JPH07233442A - Wear resistant and corrosion resistant bearing steel excellent in rolling fatigue property - Google Patents

Abstract

PURPOSE:To produce a bearing steel excellent in rolling fatigue properties without deterorating the wear resistance and corrosion resistance of the steel. CONSTITUTION:This wear resistant and corrosion resistant bearing steel excellent in rolling fatigue properties is the one having a compsn. contg., by weight, 0.5 to 1.3% C, <=1.5% Si, <=2.0% Mn, 11 to 20% Cr and 0.06 to 0.20% N, and the balance Fe with inevitable impurities, and in which hardness after tempering is regulated to >=59 HRC. If required, Mo, W, V and Nb may be added within specified ranges.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a martensitic stainless bearing steel having excellent rolling life characteristics, wear resistance and corrosion resistance.

[0002]

2. Description of the Related Art Conventionally, JIS SUS440C steel and BAS 440M steel have been used as bearing steels that can be used at relatively high temperatures and have excellent corrosion resistance even in corrosive environments.
(1.1C-14.5Cr-4Mo-Fe), 0.7C
-12Cr steel or the like is used. These martensitic stainless steels are superior to the high carbon chromium bearing steel (SUJ) specified in JIS G4805 in terms of heat resistance, corrosion resistance, and wear resistance, but they have a drawback of poor rolling fatigue characteristics. Among the above-mentioned steels, SUS440C has a problem that a huge eutectic carbide is likely to remain in the steel at the time of manufacturing, and thus rolling fatigue characteristics are deteriorated. For the purpose of solving this problem, a steel in which both C and Cr are lowered to improve rolling contact fatigue properties is proposed in JP-A-53-103917.

A bearing is an important mechanical element that guides the rotation of a shaft of a machine or the like and supports and holds the load applied to the rotary shaft, and is used in all machine tools. In recent years, in equipments, while the demands for higher performance and higher accuracy are increasing, there is a demand for bearing steels that can withstand more severe operating environments such as high-speed rotation, operating temperature, and corrosive atmosphere.

[0004]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The No. 03917 steel is superior to the SUS440C steel in rolling life, but in terms of wear resistance and corrosion resistance,
There was a problem that it was not always sufficient as bearing steel.
These deteriorations in wear resistance and corrosion resistance not only impair the performance and accuracy of equipment, but also cause noise and are one of the important properties required for bearing steel. An object of the present invention is to provide a bearing steel excellent in rolling fatigue characteristics without impairing the wear resistance and corrosion resistance of SU440C steel.

[0005]

[Means for Solving the Problems] In order to improve rolling contact fatigue characteristics, carbides effective for wear resistance are finely dispersed in a matrix and the matrix itself is strengthened to prevent unstable fracture. It is important to reduce material defects. As a result of the inventor's earnest study on refining the above-mentioned carbide and strengthening the matrix itself for high-C and high-Cr steel, the steel containing N is N in the annealed state as a nitride of Fe and Cr. It was newly found that when formed and quenched, the nitrides form a solid solution to remarkably increase the hardness of the matrix and improve the rolling fatigue characteristics and wear resistance.

That is, the present invention provides C 0.5 to 1.3% by weight.
%, Si 1.5% or less, Mn 2.0% or less, Cr 11 to 20%, N 0.0
A wear-corrosion-resistant bearing steel excellent in rolling contact fatigue characteristics, characterized by comprising 6 to 0.20%, the balance Fe and unavoidable impurities, and having a hardness after tempering of 59 HRC or more. Based on the above, the steel of the present invention has a Mo content of 5% or less and a W content of 3% when wear resistance is required or when grain refinement is required.
Hereinafter, one or more elements selected from V 2% or less and Nb 1% or less can be added in combination.
The steel of the present invention is composed of C 0.5 to 1.3% by weight, Si 1.5% or less, Mn 2.0% or less, Cr 11 to 20%, N 0.06 to 0.20%, the balance Fe and unavoidable impurities, and after annealing, Is a corrosion-resistant bearing steel excellent in rolling contact fatigue characteristics, characterized in that fine nitrides of Fe and Cr are formed in the structure of, and contains Mo, W, V and Nb within the above range. be able to.

The most important feature of the present invention is that fine nitrides of Fe and Cr are formed in the annealed state, and the bearing is prepared in such a state that it can easily form a solid solution by heat treatment after manufacturing. Conventional bearing steels such as SUS440C depend on Cr carbides mainly for imparting hardness and wear resistance, resulting in a high C and high Cr composition, and a huge eutectic carbide remains in the steel during production, causing rolling. The fatigue life was sometimes reduced. In the present invention, a large number of fine Fe and Cr nitrides during annealing dissolve into the matrix during quenching and strengthen the matrix. Therefore, the rolling fatigue characteristics and wear resistance of the bearing are not It can be significantly increased compared to steel. Therefore, the proper composition combination of the present invention can be determined in consideration of the above-mentioned effects.

[0008]

The reason for limiting the components of the steel of the present invention is described below. C is one of the most important elements in obtaining the hardness of martensitic stainless steel. In addition to Cr, Mo,
It forms carbides with W, V and Nb and contributes to the improvement of wear resistance. In order to obtain the high strength of the steel of the present invention, at least 0.5% or more is required, but if it exceeds 1.3%, the eutectic carbide is coarsened and the rolling fatigue property is deteriorated. Therefore, the range of C is 0.5 to 1.3. %
Limited to The desirable C range is 1.0 to 1.2%. Si
Is an additive element necessary as a deoxidizing element for steel. However, excessive addition of Si causes a remarkable decrease in toughness, so the content is made 1.5% or less. The desirable addition amount of Si is 1.2% or less.

Mn is used as a deoxidizer like Si,
Since it is used at the same time as nitrogen, which is an austenite stabilizing element, the residual austenite becomes excessive during quenching, so it is 2.0% or less. A desirable Mn content is 1.5% or less. Cr is an essential element for improving the corrosion resistance of the steel of the present invention, and also forms a hard Cr-based carbide,
It has the effect of improving wear resistance. Corrosion resistance to the steel of the present invention,
A minimum content of 11% is required to improve both wear resistance. However, if the Cr content is too large, the eutectic carbide becomes coarse, which causes deterioration of rolling contact fatigue characteristics.
The upper limit is 2.0%. The desirable range of Cr is 15 to 18%.

N is the most important element in the alloy of the present invention. That is, by adding N, N in the annealed state is a fine nitride of Fe and Cr, for example, (Cr · Fe) ₂
If N is formed and then quenched, these nitrides have the effect of forming a solid solution and strengthening the matrix. These features of the present invention can be clearly understood from the structure and X-ray diffraction results of Example 4 described later. Further, the addition of N also has an effect of suppressing coarse growth of primary carbides remaining in the matrix, and is particularly effective for improving rolling fatigue characteristics and wear resistance, which are important as a bearing. If N is 0.06% or less, that effect cannot be obtained, and if it exceeds 0.2%, the retained austenite phase cannot be transformed into the martensite phase, and the hardness is lowered, so the upper limit is set to 0.2%. To do. N
The desirable range of is 0.06 to 0.17%.

Mo, W, V, and Nb have the effect of forming carbides and enhancing wear resistance, and partly forming a solid solution in the matrix to enhance tempering softening resistance. One kind or two or more kinds can be added. However, if contained in a large amount, the hot workability is impaired, so M
The upper limits of o, W, V, and Nb are 5%, 3%, 2%, and 1%, respectively.
Among the above elements, Mo also contributes to the improvement of corrosion resistance, and V and Nb have the effect of promoting the refinement of crystal grains due to the N content of the present invention and enhancing rolling contact fatigue resistance. It is preferable to select it appropriately depending on the conditions.

The steel of the present invention is a high C high Cr steel containing 0.06 to 0.2 N.
%, The hardness of the matrix can be further enhanced by forming N as a nitride of Fe and Cr in the annealed state and quenching this to form a solid solution in the matrix.
A large amount of retained austenite remains during quenching.
In order to obtain a hard bearing, the residual austenite phase remaining during quenching needs to be a martensite phase.
Therefore, it is better to carry out a sub-zero treatment after quenching, followed by tempering. The bearing steel thus obtained can have a hardness of 59 HRC or more after tempering, especially for precision equipment bearings and LN used in corrosive environments and high temperatures.
It is suitable for G pumps, mini motor shafts, capstan shafts, and other members that require rolling fatigue and wear resistance.

[0013]

The present invention will be described in detail with reference to the following examples. (Example 1) Table 1 shows the chemical composition of the steel used in the examples. Each steel is blown in a vacuum melting furnace, and for nitrogen-added steel, nitrogen is added to the vacuum furnace in an atmosphere of 0.75 atm,
Blown. Of the steels shown in Table 1, Nos. 1 to 16 are steels of the present invention, No. 20 is SUS440C, No. 21 is BAS44.
0M and No. 22 are the steels disclosed in JP-A-53-103917.

[0014]

[Table 1]

The blown steel ingot was subjected to flaw removal and slab forging, and then 20
Finished and forged into a corner. Then, after carrying out an annealing treatment, it was subjected to the test shown below. In the N-containing steel of the present invention, it was confirmed by X-ray analysis in the annealed state that nitrogen was mainly present in the form of fine (Cr.Fe) ₂ N. This is also explained by showing data in Example 4. FIG. 1 shows that the invention steel No. 1 and the conventional steel No. 20 were oil-quenched at 1030 ° C., then subjected to sub-zero treatment at −75 ° C. for 2 hours, and then at temperatures of 100 to 400 ° C. 3 shows a hardness curve of a sample tempered in. As can be seen from FIG. 1, the steel of the present invention containing 0.120% N has higher hardness after subzero treatment and higher temper softening resistance than the conventional steel containing no N. Although the mechanism of N, which increases hardness, could not be fully clarified, it was inferred from the fact that the precipitate of (Cr · Fe) ₂ N, which was present in the annealed state, was not confirmed after quenching, so N is mainly It is considered to be involved in the strengthening of the base in the state of a solid solution.

Example 2 For each steel shown in Table 1, 10
After oil quenching at 30 ° C, sub-zero treatment at -75 ° C for 2 hours, and then tempering at 160 ° C for 2 hours, hardness test, Charpy impact test, rolling fatigue test, pitting potential The measurement was performed, and the results are also shown in Table 2. The Charpy impact test piece is performed with a 10R C notch, and the rolling fatigue test is a 12 mmφ × 22 mmL test piece, which is sandwiched between steel balls and the hertz maximum contact stress is 5880 MPa at 4400 rpm.
It was tested in. The life is indicated by the number of rotations until 50% damage. Further, in measuring the pitting potential, a 3.5% NaCl aqueous solution was set at 30 ° C., and a voltage value (mV) when a current of 100 mA was applied was measured. The steel of the present invention shows a significantly higher hardness of 59 HRC or more, despite the same heat treatment as compared with the conventional steel having the same level of C content. Furthermore, the steel of the present invention is
It can be seen that the impact value and rolling fatigue characteristics are superior to SUS440C, and the pitting potential is also equivalent to SUS440C.

[0017]

[Table 2]

(Embodiment 3) Steels No. 3, 6 of the present invention shown in Table 1
8 and conventional steel Nos. 20, 21, and 22 were subjected to oil quenching at 1030 ° C and then subjected to sub-zero treatment at -75 ° C for 2 hours.
Then, after tempering at 160 ° C. for 2 hours, an Ogoshi-type wear test was conducted. The results are shown in Table 3. The conditions of the Ogoshi-type wear test are as follows: JIS SCM415 annealed material is used as a mating material, and dry type is used at a friction speed of 0.78 m / s, a friction distance of 400 m, and a final load of 6.8 kg. The amount was calculated. As a result of the wear test, it can be seen that the steel of the present invention is superior in wear resistance to the conventional steel.

(Example 4) Of the steels shown in Table 1, the invention steel No. 6 and the conventional steel No. 20 were annealed by annealing at 860 ° C for 4 hours followed by extraction replica. The result of electron microscopic observation by the method is shown in FIG. Further, FIG. 3 shows an X-ray diffraction chart and analysis results of the same sample. Further, after the above sample was annealed, quenching was performed under the same conditions as in Example 2, subzero and tempering were performed, and the same electron microscopic structure was observed. The results are shown in FIG.

In the steel No. 6 of the present invention shown in FIG. 2 (a), a large amount of fine precipitates are dispersed. According to FIG. 3 showing the X-ray diffraction chart and the analysis result, (Cr · Fe) ) ₂ N. On the other hand, in the conventional steel No. 20 shown in FIG. 2 (b), fine precipitates were not observed, and the result of X-ray diffraction was also
(Cr · Fe) ₂ N could not be detected. Further, the tempered structure of the steel No. 6 of the present invention in FIG. 4 has a fine (Cr · F
e) ₂ N is not recognized. Thus, the N-containing steel of the present invention is characterized in that nitrides of Fe and Cr are formed in the structure after annealing.

[0021]

[Table 3]

[0022]

EFFECTS OF THE INVENTION The material of the present invention contains N added to a high C and high Cr composition to form fine nitrides of Fe and Cr in the annealed structure, and the bearing is easily heat-treated after forming. By preparing a state in which it forms a solid solution, it became possible to further improve the strength after tempering. As a result, SUS4, which has excellent rolling fatigue characteristics and has conventional wear resistance and corrosion resistance, is SUS4.
It is effective as a bearing steel that has the same properties as 40C.

[Brief description of drawings]

FIG. 1 is a tempering hardness curve of a material obtained by subjecting example steels No. 1 and No. 20 to oil quenching at 1030 ° C. and then performing subzero treatment at −75 ° C.

FIG. 2 is an electron microscope metallographic photograph of No. 6 and No. 20 after the annealing treatment.

FIG. 3 is a diagram showing an X-ray diffraction chart and an analysis result after annealing treatment of No. 6 and No. 20.

FIG. 4 is electron micrographs of metal structures of No. 6 and No. 20 after tempering.

Claims (4)

[Claims] 1. C 0.5 to 1.3% by weight, Si 1.5% or less,
Mn 2.0% or less, Cr 11 to 20%, N 0.06 to 0.20%, balance Fe
And unavoidable impurities, the hardness after tempering is 59 HR
A corrosion and corrosion resistant bearing steel with excellent rolling contact fatigue characteristics characterized by a C or higher. 2. C 0.5 to 1.3% by weight, Si 1.5% or less,
Mn 2.0% or less, Cr 11 to 20%, N 0.06 to 0.20%, Mo 5% or less, W 3% or less, V 2% or less, Nb 1%
A wear-and-corrosion-resistant bearing steel having excellent rolling fatigue properties, characterized by containing one or more elements selected from the following, consisting of the balance Fe and unavoidable impurities, and having a hardness of 59 HRC or more after tempering. 3. C 0.5 to 1.3% by weight, Si 1.5% or less,
Mn 2.0% or less, Cr 11 to 20%, N 0.06 to 0.20%, balance Fe
A wear-corrosion-resistant bearing steel excellent in rolling fatigue characteristics, characterized in that fine nitrides of Fe and Cr are formed in the structure after annealing, which is composed of unavoidable impurities. 4. C 0.5 to 1.3% by weight, Si 1.5% or less,
Contains Mn 2.0% or less, Cr 11 to 20%, N 0.06 to 0.20%,
Further, it contains one or more elements selected from Mo 5% or less, W 3% or less, V 2% or less, and Nb 1% or less, and the balance F
A wear-and-corrosion-resistant bearing steel excellent in rolling contact fatigue characteristics, characterized in that fine nitrides of Fe and Cr are formed in the microstructure after annealing, consisting of e and unavoidable impurities.