rotary power sources.
The present invention relates to rolling elements and rolling element materials constituting a toroidal continuously variable transmission.

[0002]

2. Description of the Related Art As a transmission used in a vehicle such as an automobile, a stepped transmission that switches the meshing state of a gear train manually or automatically is often used.
Attempts have also been made to adopt a continuously variable transmission.

Since the continuously variable transmission continuously shifts gears, it is characterized by improved fuel economy and no shift shock, but it is roughly classified into a belt type and a toroidal type according to its structure. To be done.

Among them, a toroidal type (rolling type) continuously variable transmission has a structure using metal rolling elements that come into contact with each other through lubricating oil, as shown in FIG. The toroidal type continuously variable transmission 1 includes input disks 5 and 5 that rotate integrally via a loading cam 3 and a connecting shaft 4 connected to an input shaft 2, and gears 6 and 7.
It is equipped with output disks 9 and 9 for rotating the output shaft 8 via, and power rollers 10, 10, 10 and 10 are provided between the input disks 5 and 5 and the output disks 9 and 9, and each power roller 10 is a ball. The structure is such that each is supported by a support 12 via a 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 rotation 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.).

Therefore, the input disk 5, the output disk 9 and the power roller 10 made of such metal rolling elements receive a surface pressure input on the rolling surface due to the input of the engine torque, so that the surface fatigue occurs. It is required to have excellent strength (rolling fatigue strength), and it is necessary to have a high surface hardness and a deep hardened layer depth (for example, JP-A-7-71555).

[0007]

However, in the metal rolling element (5, 9, 10) of the conventional toroidal type continuously variable transmission 1 as described above, the loading cam is loaded on the input disk 5 to transmit the torque. Load at 3,
Since it is necessary to apply a high surface pressure to the rolling surfaces, high shear stress is generated inside the rolling elements, and cracks starting from the vicinity of the maximum shear stress generation depth are generated, resulting in failure that leads to pitting separation. It happened. Further, even if the peeling does not occur, the rolling surface may be depressed due to the plastic deformation of the inside, and the shifting performance may be impaired.

Further, in the lubricating oil of the toroidal type continuously variable transmission 1 in use, there are contaminants generated from various sliding parts, and when such contaminants are caught in the rolling surface, indentations are formed. Due to the stress concentration formed around it, a crack originating from the surface may be generated, leading to pitting separation.

The back surface of the power roller 10 is respectively supported by the support 12 via the ball bearings 11. However, when a load is applied to the input disk 5, a high surface pressure is also generated. Occurrence of cracks and delamination at the surface origin sometimes occurred when foreign matter was caught.

[0010] Therefore, it has been a problem to prevent such cracks and peeling originating from the inside, and to prevent cracks and peeling originating from the surface.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and is a toroidal type continuously variable transmission that is excellent in pitting resistance and rolling fatigue strength and can have a long life. The purpose is to provide a rolling element material for a machine and a rolling element.

[0012]

The structure of the rolling element material for a toroidal type continuously variable transmission according to the present invention, which has been capable of solving the above problems, is as follows.

That is, in% by weight, C: 0.1 to 0.6
%, Si: 0.05 to 1.5%, Mn: 0.2 to 2.0
%, V: 0.03 to 1.0%, P: 0.02% or less, A
1: 0.005 to 0.10%, Ti: 0.005% or less, N: 0.004 to 0.03%, O: 0.002% or less, and optionally, Ni: 0 as another component. ．
20-5.0%, Cr: 0.20-5.0%, Mo:
0.05-1.0%, W: 0.03-2.0%, Nb:
It contains one or more elements selected from the group consisting of 0.01 to 0.10%, and optionally, as other components, S: more than 0.03 to 0.10%, Pb:
0.01-0.30%, Te: 0.005-0.10
%, Se: 0.005 to 0.10%, Ca: 0.000
5 to 0.010%, Zr: 0.005 to 0.10%, containing one or more elements selected from the group consisting of Fe and unavoidable impurities, and Veq = (V ) +1.2 (Si) -1.1 (Mn) +
0.1 (Ni) +0.3 (Cr) +0.4 (Mo) +
At 0.2 (W), Veq ≧ 0.2, and R * = − (Si) +1.5 (Mn) +0.5 (Ni) +
1.5 (Cr) + (Mo) -0.5 (V) -0.2
In (W), 0 ≦ R * ≦ 4.5, carbonitriding is performed, and the amount of C + N, which is the sum of carbon amount: C and nitrogen amount: N, of the steel material is calculated as the maximum shear stress generated in the rolling element. Generation depth is Zst
At the position of depth d ≦ 0.2Zst.
The residual austenite amount is 20 when 9 to 1.3% is set.
It is characterized in that the rolling element material for a toroidal type continuously variable transmission is up to 40% by volume.

The structure of the rolling element for a toroidal type continuously variable transmission according to the present invention, which has been able to solve the above problems, is as follows.

That is, in a toroidal type continuously variable transmission using a plurality of metal rolling elements that come in contact with each other through lubricating oil, the rolling element material for the toroidal type continuously variable transmission is used as a material of the rolling element, By carbonitriding, the N content in the rolling surface is 0.2% or more and 0.6% or less in weight%, and the depth when the maximum shear stress generated inside the rolling element due to surface contact is Zst At the position of d ≦ 0.2Zst, the amount of C + N is 0.9% or more and 1.3% or less by weight%, the amount of retained austenite is 20% or more and 40% or less by volume%,
A carbonitride having a hardness of HV 650 or more and a diameter (particle diameter) of 1.0 μm or less is 1% or more in area ratio and a depth of 0.5.
Zst ≤ d ≤ 1.4 At the position of Zst, C and N contents are 0.6% ≤ C + N ≤ 1.2% in weight% and hardness is HV7.
00 or more, the hardness at the depth d = Zst is HV7
The feature is that the rolling element for a toroidal type continuously variable transmission having a number of 60 or more is configured.

[0016]

The reasons for limiting the component composition (% by weight) of the rolling element material for a toroidal type continuously variable transmission according to the present invention will be explained together with the action of each component.

C: 0.1 to 0.6% C is an element indispensable for imparting the required hardness of the core to carbonitrided parts, and it is necessary to add 0.1% or more. is there. However, if it exceeds 0.6%, the machinability deteriorates and the toughness deteriorates, so 0.6% was made the upper limit.

Si: 0.05 to 1.5% In order to improve the rolling fatigue strength of a component, it is necessary to make it difficult for the component to soften due to friction during use or heat generated by deformation. Si has a great effect of increasing the softening resistance of parts, and is an element indispensable for this purpose, and it is necessary to add Si in an amount of 0.05% or more. However, 1.
If it exceeds 5%, the penetration of C during carbonitriding is impeded or the workability is deteriorated, so the upper limit was made 1.5%.

Mn: 0.2-2.0% Mn is added for the purpose of deoxidation during melting of steel material. However, if it is less than 0.2%, deoxidation becomes insufficient and the internal quality of the steel material deteriorates. Further, the hardenability of the carburized layer cannot be ensured, the depth of the hardened layer becomes shallow, and the strength is lowered.

On the other hand, if it exceeds 2.0%, the hardness of the material is increased and the machinability is deteriorated, so the upper limit is 2.0%.
I made it.

V: 0.03 to 1.0% V is effective for increasing the hardness and rolling fatigue strength by depositing fine carbonitrides on the surface-hardened layer by carbonitriding. In order to ensure that, 0.03% or more was added. However, if it exceeds 1.0%, a large amount of ferrite is generated in the core during quenching, the core hardness decreases, and the static strength and fatigue strength decrease, so it was made 1.0% or less.

P: 0.02% or less P deteriorates the grain boundary strength and hinders magnetism.
The upper limit was 2%.

Al: 0.005 to 0.10% Al is added for the purpose of deoxidation during melting of steel material. Further, it is an element that suppresses the growth of austenite crystal grains during heating in carbonitriding, and if it is less than 0.005%, no effect is obtained. Further, even if added in excess of 0.10%, the effect of suppressing the crystal grain growth is saturated, and excessive addition causes the formation of a large number of hard non-metallic inclusions, which reduces the rolling fatigue life. The upper limit was 10%.

Ti: 0.005% or less Ti forms hard inclusions and adversely affects the rolling fatigue life, so 0.005% was made the upper limit.

N: 0.004 to 0.03% N forms AlN to make austenite crystal grains fine and improve rolling fatigue life. However, 0.004%
If it is less than 0.03%, the effect cannot be expected, and if it exceeds 0.03%, it causes cracking defects during casting and hot rolling, so the upper limit was made 0.03%.

O: 0.002% or less When the O content is large, a large amount of oxide-based inclusions such as Al ₂ O ₃ and SiO ₂ are produced, which adversely affects fatigue strength, especially rolling fatigue life. It was set to 0.002%.

Ni: 0.20 to 5.0% Ni is effective in improving hardenability and toughness, so it is added in some cases. However, even if added, 0.20
If it is less than%, the effect cannot be expected, and if it exceeds 5.0%, the workability deteriorates, so 5.0% was made the upper limit.

Cr: 0.20 to 5.0% Cr is effective in improving hardenability and carbonitriding property. Further, carbonitride is formed and contributes to the improvement of the softening resistance, so it is added in some cases. However, even if added, the effect cannot be expected at less than 0.20%, and
If it exceeds 0%, workability deteriorates, so 5.0% was made the upper limit.

Mo: 0.05 to 1.0% Mo is effective in improving the hardenability and contributes to the improvement of the softening resistance in the formation of carbonitrides, so Mo is added in some cases. However, even if added, the effect cannot be expected if it is less than 0.05%, and if it is added over 1.0%, the workability deteriorates, so 1.0% was made the upper limit.

W: 0.03 to 2.0% W produces carbides and is effective in increasing surface hardness and softening resistance. In addition, since it also has the effect of increasing the hardness of the core, it is added in some cases. However, even if added, the effect cannot be expected if less than 0.03%, and 2.0%
If it exceeds the limit, the hardness of the material becomes high, which adversely affects the forgeability and machinability, so the upper limit was defined as 2.0%.

Nb: 0.01 to 0.10% Nb is an element effective in combining with C and N in steel to form carbonitrides and refining crystal grains to increase toughness. Add in some cases. However, even if added, the effect cannot be expected if less than 0.01%, and
%, The effect will be saturated even if added over 0.1%, so 0.10%
Was set as the upper limit.

S: more than 0.03 to 0.10% S is an element that improves machinability, so S is added in some cases. And 0.03 to get such effect
It is necessary to add more than%, but if it is too much, M
Since the amount of non-metallic inclusions of nS composition increases and adversely affects the rolling life, 0.10% was made the upper limit.

Pb: 0.01 to 0.30% Te, S
e: 0.005 to 0.10% Since Pb is a machinability improving element, it is added in some cases. Then, in order to improve machinability, it is necessary to add 0.01% or more. However, if added in excess of 0.30%, the rolling fatigue life will decrease, so 0.30% was made the upper limit.

Since Te and Se are also machinability improving elements, they are added in some cases. And, in order to improve the machinability, it is necessary to add 0.005% or more. However,
If added in excess of 0.10%, the rolling contact fatigue life will decrease, so 0.10% was made the upper limit.

Ca: 0.0005 to 0.010%, Z
r: 0.005 to 0.10% Ca is generated as CaO around Al ₂ O ₃ , suppresses deformation of MnS during hot rolling, and contributes to granulation of MnS. Since it improves machinability without lowering the value, it is added in some cases. However, the effect cannot be expected if less than 0.005%, and 0.010%
If it exceeds%, the effect will be saturated. Zr also suppresses the deformation of MnS during hot rolling and contributes to the granulation of MnS, whereby machinability can be improved without lowering the rolling fatigue life, so Zr is added in some cases. . However, if the effect is less than 0.005%, it cannot be expected.
If it exceeds 10%, a large amount of non-metallic inclusions such as ZrO ₂ is generated and the rolling fatigue life is reduced, so the upper limit was made 0.10%.

Veq: 0.2 or more In order to improve the rolling fatigue life of parts, it is necessary to prevent the parts from softening due to friction during use or heat generated by deformation. Therefore, by grasping the effect of each element on the softening resistance, Veq = (V) +1.2 (Si) -1.1 (Mn) +
0.1 (Ni) +0.3 (Cr) +0.4 (Mo) +
It was found that a rolling fatigue life can be significantly improved by setting Veq ≧ 2 at 0.2 (W).

R *: 0 or more and 4.5 or less The rolling fatigue life can be improved by generating an appropriate amount of retained austenite (γR) in the surface layer. Therefore, the effect of each element on the amount of retained austenite was clarified, and R * =-(Si) +1.5 (Mn) +0.5 (Ni) +
1.5 (Cr) + (Mo) -0.5 (V) -0.2
In (W), 0 ≦ R * ≦ 4.5, and the maximum shear stress generated inside the rolling element is C + N, which is the sum of carbon content: C and nitrogen content: N of the steel material after carbonitriding. When the generation depth of Z is Zst, 0.9 at the position of depth d ≦ 0.2Zst
~ 1.3%, the amount of retained austenite is 20 ~
It was found that a rolling fatigue life can be significantly improved by setting the content to 40% by volume.

The rolling element material for a toroidal type continuously variable transmission according to the present invention has the above-described composition, and the rolling element material for a toroidal type continuously variable transmission according to the present invention, which is made of the rolling element material described above, will be described below. The reasons for determining the amounts of C and N, the amount of retained austenite, the hardness, and the amount of carbonitride by the carbonitriding treatment of No. 1 will be sequentially described together with their respective functions. Is the depth of maximum shear stress generated in
And N content is% by weight, residual austenite content is% by volume,
The amount of carbonitride is expressed in area%.

N content on rolling surface: 0.2% or more and 0.6% or less by weight% When foreign matter in the lubricating oil is caught in the rolling surface, a small depression occurs on the surface, and stress around the depression is generated. A crack is generated in the concentrated portion.
In order to prevent this crack formation, it is necessary to relieve stress concentration and strengthen the metal structure. Retained austenite with excellent ductility is required to relax stress concentration, but if the N content is less than 0.2%, the amount is insufficient and the amount of N dissolved in the retained austenite is insufficient. Since the strength is insufficient, cracks are easily generated.
2% or more. However, if the N content exceeds 0.6%,
Since the amount of retained austenite is too large and the hardness is lowered, crack formation is facilitated. On the other hand, if the N content exceeds 0.6%, bainite may be formed during quenching, and the desired residual austenite content may not be obtained.
Below.

C + at the position of depth d≤0.2Zst
N content: 0.9% or more and 1.3% or less in weight% In this portion, impurities in the lubricating oil are caught in the rolling surface, and cracks generated on the rolling surface easily propagate. In order to prevent this, it is necessary that the metal structure of the rolling element has sufficient toughness, but if the C + N content is less than 0.9%, a sufficiently high toughness to prevent the generation and propagation of cracks is required. Since the retained austenite contained therein is not obtained and the amount of carbonitride is small, the hardness is lowered and the rolling contact surface is depressed due to plastic deformation. However, when the amount of C + N exceeds 1.3%, carbon (nitride) nitrides are formed in the crystal grain boundary in a net shape, which rather promotes the generation and propagation of cracks.
It was set to 1.3% or less.

Amount of retained austenite at the position of depth d ≦ 0.2 Zst: 20% to 40% in volume% Retained austenite is a structure having excellent toughness, and relaxes the stress at the crack tip and prevents its propagation. There is an action.
However, if the amount is less than 20% in this depth portion, it is not enough to prevent the propagation of cracks.
% And above. On the other hand, if the amount exceeds 40%, the hardness decreases and a large depression occurs, so the content was made 40% or less.

Hardness at a position of depth d ≦ 0.2 Zst: Vickers hardness of HV 650 or more If the hardness at this depth is less than HV650, the generation and propagation of cracks due to repeated loading becomes easy,
Since it causes the rolling surface to sink due to plastic deformation, HV6
It was set to 50 or more.

Carbonitride having a diameter (particle size) of 1.0 μm or less at a depth d ≦ 0.2 Zst: 1% or more in area ratio Carbonitride having a carbonitride diameter (particle size) of more than 1.0 μm Although the material is effective for maintaining hardness, it has no effect of suppressing the propagation of cracks in the rolling fatigue process. Therefore, carbonitrides with a diameter of 1.0 μm or less are required to suppress the propagation of cracks. However, if the area ratio of carbonitrides having a diameter of 1.0 μm or less is less than 1%, the hardness is lowered, and the depression of the rolling surface due to plastic deformation and the generation of surface cracks accompanying it are induced, so 1% or more is set. .

Amount of C and N at the position of 0.5 Zst ≦ d ≦ 1.4 Zst: 0.6% by weight% C + N ≦ 1.
2% Since the part of this depth is repeatedly subjected to a large shear stress, it often becomes the starting point of an internal crack, and also causes plastic deformation to cause the rolling surface to largely collapse. When the amount of C + N is less than 0.6% at this portion, the hardness of martensite is reduced, the precipitation of carbonitride is small, and plastic deformation easily occurs, causing a large depression of the rolling surface. Therefore, it is set to 0.6% or more. Also, C + N
If the amount exceeds 1.2%, an incompletely hardened structure is formed around the carbonitride growth, and cracks originating from the incompletely hardened structure are generated. Therefore, the content is set to 1.2% or less.

Hardness at a position of 0.5 Zst ≦ d ≦ 1.4 Zst: Vickers hardness of HV 700 or more When the hardness in this depth range is less than HV 700, the rolling surface of the rolling surface due to plastic deformation of this portion is The depression will be bigger,
Since it impairs the speed change performance as a rolling element for a toroidal type continuously variable transmission, the hardness must be HV 700 or more,
In particular, it is necessary that the hardness is HV760 or higher at the position of d = Zst.

[0046]

EXAMPLES Inventive steels (Nos. 1 to 19) are shown in Tables 1 and 2.
And Table 3 shows the chemical composition of the comparative steels (Nos. 20 to 29). These test steels were melted in a small furnace, subjected to hot forging and normalizing treatment, and processed into test pieces. After machining into a test piece shape, carbonitriding treatment was performed. The heat treatment conditions at that time are shown in FIG. 2 and Table 4. And N in Table 4
o. A roller pitching test piece was prepared under the H / T heat treatment condition of 1. Then, a roller pitching test was performed under the test conditions shown in Table 5. Table 6 and Table 7 show the results of the material investigation and the roller pitting test results of those test pieces.
(Invention Steel) and Table 8 (Comparative Steel).

No. 1 to 19 are Examples that satisfy all the requirements of the present invention, in which fine precipitates having a diameter of 1 μm or less are uniformly dispersed, and an appropriate amount of retained austenite (γR) is generated, The rolling surface has a large high temperature hardness and a small decrease in hardness, so it has a high resistance to softening, and a large number of roller pitching tests results in a high rolling fatigue strength.

On the other hand, no. In Nos. 20 to 29, a part of the component composition does not satisfy the specified requirements of the present invention, and the rolling fatigue strength is low, and it cannot be said that the object of the present invention is fulfilled.

That is, No. Since No. 20 steel does not contain V, precipitation of the compound is extremely small and the softening resistance is weak. No. 21 steel has a low Si content and low softening resistance. No. 22 steel has a large amount of retained austenite and a low softening resistance because the Mn content is too large. No. 23 steel has a large amount of retained austenite because the amount of Ni is too large. No. 24 steel has a large amount of retained austenite because the amount of Cr is too large. 25 steel is M
It was confirmed that the amount of retained austenite was large because the amount of o was too large.

No. No. 26 steel has a large amount of ferrite in the core due to excessive V content, and has a short fatigue life due to insufficient hardness of the core. No. 27 steel has a large amount of ferrite in the core portion because the Si content is too large, and has a short fatigue life due to insufficient hardness of the core portion. No. 28 steel has a short fatigue life because the hardness of the core is insufficient because the C content is too small. 29 steel is standard steel SCM
Although it was 420, it was confirmed that the fatigue life was short because of less precipitation of the compound and low softening resistance.

And. No. The 22 to 24 steels have an excessively large R * value, and the additive amounts of Mn, Ni, and Cr, which are additional elements for increasing the amount of retained austenite, are excessive, so that the retained austenite is too large. No. It was confirmed that the Nos. 21 to 23 steels have Veq values that are too small, and the addition amount of Si, which has a large effect of improving the softening resistance, is small, so that the softening resistance is low.

[0052]

[Table 1]

[0053]

[Table 2]

[0054]

[Table 3]

[0055]

[Table 4]

[0056]

[Table 5]

[0057]

[Table 6]

[0058]

[Table 7]

[0059]

[Table 8]

Next, steel No. which was confirmed to satisfy the object of the present invention by the results of the material examination and the roller pitting test results. A case in which four of 1 to 19 are selected and applied to the toroidal type continuously variable transmission 1 shown in FIG. 1 will be described.

As described above, the toroidal type continuously variable transmission 1 shown in FIG. 1 has the input disc 5, the output disc 9 and the power roller 10 which are metallic rolling elements as one set, and one set according to the power transmission capability. Or, it is composed of a plurality of sets (two sets in the case of the present embodiment).

In the present embodiment, among these steel rolling elements, the input disc 5, the output disc 9, and the power roller 10, among the steel materials of the present invention shown in Tables 1 and 2, No. After selecting 1, 3, 6 and 8 and machining those steel materials to the shape of parts,
~ H / T 6) carbonitriding conditions are appropriately selected, heat treatment is performed, polishing is performed, and the input / output disks 5, 9
And the power roller 10 was produced.

Next, the Vickers hardness, the amount of C, the amount of N, the amount of retained austenite (γR) on the surfaces of the disks 5 and 9 and the power roller 10 and at the position of a specific depth,
When the precipitation amount of carbonitrides having a diameter of 1.0 μm or less was measured, the results are shown in Tables 9 to 13. Zst in Tables 9 to 13 indicates the depth (mm) of maximum shear stress generated inside the rolling element due to Hertz contact (surface contact).

Next, each input disk 5 and output disk 9
The durability test was performed on the power roller 10 and the conditions shown in Table 14. The results are also shown in Tables 9 to 13.
Shown in

[0065]

[Table 9]

[0066]

[Table 10]

[0067]

[Table 11]

[0068]

[Table 12]

[0069]

[Table 13]

[0070]

[Table 14]

As shown in Tables 9 to 13, according to Examples 1 to 10 of the present invention, the number of peeling lives was greater than that of Comparative Examples 1 to 4 and the rolling fatigue characteristics were excellent. In addition, it was confirmed that the peeling morphology was all inside, and that there was no peeling at the surface origin and no deformation such as depression of the rolling surface.

As described above, as can be seen from the results confirmed in the examples of the present invention, (1) when the constituent components of the rolling element material are within the ranges specified in the present invention, V, Cr, and Mo in the hardened layer are obtained. By increasing the amount of carbonitrides such as, for example, to increase the hardness and decrease the hardness at high temperature to improve the softening resistance,
Improves rolling fatigue life.

(2) The amount of N on the surface is 0.2 to 0.6.
% And C + at the position of depth d ≦ 0.2Zst
N content is 0.9-1.3%, residual austenite content is 20
When it is in the range of up to 40%, the solid solution of N strengthens the retained austenite that relaxes the stress concentration in the minute depressions and suppresses the generation of cracks from the surface, thus improving the pitting resistance.

(3) If the area ratio of carbonitrides having a diameter of 1.0 μm or less at a depth d ≦ 0.2 Zst is 1% or more and the hardness is HV650 or more, the surface is subjected to repeated loading. Since the generation and propagation of cracks from the ground are suppressed, the pitting resistance is improved.

(4) Depth 0.5 Zst ≦ d ≦ 1.4 Zs
At the position of t, the C + N amount is 0.6% ≦ C + N ≦ 1.2.
% And the hardness is HV700 or more and the hardness is HV760 or more at the position of the depth d = Zst, the rolling surface depression due to the plastic deformation inside is suppressed by the precipitation of martensite + carbonitride, Since the generation and propagation of cracks due to repeated shear stress near the maximum shear stress generation depth Zst are suppressed, the surface fatigue strength is improved.

Since the rolling elements have the required characteristics, the rolling contact fatigue characteristics are improved, and the rolling element has a longer durable life.

Further, in the heat treatment method (H / T No. 2 shown in Table 4) in which a small amount of NH ₃ gas is caused to flow during carburizing diffusion as in Examples 1 to 4, N is diffused deeply. As a result, higher rolling contact fatigue strength can be obtained.

Furthermore, Examples 1, 4, 5, 7, 10
As described above, when the C + N amount at the position where the depth d = Zst is 0.85 to 0.91%, almost the maximum hardness becomes HV800 or higher at that position, and higher rolling fatigue strength can be obtained. I can.

On the other hand, as shown in Comparative Examples 1 and 4, the amount of N on the surface is more than 0.6% and the depth d ≦.
The amount of C + N at the position of 0.2 Zst is more than 1.3%, the amount of retained austenite is more than 40%, and the hardness is H.
If the V is less than V650, the strength of the surface layer is insufficient, resulting in peeling and depression at the surface starting point, resulting in a shorter life.

Further, as in Comparative Examples 2 and 3, the depth 0.
Hardness in the range of 5Zst ≦ d ≦ 1.4Zst is HV70.
When it is 0 or less, the critical shear strength is insufficient due to insufficient hardness, so plastic deformation occurs near Zst, and the rolling surface is depressed,
Peeling from the internal origin occurs with a short life.

Further, as in Comparative Example 3, when the N content on the surface is less than 2.0% and the depth d ≦ 0.2Zst, the C + N content is less than 0.8% and the residual austenite content is If it is less than 20% and the area ratio of the precipitate is less than 1%, the effect of alleviating the stress concentration due to the indentation or the like on the surface layer is lessened, so that peeling from the surface starting point is likely to occur and the life is remarkably shortened.

Further, as in Comparative Example 4, the depth is 0.5Z.
C + N amount is 1.2% in the range of st ≦ d ≦ 1.4Zst
If it is more than that, residual austenite is generated and the hardness is lowered, so that the depth becomes less than HV750 at Zst,
Plastic deformation occurs near Zst, and the rolling surface is depressed.

From the above, according to the present invention, a rolling element having excellent surface fatigue strength and capable of suppressing depression of the rolling surface can be obtained.

[0084]

As described above, according to the present invention, a rolling element material for a toroidal type continuously variable transmission using a plurality of metallic rolling elements that come into contact with each other through lubricating oil is used in% by weight. , C: 0.1 to 0.6%, Si: 0.05 to 1.
5%, Mn: 0.2 to 2.0%, V: 0.03 to 1.0
%, P: 0.02% or less, Al: 0.005-0.10
%, Ti: 0.005% or less, N: 0.004 to 0.0
3%, O: 0.002% or less, and in some cases, Ni: 0.20 to 5.0%, Cr: 0.
20-5.0%, Mo: 0.05-1.0%, W: 0.
03-2.0%, Nb: containing one or more elements selected from the group consisting of 0.01-0.10%,
Similarly, as other components, S: more than 0.03 to 0.10%, Pb: 0.01 to 0.30%, Te:
0.005-0.10%, Se: 0.005-0.10
%, Ca: 0.0005 to 0.010%, Zr: 0.0
Veq = (V) +1.2 (Si) -1.1 containing one or more elements selected from the group consisting of 05 to 0.10% and the balance Fe and unavoidable impurities. (Mn) +
0.1 (Ni) +0.3 (Cr) +0.4 (Mo) +
At 0.2 (W), Veq ≧ 0.2, and R * = − (Si) +1.5 (Mn) +0.5 (Ni) +
1.5 (Cr) + (Mo) -0.5 (V) -0.2
In (W), 0 ≦ R * ≦ 4.5, carbonitriding is performed, and the C + N amount, which is the sum of the carbon amount: C and the nitrogen amount: N, of the steel material at the depth d ≦ 0.2 Zst. 0.9-1.3%
And the amount of retained austenite is 20 to 40% by volume.
With such a configuration, it is possible to provide a rolling element material for a toroidal type continuously variable transmission that is excellent in rolling fatigue strength, which is a remarkably excellent effect.

Further, the rolling element for a toroidal type continuously variable transmission according to the present invention uses the above-mentioned rolling element material for a toroidal type continuously variable transmission and is carbonitrided to obtain an N value on the rolling surface.
If the amount is 0.2% or more and 0.6% or less by weight, the depth of maximum shear stress generated inside the rolling element due to surface contact is Zst.
And C + at the position of depth d ≦ 0.2Zst
The amount of N is 0.9% to 1.3% by weight, the amount of retained austenite is 20% to 40% by volume, and the hardness is H.
V650 or more and a carbonitride having a diameter of 1.0 μm or less has an area ratio of 1% or more and a depth of 0.5 Zst ≦ d ≦ 1.
At 4Zst, the C and N contents are 0.6% by weight.
% ≦ C + N ≦ 1.2%, hardness HV 700 or more, depth d
Since the hardness at the position of = Zst is HV760 or more, the hardness of the hardened layer in the rolling element is large, the hardness at high temperature is less decreased, the softening resistance is improved, and the pitting resistance is improved. It is also possible to improve the rolling contact fatigue life and further improve the deterioration of the gear shifting performance due to the depression of the rolling contact surface. And, it is possible to provide a rolling element for a toroidal type continuously variable transmission that is resistant to peeling and has a long life.

[Brief description of drawings]

FIG. 1 is an explanatory cross-sectional view illustrating the structure of a toroidal (rolling) continuously variable transmission.

FIG. 2 is an explanatory diagram showing heat treatment conditions adopted in the examples of the present invention.

[Explanation of symbols]

 1 Toroidal type (rolling type) continuously variable transmission 5 Input disc (rolling element) 9 Output disc (rolling element) 10 Power roller (rolling element)

Front page continued (72) Inventor Satoshi Abe 2 Nadahamahigashi-cho, Nada-ku, Kobe-shi, Hyogo Inside the Kido Steel Works, Ltd. Kobe Steel Works (72) Noriko Uchiyama 2 Takara-cho, Kanagawa-ku, Yokohama, Japan Nissan Motor Co., Ltd. Incorporated (72) Inventor Shinro Kino 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd. (72) Inventor Takashi Matsumoto 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd. (72 ) Inventor Shun Umegaki 2 Takara-cho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Motor Co., Ltd.

Claims (4)

[Claims] 1. C: 0.1-0.6%, S by weight%
i: 0.05 to 1.5%, Mn: 0.2 to 2.0%,
V: 0.03 to 1.0%, P: 0.02% or less, Al:
0.005-0.10%, Ti: 0.005% or less,
N: 0.004 to 0.03%, O: 0.002% or less,
The balance consists of Fe and inevitable impurities, and Veq = (V) +1.2 (Si) -1.1 (Mn) +
0.1 (Ni) +0.3 (Cr) +0.4 (Mo) +
At 0.2 (W), Veq ≧ 0.2, and R * = − (Si) +1.5 (Mn) +0.5 (Ni) +
1.5 (Cr) + (Mo) -0.5 (V) -0.2
In (W), 0 ≦ R * ≦ 4.5, carbonitriding is performed, and the amount of C + N, which is the sum of carbon amount: C and nitrogen amount: N, of the steel material is calculated as the maximum shear stress generated in the rolling element. Generation depth is Zst
At the position of depth d ≦ 0.2Zst.
The residual austenite amount is 20 when 9 to 1.3% is set.
A rolling element material for a toroidal type continuously variable transmission having excellent rolling contact fatigue strength, characterized in that the content is up to 40% by volume. 2. As another component, Ni: 0.20
~ 5.0%, Cr: 0.20 to 5.0%, Mo: 0.0
5 to 1.0%, W: 0.03 to 2.0%, Nb: 0.0
1 or 2 selected from the group consisting of 1 to 0.10%
Veq = (V) +1.2 (Si) -1.1 (Mn) +, containing at least one element and the balance being Fe and unavoidable impurities.
0.1 (Ni) +0.3 (Cr) +0.4 (Mo) +
At 0.2 (W), Veq ≧ 0.2, and R * = − (Si) +1.5 (Mn) +0.5 (Ni) +
1.5 (Cr) + (Mo) -0.5 (V) -0.2
In (W), 0 ≦ R * ≦ 4.5, carbonitriding is performed, and the C + N amount, which is the sum of the carbon amount: C and the nitrogen amount: N, of the steel material at the depth d ≦ 0.2 Zst. 0.9-1.3%
And the amount of retained austenite is 20 to 40% by volume.
The rolling element material for a toroidal type continuously variable transmission according to claim 1, which is excellent in rolling fatigue strength. 3. As other components, S: more than 0.03 to 0.10%, Pb: 0.01 to 0.30%, Te:
0.005-0.10%, Se: 0.005-0.10
%, Ca: 0.0005 to 0.010%, Zr: 0.0
Veq = (V) +1.2 (Si) -1.1 containing one or more elements selected from the group consisting of 05 to 0.10% and the balance Fe and unavoidable impurities. (Mn) +
0.1 (Ni) +0.3 (Cr) +0.4 (Mo) +
At 0.2 (W), Veq ≧ 0.2, and R * = − (Si) +1.5 (Mn) +0.5 (Ni) +
1.5 (Cr) + (Mo) -0.5 (V) -0.2
In (W), 0 ≦ R * ≦ 4.5, carbonitriding is performed, and the C + N amount, which is the sum of the carbon amount: C and the nitrogen amount: N, of the steel material at the depth d ≦ 0.2 Zst. 0.9-1.3%
And the amount of retained austenite is 20 to 40% by volume.
The rolling element material for a toroidal type continuously variable transmission having excellent rolling contact fatigue strength according to claim 1 or 2. 4. A toroidal type continuously variable transmission using a plurality of metal rolling elements that come into contact with each other through lubricating oil, wherein the toroidal type continuously variable transmission according to claim 1, 2 or 3 is used as a material for the rolling elements. The content of N on the rolling surface is 0.2% or more and 0.6% or less by weight by carbonitriding using the rolling element material for transmission, and the maximum depth of shear stress generated inside the rolling element due to surface contact. When the depth is Zst, the depth d ≦ 0.
At the 2Zst position, the C + N amount is 0.9% or more and 1.3% or less by weight% and the retained austenite amount is 20% by volume.
% Or more and 40% or less, hardness HV650 or more, diameter 1.0
The area ratio of carbonitrides of μm or less is 1% or more, and
C at a depth of 0.5 Zst ≦ d ≦ 1.4 Zst
And N content is 0.6% ≦ C + N ≦ 1.2% by weight, hardness is HV700 or more, and hardness at a position of depth d = Zst is HV760 or more, toroidal type continuously variable transmission. Rolling element for machine.