KR100610645B1 - Nitriding method and apparatus using post plasma - Google Patents

Abstract

The present invention relates to a nitriding method and apparatus using a post plasma to improve nitriding performance by a pretreatment process, perform a rapid nitriding process using a nitriding accelerator, and improve the nitriding performance by generating plasma in a screen network. .

To this end, the nitriding method using the post plasma of the present invention includes a surface activation process of generating a plasma in a screen network provided outside the specimen and then removing residual gas and impurities on the surface of the specimen by oxidizing and reducing gas; A nitride layer forming step of nitriding by injecting a nitriding agent to which nitrogen, hydrogen, and a nitriding accelerator are added to the specimens subjected to the surface activation process; It characterized in that it comprises a cooling step of cooling the specimen passed through the nitride layer forming process by lowering the temperature inside the furnace.

In addition, the nitriding apparatus using the post plasma of the present invention is a device for nitriding the specimen by passing a gas through a plasma generated outside the specimen when the specimen is loaded into the furnace and heated, whereby plasma is generated outside the specimen. A screen net is installed, and a gas pipe having a plurality of gas holes is installed outside the screen net.

Nitriding, Plasma, Oxidation, Reduction, Carbon, Screening

Description

Nitriding method and apparatus using post plasma {Method and apparatus for nitriding by post-plasma}

1 is a schematic diagram showing the structure of a nitriding device according to the prior art,

2 is a block diagram listing the order of the nitriding method according to the present invention;

3 is a block diagram listing the sequence of the surface activation process according to the present invention;

4 is a schematic view showing the structure of a nitriding device according to the present invention;

5 is an experimental photograph showing the surface shape of the specimen according to the surface activation process of the present invention,

6 is a table and a graph showing the change in surface energy according to the surface activation process of the present invention,

7a and 7b are graph diagrams and experimental photographs comparing and comparing the nitriding characteristics with and without the surface activation process of the present invention;

8 is a graph showing the hardness and cure depth of the specimen after nitriding according to the propane content of the nitriding accelerator of the present invention;

Figure 9 is a photograph showing the comparison of the specimen surface according to the propane content of the nitriding promoter of the present invention.

* Description of Major Symbols in Drawings *

10-no 20-screen net

25-plate 30-gas pipe

35-gas hole 40-gas injection part

50-Power Supply S10-Surface Activation Process

S11-Homogenization Step S12-Oxidation Step

S13-reduction treatment step S20-nitride layer forming process

S30-Cooling Process H-Heater

P-Specimen PS-Plasma

Vp-Vacuum Pump

The present invention improves the nitriding performance of a specimen by a pretreatment process, and performs a rapid nitriding process using a nitriding accelerator, while generating a plasma in a screen network to improve the nitriding performance. It is about.

In general, the surface treatment refers to a case where the treatment is performed for various purposes such as making the surface of the metal look beautiful, improving the corrosion resistance or abrasion resistance of the surface, or curing the surface.

Such hardening of the surface during surface treatment includes carburizing, nitriding, and high frequency heat treatment. Among them, in particular, nitriding method diffuses and penetrates nitrogen from the surface of the metal material to the inside in the temperature range of 500 to 600 ° C. It is a hardening technology which raises abrasion resistance, fatigue resistance, and corrosion resistance.

Unlike other surface hardening methods such as carburization and high frequency heat treatment, the nitriding method is used in precision machine parts, automobile parts, molds, etc. due to less heat treatment deformation because it is processed at low temperature below the transformation point of steel. In recent years, many studies have been actively conducted, such as being used for composite heat treatment, showing excellent adhesion to the coating layer and curing of the underlying layer.

Nitriding methods having the above characteristics are further divided into gas nitriding, salt bath nitriding, ion nitriding, plasma nitriding, and the like according to nitriding agents and nitriding properties.

In the following description, first, gas nitriding is a method of forming a compound layer and a nitride layer in a metal material by putting ammonia (NH ₃ ) gas in a closed space for about 1 to 100 hours. There is a possible advantage, but it can be applied only to the dedicated steel grade, there is a problem that not only takes a long time working, but also uses harmful ammonia gas.

Then, the salt yokjil anger cyanide (CN ^-), cyanate (CNO ^-) in a way that the nitriding process is a metallic material in a liquid phase using a salt, the compound layer and the nitride layer of high hardness in a short period of time of about 4 hours to considerable depth It has been widely applied in the mass production process of automobile parts because of the advantages that can be obtained, fast cooling speed, no limitation of steel grade, and very low equipment cost.

However, the salt yokjil anger cyanide (CN ^{-) -} since the toxicity characteristic material, there is a problem of environmental pollution, and is gradually reduced in use, a number of the pores in the nitriding product compound formed, cyanate (CNO) There is a problem that necessarily requires post-processing.

On the other hand, ion nitriding is a method of nitriding metal materials using nitrogen (N) gas, which is free from environmental pollution. It is easy to control the process and can quickly nitrify various steel grades, as well as gas and energy consumption. Small, environmentally friendly working environment continues to be developed and used.

However, the ion nitriding is applied directly to the treated specimen, so that the surface of the specimen is damaged by the arc, the electric field between the specimens are affected, and not only the temperature inside the working space is uniform, but also inside the microholes. Nitriding treatment is difficult.

On the other hand, modern nitriding technology has been developed aiming at the quality of ion nitriding and the production of gas nitriding, and a representative nitriding technique for achieving the above-mentioned goal is post plasma nitriding.

Referring to the post plasma nitriding, as illustrated in FIG. 1, the nitriding gas is passed through a plasma generated outside the specimen P to coat and nitride the specimen P, and the inside of the furnace 1. The board | substrate 2 which has a cathode power supply is installed in the center, the specimen P is provided on the board | substrate 2, and the heater H is installed in the furnace inside. In addition, the gas injection unit 4 is installed at the upper part of the furnace 1, and a vacuum pump Vp is installed at the lower part so as to generate plasma PS around the specimen P. In addition, power is supplied to the substrate 2 and the heater H through the power supply device 5.

Here, if the plasma (PS) is described briefly, the atoms are separated from the nucleus and the electrons at a temperature of millions to tens of millions, and are vigorously moved as they are, so that they are electrically neutral gas, which is called plasma.

The post plasma nitriding described above allows nitriding treatment of the specimen by passing a nitriding gas through the plasma, thereby allowing nitriding without directly applying a glow to the treated specimen. Therefore, there is no surface damage of the specimen by the arc or the like, and there is no limitation of the shape of the specimen, so that the above-mentioned disadvantages of the ion nitriding method can be solved.

However, since the post plasma nitriding is not directly applied to the surface of the specimen, there is a problem that the performance of nitriding is deteriorated because there is no surface oxide film removal and activation process due to the sputtering effect of ions as in the ion nitriding method.

The present invention has been made in order to solve the above-mentioned problems, nitriding method using a post plasma to improve the nitriding performance by performing a pre-treatment that can activate the surface of the specimen before nitriding the specimen and To provide a device.

Another object of the present invention is to nitrate the specimen by adding a nitride accelerator, thereby increasing the hardness value and the hardness depth according to the surface hardening treatment and simultaneously performing the nitriding process using the post plasma. A method and apparatus are provided.

Still another object of the present invention is to provide a method and apparatus for nitriding using a post plasma, by which radicals passing through the plasma are directly used for nitriding, thereby improving the efficacy of nitriding.

The configuration of the nitriding method using the post plasma of the present invention for achieving the above object, in the method for nitriding the specimen by passing a gas through the plasma generated outside the specimen when charging and heating the specimen inside the furnace A surface activation process of generating plasma in a screen network provided outside the specimen and then removing residual gas and impurities on the surface of the specimen by oxidizing and reducing gases; A nitride layer forming step of nitriding by injecting a nitriding agent to which nitrogen, hydrogen, and a nitriding accelerator are added to the specimens subjected to the surface activation process; It characterized in that it comprises a cooling step of cooling the specimen passed through the nitride layer forming process by lowering the temperature inside the furnace.

In addition, the structure of the nitriding apparatus using the post plasma of the present invention is a device for nitriding the specimen by passing a gas through a plasma generated outside the specimen when the specimen is loaded into the furnace and heated. The screen net is generated is installed, and the outside of the screen net is characterized in that the gas pipe having a plurality of gas holes is installed.

When described in detail with reference to the accompanying drawings a preferred embodiment of the present invention.

2 is a sequence of a method of nitriding using a post plasma of the present invention in order, and is largely divided into a surface activation step (S10), a nitride layer forming step (S20), and a cooling step (S30).

Hereinafter, the surface activation process (S10) first generates a plasma (PS) in the screen net 20 installed outside the specimen (P), and then the oxidizing and reducing gas through the gas pipe outside the screen net 20 Passing through the plasma PS to remove residual gas and impurities on the surface of the specimen (P), the surface activation step (S10) is pre-treated in three steps.

That is, the surface activation step (S10) is a pretreatment through a homogenization treatment step (S11), an oxidation treatment step (S12), a reduction treatment step (S13).

Such a surface activation step (S10) will be described with reference to FIG. 3, and the homogenization treatment step (S11) first raises the temperature in the furnace 10 to a oxidation temperature at a vacuum pressure of 1 × 10 ^-2 Torr, and then the specimen. The surface of (P) is homogenized for 5 to 10 minutes.

In the oxidation treatment step S12, the surface of the specimen P is homogenized and immediately oxidized using an oxidizing gas (eg, nitrous oxide (N ₂ O)) for 10 to 30 minutes. In addition, the reduction treatment step (S13) after raising the temperature in the furnace 10 to the nitriding temperature, the surface of the oxidized specimen (P) for 10 to 30 minutes to reduce the reducing gas (for example: hydrogen (H ₂ )) It is to reduce by using.

Here, the redox gas may be applied to air other than nitrous oxide (N ₂ O) or water (H ₂ O), and nitrogen trifluoride (NF ₃ ) or the like may be used as an activating gas having the same role.

On the other hand, the nitride layer forming step (S20) is a nitriding treatment by adding a nitrogen, hydrogen and nitriding promoter to the specimen (P) through the surface activation step (S10), the nitriding treatment, the nitriding agent is a gas pipe (30) By passing through the plasma (PS) generated in the screen net 20 through the) to nitriding the specimen (P).

Here, the nitriding accelerator is a gas containing carbon (C), and any one of propane (C ₃ H ₈ ), acetylene (C ₂ H ₂ ), methane (CH ₄ ). Among them, it is appropriate to use a propane (C ₃ H _8), according to the experimental results which will be described later, 1.0 ~ 1.5wt% of propane (C ₃ H ₈₎ by weight is contained in the case of using a.

On the other hand, Figure 4 schematically shows a nitriding device using a post plasma of the present invention, will be described below, the furnace (10) inside the heater (H) built-in to heat the specimen (P), the lower part of the vacuum pump Vp is provided to deform the atmosphere inside the furnace 10 to a vacuum state.

In addition, a gas inlet 40 for injecting a working gas into the gas pipe 30 to be described later is installed on the furnace 10, and a furnace 10 is provided between the gas inlet 40 and the furnace 10. Baratron gauge (G) for maintaining and measuring the degree of vacuum inside, and a throttle valve (Thv) for adjusting the amount of gas to be injected into the furnace (10), respectively. In addition, the furnace 10 is electrically connected to a PC or the like to measure the plasma (PS) and the power supply state in real time, thereby allowing overall control of the nitriding process.

Subsequently, a plate 25 is installed in the center of the furnace 10, and a specimen P to be nitrided on the plate 25 is provided. Further, the screen net 20 is installed outside the specimen P to cover the specimen P. The screen net 20 is the upper screen net 20a and a plurality (in the present invention, two) Separately installed by the side screen net (20b) of each of the screen net 20 to enable the supply of DC power.

At this time, by providing a plurality of power supply device 50 for supplying power to the screen net 20 to supply power to each of the screen net 20, so that a higher current can flow to the screen net 20 It was.

The screen net 20 is formed of a metal material so that the cathode power is applied to generate the plasma PS in the screen net 20. The outside of the screen net 20 is provided with a spiral gas pipe 30 into which oxidative and reducing gas and nitriding agent are injected, and a plurality of gas holes 35 are formed in the gas pipe 30. In addition, the gas pipe 30 is connected to the gas inlet outside the furnace 10 to receive the gas.

Referring to the operation and effect of the present invention configured as described in detail as follows.

In order to nitrate the specimen P through the nitriding method and apparatus using the post plasma of the present invention, the specimen P is first charged into the nitriding furnace, and the specimen P used in the present invention is a mold steel material. Quenching and tempering with any one of STD 11, STD 61, S20C, S45C, and SCM440 to maintain a constant hardness, and then mirror polished with 0.3 μm of alumina.

After charging the specimen P, the degree of vacuum inside the furnace 10 is maintained at 1 × 10 ⁻² Torr using a vacuum pump Vp, and power is supplied to the heater H to supply the inside of the furnace 10. After raising the temperature to 450-500 degreeC which is an oxidation temperature, the surface of the specimen P is homogenized (S11) for 5 to 10 minutes. Then, the oxidizing gas (for example, N ₂ O) flowing from the gas hole 35 passes through the plasma PS generated in the screen network 20 to oxidize the surface of the specimen P for 10 to 30 minutes (S12). )do.

After the oxidation treatment, the temperature in the furnace 10 is raised to 400 to 570 ° C., which is a nitriding temperature, and then a reducing gas (for example, H ₂ ) flowing from the gas hole 35 is generated in the screen net 20. By passing through (PS) and reducing the surface of the specimen (P) for 10 to 30 minutes (S13), the surface activation step (S10) of the specimen (P) is completed.

5 is a photograph of the surface of the specimen P which has undergone the surface activation process (S10) as described above. As the surface activation process (S10) proceeds, the surface of the specimen (P) is granular (granular). The new surface in the form of) is increased, and the contact angle with water is shown as the redox time elapses to confirm the activation degree of the newly increased surface. As a result, the water droplets spread widely as the redox time is increased. .

)에 대입하여 얻어진 결과를 도시한 것으로, 상기한 실험예에 따르면 표면 활성화 공정(S10)을 거치기 전에 약 37mN/m였던 표면 에너지 값이 표면 활성화 공정(S10)을 거친 이후에 약 70mN/m로 대략 2배 정도 증가하게 됨을 알 수 있다. 6 is a surface energy formula (

), The surface energy value of about 37mN / m before the surface activation process (S10) is about 70mN / m after the surface activation process (S10). It can be seen that about two times increase.

In particular, through the above experiments in which the saturation value is shown through the oxidation process and the surface energy is increased again through the reduction process, it can be seen that the optimal surface activation process (S10) is more effective when the proper oxidation and reduction process is configured. It is.

FIG. 7A is a graph illustrating a characteristic of nitriding according to the presence or absence of the surface activation process (S10) as described above. First, the surface hardness of the specimen P without undergoing the surface activation process (S10) is 770 Hv, and cured. The depth is 30 μm. On the other hand, the surface hardness of the specimen (P) after the surface activation process (S10) is 1100Hv or more, the curing depth is 55㎛, compared to the specimen (P) without the surface activation process (S10), surface activation process The hardness value of the specimen (P) subjected to (S10) is increased by 50% or more, and the curing depth is also increased by about 2 times.

In addition, as shown in FIG. 7B, the surface of the specimen P, which has undergone the surface activation process S10, is formed with a very thick and uniform nitride. Therefore, the nitriding method and apparatus of the present invention increases the surface reactivity of the specimen P by removing residual gas and impurities from the surface layer of the specimen P through a simple surface activation process (S10) using oxidizing and reducing gas. It can improve the performance of nitriding.

On the other hand, after the surface activation step (S10) described above, after setting the pressure in the furnace 10 to 1-5torr while maintaining the temperature in the furnace 10 at 450 to 570 ° C, the ratio is 1: 1 to 3: 1. Nitriding agent to which the carbon-containing gas together with nitrogen and hydrogen was passed through the plasma (PS) generated in the screen net 20 to perform the nitride layer forming process (S20) of the specimen P for about 2 to 8 hours. Done.

When the nitride layer forming step S20 is completed, the nitriding treatment of the specimen P is completed by passing through the cooling step S30 of lowering the temperature of the furnace 10. At this time, the nitride layer forming process (S20) in which the nitride is formed shows the behavior of nucleation and growth on the specimen (P), it is to promote the nucleation through the surface energy increased after the surface activation process (S10).

Here, the carbon used as the nitriding accelerator plays a role of promoting the rate of nitrogen diffusion in the steel during nitriding, thereby significantly improving the nitriding treatment rate. Wherein a carbon-containing gas was test by applying a propane (C ₃ H _8), properties of the nitride, depending on the amount of propane (C ₃ H ₈₎ is dependent.

As a result of the experiment FIG. 8 is a photograph showing the comparison of the surface hardness and the thickness of the nitride layer according to the propane (C ₃ H ₈ ) content, the content of propane (C ₃ H ₈ ) by the above experimental example is 1.0 It can be seen that when the weight is ˜1.5 wt%, the highest surface hardness and depth of cure are obtained.

Furthermore, FIG. 9 is an experimental photograph showing the characteristics of nitrides formed on the surface of the specimen P according to the content of propane (C ₃ H ₈ ), and also the content of propane (C ₃ H ₈ ) is 1.0 ~ 1 / The most densified nitriding is at 5 wt%.

Therefore, the nitriding method and apparatus using the post plasma of the present invention determine the optimum amount of propane (C ₃ H ₈ ) addition containing carbon to nitrate the specimen (P), thereby improving the nitriding ability of the specimen (P). It is possible to improve the nitriding properties of the mold steel and carbon steel which is a refractory material.

In addition, the nitriding method and apparatus using the post plasma according to the present invention can secure the nitriding technique of the specimen P having no compound layer and little change in surface roughness by nitriding by adjusting various additive gases and their gas ratios. It is.

Furthermore, the nitriding method and apparatus using the post plasma of the present invention, since the metal screen net 20 covers around the specimen P and uses the heater H to heat the specimen P, energy density and temperature In addition to increasing the uniformity, the active radicals that have passed through the plasma PS are directly used for nitriding, thereby increasing the efficiency of nitriding.

In addition, the screen net 20 is installed as an upper screen net 20a and a plurality of side screen nets 20b, respectively, and each of the screen nets 20 is connected to each of the screen nets 20 using a separate power supply device 50. By supplying power, it is possible to increase the energy density and energy efficiency by flowing a higher current than when configured as a single power supply as in the past. In addition, as described above, since power is supplied to the screen net 20 by using the individual power supply devices 50, the nitriding specimen having high hardness and hardening depth can be obtained even with the power supply device 50 having a small amount of power.

In addition, the nitriding method and apparatus using the post plasma of the present invention do not directly apply the glow to the treated specimen P, so that the surface of the specimen P is not damaged and there is no restriction in the shape of the specimen P. It is possible to process the specimen (P) at the same time and nitriding treatment even in the narrow hole.

On the other hand, the present invention has been described in detail only with respect to the specific examples described above it will be apparent to those skilled in the art that various modifications and variations are possible within the technical scope of the present invention, it is natural that such variations and modifications belong to the appended claims. .

As described above, the present invention improves the surface reactivity of the specimen by removing residual gas and impurities from the surface layer of the specimen through a simple surface activation process using an oxidizing and reducing gas, thereby promoting nitride formation to improve the performance of nitriding. It works.

In addition, by nitriding the carbon containing the optimum carbon, it is possible to improve the nitriding performance of the specimen, and to improve the nitriding characteristics of the mold steel, which is a hard nitriding material, and there is no compound layer, and the specimen has little change in surface roughness. It is also effective to secure nitriding technology.

That is, the surface roughness of the specimen mirror-polished with 0.3 μm of alumina or diamond is 0.007 to 0.009 μm, whereas the surface roughness value of 0.010 to 0.018 μm is maintained after nitriding, so that the conventional ion nitriding is 0.18 μm and radical nitridation. Shows a very good roughness compared to showing a surface roughness value of 0.03 to 0.05 µm.

Furthermore, the metal screen net covers the specimen and uses a heater to heat the specimen, increasing the energy density and temperature uniformity, as well as increasing the efficiency of nitriding because active radicals that pass through the plasma are immediately used for nitriding. It also works.

In addition, since the glow is not directly applied to the treated specimen, there is no surface damage of the specimen and there is no limitation of the shape of the specimen, so that various types of specimens can be processed simultaneously and the nitriding treatment can be performed even inside the narrow hole.

Claims (9)

delete In the case of charging and heating the specimen inside the furnace, plasma is generated in a screen net installed outside of the specimen so as to pass the gas through the plasma generated outside the specimen to nitride the specimen, and then the specimen is oxidized and reduced by gas. A surface activation process for removing residual gas and impurities on the surface, a nitriding layer formation process for nitriding by adding a nitriding agent added with nitrogen, hydrogen, and a nitriding promoter to the specimen which has undergone the surface activation process, and a temperature inside the furnace In the nitriding method using a post-plasma comprising a cooling step of dropping and cooling the test piece subjected to the nitride layer forming step, The surface activation step (S10) is to increase the temperature in the furnace 10 to the oxidation temperature at a vacuum pressure of 1 × 10 ^-2 Torr, and then homogenizing the surface of the specimen P for 5 to 10 minutes (S11). Wow; Oxidizing the surface of the specimen (P) homogenized by an oxidizing gas for 10 to 30 minutes (S12); After raising the temperature in the furnace (10) to the nitriding temperature, the post-plasma comprising the step (S13) of reducing the surface of the oxidized specimen (P) with a reducing gas for 10-30 minutes (S13) Nitriding method used. The method of claim 2, wherein the oxidizing and reducing gas is characterized in that any one of nitrous oxide (N ₂ O), water (H ₂ O), air, nitrogen trifluoride (NF ₃ ), hydrogen (H ₂ ) is applied. Nitriding method using a post plasma. The nitriding method using a post plasma according to claim 2, wherein the nitriding accelerator is a carbon-containing gas. The method of claim 4, wherein the carbon-containing gas uses propane (C ₃ H ₈ ), acetylene (C ₂ H ₂ ), or methane (CH ₄ ). The method of claim 5, wherein in the case of propane (C ₃ H ₈ ) of the carbon-containing gas, a weight of 1.0 ~ 1.5wt% is contained. In the apparatus for nitriding the specimen by charging the gas into the plasma generated outside the specimen when charging the specimen inside the furnace, Install a screen net 20 in which plasma PS is generated outside the specimen P, but the screen net 20 includes an upper screen net 20a and a plurality of side screen nets 20b, and the screen Nitriding apparatus using a post plasma, characterized in that the gas pipe (30) having a plurality of gas holes (35) is provided outside the network (20). delete 8. The nitriding apparatus using post plasma according to claim 7, wherein the screen net (20) is formed of a metal material to have a cathode power source.

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