JP2010001527A - Gear component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gear component which combines dedendum strength with tooth flank strength. <P>SOLUTION: The gear component satisfying the following inequalities (1) and (2) is manufactured by forming case-hardening steel into a prescribed gear shape, then subjecting the steel to carburizing treatment, the case-hardening steel having a composition comprising 0.10 to 0.40% C, &le;1.50% Si, 0.30 to 1.80% Mn, 0.30 to 1.50% Cr, &le;0.80% Mo, &le;0.05% Ti, &le;0.05% Al, &le;0.010% N, &le;0.10% Nb, &le;0.020% P, &le;0.020% S and 0.0005 to 0.0035% B, and the balance Fe with inevitable impurities. Here, the inequality (1) is: the dedendum part: (553.53&times;S mass%)+(34.36&times;effective hardened layer depth mm)-(0.16&times;core part hardness HV)+(123.86&times;surface layer C concentration%)&le;52, and the inequality (2) is: the tooth flank part: (0.001&times;core part hardness HV)+(0.037&times;whole hardened layer depth mm)&ge;0.460. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a gear component, particularly a gear component used in a drive system of an automobile or the like.

  Generally, gear parts typified by differential gears such as automobiles are carburized after forging or cutting case-hardened steel into a predetermined gear shape. This type of gear part is required to have high impact fatigue strength (low cycle impact bending fatigue strength). For example, Patent Document 1 discloses that impact fatigue strength is achieved by appropriately balancing the crystal grain size and the carburized hardened layer. Techniques for improvement have been proposed. For example, Patent Document 2 proposes a method for improving wear resistance as well as impact fatigue strength by setting the surface layer C concentration and the C concentration 0.4% depth to predetermined values.

JP 2003-96539 A JP 2007-231305 A

  However, the methods described in Patent Documents 1 and 2 are effective for increasing the impact fatigue strength, but are insufficient from the viewpoint of improving the plastic deformation resistance. That is, in the gear part, impact fatigue strength (tooth root strength) is required for the tooth root portion, whereas plastic deformation resistance (tooth surface strength) is required for the tooth surface portion. Therefore, as in the methods described in Patent Documents 1 and 2, if it is too important to secure the tooth root strength, the tooth surface strength may be unnecessarily lowered and plastic deformation at the tooth surface may be promoted. is there. On the other hand, if the importance of ensuring the tooth surface strength is too important, the tooth root strength may increase more than necessary, and the crack progress at the tooth root portion may be promoted at the time of impact input. As described above, in the gear part, it is ideal that both the tooth root strength and the tooth surface strength are compatible. However, since both strengths are contradictory properties, it is difficult to achieve both strengths.

  The present invention has been made to cope with the above-described problems, and an object of the present invention is to provide a gear component capable of achieving both the tooth root strength and the tooth surface strength of the gear component.

  As a result of intensive studies to solve the above problems, the present inventors have obtained the following knowledge. (A) If the strength characteristics required for the gear parts can be formulated by dividing the tooth root portion and the tooth surface portion, the strength characteristics required for the tooth root portion and the tooth surface portion can be clearly specified. (B) In order to improve the tooth root strength, it is effective to shorten the initial crack length at the time of impact input and delay the subsequent crack propagation. (C) In order to improve the tooth surface strength, it is effective to increase the hardness of the tooth surface part (suppress the amount of plastic deformation of the tooth surface part).

That is, the gear component of the present invention is in mass%, C: 0.10 to 0.40%, Si: 1.50% or less, Mn: 0.30 to 1.80%, Cr: 0.30 to 1 50%, Mo: 0.80% or less, Ti: 0.05% or less, Al: 0.05% or less, N: 0.010% or less, Nb: 0.10% or less, P: 0.020% Hereinafter, carburizing treatment that is performed after the case-hardened steel containing S: 0.020% or less, B: 0.0005-0.0035%, and the balance of Fe and inevitable impurities being made into a predetermined gear shape. Therefore, the following formulas (1) and (2) are satisfied.
Tooth base of gear parts:
(553.53 × S mass%) + (34.36 × effective hardened layer depth mm)
− (0.16 × Heart hardness HV) + (123.86 × surface layer C concentration% by mass) ≦ 52 (1)
Tooth surface of gear parts:
(0.001 × heart hardness HV) + (0.037 × total hardened layer depth mm) ≧ 0.460 (2)

  In this case, the gear part may further contain Ni: 0.20 to 2.50% by mass%, and Bi: 0.30% or less, Ca: 0.30 by mass%. % Or less, Pb: It is good to contain 1 type or 2 types or more among 0.30% or less. In addition, in this specification, the description which shows the range of an alloy composition, for example, C: 0.10-0.40% means that content of C represents 0.10 mass% or more and 0.40 mass% or less. To do.

  Hereinafter, the reasons for limiting the composition of each element and the limiting conditions will be described.

(1) C: 0.10 to 0.40%
C is an element for securing the strength of the gear part (strength of the core). In order to obtain this effect, a content of 0.10% or more is necessary. On the other hand, if it is contained excessively, the toughness and impact fatigue strength are lowered, so the upper limit is made 0.40% or less. Preferably it is 0.15-0.35%.

(2) Si: 1.50% or less Si is added as a deoxidizer during melting. This Si is an element that promotes grain boundary oxidation during carburizing, and causes a reduction in impact fatigue strength. Moreover, since excessive inclusion will remarkably impair cold forgeability or cutting workability, it is made 1.50% or less. Preferably it is 0.20% or less. In the case of carburizing treatment that can suppress grain boundary oxidation such as vacuum carburizing and plasma carburizing, 0.5% or more may be added in order to improve tempering and softening resistance.

(3) Mn: 0.30 to 1.80%
Mn is an element that promotes grain boundary oxidation at the time of carburizing, and causes a reduction in impact fatigue strength. Therefore, it is necessary to limit its content as much as possible. Specifically, the content is 1.80% or less. On the other hand, Mn is an element effective for enhancing the hardenability of steel, and moderate austenite remains after carburizing in order to improve toughness. In order to obtain these effects, a content of 0.30% or more is necessary.

(4) Cr: 0.30 to 1.50%
Cr, like Mn, is an element that promotes grain boundary oxidation at the time of carburizing, and causes a reduction in impact fatigue strength, and excessive inclusion may lead to embrittlement of grain boundaries. Specifically, the content is limited to 1.50% or less. On the other hand, Cr is an element effective for enhancing the hardenability of steel, so to obtain this effect, it is necessary to contain 0.30% or more.

(5) Mo: 0.80% or less Mo is an element effective for enhancing the hardenability of steel, and is added to supplement the hardenability of steel which is insufficient due to the limitation of the Cr content. It is also an element effective for improving the toughness of the carburized surface layer. On the other hand, excessive content increases the hardness at the time of plastic working too much and deteriorates manufacturability, so the content is made 0.80% or less.

(6) Ti: 0.05% or less Ti combines with N in carburized steel to form a nitride, and prevents N from combining with B, thereby securing solid solution B and It is an effective element for maintaining the effect of improving hardenability. However, if it exceeds 0.05%, the workability in the cold state decreases due to the enlargement of TiN, so the content is made 0.05% or less.

(7) Al (Solubility Al): 0.05% or less Al is an element effective to combine with N in carburized steel to form nitrides and prevent coarsening of austenite crystal grains during carburizing. It is. However, if it exceeds 0.05%, the effect of preventing coarsening of austenite crystal grains is saturated, so the content is made 0.05% or less.

(8) N: 0.010% or less As described above, N reacts with Ti and Al in carburized steel to form nitrides. However, if it exceeds 0.010%, large TiN is generated, which becomes a starting point of fatigue fracture and impairs fatigue characteristics. Moreover, since the effect which prevents the coarsening of an austenite crystal grain mentioned above will be saturated if it exceeds 0.010%, it is made into 0.010% or less of content.

(9) Nb: 0.10% or less Nb is an element that reacts with C and N in carburized steel to form carbonitrides and prevents coarsening of austenite crystal grains during carburizing. . However, if it exceeds 0.10%, the effect is saturated.

(10) P: 0.020% or less P is an element that deteriorates the toughness of the carburized layer. In particular, when the content exceeds 0.020%, the impact fatigue strength is significantly reduced. Further, since P is an impurity element, the content is preferably as close to 0% as possible.

(11) S: 0.020% or less S is an element that deteriorates the toughness of the carburized layer. If the content exceeds 0.020% as in the case of P, the impact fatigue strength is significantly reduced. Further, S reacts with Mn in the carburized steel to generate MnS, and this MnS becomes a crack propagation path and causes a decrease in strength. Therefore, it is desirable to reduce S as much as possible. However, if the content is 0.020% or less, MnS that causes a decrease in strength is not observed on the crack propagation path. .

(12) B (Solubility B): 0.0005 to 0.0035%
B is an element effective for improving the hardenability of the core of the carburized steel. That is, the addition of B prevents the strength from being lowered by incomplete quenching, and the effect of increasing the effective hardened layer depth described later can be obtained. B is also an element effective for preferential segregation at the grain boundaries of the carburized layer and strengthening the grain boundaries of the carburized layer. In order to obtain this effect, the content is preferably 0.0005% or more. On the other hand, excessive content not only saturates the effect of improving hardenability, but also decreases workability in hot and cold conditions, so the content is made 0.0035% or less.

Furthermore, in the present invention, the following elements can be added.
(13) Ni: 0.20 to 2.50%
Ni is an austenite generating element and contributes to the improvement of toughness. In order to acquire such an effect, the content of 0.20% or more is necessary. On the other hand, excessive inclusion increases the hardness during annealing, thus degrading cold workability. Therefore, the content is 2.50% or less.

(14) Bi: 0.30% or less, Ca: 0.30% or less, Pb: 0.30% or less Bi, Ca, and Pb are effective elements for improving machinability. However, if it exceeds 0.30%, not only the effect of improving the machinability is saturated but also the toughness may be lowered, so the content is made 0.30% or less. Note that Bi, Ca, and Pb only affect the machinability, and even if the active addition is omitted, there is almost no effect on fatigue strength and bend straightening.

  The gear component of the present invention is suitable for applications of a pinion gear (differential pinion) 10 (see FIG. 1 (a)) and a side gear 20 (see FIG. 1 (b)) constituting a differential gear of an automobile. Here, the tooth base portions 11a and 21a of the gear part in the expression (1) to be described later usually mean a portion inside the pitch circle of the teeth 11 and 21, but in this embodiment, as shown in FIG. In addition, parts extending from the root R part to the core parts 11b and 21b are collectively referred to. In addition, the tooth surface portions 11c and 21c of the gear part in the expression (2) described later usually mean all of the surfaces left in meshing of the teeth 11 and 21, but in this embodiment, as shown in FIG. Of these surfaces, the part of the contact point (pitch point) of the pitch circle of both gears was taken up as a representative.

(15) Tooth base parts 11a, 21a:
(553.53 × S mass%) + (34.36 × effective hardened layer depth mm)
− (0.16 × Heart hardness HV) + (123.86 × surface layer C concentration% by mass) ≦ 52 (1)
(A) (553.53 × S mass%)
As described above, S reacts with Mn in the carburized steel to generate MnS, and this MnS becomes a path in the crack propagation direction (D1) shown in FIG. 2 and the impact fatigue strength of the tooth root portions 11a and 21a. It becomes a factor to reduce. Therefore, by reducing the amount of S, MnS serving as a crack propagation path can be reduced and the crack growth rate can be slowed, so that the impact fatigue strength of the tooth base portions 11a and 21a can be increased.

(B) (34.36 × effective hardened layer depth mm)
The effective hardened layer depth represents the depth from the surface where the limit hardness is 513 HV (the depth in the crack propagation direction (D1) shown in FIG. 2). By reducing the effective effect layer depth of the tooth root portions 11a and 21a, the initial crack length can be set short, and the subsequent crack propagation can be delayed. Therefore, the tooth root portions 11a and 21a. The impact fatigue strength of can be increased.

(C)-(0.16 × heart hardness HV)
The core hardness is the hardness of the base material represented by the cores 11b and 21b in FIG. 2, and depends on the C amount of the base material. As the amount of C in the base material increases, the core hardness increases and the plastic deformation resistance is improved. However, as the amount of C increases, the manufacturability (forging formability or cutting workability) deteriorates and the impact fatigue strength decreases due to a decrease in toughness. Therefore, the core hardness is desirably about 400 to 500 HV.

(D) (123.86 × surface layer C concentration by mass%)
By reducing the surface layer C concentration, the toughness of the tooth root portions 11a and 21a can be improved, and the occurrence of cracks can be delayed. However, since the plastic deformation resistance is remarkably deteriorated when the surface C concentration is too small, it is desirable that the surface layer C concentration mass% of the tooth base portions 11a and 21a is about 0.5 to 0.7%.

(16) Tooth surface portions 11c, 21c:
(0.001 × heart hardness HV) + (0.037 × total hardened layer depth mm) ≧ 0.460 (2)
(A) (0.037 × total hardened layer depth mm)
The depth of the total hardened layer is the range covered by the surface-hardened hardness, that is, the depth from the surface until reaching the hardness of the base material (the depth in the normal direction (D2) of the tooth surfaces 11c and 21c shown in FIG. A). By increasing the core hardness and increasing the total hardened layer depth, the plastic deformation resistance of the tooth surface portions 11c and 21c is improved, so that the amount of plastic deformation of the tooth surface portions 11c and 21c can be suppressed. In general, in order to suppress damage (for example, a case crash) of an internal starting point that occurs from the boundary between the hardened layer and the base material, a process of imparting a total hardened layer depth of about 1.2 mm is performed. In a part to which a high impact input is applied, such as a tooth surface part, the function of the part may be impaired at such a full hardened layer depth. Therefore, in order to sufficiently secure the plastic deformation resistance of the tooth surface portions 11c and 21c, it is desirable that the total hardened layer depth of the tooth surface portions 11c and 21c is about 1.3 to 2.0 mm. Correspondingly, the effective hardened layer depth of the tooth surface portions 11c and 21c is set to be deeper than the effective hardened layer depth of the tooth base portions 11a and 21a.

  Further, the surface layer hardness (hardness at a depth position of 0.05 mm from the surface) of the tooth surface portions 11c and 21c needs to be at least 700HV from the viewpoint of ensuring surface strength. For this reason, the surface layer C concentration of the tooth surface portions 11c and 21c is set to be about 0.03 to 0.15% higher than the surface layer C concentration of the tooth base portions 11a and 21a.

a. First Example First, case-hardened steel A having the alloy composition shown in Table 1 (the balance being Fe and inevitable impurities) was melted using a vacuum melting furnace and cast into a 150 kg ingot. Next, after rolling this ingot into a bar material, the bar material was cut to produce a pinion gear 10 shown in FIG. 1 (a) and a side gear 20 shown in FIG. 1 (b). Specifically, for the pinion gear 10, the cut bar material is subjected to spheroidizing annealing, cold closed forging, carburizing quenching tempering (vacuum carburizing) with the heat pattern shown in FIG. 3, and finish grinding Was given. For the side gear 20, the bar material after cutting is warm-forged, subjected to normalization, recompressed (sizing), and subjected to cutting such as turning, followed by carburizing and quenching with the heat pattern shown in FIG. Tempering treatment was performed. In this carburizing and tempering treatment, the carburizing time or diffusion time in the carburizing and quenching process is appropriately set so that the final surface C concentration, effective hardened layer depth, and total hardened layer depth in the gears 10 and 20 respectively change. did. Of the gears 10 and 20, the pinion gear 10 is implemented by changing the surface layer C concentration and effective hardened layer depth of the tooth root portion 11 a and changing the surface layer C concentration and total hardened layer depth of the tooth surface portion 11 c. It was set as Examples 1-4 and Comparative Examples 1-5. And in the tooth base part 11a, the impact test was implemented using the testing machine shown in FIG. The testing machine includes a case 101 (corresponding to a differential case), and a pair of pinion gears 10 and 10 is incorporated into the case 101 via a pinion shaft 102, and the shaft 103 (gear-coupled to each pinion gear 10) is coupled. A pair of side gears 20 and 20 are assembled via an axle shaft). Each gear 10 and 20 is rotationally driven by a motor 104 together with a case 101 and a shaft 103. The shaft 103 is braked by the brake mechanism 105 at its output side end. Using this testing machine, the braking of the shaft 103 by the brake mechanism 105 is repeatedly performed, and an impact load is input to each of the gears 10 and 20, and the shaft 103 is generated when the tooth base portion 11a of the gear 10 is damaged. Torque (impact strength) was measured with a torque meter 106. The test results are shown in Table 3. Here, a material having an impact strength of 1350 Nm or more is considered good.

  In the tooth surface portion 11c of the gear 10, the amount of plastic deformation was obtained after a predetermined number of inputs were applied with a constant input of the plastic deformation impact test using the testing machine shown in FIG. Specifically, in the gear 10 that has been tested, the shape is obtained in the tooth profile direction perpendicular to the root, and the amount of plastic deformation is obtained by comparison with the initial state obtained in advance. The test results are shown in Table 2. Here, the absolute value of the amount of plastic deformation is 178 μm or less.

  Next, evaluation methods and tests performed to confirm the effects of the present invention will be described.

(1) Surface layer C density | concentration The surface layer C density | concentration of each test piece was measured by the emission spectroscopic analysis based on JISG1253. Here, a calibration curve was prepared so that the C content could be measured up to 1% (error is ± 0.01%). Further, the surface layer C concentration distribution of each test piece was measured by line analysis using an X-ray microanalyzer (EPMA).

(2) Effective Hardened Layer Depth The effective hardened layer depth of each test gear was measured using a Vickers hardness tester with a load of 300 g in accordance with ISO2639 (2002). However, the limit hardness of the effective hardened layer depth was set to 513HV.

(3) Total Hardened Layer Depth The depth until the hardened layer depth of each test gear is indistinguishable from the hardened layer fabric by creating a transition curve from the surface to the inside using a method in accordance with JIS G 0577 (2006). This is the total hardened layer depth. The hardness was measured using a Vickers hardness tester with a load of 300 g.

(4) Core Hardness The core hardness of each test gear was measured according to JIS Z 2244, and the hardness of the tooth cross-section at the cores 11b and 21b shown in FIG. 2 was measured using a Vickers hardness meter.

  According to Table 2, as shown in Examples 1 to 4, it can be seen that the absolute value of the amount of plastic deformation is 178 μm or less when the left term of Formula (1) is 0.460 or more. Comparative Examples 1 and 2 have lower core hardness (376 HV, 383 HV) than Examples 1 to 4 and the total hardened layer depth is shallow (0.87 mm, 1.09 mm). ) Is less than 0.460 (0.408, 0.423), and the absolute value of the amount of plastic deformation is increased (311.3, 279.4). Further, as shown in Comparative Example 3, both the core hardness and the total hardened layer depth are not large (407 HV, 1.40 mm), and the left term of the formula (1) is less than 0.460 (0. 459), the absolute value of the amount of plastic deformation exceeds 178 μm (191.2).

  According to Table 3, as shown in Examples 1 to 4, it can be seen that when the left term of Formula (2) is 52 or less, the impact strength is 1350 Nm or more. In Comparative Examples 4 and 5, since the surface layer C concentration is higher than those in Examples 1 to 4 (0.73%, 0.75%), the left term of the formula (2) exceeds 52 ( 56.2, 61.2), impact strength is reduced (1269 Nm, 1171 Nm).

b. Second Example Next, in order to determine the influence of the alloy composition, a test gear similar to that of the first example was prepared as the alloy composition shown in Table 4 (the balance being Fe and unavoidable impurities), and then FIG. Carburizing, quenching, and tempering were performed with the heat pattern shown. In the carburizing and tempering treatment, the holding time in the carburizing period (930 ° C.) in the carburizing and quenching process was set to 9 hours, the holding time in the diffusion period (850 ° C.) was set to 0.5 hours, and then oil cooling was performed. Further, in the subsequent carburizing and tempering step, the steel was kept at 180 ° C. for 2 hours and then air-cooled. This produced Examples 5-14 and Comparative Examples 6-11. And also about these test gears, the same evaluation method and test as the said 1st Example were done. The above test results are shown in Tables 5 and 6.

  According to Table 5, as shown in Examples 5 to 14, it can be seen that the absolute value of the amount of plastic deformation is 178 μm or less when the left term of the formula (1) is 0.460 or more. In particular, in Example 12, the core hardness is increased by the addition of Ni (462 HV), and the absolute value of the amount of plastic deformation is extremely reduced (4.4). Comparative Example 6 has a smaller amount of C (0.09% by mass) than Examples 5-14. For this reason, the core hardness is reduced (272 HV), the left term of equation (1) is below 0.460 (0.334), and the absolute value of the plastic deformation amount is increased (528.0). . Comparative Example 7 has a larger amount of Si (1.61% by mass) than Examples 5-14. For this reason, the total hardened layer depth is shallow (1.63 mm), the left term of formula (1) is less than 0.460 (0.456), and the absolute value of the amount of plastic deformation increases ( 186.3). Comparative Example 8 has a smaller Cr amount (0.25% by mass) than Examples 5 to 14 and Comparative Example 9 has a larger Cr amount (1.54% by mass) than Examples 5 to 14. ). In either case, the core hardness becomes low (383 HV, 394 HV), the left term of equation (1) falls below 0.460 (0.446, 0.458), and the absolute value of the amount of plastic deformation increases. (216.3, 181.7). Moreover, the comparative example 11 has little B amount (0.0003 mass%) compared with Examples 5-13. For this reason, the core hardness is lowered (377 HV), the left term of the formula (1) is less than 0.460 (0.440), and the absolute value of the plastic deformation amount is increased (232.7). .

  According to Table 6, as shown in Examples 5-14, when the left term of Formula (2) is 52 or less, it turns out that impact strength becomes 1350 Nm or more. In Comparative Example 6, the amount of C is small (0.09% by mass) compared to Examples 5 to 14 and the core hardness is extremely low (272 HV), so the left term of Formula (2) exceeds 52. (56.0), impact strength is reduced (1273 Nm). Since Comparative Example 10 has a larger amount of S compared to Examples 5 to 14 (0.026% by mass), the left term of Formula (2) exceeds 52 (54.1), and the impact strength decreases. (1310 Nm). In Comparative Example 11, although the left term of Formula (2) is 52 or less (46.7), the amount of B is small as compared with Examples 5 to 14 (0.0003 mass%). Has decreased (1310 Nm).

  As a result, in the present invention, it was confirmed that the impact strength at the tooth root portion and the plastic deformation resistance at the tooth surface portion were excellent. Therefore, by applying the present invention to a differential gear, it is possible to improve both the tooth root strength and the tooth surface strength.

  As mentioned above, although the example which applied the gear component by this invention to the differential gear was demonstrated, the application range of a gear component is not restricted to this, For example, it can apply also to the spline shaft etc. which have a spline-shaped tooth profile.

(A) is a longitudinal cross-sectional view of the pinion gear which comprises the differential gear which concerns on one Embodiment of the gear components of this invention. (B) is a longitudinal cross-sectional view of the side gear which comprises the differential gear which concerns on one Embodiment of the gear components of this invention. Explanatory drawing of the tooth base part and tooth surface part of each gear of FIG. Explanatory drawing which shows the carburizing quenching tempering process which concerns on 1st Example. Explanatory drawing which shows the carburizing quenching tempering process which concerns on 2nd Example. Schematic which shows the structure of the testing machine which makes the gear of FIG. 1 a test object.

Explanation of symbols

10 Pinion gear (gear parts)
20 Side gear (gear parts)
11, 21 tooth 11a, 21a tooth base part 11b, 21b core part 11c, 21c tooth surface part

Claims (3)

% By mass
C: 0.10 to 0.40%,
Si: 1.50% or less,
Mn: 0.30 to 1.80%,
Cr: 0.30 to 1.50%,
Mo: 0.80% or less,
Ti: 0.05% or less,
Al: 0.05% or less,
N: 0.010% or less,
Nb: 0.10% or less,
P: 0.020% or less,
S: 0.020% or less,
B: 0.0005 to 0.0035%,
And carburizing treatment that is performed after the case-hardened steel comprising Fe and inevitable impurities is formed into a predetermined gear shape, and satisfies the following formulas (1) and (2): Gear parts.
Tooth base part of the gear part:
(553.53 × S mass%) + (34.36 × effective hardened layer depth mm)
− (0.16 × Heart hardness HV) + (123.86 × surface layer C concentration% by mass) ≦ 52 (1)
Tooth surface portion of the gear part:
(0.001 × heart hardness HV) + (0.037 × total hardened layer depth mm) ≧ 0.460 (2) Furthermore, in mass%,
The gear part according to claim 1, containing Ni: 0.20 to 2.50%. Furthermore, in mass%,
Bi: 0.30% or less,
Ca: 0.30% or less,
Pb: 0.30% or less,
The gear part of Claim 1 or 2 containing 1 type, or 2 or more types.

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