JP2002356738A - High contact pressure resistant member and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high contact pressure resistant member having excellent surface fatigue strength owing to finely and uniformly precipitated M23 C6 -type carbides, and also to provide a method for manufacturing the high contact pressure resistant member by which the M23 C6 -type carbides is precipitated finely and uniformly in an intermediate step and resultantly the surface fatigue strength of the member is greatly improved. SOLUTION: In raising the temperature of steel for machine structural use in which C content is made to 0.6-1.5% or surface C content is enriched to 0.6-1.5% by a carburizing treatment or a carbonitriding treatment to an intermediate temperature of 600-750 deg.C, the steel is heated through the temperature range of 500-650 deg.C at (0.2 to 30) deg.C/min temperature-rise rate, held successively within the intermediate temperature range, then held at a temperature not lower than the Ac1 transformation temperature and not higher than the A cm transformation temperature, and quenched for hardening.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a member used as a power transmission component requiring a high surface fatigue strength, such as a gear or a rolling element of a bearing, and more particularly to an environment from a quasi-high temperature to a high temperature. 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 strength of the power transmission member as described above, for example,
Carbides that are not easily decomposed even at quasi-high to high temperatures, such as M ₃ C-type carbides, are positively precipitated to increase hardness,
There are a hypereutectoid carburizing method and a high concentration carburizing method for improving the tempering softening resistance. In Japanese Patent Application No. 11-206552, members were finely dispersed precipitating the M ₂₃ C ₆ type carbide which is excellent in resistance to surface fatigue strength than steel to precipitate M 3 _C has been proposed.

[0003] In order to precipitate such carbides, a method is used in which the amount of carbon in the surface layer is increased by carburizing the member, and then the temperature is lowered and maintained at a temperature below which carbon can be dissolved. The precipitation of carbide at this time is likely to occur at a site where chromium (Cr), which is an element essential for generating carbide, is unevenly distributed, or at an interface of austenite grains serving as precipitation nuclei. By continuing, carbides are uniformly generated in the structure on the surface of the member. As the carbide precipitation step, a holding step for making the temperature of the member uniform before quenching is usually used.

However, it is difficult to uniformly disperse the M ₂₃ C ₆ type carbide in the entire surface of the structure of the member or in the surface layer of the member whose carbon content has been increased by carburization only by the holding step, so that an unprecipitated region is easily generated. There was a problem. In a region where carbide is not precipitated, reinforcement by dispersion of carbide is not sufficiently performed, and the strength is impaired.
Further, as an effect of carbides in the quenching step, there is an effect of preventing martensite generated at the time of quenching from growing coarsely, but if carbides are not dispersed and precipitated, it is difficult to obtain a dense structure, and rolling fatigue strength is reduced. Easily damaged. On the other hand, in Japanese Patent Application No. 11-206552 Publication described above, after carburization, to hold a long time at Ac1 transformation temperature or less prior to quenching holding, _M 23 _{C 6} by providing the intermediate holding step
Trying to deposit uniformly on the entire surface of the structure of the member, or on the surface layer of the member whose carbon content has been increased by carburization, but depending on the conditions, an unprecipitated region may occur, or a very long treatment may be required. Thus, there is a problem such as an increase in manufacturing cost, and solving such a problem has been a problem in the conventional power transmission member.

[0005]

The present invention is an object of the invention, which has been made in view of the above problems in the conventional power transmission member, resistance with excellent resistance to surface fatigue strength by M ₂₃ C ₆ type carbide uniformly and finely precipitated High surface pressure member and M
The ₂₃ C ₆ type carbide uniformly and can be finely precipitated, and its object is to provide a method for producing a resistance to high surface member of the resistance to surface fatigue strength of the member can be greatly improved with.

[0006]

The high surface pressure resistant member according to the present invention has a C content of at least 0.6 to 1.5 on the surface.
%, And having a structure in which carbides having an average particle size of 0.3 μm or less are dispersed in the matrix. Such a structure in the high surface pressure resistant member is used as a means for solving the above-described problem. I have.

[0007] In a preferred embodiment of the high surface pressure resistant member according to the present invention, the high surface pressure resistant member according to claim 2 is a steel plate for machine structural use containing 0.6 to 1.5% of C. In the high surface pressure resistant member according to claim 3 as the embodiment, the surface C amount is enriched by carburizing or carbonitriding, and the high surface pressure resistant member according to claim 4 is also provided. In, C: 0.6 to 1.5
%, Cr: 1.2 to 3.2%, Mo: 0.25 to 2.0
% Consists mechanical structural steel containing, carbides and configuration is M ₂₃ C ₆ type carbide containing at least Cr, in the resistance to high surface pressure member further according to claim 5, Cr:
From 1.2 to 3.2%, Mo: carburizing or carbonitriding treatment on mechanical structural steel containing 0.25 to 2.0 percent is is applied to the surface, _M 23 _{C 6} type carbides carbide containing at least Cr Is characterized in that:

[0008] In the method of manufacturing a high surface pressure resistant member according to claim 6 of the present invention, the temperature rising rate of the steel for machine structural use containing 0.6 to 1.5% of C in a temperature range of 500 to 650 ° C. Is heated to a temperature of 600 to 750 ° C. at a rate such that the temperature becomes 0.2 to 30 ° C./min, and is kept within the temperature range. Thereafter, the temperature is higher than the Ac1 transformation temperature and lower than the Acm transformation temperature. And then quenched,
In the method for manufacturing a high surface pressure resistant member according to claim 7 of the present invention, after the carburizing or carbonitriding treatment for reducing the surface C content to 0.6 to 1.5%, the temperature is raised in a temperature range of 500 to 650 ° C. Heat at a rate such that the temperature rate becomes 0.2 to 30 ° C./min, raise the temperature to a temperature of 600 to 750 ° C., and keep the temperature within the temperature range, and thereafter, the temperature is higher than the Ac1 transformation temperature and Acm transformation. After the temperature is kept below the temperature, rapid cooling is performed. In the method for manufacturing a high surface pressure resistant member according to claim 8 of the present invention, C: 0.6 to 1.5 under reduced pressure.
%, Cr: 1.2 to 3.2%, Mo: 0.25 to 2.0
% In a temperature range of 500 to 650 ° C. at a rate such that the rate of temperature rise is 0.2 to 30 ° C./min to raise the temperature to 600 to 750 ° C.,
Subsequently, the temperature is maintained within the temperature range under reduced pressure, and thereafter, the temperature is higher than the Ac1 transformation temperature, and T (° C.) = 675 + 12
0 ・ Si (%)-27 ・ Ni (%) + 30 ・ Cr (%)
+ 215 · Mo (%) − 400 · V (%) or less and then quenching, and further, in the method for manufacturing a high surface pressure resistant member according to claim 9 of the present invention,
The steel for machine structural use containing r: 1.2 to 3.2% and Mo: 0.25 to 2.0% is subjected to a carburizing or carbonitriding treatment with a surface C amount of 0.6 to 1.5%. After that, the rate of temperature rise in the temperature range of 500 to 650 ° C. under reduced pressure is 0.2
Heating at a rate of ~ 30 ° C / min to 600 ~
The temperature was raised to a temperature of 750 ° C., and then kept within the temperature range under reduced pressure. Thereafter, the temperature was higher than the Ac1 transformation temperature, and T = 675 + 120 · Si (%) − 27 · Ni (%)
+ 30 · Cr (%) + 215 · Mo (%) − 400 · V
(%) It is configured to be rapidly cooled after being heated and held at the following temperature, and is characterized in that such a configuration in the method for manufacturing a high surface pressure resistant member is used as a means for solving the above-mentioned problem.

[0009]

The high surface pressure resistant member according to the present invention has a C content at least on the surface thereof, that is, a C content of the member itself, or a surface C amount enriched by carburizing or carbonitriding. Since the carbides having an average particle diameter of 0.3 to 1.5 μm are dispersed in the matrix, the surface fatigue strength is improved by the finely dispersed carbides. At this time, as the material steel of the member, Cr: 1.2 to 3.2%, M
o: M is preferably a steel for machine structural use containing 0.25 to 2.0%, and contains at least Cr as a carbide.
It is desirable that the ₂₃ C ₆ type carbides.

That is, if the surface C content is less than 0.6%, the area ratio (precipitation amount) of carbide cannot be sufficiently ensured, and if it exceeds 1.5%, M ₃ C type carbide precipitates. The mechanical properties are degraded due to such network precipitation of carbides. In addition, the average particle size of the carbide is 0.1.
If it exceeds 3 μm, the rolling fatigue life is reduced. If the Cr content in the base steel is less than 1.2%, M ₂₃ C
_An excellent rolling fatigue life cannot be obtained due to a decrease in the amount of precipitation of the type ₆ carbide. Conversely, if it exceeds 3.2%, the machinability during machining tends to decrease. If the Mo content is less than 0.25%, stable precipitation of M ₂₃ C ₆ type carbide may be hindered.
Like Cr, machinability tends to decrease. In addition, all content of each component in this invention means a mass percentage.

The method for producing a high surface pressure resistant member according to the present invention is suitable for producing the above high surface pressure resistant member.
Mechanical structural steel having a content of 0.6 to 1.5%, or a carbon content of 0.6 to 1.5% by carburizing or carbonitriding.
When raising the steel enriched to 1.5% to an intermediate holding temperature of 600 to 750 ° C, the temperature range of 500 to 650 ° C is heated at a rate of 0.2 to 30 ° C / min, It is kept within the intermediate holding temperature range, and then kept at a temperature higher than the Ac1 transformation temperature and lower than the Acm transformation temperature, and then quenched by quenching. A high surface pressure resistant member having surface fatigue strength can be obtained. At this time, as the material steel, Cr: 1.2 to 3.2%, Mo: 0.25 to
It is desirable to use a steel for machine structural use containing 2.0%, and to raise and hold the temperature to the intermediate holding temperature under reduced pressure.
As the cm transformation temperature, T = 675 + 120 · Si
(%)-27 · Ni (%) + 30 · Cr (%) + 215
The temperature T calculated by Mo (%)-400V (%) can be used.

That is, if the amount of surface C is less than 0.6%, the area ratio of carbide cannot be secured as described above, and if it exceeds 1.5%, M ₃ C-type carbide is liable to precipitate. And the mechanical properties deteriorate.

On the other hand, when the intermediate holding temperature is lower than 600 ° C., the diffusion rate of C becomes low, so that the growth of M ₂₃ C ₆ type carbide is remarkably slowed, and the cost is increased.
If the temperature is higher than C, C is consumed to form M ₃ C-type carbide, so that M ₂₃ C _6- type carbide cannot grow and the hardness cannot be secured. When the temperature is raised to the intermediate holding temperature, if the rate of temperature rise in the temperature range of 500 to 650 ° C. is less than 0.2 ° C./min, the processing time becomes extremely long and the cost is increased. M over
The time for precipitating the nucleus of ₂₃ C ₆ type carbide is not enough, and the amount of carbide precipitation becomes insufficient. In addition, it is more preferable that the heating rate be in the range of 0.2 to 5 ° C./min.

Further, regarding the quenching holding temperature, Ac
If the transformation temperature is lower than 1 transformation temperature, the matrix after quenching cannot have a martensite or bainite structure, and if the transformation temperature is higher than the Acm transformation temperature or the temperature T calculated by the above calculation formula, M ₂₃ C ₆ type carbide solidifies. It will melt.

Regarding the reasons for limiting the Cr and Mo contents in the base steel, as described above, when the Cr and Mo contents are less than the above lower limits, M ₂₃ C
_{This is because the} amount of precipitation of the type ₆ carbide may be reduced or its stable precipitation may be impaired, and if it exceeds the upper limit, the machinability tends to decrease.

[0016]

EXAMPLES The present invention will be described more specifically with reference to the following examples.

(Example 1) Six types of steels A to A shown in Table 1
Using F, a disk-shaped test piece (diameter: 60 mm, thickness: 5 mm) for thrust rolling fatigue test was cut out, and steel grade A,
For B and C, after performing carburizing treatment so that the surface carbon concentration becomes 0.7 to 1.4%, for steel types D, E, and F, disc-shaped test pieces were not subjected to carburizing treatment. After shaving, carbide precipitation treatment and quenching were performed according to the pattern shown in FIG. 1 or FIG. 2, followed by tempering at 170 ° C. × 2 hours, and the surface of each test piece was ground and finished.

[0018]

[Table 1]

In the rolling fatigue test, a cumulative failure probability 50% life (L50) at n = 5 until peeling occurred under the conditions shown in Table 2.

[0020]

[Table 2]

The cross section of the thrust rolling fatigue test piece thus obtained was corroded with a 3% alcohol nitric acid solution, and the cross section from the outermost surface of the test piece to a depth of 0.1 mm was magnified by 10,000 times using a scanning electron microscope. After photographing, the average particle size of the precipitated carbide was measured using an image analyzer. Further, a range of 0.1 mm ± 0.05 mm from the outermost surface was observed with an optical microscope, and an area ratio of a non-precipitated region of carbide was determined. Table 3 shows the results. In addition, Invention Example 3
After cooling to 600 ° C. after carburization, a heating treatment is immediately performed under the conditions of the present invention.

[0022]

[Table 3]

As shown in Table 3, with respect to Inventive Examples 1 to 6, which are examples of the present invention, there is no undeposited portion of carbide,
Carbide was uniformly precipitated, and excellent rolling fatigue life was obtained.

On the other hand, in Comparative Examples 1 and 5 in which the quenching holding temperature T2 is high, the precipitated carbides form a solid solution, so that a non-precipitated region of the carbide is generated, and Comparative Examples 2 and 6 in which the intermediate holding temperature T1 is high. In Comparative Example 3 where the amount of precipitation of the M ₂₃ C ₆ type carbide is small and the intermediate holding temperature T1 is low, the non-precipitated region occurs due to the slow growth of the carbide and the intermediate holding temperature T
In Comparative Example 4 in which the rate of temperature rise up to 1 was fast, the precipitation nuclei of carbides were small and uneven precipitation occurred, and all resulted in a short rolling fatigue life.

Example 2 Five types of steels G to G shown in Table 4
After normalizing this using K, a gas carburizing treatment was performed under the conditions shown in FIG. In addition, the surface carbon concentration after the carburizing treatment was adjusted to a range of 0.7 to 0.8% depending on the carburizing gas composition during carburizing (C potential). Thereafter, heat treatment was performed under any of the heat treatment symbols A to E shown in FIG. 4 and Table 5. The structure of the test piece obtained in this manner was observed with a scanning electron microscope, and the area ratio of the non-precipitated carbide region and the average particle size of the precipitated carbide were measured by an image analyzer.

[0026]

[Table 4]

[0027]

[Table 5]

Separately from this, the surface of the test piece was polished to obtain a thrust test piece (diameter: 60 mm, thickness: 5 mm). The failure probability 10% life (L10) was examined.

[0029]

[Table 6]

The results are summarized in Table 7.

[0031]

[Table 7]

As shown in Table 7, in Invention Examples 7 to 10 which are examples of the present invention, carbides were uniformly deposited,
It was confirmed that excellent rolling fatigue life was obtained. On the other hand, in Comparative Examples 7, 9, 13, and 15, since the intermediate holding temperature t1 was too low, the growth of carbide was slow, and a non-precipitated region was generated, so that sufficient rolling fatigue life was not obtained. Conversely, in Comparative Examples 10, 11, 14 and 16, the intermediate holding temperature t1 and the quenching holding temperature t2 are too high and carbides hardly precipitate, so that the rolling fatigue life is short. In Comparative Examples 8 and 12, Since the heating rate up to the intermediate holding temperature t1 was too high and the number of carbide precipitation nuclei was small, an unprecipitated region of carbide was generated, resulting in a short rolling fatigue life.

FIG. 5 is an SEM photograph of Comparative Example 1. The black portion is a carbide precipitation region, and the white portion is a carbide non-precipitation region. It can be seen that there are many carbide non-precipitated regions.

[0034]

As described above, the high surface pressure resistant member according to the present invention has a C content at least on its surface,
That is, the C content of the entire high surface pressure resistant member, or the amount of surface C enriched by carburizing or carbonitriding is 0.6 to 1.5%, and the average particle size is 0.3 μm or less. Since the carbides are dispersed in the matrix, it has excellent surface fatigue strength, and has an extremely excellent effect that it can be suitably used as a gear used under high surface pressure or a rolling element of a bearing. Things. Further, as a preferred embodiment, Cr: 1.2 to 3.2%, Mo: 0.2
Containing 5 to 2.0%, in the resistance to high surface member obtained by precipitating the _M 23 _{C 6} type carbide containing at least Cr as a _{carbide, by M} 23 _{C 6} type carbides are precipitated not Tsumura or fine, It is possible to prevent a decrease in the fatigue strength due to the unevenness of the structure, and it is possible to more reliably improve the surface fatigue strength.

In the method for manufacturing a high surface pressure resistant member according to the present invention, it is preferable that Cr: 1.2 to 3.2%,
Mo: 0.25 to 2.0%, C content is 0.6
When raising the steel for machine structural use whose surface C content is enriched to 0.6 to 1.5% by carburizing treatment or carbonitriding treatment to an intermediate holding temperature of 600 to 750 ° C, The temperature range of 500 to 650 ° C is 0.2 to 30 ° C /
heating at a temperature rising rate of min, and subsequently maintaining the temperature within the above-mentioned intermediate holding temperature range.
m transformation temperature or lower, or T (° C) (= 675 + 120)
・ Si (%)-27 ・ Ni (%) + 30 ・ Cr (%) +
215 · Mo (%) - 400 · V (%)) was held below, since so as to quenching treatment by rapid cooling, thereby evenly uniformly distributed precipitating fine _{M 2} 3 _{C 6} type carbide And an extremely excellent effect that a high surface pressure resistant member excellent in rolling fatigue life can be obtained.

[Brief description of the drawings]

FIG. 1 is a view showing carbide precipitation and quenching conditions in a first embodiment of the present invention.

FIG. 2 is a view showing other carbide precipitation and quenching treatment conditions in the first embodiment of the present invention.

FIG. 3 is a view showing gas carburizing conditions in a second embodiment of the present invention.

FIG. 4 is a view showing carbide precipitation, quenching and tempering conditions in a second embodiment of the present invention.

FIG. 5 is an SEM photograph (Nital corrosion) of Comparative Example 1 of the present invention.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshimitsu Kimura 2-30 Odomo-cho, Minami-ku, Nagoya City, Aichi Prefecture Inside the Technology Development Laboratory of Daido Steel Co., Ltd. (72) Inventor Takuro Yamaguchi Takaracho, Yokohama-shi, Kanagawa No. 2 Nissan Motor Co., Ltd. (72) Keizo Otani Inventor Keizo Oya 2 Kanagawa-ku, Kanagawa-ku, Kanagawa Prefecture 2 Nissan Motor Co., Ltd. (72) Inventor Noriko Uchiyama 2 Kanagawa-ku, Kanagawa-ku, Kanagawa-ku 2 Nissan Motor Co., Ltd.

Claims (9)

[Claims] 1. The amount of C on the surface is at least 0.6 to 1.
A high surface pressure resistant member, wherein 1.5% and carbide having an average particle size of 0.3 μm or less are dispersed in the matrix. 2. The high surface pressure resistant member according to claim 1, comprising a steel for machine structural use containing 0.6 to 1.5% of C. 3. The high surface pressure resistant member according to claim 1, wherein the surface C content is enriched by carburizing or carbonitriding. 4. C: 0.6-1.5%, Cr: 1.2-
3.2%, Mo: containing 0.25 to 2.0 percent consists machine structural steel, _{M 23} carbide containing at least Cr
Resistance to high surface pressure member of claim 1, wherein it is a C ₆ type carbides. 5. Cr: 1.2-3.2%, Mo: 0.2
Carburizing or carbonitriding treatment on mechanical structural steel containing 5 to 2.0% is has been applied, resistance of claim 1, wherein the carbide is a M ₂₃ C ₆ type carbide containing at least Cr High surface pressure member. 6. A steel for machine structural use containing 0.6 to 1.5% of C is heated at a rate such that a rate of temperature rise in a temperature range of 500 to 650 ° C. is 0.2 to 30 ° C./min. 6
The temperature is raised to a temperature of from 00 to 750 ° C., and is kept within the temperature range.
A method for producing a high surface pressure resistant member, wherein the member is rapidly cooled after being maintained at a transformation temperature or lower. 7. After the carburizing or carbonitriding treatment to reduce the surface C content to 0.6 to 1.5%, the rate of temperature rise in the temperature range of 500 to 650 ° C. is 0.2 to 30 ° C./min. The temperature is raised to a temperature of 600 to 750 ° C. by heating at a suitable rate, the temperature is kept within the temperature range, then the temperature is kept at or above the Ac1 transformation temperature and below the Acm transformation temperature, and then quenched. Manufacturing method of high surface pressure resistant member. 8. C: 0.6 to 1.5 under reduced pressure.
%, Cr: 1.2 to 3.2%, Mo: 0.25 to 2.0
% In a temperature range of 500 to 650 ° C. at a rate such that the rate of temperature rise is 0.2 to 30 ° C./min to raise the temperature to 600 to 750 ° C.,
Subsequently, the temperature is maintained within the temperature range under reduced pressure, and thereafter, the temperature is higher than the Ac1 transformation temperature, and T (° C.) = 675 + 12
0 ・ Si (%)-27 ・ Ni (%) + 30 ・ Cr (%)
A method for producing a high surface pressure resistant member, characterized in that the member is heated and maintained at a temperature of + 215 · Mo (%) − 400 · V (%) or less and then rapidly cooled. 9. Cr: 1.2-3.2%, Mo: 0.2
A machine structural steel containing 5 to 2.0% has a surface C content of 0.1%.
After performing carburizing or carbonitriding treatment at 6 to 1.5%, the mixture is heated under reduced pressure at a rate of 0.2 to 30 ° C./min in a temperature range of 500 to 650 ° C. The temperature is raised to a temperature of 600 to 750 ° C., and then kept within the temperature range under reduced pressure.
1 transformation temperature or more and T (° C) = 675 + 120 · Si
(%)-27 · Ni (%) + 30 · Cr (%) + 215
-A method for producing a high surface pressure resistant member, wherein the member is heated and held at a temperature of not more than Mo (%)-400 V (%) and then rapidly cooled.