JPS6141984B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a carbide coating layer of arbitrary thickness on the surface of a metal material, particularly a metal material with a low carbon content.

Coating a carbide layer on the surface of a metal material, such as an iron alloy material, is advantageous because the carbide layer has excellent wear resistance, seizure resistance, oxidation resistance, and corrosion resistance.
It is extremely useful industrially, and the technology for forming this carbide layer has already been put into practical use. In this case, the carbon used to form the carbide layer is carbon contained in the material, so in order to form a carbide layer with a practical thickness, at least 0.1% by weight (hereinafter % It is necessary to contain carbon of

However, the material on which the carbide coating layer is to be formed does not always contain the amount of carbon necessary for forming the carbide layer. For example, austenitic stainless steel with low magnetism and low carbon steel with good cold forging properties have a low carbon content, but they are both industrially useful materials, and the surfaces of these materials have excellent wear resistance. There is a strong need to apply a carbide coating.

In addition, even for materials that do not contain carbon at all, there are many advantages to coating them with carbide. In addition, even when using high carbon steel, if you want to form a carbide layer on the surface of a thin plate, the total amount of carbon contained inside the base material is small compared to the area where carbide is formed, so the required thickness is Sometimes you don't get it. For example, by forming carbide of only 1.5 μm on both sides of an SK4 plate with a thickness of 0.05 mm, the amount of carbon in the base material is almost eliminated.

Furthermore, in the case of steel, even if the material has the necessary amount of carbon to form carbides, if all that carbon is used to form carbides, there will be no remaining carbon in the material, so even if the steel material is quenched, the There is also the problem that it becomes impossible to give the material a predetermined hardening hardness. Therefore, in the case of steel materials, in addition to the amount of carbon necessary to form a carbide layer, it is necessary that the material contains an amount of carbon (0.5 to 1.0%) necessary to obtain quenched hardness. There is also.

However, with the conventional carbide coating method, as mentioned above, it is difficult to coat materials with a small amount of carbon that can be used for carbide formation, or on steel materials that do not contain the amount of carbon necessary to obtain quenched hardness. It is difficult to form a carbide coating layer with a certain thickness, and even if carbide is formed on steel, the quenching hardness of the base metal cannot be obtained, so the overall effect of forming a carbide coating layer is unable to demonstrate.

Therefore, the following method was previously devised by the present inventors as a method for coating such materials with carbide. That is, in the first step, the material is carburized to increase the carbon content in the material, and then in the second step, the increased carbon is used to improve the surface of the material. This is a method in which a carbide formation treatment is performed to form a carbide coating layer on the surface (Japanese Patent Publication No. 56-36703). However, with this method, even if the first step of carburizing is performed, it is not possible to make the material contain more than the solid solubility limit of carbon, so the thickness of the carbide layer that can be formed depends on the carbon hardness of each material. Limited by the melting limit, it was not always possible to form a thick carbide layer.

The present invention overcomes the above-mentioned difficulties and provides a method capable of forming a carbide coating layer of any thickness regardless of the amount of carbon in the material and without being restricted by the solid solubility limit of carbon. That is.

That is, in the present invention, after applying a carburizing agent to the surface of a metal material other than the surface on which a carbide layer is formed, the metal material is treated with one of the following elements: titanium, vanadium, niobium, tantalum, and chromium. Carrying out a carburizing process in which carbon permeates and diffuses from a carburizing agent into a metal material by heating in the presence of a carburizing agent, and a carbide forming process in which a carbide coating layer of an arbitrary thickness is formed on the surface of the metal material at the same time. A method for coating a metal material with carbide, characterized by:

According to the method of the present invention, while continuing the carburizing process in which carbon is replenished into the metal material from the outside, at the same time, both the carbon originally present in the material and the replenished carbon are used. A carbide coating layer can be formed on the surface of the material. That is, since the carburizing process and the carbide forming process are performed simultaneously and in parallel, carbon for forming the carbide can be continuously supplied. Therefore, a carbide layer of any thickness can be easily formed without being restricted by the amount of carbon originally present in the metal material and regardless of the inherent solid solubility limit of the metal material. As a result, firstly, it has become possible to form a carbide coating layer on the surface of materials that conventionally had a low carbon content and could not form carbides.
Furthermore, secondly, it has become possible to arbitrarily form a thick carbide layer on a thin plate material, whereas up until now only a thin carbide layer could be formed.

Therefore, by the method of the present invention, it has become possible to form a thick carbide layer on the surface of a thin metal plate of several microns, which is thicker than the thickness of the plate.

Furthermore, in the past, there have been materials for which it has been difficult to form carbides on all surfaces due to the special shape of the material to be treated. In other words, when knives and taps have sharp protrusions, there is a lack of carbon in the base material of the protrusions when carbide is formed.
Thick carbide formation was not possible.

However, according to the method of the present invention, by applying a carburizing agent to the surface of the material in the vicinity of such protruding parts, a sufficiently thick carbide layer can be formed even in the protruding parts.

The material to be treated to which the method of the present invention is applied may be one that does not contain carbon at all, unlike the objects to which conventional carbide forming methods are applied. However, the metal material must be capable of solidly dissolving carbon supplied from the outside into the base material. As such metal materials,
For example, there are steels that have a carbon solid solubility limit of 1.5% at 1000°C, and nickel alloys and cobalt alloys that have a carbon solid solubility limit of about 0.2%.

Furthermore, which is the greatest practical advantage of the present invention, the material to be treated according to the present invention may be a thin plate material. In the case of thin plates, it has been considered impossible to form a thick carbide layer because the total carbon content in the base material is small compared to the carbide formation area. However, by continuously supplying carbon for carbide formation as in the method of the present invention, it has become possible to form a thick carbide layer on a thin plate. Note that the thin plate here refers to approximately 1
Refers to a plate with a thickness of mm or less. If the material is thicker than 1 mm, the total amount of carbon in the base material is unlikely to be insufficient for carbide formation.

The carburizing agent applied to the material to be treated is made up of a carbon supply substance, a carburizing activator, and a binder that binds these together.Water or alcohol is further added to the carburizing agent, and the whole is kneaded into a slurry state.

Charcoal, coke, and graphite are used as carbon feed materials. These carbide supply substances are
The carburizing agent needs to be in powder form so that it can be applied to metal materials in slurry form, and the particle size is -
Approximately 50 to -100 mesh is desirable.

As the activator for carburizing, carbonates such as lithium carbonate (LiCO ₃ ), barium carbonate (BaCO ₃ ), and sodium carbonate (Na ₂ CO ₃ ) are used.

As the binder, a known adhesive such as colloidal silica, colloidal alumina, colloidal graphite, water glass, or dextrin is used.
In addition, in the molten salt bath method, these binders must not react with boric acid or borate in the bath and dissolve into the solution.

Slurry carburizing agent is practically 0.1 to 1 mm
It is preferable to apply it to the surface of the material at a thickness of .

Applying the slurry in a relatively thin layer to the metal surface in this way prevents the slurry from peeling off due to heating, maintains its binding strength as a binder even when immersed in a molten salt bath for a long time, and is easy to wash with hot water after treatment. This is because slurry can be removed. In addition, 0.1mm
If the coating thickness is less than that, the effect of carburizing will be small.

It is desirable to apply the carburizing agent to the surface of the material near the carbon-deficient portion of the base material. Therefore, when coating materials with sharp protrusions, such as knives and taps, with carbide, it is necessary to apply a carburizing agent to the surface of the material near the base material, especially at the protrusions that are deficient in carbon, to form a carbide layer. Facilitates the supply of carbon to the protrusion to be formed.

The metal material coated with the carburizing agent is heated in the presence of any one of the following elements: titanium, vanadium, niobium, tantalum, and chromium (hereinafter collectively referred to as carbide-forming elements), and eventually the material surface is heated. Form a carbide coating layer. In this heating step, carburizing treatment of the metal material and carbide formation treatment are performed simultaneously and in parallel. Therefore, the heating conditions, atmosphere, and other treatment conditions for carburizing are the same as those for carbide formation.

The carbide-forming elements are used in the form of simple metals, alloys containing these metals, or oxides of these metals. For example, alloys include ferrovanadium (Fe-V) or ferrochrome (Fe-V).
Examples of oxides include vanadium oxide (V ₂ O ₅ ) and chromium oxide (Cr ₂ O ₃ ).

Carburizing is performed by carbon released from a carbon supply substance in a carburizing agent applied to a metal material, penetrating the surface of the metal material, and then diffusing into the matrix of the material. At this time, if a portion with less carbon is generated in the base material during carbide formation, carbon diffusion is performed preferentially toward that portion.

Moreover, the carburizing process is performed continuously as long as the carbide forming process continues.

Thus, on the surface of the metal material heated in the presence of the carbide-forming element, the carbide-forming element supplied from the outside and carbon near the surface of the base material combine to form a carbide on the surface of the metal material.

The location of carbide formation is the part of the surface of the metal material to which the carburizing agent has not been applied.

In the present invention, as a specific method for forming the carbide coating layer, known carbide coating methods, ie, molten salt bath method, electrolytic method, powder method, and vapor phase method, can be used.

The molten salt bath method is a method previously developed by the inventors, in which the material to be treated is immersed and held in a molten salt bath of boric acid or borate into which carbide-forming elements have been dissolved. A method of forming a carbide layer on the surface is extremely effective. Further, an electrolytic method in which the material to be treated is immersed and held in the treatment bath and used as a cathode, and an electrode material separately inserted into the bath is used as an anode for electrolytic treatment, is effective for shortening the treatment time. The powder method uses powders of commonly used ammonium chloride (NH ₄ Cl) or fluoroborates developed by the inventors, such as potassium borofluoride (KBF ₄ ), and powders containing carbide-forming elements. An excellent method is to embed the material to be treated in a mixed powder and heat it. In this case, in the slurry method, water or alcohol is further added to the mixed powder to make the whole into a slurry state, and the slurry method is applied to the surface of the material to be treated. According to this method, it is possible to coat only a part of the material to be treated and to locally form a carbide layer in that part.

Another method is to heat and hold the material to be treated in a closed container filled with a mixed gas of titanium tetrachloride (TiCl ₄ ), methane (CH ₄ ), and hydrogen (H ₂ ) or in an air stream of these gases. In particular, titanium carbide (TiC) can also be formed.

The processing temperature for carbide formation may range from 700° C. to below the melting point of the metal material, as is generally known in the art. However, although the formation of carbides is more rapid at higher temperatures, the higher the temperature, the more severe the deterioration of the material becomes.
1100℃ is desirable.

The treatment time for carbide formation is determined in relation to the required thickness of the carbide coating layer and the treatment temperature. That is, when the purpose is to form a thick carbide layer and when the treatment temperature is low, a long treatment time is required. Generally 1 hour to 30
An appropriate amount of time is required.

The thickness of the carbide layer of the carbide-forming element to be formed must be at least 2 μm or more.
If it is thinner than 2 μm, there is concern about the wear resistance effect.
Note that the formation of the carbide layer continues as long as carbon is supplied from the carburizing agent and carbide-forming elements are present, so it is possible to form a carbide layer of any thickness by selecting the treatment temperature and treatment time. However, if the carbide layer becomes too thick, it tends to peel off easily, so it is generally desirable for practical use to have a thickness of 30 μm or less.

Example 1 Slurry carburizing agent was applied to a thickness of approximately 1 mm on only one side of a 0.05 mm thick JISSK ₄ (carbon content approximately 1% by weight, hereinafter referred to as %) plate specimen. and dried at 200°C. The carburizing agent was prepared by adding 5% colloidal aqueous solution to a mixed powder of -100 mesh 47.5% charcoal powder and -60 mesh 47.5% BaCO ₃ and stirring. This specimen was immersed in a molten bath containing 20% Fe-V powder (containing 55% vanadium) as a carbide-forming element and 80% borax and held at 900°C for 8 hours. Next, the specimen was taken out of the bath and water quenched, and then the specimen was washed with warm water to remove the adhering carburizing agent.

The specimen thus obtained was cut and the cross-sectional structure was observed. FIG. 1 is a micrograph showing the cross-sectional structure at this time. This micrograph and analysis using an X-ray microanalyzer revealed that a vanadium carbide layer (VC layer) was formed on the surface of the specimen opposite to the surface to which the carburizing agent was applied (hereinafter, this surface is referred to as the carbide-forming surface). It was recognized that In this way, on a 50 μm thick steel, approximately
A 15 μm vanadium carbide layer was formed.
Further, the base material hardness of the steel in this case was Hv820, which was the same hardness as the base material after quenching without the treatment of the present invention.

On the other hand, the same specimen was subjected to carbide coating treatment in the same bath under the same conditions without applying a carburizing agent. The cross-sectional structure of the specimen obtained as a result is shown in the micrograph of FIG. As is clear from the photograph, the vanadium carbide layer formed on both surfaces of the specimen was only 1.8 μm in thickness, and the base material hardness was only about Hv100, close to that of blunt iron.

Example 2 The same carburizing agent as in Example 1 was applied to a thickness of about 0.8 mm on only one side of a 0.1 mm thick pure nickel plate specimen, and then air-dried.

A slurry treatment agent was applied to the carbide-forming surface of this sample to a thickness of about 3 mm, and then air-dried. The above-mentioned treatment materials include -100 mesh of 95% ferroniobium (Fe-Nb, containing 65% niobium) powder as a carbide-forming element, and -100 mesh of KBF _4.
It was prepared by adding 5% colloidal silica aqueous solution to a mixed powder with 5% powder.

This specimen was placed in a heat-resistant steel covered container (diameter 130 mm, height 100 mm, wall thickness 7 mm), and ferroboron (Fe-B, boron content 20%) was placed in the gap between the lid and the container.
I put some powder on it and sealed it. The container was then placed in an electric furnace in the atmosphere and heated at 900°C for 8 hours. Thereafter, the container was taken out of the electric furnace and air cooled. Then, the sample was taken out from the container, and the treatment agent adhering to the sample was removed.

As a result of the above treatment, the carbide-forming surface of the specimen has approximately
A 10 μm niobium carbide layer was formed. The hardness of the base material at this time was approximately Hv80 because it does not harden by quenching like steel.

On the other hand, an attempt was made to coat the same specimen with the same treatment agent without applying carburizing agent under the same conditions, but no carbide layer was formed on the surface of the specimen. Ta.

Example 3 A slurry carburizing agent was applied to only one side of the same JISSK4 plate specimen as in Example 1 to a thickness of about 1.5 mm, and then dried. -100 mesh charcoal powder 30% and -60 mesh Na ₂ CO ₃ powder 60% as carburizing agent.
It was prepared by adding 10% water glass aqueous solution to 10% mixed powder.

On the other hand, -100 mesh of 65% metal chromium powder and -100 mesh of Al ₂ O ₃ powder 30% as anti-sintering agent.
A treatment agent prepared by mixing 100 mesh with 5% NH ₄ Cl powder was placed in a heat-resistant steel container with an open top, leaving 3 to 4 mm from the top. Next, the sample was embedded in the center of the treatment agent, and finally, the treatment agent was coated with -100 mesh Fe-B powder to a thickness of 3 mm. The container was then placed in an electric furnace in the atmosphere and heat treated at 950°C for 8 hours. Thereafter, the processing container was taken out of the electric furnace and air-cooled in that state. The test piece was taken out from the cooled treatment vessel, and the adhering carburizing agent and treatment agent were easily removed with a wire brush.

When the cross-sectional structure of the specimen thus obtained was observed under a microscope, it was found that the carbide forming surface of the specimen had approximately
A chromium carbide with a thickness of 15 μm was formed.
The hardness of the base material was approximately Hv800.

On the other hand, the above specimen was subjected to carbide coating treatment under the same treatment conditions without applying carburizing agent.
The thickness of the chromium carbide layer formed is only about 4
It was only μm.

Example 4 0.1mm thick JISSUS304 (carbon content approx. 0.04
The same carburizing agent as in Example 1 was applied to a thickness of about 0.6 mm on only one side of a plate-shaped specimen of %), and dried at 200°C. Next, add this sample to 20% of the total bath volume.
Immersed in a molten borax bath containing Fe-V powder,
Electrolysis was carried out for 1 hour at a current density of 0.3 A/cm ² using the specimen as a cathode and the container as an anode.

The cross-sectional structure of the specimen after the above treatment is shown in the micrograph of FIG. As is clear from the photograph, a vanadium carbide layer of about 13 μm was formed on the carbide-forming surface of the specimen. The hardness of the base material is approximately
It was Hv840.

On the other hand, the same specimen was subjected to carbide coating under the same conditions without applying any carburizing agent.
As a result, the thickness of the vanadium carbide layer formed on both sides of the specimen was only 0.2 μm.

Example 5 A slurry carburizing agent was applied to a thickness of about 0.6 mm on only one side of a 0.1 mm thick pure cobalt plate specimen, and then dried. The above carburizing agent is -60 mesh of 50% coke powder and -20 mesh of K ₂ CO ₃ powder.
It was prepared by adding a 10% aqueous dextrin solution to a 40% mixed powder. Add this sample to 50% of the total amount of bath.
% metal Ta was used as an anode and immersed in a molten borax bath which had been electrolytically infiltrated, held at 1000° C. for 2 hours, and then taken out and cooled in the air.

As a result of the above treatment, the carbide-forming surface of the specimen has
A tantalum carbide layer of about 15 μm was formed.
The hardness of this base material was approximately Hv90.

On the other hand, an attempt was made to coat the same specimen with carbide in the same bath under the same conditions without applying a carburizing agent, but no carbide layer was formed on the surface of the specimen.

Example 6 The same carburizing agent as in Example 1 was applied to a thickness of about 1.5 mm only on one side of a 0.1 mm thick pure cobalt plate specimen and dried. Next, this specimen was placed in a heat-resistant steel covered container, and further heated with TiCl ₄ 0.02 atm and CH ₄ 0.03.
A mixed gas consisting of 0.95 atm of H ₂ and 0.95 atm of H 2 was sealed in the container, and the lid was put on to make a sealed container. This container was then placed in an electric furnace in the atmosphere and heated at 1000°C for 2 hours. Thereafter, the container was taken out of the electric furnace, cooled in air, and then the specimen was taken out from the container.

Titanium carbide with a thickness of about 15 μm was formed on the carbide-forming surface of the specimen obtained by the above treatment. Moreover, the hardness of the base material was approximately Hv90.

[Brief explanation of the drawing]

FIG. 1 and FIG. 3 show Example 1, respectively.
and a cross-sectional micrograph (200x magnification) of the entire layer structure of the vanadium carbide layer formed in Example 4,
FIG. 2 is a cross-sectional micrograph (200x magnification) of the entire structure of the vanadium carbide layer formed when no carburizing agent was applied.

Claims (1)

[Claims] 1. After applying a carburizing agent to the surface of the metal material other than the surface on which the carbide layer is to be formed, the metal material is coated with titanium,
A carburizing process in which carbon permeates and diffuses from a carburizing agent into a metal material by heating in the presence of any one of the elements vanadium, niobium, tantalum, and chromium, and the surface of the metal material can be coated to an arbitrary thickness. 1. A method for coating a metal material with carbide, characterized in that a carbide forming treatment for forming a carbide coating layer is simultaneously performed in parallel. 2. The method of coating a metal material with carbide according to claim 1, wherein the metal material is a thin plate. 3. The method of coating a metal material with carbide according to claim 1, wherein the metal material is a material having an acute protrusion, and the carburizing agent is applied at least in the vicinity of the protrusion. .