JPS6138260B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for forming a carbide layer on the surface of a treated material using a molten salt method. Traditionally, this type of method was developed by the Special Publication Act in 1984
There is a method in which a Group A element of the periodic table is dissolved into a molten bath of borate to form a carbide layer of the Group A element on the surface of the material to be treated. However, this method is more difficult to work with due to the high viscosity of the salt bath, tends to have uneven temperature distribution in the furnace, and has a short pot life. Furthermore, there are other problems such as high bath loss due to high adhesion to the object to be treated, and the time required to remove the salt after treatment. Also, JP-A-53-
No. 35637 discloses a method using only neutral salt as a salt bath agent, but it is also possible to add a large amount of Group A elements of 30 wt% or more to create a precipitate layer at the bottom of the container, and to form a precipitate layer in the precipitate layer. A good coating layer cannot be formed unless the treated material is embedded. Therefore, when it is processed industrially, it is difficult to handle the material to be processed. Furthermore, it is severely lost due to evaporation and creep, and the skin does not look good after treatment. Due to these reasons, it has not been industrialized at present. Furthermore, when the group a element is vanadium, the carbide formed in the conventional neutral salt method is V ₂ C
It is a composite carbide of and V′C, and the outer layer is V ₂ C. For this reason, it has the drawbacks of inferior wear resistance and poor adhesion to the treated material compared to a carbide coating layer made only of VC. The present invention provides 5 to 30 mol of chloride of Group A element of the periodic table and one or more chlorides of Group A element.
This is a carbide coating surface treatment method that improves the above drawbacks by using a mixed salt bath agent containing % of borate. The method of the present invention does not have the problems of short pot life, high viscosity, large amount of adhesion, and difficulty in removing salts, unlike the conventional borate method. On the other hand, the formation of a precipitate layer, which was a drawback of the conventional neutral salt method, is less likely, and in particular, the coating layer can be formed without embedding the object to be treated in the precipitate layer. Evaporation and creep are also reduced, and the skin after treatment is also better. In addition, when the group a element is vanadium, the carbide formed is
Only VC, and no V ₂ C formation is observed. In the case of the present invention, the elements of group a of the periodic table and the chlorides of one or more of the elements of group a may be used alone or in combination of two or more. As the borate, it is preferable to use anhydrous borax, which is relatively inexpensive and easily available industrially, or other borates will have the same effect. NaCl, KCl, LiCl, as a group a element of the periodic table and one or more chlorides of group a elements;
When using one or more types of CaCl ₂ , a good coating layer can be obtained by adding 10 to 30 mol % of borate. If it is less than 10 mol%, the same phenomenon as the conventional neutral salt method will occur and it will be ineffective. On the other hand, 30mol%
If it exceeds 100%, the same phenomenon as the conventional borate method will occur and it will not be effective. In addition, as a chloride of a group a element of the periodic table and one or more of group a elements,
A salt bath in which BaCl ₂ is used and 5 to 15 mol % of borate is added thereto has little evaporation, almost no precipitation layer, and is industrially the best. If it is less than 5 mol %, there is no effect as described above, and if it exceeds 15 mol %, salts that are difficult to dissolve in hot water will adhere to the object to be treated, making it difficult to remove the salts after treatment. The Group A element added to the salt bath agent may be a single element or an alloy such as a ferroalloy, but it is preferable that the element be a fine powder of 60 mesh or less. The amount added is 5wt% to the base salt bath agent without adding more than 30wt% as in the conventional neutral salt method.
If the above amount is added, a good coating layer will be formed. Therefore, in order to suppress the formation of a precipitate layer as much as possible and economically, it is recommended that the amount of Group A elements be 5 to 5.
Addition of 30wt% is desirable. Of course, a good coating layer can be formed even if 30wt% or more is added, but 50wt%
% or more, the viscosity of the bath becomes extremely high, making it virtually impossible to insert the object to be treated. With the above bath composition of the present invention, a sufficiently good surface coating treatment of carbides is possible, but in addition, NaO,
Oxides or fluorides of group a and group a elements such as BaO, NaF, CaF or Na ₂ CO ₃ , Ba
When carbonate such as (Co ₃ ) ₂ is added at 15wt% or less,
The properties of the salt bath are stabilized and the skin after treatment improves, among other effects. The container used for surface treatment may be made of graphite or steel, but for practical purposes, one made of heat-resistant steel is most suitable. It is also effective to protect a part of the container with a substance that is more resistant to corrosion or to spray it with an inert gas. The treatment temperature is often selected in the atmosphere from 850°C to 1100°C depending on the chemical composition of the material to be treated, the intended use, etc. The appropriate temperature is a temperature below the upper limit that does not coarsen the heat-treated structure of the material to be treated, and a temperature that allows the treatment to be carried out economically. It is desirable that the material to be treated contains 0.3% or more of carbon, but even if it is 0.3% or less, the carbon concentration on the surface may be increased in advance by carburizing or the like. It is also possible to create a carburizing atmosphere in the salt bath. Further, even if the material to be treated is used as a cathode for electrolysis, a good carbide can be coated. After the treatment is completed, the object to be treated may be taken out of the molten salt bath and subjected to oil cooling, water cooling, or hot bath quenching in the atmosphere. Tempering can be done in the air if the temperature is below 500°C, but if it is above 500°C it must be carried out in a non-oxidizing atmosphere. To remove the salt attached to the workpiece, place the workpiece in hot water for 10 minutes.
It is sufficient to leave it on for about 60 minutes and then wipe it off with a cloth. Examples will be described below. Example 1 Five types of salt baths shown in Table 1 were prepared in an amount of 2 kg each. A and B are according to the present invention,
C and D are conventional methods, and E is a comparative method. Powdered first-class reagents were used for the salt bath agent, CaF, and Al ₂ O ₃ , and ferrovanadium was used as a fine powder with a purity of 76% since it was less than 100 mesh. The container is 60φ x 250
Using a pot made of SUS304, the salt bath prepared above was placed in the pot and heated and melted in the air in an electric furnace. The material to be treated is a SKD61 plate. After the surface has been ground and finished, it is degreased with trichlene and immersed in the above molten salt bath.
held. The treatment temperature was maintained at 1000°C for 4 hours and then cooled in oil. Next, the salt adhering to the surface of the treated material is washed and removed, and X-ray diffraction, X-ray microanalyzer,
The type, chemical composition, thickness, etc. of the coating substance formed on the surface of the treated material were measured by optical microscopic observation.

[Table] Table 2 shows the results and compares the conditions of the salt bath during treatment and the ease with which attached salts can be removed after treatment. The thickness of the coating layer was about 7μ in all cases, and except for symbol C, the others were made of VC carbide. Symbol C is on the outer layer
There were two layers of V ₂ C and VC carbide in the inner layer. Compared to the conventional method C, methods A and B of the present invention have better skin after treatment, less evaporation in the salt bath, and a smaller amount of ferrovanadium added, so the formation of a precipitate layer is minimal. It was hot. On the other hand, compared to conventional method D, the method of the present invention has a lower viscosity of the salt bath and is particularly advantageous in industrial processing in that it is easy to wash and remove adhering salts after treatment.

[Table] When treated using Comparative Method E, it was found that the carbide was not coated and the bath surface was likely to solidify, resulting in poor workability. Example 2 To a mixed salt of BaCl ₂ and anhydrous borax with a molar crude ratio of 86:14, 15 wt% of ferrovanadium powder of 100 mesh or less and 3 wt% of Na ₂ CO ₃ were added, and then heated and melted. . The container was a 60φ x 250 SUS304 pot and heated in an electric furnace. The material to be treated is
After finishing the surface with a SKD11 plate by grinding, it was degreased with trichlene and immersed in the above molten salt. The processing temperature is
After being held at 1000°C for 4 hours, it was cooled in oil. All of the above operations were performed in the atmosphere. After treatment, the treated material is washed with warm water to remove adhering salts, and then observed by X-ray diffraction, an X-ray microanalyzer, and an optical microscope to determine the substance, chemical composition, etc. of the coating layer formed on the surface of the treated material. Examined. As a result, the surface of the treated material SKD11 was approximately 9 μm thick.
It was confirmed that VC was formed. The conditions of the salt bath during treatment were almost as good as those shown in Table 2, symbol B of Example 1, and the skin after treatment was also extremely good. Example 3 Kcl, Nacl and anhydrous borax in a molar ratio of 45:42:
25wt% of ferroniobium powder of less than 100 mesh was added to the salt mixed at a ratio of 13 to 13, and the mixture was heated and melted. The treatment method was the same as in Example 2. As a result, an approximately 10μ thick NbC layer was formed on the surface of the treated material SKD11. The conditions in the salt bath were almost the same as in Table 2 A, but evaporation was slightly greater. Example 4 To a salt mixture of NaCl and anhydrous borax at a molar ratio of 70:30, 25 wt % of ferrovanadium of 100 mesh or less was added and heated and melted. The treatment method was the same as in Example 2. As a result, the treated material
A VC layer of approximately 8μ was formed on the surface of SKD11. The conditions of the salt bath were almost the same as those in Table 2 A, but as in Example 3, evaporation was somewhat large. In addition, even in the case of this bath composition, the adhered salts after treatment could be easily washed away with warm water. Example 5 The molar composition ratio of NaCl, BaCl ₂ and anhydrous borax is 38.5:
20wt% of ferrovanadium powder of 100 mesh or less and 5wt% of CaO ground to 20 mesh or less were added to the salt mixed at a ratio of 50.5:11 and heated and melted.
After processing in the same manner as in Example 2, the coating layer was investigated, and it was found that VC of about 9 μm was formed on the surface of the material to be processed SKD11. The conditions of the salt bath were almost the same as those of symbol B in Table 2, and the treated skin was also good. Example 6 The molar composition ratio of Nacl, Licl and K ₂ B ₄ O ₇ is 3:4:
15 wt % of ferrovanadium powder of 60 mesh or less was added to a salt bath agent mixed at a ratio of 1:1 and heated and melted. The processing method is the same as in Example 2. As a result, a VC layer of approximately 7μ was formed on the surface of the treated material SKH9. The condition of the salt bath and the ability to clean adhering salt are the second priority.
The results were the same as in Table A, but the evaporation was slightly larger. Example 7 The molar composition ratio of Bacl ₂ , Cacl ₂ and BaB ₄ C ₇ is 2:
6wt% of ferrovanadium powder of 60 mesh or less was added to a salt bath agent mixed at a ratio of 4:1, and the mixture was heated and melted. The method is the same as in Example 2. As a result, a VC layer of approximately 7μ was formed on the surface of the treated material SKH9. The conditions of the salt bath were the same as in Table 2 A and were good.

Claims (1)

[Scope of Claims] 1. A salt bath agent consisting of an element of group a of the periodic table, one or more chlorides of the element of group a, and 5 to 30 mol% of a borate; Adding the element or a substance containing it and heating and melting it,
A surface treatment method characterized by forming a carbide layer of a Group A element on the surface of a material to be treated immersed in a bath. 2. The surface treatment method according to claim 1, wherein the salt bath agent comprises BaCl 2 and 5 to 15 mol% borate. 3. The surface treatment method according to claim 1 or 2, wherein the Group A element is vanadium or its alloy powder, and a VC carbide is formed on the surface of the coating material. 4. A salt bath agent consisting of an element of Group A of the Periodic Table, one or more chlorides of the Group A element, and 5 to 30 mol% of borate, or containing an element of Group A of the Periodic Table. Add the substance, and then add the substance a.
By adding one or more of oxides, fluorides, or carbonates of Group A, Group A, and melting them by heating, a carbide layer of Group A elements is formed on the surface of the material to be treated that is immersed in the bath. A surface treatment method characterized by forming a surface. 5. The surface treatment method according to claim 4, wherein the salt bath agent comprises BaCl 2 and 5 to 15 mol% borate. 6. The surface treatment method according to claim 4, wherein the Group A element is vanadium or its alloy powder, and a VC carbide layer is formed on the surface of the coating material. 7. The salt bath agent is composed of BaCl 2 and 5 to 15 mol % of borate, the group a element is vanadium or its alloy powder, and a VC carbide layer is formed on the surface of the coating material, according to claim 4 surface treatment method.