JPS61272349A - Bearing steel - Google Patents

Abstract

PURPOSE:To provide excellent rolling contact fatigue life by specifying S+P content in a high-carbon chromium bearing steel having a prescribed composition containing specific amounts of carbon. CONSTITUTION:The high-carbon chromium bearing steel consists of, by weight, 0.8-1.2% C, 0.1-2.0% Si, 0.2-2.0% Mn, 0.5-2.5% Cr, and the balance Fe with impurities and further contains, if necessary, <=5% Ni and/or <=2% Mo, in which S+P content is limited to <=0.010%. Further, among the impurities, Ti, O and N are limited to <=0.003%, <=0.0010% and <=0.006%, respectively. In this way, the M3C carbide distribution in the bearing steel is made finer and more uniform, so that rolling contact fatigue life of bearings made of the above bearing steel can be prolonged.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a high carbon chromium bearing steel that is used as a material for bearings, which has particularly excellent rolling fatigue life.

(Prior art) In general, mechanical structural parts are required to have high fatigue strength, so consideration must be given to the selection of materials, but this is especially true for mechanical structural parts such as bearings where rolling fatigue strength is important. Ha, J
High carbon chromium bearing steel (SUJI~5) specified in IS G 4805 is often used as the material.

In order to increase the rolling fatigue strength and extend the life of bearings made of bearing steel, typical non-metallic inclusions that are unavoidably contained in the steel must be added. objects, i.e. A1203, S i02
, MnS, TiN, etc., and for this purpose, it is necessary to suppress the amount of 0. It is important to reduce the content of S, Ti, N, etc. as much as possible.

Furthermore, the distribution of M(Fe,Cr)ac-based carbides (hereinafter abbreviated as rN13cJ) contained in the steel also affects the rolling fatigue life, especially the huge M3C present in the positive segregation area.
is said to have a negative effect. Such a huge M
In order to eliminate 3C, it is sufficient to once solidly dissolve the huge carbides generated during casting into the matrix, and for this purpose it is effective to subject the steel ingot or slab to soaking treatment at high temperature for a long time.

(Problems to be Solved by the Invention) As mentioned above, in order to extend the rolling fatigue life of bearings, it is effective to suppress non-metallic inclusions in steel and reduce huge M3C. There has been a desire to further extend the rolling fatigue life of such bearings.

This invention was made in view of these demands.
In addition to the above-mentioned suppression of non-metallic inclusions and reduction of huge M3C, we conducted various studies on factors that extend the rolling fatigue life of bearings, and as a result, we were able to further extend the rolling fatigue life of bearings, which was our initial objective. We have developed a bearing steel that can

[Structure of the Invention] (Means for Solving the Problems) This invention provides a high carbon chromium bearing steel with a carbon content of 0.8 to 1.2% by weight, in which the S and P content is o. ,
% by weight or less.

That is, as a result of various studies on factors that extend the rolling fatigue life of bearings, the inventors have found that, in addition to suppressing the above-mentioned nonmetallic inclusions and reducing huge M3C,
By setting the +P content to 0.010% by weight or less,
The distribution of M3C can be made more uniform and finer;
They discovered that this would further improve rolling fatigue life.

Such a reduction in the S0P content in bearing steel reduces the micro-segregation of C during solidification of molten steel, makes the distribution of carbides uniform and fine in the cast state, and allows the carbides to enter the matrix in the subsequent soaking process. Facilitates solid solution of As a result, the carbide grain rafts after the subsequent thermal history of rolling, spheroidizing annealing, quenching, and tempering become smaller, and the rolling fatigue life of the bearing is significantly improved.

As the bearing steel to which this invention is applied, for example, C:0
．． 8-1, 21fL amount%, Si,: 0, 1-2
．． 0% by weight, Mn: 0, 2-2,
0% by weight, (:r: 0.5 to 2.5% by weight, and if necessary, contains one or two of Ni: 5% by weight or less, Mo: 2% by weight or less, and the balance is Fe. and impurities.

The reason why bearing steel having such a composition is particularly preferable is as follows.

C: 0. S ~ 1.2% by weight C is an effective element for improving the strength, hardness, and wear resistance of bearings and increasing their lifespan, so in order to obtain such effects, 0.8% by weight or more It is better to However, as the C content increases, the carbides in the steel tend to grow larger, reducing the rolling fatigue life of the bearing.
In addition, in the bearing steel according to the present invention, since the P+S content is reduced, the quench cracking limit is improved, and the upper limit of the C content can be increased, so that high strength and high It is now possible to obtain bearings that are prone to wear and tear without cracking.

Si: 0.1 to 2.0% by weight 5i is an element that acts as a deodorizing agent during steel melting and is effective in improving hardenability and extending the life of bearings. 0.11f to obtain such an effect.
It is preferable to set i1% or more. However, if the St content is too large, the machinability decreases, so it is preferable to keep it below z,oi-'%.

Mn: 0.2-2.0% by weight Mn acts as a deoxidizing and desulfurizing agent during steel melting, improves hardenability and increases the toughness of the base,
Since it is an effective element for extending the life of bearings, it is best to use it at 0.2% by weight or more to obtain this effect.However, even if the Mn content is increased, the life will not be improved. 2.0% by weight because it does not reduce the machinability of the
It is best to set it to the following.

Cr: 0.5 to 2.5% by weight Cr is an effective element that contributes to the uniform refinement of carbides, improves hardenability, increases the toughness of the matrix, and extends the life of the bearing. Therefore, in order to obtain such an effect, it is preferable to set the content to 0.5% by weight or more. However, if the Cr content increases too much, it becomes difficult to obtain uniform and fine carbides, making it impossible to improve the life of the bearing.
The content is preferably 5% by weight or less.

Ni: 5% by weight or less, Mo: 2% by weight or less.Ni and Mo are elements effective in improving hardenability, and are effective in increasing the toughness of the bearing. , may be added as necessary in consideration of the size of the bearing, etc. However, if it is added in a large amount, the carbides will not be finely and uniformly dispersed, which will actually reduce the toughness, so even when added, the amount of Ni is preferably 5% by weight or less, and the amount of MO is preferably 2% by weight or less.

The bearing steel according to the present invention has an S+P content of 0.010 as described above in the steel having the above-mentioned more preferable composition.
% by weight or less, to reduce micro-segregation of carbon during solidification of molten steel, to make the distribution of carbides uniform and fine in the casting state, and to facilitate the solid solution of carbides into the matrix in the subsequent soaking treatment. As a result, the grain size of the carbide after quenching and tempering is reduced, significantly improving the rolling fatigue life of the bearing.

In addition, such reduction of S+P content is achieved by careful selection of raw materials,
This is achieved by strengthening removal of S and P during refining.

The bearing steel according to the present invention extends the rolling fatigue life of bearings made of this material.

In addition to reducing the S+P content, this is also achieved by suppressing nonmetallic inclusions as described above, so AfL203
．． In order to suppress the amount of 5i02, MnS, TiN, etc., it is particularly preferable that Ti:
0.003% by weight or less, 0:0.0O10% by weight or less,
N: It is preferable that the content is 0.006% by weight or less.

(Example) After melting steel with the components shown in Table 1 by electric furnace melting and ladle refining, it was cast and heated at 1300°C x 24Hr711
After soaking with heat, it was subjected to blooming rolling, followed by small-sized rolling, and then spheroidizing annealing.

Next, after processing the above-mentioned spheroidized annealed material into the shape of a test piece for a rolling life test, it was heated and held at 850°C, then oil-cooled, tempered, heated and held at 160°C, and then air-cooled, and then polished. A test piece for the transfer life test was prepared.

Next, using each of the above test pieces, the Hertzian stress was 536k.
A thrust two transfer life test of gf/mm' was conducted to measure the transfer life (cumulative failure probability lO%) of each test piece, and M3C particle size distribution was also measured. These results are shown in Table 2.

Table 2 As shown in Table 2, bearing steel according to the present invention (No.
It is clear that samples 1 to 3) have a considerably smaller average diameter of M3C than the comparative bearing steels (No. 4, 5), and are significantly superior in rolling life.

[Effects of the Invention] As explained above, according to the present invention, in a high carbon chromium bearing steel having a hydrogen content of 0.8 to 1.2% by weight, the S+P content is 0.010%. % by weight or less, it is possible to make the distribution of M3C carbides in this bearing steel more uniform and finer, and the rolling fatigue life of bearings made from this bearing steel can be significantly extended. A very good effect is that it can be extended.

Claims (4)

[Claims] (1) In high carbon chromium bearing steel with a carbon content of 0.8 to 1.2% by weight, the S+P content is 0.010
High carbon chromium bearing steel with excellent rolling fatigue life characterized by less than % by weight. (2) The high carbon chromium bearing steel contains C: 0.8-1.2% by weight, Si: 0.1-2.0% by weight, Mn: 0.2-2.
0% by weight, Cr: 0.5-2.5% by weight, S+P
A high carbon chromium bearing steel with excellent rolling fatigue life according to claim (1), characterized in that the content is 0.010% by weight or less, with the balance consisting of Fe and impurities. (3) The high carbon chromium bearing steel contains C: 0.8-1.2% by weight, Si: 0.1-2.0% by weight, Mn: 0.2-2.
0% by weight, Cr: 0.5-2.5% by weight, and Ni:
Contains one or two of the following: 5% by weight or less, Mo: 2% by weight or less, and the S+P content is 0.010% by weight or less,
A high carbon chromium bearing steel with excellent rolling fatigue life as claimed in claim (1), characterized in that the remainder consists of Fe and impurities. (4) Among impurities, Ti: 0.003% by weight or less, 0: 0.0010% by weight or less, N: 0.006% by weight
A high carbon chromium bearing steel with excellent rolling fatigue life according to claim (2) or (3), characterized in that: