JP2002060904A - Steel excellent in rolling fatigue life - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide steel suppressed in the generation of the change in structure into the white one in steel for bearings, steel for machine structures or the like and having an excellent rolling fatigue life even under high vibration- high loads. SOLUTION: In this steel excellent in a rolling fatigue life, Ni and Mo are added to steel components in steel for bearings or steel for machine structures to improve the toughness of the steel, by which the generation of cracks is suppressed, so that the generation of the change of structure into the white one is suppressed, and the steel has a composition containing, by mass, 0.45 to 1.20% C, 0.05 to 1.50% Si, 0.20 to 2.0% Mn, 0.7 to 4.0% Ni and 0.5 to 4.0% Cr, and the balance Fe with inevitable impurities.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel having excellent rolling fatigue life which is used as a steel for machine structural use or steel for bearings. Steel with reduced structural change and improved rolling fatigue life, especially for bearings for auxiliary parts of automobile engines, bearings used under high vibration and impact loads, and steel used for rolling and sliding parts .

[0002]

2. Description of the Related Art Conventionally, SUJ2 specified by JIS for high carbon chromium steel is often used for general bearings. By the way, in recent years, the use environment of rolling parts such as drive system parts and bearings has been under high vibration and high load due to high performance, high output and downsizing and weight reduction in industrial machines or automotive parts in recent years. It has become something. When the rolling member is used under a high vibration and a high load as described above, the above-described conventional steel causes a problem that a peculiar structural change occurs below the rolling surface and the steel is damaged early. Although various theories have been raised regarding the process of generating the structural change that causes this damage, it is not yet clear.

For example, in Japanese Patent Application Laid-Open No. 5-255809, carbon atoms are diffused at the position of maximum shear stress below the rolling surface.
A white structure appears that looks white under an optical microscope due to fixation.This white structure is harder to corrode than the matrix, and is very hard and brittle compared to the matrix. It is going to reach. In order to suppress the diffusion of carbon based on this idea, a steel in which the amount of carbon in steel is reduced and Cr and Mo are added has been proposed. That is, in the conventional method, the occurrence of the above structural change is attributed to the diffusion phenomenon of C,
Although added, it has no effect on the occurrence of structural changes.

[0004] Incidentally, the white structure has no directionality in the rolling direction, the inside of the structure change is accompanied by plastic flow, and the residual carbides have disappeared. In recent studies, a close look at the white structure shows that the crystal grains have been refined to the order of nm. Even if the test bearing is made of JIS SCR420 case hardened steel with different carbon content,
It does not change even if it is made of JIS SUJ2 high carbon steel. Furthermore, since the interface between the white structure and the matrix is extremely clear, it is unlikely that the diffusion phenomenon of carbon is involved. As a matter of course, the measures aimed at preventing the diffusion of carbon cannot suppress the change in the structure of whitening, and therefore the life is not improved.

[0005]

The problem to be solved by the present invention is to suppress the occurrence of white structure change in bearing steel and steel for machine structural use, and to provide excellent rolling fatigue even under high vibration and high load. It is to provide steel having a long life.

[0006]

Means for Solving the Problems As a result of studying the mechanism of the occurrence of the white structure change, the inventors found that the occurrence of the white structure change caused cracks due to stress concentration in members such as bearings, and further cracks were applied to the cracks. It has been found that, since concentration and stress become complicated and plastic deformation occurs repeatedly along cracks, crystal grains are refined to the order of nm and a white structure change occurs. After diligent studies based on this finding, the addition of Ni and Mo to steel components such as steel for bearings and steel for machine structural use improved the toughness of the steel, thereby suppressing the occurrence of cracks and consequently the white structure. It has been found that the occurrence of change can be suppressed.

That is, according to the first aspect of the present invention, there is provided a method for solving the above-mentioned problems, wherein C:
0.45 to 1.20%, Si: 0.05 to 1.50%,
Mn: 0.20 to 2.0%, Ni: 0.7 to 4.0%,
Cr is a steel having an excellent rolling fatigue life characterized by containing 0.5 to 4.0% and being composed of a balance of Fe and unavoidable impurities.

[0008] According to the second aspect of the present invention, C: 0.
45-1.20%, Si: 0.05-1.50%, M
n: 0.20 to 2.0%, Ni: 0.7 to 4.0%, C
This steel is excellent in rolling fatigue life, characterized by containing r: 0.5 to 4.0% and Mo: 0.5 to 2.0%, the balance being Fe and unavoidable impurities.

The reasons for limiting the steel components of the present invention will be described below. In addition,% is mass%. C: 0.45% to 1.20% C is added to secure hardness after quenching and tempering.
If it is less than 0.45%, it is insufficient, and if it exceeds 1.20%, giant carbides are generated, and the life and impact value are reduced. Therefore, C is set to 0.45% to 1.20%.

Si: 0.05% to 1.50% Si is added for a deoxidizing effect in steel making and for imparting hardenability. If it is less than 0.05%, the deoxidizing effect is insufficient, and if it exceeds 1.50%, the cold workability decreases. Si is an element for increasing the tempering softening resistance, and when the object is used at a high temperature (200 ° C.), 0.5
% Or more is desired. So Si: 0.05% ~
1.50%.

Mn: 0.20% to 2.0% Mn is added to impart hardenability. 0.20%
If it is less than 2,000, the hardenability is insufficient, and if it exceeds 2.0%, the workability is reduced. Therefore, Mn is set to 0.20% to 2.0%.

Ni: 0.7% to 4.0% Ni is the most important element and enhances the toughness and suppresses the generation of cracks, which are the starting points of the white structure. If it is less than 0.7%, there is no effect. Desirably, 1% or more is added. But 4%
Exceeding the cold workability is impaired. Then Ni: 0.7
% To 4.0%.

Cr: 0.5% to 2.0% Cr is an element that strengthens the matrix. 0.5%
If it is less than 2%, it is not effective, and if it is more than 2%, a large carbide tends to be formed during solidification. In addition, the penetration of carbides deteriorates, and the quenching temperature must be increased, resulting in poor productivity. Therefore, Cr is set to 0.5% to 2.0%.

Mo: 0.5% to 2.0% Mo is an important element next to Ni and enhances toughness.
Suppress the generation of cracks that are the starting points of the white structure. By the way, if it is less than 0.5%, there is no effect, and if it exceeds 2%, giant carbide is easily generated at the time of solidification, and the life is shortened. Furthermore, since it is an expensive element, it leads to an increase in cost. Therefore, Mo is set to 0.5% to 2.0%.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the following examples. First, in the embodiment of the invention according to claim 1, C: 0.45 to 1.2 by mass%.
0%, Si: 0.05-1.50%, Mn: 0.20--20%
2.0%, Ni: 0.7 to 4.0%, Cr: 0.5 to
A steel containing 4.0% and having a chemical composition consisting of the balance of Fe and unavoidable impurities, according to an embodiment of the present invention according to claim 2, wherein C: 0.45 to 1.20% by mass, Si: 0.
05 to 1.50%, Mn: 0.20 to 2.0%, Ni:
0.7 to 4.0%, Cr: 0.5 to 4.0%, Mo:
A steel containing 0.5 to 2.0% and having a chemical composition consisting of the balance Fe and unavoidable impurities was melted by a vacuum induction furnace melting method (VIM), and heated to 1,150 ° C.
It is forged at 950 ° C., processed into a product, and quenched and tempered to obtain steel having excellent rolling fatigue life.

[0016]

Examples 1 to 7 of Examples 1 to 7 of the present invention shown in Table 1
The steels containing the chemical components of the Examples and Comparative Examples 1 to 7 are melted by VIM. Examples 1 to 3 are examples of the invention according to claim 1 containing Ni,
Examples 4 to 7 are examples of the invention according to claim 2 containing Ni and Mo. Comparative Example 6 and Comparative Example 7
Denotes steel for SUJ2 and SUJ3 bearings specified by JIS. After heating the above ingoted steel material to 1,150 ° C., it was forged at 950 ° C. and processed into a test material.
The steel is quenched by holding at 0 ° C. for 30 minutes, and tempered by holding at 180 ° C. for 90 minutes.

[0017]

[Table 1]

A bearing was prepared from the obtained test material, mounted on the pulley side of an alternator for an automobile, and operated for a maximum of 1000 hours to perform a durability life test. The test results are shown in Table 2. The durability time ratios in Table 2 are shown by comparing the life of SUJ2 steel of Comparative Example 6 with one.

[0019]

[Table 2]

As can be seen from Table 2, in each of the examples of the present invention, there is no structural change, and the durability time ratio is 3.9 or more, which is extremely excellent in toughness. On the other hand, in the case of the comparative example, there was a structural change, and the durability time ratio was about 1.

[0021]

As described above, the present invention improves the toughness of steel for medium- and high-carbon mechanical structures, especially steel for bearings, etc. by including Ni or Ni and Mo to improve the toughness of automobile electrical components. It is a steel having excellent rolling fatigue life as a steel material for a bearing used for an alternator, which is a member, and other bearings, rolling members, sliding members, and the like used under high vibration and high impact loads.

Claims (2)

[Claims] 1. A mass% of C: 0.45 to 1.20%,
Si: 0.05-1.50%, Mn: 0.20-2.0
%, Ni: 0.7 to 4.0%, Cr: 0.5 to 4.0%
A steel excellent in rolling fatigue life, characterized by containing Fe and the balance of Fe and unavoidable impurities. 2. C: 0.45 to 1.20% by mass%,
Si: 0.05-1.50%, Mn: 0.20-2.0
%, Ni: 0.7 to 4.0%, Cr: 0.5 to 4.0
%, Mo: 0.5 to 2.0%, the balance being Fe and inevitable impurities, characterized by having excellent rolling fatigue life.