JPH04349A - Bearing steel excellent in workability and rolling fatigue characteristic - Google Patents

Abstract

PURPOSE:To provide a bearing steel excellent in machinability and cold and warm workabilities as well as in rolling fatigue characteristic by limiting the compositional limit value of a steel and also controlling the amount and the form of nonmetallic inclusions existing in the steel. CONSTITUTION:A steel having a composition consisting of, by weight, 0.45-0.69% C, 0.10-2.0% Si, 0.20-2.0% Mn, <=0.015% P, <=0.015% S, <=2.0% Cr, <=0.010% Al, 0.003-0.020% N, <=0.0020% Ti, <=0.0030% O, and the balance Fe with inevitable impurities is prepared. At this time, the proportions of CaO, Al2O3, and SiO2 as nonmetallic inclusions contained in the steel are regulated to 15-70%, <=55%, and 5-70%, respectively. If necessary, 0.0003-0.010% Ca is added to the above composition. By this method, the steel excellent in machinability and cold and warm workabilities as well as in rolling fatigue characteristic required of bearings can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to bearing steel with excellent workability and rolling fatigue resistance, and more specifically, to high carbon bearing steel that has been widely used as a bearing material. It has superior machinability, cold workability, warm workability, and rolling fatigue resistance compared to The present invention relates to a bearing steel with excellent workability and rolling fatigue resistance that can be simplified or omitted.

[Prior art] Conventionally, J I 5G480 has been used as a material for bearing parts.
High carbon chromium bearing steel specified in 5UJ2 is used, and after spheroidizing annealing, cutting, cold working and warm working are performed to form bearing parts. , quenching, and tempering to adjust the structure to a few percent spherical carbide, a few percent retained austenite, and the remainder martensite, which improves bearing properties such as rolling fatigue resistance, wear resistance, and dimensional stability. In order to ensure the required properties and further improve rolling fatigue resistance, operations such as reducing alumina, which has a negative impact on rolling fatigue resistance, are carried out in the process from steelmaking to casting, which is a problem that requires high costs. There is.

However, recently, bearing parts formed by cutting have been subjected to cold working or warm working into more complex shapes compared to the conventional techniques described above in order to improve the yield of steel materials. In recent years, molding processes have begun to be carried out.

When carrying out such machining, the use of conventionally used high carbon chromium bearing steels may cause problems with machinability and cracks may occur during machining. Although it has become possible to cut at higher speeds, the use of high carbon chromium bearing steel shortens tool life and has problems with machinability.

In addition, spheroidizing annealing is always performed before forming bearing parts, and this spheroidizing annealing is used to improve workability and ensure properties such as rolling fatigue resistance for bearing parts. This is to control the carbide remaining after quenching and tempering so that it is finely, uniformly dispersed.

Since this spheroidizing annealing process takes a long time, there is a desire to simplify or omit the annealing process in order to save energy and reduce manufacturing costs of parts.

In response to this request, as an example, Japanese Patent Application Laid-Open No. 601940
Publication No. 47 proposes a high-quality bearing steel with excellent durability and cold workability, but if the spheroidizing annealing treatment is omitted or simplified, machinability, cold workability, and warm workability deteriorate. Also, deterioration of rolling contact fatigue properties could not be avoided.

Therefore, it has the same properties as high carbon chromium bearing steel subjected to spheroidizing annealing treatment, and even if the spheroidizing annealing treatment is simplified or omitted, the workability will not deteriorate. In addition, it is possible to improve rolling fatigue resistance without incurring high costs for alumina reduction treatment.
Additionally, there is a strong demand for bearing steel that can keep manufacturing costs low.

[Problems to be Solved by the Invention] In view of the various problems of the high carbon chromium bearing steel that has been conventionally used as explained above, the inventor of the present invention has conducted extensive research and studies. As a result, it has superior rolling fatigue resistance compared to conventional high carbon chromium bearing steels, improves machinability, cold workability, and warm workability, and simplifies spheroidizing annealing. Or, even if omitted, the components and component ratios of the steel are adjusted to specific amounts so that each of the above properties is equivalent to high carbon chromium bearing steel, and the amount of nonmetallic inclusions present in the steel. By controlling the shape and shape of the steel, we developed a bearing steel with excellent rolling fatigue resistance and good workability, which is important for bearing parts.

[Means for solving the problems] The bearing steel with excellent workability and rolling fatigue resistance according to the present invention has the following properties: (1) C0.45-0.69wt%, Si 0.1
0-2.0wt%, Mn 0.20-2.0wt%, P
0.015wt% or less, S 0.015wt% or less,
Cr 2.0wt% or less, Al 0.010wt% or less, N 0.003 to 0.020wt%, Ti 0.00
20wt% or less, O0.0030wt% or less, and the balance consists of Fe and unavoidable impurities, and contains nonmetallic inclusions such as CaO, AltOa, and 5iO contained in the steel.
The ratio of z is CaO 15 to 70 wt%, AltOs 55 wt% or less,
The first invention provides a steel for bearings having excellent workability and rolling fatigue resistance, characterized in that Sio is 5 to 70 wt%, (2) C0.45 to 0.69 wt%, S i 0. 1
0-2.0wt%, Mn 0.20-2.0wt%, P
0.015wt% or less, S 0.015wt% or less,
Cr 2.0wt% or less, Al 0.010wt% or less, N 0.003 to 0.020wt%, Ti 0.00
Contains 20 wt% or less, O 0.0030 wt% or less, and further contains Ni 2.0 wt% or less, Mo 1.0 wt% or less, C
u 1.0wt% or less, V 0.01-0.30wt%
, Nb 0.01 to 0.30 wt%, and the balance consists of Fe and inevitable impurities, including nonmetallic inclusions CaO, Al t O3,
The ratio of SiO2 is CaO 15 to 70 wt%, Alto, 55 wt% or less,
A second invention provides a steel for bearings having excellent workability and rolling fatigue resistance, characterized in that Siot is 5 to 70 wt%, (3) C0.45 to 0.69 wt%, Si 0. 1
0-2.0wt%, Mn 0.20-2.0wt%, P
0.015wt% or less, S 0.015wt% or less,
Cr 2.0wt% or less, Al LO 10wt% or less,
N 0.003-0.020wt%, Ti 0.002
Contains 0 wt% or less, O0,0030 wt% or less,
Contains 0.0003 to 0.010 wt% of Ca, the balance consists of Fe and unavoidable impurities, and the ratio of nonmetallic inclusions CaO1Alt03 and SrOt contained in the steel is 15 to 70 wt% of CaO and 355 wt% of AltO or less. ,
Sio! A third invention provides a steel for bearings having excellent workability and rolling fatigue resistance, characterized by having a carbon content of 5 to 70 wt%, (4) C0.45 to 0.69 wt%, Si 0.1
0-2.0wt%, Mn 0.20-2.0wt%, P
0.015wt% or less, S 0.015wt% or less,
Cr 2.01% or less, Al 0.010zL% or less,
N 0.003-0.020wt%, Ti 0.002
Contains 0 wt% or less, O0.0030 wt% or less,
Furthermore, Ni 2.0wt% or less, Mo 1.0wt% or less, C
u1. owt% or less, V 0.01-0.301%,
Contains one or more selected from 0.01 to 0.30 wt% Nb, 0.03 to 0.010 wt% Ca, and the balance is Fe and unavoidable impurities. In terms of workability and rolling contact fatigue, the ratio of CaO1Al, 03, Si, Oy included in the nonmetallic inclusions is 15 to 701% CaO, 55 wt% or less of A120s, and 5 to 70 wt% of 5iOz. This invention consists of four inventions, with the fourth invention being an excellent steel for bearings.

The bearing steel with excellent workability and rolling fatigue resistance according to the present invention will be described in detail below.

First, the components and component ratios of the bearing steel with excellent workability and rolling fatigue resistance according to the present invention will be explained.

C has a hardness of I (RC58 or higher) after quenching and tempering, and is an essential element in order to obtain bearing properties such as rolling fatigue resistance. If the content is less than 0.45 wt%, such effects will not occur. Moreover, if the content exceeds 0.69 wt%, machinability, cold workability, and warm workability will decrease, and dimensional changes due to decomposition of retained austenite during use will become significant. Therefore, the C content is 0.45 to 0.6
It is set to 9wt%.

In addition to deoxidizing, Si is an element that improves hardenability and resistance to temper softening.If the content is less than 0.1%, this effect will be small, and if it is contained in excess of 2.0wt%, it will be difficult to cut. In addition, the residual austenite generated during quenching becomes difficult to decompose during tempering, and the dimensional stability decreases because a large amount of retained austenite remains.Thus, the Si content 0.], 0
~2.0wt%.

Mn is an element that deoxidizes and desulfurizes and improves hardenability.If the content is less than 0.20wt%, such effects cannot be expected, and if the content exceeds 2.0wt%, The effect reaches saturation, and there is little further effect, and machinability and cold workability deteriorate. Therefore, the Mn content is set to 0.20 to 2.0 wt%.

P is an element that reduces toughness, so it is necessary to keep the P content as low as possible. Therefore, the P content is 0.015wt.
% or less.

S is contained in the form of MnS in steel, and is an element that improves machinability, and when contained in a large amount, MnS becomes the starting point of rolling contact fatigue fracture. Therefore, the S content is 0.01
The content shall be 5 wt% or less.

Cr is an element that improves hardenability, and the content is 2,
If the content exceeds 0 wt%, machinability, cold workability, and warm workability will be reduced. Therefore, the Cr content is 2.0w
t% or less.

Al is an element that combines with oxygen to produce Altos, and if the content exceeds 0.010 wt%, Al! 0sll increases, and the target inclusion form is not achieved. Therefore, the Al content is 0.0
The content shall be 10 wt% or less.

N is an element that combines with V etc. to form nitrides, refines the crystal grains and strengthens the steel, and the content is 0.003W.
If the content is less than t%, this effect is small, and if the content is less than 0.02
If the content exceeds 0 wt%, cold workability and warm workability will be reduced. Therefore, the N content is 0.003 to 0.0
It is set to 20wt%.

Tf is an element that combines with N to produce coarse TjN and reduces rolling fatigue resistance, cold workability, and warm workability,
Therefore, it is necessary to keep the Ti content as low as possible. Therefore, the Ti content is set to 0.0020 wt% or less.

0 is an element that combines with A25St etc. to form oxide inclusions in steel, and when it is contained in large amounts, the total amount of inclusions in steel increases, resulting in poor machinability, cold workability, and warm workability. Decreases processability. Therefore, 0 content is 0.0030wt
% or less.

Both Ni and Mo are elements that improve hardenability, and have the effect of facilitating hardening and tempering treatments for parts with large mass. If it is contained, machinability, cold workability, and warm workability are reduced, and furthermore, a large amount of retained austenite is generated after quenching and tempering, resulting in deterioration of dimensional stability. Therefore, the Ni content is 2.0 wt% or less, and the Mo content is 2.0 wt% or less.
The content shall be 1.0 wt% or less.

Cu is an element that increases hardenability and corrosion resistance, and has the effect of improving wear resistance through age hardening.
If the content exceeds 1.0 wt%, red brittleness will be promoted and cracks will occur during hot working. Therefore, the Cu content is set to 1.0 wt% or less.

■, Nb combines with CSN in steel to produce carbonitrides,
It is an element that refines crystal grains, improves rolling life, and increases toughness.■ Content, Nb content is 0.01wt
If the content is less than %, this effect will be small;
Even if the Nb content exceeds 0.30 wt%, the grain refinement effect does not increase. Therefore, ■ content is 0.
01-0.30wt%, Nb content is 0.01-0.3
It is set to 0wt%.

Ca is a strong deoxidizing element that generates CaO to form an inclusion form that is useful for target rolling contact fatigue properties, machinability, cold workability, and warm workability. is 0.0
If the content is less than 0.003 wt%, this effect is small, and
If the content exceeds 0.010 wt%, the target inclusion morphology cannot be obtained. Therefore, the Ca content is 0.0
003 to 0.010 wt%.

Next, in the bearing steel with excellent workability and rolling fatigue resistance according to the present invention, non-metallic inclusions contained in the steel to improve rolling fatigue resistance will be explained. That is, the nonmetallic inclusions Cab, Al! 03.5iOz ratio, CaO15~401%, Alt0355wt% or less, S
By controlling i0 to 5 to 70 wt%, the inclusions have a low melting point and extensibility, or the difference in thermal expansion coefficient between the matrix and the inclusions is
It was made to be smaller than tOs.

In other words, by using anorcite-based inclusions with a low melting point, they are expanded in the longitudinal direction during hot forging or hot rolling, reducing the area of the inclusions on the rolling surface, and as a result, rolling fatigue resistance is improved. In addition, the inclusion morphology was changed to 2CaO
-5ift, 2CaOAltosSin, the thermal expansion coefficients of the matrix and inclusions are reduced, and the stress concentration generated around the inclusions is reduced to A1.0. The amount of oxygen is reduced by adjusting the structure to martensite and a few percent retained austenite within a range where the hardness after quenching and tempering satisfies HRC58. It was discovered that rolling fatigue resistance equivalent to or higher than that of high carbon chromium bearing steel can be obtained without any

This means that by reducing the C content of the steel material, sufficient rolling fatigue resistance can be obtained without leaving any spheroidized carbides after quenching and tempering. When the tempered material was investigated for bearing properties such as wear resistance and dimensional stability other than rolling contact fatigue, it was found to be equivalent to conventional high carbon chromium bearing steel.

When we investigated the machinability, cold workability, and warm workability of such steel materials by subjecting them to spheroidizing annealing and normalizing, we found that the spheroidizing annealed materials had better machinability than high-carbon chromium bearing steel. It has improved properties such as hardness, cold workability, and warm workability, and the normalized material is equivalent to high carbon chromium bearing steel that has undergone spheroidizing annealing. Regarding machinability, tool wear can be suppressed by reducing the C content to lower cutting resistance and forming inclusions with a low melting point.Also, regarding cold workability and warm workability, C
By reducing the content, the deformation resistance during processing is lowered, and the deformability during cold and warm processing is improved.Furthermore, by creating an inclusion form with a low melting point, it is possible to lower the deformation resistance during processing and improve the deformability during cold and warm processing. The inclusions are expanded and cracking can be suppressed.

[Example] An example of a bearing steel having excellent workability and rolling fatigue resistance according to the present invention will be described.

Example No. 1-N of the bearing steel with excellent workability and rolling fatigue resistance according to the present invention having the contained components and component ratios shown in Table 1
Steel Nos. 0, 8 and comparative steels No. 9 to No. 20 were melted in a small vacuum furnace. In addition, comparative steel No.
20 is JISSUJ2, 1200℃ x 20 after casting
Soaking treatment was performed under certain time conditions to diffuse and eliminate giant carbides.

These sea bream are hot forged to φ60mm and φ80III.
A round bar of 11φ25III11 was forged and drawn, and A: spheroidizing annealing, B: annealing, and C: normalizing were performed under the conditions described below.

A: 760℃ x 2 hours - Furnace cooling to warm temperature of 680℃
Then, air cooling B: 850°C x 1 hour → Furnace cooling C: 850°C x 1 hour → air cooling The round bar with a diameter of 801IIl was subjected to a turning test using a carbide tool under the conditions described below to evaluate its machinability. .

Tool used: PIO Cutting speed: 150m/ff1in Feed: 0.25ma+/rev Depth of cut: 1
．． 5+a+ Cutting oil: dry type) A round bar with a diameter of 25 mm was machined on the test piece shown in FIG. 1, and its cold workability and warm workability were evaluated.

Figure 1(a) is a plan view and side view of the test piece, and Figure 1(b)
) is an enlarged view of part A in Figure 1(a), and D is an enlarged view of 20I.
II11H is 30+u+.

For deformation resistance of cold working and hot working, test specimens with no notches (V = Omm) were used, and the compression rate was 60% at temperatures of 25°C and 700°C, respectively.
It was evaluated by the deformation resistance when subjected to restraint compression deformation under the following conditions.

In addition, for deformation resistance of cold workability and warm workability, a test piece with a notch (V = 0.3 mm) was used, and the compression ratio was 25 at a temperature of 25°C and 700°C, respectively.
A restrained compressive deformation was applied by changing the compression ratio in % increments, and evaluation was performed based on the lowest compression ratio at which cracking was observed (cracking critical compression ratio).

Furthermore, in order to evaluate the rolling fatigue resistance of each sea bream, a disk with a diameter of 60 mIB and a thickness of 5 mm was cut out from the cross section.
0mm round bar 850℃ x 1 hour/oil cooling (sea bream No. 2
0 is 830℃ x 1 hour/oil cooling), 1506C x 2 hours/
After quenching, tempering, and lapping under air cooling conditions, the surface pressure is 500 kgf/1n.
A rolling fatigue test was conducted under the conditions of tr+'.

Tables 2 and 3 show test results regarding rolling contact fatigue, machinability, cold workability, and warm workability of these test pieces. Regarding rolling fatigue resistance, high carbon chromium bearing steel No. 20, B, 0 (10% cumulative failure rate), B.

(50% cumulative damage rate)! It is shown as an index when .

It can be seen from Tables 2 and 3 that the following will be explained.

Bearing steel N with excellent workability and rolling fatigue resistance according to the present invention
o, l - No. 8 has rolling fatigue resistance of No. 20 regardless of the type of heat treatment before processing.
It is superior to 5UJ2 in machinability, cold workability, and warm workability when spheroidizing annealing is performed before machining.
It is superior to USJ2, and is equivalent to 5USJ2 when annealing and normalizing are performed.

In addition, No. 9, No. 14, which have a low C content, have better machinability, cold workability, and warm workability than 5UJ2 regardless of the type of heat treatment before machining, but they are the most important as bearing parts. The rolling fatigue resistance is inferior to that of 5UJ2.

No. 10, No. 15, which have a high C content, have better rolling fatigue resistance than 5UJ2 regardless of the heat treatment before processing, but the machinability, cold workability, and warm workability are also excellent. When smoothing treatment and normalizing treatment are performed, it is lower than 5UJ2, and when spheroidizing annealing is performed, it is equivalent to 5UJ2.

In addition, No. 11, which has a high S content, is superior to 5UJ2 in terms of machinability, but inferior to 5UJ2 in terms of rolling fatigue resistance, cold workability, and deformability in warm workability. There is.

In addition, No. 12 and No. 12, which have a high Ti content and 0 content
, No. 13 is inferior to 5UJ2 in both rolling fatigue resistance, machinability, cold workability, and warm workability.

No. 16, which has a high Ca content, and No. 17, which has a low Ca content, are both superior to SUJ 2 in terms of machinability, cold workability, and warm workability, but rolling fatigue resistance is 5UJ2.
Inferior.

Furthermore, No. 18, No. 19 with high Al content
The cold workability and warm workability of the steel are equivalent to or higher than those of 5UJ2, but the rolling fatigue resistance is inferior to that of 5UJ2.

[Effects of the Invention] As explained in detail above, the bearing steel of the present invention, which has excellent workability and rolling fatigue resistance, has the above-mentioned structure. It has extremely excellent dynamic fatigue resistance, and also has excellent machinability, cold workability, and warm workability.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the shape of a test piece for evaluating cold workability and warm workability of a bearing steel having excellent workability and rolling fatigue resistance according to the present invention. Te1

Claims (4)

[Claims] (1) C0.45-0.69wt%, Si0.10-2
．． 0wt%, Mn0.20-2.01%, P0.015
wt% or less, S0.015wt% or less, Cr2.0wt
% or less, Al0.010wt% or less, N0.003~0
．． 020wt%, Ti0.0020wt% or less, O0.
0030wt% or less, the balance consists of Fe and unavoidable impurities, and contains CaO of non-metallic inclusions contained in the steel.
, Al_2O_3, and SiO_2 are as follows: 15 to 70 wt% of CaO, 355 wt% or less of Al_2O_3, and 25 to 70 wt% of SiO. Steel for bearings having excellent workability and rolling fatigue resistance. (2) C0.45-0.69wt%, Si0.10-2
．． 0wt%, Mn0.20-2.01%, P0.015
wt% or less, S0.015wt% or less, Cr2.0wt
% or less, Al0.010wt% or less, N0.003~0
．． 020wt%, Ti0.0020wt% or less, O0.
0030wt% or less, and further contains Ni2.0wt% or less, Mo1.0wt% or less, Cu1
．． 0wt% or less, V0.01-0.30wt%, Nb0
．． Contains one or more selected from 01 to 0.30 wt%, with the balance consisting of Fe and unavoidable impurities.
A steel for bearings having excellent workability and rolling fatigue resistance, characterized in that the ratio of O_2 is 15 to 70 wt% of CaO, 355 wt% or less of Al_2O_355 wt%, and 25 to 70 wt% of SiO. (3) C0.45-0.69wt%, Si0.10-2
．． 0wt%, Mn0.20-2.0wt%, P0.01
5wt% or less, S0.015wt% or less, Cr2.0w
t% or less, Al0.010wt% or less, N0.003~
0.020wt%, Ti0.0020wt% or less, O0
．． 0.0030 wt% or less, and contains Ca0.0003 to 0.010 wt%, with the balance consisting of Fe and unavoidable impurities, and contains nonmetallic inclusions CaO, Al_2O_3, and S contained in the steel.
A bearing steel with excellent workability and rolling fatigue resistance, characterized in that the ratio of iO_2 is 15 to 70 wt% CaO, 355 wt% or less Al_2O_355 wt%, and 25 to 70 wt% SiO. (4) C0.45-0.69wt%, Si0.10-2
．． 0wt%, Mn0.20-2.0wt%, P0.01
5wt% or less, S0.015wt% or less, Cr2.0w
t% or less, Al0.010wt% or less, N0.003~
0.020wt%, Ti0.0020wt% or less, O0
．． 0030wt% or less, and further contains Ni2.0wt% or less, Mo1.0wt% or less, Cu1
．． 0wt% or less, V0.01-0.30wt%, Nb0
．． Contains one or more selected from 0.01 to 0.30 wt%, and 0.0003 to 0.010 wt% of Ca, with the balance consisting of Fe and unavoidable impurities, and is a nonmetal contained in steel. Inclusions CaO, Al_2O_3, S
A bearing steel with excellent workability and rolling fatigue resistance, characterized in that the ratio of iO_2 is 15 to 70 wt% CaO, 355 wt% or less Al_2O_355 wt%, and 25 to 70 wt% SiO.