JP2002339054A - High surface pressure resistant member and method of manufacturing the same - Google Patents

Abstract

(57) [Summary] [PROBLEMS] Even when a carburizing treatment or a carbonitriding treatment with a modified gas is performed, residual hydrogen in a member can be reduced, and bending fatigue strength and rolling fatigue due to delayed fracture or hydrogen embrittlement. A high surface pressure resistant member capable of preventing a decrease in strength, and a method for manufacturing such a high surface pressure resistant member are provided. SOLUTION: After enriching the surface C content to 0.6 to 1.5% by gas carburizing or gas carbonitriding, hydrogen is reduced by maintaining the temperature below the Ac1 transformation temperature under reduced pressure, After heating and holding at a temperature not lower than the Ac1 transformation temperature, quenching is performed by rapid cooling.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a member applied as a power transmission component requiring high surface fatigue strength, such as a gear or a rolling element of a bearing, and in particular, to an environment (from 100 to 100 degrees to high temperatures). The present invention relates to a high surface pressure resistant member suitable for use under a high surface pressure at about 300 ° C.) and a method for producing such a high surface pressure resistant member.

[0002]

As a method for increasing the surface fatigue resistance of the power transmission member as described above, for example, carbides which are hardly decomposed even at a high temperature to a high temperature,
For example, there are a hypereutectoid carburizing method and a high-concentration carburizing method in which Fe ₃ C (cementite) is positively precipitated to increase the hardness to improve the tempering softening resistance. In addition, Japanese Patent Application No. 1
JP-A-206552 proposes a member in which M ₂₃ C ₆ type carbide is precipitated, which has a higher surface fatigue strength than steel in which cementite is precipitated.

[0003] As a carburizing method for producing such a member, an atmospheric heat treatment method (gas carburizing method) using a modified gas made of C ₃ H ₈ (propane) gas or the like is widely used.

However, in the gas carburizing method, H
₂ (Hydrogen) is generated and penetrates into the member during processing. Such hydrogen can be considerably reduced by tempering after carburization, but if not sufficiently reduced, delayed fracture may occur or bending fatigue strength or toughness may be reduced. . In particular, recently, it has been known that in rolling parts subjected to a high surface pressure, there is a concern that the rolling fatigue life is greatly reduced due to the presence of hydrogen, and that the above-mentioned carbides can easily adsorb hydrogen. Since it is known, it is necessary to reduce hydrogen in a carburizing member using a modified gas.

[0005] In order to reduce such residual hydrogen, there is a method called baking in which the member is kept at a temperature lower than the tempering temperature for several tens of hours. However, since a long-time treatment is required, the production efficiency is reduced. This is a cost increase factor. If the holding temperature is raised, the time can be shortened, but if the temperature is too high, the member may be softened. On the other hand, as a carburizing method in which the penetration of hydrogen during the carburizing process is extremely small, there is, for example, a vacuum carburizing method described in Japanese Patent Application Laid-Open No. H11-117059.
Coarse carbides are easily formed at austenite grain boundaries,
There is a problem that the rolling fatigue strength and the bending fatigue strength may be reduced, and solving such a problem has been a problem in the conventional power transmission member.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems in a conventional power transmission member in which the surface fatigue resistance has been enhanced by carburization. However, a high surface pressure resistant member capable of reducing residual hydrogen in the member and preventing a decrease in bending fatigue strength and rolling fatigue strength due to delayed fracture or hydrogen embrittlement, It is an object of the present invention to provide a method for manufacturing a pressure member.

[0007]

According to a first aspect of the present invention, there is provided a high surface pressure resistant member having a surface carbon content of 0.6 to 1.5% by gas carburizing or gas carbonitriding, and a temperature of 100 ° C. The total amount of hydrogen released by heating from to
Characterized in that the composition is 2 ppm or less,
The high surface pressure resistant member according to claim 3 is Cr: 1.2 to 3.
2%, Mo: 0.25 to 2.0%, and the surface C content by gas carburizing or gas carbonitriding is 0.6.
~ 1.5% of mechanical structural steel, at least C
M ₂₃ C ₆ type carbide having an average particle diameter of 0.3 μm or less containing r is dispersed in the matrix, and the total amount of hydrogen released by heating from 100 ° C. to 900 ° C. is 0.2 ppm or less. It is characterized in that such a configuration in the high surface pressure resistant member is a means for solving the above-mentioned conventional problems.

In the method for manufacturing a high surface pressure resistant member according to claim 2 of the present invention, the surface C amount is set to 0.6 to 1.5.
% After the gas-carburizing or gas-carbonitriding treatment enriched in%, the temperature is kept at a temperature lower than the Ac1 transformation temperature under reduced pressure, and the heating is continued at a temperature higher than the Ac1 transformation temperature, followed by rapid cooling. In the method for manufacturing a high surface pressure resistant member according to the above, Cr: 1.2 to 3.2%, Mo: 0.
A steel for machine structural use containing 25 to 2.0% is subjected to a gas carburizing or gas carbonitriding treatment for enriching the surface C content to 0.6 to 1.5%, and then 500 to 650 ° C under reduced pressure. Heating at a rate of 0.2 to 30 ° C./min in a temperature range of to raise the temperature to a temperature of 600 to 750 ° C.
After continuously maintaining the temperature at that temperature under reduced pressure,
Above the Ac1 transformation temperature and T (° C.) = 675 + 120 ·
Si (%)-27 · Ni (%) + 30 · Cr (%) + 2
It is configured to be heated and held at a temperature of 15 * Mo (%)-400 * V (%) or less and quenched, and to solve such a problem in the method for manufacturing a high surface pressure resistant member. It is characterized by the means.

[0009]

According to the high surface pressure resistant member according to the first aspect of the present invention, gas carburizing or gas carbonitriding is relatively inexpensive and has good controllability of carburizing concentration.
Since the surface C content is enriched to 0.6 to 1.5%, the production cost is reduced, coarse carbides are hardly generated, and high hardness is obtained, and excellent surface even under high surface pressure. It indicates fatigue strength. Also, the member is
Since the total amount of hydrogen released upon heating from 0 ° C. to 900 ° C. is 0.2 ppm or less, hydrogen embrittlement, which is a concern with high-hardness materials, is prevented.

The method for producing a high surface pressure resistant member according to a second aspect of the present invention is suitable for producing the above high surface pressure resistant member, and the surface C is formed by gas carburizing or gas carbonitriding.
After enriching the amount to 0.6-1.5%, the A
After the temperature is kept at or below the c1 transformation temperature and subsequently heated and kept at or above the Ac1 transformation temperature, it is rapidly cooled. That is, prior to the quenching step of quenching from a temperature higher than the Ac1 transformation temperature to obtain a tough martensite or bainite structure, a holding step of reducing hydrogen is performed. Even at high temperatures, the hardness is not reduced, and the hydrogen reduction processing is performed efficiently.

Further, since the holding temperature in the step of reducing hydrogen is equal to or lower than the Ac1 transformation temperature, there is no fear of coarsening of austenite crystal grains and generation of coarse carbides due to growth of only carbides at crystal grain boundaries. Surface fatigue strength.

In the high surface pressure resistant member according to claim 3 of the present invention, the surface carbon content is similarly increased to 0.6 to 1.5% by gas carburizing or gas carbonitriding, and the total hydrogen content is also increased. In addition to the amount being 0.2 ppm or less, Cr: 1.2 to 3.2%, Mo: 0.25 to 2.0
%, Containing at least Cr and having an average particle diameter of 0.3 μm
The following of the _M 23 _{C 6} type carbide are dispersed in the base. That is, by containing Cr and Mo, M ₂₃ C
Type ₆ carbides are easily precipitated, and excellent rolling fatigue strength is ensured even from a quasi-high temperature to a high temperature. Incidentally, M ₂₃ C ₆ type carbide is easily finely dispersed than other carbides, it is effective to rolling fatigue strength improvement.

[0013] In addition, since the hydrogen concentration is 0.2 ppm or less, it is excellent against hydrogen embrittlement which is concerned because hydrogen is adsorbed on M ₂₃ C ₆ type carbide.

According to a fourth aspect of the present invention, there is provided a method for manufacturing a high surface pressure resistant member, which is suitable for manufacturing the high surface pressure resistant member, wherein Cr: 1.2 to 3.2%, Mo: 0.25-2.
0% to the steel for machine structural use, the surface C content is 0.6 ~
Since the member subjected to the gas carburizing or gas carbonitriding treatment enriched to 1.5% is kept at a constant temperature of 600 to 750 ° C. under reduced pressure, hydrogen is reduced and M ₂₃ C ₆ during this time. The type carbide is uniformly deposited. Further, when the temperature is raised to the constant temperature holding temperature, M
_Since the temperature range of 500 to 650 ° C. where nuclei of ₂₃ C ₆ type carbides are generated is heated at a heating rate of 0.2 to 15 ° C./min, the number of nuclei of M ₂₃ C ₆ type carbides is larger. since the generated, so that the M ₂₃ C ₆ type carbide is more dense and uniform deposition.

Then, following the constant temperature holding at 600 to 750 ° C., T (° C.) = 675+
120 ・ Si (%)-27 ・ Ni (%) + 30 ・ Cr
(%) + 215 · Mo (%)-400 · V (%) or less and then rapidly cooled, whereby the uniformly precipitated M ₂₃ C _6- type carbide is divided without excessive solid solution. In addition to miniaturization, the matrix becomes a martensite or bainite structure, and the rolling fatigue strength is greatly improved.

The reasons for limiting various numerical values in the present invention will be described below. In addition, in this invention, each component content means a mass percentage.

Surface C concentration: 0.6 to 1.5% If the C concentration is less than 0.6%, the hardness of the member surface cannot be ensured. On the other hand, when the content exceeds 1.5%, carbides of the M ₃ C type are likely to coarsely precipitate particularly at the austenite crystal grain boundaries, and it becomes difficult to obtain excellent surface fatigue strength.

[0018] Total hydrogen content: 0.2 ppm or less When the hydrogen content exceeds 0.2 ppm, especially in steel having a high C concentration and hardness, the rolling fatigue life may be reduced due to hydrogen embrittlement.

Constant temperature holding treatment (hydrogen reduction step): If the holding temperature in the step of reducing the held hydrogen under the reduced pressure to a temperature not higher than the Ac1 transformation temperature is not less than the Ac1 transformation temperature, coarse carbides are likely to precipitate at the austenite crystal grain boundaries. Is not preferred. In addition, the reduced pressure is because hydrogen can be efficiently removed and decarburization can be prevented.

Quenching treatment: rapid cooling from the Ac1 transformation temperature or higher If the quenching temperature is lower than the Ac1 transformation temperature, the matrix cannot have a martensite or bainite structure after rapid cooling, and sufficient hardness cannot be obtained.

[0021] Cr: 1.2~3.2% Cr _is an element that forms the _M 23 _{C 6} type carbide, although desirable addition of not less than 1.2%, when too large a cost increase and cuttability Therefore, it is desirable that the content is not more than 3.2%.

Mo: 0.25 to 2.0% Mo is also an element forming M ₂₃ C ₆ type carbide,
Addition of 0.25% or more is desirable, but too much increases the cost and machinability as well, so it is preferably 2.0% or less.

Average particle size of M ₂₃ C ₆ type carbide: 0.3 μm
When the average particle size exceeds 0.3 μm, it takes a long time to obtain a uniform structure, resulting in an increase in cost. When the average particle size is too large, the rolling fatigue life tends to decrease.

Constant temperature: 600 to 750 ° C. If the temperature is lower than 600 ° C., the diffusion rate of C is low, and the growth of M ₂₃ C ₆ type carbide is remarkably slowed.
If the temperature exceeds 750 ° C., C is consumed for forming the M ₂₃ C ⁶ type carbide, so that the M ₂₃ C ₆ type carbide may not grow and the hardness may not be secured.

Rate of temperature rise to constant temperature: 0.2 to 30
If the temperature is lower than 0.2 ° C./min, the processing time becomes extremely long and the cost is increased.
_This is because nuclei of ₂₃ C ₆ type carbide are not sufficiently precipitated, and it is difficult to precipitate carbide uniformly and finely.

Hardening temperature: above the Ac1 transformation temperature, T
(° C) = 675 + 120 · Si (%) − 27 · Ni
(%) + 30 · Cr (%) + 215 · Mo (%) − 40
0 · V (%) or less If the temperature is lower than the Ac1 transformation temperature, the matrix cannot be made martensite or bainite after quenching, and T (° C.)
If the temperature is maintained at a higher temperature, the M ₂₃ C ₆ type carbide will form a solid solution.

[0027]

EXAMPLES The present invention will be specifically described below with reference to examples.

The four steel types A to D shown in Table 1 were used.
After normalizing this, a gas carburizing treatment shown in FIG. 1 was performed. The C concentration after carburizing was adjusted by the carburizing gas composition at the time of carburizing. Thereafter, heat treatment was performed in a reduced pressure atmosphere of 100 Pa under any of the conditions shown in FIG. 2 and Table 2. However, the heat treatment symbols d and e, which are part of the comparative example, were maintained at 300 ° C. and 120 ° C. for 5 hours after tempering without maintaining a constant temperature in a reduced pressure atmosphere.

[0029]

[Table 1]

[0030]

[Table 2]

The test pieces thus obtained were measured for surface hardness, surface C content, precipitated carbides and hydrogen content on cut pieces. The surface hardness was measured using a Vickers hardness meter, and the surface C amount was measured by emission spectroscopy. The structure of the precipitated carbide was identified from an electron beam diffraction image by a replica method, and the average particle size and area ratio were determined by image analysis of a structure photograph by a scanning electron microscope. Hydrogen content is from 100 ° C to 9
The total amount of hydrogen was determined from a hydrogen release curve upon heating to 00 ° C. Separately, the surface of the test piece was polished to obtain a thrust test piece shown in FIG. 3, and then a thrust rolling fatigue test was carried out under the following conditions, and a 50% (L50) failure probability of Weibull was determined as the life until peeling. Was. Some of the test pieces (sample symbols 13 to 15) were charged with hydrogen, and the influence on the rolling life was examined.

<Thrust rolling test conditions> Oil used: Nissan Traction Fluid KTF-1 Oil temperature: 150 ° C Ball used: JIS SUJ2 (3/8 inch diameter) Number of balls: 3 Balls Load: 10 kg (surface pressure 5.2 GPa) ) Rotational speed: 2000rpm

The test results are summarized in Table 3.

[0034]

[Table 3]

No hydrogen was detected in the samples 1 to 6 of the examples of the present invention, and it was confirmed that the rolling life was the best. On the other hand, in Sample 7, since the surface C concentration was too high, M ₃ C-type carbides precipitated at the crystal grain boundaries, and the rolling life was shortened. Conversely, in Sample 8, the C concentration was too low to obtain a sufficient hardness, resulting in a short rolling life. Sample 5 whose holding temperature is higher than the Ac1 transformation temperature
In Example 1, M ₂₃ C ₆ type carbide is not precipitated, and M ₃ C type carbide at the crystal grain boundary grows during holding, and the rolling life is reduced in Example 1.
Since it is lower than パ ワ ー 4, it is suitable for low power automotive applications. Further, due to insufficient nucleation heating rate fast sample 6, M ₂₃ C ₆ type carbide, there is uneven precipitation of carbides as compared to Examples 1 to 4, there is a tendency that rolling life is reduced power Suitable for low-emission vehicles. Further, since the sample 9 was not subjected to the constant temperature holding treatment, the M ₂₃ C ₆ type carbide was not precipitated, and the hardness was reduced, and the rolling life was reduced. Similarly, samples 10 to 12 which have not been subjected to the constant temperature holding process and have a low heating temperature after tempering
In this case, since the M ₂₃ C ₆ type carbide was not precipitated and the amount of hydrogen was not sufficiently reduced, the rolling life was short.

Samples 13 to 15 in which hydrogen was charged into a test piece obtained under the same conditions as Sample 1 as an example of the present invention, confirmed that the rolling life decreased as the amount of hydrogen increased. Was done.

[0037]

As described above, according to the present invention,
For high surface pressure members, use gas carburizing or gas carbonitriding.
The surface C content is 0.6 to 1.5% and the temperature is from 100 ° C.
The total amount of hydrogen released by heating up to 900 ° C is 0.2
ppm or less, the equipment cost is low,
Gas carburizing or gas carbonitriding with easy control of coal concentration
Have the advantage of a stable component and are adversely affected by hydrogen
Low cost, excellent in surface fatigue strength and rolling fatigue life
It will be. At this time, a predetermined amount of Cr and Mo is included.
Average grain size is 0.3μm or less by using raw steel
Fine M₂₃C ₆Type carbide is uniformly dispersed and deposited on the base
To improve rolling fatigue strength more reliably
The effect is excellent.

Further, in the method for manufacturing a high surface pressure resistant member according to the present invention, after enriching the surface C amount to 0.6 to 1.5% by gas carburizing or gas carbonitriding, Ac1 is reduced under reduced pressure. The temperature is maintained at a temperature lower than the transformation temperature, subsequently heated and maintained at a temperature higher than the Ac1 transformation temperature, and then quenched. That is, since the hydrogen reduction treatment is performed under reduced pressure prior to quenching, the treatment can be performed at a higher temperature, and hydrogen can be reduced with high efficiency without lowering the hardness of the member. An extremely excellent effect is obtained in that embrittlement can be prevented and a high surface pressure resistant member excellent in surface fatigue strength and rolling fatigue life can be obtained at low cost. At this time, Cr: 1.2 to 3.2%, M
o: A steel for machine structural use containing 0.25 to 2.0% is subjected to gas carburizing or gas carbonitriding treatment, and is subjected to 600 to 750 ° C.
When the temperature is raised to a constant temperature of 500 to 650 ° C.
Is heated at a heating rate of 0.2 to 30 ° C./min, and thereafter, is at or above the Ac1 transformation temperature, and T (° C.) (= 67
5 + 120 ・ Si (%)-27 ・ Ni (%) + 30 ・ C
r (%) + 215 · Mo (%) - 400 · V (%)) was held below, because as quenching, be evenly uniformly distributed precipitating fine _M 23 _{C 6} type carbide Thus, an extremely excellent effect that a high-surface-pressure-resistant member having even better surface fatigue strength and rolling fatigue life can be obtained without causing hydrogen embrittlement can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a gas carburizing step and processing conditions in an example of the present invention.

FIG. 2 is a diagram showing hydrogen reduction processing steps and processing conditions in an example of the present invention.

FIG. 3 is a diagram showing a shape of a thrust test piece used for evaluating rolling contact fatigue life in an example of the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C23C 8/32 C23C 8/32 (72) Inventor Toshimitsu Kimura 2-30 Daidocho, Minami-ku, Nagoya City, Aichi Prefecture Daido Special Steel Co., Ltd. (72) Takuro Yamaguchi, Inventor Nissan Motor Co., Ltd. (2) Nissan Motor Co., Ltd. In-company (72) Inventor Noriko Uchiyama 2F, Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Prefecture F-term in Nissan Motor Co., Ltd. 4K028 AA01 AA03 AB01 AC01

Claims (4)

[Claims] 1. A surface carbon content by gas carburizing or gas carbonitriding treatment is 0.6 to 1.5%, and 100 ° C. to 9%.
The total amount of hydrogen released by heating up to 00 ° C is 0.2p
pm or less. 2. After the gas carburizing or gas carbonitriding treatment for enriching the surface C content to 0.6-1.5%, the temperature is maintained at a temperature lower than the Ac1 transformation temperature under reduced pressure, and then maintained at a temperature higher than the Ac1 transformation temperature. A method for producing a high surface pressure resistant member, characterized by rapidly cooling after heating and holding. 3. Cr: 1.2-3.2%, Mo: 0.2
It is composed of steel for machine structural use containing 5 to 2.0% and having a surface C content of 0.6 to 1.5% by gas carburizing or gas carbonitriding, and has an average particle diameter of at least 0.3 µm containing at least Cr. are distributed in the following of the M ₂₃ C ₆ type carbide is the base, resistance to high surface member to the total amount of hydrogen released by heating from 100 ° C. to 900 ° C. is equal to or less than 0.2 ppm. 4. Cr: 1.2-3.2%, Mo: 0.2
A steel for machine structural use containing 5 to 2.0% is subjected to a gas carburizing or gas carbonitriding treatment to enrich the surface C content to 0.6 to 1.5%, and then 500 to 650 ° C under reduced pressure. Heating at a rate of 0.2 to 30 ° C./min in a temperature range of to raise the temperature to a temperature of 600 to 750 ° C.
After continuously maintaining the temperature at that temperature under reduced pressure,
Above the Ac1 transformation temperature and T (° C.) = 675 + 120 ·
Si (%)-27 · Ni (%) + 30 · Cr (%) + 2
A method for producing a high surface pressure resistant member, characterized in that the member is heated and held at a temperature of 15 * Mo (%) to 400 * V (%) or less and rapidly cooled.