JP3233674B2 - Bearing steel - 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 which is suitable for rolling bearings such as roller bearings and ball bearings and has excellent workability and rolling fatigue life characteristics. It is intended.

[0002]

2. Description of the Related Art As rolling bearing steels used for automobiles and industrial machines, high carbon chromium bearing steels (JIS standard: SU
J 2) is most often used. This SUJ 2 is 0.95
Since it is very hard because it contains C of up to 1.10 wt% (hereinafter simply referred to as%), it is first subjected to spheroidizing annealing to improve workability, then formed and then quenched. -The required hardness of the rolling bearing is secured by performing tempering. By the way, during the heat treatment several times, C on the material surface reacts with the atmospheric gas, and a low C concentration region called a decarburized layer is generated on the material surface. Such low C
Since the concentration region causes not only a decrease in the hardness of the rolling bearing but also a deterioration in the rolling fatigue life, it is usual to remove the decarburized layer by cutting or grinding after spheroidizing annealing or quenching / tempering. As a result, the yield and the productivity have been reduced.

As a method for preventing the formation of a decarburized layer as described above, there are a method of controlling a carbon potential in an atmosphere gas at the time of heat treatment, and a method of performing a carburizing treatment in an initial stage of spheroidizing annealing (Japanese Patent Laid-Open No. 2-200). No. 54717) is known.

[0004]

However, since each of the above methods is based on controlling the atmosphere during the heat treatment, not only the heat treatment cost is increased, but also the material composition, the heat treatment time, etc. A problem remains where a complicated operation of setting an appropriate gas composition is required. An object of the present invention is to provide a bearing steel which advantageously overcomes the above problems, has a low decarburized layer, and does not require any special measures for preventing the formation of a decarburized layer in a manufacturing process, and has excellent heat treatment productivity. is there.

[0005]

Means for Solving the Problems Now, the present inventors have conducted extensive research on the composition of the components in order to solve the above-mentioned problems. By adding an appropriate amount of Sb, the intended purpose can be advantageously achieved. The knowledge of what is achieved is obtained. The present invention is based on the above findings.

That is, in the present invention, C: 0.50-1.50%, Si: 0.10-2.
00%, Mn: 0.10 to 2.00%, Cr: more than 0.50 to 2.50%, Al: 0.014 to 0.050 wt% , O: 0.0030 wt% or less, and Sb: 0.0010 wt% to less than 0.0050 wt% A bearing steel comprising a balance of Fe and inevitable impurities (first invention). In the above first invention, Mo: 0.10 to 1.00%, Ni: 0.10 to 1.00%, Cu: 0.05 to
Bearing steel containing one or more selected from 0.50% (second invention). In the above first invention, Nb: 0.05 to 0.50%, V: 0.05 to 0.50%, W: 0.05 to
Bearing steel containing one or more selected from 0.50% (third invention). In the above first invention, Mo: 0.10 to 1.00%, Ni: 0.10 to 1.00%, Cu: 0.05 to
One or two or more selected from 0.50%, Nb: 0.05 to 0.50%, V: 0.05 to 0.50%, W: 0.05 to
Bearing steel (fourth invention) containing one or two or more selected from 0.50% is provided as a gist configuration.

[0007]

The reason why the composition of steel in the present invention is limited to the above range will be described below. C: 0.50 to 1.50% C forms a solid solution in the matrix to strengthen martensite,
It is a useful element that improves wear resistance and rolling fatigue life. If its content is less than 0.50%, its effect is small. On the other hand, if it exceeds 1.50%, toughness is significantly reduced, so the C content is 0.50 to 1.50%. Limited to the range.

Si: 0.10% to 2.00% Si acts as a deoxidizing agent when smelting steel, and is also useful as an element that forms a solid solution with the matrix to improve the rolling fatigue life. However, if the content is less than 0.10%, the effect is small. On the other hand, if it exceeds 2.00%, the machinability and forgeability are significantly reduced, so the Si content is set in the range of 0.10 to 2.00%.

Mn: 0.10 to 2.00% Mn enhances the toughness of base martensite by improving the hardenability of steel, and also contributes effectively to the improvement of rolling fatigue life. However, if the content is less than 0.10%, the effect of the addition is poor. On the other hand, if it exceeds 2.00%, the machinability and forgeability are significantly reduced, so the Mn content is set in the range of 0.10 to 2.00%.

Cr: more than 0.50 to 2.50% Cr not only enhances the hardenability of steel and improves the strength and toughness of the matrix, but also effectively contributes to the spheroidization of carbides, but the content is 0.50% or less. The effect is small. On the other hand, if the content exceeds 2.50%, carbides become coarse and the machinability and rolling fatigue life decrease, so the Cr content is added in the range of more than 0.50 to 2.50%.

Al: 0.014 to 0.050% Al is added as a deoxidizing agent, but it is combined with O to form hard oxide nonmetallic inclusions, so that the rolling fatigue life is reduced, so that Al is as low as possible. Is more desirable. Therefore,
Al was 0.01% as can be seen from the results of the examples shown in Table 1.
The lower limit was 4 wt% and the upper limit was 0.0030%.

O: 0.0030% or less O is desirably small because it combines with Al to form hard oxide-based nonmetallic inclusions, thereby reducing the rolling fatigue life. Therefore, the upper limit of O is set to 0.0030%.

Sb: 0.0010% Or more and less than 0.0050%  Sb is a particularly important element in the present invention, and
Decarbonization by suppressing the reaction between C in the surface layer of steel and atmospheric gas
Actively added for the purpose of suppressing the formation of a layer. Such suppression
For production, the content becomes remarkable when the content is 0.0010% or more,Especially
, 0.0050% or moreEven if added, the effect is saturatedDo. There
Where Sb is 0.0010% Or more and less than 0.0050%In the range of
It was assumed.

Although the basic components have been described above, in the present invention, one or more selected from Mo, Ni, and Cu, and / or one or more selected from Nb, V, W Two or more can be added. The preferred ranges of the amounts of the above elements are as follows.

Mo: 0.10-1.00%, Ni: 0.10-1.00%, C
u: 0.05 to 0.50% Mo, Ni and Cu are all useful elements that enhance the hardenability and improve the rolling fatigue life of steel. However, Mo, Cu
If the content is too large, the forgeability of the steel will be reduced, and if the Ni content is too large, a large amount of residual γ will be generated, the steel material hardness will be reduced, and the rolling fatigue life will be reduced. Therefore, these elements are added in each of the above ranges where there is no possibility of such an element.

Nb, V, W: 0.05 to 0.50% V, Nb and W all combine with C in the steel to improve wear resistance and to reduce rolling fatigue life and toughness due to refinement of crystal grains. It also contributes effectively to the improvement of But,
If any of these elements is too large, carbides are stabilized at high temperatures, not only lowering the hardness of the steel material and reducing the rolling fatigue life, but also deteriorating the forgeability of the steel. Therefore, these elements are also added in each of the above ranges where there is no possibility of such an element.

In the present invention, even if S, Pb, Ca, Bi, REM, etc. are added in order to improve the machinability, the suppression of the decarburized layer, which is the object of the present invention, is not hindered. In addition, the machinability can be improved.

Next, a method for producing the steel of the present invention will be described. The steel of the present invention may be produced by any method such as a converter and an electric furnace, and may be either continuous casting or ingot casting for slab production. Further, the hot rolling conditions are not particularly limited, and may be performed according to a conventional method.

[0019]

EXAMPLES Various steels having the chemical compositions shown in Table 1 were melted in a converter and made into steel slabs by a continuous casting method.
And then rolled to a 65 mmφ steel bar. D of this steel bar
After collecting cylindrical test specimens and rolling fatigue life test specimens of 15mmφ × 20mm from / 4 parts, heat treatment is performed in the order of normalizing → spheroidizing annealing → quenching → tempering without atmosphere control. went. The rolling fatigue life test specimen is
Further, in order to completely remove the decarburized layer, polishing and lapping of 1 mm or more were performed to obtain a test piece size of 12 mmφ × 22 mm. Table 2 shows the results of examining the state of the decarburized layer and the rolling fatigue life of the obtained test pieces.

The decarburized layer was obtained by cutting a cylindrical test piece of 15 mmφ × 20 mm vertically at a position of 10 mm in the height direction, then corroding with nital, and observing the microstructure to determine the maximum value of all decarburized layers on the circumference. (Hereinafter, referred to as the maximum decarburized layer). The rolling contact fatigue life was measured using a cylindrical rolling contact fatigue life tester. The maximum contact stress in Hertz was 600 kgf / mm ² and the number of repetitive stresses was about 46.
It was tested under the conditions of 500 cpm, summarized in probability paper as conforming test results on Weibull distribution, B ₁₀ of the steel No.1
The life (cumulative failure probability: the total number of loads until the occurrence of peeling at 10%) was set to 1 and relatively evaluated.

[0021]

[Table 1]

[0022]

[Table 2]

As is clear from Table 2, steel No. 16 having a C content lower than the range of the present invention has a maximum decarburized layer of 0.02 mm and N
o.1 The rolling fatigue life is N
o.1 It was only 0.7 times the conventional material. In addition, the steel material No. 17 having an Sb content lower than the range of the present invention has the rolling fatigue life of No. 1
Although it was 1.2 times as good as the conventional material, the maximum decarburized layer was 0.09
mm and not improved. In contrast, steel materials No. 2 , 4,
The maximum decarburized layer of each of the inventive materials Nos. 7 to 15 is 0.02 to
0.04mm, which is improved from 0.10mm of No. 1 conventional material.
The rolling fatigue life was 1.1 to 2.5 times that of the No. 1 conventional material. Further, as shown in this embodiment, (Mo, Ni, Cu)
And / or the addition of one or more of (Nb, V, W) improves the rolling fatigue life without hindering the suppression of the decarburized layer. It can be seen that a combination can be made.

[0024]

As described above, according to the present invention, the formation of a decarburized layer during heat treatment can be effectively suppressed without impairing the rolling fatigue life characteristics. In the above, the cutting and grinding steps conventionally performed for the purpose of removing the decarburized layer can be simplified, and the material yield and the heat treatment productivity are remarkably improved.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Mikaru Tabata 1 Kawasaki-cho, Chiba City, Chiba Prefecture Kawasaki Steel Corp. Technical Research Division (56) References JP-A-63-57749 (JP, A) JP-A JP-A-62-274058 (JP, A) JP-A-4-349 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 38/00-38/60

Claims (4)

(57) [Claims] 1. C: 0.50-1.50 wt%, Si: 0.10-2.
00 wt%, Mn: 0.10 to 2.00 wt%, Cr: more than 0.50 to 2.50 wt% , Al: 0.014 to 0.050 wt% , O: 0.0030 wt% or less, and Sb: 0.0010 wt% or more and less than 0.0050 wt% A bearing steel containing, the balance being Fe and unavoidable impurities. 2. C: 0.50-1.50 wt%, Si: 0.10-2.
00 wt%, Mn: 0.10 to 2.00 wt%, Cr: more than 0.50 to 2.50 wt% , Al: 0.014 to 0.050 wt% , O: 0.0030 wt% or less, and Sb: 0.0010 wt% to less than 0.0050 wt% Mo: 0.10 to 1.00 wt%, Ni: 0.10 to 1.00 wt%, Cu: 0.05 to 0.50 wt%.
Bearing steel comprising Fe and unavoidable impurities. 3. C: 0.50-1.50 wt%, Si: 0.10-2.
00 wt%, Mn: 0.10 to 2.00 wt%, Cr: more than 0.50 to 2.50 wt% , Al: 0.014 to 0.050 wt% , O: 0.0030 wt% or less, and Sb: 0.0010 wt% to less than 0.0050 wt% Nb: 0.05 to 0.50 wt%, V: 0.05 to 0.50 wt%, W: 0.05 to 0.50 wt%.
Bearing steel comprising Fe and unavoidable impurities. 4. C: 0.50-1.50 wt%, Si: 0.10-2.
00 wt%, Mn: 0.10 to 2.00 wt%, Cr: more than 0.50 to 2.50 wt% , Al: 0.014 to 0.050 wt% , O: 0.0030 wt% or less, and Sb: 0.0010 wt% or more and less than 0.0050 wt% One or more selected from Mo: 0.10 to 1.00 wt%, Ni: 0.10 to 1.00 wt%, Cu: 0.05 to 0.50 wt%, Nb: 0.05 to 0.50 wt%, V: A bearing steel containing one or more selected from the group consisting of 0.05 to 0.50 wt% and W: 0.05 to 0.50 wt%, with the balance being Fe and unavoidable impurities.