JP2013155438A - Rolling member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rolling member which has longer life, superior abrasion resistance and superior seizing resistance, by optimizing an Si-Mn-based nitride.SOLUTION: For instance, a rolling element 3 has an Si-Mn-based nitride formed on its surface layer through carbonitriding treatment or nitriding treatment. The surface layer is controlled so as to include 0.2 wt.% or more of nitrogen concentration, include 1% or more and less than 10% of an area rate of Si-Mn-based nitrides, and include the number of 100 pieces or more in 375 μmof the area of Si-Mn-based nitrides of 0.05 to 1 μm. Thereby, high strength is obtained by increasing the deposition amount of fine nitride to shorten a distance between the Si-Mn-based nitrides. Higher strength can be obtained by using a steel, which includes 0.3 to 2.2 wt.% Si and 0.3 to 2.0 wt.% Mn while controlling a ratio Si/Mn to 5 or less and which is subjected to carbonitriding quenching and tempering treatment.

Description

  The present invention relates to a rolling member, and is suitable for improving functions such as extending the life of rolling bearings, ball screws, and linear guides, and improving wear resistance and seizure resistance.

Conventionally, for rolling bearings, bearing steels represented by JIS SUJ2 and SUJ3 are used, and are usually used at a hardness of HRC 60 or higher by quenching / tempering treatment. However, the usage environment of rolling bearings is diversified, and under the lubrication environment where foreign matter is mixed in or the lubrication is insufficient, these bearing steels may not be able to obtain a sufficient life or may cause seizure. is there.
For this reason, the carbonitriding process called marstreshing is performed using SUJ2, and the amount of retained austenite on the raceway surface is increased by solid-dissolving nitrogen, thereby reducing the stress at the indentation edge under lubrication mixed with foreign matter. And the seizure resistance is improved by the effect of nitrogen. However, in recent years, the usage environment of rolling bearings has become more severe, and there are cases where sufficient effects cannot be obtained only by subjecting SUJ2 to carbonitriding.

  In order to solve this, in the rolling bearing described in Patent Document 1 below, a material having a large Si addition amount is used, and carbide or carbonitride containing Si-Mn is precipitated in an area ratio of 1 to 30%, and slipping is performed. Improved wear resistance and seizure resistance in environments with contact and in environments where lubricant is exhausted.

JP 2003-193200 A

However, in the rolling bearing described in Patent Document 1, an appropriate material composition and nitrogen concentration for forming a nitride containing Si and Mn (hereinafter referred to as Si / Mn nitride) are defined. In some cases, sufficient performance may not be exhibited.
The present invention has been made by paying attention to the above-mentioned problems. By optimizing the Si / Mn nitride, it has a longer life and has excellent wear resistance and seizure resistance. The object is to provide a member.

In order to solve the above-mentioned problems, a rolling member according to claim 1 of the present invention is provided with Si / Mn by carbonitriding or nitriding on at least one surface layer of an inner member, an outer member, and a rolling element. A nitrogen concentration of the surface layer is 0.2% by mass or more and 2% by mass or less, and the nitride area ratio is 1% or more and less than 10%, and 0.05 μm or more and 1 μm or less. The number of Si · Mn nitrides in the area of 375 μm ² is 100 or more.
C: 0.3% by mass or more and 1.2% by mass or less, Si: 0.3% by mass or more and 2.2% by mass or less, Mn: 0.3% by mass or more and 2.0% by mass or less, Cr: 0 It is characterized by carbonitriding and quenching and tempering steel having 5 mass% or more and 2.0 mass% or less and Si / Mn of 5 or less and the balance being Fe and inevitable impurities.

  As a result of intensive studies on the factors governing the life under the contamination with foreign matter, the present inventors have found that the life of the rolling bearing is affected by the mechanism described below. Under foreign matter-mixed lubrication, indentations are formed on the races due to the biting of foreign matter. When the rolling element repeatedly passes over the indentation, the shape collapses when the rolling element is weak. The rolling element whose shape has collapsed causes even greater damage to the raceway and leads to peeling. Therefore, in order to extend the life under the contamination with foreign matter, simply increasing the retained austenite of the bearing ring and reducing the stress at the indentation edge as in the past, the effect of extending the life is small, and formation of indentations on the surface of the rolling element It is necessary to strengthen the rolling element so that it can be suppressed.

In the present invention, a steel containing a large amount of Si and Mn added to a rolling element is used, and a carbonitriding process is performed to increase the concentration of nitrogen, so that a nitride containing hard Si and Mn, that is, a Si · Mn nitride is obtained. It is intended to reinforce the rolling element by depositing on the surface, and to remarkably suppress the shape change of the rolling element due to the indentation generated on the race.
The strength of the rolling element is attributed to the Si · Mn nitride. In order to suppress the formation of indentations, it is important to increase the resistance of deformation, and when the size of the precipitate increases, the strengthening effect decreases. That is, in order to strengthen the surface, it is necessary to finely disperse the Si · Mn nitride. In the present invention, the area ratio of the nitride is set to 1 to 10% to sufficiently precipitate, and the number of fine precipitates of 1 μm or less or 500 nm or less is increased or the ratio is set to 20% or more of the entire nitride. It is characterized by strengthening the surface.

The critical significance of numerical values for rolling elements is as follows.
[Nitrogen concentration is 0.2 mass% or more, Si / Mn nitride area ratio is 1 to 10%]
The precipitate containing Si and Mn is a thermally stable nitride, the composition ratio of Si and Mn in the nitride is about 5: 1, and the base structure has a size of 0.01 μm to 1 μm. It is characterized by uniform fine dispersion and improved hardness. With this effect, the life extension, wear resistance, and seizure resistance can be improved. Since the lifetime is remarkably improved when the area ratio of the Si · Mn nitride is 1% or more, the lower limit is set to 1% or more, and the nitrogen concentration is set to 0.2% by mass. When the area ratio of the Si · Mn nitride exceeds 10%, the effect is saturated, so the upper limit is preferably 10% and the nitrogen concentration is preferably 2% by mass.

[The number of Si · Mn nitrides with an area of 375 μm ² of 0.05 μm to 1 μm is 100 or more]
Nitride exceeding 1 μm does not contribute much to the strengthening of the material. The one where fine nitride is dispersed is strengthened. The reason for this is that the smaller the distance between precipitate particles in the theory of precipitation strengthening, the better the strengthening ability, so even if the area ratio of nitride is the same, if the number of precipitated particles is large, the distance between particles is relatively Is shortened and strengthened. That is, it is preferable to increase the number of fine nitrides of 0.05 μm or more and 1 μm or less in the range of 1 to 10% of the area ratio of Si / Mn nitride using steel with a large amount of Si and Mn. . Further, among Si · Mn nitrides having an average particle diameter of 0.05 µm or more, the ratio of the number of Si · Mn nitrides of 0.05 to 0.50 µm is further increased by 20% or more. It becomes possible.

The carbonitriding temperature is preferably 800 ° C. or more and 870 ° C. or less as a method of increasing the number of Si · Mn-based nitrides having a surface area of 375 μm ² to 0.05 or more and 1 μm or less. When this temperature is exceeded, the nitride becomes coarse and the number of fine Si · Mn nitrides decreases. Further, when the temperature is higher than the treatment temperature, the solid solubility limit of nitrogen is increased, so that the amount of nitride is reduced and a desired area ratio cannot be obtained. From the initial stage of the carbonitriding step, a mixed gas atmosphere of Rx gas, enriched gas and ammonium gas is set, the CP value is 1.2 or more, and the flow rate of ammonia gas is at least 1/5 or more of the Rx gas flow rate. Moreover, quenching after carbonitriding is performed in the oil temperature range of 60 to 120 ° C. If it is higher than this temperature, sufficient hardness may not be obtained. Tempering is performed at a temperature of 160 to 270 ° C., and the hardness range is Hv 740 or higher, preferably Hv 780 or higher. Moreover, you may perform a subzero process after a quenching process as needed.

[Si content: 0.3 to 2.2 mass%, Mn content: 0.3 to 2.0 mass%, and Si / Mn ratio: 5 or less]
In order to sufficiently precipitate Si / Mn nitride, it is necessary to use a steel containing a large amount of Si and Mn (SUJ2 (Si content 0.25 mass%, Mn content 0.4 mass%). Even if nitrogen is added excessively by carbonitriding, the amount of Si / Mn nitride is small). For this reason, content of Si and Mn makes the following values critical values.

[Si content: 0.3 to 2.2% by mass]
It is an element necessary for the precipitation of the nitride according to the present invention, and due to the presence of Mn, it effectively reacts with nitrogen and precipitates significantly when added in an amount of 0.3% by mass or more.
[Mn content: 0.3 to 2.0 mass%]
It is an element necessary for precipitation of nitride according to the present invention, and has the effect of promoting the precipitation of Si / Mn nitride by addition of 0.3% by mass or more by coexistence with Si. Further, since Mn has a function of stabilizing austenite, it is set to 2.0% by mass or less in order to prevent a problem that residual austenite increases more than necessary after the heat treatment for curing.

[Si / Mn ratio: 5 or less]
Unlike the nitride obtained by tempering, the precipitate according to the present invention is formed by reacting with Si while incorporating Mn in the austenite region where nitrogen that has entered during the carbonitriding process. Therefore, if the amount of Mn added is less than the amount of Si added, precipitation of Si / Mn nitride is not promoted even if nitrogen is sufficiently diffused. When the amount of Si and Mn added is within the range of 0.2% or more and the nitrogen content is 0.2% or more, by setting the Si / Mn ratio to 5 or less, it is effective in extending the life and improving the wear resistance and seizure resistance. It is possible to ensure the amount of precipitation of Si · Mn nitride having an area ratio of 1.0% or more.

[C: 0.3% by mass or more and 1.2% by mass or less]
C becomes a martensite structure by quenching, and has the effect of hardening the base structure. In order to obtain the core hardness necessary for the rolling member, the lower limit value of C is preferably 0.3% by mass or more. In order to shorten the carbonitriding time, 0.5% by mass or more is preferable, 0.8% by mass or more is more preferable, and 0.95% by mass or more is more preferable. On the other hand, when it is added excessively, precipitation of cementite becomes excessive, coarsening occurs by carbonitriding, and toughness is reduced. For this reason, it is preferable to make an upper limit into 1.2 mass%.

[Cr: 0.5% by mass or more and 2.0% by mass or less]
Cr is a carbide forming element as well as improving hardenability, and promotes precipitation and further refines the carbide that strengthens the material. If it is less than 0.5% by mass, the hardenability is lowered and sufficient hardness cannot be obtained, or the carbides are coarsened during carbonitriding. If it exceeds 2.0% by mass, a Cr oxide film is formed on the surface during carbonitriding to inhibit the diffusion of carbon and nitrogen. Therefore, the Cr content is preferably 0.5% by mass or more and 2.0% by mass or less.
Moreover, you may add at least 1 or more types of Mo, Ni, and V as needed.

[Mo: 0.2% by mass or more and 1.2% by mass or less]
Mo is a carbonitride-forming element as well as improving hardenability, and has the effect of promoting precipitation and further refinement of carbides, carbonitrides, and nitrides that strengthen the material. The effect becomes remarkable when 0.2% by mass or more is added. If it exceeds 1.2% by mass, the effect is saturated and the cost increases. Accordingly, the Mo content is preferably 0.2% by mass or more and 1.2% by mass or less.

[Ni: 0.5% by mass or more and 3.0% by mass or less]
Ni has an effect of improving hardenability and at the same time improving toughness, and the effect becomes remarkable when 0.5% by mass or more is added. It is an austenite stabilizing element. When 3.0% by mass or more is added, the retained austenite becomes excessive and the core hardness decreases. Therefore, the Ni content is preferably 0.5% by mass or more and 3.0% by mass or less.

[V: 0.5% by mass or more and 1.5% by mass or less]
V has the effect of improving wear resistance by forming hard carbides and carbonitrides by carbonitriding. The effect becomes remarkable when 0.5% by mass or more is added. When it is added excessively exceeding 1.5% by mass, it is combined with the solid solution carbon of the material to form a carbide and the hardness is lowered. Accordingly, the V content is preferably 0.5% by mass or more and 1.5% by mass or less.

Thus, according to the rolling member of the present invention, at least one surface layer of the inner member, the outer member, and the rolling element has a Si / Mn nitride by carbonitriding or nitriding, The nitrogen concentration of the surface layer is 0.2% by mass or more and 2% by mass or less, and the area ratio of the Si / Mn nitride is 1% or more and less than 10%, and the Si / Mn is 0.05 μm or more and 1 μm or less. By setting the number of the system nitrides in the area of 375 μm ² to 100 or more, the lifetime is longer, and the wear resistance and seizure resistance are excellent.

  C: 0.3% by mass or more and 1.2% by mass or less, Si: 0.3% by mass or more and 2.2% by mass or less, Mn: 0.3% by mass or more and 2.0% by mass or less, Cr: 0 .5% by mass or more and 2.0% by mass or less, and Si / Mn is 5 or less, and the remainder is Fe carbon and unavoidable impurities. Abrasion resistance and seizure resistance can be obtained.

It is sectional drawing which shows one Embodiment of the deep groove ball bearing using the rolling member of this invention. It is an observation photograph of Si.Mn nitride. It is explanatory drawing which shows the relationship between nitrogen concentration and the area ratio of Si * Mn type nitride. It is explanatory drawing which shows the relationship between the area ratio of Si * Mn type nitride, and L10 lifetime. It is explanatory drawing which shows the relationship between the number of 0.05 to 1 micrometer Si * Mn type nitride, and a life ratio. It is explanatory drawing which shows the relationship between Si / MN ratio and the area ratio of Si * Mn type nitride.

Next, an embodiment of the rolling member of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view of the rolling bearing of this embodiment. This rolling bearing is a deep groove ball bearing including an inner ring 1 that is an inner member, an outer ring 2 that is an outer member, rolling elements 3, and a cage 4.
First, in order to clarify the relationship between the amount of nitrogen, the amount of Si · Mn precipitates, and the performance, the materials shown in Table 1 below were turned into a 65 mm diameter and 6 mm thick disk, at 820 to 900 ° C. for 2 to 10 hours, After carbonitriding in a mixed gas of Rx gas, propane gas, and ammonia gas, oil quenching was performed, followed by tempering treatment at 160 to 270 ° C. for 2 hours. Test pieces having various nitrogen concentrations were prepared by changing the treatment temperature, treatment time, and ammonia gas flow rate. After the heat treatment, the surface was polished and lapped to give a mirror finish. In Table 1 below, steel type 1 corresponds to JIS SUJ3 and steel type 2 corresponds to JIS SUJ2.

[Measurement of surface area nitride ratio and nitrogen concentration]
Using a field emission scanning microscope (FE-SEM), the surface of the rolling element was observed at an acceleration voltage of 10 kV. As for the nitride area ratio, photographs were taken at least 3 fields of view at a magnification of 5000 times, and the area ratio was calculated using an image analyzer after binarizing the photographs. Since the target nitride is fine, if the measurement magnification is 5000 times and the measurement area is 375 μm ² , the number of nitrides of 0.05 μm or more and 1 μm or less can be measured. The nitrogen concentration was measured using an electron beam microanalyzer (EPMA) at an acceleration voltage of 15 kV.

[Life test]
Subsequently, various types of test specimens were tested under a foreign matter-mixed lubrication using a thrust type life tester. The test conditions are as follows.
Test load: 5880N (600kgf)
Rotational speed: 1000min ^-1
Lubricating oil: VG68
Hardness of foreign matter: Hv870
Foreign material size: 74 to 147 μm
Foreign matter contamination: 200ppm

  The nitrogen concentration, area ratio, and life ratio of each test piece are shown in Table 2 below. The life ratio is shown as a ratio when the L10 life of Comparative Example 1 is 1. Moreover, the observation photograph of the nitride on the rolling element surface is shown in FIG. The lower part of FIG. 2 shows the elemental analysis results of the nitride analyzed by the energy dispersive X-ray dispersive analyzer. From the analysis results, peaks of Si, Mn, and N appear, and it can be seen that the nitride on the surface is Si · Mn nitride.

  FIG. 3 shows the relationship between the nitrogen concentration and the area ratio of the Si / Mn nitride. It can be seen that the area ratio of Si.Mn nitride, that is, the amount of precipitation, increases in proportion to the nitrogen concentration. Therefore, when the amount of Si and Mn added is large, the amount of Si / Mn nitride deposited is larger when compared with the same amount of nitriding. FIG. 4 shows the relationship between the area ratio of the Si / Mn nitride and the L10 life. It can be seen that the life is remarkably improved when the area ratio of the Si · Mn nitride is 1% or more. It can also be seen that the effect is saturated when the area ratio of the Si · Mn nitride exceeds 10%.

Table 3 below shows the area ratio of the Si · Mn nitride, the number of Si · Mn nitrides of 0.05 μm to 1 μm, the life test results, and FIG. 5 shows the Si · Mn nitride of 0.05 μm to 1 μm. The relationship between the number of Mn-type nitrides and a lifetime ratio is shown. As is apparent from these, by dispersing 100 or more Si · Mn nitrides within a measurement area of 375 μm ² , the base structure is strengthened and the life under the contamination with foreign matters is extended.

  Next, as described above, various carbon steels were carbonitrided in a mixed gas of Rx gas, propane gas, and ammonia gas at 820 to 870 ° C. for 2 to 10 hours, and then subjected to oil quenching, Tempering treatment was performed at 160 to 270 ° C. for 2 hours. At that time, steel types 11 to 27 were produced by changing the heat treatment time, heat treatment temperature, and ammonia gas flow rate, and the rolling elements of JIS 6206 deep groove ball bearings were produced from the steel, and the bearing rings were also produced using SUJ2. The following life test was conducted.

[Life test]
Test load: 6223N (635kgf)
Rotational speed: 3000 min ^-1
Lubricating oil: VG68
Hardness of foreign matter: Hv590
Foreign material size: 74 to 147 μm
Foreign matter contamination: 200ppm
As a result of the life test, the chemical composition (mass%), the Si / Mn ratio, the nitrogen concentration (mass%), the Si / Mn nitride area ratio, and the number of Si · Mn nitrides of 0.05 μm to 1 μm are shown in Table 4. Shown in The life is expressed as a ratio when the L10 life of Comparative Example 21 (equivalent to SUJ2) is 1.

As is apparent from Table 4, the steel in the range of the present invention was used, and the nitrogen concentration was 0.2% by mass or more and 2.0% by mass or less, the Si / Mn nitride area ratio was 1% or more and 10% or less, 0.05 to The example in which the number of 1 μm Si · Mn-based nitrides is 100 or more has a greater life extension effect than the comparative example.
The relationship between the Si / Mn ratio in Table 4 and the Si / Mn nitride area ratio is shown in FIG. For example, Comparative Examples 13 and 14 use steel within the scope of the present invention and further have a nitrogen concentration of 0.2% by mass or more. However, the Mn content is smaller than the Si content, and Si · Mn-based nitriding is performed. The amount of precipitation of the product is 1% or less in terms of area ratio. As is apparent from FIG. 6, the Si / Mn nitride precipitation can be promoted by setting the Si / Mn ratio to 5 or less.

In addition, in the said embodiment, although the example which applied the rolling member of this invention to the rolling element was shown, the same effect is acquired even if it applies to any of an inner and outer ring | wheel, or an inner and outer ring, and all rolling elements. .
In addition to the deep groove ball bearings described above, angular ball bearings, cylindrical roller bearings, tapered roller bearings, self-aligning roller bearings, needle roller bearings, and other types of bearings can be used suitably.
Moreover, it can be used suitably also for the rolling element of a ball screw or a linear guide.

1 is the inner ring (inner member)
2 is the outer ring (outer member)
3 is a rolling element 4 is a cage

Claims (1)

At least one surface layer of the inner member, the outer member, and the rolling element has a carbonitriding or nitriding Si / Mn nitride, and the nitrogen concentration of the surface layer is 0.2% by mass or more and 2% by mass. %, The nitride area ratio is 1% or more and less than 10%, and the number of Si · Mn nitrides having an area of 375 μm ^{2 of} 0.05 μm or more and 1 μm or less is 100 or more, and C : 0.3 mass% to 1.2 mass%, Si: 0.3 mass% to 2.2 mass%, Mn: 0.3 mass% to 2.0 mass%, Cr: 0.5 mass A rolling member characterized by carbonitriding and quenching and tempering a steel composed of at least% and not more than 2.0% by mass and having Si / Mn of 5 or less with the balance being Fe and inevitable impurities.

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