KR20010034008A - High-temperature rolling bearing part - Google Patents

Abstract

The alloying element content of the high-temperature rolling bearing parts is mass%, at least 0.6% and not more than 1.3% of C, at least 0.3% and not more than 3.0% of Si, at least 0.2% and not more than 1.5% of Mn, and not less than 0.03% of P, It contains 0.03% or less of S, at least 0.3% or more and 5.0% or less of Cr, at least 0.1% or more and 3.0% or less of Ni, 0.050% or less of Al, 0.003% or less of Ti, 0.0015% or less of 0, and 0.015% or less of N. And the remainder is made of steel composed of Fe and unavoidable impurities, and also has a tempering treatment after quenching or carburizing and nitriding, and also has a hardening hardness of HRC58 or higher and a maximum carbide dimension. It is 8 micrometers or less. As a result, an excellent rolling fatigue life is obtained even under a foreign matter mixing environment and under a high temperature environment, and an inexpensive high temperature rotary bearing component is obtained.

Description

High-temperature rolling bearing part

Rotating bearings used in power transmission units or engine units in automobiles, aircraft, ships, industrial machinery, etc., are used in harsh environments, but excellent electric fatigue life and reliability are required even in such environments. In particular, foreign materials such as dust, dust and iron may be mixed in the rotary bearings used above, and it is known that the rolling fatigue life is considerably reduced in comparison with the use in a clean environment under these environments. As a countermeasure, in recent years, a carbonaceous nitriding treatment is performed on high-carbon chromium bearing steel such as SUJ2 or hardened steel such as SCM420, SNCM420, SNCM815, and a method of producing an appropriate amount of retained austenite directly under a raceway is applied. In addition, life improvement under foreign material mixing is aimed at.

However, the general carburizing nitriding treatment is a long time treatment as compared with the quench and temper treatment applied to SUJ2 steel and the like. For this reason, in these carburizing-nitriding rotary bearings, there exists a problem that manufacturing cost increases significantly compared with the rotary bearing manufactured by normal quenching and tempering process.

In addition, since rotary bearings used in automobiles and aircrafts are used under high temperature environments, excellent rolling fatigue life characteristics are demanded in foreign matter mixing environments and under extremely harsh use environments such as high temperature environments. Generally, rotary bearings used under high temperature are subjected to a quenching treatment on high-carbon chromium bearings such as SUJ2, or after carburizing and quenching treatment on superficial hardened steels such as SCM420 and SNCM815. The tempering process is performed at.

However, when these materials are tempered at a high temperature, the hardness greatly decreases, so that the predetermined hardness required for the rotating bearing cannot be obtained, and the rolling fatigue life and wear resistance decrease. For this reason, although precipitation hardening type steels, such as M50, are used for the bearing steel used in a high temperature range, such a steel material could not respond to the above requirements because manufacturing cost and material cost are high, and the use range is limited.

In the rotary bearing subjected to carburization and nitriding treatment, after the heat treatment, residual austenite is formed directly under the rolling section, and nitrogen enters the steel. This residual austenite action reduces stress concentration due to foreign matter mixing, and furthermore, tempering softening resistance is improved by nitrogen invasion into steel, thereby suppressing tissue changes generated during rolling fatigue, thereby improving rolling fatigue life. It is becoming.

However, in application to high-temperature rotating bearings, it is necessary to perform high temperature tempering in order to secure the stability of the dimensions as described above. In the case where this high temperature tempering is performed, since the retained austenite decomposes and the amount thereof decreases, the effect cannot be expected, and there is a limit in preventing tempering softening by nitrogen. You can't get performance.

In recent years, high output and miniaturization of engines are rapidly progressing in the field of automobiles and the like, and at the same time, the use environment of rotary bearings has been increasing in more severe conditions. Although the use temperature range of the rotary bearing used for an engine part is about 130 degreeC from commercial temperature, it is anticipated that temperature will rise to 160 degreeC instantaneously. Today, with the increase in engine power, it is predicted that the service temperature range of the rotary bearing rises to about 160 ° C from the commercial temperature and more than 200 ° C at the moment. Therefore, in the future, when high engine power and light weight are promoted, it is expected that the improvement of the electric fatigue life under the foreign matter mixing environment and under the high temperature environment is required.

However, current high-carbon chromium bearing steels or rotary bearings subjected to carburizing or carburizing nitriding treatments do not have sufficient heat resistance and cannot maintain sufficient rolling fatigue life under the expected foreign object mixing environment and high temperature environment. In addition, precipitation hardening bearing steel such as M50 has a problem such as high cost, and it is a situation that it is not possible to provide a rotary bearing having low cost and excellent rolling fatigue life characteristics.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a rotating bearing component for high temperature, which has excellent electric rolling fatigue life even under a foreign substance mixing environment and under a high temperature environment, and which is cheaper than the conventional example.

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a rotating bearing component used in a power transmission device such as an automobile, an aircraft, a ship, or an industrial machine, an engine part, and the like, and more specifically, in an environment where foreign matters such as dust and dust mix, The present invention relates to an inexpensive high-temperature rotating bearing component having an excellent rolling fatigue life even in a normal temperature to 300 ° C environment.

As a result of careful examination, the inventors of the present application have found a combination of compositional elements and their respective contents that can provide an inexpensive high-temperature rotating bearing component having excellent rolling fatigue life in a foreign body mixing environment and under a high temperature environment.

Therefore, the high-temperature rotary bearing component of the present invention is a high-temperature rotary bearing component having an inner ring, an outer ring, and a rolling element, the content of alloying elements being in mass%, C (carbon) of 0.6% or more and 1.3% or less, and Si ( Silicon) 0.3% or more and 3.0% or less, Mn (manganese) 0.2% or more and 1.5% or less, P (phosphorus) 0.03% or less, S (sulfur) 0.03% or less, Cr (chromium) 0.3% or more 5.0% 0.1% to 3.0% of Ni (nickel), 0.050% or less of Al (aluminum), 0.003% or less of Ti (titanium), 0.0015% or less of O (oxygen), or 0.015% or less of N (nitrogen) The remainder is made of steel composed of Fe (iron) and unavoidable impurities, and also has a structure tempered after quenching or after carburizing and nitriding, and after the tempering, the hardness is HRC58 or higher and the maximum carbide dimension is 8 μm. It is as follows.

In the high-temperature rotary bearing component of the present invention, having the above-described composition, excellent quenching and tempering treatment results in an excellent rolling fatigue life under a foreign matter mixing environment without carrying out a carburizing nitriding treatment. For this reason, a carburizing nitriding process can be omitted and manufacturing cost can be made low.

It is preferable to omit a carburizing nitriding process from a viewpoint of manufacturing cost reduction as mentioned above. However, even if it carries out a carburizing nitriding process instead of a quenching process, the outstanding rolling fatigue life can be obtained in a foreign substance mixing environment.

Moreover, since it has the said composition, even if it tempers at high temperature (for example, 350 degreeC), hardness higher than HRC58 can be obtained. Thus, by performing a tempering process at high temperature, since the amount of residual austenite can be reduced, dimensional stability in high temperature environment can be obtained and hardness higher than HRC58 can be obtained. For this reason, the rolling fatigue life and wear resistance in a high temperature environment can be improved than the conventional example.

In addition, steel of the above composition is cheaper than precipitation hardening bearing steel such as M50.

As described above, it is possible to obtain an inexpensive rolling fatigue life in a foreign material mixing environment and a high temperature environment, and to provide an inexpensive high-temperature rotating bearing component.

Moreover, it is preferable that tempering process temperature is 180 degreeC or more and 350 degrees C or less. Since the rotary bearing is usually used at a temperature of about 100 ° C, the tempering treatment temperature needs to be 180 ° C or more.

EMBODIMENT OF THE INVENTION Hereinafter, the reason for limitation of the chemical component of the high temperature rotary bearing component of this invention is demonstrated.

(1) About C content (0.6% or more and 1.3% or less)

C is an essential element for securing strength as a rotary bearing, and in order to maintain hardness after a predetermined heat treatment, it is necessary to contain C at 0.6% or more, so the lower limit of the C content is limited to 0.6%. In the present invention, although carbides play an important role in the rolling fatigue life as described below, when the C content is more than 1.3%, it has been found that large carbides are produced, leading to a reduction in rolling fatigue life. The upper limit of the C content was limited to 1.3%.

(2) About Si content (0.3% or more and 3.0% or less)

Since Si has the effect of suppressing softening in the high temperature range and improving the heat resistance of the rotary bearing, it is preferable to add Si. However, since the effect is not acquired when Si content is less than 0.3%, the minimum of Si content was limited to 0.3%. Moreover, although heat resistance improved with the increase of Si content, even if it contained in large quantity over 3.0%, since the effect became saturated and hot workability and cutting property fall, the upper limit of Si content was limited to 3.0%.

(3) About Mn content (0.2% or more and 1.5% or less)

Mn is an element used for deoxidation when manufacturing steel and an element which improves hardenability. Since Mn needs to be added 0.2% or more in order to obtain this effect, the lower limit of Mn content is limited to 0.2%. . However, when it contains a large amount exceeding 1.5%, since machinability falls significantly, the upper limit of Mn content was limited to 1.5%.

(4) About P content (0.03% or less)

P segregates at the austenite grain boundary of steel and causes toughness and reduced rolling fatigue life, so 0.03% is the upper limit of the content.

(5) About S content (0.03% or less)

Since S inhibits the hot workability of steel, forms a nonmetallic inclusion in steel, and reduces toughness and rolling fatigue life, 0.03% was made into the upper limit of S content. In addition, while S has the harmful side as described above, and also has the effect of improving the machinability, it is preferable to make it as small as possible, but it is acceptable if the content is up to 0.005%.

(6) About Cr content (0.3% or more and 5.0% or less)

Cr is an element that plays an important role in the present invention, and is added for improving hardenability, securing hardness by carbides, and improving lifetime. In order to obtain a predetermined carbide, addition of 0.3% or more is required, so the lower limit of the Cr content is limited to 0.3%. However, when a large amount exceeding 5.0% is contained, large carbides are formed to cause rolling fatigue life reduction, so the upper limit of the Cr content is limited to 5.0%.

(7) About Al content (0.050% or less)

Although Al is used as a deoxidizer in steel production, it is preferable to reduce the amount of Al since it forms a hard oxide-based inclusion and lowers the rolling fatigue life. In addition, when the amount of Al contained in a large amount exceeding 0.050%, a significant reduction in the rolling fatigue life was recognized. Therefore, the upper limit of the Al content was limited to 0.050%.

Moreover, since steel manufacturing cost rises in order to make Al content less than 0.005%, it is preferable to limit the minimum of Al content to 0.005%.

(8) About Ti content (0.003% or less), O content (0.0015% or less), and N content (0.015% or less)

Ti, O, and N form oxides and nitrides in the steel, which are the starting points of fatigue failure as nonmetallic inclusions, and thus reduce the rolling fatigue life. did.

(9) Ni content (0.1% or more and 3.0% or less)

Ni is an element which plays an important role in the present invention. In particular, Ni is an effect of suppressing the change of the structure in the rolling fatigue process when used in a high temperature environment, and suppressing the decrease in hardness in the high temperature range to improve the rolling fatigue life. Has In addition, Ni improves toughness and improves life under foreign matter environments, and is effective in improving corrosion resistance. For this reason, since it is necessary to contain Ni 0.1% or more, the minimum of Ni content was limited to 0.1%. However, when Ni is contained in a large amount exceeding 3.0%, a large amount of retained austenite is produced during the quenching treatment so that a predetermined hardness is not obtained and the steel cost increases, so the upper limit of the Ni content is set to 3.0%. Limited.

Next, reference is made to the tempering hardness and carbide of the high temperature rotary bearing component of the present invention.

(10) temper hardness

Bearings used in the high temperature range are generally subjected to a tempering treatment at a temperature above the environmental temperature in order to stabilize the dimensions under the use environment. The inventors of the present invention conducted a detailed investigation of the tempering hardness and the rolling fatigue life at a temperature environment of 200 ° C. As a result, it was recognized that there was a relationship between the tempering hardness and the rolling fatigue life, and the higher the tempering hardness, the longer the rolling fatigue life was. It was confirmed that there is a tendency to indicate. In particular, when the tempering hardness is the same, it has been found that the service life is as long as a bearing subjected to a tempering treatment at a high temperature, and that the service life is as long as a bearing having a high tempering hardness even when tempering at a high temperature. Furthermore, when the hardness after the tempering treatment is less than HRC58, the life tends to decrease rapidly, and it is found that the life gap becomes large. In order to improve the service life at high temperature and reduce the gap, it is necessary to maintain the hardness of HCR58 or more, and the tempering temperature at this time is preferably higher.

(11) carbide

Carbide was found to maintain the hardness at the time of tempering treatment, to suppress the change of the structure during rolling fatigue, and to improve the rolling fatigue life. At this time, the maximum dimensions and rolling fatigue life of carbides at a depth of 0.1 mm from the bearing surface layer were examined. As a result, large carbides were found to have a tendency to decrease their lifespan. Since it became clear that the lifetime fall, the maximum dimension of carbide was prescribed | regulated as 8 micrometers.

In the high-temperature rotating bearing component, preferably, the steel further contains at least one kind of Mo by 0.05% or more and less than 0.25% and V by 0.05% or more and 1.0% or less by mass%.

Thereby, the rolling fatigue life in a foreign material mixing environment and a high temperature environment can be improved further, and the hardness after a tempering process can be improved.

Hereinafter, the reason for limitation of the said chemical component is demonstrated.

(12) About Mo content (0.05% or more and less than 0.25%)

Mo improves the hardenability of the steel and has an effect of preventing softening during the tempering treatment by solidifying it in carbide. In particular, Mo is added because the action of improving the rolling fatigue life in the high temperature range has been found. However, when Mo is contained in a large amount of 0.25% or more, the steel cost rises and the machinability is greatly deteriorated without decreasing the hardness at the time of softening treatment for facilitating cutting, so that the Mo content is less than 0.25%. Limited. Moreover, when Mo content is less than 0.05%, since it was ineffective in carbide formation, the minimum of Mo content was limited to 0.05%.

(13) About V content (0.05% or more and 1.0% or less)

V combines with carbon to precipitate fine carbides, promotes the refinement of crystal grains, and has the effect of improving strength and toughness, while improving the heat resistance of steel by containing V, suppressing softening after high temperature tempering, and rolling It has the effect of improving the fatigue life and reducing the life gap. Since the V content at which this effect is obtained is 0.05% or more, the lower limit of the V content is limited to 0.05%. However, when V is contained in a large amount exceeding 1.0%, the machinability and hot workability deteriorate, so the upper limit of the V content is limited to 1.0%.

EMBODIMENT OF THE INVENTION Hereinafter, the Example of this invention is described.

Steel having the chemical composition shown in Table 1 was melted by a vacuum induction furnace, cast into a 150 kg weight ingot, heated for 3 hours at 1200 ° C., and hot forged to obtain a round rod having a diameter of 50 mm. Prepared. The round bar material is stored at 850 ° C. for 1 hour as a normalizing treatment, and then air cooled, and further stored at 790 ° C. for 6 hours as a softening treatment to facilitate cutting. Cooling was performed at a cooling rate, and a softening treatment was performed to air-cool to room temperature in the air to obtain a material for various investigations.

<Hardness investigation>

In order to measure the tempering hardness after quenching and the tempering hardness after carburizing and nitriding, a cylindrical test piece having a diameter of 20 mm and a length of 100 mm was manufactured by machining.

The quenching treatment was performed by heating in a salt furnace, soaking at 850 ° C. for 30 minutes, and then quenching in 80 ° C. oil. Next, as a tempering process, it heated similarly in the salt bath, and tempered process air-cooled after storing at 350 degreeC for 2 hours.

In the carburizing nitriding treatment, a gas atmosphere used in a normal production process was used to store 1.0 to 1.2% of carbon potential and 5 to 10% of NH ₃ in an RX gas atmosphere at 850 ° C. for 60 minutes. After, quenched in oil. Then, tempering for 120 minutes was performed at 350 degreeC.

A 10 mm-thick disk-shaped test piece was cut from the center of the test piece subjected to the quenching tempering treatment or the test piece subjected to the tempering treatment after carburizing and nitriding treatment, and both surfaces were ground by wet polishing to prepare a test piece for hardness measurement.

The hardness measured the hardness of 2 mm depth position from the surface in the test piece cross section using the Rockwell hardness meter, and calculated | required the average value of 7 points as tempering hardness.

<Electric fatigue life test>

In order to confirm the performance as a bearing part, the fatigue test was done by the thrust rolling contact fatigue life tester, and the life evaluation of each material was performed.

The test piece used for the life evaluation roughly processed the ring-shaped thrust type electric fatigue life test piece of 47 mm of outer diameter, 29 mm of inner diameter, and 7 mm of thickness from the round bar material of diameter 50mm by machining.

Roughly, as a heat treatment of the completed test piece, quenching tempering treatment and carburizing nitriding treatment were performed. The treatment used an experimental furnace used in a typical production process.

For quenching and tempering treatment, use a gas atmosphere furnace for 30 minutes at 850 ° C. while controlling carbon potential to prevent decarburization or carburization based on the carbon content of each steel in the RX gas atmosphere. After preservation, it was quenched in oil. Then, tempering for 120 minutes was performed at 350 degreeC.

Carburizing and nitriding treatment were heat-treated on the same conditions as said hardness test piece.

After completion of the heat treatment, both surfaces of the test piece were polished to finish in a mirror surface state. In addition, in the test piece which carburized and nitrided, the process value at the time of grinding | polishing process was set to 0.1 mm on both surfaces.

The electric fatigue life test was performed by the thrust type electric fatigue life tester. In addition, Table 2 shows all the conditions of the test. The test was performed under normal temperature environment and 200 degreeC environment, and also the test was done also in the environment which reproduced the mixed environment of a foreign material.

Motor fatigue life test condition Testing machine Thrust Type Electric Fatigue Life Tester Contact surface pressure 5.0GPa Rotational speed 2000 rpm Test temperature Room temperature, 200 ℃ Lubrication Turbo oil Foreign matter 0.4g / 1000cc

The fatigue test was repeated 15 times under the same conditions, and the lifetime which becomes 10% of the cumulative damage probability in Weibull probability was determined as the lifetime of each material. In addition, the comparative example No. in Table 2 was used. 13 is a general-purpose SUJ2, and the life value of each material was described by the ratio in the case where the lifetime of this quenching tempering treatment material was 1.0.

<Carbide>

The thrust type electric fatigue life test piece was used for the measurement of the carbide which exists in steel. In the test piece processed by the various heat processing and the thrust type electric fatigue life test piece, the ring cross section was cut | disconnected and the micro test piece for structure observation was manufactured. In order to finish this test piece to a mirror surface and to observe a carbide further, it corroded by the picral corrosion liquid. In this microsample, carbide observation in 0.1 mm depth was performed with the optical microscope from the surface of the raceway surface, and the maximum carbide in the viewing area of 50 mm ² was measured.

The results of the 350 ° C. tempering hardness, the rolling fatigue life at room temperature and 200 ° C., the rolling fatigue life under foreign matter mixing conditions, and the maximum carbide dimensions are shown in Table 3 for the examples of the present invention and Table 4 for the comparative examples.

In the example of this invention which has the composition range of this invention from the result of said Table 3 and Table 4, it turned out that hardness becomes HRC58 or more even if it tempers 350 degreeC. Moreover, in the example of this invention, even when the simple quenching tempering process (HT) was performed, it turned out that the rolling fatigue life under normal temperature and 200 degreeC, and the rolling fatigue life under foreign material conditions compared with the comparative example. It has also been found that excellent rolling fatigue life can be obtained even when carburizing-nitriding treatment is performed instead of quenching treatment. Moreover, in the example of this invention, it turned out that the largest dimension of carbide in 0.1 mm depth from a raceway surface layer will be 8.0 micrometers or less.

The disclosed embodiments are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is shown by above-described not description but claim, and it is intended that the meaning of a claim and equality and all the changes within a range are included.

As described above, the inventors of the present invention find a suitable composition element and its content, and by quenching and tempering treatment, an excellent rolling fatigue life can be obtained under foreign matter mixing conditions without performing carburizing nitriding treatment and high temperature (for example, It was possible to obtain an inexpensive high-temperature rotating bearing component capable of obtaining high hardness even if the tempering treatment was performed at 350 ° C.).

The present invention can be advantageously applied to high temperature rotary bearing parts used under foreign material mixing environments and under high temperature environments.

Claims (2)

In a high temperature rotary bearing component having an inner ring, an outer ring and a rolling element, The content of the alloying elements is in mass%, 0.6% to 1.3% C, 0.5% to 3.0% Si, 0.2% to 1.5% Mn, 0.03% or less P, 0.03% or less S, 0.3% to Cr 5,0%, 0.1% to 3.0% of Ni, 0.050% or less of Al, 0.003% or less of Ti, 0.0015% or less of O, 0.015% or less of N, each containing at least elements, the remainder being made of Fe A high-temperature rotary bearing component comprising a steel material, and having a structure that has been tempered after quenching or after carburizing and nitriding, and wherein the hardness after the tempering is HRC58 or more and the maximum carbide dimension is 8 μm or less. The method of claim 1, The steel material is a mass%, the high-temperature rotary bearing component, characterized in that it further comprises at least one of 0.05% to less than 0.25% Mo and 0.05% to more than 1.0% of V.