JPH06145897A - Steel for bearing - Google Patents

Abstract

PURPOSE:To obtain a steel for a bearing suitable for obtaining a bearing excellent in rolling fatigue properties and having a long service life. CONSTITUTION:The compsn. of this steel is constituted of, by weight, 0.10 to 0.35% C, 0.50 to 2.00% Si, <=0.30% Mn, <=0.010% S, <=0.015% P, 0.50 to 2.50% Cr, <=0.030% Al, 0.10 to 1.00% V, <=0.0010% O and 0.001 to 0.010% N (Mn+10Al<=0.50%), constituted of, at need, one or two kinds of 0.50 to 3.00% Ni and 0.10 to 0.50% Mo and furthermore constituted of, at need, one or two kinds of 0.05 to 0.50% Nb and 0.0010 to 0.0020% Ti, and the balance Fe with impurities.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention is suitable for use as a material for bearings used in a wide range of fields such as automobiles and industrial machines, and is particularly suitable for use as a material for rolling bearings. It is about.

[0002]

2. Description of the Related Art Conventionally, as a material for bearings, high carbon chromium bearing steels (JIS SUJ 1 to 5) belonging to high carbon steels have been used.
Etc.), but in addition, J
There is chrome steel for case hardening represented by ISSCr 420.

The carburized bearing member made of chrome steel for case hardening has been reduced in the amount of [O] in the steel due to the progress of the melting technology, and the rolling life has been greatly improved accordingly.

[0004]

However, as the amount of [O] in steel is reduced, the influence of factors other than the amount of [O] has become the limiting factor in extending the rolling life, which is high. There was a problem that measures for increasing the service life at the level are becoming necessary.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems. By using a bearing steel for carburizing in which inclusions are reduced as much as possible and then the composition of components is optimized. The purpose is to improve the rolling contact fatigue characteristics of bearings and to achieve even longer rolling life.

[0006]

The bearing steel according to the present invention has a weight percentage of C: 0.10 to 0.35%, Si: 0.
50-2.00%, Mn: 0.30% or less, S: 0.0
10% or less, P: 0.015% or less, Cr: 0.50
2.50%, Al: 0.030% or less, V: 0.10
1.00%, O: 0.0010% or less, N: 0.001
˜0.010% and Mn + 10Al ≦ 0.50%, and if necessary, Ni: 0.50 to 3.00%, M
o: 1 or 2 of 0.10 to 0.50%, and, if necessary, Nb: 0.05 to 0.50%, T
i: One or two of 0.0010 to 0.0020%, the balance Fe and impurities.

Next, the reasons for limiting the chemical composition (% by weight) of the bearing steel according to the present invention will be described.

C: 0.10 to 0.35% C is an element useful for securing the hardness of the bearing and maintaining the strength of the core, and it is necessary to contain C by 0.10% by weight or more. However, if it is too large, huge carbides will be formed and the toughness will deteriorate, so it was made 0.35% by weight or less so as to be suitable for carburizing.

Si: 0.50 to 2.00% Si is solid solution strengthened to improve the toughness of the bearing, and
It is an element useful for increasing the temper softening resistance, and it is necessary to contain 0.50% or more, which is higher than that of the conventional SCr 420 steel, but if it is too much, the carburizing property decreases and Since the machinability and forgeability are deteriorated, the content is set to 2.00% or less.

Mn: 0.30% or less Mn is an element that acts as a deoxidizing agent and a desulfurizing agent during melting of steel, and contributes to the improvement of hardenability.
It is also desirable to contain an appropriate amount, but if the amount is too large, the rolling life characteristics of the bearing will deteriorate, so conventional SCr
It should be kept as low as 0.30% or less, which is less than 420 steel.

S: 0.010% or less If the S content is too large, MnS will be formed and the rolling life characteristics of the bearing will be deteriorated. Therefore, it is necessary to regulate the content to 0.010% or less.

P: 0.015% or less If the P content is too large, the toughness of the bearing will be deteriorated, so it is necessary to regulate the content to 0.015% or less.

Cr: 0.50 to 2.50% Cr is an element useful for ensuring the hardenability during carburizing and quenching, and the decrease in hardenability due to the low Mn content is suppressed by Cr. Since it is an element that is useful for ensuring by the inclusion of 0.50%, it is necessary to contain 0.50% or more, but if it is too much, cold workability and machinability deteriorate, so 2.50 It must be less than or equal to%.

Al: 0.030% or less Al is normally contained as a deoxidizing agent in an amount of about 0.100%. However, a large Al content is not preferable for improving rolling life characteristics. It was decided to regulate to a low amount of 0.030% or less.

V: 0.10 to 1.00% V is an element useful for improving the toughness of steel because it has the effect of refining crystal grains, and reduces the Al content. As a result, the grain refining action due to Al cannot be obtained. Therefore, by containing V, the grain refining action can be obtained, and at the same time, the temper softening resistance is increased. It was decided to contain 10% or more. However, even if the V content is increased, the effect is saturated, so the content was made 1.00% or less.

O: 0.0010% or less If the O content is too large, the cold workability is deteriorated, and the rolling life characteristics of the bearing are deteriorated due to the formation of oxide inclusions. It was decided to regulate to 0010% or less.

N: 0.001 to 0.010% N forms a nitride together with Al, V and the like to make the crystal grains finer and improve the toughness of the steel. It was decided to contain 001% or more. However, if the N content is large, the cold workability is deteriorated and the toughness is also deteriorated, so the content is made 0.010% or less.

Mn + 10Al ≦ 0.50% If the Mn and 10Al contents are too large, the rolling contact fatigue characteristics of the bearing deteriorate and the rolling life is shortened. Therefore, Mn (%) + 10Al (%) It should be 0.50% or less.

Ni: 0.50 to 3.00% Mo: 0.10 to 0.50% Ni and Mo are useful for improving the hardenability of steel and improving the toughness, and at the same time temper softening. Since it is useful for increasing the resistance and is effective for improving the life of the bearing, one or two of these may be added to Ni.
It is also preferable to contain 50% or more and 0.10% or more for Mo. However, if the Ni and Mo contents are too high,
Since the hardness decreases due to the increase in the retained austenite, the strength of the bearing deteriorates. Therefore, even if it is contained, Ni is 3.00% or less, Mo is contained.
Is preferably 0.50% or less.

Nb: 0.05 to 0.50% Ti: 0.0010 to 0.0020% Nb and Ti are elements useful for improving the toughness of steel by refining the crystal grains. , 1% or 2% of these as needed for Nb 0.05%
As described above, Ti may be contained in an amount of 0.0010% or more. However, if the Nb content is too large, the hardness is lowered and the strength of the bearing is deteriorated.
If the content is too large, hard nitride TiN is formed and the rolling life characteristic of the bearing is deteriorated. Therefore, even if it is contained, Nb is 0.50% or less and Ti is 0.0020.
It is better to be less than or equal to%.

Circle-equivalent diameter of inclusions in steel is 15 μm or less If there are inclusions in steel having equivalent-circle diameters of more than 15 μm, the rolling fatigue characteristics are deteriorated as a starting point of failure of the bearing. Therefore, it is desirable that the equivalent circle diameters of the inclusions in the steel are all 15 μm or less.

Particles of 10 μm or more are less than 2% of the whole. If inclusions of 10 μm or more are present in 2% or more of the total inclusions in the steel, the rolling fatigue characteristics of the bearing are deteriorated. It is desirable that the number of particles having a size of 10 μm or more is less than 2% of the total amount in the material.

[0023]

In the bearing steel according to the present invention, the S content is regulated to 0.010% or less and the O content is regulated to 0.0010% or less, but the S content and the O content are reduced. Results in a reduction in the amount of inclusions that reduce the rolling life.
In addition, in the bearing steel according to the present invention, in addition to such a reduction in the S content and the O content, the alloy components are further optimized.

That is, the Si content is changed from the conventional SCr 4
By making it more than 20 steel, the tempering softening resistance is given more, and the inclusion of V makes it possible to refine the crystal grains.

In addition, as a result of various studies on the influence of alloying elements, the Mn content was made smaller than that of the conventional SCr 420 steel and also the Al content was made smaller, and these Mn content and Al content were individually determined. Not only to reduce M
By regulating the total amount of the n content and the Al content of 10 times, the rolling fatigue characteristics are further improved.

Further, if necessary, Ni and Mo are added to improve the hardenability and further improve the toughness, so that the rolling life of the bearing can be further improved.

Similarly, by containing Nb and Ti as needed, the crystal grains can be made even finer, thereby contributing to a longer life of the bearing.

Furthermore, the equivalent circle diameter of inclusions in steel is all 1
Setting the particle size to 5 μm or less and the particle size of 10 μm or more to less than 2% of the entire particles also contributes to a longer life of the bearing.

[0029]

EXAMPLES Steel Nos. Of the present invention shown in Tables 1 to 3 1-12 and comparative steel No. Steel having a chemical composition of 13 to 15 was melted in a 50 kg vacuum induction melting furnace and then ingoted to obtain an ingot.

Then, each material is forged to have a diameter of 20 mm.
Then, a cylindrical test body with a diameter of 12 mm and a length of 22 mm was manufactured by machining, and 91
Carburize at 0 ° C for 3.5 hours, perform diffusion for 2 hours, and then
After furnace cooling to 830 ° C., oil cooling from 830 ° C., quenching, heating at 160 ° C. for 2 hours and then air cooling, tempering was performed, and then the surface layer of the test body was ground and removed by 0.05 mm.

Next, the surface hardness of each test piece, the maximum diameter of inclusions (circular equivalent diameter) in steel and the ratio of the number of particles of 10 μm or more were examined, and the results shown in Tables 4 to 6 were obtained.

For each test piece, a load stress of 600 k
Performed a rolling life test of gf / mm ² and accumulated damage rate 10%
(L ₁₀ ) and 50% value (L ₅₀ ) of
No. made from conventional SCr 420 When the rolling life index was evaluated using the value in 15 as a reference, the results are also shown in Tables 4 to 6.

As shown in Tables 4 to 6, bearing steel Nos. 1-No. In the bearing made of 12,
Conventional SCr 420 steel No. It was confirmed that the rolling life index was considerably improved and the rolling fatigue characteristics were excellent as compared with the bearing made of No. 15.

Then, bearing steel No. 1 according to the present invention. 1
~ No. The bearing made of No. 12 has a Mn and Al content comparable to or slightly lower than that of SCr 420 steel. Compared with the bearings made of 13 and 14, the Mn and Al contents and the total amount (Mn + 10Al) of these are regulated to be smaller, so that the rolling life index is further improved. It was confirmed that a bearing with excellent rolling fatigue characteristics could be provided.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

[Table 3]

[0038]

[Table 4]

[0039]

[Table 5]

[0040]

[Table 6]

[0041]

EFFECTS OF THE INVENTION According to the bearing steel of the present invention, the S content and the O content are regulated and the Si content is controlled as compared with the conventional SCr 420 steel used as the material for the carburized bearing.
Since the content is increased and the Mn content and the Al content are individually reduced and the total amount is also reduced, it is suitable as a material for a bearing having excellent rolling fatigue characteristics. In particular, a particularly excellent effect that the rolling life of the rolling bearing can be further improved is brought about.

Claims (5)

[Claims] 1. C: 0.10 to 0.35% by weight,
Si: 0.50 to 2.00%, Mn: 0.30% or less,
S: 0.010% or less, P: 0.015% or less, Cr:
0.50 to 2.50%, Al: 0.030% or less, V:
0.10 to 1.00%, O: 0.0010% or less, N:
0.001 to 0.010% and Mn + 10Al ≦ 0.
Bearing steel characterized by being composed of 50% and the balance being Fe and impurities. 2. C: 0.10 to 0.35% by weight,
Si: 0.50 to 2.00%, Mn: 0.30% or less,
S: 0.010% or less, P: 0.015% or less, Cr:
0.50 to 2.50%, Al: 0.030% or less, V:
0.10 to 1.00%, O: 0.0010% or less, N:
0.001 to 0.010% and Mn + 10Al ≦ 0.
50%, Ni: 0.50 to 3.00%, Mo:
One or two of 0.10 to 0.50%, balance F
A steel for bearings, characterized by comprising e and impurities. 3. C: 0.10 to 0.35% by weight,
Si: 0.50 to 2.00%, Mn: 0.30% or less,
S: 0.010% or less, P: 0.015% or less, Cr:
0.50 to 2.50%, Al: 0.030% or less, V:
0.10 to 1.00%, O: 0.0010% or less, N:
0.001 to 0.010% and Mn + 10Al ≦ 0.
50%, Nb: 0.05 to 0.50%, Ti:
One or two of 0.0010 to 0.0020%
A bearing steel comprising a seed, the balance Fe, and impurities. 4. C: 0.10 to 0.35% by weight,
Si: 0.50 to 2.00%, Mn: 0.30% or less,
S: 0.010% or less, P: 0.015% or less, Cr:
0.50 to 2.50%, Al: 0.030% or less, V:
0.10 to 1.00%, O: 0.0010% or less, N:
0.001 to 0.010% and Mn + 10Al ≦ 0.
50%, Ni: 0.50 to 3.00%, Mo:
One or two of 0.10 to 0.50%, Nb:
0.05-0.50%, Ti: 0.0010-0.00
A bearing steel comprising one or two of 20%, the balance being Fe and impurities. 5. The equivalent circle diameter of inclusions in steel is all 15 μm.
The steel for bearings according to any one of claims 1 to 4, wherein the content of particles is 10% or less and less than 2% of the whole particles.