KR890001031B1 - Metal surface treatment method by glow discharge - Google Patents

Abstract

This process is used for glow discharge ionic surface treatment of metallic materials. The ionic treatment is available for carburizing or nitro-carburizing. Surface treatment is provided by placing the article to be processed and auxiliary electrode (cathode) to be located opposite to the anode electrode. The treating gas comprises H2, He or Ar gas and N2 or ammonia and maintains the pressure of 1-10 torr. Treating materials diffuse on the surface of metallic materials by glow discharge. By providing a uniform surface treatment for a number of articles, the process provides effective partial or complete treatment.

Description

Surface treatment method of metal by glow discharge

1 is a block diagram of a device used to implement the ion surface treatment method of the present invention.

2 is a cross-sectional view showing an example of a substance to be processed.

3 is a process chart showing an example of the treatment of the present invention.

Figure 4 is a chart showing the carbon concentration and hardness of the cross section of the carburized layer treated by the treatment method of the present invention.

* Explanation of symbols for main parts of the drawings

1: furnace body 2: object to be processed

3: DC power supply 4: Positive terminal

5: cathode terminal 6: gas cylinder for treatment

7: gas inlet 8: gas outlet

9: vacuum exhaust device 10: vacuum staircase

11: advertising thermometer 12: control panel

20: auxiliary electrode

The present invention relates to a method for treating an ion surface by glow discharge, and more particularly, to a method for carburizing or carburizing nitrous ion surface treatment. The ion treatment method introduces a gas body necessary for treatment into a pressure-reduced vessel depressurized to 10 ^-1 torr and applies a DC voltage between the anode and the anode to produce a glow discharge. It is a method of diffusing and infiltrating a treatment material on the surface of a workpiece.

The ion nitriding method introduces a treatment gas composed of at least one diluent gas of hydrogen gas, helium and argon and a nitriding gas such as nitrogen gas or ammonia while reducing the pressure to 10 ^-1 Torr or less to a predetermined pressure of 1 to 10 Torr. And a glow discharge is generated by applying a DC voltage of 300-1500V.

Ion carburizing and ion carburizing are also carried out in the same manner. As the treatment gas, a hydrocarbon carburizing gas is added to the diluent gas in the case of ion carburizing, and a nitrogen source is added thereto in the case of the ion carburizing. The treatment temperature of the ion nitriding method is relatively low at 350 to 570 ° C, the treatment temperature of the ion carburization method is 570 to 670 ° C, and the treatment temperature of the ion carburization method is 750 to 1100 ° C at the highest temperature. However, in the carburizing or carburizing ion surface treatment method, carbon is not infinitely injected as a treatment material even by infiltration treatment by only ion bombardment, and reaches a constant value. In such a composition, since an excessive processing material is formed, it is natural that toughness is low and undesirable.

In such an ion surface treatment method, there is known a method of repeatedly performing a process of stopping the ion bombardment and heating it to a predetermined temperature by diffusion with an external heating body after infiltrating the treatment material by the ion bombardment. In this method, however, during the ion bombardment, the surface of the workpiece is heated locally while the surface is always kept in a clean state, whereby the treatment material penetrates. Since the whole water is heated, the surface temperature is once lowered and it takes time to raise it to the desired temperature. Furthermore, since the object to be treated is exposed to the processing gas, oxides may form on the surface when the gas purity is low. There is a problem that an uneven state occurs in the injection of the treatment material by the ion bombardment.

In addition, it is very difficult to control the supply of the processing gas extremely accurately compared with the control of other diluent gases in order to obtain the optimum surface concentration, and it is very difficult to find the optimum gas composition, and also to process the object of complicated shape. In this case, it is very difficult to infiltrate any part at the same temperature.

Therefore, it is an object of the present invention to provide a glow discharge surface treatment method which can heat-treat a desired surface of a workpiece using less heating energy.

It is yet another object of the present invention to provide a glow discharge surface treatment method which enables partial treatment of the surface of a workpiece using reduced heating energy. Further, another object of the present invention is to provide a glow discharge surface treatment method which enables a plurality of different kinds of treatments to be processed in a processing container. It is still another object of the present invention to provide a glow discharge surface treatment method in which a workpiece is heat treated by changing the atmospheric pressure in the treatment vessel.

In addition, another object of the present invention is to provide a glow discharge surface treatment method in which the treatment temperature of the workpiece is precisely controlled.

According to the present invention, there is provided a method comprising: disposing a workpiece having a conductive surface and connected to a cathode and an auxiliary electrode having a conductive surface and connected to an anode, and a glow discharge between the anode and the conductive surface of the workpiece and the auxiliary electrode. And a glow discharge is established between the cathode and the anode to provide a surface treatment method in which the heat treatment of the workpiece is performed under reduced pressure.

The glow-cold or cold light is defined between the workpiece and the auxiliary electrode so that the workpiece and the auxiliary electrode are disposed so that the treatment effect is promoted by the combined cold light.

The auxiliary electrode is disposed so that the hollow cathode effect can occur, and the treatment portion is changed by a constant temperature or treatment temperature by ion bombardment, so that both carburizing treatment and the treatment of diffusing a high concentration of carbon on the surface are easily performed. I can do it. As a result, uniform temperature control is possible in a short time, and a uniform carburized layer with a substantially constant concentration is achieved. In addition, since the heating in the diffusion step of prioritizing diffusion can be performed by ion bombardment, the heating in the high diffusion step of surface cleaning is performed by stopping supply of the carburizing material (carburizing gas) as the processing gas, or Extremely low concentration

The carburizing step and the diffusion step may be performed by one treatment, but the repetition of the treatment step a plurality of times has a great advantage in obtaining a carburized layer having a more preferable composition.

In the glow discharge treatment method according to the present invention, in order to bring about the proper hardness and lubricity of the surface of the workpiece without adversely affecting the workpiece itself, the amount of atoms diffused into the workpiece and the surface of the workpiece The depth underneath must be precisely controlled. If the surface concentration is kept constant, the treatment temperature plays an important role. That is, for example, when steel is used as the material to be treated and nitrogen is used as the surface hardening atom, the treatment temperature must be in the range of 400 to 700 ° C. In the surface treatment of carbonization, the treatment temperature should be within the range of 700 ~ 1100 ℃.

As such, the appropriate treatment temperature varies, depending on the diffusion atom and the workpiece. Therefore, it will be appreciated that local control of the surface properties of the workpiece can be effected by appropriate temperature control for specific portions of the workpiece surface. Since the treatment temperature depends on the glow discharge state, the selected local treatment of the workpiece can be achieved by controlling the glow discharge of that portion.

According to the present invention, the irregular temperature distribution of the surface of the workpiece is such that the auxiliary electrode is positioned at regular intervals selected from the desired treatment surface of the workpiece, so that the glow discharge is coupled between the auxiliary electrode and the surface of the opposite workpiece. Cold light can be formed by positioning the auxiliary electrode (having the same potential as the workpiece) so as to increase the temperature of the opposite workpiece. This control principle of temperature is based on the fact that the mutual interaction between the auxiliary electrode and the workpiece or the combined glow discharge causes an increase in the current concentration therebetween. The inventors of the present invention call the hollow-cathodic action found in the hollow cathode of the hollow cathode tube used in the atomic absorption analyzer as mutual interference. In that portion of the workpiece facing the auxiliary electrode, the ionization concentration of the gas is increased, and the diffusion atoms are commonly acted on the surface of the workpiece.

In order to obtain optimal mutual interference, it is important to control the distance between the workpiece and the auxiliary electrode. The spacing between the workpiece and the auxiliary electrode changes the area of the negative glow in the workpiece and the bonded auxiliary electrode. The length of the secondary glow depends on the gas composition and gas pressure, and the mutual interference mainly depends on the length of the glow. The negative glow discharge is closely related to the length. In the general ion surface-hardening process, when the distance between the workpiece and the auxiliary electrode is 0 to 0.5 mm, gas reaction with the workpiece tends to be hindered, but when the interval is 50 mm or more, between the glow discharges Interference is weakened, reducing the heating effect of radiant heat from the auxiliary electrode to the workpiece, thereby increasing the heat loss of the auxiliary electrode. For this reason, the interval is preferably in the range of 2 to 25 mm.

On the other hand, any conductive material may be used as long as it as an auxiliary electrode does not adversely affect the surface reaction of the workpiece. As for the size of the auxiliary electrode, it is preferable that the surface area of the auxiliary electrode is substantially equal to or larger than the selected surface area of the workpiece. However, it will be appreciated that any auxiliary electrode provided with a conductive surface and whose area is substantially equal to or greater than the selected surface area of the workpiece can be used. The hollow cathodic action according to the invention depends on the gas pressure in the vessel. When the distance between the auxiliary electrode and the workpiece is fixed and the gas pressure can be varied, the temperature of the workpiece close to the auxiliary electrode will change with the gas pressure due to the hollow cathode action. In this case, the temperature of the workpiece that is not close to the auxiliary electrode may be left unchanged even if the gas pressure is changed. The temperature difference between the parts of the workpiece depends on the gas composition and the auxiliary electrode arrangement. If the gas pressure is within the selected range, the entire workpiece has the same temperature without irregular temperature distribution. This is because the hollow cathode does not occur. Therefore, the surface treatment for one or more portions of the workpiece is selectively effected by providing hollow cathodic action during the treatment period or by providing it only for a selected period of treatment time, so that only the selected portion is treated. It is possible to obtain a workpiece having a plurality of surfaces which may be used or give other actions. The gas pressure depending on the composition of the gas is preferably in the range of 0.1 to 10 Torr, preferably 1.0 to 7.0 Torr.

After the ion carburization treatment, a quenching treatment is performed as necessary. In this quenching treatment, an optimum temperature must be used, but quenching from the high temperature side during the carburizing treatment may cause quenching cracks, and performing in a state of a weak carburizing layer causes a large cause of quenching cracks. It is desirable to diffuse a high concentration of carbon into the interior to increase toughness and to quench from low temperatures at this stage. Therefore, the quenching temperature may be set separately, but if it is continuously carried out through the diffusion step, unnecessary steps may be omitted.

Quenching can be performed by ion treatment, high frequency quenching, laser heating, or the like.

After quenching, tempering is performed as needed, and the temperature is preferably 130 to 300 ° C.

EXAMPLE

Ion carburization was performed by the method of the present invention.

1 shows an overview of the apparatus used in the ion surface treatment method of the present invention. The to-be-processed object 2 was made into the cathode, and the furnace 1 was made into the anode. As shown in FIG. 2, the to-be-processed object 2 is a star-ater shaft of the automotive component manufactured by cutting from the cold forging of JIS standard SCM415. As shown in FIG. 2, cylindrical graphite is provided as an auxiliary electrode 20 at two places where wear resistance of the shaft is required, that is, where carburization is required (2a, 2b). The distance between 2) and graphite was 6 mm. First, while reducing the inside of the furnace body 1 to 10 ⁻¹ Torr by using the vacuum exhaust device 9, 3.5 vol% of methane gas and 96.5 vol% of hydrogen gas were introduced to make 3 Torr during carburization. At the time of diffusion, the introduction of methane gas was stopped, and the DC voltage was applied between the anodes at 4 Torr. One carburizing time was 3 minutes and one diffusion time was 9 minutes, and it repeated 5 times as shown in FIG. 3, and processed for 1 hour in total.

The temperature of the parts 2a and 2b provided with the auxiliary electrode 20 at this time was measured by the advertisement thermometer 11, and as a result, it was 950 degreeC at 3 torr, and 820 degreeC at 4 torr. The portion 2c in which the auxiliary electrode 20 was not excreted was about 600 ° C., and the temperature did not change due to the change in gas pressure, and hardly carburized. The surface of the workpiece had a metallic luster over the entire surface. The ion surface treatment method of the present invention is described in more detail.

(Heating, surface cleaning process)

In the furnace 1 under atmospheric pressure, a supporting jig of the object 2 to which the auxiliary electrode 20 is attached is provided. The furnace 1, which is a pressure reducing container, is connected to the positive electrode terminal 4, and the object 2 and the auxiliary electrode 20 are connected to the negative electrode terminal 5, respectively. The furnace body 1 is closed, and the inside of the furnace body 1 is decompressed to 0.1 Torr or less by the vacuum exhaust apparatus 9 using the vacuum terminal 10. As shown in FIG.

In the processing gas cylinder 6, 96.5 volume% of hydrogen gas of diluent gas and 3.5 volume% of methane gas of carburizing gas (process gas) are introduce | transduced into a furnace body from a gas inlet. This process gas is discharged from the gas outlet 8 to the outside of the furnace body 1 with a pump while introducing.

The control panel 12 maintains the processing gas at a predetermined pressure of 3 to 4 torr, and supports the furnace body 1 connected to the anode, the workpiece 2 connected to the cathode, and the supporting jig of the auxiliary electrode 20. And a DC voltage of 300 to 1500 V are applied from the DC power supply 3 to generate a glow discharge on the anode long. The workpiece 2 and the auxiliary electrode 20 are heated to about 800 ° C. to clean the surface of the workpiece 2, such as removal of an oxide.

Carburizing Process

After the to-be-processed object 2 has heated up to predetermined | prescribed temperature, process gas (hydrogen gas and methane gas) is hold | maintained and introduce | transduced by the predetermined pressure of 3 Torr. The process gas is set at a pressure of 3 Torr, and the current meter of the control panel 12 is controlled to bring the object 2 and the auxiliary electrode 20 to a predetermined temperature (950 ° C).

Discharge due to the hollow cathode effect occurs between the furnace body 1 connected to the anode, the object to be processed 2, and the auxiliary electrode 20, and the part where the auxiliary electrode 20 is provided (carburizing treatment The temperature of the required surface portion of the workpiece 2 was set to 950 ° C.

One carburizing time was made into 3 minutes, and the part which provided the auxiliary electrode 20 was carburized. The surface portion 2c of the workpiece 2 without the auxiliary electrode is a portion in which the hollow cathode effect does not occur, and the portion 2a, in which the auxiliary electrode 20 is provided, due to thermal diffusion into the atmosphere. Compared with 2b), the temperature was lowered to about 600 ° C.

(Diffusion process)

The introduction of the carburizing gas (methane gas) is stopped and only the diluent gas (hydrogen gas) is maintained at a pressure of 4 Torr. This dilution gas is discharged out of the furnace 1 while introducing. In addition, an extremely low concentration treatment gas may be introduced.

The ammeter of the control panel 12 was measured, and the to-be-processed object 2 and the auxiliary electrode 20 became predetermined temperature (820-850 degreeC).

Discharge due to the hollow cathode effect occurs between the furnace body 1 connected to the anode, the object to be processed 2 and the auxiliary electrode 20, and the part where the auxiliary electrode 20 is provided (diffusion treatment The temperature of the surface part of the to-be-processed object 2 required was 820-850 degreeC.

One diffusion time was set to 6 minutes, and a high concentration of carbon was diffused in the portion where the auxiliary electrode 27 was provided. The surface portion 2c of the workpiece 2 without the auxiliary electrode was a portion where the hollow cathode effect did not occur. Even if there was a change in the processing gas pressure, the temperature was about 600 ° C., not different from the carburizing process. .

(End process)

After the carburizing step and the diffusion step are processed five times for a total of one hour, the DC power supply 3 is turned off to stop the introduction of the processing gas. Exhaust by the pump of the process gas in the furnace 1 is continued to cool. After the furnace is cooled, the carburized and diffused workpiece 2 is taken out.

After the carburizing treatment, the furnace was cooled, and then the surface was heated to 930 ° C by high frequency induction heating, and spray-cooled to quench. After saccharification, low temperature tempering was performed at 180 ° C. for 1 hour, and microbikaas hardness and carbon concentration distribution were measured for the cross section of the carburized part over several places. 4 is a diagram showing the relationship between the depth from the surface and the carbon content and the vicarous hardness (Hv) for a part of the double. In addition, the cross section was observed with a microscope.

The carburized layer formed about 0.6 mm in any part where the auxiliary electrode 20 was installed, and the surface concentration of the carburized layer showed a value of about 0.8% by weight. It was approximately a constant value of 900.

This microscopic tissue was martensite. The ion carburization by the conventional glow discharge took about 1 hour even in the case of small workpieces to raise the temperature of the treatment to 900 ° C., and it required 2-3 hours in the case of large workpieces. In the treatment method, it was possible to raise the temperature to 5 to 10 minutes regardless of the size of the object by the hollow cathode effect, and the treatment was possible in a very short time. The deformation of the process is 1/100 mm or less in the vibration amount of the shaft, and the step of correcting the vibration amount of the shaft of 5 / 100-20 / 100 mm by gas carburizing which has been conventionally performed can be omitted. Moreover, regarding the surface roughness, it was confirmed that the processed goods of 4-6S are 4-6S after a process by the finishing process before a process. Therefore, except in special cases, after finishing processing, the ion treatment of the present invention can be performed as the final processing.

As mentioned above, although the description of this invention showed the example of carburization to the star-shaft for automobiles, various surface treatments can be performed by the same method with respect to other various products. Surface treatment may be carried out by appropriately changing the type of treatment gas.

According to the present invention described above, a carburized layer having a uniform concentration and uniformity can be obtained.

Claims (1)

Process gas is introduced into a pressure-reduced pressure vessel depressurized to 0.1 Torr or less, and a glow discharge is generated by applying a DC voltage to the anode of the pressure-reduced vessel, using a workpiece made of a metal material disposed in the pressure-reduced vessel as a cathode. In the method, the process gas containing the carburizing gas is maintained at a predetermined pressure (0.1 to 10 Torr) and introduced into the decompression vessel, and the to-be-processed object connected to the cathode, the to-be-processed object and a predetermined interval are And a discharge caused by the hollow cathode effect between the auxiliary electrode made of a conductive material connected to the cathode, thereby making the surface portion temperature of the carburized portion of the workpiece higher than the other surface portion temperature. A carburizing step of carburizing the surface portion of the carburizing part and stopping the introduction of the carburizing gas or introducing a low concentration of the processing gas, The method for surface treatment of metal according to the glow discharge comprises a diffusion step for diffusing a high concentration of carbon in the carburizing surface portion to the inside of the object to be treated.

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