JP7368697B2 - Steel for carburized gears, carburized gears, and method for manufacturing carburized gears - Google Patents

Description

The present invention relates to steel for carburized gears, carburized gears, and methods of manufacturing carburized gears.

Gears used in automobiles, construction machinery, industrial machinery, etc. are generally carburized and quenched after machining in order to achieve both precise dimensional accuracy and strength.
In recent years, gears have become smaller with the aim of reducing weight, and the load on gears is increasing. As a result, conventionally major forms of failure due to overload include bending fatigue failure and pitting.
Conventionally, regarding the technological development of gears, for example, Patent Document 1 discloses a technique for obtaining gas carburized steel parts that have excellent strength against pitting by increasing the Si content and adjusting the Mn and Cr contents. There is.

Patent No. 5099276

As a type of fracture different from bending fatigue fracture and pitting, fracture due to white layer formation due to structural change may occur. There is a need for a gear that has excellent strength against destruction due to the formation of a white layer that accompanies such structural changes.

An object of the present invention is to manufacture a steel for carburized gears and a carburized gear that can manufacture carburized gears that have excellent strength against destruction due to the formation of a white layer due to structural changes when gas carburizing and quenching is performed to manufacture carburized gears. It is an object of the present invention to provide a carburized gear having excellent strength against destruction due to formation of a white layer due to structural changes.

Means for solving the problems of the present invention include the following aspects.

<1> In mass%,
C: 0.26-0.35%,
Si: 0.40-1.00%,
Mn: 0.20-0.60%,
Cr: 1.00-3.00%,
Mo: 0.01-0.50%,
S: 0.001-0.050%,
N: 0.004-0.030%,
Al: 0.001-0.150%,
Ca: 0.0001-0.0100%,
O: 0.005% or less,
Carburized gear steel consisting of P: 0.05% or less, and the balance: Fe and impurities.
<2> In mass%,
Ni: 0.1 to 3.0%,
Cu: 0.05-1.0%,
Co: 0.05-3.0%,
W: 0.05-1.0%,
V: 0.01-0.3%,
Ti: 0.005-0.3%,
Nb: 0.005-0.3%, and B: 0.0005-0.005%
The carburized gear steel according to <1>, which contains one or more elements selected from the group consisting of:
<3> In mass%,
Pb: 0.09% or less,
Bi: 0.0001-0.5%,
Mg: 0.0005-0.01%,
Zr: 0.0005 to 0.05%,
Te: 0.0005 to 0.1%, and rare earth elements: 0.0005 to 0.005%
The carburized gear steel according to <1> or <2>, which contains one or more elements selected from the group consisting of:
<4> Machining the carburized gear steel according to any one of <1> to <3> into a gear-shaped member;
a step of subjecting the gear-shaped member to gas carburizing treatment;
A method for manufacturing a carburized gear having the following.
<5> At a position deeper than 3 mm from the surface, in mass%,
C: 0.26-0.35%,
Si: 0.40-1.00%,
Mn: 0.20-0.60%,
Cr: 1.00-3.00%,
Mo: 0.01-0.50%,
S: 0.001-0.050%,
N: 0.004-0.030%,
Al: 0.001-0.150%,
Ca: 0.0001-0.0100%,
O: 0.005% or less,
Carburized gear consisting of P: 0.05% or less, and the balance: Fe and impurities.
<6> At a position deeper than 3 mm from the surface, in mass%,
Ni: 0.1 to 3.0%,
Cu: 0.05-1.0%,
Co: 0.05-3.0%,
W: 0.05-1.0%,
V: 0.01-0.3%,
Ti: 0.005-0.3%,
Nb: 0.005-0.3%, and B: 0.0005-0.005%
The carburized gear according to <5>, which contains one or more elements selected from the group consisting of:
<7> At a position deeper than 3 mm from the surface, in mass%,
Pb: 0.09% or less,
Bi: 0.0001-0.5%,
Mg: 0.0005-0.01%,
Zr: 0.0005 to 0.05%,
Te: 0.0005 to 0.1%, and rare earth elements: 0.0005 to 0.005%
The carburized gear according to <5> or <6>, containing one or more elements selected from the group consisting of:

According to the present invention, when gas carburizing and quenching is performed to manufacture a carburized gear, a steel for carburized gears and a carburized gear can be manufactured which can manufacture a carburized gear that has excellent strength against destruction due to the formation of a white layer due to a change in structure. A method and a carburized gear with excellent strength against destruction due to the formation of a white layer due to structural changes are provided.

It is a micrograph showing an example of a white tissue.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment which is an example of this invention is described in detail.
In addition, in this specification, a numerical range expressed using "~" represents a range that includes the numerical values written before and after "~" as the lower limit value and upper limit value.
Furthermore, regarding the content of elements in the chemical composition, "%" means "mass%".

(Steel for carburized gears)
First, the circumstances leading to the present invention will be explained.
The present inventors conducted extensive research on a method for improving the strength against fracture due to the formation of a white layer due to structural changes in gears after gas carburizing and quenching. As a result, it was found that suppressing the tissue change itself is effective in improving strength. Therefore, the present inventors further investigated the influence of the chemical components of steel materials regarding methods of suppressing structural changes. As a result, the steel components were determined as follows: C: 0.26-0.35%, Si: 0.40-1.00%, Mn: 0.20-0.60%, Cr: 1.00-3.00%. , Mo: 0.01 to 0.50%, S: 0.001 to 0.050%,
N: 0.004 to 0.030%, Al: 0.001 to 0.150%, Ca: 0.0001 to 0.0100%, O: 0.005% or less, P: 0.05% or less, balance : It was found that by using a range consisting of Fe and impurities, structural changes were significantly suppressed.

Next, the reason for limiting the chemical composition of the steel according to this embodiment will be explained.

C: 0.26-0.35%
The C content affects the hardness of the non-carburized part of the gear. In order to ensure the required hardness, the C content is set to 0.26% or more. From the viewpoint of ensuring the hardness of the non-carburized portion of the gear, the lower limit of the C content is preferably 0.27% or more, and more preferably 0.28% or more.
On the other hand, if the C content is too large, the hardness of the non-carburized portion after carburizing becomes too high, and the strength against impact decreases, so the C content is set to 0.35% or less. From the viewpoint of suppressing the non-carburized portion after carburizing from becoming excessively hard, the preferable upper limit of the C content is 0.34% or less, and more preferably 0.33% or less.

Si: 0.40-1.00%
Si is an element effective in suppressing structural changes. To obtain this effect, the Si content needs to be 0.40 or more. From the viewpoint of suppressing structural changes, the lower limit of the Si content is preferably 0.45% or more, more preferably 0.50% or more.
On the other hand, if a large amount of Si is contained, the hardness after gas carburization is reduced, so the Si content needs to be 1.00% or less. From the viewpoint of suppressing a decrease in hardness after carburizing, the upper limit of the Si content is preferably 0.90% or less, and more preferably 0.80% or less.

Mn: 0.20-0.60%
Mn is an element effective in suppressing tissue changes. To obtain this effect, the Mn content must be within the range of 0.20 to 0.60%. From the viewpoint of suppressing structural changes, the lower limit of the Mn content is preferably 0.25% or more, and more preferably 0.30% or more. Similarly, the upper limit of the Mn content is preferably 0.55% or less, more preferably 0.50% or less.

Cr:1.00~3.00%
Cr is an element effective in suppressing structural changes. To obtain this effect, the Cr content needs to be 1.00% or more. From the viewpoint of suppressing structural changes, the lower limit of the Cr content is preferably 1.05% or more, more preferably 1.10% or more.
On the other hand, if a large amount of Cr is contained, the hardness after gas carburization decreases, so the Cr content needs to be 3.00% or less. From the viewpoint of suppressing a decrease in hardness after carburizing, the upper limit of the Cr content is preferably 2.90% or less, more preferably 2.80% or less.

Mo: 0.01~0.50%
Mo is an element effective in suppressing tissue changes. To obtain this effect, the Mo content must be within the range of 0.01 to 0.50%. From the viewpoint of suppressing structural changes, the lower limit of the Mo content is preferably 0.03% or more, more preferably 0.05% or more. Similarly, the upper limit of the Mo content is preferably 0.45% or less, more preferably 0.40% or less.

S: 0.001-0.050%
S forms MnS in the steel, thereby improving the machinability of the steel. To obtain machinability at a level that allows cutting into parts (gears), an S content equivalent to that of general mechanical structural steel is required, and the S content should be 0.001 to 0.050%. Must be within the range. From the viewpoint of improving the machinability of steel, the lower limit of the S content is preferably 0.005% or more, and more preferably 0.010% or more.
On the other hand, if the S content is excessively high, coarse MnS is formed and the mechanical performance of the gear is impaired. Therefore, the preferable upper limit of the S content is 0.040% or less, and more preferably 0.030% or less. It is.

N: 0.004-0.030%
N has a crystal grain refinement effect by forming a compound with Al, Cr, and optional components such as Ti and V, so it is contained in an amount of 0.004% or more.
However, if the N content exceeds 0.030%, the compound (nitride) becomes coarse and grain refinement effects cannot be obtained. For the above reasons, it is necessary to keep the N content within the range of 0.004 to 0.030%.
From the viewpoint of obtaining a crystal grain refinement effect, the lower limit of the N content is preferably 0.005% or more, and more preferably 0.006% or more.
On the other hand, from the viewpoint of suppressing embrittlement due to coarsening of the compound, the upper limit of the N content is preferably 0.028% or less, and more preferably 0.025% or less.

Al: 0.001-0.150%
Al is an element effective in deoxidizing steel, and is an element that combines with N to form nitrides and refine crystal grains. This effect is insufficient if the Al content is less than 0.001%. On the other hand, when the Al content exceeds 0.150%, the nitride becomes coarse and becomes brittle. Therefore, the Al content is set within the range of 0.001 to 0.150%. From the viewpoint of obtaining a crystal grain refinement effect, the lower limit of the Al content is preferably 0.004% or more, more preferably 0.007% or more.
On the other hand, from the viewpoint of suppressing embrittlement due to coarsening of nitrides, the preferable upper limit of the Al content is 0.120% or less, and more preferably 0.100% or less.

Ca:0.0001~0.0100%
Ca is an element effective in deoxidizing steel and suppressing structural changes. To obtain this effect, the Ca content needs to be 0.0001% or more. From the viewpoint of suppressing structural changes, the lower limit of the Ca content is preferably 0.0003% or more, more preferably 0.0005% or more.
On the other hand, if a large amount of Ca is contained, a large amount of coarse oxides containing Ca will appear, causing a decrease in fatigue life, so the Ca content needs to be 0.0100% or less. From the viewpoint of suppressing a decrease in fatigue life, the upper limit of the Ca content is preferably 0.0080% or less, more preferably 0.0060% or less.

O: 0.005% or less O forms oxides in steel and acts as inclusions to reduce fatigue strength, so the O content is preferably limited to 0.005% or less. The upper limit of the O content may be 0.003% or less, or 0.002% or less. Since it is preferable that the O content be small, the lower limit of the O content is 0%.

P: 0.05% or less P segregates at austenite grain boundaries during heating before quenching, thereby reducing fatigue strength. Therefore, it is preferable to limit the P content to 0.05% or less. The upper limit of the P content may be 0.04% or less, or 0.03% or less. Since it is preferable that the P content be small, the lower limit of the P content is 0%. However, if P is removed more than necessary, manufacturing costs will increase. Therefore, the practical lower limit of the P content is usually about 0.004% or more.

In order to enhance the hardenability or grain refinement effect, the steel according to the present embodiment further includes a group consisting of Ni, Cu, Co, W, V, Ti, Nb, and B in place of a part of Fe. It may contain one or more selected types. The lower limit when these elements are not contained is 0%.

Ni: 0.1-3.0%
Ni is an effective element for imparting necessary hardenability to steel. If the Ni content exceeds 3.0%, a large amount of retained austenite will remain after quenching, resulting in a decrease in hardness. Therefore, the Ni content is set to 3.0% or less. From the viewpoint of suppressing a decrease in hardness after quenching, the upper limit of the Ni content may be 2.0% or less, or 1.8% or less. When Ni is contained to improve hardenability, the lower limit of the Ni content may be 0.1% or more, or 0.3% or more.

Cu: 0.05-1.0%
Cu is an element effective in improving the hardenability of steel. When the Cu content exceeds 1.0%, hot ductility decreases. Therefore, the Cu content is set to 1.0% or less. When the above effects are obtained by containing Cu, the lower limit of the Cu content may be 0.05% or more, or 0.1% or more.

Co:0.05~3.0%
Co is an element effective in improving the hardenability of steel. When the Co content exceeds 3.0%, the effect is saturated. Therefore, the Co content is set to 3.0% or less. When the above effects are obtained by containing Co, the lower limit of the Co content may be 0.05% or more, or 0.1% or more.

W: 0.05-1.0%
W is an element effective in improving the hardenability of steel. When the W content exceeds 1.0%, the effect is saturated. Therefore, the W content is set to 1.0% or less. When the above effects are obtained by containing W, the lower limit of the W content may be 0.05% or more, or 0.1% or more.

V: 0.01~0.3%
V is an element that forms a fine compound with C and N in steel and brings about a crystal grain refinement effect. When the V content exceeds 0.3%, the compound becomes coarse and grain refinement effects cannot be obtained. Therefore, the V content is set to 0.3% or less. When the above effects are obtained by containing V, the lower limit of the V content may be 0.01% or more, or 0.15% or more.

Ti: 0.005-0.3%
Ti is an element that forms fine compounds with C and N in steel and brings about the effect of refining crystal grains. When the Ti content exceeds 0.3%, the effect is saturated. Therefore, the Ti content is set to 0.3% or less. When the above effects are obtained by containing Ti, the lower limit of the Ti content may be 0.005% or more, or 0.010% or more.
On the other hand, from the viewpoint of suppressing a decrease in machinability due to an increase in hardness, the upper limit of the Ti content may be 0.25% or less, or 0.2% or less.

Nb: 0.005-0.3%
Nb is an element that forms fine compounds with C and N in steel and brings about the effect of refining crystal grains. When the Nb content exceeds 0.3%, the effect is saturated. Therefore, the Nb content is set to 0.3% or less. When the above effects are obtained by containing Nb, the lower limit of the Nb content may be 0.005% or more, or 0.010% or more.
On the other hand, from the viewpoint of suppressing a decrease in machinability due to an increase in hardness, the upper limit of the Nb content may be 0.25% or less, or 0.2% or less.

B: 0.0005-0.0050%
B has the function of suppressing grain boundary segregation of P. B also has the effect of improving grain boundary strength and intragranular strength, and the effect of improving hardenability, and these effects improve the fatigue strength of steel. When the B content exceeds 0.005%, the effect is saturated. Therefore, the content of B is set to 0.005% or less. When containing B to obtain the above-mentioned effects, the lower limit of the B content may be 0.0005% or more, or 0.0010% or more.
On the other hand, from the viewpoint of suppressing cracking by improving hardenability, the upper limit of the B content may be 0.0045% or less, or 0.0040% or less.

The chemical composition of the steel according to the present embodiment further contains one or more selected from the group consisting of Pb, Bi, Mg, Zr, Te, and rare earth elements (REM) in place of a part of Fe. You can. The lower limit when these elements are not contained is 0%.

Pb: 0.09% or less Pb is an element that has an adverse effect on the environment, so it is desirable not to contain it. On the other hand, Pb is an element that improves machinability, and has the effect of promoting fracture of the steel material during cutting, promoting breakup of chips, and improving tool life by melting at the tool contact surface. When adding Pb to improve machinability, the Pb content is set to 0.09% or less in consideration of the impact on the environment. When the above-mentioned effects are obtained by containing Pb, the lower limit of the Pb content may be set to 0.01% or more.

Bi: 0.0001~0.5%
Bi is an element that improves machinability by finely dispersing sulfides. If Bi is contained excessively, the hot workability of the steel deteriorates and hot rolling becomes difficult, so the Bi content is set to 0.5% or less. When the above effects are obtained by containing Bi, the lower limit of the Bi content may be 0.0001% or more, or may be 0.001% or more. On the other hand, from the viewpoint of suppressing deterioration of hot workability of steel, the upper limit of the Bi content may be 0.4% or less, or may be 0.3% or less.

Mg: 0.0005-0.01%
Mg is a deoxidizing element and produces oxides in steel. Furthermore, Mg-based oxides formed by Mg tend to become nuclei for crystallization and/or precipitation of MnS. Furthermore, the Mg sulfide turns into a composite sulfide of Mn and Mg, thereby making MnS spheroidal. Thus, Mg is an effective element for controlling the dispersion of MnS and improving machinability. If the Mg content exceeds 0.01%, a large amount of MgS will be generated and the machinability of the steel will deteriorate. % or less. The upper limit of the Mg content may be 0.008% or less, or 0.006% or less. The lower limit of the Mg content may be 0.0005% or more, or may be 0.001% or more.

Zr: 0.0005-0.05%
Zr is a deoxidizing element and produces oxides. Furthermore, Zr-based oxides formed by Zr tend to become nuclei for crystallization and/or precipitation of MnS. Thus, Zr is an effective element for controlling the dispersion of MnS and improving machinability. When the amount of Zr exceeds 0.05%, the effect is saturated, so when containing Zr to obtain the above-mentioned effect, the Zr content is set to 0.05% or less. The lower limit of the Zr content may be 0.0005% or more, or may be 0.001% or more.
On the other hand, from the viewpoint of suppressing deterioration of the mechanical properties of the gear, the upper limit of the Zr content may be 0.04% or less, or 0.03% or less.

Te: 0.0005~0.1%
Te improves the machinability of steel because it promotes spheroidization of MnS. When the Te content exceeds 0.1%, the effect is saturated. Therefore, the Te content is set to 0.1% or less. The upper limit of the Te content may be 0.08% or less, or may be 0.06% or less. When the above effects are obtained by containing Te, the lower limit of the Te content may be 0.0005% or more, or 0.001% or more.

Rare earth elements: 0.0005-0.005%
Rare earth elements are elements that promote the production of MnS by producing sulfides in steel, and these sulfides become precipitation nuclei of MnS, thereby improving the machinability of steel. However, when the total content of rare earth elements exceeds 0.005%, sulfides become coarse and reduce the fatigue strength of the steel. Therefore, the total content of rare earth elements is set to 0.005% or less. The upper limit of the total content of rare earth elements may be 0.004% or less, or may be 0.003% or less.
When containing rare earth elements to obtain the above effects, the lower limit of the total content of rare earth elements may be 0.0005% or more, or 0.001% or more.

The rare earth elements referred to in this specification are the 15 elements in the periodic table from lanthanum (La) with atomic number 57 to lutetium (Lu) with atomic number 71, plus yttrium (Y) and scandium (Sc). It is a general term for elements. The content of rare earth elements means the total content of one or more of these elements.

The steel according to this embodiment contains the above-mentioned alloy components, and the remainder consists of Fe and impurities. When elements other than the alloy components mentioned above are mixed into steel as impurities from raw materials or manufacturing equipment, the amount of the mixed elements does not affect the properties of the steel. Specifically, it is due to the formation of a white layer due to structural changes. It is permissible as long as it is at a level that does not impede the improvement of strength against fracture caused by.

(Method for manufacturing carburized gear steel)
The manufacturing conditions of the carburized gear steel according to this embodiment will be explained.
The method for manufacturing the carburized gear steel according to the present embodiment is not particularly limited as long as the carburized gear steel having the above chemical composition can be manufactured, but it may be manufactured as follows, for example.
First, in a refining process, molten steel having the above chemical composition is obtained and cast. At this time, secondary refining may be performed to adjust the components and improve the cleanliness of the steel. Thereafter, rod rolling or wire rod rolling is performed to obtain a desired shape. Blooming rolling may be performed before these steps. Then, in order to improve workability into a gear shape, normalizing and annealing may be performed.
Regarding the rolling method, in order to obtain a homogeneous structure without coarse grains, the heating temperature before rolling is preferably 1150° C. or higher. On the other hand, from the viewpoint of durability of the heating furnace, the heating temperature is preferably 1350° C. or lower. In addition, in order to obtain a homogeneous structure, the reduction in cross-sectional area due to rolling is 20% or less, and the average cooling rate between 800°C and 300°C during rolling is 0.1°C/second or more and 3.0°C/second or less. It is preferable to control. The structure after rolling is preferably a mixed structure of ferrite and pearlite or a mixed structure of ferrite and bainite, and the hardness after rolling is preferably 200 or less in terms of Vickers hardness.

(carburized gear)
The carburized gear steel according to the present embodiment is suitable as a material for producing carburized gears by gas carburizing and quenching, and it is particularly preferable to produce gears by gas carburizing and quenching. For example, the carburized gear steel according to this embodiment is used to form a gear shape by machining such as cutting, and then gas carburized and quenched to produce a carburized gear. Thereby, it is possible to manufacture a carburized gear that has excellent strength against destruction due to white layer formation due to structural changes.
Note that white layer formation is determined to be "present" when, for example, a white tissue with a maximum length exceeding 5 μm is observed during tissue observation, as shown within the dotted line in FIG. 1.
For example, after cutting the carburized gear steel according to this embodiment into a gear shape, it is held at 900 to 1000°C in an atmosphere with a carbon potential of 0.7 to 1.2 for 1 to 30 hours, and then heated to 50 to 140°C. Gas carburizing treatment is performed under the same conditions as oil quenching. Next, by tempering under conditions of holding at 120 to 180°C for 0.5 to 3 hours, the same chemical as that of the carburized gear steel according to this embodiment is applied at a position deeper than 3 mm from the surface (non-carburized part). It is possible to manufacture a carburized gear that has the following components and has excellent strength against destruction due to the formation of a white layer due to structural changes.
Although it varies depending on the required depth of the part, the C content in the region approximately 0.5 to 3 mm deep from the surface (carburized part) due to gas carburizing is higher than the C content in the non-carburized part, Strength can be improved. From this point of view, the C content in the carburized part is preferably 0.6 to 0.9%.

Hereinafter, the present invention will be described in more detail with reference to Examples. Note that these Examples do not limit the present invention.
Various steel ingots having the chemical components shown in Table 1 were hot forged to a diameter of 35 mm. The heating temperature before forging was 1250°C. After forging, normalization treatment was performed under conditions of holding at 950° C. for 1 hour to completely austenite, and then allowing it to cool. After normalization, a small roller test piece having a cylindrical portion with a diameter of 26 mm and a width of 28 mm was produced by machining.
Further, using a rolled material of JIS G4052 standard SCM420H with a diameter of 140 mm, a large roller test piece with a diameter of 130 mm, a width of 18.4 mm, and a crowning of R = 150 mm on the outer periphery was produced by machining.

Thereafter, the small roller was held at 930°C for 150 minutes in an atmosphere with a carbon potential of 0.8 using a batch-type converter gas carburizing furnace (model G-161618-AFHVC) manufactured by Koyo Thermo Systems Co., Ltd. After performing gas carburizing treatment under conditions of oil quenching at 130°C, tempering was performed under conditions of holding at 150°C for 2 hours.
The large roller was subjected to the same gas carburizing treatment as the small roller except that the holding time was 360 minutes, and tempering was performed under conditions of holding at 150° C. for 2 hours.
After tempering, the parts of both the small roller and large roller other than the evaluation part were finished to eliminate the influence of runout during rotation due to heat treatment distortion.
When the C content in a region 50 μm deep from the surface of each roller (carburized part) was measured, the C content in each roller was higher than that in the non-carburized part, and the C content in the carburized part was 0.65 to 0. It was 90%.

(evaluation)
-pitching-
In order to evaluate the destruction caused by the formation of a white layer due to structural changes, a roller pitting fatigue test was conducted using the large roller and small roller produced above. This test simulates the contact state of gears.
In the roller pitting fatigue test, the large roller is pressed against the small roller with a Hertzian stress of 2000 MPa, the circumferential speed direction of both rollers at the contact part is the same direction, and the slip rate is -40% (the large roller is larger than the small roller). The circumferential speed of the contact portion was 40% higher), and the number of rotations until peeling occurred in the small roller was defined as the lifespan. The temperature of the gear oil supplied to the contact portion was 80°C. Idemitsu ZEPRO ATF ECO was used as gear oil.
The occurrence of pitching was detected using a vibration meter provided, and after the vibration was detected, the rotation of both rollers was stopped and the occurrence of pitching and the number of rotations were confirmed, and the results are listed in Table 1. If no peeling occurs even after the number of rotations reaches 20 million times, it can be evaluated that the material has sufficient strength, so the test was stopped at 20 million times, and "durability" was written in Table 1. .

-White layer formation-
In addition, in order to investigate the presence or absence of white layer formation due to structural changes, the test was stopped when the roller pitching fatigue test reached 5 million times, and a circular It was cut into cross sections, polished, and subjected to 3% nital corrosion to investigate structural changes. The presence or absence of a white layer was investigated by observing the entire circumference in a range of 0.5 mm from the surface at 100x magnification using an optical microscope, and a white tissue with a maximum length exceeding 5 μm was observed during tissue observation. In this case, it was determined that white layer formation was present.

In Table 1, "-" for the content of each component means that the element is not included (not intentionally added).
As seen in Table 1, test No. of the invention example. Nos. 1 to 19 did not peel off even after 20 million cycles, and no white layer was observed, and had good strength against destruction due to the formation of a white layer due to structural changes. Comparative Example Test No. whose chemical composition range is outside the scope of the present invention. No. 20 to 29 did not provide good strength.

Claims (7)

In mass%,
C: 0.26-0.35%,
Si: 0.40-1.00%,
Mn: 0.20-0.60%,
Cr: 1.00-3.00%,
Mo: 0.01-0.50%,
S: 0.001-0.050%,
N: 0.004-0.030%,
Al: 0.001-0.150%,
Ca: 0.0001-0.0100%,
O: 0.005% or less,
Carburized gear steel consisting of P: 0.05% or less, and the balance: Fe and impurities. In mass%,
Ni: 0.1 to 1.8 %,
Cu: 0.05-0.13 %,
Co: 0.05-0.11 %,
W: 0.05-0.41 %,
V: 0.01-0.3%,
Ti: 0.005-0.3%,
Nb: 0.005-0.3%, and B: 0.0005-0.005%
The carburized gear steel according to claim 1, containing one or more elements selected from the group consisting of: In mass%,
Pb: 0.09% or less,
Bi: 0.0001-0.5%,
Mg: 0.0005-0.01%,
Zr: 0.0005 to 0.05%,
Te: 0.0005 to 0.1%, and rare earth elements: 0.0005 to 0.005%
The carburized gear steel according to claim 1 or 2, containing one or more elements selected from the group consisting of: A step of machining the carburized gear steel according to any one of claims 1 to 3 into a gear-shaped member;
a step of subjecting the gear-shaped member to gas carburizing treatment;
A method for manufacturing a carburized gear having the following. In the non-carburized part deeper than 3 mm from the surface, in mass%,
C: 0.26-0.35%,
Si: 0.40-1.00%,
Mn: 0.20-0.60%,
Cr: 1.00-3.00%,
Mo: 0.01-0.50%,
S: 0.001-0.050%,
N: 0.004-0.030%,
Al: 0.001-0.150%,
Ca: 0.0001-0.0100%,
O: 0.005% or less,
Carburized gear consisting of P: 0.05% or less, and the balance: Fe and impurities. In the non-carburized part deeper than 3 mm from the surface, in mass%,
Ni: 0.1 to 1.8 %,
Cu: 0.05-0.13 %,
Co: 0.05-0.11 %,
W: 0.05-0.41 %,
V: 0.01-0.3%,
Ti: 0.005-0.3%,
Nb: 0.005-0.3%, and B: 0.0005-0.005%
The carburized gear according to claim 5, containing one or more elements selected from the group consisting of: In the non-carburized part deeper than 3 mm from the surface, in mass%,
Pb: 0.09% or less,
Bi: 0.0001-0.5%,
Mg: 0.0005-0.01%,
Zr: 0.0005 to 0.05%,
Te: 0.0005 to 0.1%, and rare earth elements: 0.0005 to 0.005%
The carburized gear according to claim 5 or 6, containing one or more elements selected from the group consisting of: