JP2009203526A - Rolling bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rolling bearing which is suitable for a spindle of a machine tool. <P>SOLUTION: At least one of an inner ring, an outer ring and a rolling body is manufactured by the following steps of: at first, forming an alloy steel comprising, by mass%, 0.2 to 0.7% carbon (C), 0.5 to 3.0% chromium (Cr), 0.4 to 2.0% silicon (Si), 0.5 to 3.0% molybdenum (Mo), 10 ppm or less oxygen (O), and the balance Fe with unavoidable impurities, into a predetermined shape; and subsequently subjecting the formed alloy steel to carbonitriding treatment at 840 to 920°C, induction hardening treatment, sub-zero treatment at -80 to -20°C, and tempering treatment at 200 to 400°C, in this order. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a rolling bearing used for automobiles, agricultural machines, construction machines, steel machines and the like, and more particularly to a rolling bearing for supporting a spindle of a machine tool.

Generally, in a rolling bearing, a rolling motion is performed between a race and a rolling element, and the race and the rolling element are repeatedly subjected to stress. Therefore, the materials constituting these members are required to have properties such as being hard, withstanding a load, having a long rolling fatigue life, and having good wear resistance against slipping.
Therefore, in general, the materials constituting these members often use Japanese Industrial Standard SUJ2 as bearing steel, and Japanese Industrial Standard SCR420 equivalent steel or SCM420 equivalent steel as case hardening steel. Has been.

Since these materials are repeatedly subjected to stress as described above, in order to obtain required properties such as rolling fatigue life, the bearing steel is quenched and tempered, and the case-hardened steel is carburized or Quenching and tempering are performed after carbonitriding, and the hardness is set to Hv 680 or more and 800 or less.
In recent years, various machine tools have been increasing their spindle rotation speeds and peripheral equipment feed speeds for the purpose of improving machining efficiency and productivity, and user demands for higher speeds are increasing. It has become to. In particular, the spindle of a machine tool is required to rotate at a very high speed, and the D _m n value of a grease-lubricated rolling bearing that supports the spindle (D _m is the pitch circle diameter (mm) of the rolling element, n Is a rotation speed (min ⁻¹ ), and those exceeding 1 × 10 ⁶ have recently become uncommon.

In Patent Document 1 below, in order to provide a rolling bearing having sufficient pressure resistance for a spindle of a machine tool, at least one of an inner ring, an outer ring, and a rolling element, carbon (C) is added in an amount of 0.2 mass. % To 0.7% by mass, chromium (Cr) to 0.5% to 3.0% by mass, silicon (Si) to 0.4% to 2.0% by mass, molybdenum (Mo) Carbon steel nitriding treatment using an alloy steel containing 0.5 mass% or more and 3.0 mass% or less, oxygen (O) content of 10 ppm or less, the balance being iron and inevitable impurities, By performing oil quenching , deep cooling treatment, and tempering at 240 ° C. or higher and 400 ° C. or lower in this order, the nitrogen content of the surface layer portion is 0.05% by mass or more and 0.5% by mass or less, and the amount of retained austenite in the surface layer portion is It is described that the content is 5% by volume or less.
JP 2005-76679 A

However, the rolling bearing of Patent Document 1 has a problem that cracks are likely to occur.
An object of the present invention is to provide a rolling bearing that is suitable for a spindle of a machine tool and has high pressure resistance and is not easily cracked.

In order to solve the above-mentioned problems, the present invention provides a rolling bearing comprising an inner ring, an outer ring, and a plurality of rolling elements that are movably disposed between the inner ring and the outer ring. At least one of the outer ring and the rolling element includes carbon (C) in an amount of 0.2 mass% to 0.7 mass%, chromium (Cr) in an amount of 0.5 mass% to 3.0 mass%, It contains silicon (Si) in a range of 0.4% to 2.0% by mass, molybdenum (Mo) in a range of 0.5% to 3.0% by mass, and the oxygen (O) content is 10 ppm or less, and after the balance is formed using iron and an inevitable impurity alloy steel, carbonitriding at 840 to 920 ° C., induction hardening, deep cooling at −80 to −20 ° C., By performing tempering at 200 ° C or higher and 400 ° C or lower in this order The carbon content of the surface layer part is 0.6 mass% or more and 2.0 mass% or less, the nitrogen content of the surface layer part is 0.05 mass% or more and 0.5 mass% or less, and the amount of retained austenite in the surface layer part Is a rolling bearing characterized by being made 5 volume% or less.
The rolling bearing of the present invention may be less susceptible to cracking which is a problem in Patent Document 1 by performing induction hardening instead of oil quenching after carbonitriding in the method described in Patent Document 1. The

  According to the present invention, it is possible to obtain a rolling bearing that is suitable for a spindle of a machine tool and has high pressure resistance and hardly causes cracking.

Hereinafter, embodiments of the present invention will be described.
FIG. 1 is a partial longitudinal sectional view showing a configuration of an angular ball bearing which is an embodiment of the present invention.
The angular ball bearing 10 is a rolling bearing suitable for supporting a spindle of a machine tool, and includes an inner ring 11, an outer ring 12, and a plurality of balls 13 disposed between the inner ring 11 and the outer ring 12 so as to be freely rollable. The cage 14 holds the ball 13 between the inner ring 11 and the outer ring 12. The angular ball bearing 10 has an inner diameter of 65 mm, an outer diameter of 100 mm, a width of 18 mm, a ball 13 having a diameter of 7.144 mm, a number of balls of 28, a contact angle of 18 °, and formed on the inner ring 11 and the outer ring 12. The radius of curvature of the track grooves is 52% and 56% of the diameter of the ball 13, respectively.

  The inner ring 11 and the outer ring 12 are manufactured as follows. Steel materials (A to E) having the composition shown in Table 1 are formed into a predetermined shape, and for Nos. 1 to 3, heat treatment shown in FIG. 2, that is, carbonitriding at 840 to 920 ° C., frequency 10 to 20 kHz , Induction hardening under conditions of an output voltage of 200 to 400 V and a treatment time of 5 seconds, a deep cooling treatment at −80 ° C., and a tempering treatment at 300 ° C. were performed in this order. This heat treatment corresponds to the heat treatment performed in the present invention. Next, grinding finishing and super finishing were performed.

For No. 4, the heat treatment shown in FIG. 4, that is, carbonitriding at 840 to 920 ° C., quenching at a heating temperature of 800 to 860 ° C., and tempering at 160 to 400 ° C. were performed in this order. . Next, grinding finishing and super finishing were performed.
For No. 5, the heat treatment shown in FIG. 3, ie, carbonitriding at 840 to 920 ° C., oil quenching at a heating temperature of 800 to 860 ° C., deep cooling at −80 ° C., 240 ° C. to 400 ° C. The following tempering process was performed in this order. This heat treatment corresponds to the heat treatment performed by the method of Patent Document 1. Next, grinding finishing and super finishing were performed.

For No. 6, SUJ2 (steel type E) was used, and after normal quenching and tempering, grinding finishing and superfinishing were performed.
Table 2 shows the carbon content ([C]), nitrogen content ([N]), retained austenite amount (γ _R ), and surface hardness (Hv) of the surface portions of the inner ring and outer ring thus obtained. Show.
In the present invention, the surface layer portion means a portion from the surface after superfinishing to a depth of 20 μm. Further, the carbon content and nitrogen content of the surface layer portion were measured with an emission analyzer, the surface hardness was measured with a Vickers hardness meter, and the residual austenite amount was measured with an X-ray analyzer.

And the angular ball bearing 10 is assembled using the ball | bowl 13 made from a silicon nitride, and the holder | retainer 14 made from a fluororesin, for example.
The pressure resistance of each of the inner rings and outer rings of Nos. 1 to 6 thus obtained was evaluated by the following method using a disk-shaped test piece.
The dimensions of the disk-shaped test piece were 60 mm in diameter and 6 mm in thickness, and the surface roughness was 0.01 μm or less in terms of average roughness (Ra). A sphere made of SUJ2 having a diameter of 3.76 mm (3/16 inch) was pressed against the disc surface of the test piece with various loads, and the maximum depth of the resulting indentation was measured. Then, the pressure scar resistance was evaluated at the maximum depth when the surface pressure was 4.2 GPa. Specifically, when the maximum pressure when the surface pressure is 4.2 GPa is 0.1 μm or less, the pressure resistance is very good (◎), and when the surface pressure is 0.1 to 0.2 μm, the pressure resistance is not so good. When it was not good (Δ) and 0.2 μm or more, it was evaluated that the pressure scar resistance was poor (x). Further, it was also examined whether or not cracking occurred when the surface pressure was 4.2 GPa. The results are also shown in Table 2.
Further, the amount of elliptic deformation of the outer ring outer diameter (difference between two orthogonal diameters) was measured. The results are also shown in Table 2.

In Nos. 1 to 3 corresponding to the examples of the present invention, cracks did not occur and the pressure scar resistance was high. Of Nos. 4 to 6 corresponding to the comparative example, No. 5 corresponding to the example of Patent Document 1 had crack resistance but cracks. No. 4 did not crack, but was inferior to Nos. 1 to 3 and 5 in terms of pressure resistance. No. 6 did not crack, but the pressure scar resistance was poor. In Nos. 1 to 3, since the amount of elliptical deformation is small, the machining allowance by finish polishing can be reduced. Therefore, the carbonitriding layer portion (the portion having high hardness and high nitrogen content) is used as the raceway surface. Can be used.
As described above, according to the rolling bearing of the present invention, by performing induction hardening after carbonitriding, cracking which is a problem in Patent Document 1 does not occur, and pressure resistance is high. Therefore, the rolling bearing of the present invention is suitable for a spindle of a machine tool.

It is a fragmentary longitudinal cross-section which shows the structure of the angular ball bearing which is one Embodiment of this invention. It is a figure which shows the heat processing method performed by this invention. It is a figure which shows the heat processing method (method of patent document 1) equivalent to the comparative example of this invention. It is a figure which shows the heat processing method corresponded to the comparative example of this invention.

Explanation of symbols

10 Angular Contact Ball Bearing 11 Inner Ring 12 Outer Ring 13 Ball

Claims (1)

In a rolling bearing comprising an inner ring, an outer ring, and a plurality of rolling elements arranged so as to be freely rollable between the inner ring and the outer ring,
At least one of the inner ring, the outer ring, and the rolling element is:
Carbon (C) is 0.2 mass% to 0.7 mass%, chromium (Cr) is 0.5 mass% to 3.0 mass%, and silicon (Si) is 0.4 mass% to 2.0 mass%. Less than mass%, molybdenum (Mo) is contained in each range of 0.5 mass% to 3.0 mass%, oxygen (O) content is 10 ppm or less, and the balance is iron and inevitable impurities After being formed using alloy steel,
It is obtained by performing carbonitriding at 840 to 920 ° C., induction quenching, deep cooling at −80 to −20 ° C., and tempering at 200 ° C. or more and 400 ° C. or less in this order. The ratio is 0.6 mass% to 2.0 mass%, the nitrogen content of the surface layer portion is 0.05 mass% to 0.5 mass%, and the amount of retained austenite in the surface layer portion is 5 volume% or less. A rolling bearing characterized by

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