JP6953871B2 - Carburized parts and carburized nitride parts - Google Patents

Description

The present invention relates to carburized parts and carburized nitrided parts, and more particularly to those suitable as power transmission parts such as gears.

Power transmission parts such as gears are required to have high pitching fatigue strength in addition to bending fatigue strength. As a material for such parts, JIS SCR420 or the like has been conventionally used, and the strength has been increased by various surface treatments.

The phenomenon of pitching in gears and the like is a phenomenon in which cracks occur, crack progresses, and peels off due to high stress generated by rubbing between tooth surfaces. At this time, a high surface pressure is applied to the contact surface such as the tooth surface, and the contact surface is repeatedly subjected to friction, which causes the temperature to rise to about 300 ° C. Therefore, the tooth surface strength (pitching fatigue strength) correlates with the softening resistance (difficulty of softening when held at a high temperature).

Carburizing nitriding treatment and high-concentration carburizing treatment are known as measures for improving pitching fatigue strength. The carburizing nitriding treatment is a treatment in which nitrogen is introduced into the surface layer of the treatment material together with carbon to improve the temper softening resistance. On the other hand, the high-concentration carburizing treatment is a treatment for increasing the carbon supply to the surface layer of the treatment material and dispersing and precipitating hard carbides on the surface layer to improve tempering and softening resistance.

Further, as a measure for improving the pitching fatigue strength, a high-concentration carburizing nitriding treatment combining the above-mentioned carburizing nitriding and high-concentration carburizing has also been proposed (see Patent Document 1 below). The high-concentration carburizing nitriding treatment aims to improve the temper softening resistance by controlling the amount of N in the surface layer of the treated material and the precipitated carbides.
However, since a large amount of C is dissolved in the surface layer of the steel material in the high-concentration carburizing treatment and C and N in the high-concentration carburizing nitriding treatment, a large amount of retained austenite (hereinafter referred to as residual γ) is likely to be generated after quenching. .. When a large amount of residual γ is generated, the hardness of the surface layer is locally reduced, and there is a problem that the bending fatigue strength etc. cannot be withstood the load. Regarding the carburized nitriding parts that have been subjected to the carburizing nitriding treatment, both the pitching fatigue strength and the bending fatigue strength have not been achieved, and there is still room for improvement.

Japanese Unexamined Patent Publication No. 2009-74110

Against the background of the above circumstances, the present invention provides a carburized component and a carburized nitride component in which a large amount of residual γ is suppressed in the carburized layer and the carburized nitride layer to enhance the pitching fatigue strength and the bending fatigue strength. It was made for the purpose of doing so.

Therefore, claim 1 relates to a carbonized part, and in terms of mass%, C: 0.14 to 0.38%, Si: 0.01 to 1.50%, Mn: 0.25 to 2.0%, Cu: 0.5% or less, Ni: 0.06 to 0.8 % , Cr: 0.50 to 4.5%, Mo: 0.8% or less, Al: 0.010 to 0.060%, N : Consists of steel containing 0.005 to 0.030%, having the composition of the balance Fe and unavoidable impurities, and satisfying the following formula (1).
It has a carburized layer as a surface layer, and the surface layer is the outermost layer to 0.05 mm, has a carbide area ratio of 5 to 40%, and has a residual γ content of less than 40%.
-0.19> -0.102 [Si] -0.03 [Cu] -0.01 [Ni] -0.135 [Cr] ・ ・ ・ Equation (1)
(However, each element symbol in formula (1) represents the content mass%)

The second aspect of the present invention is characterized in that, in the first aspect, the alloy component of the steel further contains Nb: 0.1% or less in mass%.

Claim 3 relates to a carbonized nitrided component, in terms of mass%, C: 0.14 to 0.38%, Si: 0.01 to 1.50% or less, Mn: 0.25 to 2.0%, Cu. : 0.5% or less, Ni: 0.06 to 0.8 % , Cr: 0.50 to 4.5%, Mo: 0.8% or less, Al: 0.010 to 0.060%, N: It is made of steel containing 0.005 to 0.030%, having the composition of the balance Fe and unavoidable impurities, and satisfying the following formula (1).
The surface layer has a carburized nitrided layer, the surface layer is the outermost layer to 0.05 mm, the N concentration is 0.05 to 0.5% by mass%, the carbide area ratio is 5 to 40%, and the residual γ is further. The amount is less than 40%.
-0.19> -0.102 [Si] -0.03 [Cu] -0.01 [Ni] -0.135 [Cr] ・ ・ ・ Equation (1)
(However, each element symbol in formula (1) represents the content mass%)

The fourth aspect of the present invention is characterized in that, in the third aspect, the alloy component of the steel further contains Nb: 0.1% or less in mass%.

The high-concentration carburizing treatment and the high-concentration carburizing nitriding treatment are performed in a treatment pattern as shown in FIG. 1, for example. First, primary carburizing and quenching are carried out, and then the temperature of the treated material is raised again to precipitate carbides. Then, carburizing (secondary carburizing) is performed again to grow carbides, and then quenching is performed.
In the high-concentration carburizing treatment, a carburizing gas such as acetylene is introduced at the time of the secondary carburizing, whereas in the high-concentration carburizing nitriding treatment, the carburizing gas and the ammonia gas for nitriding are introduced at the time of the secondary carburizing. It is introduced alternately and nitriding is performed together with carburizing.

By the way, the solid solution C concentration at the time of quenching after the secondary carburizing substantially corresponds to the concentration at the Acm point in the phase diagram. In general, it is known that when the solid solution C concentration becomes excessive, the residual γ after quenching increases and the hardness decreases, and when the solid solution N increases in addition to the solid solution C, the residual γ further increases. ing.
The present inventors aim to suppress the generation of residual γ in the high-concentration carburizing treatment in which the C concentration in the surface layer of the steel material is higher than that in the conventional carburizing treatment and the high-concentration carburizing nitriding treatment in which the C concentration and the N concentration are high. , The amount of each alloying element added was changed based on the SCR420 material, and the change in the solid solution C concentration at 850 ° C. was investigated and studied. I found it big.

The present invention is based on such findings, and Si and Cr having a large effect of suppressing the solid solution C concentration are positively added to the steel, and other components are contained according to the contribution rate to the suppression of the solid solution C concentration. This is intended to suppress the amount of residual γ after quenching. In order to suppress the amount of residual γ in the high-concentration carburizing treatment, it is desirable that the solid solution C concentration (that is, the Acm point) at around 850 ° C., which is the secondary carburizing temperature, be 0.90% or less, and in the present invention, it is solid. By incorporating an alloying element that affects the dissolved C concentration in the steel so as to satisfy the above formula (1), the solid solution C concentration at 850 ° C. is reduced to 0.90% or less, and a large amount of residual γ is present after quenching. It is intended to solve the problems that are generated.

That is, the carburized component of the present invention is made of steel whose composition has been adjusted so as to satisfy the above formula (1), and the carbide area ratio of the carburized layer formed on the surface layer of the component is 5 to 40%, and the amount of residual γ is further increased. According to the carburized parts of the present invention, it is possible to prevent a decrease in strength due to a large amount of residual γ and increase both pitching fatigue strength and bending fatigue strength. The carburized parts of the present invention are particularly suitable for application to high surface pressure resistant parts such as gears, which require particularly high pitching fatigue strength and bending fatigue strength.

The carburized nitriding component of the present invention is made of steel whose composition has been adjusted so as to satisfy the above formula (1), and the carbide area ratio of the carburized nitriding layer formed on the surface layer of the component is 5 to 40% and the residual γ content is set. It was set to less than 40%, and the N concentration was set to 0.05 to 0.5% in terms of mass%. In the case of carburized nitrided parts, increasing the N concentration on the surface layer is effective in improving the temper softening resistance, but the amount of residual γ increases. Therefore, in the carburized nitriding component of the present invention, the N concentration of the carburized nitriding layer is defined as 0.05 to 0.5%, and the residual γ amount is suppressed to less than 40%.

Next, the reasons for limiting each chemical component in the present invention will be described below.
C: 0.14 to 0.38%
C is an element necessary for ensuring the strength, and is contained in an amount of 0.14% or more in order to secure the core hardness of the part. However, if the content is too large, the toughness of the core portion is lowered and the workability such as cold forging is lowered, so the upper limit is set to 0.38%.

Si: 0.01 to 1.50% or less Si has a great effect of lowering the solid solution C concentration at the time of charcoal burning, and contains 0.01% or more. However, if the content is excessive, the toughness and machinability will decrease, so the content should be 1.50% or less.

Mn: 0.25 to 2.0%
Mn is a useful component for ensuring the hardenability of the core portion, and is contained in an amount of 0.20% or more for its function. However, if the content becomes too large, there is a concern that the machinability will decrease, so the upper limit is set to 2.0%.

Cu: 0.50% or less Cu has a function of improving hardenability. However, if the content is excessive, the hot forging property is lowered, so the content is set to 0.50% or less.

Ni: 0.06 to 0.8 %
Ni is Ri Hatarakigaa improving the hardenability, is contained more than 0.06% for that work. However, if the content becomes excessive, the residual γ increases and the processability decreases, so the content is set to 0.8% or less.

Cr: 0.50 to 4.5%
Cr is a useful component for ensuring hardenability. In addition, it has a great effect of reducing the solid solution C concentration at the time of charcoal burning together with Si. Therefore, it is contained in an amount of 0.50% or more. However, if the content is too large, the workability, particularly the machinability, deteriorates. Further, since the hardenability becomes too large and there is a concern that the quenching strain increases, the upper limit is set to 4.5%.

Mo: 0.8% or less Mo improves hardenability and enhances temper softening resistance. However, if a large amount is added, the workability, especially the machinability, will decrease, so the upper limit is set to 0.8%.

Al: 0.010 to 0.060%
Al has a pinning function of suppressing coarsening of crystal grains, and 0.010% or more is contained in order to obtain this pinning effect. However, if the content becomes too large, Al ₂ O ₃ inclusions are formed in the steel and the strength is lowered, so the upper limit is set to 0.060%.

N: 0.005 to 0.030%
N has a pinning function of suppressing coarsening of crystal grains, and is contained in an amount of 0.005% or more in order to obtain this pinning effect. On the other hand, in order to prevent blow generation during casting, the upper limit is set to 0.030%.

Nb: 0.1% or less Nb, like Al, has a pinning function of suppressing coarsening of crystal grains and can be further contained as a selective element (claims 2 and 4). However, if the content is too large, the workability is deteriorated and coarse nitrides are produced, so the upper limit is set to 0.1%.

-0.19> -0.102 [Si] -0.03 [Cu] -0.01 [Ni] -0.135 [Cr] ・ ・ ・ Equation (1)
Si, Cu, Ni, and Cr have the effect of reducing the amount of solid solution C during carburizing. The coefficients of Si, Cu, Ni, and Cr in the formula (1) represent the degree of contribution to the decrease in the amount of solid solution C, respectively. According to the investigation by the present inventors, the component so that the value on the right side of the equation (1) is less than −0.19 (in other words, the absolute value of the value on the right side is larger than 0.19). By adjusting, the solid solution C concentration (Acm point) at 850 ° C. can be suppressed to 0.90% or less, and the residual γ after quenching can be reduced. When the amount of Cu and Ni is at the impurity level, the terms of Cu and Ni may be excluded from the calculation.

Surface carbide area ratio is 5-40%
By setting the area ratio of the carbides deposited on the surface layer of the component to 5% or more, the temper softening resistance can be improved. However, if the area ratio becomes excessive, coarse carbides are likely to be generated in a mesh pattern, and there is a concern that the fatigue strength may decrease. Therefore, the upper limit is set to 40%.

The amount of residual γ in the surface layer is less than 40% When a large amount of residual γ is generated in the surface layer, the hardness of the surface layer decreases, and in particular, the bending fatigue strength decreases. Therefore, in the present invention, the amount of residual γ in the surface layer is set to less than 40%. ..

Surface N concentration is 0.05-0.5%
In the case of a carburized nitrided component, the temper softening resistance can be improved by setting the N concentration in the component surface layer (carburized nitrided layer) to 0.05% or more. However, if the N concentration becomes excessive, the residual γ increases and the hardness decreases, so the upper limit is set to 0.5%.

According to the present invention as described above, it is possible to provide a carburized component and a carburized nitriding component in which both the pitching fatigue strength and the bending fatigue strength are enhanced by suppressing the generation of a large amount of residual γ in the surface layer.

It is a figure which showed an example of the processing pattern of the high-concentration carburizing performed for obtaining the carburized part of this invention. (A) is a figure which showed the test piece used for measuring the bending fatigue strength. (B) is a figure which showed the test piece used for the measurement of the pitching fatigue strength. (A) is a figure which showed the relationship between bending fatigue strength and residual γ. (B) is a diagram showing the relationship between surface hardness and residual γ. (A) is a figure which showed the relationship between the pitching fatigue strength and the tempering hardness. (B) is a figure which showed the relationship between tempering hardness and residual γ.

Next, examples of the present invention will be described in detail below.
Steels having the chemical compositions shown in Table 1 were melted in a 150 kg high frequency induction furnace. The obtained ingot was rolled or hot forged on a round bar having a diameter of Φ90 mm, and further hot forged on a steel bar having a diameter of 22 to 32 mm to be used as a material for testing, and various items shown in Table 2 were evaluated.
In Table 1, the steel types a to p and x (15 types in total) satisfy the requirements of the component range of the present invention. On the other hand, the steel types q to w and y (8 types) do not satisfy the requirements of the component range of the present invention. Specifically, it does not satisfy at least the requirement of the formula (1).

<Solid solution C concentration>
The solid solution C concentration at 850 ° C. was evaluated for the 22 steel grades (steel grades a to x) shown in Table 1. Specifically, a round bar test piece having a diameter of 15 × 100 L was prepared from the above test material, and vacuum carburized at 850 ° C. The vacuum carburizing treatment was carried out so that the surface layer C concentration of the test piece was 1.5%, and carbides were precipitated on the surface layer. Then, the treated test piece was cut in cross section, and EPMA ray analysis was performed from the surface of the test piece to a predetermined depth. In such EPMA ray analysis, a high value is detected when the carbide is hit by the analysis beam, while a low value is detected in the matrix portion. Therefore, the obtained C concentration curve fluctuates violently up and down near the surface layer where carbides are deposited, but when the carbides disappear and C is solid-solved, the large turbulence of the curve is settled. Here, the concentration at this boundary was defined as the solid solution C concentration (Acm point) at 850 ° C. The results are shown in Table 2.

As shown in Table 2, the solid solution C concentration at 850 ° C. is a comparison in which the composition of the steel grade does not meet the requirements of the present invention (specifically, the value on the right side of the formula (1) is larger than −0.19). In Examples 3 to 9, the residual γ exceeds 0.90%, which is a guideline for an increase. On the other hand, in Examples 1 to 14 and Comparative Examples 1, 2 and 10 in which the composition of the steel grade satisfies the requirements of the present invention, the solid solution C concentration at 850 ° C. is lower than 0.90%. The effect of lowering the concentration of solid solution C was observed in the composition satisfying the formula (1).

Next, a Φ15 × 100 L round bar test piece was prepared from the above test material, subjected to the high-concentration carburizing treatment shown below, and the surface layer C concentration, residual γ content, carbide area ratio and surface hardness were evaluated. went. Further, after processing the above-mentioned test material into a predetermined shape, bending fatigue strength and pitching fatigue strength were evaluated using a test piece subjected to high-concentration carburizing treatment.
Some of the test pieces were subjected to high-concentration carburizing and nitriding treatment instead of high-concentration carburizing treatment, and the surface layer N concentration was measured in addition to the above evaluation items.

<High-concentration carburizing treatment / High-concentration carburizing nitriding treatment>
For the high-concentration carburizing treatment, a vacuum carburizing furnace was used, acetylene was used as the carburizing gas, and the primary carburizing treatment and the secondary carburizing treatment were performed in the treatment pattern as shown in FIG.
In the primary carburizing treatment, the carburizing treatment is performed at 1050 ° C. for 70 minutes so that the C concentration on the outermost surface becomes about 1.1%, and then the carburized material is rapidly cooled to a temperature range of 500 ° C. or lower by gas cooling to precipitate carbides. C was allowed to penetrate into the steel to a high concentration range where it did not occur.
In the secondary carburizing treatment, the carbides are precipitated at a temperature of 850 ° C., and then the carburizing treatment is carried out for 30 to 90 minutes depending on the target C concentration while maintaining the same temperature. Carbides precipitated in the carburized layer were grown and then oil-quenched. After quenching, a tempering treatment at 180 ° C. for 120 minutes was carried out.

In addition, Comparative Example 11 in Table 2 is an example in which a steel equivalent to JIS SCR420 was used and vacuum carburizing was performed with the C concentration on the surface as an eutectoid composition, and Comparative Example 11 was subjected to the above high concentration carburizing treatment. Not.

On the other hand, in the high-concentration carburizing nitriding treatment, the same primary carburizing treatment as in the case of the high-concentration carburizing treatment was carried out, and then the secondary carburizing nitriding treatment was carried out. In the secondary carburizing nitriding treatment, acetylene gas for carburizing and ammonia gas for nitriding are alternately flowed under the same temperature and time conditions as the secondary carburizing treatment of the above high-concentration carburizing treatment to carburize the surface layer. A nitride layer was formed.

<Surface C concentration>
Using the test piece after the high-concentration carburizing treatment or the high-concentration carburizing nitriding treatment, Dalai powder having a depth of up to 0.05 mm was collected from the surface of the test piece, and the C concentration (mass%) was measured by gas analysis. ..

<Surface N concentration>
Using the test piece after the high-concentration carburizing and nitriding treatment, Dalai powder having a depth of up to 0.05 mm was collected from the surface of the test piece, and the N concentration (mass%) was measured by gas analysis.

<Amount of residual γ>
The outermost surface of the test piece after the high-concentration carburizing treatment or the high-concentration carburizing nitriding treatment was measured by XRD to determine the amount of residual γ.

<Carbide area ratio>
After cutting and polishing the cross section of the test piece after the above high-concentration carburizing treatment or high-concentration carburizing nitriding treatment, it is corroded with piclar, and the inside of the position from the outermost surface to 0.05 mm is photographed with SEM and image analysis is performed. Therefore, the area ratio of the carbide was measured.

<Surface hardness>
The cross-sectional portion of the test piece after the high-concentration carburizing treatment or the high-concentration carburizing nitriding treatment was cut and embedded to prepare a test piece for hardness measurement. A Vickers hardness tester was used for the measurement, and the 5-point average of the hardness at a position 0.05 mm below the surface was defined as the surface hardness by the test method specified in JIS Z2244. Further, the test piece after the high-concentration carburizing treatment or the high-concentration carburizing nitriding treatment was tempered at 300 ° C. for 3 hours, and the tempering hardness of the surface layer was measured. The test load was 300 g.

<Bending fatigue strength>
The bending fatigue strength was evaluated by the Ono type rotary bending fatigue test based on JIS Z2274. After processing the above-mentioned test material into a round bar-shaped Ono-type rotary bending fatigue test piece 10 having an annular notch with a radius r = 1 mm shown in FIG. 2 (A), the above-mentioned high-concentration carburizing treatment or high-concentration carburizing It was nitrided and subjected to the test. The test conditions were a rotation speed of 3500 rpm and a test temperature of room temperature. Bending fatigue strength is the maximum stress that does not break at 10 ⁷ cycles. Further, the bending fatigue strength of the vacuum carburized material (Comparative Example 11) of JIS SCR420 was set to 1, and the bending fatigue strength improvement rate of each test piece was expressed in%.

<Pitching fatigue strength>
The pitching fatigue strength was evaluated by a roller pitching test. As shown in FIG. 2B, the above test material is applied to a small roller test piece 12 having a contact portion 12a with a diameter of φ26 mm, small diameter portions 12b on both sides thereof having a diameter of φ23 mm, and a contact portion 12a having a width of 28 mm. After processing, the above-mentioned high-concentration carburizing treatment or high-concentration carburizing nitriding treatment was performed and subjected to a test.

The large roller on the other side of the test piece 12 was subjected to quenching and tempering treatment so that the material was SUJ2 and HRC61. The radius of curvature of the large roller was set to 150R.
In the roller pitching test, the test piece 12 and the large roller on the other side are brought into contact with each other at various surface pressures of 2.0 to 4.0 GPa at a rotation speed (test piece 12): 1500 rpm, and they are contacted using a roller pitching tester. the slip ratio: rotating at -60%, and the load stress that does not cause pitting in ¹⁰⁷ cycles the surface fatigue strength (pitting fatigue strength). Then, the surface fatigue strength of the vacuum carburized material (Comparative Example 11) of JIS SCR420 was set to 1, and the surface fatigue strength improvement rate of each test piece was expressed in%.
The evaluation results are shown in Table 2 and FIGS. 3 and 4.

As shown in Table 2, Examples 1 to 14 and Comparative Examples 1 to 10 which were subjected to the high-concentration carburizing treatment or the high-concentration carburizing nitriding treatment all had a tempering hardness of 300 ° C. in Comparative Example 11 (vacuum carburizing of SCR420). The surface fatigue strength (pitching fatigue strength) was maintained higher than that of the conventional vacuum carburized material (Comparative Example 11) as shown in FIG. 4 (A). As a whole, the effect of applying the high-concentration carburizing treatment or the high-concentration carburizing nitriding treatment is obtained.

However, in Comparative Example 1, the carbide area ratio of the surface layer was lower than the lower limit of 5% of the present invention, the hardness was significantly reduced at 300 ° C. tempering from 747HV to 645HV, and the effect of improving the tempering softening resistance was another example. Not enough compared to.
On the other hand, in Comparative Example 2, the carbide area ratio of the surface layer exceeds the upper limit of 40% of the present invention. In Comparative Example 2, although the surface hardness was as high as 796 HV, the bending fatigue strength was lower than that of the conventional vacuum carburized material (Comparative Example 11) as shown in FIG. 3 (A), and pitching was performed. Achievement of both fatigue strength and bending fatigue strength is not achieved. In Comparative Example 2 in which the carbide area ratio is excessively large, it is presumed that the bending fatigue strength deteriorated because the carbide became coarse and its shape changed from a spherical shape to a net shape.

On the other hand, in Comparative Examples 3 to 8, the carbide area ratio of the surface layer was within the specified range of the present invention, but the residual γ amount was 40% or more, which exceeded the specified value of the present invention. Therefore, as shown in FIG. 3A, the bending fatigue strength is lower than that of the conventional vacuum carburized material (Comparative Example 11), and the pitching fatigue strength and the bending fatigue strength are not compatible with each other. In Comparative Examples 3 to 8 in which the residual γ content was 40% or more, although the surface hardness was apparently high, the hardness was locally reduced due to the large amount of residual γ content, and the bending fatigue strength was increased. It is presumed that it has deteriorated.

In Comparative Examples 9 and 10 subjected to the high-concentration carburizing and nitriding treatment, the carbide area ratio and the N concentration of the surface layer were within the specified range of the present invention, but the residual γ amount was 40% or more and the specified values of the present invention were obtained. As shown in FIG. 3A, the bending fatigue strength is lower than that of the conventional vacuum carburized material (Comparative Example 11), and the pitching fatigue strength and the bending fatigue strength are not compatible with each other. ..

On the other hand, Examples 1 to 12 subjected to the high-concentration carburizing treatment are made of steel whose composition has been adjusted so as to satisfy the above formula (1), and the carbide area ratio and the residual γ amount of the carburized layer are also specified in the present invention. It is within the range. As shown in Tables 2 and 4 (B), in each of Examples 1 to 12, the tempering hardness at 300 ° C. is higher than that of Comparative Example 11 (vacuum carburized material of SCR420), and the surface fatigue strength (pitching fatigue strength) is higher. ), As shown in FIG. 4A, better results than the conventional vacuum carburized material (Comparative Example 11) are obtained.
In addition, as shown in FIG. 3A, the bending fatigue strength was also improved by 1.0 to 6.5% as compared with the conventional vacuum carburized material (Comparative Example 11). That is, in Examples 1 to 12 subjected to the high-concentration carburizing treatment, both the pitching fatigue strength and the bending fatigue strength can be increased as compared with the conventional vacuum carburized material (Comparative Example 11).

Further, Examples 13 and 14 subjected to the high-concentration carburizing and nitriding treatment are made of steel whose composition has been adjusted so as to satisfy the above formula (1), and the carbide area ratio, residual γ amount and N concentration of the carburized nitride layer are the present. It is within the specified range of the invention. In each of these Examples 13 and 14, the tempering hardness at 300 ° C. is maintained higher than that of Comparative Example 11 (vacuum carburized material of SCR420). Therefore, as shown in FIG. 4A, better results are obtained for the surface fatigue strength (pitching fatigue strength) than the conventional vacuum carburized material (Comparative Example 11).
In addition, as shown in FIG. 3A, the bending fatigue strength was also improved by 1.3 to 2.6% as compared with the conventional vacuum carburized material. That is, even in Examples 13 and 14 in which the high-concentration carburizing and nitriding treatment is performed, both the pitching fatigue strength and the bending fatigue strength can be increased as compared with the conventional vacuum carburized material (Comparative Example 11).

Examples of the present invention have been described in detail above, but this is merely an example, and the present invention can be carried out in a mode in which various modifications are made without departing from the spirit of the present invention.

Claims (4)

By mass% C: 0.14 to 0.38%
Si: 0.01 to 1.50%
Mn: 0.25 to 2.0%
Cu: 0.5% or less Ni: 0.06 to 0.8 %
Cr: 0.50 to 4.5%
Mo: 0.8% or less Al: 0.010 to 0.060%
N: 0.005 to 0.030%
Consists of steel having the composition of the balance Fe and unavoidable impurities and satisfying the following formula (1).
A carburized component having a carburized layer as a surface layer, the surface layer having the outermost layer to 0.05 mm, a carbide area ratio of 5 to 40%, and a residual γ amount of less than 40%.
-0.19> -0.102 [Si] -0.03 [Cu] -0.01 [Ni] -0.135 [Cr] ・ ・ ・ Equation (1)
(However, each element symbol in formula (1) represents the content mass%) The carburized part according to claim 1, further containing Nb: 0.1% or less in mass% as an alloy component of the steel. By mass% C: 0.14 to 0.38%
Si: 0.01 to 1.50%
Mn: 0.25 to 2.0%
Cu: 0.5% or less Ni: 0.06 to 0.8 %
Cr: 0.50 to 4.5%
Mo: 0.8% or less Al: 0.010 to 0.060%
N: 0.005 to 0.030%
Consists of steel having the composition of the balance Fe and unavoidable impurities and satisfying the following formula (1).
The surface layer has a carburized nitrided layer, the surface layer is the outermost layer to 0.05 mm, the N concentration is 0.05 to 0.5% by mass%, the carbide area ratio is 5 to 40%, and the residual γ is further. A carburized nitrided component, characterized in that the amount is less than 40%.
-0.19> -0.102 [Si] -0.03 [Cu] -0.01 [Ni] -0.135 [Cr] ・ ・ ・ Equation (1)
(However, each element symbol in formula (1) represents the content mass%) The carburized nitride component according to claim 3, further containing Nb: 0.1% or less in mass% as an alloy component of the steel.

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