JP3271659B2 - High strength gear and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength gear suitable as a power transmission gear used at a high surface pressure and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for weight reduction for the purpose of reducing fuel consumption or exhaust gas of automobiles and the like, and also for higher output. In order to transmit high driving force without increasing the unit size, the surface pressure applied to the tooth surface of the power transmission gear is extremely severe, and pitching or contact surface, which is a phenomenon of contact surface separation, is occurring. It is not impossible that wear is a problem.

As a conventional technique for solving this problem, for example, there is a method of performing high concentration carburization on the surface of a gear to precipitate fine carbides to obtain a high hardness. Many applications (for example,
No. 3430).

However, in the gear, the toughness of the tooth root is required at the same time as the strength of the tooth surface, and the fatigue and impact strength due to bending stress must be ensured. Could not perform carburization at a high concentration enough to impair the toughness of the tooth root. Therefore, in order to improve the tooth surface strength by precipitating carbide, for example, as described in JP-A-6-17189, the area ratio of carbide is specified to be low, or spheroidization by a heating-cooling cycle is performed. It was necessary to add a process for controlling the shape of the carbide by the process (for example, JP-A-2-15663).

[0005] On the other hand, as a method for improving the fatigue strength of the tooth root, shot peening in which hard particles are projected onto a gear is widely used. It is considered that the main effect is that compressive residual stress on the surface of the gear is applied, and so-called hard shot peening, in which the projection speed is increased to give a large compressive residual stress, has been developed.

However, when hard shot peening is performed, the tip of the tooth is plastically deformed and crushed, and it is necessary to perform a correction process. Further, in the case where carbide is precipitated on the surface of the gear, if the correction processing is performed, the carbide on the surface layer of the gear is lost, and since the hardness is high, the wear of the tool is increased.

In addition, a method of changing the carburizing depth between the tooth surface and the tooth root has been considered in order to achieve the different strength characteristics required for the tooth surface and the tooth root. And changing the carburization depth and carbide amount at the root of the tooth to give a difference in hardness.
For example, none has focused on the effects on nitriding or shot peening.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of such a conventional problem. According to the study of the present inventors, the difference between the amount of carbide and the carbon concentration in the austenite state is reduced by the subsequent nitriding. It has been confirmed that this has a significant effect on the treatment and tempering hardness, and furthermore on the reaction when shot peening is performed.The present invention utilizes this phenomenon to reduce the tooth surface and tooth root structure of the gear. It is an object of the present invention to provide a high-strength gear that is optimally controlled, and achieves both the strength characteristics required for the tooth surface and the tooth root, and a method for manufacturing the same.

[0009]

According to the present invention, a high-strength gear according to the present invention has an outermost surface of a tooth surface in a meshing range of a tooth surface on a driving side and a driven side of the gear. From 5% to 10% in area ratio from the outermost layer to the core portion in the direction of the core portion, and from the outermost layer to the core portion at the root portion R at the driving side and the driven side of the gear. The carbonized material having a maximum area ratio of 3% is dispersed and precipitated in a spherical or pseudo spherical shape, and is subjected to a nitriding treatment. In the meshing range, the carbide from the outermost layer of the tooth surface to the core is formed. The peak of the nitrogen concentration distribution is 0.3 wt% or less, and the peak of the nitrogen concentration distribution from the outermost surface layer to the core is 0.3 wt% or more in the root corner R portion. .

In the embodiment of the high-strength gear according to the present invention, as described in claim 2, the retained austenite from the outermost surface layer of the tooth surface to the core portion in the meshing range of the tooth surface of the gear. 30w peak of quantity distribution
and the peak of the distribution of the retained austenite amount from the outermost layer to the core at the corner R of the tooth root of the gear is 25 to 45 wt%.

Similarly, in the embodiment of the high-strength gear according to the present invention, the hardness of the outermost layer of the tooth surface is Hv800 or more in the meshing range of the tooth surface as described in claim 3. In addition, the hardness of the outermost layer in the tooth corner radius R portion of the gear can be Hv700 to 800.

[0012] The method for manufacturing a high-strength gear according to the present invention comprises:
As described in claim 4, after the carburizing process of the gear material, cooling or cooling and heating processes are performed to precipitate carbides, and then the nitriding process is performed. In the meshing range, 5 to 10% of carbide is dispersed and precipitated at an area ratio from the outermost surface of the tooth surface to a depth of at least 0.2 mm in the direction of the core, and the roots on the driving side and the driven side of the gear. In the corner R part, the carbide from the outermost layer to the core is up to 3% in area ratio.
In addition, in the meshing range, the peak of the nitrogen concentration distribution from the outermost surface layer of the tooth surface to the core is set to 0.3 wt% or less in the meshing range. It is characterized in that the peak of the nitrogen concentration distribution from the outermost layer to the core is set to 0.3 wt% or more.

According to an embodiment of the method for manufacturing a high-strength gear according to the present invention, as described in claim 5, in the meshing range of the tooth surface of the gear, from the outermost surface layer of the tooth surface to the core. The peak of the residual austenite distribution of the gear is 30 wt% or less, and the tooth corner R
In the part, the peak of the amount distribution of retained austenite from the outermost layer to the core can be 25 to 45 wt%.

Similarly, in an embodiment of the method for manufacturing a high-strength gear according to the present invention, as described in claim 6, the tooth surface of the gear is formed by carburizing or tempering after carburizing and nitriding. In the meshing range, the hardness of the outermost layer of the tooth surface is Hv800 or more, and the hardness of the outermost layer is Hv700 to 8 in the tooth root radius R portion of the gear.
00.

Similarly, in an embodiment of the method for manufacturing a high-strength gear according to the present invention, as described in claim 7, after the carburizing control agent diluted in some cases is applied to the root corner R, the carburizing control agent may be applied. , Carburizing treatment can be performed.

Similarly, in an embodiment of the method for manufacturing a high-strength gear according to the present invention, the carburizing control agent is removed after the carburizing treatment, followed by the nitriding treatment and the secondary firing. Can be put in place.

Similarly, in an embodiment of the method for manufacturing a high-strength gear according to the present invention, as described in claim 9, tempering can be performed at 200 to 250 ° C.

Similarly, in an embodiment of the method for manufacturing a high-strength gear according to the present invention, as described in claim 10, hard particles having a particle size of 0.4 mm or less are formed with an arc height of 0.3 to 0. Shot peening for projection so as to be 8 mm can be performed.

Similarly, in an embodiment of the method for manufacturing a high-strength gear according to the present invention, the carburizing treatment may be performed by a plasma carburizing method.

[0020]

In the high-strength gear and the method of manufacturing the same according to the present invention, the materials used are not particularly limited.
SC material established by JIS G 4051, JIS G
SNC material specified in 4102, SNCM material specified in JIS G 4103, S specified in JISG 4104
Cr material, SCM material established by JIS G 4105, J
The SMn material and the SMnC material defined by IS G 4106 and their improved materials can be used. However, the hardening property improving element lost from the base layer due to the precipitation of carbide, for example, Cr, can be compensated. It is more desirable to use a material containing a hardenability improving element.

Therefore, in the description of the present invention, as a material, SCM420 specified in JIS G 4105 is used.
H was used, and this material was used to process various test pieces.

Next, each test piece was carburized, quenched and tempered according to the pattern shown in FIG. In carburizing, the carbon potential (Cp) of the atmosphere is set to 0.8 to 1.
By changing the ratio in the range of 4, the area ratio of carbides dispersed and precipitated in a spherical or pseudospherical shape was varied. In the subsequent measurement of the area ratio of carbide, a 10,000 × photograph was taken with a scanning electron microscope in a range of 0.2 mm from the outermost surface, avoiding the grain boundary oxide layer, and was obtained by image analysis.

In measuring the pitting and the wear strength, a life of 50% of failure was taken, and the number of rotations was 150.
A roller pitching test was performed under the conditions of 0 rpm, a slip ratio: 40%, and a surface pressure: 5000 MPa.

Further, when measuring the fatigue strength, a test piece having a shape factor of 2.0 was subjected to rotational bending, and a 107 cycle life was examined. Further, when measuring the static bending strength and the repeated impact life (1500 MPa), a 10 mm square bending test piece was used. Table 1 shows the results thus obtained.

[0025]

[Table 1]

As shown in Table 1, first, the results of the roller pitting test show that the life and the amount of wear tend to increase as the area ratio of carbide increases. This can be understood from the fact that the carbide is stable even at a high temperature, and thus has a function of suppressing a decrease in hardness as compared with a carbide having a small amount of carbide.
For example, FIG. 2 shows the relationship between the surface hardness and the roller pitting life when tempering at 300 ° C. It can be seen that the pitting strength has a good correspondence with the high temperature hardness.

However, as can be seen from the results shown in Table 1, when the area ratio of the carbide exceeds 10%, the carbides are coalesced into a lump and it is difficult to stably and finely disperse. Resulting in. Therefore, the area ratio of carbide on the tooth surface is within the range of 5 to 10 which is within the range of the present invention.
% Is considered appropriate. In addition, the depth is 0.2 mm in the case of a normal use condition, even in consideration of the maximum shear stress depth.
You only have to do it.

On the other hand, the bending fatigue strength also increases as the area ratio of carbide is increased to a certain extent, but the static bending rupture strength and the repeated impact life sharply increase when the area ratio of carbide at the root of the gear exceeds 3%. Will drop. From this, it is considered appropriate that the area ratio of carbide at the root of the gear is 3% or less.

As described above, according to the present invention, it is possible to obtain a high-strength gear in which the pitting resistance and the wear resistance of the tooth surface and the bending fatigue strength and the impact resistance of the tooth root are optimized.

In the present invention, since high-concentration carburization is required, the carburization step is preferably performed by plasma carburization.
This is because the treatment can be performed in a vacuum, so that grain boundary oxidation does not occur even at a high temperature, and carburizing can be performed quickly.

Next, the test pieces were carburized in the pattern shown in FIG. 3 and then nitrided in NH 3 gas. The carbon potential (Cp) at this time was varied under the same conditions as in the pattern of FIG. Then, the distribution of carbon and nitrogen concentrations from the outermost surface toward the core is determined by EPMA.
Table 2 shows the results of the examination.

[0032]

[Table 2]

As is clear from the results shown in Table 2, it is understood that the nitrogen concentration becomes lower as the area ratio of the carbide is larger. From this, as described above, if the carbide area ratio of the tooth surface and the tooth root is set to 5% to 10% and 3% or less, respectively, even if nitriding is carried out under the same conditions, nitrogen entering the tooth surface and the tooth root will enter. Differences in volume occur. Further, the amount of retained austenite tends to increase as the nitrogen concentration increases, and more excellent toughness can be obtained in a tooth root where the nitrogen amount is larger than the tooth surface. Conversely, on the tooth surface where high hardness is required, the amount of retained austenite is small and high hardness is easily obtained.

From the results shown in Table 2, it is considered that the hardness must be Hv 800 or more in order to effectively improve the tooth surface strength as compared with the conventional one.
%, A large amount of retained austenite is produced, and it tends to be difficult to obtain a stable and high hardness. On the other hand, at the root, the peak of the nitrogen concentration distribution is 0.3 wt% or more, the peak of the residual austenite distribution is 25 to 45 wt%, and the hardness of the outermost layer is Hv700.
By setting the range to 800, it is possible to obtain a bending fatigue strength and an impact strength equal to or higher than those of a conventional gear.

Next, the effect of the tempering temperature after carburizing and nitriding treatment on the hardness reduction of each of the above test pieces was examined using the pattern shown in FIG. Table 3 shows the results.

[0036]

[Table 3]

As described above, the carbide is stable at about the tempering temperature. Therefore, when the amount of the carbide is large, the decrease in hardness is small, and when the amount of the carbide is small, the carbide is greatly softened. For this reason, if the structure in which the carbide in the tooth surface portion is 5 to 10 area% and the carbide in the root portion is 3 area% or less, and then tempering at a high temperature, the tooth surface hardness is maintained, and Since the root hardness decreases, more excellent toughness can be provided.

As shown in Table 3, the above effects are sufficiently exhibited in tempering at 200 ° C. or higher. But 250
If the temperature exceeds ℃, it becomes a tempering embrittlement zone, and if the temperature is higher than this, it becomes difficult to maintain the tooth surface hardness. Therefore, the temperature is more preferably set to the range of 200 to 250 ° C.

Further, in the method for manufacturing a high-strength gear according to the present invention, shot peening for projecting hard particles having a particle size of 0.4 mm or less so as to have an arc height of 0.3 to 0.8 mm may be performed as necessary. Desirably, by performing such shot peening, it is possible to impart a compressive residual stress to the gear, and the fatigue strength of the gear is further improved.

[0040]

According to the present invention, there is provided a high-strength gear according to the present invention.
As described in the above, in the meshing range of the tooth surface on the driving side and the driven side of the gear, the area ratio is 5 to 10 from the outermost surface of the tooth surface to the depth of at least 0.2 mm in the core direction.
% Of carbide is dispersed and precipitated, and at the tooth corner R at the driving side and the driven side of the gear, the carbide from the outermost layer to the core has a maximum area ratio of 3%, and is spherical or pseudo. It is spherically dispersed and precipitated, and is subjected to nitriding treatment. In the meshing range of the tooth surface, the peak of the nitrogen concentration distribution from the outermost surface layer of the tooth surface to the core is 0.3 watts.
t% or less, and the peak of the nitrogen concentration distribution from the outermost layer to the core at the root portion of the tooth root is 0.3 wt%.
%, The amount of nitrogen in the tooth root portion is larger than that in the tooth surface portion, and the toughness in the tooth root portion can be improved, and the pitting resistance of the tooth surface can be improved. In addition, it is possible to provide a high-strength gear in which the wear resistance and the bending fatigue strength of the tooth root and the impact resistance are optimized.

And, as described in claim 2,
In the meshing range of the gear tooth surface, the peak of the residual austenite distribution from the outermost layer of the tooth surface to the core has a peak of 3%.
High hardness is required by setting the peak of the residual austenite amount distribution from the outermost layer to the core at 25% to 45% by weight in the tooth root radius R portion of the gear. The tooth surface has a small amount of retained austenite, and it is easy to obtain high hardness, which makes it possible to further improve the wear resistance at the tooth surface, and the pitting and wear resistance of the tooth surface and the tooth root A remarkably excellent effect is that it is possible to provide a high-strength gear with further improved bending fatigue strength and impact resistance.

Further, as described in the third aspect, in the meshing range of the tooth surface of the gear, the hardness of the outermost layer of the tooth surface is Hv800 or more, and at the tooth corner radius R portion of the gear. Means that the hardness of the outermost layer is Hv 700 to 800
, It is possible to further improve the tooth surface strength, and to further improve the pitting resistance and wear resistance of the tooth surface and the bending fatigue strength and impact resistance of the tooth root A remarkably excellent effect that it is possible to provide a high-strength gear having a reduced strength.

In the method for manufacturing a high-strength gear according to the present invention,
As described in claim 4, after the carburizing process of the gear material, cooling or cooling and heating processes are performed to precipitate carbides, and then the nitriding process is performed. In the meshing range, 5 to 10% of carbide is dispersed and precipitated at an area ratio from the outermost surface of the tooth surface to a depth of at least 0.2 mm in the direction of the core, and the roots on the driving side and the driven side of the gear. In the corner R part, the carbide from the outermost layer to the core is up to 3% in area ratio
And in a spherical or pseudo-spherical state, the peak of the nitrogen concentration distribution from the outermost surface layer of the tooth surface to the core is set to 0.3 wt% or less in the meshing range of the tooth surface, and In the R portion, the peak of the nitrogen concentration distribution from the outermost layer to the core is set to 0.3 wt% or more, so that the nitrogen amount at the root portion can be larger than that at the tooth surface portion. It is possible to make the toughness at the root part more excellent,
A remarkably excellent effect is obtained that it is possible to manufacture a high-strength gear in which the pitting resistance and the wear resistance of the tooth surface and the bending fatigue strength and the impact resistance of the root are optimized.

And, as described in claim 5,
In the meshing range of the gear tooth surface, the peak of the residual austenite distribution from the outermost layer of the tooth surface to the core is 3
0 wt% or less and the peak of the distribution of retained austenite from the outermost surface layer to the core at the corner R of the root of the gear is set to 25 to 45 wt%, so that a tooth surface requiring high hardness is required. In this case, the amount of retained austenite can be reduced, high hardness can be obtained, and the wear resistance at the tooth surface can be further improved, and the pitting resistance of the tooth surface can be improved. In addition, a remarkably excellent effect is obtained in that it is possible to manufacture a high-strength gear having even better wear resistance, root bending fatigue strength and impact resistance.

Further, as described in claim 6, the hardness of the outermost layer of the tooth surface is Hv 800 or more in the meshing range of the gear tooth surface by carburizing or tempering after carburizing and nitriding. In addition, the hardness of the outermost layer is Hv700-80 at the root corner R portion of the gear.
By setting to 0, the tooth surface strength can be further improved, and the pitting resistance and wear resistance of the tooth surface and the bending fatigue strength and impact resistance of the tooth root can be further improved. A remarkably excellent effect that a high-strength gear can be manufactured is brought about.

Further, as described in claim 7, the carburizing treatment is carried out after the carburizing control agent diluted as necessary is applied to the root corner R portion.
The carbon content at the root portion can be reduced, and a remarkably excellent effect that a high-strength gear having excellent toughness at the root portion can be manufactured can be obtained.

Further, as described in claim 8, the carburizing control agent is removed after the carburizing treatment, and then the nitriding treatment and the secondary quenching are performed, so that the nitrogen at the tooth root portion is reduced. A remarkably excellent effect is obtained that a high-strength gear having a large amount can be manufactured with higher toughness at the root portion.

Further, by performing tempering at 200 to 250 ° C., the tooth surface hardness is maintained and the root hardness is reduced. In addition, a remarkably excellent effect is obtained that a high-strength gear having more favorable pitting resistance and wear resistance of the tooth surface as well as bending fatigue strength and impact resistance of the root can be manufactured.

Still further, according to the present invention, shot peening is performed in which hard particles having a particle size of 0.4 mm or less are projected so as to have an arc height of 0.3 to 0.8 mm. Thereby, it is possible to apply a compressive residual stress to the surface of the gear, and it is possible to manufacture a high-strength gear having more excellent fatigue strength.

Furthermore, by performing the carburizing treatment by the plasma carburizing method as described in claim 11, since the treatment can be carried out in a vacuum, grain boundary oxidation occurs even at a high temperature. In addition, carburizing can be performed quickly, and a remarkably excellent effect that high-quality high-strength gears can be manufactured with high productivity can be obtained.

[0051]

EXAMPLE SCM435 specified by JIS G 4105 was used as a material, processed into a gear material having a gear shape having 12 teeth and a module 4.4, and then using a commercially available carbon-proofing agent.
The mixture was diluted to / 3 and the viscosity was adjusted with glycerin. Thereafter, carburizing and quenching is performed under the conditions shown in FIG. 5, and after removing the anti-carbonizing agent, nitriding is performed in an atmosphere of 5% by volume of NH 3 gas, and then secondary quenching and high-temperature tempering are performed to obtain the gear of the present invention. Manufactured.

For comparison, a gear material having the same gear shape as in the example was subjected to carburizing, nitriding, quenching and tempering under the conditions shown in FIG. 6 to produce a gear of a comparative example. Table 4 shows the results of examining the structure and hardness of the gears manufactured in the above Examples and Comparative Examples.

[0053]

[Table 4]

Next, the gears of the examples of the present invention and the gears of the comparative example were subjected to shot peening, and the effects of the shot particle size and the arc height on the swelling of the tip and the residual stress generated at the root were examined. Table 5 shows the results.

[0055]

[Table 5]

As shown in Table 5, when the grain size and the arc height were the same, the tooth of the comparative example had a larger amount of swelling at the tooth tip than the gear of the present invention, and the peak of the compressive residual stress at the tooth root. Is also small. This is because the gear of the present invention has a large amount of retained austenite at the tooth root, and therefore,
It is considered that high compressive residual stress is generated by the work induced transformation by shot peening.
That is, in the gear of the embodiment of the present invention, the hardness of the tooth surface is high,
In addition, since the structure has a large amount of retained austenite at the tooth root, a large compressive residual stress can be obtained at the tooth root even with small-diameter shot peening. In this small diameter shot peening,
Since a large tooth tip bulge does not occur, there is less need for subsequent correction processing.

From the results shown in Table 5, it is desirable to set the shot particle diameter to 0.4 mm or less and the arc height to 0.8 mm or less in order to suppress the rise of the tooth tip. When the arc height is less than 0.3 mm, the effect of shot peening is hardly obtained.

Next, as a shot peening condition, a steel ball having a particle diameter of 0.4 mm was projected so as to have an arc height of 0.7 mm, and then the gear of the embodiment of the present invention and the gear of the comparative example were torqued to 4 kN-m. As a result, the life of the gear of the example of the present invention was about four times as long as that of the gear of the comparative example as shown in FIG.

Further, the same heat treatment as that performed on the gears of the examples of the present invention and the gears of the comparative examples was performed on the roller pitching test pieces to obtain a structure and hardness corresponding to the respective tooth surfaces. As a result of comparing the 50% failure life at a rate of 40% and a surface pressure of 5000 MPa, as shown in FIG. 8, the life of the product equivalent to the present invention was about 12 times longer than that of the comparison product.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing carburizing and quenching conditions adopted in an experiment for investigating the effect of carbides.

FIG. 2 is a graph showing a relationship between a surface hardness and a roller pitting life when tempering at 300 ° C. is performed.

FIG. 3 is an explanatory diagram showing carburizing and nitriding conditions adopted in an experiment for examining the effect of nitriding after carburizing.

FIG. 4 is an explanatory diagram showing heat treatment conditions adopted in an experiment for examining the effect of tempering.

FIG. 5 is an explanatory diagram showing heat treatment conditions adopted in the example of the present invention.

FIG. 6 is an explanatory diagram showing heat treatment conditions adopted in a comparative example of the present invention.

FIG. 7 is a graph showing the results of comparing the fatigue strength of the gear of the present invention and the gear of the comparative example.

FIG. 8 is a graph showing the results of comparing the pitting life of a roller pitting test piece corresponding to an example of the present invention and a roller pitting test piece corresponding to a comparative example.

Continuation of front page (56) References JP-A-6-25823 (JP, A) JP-A-7-316640 (JP, A) JP-A-9-72402 (JP, A) JP-A-7-242994 (JP) JP-A-7-3430 (JP, A) JP-A-7-54050 (JP, A) JP-A-59-35630 (JP, A) JP-A-63-297866 (JP, A) 58-189368 (JP, A) JP-A-6-17189 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F16H 55/00-55/56 C21D 1/06 C21D 9 / 32 C23C 8/20 C23C 8/34

Claims (11)

(57) [Claims] 1. In the meshing range of the tooth surface on the driving side and the driven side of the gear, 5 to 10% of carbide is dispersed and precipitated at an area ratio from the outermost surface of the tooth surface to a depth of at least 0.2 mm in the direction of the core. In the toothed corners R on the driving side and the driven side of the gear, carbides from the outermost layer to the core have an area ratio of up to 3%, and are dispersed and precipitated in a spherical or pseudospherical shape. In addition, a nitriding treatment has been performed, and in the meshing range, the peak of the nitrogen concentration distribution from the outermost surface layer of the tooth surface to the core portion is 0.3 wt% or less, and the outermost layer in the root portion of the tooth root R is A high-strength gear characterized in that the peak of the nitrogen concentration distribution from the core to the core is 0.3 wt% or more. 2. In the meshing range of the gear tooth surface, the peak of the distribution of retained austenite from the outermost layer of the tooth surface to the core is 30 wt% or less, and the peak of the tooth root radius R portion of the gear is the lowest. 2. The high-strength gear according to claim 1, wherein the peak of the distribution of the retained austenite amount from the surface layer to the core portion is 25 to 45 wt%. 3. The hardness of the outermost layer of the tooth surface is Hv800 or more in the meshing range of the tooth surface of the gear, and the hardness of the outermost layer is Hv70 in the tooth corner radius R portion of the gear.
The high-strength gear according to claim 1, wherein the number is from 0 to 800. 4. 4. Carburizing treatment of the gear material, followed by cooling or cooling and heating treatment to precipitate carbides and then nitriding treatment, so that the gears can be engaged in the meshing range of the tooth surfaces on the driving side and the driven side of the gear. 5 to 10 at an area ratio from the outermost layer of the surface to a depth of at least 0.2 mm in the direction of the core.
% Of carbide is dispersed and precipitated, and in the tooth corner R at the driving side and the driven side of the gear, the carbide from the outermost layer to the core is made up to 3% in area ratio, and is spherical or pseudo spherical. In the meshing range, the peak of the nitrogen concentration distribution from the outermost surface layer of the tooth surface to the core is set to 0.3 wt% or less, and the tooth root radius R is reduced.
A method for producing a high-strength gear, wherein a peak of a nitrogen concentration distribution from the outermost layer to the core is 0.3 wt% or more in a portion. 5. The peak of the distribution of residual austenite from the outermost layer of the tooth surface to the core in the meshing range of the tooth surface of the gear is 30 wt% or less, and the outermost layer is formed at the root portion R of the tooth root. The method for manufacturing a high-strength gear according to claim 4, wherein the peak of the distribution of the amount of retained austenite from the core to the core is 25 to 45 wt%. 6. Carburizing or tempering after carburizing and nitriding, the hardness of the outermost surface of the tooth surface is set to Hv800 or more in the meshing range of the tooth surface of the gear, and at the root portion R of the tooth root of the gear. Indicates the hardness of the outermost layer is Hv7
The method for manufacturing a high-strength gear according to claim 4 or 5, wherein the number is from 00 to 800. 7. The method for producing a high-strength gear according to claim 4, wherein a carburizing treatment is performed after the carburizing control agent is applied to the root corner R. 8. The method for manufacturing a high-strength gear according to claim 7, wherein the carburizing control agent is removed after the carburizing treatment, and then the nitriding treatment and the secondary quenching are performed. 9. The method for producing a high-strength gear according to claim 4, wherein the tempering is performed at 200 to 250 ° C. 10. The production of a high-strength gear according to claim 4, wherein shot peening is performed by projecting hard particles having a particle diameter of 0.4 mm or less so as to have an arc height of 0.3 to 0.8 mm. Method. 11. The method for producing a high-strength gear according to claim 4, wherein the carburizing treatment is performed by a plasma carburizing method.