JP5251261B2 - Carburized rolling bearing - Google Patents

Description

  The present invention relates to a generally large and thick carburized rolling bearing such as a rolling bearing for a steel and paper mill, a rolling bearing for a wind turbine gear box, and the like.

  Such large and thick carburized rolling bearings are liable to have incompletely hardened structures and coarse structures with old austenite grain size due to their thickness and mass, and there is concern about the resulting decrease in fatigue strength and life. ing. That is, especially in bearings that have undergone carburizing / carbonitriding, there is residual tensile stress at the cuts in the carburized layer. Destruction occurs from the starting point. Further, it is known that when a coarse structure (inclusions) having a prior austenite grain size exists, stress concentration occurs around the inclusions, and damage starts from this.

Therefore, for example, in the following Patent Document 1, the life characteristics and the crush characteristics are obtained by defining the components of the case-hardened steel for bearings and defining the amount of retained austenite.
Moreover, in the following Patent Document 2, the number of oxide inclusions having an average particle diameter of 3 μm or more and 30 μm or less and the composition ratio are limited, thereby suppressing the flaking of the internal origin that occurs from the origin and the life of the large bearing. To improve.
JP 2004-84869 A Japanese Patent Laid-Open No. 3-100142

By the way, in order to suppress the generation of an incompletely hardened structure from the process surface centering on heat treatment, there is a method of increasing the cooling rate at the time of quenching. However, according to this method, the deformation of the bearing becomes non-uniform, which leads to an increase in grinding allowance and quench cracking. Therefore, there is a demand for a method that can suppress the incompletely hardened structure without changing the process.
Similarly, in order to suppress the coarsening of the prior austenite grain size from the process surface, there are methods such as annealing before quenching, increasing the number of times, or annealing at a temperature equal to or higher than the phase transformation point. However, since these all work in the direction of increasing the deformation, a means for suppressing the coarsening of the prior austenite grain size without depending on the process is also desirable.
Therefore, the present invention has been devised to solve the problems of the prior art as described above, and its purpose is to achieve excellent durability without almost changing the process surface centering on heat treatment. It provides a new carburized rolling bearing that can demonstrate its service life.

To the problem solution, it is carburized rolling bearing of this invention,
A carburized rolling bearing in which a plurality of rolling elements are disposed between an inner ring and an outer ring, and any one or more bearing members of the inner ring, the outer ring, and the rolling element,
C: 0.10 to 0.30 mass%, Si: 0.10 to 0.50 mass%, Mn: 0.60 to 1.00 mass%, Ni: 2.00 to 5.00 mass%, Cr: 0.50 to 2.00 mass%, Mo: 0.10 to 0.50 mass%, Cu: 0.3 mass% or less, O: 0.01 mass% or less, Al: 0.010 to 0.050 mass% %, N: 0.010 to 0.030% by mass, the balance is made of a steel material made of Fe and inevitable impurities,
And DI value of the steel material ((0.2 × C + 0.128) (1 + 0.7Si) (1 + 3.45Mn) (1 + 0.07Ni + 0.27Ni × Ni) (1 + 2Cr) (1 + 2.5Mo) (1 + 0.35Cu)) And the thickness t (mm) of the bearing member made of the steel material satisfies the relationship of DI / t> 0.45, and the core portion average hardness Hv (Vickers hardness) and the standard deviation of the hardness of the bearing member made of the steel material σ is you and satisfies the relation Hv-4σ> 400.
In addition, the content (mass%) of each component corresponding to these element symbols is substituted for the variable represented by each element symbol of the DI value.

That is, the present invention has been devised by paying attention to the relationship between the composition of the steel material constituting the bearing member, its DI value, and the thickness t of the bearing member made of this steel material. If the thickness t satisfies the condition of DI / t> 0.45, excellent durability and life can be exhibited without substantially changing the process surface centering on heat treatment.
Here, the structure of the steel material (carburized steel) is C: 0.10 to 0.30 mass%, Si: 0.10 to 0.50 mass%, Mn: 0.60 to 1.00 mass%, Ni: 2 0.00 to 5.00% by mass, Cr: 0.50 to 2.00% by mass, Mo: 0.10 to 0.50% by mass, Cu: 0.3% by mass or less, O: 0.01% by mass or less , Al: 0.010 to 0.050 mass%, N: 0.010 to 0.030 mass%, the balance Fe and unavoidable impurities are as follows.

(C: 0.10 to 0.30 mass%)
C (carbon) is an element effective for imparting necessary core strength to the steel after quenching and for ensuring sufficient surface hardness after carburizing. And if the addition amount is less than 0.1% by mass, sufficient strength and hardness cannot be obtained, and conversely if it exceeds 0.30% by mass, the toughness and machinability deteriorate, so the addition of C The amount is within this range.

(Si: 0.10 to 0.50 mass%)
Si (silicon) is an element effective for densifying the structure after quenching, toughness, fatigue resistance, and hardenability. If the addition amount is less than 0.1% by mass, these effects cannot be obtained. Conversely, if the addition amount exceeds 0.50% by mass, the toughness and workability deteriorate, so the addition amount of Si is within this range. And

(Mn: 0.60 to 1.00% by mass)
Mn (manganese) has an effect of deoxidation and desulfurization at the time of dissolution, and is an element effective for improving hardenability. And if the addition amount is less than 0.60% by mass, these effects cannot be obtained. On the other hand, if it exceeds 1.00% by mass, the workability and machinability deteriorate, so the addition amount of Mn is This range.

(Ni: 2.00 to 5.00% by mass)
Ni (nickel) is an element effective in improving the hardenability of steel and the toughness after quenching and tempering. In order to obtain a sufficient effect in hardenability, the amount added is 3% by mass, but if the amount added is too large, the workability and machinability deteriorate, so the upper limit is 5.00% by mass. To do.

(Cr: 0.50 to 2.00% by mass)
Cr (chromium) is an effective element for improving the hardenability of steel and the strength and toughness after quenching and tempering. In order to obtain a sufficient effect in hardenability, the amount added is 0.50% by mass. However, if the amount added is too large, double carbides are formed and the hardenability and machinability are impaired. Is 2.00% by mass.

(Mo: 0.10 to 0.50 mass%)
Similarly to Cr, Mo (molybdenum) is an element effective for improving the hardenability of steel and the strength and toughness after quenching and tempering. In order to obtain a sufficient effect in hardenability, the amount added is 0.10% by mass, but if the amount added is too large, double carbides are formed and the hardenability and machinability are impaired. Is 0.50 mass%.

(Cu: 0.3% by mass or less)
Cu (copper) is an element effective for improving hardenability and weather resistance. However, if the addition amount is too large, the workability and toughness are impaired and the effect is effective, so the upper limit of the addition amount is 0. .3 mass%.
(O: 0.01% by mass or less)
If there is too much O (oxygen), the cleanliness of the steel will deteriorate, and in particular, SiO ₂ -based large inclusions will increase, resulting in a decrease in fatigue strength.

(Al: 0.010-0.050 mass%)
Al (aluminum) has an effect of deoxidation at the time of dissolution, and is an element effective for refining the particle size by being finely dispersed as AlN. And if the addition amount is less than 0.010% by mass, these effects cannot be obtained. Conversely, if it exceeds 0.050% by mass, AlN becomes coarse and the effect of refining crystal grains cannot be obtained. The amount of Al added is within this range.

(N: 0.010 to 0.030 mass%)
N (nitrogen) is an element that is effective in reducing the particle size by being finely dispersed as AlN. And if the addition amount is less than 0.010% by mass, these effects cannot be obtained. Conversely, if it exceeds 0.030% by mass, the workability and machinability deteriorate, so the addition amount of N is this Range. Desirably, the addition amount of N is 0.015-0.020 mass%.

Carburizing the rolling bearing of the present invention, core average hardness Hv of the bearing member made of the steel material (Vickers hardness) The standard deviation of the hardness σ is, by satisfying the relation Hv-4 [sigma]> 400, and excellent durability Long life can be demonstrated.

The carburized rolling bearing according to the present invention has an observation range of 6.25 mm ² and a total test area of 200 mm ² , and performs extreme value statistics from the square root of the maximum area of the prior austenite crystal grains in each field of view to be converted into 1300000 mm ^2. maximum particle size d to determine Te is, by less than 140 .mu.m, it is possible to exhibit more excellent durability and long life.

Carburizing the rolling bearing of the present invention is to observe the core average hardness Hv of the bearing member made of the steel (Vickers hardness), and the standard deviation σ of hardness, 1 observation range 6.25 mm ^2, the total the test area 200 mm ² The extreme value statistics are calculated from the square root of the maximum area of the prior austenite crystal grains in each field of view, and the maximum particle size d calculated by converting to 1300000 mm ² satisfies the relationship of Hv−4σ + 2500 / (square root of particle size d)> 650. by, it can exhibit further excellent durability and long life.

  According to the present invention, it is possible to optimize the alloy composition of a steel material even for a large bearing in which an incompletely hardened structure or a coarse structure with a prior austenite grain size is likely to exist because of the thickness or mass. Excellent durability and longevity can be exhibited without substantially changing the process surface centering on heat treatment.

Next, an embodiment of a large carburized rolling bearing according to the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a partial cross-sectional view showing a configuration of a four-row tapered roller bearing applied to a backup roll of a rolling mill for steel facilities, among large-sized carburized rolling bearings 100 according to the present invention.
As shown in the figure, this four-row tapered roller bearing 100 has a plurality of frustoconical rollers 30 arranged between the inner ring 10 and the outer ring 20 along the circumferential direction so as to be rotatable at regular intervals by a cage 40. In addition, four roller arrays 50 are arranged along the width direction.

For example, a shaft (not shown) is attached to the inner ring 10, and the tapered rollers 30 are rolled along the raceway surfaces of the inner ring 10 and the outer ring 20 with the outer ring 20 attached to a housing (not shown). The radial load and the axial load can be borne simultaneously.
At least one of the bearing members constituting the four-row tapered roller bearing 100, that is, the inner ring 10, the outer ring 20, the tapered roller 30 and the cage 40, satisfies all the following four conditions.

(1) At least one of the inner ring 10, the outer ring 20, the tapered roller 30, and the cage 40 is C: 0.10 to 0.30 mass%, Si: 0.10 to 0.50 mass%, Mn: 0 .60 to 1.00% by mass, Ni: 2.00 to 5.00% by mass, Cr: 0.50 to 2.00% by mass, Mo: 0.10 to 0.50% by mass, Cu: 0.3 It is composed of a steel material composed of mass% or less, O: 0.01 mass% or less, Al: 0.010 to 0.050 mass%, N: 0.010 to 0.030 mass%, the balance Fe and unavoidable impurities, And DI value of this steel material ((0.2 × C + 0.128) (1 + 0.7Si) (1 + 3.45Mn) (1 + 0.07Ni + 0.27Ni × Ni) (1 + 2Cr) (1 + 2.5Mo) (1 + 0.35Cu)) And the thickness t of the bearing member made of this steel material is DI / t> 0 .45 relationship is satisfied.

(2) Further, in the bearing member made of the steel material, the core average hardness Hv (Vickers hardness) and the standard deviation σ of the hardness satisfy the relationship of Hv−4σ> 400.
(3) Further, the bearing member made of the steel material observes an observation range of 6.25 mm ² and a total test area of 200 mm ² , and performs extreme value statistics from the square root of the maximum area of the prior austenite crystal grains in each field of view. The maximum particle diameter d calculated in terms of 1300000 mm ² is less than 140 μm.
(4) Further, the core part average hardness Hv (Vickers hardness) of the bearing member made of the steel material , the standard deviation σ of hardness, 1 observation range 6.25 mm ² , total test area 200 mm ² were observed, The extreme value statistics are calculated from the square root of the maximum area of the prior austenite crystal grains in, and the maximum particle size d calculated by converting to 1300000 mm ² satisfies the relationship of Hv−4σ + 2500 / (square root of particle size d)> 650.

  And, in the four-row tapered roller bearing (carburized rolling bearing) 100 of the present invention that satisfies all these conditions, as can be seen from the following examples, the process surface centering on heat treatment is not changed. Excellent durability and long life can be demonstrated. For this reason, even if it is a large sized bearing with large thickness and mass like the 4-row tapered roller bearing 100 of this invention, the function can be maintained over a long period of time.

Next, specific examples of the present invention will be described.
First, three types of wall thickness (14.5 mm, 29 mm) made of steel materials having compositions (C, Si, Mn, Ni, Cr, Mo, Cu, Al, N + balance Fe + inevitable impurities) as shown in Table 1 below. , 45 mm) test pieces (Comparative Examples 1, 2, 7, 8, 13, 14, 19, 23 and Examples 3 to 6, 9 to 12, 15 to 18, 21 to 22). The piece was used for fatigue test, hardness measurement, extreme value statistics and strength of grain size, bearing life test, and the results are shown in Table 2 below.

Table 2 shows the DI value ((0.2 × C + 0.128) (1 + 0.7Si) (1 + 3.45Mn) (1 + 0.07Ni + 0.27Ni × Ni) (1 + 2Cr) (1 + 2.5Mo) ( 1 + 0.35Cu)), DI value / thickness, average hardness, hardness of the standard deviation of the value of the Hv-4 [sigma] obtained from these (the hardness of the tissue), fatigue limit, a maximum particle size, the parameters X (X = Hv −4σ + 2500 / (square root of particle diameter d)), and the life ratio in the bearing life test (comparative example 1 is 1).

As shown in FIG. 2, these test pieces are forged into a predetermined shape, and then carburized (850 to 1050 ° C.) → annealed (600 to 700 ° C.) → quenched (780 to 900 ° C.) → tempered (150 A series of conventional heat treatments (˜240 ° C.) were performed.
In addition, as a fatigue test method used in this example, rotational bending was performed with a test portion diameter of 8 mm of each test piece.

Moreover, as a hardness measuring method, the hardness measurement of the part corresponded to the test part of a fatigue test was performed. The test load was 4900N and at least 30 points were measured, and the average and standard deviation were obtained.
Further, the maximum grain size was calculated by extreme value statistics, 1 observation range 6.25 mm ^2, to observe all the test area 200 mm ^2, performs extreme value statistics than the square root of the maximum area of the particles in each field, 1300000Mm ² The maximum particle size expected when converted to was calculated.

As a life test method, a test bearing (NU228) was formed from the steel materials shown in Table 1, and a bearing life test was performed under the following conditions using this bearing (NU228). When quenching, measure the core cooling rate at the time of quenching the large bearing, change the refrigerant temperature and stirring conditions, etc. so that it is the same as the cooling rate, and the core structure of the large bearing Was reproduced.
・ Bearings: NU228
・ Radial load: P / C = 0.6
・ Rotation speed: 1000 min ^-1
・ Lubrication: Ro58

3 to 5 show the fatigue strength (fatigue limit / MP) and life ratio (L10 life ratio) in each case of the thicknesses 14.5 mm, 29 mm, and 45 mm of the test pieces among the results shown in Table 2. Is a plot of the relationship.
As shown in the figure, it can be seen that the life ratio becomes large at about 600 MPa or more at any wall thickness.
6 to 8 are plots of the relationship between the DI value / thickness t and the life ratio (L10 life ratio) for each case where the thickness of each test piece is 14.5 mm, 29 mm, and 45 mm.
As shown in the figure, it can be seen that at any thickness, if the DI value / thickness is 0.45 or more, the life ratio can be twice or more that of Comparative Example 1.

Next, FIG. 9 represents the fatigue strength (fatigue limit) of 18 test pieces from Comparative Example 1 to Example 18 with respect to Hv-4σ (structure hardness).
As can be seen from this figure, the fatigue strength increases as Hv-4σ increases, and both are in a proportional relationship. And it turns out that sufficient fatigue strength is obtained when Hv-4σ is about 400 or more.

FIG. 10 shows the relationship between the maximum particle size (μm) derived from extreme value statistics and the life ratio of the four test pieces from Comparative Example 19 to Example 22.
As can be seen from this figure, the life ratio increases as the maximum particle size (μm) decreases, and both are in an inversely proportional relationship. It can be seen that an excellent life ratio can be obtained when the maximum particle size (μm) is about 140 μm or less.

FIG. 11 shows the relationship between the parameter X and the life ratio.
As can be seen from the figure, a remarkable life ratio can be exhibited when the parameter X is about 650 or more.
That is, as shown in Table 2, Comparative Examples 1, 2, 7, 8, 13, and 14 all have a DI value / thickness t lower than the value defined in the present invention (0.45 or more). Hv-4σ indicating the relationship between the part average hardness Hv (Vickers hardness) and the standard deviation σ of hardness is lower than the value specified in the present invention (400 or more), and further, the parameter X (Hv-4σ + 2500 / (square root of particle diameter d)) ) Is lower than the value specified in the present invention (650 or more), and none of them can exhibit a sufficient life.

In Comparative Example 19, the maximum particle size measured by the measurement method derived from extreme value statistics is 180 μm, which is lower than the value specified in the present invention (less than 140 μm), and therefore can exhibit a sufficient life. There wasn't.
In Comparative Example 23, none of the DI value / thickness t, Hv-4σ, maximum particle size, and parameter X satisfied the preset values of the present invention, so the life ratio was the lowest among the examples. (0.6).
On the other hand, the life ratios of Examples 3 to 6, 9 to 12, 15 to 18, and 21 to 22 satisfying all the conditions of the present invention exhibited excellent lifespan, which is twice or more that of Comparative Example 1. . In particular, Example 6 having the highest parameter X exhibited a life ratio (2.7) nearly three times that of Comparative Example 1.

1 is a partial cross-sectional view showing an embodiment of a carburized rolling bearing (four-row tapered roller bearing) 100 according to the present invention. It is process drawing which shows the heat treatment process employ | adopted in the present Example. It is the graph which showed the relationship (wall thickness 14.5mm) of a fatigue limit and a life ratio. It is the graph which showed the relationship (thickness 29mm) of a fatigue limit and a life ratio. It is the graph which showed the relationship (thickness 45mm) of a fatigue limit and a life ratio. It is the graph which showed the relationship (wall thickness 14.5mm) of DI value / wall thickness and life ratio. It is the graph which showed the relationship (thickness 29mm) of DI value / thickness and life ratio. It is the graph which showed the relationship (thickness 45mm) of DI value / wall thickness and life ratio. It is the graph which showed the relationship between Hv-4 (sigma) (structure hardness) and a fatigue limit. It is the graph which showed the relationship between the maximum particle size and life ratio. It is the graph which showed the relationship between the parameter X and a lifetime ratio.

Explanation of symbols

100 ... Carburized rolling bearing (4-row tapered roller bearing)
DESCRIPTION OF SYMBOLS 10 ... Inner ring 20 ... Outer ring 30 ... Conical roller 40 ... Cage

Claims (3)

A carburized rolling bearing in which a plurality of rolling elements are disposed between an inner ring and an outer ring,
Any one or more bearing members of the inner ring, the outer ring, and the rolling element,
C: 0.10 to 0.30 mass%, Si: 0.10 to 0.50 mass%, Mn: 0.60 to 1.00 mass%, Ni: 2.00 to 5.00 mass%, Cr: 0.50 to 2.00 mass%, Mo: 0.10 to 0.50 mass%, Cu: 0.3 mass% or less, O: 0.01 mass% or less, Al: 0.010 to 0.050 mass% %, N: 0.010 to 0.030% by mass, the balance is made of a steel material made of Fe and inevitable impurities,
And the DI value of the steel material and the thickness t (mm) of the bearing member made of the steel material satisfy the relationship of DI / t> 0.45,
A carburized rolling bearing characterized in that an average hardness Hv (Vickers hardness) of the bearing member made of the steel material and a standard deviation σ of the hardness satisfy a relationship of Hv-4σ> 400.
However, DI value = (0.2 × C + 0.128) (1 + 0.7Si) (1 + 3.45Mn) (1 + 0.07Ni + 0.27Ni × Ni) (1 + 2Cr) (1 + 2.5Mo) (1 + 0.35Cu). The carburized rolling bearing according to claim 1,
1 observation range 6.25 mm ² , total test area 200 mm ² is observed, extreme value statistics are calculated from the square root of the maximum area of the prior austenite crystal grains in each field of view, the maximum particle diameter d calculated by converting to 1300000 mm ² , A carburized rolling bearing characterized by being less than 140 μm. The carburized rolling bearing according to claim 1,
Observe the core average hardness Hv (Vickers hardness) , hardness standard deviation σ, 1 observation range 6.25 mm ² , total test area 200 mm ² of the bearing member made of the steel material, and the old austenite crystal grains in each field of view. Carbide rolling, characterized in that extreme value statistics are calculated from the square root of the maximum area of the material and the maximum particle size d obtained by conversion to 1300000 mm ² satisfies the relationship of Hv-4σ + 2500 / (square root of particle size d)> 650 bearing.

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