JP2000087213A - Rolling part - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the toughness of a core part and moreover, to make many coarse carbides do not exist on the surface part. SOLUTION: This rolling part is obtd. by performing a stock composed of steel contg., by weight, 0.15 to 0.45% C, 1.2 to 1.6% Cr, 0.35 to 0.55% Si, 0.35 to 0.65% Mn and the balance Fe with inevitable impurities to heat treatment including carburizing treatment. The content of C in the surface part is 0.9 to 2.0 wt.% and the surface hardness is >=63 in Rockwell C hardness. Fine spheroidal carbides are precipitated on the carburizing layer, moreover, the average particle size of the spheroidal carbides is <=5 μm and the content thereof is <=40% at an area ratio. The particle size of >=70% of the spheroidal carbides is <=5 μm. The content of residual austenite in the carburizing layer is 20 to 40%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is suitable for use as a rolling part, and more particularly, as a bearing ring for a rolling bearing or a rolling element used in a dirt oil mixed with foreign matter. Related to rolling parts.

[0002]

2. Description of the Related Art As the above-mentioned rolling bearing parts, the applicant of the present invention has previously disclosed 0.5 to 1.2% by weight of C and 0.7 to 3.
It is made of steel containing 0% by weight of Cr and is carburized to make the surface C 1.5-3.0% by weight.
The surface hardness is 63 or more in Rockwell C hardness, fine spherical carbides are precipitated on the carburized layer, and the diameter of the spherical carbides is 10 μm or less and the amount is 1% in area ratio.
It has been proposed that the carbon content of the carburized layer matrix be 0.6 to 0.7% by weight (see Japanese Patent Application Laid-Open No. 7-41934).

[0003]

However, it has been found that the conventional rolling bearing parts have the following problems. That is, since such a rolling bearing component has a relatively high C content of 0.5 to 1.2% by weight in steel as a material thereof, the strength and hardness of the core can be secured. The toughness is inferior, and when a rolling bearing assembled using this bearing component is used in a machine that is easily subject to vibration or impact, it may be damaged. In addition, since the C content in the steel used as the material is relatively large at 0.5 to 1.2% by weight,
During the carburizing treatment, C in the carburizing atmosphere hardly penetrates into the material, so that C is collected on the surface of the obtained bearing component, and the amount of C in the surface portion is described in Examples of the above publication. As such, it actually amounts to more than 2.1% by weight. Therefore, the amount of coarse carbides and the amount of retained austenite on the surface are increased, which contributes to a decrease in strength. In addition, if C is collected on the surface of the bearing component, the carbide generated there is coarsened. Therefore, even if the average particle size is 4 μm as described in the example of the above publication, the particle size is actually Spherical carbide having a diameter exceeding 5 μm is about 30% of the whole,
In some cases, the maximum particle size is 10 μm, and as a result, stress is concentrated on the spherical carbide having a particle size exceeding 5 μm, and fracture may occur from this portion.

[0004] It is an object of the present invention to solve the above-mentioned problems, to improve the toughness of the core, and to provide a rolling part in which a large amount of coarse carbide does not exist on the surface.

[0005]

The rolling component according to the present invention has a C content of 0.15 to 0.45% by weight,
1.2 to 1.6% by weight, Si 0.35 to 0.55% by weight
And 0.35 to 0.65% by weight of Mn, and the balance Fe
And a heat treatment including a carburizing treatment, wherein the C of the surface is 0.9 to 2.0% by weight.
At the same time, the surface hardness is 63 or more in Rockwell C hardness, fine spherical carbides are precipitated on the carburized layer, and the average particle size of the spherical carbides is 5 μm or less and the amount is 40% in area ratio. And the particle size of 70% or more of the spherical carbide is 5 μm or less,
Further, the amount of retained austenite in the carburized layer is set to 20 to 40%.

[0006] In the above description, the rolling parts are usually used after the rolling surface is subjected to a polishing finish treatment of several tens to one hundred and several tens μm. Therefore, in the above, C is 0.9 ~
The surface portion of 2.0% by weight means a portion from the outermost surface after the polishing finish treatment to a portion having a depth of 50 μm. Note that the depth of the carburized layer is considerably deeper than the above-mentioned polishing amount, and therefore, the properties of the carburized layer are not affected by the polishing.

[0007] The reasons for limiting the alloy components in the steel used as the material in the above-mentioned rolling parts are as follows.

C: 0.15 to 0.45% by weight C has the property of securing the core hardness and strength required for a rolling part, but if the content is less than 0.15% by weight, Effect is not obtained, and if it exceeds 0.45% by weight, the toughness decreases. Further, when the content exceeds 0.45% by weight, C in the carburizing atmosphere hardly penetrates into the material during the carburizing treatment, so that C is collected on the surface of the obtained rolling component, and the C content of the surface portion is 2%. More than 1% by weight. When C collects on the surface of the rolling component, the carbide generated here becomes coarse, so that the spherical carbide having a particle size of 5 μm or less cannot be made 70% or more of the whole. Therefore, C
The content should be chosen in the range of 0.15 to 0.45% by weight.

Cr: 1.2 to 1.6% by weight Cr has a property of precipitating spherical carbides by carburizing treatment, but if its content is less than 1.2% by weight, such an effect cannot be obtained. If it exceeds 1.6% by weight, the spherical carbides become coarse. Therefore, the Cr content is 1.2 to
It should be chosen within the range of 1.6% by weight.

Si: 0.35 to 0.55% by weight Si has a property of refining spherical carbides precipitated by carburizing treatment. If the content is less than 0.35% by weight, such an effect is not obtained. If it exceeds 0.55% by weight, the required carburizing depth cannot be obtained. Therefore, the Si content should be selected within the range of 0.35 to 0.55% by weight.

Mn: 0.35 to 0.65% by weight Mn has a property of improving hardenability, but if its content is less than 0.35% by weight, such an effect cannot be obtained, and If it exceeds 0.65% by weight, the amount of retained austenite on the surface will exceed 40%, and the hardness will decrease. Therefore, the Mn content should be selected within the range of 0.35 to 0.65% by weight.

V: 0.3% by weight or less The above steel may further contain V by 0.3% by weight or less. V, like Cr, has the property of precipitating spherical carbides by carburizing, but if its content exceeds 0.3% by weight, the spherical carbides become coarse.
Therefore, the V content should be 0.3% by weight or less.

In the above rolling parts, the amount of C in the surface portion, the surface hardness, the average particle size of the spherical carbide, the amount of those having a particle size of 5 μm or less in the spherical carbide, the area ratio of the spherical carbide,
The reasons for limiting the amount of retained austenite are as follows.

If the amount of C on the surface is less than 0.9% by weight, carbides cannot be uniformly dispersed. If the amount of C exceeds 2.0% by weight, the amount of coarse carbides on the surface and the amount of retained austenite As the amount increases, the strength decreases. When C collects on the surface of the bearing component, the carbide generated here becomes coarse, so that spherical carbide having a particle size exceeding 5 μm actually accounts for about 40% of the whole,
In some cases, the maximum particle size is 10 μm, and as a result, stress is concentrated on the spherical carbide having a particle size exceeding 5 μm, and fracture may occur from this portion. Therefore, the amount of C on the surface is in the range of 0.9 to 2.0% by weight, preferably 0.1 to 2.0% by weight.
It should be selected within the range of 9-1.4% by weight.

The surface hardness surface hardness Rockwell C hardness (hereinafter, HRC referred to as) In is not sufficient surface hardness is less than 63, the foreign matter component, for example a bearing using the rolling bearing part this rolling This is because, when used in contaminated oil mixed with water, the surface of the rolling bearing component is liable to be scratched by an indentation or the like due to a foreign substance serving as a separation starting point, and the wear resistance is reduced to shorten the life of the bearing. Therefore, the surface hardness should be HRC63 or more. Note that the upper limit of the surface hardness is preferably about HRC68 in consideration of toughness.

Average particle size of spherical carbide and in spherical carbide
When the average particle size of the spherical carbide exceeds 5 μm, the particle size becomes 5 μm.
m is about 80% of the total, and as a result, stress is concentrated on the spherical carbide having a particle size exceeding 5 μm,
Destruction may occur from this part. Therefore,
The average particle size of the spherical carbide is 5 μm or less, preferably 3 μm.
m. In addition, the particle size in the spherical carbide is 5μ.
If the amount is less than 70%, the spherical carbide having a particle size exceeding 5 μm accounts for 30% or more of the whole, and in some cases, the maximum particle size becomes 10 μm, and as a result, the particle size becomes 5 μm.
Stress concentrates on the spherical carbide exceeding m, and fracture may occur from this portion. Therefore, the amount of those having a particle size of 5 μm or less in the spherical carbide should be 70% or more of the entire spherical carbide.

If the area ratio of the spherical carbide exceeds 40%, the strength of the carburized layer matrix decreases, so that the area ratio of the spherical carbide is 40%.
%, Preferably not more than 25%. In addition,
The lower limit of the area ratio is 5 to secure the required surface hardness.
% Is preferable. Here, the area ratio refers to an average value of the area ratios of the above-mentioned five locations, each of which is observed by image analysis at five locations of a visual field of 40 × 30 μm observed at 3,000 times.

If the amount of retained austenite is less than 20%, the toughness is reduced and the cracking speed is increased to shorten the life of the bearing using this component. If it exceeds 40%, the required surface hardness is reduced. I can't secure it. Therefore, the amount of retained austenite is 2
It should be selected within the range of 0-40%.

In the rolling part of the present invention, the heat treatment including the carburizing treatment applied to the steel used as the material includes, for example, a first step of performing carburizing or carburizing and quenching, and a step of performing quenching to form a fine spherical carburized layer. A method comprising: a second step of depositing carbide; and a third step of performing a high-concentration carburizing and quenching treatment so that the carbon concentration of the surface portion is higher than the carbon concentration of the surface portion obtained in the first step. There is. The heating temperature in the third step is preferably equal to or lower than the heating temperature in the second step. If the heating temperature in the third step is higher than the heating temperature in the second step, a part of the carbide precipitated in the second step may be dissolved in the matrix. The following is a more specific description of such a method. That is, C ₃ H
930 in a carburizing atmosphere containing ₁₀ to 17 vol%
A first step of oil-cooling after heating at a temperature of ~ 950 ° C for 3-5 hours, a second step of oil-cooling after heating at a temperature of 800-840 ° C for 0.5-0.8 hours, C ₃ H ₈ to 10
790-840 ° C in a carburizing atmosphere containing 17vol%
And heating at a temperature not higher than the heating temperature of the second step for 3 to 5 hours, followed by oil cooling. In the third step, C ₃ H ₈ is added in an amount of ₁₀ to 17 vol.
%, At a temperature of 790 to 820 ° C. and a temperature not higher than the heating temperature of the second step for 3 to 5 hours, and then increasing the temperature to 0.5 to 830 to 840 ° C.
It is preferred to heat for 0.8 hours and then oil cool. In this case, it is possible to increase the amount of carbide without coarsening the carbide.

According to the rolling component of the present invention, C0.1
5 to 0.45% by weight, Cr 1.2 to 1.6% by weight, Si
0.35 to 0.55% by weight and Mn 0.35 to 0.6
Since it is made of steel containing 5% by weight and the balance being Fe and unavoidable impurities, the strength and hardness of the core are ensured, and a decrease in toughness is prevented. In particular, since the C content in the steel material is 0.15 to 0.45% by weight,
The C content of the surface portion becomes 2.0% by weight or less, and the carbide generated on the surface portion of the rolling component can be prevented from becoming coarse. Therefore, destruction due to concentration of stress on the coarsened spherical carbide can be prevented. The steel is subjected to a heat treatment including a carburizing treatment so that the surface portion has a C of 0.9 to 2.0% by weight, and the surface hardness is 63 or more in Rockwell C hardness. Fine spherical carbides are precipitated in the layer, and the average particle size of the spherical carbides is 5
μm or less and the amount is 40% or less in area ratio, and the particle size of 70% or more of the spherical carbide is 5 μm or less.
And the amount of retained austenite is 2
Since the ratio is set to 0 to 40%, the life of the rolling bearing using this component in dirty oil is improved.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described together with comparative examples.

Examples 1 to 8 A track for a thrust ball bearing using a steel containing 0.2% by weight of C, 1.4% by weight of Cr, 0.45% by weight of Si and 0.50% by weight of Mn, the balance being Fe and inevitable impurities. A ring material and a ball material are prepared for eight sets, and four of these materials are subjected to heat treatment under the conditions shown in FIG. 1 (heat treatment condition 1), and the remaining four sets are subjected to the conditions shown in FIG. Heat treatment was performed under (heat treatment condition 2). Then, 16
After heating and tempering at 0 ° C for 2 hours, the surface of each material is polished, and the polishing amount is changed to produce eight sets of races and balls for thrust ball bearings with different surface properties. These were used to assemble eight thrust ball bearings. Note that the tempering is a process that is generally performed after the quenching process to improve the toughness of the material, and is not illustrated.

The heat treatment condition 1 was performed using a fluidized bed furnace, and N ₂ gas was supplied as a fluidizing gas at a flow rate of 4.5 × 10 ⁻⁴ m ³ / s and C was supplied. _While supplying ₃ H ₈ gas at a flow rate of 0.5 × 10 ⁻⁴ m ³ / s (C ₃ H ₈ concentration in the atmosphere is 10 vol%
), Heated at 930 ° C. for 3 hours, oil-cooled to 80 ° C., and carburized and quenched, and a flow rate of N ₂ gas as a fluidizing gas of 5.0 × 10 ⁻⁴ m ³ / After heating at 840 ° C. for 0.5 hour while supplying so that
A second step of oil-cooling to ℃ and quenching, supplying N ₂ gas as a fluidizing gas at a flow rate of 4.2 × 10 ⁻⁴ m ³ / s, and flowing C ₃ H ₈ gas Is 0.8 ×
While supplying at a ^{rate of} 10 ⁻⁴ m ³ / s (C in atmosphere)
₃ H ₈ concentration is 16 vol%), was heated for 5 hours at 830 ° C., the more the third step of cooled oil 80 ° C. subjected to high-concentration carburizing and quenching treatment.

The heat treatment condition 2 was performed using a fluidized bed furnace, and N ₂ gas was supplied as a fluidizing gas at a flow rate of 4.5 × 10 ⁻⁴ m ³ / s and C _While supplying ₃ H ₈ gas at a flow rate of 0.5 × 10 ⁻⁴ m ³ / s (C ₃ H ₈ concentration in the atmosphere is 10 vol%
), Heated at 930 ° C. for 3 hours, oil-cooled to 80 ° C., and carburized and quenched, and a flow rate of N ₂ gas as a fluidizing gas of 5.0 × 10 ⁻⁴ m ³ / After heating at 840 ° C. for 0.5 hour while supplying so that
A second step of oil-cooling to ℃ and quenching; supplying a N ₂ gas as a fluidizing gas at a flow rate of 4.5 × 10 ⁻⁴ m ³ / s and a C ₃ H ₈ gas flow rate Is 0.5 ×
While supplying at a ^{rate of} 10 ⁻⁴ m ³ / s (C in atmosphere)
₃ H ₈ concentration is 10 vol%), was heated for 5 hours at 830 ° C., the more the third step of cooled oil 80 ° C. subjected to high-concentration carburizing and quenching treatment.

Examples 9-16 0.2% by weight of C, 1.4% by weight of Cr, 0.4% by weight of Si
And thirteen sets of thrust ball bearing material and ball material are made from steel containing 0.50% by weight of Mn and Mn, the balance being Fe and unavoidable impurities, and heat treatment conditions are applied to four sets of these materials. 1 and a heat treatment was performed on the remaining four sets under a heat treatment condition 2. Then
After each material is heated at 160 ° C. for 2 hours and tempered, the surface of each material is polished, and the amount of polishing is changed to thereby provide eight sets of thrust ball bearing races having different surface properties. Balls were manufactured and used to assemble eight thrust ball bearings. Note that the tempering is a process that is generally performed after the quenching process to improve the toughness of the material, and is not illustrated.

Comparative Examples 1-4 JIS SUJ2 materials were used to make four sets of thrust ball bearing race and ball materials, and these materials were subjected to heat treatment under the conditions shown in FIG. 3 (heat treatment conditions 3). did. Then
By polishing the surface of each material and changing the polishing amount, four sets of thrust ball bearing orbits and balls having different surface properties were manufactured, and four thrust ball bearings were assembled using these.

The heat treatment conditions 3 include a first step of heating at 830 ° C. for 0.5 hour, followed by oil cooling and quenching,
A second step of performing a tempering treatment by heating at 80 ° C. for 2 hours.

Comparative Examples 5-8 Tracks for thrust ball bearings using a steel containing 0.2% by weight of C, 1.4% by weight of Cr, 0.45% by weight of Si and 0.50% by weight of Mn, the balance being Fe and unavoidable impurities. Four sets of ring materials and ball materials were prepared, and these materials were subjected to heat treatment under the conditions shown in FIG. 4 (heat treatment conditions 4). Then, each material is heated at 160 ° C. for 2 hours to perform a tempering process, and then the surface of each material is polished, and the amount of polishing is changed so that four sets of raceways for thrust ball bearings having different surface properties. Rings and balls were manufactured and used to assemble four thrust ball bearings. Note that the tempering is a process that is generally performed after the quenching process to improve the toughness of the material, and is not illustrated.

The heat treatment condition 4 is performed using a fluidized-bed furnace. N ₂ gas is supplied as a fluidizing gas at a flow rate of 3.5 × 10 ⁻⁴ m ³ / s and C is supplied. _While supplying ₃ H ₈ gas at a flow rate of 1.5 × 10 ⁻⁴ m ³ / s (C ₃ H ₈ concentration in the atmosphere is 30 vol%
), Heated at 930 ° C. for 3 hours, oil-cooled to 80 ° C., and carburized and quenched, and a flow rate of N ₂ gas as a fluidizing gas of 5.0 × 10 ⁻⁴ m ³ / After heating at 830 ° C. for 0.5 hour while supplying so that
A second step of performing oil-cooling and quenching at 830 ° C. while supplying N ₂ gas as a fluidizing gas at a flow rate of 5.0 × 10 ⁻⁴ m ³ / s. After heating for hours,
A third step of performing oil-cooling and quenching at 80 ° C., supplying N ₂ gas as a fluidizing gas at a flow rate of 4.2 × 10 ⁻⁴ m ³ / s, and supplying C ₃ H ₈ gas. The flow rate is 0.
While heating at 8 × 10 ⁻⁴ m ³ / s (the C ₃ H ₈ concentration in the atmosphere is 16 vol%), the mixture was heated at 930 ° C. for 5 hours, and then cooled to 80 ° C. to obtain a high concentration. A fourth step of performing carburizing and quenching, and supplying N ₂ gas as a fluidizing gas at a flow rate of 5.0 × 10 ⁻⁴ m ³ / s,
After heating at 0 ° C. for 0.5 hour, a fifth step of oil cooling to 80 ° C. and quenching is performed.

The surface hardness of the thrust ball bearing races and balls of Examples 1 to 16 and Comparative Examples 1 to 8 described above,
The amount of C in the surface, the area ratio of carbide in the carburized layer, the average particle diameter of the carbide, the amount of spherical carbide having an average particle diameter of 5 μm or less,
Tables 1 and 2 also show the amount of retained austenite.

[0031]

[Table 1]

[0032]

[Table 2]

Evaluation Test Using the ball bearings of Examples 1 to 16 and Comparative Examples 1 to 8, a life test was performed in dirty oil containing foreign matter. In the life test, the ball bearing was immersed in # 60 spindle oil containing 0.12% by weight of high-speed tool steel powder having an average particle diameter of 27 μm, a maximum particle diameter of 50 μm and a surface hardness of HRC65, and a thrust load of 3.92 kN. (maximum contact stress P _{ma x} = 5.24G
Pa), rotation speed 1200 rpm (stress repetition rate 30H)
z) was carried out using a thrust type testing machine. A vibration meter is connected to the tester so that if an abnormality such as peeling occurs during the test, the tester stops automatically when the vibration value increases and reaches twice the initial vibration value. I had it. The oil was not filtered or replenished during the test, and a predetermined amount was replaced with new oil for each test. Tables 1 and 2 also show the life of the ball bearings of Examples 1 to 16 and Comparative Examples 1 to 8.

First, the relationship between the ratio between the surface hardness of the race and the ball and the surface hardness of the foreign matter (hardness ratio R) and the rolling life L in Examples 1 to 16 and Comparative Examples 5 to 8 was determined. . The result is shown in FIG. As is apparent from FIG. 5, in the case of Examples 1 to 16, it is needless to say that the hardness ratio R is larger than 1, that is, the surface hardness of the bearing ring and the ball is larger than the surface hardness of the foreign matter. It can be seen that even when the hardness ratio R is 1 or less, the life L is extended as compared with Comparative Examples 5 to 8. In contrast, in Comparative Examples 5 to 8,
Although the hardness ratio R may be 1 or more, the life is half or less of Examples 1 to 16.

As can be seen from Table 2, the hardness ratios R of Comparative Examples 1 to 4 are all 0.96 or less.
The life is 0.85 × 10 ⁶ cycles or less.

Next, the relationship between the carbide area ratio and the rolling life L in the life test was determined. FIG. 6 shows the result. As is clear from FIG. 6, in Examples 1 to 16, the lower the carbide area ratio, the longer the rolling life L tends to be. On the other hand, in the case of Comparative Examples 1 to 4, despite the low carbide area ratio, the rolling life L was low because the surface carbon amount was small and the surface hardness was less than HRC63.
Is less than half of Examples 1 to 16. Further, in the case of Comparative Examples 5 to 8, the rolling life L was shortened because the carbide area ratio was high, although the same steel as in Examples 1 to 8 was used.

Further, the relationship between the average particle diameter of the carbide and the rolling life in the life test was determined. FIG. 7 shows the result. As is clear from FIG. 7, in Examples 1 to 16, the smaller the average particle diameter of the carbide, the longer the rolling life tends to be. The tendency is particularly remarkable when the hardness ratio R is 1 or more. On the other hand, in the case of Comparative Examples 1 to 4, the rolling life L was smaller than that of Examples 1 to 4 because the surface carbon content was small and the surface hardness was less than HRC 63 despite the small carbide average particle size. 16 or less. Further, in the case of Comparative Examples 5 to 8, the rolling life L was shortened because the carbide average particle diameter was large even though the same steel as in Examples 1 to 8 was used.

In FIGS. 5 to 7, actual 1 to 16 and ratios 1 to 8 represent Examples 1 to 16 and Comparative Examples 1 to 8.

From the above results, it can be seen that the carbide area ratio and the carbide average particle diameter are both low values despite the large surface carbon content, in other words, the minute spherical carbides are contained in the carburized layer matrix. It can be seen that the roller in a state of being uniformly dispersed has a longer rolling life L.

[Brief description of the drawings]

FIG. 1 is a diagram showing a heat treatment condition 1 of an example.

FIG. 2 is a diagram showing a heat treatment condition 2 of an example.

FIG. 3 is a diagram showing heat treatment conditions 3 of Comparative Examples 1 to 4.

FIG. 4 is a diagram showing heat treatment conditions 4 of Comparative Examples 5 to 8.

FIG. 5 is a graph showing the relationship between the hardness ratio and the rolling life in Examples 1 to 16 and Comparative Examples 5 to 8.

FIG. 6 is a graph showing the relationship between the carbide area ratio and the rolling life in Examples 1 to 16 and Comparative Examples 1 to 8.

FIG. 7 is a graph showing the relationship between the average carbide particle size and the rolling life in Examples 1 to 16 and Comparative Examples 1 to 8.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F16C 33/62 F16C 33/62 (72) Inventor Shinichi Yasuki 1-3-18 Wakihamacho, Chuo-ku, Kobe-shi No. Kobe Steel, Ltd. (72) Inventor Yoshitake Matsushima 1-3-18, Wakihama-cho, Chuo-ku, Kobe Stock Company Kobe Steel, Ltd. F term in Kobe Steel (reference) 3J101 AA53 BA10 BA70 DA02 EA03 FA60 4K028 AA01 AB01 AB06 AC08

Claims (5)

[Claims] C. 0.15 to 0.45% by weight of C1.
2 to 1.6% by weight, 0.35 to 0.55% by weight of Si and 0.35 to 0.65% by weight of Mn, the balance being made of steel comprising Fe and unavoidable impurities, and subjected to heat treatment including carburizing. The C of the surface portion is 0.9 to 2.0% by weight, and the surface hardness is 63 in Rockwell C hardness.
As described above, fine spherical carbides are precipitated on the carburized layer, the average particle size of the spherical carbides is 5 μm or less and the amount thereof is 40% or less in area ratio, and the particle size of 70% or more of the spherical carbides The rolling part is characterized in that the carburized layer has a residual austenite amount of 20 to 40%. 2. The rolling part according to claim 1, wherein the steel further contains V of 0.3% or less. 3. The rolling component according to claim 1, wherein C of the surface portion is 0.9 to 1.4% by weight. 4. The rolling part according to claim 1, wherein the average particle diameter of the spherical carbide is 3 μm or less. 5. The rolling part according to claim 1, wherein the amount of the spherical carbide is 25% or less in area ratio.