JPH0987740A - Production of bearing parts excellent in cold workability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently produce bearing parts having bearing characteristics such as good cold workability, machinability, a long rolling fatigue life or the like even if spherodizing annealing treatment is simplified or eliminated by specifying the compsn. of a steel, the amt. of nonmetallic inclusions and quenching and tempering temps. SOLUTION: A steel satisfying contg., by mass, 0.5 to 0.9% C, Si<=1.0% (including zero), 0.2 to 1.5% Mn, P<=0.03% (including zero), Ni<=0.25% (including zero), Mo<=0.08% (including zero) and Cu<=0.25% (including zero), and in which nonmetallic inclusions in the steel prescribed by the method A in the ASTM method satisfy A series (Thin)<=3.0%, A series (Heavy)<=2.0%, B series (Thin)<=3.0%, B series (Heavy)<=1.0%, C series (Thin)<=0.5%, C series (Heavy)<=0.5%, D series (Thin)<=1.0%, D series (Heavy)<=1.0% and A series + B series + C series + D series <=8.0% (including zero as for all of the above inclusions) is formed. After that, heat treatment is executed at the quenching and tempering temps. satisfying the index of surface hardness prescribed by the formula.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for efficiently producing bearing parts such as ball bearings and roller bearings used in automobiles and various industrial machines. The present invention relates to a method of manufacturing a bearing component having excellent cold workability even when the spheroidizing annealing treatment is simplified or omitted.

[0002]

2. Description of the Related Art Conventionally, JIS G48 has been used as a bearing steel.
High carbon chromium bearing steel such as SUJ2 specified in No. 05 is used. In manufacturing a bearing component using such a bearing steel, first, after performing a spheroidizing annealing treatment,
Cold forging and cutting are sequentially performed to form bearing parts, which are then quenched and tempered to adjust the structure of the parts to the specified properties (that is, containing a few percent of spherical carbides and residual austenite. However, by making the balance martensite), various characteristics (hereinafter sometimes referred to as bearing characteristics) required for the bearing component such as rolling fatigue resistance, wear resistance, and dimensional stability have been secured.

As described above, in the conventional manufacturing process, the spheroidizing annealing treatment is always performed, and thereby the cold workability is improved and the spherical carbide remaining after the quenching / tempering performed after the forming process is performed. Are dispersed finely and uniformly to secure the above-mentioned bearing characteristics required for bearing parts. However, since this spheroidizing annealing consumes a lot of time and consumes a lot of energy, there is an increasing demand for simplifying or omitting the spheroidizing annealing in order to save energy and reduce the manufacturing cost. .

However, in the case of using the conventional high carbon chromium bearing steel, when the bearing parts are manufactured by simplifying or omitting the spheroidizing annealing treatment, the bearing characteristics such as cold workability and rolling fatigue property are deteriorated. There is a problem of decrease. Problems like this
For example, like the bearing steel described in Japanese Patent Publication No. 5-85629,
The same can be seen in the case of using a bearing steel in which the content of P, S, O, and Ti is reduced and the amount and size of nonmetallic inclusions in the steel are controlled to improve the durability life.

Therefore, even if the spheroidizing annealing treatment is simplified or omitted, the same degree as in the case of using the conventional high carbon chromium bearing steel or There is a strong demand for a new method capable of manufacturing a bearing component having cold workability and machinability higher than that.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to obtain good cold workability even when the spheroidizing annealing treatment is simplified or omitted. Another object of the present invention is to provide a method for efficiently manufacturing a bearing component having bearing properties such as machinability, rolling fatigue life, and the like.

[0007]

The manufacturing method of the present invention which has been able to solve the above-mentioned problems is C: 0.5-0.9%,
Si: 1.0% or less (including 0%), Mn: 0.2 to
1.5%, P: 0.03% or less (including 0%), Ni:
0.25% or less (including 0%), Mo: 0.08% or less (including 0%), Cu: 0.25% or less (including 0%)
And non-metallic inclusions in the steel specified by the method A of the ASTM method are A type (Thin): 3.0 or less, A
System (Heavy): 2.0 or less, B system (Thin): 3.0 or less, B system (Heavy): 1.0 or less, C system (Thin): 0.
5 or less, C system (Heavy): 0.5 or less, D system (Thin):
1.0 or less, D system (Heavy): 1.0 or less, A system + B system + C system + D system: 8.0 or less (all non-metallic inclusions of A system, B system, C system and D system are 0) After forming a steel satisfying the following conditions (1) and (2), heat treatment is performed at a quenching / tempering temperature satisfying the surface hardness index defined by the following formula (1). H = -14.8 + √ [C] + 0.12 [Mn] + 0.11 [Cr] + 5.8 · log (T ₁ ) -8.2 × 10 ^-4 × (T ₂ ) ≧ 3.48 (1) ( In the formula, H is the surface hardness index, [] is the mass% of each element,
(T ₁ means tempering temperature (K), T ₂ means tempering temperature (K), respectively)

In the present invention, in order to obtain a more excellent rolling contact fatigue life, Cr:
At least selected from the group consisting of 1.2% or less (not including 0%), V: 0.3% or less (not including 0%), Nb: 0.1% or less (not including 0%). Pb: 0.1 for the purpose of containing one kind or improving the machinability.
% Or less (not including 0%), Ca: 0.01% or less (0
%), Te: 0.1% or less (not including 0%), Bi: 0.1% or less (not including 0%), at least one selected from the group consisting of It is a preferred embodiment of the present invention.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION As a result of searching for a new bearing steel capable of solving the above-mentioned problems, the present inventors have found that by controlling the chemical composition of the steel from a viewpoint different from that of the conventional bearing steel. It has been found that the purpose of the term can be achieved, and the application has already been completed (Japanese Patent Laid-Open No. 2-54739).
issue). Specifically, even if the amount of C in steel is controlled to a small amount (that is, even if spheroidized carbide does not remain in the structure after quenching / tempering), the content of O or Ti is minimized. Al ₂ O ₃ and Ti which are lowered to adversely affect rolling fatigue
It has been found that sufficient rolling contact fatigue resistance can be obtained by reducing the amount of N produced.

After the above-mentioned application, the inventors of the present invention have further conducted studies for the purpose of providing a bearing component having more excellent cold workability and bearing characteristics. In particular, the inventors have found that controlling the steel composition, the amount of non-metallic inclusions, and the quenching / tempering temperature as described below is very effective in improving the above-mentioned properties, and completed the present invention.

(I) The chemical composition of steel is C, Ni,
In addition to Mo and Cu, if necessary, the amount of Cr is controlled to be as small as possible to suppress the generation of a bainite structure that adversely affects cold workability, and it is a pearlite structure that does not adversely affect cold workability. Even hard Fe ₃ C
By reducing the amount, generation of bainite structure is suppressed and deformation resistance, cutting resistance, etc. are reduced. (Ii) Al ₂ O ₃ and TiN measured according to the ASTM method
By controlling the amount of hard inclusions such as, the wear of the cutting tool is suppressed and the occurrence of cracks during cold working is suppressed. (Iii) Surface hardness index (H) calculated by the following formula (1)
By controlling the quenching / tempering temperature so that the value becomes 3.48 or more, rolling fatigue resistance equivalent to or more than that in the case of using the conventional high carbon chromium bearing steel can be obtained. H = -14.8 + √ [C] + 0.12 [Mn] + 0.11 [Cr] + 5.8 · log (T ₁ ) -8.2 × 10 ^-4 × (T ₂ ) ≧ 3.48 (1) ( In the formula, [] means mass% of each element, T ₁ means quenching temperature (K), and T ₂ means tempering temperature (K), respectively.)

The requirements that characterize the present invention will be described below. First, the reason for defining the chemical composition of the bearing steel in the present invention will be described. C: 0.5 to 0.9% C is an element necessary to obtain hardness (HRC) of 58 or higher after quenching / tempering and to secure bearing characteristics such as rolling fatigue. If the C content is less than 0.5%, such an effect cannot be effectively exhibited. A preferable lower limit value is 0.7%. However, if added in excess, the cold workability and machinability deteriorate, so the upper limit is made 0.9%.

Si: 1.0% or less (including 0%) Si acts as a deoxidizing agent and enhances the hardenability and the softening resistance after tempering. Since the inter-workability and machinability deteriorate, the upper limit is 1.
Set to 0%. A preferable upper limit value is 0.5%.

Mn: 0.2-1.5% Mn acts as a deoxidizing / desulfurizing element, and also improves the hardenability to increase the hardness of the surface layer and the interior, thereby improving the rolling fatigue life. It is an element effective in preventing the depression of the surface. 0.2 is effective to exert such action effectively.
% Or more is required. The preferred lower limit is 0.5%
It is. However, even if added in excess of 1.5%, the effect reaches saturation, and rather there arises a problem that cold workability and machinability deteriorate. The preferable upper limit value is 1.1%.

P: 0.03% or less (including 0%) P is an element that reduces toughness, so it is desirable that the content thereof be as small as possible. However, in order to further reduce the P content in the low concentration range from the beginning, a large amount of burden is required for the deP treatment, so for economic reasons, the P level obtained by the ordinary deP treatment, that is, 0.03% or less is set. At this level, there is no particular adverse effect in the present invention.

Ni: 0.25% or less and Mo: 0.0
8% or less (including both 0%) Ni and Mo are both elements that improve the hardenability, and are elements useful for easily performing the quenching / tempering treatment on a part having a large mass. However, when the upper limits thereof exceed Ni: 0.25% and Mo: 0.08%, cold workability and machinability are deteriorated, and quenching /
After tempering, a large amount of retained austenite is generated, which deteriorates dimensional stability. A preferable upper limit value is Ni: 0.10%
And Mo: 0.05%.

Cu: 0.25% or less (including 0%) Cu is an element useful for improving hardenability and corrosion resistance, and also for increasing wear resistance by age hardening.
If it is added in excess of 0.25%, cold workability and machinability are deteriorated, and red hot embrittlement is promoted to cause cracking during hot working. A preferable upper limit value is 0.10%.

The bearing steel used in the present invention essentially contains the above chemical components, but for the purpose of further improving rolling fatigue life and machinability, the following (a) and / or The chemical component (b) can be positively added as a selectively acceptable component.

(A) Cr: 1.2% or less, V: 0.3%
Or less and / or Nb: 0.1% or less (any element is 0
% Is not included) All of these elements are elements that contribute to the improvement of rolling contact fatigue life. Hereinafter, each element will be described.

Cr: 1.2% or less Cr is an element effective for improving the hardenability and increasing the hardness of the surface layer and the inside to improve the rolling contact fatigue life and prevent the depression of the surface. . Addition of 0.2% or more is preferable to effectively exhibit such an effect. On the other hand, if added in excess, cold workability and machinability deteriorate, so the upper limit is preferably made 1.2%. It is more preferably 1.0% or less.

V: 0.3% or less, Nb: 0.1% or less V and Nb both combine with C and N in the steel to form carbonitrides, and refine the crystal grains to cause rolling fatigue. To improve
It is an element effective in increasing toughness. In order to exert such an effect effectively, it is recommended to add both V and Nb in an amount of 0.01% or more. However, V: 0.
Even if added in excess of 3% and Nb: 0.1%, the effect of refining the crystal grains is saturated, which is economically useless.

(B) Pb: 0.1% or less, Ca: 0.0
1% or less, Te: 0.1% or less and / or Bi: 0.1
% Or less (all elements do not include 0%) All of these elements are machinability improving elements, and if each is within the above range, machinability can be improved. Even if it is added, its action is saturated, and it is useless, and adversely, such as a decrease in rolling contact fatigue life, and the like, which adversely affects it. Therefore, the upper limits are defined as above.

In addition, in the present invention, the amount of non-metallic inclusions is specified (to be described later) for the purpose of improving cold workability and rolling contact fatigue resistance. It is preferable to reduce the content of certain S, Ti, O, etc.,
S: 0.03% or less, Ti: 0.005% or less, O:
It is recommended to be 0.002% or less.

Furthermore, in the present invention, it is necessary to control the amount of non-metallic inclusions in the steel specified in ASTM method A as follows. A system (Thin): 3.0 or less, A system (Heavy): 2.0 or less B system (Thin): 3.0 or less, B system (Heavy): 1.0 or less C system (Thin): 0. 5 or less, C system (Heavy): 0.5 or less D system (Thin): 1.0 or less, D system (Heavy): 1.0 or less A system + B system + C system + D system: 8.0 or less (above A All non-metallic inclusions in the system, B system, C system and D system include 0) Note that the sum of (A system + B system + C system + D system) is the total value including both thin system and heavy system. Means

In the present invention, the amount of non-metallic inclusions that adversely affect cold workability, rolling contact fatigue resistance, etc. is controlled by the ASTM method instead of the JIS method.
Here, the JIS method and the ASTM method are the same in the broad sense of "measuring the amount of non-metallic inclusions by a microscope method", but the total number of various inclusions occupied by the JIS method in one visual field is In contrast to the measurement, the ASTM method
Each view of the test piece is compared with the view of the standard view, and the morphology of inclusions (A to D system) and Thin system and Heav observed in one view
It records the evaluation numbers described in the standard diagram that most closely resembles both y systems, and calculates the average value.
JIS method to measure "total number" and "size (width,
Select the most similar standard drawing based on (length) "A
It can be said that the measuring method is strictly different from the STM method. Then, in the present invention, for each of various inclusion forms A to D systems calculated based on the ASTM method, the upper limits of the Thin system and the Heavy system are finely controlled, and
Total amount of inclusions (A type + heavy type)
By defining the upper limit of (B type + C type + D type) as well, it is possible to reduce the amount of inclusions that adversely affect cold workability and rolling fatigue, and as a result, prevent the occurrence of cracks during cold working. It is what

Next, after forming the steel satisfying the above requirements, the surface hardness index (H) defined by the above formula (1).
Although the heat treatment is performed at a quenching / tempering temperature that satisfies the above conditions, the present invention has the greatest feature in performing such heat treatment.

That is, the above equation (1) ensures the same or better bearing characteristics as in the case of using the conventional high carbon chromium bearing steel even when the spheroidizing annealing treatment is simplified or omitted. The content of C, Mn, and Cr, which are steel components that have a great influence on the improvement of rolling fatigue life, and the quenching / tempering temperature are determined. When the surface hardness index calculated by this formula is 3.48 or more, good rolling contact fatigue life can be obtained. A preferred lower limit value is 3.50. Although Cr in the formula is a selectively permissible component, even if the amount of unavoidable impurities is contained, the rolling fatigue life achieved by determining the quenching / tempering temperature and by setting the above formula. Is a component that has a great influence on the improvement of the above, and is a major factor constituting the above equation.

Next, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples, and changes may be made within a range compatible with the spirit of the preceding and following statements. Of course, it is possible to carry out, and all of them are included in the technical scope of the present invention.

[0029]

【Example】

Example 1 After the steel having the chemical composition shown in Table 1 was melted in a small vacuum furnace, it was forged into a round bar of φ65 mm or φ25 mm by hot forging. Further, No. 28 is a conventional steel equivalent to JIS SUJ2, and after being melted in the same manner as above, 1200
The soaking treatment was performed under the condition of ° C x 20 hours to carry out diffusion disappearance treatment of the giant carbide, and then forged into a round bar in the same manner as above.

The following characteristics of each round bar thus obtained were evaluated. The heat treatments A (spheroidizing annealing), B (annealing), and C (normalizing) performed in evaluating the following characteristics are the following heat treatments. A: 790 ° C x 2 hours → temperature of 680 ° C up to 20 ° C / h
Furnace cooling at r, then air cooling B: 700 ° C × 3 hours → air cooling C: 870 ° C × 1 hour → air cooling

[Rolling Fatigue Property] Regarding each round bar forged to φ65 mm, heat treatment A was applied to No. 28 and heat treatment B was applied to the other steels. Next, from the cross section, a diameter of 60 mm,
A disk with a thickness of 5 mm is cut out, quenched at 840 ° C., tempered at 160 ° C., and subjected to lapping,
A rolling fatigue test was carried out under the condition of a surface pressure of 527 kgf / mm ² .

[Machinability] For each round bar forged to φ65 mm, No. 28 was subjected to heat treatment A, No. 1 and No. 2 of the steels of the present invention were subjected to heat treatments A to C, and other steels. For the above, heat treatment B was performed. Next, a machinability was evaluated by performing a cutting test using a cemented carbide tool under the following conditions. Tool used: P10 Cutting speed: 150 m / min Feed: 0.25 mm / rev Cutting depth: 1.5 mm Cutting oil: None (dry type) Tool life standard: VB = 0.2 mm

[Cold workability (deformation resistance and deformability)]
With respect to each round bar forged to φ25 mm, No. 28 was subjected to heat treatment A, No. 1 and No. 2 of the invention steels were subjected to heat treatments A to C, and other steels were subjected to heat treatment B. Next, after machining was performed to prepare the test piece shown in FIG. 1, the cold workability was evaluated. In the figure, (a) shows a plan view and a side view of the test piece, and (b) is an enlarged view of a portion A. In the figure, D is 20 mm and H is 30 mm.

Regarding the deformation resistance in the cold workability, a test piece without notch (V = 0 mm) is used, and the deformation resistance when constrained compression deformation is performed under the condition of a compression rate of 60%. It was evaluated by On the other hand, regarding the deformability, a test piece with a notch (V = 0.3 mm) was used, the compressive ratio was changed by 2.5%, and constrained compressive deformation was applied, and the minimum compression at which cracking was observed. The deformability was evaluated by the rate (cracking limit compression rate).

Table 2 shows various characteristic results and surface hardness index (H) thus measured. In the evaluation of rolling contact fatigue resistance, the ratio when L ₁₀ (10% cumulative failure rate) of No. 28 was set to 1 was used.

[0036]

[Table 1]

[0037]

[Table 2]

From these results, the following can be considered. Nos. 1 to 15 are examples satisfying all the prescribed requirements of the present invention. Even if the spheroidizing annealing treatment is simplified (heat treatment B), machinability and cold workability are No. 28 of the conventional example.
Even when the treatment was omitted (heat treatment C), the effect was comparable to that of the conventional example. Then, similarly to the conventional example, a spheroidizing annealing process is performed (heat treatment A).
Then, it was found that the effect was remarkably improved. Regarding the rolling fatigue property, regardless of the type of heat treatment conditions, the rolling fatigue property was as good as or better than that of the conventional example.
On the other hand, Comparative Example No. 1 which does not satisfy the requirements of the present invention
6 to 27 are accompanied by the following problems.

Low C content and surface hardness index (H)
No. 16 having a small number is excellent in machinability and cold workability as compared with Conventional Example No. 28, but the rolling fatigue life is inferior.

Further, No. 17 having a high C content, No. 18 having a high Si content, No. 19 having a high Mn content, No. 21 having a high Ni content, No. 22 having a high Cu content and No. 23, which has a high Mo content, is inferior to the conventional example in machinability and cold workability. In addition, No. 20, which has a large P content, is inferior to the conventional example in cold workability and rolling fatigue life.

Further, No. 24, which has a large amount of A type inclusions, has improved machinability as compared with the conventional example, but has reduced rolling fatigue life and cold workability. No. 25, which has a large amount of B-type inclusions, No. 26, which has a large amount of C-type inclusions, and No. 27, which has a large amount of D-type inclusions, have the conventional rolling fatigue life, machinability, and cold workability. Inferior to the example.

Example 2 Of the steel materials having the chemical composition shown in Table 1, No. 1 was used,
After quenching and tempering treatments at various temperatures shown in Table 3, a rolling fatigue test was conducted in the same manner as in Example 1. The obtained results and the surface hardness index (H) are shown in Table 3.

[0043]

[Table 3]

As is clear from Table 3, when the steel composition and the surface hardness index satisfy the requirements of the present invention, the rolling fatigue life shows the same good value as that of the conventional example, but the surface hardness Quenching so that the hardness index is less than 3.48 specified in the present invention.
It can be seen that when the tempering treatment is performed, the rolling fatigue resistance is significantly reduced.

[0045]

The present invention is configured as described above, and even when the spheroidizing annealing treatment is simplified or omitted,
Efficiently manufacture bearing parts with cold workability and machinability equivalent to or better than when using conventional high carbon chromium bearing steel without degrading bearing characteristics such as rolling fatigue life. be able to.

[Brief description of drawings]

FIG. 1 is a diagram showing a shape of a test piece for evaluating cold workability in Examples.

Claims (3)

[Claims] 1. C: 0.5 to 0.9% (mass%, the same hereinafter), Si: 1.0% or less (including 0%), Mn: 0.
2 to 1.5%, P: 0.03% or less (including 0%),
Ni: 0.25% or less (including 0%), Mo: 0.08
% Or less (including 0%), Cu: 0.25% or less (including 0%), and the non-metallic inclusions in the steel specified in the ASTM method A are A type (Thin): 3.0 or less,
A system (Heavy): 2.0 or less, B system (Thin): 3.0 or less, B system (Heavy): 1.0 or less, C system (Thin): 0.
5 or less, C system (Heavy): 0.5 or less, D system (Thin):
1.0 or less, D system (Heavy): 1.0 or less, A system + B system + C system + D system: 8.0 or less (all non-metallic inclusions of A system, B system, C system and D system are 0) Bearing having excellent cold workability, which is characterized by performing heat treatment at a quenching / tempering temperature satisfying a surface hardness index defined by the following formula (1) after forming and processing a steel satisfying Manufacturing method of parts. H = -14.8 + √ [C] + 0.12 [Mn] + 0.11 [Cr] + 5.8 · log (T ₁ ) -8.2 × 10 ^-4 × (T ₂ ) ≧ 3.48 (1) ( In the formula, H is the surface hardness index, [] is the mass% of each element,
(T ₁ means tempering temperature (K), T ₂ means tempering temperature (K), respectively) 2. The steel further comprises Cr: 1.2% or less (0
%), V: 0.3% or less (0% is not included), Nb: 0.1% or less (0% is not included), and at least one selected from the group consisting of The manufacturing method according to claim 1. 3. The steel further comprises Pb: 0.1% or less (0
%), Ca: 0.01% or less (0% is not included), Te: 0.1% or less (0% is not included), Bi:
The production method according to claim 1 or 2, which contains at least one selected from the group consisting of 0.1% or less (not including 0%).