JP2003183772A - Steel to be carburized superior in torsional fatigue characteristics - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve torsional fatigue characteristics in steel to be carburized. <P>SOLUTION: In the steel to be carburized, which has a carbon content of 0.1-0.3 mass% and contains Cr, this steel includes at least one element selected among Co, Ni, and Cu, in a range satisfying the expression (1): [Co]+2.1×[Ni]+2.8×[Cu]-2.4×[Cr]>0, (where [Co], [Ni], [Cu], or [Cr] indicates respectively Co content in the steel (mass%), Ni content (mass%), Cu content (mass%), or Cr content (mass%)). <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to carburizing steel having excellent torsional fatigue properties, which is useful for manufacturing shaft-shaped members used for automobile parts, building machine parts, industrial machine parts and the like. Is.

[0002]

2. Description of the Related Art In automobiles, construction machines, industrial machines, etc., power output has been increased. For example, in automobiles, engine output has been increasing. As these outputs increase, it is required to improve the torsional fatigue strength of the shaft-like member (shaft or the like) used for power transmission in the automobile and the like.

As the shaft-shaped member, in most cases, a member whose surface strength is increased by induction hardening is used. Induction hardening is widely used because it can be hardened with relatively simple equipment and has high productivity.
Therefore, many inventions relating to induction hardening have been made, and many inventions having high torsional fatigue strength in induction hardened steel have also been made. For example, in Japanese Patent No. 2774118, Cr and Ni are elements useful for improving the torsional fatigue strength by induction hardening, and Cr is 1.0
It is described that a high torsional fatigue strength can be obtained by containing at least wt%, Ni at 0.10 wt% or more, and Ni + 0.70Cr at 0.250 wt% or more.

However, steel for induction hardening generally has a problem in machinability because it has a large amount of C. Further, since induction hardening is a method of heating only the surface of a member by high frequency, it is difficult to quench a member having a complicated shape. Therefore, for example, when manufacturing a member having a hole or a groove, it is difficult to use induction hardening.

In the case of hardening the surface of a member having a complicated shape such as having holes and grooves, in recent years, cases where carburizing and quenching are performed have been increasing. By carburizing and quenching, the surface of a member having a complicated shape can be easily hardened. However, while various inventions have been made to improve the torsional fatigue strength with respect to induction hardening, few inventions have been found to improve the torsional fatigue strength with respect to carburization.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to improve torsional fatigue characteristics in carburizing steel.

[0007]

In order to solve the above problems, the present inventors have conducted a detailed study on torsional fatigue fracture of a carburized and quenched shaft-shaped member, and as a result, bending fatigue in a conventional carburized member has been investigated. It was discovered that the amount of carbide in the carburized layer, which was not considered important in terms of improving the properties, had an extremely large effect in terms of torsional fatigue properties. Hereinafter, this point will be described in detail with reference to FIG.

That is, as shown in FIG. 1, in the carburizing steel, the harder the carburized layer is and the more the surface hardness is improved as the Cr content is increased, resulting in improved pitting resistance and wear resistance. (See the solid line in FIG. 1). This is because Cr has the property of forming a solid solution with cementite in the steel to harden the steel. Therefore, from the viewpoint of pitting resistance and wear resistance, it can be said that the larger the amount of Cr added, the more preferable.

However, according to the study by the present inventors, unlike the induction hardened member, it was discovered that the torsional fatigue characteristics of the carburized member deteriorate as the Cr addition amount increases (see the thin broken line in FIG. 1). . As a result of further study, it was found that the torsional fatigue characteristics deteriorate as the amount of Cr carbide in the carburized layer increases, not the amount of Cr itself added. That is, Cr is an element that easily forms a carbide even if it is used alone. Normally, when the amount of addition is increased, Cr and carbon are combined with each other in the outermost surface layer of the carburized portion having a high carbon concentration to form C.
A large amount of r carbide is also generated (see the thin chain line in FIG. 1). Then, in the torsional fatigue, it is considered that the increased Cr carbide promotes the development of fatigue cracks and reduces the fatigue strength. Therefore, it has been found that the torsional fatigue strength is improved as compared with the conventional case by suppressing the amount of carbides generated (see the thick chain line in FIG. 1) even if the amount of Cr added is increased (large range in FIG. 1). (See dashed line). In summary, the inventors have found that in carburizing steels where it is desirable to increase the Cr loading, it is important to suppress the formation of Cr carbides in order to improve the torsional fatigue properties. Of.

Further, as a result of further intensive studies in order to suppress the generation amount of Cr carbide, when the addition amount of Co, Ni, or Cu increases as the addition amount of Cr increases, the carbide (particularly, grain The inventors have found that it is possible to suppress the formation of carbide that precipitates in the form of a film in the boundary) and improve the torsional fatigue strength, and completed the present invention.

That is, the carburizing steel of the present invention which has achieved the above objects and is excellent in torsional fatigue characteristics has a carbon content of 0.
1 to 0.3% by mass, in a carburizing steel containing Cr, at least one selected from Co, Ni, and Cu is contained in a range satisfying the following formula (1). I have.

[Co] + 2.1 × [Ni] + 2.8 × [Cu] −2.4 × [Cr]> 0 (1) [wherein [Co], [Ni], [Cu], Or [Cr]
Respectively indicate Co content (mass%), Ni content (mass%), Cu content (mass%), or Cr content (mass%) in the steel.] Co, Ni, Cu and Cr The preferred content of C is
o: 7 mass% or less (including 0%), Ni: 4.5 mass%
The following (including 0%), Cu: 4 mass% or less (including 0%), Cr: 0.5 to 2 mass% (however, Co,
Ni and Cu do not become 0% at the same time.) The carburizing steel further contains Mo: 0.45 mass% or less (0
%), B: 0.003 mass% or less (0% is not included), Ti: 0.1 mass% or less (0% is not included), Nb: 0.1 mass% or less (0% is Not included), A
l: 0.1% by mass or less (not including 0%) may be contained.

The carburizing steel usually has a Si: 0.
5 mass% or less (0% is not included), Mn: 2 mass% or less (0% is not included), N: 0.05 mass% or less (0% is not included), P: 0.03 mass% or less (0% is not included), S: 0.03 mass% or less (0% is not included) is contained.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The carburizing steel of the present invention has a carbon content of 0.1 to 0.3 mass% and contains Cr.
The carbon content is set to 0.1% by mass or more because the strength of the obtained member is insufficient when the carbon content is low. The carbon content is preferably 0.10 mass% or more, and more preferably 0.15 mass% or more.
Further, the upper limit of the carbon content is set to 0.3% by mass, because the carbon concentration on the surface can be increased due to carburization in the manufacturing process of the member, so machinability is maintained at the steel material stage. Therefore, it is desirable to suppress the carbon concentration. The upper limit of the carbon content is preferably 0.25% by mass.

The content of Cr is not particularly limited, but considering that it is a carburizing steel, the higher the content, the better the wear resistance and pitting resistance of the obtained member, which is desirable. The Cr content is, for example, 0.5% by mass or more, preferably 0.6% by mass or more, and more preferably 0.7% by mass or more. If the Cr content is too large, the carbides may not be sufficiently suppressed even if the Cr carbide suppression measure described below is applied, and the torsional fatigue strength of the member may be reduced.
Therefore, the Cr content is, for example, 3 mass% or less, preferably 2 mass% or less, more preferably 1.5 mass% or less,
It is particularly desirable to suppress the content to 1.2% by mass or less.

In the present invention, elements such as Co, Ni and Cu are also added to the carburizing steel containing Cr as described above. The higher the Cr content, the more Cr
In spite of the fact that a large amount of carbide is easily generated and the torsional fatigue strength is easily reduced, in the present invention, the addition amount of elements such as Co, Ni, Cu is increased according to the addition amount of Cr. , Cr carbides can be suppressed and the torsional fatigue strength can be prevented from decreasing. Co, Ni, Cu, etc. are elements that suppress the formation of carbides, and addition of these elements can also suppress the formation of Cr carbides. C
The addition amounts of o, Ni, and Cu can be appropriately determined according to the carbide suppressing ability of these elements and the addition amount of Cr.
It is added in a range that satisfies the following formula (1), preferably the following formula (2), and more preferably the following formula (3).

[Co] + 2.1 × [Ni] + 2.8 × [Cu] −2.4 × [Cr]> 0 (1) [Co] + 2.1 × [Ni] + 2.8 × [Cu ] -2.4 * [Cr]> 1 ... (2) [Co] + 2.1 * [Ni] + 2.8 * [Cu] -2.4 * [Cr]> 2 ... (3) [In Formula, [Co], [Ni], [Cu], or [Cr]
Respectively represent Co content (mass%), Ni content (mass%), Cu content (mass%), or Cr content (mass%) in the steel.] The above formulas (1) to (3) The larger the value on the left side of (), the more the amount of Cr carbide in the carburized layer after carburization can be suppressed, and the torsional fatigue strength of the carburized member can be increased.
The above Co, Ni, and Cu may be added alone, and 2
You may add in combination of 1 or more types.

As long as the above equations (1) to (3) are satisfied, C
Although the addition amount of o is not particularly limited, for example, 7 mass% or less (including 0%), preferably 6 mass% or less, more preferably 5 mass% or less, and particularly 3 mass% or less (eg,
It is desirable to suppress it to 1.5 mass% or less). Even if Co is added too much, the effect is saturated as compared with the addition amount, and further, since it is an expensive element, the manufacturing cost is improved.

Further, the addition amount of Ni also depends on the above formulas (1) to (3).
It is not particularly limited as long as it satisfies, but for example, 4.5 mass% or less (including 0%), preferably 3.5 mass% or less,
More preferably 2.5 mass% or less, especially 1.7 mass%
It is desirable to suppress it to the following. If Ni is added too much, the effect will be saturated compared to the amount added.

The addition amount of Cu is not particularly limited as long as it satisfies the above formulas (1) to (3), but is, for example, 4% by mass or less,
It is desirable to suppress the content to 3% by mass or less, more preferably 2% by mass or less, and especially 1.5% by mass or less. C
If u is added too much, the effect will be saturated as compared with the amount added, and further the rescrewability of the product will decrease.

The carburizing steel is usually Si: 0.5% by mass or less (not including 0%), Mn: 2% by mass or less (0%).
Is not included), and N: 0.05 mass% or less (0% is not included), and P: 0.03 mass% or less (0
%), S: 0.03 mass% or less (not including 0%), and the balance may be Fe and inevitable impurities, and various additions may be made as necessary. You may contain the component. The reasons for limiting the above components will be described below.

Si: 0.5% by mass or less (not including 0%
It is desirable that Si is not contained more than necessary because Si may cause the formation of a grain boundary oxide layer and may reduce fatigue strength.
The Si content is, for example, 0.5% by mass or less, preferably 0.35% by mass or less, and more preferably 0.15% by mass or less. Since Si is useful as a deoxidizing element, it may be added positively. When positively added, the Si content is, for example, 0.05% by mass or more,
It is preferably about 0.10 mass% or more.

Mn: 2% by mass or less (not including 0%) If the Mn content is too large, it may lead to defects or center segregation depending on the steelmaking conditions, and may deteriorate the quality of the steel material. It is desirable not to include it in. Therefore Mn
Content of, for example, 2% by mass or less, preferably 1.5
It is at most mass%, more preferably at most 1.2 mass%. Note that Mn is useful for deoxidizing steel materials, and is an element for improving hardenability, so it is effective for increasing the depth of the carburized layer and may be added positively. When positively added, the Mn content is, for example, 0.5% by mass or more,
Preferably 0.6% by mass or more, more preferably 0.8
It is at least mass%.

N: 0.05% by mass or less (not including 0%
B) When N is excessive, nonmetallic inclusions are formed and the toughness decreases. Therefore, the content of N is, for example, 0.05% by mass.
The content is preferably 0.03% by mass or less, more preferably 0.02% by mass or less. When the steel contains Al or Ti, if N is present, it has the effect of preventing the coarsening of crystal grains by increasing AlN or TiN and enhancing the pitting resistance. In this case, the content of N is
For example, 0.005 mass% or more, preferably 0.01 mass% or more, and more preferably 0.015 mass% or more.

P: 0.03% by mass or less (not including 0%
B) P segregates at the grain boundaries and deteriorates the fatigue strength of the steel material, so it is desirable to suppress it as much as possible. For example, the P content is
0.03 mass% or less, preferably 0.02 mass% or less,
More preferably, it is desirable to suppress it to 0.015 mass% or less.

S: 0.03% by mass or less (not including 0%
S ) S combines with Mn in steel to form MnS inclusions, which may cause a decrease in fatigue strength depending on the shape of the part.
It is desirable to suppress it as much as possible. For example, the S content is 0.03 mass% or less, preferably 0.025 mass%
Hereafter, it is desirable to suppress the content to 0.02 mass% or less.

The carburizing steel further comprises Mo: 0.45.
It is desirable to contain at least one selected from mass% or less (not including 0%) and B: 0.003 mass% or less (not including 0%).

Mo is useful for improving the hardenability of the carburized layer, and can reduce the abnormal carburized layer to improve the fatigue strength. The content of Mo is, for example, 0.1% by mass or more, preferably 0.2% by mass or more, and more preferably 0.25% by mass or more. On the other hand, when Mo is excessively added, the cost is increased, and further, the hardness of the rolled material is increased and the machinability and workability are deteriorated. Therefore, the content of Mo is, for example, 0.45 mass% or less, preferably 0.4
The content is set to not more than mass%, more preferably not more than 0.3 mass%.

B is also useful for improving the hardenability of the carburized layer. The content of B is, for example, 0.0005 mass% or more, preferably 0.001 mass% or more. On the other hand, B
Even if a large amount of is added, the effect of improving the hardenability is saturated and only the cost is increased. Therefore, the content of B is, for example,
The content is 0.003 mass% or less, preferably 0.002 mass% or less, and more preferably 0.0015 mass% or less.

The carburizing steel of the present invention further comprises Ti: 0.
1% by mass or less (not including 0%), Nb: 0.1% by mass
It is desirable to contain at least one selected from the following (excluding 0%) and Al: 0.1 mass% or less (excluding 0%). Ti is useful for fixing N in steel and refining γ grains. Nb forms fine carbide and is useful for refining γ grains. Al, like Ti, fixes N and is useful for refining γ grains. The preferable addition amounts of these components are as follows.

Ti: preferably 0.01 mass% or more (more preferably 0.02 mass% or more), 0.1 mass% or less (more preferably 0.05 mass% or less) Nb: preferably 0.01 mass% % Or more (more preferably 0.02 mass% or more), 0.1 mass% or less (more preferably 0.05 mass% or less) Al: preferably 0.01 mass% or more (more preferably 0.02 mass%) Above, 0.1 mass% or less (more preferably 0.05 mass% or less) The shape of the carburizing steel is not particularly limited, but in consideration of processing into a shaft-shaped member, it is linear or rod-shaped. Is desirable.

The carburizing steel is subjected to various conventional treatments such as rolling, wire drawing, forging, heat treatment and cutting, if necessary, and then carburized to form a carburizing member (axial member).
Can be processed into

The carburizing conditions are not particularly limited, and the carburizing may be performed under general conditions. The carburizing temperature is, for example, 750 to 110.
It can be appropriately selected from the range of about 0 ° C, preferably about 800 to 1000 ° C, and more preferably about 850 to 950 ° C. The carbon potential during carburization (equilibrium carbon concentration in the atmosphere) is about 0.5 to 1.6% by mass, preferably about 0.6 to 1.4% by mass, and more preferably 0.7 to
It can be appropriately selected from the range of about 1.0% by mass. In the present invention, even if carburized under such general-purpose conditions, since the steel contains a predetermined amount of Co, Ni, and / or Cu according to the amount of Cr added, the production amount of Cr carbide is suppressed. Therefore, the torsional fatigue strength of the carburized member is enhanced.

The carburizing conditions are conditions under which the formation of carbides can be suppressed as long as the hardness of the surface of the member can be maintained at a predetermined hardness or higher by carburizing, that is, the carbon concentration in the carburized portion can be maintained at a predetermined or higher concentration. You may go in. For example, the carbon potential of the carburizing atmosphere may be suppressed to about 0.5 to 0.8% by mass, preferably about 0.5 to 0.7% by mass.

The carbon concentration on the surface of the carburized portion of the carburized member obtained by the present invention is, for example, about 0.6 to 1.2% by mass, preferably about 0.7 to 1.0% by mass, and more preferably 0.1. It is about 8 to 0.9 mass%.

Since the carburized member is excellent in torsional fatigue strength, for example, a shaft member, preferably a shaft used for transmitting power in automobile parts, building machine parts, industrial machine parts, etc. It is extremely useful as a strip-shaped member.

The torsional fatigue strength of the carburized member is determined, for example, by cutting out a dumbbell-shaped test piece shown in FIG. 2 and applying a load torque of 70 to 120 kgf · m at a repetition rate of 5 Hz.
It can be evaluated by obtaining the stress (100,000 times fatigue strength) that can withstand the fatigue test of 100,000 times by performing the one-sided drop test. The torsional fatigue strength (100,000 times fatigue strength) of the carburized member obtained in the present invention is, for example, 680 MPa or more (preferably 700 MPa or more, more preferably 7 MPa).
20 MPa or more, particularly 740 MPa or more), and usually 1000 MPa or less.

Further, according to the present invention, the Cr content can be increased while maintaining high torsional fatigue strength. Therefore, when a high Cr steel material is used, the pitting resistance of the shaft-shaped member can be improved. This pitting resistance can be specifically measured by the two-roller test method shown in the following 1) to 4).

1) A cylindrical test piece (however, a semi-cylindrical protrusion having a radius of 12 mm is provided so as to make one turn in the circumferential direction on the side wall portion of the cylindrical test piece by the same method as the method for manufacturing the shaft-shaped member. The diameter of the test piece including the above-mentioned protruding portion = 70 cm was manufactured, and the other cylindrical member (however, height 12 mm, width 1) was manufactured.
A rectangular parallelepiped projection of 0 mm is provided so as to make one round in the circumferential direction on the side wall of the cylindrical test piece. The diameter of the test piece including the protrusion is 70 cm. (Made of JIS SUJ2 steel)
, And juxtaposed in parallel so that the protrusions contact each other.

2) The cylindrical test piece and the counterpart cylindrical member are pressed with a surface pressure of 5000 MPa, and a gear oil for an automatic transmission is applied to the sliding portion (contact portion) at a flow rate of 2 L.
Number of revolutions of cylindrical test piece is 1910 while supplying at 10 / min.
Rotate at rpm to rotate the partner's cylindrical member at 1364
Rotate at rpm (sliding speed; 2.0 m / s).

3) The number of rotations of the cylindrical test piece before the occurrence of abnormal vibration due to pitching on the sliding surface is measured.

4) Using a plurality of cylindrical test pieces, the above 1)
~ 3) is performed, and the number of rotations at which abnormal vibration occurs in 10% of the test pieces is determined (L10 life).

According to the present invention, the L10 life obtained by the above test can be, for example, 5 × 10 ⁷ times or more, preferably 7 × 10 ⁷ times or more, and more preferably 9 × 10 ⁷ times or more. .

[0044]

The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to the following examples, and may be appropriately applied within the scope of the above and the following points. It is of course possible to make changes and implement them, and all of them are included in the technical scope of the present invention.

Experimental Examples 1 to 23 In a vacuum induction melting furnace (VIF furnace), 1 steel containing the chemical composition shown in Table 1 (the balance being Fe and inevitable impurities) was used.
After 50 kg was melted and made into a round steel bar having a diameter of 50 mm by hot forging, solution treatment (1300 ° C. × 1 hour) and heat leveling treatment (900 ° C. × 2 hours) were performed. This round bar steel was cut and cut into a test piece shape (dumbbell shape) shown in FIG.

The dumbbell-shaped steel material was subjected to the first step (temperature 900 ° C., 150 minutes, carbon potential: 0.9).
5% by mass), a second step (temperature 840 ° C., 30 minutes, carbon potential: 0.85% by mass), and a third step (water cooling) for carburizing and quenching, and then temperature 180 ° C. ×
Tempered under conditions of 2 hours, 0.1 mm (±
The surface was polished to a depth of 0.025 mm.

The obtained dumbbell-shaped carburized member was set in a torsion fatigue tester, and a load torque of 70 to 120 kgf.
In the range of m, a one-way test with a repetition rate of 5 Hz
Stress to withstand 100,000 fatigue tests (100,000 fatigue strength)
I asked.

Further, similarly to the dumbbell-shaped carburizing member, a cylindrical carburizing member (provided that a semicylindrical protrusion having a radius of 12 mm is provided so as to make one round in the circumferential direction on the side wall of the cylindrical test piece. Diameter of the test piece including the protrusion = 7
0 cm) was produced. Using this cylindrical carburized member, the above-mentioned pitching resistance test (two-roller type test) was performed to measure the pitching resistance (L10 life).

The results are shown in Table 2 and FIGS. 3 and 4. In addition, in FIG. 3, a circle indicates [Co] + 2.1 × [Ni] + 2.8 ×.
Corresponding to the experimental result of [Cu] -2.4 [Cr]> 0, the x mark indicates [Co] + 2.1 × [Ni] + 2.8 × [C
u] −2.4 [Cr] ≦ 0.

[0050]

[Table 1]

[0051]

[Table 2]

As is clear from Table 2 and FIG. 3, [C
o] + 2.1 × [Ni] + 2.8 × [Cu] -2.4
When [Cr] ≦ 0 (Co, N relative to the amount of Cr added)
When the amount of i or Cu added is insufficient; × in FIG.
Mark), the torsional fatigue strength rapidly decreases as the amount of Cr added increases. On the other hand, [Co] + 2.1 ×
In the case of [Ni] + 2.8 × [Cu] -2.4 [Cr]> 0 (circle mark in FIG. 3), the decrease in torsional fatigue strength is suppressed even if the Cr addition amount increases.

As is clear from FIG. 4, the pitting resistance also improves as the Cr content increases. Therefore, the Cr content is divided into about 0.5 mass% or more, and in the test piece excellent in pitting resistance, the formula [Co] +2.
The relationship between 1 × [Ni] + 2.8 × [Cu] -2.4 [Cr] and the torsional fatigue strength was arranged. Results are shown in FIG.
As is clear from FIG. 5, the Cr content is 0.5% by mass or more, and [Co] + 2.1 × [Ni] + 2.8 × [C
If u] -2.4 [Cr]> 0, both pitting resistance and torsional fatigue strength can be achieved.

In Experimental Example 14, although the fatigue strength is excellent at 100,000 cycles, the C content is low, and therefore the Experimental Example having a large amount of other C content is superior in terms of strength (static strength). There is. In Experimental Example 15, although the fatigue strength is excellent at 100,000 cycles, since the C content is high, the Experimental Example in which the other C content is small is superior in terms of machinability.

[0055]

According to the steel of the present invention, as the amount of Cr added increases, the amount of Co, Ni, Cu, etc. also increases. Therefore, the amount of Cr carbide formed in the carburized layer during the carburizing treatment is increased. Can be suppressed, and the torsional fatigue strength of the carburized member can be improved.

[Brief description of drawings]

FIG. 1 is a graph conceptually showing the relationship between Cr content and steel material characteristics.

FIG. 2 is a schematic view of a test piece used in a torsion fatigue test.

FIG. 3 is a graph showing the relationship between the Cr content and the torsional fatigue strength (MPa) of the steel materials tested in the examples.

FIG. 4 is a graph showing the relationship between Cr content and roller pitting life for the steel materials tested in the examples.

FIG. 5 is a calculation formula [Co] + 2.1 × [Ni] +
It is a graph which shows the relationship between the value of 2.8 [Cu] -2.4 [Cr], and torsional fatigue strength.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroshi Ieguchi             1-5-5 Takatsukadai, Nishi-ku, Kobe City Stock Association             Company Kobe Steel Works, Kobe Research Institute (72) Inventor Masao Kuchibuchi             1-5-5 Takatsukadai, Nishi-ku, Kobe City Stock Association             Company Kobe Steel Works, Kobe Research Institute

Claims (6)

[Claims] 1. In a carburizing steel having a carbon content of 0.1 to 0.3 mass% and containing Cr, at least one selected from Co, Ni, and Cu satisfies the following formula (1). A steel for carburizing which is excellent in torsional fatigue characteristics and is contained in a range. [Co] + 2.1 × [Ni] + 2.8 × [Cu] -2.4 × [Cr]> 0 (1) [wherein [Co], [Ni], [Cu], or [Cr] ]
Indicates the Co content (mass%), Ni content (mass%), Cu content (mass%), or Cr content (mass%) in the steel, respectively.] 2. The carburizing steel according to claim 1, wherein the content of Cr is 0.5 to 2 mass%. 3. The content of Co is 7 mass% or less (0%
, And the Ni content is 4.5% by mass or less (0%
, And the Cu content is 4 mass% or less (0%
(Including Co, Ni, Cu at 0% at the same time)
The carburizing steel according to claim 1 or 2, wherein 4. Further, Mo: 0.45 mass% or less (0
%) And B: 0.003 mass% or less (0%
The steel for carburizing according to any one of claims 1 to 3, containing at least one selected from 5. Further, Ti: 0.1% by mass or less (not including 0%), Nb: 0.1% by mass or less (not including 0%), and Al: 0.1% by mass or less (0%). Not included)
5. Containing at least one selected from
The steel for carburizing according to any one of 1. 6. Si: 0.5% by mass or less (not including 0%), Mn: 2% by mass or less (not including 0%),
And N: 0.05% by mass or less (0% is not included), P: 0.03% by mass or less (0% is not included), S:
The carburizing steel according to claim 1, wherein the content is controlled to 0.03 mass% or less (not including 0%), and the balance is Fe and inevitable impurities.