JP2005325398A - High-strength gear and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mass-manufacturable high-strength gear which has a higher bending fatigue strength of a dedendum than a conventional gear has, and besides, superior bearing fatigue characteristics, and to provide a manufacturing method therefor. <P>SOLUTION: This high-strength gear is made of a steel material comprising 0.10-0.25% C, 0.8-1.2% Si, 0.6-2.0% Mn, 0.006% or more S, 1.0-2.0% Cr, 0.2-0.8% Mo, 0.005-0.200% Al, 0.0050-0.0200% N (by mass%) and the balance Fe with unavoidable impurities; is formed into a gear shape by forging or machining the steel material and then carburizing or carbonitriding it, so that the surface layer of the formed gear can contain less than 0.9 mass% C, and so that the layer of the gear between the surface layer and a 100 μm deep layer can contain less than 40 vol.% of retained austenite and have a structure of a martensite single phase. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a high-strength gear having high bending fatigue strength and surface fatigue strength used for automobiles and various industrial equipment, and a method for manufacturing the same.

  In recent years, gears used in automobiles and the like have been required to be smaller in size as the weight of the vehicle body has been reduced due to energy saving, and the load on the gears has increased as the output of the engine has increased. ing. The durability of a gear is mainly determined by the bending fatigue failure of the tooth root and the surface pressure fatigue failure of the tooth surface.

  Conventionally, gears have been manufactured by preparing gear materials using case-hardened steel defined by JIS SCM420H, SCM822H, etc., and subjecting the gear materials to surface treatment such as carburization. However, such gears cannot withstand use under high stress, and therefore, by changing steel materials, changing heat treatment methods, surface work hardening treatments, etc., tooth root bending fatigue strength and pitting resistance can be improved. I was trying to improve.

  For example, in Japanese Patent Publication No. 07-122118 (Patent Document 1), by reducing Si in steel and controlling Mn, Cr, Mo and Ni, a grain boundary oxide layer on the surface after carburizing heat treatment is provided. By reducing the generation of cracks and suppressing the generation of incompletely hardened layers, the reduction of surface hardness is suppressed and the fatigue strength is increased. Furthermore, Ca is added to promote the generation and propagation of cracks. A method for controlling the stretching of MnS is disclosed. Hereinafter, this method is referred to as Prior Art 1.

  Japanese Patent No. 2945714 (Patent Document 2) discloses a method of increasing temper softening resistance using a steel material to which 0.25 to 1.50% of Si is added as a material. Hereinafter, this method is referred to as Prior Art 2.

Japanese Patent Publication No. 07-122118 Japanese Patent No. 2945714

  However, the above-described prior art has the following problems.

  According to Prior Art 1, since the grain boundary oxide layer and the incompletely hardened layer are reduced by reducing Si, it is possible to suppress the occurrence of bending fatigue cracks at the tooth root. However, the temper softening resistance decreases, and the occurrence of fracture shifts from the tooth base to the tooth surface. As a result, temper softening due to frictional heat on the tooth surface cannot be suppressed, and the surface softens. For this reason, there has been a problem that pitching is likely to occur.

  In Prior Art 2, Si or the like is added to increase the temper softening resistance, and the carburizing method is limited to vacuum carburizing or plasma carburizing to suppress the progress of grain boundary oxidation. It is unsuitable for mass production due to increased costs.

  Accordingly, an object of the present invention is to solve the above-described problems, and provide a high-strength gear capable of mass production that has a higher root bending fatigue strength than that of a conventional gear and that is excellent in surface pressure fatigue characteristics, and a method for manufacturing the same. There is to do.

  The inventors of the present application have earnestly studied to solve the above-mentioned problems, and as a result, obtained the following knowledge.

  (1) By increasing the amount of Si and Cr in the steel material, the temper softening resistance is increased, and if the softening due to heat generation at the gear contact surface is suppressed, the generation of cracks in the tooth surface that occurs during gear driving can be suppressed. .

  (2) For the grain boundary oxide layer that can be the starting point of bending fatigue and fatigue cracks, the growth direction of the grain boundary oxide layer changes from the depth direction to the surface density increase direction by adding a certain amount or more of Si. Therefore, since there is no oxide layer grown in the depth direction as a starting point, it becomes difficult to be a starting point for bending fatigue and fatigue cracks. Furthermore, this oxide layer is easy to peel off, and is almost unpeeled by shot peening, so there is no influence.

  (3) As described in the above (1) and (2), Si is effective in improving the temper softening resistance and controlling the grain boundary oxide layer, but there is an appropriate value of the Si amount to satisfy both.

  (4) The surface of the carburized portion of the tooth surface can be reduced in hardness by using martensite and retained austenite of 40% by volume or less. Further, the generation of fatigue cracks in bending fatigue and surface pressure fatigue can be suppressed by setting the C content of the surface layer to less than 0.9 mass% and suppressing the formation of grain boundary cementite in the surface layer.

  The present invention has been made on the basis of the above findings, and is characterized by the following.

  The invention according to claim 1 includes C: 0.10 to 0.25%, Si: 0.8 to 1.2%, Mn: 0.6 to 2.0%, S: 0.006% or more, Cr : 1.0-2.0%, Mo: 0.2-0.8%, Al: 0.005-0.200%, N: 0.0050-0.0200% (above, mass%) contained In addition, the steel material comprising the balance Fe and inevitable impurities is formed into a gear shape by forging or machining, and after forming into a gear shape, carburizing treatment or carbonitriding treatment is performed, and C content in the surface layer The amount is less than 0.9 mass%, the amount of retained austenite from the surface layer of the gear to the depth of 100 μm is 40% by volume or less, and the structure is characterized by a martensite single phase.

  The invention according to claim 2 is the invention according to claim 1, wherein the steel material is at least one of Nb: 0.010 to 0.060% and V: 0.05 to 0.20% (more than mass%). It is characterized by further containing.

  The invention according to claim 3 is the invention according to claim 1 or 2, wherein the steel material further includes Ti: 0.005 to 0.050%, B: 0.0005 to 0.0100% (more than mass%). It is characterized by containing.

  Invention of Claim 4 is C: 0.10-0.25%, Si: 0.8-1.2%, Mn: 0.6-2.0%, S: 0.006% or more, Cr : 1.0-2.0%, Mo: 0.2-0.8%, Al: 0.005-0.200%, N: 0.0050-0.0200% (above, mass%) contained Then, a steel material having the balance of Fe and inevitable impurities is formed into a gear shape by forging or machining to prepare a gear material, and then the carburizing treatment or carbonitriding treatment is applied to the gear material, and the arc height is further increased. Shot peening of 0.3 mmA or more is performed, the C content of the surface layer is less than 0.9 mass%, the amount of retained austenite from the surface layer of the gear to the 100 μm depth position is 40% by volume or less, and the structure is a martensite single phase. Is characterized by

  The invention according to claim 5 is the invention according to claim 4, wherein the steel material is at least one of Nb: 0.010 to 0.060%, V: 0.05 to 0.20% (more than mass%). It is characterized by using what further contains.

  The invention according to claim 6 is the invention according to claim 4 or 5, wherein Ti: 0.005 to 0.050%, B: 0.0005 to 0.0100% (above, mass%) is further added as the steel material. It is characterized by using what it contains.

  According to the present invention, it is possible to manufacture a gear that is excellent in bending fatigue characteristics and surface pressure fatigue characteristics and that is used in automobiles, various industrial equipment, and the like that require a high surface pressure of 3000 MPa or more.

  Below, each reason for limitation is described.

C: 0.10 to 0.25 mass%
C is necessary for securing the strength, and the amount thereof determines the internal hardness after carburizing and tempering. However, if the amount is less than 0.10 mass%, the internal hardness is excessively reduced, so that the gear is used. Can not secure the strength of. On the other hand, if it exceeds 0.25 mass%, the toughness inside the gear is lowered and fatigue cracks are likely to progress, so that not only the bending fatigue characteristics are lowered, but also workability is deteriorated. Therefore, the C content is limited to a range of 0.10 to 0.25 mass%.

Si: 0.8-1.2 mass%
Si is an element effective for increasing the temper softening resistance and has an effect of suppressing the depth of the grain boundary oxide layer. If the softening resistance is low, the gear surface layer is tempered and softened by friction between the gears when the gears are driven, and the surface pressure fatigue characteristics are deteriorated. If the grain boundary oxide layer depth is large, it tends to become a fatigue starting point, so both the bending fatigue characteristics and the surface pressure fatigue characteristics are lowered.

  In order to investigate the appropriate range of Si, the following tests were conducted.

  Only the amount of Si added was changed to dissolve the materials, and these materials were subjected to carburizing treatment according to the pattern shown in FIG. In addition, a roller pitching test, which is an index of surface pressure fatigue characteristics, was performed using a test piece having the shape and dimensions shown in FIG. Furthermore, the softening amount and the grain boundary oxide layer depth by tempering at 300 ° C. were investigated for each material.

  The result of arranging the bending fatigue strength by the grain boundary oxide layer depth is shown in FIG. FIG. 3 indicates that the bending fatigue strength is improved when the grain boundary oxide layer is 10 μm or less.

  Next, FIG. 4 shows the results of arranging the surface pressure fatigue strength by the temper softening amount at 300 ° C. From FIG. 4, it was found that the surface pressure fatigue strength is improved when the softening amount ΔHV by tempering at 300 ° C. is 100 HV or less.

  FIG. 5 shows the relationship between the Si amount, the grain boundary oxide layer depth, and the 300 ° C. temper softening amount.

  From FIG. 5, it can be seen that Si has an effect of suppressing hardness reduction at 0.8 mass% or more in tempering at 300 ° C., which is about the temperature of heat generation due to friction of the tooth surface, and exceeds 2.0 mass%. And the effect was saturated.

  From FIG. 5, it was found that the effect of Si amount on the grain boundary oxide layer depth was 0.1 mass% or less and 0.6 mass% or more. Moreover, it turned out that the effect will be saturated when it exceeds 1.2 mass%.

  From the above experimental results, the range of Si addition amount in which both the grain boundary oxide layer depth and the 300 ° C. temper softening effect can be obtained is 0.8 to 1.2 mass%, and less than 0.8 mass%, The surface fatigue strength cannot be improved, and even if added over 1.2 mass%, these effects are saturated, and this is wasteful in cost. Therefore, the Si content is limited to the range of 0.8 to 1.2 mass%.

Mn: 0.6 to 2.0 mass%
Mn is an element that enhances the hardenability of steel. In order to ensure hardenability, the amount of Mn added must be 0.6 mass% or more, but even if added over 2.0 mass%, the hardenability is excessively increased and the amount of retained austenite becomes excessive. Therefore, the upper limit of the Mn addition amount is set to 2.0 mass%.

S: 0.006 mass% or more S combines with Mn to form MnS and has an effect of improving machinability. However, if it is less than 0.006 mass%, the generated MnS is so small that the effect does not appear. . Therefore, the S content is limited to 0.006 mass% or more.

Cr: 1.0-2.0 mass%
Cr is an element that enhances hardenability and increases temper softening resistance. In order to exhibit both performances, addition of 1.0 mass% or more is necessary. However, when the addition amount exceeds 2.0 mass%, the effect of increasing the softening resistance is saturated and the hardenability becomes too high. For this reason, the toughness inside the gears deteriorates and the fatigue cracks progress more quickly, so the bending fatigue strength decreases. Therefore, the Cr content is limited to a range of 1.0 to 2.0 mass%.

Mo: 0.2-0.8 mass%
Mo is a hardenability improving element. For that purpose, addition of 0.2 mass% or more is necessary, but even if added in excess of 0.8 mass%, the effect is saturated, and since it is an expensive alloy, the economy is poor. Therefore, the Mo content is limited to the range of 0.2 to 0.8 mass%.

Al: 0.005 to 0.200 mass%
Al is an element effective for deoxidation, and the effect is exhibited by addition of 0.005 mass% or more. In addition, it combines with N to produce AlN, and has a function of suppressing coarsening of crystal grains. The effect is effective when added up to 0.200 mass%, and if it exceeds that, coarse grains are generated and fatigue cracks tend to progress, so that the bending fatigue strength and the surface pressure fatigue strength are reduced. Therefore, the Al content is limited to a range of 0.005 to 0.200 mass%.

N: 0.0050-0.0200 mass%
N combines with Al to produce AlN, and suppresses coarsening of crystal grains to improve fatigue strength. In order to obtain the effect, 0.005 mass% or more is necessary. However, if it exceeds 0.0200 mass%, the effect is not only saturated, but also defects such as blow balls are generated inside, resulting in bending fatigue strength. Incurs a decline. Therefore, the N content is limited to a range of 0.005 to 0.0200 mass%.

Nb: 0.010 to 0.060 mass%
Nb refines crystal grains by forming carbonitrides. As a result, the root bending fatigue strength is improved. In order to refine crystal grains, 0.010 mass% or more is necessary, and the effect is saturated even if 0.060 mass% or more is added. Therefore, the Nb content is limited to the range of 0.010 to 0.060 mass%.

V: 0.05-0.20 mass%
V increases the temper softening resistance in the same manner as Si and Cr. At the same time, carbonitrides are formed to refine crystal grains and to suppress the segregation of Si. In order to exhibit the effect, addition of 0.05 mass% or more is necessary. However, this effect is saturated even if added in excess of 0.20 mass%, a sufficient effect cannot be obtained, and the manufacturing cost only increases. Therefore, the V content is limited to the range of 0.05 to 0.20 mass%.

Ti: 0.005-0.050 mass%, B: 0.0005-0.0100 mass%
B is effective in increasing the hardenability. The effect is obtained at 0.0005 mass% or more, and when it exceeds 0.0100 mass%, the effect is saturated. Therefore, the B content is limited to a range of 0.0005 to 0.0100 mass%. However, the effect of improving the hardenability of B is ineffective when B is an N compound, so Ti is added to fix N simultaneously with the addition of B. The appropriate addition amount varies depending on the N amount, but is in the range of 0.005 to 0.050 mass%.

  The P and oxygen contents as inevitable impurities are preferably as low as possible.

  Moreover, you may contain free-cutting elements, such as S, Pb, Se, and Ca, as needed in order to improve machinability.

Surface layer C content: less than 0.9 mass% The C content of the surface layer is increased by carburization. As a result, the surface hardness is increased, and bending fatigue and surface fatigue strength are improved. However, if the surface layer C content is 0.9 mass% or more, cementite is precipitated at the grain boundary near the surface layer and becomes a starting point of fatigue, so that the bending fatigue strength and the surface pressure fatigue strength are lowered. Therefore, the surface layer C content is limited to less than 0.9 mass%.

Residual austenite content of the tooth surface surface layer ≦ 40 volume% or less Residual austenite is soft by itself, but when it exists on the surface layer of the tooth surface, it transforms into martensite due to stress during driving of the gear and hardens. Therefore, it has the effect of suppressing crack propagation against bending and surface pressure fatigue. However, when the amount of retained austenite exceeds 40% by volume, the hardness of the surface layer is excessively decreased, and the bending fatigue characteristics and the surface pressure fatigue characteristics are deteriorated. Therefore, the amount of retained austenite is limited to 40% by volume or less.

Structure: Martensite single phase structure When Si, V, or the like is added, an austenite single phase is not formed even at the quenching heating temperature due to an increase in the transformation point, and ferrite is generated. Ferrite accelerates the progress of cracks due to bending fatigue failure, and fatigue strength tends to decrease. Therefore, the structure was limited to the martensite single phase. It should be noted that the generation of ferrite can be avoided by adjusting the addition amount of various elements.

Shot peening arc height: 0.3 mmA or more Shot peening imparts compressive residual stress in the vicinity of the surface layer to further increase bending fatigue strength and surface fatigue strength. When this treatment is performed, if the arc height is 0.3 mmA or less, the application of compressive residual stress is too small, so that the bending fatigue strength and the contact pressure fatigue strength cannot be further increased. Therefore, shot peening should be performed at an arc height of 0.3 mmA or more.

  The present invention will be described in more detail in comparison with comparative examples by way of examples.

  Steel having the chemical composition shown in Table 1 was melted. No. shown in Table 1. Nos. 1 to 10 are steels of the present invention used for manufacturing the gears of the present invention. 11 to 19 are comparative steels that are outside the scope of the present invention. And No. 20 and 21 are conventional steels, which are JIS SCM420H and SCM822H, respectively, which are also outside the scope of the present invention.

  Each ingot made of the invented steel of the present invention, comparative steel and conventional steel is hot-rolled to prepare a round bar steel, and the obtained round bar steel is subjected to a normalizing treatment. 1-10, comparative specimen No. 11-19 and the conventional specimen No. 20, 21 were obtained.

  From each specimen after the normalizing treatment, a round bar steel for various characteristic tests of 20 mmφ, an Ono type rotating bending fatigue test piece and a roller pitching test piece were collected. Carved quenching and tempering treatments are performed according to the pattern shown in Fig. 1 on the round bar steel and various test pieces for various characteristic tests, and then the surface is subjected to shot height peening with an arc height of 0.3 mmA to perform various characteristic tests and rotational bending fatigue. Tests and roller pitching tests were performed. The results are shown in Table 2 together with the results of the grain boundary oxide layer, the carburized portion γ grain size, and the surface layer C content.

  The contents of each survey are described below.

(1) Effective hardened layer depth, internal structure, internal toughness, internal hardness Cut 20mmφ round bar steel, measure the hardness distribution of the cross section, investigate the depth to obtain 550HV in Vickers hardness, effective hardening It was the depth. Moreover, the inside (non-carburized part) structure in the carburizing and quenching and tempering of each round bar steel was observed with a spectroscopic test to confirm the presence or absence of ferrite precipitation. Furthermore, a JIS No. 3 impact test piece was produced from the inside, and the impact value at 20 ° C. was investigated. The internal hardness was measured using a Vickers hardness tester.

(2) Surface layer retained austenite Using another round steel bar, the amount of residual γ at a position 20 μm below the surface layer was measured. Note that electrolytic polishing was used for polishing the measurement surface, and an X-ray diffractometer was used for measurement.

(3) Rotating bending fatigue characteristics A test piece with a parallel part diameter of 10 mm was sampled from a round steel bar with a diameter of 32 mm, and a notch with a depth of 3 mm perpendicular to the parallel part was obtained (notch coefficient: 1.4). Was prepared for a rotating bending fatigue test piece. Carburization quenching and tempering were performed on all the test pieces. Thereafter, half of the test pieces of each specimen were subjected to shot peening treatment (arc height: 0.3 mmA). And about the test peened execution goods of each test piece, and the non-execution goods, the rotation bending fatigue strength was measured by using the Ono-type rotation bending fatigue tester with 10 ⁷ times as a fatigue limit, and the rotation bending fatigue strength was measured.

(4) Roller pitching test (surface fatigue characteristics)
A test piece having a cylindrical portion having a diameter of 26 mm and a width of 28 mm as shown in FIG. 2 was prepared from a round steel bar having a diameter of 32 mm. Furthermore, after using a round steel bar with a diameter of 70 mm to obtain a diameter of 135 mm by forging, a normalizing process was performed to produce a large roller with a diameter of 130 mm and a width of 18 mm. Next, carburizing and tempering treatment of the roller-shaped test piece and the large roller was performed. Thereafter, a shot peening treatment (arc height: 0.3 mmA) was carried out under the same conditions as for the rotating bending fatigue test piece for each half. Then, the shot peened product and the unexecuted product of each test piece were tested using a roller pitching tester with 10 ⁷ times as the fatigue limit. The test conditions at that time were as follows: rotation speed: 1500 rpm, slip rate of 40%, lubricant: mission oil, oil temperature: 120 ° C.

  From Table 1 and Table 2, the following matters became clear.

  Specimen No. of the present invention. 1 to 10 are conventional specimen Nos. Compared to 20 and 21, the internal toughness, carburized part γ grain size, and residual γ amount were the same, but the grain boundary oxide layer was smaller, and therefore the rotational bending fatigue strength was improved. Moreover, since the temper softening resistance is high due to Si, the surface pressure fatigue strength is remarkably increased.

  In contrast, comparative specimen No. In No. 11, since the C content was lower than the range of the present invention and the Si content exceeded the range of the present invention, ferrite precipitated inside. Therefore, the internal hardness was too low, and the rotational bending fatigue strength was reduced.

  Comparative specimen No. No. 12, the C content exceeds the range of the present invention, and the hardenability is too high. Therefore, the internal toughness decreased. Further, the amount of residual γ increased too much, and the hardness of the carburized layer decreased, and both the rotary bending fatigue strength and the surface pressure fatigue strength decreased.

  Comparative specimen No. No. 13 has a high Cr content exceeding the range of the present invention. Therefore, since the internal impact value became too low, the rotational bending fatigue strength decreased. Moreover, since the Al content was too low and the carburized portion γ grains were large, the surface pressure fatigue strength was reduced.

  Comparative specimen No. No. 14 had a Mn content greater than the range of the present invention, and therefore the hardenability was too high. For this reason, the effective hardened layer depth became too deep, and there was too much residual γ in the carburized layer. As a result, both the rotary bending fatigue strength and the contact pressure fatigue strength decreased.

  Comparative specimen No. In No. 15, since the Mn content was lower than the range of the present invention, the hardenability was too low and the effective hardened layer depth was too shallow. As a result, the strength of the matrix was insufficient and the rotational bending fatigue strength was lowered.

  Comparative specimen No. In No. 16, the Cr content was less than the range of the present invention, so the temper softening resistance was low, and the hardenability was low, so the effective hardened layer was shallow. For this reason, both the rotary bending fatigue strength and the contact pressure fatigue strength decreased.

  Comparative specimen No. In No. 17, since the Si content was less than the range of the present invention, the temper softening resistance was low, and therefore the surface pressure fatigue strength was reduced.

  Comparative specimen No. In No. 18, the Mo content was lower than the range of the present invention, so that the hardenability was too low, the internal hardness was low, and the effective hardened layer depth was shallow, so the rotational bending fatigue strength was lowered.

  Comparative specimen No. No. 19 has an Al content higher than the range of the present invention. Therefore, the crystal grains became too large, and both the rotational bending fatigue strength and the surface pressure fatigue strength were reduced.

  Comparative specimen No. 20 and 21 are JIS SCM420H and SCM822H of conventional steels, but the Si content is lower than the range of the present invention. As a result, the grain boundary oxide layer becomes deep, and both the rotational bending fatigue strength and the surface pressure fatigue strength are reduced. .

It is a figure which shows the pattern of a carburizing process. It is a figure which shows an example of a pitching test piece. It is a graph which shows the relationship between a grain boundary oxide layer depth and bending fatigue strength. It is a graph which shows the relationship between 300 degreeC temper softening amount and surface pressure fatigue strength. It is a graph which shows the relationship between the addition amount of Si, 300 degreeC temper softening amount, and a grain boundary oxide layer depth.

Claims (6)

C: 0.10 to 0.25%,
Si: 0.8 to 1.2%,
Mn: 0.6 to 2.0%,
S: 0.006% or more,
Cr: 1.0-2.0%,
Mo: 0.2 to 0.8%,
Al: 0.005 to 0.200%,
N: 0.0050-0.0200% (above, mass%)
And the balance of Fe and inevitable impurities is formed into a gear shape by forging or machining, and after forming into a gear shape, carburizing treatment or carbonitriding treatment is performed. A high-strength gear having a C content of less than 0.9 mass%, a retained austenite amount of 40% by volume or less from the gear surface to a depth of 100 μm, and a martensite single phase. The steel material is
Nb: 0.010 to 0.060%,
V: 0.05-0.20% (above, mass%)
The high-strength gear according to claim 1, further comprising at least one of the following. The steel material is
Ti: 0.005 to 0.050%,
B: 0.0005 to 0.0100% (above, mass%)
The high-strength gear according to claim 1, further comprising: C: 0.10 to 0.25%,
Si: 0.8 to 1.2%,
Mn: 0.6 to 2.0%,
S: 0.006% or more,
Cr: 1.0-2.0%,
Mo: 0.2 to 0.8%,
Al: 0.005 to 0.200%,
N: 0.0050-0.0200% (above, mass%)
A steel material containing the balance Fe and inevitable impurities is formed into a gear shape by forging or machining, and then the gear material is subjected to carburizing treatment or carbonitriding treatment, Shot peening with an arc height of 0.3 mmA or more is performed, the C content of the surface layer is less than 0.9 mass%, the amount of retained austenite from the surface layer of the gear to the 100 μm depth position is 40% by volume or less, and the structure is martensite. A method for producing a high-strength gear, characterized by being a single phase. As the steel material,
Nb: 0.010 to 0.060%,
V: 0.05-0.20% (above, mass%)
The method for producing a high-strength gear according to claim 4, wherein a material further containing at least one of the above is used. As the steel material,
Ti: 0.005 to 0.050%,
B: 0.0005 to 0.0100% (above, mass%)
The method for producing a high-strength gear according to claim 4 or 5, characterized in that a material further containing

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