JP2007154281A - Rolling-support apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rolling-support apparatus with which even in the case of using this apparatus under lubrication mixed with foreign matter, early exfoliation is hardly caused and long service life can be obtained. <P>SOLUTION: At least one of rolling members among an inner race 1, an outer race 2 and a ball 3 constituting a deep groove ball bearing, are produced by applying a heat-treatment including carbo-nitriding or nitriding after working a blank composed of a steel into a prescribed shape, and the abundance ratio of the nitride containing Si and Mn on this rolling surface is 1.0-20.0% area ratio and N content on the surface layer part forming the rolling surface is made ≥0.2 mass%. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a rolling support device such as a rolling bearing, a ball screw, and a linear guide.

Rolling bearings used in transmissions and engines of automobiles, agricultural machinery, construction machinery, steel machinery, etc. are under conditions where foreign matters such as metal chips, shavings, burrs, and abrasion powder are mixed in the lubricating oil (hereinafter referred to as “ In many cases, it is used as "under lubrication mixed with foreign matter."), And there is a case where the raceway or rolling element is prematurely peeled off by foreign matter, resulting in a significant decrease in service life.
Such early peeling under foreign matter-mixed lubrication is performed on the edge portion of the indentation (hereinafter referred to as “indentation edge”) formed on the rolling surface by foreign matter biting between the raceway and the rolling element. It is said that the cause is stress concentration.

Therefore, in order to alleviate the stress concentration on the indentation edge even in the case where the indentation is formed on the rolling surface under the contamination with foreign matters, the applicant of the present application disclosed in Patent Document 1 at least one of the inner and outer rings. The amount of retained austenite of the surface layer portion forming the raceway surface and the surface layer portion forming the rolling surface of the rolling element is set to 20% by volume or more and 45% by volume or less, and the carbonitride of the surface layer portion forming the rolling surface of the rolling element It has been proposed that the content is 5% to 15% by volume.
Japanese Patent Laid-Open No. 64-55423

  By the way, in recent years, it has been found that the early peeling that occurs under the contamination with foreign matter is caused not only by the stress concentration on the indentation edge described above but also by the tangential force acting on the rolling surface between the race and the rolling element. ing. Factors affecting the tangential force include the surface shape and surface roughness of the rolling surface in addition to the sliding speed and surface pressure of the rolling surface. That is, in order to make it difficult for early peeling to occur under lubrication mixed with foreign matter, it is necessary to suppress stress concentration on the indentation edge formed on the rolling surface and to reduce the tangential force acting on the rolling surface.

  However, in Patent Document 1 described above, in order to suppress stress concentration on the indentation edge, the amount of retained austenite in the surface layer portion that forms the rolling surface is increased, so that the hardness of the surface layer portion is reduced and wear resistance is increased. In some cases, the indentation resistance is lowered, and the indentation due to the foreign matter is easily formed on the rolling surface. As a result, as the size and number of indentations to be formed increase, the shape of the rolling surface tends to collapse and the surface roughness increases, so the tangential force acting on the rolling surface increases.

  Here, even when the tangential force acting on the rolling surface is increased, in the rolling bearing described in Patent Document 1 described above, early peeling is unlikely to occur in the rolling element having a large amount of retained austenite in the surface layer portion. . However, since the same tangential force acts between the two members that are in rolling contact, the amount of retained austenite in the surface layer portion of the inner and outer rings that is in rolling contact with the rolling element described above is less than the surface layer portion of the rolling element. As a result, early peeling due to an increase in tangential force occurs on the rolling surfaces of the inner and outer rings, and as a result, the life of the entire rolling bearing cannot be extended.

Moreover, since retained austenite existing in the surface layer part deteriorates dimensional stability, the rolling bearing described in Patent Document 1 described above is preferably used when it is used under foreign matter lubrication and at high temperature. difficult.
Accordingly, an object of the present invention is to provide a rolling support device that is less likely to cause early peeling even when used under foreign matter lubrication and has a long life.

  In order to solve such a problem, the present invention is arranged between a first member and a second member having raceway surfaces arranged opposite to each other, and between the first member and the second member so as to be freely rollable. A rolling element having a rolling surface with respect to the raceway surface, and one of the first member and the second member moves relative to the other when the rolling element rolls. The at least one rolling member of the first member, the second member, and the rolling element is obtained by performing a heat treatment including carbonitriding or nitriding after processing a material made of steel into a predetermined shape. In addition, the abundance ratio of the nitride containing Si and Mn on the rolling surface is 1.0% or more and 20.0% or less in terms of area ratio, and the N content in the surface layer portion forming the rolling surface is 0. Rolls characterized by being 2% by mass or more To provide a support device.

  In addition, the rolling support apparatus of this invention points out a rolling bearing, a ball screw, and a linear guide, for example. Here, when the rolling support device is a rolling bearing, the first member and the second member refer to the inner ring and the outer ring. Similarly, when the rolling support device is a ball screw, the first member and the second member are When the rolling support device is a linear guide, the first member and the second member indicate a guide rail and a slider, respectively. Moreover, the rolling surface of this invention points out the track surface of a 1st member or a 2nd member, and the rolling surface of a rolling element. Furthermore, the surface layer portion of the present invention refers to a portion from the rolling surface to a predetermined depth (for example, 50 μm).

  According to the present invention, in at least one rolling member among the first member, the second member, and the rolling element constituting the rolling support device, a nitride containing Si and Mn on the rolling surface (hereinafter referred to as “Si-Mn”). )) And the N content of the surface layer portion forming the rolling surface, the stress concentration suppressing action, the scratch resistance and the wear resistance excellent in the rolling member itself are specified. Since the tangential force acting between the rolling member and the mating member that is in rolling contact can be reduced, early peeling on the rolling surface is less likely to occur when foreign matter is mixed.

In addition, according to the present invention, early peeling is suppressed by specifying a configuration other than the amount of retained austenite in the surface layer portion of the rolling surface (the abundance and N content of Si-Mn nitride). Excellent dimensional stability is obtained even when used at high temperatures.
Therefore, even if the rolling support device of the present invention is used under foreign matter-mixed lubrication, early peeling is unlikely to occur and the life is extended.

  Hereinafter, the rolling member which comprises the rolling support apparatus in this invention is demonstrated in detail. In the rolling member used in the present invention, the abundance ratio of the Si—Mn nitride on the rolling surface is 1.0% or more and 20.0% or less after the heat treatment, and the N content of the surface layer portion forming the rolling surface Is obtained by performing a heat treatment including carbonitriding or nitriding, after processing the material made of steel into a predetermined shape so that the amount becomes 0.2 mass% or more.

<About the steel used as the material>
As the steel constituting the material, the Si content is 0.3 to 2.2% by mass, the Mn content is 0.3 to 2.0% by mass, the Si content and the Mn content It is preferable to use steel having a mass ratio Si / Mn of 5 or less. Further, in order to efficiently precipitate Si-Mn nitride on the rolling surface and to dissolve N within the scope of the present invention in the surface layer portion forming the rolling surface, the sum of the Si content and the Mn content is calculated. It is preferable to set it as 1 mass% or more.

  Here, the Si content and the Mn content are each 0.3% by mass or more in order to precipitate Si—Mn nitride efficiently. On the other hand, if the Si content is too high, not only the workability and machinability are lowered, but also the carbonitriding characteristics and nitriding characteristics are lowered, and the N content of the surface layer portion forming the rolling surface is within the scope of the present invention. It becomes impossible to. Moreover, when there is too much Mn content, the amount of retained austenite of the surface layer part which makes a rolling surface after heat processing will increase, and hardness, abrasion resistance, and pressure dent will deteriorate. Therefore, the Si content is preferably 2.2% by mass or less, and the Mn content is preferably 2.0% by mass or less.

  Further, the Si—Mn-based nitride can be obtained by nitrogen that has entered during carbonitriding or nitriding reacting with Si while taking in Mn in the austenite region and being precipitated. For this reason, when the Mn content is small with respect to the Si content, it is difficult to promote the precipitation of Si—Mn nitride even if nitrogen is sufficiently diffused. Therefore, it is preferable that the content ratio (Si / Mn) of Si and Mn in the steel constituting the material is 5 or less in mass ratio.

Furthermore, it is preferable that the steel constituting the material has a C content of 0.3 mass% to 1.2 mass% and a Cr content of 0.5 mass% to 2.0 mass%.
Here, C which exists in the steel which makes a raw material is an element required in order to provide the intensity | strength and lifetime which are required for steel. Heat treatment time for obtaining the necessary hardened layer depth on the rolling surface when performing nitriding or carbonitriding as well as not giving the necessary strength to the rolling member if the C content of the steel constituting the material is too small Increases the heat treatment cost. Therefore, the C content of the steel constituting the material is preferably 0.3% by mass or more, and more preferably 0.5% by mass or more.

  On the other hand, if the C content of the steel material is too large, huge carbides are produced during steelmaking, which not only adversely affects the subsequent quenching characteristics and rolling fatigue life, but also reduces the header workability and reduces the cost. Invite rise. Therefore, the C content is preferably 1.2% by mass or less. In addition, Cr present in the steel constituting the material is dissolved in the base and has the effect of improving the hardenability and temper softening resistance, and forms fine carbides and carbonitrides with high hardness, In order to suppress the hardness of the rolling member and the coarsening of crystal grains during heat treatment, it has the effect of improving the rolling fatigue life. In order to obtain these effects, the Cr content of the material steel is preferably 0.5% by mass or more, and more preferably 1.3% by mass or more.

On the other hand, if the Cr content of the material steel is too high, huge carbides are produced during steelmaking, which adversely affects the subsequent quenching characteristics and rolling fatigue life, and reduces the header workability and machinability. There is. Therefore, the Cr content of the steel constituting the material is preferably 2.0% by mass or less, and more preferably 1.6% by mass or less.
In addition to the elements described above, carbide forming promoting elements such as Mo and V, which have the same action as Cr, are included in the steel that forms the material in a range that does not cause an increase in cost due to an increase in material cost or a decrease in workability. You may contain. The balance of the steel constituting the material is substantially made of Fe, but may contain S, P, Al, Ti, O, etc. as inevitable impurities. These elements are said to have no particularly remarkable inhibitory effect on surface-initiated peeling starting from the indentation edge. Origin-type peeling occurs. For this reason, strict impurity regulation that causes a significant increase in cost is not performed, but the content of inevitable impurities is set to a quality level that satisfies the cleanliness regulation of high carbon chromium bearing steel defined in JIS G 4805.

<About heat treatment>
First, after the above-described material made of steel is processed into a predetermined shape by forming or rough grinding or the like, “nitriding” is performed by heating and holding in a furnace into which ammonia gas is introduced, or a mixed gas (for example, RX) “Carbonitriding” is performed by heating and holding in a furnace in which (gas + enrich gas + ammonia gas) is introduced. In these treatments, after the heat treatment, the abundance ratio of the Si—Mn nitride on the rolling surface is 1.0% or more and 20.0% or less, and the N content of the surface layer portion forming the rolling surface is 0.2% by mass. The conditions are as described above.
Next, quenching and tempering are performed. These treatments are preferably performed under such conditions that the surface layer portion that forms the rolling surface after the heat treatment has a hardness necessary for a rolling member (for example, Hv 750 or more).

<About the N content of the surface layer portion forming the rolling surface>
N present in the surface layer forming the rolling surface not only acts on solid solution strengthening of martensite and ensuring the stability of retained austenite, but also forms nitrides and carbonitrides to provide wear resistance and scratch resistance. It has the effect of improving and reducing the tangential force acting on the rolling surface. In order to obtain these effects, the N content of the surface layer portion forming the rolling surface is 0.2% by mass or more, preferably 0.3% by mass, more preferably 0.45% by mass or more.
On the other hand, if the N content of the surface layer is too large, the toughness and strength required as a rolling member cannot be obtained. In particular, since the rolling element of the rolling support device needs sufficient toughness and strength, the N content of the surface layer portion forming the rolling surface is preferably 2.0% by mass or less.

<About the abundance ratio of Si-Mn nitride on the rolling surface>
As a result of intensive studies by the present inventors, it has been found that the Si—Mn nitride existing on the rolling surface has the effect of improving the wear resistance and pressure scar resistance and improving the rolling fatigue life. . In order to obtain these effects, the abundance ratio of the Si—Mn nitride on the rolling surface is set to 1.0% or more.
On the other hand, if there is too much Si—Mn nitride present on the rolling surface, the toughness and strength required as a rolling member cannot be obtained. Therefore, the abundance ratio of the Si—Mn nitride on the rolling surface is 20.0% or less, preferably 10.0% or less.

<Regarding the amount of retained austenite in the surface layer portion forming the rolling surface>
The amount of retained austenite in the surface layer portion that forms the rolling surface is preferably increased in order to suppress stress concentration on the indentation edge, but the surface surface portion is provided with excellent wear resistance and pressure dent resistance, and the rolling surface In order to reduce the tangential force acting on the surface, it is preferable to reduce the tangential force.
Therefore, as a result of intensive studies, the present inventors have determined that the amount of retained austenite in the surface layer portion forming the raceway surface of the first member and the second member is γ _RAB and the retained austenite in the surface layer portion forming the rolling surface of the rolling element. When the amount is γ _RC , 0 ≦ γ _RAB and 0 ≦ γ _RC ≦ 50 are satisfied, and γ _RAB −15 ≦ γ _RC ≦ γ _RAB +15 is satisfied so that the indentation in the surface layer portion forming the rolling surface is satisfied. It was found that the tangential force acting on the rolling surface can be made smaller while reliably suppressing the stress concentration on the edge. Here, γ _RC is 50 in order to give the rolling surface the necessary hardness, to obtain excellent pressure scar resistance and wear resistance, and to provide excellent dimensional stability when used at high temperatures. Volume% or less.

  According to the rolling support device of the present invention, in at least one rolling member among the first member, the second member, and the rolling element, the abundance ratio of the nitride containing Si and Mn on the rolling surface is 1. Since the tangential force acting on the rolling surface can be reduced by setting the N content of the surface layer portion forming the rolling surface to 0.2% by mass or more by setting it to 0% or more and 20.0% or less. Peeling can be made difficult to occur.

Hereinafter, the results of verifying the effects of the present invention based on examples will be described.
<First embodiment>
First, a material composed of two types of high carbon chromium bearing steel (SUJ2) is processed into a predetermined shape, and then in a furnace in which a mixed gas (Rx gas + enrich gas + ammonia gas) is introduced, at 830 to 850 ° C. for 1 to 3 hours. Cylindrical specimens (inner diameter: 16 mm, outer diameter: 30 mm, width: 7 mm) by performing carbonitriding by heating and holding, oil quenching, and tempering by heating and holding at 180 to 240 ° C. for 2 hours. Was made.

In addition, the material which consists of SUJ2 is C content rate 0.99 mass%, Si content rate is 0.25 mass%, Mn content rate is 0.40 mass%, Cr content rate is 1.49 mass%. Of steel.
At this time, by changing the carbonitriding conditions, the N content of the surface layer portion (portion from the surface to a depth of 50 μm) forming the outer peripheral surface (surface) of the specimen after heat treatment was adjusted.
In the test body thus obtained, the N content of the surface layer portion forming the outer peripheral surface was measured using an electron beam microanalyzer (EPMA) at an acceleration voltage of 15 kv.
In the obtained specimen, the hardness of the surface layer portion was Hv 750-780, and the amount of retained austenite of the surface layer portion was 20-30% by volume.
And using the obtained test body, the pressure-dentation test, the abrasion resistance test, and the Charpy impact test were done.

[About pressure resistance test]
As shown in FIG. 1, the pressure scar test was performed by placing a steel ball 20 having a diameter of 2 mm on the outer peripheral surface of the test body 10 and pressing it at 5 GPa. In this test, the indentation depth formed on the outer peripheral surface of the test body 10 after pressing the steel ball 20 was measured.
And based on the obtained result, the graph of FIG. 2 which shows the relationship between N content rate of a surface layer part and indentation depth was created.
From the graph of FIG. 2, the indentation depth becomes shallower as the N content in the surface layer increases, and the indentation depth may be 250 nm or less when the N content in the surface layer is 0.2% by mass or more. I understood.

[Abrasion resistance test]
As shown in FIG. 3, the wear resistance test is carried out under the conditions of a surface pressure of 0.8 GPa and a slip rate of 30% after the two outer peripheral surfaces of the pair of test bodies 11 and 12 are placed in contact with each other. The test specimen 11 on the side was rotated at a rotational speed of 10 min ⁻¹ and the test specimen 12 on the driven side was rotated at a rotational speed of 7 min ⁻¹ for 20 hours. In this test, the mass difference between the test specimens 11 and 12 before and after rotation was measured, and the average value of these was measured as the amount of wear. The test bodies 11 and 12 were rotated by the motor 30 and the rotational speed of the driven test body 12 was adjusted by the gear 40.
And based on the obtained result, the graph of FIG. 4 which shows the relationship between N content rate of a surface layer part and wear amount was created.
From the graph of FIG. 4, it can be seen that as the N content in the surface layer portion increases, the wear amount decreases, and when the N content rate in the surface layer portion is 0.2 mass or more, the wear amount is 0.02 g or less. It was.

[Charpy impact test]
The Charpy impact test was conducted by the Charpy impact test method defined in JIS Z 2242. And based on the obtained result, the graph of FIG. 5 which shows the relationship between N content rate of a surface layer part and absorbed energy was created.
From the graph of FIG. 5, it was found that when the N content in the surface layer portion is larger than 2.0 mass%, the absorbed energy is decreased and sufficient toughness cannot be obtained in the surface layer portion.
From the above results, in order to impart all of the scratch resistance, wear resistance, and toughness to the surface layer portion, the N content of the surface layer portion may be 0.2% by mass or more and 2.0% by mass or less. I was able to confirm.

<Second embodiment>
First, after processing a material made of SUJ2 into a predetermined shape, a heat treatment similar to that in the first embodiment was performed to produce a cylindrical test body similar to that in the first embodiment.
At this time, the hardness of the surface layer portion (portion from the surface to a depth of 50 μm) forming the outer peripheral surface of the test body after the heat treatment was adjusted by changing the carbonitriding conditions.
In the test body thus obtained, the hardness of the surface layer portion forming the outer peripheral surface was measured using the Vickers hardness test method defined in JIS Z 2244.
In the obtained specimens, the N content in the surface layer part was 0.3 to 0.5% by mass, and the amount of retained austenite in the surface layer part was 20 to 30% by volume.
And using the obtained test body, the pressure-proof dent test and the abrasion resistance test were done on the same conditions as the 1st example mentioned above.
Then, based on the obtained result, the graph of FIG. 6 which shows the relationship between the hardness of a surface layer part and an indentation depth was created.

From the graph of FIG. 6, it was found that as the hardness of the surface layer portion was increased, the indentation depth became shallower, and when the hardness of the surface layer portion was Hv 750 or more, the indentation depth was 200 nm or less.
Moreover, based on the obtained results, the graph of FIG. 7 showing the relationship between the hardness of the surface layer and the amount of wear was created.
From the graph of FIG. 7, it was found that as the hardness of the surface layer portion increased, the wear amount decreased, and when the hardness of the surface layer portion was set to Hv 750 or more, the wear amount became 0.011 g or less.
From the above results, it was confirmed that the hardness of the surface layer portion should be Hv 750 or more in order to reliably impart pressure scar resistance and wear resistance to the surface layer portion.

<Third embodiment>
First, after processing a material made of steel containing Si and Mn into a predetermined shape, a heat treatment similar to that in the first embodiment described above is performed to produce a cylindrical test body similar to that in the first embodiment described above. did.
At this time, by changing the Si content and the Mn content in the steel constituting the material, the abundance of Si—Mn nitrides on the outer peripheral surface (surface) of the specimen after the heat treatment was varied.
On the outer peripheral surface of the specimen thus obtained, a photograph of at least three fields of view under a condition of an acceleration voltage of 10 kV and a magnification of 5000 using a field emission scanning microscope (Fe-SEM) (FIG. 8). Reference) was taken. Then, using an image analysis apparatus, the obtained photograph was binarized, and then the abundance (area ratio) was measured.

In the obtained specimen, the hardness of the surface layer part (part from the surface to a depth of 50 μm) is Hv 780 to 820, and the N content of the surface layer part is 0.3 to 0.7% by mass. The amount of retained austenite in the surface layer was 20-30% by volume.
And using the obtained test body, the indentation test, the abrasion resistance test, and the Charpy impact test similar to the above-mentioned 1st Example were done.
Then, based on the obtained result, the graph of FIG. 9 which shows the relationship between the presence rate of the Si-Mn type nitride of the outer peripheral surface of a test body, and an indentation depth was created.
From the graph of FIG. 9, as the abundance ratio of the Si—Mn nitride on the outer peripheral surface is increased, the indentation depth becomes shallower. When the abundance ratio of the Si—Mn nitride is 1.0% or more, the indentation depth is Was found to be 100 nm or less.

Moreover, based on the obtained result, the graph of FIG. 10 which shows the relationship between the abundance of the Si-Mn system nitride of the outer peripheral surface of a test body and the amount of wear was created.
From the graph of FIG. 10, as the abundance ratio of the Si—Mn nitride on the outer peripheral surface is increased, the amount of wear decreases, and when the abundance ratio of the Si—Mn nitride on the outer peripheral surface is 1.0% or more, It was found that the wear amount was 0.005 g or less.
Furthermore, based on the obtained results, the graph of FIG. 11 showing the relationship between the abundance ratio of Si—Mn nitrides on the outer peripheral surface of the specimen and the absorbed energy was created.

  From the graph of FIG. 11, it was found that when the abundance ratio of the Si—Mn nitride on the outer peripheral surface exceeds 20.0%, the absorbed energy becomes small and sufficient toughness cannot be obtained on the rolling surface. From the above results, in order to give the surface layer part all of pressure scar resistance, wear resistance, and toughness, the abundance ratio of the Si—Mn nitride on the outer peripheral surface is 1.0% or more, preferably 2. It was confirmed that it should be 0% or more and 20.0% or less.

<Fourth embodiment>
First, a material composed of three types of high carbon chromium bearing steel (SUJ3) and a material composed of SUJ2 were each turned to be processed into a predetermined shape.
Next, carbonitriding by heating and holding at 820 to 900 ° C. for 2 to 10 hours in an oven into which a mixed gas (Rx gas + propane gas + ammonia gas) is introduced, oil quenching, and 160 to 270 ° C. And tempering by heating and holding for 2 hours.
Next, by subjecting them to mirror finishing by polishing and lapping, disk-shaped test bodies (diameter 65 mm, thickness 6 mm) were produced.

In addition, the material which consists of SUJ3 is C content rate 1.01 mass%, Si content rate is 0.56 mass%, Mn content rate is 1.10 mass%, Cr content rate is 1.10 mass%. Of steel.
At this time, by changing the carbonitriding conditions, as shown in Table 1, the N content of the surface layer portion forming the surface of the test body after the heat treatment was adjusted.
In the obtained specimen, the hardness of the surface layer portion was Hv 750 to 820, and the amount of retained austenite of the surface layer portion was 20 to 30% by volume.

In the specimen thus obtained, under the same conditions as described above, the N content in the surface layer portion forming the surface and the abundance of the Si—Mn nitride on the surface were measured. The results are also shown in Table 1.
Then, after the obtained specimen was incorporated in a thrust type life tester manufactured by NSK Ltd., a life test was performed under the following conditions assuming use under the contamination with foreign matter. In this test, the rotation time of the test body until peeling occurred on the surface of the test body was measured as the life, and the L10 life based on the Weibull distribution curve was calculated. This result is shown in No. Table 1 also shows the ratio when the L10 life of 11 is 1.
[Life test conditions]
Test load: 5880N (600kgf)
Rotational speed: 1000min ^-1
Lubricating oil: VG68
Foreign matter: (Hardness) Hv870
(Dimensions) 74-147 μm
(Mixing amount) Mixing so that it becomes 200ppm with respect to the whole lubricant.

From the results of Table 1, the N content of the surface layer portion forming the surface of the test specimen is 0.2% by mass or more, and the abundance of Si—Mn nitride on the surface of the test specimen is 1.0% by mass or more. If it is, a long life is obtained. It turns out that it is 2.1 times or more of 11.
Moreover, based on the obtained results, FIG. 12 showing the relationship between the N content of the surface layer portion forming the surface of the specimen and the abundance of Si—Mn nitride on the surface of the specimen was created.

  From the graph of FIG. 12, it can be seen that the abundance of Si—Mn nitride on the surface of the test specimen increases as the N content in the surface layer portion forming the surface of the test specimen increases. In addition, when a material made of SUJ3 having a higher Si content or Mn content than SUJ2 is used, even if the N content of the surface layer is the same as SUJ2, the abundance of Si-Mn nitride on the surface is high. You can see that it is getting bigger.

Furthermore, based on the obtained results, the graph of FIG. 13 showing the relationship between the abundance of Si—Mn nitrides on the surface of the test specimen and the lifetime was prepared.
From the graph of FIG. 13, it can be seen that the lifetime increases as the abundance ratio of the Si—Mn nitride on the surface of the specimen increases. In addition, when a material made of SUJ3 having a higher Si content or Mn content than SUJ2 is used, the lifetime may be longer even if the surface Si-Mn nitride abundance is the same as SUJ2. I understand.

  From the above results, the rolling member of the rolling support apparatus has an N content of 0.2% by mass or more on the surface layer portion forming the surface, and an abundance of Si—Mn nitride on the surface of 1.0%. It has been confirmed that the life of the rolling support device can be extended by using the same configuration as that of the test body of 20.0% or less even when used under foreign matter-mixed lubrication.

<Fifth embodiment>
In this example, a deep groove ball bearing (inner diameter: 30 mm, outer diameter: 62 mm, width: 16 mm) having a designation number of 6206 manufactured by NSK Ltd. was produced by the following procedure. As shown in FIG. 14, the deep groove ball bearing includes an inner ring 1, an outer ring 2, a ball 3, and a cage 4.
The ball 3 was produced by processing a material made of steel having each composition shown in Table 2 into a predetermined shape and then performing the same heat treatment and mirror finishing as in the fourth embodiment described above. In the ball 3 thus obtained, the N content of the surface layer portion that forms the rolling surface (rolling surface) is measured under the same conditions as in the first embodiment, and the same as in the third embodiment. Under these conditions, the abundance of Si—Mn nitride on the rolling surface was measured. The results are also shown in Table 2.

And after assembling the deep groove ball bearing using the obtained ball 3, the inner ring 1 and outer ring 2 made of SUJ2, and the cage 4 made of plastic, the following is assumed to be used under the contamination with foreign matter A life test was conducted under the conditions shown.
In this test, the rotation time until peeling occurred on any of the rolling surfaces of the inner ring 1, the outer ring 2 and the ball 3 was measured as a life, and the L10 life based on the Weibull distribution curve was calculated. This result is shown in No. Table 2 also shows the ratio when the L10 life of 40 is 1.
[Life test conditions]
Test load: 6223N (635kgf)
Rotational speed: 3000min ^-1
Lubricating oil: VG68
Foreign matter: (Hardness) Hv590
(Dimensions) 74-147 μm
(Mixing amount) Mixing so that it becomes 200ppm with respect to the whole lubricant.

  From the results of Table 2, the Si content is 0.3 mass% or more and 2.2 mass% or less, the Mn content is 0.3 mass% or more and 2.0 mass% or less, and Si / Mn is in mass ratio. It is produced using a material made of steel that is 5 or less, the N content of the surface layer portion forming the rolling surface is 0.2 mass% or more, and the abundance of Si—Mn nitride on the rolling surface is 1 0.0% or more and 20.0% or less. 21-No. In No. 39, no. 40-No. Compared to 44, it can be seen that a long life is obtained.

Moreover, based on the obtained result, the graph of FIG. 15 which shows the relationship between Si / Mn in the steel which comprises the raw material of the ball | bowl 3, and the Si-Mn type | system | group nitride existing rate of the rolling surface of the ball | bowl 3 is shown. Created.
From the graph of FIG. 15, the material of the ball 3 having the N content of the surface layer part forming the rolling surface within the scope of the present invention using the material made of steel having the Si content and the Mn content within the scope of the present invention. It was found that when the Si / Mn in the formed steel was 5 or less in mass ratio, the abundance of Si—Mn nitride on the rolling surface of the balls 3 was 1.0% or more.

<Sixth embodiment>
In this example, a roller of a tapered roller bearing (inner diameter: 26.988 mm, outer diameter: 50.292 mm, width: 14.224 mm) having a designation number of L44649 / 610 manufactured by NSK Ltd. was produced by the following procedure.
First, a wire rod (material) made of steel having each composition shown in Table 3 is processed into a predetermined shape by header processing and rough grinding processing, and then in a furnace in which a mixed gas (Rx gas + propane gas + ammonia gas) is introduced 830. Carbonitriding by heating and holding at 5 ° C. for 5 to 20 hours, oil quenching, and tempering by heating and holding at 180 to 270 ° C. for 2 hours were performed. Next, these rolling surfaces were mirror finished by polishing and lapping.

In the roller thus obtained, in the surface layer portion forming the rolling surface (rolling surface), the N content is measured under the same conditions as in the first embodiment described above, and the amount of retained austenite is determined by the X-ray diffraction method. Was measured. Further, the abundance ratio of the Si—Mn nitride on the rolling surface of the roller was measured under the same conditions as in the third example. These results are also shown in Table 3.
The inner ring and the outer ring were produced by the following procedure.

First, carbonitriding by processing a material composed of SUJ2 into a predetermined shape and then heating and maintaining at 830 to 850 ° C. for 1 to 3 hours in a furnace in which a mixed gas (Rx gas + propane gas + ammonia gas) is introduced. Then, heat treatment including oil quenching and tempering by heating and holding at 180 to 240 ° C. for 2 hours was performed. Next, these track surfaces were mirror finished by polishing and lapping.
At this time, by changing the carbonitriding conditions, the amount of retained austenite in the surface layer portion forming the raceway surface (rolling surface) of the inner ring and the outer ring was adjusted to three types (10 vol%, about 20 vol%, 30 vol%). .

Then, after assembling the tapered roller bearing using the obtained roller, the inner ring, and the outer ring, a life test was performed under the following conditions assuming use under the contamination with foreign matter. In this test, the rotation time until peeling occurred on any of the rolling surfaces of the roller, the inner ring, and the outer ring was measured as the life, and the L10 life based on the Weibull distribution curve was calculated. This result is shown in No. Table 3 shows the ratio when the L10 life of 96 is 1.
[Life test conditions]
Test load: Fr = 12kN, Fa = 3.5kN
Rotational speed: 3000min ^-1
Lubricating oil: VG68
Foreign matter: (Hardness) Hv870
(Dimensions) 74-134 μm
(Mixed amount) Number of tests for each mixed sample to be 0.1 g with respect to the entire lubricant: 12 times

From the results in Table 3, the N content of the surface layer portion forming the rolling surface is 0.2% by mass or more, and the abundance of Si—Mn nitride on the rolling surface is 1.0% or more and 20.0%. No. using the following rollers. 51-No. In No. 91, No. using rollers other than the above. 92-No. It can be seen that a longer life is obtained compared to 96.
Among these, No. 1 was obtained by variously changing the amount of retained austenite γ _RAB in the surface layer portion forming the raceway surface of the inner and outer rings. 67-No. 74, no. 75-No. 82, no. 83-No. From the results of the 91, as gamma _RAB is large, it can be seen that there is a tendency that the life is prolonged.

That is, No. 1 using an inner and outer ring having a γ _RAB of 10% by volume. 67-No. 74, no. A lifetime of 96 to 1.7 to 2.8 times was obtained. Similarly, No. using inner and outer rings with 20% by volume of γ _RAB . 75-No. 82, no. No. 96 using 2.4 to 4.5 times the life of No. 96 and using inner and outer rings with γ _RAB of 30% by volume. 83-No. 91, no. A life of 96 to 2.9 to 6.1 times longer was obtained.

No. 67-No. Of 74, and gamma _RAB, the difference between the amount of retained austenite gamma _RC of the surface layer portion of the roller (hereinafter, referred to as "the difference between the gamma _RAB and gamma _RC".) Was used a larger rollers than 15 vol% No . 73, no. No. 74 has a short life. It turns out that it is 1.8 times or less of 96.
Similarly, no. 75-No. No. 82 using a roller having a difference between γ _RAB and γ _RC larger than 15% by volume. 75, no. 81, no. No. 82 has a short life. No. 96 is 2.4 times or less. 83-No. No. 91 in which the difference between γ _RAB and γ _RC is larger than 15% by volume. 83, no. 84, no. 90, no. No. 91 has a short life. It turns out that it is 2.9 times or less of 96.

From these results, it can be seen that the life of the tapered roller bearing can be further extended by setting the difference between γ _RAB and γ _RC to 15 volume% or less.
Based on the results shown in Table 3, the graph of FIG. 16 showing the relationship between the abundance ratio of the Si—Mn nitrides on the rolling surfaces of the rollers and the service life was prepared.
From the graph of FIG. 16, when the abundance ratio of the Si—Mn nitride on the rolling surface of the roller is 1.0% or more and 20.0% or less, No. It can be seen that a life of 2.0 times that of 96 is obtained.

Further, based on the results shown in Table 3, the graph of FIG. 17 showing the relationship between the amount of retained austenite of the surface layer portion forming the raceway surface of the inner ring and the outer ring and the surface layer portion forming the rolling surface of the roller and the life was prepared. .
From the graph of FIG. 17, the relationship between the retained austenite amount γ _{RC in the} surface layer portion that forms the rolling surface of the roller and the retained austenite amount γ _{RAB in the} surface layer portion that forms the raceway surfaces of the inner ring and the outer ring is expressed as γ _RAB −15 ≦ γ It can be seen that the lifetime is shortened in the portion that does not satisfy _RC ≦ γ _RAB +15 (the broken line portion in FIG. 17).

From the above results, in addition to specifying the N content of the surface layer part forming the rolling surface of the roller and the abundance of Si-Mn nitride on the rolling surface of the inner and outer rings, the surface layer part forming the roller rolling surface By identifying the retained austenite amount γ _RC and the retained austenite amount γ _RAB of the surface layer forming the raceway surface of the inner and outer rings, it has been confirmed that the life of the tapered roller bearing used under the foreign matter lubrication can be further extended.

It is explanatory drawing shown about a pressure | voltage resistant test. It is a figure which shows the relationship between N content rate of a surface layer part, and indentation depth. It is explanatory drawing shown about an abrasion resistance test. It is a figure which shows the relationship between N content rate of a surface layer part, and the amount of wear. It is a figure which shows the relationship between N content rate of a surface layer part, and absorbed energy. It is a figure which shows the relationship between the hardness of a surface layer part, and indentation depth. It is a figure which shows the relationship between the hardness of a surface layer part, and the amount of wear. It is a scanning micrograph in the surface of a test body. It is a figure which shows the relationship between the abundance rate of Si-Mn type nitride, and indentation depth. It is a figure which shows the relationship between the abundance of Si-Mn type nitride, and the amount of wear. It is a figure which shows the relationship between the abundance of Si-Mn type nitride, and absorbed energy. It is a figure which shows the relationship between N content rate of a surface layer part, and the abundance rate of Si-Mn type nitride. It is a figure which shows the relationship between the abundance rate of Si-Mn type nitride, and lifetime. It is sectional drawing which shows a deep groove ball bearing as an example of the rolling support apparatus which concerns on this invention. It is a figure which shows the relationship between Si / Mn in steel, and the abundance of Si-Mn type nitride. It is a figure which shows the relationship between the abundance rate of Si-Mn type nitride, and lifetime. It is a figure which shows the relationship between the amount of retained austenite of a surface layer part, and a lifetime.

Explanation of symbols

1 Inner ring (first member)
2 Outer ring (second member)
3 balls (rolling elements)
4 Cage

Claims (3)

A first member and a second member having raceway surfaces arranged to face each other; a rolling element which is disposed between the first member and the second member so as to freely roll and has a rolling surface with respect to the raceway surface; In the rolling support device in which one of the first member and the second member moves relative to the other by rolling the rolling element,
At least one rolling member among the first member, the second member, and the rolling element is obtained by processing a raw material made of steel into a predetermined shape and then performing a heat treatment including carbonitriding or nitriding,
The abundance ratio of the nitride containing Si and Mn on the rolling surface is 1.0% or more and 20.0% or less in terms of area ratio, and the N content of the surface layer portion forming the rolling surface is 0.2 mass. % Rolling support device characterized in that it is at least%.   The steel has a Si content of 0.3 mass% or more and 2.2 mass% or less, a Mn content of 0.3 mass% or more and 2.0 mass% or less, and a content ratio of Si and Mn. The rolling support device according to claim 1, wherein the ratio (Si / Mn) is 5 or less by mass ratio. When the amount of retained austenite of the surface layer portion forming the raceway surface is γ _RAB and the amount of residual austenite of the surface layer portion forming the rolling surface is γ _RC , 0 ≦ γ _RAB and 0 ≦ γ _RC ≦ 50 are satisfied, The rolling support device according to claim 1, wherein γ _RAB −15 ≦ γ _RC ≦ γ _RAB +15 is satisfied.

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