JP2002339041A - Highly clean steel with excellent finish machinability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide highly clean steel which has excellent fatigue life time and acoustic characteristics, and by which finish machining time can be shortened without reducing the accuracy. SOLUTION: The highly clean steel with excellent final polishability is hypereutectoid high-carbon chromium steel of specified by JIS G 4805. In this steel, the amount of Ti contained in the chemical composition is <=20 ppm by mass and the average grain size of spheroidal carbides is <=0.60 μm, and further, the number of clusters of TiN continued over a range >=2.5 μm in width and >=10 μm in length in 200 mm<2> inspection area are <=50 pieces.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to bearing steel, which is a material for bearing parts such as races, balls and rollers of bearings.

[0002]

2. Description of the Related Art Bearing races, balls, rollers, and other bearing components are subjected to quenching / tempering, carburizing, and nitriding after predetermined plastic working and cutting from a bearing steel material. Thereafter, heat treatment such as quenching and tempering is performed, and then finishing such as fine polishing and lapping is performed. By the way, as the demands on the product shape accuracy, that is, the dimensional accuracy, are increasing more and more in the world, the final finishing is particularly problematic. In response to this need and more precise processing is required, finish shape accuracy,
There is a demand for an improvement in productivity and a streamlining process by shortening the processing time while maintaining the surface roughness and undulation.

[0003] Conventionally, bearing steel, which is a material for manufacturing bearing components, is manufactured without particularly limiting the particle diameters of Ti and spherical carbides in the chemical components of the steel. It takes a long time to process a predetermined processing allowance in final finishing polishing such as fine polishing and lapping. At present, as a countermeasure against this, there is a case where the free-cutting element S is increased to supplement the workability.
In addition to the effect of the content, this is a direction that goes against the needs for improving the fatigue life and acoustic characteristics of bearing steel, and is not inherently a desirable measure. In addition, when the processing surface pressure is increased in order to shorten the time of the final finish polishing, the accuracy of the finished shape is reduced, so that the use is limited.

With respect to the improvement of the finish workability of the bearing steel, the reduction of the size and amount of the eutectic carbide is mainly intended to improve the accuracy of the finished shape for improving the acoustic characteristics and quietness and to improve the aging characteristics. Japanese Patent Application Laid-Open No. 11-27
Japanese Patent Application Laid-open No. S61-9710 discloses an example that focuses only on the reduction of oxynitride-based nonmetallic inclusions and eutectic carbide.
Japanese Patent Application Laid-Open No. 11-163244 discloses an example in which attention is paid only to the reduction of the size and amount of oxide-based nonmetallic inclusions.
No. 303874. However, while maintaining the finished shape accuracy, which is the gist of the present invention, all of these "reduce the amount of Ti + shorten the finish processing time by making the spherical carbide (eutectoid carbide) finer + improve the cleanliness". No mention was made, and no disclosure was made.

[0005]

SUMMARY OF THE INVENTION The problem to be solved by the present invention is to solve the above-mentioned conventional problems, that is, to achieve a fatigue life and an acoustic sound in which the finishing time can be shortened without lowering the finishing accuracy. An object of the present invention is to provide bearing steel with excellent characteristics and high cleanliness.

[0006]

Means for Solving the Problems According to the present invention, there is provided a high-carbon chromium bearing steel defined by JIS G 4805 which is a hypereutectoid system. And the content chemical component Ti is 20pp
and m or less, an average particle size of globular carbides was limited to less than 0.60 .mu.m, the width 2.5μm in a test area 200 mm ²
TiN whose length is continuous over 10 μm
Is a high cleanliness bearing steel excellent in finish polishing workability, wherein the number of groups is 50 or less.

In the present invention, the average particle size of the spherical carbides (eutectoid carbides) is set to 0.60 μm or less. However, in the present invention, it is difficult to reduce coarse and hard eutectic carbides and oxide-based inclusions. This is a prerequisite, which is generally clear if the oxygen level of steel materials that have been subjected to soaking and diffusion treatment, which is commonly used today and is commonly known as soaking, and general-purpose bearing steels for automobiles and industrial machines.

The effect of Ti and spherical carbide on finish workability will be described. Ti is mainly crystallized as TiN in a matrix, and is hard like eutectic carbide on the order of several tens of μm. Invitation, finishing accuracy,
That is, it is conventionally said that the polishing accuracy is affected. However, when finishing a high-precision product shape as in the present invention, not only TiN but also a spherical carbide having a size two orders of magnitude smaller than a eutectic carbide, that is, polishing unevenness due to a spheroidized eutectoid carbide, and finish polishing, It is considered that the influence on the polishing finish shape accuracy and finish processing time through phenomena such as abrasion and clogging of the grinding stone cannot be ignored. That is, as described above, if hard particles such as spherical carbides as well as TiN are large or large, polishing unevenness occurs, and abrasion / clogging of the finish grinding wheel is accelerated, and as a result, a predetermined shape is not obtained. Or the finishing time may be long. The present invention has focused on this phenomenon and has solved the problem by limiting the amount of Ti and the particle size of the spherical carbide to the above ranges.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The embodiment of the present invention relates to a high carbon chromium bearing steel specified by JIS G 4805 of a hypereutectoid system, in which the chemical component Ti contained in a mass ratio of 20p is used.
and pm or less, an average particle size of globular carbides was limited to less than 0.60 .mu.m, the width of the inspection area 200 mm ² 2.5 [mu]
m and a continuous length of 10 μm or more
Cleanliness bearing steel in which the number of groups of N is 50 or less. These are shown in Table 1 below. The present invention will be described through invention steels 1 to 3 and examples.

[0010]

[Example] In a mass production melting furnace, a steel for bearings whose base is JIS SUJ2 and whose contents are shown in Table 1 in a mass ratio of Ti and S is smelted, refined, degassed, and cast. Then, it was subjected to soaking diffusion treatment, hot-rolled to a steel material, and subjected to a predetermined spheroidizing heat treatment to obtain an invention steel and a comparative steel. Further, a ring-shaped test piece of φ60 × φ20 × L6 is cut out from this steel material by cutting, and then rough polishing (φ60 × φ20 surface) → quenching at 835 ° C. → tempering at 170 ° C. → polishing (φ60 ×
(φ20 surface), and the time required for the final lapping and the surface roughness of the lapping were evaluated.

The above embodiment is an example of the manufacturing process of bearing parts (races, balls, rollers, etc.), ie, cutting (or plastic working) → quenching and tempering → final finishing (polishing → fine polishing, lapping, etc.). What is currently a problem is the time required for final finishing (fine polishing, lapping, etc.) and the finishing accuracy,
It is important to evaluate the surface roughness of the final lapping finish as in the above example.

Table 1 shows the final lapping time, the surface roughness (Rmax) of the lapping surface and the surface roughness (Ra) of the lapping surface.

[0013]

[Table 1]

In Table 1, the circle of cleanliness means that the number of TiN groups continuous over 2.5 μm in width and 10 μm or more in a test area of 200 mm ² specified by the present invention is 50 or less. Those that satisfy a certain degree of cleanliness are shown.

As can be seen from Table 1, No. 1 of the invention steel according to the embodiment of the present invention. 1 to 3, when the processing time of the final finish processing is 1 for the conventional bearing steel, 0.2 to
It can be greatly reduced to 0.6, and the surface roughness is small and excellent.

[0016]

As described above, the bearing steel according to the present invention can reduce the time required for the processing at the same processing surface pressure in the final finishing of bearing parts such as races, balls, rollers, etc. Accuracy is maintained well, and free-cutting element S is extremely low (for example, 0.003% by mass or less).
Good workability is maintained even if it is suppressed to a minimum, and together with the reduction of Ti which is the most characteristic of the present invention, the improvement of cleanliness which is important for the fatigue life, acoustic characteristics, etc., which are the main characteristics of the bearing, is also required. It has excellent effects that have not been achieved in the past, for example.

Claims (1)

[Claims] 1. A high-carbon chromium bearing steel specified in JIS G 4805 of a hypereutectoid system, in which the content of Ti as a chemical component is set to 20 ppm or less and the average particle diameter of the spherical carbide is set to 0.60 μm or less. Restrict, test area 200m
A high cleanliness bearing steel excellent in finish polishing workability, characterized in that the number of TiN clusters continuous over 2.5 μm in width and 10 μm or more in m ² is 50 or less.