JP2013155423A - Method for producing gear - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a forged gear that has suitable strength, and furthermore is inexpensive.SOLUTION: A raw material which is heated to a transformation point A3 or higher or remains unheated, depending on steel components thereof, is subjected to forging in the temperature range of 350-600°C. Alternatively, a forged intermediate obtained by hot forging or cold forging depending on the steel components is subjected to the same forging in the temperature range of 350-600°C.

Description

  The present invention relates to a forging technology for steel parts, and more specifically to a manufacturing method by forging a gear excellent in fatigue strength and impact strength.

  Carburizing, quenching and tempering are generally used to improve the strength of forgings, such as fatigue strength and impact strength, and as a surface modification to improve surface strength. There is a problem of deterioration in (dimensional accuracy), cost associated with this correction, and increase in required time.

  For this reason, for example, Patent Document 1 discloses that a desired strength is obtained by performing forging processing in a temperature range from the Ar1 transformation point to 200 ° C. in a cooling process after hot forging in a site that requires a high level of strength. It is disclosed to ensure.

JP 2003-055714 A

  However, when the forging process is performed in a blue-hot brittle region, heat treatment is necessary for embrittlement recovery, resulting in an increase in manufacturing cost. On the other hand, when forging is performed in a temperature range of 600 ° C. or higher, processing is performed at a temperature close to the A1 transformation point, and thus the previously obtained ferrite + pearlite structure starts to grow, and pearlite grains are coarsened. Begins. Moreover, it is difficult to obtain the target strength due to the precipitation of ferrite in the pearlite grains based on the strain after processing.

  Moreover, surface modification heat treatment such as carburizing, quenching, and tempering is performed on components that require fatigue strength and impact strength inside, such as gears, and that require wear resistance and fatigue resistance on the surface. However, when the processing temperature is 900 ° C. or higher, and heat treatment distortion due to quenching (rapid cooling) is unavoidable, correction of quality deterioration, atmospheric temperature heating, mass consumption of energy by tempering and reheating after quenching, over 10 hours It is difficult to reduce costs such as heat treatment time.

  The present invention has been made to solve the above-described problems in the conventional forging method, and the object of the present invention is to provide a method for producing a forged gear having good strength and low cost. There is to do.

  As a result of repeating earnest studies to achieve the above object, the present inventors have obtained a material heated or not heated to the A3 transformation point or higher, or hot or cold forging depending on the steel type. It has been found that the above object can be achieved by subjecting the intermediate forged product to a forging process in a temperature range of 350 to 600 ° C., and the present invention has been completed.

That is, the present invention is based on such knowledge, and the gear manufacturing method according to the present invention includes C: 0.10 to 0.60 mass%, Si: 0.05 to 1.50 mass%, Mn : A steel containing 0.30 to 2.0% by mass, with the balance being Fe and inevitable impurities, heated to the A3 transformation point or higher, and then forged in a temperature range of 350 to 600 ° C. Yes.
At this time, if necessary, at least one selected from the group consisting of V: 0.30% or less, S: 0.10% or less, and Bi: 0.30% or less may be added to the steel. it can.

  Further, C: 0.10 to 0.60 mass%, Si: 0.05 to 1.50 mass%, Mn: 0.30 to 2.0 mass%, Ni: 2.50 mass% or less, Cr: It contains at least one selected from the group consisting of 2.0% by mass or less and Mo: 1.00% by mass or less, and a ferrite + pearlite steel consisting of Fe and unavoidable impurities in the temperature range of 350 to 600 ° C. A gear can also be manufactured by forging.

  Furthermore, the manufacturing method of the gear of the present invention is as follows: C: 0.10 to 0.60%, Si: 0.05 to 1.50%, Mn: 0.30 to 2.0%, Further, steel containing at least one selected from the group consisting of V: 0.30% or less, S: 0.10% or less, and Bi: 0.30% or less, with the balance being Fe and inevitable impurities, or C : 0.10 to 0.60 mass%, Si: 0.05 to 1.50 mass%, Mn: 0.30 to 2.0 mass%, Ni: 2.50 mass% or less, Cr: 2.0 An intermediate having a ferrite pearlite structure obtained by hot forging a steel containing at least one selected from the group consisting of less than mass% and Mo: 1.00 mass%, with the balance being Fe and inevitable impurities It is characterized by forging a forged product in a temperature range of 350 to 600 ° C. That.

  And the manufacturing method of the gear of this invention is C: 0.10-0.60 mass%, Si: 0.05-1.50 mass%, Mn: 0.30-2.0 mass%, Ni: 2. Cold containing steel containing at least one selected from the group consisting of 50% by mass or less, Cr: 2.0% by mass or less, and Mo: 1.00% by mass or less, with the balance being Fe and inevitable impurities It is characterized in that a forging process is performed in a temperature range of 350 to 600 ° C. on an intermediate forged product obtained by forging.

  According to the present invention, depending on the steel type, the intermediate forged product obtained by performing hot forging or cold forging on the raw material heated to the A3 transformation point or higher, or the raw material without heating, is 350 to Since the forging process is performed in the temperature range of 600 ° C., it is possible to manufacture a gear that is inexpensive and has good strength.

(A)-(d) is each process drawing which shows the manufacture procedure of the gear of this invention. It is a perspective view which shows the shape of the intermediate forge product (a) and the forge rough material (b) in the manufacturing method of the gear of this invention, respectively. It is explanatory drawing which each shows the extraction position and hardness measurement position of the impact test piece from the tooth | gear part (a) of a gear manufactured in Example 1 of this invention, and a tooth bottom part (b). It is a graph which shows the influence of the forging process temperature which acts on the internal hardness in the tooth | gear part of a gear manufactured in Example 1 of this invention, and a tooth bottom part. It is a graph which shows the influence of the forging process temperature on the impact strength in the tooth | gear part and tooth root part of the gear which were manufactured in Example 1 of this invention. It is a perspective view which shows the shape of the test forge rough material manufactured in Example 2 of this invention. It is a graph which shows the influence of the forge processing temperature which acts on the internal hardness in the forge rough material manufactured in Example 2 of this invention. It is a graph which shows the influence of the forging process temperature which has on the impact strength in the forge rough material manufactured in Example 2 of this invention.

  Below, the manufacturing method of the gear of this invention is demonstrated still in detail with the steel component etc. which are used for this. In the present specification, “%” means mass percentage unless otherwise specified.

FIG. 1 is a process diagram showing the procedure of the gear manufacturing method of the present invention, and the manufacturing method can be roughly divided into a cutting process, a forging process, and a machining process.
That is, in the cutting step, steel materials having components described later are cut to obtain materials such as various gears, such as side gears and pinion mate gears in differential gears, and drive pinions and ring gears in hypoid gears.

  In the forging process, as will be described later, forging consisting of various processes as shown in FIGS. 1 (a) to 1 (d) is applied to the cut material according to the material steel components. The fatigue strength and impact strength of the material and target part are improved.

  And in a machining process, with respect to the normal temperature forged product which passed through the forging process, cutting and grinding are given, and various gears are obtained. In the cutting process, for example, protruding burrs and the like are removed. In the grinding process, for example, a bevel tooth or a helical is formed.

Thereafter, when further surface strength is required, it is desirable to perform surface hardening treatment, for example, nitriding treatment (500 to 600 ° C.), whereby the features of the method of the present invention can be maximized.
That is, since nitriding is performed at a temperature below the transformation point, expansion due to phase transformation can be prevented, and a gear having high shape quality with little influence of heat treatment strain can be obtained. In addition, since the processing temperature is low and processing can be performed in a short time compared to carburizing processing, energy consumption can be suppressed and processing can be performed at low cost. Note that DLC coating, plating, or the like can be appropriately performed instead of nitriding.

  Next, with reference to FIGS. 1A to 1D and FIGS. 2A and 2B, the forging process described above will be described in detail by taking as an example the manufacture of a side gear that constitutes a differential gear.

  First, steel containing 0.10 to 0.60% C, 0.05 to 1.50% Si, and 0.30 to 2.0% Mn (hereinafter referred to as “first steel”) Is applied), the process shown in FIG. 1A is employed.

That is, the gear material cut into a predetermined shape in the cutting step is first heated to a temperature exceeding the A3 transformation point, as shown in FIG.
Next, forging is performed when the raw material temperature reaches a temperature range of 350 to 600 ° C., for example, a forged rough material having a shape as shown in FIG. 2 (b), which can give high strength. . In this forging process, for example, a relative strain of 0.1 mm / mm or more is given in a time of about 1 minute.

And the forge rough material forged in the said temperature range is cooled to normal temperature, and a cutting process and a grinding process are given in a machining process.
And if necessary, surface hardening treatment such as nitriding treatment is performed to complete the side gear.

  In the cooling process after the material is heated to a temperature exceeding the transformation point and then lowered to a temperature range of 350 to 600 ° C., the cooling rate is 5 ° C./second or less so that a mixed structure of ferrite and pearlite is obtained. It is preferable to perform proper cooling. This is because at a cooling rate exceeding 5 ° C./second, a bainite structure may be formed and forgeability and machinability may be significantly impaired.

In the above steel material (first steel), that is, steel containing 0.10 to 0.60% C, 0.05 to 1.50% Si, 0.30 to 2.0% Mn If necessary, at least one selected from the group consisting of V of 0.30% or less, S of 0.10% or less, and Bi of 0.30% or less can be added (hereinafter referred to as “steel”). Sometimes called "second steel").
Also in this case, the process shown in FIG. 1A is adopted as described above.

As the material steel, 0.10 to 0.60% C, 0.05 to 1.50% Si, 0.30 to 2.0% Mn, 2.50% or less Ni, 2.0% When a steel containing at least one selected from the group consisting of the following Cr and 1.00% or less Mo (hereinafter sometimes referred to as “third steel”) is applied, FIG. The process shown in b) is employed.
That is, in this case, it is not necessary to heat the gear material cut into a predetermined shape to a temperature exceeding the A3 transformation point, and the material is heated as it is to a temperature of 350 to 600 ° C., and forging is performed in the temperature range. Applied. Other than this, the side gear is completed by the same process as described above.

When the first to third steels are applied, the step shown in FIG.
That is, the gear material cut into a predetermined shape is first subjected to hot forging for about 1 minute, for example, in a temperature range that does not fall below the transformation point. Thereafter, as described above, controlled cooling is performed at a cooling rate of 5 ° C./second or less, whereby an intermediate forged product having a ferrite + pearlite structure having a shape as shown in FIG. 2A is obtained.

  Then, after 1 to 10 minutes have passed, when the temperature of the intermediate forged product reaches the temperature range of 350 to 600 ° C., the forging process is performed on the target portion in the intermediate forged product, that is, the portion where the teeth are formed. A rough forged material as shown in 2 (b) is obtained, and high strength can be imparted to the tooth portion. In the forging process in the temperature range of 350 to 600 ° C., for example, as described above, a relative strain of 0.1 mm / mm or more is applied in about 1 minute.

  Thereafter, the forged rough material at room temperature is similarly machined and, if necessary, surface hardened to complete the side gear.

In addition, in the said manufacturing method, since it is trying to perform a forging process when the temperature falls to the temperature range of 350-600 degreeC using the residual heat at the time of the hot forging of an intermediate forging product, Energy can be saved and low-cost manufacturing is possible.
On the other hand, after lowering the temperature of the intermediate forged product after hot forging to room temperature, it can be heated again in the above temperature range to perform forging, improving the freedom of the forging process Will do.

When the third steel containing one or more of Ni, Cr, and Mo is used as the material steel, the forging of the intermediate forged product can be performed cold, and the process shown in FIG. 1 (d) Is adopted.
That is, the gear material cut into a predetermined shape is cold forged at a temperature of about 200 ° C. or lower, and an intermediate forged product having a shape as shown in FIG. 2A is obtained.

  The intermediate forged product that has been cold forged is either directly or once cooled to room temperature, and then heated to a temperature of 350 to 600 ° C., and the forging process is performed on the tooth mold forming portion of the intermediate forged product in the temperature range. The forged coarse material as shown in FIG. 2B is obtained in the same manner as described above.

  Thereafter, the forged rough material at room temperature is similarly machined and, if necessary, surface hardened to complete the side gear.

In the gear manufacturing method of the present invention, in any of the above cases, since the forging process applied to the raw steel or the intermediate forged product is a process at 600 ° C. or lower, austenite precipitates even if heat is generated by the forging process. The temperature is never reached. Further, since pearlite coarsening and ferrite growth in pearlite grains are suppressed, target strengths (fatigue strength and impact strength) can be obtained by forging.
And since it is a forging process at a temperature of 350 ° C. or higher, the temperature is higher than that of the blue-hot brittle region, and heat treatment (for example, tempering and sub-zero treatment) for recovery from embrittlement is unnecessary, thereby reducing manufacturing costs. Therefore, it is possible to manufacture a gear having good strength and inexpensive.

  In addition, since the forging temperature is relatively low and the material thermal expansion coefficient is small, the dimensional accuracy is improved. In addition, since the material deformation resistance in the forging process is smaller than that in the cold, it is possible to reduce the equipment scale and increase the deformation amount (for example, strong processing capable of imparting strain to the core part).

As described above, the gear manufacturing method of the present invention includes the first steel (C: 0.10 to 0.60%, Si: 0.05 to 1.50%, Mn: 0.30 to 2.0. %, The balance being Fe and inevitable impurities), second steel (C: 0.10-0.60%, Si: 0.05-1.50%, Mn: 0.30-2.0 %, V: 0.30% or less, S: 0.10% or less and Bi: 0.30% or less, and the balance is Fe and inevitable impurities), and 3 steel (C: 0.10 to 0.60%, Si: 0.05 to 1.50%, Mn: 0.30 to 2.0%, Ni: 2.50% or less, Cr: 2. It contains at least one selected from the group consisting of 0% or less and Mo: 1.00% or less, with the balance being Fe and inevitable impurities).
Below, the effect | action of each component in these steel is demonstrated with the reason for limitation of a component value.

C: 0.10 to 0.60%
C is an important component as a strength-enhancing element, and if it is less than 0.10%, the strength may be insufficient, and if it exceeds 0.60%, the toughness decreases and the tensile strength becomes excessively large. There is a possibility that the machinability is lowered. Therefore, the content of C is preferably 0.10 to 0.60%.

Si: 0.05 to 1.50%
Si acts as a deoxidizing element and is effective in improving the yield strength and fatigue strength by dissolving in ferrite ground, but if it is less than 0.05%, the effect is not significant, and if it exceeds 1.50% There is a concern that the machinability is lowered and decarburization after hot forging is increased. Therefore, the content of Si is preferably 0.05 to 1.50%.

Mn: 0.30 to 2.0%
Mn is an element that increases the strength and toughness after hot forging. However, if it is less than 0.30%, the effect is not significant, and if it exceeds 2.00%, bainite may be generated and machinability may be reduced. is there. Therefore, the content of Mn is preferably 0.30 to 2.0%.

V: 0.30% or less V precipitates carbides after hot forging and contributes to improvement of strength and proof stress, but its action is saturated at about 0.30%, and addition exceeding it increases the cost. Therefore, when V is added, the content is made 0.30% or less.

S: 0.10% or less S is added as necessary to improve the machinability of steel, as with Bi. However, addition over 0.10% tends to cause cracking during hot forging. Therefore, the content is made 0.10% or less.

Bi: 0.30% or less Bi is also a component added as necessary to improve the machinability of steel, but even if added over 0.30%, the effect is saturated and wasted Therefore, the content is made 0.30% or less. In addition to these, Pb is known as an element for improving machinability, but it is desirable not to add it from the viewpoint of reducing the environmental load.

Ni: 2.50% or less Cr: 2.0% or less Mo: 1.00% or less These components improve quench hardenability and toughness, increase steel strength, and improve wear resistance and impact resistance. Therefore, one or more of the above elements are added as necessary.

However, if the Ni content exceeds 2.50%, the machinability is significantly impaired, so the Ni content is set to 2.50% or less.
In addition, when the Cr content is excessive, bainite is generated and the machinability may be reduced. Therefore, the Cr content is set to 2.0% or less. About Mo, since it is expensive compared with Cr and Ni, it is made into 1.00% or less.

  In the present invention, N causes hydrogen embrittlement by adsorbing hydrogen to the solute N after aging, so N is not intentionally added to the material steel used in the present invention, and the N content is Inevitable level.

  Hereinafter, the present invention will be described in detail based on examples. Needless to say, the present invention is not limited to these examples.

(1) Example 1
[Invention Example 1, Comparative Example 1]
A gear material is cut out from steel A (corresponding to the third steel) having the component composition shown in Table 1, and forged at 900 ° C., 750 ° C. and 500 ° C., and at room temperature, respectively, as shown in FIG. A shape (lower surface diameter: about 70 mm, upper surface diameter: about 40 mm, height: about 30 mm, inner diameter: about 25 mm) was obtained. Forgings processed at 900 ° C., 750 ° C., and 500 ° C. were allowed to cool at a cooling rate of about 4 ° C./second.
The obtained forged product was confirmed to have a ferrite + pearlite structure.

In addition, about P content in each steel shown in Table 1, Cu content, Ni content, Cr content in steel B and C, S content in steel A, C, and D originates in raw materials, such as scrap However, they are not intentionally added, and all of them correspond to inevitable impurities.
In addition, nitrogen was not added to each of the above steels, and the N content was analyzed by an active gas dissolution-thermal conductivity method (TDC method) in accordance with JIS. It was confirmed that.

And about each forged rough material obtained by the above, the internal hardness (Rockwell hardness B scale) and impact strength of a tooth part and a tooth bottom part were investigated, respectively.
In addition, the hardness measurement position in the tooth part and the sampling position of the impact test piece (□ 1 mm × 20 mm size) are shown in FIG. 3A, and the measurement position and sampling position in the tooth bottom part are shown in FIG.

  As the test results, the influence of the forging temperature on the internal hardness of the tooth part and the tooth bottom part is shown in FIG. FIG. 5 shows the influence of the forging temperature on the impact strength of the tooth part and the tooth bottom part.

The following can be said from the results shown in FIGS.
That is, when forging is performed at a high temperature such as 750 ° C. or 900 ° C., the impact strength is high, but the hardness is low, and carburizing, quenching and tempering are necessary to increase the surface and internal hardness, and the heat treatment distortion It is predicted that product quality (accuracy) will deteriorate.

  On the other hand, forging at 100 ° C. shows high hardness as a result of cold work hardening. However, when the surface hardening treatment is a nitriding treatment, the work-hardened product has a significant decrease in the base material hardness due to the annealing effect in the nitriding temperature range, so carburizing quenching and tempering must be adopted, In that case, the product quality deteriorates as described above.

In contrast, when forging is performed at 500 ° C., which is the temperature range of the present invention, the impact strength is increased while the hardness is improved to a cold equivalent level, and the hardness (fatigue strength) is increased. It was confirmed that the balance of impact strength was excellent.
In addition, since the impact value has improved, a recovery (aging) phenomenon has occurred, tempering treatment is no longer necessary, and internal formation (aging) has already been performed at the nitriding temperature. It is considered that surface hardening treatment by nitriding is possible.

(2) Example 2
[Invention Example 2]
From the steel B (corresponding to the second steel), steel C (corresponding to the first steel) and steel D (corresponding to the third steel) having the composition shown in Table 1, the raw materials were cut out from 400 ° C. to 600 ° C., respectively. The forging process temperature is set every 100 ° C., heated to a temperature obtained by adding 100 ° C. to the processing temperature, and after waiting for the temperature to fall to the set temperature, forging is performed, the test piece shape shown in FIG. A forged rough material was obtained. The forging time at this time was 1 minute, and the relative strain was 0.1 to 0.5 mm / mm.
And about each obtained forging rough material, the internal hardness of the center part of the site | part used as a relative strain of 0.1 mm / mm was investigated, respectively. The result is shown in FIG. Moreover, the impact strength of the forged rough material by the steel D was investigated, and the result is shown in FIG.

[Comparative Example 2]
The same forging rough as shown in FIG. 6 is repeated by repeating the same operation as in Example 2 except that the raw materials are cut out from the steels B, C and D shown in Table 1 and the forging temperature is set to 300 ° C. The material was obtained. The forging time at this time was also 1 minute.
And about each obtained forged rough material, internal hardness of the center part of the site | part used as a relative strain of 0.1 mm / mm was investigated similarly to the above. The results are also shown in FIG. Moreover, the investigation result of the impact strength of the forged rough material by the steel D is shown in FIG.

[Comparative Example 3]
Moreover, each material is cut out from each of steels B, C and D shown in Table 1, the forging temperature is set to 100 ° C. from 700 ° C. to 1000 ° C., and each is heated to a temperature obtained by adding 100 ° C. to the processing temperature. By allowing to cool to a temperature at a cooling rate of about 4 ° C./second, a forged coarse material having a test piece shape was obtained through cooling conditions having a ferrite + pearlite structure. A similar forged coarse material was obtained by repeating the same operation as in Example 2 except that the material was allowed to cool at a cooling rate of about 4 ° C./second. The forging time at this time was also 1 minute.
And about each obtained forged rough material, internal hardness of the center part of the site | part used as a relative strain of 0.1 mm / mm was investigated similarly to the above. The results are also shown in FIG. And the investigation result of the impact strength of the forge rough material by the steel D is shown in FIG.

  However, in steel B, C, and D, the test piece having a forging temperature of 700 ° C. to 1000 ° C. has a bainite structure because the temperature rapidly decreases due to heat absorption by the mold during molding. It was predicted that the workability was impaired.

[Invention Example 3]
From the steel D shown in Table 1, the material was cut out, heated to 800 ° C., allowed to cool at a cooling rate of about 4 ° C./second until lowered to a temperature of 500 ° C., and then forged. A forged rough material having a specimen shape as shown in FIG. 6 having a pearlite structure was obtained. The forging time at this time was 1 minute, and the relative strain was 0.1 to 0.5 mm / mm.
And about each obtained forged rough material, internal hardness and impact strength were investigated in the same way as the above, respectively. The result of the internal hardness is shown as white ◇ in FIG. Also, the impact strength is shown in FIG.

  From the results of FIG. 7 and FIG. 8, although the absolute value and the extreme point processing temperature are different due to the difference in the amount of C in the steel components, regardless of the type of steel such as carbon steel or alloy steel, heating, cooling (residual heat) It was confirmed that there exists a processing temperature range that satisfies the hardness and impact strength.

Claims (11)

  Steel containing, by mass%, C: 0.10 to 0.60%, Si: 0.05 to 1.50%, Mn: 0.30 to 2.0%, the balance being Fe and inevitable impurities Is heated to a temperature exceeding the A3 transformation point, and then forged in a temperature range of 350 to 600 ° C.   In mass%, C: 0.10 to 0.60%, Si: 0.05 to 1.50%, Mn: 0.30 to 2.0%, V: 0.30% or less, S: 0.00. 350 to 600 ° C. after heating a steel containing at least one selected from the group consisting of 10% or less and Bi: 0.30% or less, with the balance being Fe and inevitable impurities to a temperature exceeding the A3 transformation point A gear manufacturing method, wherein forging is performed in a temperature range of   In mass%, C: 0.10 to 0.60%, Si: 0.05 to 1.50%, Mn: 0.30 to 2.0%, Ni: 2.50% or less, Cr: 2. It contains at least one selected from the group consisting of 0% or less and Mo: 1.00% or less, and the forging is performed in a temperature range of 350 to 600 ° C. with the balance being Fe and unavoidable impurities. A manufacturing method of a gear.   Steel containing, by mass%, C: 0.10 to 0.60%, Si: 0.05 to 1.50%, Mn: 0.30 to 2.0%, the balance being Fe and inevitable impurities A method for producing a gear, characterized by subjecting an intermediate forged product having a ferrite and pearlite structure obtained by hot forging to a forging process in a temperature range of 350 to 600 ° C.   In mass%, C: 0.10 to 0.60%, Si: 0.05 to 1.50%, Mn: 0.30 to 2.0%, V: 0.30% or less, S: 0.00. Intermediate forging having ferrite pearlite structure obtained by hot forging steel containing at least one selected from the group consisting of 10% or less and Bi: 0.30% or less, the balance being Fe and inevitable impurities A method for producing a gear, wherein the product is forged in a temperature range of 350 to 600 ° C.   In mass%, C: 0.10 to 0.60%, Si: 0.05 to 1.50%, Mn: 0.30 to 2.0%, Ni: 2.50% or less, Cr: 2. Intermediate forging having a ferrite pearlite structure obtained by hot forging steel containing at least one selected from the group consisting of 0% or less and Mo: 1.00% or less, the balance being Fe and inevitable impurities A method for producing a gear, wherein the product is forged in a temperature range of 350 to 600 ° C.   The gear manufacturing method according to any one of claims 4 to 6, wherein the forging process is performed in the temperature range by using a residual heat during forging of the intermediate forged product.   The method for manufacturing a gear according to any one of claims 4 to 6, wherein after the temperature of the intermediate forged product is lowered to room temperature, the forging process is performed by heating to the temperature range.   In mass%, C: 0.10 to 0.60%, Si: 0.05 to 1.50%, Mn: 0.30 to 2.0%, Ni: 2.50% or less, Cr: 2. An intermediate forged product obtained by cold forging steel containing at least one selected from the group consisting of 0% or less and Mo: 1.00% or less, with the balance being Fe and inevitable impurities, is 350 to 600 ° C. A gear manufacturing method, wherein forging is performed in a temperature range of   The gear manufacturing method according to claim 9, wherein the forging process is performed by heating the intermediate forged product to the temperature range.   The method for manufacturing a gear according to any one of claims 1 to 10, wherein a surface hardening treatment selected from nitriding treatment, coating and plating treatment is performed.

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