JPH02125838A - Rolling bearing - Google Patents

Abstract

PURPOSE:To prevent the generation of cracks in the title bearing at the time of plastic working and to prolong its service life by forming at least either of the inner ring and outer ring of a rolling bearing with the compsn. of a steel having specified contents ot C, Si, Mn, Cr, P, S and O. CONSTITUTION:At least either of the inner ring and outer ring of a bearing is formed by subjecting a steel constituted of, by weight, 0.4 to 0.7% C, <=0.04% Si, 0.4 to <=1.0% Mn, 0.4 to 1.0% Cr, <=0.025% P, <=0.003% S, <=0.0015% O and the balance Fe with inevitable impurities to plastic working. Then, the steel is subjected to surface hardening heat treatment if necessary. In this way, the rolling bearing having no generation of cracks even if subjected to forming working into the final shape by cold forging, etc., can be obtd. At least either of <=0.2% Nb or V is furthermore incorporated into the above steel, by which the rolling service life can moreover be improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to rolling bearings used in automobiles, agricultural machinery, construction machinery, steel machinery, etc., and in particular, rolling bearings that have a long life required for transmissions and engines. Regarding rolling bearings.

[Conventional technology]

Conventionally, when manufacturing the inner and outer rings of rolling bearings such as rolling ball bearings and 7 spherical roller bearings using bearing steel (for example, JIS5UJ-2), cold rolling is used to manufacture cylindrical blanks. It has been practiced to plastically process steel into a ring shape until turning after cold rolling becomes unnecessary.

However, when the above plastic working was performed, the inner ring.

It has been known that minute cracks or cracks occur on the inside of the outer ring, and this becomes the starting point for the crank. Therefore,
The applicant of this application has proposed a rolling bearing that can prevent the occurrence of cranks during plastic working such as cold rolling and upsetting (Japanese Patent Application No. 172030/1982).

[Problem to be solved by the invention]

When the above crank occurs, it causes the inner race,
This causes cracking of the outer ring. Therefore, 0.4 to 0.7 mm of extra metal is added to the skin of the inner and outer rings in advance, and since this excess metal causes cranking, machining has been carried out in which the excess metal is scraped off after the plastic working is completed. .

On the other hand, in order to omit the addition and deletion of such extra thickness, it is necessary to perform plastic working with a certain degree of reduction in processing power, and then add turning work to form the product into the final shape.

However, this not only complicates the rolling bearing manufacturing process but also increases material yield and production costs. Therefore, the conventional problem has been how to obtain a rolling bearing that is less prone to cranking during plastic working and has a longer life.

In order to solve these conventional unresolved problems, the present invention aims to provide a rolling bearing that does not generate cracks during plastic working, and in addition, provides a rolling bearing that has a longer service life. The second purpose is to

[Means to solve the problem]

The invention according to claim (1) for achieving the above first object is a rolling bearing comprising an inner ring, an outer ring, and a rolling element, in which at least one of the inner ring and the outer ring has a weight percentage of
CiO, 4-0.7%, si; 0.04% or less, Mn;
0.4-1.0%, Cr; 0.4%-1.0%, P; 0
．． 025% or less, siQ, 003% or less, O; 0.00
It is characterized by being made of steel that has been plastically worked, with the content being 15% or less, and the remainder being Fe and unavoidable impurities.

Further, the invention according to claim (2) to achieve the above second object provides a rolling bearing comprising an inner ring, an outer ring, and a rolling element, in which at least one of the inner ring and the outer ring has a C; , 4-0. 7%, Si: 0.04% or less, Mn: 0.4-1.0%, Cr: 0.4%-1.
0%, P: 0.025% or less, Sin, 003% or less,
The steel is characterized in that the steel is plastically worked and then subjected to surface hardening heat treatment, with an O content of 0.015% or less, and the remainder consisting of Fe and unavoidable impurities.

Furthermore, claim (3) for achieving the second objective above.
The described invention provides a rolling bearing comprising an inner ring, an outer ring, and a rolling element, in which at least one of the inner ring and the outer ring contains C: 0.4 to 0.7%, Si: 0.04% or less, Mn in weight percent. ; 0. 4-1. 0%, Cr; 0.4%~
1.0%, P: 0.025% or less, S: 0,003% or less, O: 0.0015% or less 1, at least one of Nb or ■; 0.2% or less, the remainder being Fe and unavoidable It is characterized by being made of steel made of impurities that is plastically worked and then subjected to surface hardening heat treatment.

[Effect]

The inventors of the present application have conducted various studies on the occurrence of cracks during plastic working of rolling bearings and the extension of the life of rolling bearings, and have found that the relationship between the S content and the crack incidence during plastic working,
We have obtained various new knowledge regarding the relationship between crystal grain size and life, and based on this knowledge, we have arrived at the present invention as described in the claims.

Next, the effects of various elements used in the present invention and the critical significance of their content will be explained.

(C) C becomes longer than 0.4% by weight (hereinafter simply referred to as %), and heat treatment productivity decreases. Furthermore, if the content exceeds 0.7%, the deformation resistance increases and the plastic workability, especially the cold rolling property, deteriorates, resulting in the occurrence of cranks. Therefore,
Based on the above, the amount of C was limited within the range of the above values.

(Sl) Si is necessary as a deoxidizing agent, but if it is contained in an amount exceeding 0.04%, plastic workability will decrease and cracks will occur, so the amount of Si was limited to within the above range. .

(Mn) Mn is an element necessary to improve the hardenability of steel, but if it is less than 0.4%, the hardenability decreases, and if it is contained more than 1.0%, the hardness increases. , machinability such as machinability and forgeability, especially hot workability, are reduced, so its content was limited to within the range of the above values.

(Cr) Cr is an element necessary to improve the hardenability and wear resistance of steel, but if it is less than 0.4%, the hardenability is insufficient, and if it is contained more than 1.0%, the hardenability is insufficient. A large amount of Cr carbide is generated, resulting in a decrease in rolling fatigue life. Therefore, its content was limited to within the range of the above values.

(P) If the P content is more than 0.025%, machinability decreases, so the upper limit of the content was limited to "-plantation".

(S) S causes the formation of sulfide-based nonmetallic inclusions such as MnS. Since MnS has low hardness and high plastic deformability, it acts as a starting point for crank generation during plastic working such as cold rolling. Therefore, in order to prevent cracking during plastic working of rolling bearings and enable stronger working, it is necessary to reduce the S content, and the upper limit is set to less than 0.003%.

Since 0 is an oxide-based nonmetallic inclusion-generating element that reduces the rolling fatigue life of rolling bearings, it is necessary to reduce its content as much as possible, so the upper limit was set at 0.0015%.

(Nb, V) Nb and V are effective elements for precipitating at grain boundaries and suppressing their coarsening, making the grains finer, and extending the life of the bearing. In particular, if high-temperature heat treatment (950 to 970°C) is performed to shorten the carburizing and carbonitriding time, crystal grains tend to become coarse, but even in this case it is effective in preventing coarse grains.

Therefore, at least one of Nb or (2) was contained in an amount of 0.2% or less. Even if the content exceeds 0.2%, there is little improvement in the effect of refining crystal grains, and the cost increases.
The upper limit of its content was limited to the above value.

Note that the lower limits of the contents of Nb and V mentioned above are desirably 0.03% for Nb and 0.1% for ■. ” In the invention described in claim (1), since the rolling bearing has an S content of 0.003% or less, M, which is the starting point of the crank,
It is made of steel that suppresses the generation of sulfide-based nonmetallic inclusions such as nS and has improved formability. Therefore, even if the final shape is formed by plastic working such as cold rolling, the occurrence of cracks can be prevented.

In the invention described in claim (2), since the steel described in claim (1) is subjected to surface hardening heat treatment such as quenching, carburizing, carbonitriding, etc., cranking does not occur during plastic working, and moreover, bearing It is possible to improve the lifespan of people.

Furthermore, in the invention described in claim (3), since the steel described in claim (2) contains Nb and V that can prevent coarsening of crystal grains, the life of the bearing can be further extended. .

〔Example〕

Next, examples of the present invention will be described.

Example steels (Al to A8) and comparative steels (Bl to B4) having the compositions shown in Table 1 below were melted in a 100 kgf vacuum melting furnace, and after soaking the steel ingots, they were forged to φ50.

(Hereinafter, blank space) Next, the steel listed in Table 1 is annealed to form a spheroid, then turned into a predetermined blank shape, and then cold rolled without constraining the outer diameters of the inner and outer rings of the single-row deep groove ball bearing. The molding process was performed at.

FIG. 1 shows a half cross section of the inner ring and the outer ring in the thickness direction. FIG. 1 (1) shows a cylindrical blank before cold rolling of the outer ring, and FIG. 1 (2) shows an outer ring obtained by cold rolling this cylindrical blank. (
1) In the figure, dl is the outer ring radius before cold rolling, and (2) in the figure, d2 is the outer ring radius after cold rolling. Furthermore, in Figure (2), numeral 1 indicates a deep groove on the outer ring side formed as a result of cold rolling.

Further, FIG. 1(3) shows a cylindrical blank before cold rolling of the inner ring, and FIG. 1(4) shows an inner ring obtained by cold rolling this cylindrical blank.

In the figure (3), dl is the radius of the inner ring before cold rolling, and in the figure (4), d2 is the radius of the inner ring after cold rolling. Moreover, in FIG. (4), 2 is a groove on the inner ring side formed as a result of cold rolling.

In FIG. 1, the radius of the blank before cold rolling (d
) and the radius (d2) of the molded product after cold rolling (dz/
d+) is a rolling ratio, and the larger this ratio is, the greater the working strength in cold rolling is.

Therefore, the molding process was performed while changing the cold rolling ratio, and the presence or absence of cranks occurring in the inner and outer rings was visually inspected. The results are shown in Table 2 below. It is known that this crack occurs on the inner diameter side (3 in FIG. 1) as a symbiotic relationship between the inner and outer rings.

(Hereinafter, blank space) Table 2 In Table 2, (1) indicates that the rolling ratio (d+/dz) is -1
, 45, and (2) is the rolling ratio (d+/dz)! =i
It shows that it is 1.6.

Looking at Table 2, it can be seen that in comparative steels Bl and B2, the Si content was outside the range of the present invention, so the plastic workability decreased.
When the processing strength during cold rolling increases (rolling ratio is approximately 1
．． 6) It can be seen that cranking occurs on both the inner and outer rings.

In addition, in comparative example steel B3, the content of C, the content of Si,
Since the Cr content is outside the range of the present invention, the deformation resistance is high (the deformation resistance becomes large), and the working strength during cold rolling is low (rolling ratio is about 1.45) and when the working strength is high. (When the rolling ratio was approximately 1.6), cracks were found in both the inner and outer rings.

In addition, in Comparative Example Steel B4, since the S content is outside the range of the present invention, many sulfide-based nonmetallic inclusions are generated, and the working strength during cold rolling is low and the working strength is high. In this case, it can be seen that the crank occurs on both the inner and outer rings.

On the other hand, it can be seen that in the example steel, no cracks occurred in either the inner ring or the outer ring, not only when the working strength during cold rolling was low, but also even when the working strength was high.

The example steel Al-A3 shown in Table 2 above has good formability, and even when plastic forming is performed to the final shape by cold rolling, the rolling ratio is in the range of, for example, 1.45 to 1.6. Since no cracks occur, the process of adding extra thickness to the cylindrical blank material and removing this extra thickness after rolling can be omitted, which simplifies the bearing manufacturing process. As a result, it is possible to improve material yield and reduce production costs.

Next, a rolling bearing is completed using the formed rings (inner ring, outer ring) that have been cold rolled at the rolling ratio of 1.45,
This was subjected to heat treatment of quenching or carburizing (carbonitriding may also be used) followed by quenching and then tempering as shown in Table 3 below.

Among the heat treatments shown in Table 3, carburizing heat treatment is R,
Approximately 3 hours at 930°C in a gas + enriched gas atmosphere
Heat treated at ±5°C, then oil quenched, and further heated to 160°C.
Tempering was carried out at °C for 2 hours.

In addition, Comparative Example Steel B2. B3. Since B4 had minute racks densely grown after cold rolling, the crank-generating portion was removed by turning and then subjected to the above-mentioned surface hardening heat treatment.

Then, the surface hardness of the heat-treated rolling bearings was measured, and "Special Steel Handbook (1st edition), Electric Steel Research Institute Line, Rigakusha, May 25, 1965, 10th
Rolling fatigue life (L+
(denoted by o) test was conducted. The test conditions are as follows.

Radial load (Fr) = 1400kg-f/mm2N
=400Or, p, m Lubricant oil #68 Turbine oil bath The results are shown in Table 3 below.

(Hereinafter, blank space) In Table 3, Example steel A2. A3. A8 contains Nb or ■, which makes the crystal grains fine, so these N
It can be seen that the transfer life is further improved compared to other example steels that did not contain B or V and were simply heat treated.

〔Effect of the invention〕

As explained above, according to the invention described in claim (1),
It is possible to provide a rolling bearing in which cranking does not occur even when the final shape is formed by plastic working such as cold rolling.

Furthermore, according to the invention described in claim (2), claim (1)
Since the steel described above is subjected to surface hardening heat treatment such as quenching or carburizing/carbonitriding quenching, it is possible to provide a rolling bearing that does not generate cracks during plastic working and has an improved lifespan.

Furthermore, according to the invention described in claim (3), claim (2)
) Nb or ■ which can prevent coarsening of crystal grains in the steel described
Because it contains at least one type of Nozuku, it is possible to provide rolling bearings that do not cause cranking during plastic working and have a further improved lifespan.

[Brief explanation of the drawing]

FIG. 1 is a half-sectional view in the thickness direction of an inner ring and an outer ring before and after cold rolling.

Claims (3)

[Claims] (1) In a rolling bearing consisting of an inner ring, an outer ring, and a rolling element, at least one of the inner ring and the outer ring has a weight percentage of
C; 0.4 to 0.7%, Si; 0.04% or less, Mn;
0.4-1.0%, Cr; 0.4-1.0%, P; 0.
025% or less, S; 0.003% or less, O; 0.001
A rolling bearing characterized in that the content is 5% or less, and the remainder is made of plastically worked steel containing Fe and unavoidable impurities. (2) In a rolling bearing consisting of an inner ring, an outer ring, and a rolling element, at least one of the inner ring and the outer ring has a weight percentage of
C; 0.4 to 0.7%, Si; 0.04% or less, Mn;
0.4-1.0%, Cr; 0.4-1.0%, P; 0.
025% or less, S; 0.003% or less, O; 0.001
5% or less, the remainder being Fe and unavoidable impurities. A rolling bearing characterized in that the steel is plastically worked and then subjected to surface hardening heat treatment. (3) In a rolling bearing consisting of an inner ring, an outer ring, and a rolling element, at least one of the inner ring and the outer ring has a weight percentage of
C; 0.4 to 0.7%, Si; 0.04% or less, Mn;
0.4-1.0%, Cr; 0.4-1.0%, P; 0.
025% or less, S; 0.003% or less, O; 0.001
5% or less, at least one of Nb or V; 0.2% or less, the remainder being Fe and unavoidable impurities. A rolling bearing comprising steel that is plastically worked and then subjected to surface hardening heat treatment.