JP2011117489A - High strength rolling bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the required mechanical strength from being deteriorated by the oxide film when an oxide film is formed on the surface of a steel-made rolling bearing by heat treatment for strengthening a steel material. <P>SOLUTION: In a high strength rolling bearing, a thermal oxide film 3 formed by heat treatment for strengthening steel material partially remains on the surface of both components of an outer ring 1 and inner ring of a deep groove ball bearing made of steel material even after surface grinding to achieve necessary dimensions. A chemical oxide film 4 made of a triiron tetroxide oxide by reaction with a strong base aqueous solution is provided on a steel material inside the remaining thermal oxide film 3. An oxide film composed mainly of the chemical oxide film 4 resists cracks even when receiving a load so that the outer ring, inner ring or both components prevents the deterioration of strength in a part containing the oxide film even after a heat treatment for strengthening steel material. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a rolling bearing used for an automobile transmission and the like, and more particularly to a high-strength rolling bearing that has been surface-treated to improve its strength.

  In general, it is well known that carburizing treatment, nitriding treatment or carbonitriding treatment for strengthening the steel material is performed on the outer ring or inner ring of a rolling bearing made of a steel material, and further quenching to 830 to 870 ° C. after the carbonitriding treatment, It is known to improve the life of rolling bearings lubricated with lubricating oil in the presence of foreign matter, such as automobile transmissions, by tempering to 160-190 ° C. and making the retained austenite of the surface layer 25% or more. (Patent Document 1).

  In addition, in rolling bearings filled with grease, in order to suppress the phenomenon that hydrogen separates from the grease and cracks due to peeling occur on the inner and outer race rings made of steel, the race rings are immersed in an aqueous caustic soda solution by the black dyeing method. It is known that a triiron tetroxide film is formed on a rolling surface (Patent Document 2).

  Further, it is known to use a basic treatment liquid containing sodium nitrite and sodium hydroxide as a treatment for forming an oxide film for imparting insulation to the surface of a rolling bearing (Patent Document 3).

JP 7-190072 (Claim 1, paragraph 0028) Japanese Patent Publication No. 6-89783 (page 3, column 5, lines 4-6) JP 2008-57602 A (Claim 3)

  However, the surface of the steel subjected to the heat treatment such as quenching described above is formed with an oxide film formed by heating, unlike an oxide film formed by a basic treatment liquid called black dyeing. Since this oxide film increases crack sensitivity, if it is formed on a surface other than the required surface such as insulation and lubricating oil contact surface, there is a problem that the mechanical strength of the inner and outer races of the rolling bearing is reduced. There is a point.

  Referring to a part of FIG. 1, when a recess such as a circumferential groove 5 for locking is formed on the outer surface of the inner and outer races of the rolling bearing, the recess is partially In addition, since the thickness in the radial direction is reduced, it is necessary to increase the mechanical strength by designing such as increasing the thickness if possible.

  However, rolling bearings are limited in size, such as being matched to predetermined mounting dimensions, and there is also a demand for miniaturization, so it is easy to produce rolling bearings with a design that increases the wall thickness. Not that.

  In general, the surface of the rolling bearing is adjusted to a desired dimension by grinding. However, the oxide film in the recess is a portion that cannot be easily removed by grinding. The formed oxide film is in a state where cracks are likely to occur, that is, a state in which cracks are highly sensitive.

  In addition, the surface on which the oxide film is formed on the rolling bearing is limited to the surface that is liable to be brittle when in contact with the lubricating oil or the surface that requires insulation, and for these surfaces, an oxide film formed by heating, It was not used separately from the oxide film formed by black dyeing using a basic aqueous solution.

  Therefore, the object of the present invention is to solve the above-mentioned problems, and when an oxide film is formed on the surface of a steel rolling bearing by a heat treatment for strengthening the steel material, the machine of the key point is formed by such an oxide film. It is to prevent the strength from being weakened.

  In particular, when the outer ring or inner ring of the rolling bearing or both components have a recess such as a circumferential groove on the surface, the mechanical strength is prevented from being weakened by the oxide film formed in the recess.

  In order to solve the above-mentioned problems, in the present invention, in a high-strength rolling bearing having an oxide film formed by heat treatment for strengthening the steel material on the outer ring or inner ring of the rolling bearing made of a steel material or the surface of both parts. Thus, a high-strength rolling bearing is provided in which a chemical oxide film made of triiron tetroxide is provided on the steel material inside the oxide film by reaction with a strong base aqueous solution.

  A high-strength rolling bearing constructed as described above is formed on a steel material inside an oxide film (hereinafter referred to as a thermal oxide film) formed by heat treatment, by a reaction with a strong base aqueous solution before the heat treatment. Since the formed chemical oxide film made of triiron tetroxide is provided, the reaction rate of the oxide film formation by heat treatment is slow, and it is difficult to form the entire oxide film to be thicker than about 3 μm. Therefore, the thickness of the thermal oxide film on the chemical conversion oxide film is relatively thin.

  In this way, the outer ring or inner ring, or both parts, the thermal oxide film does not adhere to the surface indefinitely even after the heat treatment for strengthening the steel material, the thermal oxide film is formed thinly, and the chemical oxide film is formed. It becomes the outer ring or inner ring or both parts on which the main oxide film is formed.

  Since the oxide film mainly composed of such a chemical oxide film is resistant to cracking even when subjected to a load, the outer ring or the inner ring or both parts have an oxide film even after heat treatment for strengthening the steel material. There will be no reduction in strength in the part.

The film thickness of the above-mentioned chemical conversion oxide film is preferably formed to a thickness of 1.5 to 2.5 μm so that the above-described effects can be sufficiently achieved. This is because the formation of the film thickness of the oxide film made of triiron tetroxide on the steel material is generally considered to be about 1 to 3 μm in the case of both heat treatment and chemical conversion treatment, and is formed to be thicker than 3 μm. It is difficult and impractical.
Therefore, by forming the chemical conversion oxide film as thick as a predetermined film thickness, the thermal oxide film is formed relatively thin, preferably 1.5 μm or less. Such a relatively thin thermal oxide film does not weaken the mechanical strength of the steel material.

  In addition, the surface of the outer ring or inner ring of the rolling bearing or the surfaces of both parts can be removed by normal grinding. However, it is difficult to remove the oxide film in the recess in a rolling bearing having a recess on the surface. is there.

  However, in the present invention, the oxide film remaining in the recess is formed by a conversion oxide film mainly composed of triiron tetroxide having low crack sensitivity, and the mechanical strength of the steel material is weakened by a relatively thin thermal oxide film. Since there is no, the intensity | strength of a recessed part is raised. Such a recess includes, for example, a locking circumferential groove formed on the outer diameter surface of the outer ring.

  As the rolling bearing in the present invention, for example, a deep groove ball bearing, a cylindrical roller bearing or a tapered roller bearing can be adopted, and these can be used as a high-strength rolling bearing.

The heat treatment for strengthening the steel material is, for example, a heat treatment involving carburizing of the steel material, a heat treatment involving nitriding of the steel material, or a heat treatment involving carbonitriding of the steel material. Therefore, it is preferable that the heat treatment for strengthening the steel material is a high-strength rolling bearing that employs heat treatment accompanied by refinement of crystal grains of the steel material.
The rolling bearing as described above is a high-strength rolling bearing that can be applied as a rolling bearing for an automobile transmission.

  This invention is a rolling bearing provided with a chemical oxide film made of triiron tetroxide by reaction with a strong base aqueous solution on the steel material inside the oxide film by heat treatment, and then heat treatment for strengthening the steel material. The thermal oxide film formed on the oxide film is thin even after passing through this process, and there is an advantage that it becomes a high-strength rolling bearing that does not weaken the mechanical strength of important parts by such an oxide film.

  In particular, when the outer ring or inner ring of the rolling bearing or both parts have a concave portion such as a circumferential groove on the surface, it becomes a high strength rolling bearing in which the mechanical strength is not weakened by the oxide film formed in the concave portion. There are advantages.

Sectional drawing of embodiment of the invention which concerns on a high intensity | strength rolling bearing Sectional drawing of the outer ring of the embodiment of the invention related to the high-strength rolling bearing 2 is an enlarged cross-sectional view of the main part Explanatory drawing of test method of thrust breaking load The chart which shows the measurement result of the thrust breaking load of Example 1 and Comparative Example 1 The chart which shows the measurement result of the radial breaking load of Example 1 and Comparative Example 1

Embodiments of the present invention will be described below with reference to the accompanying drawings.
As shown in FIGS. 1 to 3, in the embodiment, a thermal oxide film 3 (FIG. 3) formed on the surfaces of both the outer ring 1 and the inner ring 2 of a deep groove ball bearing made of a steel material by heat treatment for strengthening the steel material. 3) is a high-strength rolling bearing that remains partially even after surface grinding for required dimensioning. Tetraoxidation occurs on the steel material inside the remaining thermal oxide film 3 by reaction with a strong base aqueous solution. A chemical conversion oxide film 4 made of triiron is provided.

  A concave portion made up of a circumferential groove 5 for locking is formed in advance on the surface of the material on the outer diameter surface of the outer ring 1 of the rolling bearing shown in FIG. 1, and reference numeral 6 in the figure denotes a rolling element. (Ball), 7 indicates a cage.

  The form (type) of the rolling bearing used in the present invention is not particularly limited. For example, a cylindrical roller bearing or a tapered roller bearing can be adopted in addition to the deep groove ball bearing as described above. In addition, steel materials that can be used for the above-described bearings can be selectively employed depending on the purpose, and the composition of the metal elements constituting the steel is not particularly limited. A steel material can be used.

  Moreover, the chemical oxide film 4 made of triiron tetroxide formed on such a steel material is formed by a reaction between the steel material and a strong base aqueous solution, and the reaction is published by Nikkan Kogyo Shimbun, As described in Metal Surface Technology Handbook (new edition), page 818, this is based on the following chemical formulas (a), (b), and (c).

  The strong base aqueous solution used to advance this reaction is, for example, a strong base aqueous solution in which sodium nitrite or the like is blended as a reducing agent in an aqueous sodium hydroxide solution, and is well known as a so-called “black dyeing solution”. As the black dyeing solution, not only sodium hydroxide but also a cyanide compound may be used. When heated to 120 to 150 ° C., scaly triiron tetroxide is efficiently produced.

The reducing agent such as sodium nitrite and sodium arsenite adjusts the reaction rate of the above formulas (a) and (b) and quickly generates Na ₂ FeO ₄ generated by the formula (b) by the formula (c). The production of ferric trioxide Fe ₂ O ₃ can be suppressed by reducing the iron trioxide to produce triiron tetraoxide Fe ₃ O ₄ .

  The circumferential groove 5 for locking formed on the outer diameter surface of the outer ring is a single annular shape, but a plurality of the circumferential grooves 5 may be arranged, and may be a recess formed in a discontinuous manner ( (Not shown). In addition, the oxide film formation according to the present invention can be applied to the concave portion formed to reduce the wall thickness for other purposes as required for locking, and such a concave portion can be formed on the inner surface of the inner ring 2 as well. It is possible to provide.

  The heat treatment for reinforcing the steel material in the present invention is a heat treatment in which an oxide film is formed as a secondary as described above, and examples thereof include nitriding, carburizing, or carbonitriding. Moreover, the heat processing accompanied by refinement | miniaturization of the crystal grain of a steel raw material may be sufficient with these processes or independently.

  For example, the carbonitriding process is a process in which C and N are simultaneously infiltrated and diffused in an atmosphere obtained by adding 5 to 15% ammonia gas to a carburizing gas modified by burning propane or butane. Nitrogen diffused in the surface layer stabilizes retained austenite, so that the amount of retained austenite increases after quenching, and temper softening resistance increases due to solid solution of nitrogen, so that the rolling fatigue life is improved.

  Moreover, the heat treatment accompanied by the refinement of the crystal grain of the steel material can be achieved by, for example, dividing the quenching process into two times, thereby reducing the heating temperature and ensuring the refinement of the crystal grain while ensuring the solid solution amount of carbon. It is intended. That is, nitriding is performed for the purpose of lowering the Ac1 transformation point of the steel while sufficiently dissolving carbon in the martensite in the primary quenching, and then the heating and holding temperature in the secondary quenching step is set to 2 at 180 ° C., for example. In this method, the temperature is lowered as time passes to obtain fine crystals having an average particle diameter of 5 μm or less, for example.

  As shown in FIG. 2, as a manufacturing process of a high-strength rolling bearing, first, a rolling base made of a steel material is applied to a strong base aqueous solution heated to about 120 to 150 ° C. which is made of a black dyeing liquid mainly composed of sodium hydroxide. The outer ring 1 and the inner ring 2 of the bearing are immersed, and a chemical oxide film made of triiron tetroxide having a thickness of about 1.5 to 2.5 μm is provided. And the said heat processing is performed and steel raw material reinforcement | strengthening is performed, but the oxide film 3 is formed in the surface by this at the time.

  As shown in FIG. 3, the thermal oxide film 3 formed on the oxide film 4 at that time is as thin as about 0.5 to 1.5 μm. There is no weakening.

  As shown in FIG. 2, when the outer ring rolling surface 1a, the width surface 1b, and the outer diameter surface 1c are ground, the oxide film 8 composed of two layers of the chemical oxide film 4 and the thermal oxide film 3 becomes a circumferential groove. 5 remains on the inner diameter surface 10 excluding the inner surface 5 and the outer diameter edge portion 9 and the rolling surface.

  After the outer ring 1 shown in FIG. 2 is washed with alkali and water, a black dyeing solution of about 140 ° C. (sodium hydroxide (manufactured by Wako Pure Chemical Industries) 60 parts by weight, sodium nitrite (manufactured by Wako Pure Chemical Industries) 25 Part by weight and 15 parts by weight of sodium nitrate (manufactured by Wako Pure Chemical Industries, Ltd.) were mixed to prepare a treatment agent, which was diluted with water to a concentration of 1.0 kg / L to obtain a basic treatment solution. ) To provide a chemical oxide film having a thickness of about 2 μm.

  Thereafter, as heat treatment, after quenching at 800 to 850 ° C., tempering was performed at 170 to 200 ° C. to form a thermal oxide film.

  Next, the outer ring rolling surface 1a, the width surface 1b, and the outer diameter surface 1c were ground, and a deep groove ball bearing applicable to an automobile transmission was fabricated by assembling the inner ring, rolling elements and cage.

[Comparative Example 1]
A deep groove ball bearing was produced in the same manner as in Example 1 except that the immersion treatment was not performed in the black dyeing solution before the heat treatment.

  For Example 1 and Comparative Example 1, the snap ring 11 was attached and the outer ring 1 was fixed, and the thrust breaking load F was measured by the method shown in FIG. 4, and the results are shown in FIG. Further, the radial ring breaking load was also measured, and the result is shown in FIG.

  As apparent from the results of FIGS. 5 and 6, the rolling bearing of Example 1 has an improved breaking strength of 20% or more compared to Comparative Example 1, and the chemical oxide film reduces crack sensitivity. It has been found.

In addition, under the temperature conditions of the heat treatment, a test product was prepared that was subjected to heat treatment accompanied by carburizing, nitriding, carbonitriding, or refinement of crystal grains (5 μm or less) of the steel material in the same manner as in the above example. Deep groove ball bearings applicable to automobile transmissions were fabricated.
Regarding these bearings, the radial ring breaking load was also measured, but the breaking strength was improved in the same manner as described above, and the chemical oxide film reduced the crack sensitivity.

DESCRIPTION OF SYMBOLS 1 Outer ring 1a Rolling surface 1b Width surface 1c Outer diameter surface 2 Inner ring 3 Thermal oxide film 4 Chemical conversion film 5 Circumferential groove 6 Rolling element 7 Cage 8 Oxide film 9 Outer diameter edge 10 Inner diameter surface 11 Snap ring

Claims (10)

In a high-strength rolling bearing having an oxide film formed by heat treatment for strengthening the steel material on the outer ring or inner ring of the rolling bearing made of steel material or the surface of both parts,
A high-strength rolling bearing characterized in that a chemical oxide film made of triiron tetraoxide is provided on a steel material inside the oxide film by reaction with a strong base aqueous solution.   The high-strength rolling bearing according to claim 1, wherein the chemical oxide film has a thickness of 1.5 to 2.5 μm.   The high-strength rolling bearing according to claim 1 or 2, wherein the outer ring or inner ring or both parts of the rolling bearing are outer rings, inner rings or both parts of the rolling bearing having a concave portion on the surface.   The high-strength rolling bearing according to claim 3, wherein the concave portion is a circumferential groove for locking formed on the outer diameter surface of the outer ring.   The high-strength rolling bearing according to any one of claims 1 to 4, wherein the rolling bearing is a deep groove ball bearing, a cylindrical roller bearing, or a tapered roller bearing.   The high-strength rolling bearing according to any one of claims 1 to 5, wherein the heat treatment for strengthening the steel material is a heat treatment involving carburization of the steel material.   The high-strength rolling bearing according to any one of claims 1 to 5, wherein the heat treatment for strengthening the steel material is a heat treatment involving nitriding of the steel material.   The high-strength rolling bearing according to any one of claims 1 to 5, wherein the heat treatment for strengthening the steel material is a heat treatment involving carbonitriding of the steel material.   The high-strength rolling bearing according to any one of claims 6 to 8, wherein the heat treatment for strengthening the steel material is a heat treatment involving refinement of crystal grains of the steel material.   The high-strength rolling bearing according to any one of claims 1 to 9, wherein the rolling bearing is a rolling bearing for an automobile transmission.

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