WO2000028100A1

WO2000028100A1 - Bearing steel excellent in rolling fatigue life

Info

Publication number: WO2000028100A1
Application number: PCT/JP1999/005986
Authority: WO
Inventors: Takuya Atsumi; Toshiyuki Hoshino; Keniti Amano; Satoshi Yasumoto; Masao Gotoh
Original assignee: Kawasaki Steel Corporation; Koyo Seiko Co., Ltd.
Priority date: 1998-11-10
Filing date: 1999-10-28
Publication date: 2000-05-18
Also published as: JP2000144326A; CA2317658A1; EP1048744A1; KR20010033504A; KR100508463B1; EP1048744A4; TW454042B; JP3779078B2

Abstract

A bearing steel excellent in rolling fatigue life which can provide a bearing member used for a rolling bearing (roller bearing and ball bearing) element member and particularly excellent in rolling fatigue life, characterized by containing 0.95 to 1.10 mass% of C, over 1.60 to 3.50 mass% of Cr, up to 0.0015 mass% of O, up to 0.0010 mass% of Sb and the remaining components of Fe and unavoidable impurities, one or at least two components selected from a group consisting of up to 2.5 mass% of Si, up to 2.5 mass% of Mn, up to 2.5 mass% of Mo, up to 3.0 mass% of Ni, up to 1.5 mass% of Nb, up to 1.5 mass% of V, up to 2.0 mass% of Cu and up to 0.08 mass% of Al being permitted to be contained.

Description

The excellence of labor ^ Steel

The present invention relates to bearing steel used as an element member of a rolling bearing such as a roller bearing or a ball bearing. In particular, it is a bearing steel for providing bearing members with excellent rolling fatigue life. Background art

Bearing steel used for rolling bearings and the like is required to have a long rolling fatigue life. In general, it is well known that hard oxide nonmetallic inclusions present in steel have an adverse effect on the rolling contact fatigue life of bearings.

Therefore, in order to improve the rolling contact fatigue life by reducing the amount of nonmetallic inclusions, efforts have been made mainly to reduce the oxygen content in steel in the past. Advances in steelmaking technology have made it possible to reduce the oxygen content of steel to 0.0010 mass or less in steels containing Si or A1 as a deoxidizing agent. As a result, the amount of hard oxide-based nonmetallic inclusions present in the steel was significantly reduced, and the rolling fatigue life was improved.

However, the improvement in rolling fatigue life due to such low oxygen has already reached its limit.

However, recently, there has been a movement to further improve the rolling fatigue life. For example, JP-A-3-126839 discloses a method of adjusting the number of oxide-based nonmetallic inclusions in a unit area or a unit volume, that is, a method of adjusting their distribution. Also, in JP-A-5-25587, extreme value statistics A method of adjusting the predicted maximum diameter of oxide-based nonmetallic inclusions estimated by the above, that is, a method of adjusting these forms is disclosed. In each case, the distribution or form other than the amount of the oxide-based nonmetallic inclusions is adjusted to reduce the influence of the oxide-based nonmetallic inclusions.

However, in order to further reduce the number and the maximum diameter of the oxide-based nonmetallic inclusions per unit area in accordance with the above-mentioned known technology, it is necessary to further improve steelmaking equipment or remodel the manufacturing process. Therefore, in order to achieve these, a huge investment is required, which inevitably leads to an increase in manufacturing costs. In addition, in order to guarantee the rolling fatigue life, a detailed evaluation of non-metallic inclusions is required, and a reduction in productivity is inevitable.

On the other hand, techniques for improving the rolling fatigue life by reducing impurities are disclosed in JP-A-10-68047, JP-A-10-158790, JP-A-10-168547 and the like. Also, a method for controlling sulfide-based nonmetallic inclusions, which are hard nonmetallic inclusions other than oxides, is disclosed in Japanese Patent Application Laid-Open No. 9-291340 (PCT / JP97 / 00549). In both cases, the aim is to reduce substances that can cause fatigue fracture. However, in each case, steel containing Si or A1 as a deoxidizing agent is targeted, and the formation of Si or A1 oxide is inevitable, and the rolling fatigue life varies, and its improvement is limited. Was.

Therefore, a main object of the present invention is to provide a bearing steel that can be manufactured only by adjusting the component composition, is advantageous in terms of productivity, and has an excellent rolling fatigue life. Disclosure of the invention

The present invention has been made to achieve the above in view of the above-mentioned objects. Most According to recent steelmaking technology, even when Si and A1 are not added as deoxidizers, when C is included at about 1 mass%, O can be reduced to about 0.0010 mass%. In addition, the improvement of hardenability and the improvement of rolling fatigue life by adding Si or A1 can be replaced by adding a large amount of Cr. Therefore, the inventors examined the effect of impurity elements using a material containing about lmass% of C, not containing Si and A1, reducing ◦ to about lOppm, and using a material containing a large amount of Cr. As a result, they found that the presence of Sb as an impurity element in steel had an adverse effect on rolling fatigue life.

C: 0.998-1.05 mass%, Cr: 1.65-3.45 mass%, Ο: 0.0008-0.0012 mass ⁰ Sb: 0.000 1-0. 0100 mass% Then, the rolling fatigue life of the sample substantially consisting of Fe was examined. The number of oxide-based nonmetallic inclusions was 100 to 200 / ^ SOmm, and the maximum diameter was 8 to 12 / zm when the test area was 320 mm. Figure 1 shows the effect of Sb content in steel on rolling fatigue life. When the Sb content in steel was reduced to less than 0.0015 mass%, the rolling fatigue life was improved. This improvement effect was saturated at about 0.10010 mass ° / _o . The reason for such a phenomenon is not always clear, but if the amount of Sb in steel exceeds a certain limit, excess Sb segregates at the grain boundaries, promoting the growth of fatigue cracks and accelerating fracture. It is considered to be.

The gist configuration of the present invention developed based on the above knowledge is as follows.

C: 0.95 to 1.10 mass%, Cr: more than 1.60 to 3.5 mass%, O: less than 0.0015 mass% and Sb: less than 0.0010 mass%, balance Fe and unavoidable impurities It is a bearing steel excellent in rolling fatigue life characterized by comprising: In addition, Si: 2.5 mass% or less, Mn: 2.5 mass% or less, Mo: 2.5 mass% or less, i: 3.0 mass% or less, Nb: 1.5 mass% or less, V: One or two selected from 1.5 mass% or less, Cu: 2. mass% or less and A1: 0.08 mass% or less More than one species may be included.

The reasons for limiting the components in the present invention are shown below.

C: 0.95 to 1.10raass%

C is an element that forms a solid solution in the matrix and effectively acts to strengthen martensite. It is included to secure the strength after quenching and tempering and to improve the rolling fatigue life due to it. If the content is less than 0.95 mass ° / o, these effects cannot be obtained. On the other hand, if the C content exceeds 1.10raass%, giant carbides will be generated during fabrication, reducing workability and rolling fatigue life. Therefore, the range is 0.95 to 1.10 mass%.

Cr: 1.60 ~ 3.50mass%

Cr is useful for stabilizing carbides and improving wear resistance by leaving carbides after quenching. In addition to improving the hardenability, the cold workability is improved by promoting the spheroidized structure. These effects cannot be obtained if the Cr content is 1.60 mass% or less. 3. If more than 50 mass% is added, the amount of carbide remaining by quenching increases. As a result, the amount of C dissolved in the matrix decreases, and the strength and, consequently, the rolling fatigue life decrease. Therefore, the Cr content is set to be more than 1.60 to 3.50 raass%, preferably more than 1.60 to 2.50 mass%. O: 0.0015 mass% or less

O is desirably low because it forms hard oxide-based nonmetallic inclusions and reduces the rolling fatigue life, but is allowable up to 0.0015 mass ° / o. Therefore, the O content is 0.0015 mass% or less, and preferably 0.0010 mass% or less. Sb: 0.0001 mass% or less

Sb is a particularly important element in the present invention. This is preferable in that it has the effect of suppressing the formation of a decarburized layer and improving the heat treatment productivity. However, it reduces the hot workability and toughness and significantly reduces the rolling fatigue life. Therefore, Sb The amount must be limited to 0.000010 mass% or less. Further, one or more of the following elements can be contained.

Si: 2.5 mass% or less

Si is an element that increases tempering softening resistance. As a result, the strength after quenching and tempering is increased, and the rolling fatigue life is improved. It is also an element that contributes to the reduction of oxygen in steel as a deoxidizing agent during smelting. However, if added in excess of 2.5 mass%, workability and toughness decrease. For this reason, Si is added at 2.5 ma ss% or less. Preferably, it is added in the range of 0.15 to 2.0 mass%. Mn: 2.5 mass% or less

Mn is an element that improves the hardenability of steel. As a result, the toughness and strength of the base martensite are improved, and the rolling fatigue life is improved. However, when added in excess of 2.5 mass%, machinability and toughness decrease. For this reason, Mn is added at 2.5 mass% or less. Preferably, it is added in the range of 0.10 to 2.0 mass%.

Mo: 2.5 mass% or less

Mo is an element that improves hardenability. As a result, the strength is improved and the rolling fatigue life is improved. However, adding more than 2.5 mass% stabilizes the carbides. As a result, the strength is reduced and the rolling fatigue life is reduced. Mo is also an expensive element. Therefore, Mo is added at 2.5 mass% or less. Preferably, it is added in the range of 0.10 to 1.5 mass%.

Ni: 3.0 mass% or less

Ni is an element that improves hardenability. As a result, the strength is improved and the rolling fatigue life is improved. However, the effect of adding over 3.0 mass% Saturated. Ni is also an expensive element. Therefore, Ni is added in an amount of not more than 3.0 mass% in consideration of the obtained effect and cost. Preferably, it is added in the range of 0.1 to 2.0 mass%.

Nb: 1.5 mass% or less

Nb is an element that improves hardenability. As a result, the strength is improved and the rolling fatigue life is improved. However, if added in excess of 1.5 mass%, the carbohydrate is stabilized. As a result, the strength is reduced and the rolling fatigue life is reduced. Nb is also an expensive element. Therefore, Nb is added at 1.5 mass% or less. Preferably, it is added in the range of 0.05 to 1.0 mass%.

V: 1.5 mass% or less,

V is an element that improves hardenability. As a result, the strength is improved and the rolling fatigue life is improved. However, if added in excess of 1.5 mass%, the carbohydrate is stabilized. As a result, the strength is reduced and the rolling fatigue life is reduced. V is also an expensive element. Therefore, V is added at 1.5 mass% or less. Preferably, it is added in the range of 0.05 to 1.0 mass%.

Cu: 2.0 mass% or less

Cu is an element that improves hardenability. As a result, the strength is improved and the rolling fatigue life is improved. However, if added in excess of 2.0 raass%, the forgeability decreases. Therefore, Cu is added at 2.0 mass% or less. Preferably, it is added in the range of 0.10 to 1.5 mass%.

A1: 0.08 mass ° / o or less

A1 is an element that increases tempering softening resistance. As a result, the strength after quenching and tempering is increased, and the rolling life is improved. It is also an element that contributes to the reduction of oxygen in steel as a deoxidizer during smelting. On the other hand, if added in excess of 0.08 mass ° / _o , workability and toughness are reduced. Therefore, A1 is 0.08mass% Add below. Preferably, it is added in the range of 0.005 to 0.05 mass%. Although the present invention is constituted by each of the above elements, as a more preferred embodiment, it is desirable that P, S, Ti and N as the impurity elements be suppressed to the following ranges.

P: 0.025 mass% or less

P decreases the toughness and rolling fatigue life of steel. Therefore, it is desirable to be as low as possible. The allowable upper limit is 0.025 mass%, preferably 0.015 mass%.

S: 0.025 mass% or less

S combines with Mn to form MnS and improves machinability. However, when contained in a large amount, the rolling fatigue life is reduced. The allowable upper limit is 0.025 mass%, preferably 0.010 mass%.

Ti: 0.010 mass% or less

Ti forms hard nitrides and reduces the rolling fatigue life. Therefore, it is desirable to be as low as possible. The allowable upper limit is 0.001 raass%, preferably 0.005 raass%.

N: 0.015 mass% or less

N forms hard nitrides and reduces the rolling fatigue life. Therefore, it is desirable to be as low as possible. The allowable upper limit is 0.015 mass%, preferably 0.008 raass%. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a graph showing the effect of the amount of Sb on the B10 life. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, examples of the present invention will be described. The embodiment of the present invention is not limited to this embodiment.

Steels having the chemical compositions shown in Tables 1 and 2 were melted in a converter, and then made into 400 X 560 orchids bloom by continuous casting. The bloom was subjected to diffusion annealing at 1200 ° C. for 30 hours, and then hot rolled to obtain a steel bar having a diameter of 65 mm. The steel bar is subjected to normalizing at 860 ° C, spheroidizing annealing at 760 to 800 ° C, further holding at 830 ° C for 30 minutes, oil quenching, and tempering at 180 ° C for 2 hours. gave. The tempered material was cut and rubbed to obtain 12 disk-type rolling fatigue life test specimens of 60πιπιφX 5mm for each steel.

The rolling fatigue test was carried out using a forest-type thrust rolling fatigue tester under the following conditions: Hertz maximum contact stress: 5260 MPa, cyclic stress number: 30 Hz, and lubricating oil: # 68 turbine oil. The test results were summarized on a probability paper according to the Weibull distribution, and the B10 life (cumulative failure probability: the total number of loads until peeling occurred at 10%) was determined. The life ratio of steel 1 (JIS steel type: SUJ2), which is a conventional steel, was evaluated by a relative ratio when the life was set to 1.

The evaluation results are shown in Tables 1 and 2. As clearly shown in Tables 1 and 2, the invention steels of steel 2 and steels 6 to 25 have a B10 life ratio 1.7 to 5.6 times that of the conventional steel (steel 1). It has an excellent value.

On the other hand, the steel 4 as the comparative steel has C and the steel 5 has O, which is out of the range of the present invention, and the B10 life ratio is inferior to the conventional steel. In addition, steel 3 as the comparative steel does not differ much from steel 2 as the invention steel except for the chemical composition of Sb. Nevertheless, the B10 life ratio of steel 3 is 1.1, which is inferior to 3.2 of steel 2. Clearly, the effect of reducing the amount of Sb is apparent. Chemical composition of test material (mass%) B,. Life ratio

No equipment

Si n S Cr Mo Nb Ni Cu Al Ti Sb N O (Steel No. 1: 1)

0.99 0.21 0.46 0.015 0.005 1.34 0.021 0.003 0.0030 0.0052 0.0009 1.0

01 0.010 0.003 2.46 0.002 0.0008 0.0040 0.0007 3.2 Issue 00 0.015 0.004 2.43 0.004 0.0028 0.0042 0.0009 Ratio

0.40 0.015 0.005 2.20 0.005 0.0008 0.0042 0.0011 0.8 Ratio

1.02 0.013 0.008 2.21 0.005 0.0009 0.0055 0.0024 0.6 Ratio

1.02 0.012 0.004, 68 0.003 0.0008 0.0044 0.0010 1.7

1.02 1.75 0.014 0.003 2.00 0.003 0.0008 0.0041 0.0008 4.6

1.06 1.87 0.009 0.004 2.04 0.004 0.0007 0.0037 0.0007 3.9

1.04 0.010 0.004 1.99 1.24 0.005 0.0007 0.0048 0.0009 4.6

10 1.03 0.010 0.003 1.96 0.83 0.003 0.0008 0.0038 0.0007 3.9

11 1.03 0.008 0.003 1.97 0.79 0.004 0.0008 0.0043 0.0008 3.2

12 1.00 0.013 0.008 2.02 1.96 0.003 0.0008 0.0041 0.0006 5.5

13 1.02 0.012 0.005 2.01 1.32 0.003 0.0007 0.0041 0.0008 4.6

14 1.00 0.011 0.004 2.01 0.047 0.002 0.0006 0.0036 0.0004 4.2

15 0.99 0.23 0.42 0.009 0.005 1.97 0.023 0.002 0.0008 0.0038 0.0006

Table 2

B _{1 ()} Life ratio

vm c Si Mn P S Cr Mo V Nb Ni Cu Al Ti Sb N O (Steel No.1: 1.)

16 0.98 0.79 0.11 0.008 0.004 1.96 0.023 0.005 0.0008 0.0038 0.0006 3.4 Invention

17 1.03 0.12 1.44 0.Oil 0.003 1.96 0.025 0.002 0.0009 0.0042 0.0007 3.6 Invention

18 0.99 1.01 1.03 0.010 0.003 1.98 0.021 0.003 0.0007 0.0041 0.0008 3.9 Invention

19 1.05 1.02 0.47 0.010 0.004 2.01 0.47 0.022 0.002 0.0009 0.0038 0.0007 4.5 Invention

20 1.07 0.27 0.42 0.008 0.005 1.76 0.26 0.31 0.022 0.004 0.0007 0.0039 0.0007 4.4 Invention

21 1.01 0.27 0.48 0.012 0.002 1.79 0.25 0.028 0.002 0.0006 0.0040 0.0005 3.7 Invention

22 0.99 0.25 0.42 0.012 0.003 1.85 0.88 0.48 0.023 0.003 0.0007 0.0039 0.0006 4.2 Invention

23 1.00 0.26 0.38 0.010 0.005 1.82 0.49 0.79 0.37 0.025 0.004 0.0009 0.0042 0.0008 5.4 Invention

24 1.04 0.26 0.86 0.Oil 0.004 1.77 0.25 0.76 0.41 0.021 0.004 0.0007 0.0042 0.0007 4.3 Invention

25 0.97 0.24 0.42 0.009 0.005 1.64 0.43 0.21 0.18 0.51 0.28 0.024 0.004 0.0007 0.0038 0.0009 5.6 Invention

Industrial applicability

According to the present invention, a bearing steel having significantly superior rolling fatigue life can be obtained only by adjusting the composition by adding a large amount of Cr and suppressing the amount of Sb in the steel to 0.0010 mass% or less. be able to. Limiting the amount of Sb can be easily achieved by managing scrap, which is favorable in terms of productivity and greatly contributes to the industry.

Claims

The scope of the claims

1. C: 0.95-1.10mass%,

Cr: over 1.60 ~ 3.50mass%,

O: 0.0015 mass% or less and

Sb: 0.0010mass% or less

A bearing steel with excellent rolling fatigue life, characterized by containing Fe and the balance consisting of Fe and unavoidable impurities.

2. C: 0.95-1.10mass%,

Cr: over 1.60 ~ 3.50mass%,

O: 0.0015 mass% or less and

Sb: 0.0010mass% or less

And further

Si: 2.5 mass% or less,

Mn: 1.5 mass% or less,

Mo: 2.5 raass% or less,

Ni: 3.0 raass% or less,

Nb: 1.5 mass ° /. Less than,

V: 1.5 mass ⁰ /. Less than,

Cu: 2.0 mass% or less and

A1: 0.08mass% or less

Bearing steel with excellent rolling fatigue life, characterized by containing one or more selected from the group consisting of Fe and unavoidable impurities.