JPS6137352B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a glow discharge surface treatment method for a metal material, and in particular, the glow discharge state of one part of the metal material to be treated is made different from that of other parts to improve the diffusion distance or diffusion of atoms. It concerns a method of obtaining surfaces with different functions by changing the ratio of atoms.

Glow discharge surface treatment, which is a type of surface treatment technology for metal materials, has been attracting attention in recent years. A typical example is ion nitriding. In the ion nitriding method, the gas necessary for the treatment is introduced into a reduced pressure vessel (hereinafter sometimes referred to as a furnace body) whose pressure is reduced to at least 10 ^-1 Torr or less, and an electrode is installed so that the product to be treated becomes a cathode. (The furnace body may be used as a cathode)
A voltage is applied to this from an external DC power source to generate glow discharge and perform surface hardening treatment. FIG. 1 shows an outline of the ion nitriding apparatus. Generally, the product to be treated 2 becomes the cathode,
The furnace body 1 serves as an anode. The furnace body 1 has a water-cooled structure to prevent various equipment and parts (such as airtight packing) from being overheated due to heating during processing. In the ion nitriding process, the pressure inside the furnace is reduced to at least 10 ^-1 Torr or less using a vacuum device 9, and a processing gas 6 such as hydrogen gas and nitrogen gas or ammonia gas is introduced to maintain a predetermined pressure in the range of 1 to 10 Torr. The nitriding process is then performed by applying a voltage of 300 to 1500 V from a DC power supply to generate glow discharge. In FIG. 1, 3 is a DC power supply, 4 is an anode terminal, 5 is a cathode terminal, 7 is a gas inlet, 8 is a gas exhaust port to which a vacuum device 9 is connected, 1
0 is a vacuum gauge terminal, 11 is an optical pyrometer, and 12 is a control panel.

Since the object to be processed is heated by glow discharge energy, no external heat source is required. Therefore, since the surface generating the glow becomes the heating source, the temperature of the object to be treated changes depending on the ratio of the surface to the volume. In other words, if the workpiece is of the same shape and has a relatively simple shape, the temperature will be almost uniform throughout and uniform processing will be possible, but if the workpiece has a complex shape, especially parts with different surface areas relative to volume, the temperature will vary depending on the location even if the workpiece is the same. However, the disadvantage is that the concentration and depth of the diffused atoms vary greatly as a result, making uniform processing impossible.

On the other hand, depending on the intended use of the article to be treated, it may be necessary to perform treatments having multiple functions within the same article, rather than subjecting the entire surface to a surface treatment with the same function. In conventional ion surface treatment, such treatment cannot be performed continuously in one step in the same furnace, but is performed in multiple steps.

In the ion surface treatment method, as a method of obtaining partially different surface treatment layers (for example, the depth and hardness of the nitrided layer in nitriding treatment), as shown in Japanese Patent Application Laid-Open No. 47-6956, An additional metal electrode (anode for the workpiece) is placed between the (cathode) and the wall of the vacuum container (anode) via a resistor to the anode power source.
A method is also known in which the potential of this portion is changed to partially change the ion impact energy. In this method, for example, in the case of ion nitriding, additional metal electrodes are provided at parts that require different nitriding, and the potential of these parts is changed by an external circuit to change the ion bombardment energy to the surface parts. The amount of nitrogen adsorbed and diffused is adjusted to form nitrided layers with partially different depths. However, with this method of partially changing the ion bombardment energy using an external circuit, it is difficult to control the bombardment energy and the device becomes complicated. Since the influence of

The purpose of the present invention was to solve the above-mentioned drawbacks of the prior art, and to easily perform surface treatments having a plurality of different functions on a metal material to be treated in succession in the same container. It is an object of the present invention to provide a glow discharge surface treatment method for metal materials, which can save a large amount of energy required for heating.

The present invention provides a method for surface-treating a metal material by generating glow discharge between a cathode and an anode made of a metal material, which are objects to be treated, in a reduced pressure container. The metal material and the auxiliary electrode are arranged at a predetermined distance from the surface of the metal material so that the glow discharge generated between them interacts with each other, and the glow discharge is generated at a predetermined gas pressure to produce a predetermined result. After surface-treating the auxiliary electrode-equipped portion of the metal material at a temperature, the auxiliary-electrode-equipped portion of the metal material is then surface-treated at a temperature different from the gas pressure by glow discharge at a gas pressure different from the gas pressure. In particular, the above objective has been achieved. Note that by changing the gas pressure and type of gas, the temperature of the surface to be treated in the auxiliary electrode portion can be made higher than that in other portions.

The principle of the present invention will be explained below. First, when diffusing atoms from the surface of a workpiece to provide a function such as surface hardening or surface lubrication, the amount of atoms to be diffused, There are appropriate values for depth etc.
If the surface concentration is kept constant, processing temperature plays an important role. Taking steel materials as an example, when surface hardening is performed with nitrogen, the temperature is generally in the range of 400 to 700°C. Surface hardening by carburizing using carbon is 700-1100°C, and boron is 800-1200°C. On the other hand, surface lubrication during sulfurization using sulfur is 150 to 600°C. As described above, there is an appropriate processing temperature depending on the atoms to be diffused and the materials to be processed. In the ion surface treatment method, methods such as using an external heat source to partially make the surface temperature of the object to be treated non-uniform are also possible, but in the present invention, the method of making the surface temperature of the object to be treated partially non-uniform is possible. The electrode is placed on the cathode side at a predetermined distance from the surface of the workpiece, and by varying the pressure and type of gas introduced during ion treatment, the necessary distance between the auxiliary electrode and the workpiece is created. The process is performed by generating negative glow with different current densities depending on the current density. Here, heat absorption from the workpiece is through heat exchange of glow discharge energy and radiant heat from between the workpieces and the electrodes, while heat loss due to heat release is through radiant heat, convection of the process gas, and heat from the electrodes. These include conduction (flow from the electrode cooling water). Among these factors, possibilities that can be used to heat only the necessary portions of the workpiece to a predetermined temperature include discharge energy between workpieces, radiant heat, and the like. This can be achieved by making the cathode spacing constant, setting the introduced gas pressure to a predetermined value, and causing interaction between the two negative glows to make the current density higher than on other glow surfaces.

Therefore, a counter auxiliary electrode with approximately the same potential is installed on the surface part of the object to be treated (cathode) where it is desired to impart a function different from the others. The surface of the workpiece in this area receives radiant heat due to interaction with this auxiliary electrode.
It is heated and kept warm by glow discharge such as hollow cathode effect. In this case, the ionization density of the gas between the object to be treated and the auxiliary electrode is increased, and the surface reaction with the target active atoms to be diffused becomes active.
In order to effectively carry out this phenomenon, important factors are the distance from the surface of the object to be treated to the auxiliary electrode and the setting of the gas pressure according to the composition of the gas. First of all, the distance from the surface of the workpiece to the auxiliary electrode varies depending on the gas pressure, but if the negative glow generated between the workpiece and the installed auxiliary electrode does not interact in some way, it will not work. This effect does not occur. This is because the width of the negative glow varies depending on the gas composition and gas pressure, which strongly influences the interaction. Furthermore, the negative glow discharge area of the auxiliary electrode, which is closely related to these, must also be considered. Therefore, in general ionic surface hardening treatment, if this distance is less than 0.5 mm, the reaction of the processing gas to the treated object tends to be inhibited, while if the distance is more than 50 mm, the interaction between the glows will be inhibited. As the influence becomes weaker, the heating effect due to radiated heat from the auxiliary electrode to the workpiece decreases, and there is also heat loss to the auxiliary electrode side, resulting in a loss of energy.
Here, a glow discharge is generated at a pressure of 3.5 Torr using a mixed gas of nitrogen gas, hydrogen gas, argon gas, and methane gas, and the temperature of the surface without the auxiliary electrode is increased to 600 m
℃, and the temperature of the surface of the treated material directly under the auxiliary electrode section was measured. FIG. 2 shows the relationship between the distance (gap) between the auxiliary electrode and the surface of the material to be treated and the temperature. The relationship between distance and temperature varies greatly depending on the ratio of introduced gas, gas pressure, the shape of the material to be treated, the material of the auxiliary electrode material, its shape, etc. In the case of Figure 2, when the distance is less than 0.5 mm, the auxiliary electrode part also has a temperature of 600°C, which is almost the same temperature as the other glow surfaces. When the distance becomes larger than that, the temperature of the auxiliary electrode part rises rapidly, reaching a peak value at a distance of 2 to 5 mm.
At this distance, the temperature of the surface of the treated material directly under the auxiliary electrode is about 1000°C or higher, which is about 400°C higher than the other glow surfaces. As the distance increases further, the temperature difference gradually decreases, and at about 50 mm it is almost the same value as other glow surfaces. As mentioned above, it is desirable that the distance to the auxiliary electrode be within the range of 0.5 to 50 mm, more preferably within the range of 2 to 25 mm.

Next, regarding gas pressure, there is an appropriate value depending on the gas mixture ratio and the desired characteristics. For example, FIG. 3 shows a case where deep carburizing and hardening is required on the surface of only one part of a product in a general carbonitriding process. In this example, the area within 40 mm from each end surface of a shaft-shaped workpiece with a diameter of 25 mm and a length of 250 mm serves as the bearing part of the ball bearing, and requires a deep hardened layer. For other parts, general carbonitriding or nitriding is sufficient. In this case, 40mm on both end faces
A cylindrical auxiliary electrode with a diameter of 31 mm, which is 6 mm larger than the diameter of the product to be processed, a length of 40 mm, and a wall thickness of 4 mm is installed at a position within the range of . This is an example in which the temperature of the auxiliary electrode part was determined by maintaining the temperature at 600°C and varying the gas pressure. If the gas pressure is maintained at less than 0.5 Torr during the treatment process, some parts of the auxiliary electrode will have approximately the same temperature as other parts. On the other hand, when the gas pressure is set to 0.5 Torr or more, the current density of the glow discharge in the auxiliary electrode part becomes high, and the temperature becomes higher than that in other parts. In this example, the gas pressure is approximately
When maintained at 2 Torr, the auxiliary electrode part can be maintained at a temperature approximately 320°C higher than other parts. Note that the temperature difference can be varied widely depending on the composition of the gas, the structure of the auxiliary electrode, etc. In this example, if the gas pressure is maintained at 2 Torr, the auxiliary electrode part will be 920
℃, and other parts are kept at 600℃. Therefore, in this state, the auxiliary electrode part is made of austenite in steel, and the solid solubility limit of carbon becomes extremely large, so that the carburization phenomenon takes priority. On the other hand, other parts are ferrite until carbon and nitrogen diffuse, so there is no solid solution of nitrogen and a carbonitrided layer is formed. Generally, when surface hardening is carried out by carbonitriding, it is carried out at a low temperature of 600° C. or less, and the diffusion rate is slow, so the treatment is carried out for 2 to 5 hours in order to obtain an effective depth.
However, if the auxiliary electrode portion is kept at a high temperature, the carburization depth increases and the crystal grains also become coarse, which may make the mechanical properties undesirable. Therefore, in this process, the initial carbonitriding treatment is
The auxiliary electrode part was heated to 600°C to form a carbonitrided layer like the other parts, and the auxiliary electrode part was heated to 2 Torr for 10 to 20 minutes during the treatment process.
A thick carburized layer of approximately 0.5 mm is formed at 920°C.

As described above, the processing pressure is an extremely important factor in the present invention. Generally, it is desirable to vary it in the range of 0.1 to 10 Torr, more preferably in the range of 1.0 to 7.0 Torr.

Other incidental factors in the present invention include the size and material of the auxiliary electrode. First, the size of the auxiliary electrode is preferably approximately equal to or larger than the area of the surface portion of the object to be treated that is different from other treatments. Next, the material of the auxiliary electrode may be any material that does not adversely affect the surface of the object to be processed during processing, and the glow-generating surface of the auxiliary electrode may be only the surface facing the object to be processed.

On the other hand, as a method similar to the present invention, a method of installing an auxiliary heating source such as a heater can be considered.
In this case, it is difficult to partially provide the auxiliary heating source when processing a large number of units at the same time, and even when a single unit is used, the number of equipment etc. increases, which is not effective.

Embodiments of the present invention will be described in detail below with reference to the drawings.

Embodiment 1 As shown in FIGS. 4 and 5, a treatment section 2a, in which deep surface hardening is to be performed on a workpiece 2 set inside the conventional ion surface treatment apparatus shown in FIG.
An auxiliary electrode 20 for partial heating was set only in the portion 2b, and ion carbonitriding treatment was performed.

The product to be treated is a chromium molybdenum steel shaft (diameter 15 to 20 mm, length 205 mm) of JIS standard SCM21.
I used this book. As shown in FIG. 5, parts 2a of the shaft to be treated that require a deep hardened layer
2b is a position 25mm from the middle part and a position 25mm from the end, and the other part 2c is general carbonitriding.
Approximately 0.05mm is sufficient. Therefore, the processed part 2 of the processed product
An auxiliary electrode 20 was installed opposite to a and 2b. The auxiliary electrode 20 was made of SUS304, and the distance from the object to be processed was 5 mm.

The process involves reducing the pressure inside the vacuum container 1 to 10 ^-2 Torr or less, and in that state nitrogen gas, hydrogen gas, methane gas, and argon gas are introduced to bring the pressure to 1 Torr.
A direct current voltage of 800V was applied to generate glow discharge, and carbonitriding treatment was performed at 600°C for 4.5 hours. In this state, the surface of the treated material where the auxiliary electrode 20 was set was almost the same as other glow discharge surfaces.
In this state, the gas pressure was subsequently increased to approximately 4 Torr, and treatment was continued for another 30 minutes. In this state, the temperature of the auxiliary electrode part is 900℃, and the temperature of the other glow surfaces is 600℃.
(set temperature). After the treatment, the treated product was rapidly cooled and the hardness distribution of its cross section was measured. FIG. 6 shows the hardness distribution. In FIG. 6, curves 2a and 2b represent the hardness of the workpiece in the portion where the auxiliary electrode is installed, and curve 2c represents the hardness distribution of the other glow discharge portion. Processed parts 2a and 2b heated by varying the gas pressure during the processing process according to the present invention
The hardness distribution of the part shows a Vickers hardness of Hv513 or higher up to about 1.1 to 1.2 mm from the surface. On the other hand, in conventional carbonitriding, the depth to the same hardness is 0.2 mm or less. In other words, since the auxiliary electrode part was heated to 900℃ to the austenite region of steel, carbon diffused deeply from the surface and a carburized layer was formed in this part, resulting in a hardness distribution depending on the carbon concentration. It is something that On the other hand, since the other surfaces were treated in the ferrite region at a low temperature of 600°C, the solid solubility limit of nitrogen and carbon is small and the diffusion rate is low, resulting in a thin carbonitrided layer. As described above, it can be seen that according to the method of this example, the intended carburizing treatment was partially performed in the heat treatment section. On the other hand, it has conventionally been almost impossible to form different hardened layers of this type, or the process has been divided into two steps and the
After carburizing (general gas carburizing) with parts other than the a and 2b parts masked, the 2aa and 2b parts were masked and the other parts were carbonitrided with ions or gas. Therefore, when compared with the conventional method, it can be seen that this method is extremely desirable in terms of resource and energy saving.

As explained above, according to the glow discharge surface treatment method of the present invention, it is possible to continuously perform surface treatments with a plurality of different functions on the metal material to be treated in the same container. Moreover, it has become possible to significantly reduce the energy required for heating.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of an ion nitriding apparatus that performs conventional ion nitriding treatment, Figure 2 is a diagram showing the relationship between the distance from the surface of the workpiece to the auxiliary electrode and temperature, and Figure 3: A diagram showing the relationship between gas pressure and temperature, FIG. 4 is a sectional view showing an example of an apparatus in which the glow discharge surface treatment method of the present invention is carried out, and FIG. 5 is a diagram showing the relationship between gas pressure and temperature. FIG. 6 is a schematic diagram of the processed object to be processed, and FIG. 6 shows the relationship between the distance from the surface of the processed object to the auxiliary electrode and hardness when the processed object shown in FIG. 5 is treated by the glow discharge surface treatment method of the present invention. FIG. 1...Reduced pressure container, 2...Product to be processed, 2a, 2b
...Treatment section where deep surface hardening is desired, 3...DC power supply, 4...Anode terminal, 6...Processing gas, 9...
Vacuum device, 12... control panel, 20... auxiliary electrode.

Claims (1)

[Scope of Claims] 1. A method for surface-treating a metal material by generating glow discharge between a cathode and an anode made of a metal material, which is an object to be treated, in a reduced pressure container. An auxiliary electrode connected to a cathode near the surface is disposed at a predetermined distance from the surface of the metal material so that glow discharges generated between the metal material and the auxiliary electrode interact with each other;
After generating glow discharge at a predetermined gas pressure and surface-treating the auxiliary electrode disposed portion of the metal material at a predetermined temperature, the glow discharge is then caused to occur at a gas pressure different from the gas pressure, and the surface treatment is performed at a temperature different from the gas pressure. A glow discharge surface treatment method for a metal material, comprising surface-treating a portion of the metal material where the auxiliary electrode is provided. 2. The method according to claim 1, in which glow discharge is generated by varying the pressure inside the vacuum container in the range of 0.1 to 10 Torr during the treatment. 3. Claim 1, wherein the auxiliary electrode is disposed at a distance of 0.5 to 50 mm from the surface of the metal material.
The method described in section. 4. Claim 1, in which there are two or more components of diffused atoms that contribute to surface treatment, and the amount of diffused atoms in the part of the metal material where the auxiliary electrode is installed is different from that in other parts, so that the atoms penetrate deeply. The method described.