JPH0432548A - Manufacture of power transmission parts - Google Patents

Abstract

PURPOSE:To improve the pitching resistance and fatigue properties by subjecting steel parts having specified Cr content to plasma carburizing treatment to specify the surface carbon concn. and the areal rate of surface carbide and thereafter subjecting this steel parts to quenching, tempering and shot peening. CONSTITUTION:A steel having, by weight, 1.5 to 15.0% Cr content is formed into the shape of power transmission parts. This formed part is subjected to plasma carburizing treatment to regulate its surface carbon concn. to >=1.3% and the areal rate of surface carbide to >=15%. Next, this formed part is subjected to quenching and tempering treatment and is thereafter subjected to shot peening. If required, the above steel is incorporated with one or more kinds among <=1.0% Ni, <=2.0% V and <=3.0% W. In this way, small-sized power transmission parts having high strength can be manufactured.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing power transmission parts, in which carburized steel is molded into the shape of power transmission parts such as gears and bearings. The present invention relates to a method of manufacturing a power transmission part with excellent pitting resistance and fatigue characteristics by carburizing a molded product, quenching and tempering the molded product, and then subjecting it to shot peening.

[Prior Art] Conventionally, power transmission parts such as gears and bearings have been processed by gas carburizing to reduce the surface carbon concentration to 0. By quenching and tempering the parts adjusted to 8%,
Materials that have been given high surface hardness and compressive residual stress and have improved pitting resistance and fatigue properties have been used.

In recent years, there has been a growing demand for parts with higher strength and smaller size, and parts with even better fatigue characteristics have become necessary. Therefore, a method has been adopted in which the parts that have been quenched and tempered after gas carburizing are further subjected to shot peening to increase their compressive residual stress and improve their fatigue characteristics.

[Problems to be Solved by the Invention] However, the requirements for pitting resistance and fatigue properties tend to become even higher, and it has become difficult for the above-mentioned conventional methods to meet these demands.

The manufacturing method of the present invention (above) aims to make it possible to manufacture power transmission components that can meet these additional demands.

[Means for Solving the Problems] In order to achieve the above object, the inventors performed plasma carburization on parts formed from carburized steel made of specific components to achieve a predetermined surface carbon concentration and area. We found that by forming a carbide layer with a certain ratio, quenching and tempering it, and then subjecting it to shot pinning, the surface hardness and residual compressive stress could be increased compared to conventional products, and we summarized the structure below. This invention has been made.

That is, in the method for manufacturing power transmission parts of the present invention, a molded product made of carburized steel material into the shape of a power transmission part such as a gear or a bearing is carburized, and then quenched and tempered. Later, in the method for manufacturing power transmission parts that performs shot peening, the steel material for carburizing has a Cr content of 1.5% by weight to 1.5% by weight.
15.0% by weight, plasma carburization is adopted as the carburizing treatment, and the surface carbon concentration of the molded article is made to be 1.3% or more by the plasma carburization treatment,
The method is characterized in that after the area ratio of surface carbides is set to 15% or more, the above-mentioned baking tender tempering and shot peening are carried out.

In addition, in the method for manufacturing such a power transmission part, the carburizing steel material further contains 1.0% by weight or less of Ni, 2.0% by weight or less of V, or 3.0% by weight or less of V.
It may also be characterized by containing one or more components selected from W at 0% by weight or less.

[Function] According to the method for manufacturing a power transmission component of the present invention having such a configuration, the steel material for carburizing is particularly made with a Cr content of 1.5.
By using a material containing 15.0% to 15.0% by weight and using plasma carburizing treatment, the surface carbon concentration of the molded product was reduced to 1.3%.
% or more and the surface carbide area ratio is 15% or more, and then performs tempering, tempering, and shot peening to produce power transmission parts with excellent pitting resistance and fatigue characteristics. The surface carbon concentration and the area ratio of surface carbides can be adjusted by the relationship between the steel type and the plasma carburizing treatment temperature and treatment time.

In addition, this carburizing steel material further contains as other components:
1. N1 or 2.0% by weight or less. It may contain one or more components selected from 0% by weight or less of V or 3.0% by weight or less of W, and in this case, it also has excellent pitting resistance and fatigue properties. power transmission parts can be manufactured.

Here, if the type of steel material for carburizing is simply specified and gas carburizing is performed in the same way as before, even if the surface carbon concentration satisfies the above conditions, the pitting resistance and fatigue properties of the surface will be affected. The characteristic values obtained are comparable to those of the conventional product in which the carbon concentration is adjusted to 0.8% or less, which is inferior to the method of the present invention.

Furthermore, even if plasma carburizing is performed, if the above-mentioned conditions such as surface carbon concentration are not satisfied, the pitting resistance and fatigue properties will still be inferior to those obtained by the method of the present invention.

Furthermore, if the Cr content is lower than the range of the present invention, it may not be possible to carry out carburizing treatment that satisfies conditions such as surface carbon concentration, or even if it is possible, it will require an extremely long treatment time. Become.

On the other hand, if the Cr content is higher than the above range, the material cost will increase and the amount of carbides formed will be saturated, which will affect the workability and other properties of the steel material, which is not preferable.

In addition, the steel material for carburizing has the following content as the amount of components other than Cr:
C to 0. Desirably, the content is 1 to 0.4%, Sl is O to 1.0%, Mn is O to 1.0%, and Mo is 0 to 2.0%. Table 1 summarizes the reasons for setting upper and lower limits for these and the Cr content.

Table 1 [Examples] Next, in order to further clarify the present invention, preferred examples to which the present invention is applied will be described.

The inventors performed plasma carburizing, quenching, and tempering on Ono rotary bending test pieces and roller pitting test pieces made of carburizing steel using the treatment pattern shown in Figure 1. After setting the piece in a plasma carburizing furnace and raising the temperature to T['C], Ar gas and H2 gas were introduced into the furnace and plasma discharge was performed to perform sputter cleaning for 30 minutes, followed by carbon carburizing.
Carburizing was carried out for t [hours] by switching to 3H5 gas. Thereafter, the temperature was lowered to 830'C over 20 minutes by furnace cooling, held at that temperature for 30 minutes, cooled with oil, heated again to 160°C, held for 2 hours, and then air cooled.

After carburizing, quenching, and tempering in this manner, shot peening was performed under the following conditions.

Shot peening conditions: Arc height 1. OmmA mm upper diameter 100% Projection speed 80m/s Shot ball ψ0.8 shot A test piece that has been carburized, quenched, tempered, and shot peened is subjected to an Ono rotary bending tester and a roller pitting test using a procedure of HRC50 or higher. The fatigue characteristics and roller pitching characteristics were measured. The conditions for each test are as follows.

Ono type rotary bending test conditions: Test piece Fatigue test piece with a notch with a notch factor of 1.8 Test temperature Room temperature measurement items 107 times fatigue limit Roller pitting test conditions: Number of rotations 150 Orpm Surface pressure 350 kgf/mm2 Slip rate -40 % Measurement Item Steel materials used in the 50% failure rate life (B50 life) test are shown in Table 2.

Table 2 Using these steel materials B to K, carburizing temperature T and carburizing time t
Plasma carburizing was carried out using the above-mentioned pattern with various changes.For steel materials A and H, gas carburizing was performed instead of plasma carburizing.
As shown in the figure. As shown in the figure, the temperature of gas carburizing was 910'C, and after carburizing for 3.5 hours, diffusion was performed for 2 hours, and then quenching and tempering were performed in the same way as in the case of plasma carburizing. Table 3 shows the carburizing conditions and the results of various measurements.

In addition, "P" in the carburizing method column in the table means plasma carburizing, and rGJ means gas carburizing. Furthermore, the reason why the T and t columns for materials Nα12 and Nα13 are marked with “-” is because, as described above, gas carburizing is performed using a different treatment pattern from that shown in FIG. Furthermore, those marked "10~" in the 850 lifespan column are 107
The measurement was stopped at

Table 3 As is clear from Tables 2 and 3, the Cr content is 1.5
~15.0% of steel materials were subjected to plasma carburization, and the carburizing conditions resulted in a surface carbon concentration of 1.3% or more and an area ratio of 15%, with a 107-cycle fatigue limit of 90 kgf/ mm2 and B50 life is 7.2X10
"It showed excellent fatigue properties and pitting resistance compared to recovered balls (Test No. 1~]).The surface carbon concentration referred to here refers to the carbon concentration within 0.1 mm from the surface of the test piece. The area ratio is the area ratio of carbide at a position of 0°1 mm from the surface of the test piece.

On the other hand, with the conventional one whose surface carbon concentration was adjusted to 0.8% by gas carburizing, the fatigue limit was 81 kgf/mm2 for 107 cycles and the B50 life was 4.2 x 106 cycles (test Nα]2).

In addition, although it was gas carburized, the steel H
When the surface carbon concentration was adjusted to 1.4% and the area ratio was adjusted to 15% using
B50 life in mm2 is 5. It was 1×106 times (test Nα13).

Furthermore, plasma carburization was performed using steel C as in test Nα3, but the surface carbon concentration was 1.2% and the area ratio was
When adjusted to %, the fatigue limit for 107 times is 84 kgf.
/mm2, and the B50 life was 6.2 x 106 times (test Nα]4).

In this way, test No. 1~]] is test No. 12~
Compared to 13, the fatigue limit value of 107 times is about 1
A comparative improvement in characteristics was observed, and in the 1B50 life span, it was confirmed that the life span was approximately twice as long.

Considering this difference, it is considered that in order to improve such characteristic values, it is necessary to satisfy the following requirements (1) and (2).

Requirements: Must be plasma carburized.

Requirement ■: The surface carbon concentration is adjusted to 1.3% or more and the area ratio is adjusted to 15% or more.

Further, in steel materials with a Cr content of less than 1.5%, it is difficult to increase the surface carbon concentration to 1.3% or more even if plasma carburizing is performed.

Therefore, Requirements: The Cr content of the steel material for carburizing is 1.5% or more.

is considered necessary.

In addition, since steels with a Cr content of 15.0% or more are expensive and the formation of carbides reaches a saturated state, Requirement ■: The Cr content of the steel for carburizing is 15.0% or less. thing.

can also be a requirement.

As explained above, test N that meets all requirements
α] ~ 11 exhibit superior anti-pitching characteristics and fatigue characteristics compared to the others, and if such a manufacturing method is adopted, power transmission parts with good properties can be manufactured without increasing costs. I can do it.

Although the present invention has been described above in detail, it goes without saying that the present invention is not limited thereto and can be implemented in various forms without departing from the spirit thereof.

For example, the processing pattern of plasma carburization is not limited to that of the example, and any pattern that can form a carbide with a surface carbon concentration of 1.3% or more and an area ratio of 15% or more is sufficient.

Further, as for components other than Cr, the mixing ratio thereof may be appropriately selected, and in this case, it is preferable to refer to Table 1 mentioned above. However, it does not matter if the range is not shown in this table.

Effects of the Invention According to the method for manufacturing a power transmission component of the present invention, it is possible to manufacture a product that satisfactorily meets the demand for manufacturing high-strength, compact power transmission components that has been increasing in recent years.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the procedure of plasma carburizing treatment in an example, and FIG. 2 is an explanatory diagram showing the procedure of gas carburizing treatment adopted as a comparative example. T...Processing temperature t...Processing time

Claims (1)

[Claims] 1 Carburizing a molded product made of carburized steel into the shape of a power transmission part such as a gear or bearing, followed by quenching and tempering, followed by shot peening. In the method for manufacturing power transmission parts, the steel material for carburizing has a Cr content of 1.5% by weight or more.
15.0% by weight, plasma carburization is adopted as the carburizing treatment, and the surface carbon concentration of the molded article is set to 1.3% or more by the plasma carburization treatment,
A method for manufacturing a power transmission part, characterized in that the baking-tempering and shot-peening are performed after the area ratio of surface carbide is 15% or more. 2. A method for manufacturing a power transmission component according to claim 1, comprising:
The steel material for carburizing further contains 1.0 as another component.
A method for producing a power transmission component, characterized in that it also contains one or more components selected from Ni at or below 2.0% by weight, V at or below 3.0% by weight, or W at or below 3.0% by weight. .