JPS62274055A - Bearing steel - Google Patents

Abstract

PURPOSE:To improve the rolling fatigue characteristics of a bearing made of undermentioned material and also to prolong the rolling life of the above, by providing a composition in which the amounts of C, Si, Mn, Cr, Mo, and Fe are specified and the amounts of Cu and Ni as impurities are reduced and limited to the prescribed quantities or below. CONSTITUTION:This bearing steel has a composition consisting of, by weight, 0.8-1.2% C, <=2% Si, <=2% Mn, 0.3-2.5% Cr, 0.05-1% Mo, and the balance Fe with impurities. Moreover, among the above impurities, Cu and/or Ni is limited to <=0.1%, respectively.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Purpose of the Invention] (Field of Industrial Application) The present invention relates to a steel for bearings that is used as a material for bearings that has particularly excellent rolling life. be.

(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 transfer fatigue properties are important. , J.I.
High carbon chromium bearing steel (SUJ1-5) specified in S G 4805 is often used as the material.
However, in recent years, the load on bearings has become heavier due to the high-speed operation of automobiles, industrial machinery, etc., and it is desirable to develop bearings with even better transfer fatigue properties and the steel used for bearings. It is rare.

Therefore, in order to further improve the transfer fatigue characteristics of bearings made of such bearing steel and extend its life, it is necessary to incorporate typical non-containing materials that are unavoidably contained in the steel. Metal inclusions, i.e. 5i02, M
It is necessary to suppress the amount of nS, TiN, etc., and for this purpose, it is important to reduce the content of O, S, Ti, N, etc. in the steel as much as possible.

(Problems to be Solved by the Invention) Therefore, when producing steel for bearings, which is a material for bearings that are particularly required to have excellent transfer fatigue properties, the VIM method, VAR method, ESR method, PAM method, etc. So-called special melting and refining methods such as
■ Pig making/steel making (described on pages 728 to 764) may be used alone or in combination, but this significantly increases the material cost, making the bearing price high, and making mass production difficult. It has the problem of not being oriented properly.

Further, as mentioned above, although the transfer fatigue characteristics can be improved by reducing the content of impurities such as O, S, Ti, and N as much as possible, there is still a problem that it is still insufficient.

(Purpose of the Invention) The present invention has been made in view of these conventional problems, and in particular, it is possible to significantly improve the rolling fatigue characteristics of bearings and extend their life, while reducing material costs. The object of the present invention is to provide a steel for bearings that is capable of suppressing the increase in .

[Structure of the Invention] (Means for Solving the Problems) The bearing steel having excellent transfer fatigue properties according to the present invention has a weight percentage of
So, C: 0.8 to 1.2%, Si: 2.0% or less, Mn
: 2.0% or less, Cr: 0.3 to 2.5%, and if necessary, So and A: 0.016 to 0.070%, with the balance consisting of Fe and impurities. Cu: O, 10% or less and/or Ni: 0.10%
It is characterized by the following regulation, and if necessary, further include MO20.05 to 1.0% in the balance Fe, and P:0.006 in impurities if necessary.
% [F, S: 0.005% or less, O: 0.0007% or less, N: 0.0060% or less, Ti = 0.0020% or less.

Next, the reason for limiting the composition (weight %) of the bearing steel having excellent transfer fatigue properties according to the present invention will be explained.

C: 0.8 to 1.2% C is an effective element for improving the strength, hardness and wear resistance of bearings and increasing their lifespan, so to obtain such effects, 0.8 to 1.2% % or more. However, as the C content increases, the carbides in the steel tend to become large, and M
3C(M: Fe.

Since giant Cr)-based carbides precipitate and reduce the rolling fatigue life of the bearing, the content was set at 1.2% or less. Note that by reducing the amount of P+S, the limit of quench cracking can be improved and the upper limit of the C content can be increased, so that a bearing with high strength and high wear resistance can be obtained without quench cracking.

Si: 2.0% or less Sl is an element that acts as a deoxidizing agent during steel melting and is effective in improving hardenability and extending the life of bearings. If it is too high, machinability deteriorates, so it is set to 2.0% or less.

Mn: 2.0% or less Mn acts as a deoxidizing and desulfurizing agent during steel melting, and is an effective element for improving hardenability, increasing the toughness of the base, and extending the life of bearings. However, even if the Mn content is increased, no improvement in service life is observed, and on the contrary, the machinability is reduced, so the Mn content is set at 2.0% or less.

Cr: 0.3-2.5% Cr is an effective element that contributes to uniform refinement of carbides, improves hardenability, increases the toughness of the matrix, and extends the life of the bearing. In order to obtain such an effect, the content was set to 0.3% or more. However, if the Cr content becomes too large, it becomes difficult to obtain uniform fine carbides, making it impossible to improve the life of the bearing, so it is set at 2.5% or less.

Mo: 0.05-1.0% Mo is an element that is effective in improving hardenability and is effective in increasing the toughness of bearings. 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 if it is added, it is preferably 1.0% or less.

So! L-bag A1: 0.016-0.070% In order to reduce oxide-based inclusions that have a large effect on transfer fatigue of bearings, it has conventionally been thought that it is better to reduce the amount of AfL as much as possible. However, when the 0 content is reduced to a considerably small amount, preferably 0.0007% or less, a certain amount of AfL does not exist in the steel as oxide-based inclusions, but rather has the effect of refining the crystal grains. This improves the toughness and fatigue strength of bearings.

In addition, spheroidization progresses completely even at a relatively high cooling rate.
It was found that it becomes easier to perform spheroidizing annealing. and,
By containing at least 0.016%, toughness, fatigue strength, and spheroidizing annealing characteristics can be improved without adversely affecting the transfer fatigue characteristics of the bearing.

However, if 5ofL/A standing exceeds 0.070%, 0
Even if the content is less than 0.0007%, it will combine with oxygen in the air during casting, etc., or spread with large ladle-resistant materials, producing oxide-based inclusions. Unfavorable, therefore, in order to obtain the above effect, 5
The amount ofLeAn was limited to a range of 0.016% to 0.070%.

Cu: 0.10% or less Cu reduces the base strength of bearing steel and has a negative effect on transfer fatigue properties, so in order to increase the transfer life of bearings, the upper limit should be 0.10%. It is desirable to reduce the amount of Cu as much as possible, and since it is difficult to remove by ordinary refining, reducing the amount of Cu is achieved by selecting raw materials.

Ni: 0.10% or less Although Ni is an element that contributes to improving hardenability, it is limited to 0.10% or less in the steel for bearings according to the present invention from the viewpoint of strictly controlling hardenability. In some cases, restrictions on the amount of Ni may be difficult to remove through normal refining, so in such cases, the raw material should be analyzed in advance to ensure that the amount of Ni is sufficient to the extent that it does not affect hardenability. It is desirable to select materials with low

P: 0.006% or less.

Since P precipitates at grain boundaries and reduces the rolling life of the bearing, it is desirable to set the upper limit to 0,00% or less and to reduce it as much as possible.In this case, the P content can be sufficiently reduced in the melting furnace. In addition, by removing the slag from the melting furnace into a separate container and tapping the melt, or by removing the sludge after tapping the melt into a separate container, CaO or Na2 CO3 is removed from the molten metal.
This is achieved by performing oxidative refining, in which a flux whose main component is blown into a flow of oxygen-containing gas.

S: 0.005% or less S combines with Mn to form MnS, and exists in the steel in a stretched stringer-like state, which promotes mechanical anisotropy and improves bearing performance. Since it reduces the transfer life of S, it is desirable to set the upper limit to o, oos% or less and to reduce it as much as possible. In this case, reduction of S content can be achieved by strengthening reduction refining by ladle refining (LF), etc. .

0: o, ooo 7% or less If a large amount of 0 is contained, AJL203. SiO, Ti
Oxide-based inclusions such as O2 are generated and reduce the transfer life of the bearing, so it is desirable to keep the upper limit to 0.0007% or less and to reduce it as much as possible.In this case, LF (ladle refining) and DH, Zero tolerance can be reduced by enhancing RH (vacuum degassing).

N: 0.006.0% or less N produces lumpy nitrides such as TiN, and the edges of the nitrides become the starting point of transfer fatigue fracture, reducing the transfer life of the bearing, so the upper limit should be set to o. , less than ooso%,
It is desirable to reduce it as much as possible. In this case, DH,
The N content can be reduced by strengthening RH (vacuum degassing).

Ti: 0.0020 or less Ti combines with N to form a lumpy nitride TiN, and the edge of the nitride becomes a starting point for transfer fatigue fracture, reducing the transfer life of the bearing, so the upper limit is set to 0. .0020%
It is desirable to reduce the Ti content as much as possible. In this case, the Ti content can be reduced by carefully selecting raw materials and strengthening oxidation refining in a container separate from the melting furnace (02 supply).

(Example) First, raw materials were melted in an electric arc furnace.
Ti by carefully selecting raw materials.

While ensuring that the amounts of Cu and Ni are below the desired values,
DeP by sufficient oxidation refining using 2.

Next, the slag was removed and then transferred into a ladle. After the steel has been tapped into the ladle, N is placed on the flow of 02 from the lance installed above.
A2CO3 powder was supplied at a rate of 2 kg/lon, and at the same time Ar gas was supplied from the bottom for stirring. Then, slag removal was carried out, but at this time, sufficient slag removal was performed to prevent back-up. Next, an electrode was installed and ladle refining was carried out, and the de[3] , promoted de[01].

Next, the molten steel is transferred to a vacuum degassing (RH) device.

By equalizing the temperature and promoting [N] removal.

After adjusting the components, the slab was transferred into a tundish and subjected to continuous broiling.The obtained slab was then subjected to blooming rolling and product rolling, and then spheroidizing annealing.

The chemical composition of the bearing steel thus obtained is shown in Table 1.

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.
gf/mm2 thrust type transfer life test was conducted to measure the transfer life (cumulative failure probability lO%) of each test piece, and the transfer life was evaluated using comparison steel No. 19 as a standard. Shown in the table.

As shown in Table 1, bearing steel according to the present invention (No.
It is clear that steels No. 1 to B) are significantly superior in transfer life compared to comparative bearing steels (Nos. 9 to 11).

[Effects of the Invention] As explained above, the bearing steel according to the present invention contains, in weight percent, C: 0.8 to 1.2%, Si: 2.0% or less,
Mn: 2, 0% or less, Cr: 0.3-2.5%
, and if necessary, 5 oil・A sentence: 0. O16～0
．． 070%, also as necessary M o: 0, 0
Contains 5 to 1.0%, the balance consists of Fe and impurities,
In impurities.

Cu: 0.10% or less and/or Ni: 0.10%
P: 0 in impurities, preferably as follows:
．． 006% or less, S: o, oos% or less, O: O, 0.
0007% or less, N: 0.0060% or less, Ti: 0.0007% or less, N: 0.0060% or less, Ti: 0.
0.0020% or less, it is possible to significantly improve the rolling fatigue characteristics of bearings made from this bearing steel, and to significantly extend the rolling life of the bearings. Excellent effects are brought about.

Claims (6)

[Claims] (1) Contains C: 0.8 to 1.2%, Si: 2.0% or less, Mn: 2.0% or less, Cr: 0.3 to 2.5%, and the balance is Fe and 1. Steel for bearings comprising impurities, the impurities being regulated to Cu: 0.10% or less and/or Ni: 0.10% or less. (2) The steel for bearings according to claim (1), characterized in that Mo: 0.05 to 1.0% is contained in the balance Fe. (3) Among impurities, P: 0.006% or less, S: 0.005% or less, O: 0.0007% or less, N: 0.0060% or less, Ti: 0.0020% or less A bearing steel according to claim (1) or (2), characterized in that: (4) In weight%, C: 0.8 to 1.2%, Si: 2.0% or less, Mn: 2.0% or less, Cr: 0.3 to 2.5%, Sol/Al: 0 .016 to 0.070%, the balance consists of Fe and impurities, Cu: 0 in the impurities
．． Steel for bearings, characterized in that it is regulated to 10% or less and/or Ni: 0.10% or less. (5) The steel for bearings according to claim (4), characterized in that the balance of Fe contains Mo: 0.05 to 1.0%. (6) Among impurities, P: 0.006% or less, S: 0.005% or less, O: 0.0007% or less, N: 0.0060% or less, Ti: 0.0020% or less Steel for bearings according to claim 4 or 5, characterized in that: