JP2011032556A - Method of carburizing steel member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of carburizing a steel member capable of partially controlling a carburizing depth (carburization concentration distribution) only by changing carburizing conditions without allowing the steel member to pass through specific processes and, thereby, capable of manufacturing a gear having a high bending fatigue strength, in particular on the dedendum. <P>SOLUTION: The method of carburizing a steel member includes steps of: filling a carburizing gas into the interior of a carburizing furnace in which an environmental pressure is set to be a low pressure condition; and feeding a gear into the carburizing furnace to perform the carburization. Therein, a flow rate of the carburizing gas per 1 m<SP>3</SP>of volume of the carburizing furnace is desirably made to be 60 L/min or less. More desirably, the flow rate of the carburizing gas per 1 m<SP>3</SP>of volume of the carburizing furnace is made to be 20 L/min or less. In such a case, 100% acetylene C<SB>2</SB>H<SB>2</SB>is desirably used as the carburizing gas. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a carburizing method for a steel member, and more particularly, to a technique for partially changing the carburizing depth in a steel member that is an object of carburizing treatment.

  Conventionally, carburizing treatment is known as one of the surface hardening methods applied to steel members, and the carburizing treatment is also applied to gears used as machine parts. In carburizing treatment, the steel material that is the object to be treated is sent to a carburizing furnace filled with hydrocarbon gas such as acetylene, and carbon is penetrated and diffused on the surface of the object to be treated, followed by quench hardening. It is a technique to perform. Thereby, the wear resistance of the surface is improved while ensuring the toughness of the workpiece. In such a general carburizing method for steel members, the carburizing depth is uniform over the entire object to be processed, so it is difficult to manufacture parts with partially different carburizing depths.

  Further, regarding a steel member having a groove portion such as a gear, in general, in a protruding portion (a tooth surface in the case of a gear, hereinafter referred to as a tooth surface), the surface pressure fatigue strength is the base end portion (of the gear). In this case, the bending fatigue strength is required. The carburizing treatment is effective for improving the surface fatigue strength at the tooth surface, and on the other hand, applying the compressive residual stress is effective for improving the bending fatigue strength at the tooth root. Here, in order to impart compressive residual stress at the tooth root, it is desirable to make the carburization depth in the carburizing process shallow at the tooth base (increase the carburization concentration gradient).

  For the purpose of manufacturing parts having partially different carburization depths (carburization concentration distribution) as described above, a technique for performing vacuum carburization after forming an oxide film on the surface of the object to be processed has been proposed (for example, Patent Document 1).

JP 2008-231563 A

  However, in the method of vacuum carburizing after forming an oxide film on the surface of the object to be processed as in the prior art, precise control is performed so that the thickness of the oxide film is in the range of 0.05 μm to 5 μm. Therefore, it is difficult to obtain a desired effect if it is out of this range.

  On the other hand, an oxide film generally causes carburization to be inhibited, and the formation state of the oxide film is strongly influenced by the surface properties of the object to be treated. It is difficult. That is, it has been difficult in terms of quality control to manufacture parts with partially different carburization depths (carburization concentration distribution) by the above-described prior art.

  Therefore, in the present invention, in view of the above situation, the carburization depth (carburization concentration distribution) can be partially adjusted only by changing the carburizing conditions without going through a special process, and in particular, the base end. The present invention provides a carburizing method for a steel member, which makes it possible to manufacture a steel member (gear) having a high bending fatigue strength at the portion (tooth base).

  The problem to be solved by the present invention is as described above. Next, means for solving the problem will be described.

That is, in claim 1, a carburizing furnace filled with a hydrocarbon-based gas as a carburizing gas in which the atmospheric pressure condition is set to a low pressure condition, and a steel member having a groove portion is fed into the carburizing furnace. The method of carburizing a steel member, wherein the flow rate of the hydrocarbon-based gas per 1 m ^{3 of the} carburizing furnace is 60 L / min or less.

  In the present invention, the steel member is a gear.

In claim 3, it is to use 100% of _C 2 _{H 2} as the hydrocarbon gas.

According to a fourth aspect of the present invention, the flow rate of the hydrocarbon-based gas per 1 m ^{3 of the} carburizing furnace is 20 L / min or less.

  In claim 5, the carburizing temperature inside the carburizing furnace is set to 1050 degrees or more.

  As effects of the present invention, the following effects can be obtained.

  According to the present invention, the carburization depth (carburization concentration distribution) can be partially adjusted only by changing the carburizing conditions without passing through a special process, and thereby, the bending fatigue strength particularly at the tooth root is large. Gears can be manufactured.

(A) is the figure which shows the test piece which cut out the gearwheel which is a to-be-processed object of this invention, (b) is the schematic which showed the carburizing furnace, (c) showed the heating cycle in one Embodiment of this invention. Figure. The expanded sectional view of the gearwheel which is a processed material of the present invention. The figure which showed the 1st experimental condition and 1st experimental result which concern on this invention. The figure which showed the relationship between the flow volume of the carburizing gas in the 1st experiment which concerns on this invention, and the carburizing depth of a tooth root part. The figure which showed the 2nd experimental condition which concerns on this invention, and the 2nd experimental result. The figure which showed the relationship between the density | concentration of the carburizing gas in the 2nd experiment which concerns on this invention, and the carburizing depth of a tooth root part. The figure which showed the 3rd experimental condition and 3rd experimental result which concern on this invention. The figure which showed the relationship between the density | concentration of the carburizing gas in the 3rd experiment which concerns on this invention, and the carburizing depth of a tooth root part.

Next, embodiments of the invention will be described.
It should be noted that the technical scope of the present invention is not limited to the following examples, but broadly covers the entire scope of the technical idea that the present invention truly intends, as will be apparent from the matters described in the present specification and drawings. It extends.

[First experiment]
A first experiment conducted by the present applicant regarding a carburizing method for a steel member according to an embodiment of the present invention will be described with reference to FIG.
In the carburizing method for a steel member according to the present embodiment, a steel member having a groove is used as an object to be processed. In this experiment, as shown in FIG. 1A, a test piece TP cut out from a gear made of SCM420 was used as an object to be processed. The object to be processed is not limited to a gear, and the present invention can be applied to any member that has a groove formed, such as a bolt or a nut.

Then, as shown in FIG. 1 (b), the test piece TP, after acetylene C ₂ H ₂ is carburizing gas is fed into the carburizing furnace filled with a concentration of 100%, by heating with a heater, the Carburizing treatment was performed on the test piece TP. As shown in FIG. 1 (c), the carburizing condition was such that the carburizing temperature was 950 degrees. In the carburizing furnace, the atmospheric pressure was set to a low pressure condition of about 500 Pa. The carburizing furnace used was a cylinder having an inside diameter of about 8 cm and a height of about 1.5 m, and a volume of about 7.5 × 10 ⁻³ m ³ .
The carburizing gas is not limited to acetylene C ₂ H ₂ , and other hydrocarbon gases such as methane CH ₄ , ethylene C ₂ H ₄ , propane C ₃ H ₈ , butane C ₄ H ₁₀ are used. It is also possible.

For the first experiment conducted by the applicant of the present application, test no. 1 to test no. Five types of test pieces TP up to 5 were prepared, and carburizing treatment was performed under different conditions. Specifically, as shown in FIG. 3, the flow rate of the carburizing gas per 1 m ^{3 of the} carburizing furnace was measured according to Test No. The test piece TP of 1 is 5 L / min. 2 to test no. The test pieces TP up to 5 were, in order, 10 L / min, 20 L / min, 60 L / min, and 100 L / min. For example, test no. In the case of the test piece TP of 5, the volume of the carburizing furnace is about 7.5 × 10 ⁻³ m ³ , and therefore the flow rate of the carburizing gas is 100 L / min × 7.5 × 10 ⁻³ m ³ = about 0. .75 L / min. In addition, Test No. The condition of the test piece TP 5 is the same as the condition for manufacturing the conventional product.

Next, the result regarding the carburizing method of the steel member which concerns on this experiment is demonstrated using FIGS.
As shown in FIG. 2, each experiment according to the present specification, as shown in FIG. 2, for the gear as the test piece TP, the depth of the carburized portion in the protruding portion (tooth surface) of the tooth portion is defined as the tooth surface depth, and the base end of the tooth portion. The depth of the carburized portion in the portion (tooth root) was measured as the tooth root depth.

Then, by changing the flow rate of the carburizing gas per 1 m ³ of the carburizing furnace volume as described above and performing the carburizing process on the test piece TP, the tooth root depth is changed as shown in FIGS. I was able to. Specifically, each test No. The tooth root depth when the carburizing process is performed so that the tooth surface depth of the test piece TP in the test piece TP becomes a constant value of 0.50 mm, 1 to test no. In this order, the test pieces TP of 5 could be changed to 0.19 mm, 0.32 mm, 0.36 mm, 0.44 mm, and 0.47 mm.
In other words, by reducing the flow rate of the carburizing gas, the tooth root depth can be made smaller than the tooth surface depth. This is considered to be an effect that the carburizing gas does not easily reach the tooth root portion by reducing the flow rate of the carburizing gas.

In the present experiment, the flow rate of the carburizing gas per 1 m ^{3 of the} carburizing furnace is changed. However, it is possible to adopt other configurations that make it difficult for the carburizing gas to reach the tooth root portion. is there. Specifically, a method of controlling the flow rate of the carburizing gas in the vicinity of the surface of the test piece TP and a method of controlling the weight increase (F value) before and after carburizing of the test piece TP per unit time and unit surface area are possible. is there.

  As described above, by using the carburizing method for steel members according to this experiment, it was possible to adjust the carburization concentration distribution in the tooth root portion. As a result, sufficient compressive residual stress can be imparted at the tooth root, so that a gear having high bending fatigue strength at the tooth root can be produced.

Specifically, in this experiment, test No. 1 with a carburizing gas flow rate of 100 L / min per 1 m ^{3 of the} carburizing furnace volume was used. The test piece TP of No. 5 gave a compressive residual stress of −1102 kN / mm ² , whereas the test piece TP with a flow rate of 20 L / min. No. 3 test piece TP was able to impart a compressive residual stress of −1330 kN / mm ² .

As described above, in the carburizing method for steel members according to the present invention, the carburizing furnace is filled with the carburizing gas and the gear is fed into the carburizing furnace. is there. From the above experimental results, in order to reduce the flow rate of the carburizing gas and make it difficult for the carburizing gas to reach the tooth root portion, the flow rate of the carburizing gas per 1 m ^{3 of the} carburizing furnace is set to 60 L / min or less. Is desirable. Specifically, in the carburizing furnace in this experiment, since the volume of the carburizing furnace is about 7.5 × 10 ⁻³ m ³ , the flow rate of the carburizing gas is 60 L / min × 7.5 × 10 ⁻³ m ³ = About 0.45 L / min.
More desirably, the flow rate of the carburizing gas per 1 m ^{3 of the} carburizing furnace is set to 20 L / min or less in order to reduce the flow rate of the carburizing gas and make it difficult for the carburizing gas to reach the tooth root portion. Is desirable. Specifically, in the carburizing furnace in this experiment, the flow rate of the carburizing gas is 20 L / min × 7.5 × 10 ⁻³ m ³ = about 0.15 L / min.
Further, in this way, when the flow rate of the carburizing gas is smaller than the flow rate in the conventional carburizing process (100 L / min per 1 m ³ ), it is desirable to use 100% acetylene C ₂ H ₂ as the carburizing gas.

  In this experiment, by configuring as described above, the carburization depth (carburization concentration distribution) can be partially adjusted by changing the carburizing conditions without passing through a special process. The original gear with high bending fatigue strength could be manufactured.

[Second experiment]
Next, a second experiment conducted by the applicant of the present application regarding a carburizing method for a steel member according to an embodiment of the present invention will be described with reference to FIGS. 5 and 6.
In the experiment of the carburizing method for steel members according to the present embodiment, the test piece TP cut out from the gear made of SCM420 was used as the object to be processed, as in the first experiment.
Then, the test piece TP, and fed into the carburizing furnace filled with varying concentrations of acetylene C ₂ H ₂ is carburizing gas and subjected to carburizing for the test piece TP. The carburizing conditions were a carburizing temperature of 950 ° C., and the carburizing furnace was set to a low pressure condition of an atmospheric pressure of about 500 Pa. The flow rate of the carburizing gas per 1 m ^{3 of the} carburizing furnace was 100 L / min.

For the second experiment conducted by the applicant of the present application, test no. 11 to test no. Five types of test pieces TP up to 15 were prepared, and carburizing treatment was performed under different conditions. More specifically, as shown in FIG. 5, the concentration of acetylene C ₂ H ₂ is carburizing gas, Test No. No. 11 test piece TP was 5%. No. 12 to Test No. Up to 15 test pieces TP are set to 10%, 30%, 50%, and 100% in order. The acetylene C ₂ H ₂ having a concentration of less than 100% was diluted with an inert gas such as nitrogen N ₂ , helium He, or argon Ar. In addition, Test No. The carburizing conditions for the 15 test pieces TP are the same as the conditions for manufacturing the conventional product.

Next, the result regarding the carburizing method of the steel member which concerns on this experiment is demonstrated using FIG.5 and FIG.6.
In this experiment, as shown in FIGS. 5 and 6, the root depth could be changed by changing the concentration of acetylene C ₂ H ₂ which is a carburizing gas. Specifically, each test No. The tooth root depth when the carburizing process is performed so that the tooth surface depth of the test piece TP in the test piece TP becomes a constant value of 0.50 mm, 11 to Test No. The test pieces TP could be changed to 0.23 mm, 0.30 mm, 0.39 mm, 0.44 mm, and 0.47 mm in the order of 15 test pieces TP.
In other words, by reducing the concentration of acetylene C ₂ H ₂ that is a carburizing gas, the tooth root depth can be made smaller than the tooth surface depth. This is considered to be an effect that the carburizing gas does not easily reach the tooth base portion due to the lower concentration of the carburizing gas.

  As described above, by using the carburizing method for steel members according to this experiment, it was possible to adjust the carburization concentration distribution in the tooth root portion. As a result, sufficient compressive residual stress can be imparted at the tooth root, so that a gear having high bending fatigue strength at the tooth root can be produced.

Specifically, in this experiment, test No. 1 with the concentration of acetylene C ₂ H ₂ as 100% was used. Test piece TP No. 15 applied compressive residual stress of −1102 kN / mm ² , whereas test No. 15 with a concentration of 30%. Thirteen test pieces TP were able to impart a compressive residual stress of −1380 kN / mm ² .

As described above, in the carburizing method for a steel member according to the present invention, the carburizing gas is filled into the carburizing furnace with the atmospheric condition set to the low pressure condition, and the gear is fed into the carburizing furnace. is there. From the above experimental results, it is desirable to use acetylene C ₂ H ₂ having a concentration of 50% or less, more preferably 10% or less as the carburizing gas.

  In this experiment, by configuring as described above, the carburization depth (carburization concentration distribution) can be partially adjusted by changing the carburizing conditions without passing through a special process. The original gear with high bending fatigue strength could be manufactured.

[Third experiment]
Next, a third experiment conducted by the applicant of the present application regarding the carburizing method for a steel member according to an embodiment of the present invention will be described with reference to FIGS.
In the experiment of the carburizing method for steel members according to the present embodiment, the test piece TP cut out from the gear made of SCM420 was used as the object to be processed, as in the first experiment.
Then, the test piece TP, and fed into the carburizing furnace filled with varying concentrations of acetylene C ₂ H ₂ is carburizing gas and subjected to carburizing for the test piece TP. The carburizing conditions were such that the carburizing temperature inside the carburizing furnace was 1100 degrees, and the atmospheric pressure in the carburizing furnace was a low pressure condition of about 500 Pa. The flow rate of the carburizing gas per 1 m ^{3 of the} carburizing furnace was 100 L / min.

For the third experiment conducted by the applicant of the present application, test no. 21 to test no. Five types of test pieces TP up to 25 were prepared, and carburizing treatment was performed under different conditions. More specifically, as shown in FIG. 7, the concentration of acetylene C ₂ H ₂ is carburizing gas, Test No. The test piece TP No. 21 was 5%, and the following test No. No. 22 to Test No. Up to 25 test pieces TP are set to 10%, 30%, 50%, and 100% in order.

Next, the result regarding the carburizing method of the steel member which concerns on this experiment is demonstrated using FIG.7 and FIG.8.
In this experiment, as shown in FIG. 7 and FIG. 8, the tooth depth could be changed by changing the concentration of acetylene C ₂ H ₂ which is a carburizing gas. Specifically, each test No. The tooth root depth when the carburizing process is performed so that the tooth surface depth of the test piece TP in the test piece TP becomes a constant value of 0.50 mm, 21 to test no. The test pieces TP of 25 were able to be changed to 0.13 mm, 0.21 mm, 0.35 mm, 0.46 mm, and 0.47 mm in this order. In other words, by reducing the concentration of acetylene C ₂ H ₂ that is a carburizing gas, the tooth root depth can be made smaller than the tooth surface depth.

  Furthermore, by setting the carburizing temperature inside the carburizing furnace to 1050 ° C. or higher, the carburizing depth could be further reduced as compared with the second experimental result in which the carburizing temperature was 950 ° C. This is considered to be an effect that the carburizing gas is thermally decomposed before reaching the tooth root part due to an increase in the carburizing temperature inside the carburizing furnace, thereby making it difficult to reach the tooth root part.

  As described above, by using the carburizing method for steel members according to this experiment, it was possible to adjust the carburization concentration distribution in the tooth root portion. As a result, a larger compressive residual stress can be applied at the tooth root, so that a gear having a higher bending fatigue strength at the tooth root can be produced.

  In this experiment, by configuring as described above, the carburization depth (carburization concentration distribution) can be partially adjusted by changing the carburizing conditions without passing through a special process. A gear having a higher bending fatigue strength can be produced.

  TP test piece

Claims (5)

A steel member that is filled with a hydrocarbon-based gas as a carburizing gas inside a carburizing furnace having a low atmospheric pressure condition, and that feeds a steel member having a groove into the carburizing furnace. A carburizing method,
The flow rate of the hydrocarbon-based gas per 1 m ^{3 of the} carburizing furnace is 60 L / min or less.
A method for carburizing a steel member. The steel member is a gear;
The carburizing method for a steel member according to claim 1, wherein 100% C ₂ H ₂ is used as the hydrocarbon-based gas,
The carburizing method for a steel member according to claim 1 or 2, characterized by the above. The flow rate of the hydrocarbon-based gas per 1 m ^{3 of the} carburizing furnace is 20 L / min or less.
The carburizing method for a steel member according to any one of claims 1 to 3, wherein the carburizing method is performed. The carburizing temperature inside the carburizing furnace is 1050 ° C. or higher.
The carburizing method for a steel member according to any one of claims 1 to 4, wherein the carburizing method is performed.

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