JPH02175836A - Carburizing steel for bearing - Google Patents

Abstract

PURPOSE:To obtain the carburizing steel for a bearing stock having suppressed generation and progress of fine fractures and having prolonged service life by specifying the contents of C, Si, Ni, Cr and S. CONSTITUTION:The compsn. of a carburizing steel is constituted of, by weight, 0.1 to 0.25% C, 0.5 to 1.5% Si, 1.0 to 2.0% Ni, 0.5 to 1.5% Cr, <=0.03% S and the balance Fe with inevitable impurities. The steel is carburized to regulate the surface hardness to about 60 to 64 HRC and the surface C concn. to about 0.8 to 1.0%. In the steel having the above compsn., S which is the. element forming A series inclusions regarded as the one of the main causes for the deterioration of the service life in a conventional bearing is utilized for the improvement of machinability, by which machinability equal to that of a carburizing steel contg. no Si and Ni can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to carburized steel used as a material for bearings that has a significantly superior rolling fatigue life.

BACKGROUND OF THE INVENTION The rolling fatigue life (hereinafter referred to as life) of a rolling bearing generally ends with peeling of the raceway surface that receives rolling contact from rolling members. The forms of this tll separation include surface-originated peeling that originates from scratches that occur on the surface during use, and internally-originated peeling that originates from nonmetallic inclusions that exist near the maximum shear stress position on the surface of the raceway surface. There are 2 f'R types of peeling. In order to extend the lifespan, the hardness should be increased to prevent surface scratches from forming on the surface, and the content of non-metallic inclusions should be reduced to prevent internal flaking from occurring. The effectiveness of nails is to reduce the number of sources of cracks.

However, there is a problem in that there is a limit to the hardness related to the above-mentioned surface-originated peeling, and the hardness cannot be made any harder. Furthermore, the reduction in the content of nonmetallic inclusions related to internally initiated flaking is almost reaching its limit under current steelmaking methods, and further significant reductions in the content of nonmetallic inclusions are expected. The problem is that there is no.

The purpose of this invention is to suppress the occurrence and propagation of microcracks by focusing on the process in which microcracks occur from their origin, propagate, and lead to peeling, and by strengthening the matrix from the material perspective. The object of the present invention is to provide a carburized steel for bearings that can be used for bearings and, therefore, can have a long service life.

Means for Solving the Problems The carburized steel for bearings according to the present invention has a carbon content of 0. 1-0.2
5 weight%, SI 0.5 to 1.5 weight%, Nl 1.0
~2.0% by weight, Cr: 0°5-1.5mm%, S: 0
．． It is characterized by having 0.03 times or less, and the remainder consisting of Fe and unavoidable impurities.

The reason for limiting the content of each element will be described below.

C: 0.1 to 0.25 overlapping fire In the present invention, C is an element that affects the hardness and hardenability of the core after carburizing and quenching. Normally, 11 core hardness is Il
l? It is desirable that C is about 030 to 45.
．． 1-0.25ffi1% is required. However, 0.2
If the amount exceeds 5% by weight, the toughness will decrease, so the upper limit should be set at 0.
The amount is 25% by weight.

Si: 0.5 to 1.5% by weight Si is a matrix-strengthening element and increases temper softening resistance, so it is an effective element for improving service life.

In the present invention, the life is significantly improved due to the synergistic effect with the toughness improvement by N1, which will be described later. If the content is less than 0.5 ffim%, the effect of improving the synergistic effect with Nl will be reduced, so the lower limit is set to 0.5 wt%. However, since Sl has a carburization inhibiting effect, the upper limit was set at 1.5ff1m%.

Ni:1. O ~ 2.0% by weight Ni is an effective element for improving toughness, and has a synergistic effect with the improvement in temper softening resistance by 81 mentioned above, which significantly improves the life. 1. C) Below fffffi%, the lifespan improvement effect due to the synergistic effect decreases, so the lower limit is set to 1. C
1ff1ffi96. In addition, since NI promotes the diffusion of C to the center during carburization, if it increases too much, it lowers the surface C concentration. Therefore, the upper limit is set to 2.0% by weight.

Cr: 0.5 to 1.5% by weight Cr is an element that improves hardenability and carburizability, and therefore 0.5 to 1.5% by weight. 5ffiffi% or more is required.

However, if the amount is too large, giant carbides will be formed during carburizing.
This becomes a stress concentration source, leading to a shortened lifespan. Therefore,
The upper limit is 1.5% by weight.

S: 0.03% by weight or less S is an element that improves machinability. In the present invention, since the Si content is high, machinability may be reduced. To improve this, S is added. However, if the amount is too large, A-based inclusions will increase. In general, it is B-based and C-based inclusions that affect the service life, and the effect of A-based inclusions is small.

However, if the A-based inclusions exceed 0.1% by weight, the influence cannot be ignored, so the upper limit is set at 0°03ffl%.

Japanese Patent Publication No. 1339/1986 is an example of a material that extends the service life by improving toughness and resistance to temper softening. However, this is due to the synergistic effect of Sl and Mn, which is completely different from the synergistic effect of Sl and Nl of the present invention.

Furthermore, in the present invention, Mn is not particularly added, but is treated as an unavoidable impurity. One of the features of the present invention is that S is added to improve machinability, and therefore, M n
This is because adding MnS increases the amount of MnS in the A-based inclusions, resulting in a decrease in service life.

Furthermore, since Mn is also an element that reduces grindability, it is particularly preferable not to add it.

Japanese Patent Publication No. 11423/1983 proposes a steel with similar composition, although the purpose of use is different. However, this also contains 0.2 to 2.0% by weight of Mn, and is different from the present invention for the same reason as above.

Example Hereinafter, this invention will be explained in detail with reference to Examples.

Tables 1 and 2 show the results of the chemical composition, carburizing quality, and rolling life of the steel of the present invention and the comparative steel.

In these tables, Sample 1, Sample 2, Sample 3, and Sample 4 are the invention steel, Sample 5, and Sample 6.
indicates comparative steel.

These samples were cut into a predetermined shape and then carburized. For rolling bearings, what hardness is usually required to suppress plastic deformation due to high contact surface pressure? 05
It is said to be about 8 to 64, but preferably IIRc
60-64.

Further, the optimum surface angle of 015 degrees is 0.8 to 1.0% by weight. Therefore, in this example, the surface hardness is IIl? C6
Carburizing treatment was carried out so that the surface C concentration was 0.8 to 1.0 mm%.

(Margins below) Table 1 Table 2 Figure 1 shows inventive steel sample 2 and comparison steel sample 5.
The results of the life test are shown as an example.

This life test is a rolling fatigue life test using a cylindrical roller test piece with a diameter of 20 and a length of 20 mTa, and the test conditions were such that the maximum contact surface pressure (PIlax) was 4401:gl.
/ stop 2, stress repetition rate is 3 x 10' cpm.

As is clear from Table 2 and FIG. 1, it can be seen that the B1° life (cycle) of the steel of the present invention is dramatically improved compared to the comparative steel. This improvement in life can be said to be due to the synergistic effect of Sl and N1.

In this example, the test piece was manufactured by cutting, but it can be manufactured by any of hot forging, warm forging, and cold forging.

FIG. 2 shows an example of test results in which the machinability of the steel sample 2 of the present invention was compared with that of the comparative steel sample 5.

The machinability test was conducted using cemented carbide P 20 (JIS B12O
3) Feed 0, 311IIl using a tool consisting of
/rev.

Cut ix, on+1. Cutting speed 150-250m/si
This was done by machining without cutting oil and comparing the tool life. The tool life standard VB (average wear width of front flank face) is 0.3 mm.

The horizontal axis in FIG. 2 represents tool life (IIlin), and the vertical axis represents cutting speed (m/win). This shows that the steel of the present invention has machinability equivalent to that of the comparative steel.

This shows the effect of adding S.

As described above, it can be seen that the steel of the present invention has a significantly improved life compared to the comparative steel due to the effects of Sl and Ni, and the effect of S prevents deterioration in machinability.

Effects of the Invention As is clear from the above, the carburized steel for bearings of the present invention has a
．． 5-1.5 wt% Si, 1.0-2.0 wt% N
i, 0.5-1.5% by weight of Cr, 0.03ffl amount%
Contains the following S, which improves temper softening resistance and matrix toughness, and its synergistic effect:
It suppresses the occurrence and propagation of cracks and dramatically extends the rolling fatigue life by more than 10 times compared to conventional bearings. By using a certain S to improve machinability, it is possible to obtain machinability equivalent to that of carburized steel that does not contain SI Ni.

[Brief explanation of the drawing]

Figure 1 is a diagram showing an example of test results comparing the life of the invention steel with comparison steel, and Figure 2 is a diagram showing an example of test results comparing the machinability of invention steel with comparison steel. . Patent applicant: Koyo Seiko Co., Ltd.

Claims (2)

[Claims] (1) C: 0.1-0.25% by weight, Si: 0.5-1%
．． 5% by weight, Ni 1.0-2.0% by weight, Cr 0.
5 to 1.5% by weight, S is 0.03% by weight or less, and the balance is Fe and unavoidable impurities. (2) Surface hardness is HRC60-64, surface C concentration is 0.
The carburized steel for bearings according to claim 1, which is carburized to a content of 8 to 1.0% by weight.