JP6155829B2 - ROLLING MEMBER, MANUFACTURING METHOD THEREOF, AND ROLLING BEARING - Google Patents

Description

  The present invention relates to a rolling member, a manufacturing method thereof, and a rolling bearing.

  The main cause of rolling fatigue failure in rolling bearings is internal origin type surface peeling. This internal origin type surface delamination is caused by stress that acts due to rolling contact on impurity parts such as non-metallic inclusions contained in the material, and this causes surface damage caused by crack initiation and propagation. It is.

Highly clean steel may be used as a raw material as a measure for suppressing internal-origin-type surface peeling and improving rolling fatigue life (see, for example, Patent Document 1).
High cleanliness steel is a steel material in which the content of oxide-based nonmetallic inclusions is suppressed by reducing the amount of oxygen in the steel. By using this high cleanliness steel, it becomes the starting point of cracks. Non-metallic inclusions can be reduced, and fatigue life can be improved by suppressing the occurrence of surface peeling.
Moreover, even if non-metallic inclusions exist by strengthening the material itself, an alloy steel that has been strengthened to such an extent that cracks can be suppressed and their growth can be used.

Japanese Patent Laying-Open No. 2005-8987

  The above-mentioned high cleanliness steel is different in production method from general steel materials, so the cost as a material is high, and further, the cost for quality control is also required, which increases the production cost of the product. Had. Moreover, even in high-strength alloy steel, since expensive rare metals are added as alloy elements, the cost of the material is high, and the problem of increasing the production cost of the product as in the case of high cleanliness steel Had.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a rolling member, a manufacturing method thereof, and a rolling bearing capable of ensuring a long life against rolling fatigue at a lower cost. To do.

  The present invention for achieving the above object is a rolling member that is formed of a material made of bearing steel and has a rolling contact surface that makes rolling contact with a mating member, and the rolling contact surface has a carbonitriding treatment. The treatment layer is formed on the surface of the rolling contact surface, the surface layer having a residual austenite amount of less than 15% by volume, and positioned closer to the core than the surface layer. A base material layer having a residual austenite amount of less than 15% by volume, and an intermediate layer having a residual austenite content of 25% by volume or more interposed between the surface layer and the base material layer. It is characterized by that.

  According to the rolling member having the above configuration, the intermediate layer having a large amount of retained austenite as compared with the surface layer and the base material layer is formed in a range located in the depth direction from the surface of the rolling contact surface by the depth of the surface layer. Therefore, the shear stress generated when the intermediate layer is brought into rolling contact with the mating member can be applied. Thereby, the retained austenite contained in the intermediate layer can be positively transformed into stress-induced martensite by the shear stress due to rolling contact.

Furthermore, when austenite is transformed into martensite, the hardness increases and volume expansion occurs. For this reason, in the intermediate layer containing more retained austenite than the surface layer and the base material layer, more stress-induced martensite is generated, and the volume expansion appears remarkably.
On the other hand, the surface layer and the base material layer provided via the intermediate layer have less retained austenite and lower shear stress due to rolling contact than the intermediate layer, so that stress-induced martensite is not generated as much as the intermediate layer. Volume expansion does not appear significantly. The intermediate layer is interposed between the surface layer and the base material layer where the volume expansion does not occur remarkably even though the intermediate layer is about to expand in volume, so that the volume expansion is limited. For this reason, compressive stress is generated in the intermediate layer.
As a result, even if impurities such as non-metallic inclusions are present in the material, the improvement in hardness and compressive stress in the intermediate layer suppresses the generation of cracks originating from the impurities or their extension, Even if the maximum shear stress due to rolling contact is continuously applied to the intermediate layer, a long life can be secured against rolling fatigue.

  Furthermore, according to the present invention, even if impurities such as non-metallic inclusions are present in the material, a long life can be ensured against rolling fatigue. There is no need to use special steel such as pre-heated steel. For this reason, it is possible to secure a long life against rolling fatigue at a lower cost than the conventional example.

In the rolling member, it is preferable that the intermediate layer is formed in a depth region where a maximum shearing stress generated when the intermediate layer is brought into rolling contact with the counterpart member.
In this case, the intermediate layer is present in a depth region where the maximum shearing stress generated when the intermediate layer is brought into rolling contact with the counterpart member. Thereby, the retained austenite contained in the intermediate layer can be more positively transformed into stress-induced martensite by the shear stress due to rolling contact.

In the rolling member, the surface layer is formed over a range from the surface of the rolling contact surface to a position where the depth from the surface is 0.05 mm, and the intermediate layer is at least the The rolling contact surface is preferably formed over a range from a position where the depth from the surface is 0.1 mm to a position where the depth is 0.3 mm.
In this case, the intermediate layer can be formed in a depth region where the maximum shear stress generated when the intermediate layer is brought into rolling contact with the counterpart member.

In the rolling member, the nitrogen concentration of the surface layer and the base material layer is less than 0.1 wt%, the nitrogen concentration of the intermediate layer is 0.15 to 0.6 wt%, micro Vickers hardness of the base material layer is not less than 700 Hv, the der micro Vickers hardness than 600Hv intermediate layer is, the micro-Vickers hardness of the intermediate layer is micro-Vickers of the surface layer and the base material layer The hardness is preferably lower than the hardness .
In this case, the amount of retained austenite in each layer can be made appropriate, and the cross-sectional hardness necessary for ensuring a long life against rolling fatigue can be ensured.

The present invention also provides an inner ring having an inner ring raceway surface, an outer ring having an outer ring raceway surface concentrically disposed on the outer peripheral side of the inner ring and facing the inner ring raceway surface, the inner ring raceway surface and the outer ring raceway surface. A plurality of rolling elements interposed between the outer ring, the outer ring, the inner ring, and the rolling elements as described above. Yes.
According to the rolling bearing having the above-described configuration, as described above, it is possible to ensure a long life against rolling fatigue at a low cost.

  The present invention also relates to a method of manufacturing a rolling member having a rolling contact surface that is in rolling contact with a mating member, wherein the material made of bearing steel is heated and held in a carbonitriding atmosphere. A first step of providing a high nitrogen concentration layer obtained by diffusion on the material surface side, and changing the carbonitriding atmosphere in the first step to a hydrogen atmosphere, and maintaining the material in a hydrogen atmosphere, the high nitrogen concentration A second step of reducing the nitrogen concentration of a part of the surface side of the high nitrogen concentration layer while leaving a part of the core side of the layer, and a third step of quenching the material that has undergone the second step; It is characterized by including.

  According to the manufacturing method of the rolling member having the above-described configuration, the second step reduces the nitrogen concentration on the surface side while leaving a portion on the core side of the high nitrogen concentration layer obtained in the first step. A denitrification layer having a low nitrogen concentration can be provided on the outermost surface. Further, in the lower layer of the denitrification layer, a part of the high nitrogen concentration layer remains, and in the lower layer of the high nitrogen concentration layer, the nitrogen concentration does not reach the first step, so the nitrogen concentration is low. The portion is a base material layer having a low nitrogen concentration.

If the concentration of nitrogen diffused in the steel is high, the amount of retained austenite during quenching is increased. Therefore, when quenching is performed in the third step, the high nitrogen concentration layer has a higher nitrogen concentration than the denitrification layer and the base material layer, so that the amount of retained austenite is larger than that of the denitrification layer and the base material layer.
Therefore, the denitrification layer and the base material layer become a surface layer and a base material layer with a relatively small amount of retained austenite by quenching, and the high nitrogen concentration layer has a retained austenite by quenching as compared with the surface layer and the base material layer. The middle layer contains a lot.

  As a result, the surface layer, the base material layer located closer to the core than the surface layer, and the surface layer and the base material layer are interposed between the surface layer and the base material layer. A treatment layer having an intermediate layer containing a large amount of can be formed on the material, and a rolling member that can ensure a long life against rolling fatigue can be obtained.

  According to the rolling member and the rolling bearing of the present invention, it is possible to secure a long life against rolling fatigue at a lower cost. Moreover, according to the manufacturing method of the rolling member of this invention, the rolling member which can ensure a long life with respect to rolling fatigue at lower cost can be obtained.

It is sectional drawing of the ball bearing which concerns on one Embodiment of this invention. (A) is a partial sectional view of an outer ring raceway surface schematically showing a treatment layer formed on an outer ring of an unused ball bearing, and (b) is an outer ring of the ball bearing after being used for a predetermined time. It is a fragmentary sectional view of an outer ring raceway surface showing typically the formed processing layer. (A) is process drawing which shows an example of the manufacturing method of an outer ring | wheel, (b) is a figure which shows the process included in a carbonitriding process. It is a figure which shows the heat processing conditions of a carbonitriding process. (A) is the fragmentary sectional view which typically showed the state of the surface vicinity of the intermediate material after a carbonitriding process, (b) is the state of the surface vicinity of the intermediate material after a denitrification process typically. It is the fragmentary sectional view shown. It is a graph which shows the result of having measured the cross-sectional hardness of the test piece, and the amount of retained austenite, (a) is the measurement result of an unused test piece, (b) is the measurement of the test piece after using for a predetermined time. Results are shown. It is a graph which shows the result of the line analysis of the nitrogen concentration by EPMA. It is sectional drawing which shows the testing machine used for the rolling fatigue life test.

Next, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a cross-sectional view of a ball bearing according to an embodiment of the present invention.
The ball bearing 1 includes an inner ring 2, an outer ring 3 disposed concentrically on the outer peripheral side of the inner ring 2, and a plurality of balls 4 as a plurality of rolling elements arranged between the inner and outer rings 2 and 3. .

The inner ring 2 is an annular member formed using high carbon chromium bearing steel such as SUJ2 (JIS G4805), and an inner ring raceway surface 2a on which a plurality of balls 4 roll is formed on the outer periphery thereof. .
The outer ring 3 is also an annular member formed using high carbon chrome bearing steel such as SUJ2 like the inner ring 2, and the inner ring faces the inner ring raceway surface 2a and a plurality of balls 4 A rolling outer ring raceway surface 3a is formed.
The ball 4 has a rolling surface 4a which is a surface thereof in contact with the inner ring raceway surface 2a and the outer ring raceway surface 3a, and is interposed between the raceway surfaces 2a and 3a so as to be freely rollable. The balls 4 are also formed using high carbon chrome bearing steel such as SUJ2 as with the inner and outer rings 2 and 3.

  The inner ring 2 and the outer ring 3 have an inner ring raceway surface 2a and an outer ring raceway surface 3a as rolling contact surfaces that make rolling contact with a ball 4 that is a counterpart member, and constitute a rolling member. . The ball 4 also has a rolling surface 4a as a rolling contact surface that is in rolling contact with the inner and outer rings 2 and 3 that are counterpart members, and constitutes a rolling member.

A plurality of layers are formed on the surface of at least one member of the inner and outer rings 2 and 3 and the balls 4 constituting the rolling members by carbonitriding according to the present embodiment described below.
In the following description, a case where the carbonitriding process is performed on the outer ring 3 will be described.

FIG. 2A is a partial cross-sectional view of the outer ring raceway surface 3 a schematically showing a treatment layer formed on the outer ring 3 of the unused ball bearing 1.
As shown in FIG. 2, a plurality of treatment layers are formed on the outer ring raceway surface 3a by carbonitriding according to the present embodiment.

The treatment layer L includes a surface layer L1 located on the outermost surface side of the outer ring raceway surface 3a, a base material layer L3 located closer to the core than the surface layer L1, and a surface layer L1 and a base material layer L3. And an intermediate layer L2 interposed therebetween.
The surface layer L1 is formed over at least a range from the surface S of the outer ring raceway surface 3a to a position where the depth from the surface S is 0.05 mm.
The intermediate layer L2 is formed over at least a range from a position where the depth from the surface S is 0.1 mm to a position where the depth is 0.3 mm.
The base material layer L3 is formed as a lower layer of the intermediate layer L2.

  The surface layer L1 and the base material layer L3 in the unused ball bearing 1 are hardened and hardened containing martensite generated by quenching during carbonitriding and residual austenite (γ phase) of less than 15% by volume. The section hardness is 700 Hv or more in micro Vickers hardness.

Further, the intermediate layer L2 in the unused ball bearing 1 is a quenching containing martensite generated by quenching during carbonitriding and residual austenite (γ phase) of 25 volume% or more and less than 50 volume%. The hardened layer has a cross-sectional hardness of 600 Hv or more in terms of micro Vickers hardness.
The surface layer L1 and the base material layer L3 are values of general cross-sectional hardness obtained when the high carbon chromium bearing steel is quenched. Since the intermediate layer L2 contains more austenite (residual austenite) having lower hardness than martensite than the surface layer L1 and the base material layer L3, the intermediate layer L2 has a hardness value higher than that of the surface layer L1 and the base material layer L3. Appears low.

  FIG. 2B is a partial cross-sectional view of the outer ring raceway surface 3a schematically showing a treatment layer formed on the outer ring 3 of the ball bearing 1 after being used for a predetermined time. Each layer L1-L3 does not change in the cross-sectional depth formed before and after use.

When the ball bearing 1 is used for a predetermined time, the outer ring raceway surface 3a comes into rolling contact with the balls 4, and therefore, shear stress due to rolling contact acts on the outer ring raceway surface 3a.
In a raceway surface of a rolling bearing such as a ball bearing, the maximum shear stress generated by rolling contact generally acts on a depth region having a cross-sectional depth of about 0.1 to 0.2 mm from the raceway surface.
Therefore, when the ball bearing 1 of the present embodiment is used for a predetermined time, the maximum shear stress generated by the rolling contact with the ball 4 on the outer ring raceway surface 3a mainly acts on the intermediate layer L2.

In the present embodiment, this maximum shear stress acts on the intermediate layer L2, so that the residual austenite contained in the intermediate layer L2 is transformed into stress-induced martensite.
For this reason, as shown in FIG. 2B, the amount of retained austenite contained in the intermediate layer L <b> 2 is reduced as compared with that before use of the ball bearing 1. The retained austenite is transformed into stress-induced martensite by the reduced amount.
The intermediate layer L2 contains more residual austenite than the other layers, and the intermediate layer L2 of the ball bearing 1 after use contains a relatively large amount of stress-induced martensite transformed from the residual austenite.

  On the other hand, the surface layer L1 and the base material layer L3 contain less residual austenite than the intermediate layer L2, and the shear stress acting by rolling contact is also smaller than that of the intermediate layer L2. Therefore, as shown in FIG. 2B, the retained austenite slightly decreases in the surface layer L1, but the stress-induced martensite does not occur in the surface layer L1 and the base material layer L3 as much as in the intermediate layer L2.

  That is, according to the present embodiment, at least the depth from the surface S of the outer ring raceway surface 3a is 0.1 mm in the intermediate layer L2 having a larger amount of retained austenite than the surface layer L1 and the base material layer L3. Since the intermediate layer L2 is formed over the range from the position to the position of 0.3 mm, the intermediate layer L2 exists in a depth region where the maximum shear stress generated when it makes rolling contact with the ball 4 acts. Become. Thereby, the retained austenite contained in the intermediate layer L2 can be positively transformed into stress-induced martensite by the shear stress due to rolling contact.

When austenite is transformed into martensite, hardness increases and volume expansion occurs.
That is, in the surface layer L1 and the base material layer L3 in which stress-induced martensite does not occur as much as the intermediate layer L2, volume expansion associated with the stress-induced martensite is not significant, but the intermediate layer L2 contains more retained austenite. Since more stress-induced martensite is generated, the volume expansion also appears significantly as compared with the surface layer L1 and the base material layer L3.

  Since the intermediate layer L2 in which the volume expansion appears remarkably is interposed between the surface layer L1 and the base material layer L3 in which the volume expansion does not appear significantly as compared with the intermediate layer L2, the volume expansion is limited. . For this reason, a compressive stress is generated in the intermediate layer L2.

As a result, even if impurities such as non-metallic inclusions are present in the material, the crack generation starting from the impurities or its extension is suppressed by the improvement in hardness and compressive stress in the intermediate layer L2, Even if the maximum shear stress due to rolling contact is continuously applied to the intermediate layer L2, a long life against rolling fatigue can be ensured.
As described above, in the present embodiment, a large amount of retained austenite is intentionally left in the intermediate layer L2, and the compressive stress is applied while the intermediate layer L2 is secondarily cured by using the shear stress acting at the time of rolling contact. Fatigue life due to is improved.

  Furthermore, according to the present embodiment, even if impurities such as non-metallic inclusions are present in the material, a long life can be ensured against rolling fatigue. Since it is not necessary to use special steel materials such as cleanliness steel, it is possible to secure a long life against rolling fatigue at a lower cost than the conventional example.

In the present embodiment, the nitrogen concentration of the surface layer L1 and the base material layer L3 is less than 0.1% by weight, and the nitrogen concentration of the intermediate layer L2 is 0.15 to 0.6% by weight.
The reason is that in the carbonitriding process, if the concentration of nitrogen diffused in the steel is high, the amount of retained austenite at the time of quenching can be increased. For this reason, the nitrogen concentration of the intermediate layer L2 is 0.15 to 0.6% by weight, which is a larger value than the surface layer L1 and the base material layer L3.

In the above embodiment, the surface hardness of the surface layer L1 is set to 700 Hv or more in terms of micro Vickers hardness. However, since the surface layer L1 is in direct contact with the ball 4, if it is less than 700 Hv, the wear resistance is reduced and the rolling life is reduced. May decrease. Therefore, the cross-sectional hardness of the surface layer L1 is preferably 700 Hv or more.
In the above embodiment, the amount of retained austenite contained in the surface layer L1 is less than 15% by volume. However, when the amount of retained austenite is 15% by volume or more, stress-induced martensite transformation occurs to a degree that cannot be ignored. The effect which restrict | limits the volume expansion of L2 will be reduced. For this reason, it is preferable that the amount of retained austenite contained in the surface layer L1 is less than 15% by volume.
The reason why the nitrogen concentration of the surface layer L1 is less than 0.1% by weight is related to the amount of retained austenite. When the nitrogen concentration is 0.1% by weight or more, the amount of retained austenite is less than 15% by volume. It is because it becomes difficult to suppress it.

Moreover, in the said embodiment, although the cross-sectional hardness of the base material layer L3 was 700 Hv or more in micro Vickers hardness, when it is less than 700 Hv, the hardness as the whole process layer L will fall and abrasion resistance will fall. In addition, the rolling life may be reduced. Therefore, the cross-sectional hardness of the base material layer L3 is preferably 700 Hv or more.
In the above embodiment, the amount of retained austenite contained in the base material layer L3 is less than 15% by volume. However, as with the surface layer L1, when the amount of retained austenite is 15% by volume or more, stress-induced martensite transformation is ignored. It occurs to the extent that it cannot be performed, and the effect of limiting the volume expansion of the intermediate layer L2 is reduced. For this reason, it is preferable that the amount of retained austenite contained in the base material layer L3 is less than 15% by volume.
Further, the nitrogen concentration of the base material layer L3 is less than 0.1% by weight, which is related to the amount of retained austenite. Like the surface layer L1, when the nitrogen concentration is 0.1% by weight or more, This is because it becomes difficult to suppress the amount of retained austenite to less than 15% by volume.

In the above embodiment, the cross-sectional hardness of the intermediate layer L2 is set to 600 Hv or more in terms of micro Vickers hardness, but if it is less than 600 Hv, stress-induced martensite is generated due to the action of shear stress generated by the rolling contact of the balls 4. There is a possibility that the value of the later section hardness is insufficient. For this reason, it is preferable that the cross-sectional hardness of the intermediate layer L2 is 600 Hv or more.
In the above embodiment, the amount of retained austenite contained in the intermediate layer L2 is set to 25% by volume or more and less than 50% by volume. However, when the amount of retained austenite is less than 25% by volume, sufficient stress-induced martensite is obtained. There is a risk of not. On the other hand, if the amount of retained austenite is 50% by volume or more, the amount of retained austenite is increased without being transformed into stress-induced martensite, which may reduce the value of cross-sectional hardness. For this reason, it is preferable that the amount of retained austenite contained in the intermediate layer L2 is 25% by volume or more and less than 50% by volume.
The reason why the nitrogen concentration of the intermediate layer L2 is in the range of 0.15 to 0.6% by weight is related to the amount of residual austenite. When the nitrogen concentration is less than 0.15% by weight, the amount of residual austenite is This is because it is difficult to make the content of 25 volume% or more, and when the nitrogen concentration is larger than 0.6% by weight, it becomes difficult to make the amount of retained austenite less than 50 volume% and embrittle.

Next, a method for manufacturing the outer ring 3 will be described.
FIG. 3A is a process diagram illustrating an example of a method for manufacturing the outer ring 3.
First, a material made of high carbon chromium bearing steel such as SUJ2 is formed in a predetermined shape as the outer ring 3 to obtain an intermediate material of the outer ring 3 (step S1).

Next, carbonitriding is performed on the intermediate material (step S2). In this carbonitriding process, since quenching is performed, tempering is performed after the carbonitriding process (step S3).
Thereafter, finishing such as polishing is performed on the intermediate material that has been subjected to each heat treatment (step S4), and a finished product of the outer ring 3 is obtained.

  The carbonitriding process in step S2 includes a carbonitriding process (step S21), a denitrification process (step S22), and a quenching process (step S23), as shown in FIG. After placing the material in the carbonitriding furnace, these steps are performed continuously.

FIG. 4 is a diagram showing heat treatment conditions for carbonitriding.
In the carbonitriding process, first, the intermediate material obtained in step S1 is placed in a carbonitriding furnace. Then, the inside of the furnace in which the intermediate material is arranged is adjusted to a carbonitriding atmosphere with a carbon potential of 1.1 (CP = 1.1) and an ammonia concentration of 3% by volume, and heated and held at 830 ° C. for 3 hours or more. (Carbonitriding step (first step)).
Thereby, nitrogen is diffused on the surface of the intermediate material, and a high nitrogen concentration layer having a higher nitrogen concentration than the core is formed.
The holding time is appropriately adjusted according to the size and shape of the intermediate material so that the high nitrogen concentration layer is formed in the necessary depth range.

Fig.5 (a) is the fragmentary sectional view which showed typically the state of the surface vicinity of the intermediate raw material after a carbonitriding process.
As shown in FIG. 5A, the intermediate material after the carbonitriding step is formed with a high nitrogen concentration layer L12 having a higher nitrogen concentration than the core side base material layer L13 on the surface side.
At this time, the high nitrogen concentration layer L12 is formed over at least a range from the surface of the intermediate material to a position where the depth is 0.3 mm. Thereby, when the intermediate material is the outer ring 3 that is a finished product, the range of the cross-sectional depth in which the intermediate layer L2 (FIG. 2) is formed can be set to an appropriate range.

  Returning to FIG. 4, when the carbonitriding process is completed as described above, the introduction of ammonia is stopped while the intermediate material is set in the carbonitriding furnace, and further the hydrogen gas atmosphere is adjusted to adjust the inside of the carbonitriding furnace. Change the setting so that the atmosphere is reduced. Thereby, nitrogen diffused on the surface of the intermediate material can be diffused inside the furnace (denitrification step (second step)), and the nitrogen concentration on the surface side of the high nitrogen concentration layer can be reduced.

As shown in FIG. 4, in the denitrification step, the atmosphere in the furnace is set as described above, and heated and held at 830 ° C. for 0.5 hour or more.
The holding time is appropriately adjusted according to the size and shape of the intermediate material so that the denitrification layer is formed in the necessary depth range.

FIG.5 (b) is the fragmentary sectional view which showed typically the state of the surface vicinity of the intermediate raw material after a denitrification process.
As shown in FIG. 5B, the intermediate material after the denitrification step is formed with a denitrification layer L11, a high nitrogen concentration layer L12, and a base material layer L13 in order from the outermost surface side.
The denitrification layer L11 is a layer formed by a denitrification process. The denitrification layer L11 is formed by lowering a partial nitrogen concentration on the surface side of the high nitrogen concentration layer L12 formed after the carbonitriding step by the denitrification step.
The denitrification layer L11 is formed over at least a range from the surface of the intermediate material to a position where the depth from the surface is 0.05 mm. This is because when the intermediate material is the outer ring 3 that is a finished product, the depth range in which the surface layer L1 and the intermediate layer L2 (FIG. 2) are formed can be set to an appropriate range.

Returning to FIG. 4, when the denitrification process is completed, the intermediate material is put into a quenching oil maintained at about 180 ° C. and quenched (quenching process (third process)), for example.
Thereafter, the intermediate material is tempered as described above (step S3 in FIG. 3). As conditions for tempering, as shown in FIG. 4, the quenched intermediate material is put into an oil tank maintained at 190 ° C. and held for 2 hours.

  The intermediate material quenched and tempered as described above has a denitrification layer L11, a high nitrogen concentration layer L12, and a base material layer L13 (FIG. 5B) formed before quenching by quenching and tempering, respectively. The surface layer L1, the intermediate layer L2, and the base material layer L3 (FIG. 2) are used.

  According to the manufacturing method of the outer ring 3 having the above-described configuration, a part of the nitrogen concentration on the surface side while leaving a part on the core side of the high nitrogen concentration layer L12 (FIG. 5) obtained in the carbonitriding step by the denitrification step. Therefore, a denitrification layer L11 (FIG. 5) having a low nitrogen concentration can be provided on the outermost surface. Further, in the lower layer of the surface layer, a part of the high nitrogen concentration layer L12 remains, and further, in the lower layer of the high nitrogen concentration layer L12, the nitrogen diffusion by the carbonitriding process does not reach, so the nitrogen concentration becomes low. This portion is the base material layer L13 (FIG. 5) having a low nitrogen concentration.

If the concentration of nitrogen diffused in the steel is high, the amount of retained austenite during quenching is increased. Therefore, when quenching is performed by the quenching process, the high nitrogen concentration layer L12 has a higher nitrogen concentration than the denitrification layer L11 and the base material layer L13, and therefore the amount of retained austenite is larger than that of the denitrification layer L11 and the base material layer L13. Become.
Therefore, the denitrification layer L11 and the base material layer L13 become the surface layer L1 (FIG. 2) and the base material layer L3 (FIG. 2) with a relatively small amount of retained austenite by quenching, and the high nitrogen concentration layer L12 by quenching. The intermediate layer L2 (FIG. 2) contains more retained austenite than the surface layer L1 and the base material layer L3.

  As a result, the surface layer L1, the base material layer L3 located on the core side of the surface layer L1, and the surface layer L1 and the base material layer L3 are interposed between the surface layer L1 and the base material. The treatment layer L having the intermediate layer L2 containing more retained austenite than the layer L3 can be formed on the intermediate material, and the outer ring 3 that can ensure a long life against rolling fatigue can be obtained.

  The present invention is not limited to the above embodiment. In the above description, the case where the rolling member according to the present invention is used for the inner and outer rings and balls of a ball bearing has been illustrated. However, for example, it can be used for a raceway ring of a tapered roller bearing or a tapered roller, or it can be in rolling contact with a counterpart member. If it is a member to perform, the rolling member by this invention is applicable.

The present inventors conducted an evaluation test to confirm the state of the treatment layer formed on the rolling member and the effect on rolling fatigue by the rolling member.
For the evaluation test, an annular test piece formed in the following dimensions was subjected to carbonitriding treatment by the above-described manufacturing method and used as a rolling member. In addition, the following test piece dimension was formed according to the test piece dimension used for the rolling fatigue life tester mentioned later.
Test piece dimensions: outer diameter 60 mm, inner diameter 20 mm, thickness 11 mm
Specimen material: SUJ2

As an evaluation method, the cross-sectional hardness, the amount of retained austenite, and the nitrogen concentration of the test piece manufactured as a rolling member were measured, and these values were evaluated.
The cross section hardness was measured by embedding the test piece in a resin or the like and then mirror polishing the cross section of the test piece, and then measuring a predetermined depth position from the surface with a load of 300 gf using a micro Vickers hardness meter.
The amount of retained austenite was quantitatively analyzed by X-ray diffraction from the surface side of the test piece. The surface of the test piece was scraped off to a predetermined dimension by electrolytic polishing or the like to obtain a predetermined depth position, and a quantitative analysis of the amount of retained austenite was performed at each predetermined depth position.
For the nitrogen concentration, line analysis (quantitative analysis) was performed for each predetermined depth position in the cross section of the test piece by a calibration curve method using EPMA (Electron Probe MicroAnalyser) using a test piece embedded in a resin.

FIG. 6 is a graph showing the results of measuring the cross-sectional hardness and the amount of retained austenite of a test piece, (a) is the measurement result of an unused test piece, and (b) is the result after use for a predetermined time. The measurement result of the test piece is shown. In addition, as a test piece after using for this predetermined time, the test piece which carried out the rolling contact by implementing the fatigue life test mentioned later for 48 hours was used.
In the figure, the horizontal axis indicates the depth from the surface, and the vertical axis indicates the cross-sectional hardness and the amount of retained austenite. Moreover, the measurement result of the amount of retained austenite is indicated by a square point and a solid line, and the measurement result of the cross-sectional hardness is indicated by a round point and a broken line.

In FIG. 6 (a), when the measurement result of the residual austenite amount of the unused test piece is seen, the depth from the surface is 0.05 mm (corresponding to the surface layer L1 (FIG. 2)), and from the surface. The amount of retained austenite at a position where the depth of 0.5 mm is equivalent to the base material layer L3 (FIG. 2) is less than 10% by volume.
On the other hand, the amount of retained austenite at a position where the depth from the surface is in the range of 0.1 to 0.3 mm (corresponding to the intermediate layer L2 (FIG. 2)) is 25 to 35% by volume, compared with the other layers. Many are included.
From this result, in the unused test piece, the surface layer L1 with a small amount of residual austenite, the base material layer L3 which is located on the core side with respect to the surface layer L1 and has a small amount of residual austenite, the surface layer L1 and the base material It can be confirmed that a treatment layer having an intermediate layer L2 having a relatively large amount of retained austenite present in the material layer L3 is formed.

In FIG. 6 (a), when the measurement result of the cross-sectional hardness is seen, the cross-sectional hardness at the position where the depth from the surface is 0.05 mm and at the position where the depth from the surface is 0.5 mm is about It is about 720 Hv, and it can be seen that the general quenching hardness of the high carbon chromium bearing steel is obtained in the surface layer L1 and the base material layer L3.
Further, the cross-sectional hardness at a position where the depth from the surface is in the range of 0.1 to 0.3 mm, which corresponds to the intermediate layer L2, is 620 to 650 Hv, and the amount of retained austenite is larger than that of the other layers. The value of the cross-sectional hardness is lower than the other parts.

  In FIG. 6B, when the measurement result of the residual austenite amount of the test piece after use is seen, the residual austenite amount at a position where the depth from the surface is 0.5 mm is the residual austenite amount of the unused test piece. Almost the same as the amount. However, the amount of retained austenite at a position where the depth from the surface is 0.05 mm is slightly reduced as compared with the amount of retained austenite (about 8% by volume) of the unused test piece. This is presumably because a part of the retained austenite contained slightly is transformed into martensite due to the shear stress acting by rolling contact during use acting on the outermost surface layer L1.

In FIG. 6B, the amount of retained austenite at a position where the depth from the surface is in the range of 0.1 to 0.3 mm is compared with the amount of retained austenite of the unused test piece (25 to 35% by volume). Thus, it is about 10% by volume and it can be confirmed that it is greatly reduced.
From this result, it is considered that in the intermediate layer L2, shear stress due to rolling contact acts, and the retained austenite contained relatively much when not in use is transformed into stress-induced martensite, which is greatly reduced. It is done.

In FIG. 6B, when the measurement result of the cross-sectional hardness of the test piece after use is seen, the cross section at a position corresponding to the intermediate layer L2 and having a depth from the surface in the range of 0.1 to 0.3 mm. It can be seen that the hardness is a very hard value of 730 to 770 Hv compared to the cross-sectional hardness (620 to 650 Hv) of an unused test piece. This seems to be secondary hardening due to the transformation of the retained austenite contained in the intermediate layer L2 into stress-induced martensite.
Thus, from the measurement results of the cross-sectional hardness and residual austenite amount of the test piece after use, the austenite contained in the intermediate layer L2 is transformed into stress-induced martensite by the shear stress acting by rolling contact, Can be confirmed.
In addition, although the value of the cross-sectional hardness at a position where the depth from the surface is 0.05 mm is slightly high, this is due to the fact that the retained austenite is slightly transformed into martensite and is due to work hardening. Conceivable.

  As described above, from the measurement results of the cross-sectional hardness and the retained austenite amount, it is confirmed that the unused test piece is formed with the treatment layer L including the surface layer L1, the intermediate layer L2, and the base material layer L3. It can be confirmed that the residual austenite is transformed into stress-induced martensite and improves the hardness of the intermediate layer L2 due to the shear stress due to rolling contact acting on the intermediate layer L2 of the test piece after use. It could be confirmed.

FIG. 7 is a graph showing the results of line analysis of nitrogen concentration by EPMA. In the figure, the horizontal axis indicates the depth from the surface, and the vertical axis indicates the concentration. Further, in the figure, a diagram N is a line analysis result of nitrogen concentration. Moreover, in FIG. 7, the carbon analysis line analysis result is also shown (line C).
Referring to FIG. 7, the nitrogen concentration at a position where the depth from the surface is in the range of 0.1 to 0.3 mm corresponding to the intermediate layer L2 is in the range of 0.2 to 0.5% by weight, The nitrogen concentration in the range corresponding to the surface layer L1 and the base material layer L3 in the range of 0 to 0.05 mm from the surface and in the range of 0.5 mm or more from the surface is 0.1% by weight. It can confirm that it is less than.
Further, it can be confirmed that the carbon concentration is stable at about 1% by weight which coincides with the carbon concentration of SUJ2 in the analyzed range.

  As described above, from FIG. 7, the nitrogen concentration of the surface layer L1 is substantially the same value as the base material layer L3 where the diffusion of nitrogen by carbonitriding hardly reaches, and the nitrogen concentration of the intermediate layer L2 is It can be seen that the height is higher than that of the surface layer L1 and the base material layer L3. From this, in the test piece before quenching, the high-concentration nitrided layer L12 is obtained by the carbonitriding process, and the denitrification layer L11 having a lower nitrogen concentration than the high-concentration nitrided layer L12 is formed by the denitrification process. It can be confirmed.

In addition, the present inventors conducted a rolling fatigue life test using the above test piece.
FIG. 8 is a cross-sectional view showing a testing machine used in the rolling fatigue life test.
The rolling fatigue life tester 50 includes a casing 51 to which a test piece 60 is fixed, an annular member 52 disposed to face the test piece 60, a raceway surface 60a of the test piece 60, and a raceway surface 52a of the annular member 52. And a plurality of balls 53 that roll between them and a drive shaft 54 that rotates the annular member 52 relative to the test piece 60, and the track of the test piece 60 while applying a load in the thrust direction. The balls 53 are configured to roll on the surface 60a.

  The test piece 60 is fixed to the casing 51 as shown in FIG. Lubricating oil O is stored in the casing 51, and the test piece 60 is immersed in the lubricating oil O.

As shown in FIG. 8, the test piece 60 incorporated in the rolling fatigue life tester 50 is applied with a load from the lower side of the casing 51, and rotates the drive shaft 54 to apply the load while applying the load. A plurality of balls 53 are rolled up.
The test piece 60 was peeled off until the stress repetition number reached 100 × 10 6 cycles. The test conditions were set as follows.
Load: 3920N
Maximum contact stress: 5230 MPa
Stress repetition rate: 30Hz
Lubricating oil: Machine oil VG8 equivalent

  As a test piece used in the rolling fatigue life test, in addition to a test piece (Example product) formed as a rolling member by performing carbonitriding treatment according to the present invention, a general quenching treatment is performed as a comparative product. The test pieces thus formed were also tested under the same conditions, and the life performance was evaluated by comparing these Example products with the Comparative Example products.

As a result of the rolling fatigue life test, the life of the example product was about 4 times that of the comparative product.
From this result, it was confirmed that the rolling member according to the present invention can ensure a long life against rolling fatigue as compared with a conventional general heat-treated product.

2 Inner ring 2a Inner ring raceway surface 3 Outer ring 3a Outer ring raceway surface 4 Ball 4a Rolling surface L1 Surface layer L2 Intermediate layer L3 Base material layer L11 Denitrification layer L12 High nitrogen concentration layer L13 Base material layer

Claims (6)

A rolling member that is formed of a material made of bearing steel and has a rolling contact surface that makes rolling contact with a mating member,
A treatment layer by carbonitriding is formed on the rolling contact surface,
The treatment layer is
A surface layer having a residual austenite amount of less than 15% by volume formed on the surface of the rolling contact surface;
A base material layer having a residual austenite amount of less than 15% by volume located on the core side of the surface layer;
A rolling member, comprising: an intermediate layer having a residual austenite amount of 25% by volume or more interposed between the surface layer and the base material layer.   The rolling member according to claim 1, wherein the intermediate layer is formed in a depth region where a maximum shearing stress is generated when the intermediate layer is in rolling contact with the counterpart member. The surface layer is formed over a range from the surface of the rolling contact surface to a position where the depth from the surface is 0.05 mm,
The said intermediate | middle layer is formed over the range from the position where the depth from the surface of the said rolling contact surface is 0.1 mm to the position which is 0.3 mm at least. Rolling member. The nitrogen concentration of the surface layer and the base material layer is less than 0.1% by weight,
The intermediate layer has a nitrogen concentration of 0.15 to 0.6% by weight;
The micro Vickers hardness of the surface layer and the base material layer is not less than 700 Hv, the micro Vickers hardness of the intermediate layer is Ri der than 600 Hv,
The rolling member according to claim 1 , wherein a micro Vickers hardness of the intermediate layer is lower than a micro Vickers hardness of the surface layer and the base material layer . Rolling between an inner ring having an inner ring raceway surface, an outer ring having an outer ring raceway surface concentrically disposed on the outer peripheral side of the inner ring and facing the inner ring raceway surface, and the inner ring raceway surface and the outer ring raceway surface A rolling bearing provided with a plurality of freely intervening rolling elements,
The rolling bearing according to claim 1, wherein at least one of the outer ring, the inner ring, and the rolling element is the rolling member according to claim 1. A method for manufacturing a rolling member having a rolling contact surface that is in rolling contact with a mating member,
A first step of providing a high nitrogen concentration layer obtained by nitrogen diffusion on the material surface side by heating and holding in a carbonitriding atmosphere for the material made of bearing steel;
By changing the carbonitriding atmosphere in the first step to a hydrogen atmosphere and holding the material in a hydrogen atmosphere, the surface side of the high nitrogen concentration layer remains part of the core side of the high nitrogen concentration layer A second step of reducing the nitrogen concentration of a portion of
And a third step of performing a quenching treatment on the material that has undergone the second step.

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