JP2006328514A - Rolling supporting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To elongate the rolling fatigue life of a rolling supporting device used under a severe environment such as a rolling bearing for a rolling mill. <P>SOLUTION: At least one selected from an inner race 1, an outer race 2 and a roller 3 is produced by working a stock composed of a steel comprising, by mass, 0.1 to 0.6% C, 0.3 to 2.0% Cr, 0.1 to 0.6% Si, 0.3 to 2.0% Mn, ≤2.0% Mo, ≤5.0% Ni and 0.1 to 4.0% Cu, and the balance Fe with inevitable impurities into a prescribed shape, and thereafter performing heat treatment. Then, in the core part, the average grain size of old austenite crystal grains present per mm<SP>2</SP>is controlled to ≤30 μm, and also, the maximum grain size thereof is controlled to ≤100 μm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a rolling support device such as a rolling bearing, a ball screw, and a linear guide.

Rolling bearings used in steel facilities are often used in harsh environments such as high loads and high surface pressures, so it is necessary to increase the rolling fatigue life even in such harsh environments. Has been.
For this reason, in a rolling bearing used in such a harsh environment, the effective hardened layer depth capable of withstanding the shear stress with respect to the case-hardened steel such as SNC815 to which Ni (nickel) or Mo (molybdenum) is added. A rolling member is used in which the surface layer portion forming the rolling surface is provided with the necessary hardness by performing a long-term carburizing or carbonitriding treatment for obtaining a thickness and quenching and tempering.

  Moreover, in patent document 1, in order to suppress the surface damage which arises in severe environments, such as under a heavy load, high surface pressure, and foreign material mixing, at least one of an inner ring, an outer ring, and a rolling element is unit. It is made of steel in which the number and size of non-metallic inclusions (oxide inclusions) existing per area is specified, and the amount of retained austenite in the surface layer is 20% by volume or more and 45% by volume or less. Has been proposed.

Furthermore, in Patent Document 2, a bearing that constitutes a rolling member is used to suppress internal damage originating from non-metallic inclusions that occur under severe environments such as high loads, high surface pressures, and clean environments. It has been proposed to define the number and size of non-metallic inclusions (oxide inclusions or Ti inclusions) present per unit area or unit volume in steel.
By the way, in recent years, rolling bearings for rolling mills have been used under higher load environments, and in addition to the above-mentioned surface damage due to the contamination of foreign matter, a unique form different from the above-mentioned internal damage. As internal damage occurs in the rolling member, it is a problem that the rolling fatigue life cannot be extended.
Japanese Patent Laid-Open No. 6-145883 JP 2004-84869 A

However, in the technique described in Patent Document 1 and Patent Document 2 described above, the rolling fatigue life of a rolling support device that causes unique internal damage to a rolling member, such as a rolling bearing for a rolling mill, is increased. There is room for further improvement.
An object of the present invention is to prolong the rolling fatigue life of a rolling support device used in a severe environment such as a rolling bearing for a rolling mill under a heavy load, a high surface pressure, and a foreign matter. .

In order to solve such a problem, as a result of intensive investigations by the present inventors, unique internal damage caused by rolling members such as rolling mill rolling bearings is deeper than the surface (core part). It was discovered that cracks originated from crystal grains coarsened by carburizing or carbonitriding for a long time.
Accordingly, the present inventors have found that the above-described unique internal damage can be suppressed by refining the prior austenite crystal grains constituting the martensite structure in the core portion of the rolling member, Invented the invention.

In addition, the present inventors have devised a heat treatment method for steel as a method for refining prior austenite crystal grains even after long-term carburizing or carbonitriding (for example, A after carburizing or carbonitriding). _The heat treatment cost is reduced by adopting a method of adding Cu (copper) to the material steel and remarkably delaying the growth of austenite grains, instead of once quenching below ₁ transformation point and further quenching. The present invention has been completed by finding that the above-mentioned unique internal damage can be suppressed without increasing.

That is, the present invention is arranged such that the first member and the second member having raceway surfaces arranged to face each other, and the first member and the second member are movably disposed between the first member and the second member. A rolling support device having a surface, wherein the rolling member rolls so that one of the first member and the second member moves relative to the other, the first member, At least one of the second member and the rolling element has a C content of 0.1% by mass to 0.6% by mass, a Cr content of 0.3% by mass to 2.0% by mass, Si content is 0.1% by mass or more and 0.6% by mass or less, Mn content is 0.3% by mass or more and 2.0% by mass or less, Mo content is 2.0% by mass or less, and Ni content is 5%. 0.0 mass% or less, Cu content is 0.1 mass% or more and 4.0 mass% or less, and the balance is Fe After processing the material made of steel is fine unavoidable impurities into a predetermined shape, the heat treatment is obtained is subjected, at its core, the old austenite crystal grains existing per 1 mm ² is an average particle diameter of 30μm or less, And the rolling support apparatus characterized by the maximum particle size being 100 micrometers or less is provided.

The present invention also includes a first member and a second member having raceway surfaces arranged opposite to each other, and a rollable member disposed between the first member and the second member, and rolling relative to the raceway surface. A rolling support device having a surface, wherein the rolling member rolls so that one of the first member and the second member moves relative to the other, the first member, At least one of the second member and the rolling element has a C content of 0.1% by mass to 0.6% by mass, a Cr content of 0.3% by mass to 2.0% by mass, Si content is 0.1% by mass or more and 0.6% by mass or less, Mn content is 0.3% by mass or more and 2.0% by mass or less, Mo content is 2.0% by mass or less, and Ni content is 5%. 0.0 mass% or less, Cu content is 0.1 mass% or more and 4.0 mass% or less, and the balance is Fe and After processing the material made of steel which is soluble avoid impurities into a predetermined shape, the heat treatment is obtained is subjected, at its core, with an average grain size of prior austenite crystal grains existing per 1 mm ² is 30μm or less There is provided a rolling support device characterized in that the number of old austenite crystal grains of 60 μm or more present per 1 mm ² is 5 or less.

The present invention further includes a first member and a second member having raceway surfaces arranged opposite to each other, and a rollable member disposed between the first member and the second member, and rolling relative to the raceway surface. A rolling support device having a surface, wherein the rolling member rolls so that one of the first member and the second member moves relative to the other, the first member, At least one of the second member and the rolling element has a C content of 0.1% by mass to 0.6% by mass, a Cr content of 0.3% by mass to 2.0% by mass, Si content is 0.1% by mass or more and 0.6% by mass or less, Mn content is 0.3% by mass or more and 2.0% by mass or less, Mo content is 2.0% by mass or less, and Ni content is 5%. 0.0 mass% or less, Cu content is 0.1 mass% or more and 4.0 mass% or less, and the balance is Fe and After processing the material made of steel is inevitable impurities into a predetermined shape, the heat treatment is obtained is subjected, at its core, the old austenite crystal grains existing per 1 mm ² is an average particle diameter of 30μm or less, and The rolling support device is characterized in that the maximum grain size is 100 μm or less and the number of old austenite crystal grains of 60 μm or more present per 1 mm ² is 5 or less.

The rolling support device in the present invention can be suitably used as a rolling bearing used for supporting a rotating part of a rolling mill.
In the present invention, the “rolling support device” refers to, for example, a rolling bearing, a ball screw, and a linear guide. Here, when the rolling support device is a rolling bearing, the first member and the second member indicate an inner ring and an outer ring. When the rolling support device is a ball screw, the first member and the second member indicate a screw shaft and a nut. Furthermore, when the rolling support device is a linear guide, the first member and the second member indicate a guide rail and a slider.

In the present invention, the “core portion” refers to a portion where there is no difference between the material and the contained component.
Further, in the present invention, “old austenite crystal grains” refers to austenite crystal grains before quenching, and can be manifested by corroding the martensite structure after quenching and tempering.
The rolling support device according to the present invention is a rolling member (first member,) in which a specific core portion is obtained after the following heat treatment is performed after processing a material made of the following specific steel into a predetermined shape. (Second member, rolling element).

First, the steel used in the present invention will be described.
<C content: 0.1 mass% or more and 0.6 mass% or less>
C (carbon) has the effect | action which provides the intensity | strength and lifetime which are required for steel by converting a base into a martensite. Here, since the C content of the surface layer portion can be added when carburizing or carbonitriding is performed as a heat treatment, the C content of steel forming the material is in the core of the rolling member in a completed state. It is necessary to make the amount that can provide the required strength. Therefore, the C content of the steel constituting the material is 0.1% by mass or more.

On the other hand, if the C content of the steel constituting the material is too large, coarse carbides may be generated during steel making and the fatigue characteristics may be reduced. Therefore, the C content of the steel constituting the material is 0.6% by mass or less.
<Cr content: 0.3 mass% or more and 2.0 mass% or less>
Cr (chromium) improves the hardenability and temper softening characteristics, thereby strengthening the base and improving the rolling fatigue life. In addition, Cr has the effect of generating high hardness and fine carbides and carbonitrides to improve wear resistance. Further, Cr is a surface layer part when performing carburizing treatment or carbonitriding treatment as heat treatment. It also has the effect of increasing the C content and improving the carburizing characteristics and carbonitriding characteristics. In order to obtain these effects, the Cr content is set to 0.3% by mass or more.

On the other hand, when the Cr content is too high, not only the above-described effect is saturated, but also a passive film is formed on the surface layer portion, which may hinder carburizing characteristics and carbonitriding characteristics. Therefore, Cr content rate shall be 2.0 mass% or less.
<Si content: 0.1% by mass or more and 0.6% by mass or less>
Si (silicon) has an action as a deoxidizer and a desulfurizer during steelmaking. In order to obtain this effect, the Si content is set to 0.1% by mass or more.

On the other hand, when there is too much Si content rate, machinability, such as a forgeability and machinability of a raw material, will fall. Therefore, Si content rate shall be 0.6 mass% or less.
<Mn content: 0.3 mass% or more and 2.0 mass% or less>
Similar to Si, Mn (manganese) has the effect of improving the hardenability in addition to the action as a deoxidizing agent and a desulfurizing agent during steelmaking. In order to obtain these effects, the Mn content is set to 0.3% by mass or more, preferably 0.5% by mass or more.

On the other hand, when there is too much Mn content, many nonmetallic inclusions will be produced | generated and there exists a possibility that a rolling fatigue life characteristic may fall, and machinability, such as a forge property and a machinability of a raw material, will fall. Therefore, the Mn content is 2.0% by mass or less.
<Mo content: 2.0 mass% or less, Ni content: 5.0 mass% or less>
Mo (molybdenum) and Ni (nickel) have the effect of strengthening the base and improving the rolling fatigue life by improving the hardenability. In particular, when the wall thickness of the bearing ring is large, such as a rolling bearing for a rolling mill, it is necessary to add at least one element of Mo and Ni.

On the other hand, when there are too many Mo content rates and Ni content rates, it will cause deterioration of hot workability and a raise of manufacturing cost. Therefore, the Mo content is 2.0% by mass or less, and the Ni content is 5.0% by mass or less.
<Cu content: 0.1% by mass or more and 4.0% by mass or less>
Cu has the effect of making it difficult to form carbides and nitrides in steel, and the effect of suppressing grain growth by segregating to austenite grain boundaries and reducing the grain boundary energy. In order to obtain these effects, the Cu content is set to 0.1% by mass or more. The Cu content is preferably 0.6% by mass or more, and more preferably 1.0% by mass or more.

On the other hand, if the Cu content is too high, the hot workability is deteriorated, so the Cu content is 4.0 mass% or less.
Next, an example of the heat treatment performed in the present invention will be described.
Although it does not specifically limit as heat processing for making the core part of a rolling member into the range of this invention using the specific steel mentioned above, For example, the carburizing process hold | maintained at about 850-1150 degreeC for 50 to 120 hours, or Examples of the heat treatment include performing carbonitriding and then quenching, and further performing tempering at 160 to 240 ° C. for 2 hours.

Next, the structure of the core part of the rolling member specified by the present invention will be described.
In order to suppress unique internal damage starting from the above-mentioned crystal grains, in the core portion, “the prior austenite crystal grains existing per 1 mm ² have an average grain size of 30 μm or less and a maximum grain size of 100 μm. Or “the average grain size of the prior austenite crystal grains existing per 1 mm ^{2 is set} to 30 μm or less, and 5 or less old austenite crystal grains of 60 μm or more existing per 1 mm ² ”. is there.

Further, in order to effectively suppress the unique internal damage starting from the above-mentioned crystal grains, in the core portion, “the prior austenite crystal grains existing per 1 mm ² have an average grain size of 30 μm or less, and The maximum grain size is preferably 100 μm or less, and is preferably 5 or less old austenite crystal grains of 60 μm or more present per 1 mm ² .
Here, if the average grain size of the prior austenite crystal grains present per 1 mm ² of the core exceeds 30 μm, unique internal damage starting from the coarse crystal grains described above tends to occur.

Even if the average grain size of the prior austenite crystal grains existing per 1 mm ^{2 of} the core is 30 μm or less, the maximum grain size of the prior austenite crystal grains present per 1 mm ^{2 of} the core is over 100 μm. If there are more than 5 old austenite crystal grains of 60 μm or more present per 1 mm ^{2 of} the core part, unique internal damage starting from the coarse crystal grains described above tends to occur.

The average grain size and the maximum grain size of the prior austenite crystal grains existing per 1 mm ^{2 of} the core are preferably as small as possible within a range where the heat treatment cost is not significantly increased, and per 1 mm ^{2 of} the core. It is preferable to reduce the number of existing austenite crystal grains of 60 μm or more as much as possible without causing a significant increase in heat treatment cost.
Moreover, it is preferable to form an effective hardened layer of Hv550 or more with a thickness of 3 mm or more on the surface layer part forming the rolling surface of the rolling member so as to be able to withstand even in a high load environment. On the other hand, considering the heat treatment cost, it is preferable to form an effective hardened layer of Hv550 or higher with a thickness of 6 mm or lower.

According to the rolling support device of the present invention, the “average grain size” of the prior austenite crystal grains present per 1 mm ² in at least one core portion of the rolling member (first member, second member, rolling element) By specifying at least one of “maximum grain size” and “number of predetermined grain sizes”, it is possible to suppress surface damage due to contamination by foreign substances and to prevent internal damage starting from coarse crystal grains in the core. Can be suppressed.

  Therefore, the rolling support device of the present invention has a rolling fatigue life even when it is used in a severe environment such as a rolling bearing for a rolling mill under a heavy load, a high surface pressure, and contamination. Can be long.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In the present embodiment, a cylindrical roller bearing (reference number NU228: inner diameter 140 mm, outer diameter 250 mm, width 42 mm, roller diameter 26 mm) having the configuration shown in FIG. 1 was produced by the method described below.
As shown in FIG. 1, this cylindrical roller bearing (rolling support device) 10 includes an inner ring (first member) 1, an outer ring (second member) 2, and between the raceway surfaces 1 </ b> A and 2 </ b> A of the inner ring 1 and the outer ring 2. And a plurality of cylindrical rollers (rolling elements) 3 and a cage 4.

The inner ring 1, the outer ring 2, and the roller 3 were produced by the following procedure.
First, a material made of steel to which C, Cr, Si, Mn, Mo, Ni, and Cu having respective contents shown in Table 1 were added was processed into a predetermined shape by forging, turning, or the like.

  Next, these were subjected to heat treatment including carburizing, quenching, and tempering. Here, the cylindrical roller bearing 10 manufactured in the present embodiment is extremely small as compared with a normal rolling mill rolling bearing (for example, reference number 850RV1133: inner diameter 850 mm, outer diameter 1180 mm, width 650 mm, roller diameter 80 mm). Therefore, in this embodiment, in the rolling members (inner ring 1, outer ring 2, roller 3) constituting the cylindrical roller bearing 10, the above-described rolling member for the reference number 850RV1133 is mixed gas (RX gas + propane gas) atmosphere. The heat treatment was performed so that the effective hardened layer depth and the crystal grain size similar to those obtained when carburizing for 100 hours was performed.

Specifically, carburizing treatment was performed by heating and holding at 850 to 1150 ° C. for 50 to 120 hours in an atmosphere of a mixed gas (RX gas + propane gas). Next, after performing oil quenching, tempering treatment was performed by holding at 200 ° C. for 2 hours. Next, grinding finishing was performed.
Next, the hardness of the core (the portion where the carburized layer is not formed) and the unit area (1 mm ² ) per sample for the fracture test among the obtained inner ring 1, outer ring 2 and roller 3 The average grain size, the maximum grain size, and the number of old austenite crystal grains having a grain size of 60 μm or more (the number of crystals of 60 μm or more) were measured by the methods described below. The results are also shown in Table 1.

The crystal grain size of the prior austenite present in the core was measured as follows. First, the inner ring 1, the outer ring 2, and the roller 3 are cut, and the cut surface is corroded with a picric acid solution (picral: laurylbenzene sulfonic acid = 1: 1), thereby revealing the core structure. I made it come out.
Then, this structure is observed with an optical microscope, and the grain boundaries are traced and image-processed, whereby the average grain size of the prior austenite crystal grain size per 1 mm ² , the maximum grain size, and the grain size is 60 μm. The number of the above crystal grains was calculated.

Moreover, the hardness of the said core part was computed using the Vickers hardness test method in the part in which the carburized layer is not formed.
The hardness of the surface layer portion (the portion from the surface to a depth of 1000 μm) and the amount of retained austenite of the obtained inner ring 1, outer ring 2, and roller 3 were carburized for 100 hours on the rolling member for the above-mentioned reference number 850RV1133. It was almost the same as the product that had been subjected to.

Then, the cylindrical roller bearing 10 was assembled using the sample for a life test among the obtained inner ring | wheel 1, the outer ring | wheel 2, and the roller 3, and the holder | retainer 4 made from copper. And the lifetime test was done by making this cylindrical roller bearing 10 operate | move on the conditions shown below assumed using it under a high load and a high surface pressure.
This life test was performed by rotating the inner ring 1 until at least one of the inner ring 1, the outer ring 2 and the roller 3 was damaged, and the rotation time until the damage occurred was defined as the life. As a result of this life test, the L ₁₀ life based on the Weibull distribution function was calculated. The ratio of when the 1 of 12 L ₁₀ life, also shown in Table 1.
<Life test conditions>
Radial load: P / C = 0.6
Rotational speed: 1000min ^-1
Lubricating oil: # 68 Turbine oil (oil bath)

As shown in Table 1, in Example No. 1 in which the inner ring 1, the outer ring 2, and the roller 3 have the core configuration of the present invention. 1-No. 11, Comparative Example No. 1 outside the configuration of the present invention. Compared with 12-18, it has a long service life. A life of 2.0 or more times 12 was obtained.
Among these, in the core parts of the inner ring 1, the outer ring 2, and the roller 3, the average particle diameter, the maximum particle diameter, and the number of grains of 60 μm or more are all No. 1-No. In No. 9, only the average particle size and the maximum particle size are within the scope of the present invention. No. 10 and the average particle diameter and the number of grains of 60 μm or more are within the scope of the present invention. Compared to 11, it had a longer life.

Also, performed from the results shown in Table 1, heat treatment for refining the crystal grains carburizing immediately after quenching without (once cooled to below the A ₁ transformation point after carburizing, and thereafter quenching processes) However, it was found that the crystal grains could be refined. Thereby, it turned out that the crystal grain of the steel which makes the raw material of a rolling member can be refined | miniaturized, without raising heat processing cost by using specific steel as a raw material.

Subsequently, based on the results obtained in Table 1, the graph of FIG. 2 showing the relationship between the Cu content in the steel constituting the material and the lifetime was prepared.
From the graph of FIG. 2, by setting the Cu content in the steel to 0.1 μm or more, No. It can be seen that a life of 3 times longer than 12 is obtained.
Further, based on the results obtained in Table 1, the graph of FIG. 3 showing the relationship between the Cu content in the steel constituting the material and the average grain size of the prior austenite grains present per 1 mm ^{2 of} the core. It was created.

From the graph of FIG. 3, it can be seen that by setting the Cu content to 0.1 μm or more, the average particle size of the prior austenite grains existing per 1 mm ² of the core is 30 μm or less.
Further, based on the results shown in Table 1, the graph of FIG. 4 showing the relationship between the Cu content in the steel constituting the material and the maximum grain size of the prior austenite grains existing per 1 mm ^{2 of} the core is prepared. did.

From the graph of FIG. 4, it can be seen that the maximum grain size of the prior austenite grains existing per 1 mm ² of the core is 100 μm or less by setting the Cu content to 0.1 μm or more.
Furthermore, based on the results shown in Table 1, the graph of FIG. 5 showing the relationship between the Cu content in the steel constituting the material and the number of old austenite grains of 60 μm or more present per 1 mm ^{2 of} the core part. Created.

From FIG. 5, it is understood that the number of old austenite grains of 60 μm or more existing per 1 mm ² of the core is 5 or less by making the Cu content in the steel constituting the material 0.1 μm or more. .
From the above results, it is possible to extend the rolling fatigue life of the cylindrical roller bearing 10 used under high load, high surface pressure, and the like by configuring the core portions of the inner ring 1, outer ring 2 and roller 3 according to the present invention. I understood.

  That is, from the results of the present embodiment, it was confirmed that the rolling fatigue life can be extended even in a rolling mill rolling bearing used in a severe environment under high load and high surface pressure.

It is sectional drawing which shows the cylindrical roller bearing which is an example of the rolling support apparatus which concerns on this invention. It is a figure which shows Cu content rate in steel, and a relationship with a lifetime. It is a figure which shows the relationship between Cu content rate in steel, and the average particle diameter of the prior austenite crystal grain which exists per 1 mm < ² > of a core part. It is a figure which shows the relationship between Cu content rate in steel, and the largest grain size of the prior austenite crystal grain which exists per 1 mm < ² > of a core part. It is a figure which shows the relationship between Cu content rate in steel, and the number of the former austenite crystal grains of 60 micrometers or more which exist per 1 mm < ² > of a core part.

Explanation of symbols

1 Inner ring (first member)
1A Raceway surface 2 Outer ring (second member)
2A raceway surface 3 rollers (rolling elements)
4 Cage 10 Cylindrical roller bearing (rolling support device)

Claims (4)

A first member and a second member having raceway surfaces disposed opposite to each other; a rolling element which is disposed between the first member and the second member so as to be freely rollable and has a rolling surface with respect to the raceway surface; In the rolling support device in which one of the first member and the second member moves relative to the other by rolling the rolling element,
At least one of the first member, the second member, and the rolling element is:
C content is 0.1 mass% or more and 0.6 mass% or less, Cr content is 0.3 mass% or more and 2.0 mass% or less, and Si content is 0.1 mass% or more and 0.6 mass% or less. The Mn content is 0.3% by mass or more and 2.0% by mass or less, the Mo content is 2.0% by mass or less, the Ni content is 5.0% by mass or less, and the Cu content is 0.1% by mass or more. 4.0% by mass or less, the balance being obtained by processing a material made of steel with Fe and inevitable impurities into a predetermined shape, followed by heat treatment,
A rolling support device characterized in that, in the core portion, the prior austenite crystal grains present per 1 mm ² have an average particle size of 30 μm or less and a maximum particle size of 100 μm or less. A first member and a second member having raceway surfaces disposed opposite to each other; a rolling element which is disposed between the first member and the second member so as to be freely rollable and has a rolling surface with respect to the raceway surface; In the rolling support device in which one of the first member and the second member moves relative to the other by rolling the rolling element,
At least one of the first member, the second member, and the rolling element is:
C content is 0.1 mass% or more and 0.6 mass% or less, Cr content is 0.3 mass% or more and 2.0 mass% or less, and Si content is 0.1 mass% or more and 0.6 mass% or less. The Mn content is 0.3% by mass or more and 2.0% by mass or less, the Mo content is 2.0% by mass or less, the Ni content is 5.0% by mass or less, and the Cu content is 0.1% by mass or more. 4.0% by mass or less, the balance being obtained by processing a material made of steel with Fe and inevitable impurities into a predetermined shape, followed by heat treatment,
In the core, the average grain size of the prior austenite crystal grains present per 1 mm ² is 30 μm or less, and the number of the prior austenite crystal grains 60 μm or greater present per 1 mm ² is 5 or less. Rolling support device. A first member and a second member having raceway surfaces disposed opposite to each other; a rolling element which is disposed between the first member and the second member so as to be freely rollable and has a rolling surface with respect to the raceway surface; In the rolling support device in which one of the first member and the second member moves relative to the other by rolling the rolling element,
At least one of the first member, the second member, and the rolling element is:
C content is 0.1 mass% or more and 0.6 mass% or less, Cr content is 0.3 mass% or more and 2.0 mass% or less, and Si content is 0.1 mass% or more and 0.6 mass% or less. The Mn content is 0.3% by mass or more and 2.0% by mass or less, the Mo content is 2.0% by mass or less, the Ni content is 5.0% by mass or less, and the Cu content is 0.1% by mass or more. 4.0% by mass or less, the balance being obtained by processing a material made of steel with Fe and inevitable impurities into a predetermined shape, followed by heat treatment,
In the core portion, the prior austenite crystal grains present per 1 mm ² have an average grain size of 30 μm or less and a maximum grain size of 100 μm or less, and 60 μm or more prior austenite crystal grains present per 1 mm ^2. Is a rolling support device characterized by having 5 or less. It is a rolling bearing used in order to support the rotation part of a rolling mill, The rolling support apparatus of any one of Claims 1-3 characterized by the above-mentioned.

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