JP3426495B2 - Long-life bearing steel excellent in delayed fracture resistance and method of manufacturing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a bearing, a linear motion shaft, and the like.
The present invention relates to a bearing steel which is used in a high hardness state and has excellent resistance to delayed fracture due to hydrogen invading from a steel material, heat treatment and an environment in use, and a method for producing the bearing steel.

[0002]

2. Description of the Related Art Delayed fracture is often generated from hydrogen invading from a use environment such as bolts in a tensile stress state, and it is often the case that materials such as temper hardness and adjustment of alloying elements are taken, but high hardness state. In the bearings used in, delayed fracture was not a problem. However, recently, early damage due to hydrogen invading from heat treatment and use atmosphere has become a problem, and although the lubricating oil has been changed, the above-mentioned materials have tensile strength. Strength is 140-150
(equivalent to 43 to 45 HRC in terms of kgf / mm ² hardness), it cannot withstand a high load such as a bearing, and no measures have been taken from a bearing material excellent in delayed fracture resistance.

[0003]

SUMMARY OF THE INVENTION The present invention is intended to provide a bearing steel which is suitable for such applications and has a long life and excellent delayed fracture resistance. It is to develop a manufacturing method that enables

[0004]

[Means for Solving the Problems] The inventors of the present invention have made intensive studies on the delayed fracture behavior in bearing steel, and by trapping hydrogen in the steel, which causes delayed fracture, with fine Ti-based precipitates, It was found that it can be invalidated to increase the resistance to delayed fracture and prolong the service life. In that case, it has been found that the smaller the particle size of the precipitate, the stronger the force for trapping hydrogen, and that it is effective to disperse the particles as uniformly and finely as possible. However, increasing the addition amount does not increase the effective fine precipitates, coarsens and weakens the hydrogen trapping force, and also becomes a source of stress concentration, which adversely reduces life characteristics and the like. It was found that the optimization of manufacturing conditions in order to produce steel and steel materials is necessary.

That is, the means of the invention for achieving the above object is, in the invention of claim 1, a mass ratio of C: 0.65 to 0.65.
1.2%, Si: 0.05 to 0.50%, Mn: 0.2
.About.2.0%, T1: 0.05 to 0.20%, Al: 0.
005 to 0.50%, N: 0.0120% or less, O: 2
Contains 0 ppm or less, preferably 10 ppm or less,
It is a long-life bearing steel having excellent delayed fracture resistance in which Ti carbide and Ti carbonitride having an average size of 70 nm or less, which is composed of the balance Fe and unavoidable impurities, are finely dispersed in the steel.

According to the second aspect of the invention, the mass ratio of C:
0.65 to 1.2%, Si: 0.05 to 0.50%, M
n: 0.2 to 2.0%, Ti: 0.05 to 0.20%,
Al: 0.005-0.050%, N: 0.0120%
Hereinafter, O: 20 ppm or less, preferably 10 ppm or less is contained, and further Ni: 0.1 to 2.0%, C
r: 0.20 to 2.0%, Mo: 0.05 to 1.0%, and one or more selected from the balance Fe.
And unavoidable impurities, the average size is 70 nm
It is a long-life bearing steel having excellent delayed fracture resistance in which the following Ti carbide and Ti carbonitride are finely dispersed in the steel.

According to the invention of claim 3, in the long-life bearing steel according to the means of claim 1 or 2, B: 0.0005 to 0.0050% by mass is further contained as an alloy component, and the balance Fe. and consists inevitable impurities, the size
It is a long-life bearing steel having excellent delayed fracture resistance, characterized in that Ti carbide and Ti carbonitride having an average of 70 nm or less are finely dispersed in the steel.

According to the invention of claim 4, in a mass ratio, C:
0.65 to 1.2%, Si: 0.05 to 0.50%, M
n: 0.2 to 2.0%, Ti: 0.05 to 0.20%,
Al: 0.005-0.050%, N: 0.0120%
Hereinafter, a steel material containing O: 20 ppm or less, preferably 10 ppm or less, and the balance Fe and unavoidable impurities is heated and rolled to a temperature range of 1200 to 1350 ° C.,
Further, by rolling or forging into a predetermined steel material or component at the same temperature or a temperature of 800 to 1050 ° C, Ti carbide and Ti carbonitride having an average size of 70 nm or less are finely dispersed in the steel in the subsequent heat treatment step. Is a method for producing long-life bearing steel having excellent delayed fracture resistance.

According to the invention of claim 5, in a mass ratio, C:
0.65 to 1.2%, Si: 0.05 to 0.50%, M
n: 0.2 to 2.0%, Ti: 0.05 to 0.20%,
Al: 0.005-0.050%, N: 0.0120%
Hereinafter, O: 20 ppm or less, preferably 10 ppm or less is contained, and further Ni: 0.1 to 2.0%, C
r: 0.20 to 2.0%, Mo: 0.05 to 1.0%, and one or more selected from the balance Fe.
And a steel material consisting of inevitable impurities from 1200 to 1350
Heating and rolling in the temperature range of ℃, and the same temperature or 8
By rolling or forging to a predetermined steel or component at a temperature of 00-1,050 ° C., a heat treatment step the size of the later
It is a method for producing a long-life bearing steel having excellent delayed fracture resistance by finely dispersing Ti carbide and Ti carbonitride having an average of 70 nm or less in the steel.

[0010] In the present invention of claim 6, the alloy components of the steel material in the production process of steel long life bearing means according to claim 4 or claim 5, further at a mass ratio B: 0.0005-0.0
Heating and rolling a steel material containing 050% and the balance Fe and unavoidable impurities in a temperature range of 1200 to 1350 ° C, and further rolling or forging into a predetermined steel material or component at the same temperature or 800 to 1050 ° C. As a result, in the subsequent heat treatment step, T having an average size of 70 nm or less
A method for producing a long-life bearing steel having excellent delayed fracture resistance, characterized in that i carbide and Ti carbonitride are finely dispersed in the steel.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described through examples. Regarding the reasons for limiting the present invention, first, the reasons for limiting the chemical components (hereinafter referred to as “ mass ratio”) will be described.

Regarding C: 0.65 to 1.2%, C is an element that imparts hardness necessary for a bearing, but 0.65
If it is less than%, the hardness HRC59 or more required as a bearing may not be obtained, so the lower limit is made 0.65%. Also,
If it exceeds 1.2%, large carbides and coarse Ti carbonitrides are likely to crystallize during solidification, and the effect cannot be removed even in the subsequent step, so the upper limit is made 1.2%.

Si: 0.05 to 0.50%, S
i is added to improve the deoxidizer and hardenability, but 0.0
If it is less than 5%, the deoxidizing effect is not sufficient, and if it exceeds 0.50%, the workability deteriorates, so the lower limit is made 0.05% and the upper limit is made 0.50%.

Regarding Mn: 0.2 to 2.0%, Mn is also added to improve the deoxidizing agent and hardenability, like Si, but if it is less than 0.20%, the hardenability is insufficient. If it exceeds 2.0%, the workability is remarkably reduced, so the lower limit is 0.20.
%, And the upper limit is 2.0%.

For Ti: 0.05 to 0.20%, T
By finely dispersing i as Ti carbide or Ti carbonitride in the steel, the grain size can be made finer and the matrix strengthening can improve the fatigue characteristics and life characteristics.
Further, fine Ti carbide or Ti carbonitride acts as a hydrogen trap site, and thus reduces the harmfulness of hydrogen. If it is less than 0.05%, the effect is not sufficient, and if it exceeds 0.20%, Ti carbide and Ti carbonitride are coarsened and no sufficient effect is exhibited, so the lower limit is set to 0.
05% and the upper limit is 0.20%.

Al: About 0.005 to 0.050%, Al is added as a deoxidizing agent, but if it is less than 0.005%, it has no effect, and if it exceeds 0.050%, alumina-based oxide is formed. In order to increase the fatigue strength and workability, the lower limit is made 0.005% and the upper limit is made 0.050%.

N: 0.0120% or less, it is desirable that the amount of N be as small as possible, because if the amount is large, N will be precipitated as coarse Ti nitride or Ti carbonitride. The upper limit is set to 0.0120% in consideration of the manufacturing conditions.

O: 20 ppm or less, O is present in the steel as an oxide inclusion and may be considered to function as a hydrogen trap site, but rather as a coarse precipitate,
The role of reducing fatigue strength is large, and it is desirable that it be as small as possible. Therefore, the upper limit is 20 ppm, preferably 10
ppm.

In addition to the above components, in the steel of the present invention, Ni, C
r and Mo can be contained alone or in combination. These actions are as follows.

Ni: About 0.1 to 2.0%, Ni improves hardenability and improves fatigue strength, toughness and the like.
If it is less than 0.1%, the effect is not sufficient, and if it exceeds 2.0%, it becomes difficult to soften the material and the workability is significantly reduced, so the upper limit is made 2.0%.

Cr: About 0.20 to 2.0%, Cr
Improves hardenability and spheroidization of carbides, and improves fatigue strength and toughness. If it is less than 0.2%, the effect is not sufficient, and if it exceeds 2.0%, it becomes difficult to soften the material and the workability is remarkably lowered, so the upper limit is made 2.0%.

Mo: About 0.05 to 1.0%, Mo
Improves hardenability and improves fatigue strength and toughness.
If less than 0.05%, the effect is not sufficient, 1.0%
If it exceeds, the softening of the material becomes difficult and the workability is significantly lowered. Further, the above effect is saturated and it becomes disadvantageous in terms of cost, so the upper limit is made 1.0%.

Further, in addition to the above components, in the steel of the present invention, B
Can be included. This action is as follows.

B: About 0.0005 to 0.0050%, B is added as an element for improving induction hardenability. If less than 0.0005%, the effect is not sufficient,
If it exceeds 0.0050%, the hot workability is deteriorated, so the upper limit is made 0.0050%.

When a steel material having the above chemical composition is produced under the following conditions, the most effective fine Ti-based precipitate is obtained,
It exhibits excellent delayed fracture characteristics and long life.

That is, when the steel melted in the above composition range is rolled into a billet or a steel material, 1200 to 1350
By heating / rolling to a temperature range of ℃, and then rolling or forging into a steel material of a predetermined size in the same temperature range or a lower temperature range of 800 to 1050 ° C, the subsequent heat treatment without tempering and tempering is performed. Even after that, Ti carbide and Ti carbonitride having an average size of 70 nm or less can be finely dispersed in the steel, and a method for producing a long-life bearing steel having excellent delayed fracture resistance can be obtained. .

[Examples] Sample materials having the chemical components shown in Table 1 were melted in a 100 kg vacuum melting furnace, and the temperature range was 1200 to 1350 ° C, and some were in the same temperature range and 800 to 1050 ° C.
65mmφ and 30m in the temperature range of
Finished to mφ. Furthermore, after normalizing and spheroidizing annealing, it was processed into a test piece and subjected to quenching and tempering to obtain a final use state.

Thrust life characteristics (test piece size: 60 mm × 40) of the obtained steel material under normal clean lubrication and lubrication containing 0.5% pure water (under hydrogen infiltration environment)
mm x 5 mm) and 5% as a standard for delayed fracture resistance
A hydrogen cracking resistance susceptibility test by immersion in hydrochloric acid was performed.

[0028]

[Table 1]

Table 2 shows the production conditions, the precipitate particle size, and the characteristic test results for each test material. In the manufacturing conditions, two rolling temperatures are entered, and forging is performed twice.

[0030]

[Table 2]

FIG. 1 schematically shows the structure of the thrust life tester, Table 3 shows the test conditions, and FIG. 2 shows the shape of the test piece used for the hydrogen cracking susceptibility test. In FIG. 1, 1 is a test piece holding frame, 2 is a thrust test piece (60φ ×
5 to 10 mm), 3 is a retainer, 4 is 3/8 inch (9.
(525mmφ) steel ball, 5 upper race (# 5130 thrust bearing race), 6 rotating shaft (1200r.p.
m.) and 7 are lubricating oils (# 60 spindle oil).

[0032]

[Table 3]

It can be seen from Table 2 that the steels of the present invention show little deterioration in life characteristics in a hydrogen invading environment, show high resistance to hydrogen cracking resistance, and have excellent delayed fracture characteristics.

[0034]

As described above, the present invention can provide a long-life bearing steel having excellent delayed fracture resistance by effectively adding Ti and optimizing manufacturing conditions. Have.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing the structure of a thrust life tester.

FIG. 2 is a diagram showing a test piece shape of a hydrogen cracking susceptibility test.

[Explanation of symbols]

1 Test piece holding frame 2 Thrust test piece 3 cage 4 3/8 inch steel ball 5 upper race 6 rotation axes 7 Lubricating oil

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) C22C 38/00 C21D 8/00

Claims (6)

(57) [Claims] 1. A mass ratio of C: 0.65 to 1.2%,
Si: 0.05 to 0.50%, Mn: 0.2 to 2.0
%, Ti: 0.05 to 0.20%, Al: 0.005 to
0.50%, N: 0.0120% or less, O: 20 ppm
Containing the following, consisting of the balance Fe and unavoidable impurities,
A long-life bearing steel having excellent delayed fracture resistance, characterized in that Ti carbide and Ti carbonitride having an average size of 70 nm or less are finely dispersed in the steel. 2. A mass ratio of C: 0.65 to 1.2%,
Si: 0.05 to 0.50%, Mn: 0.2 to 2.0
%, Ti: 0.05 to 0.20%, Al: 0.005 to
0.050%, N: 0.0120% or less, O: 20pp
m or less, and further Ni: 0.1 to 2.0%, C
r: 0.20 to 2.0%, Mo: 0.05 to 1.0%, and one or more selected from the balance Fe.
And unavoidable impurities, the average size is 70 nm
A long-life bearing steel having excellent delayed fracture resistance, characterized in that the following Ti carbide and Ti carbonitride are finely dispersed in the steel. 3. The long-life bearing steel according to claim 1 or 2, further comprising B as a mass ratio as an alloy component:
0.0005 to 0.0050% content, consisting of balance Fe and unavoidable impurities, Ti carbide and Ti carbonitride having an average size of 70 nm or less are finely dispersed in steel, which is excellent. Long-life bearing steel with delayed fracture resistance. 4. A mass ratio of C: 0.65 to 1.2%,
Si: 0.05 to 0.50%, Mn: 0.2 to 2.0
%, Ti: 0.05 to 0.20%, Al: 0.005 to
0.050%, N: 0.0120% or less, O: 20pp
A steel material containing m or less and consisting of balance Fe and unavoidable impurities is heated and rolled in a temperature range of 1200 to 1350 ° C., and further rolled or forged into a predetermined steel material or component at the same temperature or 800 to 1050 ° C. As a result, in the subsequent heat treatment step, T having an average size of 70 nm or less is obtained.
A method for producing a long-life bearing steel having excellent delayed fracture resistance, characterized in that i carbide and Ti carbonitride are finely dispersed in the steel. 5. A mass ratio of C: 0.65 to 1.2%,
Si: 0.05 to 0.50%, Mn: 0.2 to 2.0
%, Ti: 0.05 to 0.20%, Al: 0.005 to
0.050%, N: 0.0120% or less, O: 20pp
m or less, and further Ni: 0.1 to 2.0%, C
r: 0.20 to 2.0%, Mo: 0.05 to 1.0%, and one or more selected from the balance Fe.
And a steel material consisting of inevitable impurities from 1200 to 1350
Heating and rolling in the temperature range of ℃, and the same temperature or 8
By rolling or forging to a predetermined steel or component at a temperature of 00-1,050 ° C., a heat treatment step the size of the later
A method for producing a long-life bearing steel having excellent delayed fracture resistance, characterized in that Ti carbide and Ti carbonitride having an average of 70 nm or less are finely dispersed in the steel. 6. The alloy component of the steel material in the method for producing a long-life bearing steel according to claim 4 or 5, further containing B: 0.0005 to 0.0050% in a mass ratio, A steel material composed of the balance Fe and unavoidable impurities is set to 1200 to 13
By heating and rolling in a temperature range of 50 ° C, and further rolling or forging into a predetermined steel material or part at the same temperature or a temperature of 800 to 1050 ° C, Ti carbide having an average size of 70 nm or less in the subsequent heat treatment step. A method for manufacturing a long-life bearing steel having excellent delayed fracture resistance, characterized in that Ti carbonitride is finely dispersed in the steel.