JP2001262313A - Vacuum carburizing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vacuum carburizing method by which, even in the case a large quantity of the objects to be treated are arranged in the effective space of a heating chamber, and carburizing is performed, the generation of the irregularity of the carburizing on all objects to be treated can be prevented. SOLUTION: In this vacuum carburizing method, as carburizing gas, a gaseous mixture of gaseous ethylene and gaseous hydrogen is used. The mixing ratio of the gaseous hydrogen in the gaseous mixture is controlled to 15 to 50%. The carburizing is performed under the pressure of 40 to 65 Torr.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a vacuum carburizing method performed under reduced pressure.

[0002]

2. Description of the Related Art For example, as a vacuum carburizing method for carburizing steel parts such as gears, bearings, fuel injection nozzles, constant velocity joints, etc. under reduced pressure, a carburizing gas composed of ethylene gas is used. (See Japanese Patent Application Laid-Open No. 11-315363).

[0003]

However, it has been found that the following problems occur in the conventional method. That is, when vacuum carburizing is performed by placing a basket loaded with a large amount of articles to be processed in an effective space where temperature uniformity is ensured in a heating chamber of a vacuum carburizing furnace, uneven carburization occurs due to a loading position on the basket, There is a problem that carburizing quality such as carburizing depth and surface carbon concentration of articles to be processed at different loading positions varies. Moreover, controllability and reproducibility of carburizing quality are not sufficient.

[0004] An object of the present invention is to solve the above-mentioned problem, and even when carburizing is performed by disposing a large amount of articles to be treated in an effective space of a heating chamber, uneven carburizing occurs in all articles to be treated. It is an object of the present invention to provide a vacuum carburizing method capable of preventing the occurrence of the problem.

[0005]

The vacuum carburizing method according to the first aspect of the present invention is characterized in that a mixed gas of ethylene gas and hydrogen gas is used as the carburizing gas.

In the above vacuum carburizing method, the article to be treated is placed in the flow of the carburizing gas so that the carburizing gas directly hits all the articles to be treated, and the carburizing gas is supplied at a constant flow rate during the carburizing process. It is good to flow in. In order to achieve this, a plurality of gas blowing pipes each having a plurality of gas blowing ports formed at intervals in the length direction are arranged in parallel in one horizontal plane above the effective space in the heating chamber. At the same time, it is preferable that a plurality of gas suction pipes are arranged in a penetrating manner on the bottom wall of the heating chamber so as to be uniformly scattered. For example, the size of the effective space is 610 mm long, 460 mm wide,
When the height is 460 mm, the distance between the effective space and the gas blowing pipe is 100 to 150 mm, and the diameter of the gas blowing port is 3
mm, and the pitch of the gas outlets is preferably 32 to 53 mm. Further, it is preferable that the number of gas suction pipes is 10, and the diameter of the gas suction pipe is 20 mm.

According to the vacuum carburizing method of the first aspect,
Since a carburizing gas consisting of a mixed gas of ethylene gas and hydrogen gas is used, even if a large amount of articles to be treated are placed in the effective space of the heating chamber and carburizing is performed, carburizing unevenness occurs in all the articles to be treated. It can be prevented from occurring, and as a result, the carburizing quality of all the articles to be treated can be made uniform. Here, it is possible to prevent occurrence of uneven carburization in all the articles to be treated arranged in the effective space by using a carburizing gas composed of a mixed gas of ethylene gas and hydrogen gas. Is a matter that was found by repeating various experimental studies, and the reason is considered to be as follows.
That is, the uneven carburization is caused by the C ₂ H in the heating chamber.
The partial pressure of ₂ the case is _high, the partial pressure of C 2 _{H 2} becomes high _is considered to decomposition reaction of _{C 2 H 4 → C 2 H} 2 + H 2 is due to take place actively. When hydrogen gas is contained in the carburizing gas, such a decomposition reaction can be suppressed, and as a result, uneven carburizing is reduced.

[0008] In a vacuum carburizing method according to the second aspect of the present invention, the mixing ratio of hydrogen gas in the mixed gas is set to 15 to 50% in the first aspect of the invention. If the mixing ratio of hydrogen gas in the mixed gas is less than 15%, the above-described effect of reducing carburization unevenness cannot be obtained, and a large amount of soot is generated in the heating chamber. Carbide quality such as layer depth and surface carbon concentration may not satisfy the required conditions.

The vacuum carburizing method according to the third aspect of the present invention is the vacuum carburizing method according to the first or second aspect of the present invention, wherein the pressure is 40 to 65 Torr (5.
33 to 8.67 kPa). If the pressure in the heating chamber is less than 40 Torr, uneven carburization occurs and the carburizing quality becomes non-uniform. If the pressure exceeds 65 Torr, the amount of free carbon generated increases and a large amount of soot is generated in the heating chamber.

A vacuum carburizing method according to a fourth aspect of the present invention is a vacuum carburizing method for performing a carburizing process on an article to be processed having a bottomed hole from an end face, wherein an ethylene gas and a hydrogen gas are used as the carburizing gas. Using a mixed gas, at a temperature of 870 to 880 ° C. and 25 to 35 Torr (3.33 to 4.67 kPa)
This is characterized in that the process is performed under the following pressure.

According to the vacuum carburizing method of the invention of claim 4,
The same effect as that of the first aspect is obtained. In addition, the carburizing quality of each part of the article to be treated can be made uniform.
In particular, the carburizing quality in the vicinity of the bottom of the inner peripheral surface of the bottomed hole can be improved. However, the carburizing temperature is 8
If the temperature is lower than 70 ° C., the carburizing time becomes longer, the amount of soot generated becomes larger, and the diffusion of carbon into steel becomes slower, making it difficult to control the surface carbon concentration. On the other hand, if the temperature exceeds 880 ° C., decomposition of ethylene gas and diffusion of carbon into steel become faster, and the amount of ethylene gas consumed near the entrance of the bottomed hole increases, resulting in insufficient carbon near the bottom of the bottomed hole. However, the required carburizing quality is not obtained. Furthermore, the pressure in the heating chamber is 25
If the pressure is lower than Torr, the carburizing quality varies greatly and becomes non-uniform. If the pressure exceeds 35 Torr, the amount of soot generated in the heating chamber increases.

A vacuum carburizing method according to a fifth aspect of the present invention is the method according to the fourth aspect, wherein the mixing ratio of hydrogen gas in the mixed gas is 30 to 50%. If the mixing ratio of hydrogen gas in the mixed gas is less than 30%, the effect of reducing the uneven carburization described in the first aspect of the present invention cannot be obtained, and more soot is generated in the heating chamber, and exceeds 50%. Then, there is a possibility that the carburized depth of each part in each article to be processed becomes non-uniform. The mixing ratio of hydrogen gas in the mixed gas is 33
It is preferably about 40%.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described.

Example 1 In an effective space in a heating chamber of a carburizing furnace, JIS SCM4
A basket in which a number of constant velocity joints for automobiles composed of 20 H2 materials were loaded 92.3% of the maximum loading weight was arranged. The weight of the constant velocity joint for automobiles is 190 kg, and the total weight including the basket and tray is 240 kg.
kg.

Next, the car constant velocity joint was subjected to vacuum carburization under the following conditions. That is, after the pressure in the heating chamber is reduced to 1 Torr (133.3 Pa) or less, a pre-heat treatment is performed by heating and holding at 950 ° C. for 100 minutes, and after the pre-heat treatment, ethylene gas and hydrogen gas are introduced into the heating chamber to 50 Torr (6 70 at 950 ° C. under a pressure of .67 kPa).
Carburizing treatment was performed by heating and holding for minutes. At this time, the flow rate of ethylene gas was 10 L / min, and the flow rate of hydrogen gas was 5 L / min.
These flow rates were controlled to be constant during the carburizing process. Following the carburizing treatment, the heating chamber was heated to 1 Torr (13
The pressure is reduced to 3.3 Pa) or less, and diffusion treatment is performed by heating and holding at 950 ° C. for 50 minutes.
After performing a soaking process of heating and holding at 50 ° C. for 30 minutes, 6
The quenching treatment was performed under a pressure of 00 Torr (80.0 kPa). Finally, as a post-treatment, a tempering treatment of heating and holding at 160 ° C. for 90 minutes was performed.

Then, the effective hardened layer depth (the maximum depth of the portion having the hardness of HV513) and the surface carbon concentration of the five automotive constant velocity joints loaded at different positions in the height and the depth direction of the heating chamber. And the surface hardness was measured. The result is shown in FIG. As is clear from FIG. 1, the effective hardened layer depth of the five automotive constant velocity joints,
Variations in surface carburizing concentration and surface hardness are small and uniform.

Further, when a sectional hardness distribution curve of a constant velocity joint for an automobile arranged at the center in the depth direction of the height and the heating chamber was prepared, no decrease in hardness was observed near the outermost surface. In the latter case, a smooth sectional hardness distribution curve was obtained. Further, when a cross-sectional structure near the surface after tempering treatment of the same automotive constant velocity joint was observed, no grain boundary oxidation was observed, and a fine martensite structure in which fine granular cementite was dispersed was observed.

Example 2 A rod-shaped automotive fuel injection nozzle (1) made of JIS SCM415 material and having a bottomed hole (2) as shown in FIG. 2 was produced. As shown in FIG. 2, the length a of the fuel injection nozzle (1) is 52.1 mm, and the outer diameter b of the large diameter portion (1a) is 16.9 m.
m, the length c of the large diameter portion (1a) is 25 mm, the outer diameter d of the small diameter portion (1b) is 8.4 mm, the inner diameter e of the bottomed hole (2) is 6.0 mm, and the bottomed hole (2) is The depth f is 50 mm.

Then, this fuel injection nozzle (1) is
The basket was loaded in a basket together with 10 kg of the dummy with the opening end of (2) facing downward, and this basket was placed in the effective space in the heating chamber of the carburizing furnace.

Next, the inside of the heating chamber is set to 1 Torr (133.3 P).
a) After the pressure is reduced to the following, a pre-heat treatment is performed by heating and holding at 870 ° C. for 40 minutes. Subsequently to the pre-heat treatment, ethylene gas and hydrogen gas are introduced into the heating chamber to 30 to 35 Torr.
Carburizing treatment was performed by heating and holding at 870 ° C. under a pressure of (4.0 to 4.67 kPa) for tc minutes. At this time, the flow rate of the ethylene gas was set to 10 L / min, and the flow rate of the hydrogen gas was set to 5 L / min, and these flow rates were controlled to be constant during the carburizing process. Following the carburizing treatment, the heating chamber was heated to 1 Torr (13
The pressure is reduced to 3.3 Pa) or less, and a diffusion treatment is performed by heating and holding at 870 ° C. for td minutes.
After performing a soaking heat treatment by heating and holding at 0 ° C. for 30 minutes,
Quenching was performed under a pressure of 0 Torr. Further, as post-processing, a sub-zero treatment of holding at -79 ° C for 120 minutes and a tempering treatment of heating and holding at 200 ° C for 120 minutes were performed. In the above, two cases were performed: tc = 120 and td = 60 (case 1) and tc = 112 and td = 68 (case 2).

For each of the fuel injection nozzles (1) of the cases 1 and 2, a point P1 on the outer peripheral surface of the small diameter portion (1b) and a point P2 on the inner peripheral surface of the bottomed hole (2) shown in FIG. Hole with bottom (2)
The hardness of a portion having a depth of 0.05 to 1.0 mm was measured with reference to the outermost surface at the point P3 of the bottom surface (sheet portion) (2a) of Example 2 to obtain a sectional hardness distribution curve. FIG. 3 shows the case 1
The case 2 is shown in FIG. Note that point P1
And the distance g from the sheet portion (2a) of P2 is g = 10 mm.

Since the use environment of this type of fuel injection nozzle is high in temperature, a post-treatment including a sub-zero treatment at 120 ° C. for 120 minutes and a tempering treatment at 200 ° C. for 120 minutes after vacuum carburization is performed. However, the following surface quality is required after the post-treatment. That is,
This cross-sectional hardness distribution curve is 0.15 based on the outermost surface.
HV690-780, 0.4-
It is required to pass through the range of HV350 to 450 at a depth of 0.6 mm or more and HV550 or more at a depth of 0.6 mm.

As is clear from FIGS. 3 and 4, in both cases 1 and 2, the sectional hardness distribution curve passes through the above required range. The required range is shown by a chain line in FIGS.

Example 3 A bearing race (191.5) made of SAE5120 material
g) was placed in an effective space in a heating chamber of a carburizing furnace, with a basket packed with 240 pieces.

Next, the bearing race was vacuum carburized under the following conditions. That is, 1 Torr (1
After reducing the pressure to 33.3 Pa) or less, a pre-heat treatment is performed by heating and holding at 950 ° C. for 100 minutes. Subsequently to the pre-heat treatment, ethylene gas and hydrogen gas are introduced into the heating chamber to 50 Torr.
Carburizing treatment was performed by heating and holding at 950 ° C. for 200 minutes under a pressure of (6.67 kPa). At this time, the flow rate of the ethylene gas was set to 10 L / min, and the flow rate of the hydrogen gas was set to 5 L / min, and these flow rates were controlled to be constant during the carburizing process.
Following the carburizing treatment, the heating chamber was heated to 1 Torr (133.3P
a) A diffusion treatment is performed in which the pressure is reduced to the following, and the mixture is heated and held at 950 ° C. for 10 minutes.
After performing soaking for 30 minutes, 600 To
The quenching treatment was performed under a pressure of rr (80.0 kPa). Further, as a post-treatment, heat and hold at 180 ° C. for 90 minutes 1
Next tempering treatment and heating and holding at 180 ° C for 120 minutes 2
Next tempering treatment was performed.

Then, the surface hardness (HRC) and the effective hardened layer depth (the maximum depth of the portion having the hardness of HV550) of the fifteen bearing rings loaded at different positions in the height and the depth direction of the heating chamber are different. ) Was measured. The result is shown in FIG. As is clear from FIG. 5, variations in the surface hardness and effective hardened layer depth of the 15 races are small and uniform. Further, when the sectional hardness distribution curves of these 15 races were determined, no decrease in hardness was observed near the outermost surface, and a smooth sectional hardness distribution curve was obtained.

Further, the surface carbon concentration and the 0.3% C carburized depth of five races loaded at different positions in the height and the depth direction of the heating chamber were measured. In addition,
The 0.3% C carburizing depth is a distance from the outermost surface of a portion where the carbon concentration is 0.3%. FIG. 6 shows the result. As is clear from FIG. 6, the variations in the surface carbon concentration and the 0.3% C carburizing depth of the five races are small and uniform.

From the results shown in FIGS. 5 and 6, it can be seen that all the bearing rings are uniformly carburized without carburization.

[Brief description of the drawings]

FIG. 1 is a graph showing the results of Example 1.

FIG. 2 is a longitudinal sectional view showing a fuel injection nozzle used in a second embodiment.

FIG. 3 is a graph showing the result of Case 1 of Example 2.

FIG. 4 is a graph showing the result of Case 2 of Example 2.

FIG. 5 is a graph showing the results of Example 3.

FIG. 6 is a graph showing another result of Example 3.

[Explanation of symbols]

 (1): Fuel injection nozzle (workpiece)

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[Procedure amendment]

[Submission date] October 13, 2000 (2000.10.
13)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0019

[Correction method] Change

[Correction contents]

Then, this fuel injection nozzle (1) is
In a posture in which the opening end facing downward of (2), stacked in a basket with a dummy 10 kg, was placed the basket in the effective space of the heating chamber of the carburizing furnace.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazuka Yamaguchi 229 Kahata-cho, Tenri-shi, Nara Prefecture Inside Koyo Thermo System Co., Ltd. F term (reference) 4K028 AA01 AB01 AC03 AC08

Claims (5)

[Claims] 1. A vacuum carburizing method using a mixed gas of ethylene gas and hydrogen gas as a carburizing gas. 2. The mixing ratio of hydrogen gas in the mixed gas is 15
The vacuum carburizing method according to claim 1, wherein the amount is set to 50%. 3. The method according to claim 1, which is performed under a pressure of 40 to 65 Torr.
Or the vacuum carburizing method of 2. 4. A vacuum carburizing method for carburizing a workpiece having a bottomed hole from an end face, wherein a mixed gas of ethylene gas and hydrogen gas is used as a carburizing gas.
A vacuum carburizing method which is carried out at a temperature of 70 to 880C and a pressure of 25 to 35 Torr. 5. The mixing ratio of hydrogen gas in the mixed gas is 30.
The vacuum carburizing method according to claim 4, wherein the amount is set to 50%.