KR100996285B1 - Method for treating vacuum carburization - Google Patents

Abstract

The present invention relates to a workpiece vacuum carburizing method which presents a process technology of vacuum heat treatment for removing sooting which is one of defects of vacuum carburizing treatment of a workpiece, that is, a carbon steel component material.

Carbon steel parts material, vacuum carburizing, shooting

Description

Method for treating vacuum carburization

The present invention relates to a vacuum carburizing method of a workpiece, and more particularly, to a vacuum carburizing method in which shooting, which is one of the defects of vacuum carburizing treatment of a carbon steel component material, is not generated.

In general, the surface hardening treatment method which hardens the surface of a workpiece to improve mechanical properties such as abrasion resistance and fatigue resistance includes a method of locally heat treating only the surface of the workpiece, and spreading, penetrating or forcing a new material into the workpiece. The method of forming a hard alloy layer by injecting and reacting with a base metal, the method of coating a high hardness material layer on the surface, and forming a separate layer, etc. are mentioned.

On the other hand, the core hardening is to cure the whole inside and the outside through quenching the whole to be processed, etc. In contrast, the surface hardening is a method of curing the outer surface while maintaining the properties of the core as it is.

Such surface hardening can be roughly divided into nitriding method for injecting nitrogen and carburization method for injecting carbon from the surface of the workpiece, and the nitriding method includes gas nitriding, salt bath nitriding and ion nitriding, and the carburizing method is gas Carburizing, salt bath carburizing and vacuum carburizing.

The carburizing method which is widely used at present is gas carburizing method, and the surface abnormality layer and the non-quenching layer which reduce durability on the surface are produced in 15 ~ 25㎛, and high temperature carburization is not possible, which leads to an increase in heat treatment time and cost, and manufacturing process. Various problems, such as generation of carbon dioxide, salt bath or oil, and post-treatment costs have been raised.

Among the new carburizing methods to cope with the problem of gas carburizing, the most attention-getting method is vacuum carburizing.

The vacuum carburizing method is a new heat treatment method for carburizing in a vacuum atmosphere and quenching with a high-pressure gas. Since the surface abnormality layer is not generated, durability (fatigue resistance and abrasion resistance) is dramatically improved, and carbon dioxide is generated during carburization. Almost no, there is no waste oil / waste water treatment, and there is no need for post-processing to remove foreign substances, which has the advantage of improving productivity.

However, when the surface hardening of the workpiece by the vacuum carburizing method inevitably causes a sorting on the surface, such sorting degrades characteristics such as surface hardness, wear resistance and lubricity of the workpiece.

Accordingly, the present invention is to solve all the disadvantages and problems of the prior art as described above, not only does not sort out on the surface of the workpiece in the surface treatment of the workpiece by vacuum carburizing method, but also surface hardening SUMMARY OF THE INVENTION An object of the present invention is to provide a vacuum carburizing method of an object which presents a vacuum carburizing method having excellent characteristics.

The object of the present invention is the step of preheating the preheating process for a first time after the temperature of the object to be heated to the preheating temperature in a vacuum atmosphere; Heating the workpiece to a carburizing temperature and supplying a hydrocarbon-based carburizing gas to a process pressure of 10 ⁻³ torr or less; Performing a carburizing process of permeating and diffusing carbon into the workpiece while maintaining the carburizing temperature and the process pressure for a second time; Cooling the object to be treated after the carburizing process; Heating the cooled object to a tempering temperature, and then performing a tempering process of maintaining the tempering temperature for a third time; And subjecting the workpiece to air-cooling after the tempering process.

In addition, the object of the present invention, the first time is 60 minutes to 120 minutes, the second time is 90 minutes to 150 minutes, the third time is a vacuum carburizing method, characterized in that 210 minutes to 270 minutes It is also achieved by

The above object of the present invention is also achieved by the vacuum carburizing method of the workpiece, wherein the first time is 90 minutes, the second time is 120 minutes, and the third time is 240 minutes.

In addition, the object of the present invention is the preheating temperature is 800 ℃ to 900 ℃, the carburizing temperature is 980 ℃ to 1080 ℃, the tempering temperature vacuum treatment carburizing method, characterized in that the 470 ℃ to 550 ℃ It is also achieved by

In addition, the object of the present invention is also achieved by the vacuum carburizing method to be treated, characterized in that the preheating temperature is 850 ℃, the carburizing temperature is 1030 ℃, the tempering temperature is 520 ℃.

In addition, the object of the present invention is achieved by the vacuum carburizing method of the workpiece, characterized in that the carburizing gas is any one or more of CH ₄ (methane), C ₃ H ₈ (propane) and C ₄ H ₁₀ (butane). do.

The workpiece vacuum carburizing method of the present invention has an effect of providing a workpiece vacuum carburizing method which is excellent in the surface hardening property of the workpiece but does not generate a sort on the surface.

Details of the above objects and technical configurations and the effects thereof according to the present invention will be more clearly understood by the following detailed description with reference to the drawings showing preferred embodiments of the present invention. Like numbers refer to like elements throughout.

1 is a flowchart illustrating a method of vacuum carburizing a workpiece according to an exemplary embodiment of the present invention, and FIG. 2 is a graph showing a temperature change of a workpiece of the workpiece vacuum carburizing method according to an embodiment of the present invention. .

Referring to FIGS. 1 and 2, the vacuum carburizing method of the workpiece is described. First, the workpiece is charged into the vacuum carburizing apparatus.

Subsequently, the inside of the vacuum carburizing apparatus into which the said to-be-processed object was charged is exhausted in a vacuum atmosphere.

Subsequently, the to-be-processed object is heated and heated up to preheating temperature. And the preheating process (S100) for preheating the object to be treated for the first time at the preheating temperature.

At this time, as shown in Figure 2 and the preheating temperature is 800 ℃ to 900 ℃, preferably 850 ℃. In addition, the first time is 60 minutes to 120 minutes, preferably 90 minutes.

The preheating process (S100) is a process for heating the entire workpiece to the preheating temperature, which is not only necessary to obtain a desired carburizing depth and a uniform carburizing layer during the carburizing process, which will be described later, but also a workpiece by thermal shock. It is necessary to prevent deformation.

Subsequently, the workpiece is heated to a carburizing temperature, and at the same time or sequentially, the hydrocarbon-based carburizing gas is supplied into the vacuum carburizing apparatus, and the vacuum degree inside the vacuum carburizing apparatus is supplied at a process pressure of 10 ^-3 torr or less. (S200).

At this time, the carburizing gas uses a hydrocarbon gas such as CH ₄ (methane), C ₃ H ₈ (propane) and C ₄ H ₁₀ (butane), and any one or two or more of these hydrocarbon gases are used. .

As described above, when the vacuum carburizing process has a process pressure of 10 ⁻³ torr or less, shooting may not occur on the surface of the workpiece.

The shooting is caused by an imbalance in the internal diffusion rate and surface accumulation of carbon derived from the carburizing gas on the surface of the workpiece as the carburizing gas is excessive (ie, high process pressure) or undecomposed in the vacuum carburizing apparatus. Therefore, when the process pressure, that is, the pressure of the carburized gas is controlled to 10 ⁻³ torr or less as in the present invention, the above-described shooting is not generated.

Subsequently, the carburizing temperature and the process pressure are maintained for a second time to carry out the carburizing process (S300) of infiltrating and diffusing carbon into the object.

At this time, as shown in Figure 2, the carburizing temperature is 980 ℃ to 1080 ℃, preferably 1030 ℃.

The second time is 90 minutes to 150 minutes, preferably 120 minutes.

Subsequently, when the carburization process (S300) is completed, the object is cooled (S400).

Subsequently, the oil-cooled object is heated to a tempering temperature, and then a tempering process (S500) of maintaining the third tempering temperature at the tempering temperature is performed.

Subsequently, after the tempering process (S500) is completed, the air cooling process (S600) for cooling the workpiece in air is performed to complete the step of vacuum carburizing the workpiece.

In this case, as shown in FIG. 2, the tempering temperature is 470 ° C to 550 ° C, preferably 520 ° C.

Further, the third time is 210 minutes to 270 minutes, preferably 240 minutes.

At this time, the tempering process (S500) and the air-cooling process (S600) may be repeated once or several times.

Experimental Example 1

3A and 3B are tissue photographs showing fracture surfaces showing a result of vacuum carburizing SKD11, which is a cold mold material, by using a vacuum carburizing method of a workpiece according to an embodiment of the present invention.

At this time, the present experimental example shows the results of the carburizing process time change in the vacuum carburizing method.

The electron micrographs of SKD11 shown in FIGS. 3A and 3B show the results of vacuum carburizing at 100 ° C. for 100 minutes (for FIG. 3A) or 120 minutes (for FIG. 3B) at 1030 ° C., respectively. In this case, as shown in FIG. 3A, the shape of the carbide is close to a spherical shape, and as shown in FIG. 3B, the shape of the carbide shows a rod shape and a mixture of spheres.

In this case, the more spherical the shape of the carbide shows excellent material properties, the more the spherical carbide appears to be 100 minutes when the vacuum carburizing is carried out for 100 minutes than the case of 120 minutes.

Experimental Example 2

4A and 4B are tissue photographs showing fracture surfaces showing a result of vacuum carburizing SKD11, which is a cold mold material, by using a vacuum carburizing method of a workpiece according to an embodiment of the present invention.

In this case, the experimental example shows the effect of the tempering process in the vacuum carburizing method.

4A and 4B are microscopic histograms of SKD11 shown in FIGS. 4A and 4B, respectively, after the carburizing process was performed at 1030 ° C. for 100 minutes, and the tempering process was performed at 520 ° C. for 180 minutes, respectively.

As shown in FIG. 4A, as a result of performing the tempering process under the above conditions, it can be seen that the orientation and self-decomposition of the carbide occurs as the carbides are arranged in an orderly manner.

In addition, in Fig. 4b, not only shows the formation of secondary carbides and the refinement of secondary carbide particles, but also the undissolved primary carbides are widely distributed, and the particle size of the carbides is uniformly shown so that the primary carbides are short-lived. It shows that it is not showing uniformity or showing band structure.

When the primary carbides are aligned in the short-length direction or form a band structure, there are not only problems of anisotropy of various mechanical properties, but also anisotropy of dimensional change, which makes it difficult to predict the dimensional change in the longitudinal direction and the width direction during heat treatment. Generate.

However, as shown in FIGS. 4A and 4B, when the carburized material is carburized using the vacuum carburizing method according to an embodiment of the present invention, the carbides are arranged in an orderly manner, and thus the orientation and self decomposition of the carbides are generated. The same problem does not occur.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, Various changes and modifications will be possible.

1 is a flowchart illustrating a method of vacuum carburizing a workpiece according to an exemplary embodiment of the present invention, and FIG. 2 is a graph showing a temperature change of a workpiece of the workpiece vacuum carburizing method according to an embodiment of the present invention. .

3A and 3B are tissue photographs showing fracture surfaces showing a result of vacuum carburizing SKD11, which is a cold mold material, by using a vacuum carburizing method of a workpiece according to an embodiment of the present invention.

4A and 4B are tissue photographs showing fracture surfaces showing a result of vacuum carburizing SKD11, which is a cold mold material, by using a vacuum carburizing method of a workpiece according to an embodiment of the present invention.

Claims (6)

Heating the workpiece to a preheating temperature in a vacuum atmosphere, and then performing a preheating process of preheating the first time; Heating the workpiece to a carburizing temperature and supplying a hydrocarbon-based carburizing gas to a process pressure of 10 ⁻³ torr or less; Performing a carburizing process of permeating and diffusing carbon into the workpiece while maintaining the carburizing temperature and the process pressure for a second time; Cooling the object to be treated after the carburizing process; Heating the cooled object to a tempering temperature, and then performing a tempering process of maintaining the tempering temperature for a third time; And And air-cooling the workpiece after the tempering process. And said first time is 90 minutes, said second time is 120 minutes, and said third time is 240 minutes. delete delete delete Heating the workpiece to a preheating temperature in a vacuum atmosphere, and then performing a preheating process of preheating the first time; Heating the workpiece to a carburizing temperature and supplying a hydrocarbon-based carburizing gas to a process pressure of 10 ⁻³ torr or less; Performing a carburizing process of permeating and diffusing carbon into the workpiece while maintaining the carburizing temperature and the process pressure for a second time; Cooling the object to be treated after the carburizing process; Heating the cooled object to a tempering temperature, and then performing a tempering process of maintaining the tempering temperature for a third time; And And air-cooling the workpiece after the tempering process. The preheating temperature is 850 ° C, the carburizing temperature is 1030 ° C, the tempering temperature is 520 ° C to be treated. The method according to claim 1 or 5, The carburizing gas is any one or more of CH ₄ (methane), C ₃ H ₈ (propane) and C ₄ H ₁₀ (butane).

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