JPS601932B2 - Manufacturing method of rolling bearing steel pipe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a high carbon chromium bearing steel pipe with excellent rolling fatigue strength.

In the bearing manufacturing industry, there is always a demand for steel materials with excellent rolling fatigue strength (hereinafter referred to as life).

For this reason, degassing is performed for normal applications, and for applications requiring a longer life, vacuum remelting is performed to further lower the oxygen content in the steel.
However, vacuum remelting increases costs and is not necessarily the best method. Additionally, oxygen and the like once remaining in the steel cannot be removed except by methods such as vacuum remelting.

Therefore, the present invention was developed as a result of research on a method for making these non-metallic inclusions (hereinafter referred to as inclusions) harmless, which inevitably remain and have a negative effect on the lifespan, and thereby improving the lifespan. In other words, the gist of the present invention is that CO
．． 80-1.20%, Sio. 05-1.50%, Mn
o. 20-2.00%, P<0.030, Cro. 8～
2.0%, SO. 010-0.050%, 0<0.00
17%, N < 0.0100%, Ti < 0.007%, the balance is Fe and inevitably remaining impurities, and the rolling bearing steel has a sulfur to oxygen ratio (S/○) of 8 or more. A steel pipe with rolling fatigue strength characterized by making a base material steel pipe by rolling or hot extrusion, and then subjecting it to European annealing and then cold rolling with a surface loss ratio of 50% or more to finish it into a finished product. Excellent method for manufacturing rolling bearing steel pipes and CO. 80-1.20%, S core 05-1.50%, Mn
o. 20-2.00%, Cro. 8-2.0%, P<0
．． 030, SO. 010-0.050%, 0<0.00
17%, N<0.0100%, Ti<0.007%, M
OO. 05 to 0.30%, the balance is Fe and inevitably remaining impurities, and the ratio of sulfur to oxygen (S/○) is 8
The above-mentioned rolling bearing steel is hot-rolled or hot-extruded to form a base material steel pipe, and after softening and annealing, it is subjected to one round rolling process with an area reduction rate of 50% or more to finish it into finished product dimensions. This is a method for manufacturing rolling bearing steel pipes with excellent rolling fatigue strength.

That is, a high carbon chromium bearing steel pipe having the above-mentioned chemical composition and composition ratio is subjected to cold rolling with a strength of an area reduction of 50% or more in one step using a steel pipe cold rolling machine such as a cold Pilger mill. We have discovered that crushing inclusions eliminates their harmful effects on the lifespan and nearly doubles the lifespan, leading to the present invention.

In general, large oxide-based inclusions such as AI203 and Si02, and Ti-based carbonitrides act as stress concentration sources in steel, promoting crack formation and reducing service life.

Therefore, if these inclusions are made finer, their harmfulness can be considerably reduced. Regarding this point, in the present invention, it has been found that it is possible to achieve this by subjecting steel having the components specified in the present invention to cold working once with an area reduction rate of 50% or more. As will be described later, even if processing is performed such that the total area reduction rate becomes 50% or more by, for example, several drawings, no improvement in life will be obtained.

Further, sulfides usually exist alone in steel as MnS or as MnS containing oxide inclusions. In order to improve the lifespan, it is better to wrap the peak 203 etc. with MnS to reduce the stress concentration effect of the AI 203 etc. and improve the lifespan.

Furthermore, even if large MnS exists alone, it is just an inclusion, and it reduces the lifespan, similar to AI203 and the like. Therefore, the lifetime can be improved by making MnS finer. In the present invention, it has been found that this point can also be achieved by performing processing with a surface reduction rate of 50% or more in one operation.

In addition, for MnS containing AI203, etc., if the S/○ ratio in the steel is 8 or more, even if cold working with a strength of 50% or more is applied, the N203 etc. contained in MnS will separate and have a negative effect on the life. It was found that there was no effect on

In addition, Ti-based carbonitrides are strong inclusions, and large ones can be crushed during cold rolling, which can reduce the negative effect on life to some extent, but it is difficult to make them harmless, so large ones are It is necessary to adjust the content so that it does not form.

It is for this reason that Ti and N are limited in the present invention. The reasons for limitations regarding the production of the high carbon chromium bearing steel pipe of the present invention will be described below.

First, the components of the steel that is the object of the present invention will be described.

○'Minimum HRC when quenched and tempered for carbon rolling bearing steel
It requires a hardness of 57.

For this purpose, it is necessary to contain 0.80% of C. Therefore, the lower limit of C is set to 0.80%. Also, if it exceeds 1.20%, giant carbides are likely to be formed, so the upper limit is set at 1.2%.
Set to 0%. (2) In the steel for rolling bearings, Si is added as a deoxidizing agent and as an element that improves flatness.

For this purpose, the objective can be achieved with a content of 0.05 to 1.50%.

Therefore, the lower limit of Si is 0.05% and the upper limit is 0.50%.

-{3- Mn Mn is used as an element to improve hardenability in steel for rolling bearings.

For this purpose, the objective can be achieved with a content of 0.20 to 2.00%.

Therefore, the lower limit of Mn is 0.05% and the upper limit is 2.00%. (Cr) In steel for rolling bearings, since it is necessary to spheroidize carbides, Cr is used as an element that promotes spheroidization of carbides and improves hardenability.

For this purpose, the objective can be achieved with a content of 0.80 to 2.00%.

Therefore, the lower limit of Cr is 0.80% and the upper limit is 2.00%. (Mo) In the rolling bearing steel according to the second invention, Mo is used as a hardenability improving element.

For this purpose, the objective can be achieved with a content of 0.05 to 0.30%.

Therefore, the lower limit of Mo is 0.05% and the upper limit is 0.30%.

(S) S becomes MnS in steel and affects service life and machinability.

In the present invention, S becomes MnS and AI2Q, Si0
It is used to encapsulate oxide-based inclusions such as No. 2, etc., and reduce their adverse effects on the lifespan.

For this purpose, S of 0.010% or more is required in relation to 0, which will be described later, and if there is a large amount of AI203, etc., S should be set high. Furthermore, the present invention is directed to bearing steel pipes for mass production, and machinability is also an important characteristic item.

Normally, in high carbon chromium bearing steel, if the S content falls below 0.010%, the machinability decreases significantly, so it is preferable that the S content is 0.010% or more.

For these reasons, the lower limit of S is set to 0.010%.

On the other hand, if S contains 0.050% or more, large individual Mn
S is generated, and even if 50% or more of the gap is processed as described later, no improvement in the life will be seen. Therefore, the upper limit of S is set to 0.050%. (〇) 0 produces oxide-based inclusions such as mountains 203 and Si02 in the steel, which adversely affects the service life.

Therefore, it is generally better to have fewer 0s. In the present invention, if ○ is 0.0017% or less, the life can be improved by cold working of 50% or more, so the upper limit of ○ is set to 0.00.
It will be 17%.

The lower limit is set to the level that normally remains. (Ti) Ti forms nitrides or carbonitrides in steel, which adversely affects the service life.

In addition, these are strong inclusions, and if they are very large, they can be crushed by cold rolling and rendered harmless to some extent, but it is quite difficult to do so, and it is better to keep the amount of Ti in the steel as low as possible. good.

In the present invention, the upper limit of Ti is set to 0.007% because if it is 0.007% or less, the life can be improved by cold rolling by 50% or more. (N) N exists in steel as a carbonitride with Ti or as a nitride with Ti.

In the present invention, if it exceeds 0.0100%, large Ti carbonitrides or titanium oxides are formed, and as described below, 50%
Even if the above processing is carried out, the life cannot be improved.

Therefore, the upper limit of N is set to 0.0100%. Note that the lower limit is the level that normally remains. Next, the reason for defining the S/○ ratio in the present invention will be described.

As already mentioned in the section on S, S combines with Mn to form MnS
is produced in steel.

This MnS often combines with oxides such as AI203 and Si02 and exists in a form that includes them. In such a case, the action of AI203 etc. as a stress concentration source is reduced, which has a positive effect on the life span. In the present invention, S/○ is set to S or more because inclusions of oxides with S/○ of 8 or more are mostly included in MnS, and even if cold rolling is performed by 50% or more, N203 etc. are sulfurized. This is to ensure that the M-hawk remains encapsulated with N203 without being exposed from objects, improving its lifespan.

Next, in the present invention, the reason why the area reduction rate is set to 50% or more is that the effect of improving life by crushing inclusions becomes apparent at 50% or more.

In addition, from the technical idea of the present invention, the higher the grade ratio is, the better.
In actual manufacturing, cracks occur, so the limit is about 85%. Next, the present invention will be explained in detail based on examples.

Table 1 shows the chemical composition of the steel in the 24 heats conducted. Table 1 The chemical components of the sample materials are outside the composition regulations of the present invention.

All of these are high carbon chromium steels, among which No. 1
The series is low ○ level with different S content, No.
．． Series 2 is medium ○ level with different S content,
No. Series 3 has a high 0 level with different S content.

Furthermore, No. In series No. 4, only the ○ content is out of the claimed scope. The No. 5 series is one in which only the N content is outside the claimed range. 6
In the series, only the Ti content is outside the scope of the claims. All of these series are melted using a vacuum melting furnace for ease of composition adjustment, formed into a 100K9 steel ingot, forged, and then manufactured into a mother pipe by hot extrusion, and then subjected to pricking and spheroidizing annealing. I did it.

Next, this was cold-rolled once using a cold Pilger mill so that the area reduction ratio was 20%, 40%, 60%, and 80%, respectively, to produce steel pipes.

As described above, life test specimens were collected and prepared for the mother tube as hot rolled and the mother tube subjected to cold pilger rolling. Next, these were immersed in 83030 oil, tempered at 180 qo, adjusted to hardness HRC 62-63, and tested using a thrust type life tester, Hertz maximum contact stress Pmax = 500 k9f/m, lubricating oil was immersed in spindle 6 sesame oil. A life test was conducted on the outer surface side of the steel pipe under thin conditions.

The rolling fatigue life L of these materials. (The lifespan when 10% of the test piece undergoes flaking) is shown in Table 2 and 1.
As shown in the figure. Table 2 Transfer fatigue life (◎Applicable to the present invention) (
); Magnification for the value of area reduction rate of zero In Table 2, those marked with ◎ are those obtained by the method of the present invention.

Series No. 1 is heat no. 2, 3, and 4 are within the specified range of the components of the present invention, and the improvement in the life of these heats at an area reduction rate of 80% is 1.9 to 2.3 times. On the other hand, heat no. 1 is 1.2 times, heat no. 5
The improvement in life is 1.1 times, which is hardly recognized, but this is because the S/○ ratio of the former is small at 5, and the S content of the latter is 0.0.
This is because it is high at 61%. Series No. In 2, heat no. 7, 8, and 9 are steels with compositions regulated by the present invention, and the improvement in life of these heats at an area reduction rate of 80% is 1.8 to 3. It has a string sound. On the other hand, heat no. 6 is 1.4 times, heat no. 10 has a lifespan of 1.2 times, which is not much of an improvement in life, but this is series No. Like 1, the former has a small S/○ ratio of 6, and the latter has a S content of 0.06.
This is due to the high rate of 6%. Series No. 3 is heat no. Steels Nos. 12, 13, and 14 have the compositions regulated by the steel of the present invention, and the improvement in the life of these heats is 2.0 to 3.0 times when the surface area ratio is 80%. On the other hand, heat ground.
11 is 1.3 times, heat No. 15 has a lifespan of 1.1 times, which shows almost no improvement in life, but this is because the former has an S/○ of 7.
This is because the latter has a high S content of 0.067%. Series No. 4, 5, and 6 have improved lifespan as 1.
Although it is between 1 and 1.2 times and is hardly recognized, the series No. 4: ○ content is 0.0020-0.0028%
Highly ranked, series No. 5 has an N content of 0.011 to 0
．． It is high at 0.013%. Also series no. No. 6 has a high Ti content of 0.01 to 0.020%.

The improvement in life due to cold working is due to the change in shape of sulfide inclusions (mainly MnS), oxide inclusions (mainly AI203), and Ti inclusions (mainly Ti(C,N)) due to cold working. I can't wait. Heat No. in Figure 2
．． Sulfide-based, oxide-based, and Tj-based inclusions in steel pipes that have been hot-worked by the hot extrusion method in step 8 and steel pipes that have been cold-worked once with an area reduction rate of 80% in a cold Pilger mill. Shows a microscopic photograph of an object.

The sulfide inclusions are stretched by cold working, and the oxide and T
The i-based inclusions are finely crushed and dispersed. Next heat N
o. Using the mother pipe of No. 8, the cold drawing process was repeated four times with an area reduction rate of about 25% each time, and the process of cold drawing was repeated four times, and the total area reduction rate was about 70%. When a life test was conducted under exactly the same conditions as the life test results shown in the table, the improvement in life was 1.5 sounds, and no significant improvement in life was observed.

In addition, heat No. of the components regulated in the present invention. 2, 3, 4
, 7, 8, 9, 12, 13, and 14, as is clear from FIG. 1, the lifespan of all of them increases rapidly when the grade ratio is between 40% and 60%.

Therefore, when considered in conjunction with the above-mentioned life improvement ratio in lining drawing, in order to obtain a significant improvement in life, it is necessary to ensure a surface reduction rate of 50% or more in one cold working process, rather than in a total of several cold working processes. It turns out that this is necessary. The life improvement factor is set as 1 for the case without cross-rolling as shown in Table 2 (
), of which the mark ◎ is based on the method of the present invention. According to this, by using the method of the present invention, for example, it became possible to obtain an improvement in life of about 1.9 to 3.3 tones at a surface reduction rate of 80%.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the relationship between the weave surface ratio of cold working and the service life, and Fig. 2 is a diagram showing the relationship between the weave surface ratio of cold working and the life. Fig. 8 is a microphotograph of inclusions in Fig. 8. Figure 1 Figure 2

Claims (1)

[Claims] 1 C0.80-1.20% Si0.05-1.50% Mn0.20-2.00% Cr0.8-2.0% P<0.030 S0.010-0. 050% O < 0.0017% N < 0.0100% Ti < 0.007% A rolling bearing with the balance consisting of Fe and inevitably remaining impurities, and with a sulfur to oxygen ratio (S/O) of 8 or more A rolling machine characterized in that steel is made into a base material steel pipe by hot rolling or hot extrusion, which is softened and annealed and then cold rolled once with an area reduction rate of 50 to 85% to finish it into finished product dimensions. A method for manufacturing rolling bearing steel pipes with excellent fatigue strength. 2 C0.80-1.20% Si0.05-1.50% Mn0.20-2.00% Cr0.8-2.0% P<0.030 S0.010-0.050% O<0. 0017% N<0.0100% Ti<0.007% Mo0.05-0.30% The balance consists of Fe and inevitably remaining impurities, and the sulfur to oxygen ratio (S/O) is 8 or more Rolling bearing steel is hot-rolled or hot-extruded to form a base steel pipe, which is then softened and annealed and then cold-rolled once with an area reduction rate of 50 to 85% to finish it into finished product dimensions. A method for manufacturing rolling bearing steel pipes with excellent rolling fatigue strength.