JP3233726B2 - Bearing steel with excellent heat treatment productivity and delayed microstructural change due to repeated stress loading - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bearing steel used as an element of a rolling bearing such as a roller bearing or a ball bearing. We propose a bearing steel that is excellent in delay characteristics against microstructural change (deterioration) occurring under the dynamic contact surface and also has an effect of suppressing the formation of a decarburized layer that occurs during heat treatment.

[0002]

2. Description of the Related Art Rolling bearings used in automobiles, industrial machines, and the like are conventionally known as high carbon chromium bearing steel (JI).
S: SUJ 2) is used the most. In general, bearing steel is one of the important properties to have a long rolling fatigue life, but it is considered that the factor affecting the rolling fatigue life is the largest effect of nonmetallic inclusions in steel. I was
Therefore, the mainstream of recent research has been to improve the bearing life by controlling the amount and size of nonmetallic inclusions by reducing the amount of oxygen in steel. For example, Japanese Unexamined Patent Publication Nos. Hei. 1-306542 and Hei. 3-1268 disclose developments aimed at further improving the rolling fatigue life of bearings.
There are proposals such as Japanese Patent Publication No. 39, which are techniques for controlling the composition, shape or distribution of oxide-based nonmetallic inclusions in steel. However, in order to produce bearing steel with a small amount of nonmetallic inclusions, it is necessary to install expensive smelting equipment or to significantly improve conventional equipment, resulting in a large economic burden.

Another move to improve the characteristics of the high-carbon bearing steel (JIS-SUJ2) is a study of workability, particularly suppression of the formation of a decarburized layer during heat treatment. Generally, the bearing steel specified in JIS-SUJ2 above is 0.95-1.
Since it contains 10wt% of C, it is very hard. Therefore, it is subjected to spheroidizing annealing to improve workability, and then molded, then quenched and tempered to provide a rolling bearing. The required strength and toughness were obtained. However, when such heat treatment for improving the characteristics is repeated many times, it is known that a "low C concentration region" called a decarburized layer is generated on the surface of the material due to a reaction between C and the atmospheric gas. I have. This decarburized layer is not only reduced in hardness of the rolling bearing but also causes deterioration in rolling contact fatigue life. Therefore, the decarburized layer is usually removed by cutting or grinding. As a result, the material yield and the productivity had to be reduced. On the other hand, conventionally, as means for preventing the formation of the decarburized layer, a method of controlling the carbon potential in the atmosphere gas in the furnace during the heat treatment and a method disclosed in JP-A-2-54717, A method of performing a carburizing treatment at an early stage of annealing has been proposed. However, since each of the above methods is based on cleaning the atmosphere during heat treatment or pre-treatment, not only does the heat treatment cost increase, but also setting of an appropriate gas composition according to the material composition, heat treatment time, and the like. There is a problem where such complicated operations are required.

[0004]

The present inventors have recently conducted various studies on the above-mentioned prior art. as a result,
Surprisingly, the factors that determine the rolling life are the above-described phenomena that have been generally discussed in the past; that is, the existence of the above-mentioned “non-metallic inclusions” and the “decarburized layer” (low C concentration region) generated during heat treatment. ) Was found to be due to factors other than generation. The reason is that simply reducing the amount of nonmetallic inclusions and decarburized layers under the conventional technology does not improve the rolling contact fatigue life of the bearing, especially under the severe conditions such as high load or high temperature. Has experienced many cases where significant effects cannot be obtained. From this,
He was convinced that there were other factors that govern the bearing life.

Therefore, the present inventors have investigated the bearing life in consideration of the recent bearing operating environment, particularly the cause of peeling of the rolling bearing. As a result, the shear stress generated during the contact rolling between the inner and outer races of the bearing, the rolling elements, and the rolling elements in accordance with the intensified use environment of the bearings causes the lower layer (surface layer) of the rolling contact surface to be formed as shown in FIG. As shown in (a), it was found that a microstructure-change layer composed of a band-like white product and a rod-like precipitate was generated. This microstructure-changed layer gradually grows as the number of rollings increases, and finally, from this microstructure-changed portion, fatigue delamination as shown in FIG. all right. In addition, the harsh operating environment of the bearing, that is, high surface pressure (miniaturization) and increase in operating temperature, shorten the number of rollings before these microstructure changes occur, leading to a significant reduction in bearing life. Ascertained. In other words, the life of the bearing due to the harsh operating environment is not sufficient just by controlling the decarburized layer and nonmetallic inclusions as in the conventional technology.For example, simply reducing the nonmetallic inclusions is not sufficient. ,
It is not possible to delay the time until the microstructure change occurring under the rolling contact surface described above occurs. As a result, they found that the bearing life could not be further improved.

Accordingly, an object of the present invention is to delay the microstructure change expected to occur during the use of a bearing under severe operating conditions, and thereby to significantly improve the life of the bearing, and at the same time to reduce the time required for heat treatment. An object of the present invention is to provide a bearing steel capable of improving heat treatment productivity (reducing machining removal) by suppressing the formation of a decarburized layer.

[0007]

The inventors of the present invention have focused on a new "microstructure change delay characteristic" as a bearing life based on the above-mentioned knowledge, and it is natural to aim for improvement of the characteristic. It is recognized that a new alloy design (composition composition) is necessary, and further improvement in bearing life cannot be achieved without realizing this. In addition, various alloys that suppress formation of a decarburized layer are realized. Experiments and examinations were conducted. As a result, surprisingly, if a proper amount of Mo and Sb are added in combination, the above-mentioned microstructure change generated below the rolling contact surface due to repeated stress loading can be significantly delayed, and furthermore, the occurrence of a decarburized layer during heat treatment The inventors have found that the bearing steel can be suppressed, and have developed the bearing steel of the present invention.

That is, the bearing steel of the present invention requires the following
That is, it has a configuration to the effect. (1) C: 0.5 to 1.5 wt%, Mo: more than 0.5 to 2.0 wt%, Al: 0.005
0.00.07 wt%, Sb: 0.001 to less than 0.005 wt% and O: 0.002
0wt% or less, the balance being Fe and unavoidable impurities
Depending on heat treatment productivity and repeated stress loading
Bearing steel with excellent microstructure change delay characteristics (first
Akira). (2) C: 0.5 to 1.5 wt%, Mo:1.0Super-2.0wt%, Al: 0.005
~ 0.07wt%, Sb: 0.001 ~ less than 0.005wt% and O: 0.00
20% by weight or less, Si: 0.05 to 0.5% by weight, Mn:
0.05 ~ 2.0wt%, Cr: 0.05 ~ 2.5wt%, Ni: 0.05 ~ 1.0wt%,
Cu: 0.05-1.0 wt%, B: 0.0005-0.01 wt%, and N: 0.
0005 ~ 0.012wt% Any one selected from
Contains two or more, the balance being Fe and inevitable impurities
Heat treatment productivity and repetitive stress loading
Bearing steel excellent in the delay characteristic of black structure change (second invention). (3) C: 0.5 to 1.5 wt%, Mo: more than 0.5 to 2.0 wt%, Al: 0.005 to
0.07 wt%, Sb: 0.001 to less than 0.005 wt% and O: 0.0020 w
t: up to 2.5 wt%, Cr: 2.5 wt%
More than 8.0wt%, Ni: more than 1.0 to 3.0wt%, N: more than 0.012 to 0.050w
t%, V: 0.05-1.0 wt%, Nb: 0.05-1.0 wt%, W: 0.05-
1.0 wt%, Zr: 0.02 to 0.5 wt%, Ta: 0.02 to 0.5 wt%, Hf: 0.
02-0.5wt% and Co: selected from 0.05-1.5wt%
One or more of them, the balance being Fe and
Heat treatment productivity and repetition consisting of unavoidable impurities
Bearings with excellent microstructure change delay characteristics due to stress load
Steel (third invention). (4) C: 0.5 to 1.5 wt%, Mo:1.0Super ~ 2.0wt%, Al: 0.005 ~
0.07 wt%, Sb: 0.001 to less than 0.005 wt% and O: 0.0020 w
t% or less,Ingredients of the following (Group I)Inside
Including one or more selected from the group consisting of:
Also,Ingredients of the following group (II) (however,
Excluding elements that are present)Any one selected from
Contains two or more, the balance being Fe and inevitable impurities
Heat treatment productivity and repetitive stress loading
A bearing steel having an excellent property of delaying the change in the microstructure (the fourth invention).Record (Group I)  Si: 0.05 to 0.5 wt%, Mn: 0.05 to 2.0 wt%, Cr: 0.05 to 2.5 w
t%, Ni: 0.05 to 1.0 wt%, Cu: 0.05 to 1.0 wt%, B: 0.0005
~ 0.01wt%, and N: 0.0005 ~ 0.012wt%(Group II) S i: more than 0.5 to 2.5 wt%, Cr: more than 2.5 to 8.0 wt%, Ni: more than 1.0
3.0 wt%, N: more than 0.012 to 0.050 wt%, V: 0.05 to 1.0 wt%,
Nb: 0.05-1.0 wt%, W: 0.05-1.0 wt%, Zr: 0.02-0.5 w
t%, Ta: 0.02-0.5 wt%, Hf: 0.02-0.5 wt% and Co:
0.05-1.5wt%

[0009]

The background that led to the bearing steel of the present invention having the above alloy design will be described below based on the results of experiments conducted by the present inventors. First, in the experiment, SUJ 2 (C: 1.02 wt%, Si: 0.25 wt%, Mn: 0.45 wt%
%, Cr: 1.35wt%, Ni: 0.0040wt%, O: 0.0012wt%)
And two kinds of materials to which Mo, Sb and Al are added (C: 1.00 wt%, Si: 0.23 wt%, Mn: 0.46 wt%, C
r: 1.33wt%, O: 0.0009wt%, Mo: 0.75wt%, Sb: 0.0
015wt%, Al: 0.018wt%, N: 0.0042wt%) (C: 1.00wt%, Si: 0.20wt%, Mn: 0.43wt%, C
r: 1.30 wt%, O: 0.0008 wt%, Mo: 1.28 wt%, Sb: 0.0
040 wt%, Al: 0.047 wt%, N: 0.0032 wt%). Next, after normalizing these test materials, spheroidizing normalizing, and performing each treatment of quenching and tempering, a cylindrical test piece of 15 mm φ × 22 mm and a 12 mm φ × 22 mm A test piece for a rolling fatigue test was prepared.

In the rolling fatigue life test, the above-mentioned rolling fatigue test piece was tested using a radial type rolling fatigue life tester. The maximum contact stress in Hertz was 600 kgf / mm ² and the number of repetitive stresses.
Tested under 46500 cpm load conditions. The results of the tests are plotted on a Weibull distribution establishment paper, by repeated stress load at B ₁₀ seen a numerical value indicating the improvement in rolling fatigue life due to an increase in the material strength (10% cumulative failure probability) a high load rolling B ₅₀ (50) which is considered to be a numerical value indicating an improvement in rolling fatigue life by delaying the occurrence of microstructure change.
% Cumulative failure probability). In addition, for the test of the decarburized layer, after cutting the above cylindrical test piece vertically at the position of 10 mm in the height direction, corroded with nital, the maximum value of all decarburized layers on the circumference due to microstructure change ( Hereinafter, it is referred to as “maximum decarburized layer”.

The results are shown in Table 1. As it can be seen from the results shown in Table 1, for the high Mo additives, wherein at not so large improvement for the B ₁₀ value, B ₅₀ value exhibited significantly higher numbers for bearing life expectancy compared to SUJ 2 about 1.4 to 1.8-fold in B ₁₀ value each, to exhibit improved by about 15.0 to 23.4 times B ₅₀ values were observed. In particular, the addition of a large amount of Mo has a remarkable effect on the delay characteristics of microstructure change generated during high-load rolling, and can be expected to delay the breakage (life) by that much. Regarding the maximum decarburized layer, SUJ
2 was 0.10mm, Al: 0.018wt%, Sb: 0.0015wt
%: 0.03mm, Al: 0.047 wt%, Sb: 0.0040wt
%, Which was 0.01 mm, it was found that the appropriate Sb content was effective in suppressing the generation of decarburized layers.

[0012]

[Table 1]

FIG. 2 summarizes the experimental results of the above-mentioned bearing rolling fatigue life, and shows the relationship between the bearing life caused by non-metallic inclusions and the life change caused by microstructural change. It is a schematic diagram. As is evident in this figure, the bearing life represented by the cumulative failure probability of 10% B ₁₀ value (hereinafter referred to as "B ₁₀ rolling contact fatigue life") is simply not improved by merely adding a large amount of Mo but, looking at the B ₅₀ value, this
The effect of adding a large amount of Mo is extremely remarkable. Therefore, based on such knowledge, the inventors have calculated the cumulative damage probability
Bearing life indicated by 50% B ₅₀ value (hereinafter referred to as “B ₅₀
In order to improve the “high-load rolling fatigue life” and to suppress the growth of the decarburized layer during heat treatment, from the viewpoint of what kind of alloy design is effective, Range was determined.

C: 0.5-1.5 wt% C is an element which forms a solid solution in the matrix and effectively acts to strengthen martensite. In order to secure strength after quenching and tempering and to improve the rolling fatigue life. To be contained. If the content is less than 0.5 wt%, such effects cannot be obtained. On the other hand, if the content exceeds 1.5 wt%, machinability and forgeability deteriorate, so the content is limited to the range of 0.5 to 1.5 wt%.

Si: 0.05-0.5 wt%, more than 0.5-2.5 wt% or less Si is used as a deoxidizing agent in steel smelting, and is also dissolved in a matrix and tempered by an increase in tempering softening resistance. It is effective as an element for increasing the strength after tempering and improving the rolling fatigue life. The content of Si added for such a purpose is in the range of 0.05 to 0.5 wt%. In addition, this Si
Addition of more than 0.5 wt% has an effect of delaying microstructure change under repeated stress load and improving rolling fatigue life. However, if the content exceeds 2.5 wt%, the effect is saturated and the workability and toughness are reduced. Therefore, in order to further improve the microstructure change delay characteristics, it is necessary to use more than 0.5 to 2.5 wt%. Is effective.

Mn: 0.05-2.0 wt% Mn is an element that acts as a deoxidizing agent during melting of steel and is effective in reducing oxygen in steel. In addition, by improving the hardenability of steel, the toughness and hardness of the base martensite are improved, which effectively works to improve the rolling fatigue life. For this purpose, Mn is added in the range of 0.05 to 2.0 wt%.

Cr: 0.05-2.5 wt%, more than 2.5-8.0 wt% Cr is formed by improving hardenability and forming stable carbides.
It is a component that improves strength and abrasion resistance, and thereby improves rolling fatigue life. To obtain this effect, the addition of 0.05 to 2.5 wt% is sufficient. Further, when this Cr is added in a large amount exceeding 2.5 wt%, it is effective to delay the microstructural change due to the repeated stress load and to improve the rolling fatigue life on this surface. The effect of the addition of Cr for this purpose not only saturates when the content exceeds 8.0 wt%, but also causes a decrease in the amount of solid solution C during quenching, resulting in a decrease in strength. Therefore, when added for this purpose, it must be more than 2.5 to 8.0 wt%.

Mo: more than 0.5 (more than 1.0) to 2.0 wt% Mo is an element which basically improves the wear resistance by stabilizing the residual carbide. Moreover, this Mo is particularly 0.5 wt% greater than in the present invention, or when performing a large amount of addition of 1.0 wt% greater than the effect of delaying the microstructure changes during rolling becomes remarkably, B ₅₀ rolling in this area Significantly improves fatigue life. However, if the amount exceeds 2.0 wt%, the machinability and forgeability are reduced, and the cost is increased. For this purpose, more than 0.5 or more than 1.0 to 2.0 wt %
% Need to be added.

Ni: 0.05-1.0 wt%, more than 1.0-3.0 wt% Ni increases the hardenability, increases the strength after quenching and tempering, improves the toughness, and improves the rolling fatigue life. Is added in the range of 0.05 to 1.0 wt%. Furthermore, when this Ni is added in excess of 1.0 wt%, the microstructure change during rolling is delayed, thereby improving the rolling fatigue life. However, even in this case, if it is added in excess of 3 wt%, a large amount of residual γ is precipitated, which lowers strength and impairs dimensional stability.
If this effect is expected, it is necessary to add in a range of more than 1.0 to 3.0 wt% because the cost is increased.

Cu: 0.05 to 1.0 wt% Cu is added to increase the strength after quenching and tempering by increasing the quenching and to improve the rolling fatigue life. When Cu is added for this purpose, it should be in the range of 0.05-1.0 wt%.

Sb: 0.001 to less than 0.005 wt% Sb is an element which plays an important role together with Al in the present invention. In particular, Sb contributes to an improvement in heat treatment productivity by suppressing the reaction between C in the surface layer of the steel material and the atmosphere gas to prevent the formation of a decarburized layer during the heat treatment. In addition, the addition of Al in combination with the suppression of the decarburized layer also has an effect on the delay of the change in microstructure, so that it is added positively. These two effects become remarkable when the Sb content is 0.001 wt% or more. However, even when 0.005 wt% or more is added, the effect is saturated, and in addition, hot workability and toughness are rather increased. Is caused to deteriorate. Therefore, Sb is contained in the range of 0.001 to less than 0.005 wt%.

B: 0.0005 to 0.01 wt% B is added in an amount of 0.0005 wt% or more because B increases the strength after quenching and tempering due to the increase in hardenability and improves the rolling fatigue life. However, if added in excess of 0.01 wt%, the workability is degraded, so the range is limited to 0.0005 to 0.01 wt%.

Al: 0.005 to 0.07 wt% Al is used as a deoxidizing agent at the time of melting steel,
It combines with N in the steel to refine the crystal grains and contribute to improving the toughness of the steel. In addition, it effectively acts to improve the rolling fatigue life by increasing the strength after quenching and tempering. For such an effect, it is effective to add 0.005 to 0.07 wt% of Al.

N: 0.0005 to 0.012 wt%, more than 0.012 to 0.05
wt% N combines with the nitride-forming element to refine the crystal grains, and dissolves in the matrix to increase the strength after quenching and tempering.
Improves rolling fatigue life. 0.0005 for this purpose
It is added within the range of ~ 0.012 wt%. This N is 0.
When added in excess of 012 wt%, rolling fatigue life is improved by delaying microstructural changes due to repeated stress. However, if the amount exceeds 0.05 wt%, the workability is reduced, and for this purpose, it exceeds 0.012 to 0.
Add 05 wt%.

P ≦ 0.025 wt% P is desirably as low as possible from the viewpoint of lowering the toughness and rolling fatigue life of steel.
0.025 wt%.

S ≦ 0.025 wt% S combines with Mn to form MnS and improves machinability. However, if contained in a large amount, the rolling fatigue life is reduced, so the upper limit must be 0.025 wt%.

O: 0.0020 wt% or less O forms hard non-metallic inclusions, so even if the control of other components delays the microstructure change due to repeated stress loading, the rolling fatigue life Therefore, it is desirable to be as low as possible. However, a content of 0.0020 wt% or less is acceptable.

As described above, the component for improving the rolling fatigue life by delaying the microstructure change due to the repeated stress load, the component for improving the rolling fatigue life by increasing the strength, and the formation of the decarburized layer to suppress the bearing The reason for limiting the components for improving the processability and productivity of the above has been described. Incidentally, in the present invention, V, Nb, W, Zr, T
One, two or more selected from a, Hf and Co may be added to further improve the bearing life. Table 2 summarizes the preferable addition ranges of the above elements, the purpose of the addition, and the reasons for limiting the upper and lower limits.

[0029]

[Table 2]

In the present invention, in order to improve machinability, S, Se, Te, REM, Pb, Bi, Ca, Ti, Mg, P,
Even if Sn, As, etc. are added, the above-mentioned object of the present invention does not hinder the retardation characteristics due to the change in microstructure due to the repeated stress load, and the machinability can be easily improved. You may add according to it.

[0031]

EXAMPLE Steels having the chemical compositions shown in Tables 3, 4 and 5 were melted in a converter and then continuously cast.
And then rolled into a 65 mmφ bar after diffusion annealing for 30 hours. Next, a cylindrical test piece of 15 mmφ × 20 mm and a test piece for rolling fatigue were collected from the D / 4 part of the steel bar by cutting. Thereafter, these test pieces were tested in the order of normalizing, spheroidizing annealing, quenching, and tempering without controlling the atmosphere (in the air atmosphere). Further, the test piece for rolling fatigue was polished and lapping finished to 1 mm or more for the purpose of completely removing the decarburized layer, and the test piece size was 12 mmφ × 22 mm. The depth of the decarburized layer after heat treatment was the maximum of all decarburized layers on the circumference by cutting a cylindrical test piece of 15 mm φ × 20 mm at a position of 10 mm perpendicular to the height direction, corroding with nital, and observing the microstructure. The value (hereinafter, referred to as “maximum decarburized layer”) was evaluated. The rolling fatigue life test was carried out by a radial type rolling fatigue life tester under the conditions of Hertz maximum contact stress: 600 kgf / mm2 ^, number of repeated stress: about 46500 cpm. The test results are summarized on a probability paper assuming a Weibull distribution, and the average life of steel No. 1 (cumulative failure probability: 50%
, The total number of loads until peeling occurred) was set to 1. The evaluation results are shown in Tables 3, 4, and 5.

[0032]

[Table 3]

[0033]

[Table 4]

[0034]

[Table 5]

As is clear from the results shown in Tables 3, 4, and 5, steel No. 3 in which the C content in steel is out of the range of the present invention, and steel No. 4 and 4 in which the Mo content in steel is out of the range of the present invention. Steel No. 2 in which the amount of Al in the steel is out of the range of the steel of the present invention and steel No. 5 in which the amount of O in the steel is out of the range of the steel of the present invention have a maximum decarburized layer of 0.01 to 0.10 mm and the conventional steel (steel No. .1), but the bearing life ( _B50 life ratio) has been improved over conventional steel (steel material).
Lower than No.1). On the other hand, B ₅₀ rolling fatigue life of the steel No.2 amount in the steel Sb is outside the present invention steels ranges conventional steels (steel N
o.1), but the maximum decarburized layer is 0.10m
m and not much improved compared to the conventional example (SUJ2). In contrast, steel No.6 is the invention steels, 7 B ₅₀ rolling fatigue life is about as compared with the conventional steels (steel No.1) 4 to 8
This indicates that the addition of Mo significantly delayed the microstructure change, and as a result, effectively acted to improve the rolling fatigue life. In addition, the maximum decarburized layer depth is 0.01 to 0.02 mm, which is far less than that of conventional steel No. 1, and is about 1/10 improved compared to steel No. 2 in which Sb is out of the proper range of the present invention. The effect is remarkable.

Further, in addition to the Al, Mo and Sb, Si, Mn, C
r, Mo, Ni, Cu, B, or added to become steel No.8~17 to by one or more N not only improve the B ₅₀ rolling contact fatigue life characteristics, even up decarburized layer depth 0.02 It was found to be significantly improved to less than mm.

Further, in addition to Al, Mo, Sb, Si, Cr, W, V,
In the case of steel Nos. 18 to 30 in which Nb, Zr, Ta, Hf, Ni, Co, and N are positively added in a predetermined amount or more, the average life (B ₅₀ rolling) It was confirmed that the fatigue life was further improved. This is the same in the case of steels Nos. 31 to 44 in which all of the above-mentioned respective improving components are selectively added, and it has been found that this is effective in improving both the bearing steel life and the heat treatment productivity. .

[0038]

As described above, according to the present invention,
Basically, by adding Sb and using a high Mo-containing composite steel bearing steel with a high content of more than 0.5 to 2.0 wt%, the processing load during heat treatment can be reduced (addition effect of Sb), and high load rolling fatigue life introduces a delay of microstructural changes due to repeated stress load when (high Mo content effect), to achieve an improvement in the so-called B ₅₀ high load rolling contact fatigue life, a steel for high heat treatment productivity of long life bearing Can be provided. Therefore, it is necessary to further reduce the oxygen content in steel or control the composition, shape, and distribution of oxide-based nonmetallic inclusions present in steel, which were indispensable under the conventional technology. It is not necessary to improve or construct steelmaking equipment. Further, the development of the bearing steel according to the present invention makes it possible to reduce the size of the rolling bearing and further increase the operating temperature of the bearing.

[Brief description of the drawings]

1 (a) and 1 (b) are micrographs of a metal structure showing a change in microstructure generated under repeated stress loading.

FIG. 2 is an explanatory diagram showing the effect of the addition of Mo and Sb on the bearing life caused by nonmetallic inclusions and the bearing life caused by microstructural changes.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenichi Amano 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Corp. Technical Research Division (56) References JP-A-5-271866 (JP, A) JP-A-5-306432 (JP, A) JP-A-6-287703 (JP, A) JP-A-5-306432 (JP, A) JP-A-2-156045 (JP, A) JP-A-63-57749 (JP) JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C22C 38/00-38/60

Claims (4)

(57) [Claims] C: 0.5 to 1.5 wt%, Mo: more than 0.5 to 2.0
wt%, Al: 0.005 to 0.07 wt%, Sb: 0.001 to 0.005 wt%
Less than and O: 0.0020 wt% or less, the balance being Fe and unavoidable impurities, excellent in heat treatment productivity and excellent in microstructure change delay characteristics due to repeated stress load. 2. C: 0.5 to 1.5 wt%, Mo: more than 1.0 to 2.0 wt%, Al: 0.005 to 0.07 wt%, Sb: 0.001 to less than 0.005 wt%, and O: 0.0020 wt% or less. Si: 0.05-0.5 wt%, Mn: 0.05-2.0 wt%, Cr: 0.05-2.5 wt%, Ni: 0.05-1.0 wt%, Cu: 0.05-1.0 wt%, B: 0.0005-0.01 wt%, and N: contains at least one selected from the group consisting of 0.0005 to 0.012 wt%, with the balance being Fe and unavoidable impurities, and having excellent heat treatment productivity and excellent microstructure change delay characteristics due to repeated stress loading. Bearing steel. (3) C: 0.5 to 1.5 wt%, Mo: more than 0.5 to 2.0
wt%, Al: 0.005 to 0.07 wt%, Sb: 0.001 to 0.005 wt%
And O: 0.0020 wt% or less, and further, Si:
More than 0.5 to 2.5 wt%, Cr: More than 2.5 to 8.0 wt%, Ni: More than 1.0 to 3.0 wt%, N: More than 0.012 to 0.050 wt%, V: 0.05 to 1.0
wt%, Nb: 0.05-1.0 wt%, W: 0.05-1.0 wt%,
Zr: 0.02-0.5 wt%, Ta: 0.02-0.5 wt%, Hf: 0.02
-0.5 wt% and Co: 0.05-1.5 wt%, containing one or more selected from the group consisting of Fe and unavoidable impurities, the balance comprising Fe and unavoidable impurities. Bearing steel with excellent delay characteristics. 4. C: 0.5 to 1.5 wt%, Mo:1.0Super ~ 2.0wt%, A
l: 0.005 to 0.07 wt%, Sb: 0.001 to less than 0.005 wt% and
O: 0.0020 wt% or less,The following (group I)
componentAny one or two or more selected from
Including, and also,Components of the following (Group II) (however, Group I
Excluding the element selected in)Which one to choose from
Including one or two or more, the balance being Fe and inevitable
Heat treatment productivity and repetitive stress composed of chemical impurities
Bearing steel with excellent microstructure change delay characteristics due to load.Record (Group I)  Si: 0.05 to 0.5 wt%, Mn: 0.05 to 2.0 wt%, Cr: 0.05 to 2.5 w
t%, Ni: 0.05 to 1.0 wt%, Cu: 0.05 to 1.0 wt%, B: 0.0005
~ 0.01wt%, and N: 0.0005 ~ 0.012wt%(Group II)  Si: more than 0.5 ~ 2.5wt%, Cr: more than 2.5 ~ 8.0wt%, Ni: more than 1.0 ~
3.0 wt%, N: more than 0.012 to 0.050 wt%, V: 0.05 to 1.0 wt%,
Nb: 0.05-1.0 wt%, W: 0.05-1.0 wt%, Zr: 0.02-0.5 w
t%, Ta: 0.02-0.5 wt%, Hf: 0.02-0.5 wt% and Co:
0.05-1.5wt%