JP2016151057A - Hydrogen embrittlement type carbonitrided bearing component excellent in surface fatigue strength - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbonitrided bearing component capable of securing excellent surface fatigue strength even when hydrogen embrittlement separation occurs.SOLUTION: The carbonitrided bearing component contains, by mass%, C:0.10 to 0.50%, Si:0.05 to 1.00%, Mn:0.10 to 1.00%, P:0.030% or less, S:0.030% or less, Cr:4.00 to 8.00%, Mo:0.10 to 1.00%, Al:0.050% or less, O:0.0015% or less, N:0.025% or less, Cr+Mo:5.00 to 8.10% and the balance Fe with inevitable impurities, and undergoes a carbonitriding treatment and a hardening and tempering treatment. After the tempering treatment, the surface layer of the carbonitrided bearing component has, by mass%, a C concentration of 0.80 to 2.00%, a N concentration of 0.05 to 1.50% and a C+N concentration of 1.10 to 3.00%. In the carbonitrided bearing component, a surface hardness is HRC 58 or more and less than 64 and the number of coarse nitride with particle diameter of 2 μm or more of nitride dispersed and deposited on the surface layer is 10/mmor less.SELECTED DRAWING: None

Description

  The present invention relates to a carbonitrided bearing component capable of suppressing a reduction in life due to surface fatigue peeling of a hydrogen embrittlement type.

  In recent years, parts subjected to surface fatigue loads such as gears, CVT (Continuously Variable Transmission), bearing parts, etc. used in automobiles and industrial equipment have become harsher due to higher performance and higher speed. . Furthermore, the types of lubricating oil including CVT traction oil are diversified, and there is a problem in that early peeling due to a peeling form different from the conventional one occurs.

For example, a bearing for automotive alternator, a tree-like white layer along a grain boundary different from the inclined white band (30 ° band, 80 ° band) due to the Hertzian stress field which is a conventional structural change There is a case where premature exfoliation accompanied by a tissue change occurs.
This is because under severe load conditions such as high vibration, high load, and sudden acceleration / deceleration, the oil film thickness becomes insufficient, metal contact occurs in part, the lubricating oil decomposes, and hydrogen is generated on the rolling surface. This is thought to be due to hydrogen brittle exfoliation caused by entering the inside. Alternator bearings have prevented this early peeling by changing the lubricating oil. However, by simply changing the lubricating oil, it is becoming impossible to suppress the early peeling due to hydrogen, and there has been a demand for the development of a material with excellent hydrogen embrittlement.

As disclosed in the following Patent Document 1, the applicant of the present invention is for carbonitriding excellent in surface fatigue strength of a hydrogen embrittlement type using a hydrogen trap of CrN that is Cr-based nitride and MnSiN ₂ that is Mn-based nitride. Steel is being developed. In the carbonitriding steel described in Patent Document 1, a large number of CrN nitrides having a particle diameter of less than 300 nm and MnSiN ₂ being Mn-based nitrides are dispersed and precipitated to trap diffusible hydrogen well. Thus, the surface fatigue strength is improved.
Furthermore, as disclosed in the following Patent Document 2, in order to further extend the hydrogen brittle exfoliation life, it is necessary to increase the number of fine hydrogen trap sites. That is, appropriate conditions of the surface layer N concentration and the surface layer C concentration for obtaining a long life in rolling fatigue of hydrogen embrittlement type were found by various tests. Specifically, since the surface layer C concentration is lowered by the diffusion of C accompanying nitriding, 0.80 to 2.00% higher than normal carburizing is suitable. On the other hand, when the surface layer N concentration is too high, coarse nitrides are generated, and thus it has been clarified that the surface layer N concentration is suitably 0.10 to 1.50%. In addition, in order to increase the number of fine nitrides that are effective as hydrogen traps, various tests have been conducted not only to increase the surface nitrogen amount but also to optimize the chemical components and to devise the nitrides that are produced. It was found by. That is, it has been found that it is necessary to maximize the amount of MnSiN ₂ that is a Mn-based nitride that is simultaneously generated in addition to CrN that is a Cr-based nitride as a fine nitride. Specifically, since MnSiN ₂ which is a Mn-based nitride is formed as a composite nitride of Mn and Si, the Si amount is added to 0.50 to 1.50%, and the Mn amount is added to 0.80 to 1.50%. Clarified that there is a need to do. Furthermore, in order to maximize the effect, it has been clarified that the Si + Mn amount needs to be over 1.8 to 2.50% and the Mn + Cr amount needs to be 3.00 to 4.50%.

On the other hand, in Patent Document 3 below, the amount of C is 0.4 to less than 0.8%, the amount of Cr is 4.0 to 8.0%, other predetermined amounts of Si, Mn, and Mo are contained, and the balance is Fe and inevitable. There has been disclosed a technique for prolonging the rolling fatigue life by performing carburizing or carbonitriding treatment on high chromium bearing steel as impurities. By increasing the C content and the Cr content in the art, to generate a M ₇ C ₃ type carbides or carbonitrides, and strengthen the surface, rolling especially under lubricated environment foreign matter under high load is mixed fatigue The life expectancy is increased.

JP 2011-225936 A JP 2014-185379 A Japanese Patent Publication No. 6-11899

  However, the early peeling phenomenon caused by hydrogen is still a problem in CVT pulley bearings. The environmental conditions generated in bearing parts tend to increase due to high-speed rotation and high load of parts subjected to surface fatigue load, severe use conditions, diversification of lubricating oil, and the like. For this reason, there has been a demand for the development of a bearing component that further improves the surface fatigue strength of the hydrogen embrittlement type.

  The present invention has been made in the background as described above, and its purpose is to perform carburizing and nitriding, and carburizing having excellent surface fatigue strength even when hydrogen embrittlement delamination occurs depending on use conditions. It is to provide a nitride bearing component.

The present inventors considered that it is necessary to increase the number of fine hydrogen trap sites in order to further extend the hydrogen brittle exfoliation life. That is, the fine nitrides in addition to CrN a Cr-based nitride, although MnSiN ₂ is a Mn-based nitride becomes possible to generate simultaneously, in order to increase the nitriding amount is of CrN due to the increase in Cr content We found that the increase was effective. This is because the production of MnSiN ₂ requires an amount of N twice that of CrN. Specifically, it has been clarified that it is necessary to add 4.00 to 8.00% of Cr in order to increase the amount of CrN produced. Furthermore, in order to enhance the effect, it has been clarified that it is effective to add Mo in an amount of 0.01 to 1.00%.
However, when the amount of Cr + Mo exceeds 8.10%, the productivity is remarkably lowered. Therefore, it has been clarified that the amount of Cr + Mo needs to be 5.00 to 8.10%. Further, while effectively using CrN, the amount of Mn and Si that generate MnSiN ₂ is not actively added, and the amount of Mn and Si is preferably reduced to 1.00% or less from the viewpoint of manufacturability. It revealed that.
In the technique described in Patent Document 3, the Cr amount is added from 4.00 to 8.00%, and the Mo amount is added from 0.01 to 1.00%. to ₇ C ₃ type of those that actively generate carbides or carbonitrides of the present invention is to produce actively CrN a Cr-based nitride, CrN the M ₇ C ₃ The technical idea of the present invention is different from that of Patent Document 3 described above in that the number of finer hydrogen traps is increased because it is finer.

Based on the above knowledge, the hydrogen embrittlement type carbonitrided bearing component of the present invention having excellent surface fatigue strength is mass%, C: 0.10 to 0.50%, Si: 0.05 to 1.00. %, Mn: 0.10 to 1.00%, P: 0.030% or less, S: 0.030% or less, Cr: 4.00 to 8.00%, Mo: 0.10 to 1.00% , Al: 0.050% or less, O: 0.0015% or less, N: 0.025% or less, Cr + Mo: 5.00 to 8.10%, the balance consisting of Fe and inevitable impurities, carbonitriding and quenching Carbonitrided bearing parts that have been tempered, and the surface layer C concentration after tempering is mass%, 0.80 to 2.00%, the surface layer N concentration is 0.05 to 1.50%, and the surface layer C + N concentration 1.10 to 3.00% and the surface hardness is HRC58 or more and less than 64, The number of out particle size 2μm or more coarse nitrides dispersed precipitated nitrides, characterized in that it is 10 ³ / mm ² or less. In this case, the composition further includes one or more of Ni: less than 0.50%, Ti: 0.10% or less, and Nb: 0.10% or less. You can also.

  According to the carbonitrided bearing component of the present invention, the surface fatigue strength of the hydrogen embrittlement type is increased compared to the prior art by increasing the number of fine nitrides effective as hydrogen trap sites and further suppressing the formation of coarse nitrides. Thus, it can be further improved.

Explanatory drawing of the hydrogen charge thrust rolling fatigue test method. Explanatory drawing of the 2 cylindrical rolling fatigue test method.

  Hereinafter, the reason for addition and limitation of each chemical component of the carbonitrided bearing component excellent in surface fatigue strength of the hydrogen embrittlement type of the present invention will be described.

(1) C: 0.10 to 0.50%
C (steel material C concentration) is an element necessary for securing the core hardness of, for example, a rolling bearing as a bearing component. In order to ensure the required core hardness after a predetermined heat treatment, the C content needs to be 0.10% or more, so the lower limit of the C content is defined as 0.10%. On the other hand, if the C content exceeds 0.50%, the manufacturability such as forging and turning decreases, so the upper limit of the C content is set to 0.50%. Preferably it is 0.30 to less than 0.40%, more preferably 0.33 to 0.38%.

(2) Si: 0.05 to 1.00%
Si forms a complex nitride (for example, MnSiN ₂ or the like) with Mn by carbonitriding and acts as a hydrogen trap site, thereby improving hydrogen embrittlement type surface fatigue strength. In order to obtain this effect, since the Si content is required to be 0.05% or more, the lower limit of the Si content is defined as 0.05%. On the other hand, when the Si content exceeds 1.00%, as in the case of C, manufacturability such as forging and turning decreases, so the upper limit of the Si content is set to 1.00%. Preferably it is 0.10 to 0.50%.

(3) Mn: 0.10 to 1.00%
Mn forms Si and Mn nitride (for example, MnSiN ₂ or the like) by carbonitriding to serve as a hydrogen trap site, thereby improving the hydrogen embrittlement type surface fatigue strength. In order to obtain this effect, the Mn content is required to be 0.10% or more, so the lower limit of the Mn content is defined as 0.10%. On the other hand, when the Mn content exceeds 1.00%, as in the case of Si, manufacturability such as forging and turning is lowered, so the upper limit of the Mn content is set to 1.00%. Preferably it is 0.20 to 0.50%.

(4) P: 0.030% or less P segregates at the austenite grain boundary of the steel and causes a decrease in toughness and rolling fatigue life. In particular, the upper limit of the P content is set to 0.030% in order to greatly reduce the grain boundary strength, which is a characteristic of hydrogen embrittlement type rolling fatigue.

(5) S: 0.030% or less S impairs hot workability of steel, forms non-metallic inclusions in the steel to reduce toughness and rolling life, and hydrogen embrittlement type rolling fatigue strength. It is desirable to reduce it as much as possible. For this reason, the upper limit of the S content is set to 0.030%. On the other hand, since S also has an effect of improving the machinability, the lower limit is preferably set to 0.010%.

(6) Cr: 4.00 to 8.00%
Cr is an important additive element in the present invention, and forms a nitride by carbonitriding to serve as a hydrogen trap site to improve hydrogen embrittlement type surface fatigue strength. Cr is added to improve hardenability, secure hardness by carbides, and improve life. In order to obtain a predetermined nitride for high hydrogen embrittlement resistance, it is necessary to add a Cr amount of 4.00% or more. Therefore, the lower limit of the Cr content is defined as 4.00%. On the other hand, if the Cr content exceeds 8.00%, the carburizing property is deteriorated, large carbonitrides are formed, and the rolling fatigue life is reduced. Therefore, the upper limit of the Cr content is 8.00%. It was. Preferably it is 5.00 to 7.00%.

(7) Mo: 0.10 to 1.00% or less Mo improves the surface fatigue strength of the hydrogen embrittlement type by suppressing grain boundary fracture. Further, Mo improves the hardenability of the steel and has the effect of suppressing the decrease in hardness during tempering by dissolving in the carbide. In order to obtain the effect, it is necessary to add an amount of Mo of 0.10% or more, so the lower limit of the Mo content is defined as 0.10%. On the other hand, if the Mo content exceeds 1.00%, the cost of the steel material increases, and the manufacturability such as forging and turning decreases, so the upper limit of the Mo content is set to 1.00%. Preferably it is 0.20 to 0.50%.

(8) Al: 0.050% or less Al is used as a deoxidizer during the production of steel, but it is desirable to reduce it to produce hard non-metallic inclusions and reduce the rolling fatigue life. . When the Al content exceeds 0.050%, a significant decrease in rolling fatigue life is observed, so the upper limit of the Al content was set to 0.050%. In addition, since the cost of steel materials will raise when Al content is made less than 0.005%, it is preferable to make the minimum of Al content into 0.005%.

(9) O: 0.0015% or less, N: 0.025% or less O and N form oxides and nitrides in the steel, and serve as starting points for fatigue failure as non-metallic inclusions. Therefore, the upper limit of the O content was 0.0015% and the upper limit of the N content was 0.025%.

(10) Cr + Mo: 5.00 to 8.10%
Even if Cr and Mo are added alone, the surface fatigue strength of the hydrogen embrittlement type is improved. However, in order to obtain a sufficient effect, it is necessary to add both appropriately and in combination. When the content of Cr + Mo is less than 5.00%, the improvement effect on hydrogen embrittlement cannot be obtained sufficiently, so the lower limit was made 5.00%. On the other hand, if the content of Cr + Mo exceeds 8.10%, productivity such as forging and turning decreases, so the upper limit was made 8.10%. Preferably it is 5.50-7.50%.

(11) Surface hardness: HRC 58 or more and less than 64 There is a correlation between the surface hardness after tempering and the rolling fatigue life, and the higher the surface hardness, the longer the rolling fatigue life. In particular, when the surface hardness after the tempering treatment is less than HRC58, the rolling fatigue life is drastically reduced and the variation in the life is increased. Therefore, the surface hardness after the tempering treatment is set to HRC58 or more. On the other hand, when the surface hardness is increased, the sensitivity to hydrogen embrittlement is increased, and when the surface hardness is HRC64 or more, the surface fatigue strength of the hydrogen embrittlement type is significantly decreased. In terms of Hv hardness, this corresponds to about 650 Hv or more and less than 800 Hv.

(12) The number of coarse nitrides having a particle size of 2 μm or more is 10 ³ pieces / mm ² or less. In order to improve the hydrogen embrittlement surface fatigue strength, it is necessary to precipitate a large number of fine nitrides. That is, of the nitrides, nitrides effective for hydrogen trapping are fine Cr nitrides (eg, CrN) having a particle size of 300 nm or less, and composite nitrides of Mn and Si (eg, MnSiN ₂ ). However, increasing the surface layer N concentration and the alloy element facilitates the formation of coarse nitrides having a large particle size, which causes a decrease in strength. If the number ratio of coarse nitrides having a particle size of 2 μm or more exceeds 10 ³ pieces / mm ² , the hydrogen embrittlement type surface fatigue strength is remarkably lowered. Therefore, the upper limit of the number ratio of coarse nitrides having a particle size of 2 μm or more is limited. 10 ³ pieces / mm ² .

(13) Surface layer C concentration (surface layer carbon concentration): 0.80 to 2.00%
The surface layer C is an essential element for securing strength as a rolling bearing, and the surface layer C concentration of 0.80% or more is necessary to maintain the hardness after a predetermined heat treatment. The lower limit was defined as 0.80%. On the other hand, when the surface layer C concentration exceeds 2.00%, it has been found that large carbides are generated and the rolling fatigue life is reduced, so the upper limit of the surface layer C concentration is 2.00%. Preferably it is 1.20 to 1.40%.

(14) Surface layer N concentration (surface layer nitrogen concentration): 0.05 to 1.50%
The surface layer N works as a hydrogen trap site by generating fine nitride in the surface layer, and improves hydrogen embrittlement resistance. It also improves the rolling life by improving the softening resistance of the steel. In order to obtain these effects, the surface layer N concentration needs to be 0.05% or more, so the lower limit of the surface layer N concentration was set to 0.05%. On the other hand, when the surface layer N concentration exceeds 1.50%, the surface hardness is lowered due to the formation of retained austenite, and a predetermined surface hardness cannot be obtained. Therefore, the upper limit of the surface layer N concentration is set to 1.50%. Preferably it is 0.60 to 0.90%.

(15) Surface layer C + N concentration (surface layer carbon / nitrogen concentration): 1.10 to 3.00%
By optimizing the surface layer C + N concentration, it is possible to achieve both necessary surface layer hardness and precipitation of fine nitrides and improve hydrogen embrittlement surface fatigue strength. In order to obtain this effect, the surface layer C + N concentration needs to be 1.10% or more, so the lower limit of the surface layer C + N concentration is defined as 1.10%. On the other hand, when the surface layer C + N concentration exceeds 3.00%, coarse carbonitrides are generated and the hydrogen embrittlement surface fatigue strength is lowered. Therefore, the upper limit of the surface layer C + N concentration is defined as 3.00%. Preferably it is 1.80 to 2.30%.

In the present invention, any one or more of the following chemical components can be added.
(16) Ni: Less than 0.50% Ni suppresses structural changes in the rolling fatigue process and improves the rolling fatigue life. Further, the addition of Ni is effective in improving toughness and corrosion resistance. On the other hand, if the Ni content exceeds 0.50%, a large amount of retained austenite is generated during quenching of the steel, and a predetermined hardness cannot be obtained, and the cost of the steel material is increased. Less than 50%.

(17) Ti: 0.10% or less Ti carbide is fine and effectively acts as a hydrogen trap site, thereby improving the surface fatigue strength of the hydrogen embrittlement type. On the other hand, Ti forms oxides and nitrides in the steel and serves as a starting point for fatigue failure as a non-metallic inclusion and lowers the rolling fatigue life. Therefore, the upper limit of Ti content is set to 0.10%.

(18) Nb: 0.10% or less Nb carbide is also fine, and effectively acts as a hydrogen trap site, thereby improving the surface fatigue strength of the hydrogen embrittlement type. Nb suppresses the coarsening of crystal grains. Refinement of crystal grains is effective in improving hydrogen embrittlement resistance. On the other hand, since the effect is saturated even if the Nb content exceeds 0.10%, the upper limit of the Nb content is set to 0.10%.

(19) Remainder: Fe and inevitable impurities The inevitable impurities here (inevitable impurities) indicate impurity levels represented by Ni in Table 1 (indicated by “-” in the column of Ni shown in Table 1). In Table 1, the balance is Fe.

Examples of the present invention will be described below.
The material of the chemical component shown in Table 1 was melted by vacuum melting of 150 kg, and steel bars having a diameter of 70 mm and a diameter of 28 mm were manufactured by hot forging. Then, as a spheroidizing annealing treatment, it was heated to 850 ° C., held for 4 hours, cooled to 650 ° C. at −15 ° C./hour, and then air-cooled to obtain materials for each test.

  A test piece having a diameter of 25 mm and a length of 100 mm was cut out from the material and subjected to carbonitriding and quenching and tempering. The carbonitriding process was performed in a mixed atmosphere in which ammonia gas was added to the carburizing gas, followed by quenching and tempering.

  First, after installing a test piece in the processing chamber, a mixed gas obtained by adding ammonia gas to carburizing gas was introduced into the processing chamber, and carbonitriding was performed at 930 ° C. Then, soaking was continued in a state where the temperature in the processing chamber was lowered to 850 ° C., and the test piece was oil-cooled.

  Next, secondary quenching at 850 ° C. and tempering treatment at 200 ° C. were performed. The carbon potential in the processing chamber during the carbonitriding process was 0.8% by volume, and the ammonia gas concentration was 1.0% by volume.

  After performing the carbonitriding process and the quenching and tempering process, the outer periphery of the test piece was ground by a depth of 0.1 mm, and the Rockwell hardness (conforming to JIS Z2245) was obtained by averaging five points. Thereafter, the longitudinal section of the test piece was embedded and polished, and the surface layer C concentration and the surface layer N concentration in the surface layer portion were analyzed by EPMA. Here, the surface layer C concentration and the surface layer N concentration were set to the maximum value (peak value) of the C concentration and N concentration from the outermost layer to a depth of 10 μm.

Further, using a scanning electron microscope, the number of nitrides having a particle diameter of 2 μm or more existing from the surface layer of the embedded and polished specimen to a position of 100 μm in depth is measured and divided by the area of the observation region, The number density (pieces / mm ² ) of coarse nitrides having a diameter of 2 μm or more was determined.

In addition, a 61 mm diameter and 6 mm thick thrust type rolling fatigue test piece is roughly processed from the 70 mm diameter material, and each steel type is subjected to carbonitriding and quenching and tempering under the same carbonitriding conditions as described above. The surface was ground to a thickness of 5.5 mm and buffed to produce a test piece. The test piece was subjected to a cathode charge (hydrogen charge) for 20 hours at a current density of 0.4 mA / cm ² using a diluted sulfuric acid electrolyte solution in which 1.4 g of ammonium thiocyanate was dissolved in 1 L. After the cathode was charged with hydrogen, the paper was polished and a rolling fatigue test was started.

In the rolling fatigue test, as shown in FIG. 1, lubricating oil 15 is injected into an oil tank provided with a disk-shaped test piece 13, the table 14 is pushed up, and a steel ball 12 supported by a cage is attached to a thrust bearing 11. In this state, a predetermined surface pressure is applied, and the shaft 10 that transmits power from the motor is rotated in that state.
Test conditions were a surface pressure of 4.9 GPa, lubrication was performed using a naphthenic mineral oil and a load speed of 1800 rpm. Were tested about 10 points under the same conditions, the cumulative failure probability of the Weibull distribution was evaluated life seeking 10% become L ₁₀ life.

  Further, after roughing from a material having a diameter of 28 mm, each steel type was subjected to the same carbonitriding treatment as described above to produce a cylindrical specimen having a test surface diameter of 26 mm, and a two-cylinder rolling fatigue test was conducted using the specimen. . In the two-cylinder rolling fatigue test, as shown in FIG. 2, the mating cylinder 20 is pressed against the cylindrical test piece 18 with a predetermined surface pressure, and the test piece 18 is pushed by the motor 22 via the shaft portion 24 in this state. While rotating, the rotation of the motor 22 is transmitted to the shaft 30 via the gears 26 and 28 to rotate the counterpart cylinder 20. The counterpart cylinder 20 is made of a quenching and tempering material made of SUJ2, and is formed into a shape with a diameter of 130 mm having a crowning with a curvature radius of 150 mm in the axial direction.

  The test was performed under test conditions (oil temperature 90 ° C., slip rate −60%, surface pressure 3 GPa, rotation speed 1500 rpm) in which hydrogen brittle type early rolling fatigue failure occurs. Even under the same test conditions, the amount of hydrogen intrusion was changed by the lubricating oil and affected hydrogen brittle exfoliation. Therefore, a lubricating oil that was more likely to cause hydrogen brittle exfoliation was used. Here, the slip ratio is a ratio of the difference between the peripheral speeds of the test piece 18 and the counterpart cylinder 20 and the peripheral speed of the test piece 18. The test was performed at four points under the same conditions, and the average life was obtained. Table 2 shows the test results.

In all the inventive examples, the surface hardness is HRC58 or more and less than 64, the surface layer C concentration is in the range of 0.80 to 2.00% by mass, the surface layer N concentration is in the range of 0.05 to 1.50% by mass, and the surface layer C + N The concentration is in the range of 1.10 to 3.00% by mass, and 10 ³ pieces / mm ² or less of coarse nitrides having a particle size of 2 μm or more.

The L ₁₀ life of rolling fatigue of the hydrogen charge material of the inventive example is excellent as 24.05 to 30 × 10 ⁶ times. On the other hand, in the comparative example, the _{L 10} life and 2.92 to 6.77 × 10 ⁶ times, both of which are low-life cause premature rolling fatigue fracture of hydrogen embrittlement type. It can be seen that the rolling life of the hydrogen brittle type is improved by the present invention.

Moreover, the average life of the two-cylinder test of the invention example is excellent at 18.1 to 20 or more × 10 ⁶ times. On the other hand, in the comparative example, the average life is 3.5 to 5.7 × 10 ⁶ times, both of which are low life due to hydrogen embrittlement. It can be seen that the rolling life of the hydrogen embrittlement type is improved by about one order according to the present invention.

  Among the comparative examples in Table 2, steel types Nos. 14 and 16 are examples in which the amount of Cr in the chemical components is low, and since steel type No. 15 has a low amount of Mo, both have a low life. Further, among the comparative examples, steel types No. 1 to No. 3 are examples in which the chemical components are within the scope of claims but have a low life due to the following reasons.

That is, since the carbonitriding condition was not appropriate for the steel type No. 1 in the comparative example, the number of nitrides having a particle size of 2 μm or more was 10 ³ pieces / mm ² or more, and the life was shortened. Steel type No. 2 in the comparative example has a low surface layer C concentration, and steel type No. 3 in the comparative example has a low surface layer N concentration, so that both have a short life.

  As is clear from the above description, according to the carbonitrided bearing component of the present invention that increases the fine nitride effective as a hydrogen trap site and further suppresses the formation of coarse nitride, the hydrogen embrittlement The surface fatigue strength of the mold can be further improved as compared with the prior art.

13, 18 Specimen

Claims (2)

% By mass
C: 0.10 to 0.50%,
Si: 0.05-1.00%,
Mn: 0.10 to 1.00%,
P: 0.030% or less,
S: 0.030% or less,
Cr: 4.00 to 8.00%,
Mo: 0.10 to 1.00%,
Al: 0.050% or less,
O: 0.0015% or less,
N: 0.025% or less,
Cr + Mo: 5.00 to 8.10%,
Carbonitriding bearing parts that have been carbonitrided and quenched and tempered, with the balance being Fe and inevitable impurities, the surface layer C concentration after the tempering treatment being mass%, 0.80 to 2.00%, surface layer N Concentration is 0.05 to 1.50%, surface layer C + N concentration is 1.10 to 3.00%, surface hardness is HRC58 or more and less than 64, and the particle size among the nitrides dispersed and deposited on the surface layer A carbon-nitrided bearing part excellent in surface fatigue strength of a hydrogen embrittlement type, characterized in that the number of coarse nitrides of 2 μm or more is 10 ³ / mm ² or less. In claim 1, in mass%,
Ni: less than 0.50%,
Ti: 0.10% or less,
Nb: 0.10% or less,
A carbon-nitrided bearing part excellent in surface fatigue strength of a hydrogen embrittlement type, characterized by further containing any one or more of these.

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