KR20200049304A - Low-Temperature Carburizing Method by Controlling Carbon Potential - Google Patents

Abstract

The present invention is to provide a low-temperature carburizing method for effectively preventing soot generated on the final product of a low-temperature carburizing process. The low-temperature carburizing method according to the present invention comprises a step (a) of performing pretreatment on a target metal, a step (b) of introducing the target metal into a reaction chamber and raising the temperature to a set temperature, and a step (c) of forming a vacuum atmosphere in the reaction chamber and supplying a reaction gas containing at least hydrocarbon gas to perform carburization. In the step (c), the hydrocarbon gas is supplied below a preset reference threshold considering relationship between a plurality of carburizing processes during carburization.

Description

Low-temperature carburizing method by controlling carbon potential {Low-Temperature Carburizing Method by Controlling Carbon Potential}

The present invention relates to a low-temperature carburizing method, and more particularly, to a low-temperature vacuum carburizing method capable of minimizing soot generated in the final result through carburizing carbon potential control.

In general, austenitic stainless steels exhibit relatively good corrosion resistance, but are susceptible to fitting corrosion in aqueous solutions with Cl groups, and are relatively vulnerable to wear due to their relatively low hardness, especially limited in seawater conditions. There is.

Therefore, in order to solve this problem, nitriding or carburizing is conventionally performed by applying various surface modification methods.

However, when the nitriding or carburizing process is performed at a high temperature (salt bath nitriding, high temperature carburizing process, etc.), a problem occurs in that corrosion resistance is lowered due to precipitation of nitrides and carbides.

In addition, when the nitriding or carburizing process is performed at a low temperature condition, there is a problem that it is difficult to form a carburizing and nitriding layer by a natural oxide film existing on the surface of the metal.

In addition, since the low temperature nitridation or low temperature carburization process uses a reactive gas having high reactivity, there is a problem in that soot (soot, metal dust) is easily generated on the product surface. Such a suit is vulnerable to a corrosive environment, and once it is generated, it is difficult to remove it, which greatly degrades the product quality.

Therefore, a method for solving these problems is required.

Korean Patent Publication No. 10-2011-0104631

The present invention has been made to solve the problems of the prior art described above, and has an object to provide a low-temperature carburization treatment method for effectively preventing the occurrence of soot in the final product in the process of performing low-temperature carburization treatment.

The problems of the present invention are not limited to the problems mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the following description.

A low-temperature carburization treatment method through carbon potential control of the present invention for achieving the above object is a step (a) of performing a pre-treatment on the target metal, the target metal is introduced into the reaction chamber, and the temperature is raised to a set temperature (b ) And the step (c) of forming the reaction chamber in a vacuum atmosphere and supplying a reaction gas containing at least hydrocarbon gas to perform carburization, wherein step (c) comprises a plurality of steps during the carburizing process. Considering the relationship between the carburizing process conditions, the hydrocarbon gas is supplied below a preset reference threshold.

In addition, the plurality of carburizing process conditions may include at least one of a relative flow rate of the hydrocarbon gas, a carburizing treatment time, a process pressure, and a process temperature in the reaction gas.

In addition, the threshold value may be calculated through multiplication between the plurality of process conditions.

And the threshold is,

(α: relative flow of hydrocarbon gas, SLM: Standard Liter per Minute, t: process time, p: process pressure exp (-ΔG / RT): equilibrium constant)

It can be calculated through the formula of.

Further, the reference threshold may be 1.60 × 10 ¹¹ ℓ · atm.

In addition, the reaction gas may further include an atmosphere control gas.

In addition, the atmosphere control gas may include hydrogen.

And the atmosphere control gas may further include nitrogen.

In the step (c), the reaction chamber is formed in a vacuum atmosphere, and the reaction gas is injected at a predetermined pressure to accelerate carburization (c-1). (C-3) step (c-2) and (c-1) and (c-2) steps for diffusing carburizing by supplying a pressure below the reaction gas in step (c-3) are repeated at predetermined time intervals. ).

And the step (c-1) is to accelerate the carburization by supplying the reaction gas to the reaction chamber at a pressure of 5 mbar or less, and in the step (c-2), the reaction gas is 0.5 mbar or more to the reaction chamber (c). It can be made to diffuse carburizing by supplying below the pressure of the reaction gas of the step.

In addition, the step (c-3) may be to shorten the total process time of the step (c-1) to be repeated.

And the (c-3) step, it can be said to gradually increase the total process time of the (c-2) step is repeated.

In addition, the step (a), by supplying a natural oxide removal gas to the target metal to relieve the stress of the target metal, it is possible to weaken the bonding force of the natural oxide film and the target metal.

In addition, the natural oxide removal gas may be an oxidizing gas having a faster spontaneous oxidation reaction than the reaction gas.

In addition, the oxidizing gas may include carbon monoxide (CO).

In addition, the natural oxide removal gas may be a carbonaceous gas that reacts with the oxide by radicalizing.

In addition, the carbonaceous gas may include methane (CH ₄ ).

In addition, step (a) may be performed at a process temperature lower than the process temperature of step (c).

In addition, step (a) may be performed in a stress relaxation temperature atmosphere of the target metal.

Further, the target metal is formed of austenitic stainless steel, and step (a) may be performed in a temperature atmosphere of 250 ° C to 500 ° C.

In addition, in step (a), prior to the supply of the natural oxide removal gas, the target metal may be subjected to at least one or more treatments of electropolishing and salt bath.

The low-temperature carburization treatment method through the carbon potential control of the present invention for solving the above problems has the following effects.

First, by suppressing the generation of soot generated during the low-temperature carburization process, there is an advantage of forming a low-temperature carburization layer having a more homogeneous and high quality.

Second, since the formation of the soot is suppressed, there is an advantage of omitting or minimizing post-processing of the product.

Third, there is an advantage in that it is easy to apply to a product having a complicated shape, and thus, it is possible to reduce consideration of a structural design that is difficult to post-process.

The effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description of the claims.

1 is a flow chart showing each step of the low-temperature carburizing method according to an embodiment of the present invention;
2 is a view showing a state of a ferrule as a target metal for applying a low temperature carburizing method according to an embodiment of the present invention;
Figure 3 is a low-temperature carburization method according to an embodiment of the present invention, a view showing a state of performing a pre-treatment on the target metal;
Figure 4 is a low temperature carburizing method according to an embodiment of the present invention, a graph showing the change in the amount of oxygen remaining over time when the natural oxide removal gas is added;
5 is a low-temperature carburizing method according to an embodiment of the present invention, showing a state in which the target metal is charged in the reaction chamber;
6 is a graph showing a process of repeating a carburizing acceleration process and a carburizing diffusion process in a low-temperature carburizing method according to an embodiment of the present invention; And
7 to 10 in the low-temperature carburization method according to an embodiment of the present invention, a diagram showing the results of performing the carburization treatment while changing the conditions in pre-treatment conditions; And
11 to 15 is a view showing the results of performing the carburization treatment in a low-temperature carburization method according to an embodiment of the present invention, variously changing the conditions in the carburization process.

Hereinafter, preferred embodiments of the present invention, in which the object of the present invention can be specifically realized, will be described with reference to the accompanying drawings. In describing this embodiment, the same name and the same code are used for the same configuration, and additional description will be omitted.

1 is a flow chart showing each step of the low-temperature carburizing method according to an embodiment of the present invention.

As shown in Fig. 1, the low-temperature carburizing method according to the present invention includes (a) a step of pre-treating a target metal, (b) a step of introducing the target metal into a reaction chamber, and raising the temperature to a set temperature. And (c) performing carburization by injecting a reaction gas into the reaction chamber.

And in this embodiment, after the step (c), the step of cooling the target metal may be further performed.

Hereinafter, each step will be described in detail.

And, as shown in Figure 2, the target metal 10 for applying a low-temperature carburizing method according to an embodiment of the present invention was to be a stainless steel ferrule (ferrule).

The ferrule has a disadvantage in that the shape of the ferrule is more complicated than that of a general object, thereby forming an uneven surface layer during carburizing, and also difficult to control process parameters. Therefore, there is a problem that it is difficult to apply a general carburizing method.

In the low-temperature carburizing method according to this embodiment, first, a step of pre-treating the target metal is performed.

As shown in FIG. 3, this step may be performed by filling an organic solvent 52 in a predetermined container 50 and then washing the target metal 10 by introducing it into the organic solvent 52.

The reason for doing this is that various lubricants and foreign substances remain on the surface of the target metal 10 due to the grinding process. Therefore, for an effective carburizing process, washing is performed using an organic solvent 52.

At this time, acetone, ethanol, etc. may be applied as the organic solvent 52. In the present embodiment, vibration is applied using the ultrasonic vibrator 55 provided at the bottom of the container 50, and the target metal 10 is acetone or It was decided to wash in ethanol for about 5 minutes.

In addition, in this step, a process of performing a pickling process on the target metal may be further performed. The pickling process is a process of cleaning after immersion in an acid solution, and is intended to remove or weaken the natural oxide film formed on the surface of the target metal 10. In addition, the reason for doing so is to obtain an excellent carburizing effect in a low-temperature atmosphere.

And the pickling solution used in the pickling process includes a first solution containing ammonium hydrogen fluoride ((NH ₄ ) (HF ₂ )), nitric acid, water, and a second solution containing hydrogen peroxide and water 7: 3 It may have a component mixed in a ratio of.

In addition, a solution mixed in a weight ratio of 10% sulfuric acid, 4% sodium chloride, and 86% distilled water may be used as the pickling solution.

Alternatively, as the pickling solution, a solution in which 6 to 25% of nitric acid, 0.5 to 8% of hydrogen fluoride (HF), and distilled water in the remaining proportions according to the ratio of nitric acid and hydrogen fluoride are mixed in a volume ratio may be used.

On the other hand, in the step of performing pretreatment on the target metal 10, in order to remove the natural oxide film in addition to the above-described processes, by supplying the natural oxide film removal gas to the target metal 10 to relieve the stress of the target metal 10 And, a process of weakening the bonding force between the natural oxide film and the target metal 10 may be further performed.

At this time, the natural oxide film removal gas may include at least one of an oxidizing gas having a faster oxidation reaction than the reaction gas and a carbonizing gas radically reacting with the oxide film.

For example, the oxidizing gas may be carbon monoxide (CO), and the carbonizable gas may be methane (CH4). Of course, the types of the oxidizing gas and the carbonizable gas are not limited thereto.

In this process, the target metal 10 is placed in a reaction chamber 60 (refer to FIG. 5), and the natural oxide removal gas is charged in the reaction chamber 60, and when the natural oxide removal gas is an oxidizing gas By lowering the oxygen partial pressure in the reaction chamber 60 to an extremely low oxygen partial pressure in the reaction chamber 60 lower than the equilibrium oxygen pressure such as Cr ₂ O ₃ and Fe ₃ O ₄ , which are the main compounds of the stainless steel natural oxide film Natural oxides are decomposed naturally.

In addition, this process may be performed at a process temperature lower than the process temperature in step (c), that is, a carburizing process, which will be described later, which may be an atmosphere of stress relaxation temperature of the target metal 10.

In this embodiment, since the target metal 10 is austenitic stainless steel, this process can be performed in a temperature atmosphere of 250 ° C to 500 ° C.

In general, strain-hardening the austenitic thickness of the stainless steel, the native oxide film is composed of from about 5-10 times the Cr thick, the composition of the outermost surface of the lower equilibrium oxygen pressure ₂ O ₃ as compared to a fully annealed product effective to remove Is difficult

In order to solve this problem, in this embodiment, at least one of oxidizing gas and carbonizing gas is injected at a stress relaxation temperature of 250 ° C to 500 ° C, which is a stress relaxation temperature of austenitic stainless steel, which is lower than the carburizing process temperature. It is to be able to perform efficient low-temperature carburization by decomposing.

In more detail, in general, in order to naturally decompose the oxide film, the equilibrium oxygen pressure is 2.8 × 10 ^-46 bar for Cr ₂ O ₃ , 2.6 × 10 ^-32 bar for Fe ₃ O ₄ , and FeCr ₂ O ₄ Since it is 1.5 × 10 ^-44 bar, it is close to impossible because the process pressure must be kept lower to remove the natural oxide film.

In addition, even in the case of a heat treatment furnace using a low vacuum, since the vacuum degree of 10 ^-6 bar is limited, the amount of oxygen remaining in the reaction chamber 60 is expected to reach tens of ppm or more.

However, maintaining the vacuum of 10 ^-6 bar and introducing the carbon monoxide (CO) gas, which is an oxidizing gas, into the reaction chamber 60 heated to the stress relaxation temperature causes the following reaction.

Since the reaction is spontaneous reaction with G ^o = -220.4KJ / mol, it reacts with oxygen inside the reaction chamber 60 to produce carbon dioxide and can gradually remove oxygen, and thus the equilibrium oxygen pressure is extremely It can be lowered so that it can effectively decompose the natural oxide film of stainless steel.

Referring to the CO / CO ₂ Ellingham diagram shown in FIG. 4, the decomposition reaction of Cr ₂ O ₃ at 350 ° C. appears to decompose naturally when the ratio of CO / CO ₂ is 10 ^{8 or} more.

And to the residual oxygen in the introduced beginning of the oxidizing gas, the reaction chamber 60 to react with CO CO ₂ is generated, and the CO / ratio of increase of CO _2, however, the residual oxygen is consumed As the ratio is gradually increased as the CO / CO ₂ in accordance with 10 ^{If a} certain time is maintained from when it reaches ⁸ or more, the natural oxide film decomposes naturally.

At this time, this process may vary the retention time according to the volume of the reaction chamber 60, the degree of vacuum, the amount of oxygen remaining, and the purity of the natural oxide removal gas to be input.

When the natural oxide film of the target metal 10 is removed using the natural oxide removal gas, the time of the low-temperature carburization process can be reduced to less than half, and this process is performed in the reaction chamber 60. No equipment cost is required, and the risk of toxic substances can be reduced.

On the other hand, in this step, prior to the supply of the natural oxide removal gas, the target metal 10 may be subjected to at least one or more treatments of electropolishing and salt bath, and when the natural oxide film is removed through such a process Alternatively, when the bonding strength is lowered or the thickness is thinned, the exposure time of CO can be reduced to less than half compared to the target metal 10 that is hardened by processing.

The experiment process according to the supply of the natural oxide removal gas will be described later.

Next, step (b) of introducing the target metal into the reaction chamber and raising the temperature to the set temperature is performed.

As shown in FIG. 5, in this step, the target metal 10 is placed in the reaction chamber 60 to properly match the surface temperature of the target metal 10.

In this embodiment, the reaction chamber 60 includes a stage 65 on which the target metal 10 is seated, a first gas inlet 70a, and a second gas inlet 70b. However, it is of course that various reaction chambers 60 may be applied as one embodiment.

Next, step (c) of performing carburization by performing a reaction gas containing at least hydrocarbon gas into the reaction chamber 60 is performed.

In the case of this step, the hydrocarbon gas is supplied below a preset reference threshold value considering the relationship between a plurality of carburizing process conditions during the process of performing carburizing. In this embodiment, the hydrocarbon gas is assumed to be acetline, but the type of the hydrocarbon gas is not limited thereto.

The reason for this is to form a low-temperature carburizing layer having a more homogeneous and high quality by suppressing the production of soot generated during the low-temperature carburizing process.

And the plurality of carburization process conditions considered in this step may include at least one of the relative flow rate of the hydrocarbon gas, the carburization treatment time, the process pressure, and the process temperature among the reaction gases, and the threshold is the plurality of It can be calculated through multiplication between process conditions.

Specifically, in this embodiment, the threshold may be calculated through the following equation.

(α: relative flow of hydrocarbon gas, SLM: Standard Liter per Minute, t: process time, p: process pressure exp (-ΔG / RT): equilibrium constant)

This formula can be established when the hydrocarbon gas is supplied sufficiently to carburize the target metal 10 irrespective of the decomposition rate of the hydrocarbon gas according to temperature.

In addition, as a result of performing experiments with various changes in the carburizing process conditions, the reference threshold for suppressing soot generation was calculated to be 1.60Х10 ¹¹ ℓ · atm. That is, in this step, it is possible to carry out a carburizing process by supplying the hydrocarbon gas at 1.60Х10 ¹¹ ℓ · atm or less.

The experimental process for deriving such a reference threshold will be described later.

In addition, in the present embodiment, the reaction gas may further include an atmosphere control gas in addition to the hydrocarbon gas, and the atmosphere control gas may include at least one or more of hydrogen and nitrogen.

Meanwhile, the step (c) may be performed while continuously supplying the reaction gas throughout the carburizing process, but may also be performed while changing the supply pattern of the reaction gas.

For example, in step (c), the reaction chamber 60 is formed in a vacuum atmosphere, and the reaction gas is injected at a predetermined pressure to accelerate carburization (c-1) and the reaction chamber 60 is reacted. Repeat steps (c-2) and (c-1) and (c-2) at predetermined time intervals by supplying gas below the pressure of the reaction gas in step (c) to diffuse carburization. It may include (c-3) to perform.

 These steps are processes for effectively forming a carburized layer on the surface of the target metal 10.

Specifically, in step (c-1), the reaction gas may be injected while maintaining a pressure of 2 to 10 mbar in an atmosphere of 400 ° C to 500 ° C. At this time, the reaction gas was supposed to be a mixed gas of 20-70% hydrogen gas and 30-80% acetylene gas.

Particularly in the case of the step (c-2) in this embodiment, the reaction chamber 60 is maintained at a pressure of 0 to 2 mbar, and a low pressure state is diffused. However, the injection of the reaction gas may be completely stopped in step (d), but the supply of hydrogen gas among the reaction gases may be maintained.

Alternatively, the supply of hydrocarbons with hydrogen gas may be maintained, and a method of forming a vacuum atmosphere without a reaction gas may be used.

Preferably, step (c-1) accelerates carburization by supplying a reaction gas to the reaction chamber at a pressure of 5 mbar or less, and in step (c-2), the reaction gas is 0.5 mbar or more to the reaction chamber. It can be made to diffuse the carburized by supplying it below the pressure of the reaction gas in step (c-1).

And the (c-3) step is to repeat the above steps (c-1) and (c-2) for about 5 to 30 hours, and then carburize the surface of the target metal 10 A layer is formed. Of course, the number and duration of repetitions in step (c-3) can be set in various ways.

And in this embodiment, the repeating patterns of steps (c-1) and (c-2) may be made at predetermined time intervals. Referring to FIG. 6, in a low temperature vacuum carburizing method according to an embodiment of the present invention, a graph showing a process of repeating a carburizing acceleration process and a vacuum diffusion process is shown.

As shown in FIG. 6, the (c-3) step may be made to gradually shorten the total process time of the (c-1) step being repeated, and the total of the (c-2) step is repeated. It can be said that the process time is gradually increased.

In this case, a better carburizing effect can be obtained, and the time interval of each step may be set according to the characteristics of the target metal 10 and the process environment.

In the case of the present embodiment, the method of gradually shortening the total process time in step (c-1) and the method of gradually increasing the total process time in step (c-2) were applied simultaneously, but unlike this, only one method is used. It goes without saying that this may be performed.

In addition, in the case where steps (c-1) to (c-3) are repeatedly performed, the threshold value is determined for each of the carburizing process conditions in the total process time of step (c-1) and step (c-2). It can be calculated for based on the total sum of each carburizing process conditions in the total process time.

Meanwhile, after this step, a step of cooling the target metal 10 may be further performed. In step (e), the target metal 10 may be naturally cooled, but a method of rapidly cooling using a separate cooling device or a low temperature fluid may be applied.

Hereinafter, the experimental results according to the change in the supply amount of the natural oxide removal gas in step (a) among the aforementioned steps, and the experimental results according to the threshold value change in step (c) will be described.

First, FIGS. 7 to 10 are views showing results of performing carburization treatment while variously changing conditions in pretreatment conditions in a low-temperature carburization method according to an embodiment of the present invention.

Specifically, FIG. 7 is a result of performing carburization treatment without applying a pretreatment process through CO, which is an oxidizing gas, and FIG. 8 is a result of performing carburization for 5 hours while applying a pretreatment process through CO. In addition, FIG. 9 is a result of performing carburization for 10 hours in a state in which a pretreatment process through CO is applied, and FIG. 10 is performing carburization for 5 hours in a state in which a pretreatment process such as electropolishing and salt bath and a pretreatment process through CO are applied. One result.

As shown in FIG. 7, in the case of a target metal that has undergone a carburization process without applying a pre-treatment process through CO, the carburization layer is not visually confirmed, whereas CO as shown in FIGS. 8 to 10 It can be seen that the carburized layer is visually identified in the target metal that has undergone the carburization process with the pretreatment process applied.

In addition, it can be seen from FIG. 8 to FIG. 10 that the carburized layer appears more clearly and the thickness of the carburized layer becomes thicker.

Next, FIGS. 11 to 15 are views showing results of performing a carburizing treatment while variously changing conditions in a carburizing process in a low-temperature carburizing method according to an embodiment of the present invention.

Specifically, the result shown in FIG. 11 uses acetylene as a hydrocarbon gas, and hydrogen is charged into the reaction chamber for controlling the atmosphere. In addition, the process temperature was 450 ° C, the process pressure was 8 mbar, the process time was 45 minutes, and acetylene and hydrogen were charged with 60 SLH (Standard Liter per Hour) and 240 SLH, respectively.

Accordingly, the threshold value calculated through the equation was derived as 1.44Х10 ¹² ℓ · atm, which is higher than the reference threshold.

As a result, as shown in Fig. 11, the surface of the sample was covered with a black suit, which lost the luster of the metal and was not easily erased.

Next, in the result shown in FIG. 12, acetylene was used as a hydrocarbon gas, and hydrogen and nitrogen were charged into the reaction chamber to control the atmosphere. In addition, the process temperature was 450 ° C, the process pressure was 1.8 mbar, the process time was 840 minutes, and acetylene, hydrogen, and nitrogen were charged with 15 SLH, 60 SLH, and 600 SLH, respectively.

Accordingly, the threshold value calculated through the equation was derived as 1.68Х10 ¹¹ ℓ · atm, which is slightly above the reference threshold.

As a result, as shown in FIG. 12, the surface of the sample was thinly covered with a black suit, which could be easily removed through post-treatment, and a low-temperature carburizing layer of about 13 μm was formed.

Next, in the result shown in FIG. 13, acetylene was used as a hydrocarbon gas, and hydrogen was charged into the reaction chamber for controlling the atmosphere. In addition, the process temperature was 450 ° C, the process pressure was 8 mbar, the process time was 5 minutes, and acetylene and hydrogen were charged at 60 SLH and 240 SLH, respectively.

Accordingly, the threshold value calculated through the formula was derived as 1.60Х10 ¹¹ ℓ · atm, which is a value that matches the reference threshold.

As a result, it can be seen that the result was hardly any numerical value on the surface of the sample as shown in FIG. 13.

Next, in the result shown in FIG. 14, acetylene was used as a hydrocarbon gas, and hydrogen and nitrogen were charged into the reaction chamber for controlling the atmosphere. In addition, the process temperature was 450 ° C, the process pressure was 3 mbar, the process time was 300 minutes, and acetylene, hydrogen, and nitrogen were charged with 15 SLH, 100 SLH, and 600 SLH, respectively.

Accordingly, the threshold value calculated through the formula was derived as 9.46Х10 ¹⁰ ℓ · atm, which is the value below the reference threshold.

As a result, as shown in Fig. 14, the sample had no soot on the surface of the sample, and metallic luster was maintained, and as shown in Fig. 15, a clear low-temperature carburizing layer of about 10 mu m was formed.

Through these experimental results, it is possible to set the threshold of 1.60Х10 ¹¹ ℓ · atm, which does not cause soot, as a reference threshold in the carburizing process.

As described above, the preferred embodiments according to the present invention have been examined, and the fact that the present invention may be embodied in other specific forms without departing from the spirit or scope of the embodiments described above has ordinary knowledge in the art. It is obvious to them. Therefore, the above-described embodiments are to be regarded as illustrative rather than restrictive, and accordingly, the present invention is not limited to the above description and may be modified within the scope of the appended claims and their equivalents.

10: target metal
12: Hollow
50: courage
52: organic solvent
55: ultrasonic oscillator
60: reaction chamber
65: Stage
70a: 1st gas inlet
70b: second gas inlet

Claims (21)

(A) performing pre-treatment on the target metal;
Step (b) of introducing the target metal into the reaction chamber and raising the temperature to a set temperature; And
(C) forming the reaction chamber in a vacuum atmosphere and performing carburization by supplying a reaction gas containing at least hydrocarbon gas;
It includes,
Step (c) is,
A low-temperature carburizing treatment method for supplying the hydrocarbon gas below a preset reference threshold in consideration of a relationship between a plurality of carburizing process conditions during the process of performing carburizing. According to claim 1,
The plurality of carburizing process conditions,
Low-temperature carburization treatment method comprising at least one of the relative flow of the hydrocarbon gas, the carburization treatment time, the process pressure, the process temperature of the reaction gas. According to claim 2,
The threshold value is a low-temperature carburization treatment method calculated through multiplication between the plurality of process conditions. According to claim 3,
The threshold is,

(α: relative flow of hydrocarbon gas, SLM: Standard Liter per Minute, t: process time, p: process pressure exp (-ΔG / RT): equilibrium constant)
Low temperature carburization treatment method calculated through the formula of. The method of claim 4,
The reference threshold value is 1.60 × 10 ¹¹ ℓ · atm low temperature carburization treatment method. According to claim 1,
The reaction gas is a low-temperature carburization treatment method further comprising an atmosphere control gas. The method of claim 6,
The atmosphere control gas low-temperature carburization treatment method containing hydrogen. The method of claim 7,
The atmosphere control gas low-temperature carburization treatment method further comprises nitrogen. According to claim 1,
Step (c) is,
Forming the reaction chamber in a vacuum atmosphere and injecting a reaction gas at a predetermined pressure to accelerate carburization (c-1);
Step (c-2) of supplying the reaction gas to the reaction chamber below the pressure of the reaction gas in step (c-1) to diffuse carburization; And
Step (c-3) of repeatedly performing steps (c-1) and (c-2) at predetermined time intervals;
Low temperature carburization treatment method comprising a. The method of claim 9,
In step (c-1), the reaction gas is supplied to the reaction chamber at a pressure of 5 mbar or less to accelerate carburization,
The (c-2) step is a low-temperature carburization treatment method in which the reaction gas is supplied to the reaction chamber at a pressure of 0.5 mbar or more and less than the pressure of the reaction gas in the step (c) to diffuse carburization. The method of claim 9,
Step (c-3) is,
Low-temperature carburization treatment method to gradually shorten the total process time of step (c-1) is repeated. The method of claim 9,
Step (c-3) is,
Low-temperature carburization treatment method to gradually increase the total process time of the (c-2) step is repeated. According to claim 1,
Step (a) is,
Low-temperature carburization treatment method to supply natural oxide removal gas to the target metal to relieve stress of the target metal and weaken the bonding force between the natural oxide film and the target metal. The method of claim 13,
The natural oxide film removal gas is a low-temperature carburization treatment method, which is an oxidizing gas having a faster spontaneous oxidation reaction than the reaction gas. The method of claim 14,
The oxidizing gas is a low-temperature carburization treatment method comprising carbon monoxide (CO). The method of claim 13,
The natural oxide removal gas is a low-temperature carburization treatment method, which is a carbonaceous gas that reacts with the oxide by radicalizing. The method of claim 16,
The carbonaceous gas is low-temperature carburization treatment method comprising methane (CH ₄ ). The method of claim 13,
Step (a) is,
Low temperature carburization treatment method performed at a process temperature lower than the process temperature of step (c). The method of claim 18,
Step (a) is,
Low temperature carburization treatment method performed in the stress relaxation temperature atmosphere of the target metal. The method of claim 19,
The target metal is formed of austenitic stainless steel,
The step (a) is a low-temperature carburization treatment method performed in a temperature atmosphere of 250 ° C to 500 ° C. The method of claim 13,
Step (a) is,
Low-temperature carburization treatment method of performing at least one or more treatments of electropolishing and salt bath on the target metal before supplying the natural oxide removal gas.

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