JP2006124780A - Rolling and sliding part and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide rolling and sliding parts excellent in dimensional stability and a manufacturing method therefor. <P>SOLUTION: After applying carburizing-treatment to a material for parts already formed into a prescribed shape from a bearing steel, by heating at 840-870°C for ≥3 hr under carburizing atmosphere having ≥1.2% carbon potential, the carburized material is cooled to ≤830°C and successively, rapidly cooled. In this way, the total carbon content on the surface layer part from the surface to such depth that the maximum shearing stress acts is made to 1.0-1.6 wt% and solid-solution carbon content in a matrix on the surface layer part is made to 0.6-1.0 wt% and also, carbide is precipitated on the surface layer part and thus, the quantity of the carbide is made to 5-20% as the area ratio and the grain diameter of the carbide is made to ≤3μm. Further, the hardness at the deeper portion from the surface layer part is made to 30-64 Rockwell C hardness, and the amount of retained austenite at the deeper portion from the surface layer part is made to ≤15%. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is used as a rolling and sliding component and a manufacturing method thereof, and more specifically, as a rolling component used as a bearing ring and a rolling element of a rolling bearing that uses, for example, lubricating oil mixed with foreign matter, or a sliding bearing component. The present invention relates to a rolling and sliding component suitable for the above and a manufacturing method thereof.

  In this specification and claims, a rolling and sliding part means a part that performs pure rolling contact, pure sliding contact, and contact in which rolling contact and sliding contact are mixed.

  For example, as part of measures to improve the life of rolling bearings that are used with lubricating oil mixed with foreign matter, the present applicant has previously made rolling and sliding parts used in rolling bearing races and rolling elements. It is made of bearing steel (high carbon chrome bearing steel) such as JIS SUJ2, carburized, and the total carbon content of the surface layer in the range from the surface to the depth at which the maximum shear stress acts is 1.0-1 .6 wt%, and the amount of dissolved carbon in the matrix of the surface layer portion is 0.6 to 1.0 wt%. Further, carbide is deposited on the surface layer portion, and the amount of the carbide is the area. A rolling component was proposed in which the ratio was 5 to 20% and the particle size was 3 μm or less, and the amount of retained austenite in the surface layer portion was 20 to 40% (see Patent Document 1).

The rolling and sliding parts described in Patent Document 1 have a low cost and a long life, but when used under severe conditions such as high temperature and high load, or when used in high precision equipment, It is desirable to further suppress dimensional changes and improve dimensional stability.
Japanese Patent Laid-Open No. 2004-52101

  An object of the present invention is to provide a rolling and sliding component that is low in cost and has a long life and excellent in dimensional stability, and a method for manufacturing the same.

  The rolling and sliding component according to the invention of claim 1 is made of bearing steel, and is subjected to carburizing or carbonitriding so that the total carbon content of the surface layer from the surface to the depth at which the maximum shear stress acts is 1.0. The amount of solid solution carbon in the matrix of the surface layer portion is 0.6 to 1.0 wt%, and further, carbide or carbonitride is precipitated in the surface layer portion, The amount of the carbide or carbonitride is 5 to 20% in terms of area ratio and the particle size is 3 μm or less, and the hardness of the portion deeper than the surface layer portion (hereinafter referred to as the deep portion) is Rockwell C. The hardness (hereinafter referred to as HRC) is 30 to 64, and the amount of retained austenite in the deep part is 15% or less.

  In the first aspect of the present invention, the reasons for limiting each numerical value are as follows.

The total amount of carbon in the surface layer is limited to 1.0 to 1.6 wt% because when the amount exceeds the upper limit, the carbide or carbonitride becomes extremely coarse and cannot be refined. The lower limit is inevitably determined because it is based on bearing steel (high carbon chromium bearing steel) such as JIS SUJ2.

The amount of solute carbon in the matrix of the surface layer portion is limited to 0.6 to 1.0 wt% because if it is less than the lower limit value, the desired surface hardness cannot be obtained and lubrication is performed. This is because indentations are likely to be generated by foreign matters mixed in the oil, and when the upper limit is exceeded, the amount of fine carbides or carbonitrides in the surface layer becomes less than 5% in terms of area ratio, and wear resistance decreases. .

The amount of fine carbide or carbonitride in the surface layer part The amount of fine carbide or carbonitride is limited to 5 to 20% in terms of the area ratio. If it exceeds, coarse carbide or carbonitride is generated, and this coarse carbide or carbonitride rolls as a starting point for fatigue cracks, leading to a shortened life of the sliding component.

Particle size of fine carbide or carbonitride in surface layer This particle size is limited to 3 μm or less. If it exceeds 3 μm, it becomes the starting point of fatigue cracks as well as non-metallic inclusions, and toughness can be secured. It is not possible.

Hardness of the deep part The hardness of the deep part is limited to HRC30 to 64. Regarding the lower limit value, when the HRC is less than 30, rolling when the bearing receives a load, sliding parts, that is, rolling elements and This is because the amount of elastic deformation of the bearing ring is increased, causing a problem in bearing rigidity. As for the upper limit value, if the hardness of the deep part exceeds 64 in the bearing steel having a carbon content of 1% without sub-zero treatment, the amount of retained austenite exceeds 15%, resulting in a problem in dimensional stability. Because.

This is because if the amount of retained austenite in the deep part exceeds 15% or less, the amount of decomposed retained austenite that affects the dimensional change over time is obviously increased, and the dimensional stability is lowered.

  The rolling bearing according to the invention of claim 2 comprises both inner and outer wheels and rolling elements, and at least one of the inner and outer wheels and rolling elements comprises the parts of the invention of claim 1.

According to a third aspect of the present invention, there is provided a method for manufacturing a rolling / sliding component, in which a processed component material formed into a predetermined shape from bearing steel is 840-800 in a carburizing or carbonitriding atmosphere having a carbon potential of 1.2% or more. After heating at 870 ° C. for 3 hours or more and carburizing or carbonitriding, the temperature is lowered to 830 ° C. or less, and then rapidly cooled, so that the total amount of carbon in the surface layer from the surface to the depth where the maximum shear stress acts is reduced. 1.0 to 1.6 wt%, and the amount of solid solution carbon in the matrix of the surface layer portion is 0.6 to 1.0 wt%, and carbide or carbonitride is further precipitated on the surface layer portion to form the carbide. Alternatively, the amount of carbonitride is 5 to 20% in terms of area ratio, the particle size is 3 μm or less, the hardness in the deep portion is 30 to 64 in Rockwell C hardness, and the amount of retained austenite in the deep portion is 15% or less. This The one in which the features.
The reason for limiting each numerical value in the invention of claim 3 is as follows. Regarding the total carbon amount of the surface layer part, the amount of solid solution carbon in the matrix of the surface layer part, the amount of carbide or carbonitride of the surface layer part and the particle size of the carbide or carbonitride of the surface layer part, the reason for limitation is claimed This is the same as the case of the first invention.

Carbon potential in the carburizing or carbonitriding atmosphere This carbon potential is limited to 1.2% or more because if it is less than 1.2%, it is hardly carburized with respect to bearing steel having a carbon content of about 1 wt%. This is because the hardness of the surface layer portion and the area ratio of the carbide or carbonitride cannot be made desired, and the carbide or carbonitride cannot be refined. In addition, since a large amount of soot is generated when the carbon potential is excessive, the upper limit is preferably about 1.4%.

Carburizing or carbonitriding temperature This temperature is limited to 840 to 870 ° C. If the temperature is less than the lower limit, the necessary carburization as described in the carbon potential cannot be performed. This is because the crystal grain size becomes too large and giant carbides or carbonitrides precipitate to lower the strength. That is, since the yield strength is proportional to the -1/2 power of the crystal grain size, the strength decreases when the crystal grain size becomes too large.

Carburizing or carbonitriding time This time is limited to 3 hours or more. If it is less than 3 hours, the carburizing depth required for general rolling, sliding parts rolling, and strengthening of the surface layer on the sliding surface is obtained. Because it is not possible. In addition, this surface layer part is generally a range from the surface to a depth of about 0.5 mm.

  The reason why the temperature is lowered to 830 ° C. or lower after the carburizing or carbonitriding treatment and then rapidly cooled is to reduce the amount of retained austenite in the deep portion to 15% or less.

  In the above description, the surface layer portion from the surface to the depth at which the maximum shear stress acts refers to, for example, a portion having a depth of 50 μm from the outermost surface of the sliding contact surface.

  According to the rolling and sliding part of the invention of claim 1, since the hardness of the deep part is HRC 30 to 64 and the amount of retained austenite in the deep part is 15% or less, the rolling and the dimensional stability of the sliding part are improved. , Dimensional changes over time can be suppressed.

  In addition, since the surface layer portion is as described above, the surface hardness increases and foreign matter mixed in the lubricating oil does not generate indentation, and wear resistance is improved, resulting in rolling and sliding parts. It is possible to extend the life of rolling bearings and sliding bearings using Moreover, since it is made of bearing steel (high carbon chromium bearing steel) that is mass-produced for bearings, the material cost is reduced, and as a result, the total manufacturing cost is reduced. Among bearing steels, JIS SUJ2 is particularly mass-produced, and therefore, using it is preferable because the material cost is extremely low. In particular, in the case of an inner ring of a rolling bearing, the raceway surface and the rolling element are in contact with each other, so that the generated contact pressure increases and is easily damaged. According to the rolling bearing using the rolling and sliding parts of the present invention for the inner ring, the inner ring can be prevented from being damaged, and as a result, the life of the rolling bearing can be extended.

  According to the rolling bearing of the invention of claim 2, the dimensional stability is improved and the life can be extended.

  According to the rolling and sliding part manufacturing method of the third aspect of the present invention, since material parts made of bearing steel often used for bearings are used, the material cost is reduced. In addition, since the carburization or carbonitriding temperature is 840 to 870 ° C., and only after the single carburizing or carbonitriding treatment, the heat treatment is performed by cooling to 830 ° C. or lower and quenching, the heat treatment cost is reduced. . Therefore, the total manufacturing cost of the bearing parts is reduced. Among bearing steels, JIS SUJ2 is particularly mass-produced, and therefore, using it is preferable because the material cost is extremely low.

Embodiments of the Invention

  Hereinafter, specific examples of the present invention will be described together with comparative examples.

Example 1 and Comparative Examples 1-2
JIS SUJ2 was used to form three types of inner ring materials used for the type 6206 rolling bearing, and these inner ring materials were subjected to heat treatment to produce three types of inner rings (Example 1 and Comparative Examples 1 and 2).

  The heat treatment applied to the inner ring of Example 1 is as shown in FIG. 1, and after heating and holding at 850 ° C. for 4 hours in a carburizing atmosphere with a carbon potential of 1.3%, the temperature was lowered to 820 ° C. It is heated and held in the atmosphere for 0.5 hours, and then oil-cooled to 80 ° C.

  The heat treatment applied to the inner ring of Comparative Example 1 is shown in FIG. 2, and is heated at 850 ° C. for 3 hours in a carburizing atmosphere with a carbon potential of 1.3%, and then oil-cooled to 80 ° C.

  In addition, in the heat treatment of Example 1 and Comparative Example 1 described above, although not shown, a tempering process is performed in which heating is performed at 160 ° C. for 2 hours.

  The heat treatment applied to the inner ring of Comparative Example 2 is a normal quenching process, in which it is heated at 830 ° C. for 40 minutes, then oil cooled to 80 ° C., and then tempered by heating at 180 ° C. for 2 hours. .

  In all the heat treatments described above, although not shown, a tempering process is performed in which heating is performed at 160 ° C. for 2 hours.

The surface hardness (HRC) of the raceway surface of the inner ring of Example 1 and Comparative Examples 1 and 2 manufactured in this way, the total carbon content of the outermost track surface, the amount of solute carbon in the matrix of the outermost track surface, the track the amount of carbides precipitated in the uppermost surfaces (area ratio), the maximum grain size of carbides precipitated in the track outermost surface retained austenite amount of the surface layer portion, the amount of retained austenite of hardness and deep deep (gamma _R amount), Table As shown in FIG.

Evaluation test 1
The shaft was press-fitted into the inner rings of Example 1 and Comparative Examples 1 and 2, and kept at 120 ° C. in a thermostatic bath. The tensile stress at the time of shaft press-fitting is 100 to 150 MPa. Then, after 50 hours, 100 hours, 200 hours, 500 hours, 1000 hours and 2000 hours have passed, 6 points on the inner ring inner diameter surface (2 spaced apart in the axial direction at 3 points equally spaced in the circumferential direction). The inner diameter of the point) was measured, and the change rate (%) of the dimension after the passage of time with respect to the dimension of the six points on the inner ring inner diameter surface before heating and holding was determined. The result is shown in FIG. The dimensional change rate is (the dimension after each time-the dimension before the test) / the dimension before the test.

Evaluation test 2
A ball bearing of model number 6206C3 was assembled by combining the inner ring of Example 1 and Comparative Examples 1 and 2 with an outer ring and balls made of JIS SUJ2 and subjected to normal carbonitriding. And these ball bearings were used, and the life test was done using the lubricating oil in which the foreign material was mixed. The test conditions are as shown in Table 2.

  The testing machine shown in Table 2 can simultaneously test two ball bearings, and the radial load in Table 2 means the radial load of one ball bearing. The results of the life test are also shown in Table 1.

The L ₁₀ life and L ₅₀ life in Table 1 are set to 5 ball bearings equipped with the same inner ring in the test machine and the time until the inner ring of one of the ball bearings is broken is measured 5 times. It is a cumulative failure probability life (L ₁₀ life) of ₁₀ % and a cumulative failure probability life (L ₅₀ life) of 50% obtained by carrying out.

  As is apparent from the above results, Example 1 which is the product of the present invention is equivalent to Comparative Example 1 which is the same as the rolling and sliding component described in Patent Document 1 in terms of life, and is dimensionally stable. It is equivalent to Comparative Example 2 which is a standard product made of JIS SUJ2 and is superior to Comparative Example 1.

  The above-described effects of the product of the present invention are particularly remarkable in a high temperature environment of 120 ° C. or higher and a tensile stress environment of 100 MPa or higher.

It is a diagram which shows the heat processing conditions given to the inner ring | wheel of Example 1. FIG. It is a diagram which shows the heat processing conditions given to the inner ring | wheel of the comparative example 1. 6 is a graph showing the results of Evaluation Test 1.

Claims (3)

It is made of bearing steel and is subjected to carburizing or carbonitriding so that the total carbon content of the surface layer part from the surface to the depth at which the maximum shear stress acts is 1.0 to 1.6 wt%, and the surface layer part The amount of dissolved carbon in the matrix is 0.6 to 1.0 wt%, and further, carbide or carbonitride is precipitated on the surface layer portion, and the amount of carbide or carbonitride is 5 by area ratio. ˜20% and the particle size is 3 μm or less, the hardness of the portion deeper than the surface layer portion is 30 to 64 in Rockwell C hardness, and the amount of retained austenite in the portion deeper than the surface layer portion is 15 % Or less rolling and sliding parts. A rolling bearing comprising both inner and outer wheels and rolling elements, wherein at least one of the inner and outer wheels and rolling elements comprises the component of claim 1. Carved or carbonitrided by heating the processed part material formed from the bearing steel to a predetermined shape in a carburizing or carbonitriding atmosphere with a carbon potential of 1.2% or more at 840 to 870 ° C. for 3 hours or more. Then, the temperature is lowered to 830 ° C. or lower, and then rapidly cooled, so that the total carbon content of the surface layer portion from the surface to the depth at which the maximum shear stress acts is 1.0 to 1.6 wt%, and the surface layer portion The amount of solid solution carbon in the matrix is 0.6 to 1.0 wt%, and further, carbide or carbonitride is precipitated on the surface layer portion, and the amount of carbide or carbonitride is 5 to 20% in area ratio and The grain size is 3 μm or less, the hardness of the portion deeper than the surface layer portion is 30 to 64 in Rockwell C hardness, and the amount of retained austenite in the portion deeper than the surface layer portion is 15% or less. That rolling, the production method of the sliding parts.

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