JPS6138263B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for coating the surface of a material to be treated with a carbide layer using a molten salt method.

Conventionally, the above-mentioned surface treatment methods include a method in which a group A element is dissolved in a molten bath of borate to form a group A carbide layer on the surface of the material to be treated, and a method in which a group A or a carbide layer is formed in a molten bath of a neutral salt. A method is known in which a group a carbide layer or a group a carbide layer is formed on the surface of a material to be treated by infiltrating a group element. However, all of the above methods relate to coating a single carbide layer. Moreover, in the method using a borate bath as the main ingredient, the A-group elements reduce the borate, so it is difficult to coat the A-group element with a carbide layer, or the life of the pot is short.
There are many operational problems, such as the high viscosity of the bath and the time it takes to remove salt deposits after treatment. On the other hand, in the conventional method using a neutral salt bath, a large amount of Group A elements or their alloys of 30 wt% or more are added to form a precipitate layer at the bottom of the container, and the material to be treated is embedded in the precipitate layer. Otherwise, a good coating layer will not be formed. Therefore, when processing industrially, various difficulties arise in handling the objects to be processed. In addition, although it is possible to coat a carbide layer of group A elements with the neutral salt bath method, a precipitate layer is formed in this case as well, and carbides of group A elements are very easily oxidized, so they should not be treated in an inert atmosphere. Must be.

The present invention involves reducing the oxide of the Group A element with the Group A element or a substance containing the same in a molten salt bath, so that the Group A element is dissolved in the salt bath, and at the same time, the Group A element is dissolved in the salt bath. This is a surface treatment method of forming a double carbide layer of a group A element and a group A element on the surface of a material to be treated by infiltrating a portion of the metal. The double carbide layer formed by the present invention has better wear resistance than a single carbide of a group A element, and has better oxidation resistance than a single carbide of a group A element, so it can be treated in the atmosphere. It has the following characteristics.

Group a oxides in the present invention include V ₂ O ₅ ,
Nb ₂ O ₅ , V ₂ O ₃ , Ta ₂ O ₅ etc., 3wt%~20wt
It is preferable to add it within a range of %. If it is less than 3 wt%, no coating layer will be formed, and if it is more than 20 wt%, as will be described later, it is necessary to add a large amount of Group A elements, so the viscosity of the salt bath increases significantly, making it virtually impossible to process.

A substance containing the Group A element, such as a compound, may be added to the Group A element as long as it has the ability to reduce the Group A element oxide. For example, ferroalloys of Group A elements are also effective. The amount of the Group A element added must be greater than the stoichiometric amount sufficient to reduce 80% of the Group A element oxide added above. Therefore, when adding a large amount of the group a element oxide, a large amount of the group a element must also be added at the same time. The addition method may be to mix the above Group A element oxide and the Group A element or a substance containing them with the base salt bath agent at room temperature and then heat and melt them at the same time. Only the substance contained in the salt bath may be added later into a pre-molten salt bath and mechanically stirred.

It is desirable to use a fine powder of 60 mesh or less for the Group A element or a substance containing it. The Group A element oxide may be in any form as long as it has a melting point of 1000° C. or less, such as V ₂ O ₅ , but if a high melting point oxide is used, it must be in the form of a fine powder of 60 mesh or less.

The base salt bath agent may be one that forms a stable melt at 850°C to 1100°C;
When one or more chlorides of Group A and Group A are used as a salt bath agent, the viscosity of the bath is low, the amount of adhesion to the object to be treated is small, and the salt can be easily removed after treatment. This makes it easier to work. More preferably, if a salt bath containing a mixture of 5 to 30 mol% borate and one or more chlorides of Group A and Group A of the Periodic Table is used, evaporation and creep phenomena in the salt bath will be reduced. , the surface of the treated material also becomes better. In this case, since the main component is one or more chlorides from Group A and Group A of the Periodic Table,
It does not have the short pot life, high viscosity of the bath, large amount of adhesion to the object to be treated, and difficulty in removing salt after treatment, which are the shortcomings of conventional methods mainly using borate. It is an extremely practical salt bath agent because group elements do not reduce borates.

Furthermore, adding a small amount of Group A elements of 15 wt% or less to the above salt bath stabilizes the life of the bath.
This has the effect of keeping the growth rate of the coating layer constant over a long period of time. Addition of a group a element or a fluoride of a group a element is also effective in stabilizing the properties of the bath.

Containers used for processing include graphite, refractories, steel, etc.
There are various types, 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 material that is more resistant to corrosion or to spray it with an inert gas.

The processing temperature is 850°C to 1100°C, which varies depending on the chemical composition of the material being treated. A guideline for determining the appropriate processing temperature is the upper limit that can process the target coating layer thickness (usually 15μ or less) in the shortest possible holding time and that does not coarsen the heat-treated structure of the material to be processed. It should be experimentally determined in advance for each material to be below the temperature.
The material to be treated preferably contains 0.3% or more of carbon, but even if it contains 0.3% or less, it is sufficient if the carbon concentration on the surface has been increased in advance by carburizing or the like.
It is also possible to form a carbide layer on the surface of the material to be treated by using the salt bath agent in a carburizing atmosphere.

After the treatment is completed, the object to be treated is taken out of the molten salt bath and cooled in the atmosphere with oil, water, or at 600°C.
The following hot bath quenching is sufficient. Tempering is at 500℃
In the following cases, it may be carried out in the air, but if the temperature is 500°C or higher, it must be carried out in a non-oxidizing atmosphere.

Examples will be described below.

Example 1 A mixed salt of KCl and BaCl ₂ with a molar composition ratio of 60:40
V ₂ O ₅ and powdered Fe-Ti of 100 mesh or less were mixed in various proportions and then heated and melted together with a salt bath agent. The container is made of SUS304 and the bottom of the pipe is also made of SUS304.
The plate was welded by plate making and heated in an electric furnace. The materials to be treated were plates of SKD11 and SKD61, the surfaces of which were ground, degreased, and immersed in the molten salt bath. The treatment temperature was 1000°C, which was maintained for 4 hours and then cooled with oil in the atmosphere. After washing the treated material with warm water to remove the attached salt, the presence or absence of a coating layer and its type of composition were examined by X-ray diffraction, X-ray microanalyzer, and optical microscope observation. FIG. 1 is a diagram showing the results in terms of the relationship between the addition ratio of V ₂ O ₃ and Ti. In the figure, ○ indicates the case where the composition is (VTi)C and the crystal structure is VC, ● indicates the formation of a double carbide layer with the composition (VTi)C and the crystal structure TiC, and × indicates the case where no carbide layer is formed. . Ti (%) was calculated from the purity of added Fe-Ti (71.0% Ti).

From this example, the amount of Ti added is 1/2 of the amount of V ₂ O ₅ added.
It was found that the carbide layer was not formed unless the above conditions were met. In addition, the carbide layers formed are both V and V.
It is a Ti double carbide layer, but the amount of Ti added is 1/2V ₂ O ₅
When ≦Ti<V ₂ O ₅ , the crystal structure is close to VC, and Ti≧
It was found that when V ₂ O ₅ is used, it is close to TiC. Second
The figure shows an example of the results of line analysis of each element using an X-ray microanalyzer on a double carbide layer formed when 1/2V ₂ O ₅ ≦Ti<V ₂ O ₅ . In this case V.C.
Ti is in a solid solution state. Figure 3 shows Ti
This is an example of a line analysis result of a double carbide layer formed when ≧V ₂ O ₅ , and in this case, the double carbide is a double carbide in which V is fixed to TiC. Note that the thickness of the formed double carbide layer varied to some extent from 3 to 7.3μ.

Example 2 8wt% _V2O5 and _7wt % Fe-Ti were added to a mixed salt of anhydrous borax and _BaCl2 with a molar composition ratio of 14:86,
The material to be treated, SKD11, was immersed and held at 1000°C for 4 hours, and then cooled in oil. After washing with warm water, X-ray diffraction, X-ray microanalyzer analysis, and optical microscope observation were performed in the same manner as in Example 1, and the result was approximately 7.5
A coating layer of μ was formed. This layer was a double carbide of V and Ti close to the crystal lattice of VC. In the case of the salt bath composition, the evaporation of the bath, the condition of the precipitated layer, the texture of the treated material after treatment, etc. were all superior to the case of Example 1 in which only the neutral salt was used as the base.

Example 3 Mixed salt of KCl and BaCl ₂ with a molar composition ratio of 60:40
5wt% _{V2O5 and} less than 100 mesh powdered Fe-Ti
When treated in the same manner as in Example 2 using a salt bath composition containing 5 wt% of Fe-V and Fe-V, approximately 7μ
A uniform coating layer was formed. This layer was a double carbide of V and Ti close to the crystal lattice of VC.

Example 4 A mixed salt of NaCl and BaCl ₂ with a molar composition ratio of 61:39, 10 wt% V ₂ O ₅ , 5 wt% Ti, and 5 wt% NaF
(both in powder form) were added, heated and melted, and treated in the same manner as in Example 2, forming a coating layer of about 6 μm. This layer is also close to the crystal lattice of VC
It was a double carbide of Ti and Ti.

[Brief explanation of the drawing]

Figure 1 shows the relationship between the mixing ratio of Ti and V ₂ O ₅ , the composition and crystal structure of the coated material, and Figure 2 shows the relationship between the mixing ratio of Ti and V 2 O 5 and the composition and crystal structure of the coated material. V by X-ray microanalyzer,
Figure 3 shows the results of line analysis of Ti and C elements.
It is a figure which shows the result of the line analysis of Ti and C each element.

Claims (1)

[Claims] 1. 3wt% to 20wt% oxide of group a element of the periodic table
and one or two of the Group A and Group A elements of the Periodic Table containing the Group A element or a substance containing it in a stoichiometric amount or more sufficient to reduce 80% of the Group A element oxide. A surface treatment method characterized by immersing a material to be treated in the above chloride bath to form a double carbide layer of a group A element and a group A element on the surface thereof. 2 Oxides of Group A elements of the periodic table 3wt% to 20wt%
and 5 to 30 mol% borate containing a Group A element or a substance containing it in a stoichiometric amount or more sufficient to reduce 80% of the Group A element oxide, and the remaining Group A and Group A borate of the periodic table. The material to be treated is immersed in a salt bath containing one or more chlorides of group A elements to form a double carbide layer of group A elements and group A elements on its surface. surface treatment method. 3 Oxides of Group A elements of the periodic table 3wt% to 20wt%
Add up to 15 wt% of a Group A element or a substance containing it to a mixture of a Group A element or a substance containing it in an amount greater than the stoichiometric amount sufficient to reduce 80% of the Group A element oxide. As the amount of group a elements
Group A elements and Group A elements are added to the surface of the material to be treated, which is immersed in a bath of one or more chlorides from Group A and Group A of the Periodic Table, which is heated and melted with the addition of 15 wt% or less. A surface treatment method characterized by forming a double carbide layer. 4 Oxides of Group A elements of the periodic table 3wt% to 20wt%
Add up to 15 wt% of a Group A element or a substance containing it to a mixture of a Group A element or a substance containing it in an amount greater than the stoichiometric amount sufficient to reduce 80% of the Group A element oxide. As the amount of group a elements
5 to 30 mol, heated and melted with 15 wt% or less added
% of borates and the rest of groups a and a of the periodic table
A surface treatment characterized by forming a double carbide layer of a group a element and a group a element on the surface of a material to be treated immersed in a salt bath containing one or more chlorides of the group a. Method.