JP2726440B2 - Bearing steel with excellent workability and capable of simplifying or omitting spheroidizing annealing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a bearing steel excellent in workability, and more specifically, to a high carbon chromium bearing steel which is widely used as a bearing material. It has properties and is excellent in machinability, cold workability, and warm workability, and further simplifies or eliminates spheroidizing annealing performed before cutting, cold working, and warm working. The present invention relates to a bearing steel which has excellent workability and can simplify or omit spheroidizing annealing.

[Conventional technology]

Conventionally, bearing parts are made of high-carbon chromium bearing steel represented by SUJ2 stipulated in JIS G 4805, and after spheroidizing annealing, cutting, cold working, and warm working are performed. Then, quenching and tempering are performed to adjust the structure to several percent of spherical carbide and several percent of retained austenite and the rest to martensite, to provide rolling fatigue resistance, wear resistance, and dimensions. The characteristics required for bearings, such as stability, have been secured.

However, in recent years, bearing parts that have been formed by the cutting method have been cold-worked and warm-worked to more complex shapes than before, with the aim of improving the yield of steel materials. It is being processed.

In this case, if the conventional high carbon chromium bearing steel is used, there is a problem in workability, cracks may occur during the processing, and in the field of cutting, the tool material is improved, so that cutting can be performed at a higher speed. At this time,
The conventional high carbon chromium bearing steel has a short tool life and is problematic in terms of machinability.

In addition, spheroidizing annealing is always performed before forming a bearing component. This process is intended to improve workability and harden the bearing component to ensure its characteristics such as rolling fatigue. This is performed to control the spheroidized carbide remaining after the tempering treatment to be finely and uniformly dispersed.

However, since the spheroidizing annealing process requires a long time, there is a demand to simplify or omit the spheroidizing annealing process in order to save energy and reduce the manufacturing cost of parts.

In response to these demands, high-quality bearing steels having excellent durability and cold workability, as described in Japanese Patent Application Laid-Open No. 60-194047, have been proposed. If omitted or simplified, it is inevitable that the machinability, cold workability, warm workability and rolling fatigue resistance will decrease, and therefore, the properties equivalent to high carbon chromium bearing steel subjected to spheroidizing annealing treatment Further, there is a demand for a bearing steel which has a simplified spheroidizing annealing process and which does not reduce the workability even if it is omitted.

[Problems to be solved by the invention]

In view of the various problems of the conventional high-carbon chromium bearing steel described above, the present invention has intensively studied by the inventor, and as a result of repeated studies, it has been found that bearing characteristics equivalent to those of the conventional high-carbon chromium bearing steel are obtained. Bearing properties such as rolling fatigue and machinability,
While improving cold workability and warm workability, and simplifying or omitting spheroidizing annealing, the machinability, cold workability and warm workability are equivalent to high carbon chromium bearing steel. In order to adjust the content and content of steel,
The company developed bearing steel with excellent rolling workability, which is the most important bearing component, and excellent workability.

[Means for solving the problem]

Bearing steel excellent in workability according to the present invention and capable of simplifying or omitting spheroidizing annealing treatment is as follows: (1) C 0.45 wt% or more, less than 0.70 wt%, Si 0.10 to 2.0 wt%
%, Mn 0.20 ~ 2.0wt%, P 0.015wt% or less, S 0.015wt%
Below, Cr 2.0 wt% or less, Al 0.015 to 0.060 wt%, N 0.003
~ 0.020wt%, Ti 0.0020wt% or less, O 0.0006 ~ 0.0015wt
%, With the balance being Fe and unavoidable impurities, and having excellent workability and capable of simplifying or omitting the spheroidizing annealing treatment as the first invention, and (2) C 0.45 wt. % Or more, less than 0.70wt%, Si 0.10-2.0wt
%, Mn 0.20 ~ 2.0wt%, P 0.015wt% or less, S 0.015wt%
Below, Cr 2.0 wt% or less, Al 0.015 to 0.060 wt%, N 0.003
~ 0.020wt%, Ti 0.020wt% or less, O 0.0006 ~ 0.0015wt
%, Ni 2.0% by weight or less, Mo 1.0% by weight or less, Cu 1.0% by weight or less, V 0.01 to 0.30% by weight, Nb 0.01 to 0.3%
A bearing steel containing one or more selected from 0 wt%, with the balance being Fe and unavoidable impurities, and having excellent workability and capable of simplifying or omitting spheroidizing annealing. The present invention comprises two inventions as a second invention.

BEST MODE FOR CARRYING OUT THE INVENTION A bearing steel having excellent workability according to the present invention and capable of simplifying or omitting spheroidizing annealing will be described in detail below.

In the bearing steel having excellent workability according to the present invention and capable of simplifying or omitting the spheroidizing annealing treatment, the content of O and Ti is reduced as much as possible in order to improve the rolling fatigue. The content of Al ₂ O ₃ and TiN, which have an adverse effect on steel, should be less than or equal to that of high carbon chromium bearing steel, and the structure should be as low as martensite as long as the hardness after quenching and tempering satisfies HRC58. It has been found that by adjusting the content of retained austenite to 0.1%, traditional fatigue resistance equivalent to that of a high carbon chromium bearing steel can be obtained.

This means that even after quenching and tempering, sufficient rolling fatigue resistance can be obtained without leaving spheroidized carbides, and
Investigation of bearing properties such as wear resistance and dimensional stability other than rolling fatigue resistance for quenched and tempered materials that means reducing the C content of the material and satisfying the above conditions. It turned out to be equivalent to chromium bearing steel.

In such steel materials, spheroidizing annealing and normalizing were performed, and the machinability, cold workability, and warm workability were investigated.The spheroidizing annealing process was compared to high carbon chromium bearing steel. , Machinability, cold workability and warm workability have been improved, and the normalizing material is equivalent to high carbon chromium bearing steel that has been subjected to spheroidizing annealing. Al ₂ O by reducing the amount to reduce the cutting force and the O content
Tool wear due to ₃ can be suppressed, and for cold workability and warm workability, the C content is reduced to lower the deformation resistance during cold work, and cold workability and warm workability are reduced. By improving the deformability at the time and reducing the O content, it is possible to suppress the amount of Al ₂ O ₃ that becomes the starting point of cracking during cold working and warm working.

The components and proportions of the bearing steel according to the present invention, which are excellent in workability and can simplify or omit the spheroidizing annealing treatment, will be described.

C is an essential element for securing the hardness after quenching and tempering treatment of HRC 58 or more and obtaining bearing characteristics such as rolling fatigue, and such an effect is expected if the content is less than 0.45 wt%. In addition, if the content is 0.70wt% or more, machinability, cold workability and warm workability decrease, the amount of retained austenite increases after quenching and tempering, and the decomposition of residual austenite during use as a bearing The change in dimensions due to Therefore, the C content is set to 0.45 wt% or more and less than 0.70 wt%.

Si is an element that enhances hardenability and temper softening resistance in addition to deoxidation. If its content is less than 0.10 wt%, this effect is small. Workability and warm workability are remarkably deteriorated, and retained austenite generated during quenching is hardly decomposed during tempering, and dimensional stability is reduced because a large amount of retained austenite remains. Therefore, the Si content is set to 0.10 to 2.0 wt%.

Mn is a deoxidizing and desulfurizing element that improves quenching properties. Such an effect cannot be expected if the content is less than 0.20 wt%. Is less effective, and the machinability and cold workability decrease.
Therefore, the Mn content is set to 0.20 to 2.0 wt%.

Since P is an element that lowers toughness, it is necessary to reduce the P content as much as possible.
5 wt% or less.

S is mostly contained in the form of MnS in steel,
It is an element that improves machinability, and when the O content is small, it lowers rolling fatigue, and also has a bad effect on cold workability and warm workability. Therefore, in consideration of these points, the S content is set to 0.015 wt% or less.

Cr is an element that improves the hardenability and has a content of 2.0 w
If the content exceeds t%, the machinability, cold workability and warm workability are reduced. Therefore, the Cr content is set to 2.wt% or less.

Al is an effective element for deoxidation and grain refinement. If its content is less than 0.015 wt%, such effect is small, and if it exceeds 0.060 wt%, the grain refinement effect is obtained. Is saturated, and when it is contained in a larger amount, crystal grains are more likely to grow. Therefore, the Al content is 0.015 to 0.060
wt%.

N is an element that combines with Al and V to form nitrides, refines crystal grains and increases the toughness of steel, and has a content of 0.
If the content is less than 003% by weight, such an effect is small.
If the content exceeds wt%, cold workability and warm workability are reduced. Therefore, the N content is set to 0.003 to 0.020 wt% or less.

Ti combines with N to form coarse TiN,
It is an element that lowers cold workability and warm workability, so that the Ti content needs to be as low as possible. Therefore, the Ti content is set to 0.0020 wt% or less.

O is an element that combines with Al, Si, etc. to form oxide-based inclusions in the steel. When the content in the steel increases, the rolling fatigue resistance is reduced, and the machinability, cold workability and O adversely affects the warm workability, so the O content needs to be reduced as much as possible. However, in order to reduce the O content, it is necessary to deoxidize the steel for a long time at the time of steel making, which increases the production cost. Therefore, the O content is 0.00
06-0.0015wt%.

Both Ni and Mo are elements that increase the quenchability, and are elements that facilitate quenching and tempering in large-mass components. Ni content is 2.0 wt% and Mo content is 1.0 wt%
%, The machinability, the cold workability and the warm workability are reduced, and further, a large amount of retained austenite is generated after quenching and tempering, thereby deteriorating dimensional stability. Therefore, Ni content is 2.0 wt% or less, Mo content is 1.0 wt%
% Or less.

Cu is an element that increases hardenability and corrosion resistance, and is an element that improves wear resistance by age hardening. If the content exceeds 1.0 wt%, it promotes red hot brittleness and causes hot working. Cracks occur during processing. Therefore, the Cu content is set to 1.0 wt% or less.

V and Nb combine with C and N in steel to form carbonitride,
It is an element that refines crystal grains to improve rolling fatigue life and increases toughness. Therefore, if the V content and Nb content are less than 0.01 wt%, such effects are small, and 0.30 wt%.
If the content exceeds the range, no increase in the effect of crystal grain refinement is observed. Therefore, the V content is 0.01 to 0.30 wt% and Nb
The content is 0.01 to 0.30 wt%.

〔Example〕

An example of a bearing steel according to the present invention, which has excellent workability and can simplify or omit the spheroidizing annealing treatment, will be described.

Examples Steels which are excellent in workability according to the present invention and whose content and proportion shown in Table 1 are applied to bearing steels 1-4 and comparative steels 5-10 in which spheroidizing annealing treatment can be simplified or omitted. Was melted in a small vacuum furnace.

The comparative steel 10 was JIS SUJ2, which was subjected to a soaking treatment at 1200 ° C. for 20 hours after casting to perform a diffusion and disappearance treatment of a large carbide.

Φ60mm, φ80mm, φ25mm by hot forging these steels
Was rounded and subjected to A: spheroidizing annealing, B: annealing, C: normalizing, and D: low-temperature annealing under the following conditions.

A: 760 ° C x 2 hours → Furnace cooling to 680 ° C, then air cooling B: 850 ° C x 1 hour → Furnace cooling C: 850 ° C x 1 hour → Air cooling D: 700 ° C x 1 hour → Air cooling Round bar with a diameter of 80mm For the following conditions,
A cutting test was performed with a carbide tool to evaluate the machinability.

Tool: P10 Cutting speed: 150m / min Feed: 0.25mm / rev Depth of cut: 1.5mm Cutting oil: None (dry type) Tool life standard: VB = 0.2mm For a round bar with a diameter of 25mm, the test piece shown in Fig. 1 Then, cold workability and warm workability were evaluated. FIG. 1 (a) is a plan view and a side view of a test piece, and FIG. 1 (b)
2 is an enlarged view of a portion A in FIG. 1 (a). D is 20mm, H
Is 30mm.

Among the cold workability and warm workability, the deformation resistance was determined by using an unnotched specimen (V = 0 mm) under the conditions of a compressibility of 60% at a temperature of 25 ° C and 700 ° C, respectively. Evaluation was made based on the deformation resistance at the time of constrained compression deformation. In addition, the deformability of the cold workability and the warm workability was determined using a notched test piece (V = 0.3 mm).
At a temperature of 25 ° C and 700 ° C, respectively, changing the compressibility by 2.5%,
Restrained compression deformation was applied, and the evaluation was made based on the lowest compression ratio (crack limit compression ratio) at which cracking was observed.

Furthermore, in order to evaluate the rolling fatigue properties of each steel, a disk with a diameter of 60 mm and a thickness of 5 mm was cut out from the cross section, and a disk with a diameter of 60 mm was cut at 850 ° C for 1 hour → oil cooling (830 ° C for steel 10 only). 1 hour → oil cooling), 150 ° C × 2 hours → air cooling, quenching, tempering, lapping, and surface pressure 500k
A rolling fatigue test was performed under the condition of gf / mm ² .

Table 2 shows the test results of these test pieces for rolling fatigue, machinability, cold workability, and warm workability. Note that the rolling contact fatigue resistance, B ₁₀ (10% cumulative failure rate) of steel 10, in which B ₅₀ (50% cumulative failure rate) indicated by an index when the 1.

It is clear from the results in Table 2 that the following is explained.

That is, excellent workability according to the present invention, and spheroidizing annealing treatment can be simplified or omitted bearing steel No. 1 ~ No. 4,
Regardless of the type of heat treatment before processing, the rolling fatigue resistance is equivalent to that of No.10 SUJ2 in any case, and the machinability, cold workability and warm workability are spherical before processing. Superior to SUJ2 when annealed and annealed,
When the normalizing process and the low-temperature annealing process are performed, it is equivalent to SUJ2.

In addition, No. 5 with a low C content has the same machinability, cold workability and warm workability as SU regardless of the type of heat treatment before working.
Although it is equal to or higher than J2, the most important rolling fatigue as a bearing component is inferior to SUJ2.

No. 6, which has a high C content, has almost the same rolling fatigue resistance as SUJ2, regardless of the type of heat treatment before processing. However, the cutting property, cold workability, and warm workability are both annealing and annealing. If the annealing treatment or low-temperature annealing treatment is performed, the SU
It is lower than J2 and becomes equivalent to SUJ2 when spheroidizing annealing is performed.

Further, No. 7, which has a high S content, is superior to SUJ2 in terms of machinability, but is inferior to SUJ2 in terms of rolling fatigue and deformability during cold working and warm working.

In addition, No. 8 and No. 9 with high Ti and O contents all have the same rolling fatigue, machinability, cold workability and warm workability.
SUJ2 or less.

[Effects of the Invention] As described above, excellent workability according to the present invention,
And since the bearing steel which can simplify or omit the spheroidizing annealing process has the above-mentioned configuration, even if the spheroidizing annealing process before processing is simplified or omitted, it is the most important as a bearing. It has an effect of being extremely excellent in rolling fatigue property, which is a characteristic, and also excellent in machinability, cold workability and warm workability.

[Brief description of the drawings]

FIG. 1 shows a test piece shape for evaluating cold workability and warm workability in an embodiment of a bearing steel having excellent workability according to the present invention and capable of simplifying or omitting spheroidizing annealing. FIG.

Claims (2)

(57) [Claims] (1) C 0.45 wt% or more, less than 0.70 wt%, Si 0.10
~ 2.0wt%, Mn 0.20 ~ 2.0wt%, P 0.015wt% or less, S 0.
015wt% or less, Cr 2.0wt% or less, Al 0.015-0.060wt%,
N 0.003 to 0.020 wt%, Ti 0.0020 wt% or less, O 0.0006 to
A bearing steel containing 0.0015wt%, with the balance being Fe and unavoidable impurities, and having excellent workability and capable of simplifying or omitting spheroidizing annealing. 2. C 0.45 wt% or more, less than 0.70 wt%, Si 0.10
~ 2.0wt%, Mn 0.20 ~ 2.0wt%, P 0.015wt% or less, S 0.
015wt% or less, Cr 2.0wt% or less, Al 0.015-0.060wt%,
N 0.003 to 0.020 wt%, Ti 0.0020 wt% or less, O 0.0006 to
0.0015 wt%, Ni 2.0 wt% or less, Mo 1.0
wt% or less, Cu 1.0 wt% or less, V 0.01 to 0.30 wt%, Nb 0.0
Bearings that contain one or more selected from 1 to 0.30 wt%, are excellent in workability characterized by the balance of Fe and unavoidable impurities, and can simplify or omit the spheroidizing annealing treatment. For steel.