JPH06293939A - Bearing parts excellent in high temperature rolling fatigue characteristic - Google Patents

Abstract

PURPOSE:To provide bearing parts superior in high temp. rolling fatigue characteristic to the ones prepared by using conventional high carbon chromium bearing steel and case hardening steel as a stock. CONSTITUTION:A steel, having a composition which consists of 0.7-1.3% C, <0.5% Si, 0.3-2% Mn, <=0.02% S, 0.51-6% Cr, 0.015-0.06% Al, 0.003-0.02% N, and the balance Fe with inevitable impurities and contains, if necessary, prescribed amounts of Mo, W, V, Nb, Ni, Cu, Co, etc., and in which the contents of P, Ti, and O among the inevitable impurities are controlled to <=0.02%, <=0.003%, and <=0.003%, respectively, is used as a stock. The parts can be obtained by subjecting parts, prepared by using the stock, to quench-and-temper treatment. Further, the average grain size of carbide in the steel is regulated to <=2mum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bearing component having a rolling fatigue resistance superior to that of a high carbon chrome bearing component or a case hardening bearing component, and in particular, it has an excellent bearing life even in a use environment at high temperature. The present invention relates to a bearing component that exhibits rolling fatigue.

[0002]

2. Description of the Related Art Conventionally, high carbon chromium bearing steel has been widely used as a raw material for bearing parts used in automobiles and industrial machines. For example, SUJ1 (JISG 4805).
The SUJ2 with an increased amount of Cr has been widely used for medium and small-sized bearing parts, and the SUJ3 with an increased amount of Mn and Si has been used for large-sized bearing parts. In addition, SCr420 (JISG 41
Case-hardened bearing steel represented by 04) has also been used as a material for bearing parts.

However, in recent years, the temperature around the bearing has tended to rise with the increase in the output of the engine, the increase in the rotation speed, the miniaturization of mechanical parts, etc. Under these circumstances, the SUJ2 A bearing component made of, for example, SCr420 or the like has a problem that a sufficient rolling contact fatigue life cannot be obtained in a high temperature use environment.

On the other hand, AISI M50 or the like has been used as a material for bearing parts used under severe conditions. A bearing component made of AISI M50 has excellent rolling contact fatigue resistance even when used in a high temperature environment. However, AISI M50 contains a large amount of alloying elements, resulting in high material cost and workability. However, there is a problem that the processing cost becomes high.

For these reasons, there is a demand for the realization of a bearing component which is excellent in rolling contact fatigue at high temperatures (300 ° C. or lower) and which is lower in material cost and processing cost than the conventional AISI M50.

[0006]

SUMMARY OF THE INVENTION The present invention has been made under these circumstances, and its purpose is to provide a high temperature which is superior to that of a conventional high carbon chromium bearing steel or case hardening steel. An object of the present invention is to provide a bearing component which has rolling fatigue properties and which has a lower material ratio and a lower processing cost than AISI M50.

[0007]

According to the present invention which has achieved the above object, C: 0.7 to 1.3%, Si: less than 0.5%, Mn: 0.3 to 2%, S : 0.02% or less, Cr:
0.51-6%, Al: 0.015-0.06%, N:
0.003 to 0.02%, respectively, with the balance Fe and unavoidable impurities, and P: 0.02 in the unavoidable impurities.
%, Ti: 0.003% or less, O: 0.003% or less are used as raw materials, and the parts made of the materials are subjected to quenching and tempering treatment, and carbides. It has a gist that the average particle diameter of is less than 2 μm.

The bearing component according to the present invention contains the above-mentioned elements as basic components.
It may contain W, V, Nb, Ni, Cu, Co or the like. Further, in the bearing component according to the present invention, a treatment for infiltrating nitrogen into the surface layer portion at the time of quenching heating is performed, and a carbon nitride having an average particle size of 2 μm or less has high temperature rolling fatigue resistance. It can be further improved.

[0009]

The present invention is constructed as described above, but in short,
In order to suppress the decrease in hardness, which is a problem in use at high temperatures, the amount of various alloy elements is adjusted to improve the temper softening resistance, and the carbide forming element Cr (if necessary, Mo, W, V and Nb) are added to cause carbides to positively break out, and the average grain size of carbides is adjusted to 2 μm or less by quenching and tempering treatment. Bearing parts have excellent rolling characteristics even under high temperature use conditions. The inventors have found that they exhibit fatigue properties and completed the present invention. Further, in the above-mentioned bearing component, the one in which nitrogen is infiltrated into the surface layer portion during quenching and heating so that the average grain size of carbonitride is adjusted to 2 μm or less, further improves the high temperature rolling fatigue resistance of the bearing component. It also turned out to be possible. First, the reasons for limiting the chemical components in the bearing component according to the present invention are as follows.

C: 0.7-1.3% C is a solid solution in the matrix to strengthen martensite,
It is also an element necessary to increase the amount of carbide and improve the hardness after tempering. In order to exert such an effect, the content of C needs to be 0.7% or more. However, if the C content exceeds 1.3%, the carbides are coarsened, the rolling fatigue is deteriorated, and the toughness, machinability, cold workability, warm workability, etc. are deteriorated.

Si: Less than 0.5% Si is the end of the first stage of tempering (the step in which C dissolved in martensite as carbides is extruded) and the second step (the stage in which residual austenite decomposes). Is an element that delays the onset of heat treatment and improves temper softening resistance resistance.
Even if contained in an amount of 5% or more, the effect is saturated and the machinability, cold workability and warm workability are significantly reduced. Therefore, S
The content of i needs to be less than 0.5%.

Mn: 0.3-2% Mn is a deoxidizing / desulfurizing element and also an element for improving hardenability. If the Mn content is less than 0.3%, such an effect cannot be expected, and if the Mn content exceeds 2%, the effect is saturated, and rather the cutting raw and cold-warm workability deteriorates.

S: 0.02% or less S is mostly contained in the steel in the form of MnS,
It is an element that improves machinability. However, when the O content is low, the rolling fatigue property is rather deteriorated and the cold workability and the warm workability are adversely affected. Therefore,
Considering these points, the S content is 0.02% or less.

Cr: 0.51-6% Cr combines with C to form fine carbides, which improves hardness at high temperatures and improves high temperature rolling fatigue. If the Cr content is less than 0.51%, the carbides are coarsened and the rolling fatigue resistance deteriorates. If the Cr content exceeds 6%, the machinability, cold workability and warm workability are deteriorated. Therefore, the Cr content is 0.51 to 6%.

Al: 0.015 to 0.06% Al is an element effective in deoxidizing and refining crystal grains.
If the content is less than 0.015%, there is no such effect,
If it exceeds 0.06%, the effect of refining the crystal grains is saturated, and if the content is further increased, the crystal grains tend to grow. Therefore, the content of Al is 0.015
It is set to 0.06%.

N: 0.003 to 0.02% N is an effective element for combining with Al, V, Nb and the like to form a nitride and refining the crystal grains to strengthen the steel. . When the N content is less than 0.003%, such an effect is small, and when the N content exceeds 0.02%, cold workability and warm workability are deteriorated. Therefore, the N content is
It is set to 0.003 to 0.02%.

The bearing component of the present invention comprises the above elements as basic components and the balance iron and unavoidable impurities. P, Ti, O, etc. in the unavoidable impurities must be suppressed as described below.

P: 0.02% or less Since P is an element that reduces toughness, it is necessary to reduce the P content as much as possible, and the P content is 0.02% or less.

Ti: 0.003% or less Ti is an element that combines with N to form coarse TiN and deteriorates rolling fatigue resistance, cold workability and warm workability, and it is necessary to reduce it as much as possible. is there. From this viewpoint, Ti
The content is 0.003% or less.

O: 0.003% or less O is an element that combines with Al and Si and forms oxide inclusions in the steel. When the content in the steel increases, the rolling fatigue resistance decreases and It also has an adverse effect on machinability and cold workability, so it is necessary to reduce it as much as possible. Therefore, O content

Is 0.003% or less.

If necessary, the bearing component of the present invention may have M
You may contain o, W, V, Nb, Ni, Cu, Co etc. The contents when these elements are added are as follows.

Mo: 1% or 2 selected from the group consisting of 2% or less and W: 1% or less Mo and W are effective in increasing the hardness by dispersion strengthening by forming carbides like Cr. It is an element. However, when the Mo content exceeds 2% and the W content exceeds 1%, the effect is saturated and the machinability,
Cold workability and warm workability are reduced.

V: 0.03 to 2% and Nb: 0.01
~ 1% or 2 kinds selected from the group consisting of 0.5% V and Nb both combine with C and N in the steel to form carbonitrides, refine the crystal grains, and temper softening resistance. It is an effective element to improve. V content is 0.03
%, And the Nb content is less than 0.01%, such an effect is not exhibited. Conversely, even if the V content is more than 2% and the Nb content is more than 0.5%, The effect is saturated.

Ni: 3% or less Ni is an element that improves the hardenability, and is an element that facilitates the quenching / tempering treatment in a component having a large mass. It is also an element that improves toughness. However, if it is contained in excess of 3%, the machinability, cold workability and warm workability are deteriorated, and a large amount of retained austenite is generated after quenching and tempering, which deteriorates the dimensional stability.

Cu: 1% or less Cu is an element that increases hardenability and corrosion resistance, and is an element that improves wear resistance. However, if it exceeds 1%, red hot brittleness is promoted to promote hot working. Cracks occur. Therefore,
The Cu content needs to be 1% or less.

Co: 0.03 to 3% Co is an element that improves the corrosion resistance and also increases the temperature of the eutectoid point to refine the carbides and carbonitrides. In order to exert such an effect, it is necessary to contain 0.03% or more, but if it exceeds 3%, the effect is saturated. Therefore, the Co content needs to be 0.03 to 3%.

In the bearing component of the present invention, the high temperature rolling contact fatigue resistance can be further improved if the bearing part is subjected to the treatment of infiltrating nitrogen into the surface layer portion at the time of quenching and heating. Hereinafter, the present invention will be described in more detail with reference to Examples, but the following Examples are not intended to limit the scope of the present invention, and it is technically within the scope of the present invention to change the design in view of the gist of the preceding and the following. Are included in.

[0029]

EXAMPLES Steels No. 1 to 9 of the present invention and comparative steels No. 10 to 18 having the chemical composition shown in Table 1 were melted in a small vacuum furnace. The comparative steel No. 17 is JIS SUJ2, and the comparative steel No. 18 is JIS SCr420.

[0030]

[Table 1]

The above steel was hot forged to a diameter of 60 m.
m and 20 mm round bar, after forging, comparative steel No. 1
For No. 17, soaking treatment was performed after forging, diffusion disappearance treatment of giant carbide was performed, and then spheroidizing annealing was performed. Steel No. 18 was annealed after hot forging.

Then, for a round bar having a diameter of 60 mm,
After processing into a test piece having a diameter of 60 mm and a thickness of 5 mm, the following heat treatment is performed, the surface is lapped, and the surface pressure is 53
A rolling fatigue test was carried out at a temperature of 130 ° C. under the condition of 0 kgf / mm ² .

On the other hand, for a round bar having a diameter of 20 mm, a test piece having a diameter of 20 mm and a thickness of 5 mm was processed and subjected to the heat treatment described below, followed by measurement of high temperature hardness (300 ° C.) and average grain size of carbide in the surface layer portion. The diameter was measured. The average particle size of the carbide was measured by taking an SEM photograph and then determining the average particle size by image analysis.

<Heat treatment conditions for each steel> (1) Steel No. 1 to 17 Quenching: 840 ° C x 40 min / oil cooling Tempering: 220 ° C x 2 hr / air cooling (2) Steel No. 18 Quenching: 925 ° C x 10 hr ( Carburizing treatment / oil cooling (carbon potential: 0.8% by weight) Tempering: 250 ° C x 2 hr / air cooling Table 2 shows the high temperature hardness and high temperature rolling fatigue test results of these test pieces.
Shown in. The rolling fatigue test results were evaluated by the L ₁₀ (10% cumulative damage rate) life.

[0035]

[Table 2]

From these results, it can be considered as follows. Each of the examples of the present invention (Steel Nos. 1 to 9) has a rolling fatigue life superior to those of the conventional steels of Steel Nos. 17 and 18. On the other hand, comparative steel No.
The steel using No. 10 had a lower high-temperature hardness due to the formation of coarse carbides and the rolling fatigue life was shorter than that using the steel No. 1. Comparative steel No. 1 with low C content
Compared with the one using steel No. 1, the high temperature hardness was lower, and the rolling fatigue life was shorter than that using the conventional steel of steel No. 16 and 17. There is. Compared with the one using steel No. 2, the one using steel No. 12 with a high Cr content has no difference in high temperature hardness and rolling fatigue life, and the effect is saturated. Steel with high Mo content No.13
Compared with the one using steel No. 3, there was no difference in high temperature hardness and rolling fatigue life, and the effect was saturated. Steel No. 14 having a high V content was used.
There is no difference between the high temperature hardness and the rolling fatigue life, and the effect is saturated, as compared with the one using No. Further, the steels using the steel Nos. 15 and 16 having a large content of Ti or O have shorter rolling fatigue life than the steels using steels Nos. 17 and 18 of the conventional steels.

Next, using steel No. 1, by changing the spheroidizing treatment condition and the quenching condition, the average grain size of the carbide was changed, and the average grain size of the carbide and the high temperature hardness (30
The relationship of 0 ° C.) was investigated. The result is shown in FIG. From this, it is understood that controlling the average grain size of the carbides to 2 μm or less is effective in increasing the high temperature hardness and improving the rolling contact fatigue life.

Further, the invention steel Nos. 1 and 2 and the comparative steel N
For o.15, the following heat treatment was performed, and then high temperature hardness measurement and rolling fatigue test were performed. The results are shown in Table 3. As is apparent from Table 3, it is understood that more excellent rolling contact fatigue resistance can be obtained by injecting nitrogen into the surface layer portion. <Heat treatment conditions> Carbonitriding / quenching: 870 ° C x 5 hr / oil cooling (carbon potential: 1.0%, ammonia flow rate: 2 liter / min) Tempering: 220 ° C x 2 hr / air cooling

[0039]

[Table 3]

[0040]

As described above, according to the present invention, it is possible to realize a bearing component having excellent rolling fatigue resistance even at high temperature without using a conventional high alloy bearing steel such as M50. In addition, since the bearing component of the present invention has a high hardness due to the refinement of carbides or carbonitrides, even if it is used under a lubricating condition such that foreign matter such as gear powder of an automobile is mixed, indentation due to foreign matter entrapment may occur. It also has the advantage of being difficult to stick to.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the average grain size of carbides and high-temperature hardness.

Claims (7)

[Claims] 1. C: 0.7 to 1.3% (meaning% by weight,
The same shall apply hereinafter), Si: less than 0.5%, Mn: 0.3 to 2
%, S: 0.02% or less, Cr: 0.51 to 6%, A
1: 0.015-0.06%, N: 0.003-0.0
2% of each, and the balance Fe and unavoidable impurities, P: 0.02% or less in the unavoidable impurities, Ti: 0.
003% or less and O: 0.003% or less are used as raw materials, and the parts made of the materials are subjected to quenching and tempering treatments, and the average grain size of the carbides is 2 μm or less. A bearing component with excellent high temperature rolling fatigue. 2. The bearing component according to claim 1, further comprising a steel containing one or two selected from Mo: 2% or less and W: 1% or less. 3. The bearing component according to claim 1, further comprising V: 0.03 to 2% and Nb: 0.01 to.
Bearing parts made of steel containing one or two kinds selected from 0.5%. 4. The bearing component according to claim 1, which is made of steel containing Ni: 3% or less. 5. The bearing component according to claim 1, which further comprises Cu: 1% or less of steel. 6. The bearing component according to claim 1, which is made of steel containing Co: 0.03 to 3%. 7. A carbonitride having an average particle size of 2 μm, which has been subjected to a treatment in which nitrogen is infiltrated into the surface layer during quenching and heating.
The bearing component according to any one of claims 1 to 6, which has a m or less.