JPH0365435B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a surface treatment method for forming a chromium nitride or carbonitride layer on the surface of iron alloy materials such as molds, jigs, tools, and machine parts. It is something.

[Conventional technology]

When a surface treatment layer consisting of chromium carbonitride, nitride, or carbonitride is coated on the iron alloy material, various properties such as wear resistance, seizure resistance, oxidation resistance, and corrosion resistance of the iron alloy material are improved. It is well known that Many proposals have been made in recent years regarding methods of coating this surface layer. For example, a method attempts to form a chromium carbide layer by immersing an iron alloy material in a chloride-based molten salt bath (Japanese Unexamined Patent Publication No. 57
-200555, Japanese Unexamined Patent Application Publication No. 1972-20055) or chromizing treatment after nitriding the iron alloy material in advance to form a surface layer consisting of chromium carbonitride (Japanese Patent Publication No. 1972-1972) −24967
No., USP No. 4242151).

However, in all the above methods, iron
A Because the heat treatment is performed at a temperature higher than _{the C1} transformation point of approximately 700℃, distortion occurs in the base material of the iron alloy material, and there is a risk that materials with complex shapes may crack. There are also other problems, such as the high heat and poor working environment.

On the other hand, methods that attempt to form a surface layer containing chromium at temperatures below 700°C include CVD (chemical vapor deposition) and PVD (physical vapor deposition), which utilize chromium halides. is proposed. However, with these methods, it is difficult to obtain a formed surface layer with good throwing power and adhesion. Furthermore, the processing steps are complicated and the equipment is expensive. Furthermore, it is inefficient because it must be carried out in hydrogen or reduced pressure.

[Problem that the invention seeks to solve]

The present invention solves the above-mentioned conventional problems, and uses an extremely simple device to perform efficient low-temperature heat treatment to produce iron alloy materials with excellent adhesion to the base material without causing distortion to the base material. The object of the present invention is to provide a method for forming a surface layer of chromium nitride or carbonitride.

[Means for solving problems]

In the present invention, after performing a nitriding treatment to form a nitride layer of iron/nitrogen or iron/carbon/nitrogen on the surface of an iron alloy material, the iron alloy material, a chromium material, and an alkali metal or alkaline earth metal are combined. Chloride, borofluoride, fluoride, oxide, bromide, iodide,
Chromium is removed by heat treatment at 680°C or below in the presence of a treatment material consisting of one or more of carbonates, nitrates, borates, one or both of ammonium halides and metal halides. This is a method for surface treatment of an iron alloy material, characterized by forming a surface layer made of chromium nitride or carbonitride on the surface of the iron alloy material by diffusing it onto the surface of the iron alloy material.

In the present invention, the iron alloy material is a material to be treated on which a chromium nitride or carbonitride layer is formed. The iron alloy material may be one containing carbon, such as carbon steel, alloy steel, cast iron, sintered alloy, or the like, or one containing very little carbon, such as pure iron. Furthermore, the greater the carbon content of the cast iron alloy material, the greater the amount of carbon in the formed chromium carbonitride layer. Therefore, in order to increase the amount of carbon in the surface layer formed, the carbon content of the surface portion may be increased by carburizing or the like prior to nitriding, or carburizing may be performed during nitriding. Note that when industrial pure iron is used as the material to be treated, a very small amount of carbon contained in the base material enters the chromium carbonitride layer.

Nitriding treatment is to diffuse nitride (N) onto the surface of an iron alloy material to form nitrides. This nitride layer is made of iron nitride, which is the reaction between iron and nitrogen, or iron carbonitride, which is the reaction between iron, nitrogen, and carbon in the base material. Note that a solid solution layer (diffusion layer) of nitrogen into iron is formed directly below the nitride layer. Then, by heat-treating this iron alloy material together with a chromium material, chromium diffuses into the nitride layer, and a substitution reaction between chromium and iron in the nitride layer occurs.
At this time, if the nitride layer is an iron carbonitride layer, a surface layer consisting of chromium carbonitride is formed, and if the nitride layer is an iron nitride layer, a surface layer consisting of chromium nitride is formed. A layer is formed. The maximum thickness of the surface layer that can be formed on the nitrided iron alloy material is the same as the layer thickness of the nitride layer, and therefore the thickness of the surface layer is defined by the nitriding treatment.

Any method such as gas nitriding, gas soft nitriding, salt bath soft nitriding, glow discharge nitriding, etc. may be used as the nitriding method. It is desirable that the nitride concentration of the nitride layer be high, and that the nitride layer be thick.
Most preferably, the nitride layer thickness is in the range of 3 to 15 μm. If the nitride layer thickness is too shallow, the thickness of the chromium nitride or carbonitride layer formed will be thin, while if it is too deep, the toughness of the iron grade material may decrease.

After subjecting the iron alloy material to the above-mentioned vertical treatment, the iron alloy material and the chromium material are allowed to coexist and are heat treated.

This heat treatment diffuses chromium onto the surface of the iron alloy material to form a surface layer made of chromium nitride or carbonitride.

The above-mentioned chromium material supplies chromium that diffuses onto the surface of the iron alloy material, and uses a metal containing chromium, a chromium compound, or the like. Examples of metals containing chromium include chromium alloys such as pure chromium and ferrochrome, and examples of chromium compounds include:
Examples include chlorides, fluorides, and oxides of chromium such as CrCl ₃ , CrF ₆ , Cr ₂ O ₃ , and K ₂ CrO ₃ . However,
Although one or more of these chromium materials are used, it is most practical to use pure chromium.

Further, the treatment agent has the function of acting as a medium for chromium to diffuse into the surface of the iron alloy material. The treatment agent consists of one or more of alkali metal or alkaline earth metal chlorinating agents, fluorides, boric fluorides, oxides, bromides, iodides, carbonates, nitrates, and borates. It consists of an alkali metal or alkaline earth metal compound, or one or both of an ammonium halide salt and a metal halide, and is appropriately selected and used depending on the heat treatment method.

For example, the alkali metal or alkaline earth metal compounds include NaCl, CaCl ₂ , LiCl,
NaF, KF, LiF, _KBF4 , _{Na2CO3 , LiCO3} ,
Examples include KCO ₃ , NaNO ₃ , Na ₂ O, etc., and one or more of these are used. In addition, halogenated ammonium salts include NH ₄ Cl,
Examples include NH ₄ Br, NH ₄ I, NH ₄ F, etc., and examples of metal halides include CrI ₂ , CrBr ₃ , TiF ₄ , VCl ₃ ,
Examples include TiBr ₄ and the like, and one or more of these are used. Note that when using a compound containing Ti or V, there is a possibility that a surface layer containing Ti and V at the same time as Cr is formed.

Further, when a chromium halide such as CrCl ₃ is used as a treatment agent, it can also be used as the chromium material.

Heat treatment methods include a molten salt immersion method, a molten salt electrolysis method, a powder method, and the like, depending on whether the processing agent is in a molten state or a solid state at the treatment temperature.

The molten salt immersion method is a method in which the treatment agent is melted to form a molten bath, and the chromium material and the iron alloy material are immersed in the molten bath. The processing agent used in this method includes one or more of the above-mentioned processing agents, including chlorides, fluorides, borate fluorides, carbonates, nitrates, oxides, and borates of alkali metals or alkaline earth metals; Alternatively, a metal halide that melts and does not evaporate at a temperature below the heat treatment temperature is used.
In addition, in order to improve the melting state, NaCl and
It is desirable to use two or more of the above compounds, such as in combination with CaCl ₂ . Furthermore, oxides such as Al ₂ O ₃ and ZrO ₂ and cyanide compounds such as NaCN may be added for the purpose of adjusting the viscosity of the molten bath.

The reason why the chromium material is immersed in the molten bath is to dissolve chromium into the molten bath. As a means of dipping the chromium material, the chromium material such as the above-mentioned pure chromium is immersed in powder form (preferably 200 mesh or less).
Alternatively, there are methods such as adding it to the molten bath in the form of a thin plate, or immersing a rod-shaped or plate-shaped chromium material as an anode in the molten bath and electrolyzing it to dissolve the chromium anode. However, when chromium is dissolved by the above-mentioned anodic dissolution, This is advantageous in that chromium can be dissolved quickly to improve work efficiency, and undissolved chromium material is not deposited on the bottom of the bath.
In this case, as the anode, a conductive substance inserted into the molten bath container or elsewhere is used. If the anode current density during anodic melting is increased, the infiltration rate will increase, but considering that infiltration occurs even without electrolysis, a relatively low current density is sufficient. Practically speaking, 0.1 to 0.8 A/cm ² is appropriate.

The chromium dissolved in the bath diffuses onto the surface of the nitride layer formed by nitriding the iron alloy material, forming a chromium nitride or carbonitride layer.

Graphite, steel, etc. are used as the container for the molten bath, but steel is sufficient for practical use.

The above-mentioned molten salt electrolysis method is a method in which a chromium material is immersed in a bath in which a treatment agent is melted to infiltrate the chromium, and an iron alloy material is immersed as a cathode in the molten bath to perform electrolytic treatment. be. In this case, a bath container or a separately inserted conductive substance is used as the cathode.

As the treatment agent, the same one as in the molten salt immersion method is used, and the means for infiltrating chromium by immersing the chromium material in a bath containing the treatment agent is also the same as in the molten bath salt immersion method. good. Alternatively, electrolytic treatment can be carried out by immersing a chromium material in a molten bath of a treatment agent as an anode and an iron alloy material as a cathode. in this case,
It has the advantage that the anodic melting of chromium and the formation of the surface layer can be performed simultaneously.

In addition, the cathode current density for electrolytic treatment by immersing iron alloy materials is 2A/ ^cm2 or less, and practically 0.8~
0.05A/cm ² is appropriate.

It should be noted that both the molten salt immersion method and the molten salt electrolysis method described above can be carried out in the air or in a protective gas (N ₂ , Ar, etc.).

Next, in the powder method, a mixed powder of the treatment agent, a chromium material, and an iron alloy material are allowed to coexist and heated.

In the powder method, the following methods can be used to make the treatment agent coexist with the mixed powder of the chromium material and the iron alloy material. In other words, there are two methods: embedding the iron alloy material in the mixed powder, which is generally called the embedding method, coating the surface of the iron alloy material with the mixed powder, which is generally called the paste method, and the non-contact method, which is generally called the paste method. A method of arranging an iron alloy material and the above mixed powder in a non-contact state in a certain space,
There is also a method generally called the fluidized bed method, in which the mixed powder is brought into a fluidized state to form a fluidized bed, and an iron alloy material is inserted into the fluidized bed.

The processing agents used in the above powder method include alkali metal or alkaline earth metal chlorinating agents, fluorides, bromides,
It consists of one or more of iodide, boron fluoride, ammonium halide salt, or metal halide, or both. In addition, among the powder methods, in the case of a fluidized bed, the above-mentioned metal halides are those that sublimate or evaporate at a temperature below the heat treatment temperature (TlF ₄ , VF ₃ , TiBr ₄
etc.). This is because when a metal halide that does not sublimate or evaporate at temperatures below the heat treatment temperature is used, the amount of gas generated from the treatment agent that contributes to the diffusion of chromium is reduced, resulting in a thinner layer. It is.

The mixing ratio of the treatment agent and the chromium material is preferably within a range of 0.5 to 20% by weight (hereinafter referred to as % by weight) of the treatment agent relative to the chromium material. Outside this range, it becomes difficult to form a continuous surface layer consisting of chromium nitride or carbonitride, and as you approach the center of this range, it tends to become easier to form a continuous surface layer. It is in.

In addition, the particle size of the mixed powder of the treatment agent and chromium material may be such that it can pass through a JIS No. 100 sieve when using the embedding method, paste method, or non-contact method. Whether it is coarser or finer than this, there is no particular effect. Further, when carrying out the fluidized bed method, particles having a particle size in the range of 60 to 350 mesh are preferred. If the mesh is coarser than 60, a large amount of gas is required to fluidize the mixed powder, and the formation of a surface layer is difficult to proceed. On the other hand, if the powder is finer than 350 mesh, the mixed powder tends to float and becomes difficult to handle.

In the mixed powder method, additives can be added in addition to the above-mentioned processing agent and chromium material. For example, when carrying out a paste method, an adhesive such as dextrin or water glass can be added. Furthermore, some types of processing agents tend to solidify easily during heat treatment. In this case, inert powder such as alumina (Al ₂ O ₃ ) can be added. Furthermore, some combinations of chromium materials and treatments have poor surface layer formation effects. In such cases, a conventionally known halide as an activator can be added to increase the cost of forming the surface layer. The amount of these additives added can be arbitrarily selected depending on the purpose.

Hereinafter, concrete examples of the powder method, such as the embedding method, the paste method, the non-contact method, and the fluidized bed method, will be explained in detail.

In the burying method, a mixed powder of a treatment agent and a chromium material is placed in a certain container, the iron alloy material to be treated is embedded in the powder, the container is placed in a heating furnace in the atmosphere or an atmosphere furnace, and the iron alloy material is removed together with the container. This is a method of heating. In order to prevent outside air from entering the opening of the container, an inert powder such as alumina or a metal layer such as iron-boron powder may be provided.

In the paste method, an adhesive such as an aqueous dextrin solution, glycerin, water glass, ethylene glycol and alcohol is added to the mixed powder to form a paste. The paste of this mixed powder is coated on the surface of the iron alloy material to a thickness of usually 1 mm or more. The paste-coated iron alloy material is usually placed in a container and heated in a heating furnace. The atmosphere may be air, but the skin layer of the paste can be made thinner in a non-oxidizing atmosphere.
Further, in this paste method, the surface layer is formed only on the surface portion covered with the paste, so the surface layer can be formed only on an arbitrary part of the surface portion of the iron alloy material.

The non-contact method involves making the iron alloy material and mixed powder coexist in a certain closed space. Specifically, the heat treatment is performed by placing the mixed powder near the opening of the container to prevent outside air from entering, and placing the iron alloy material at a position where it does not come into contact with the mixed powder in the container. This method has operational advantages because the iron alloy material and the mixed powder are not in contact with each other.

The fluidized bed method uses a fluidized bed furnace, in which a refractory material such as alumina is added to the mixed powder to prevent the mixed powder from forming lumps during fluidization, and the above-mentioned iron alloy material is added to the mixed powder. The powder is placed in a furnace and fluidized gas is introduced to create a fluidized bed state in which the powder is fluidized. When heat-treated using this method, an extremely smooth surface layer can be obtained.
Furthermore, since the temperature distribution of the fluidized bed is uniform, a surface layer of uniform thickness can be formed. As the fluidizing gas, an inert gas such as argon gas or a non-oxidizing gas such as nitrogen gas can be used. Further, it is desirable that the flow rate of the fluidizing gas be 50 cm/min or more in the fluidized bed to avoid adhesion of powder on the surface layer. Gas pressure is 0.5-2Kg/cm ² for handling purposes.
A range of is good.

The heating temperature of the above heat treatment needs to be 680°C or less. At temperatures higher than 680°C, the matrix of the iron alloy material is subject to distortion. Further, it is desirable that the lower limit temperature is 450°C. 450℃
When heat treatment is performed at a lower temperature, the rate of formation of a surface layer of chromium nitride or carbonitride is very slow. Practically speaking, the high temperature tempering temperature for die steel is preferably 500 to 650°C, which is the tempering temperature for structural steel.

As the heat treatment time increases, the chromium content in the surface layer increases. Therefore, the treatment time is determined depending on the desired chromium content, and is selected within the range of 1 to 50 hours.

Further, the practical thickness of the surface layer to be formed is about 3 to 45 μm.

[Effect]

Although the formation mechanism of the surface layer made of chromium nitride or carbonitride according to the present invention is not clear, the inventors have determined from microanalyzer analysis and the relationship between processing time and thickness that it is as follows. It is thought that Note that the following explanation is about the mechanism of forming a chromium carbonitride layer (m, n, o, and p below each represent a number).

First, by applying nitriding treatment to the iron alloy material, which is the material to be treated, nitrogen (N) supplied from the outside reacts with iron (Fe) and carbon (C) on the surface of the iron alloy material. , N) _o a nitride layer is formed.
Also, directly below this nitride layer is a nitrogen solid solution (Fe
-N shape) is also formed.

Thereafter, by subjecting the iron alloy material to heat treatment, chromium (Cr) from the outside is diffused into the nitride layer. This diffusion is a reaction in which Fe and Cr in Fem(C,N) _o are substituted, and the nitride layer is (Cr,Fe) _p
(C, N) changes to _p . When all the Fem (C, N) _o layers change to (Cr, Fe) _p (C, N) _p , there is no further growth of (Cr, Fe) _p (C, N) _p layers. Note that in the (Cr, Fe) _p (C, N) _p layer, there is a tendency for the surface to have more Cr, and the closer to the base material, the more Fe. Therefore, depending on the conditions, the amount of Fe at the surface may be extremely small, and it may be appropriate to express it as Cr _p (C, N) _p .

Therefore, the thickness of the surface layer formed is the same as the thickness of the nitride layer formed by the initial nitriding process. Therefore, the maximum layer thickness of the surface layer can be determined by the conditions of the nitriding treatment. Also all
Until the Fem (C, N) _o layer changes to (Cr, Fe) _p (C, N) _p , (Cr, Fe) _p (C, N) _p
On the base material side, there is a surface layer consisting of two layers, the Fem(C,N) layer and _{the other} layer. The thickness of this surface layer is approximately equal to the thickness of the first Fem(C,N) _o layer.

Also, when forming a surface layer made of chromium nitride, the surface layer formation mechanism is the same as described above.

This is because the method of the present invention performs heat treatment at a low temperature of 680°C or less, and thus the formation of a surface layer with such a treatment time-thickness relationship using such a mechanism has never been done before. unknown.
In the method of the present invention, as shown in FIG. 1 of Example 1, when the heat treatment is performed at 550°C (curve A), the surface layer thickness (Fem(C,N ₎ ,
Fe) _p (total thickness of C, N) _p layer thickness) is not affected by heat treatment time. On the other hand, when heat treatment is performed at a high temperature of 1000° C. (curve S1), the longer the heat treatment is, the more the surface layer thickness generally increases, as in the case of diffusion treatment.

In addition, in practical use, it is not necessary to change all the iron, carbon, and nitrogen nitride layers to (Cr, Fe) _p (C, N) _p layers. Even in the state where two layers coexist, all (Cr,
Fe) _p (C, N) It may be in a state changed to _p layer (Fe)
The same applies to the case where the nitrogen nitride layer is changed to a surface layer consisting of chromium nitride).

〔Effect of the invention〕

According to the present invention, iron/nitrogen or iron/carbon/
After forming the nitrogen nitride layer, chromium diffusion treatment is performed using the above-mentioned specific treatment material at a temperature below 680°C, so an excellent surface layer consisting of chromium nitride or carbonitride can be formed on the iron alloy material even at low temperatures. can do.

Additionally, since the iron alloy material is heated at a low temperature, distortion is less likely to occur in the base material. Furthermore, it has good operability due to low temperature treatment and does not require a large amount of energy.

In addition, since the layer according to the present invention is formed by diffusion, it has excellent adhesion to the base material and is dense even though it is processed at low temperatures, unlike the case of carbide and nitride layers made by PVD, which do not have a diffusion reaction. A surface image can be formed.

In addition, the nitride layer etc. formed by the present invention has a large amount of iron at the layer boundary and the thermal expansion coefficients of the layer and the base material are close to each other, so it has excellent thermal collision resistance and Peeling is less likely to occur even when subjected to thermal collisions, such as when used in aluminum.

〔Example〕

Examples of the present invention will be described below. Note that % means weight %.

Example 1 A JIS/SKH51 round bar specimen with a diameter of 6 mm and a length of 30 mm
Salt bath nitriding treatment was performed by immersing the sample in a salt bath at 570°C for 2 hours. Next, a heat-resistant steel container containing a mixture of 52 mol% CaCl ₂ and 48 mol% NaCl was heated in an electric furnace in the atmosphere to form a molten salt bath at 550°C, and -100 mesh of pure salt was added to the bath. 20% chromium powder was added to the molten salt bath. The nitrided sample was immersed in this 550°C molten salt bath for 1 to 25 hours, then taken out and cooled in oil. After washing off the adhering bath agent, the cross section was polished and the thickness of the layer formed on the surface was measured by observing the cross-sectional structure. The results are shown in curve A in FIG. In this curve A, the thickness at immersion time 0 is the thickness of the nitride layer formed by the first nitriding treatment, and the thickness after 1 hour is the total thickness of the nitride layer and the chromium carbonitride layer. (the thickness of the entire surface layer) (the thickness of the Cr carbonitride layer is shown in curve B). The thickness of the total surface layer was almost the same for different treatment times and was approximately 4 μm.

FIG. 2 shows a micrograph (400x magnification) of the cross-sectional structure of the surface layer formed after 9 hours of immersion treatment. The surface layer is a layer with a smooth surface, and the boundary between the layer and the base material is intricately intricate, making it a coating layer with excellent adhesion. Furthermore, analysis using an X-ray microanalyzer reveals that there are
N and C were recognized along with Cr. According to the surface analysis results, approximately 60% Cr content was present.
Furthermore, a diffraction line corresponding to Cr ₂ N was observed in X-ray diffraction. The surface layer formed from this is
It was confirmed that it was a chromium carbonitride layer consisting of (Cr, Fe) ₂ (N, C) + (Cr, Fe) (N, C).

For comparison, nitrided samples were also prepared using the same process as above.
When a JIS/SKH51 specimen was immersed in a molten salt bath heated to 1000°C and treated, a chromium carbonitride layer with the thickness shown by curve S1 in Figure 1 was formed. . As is clear from this comparative example,
The layer thickness increases as the immersion time increases, but in the present invention, the total surface thickness does not increase as the immersion time increases. Therefore, it has become clear that the formation mechanism of the carbonitride layer in the present invention is different from that in the case of high-temperature treatment in the comparative example.

Example 2 A JIS/S45C specimen (diameter 7
mm, length 50 mm) was subjected to salt bath nitriding treatment. Next, a CaCl ₂ +NaCl molten salt bath having the same composition as in Example 1 was prepared, and CrCl ₃ powder (-320 mesh) was added in an amount of 15% based on the molten salt bath. The molten salt bath was heated to 500° C. and the specimen was immersed in the bath for 1 to 16 hours, and then taken out from the bath and cooled in oil.

The surface layer formed had almost the same thickness and texture regardless of the immersion time. As an example, when we examined a sample that had been soaked for 4 hours, we found that a surface layer with a thickness of about 8 μm was formed, as shown in the micrograph of the cross-sectional structure of the surface layer (400x magnification) in Figure 4. Ta. X-ray diffraction and X shown in Figure 5
According to the results of line microanalyzer analysis, this surface layer is (Cr, Fe) ₂ (N, C) + (Cr, Fe) (N, C)
It was confirmed that it was a chromium carbon nitride layer consisting of.

Example 3 Cylindrical shape with outer diameter φ10mm, inner diameter φ6mm, length 25mm
A JIS/S48C specimen was subjected to gas nitrocarburizing treatment at 570°C for 6 hours.

Next, a molten salt bath of CaCl ₂ +NaCl with the same composition as in Example 1 was prepared, and in this bath, 3% Al ₂ O ₃ (-320 mesh) and 20% ferrochrome alloy were added to the salt bath. Powder (-200 mesh) was added. The above sample was heated to 550℃ in a molten salt bath.
The samples were immersed for 9, 25, and 50 hours, respectively, and then taken out of the bath and cooled in oil.

When the roundness of these four types of specimens was measured, they all had almost the same roundness, and both the upper and lower parts of the specimen were as small as about 5 μm. For comparison, the roundness of the specimen when immersed in a molten salt bath at a temperature of 850℃ (immersion time was 4 hours) was approximately
It was 20 μm, which was about 4 times larger than the specimen treated with the present invention.

FIG. 6 shows a micrograph (magnification: 400 times) of a cross-sectional structure obtained by cutting a specimen treated according to the present invention (immersion temperature: 550° C., immersion time: 50 hours) and observing the surface layer.
Furthermore, analysis using an X-ray microanalyzer revealed that the formed surface layer had a thickness of approximately 8 μm, as shown in Figure 7.
m, and (Cr, Fe) ₂ (N, C) + (Cr, Fe) (N,
It was confirmed that the layer was a chromium carbonitride layer consisting of C).

Example 4 JIS/SKH51 specimen (diameter 6 mm, length 30 mm)
Ion nitriding treatment was performed at 550°C for 3 hours.

Next, a molten salt bath of CaCl ₂ +NaCl with the same composition as in Example 1 was prepared in a graphite container, and a pure chromium plate of 40 mm x 35 mm x 4 mm was inserted in the center of this bath, and this was used as the anode and the graphite container. was used as a cathode, and current was applied at an anode current density of 0.8 A/cm ² for about 15 hours. Due to this anodizing of chromium, approximately 7% of chromium was dissolved into the bath based on the total amount of salt bath, calculated from the weight loss of the chromium plate. The above specimen was placed in this molten salt bath at 550℃ for 9 hours.
After soaking for an hour, it was taken out and cooled in oil.

When the treated specimen was cut and examined using an X-ray microanalyzer, C was also found in the surface layer in addition to Cr and N, as shown in FIG. Furthermore, the X-ray diffraction results showed good agreement with the diffraction of CrN and Cr ₂ N, confirming that the surface layer was a chromium carbonitride layer.

Example 5 A JIS/S45C specimen with a diameter of approximately 7 mm and a length of 50 mm was
Salt bath nitriding treatment was performed at 570°C for 1 hour.

Next, a graphite container containing a mixture of 50 mol% KF and 50 mol% LiF was heated in the atmosphere to 600°C in an electric furnace to prepare a molten salt bath, and -100 mesh of pure chromium powder was further melted into this bath. Added 25% to the salt bath. The nitrided sample was immersed in this 600° C. bath, and electrolysis was carried out by applying current at a cathode current density of 0.1 A/cm ² for 8 hours using this as a cathode and the graphite container as an anode.

The specimen was taken out of the bath and cooled in oil, and the surface layer formed was analyzed using an X-ray microanalyzer. The surface layer was (Cr, Fe) ₂ (C, N) + (Cr,
It was confirmed that it consists of Fe)(C,N). In addition, the analysis results from the surface show that in addition to about 60% Cr,
N and C were confirmed.

Example 6 A JIS/SKH51 specimen was subjected to salt bath nitriding treatment in the same manner as in Example 1.

Next, a heat-resistant steel container containing a mixture of 45% Li ₂ CO ₃ , 25% K ₂ CO ₃ , and 30% Na ₂ CO ₃ was heated to 550°C in an atmospheric furnace to prepare a molten salt bath. Further, -100 mesh of pure chromium powder was added to this bath in an amount of 30% based on the molten salt bath. After thoroughly stirring this bath, the specimen was kept immersed in this 550°C bath for 4 hours.

The specimen was taken out of the bath and cooled in oil, and the surface layer formed was analyzed using an X-ray microanalyzer. The surface layer was (Cr, Fe) ₂ (C, N) + (Cr,
It was confirmed that it consists of Fe)(C,N).

Example 7 A JIS/S45C specimen with a diameter of 8 mm and a length of 30 mm was 570%
Gas nitrocarburizing treatment was performed for 150 minutes.

Next, -100 mesh of pure chromium potassium borofluoride (KBF ₄ ) 10 at 90°C was placed in a stainless steel container.
The specimen was embedded in a mixed powder consisting of %. Furthermore, to prevent oxidation, the mixed powder was coated with -100 mesh ferroboron powder to a thickness of 3 to 4 mm.
The whole container was heated at 600°C for 16 hours in an atmospheric furnace.
The container was taken out of the furnace and cooled in air, and then a test piece was taken out from the powder.

When the surface layer formed on the specimen was analyzed using an X-ray microanalyzer, Cr, N, and C were found in the surface layer, as shown in Figure 9, and the analysis results from the surface showed that about 60% of Cr was present in the surface layer. This layer was confirmed to be a chromium carbonitride layer.

Example 8 A JIS/SK4 specimen with a diameter of 7 mm and a length of 30 mm was heated at 570°C.
Gas nitriding treatment was performed for 60 hours.

Next, the sample was embedded in the same powder as in Example 7 and heated at 650°C for 16 hours. When the formed surface layer was analyzed with an X-ray microanalyzer, it was found that
As shown in Figure 10, the surface layer consists of Cr, N, and C, and the analysis results from the surface show that about 50% of the
Cr was detected and it was confirmed that it was a chromium carbonitride layer.

Example 9 A mixed powder consisting of 40% alumina (Al ₂ O ₃ -200 mesh), 55% ferrochrome alloy (-100 mesh), and 5% ammonium chloride (NH ₄ Cl -80+100 mesh) was dissolved in ethyl cellulose with ethyl alcohol. It was made into a paste using a solvent. Gas nitriding treatment was performed under the same conditions as Example 8.
3 to 5 on JIS/SK4 specimen (diameter 20 mm, length 10 mm)
After applying the above paste to a thickness of mm, it was placed in a stainless steel container and heated at 600℃ in an argon atmosphere.
Heated for 16 hours.

When the formed surface layer was analyzed with an X-ray microanalyzer, it was confirmed that the surface layer was made of chromium carbonitride.

Example 10 Al ₂ O ₃ (-80 mesh) 60%, pure chromium (-100
38.8%, NH ₄ Cl (−80 mesh) 12%
A mixed powder consisting of was placed in a fluidized bed furnace, and argon gas (flow rate in the furnace of
cm/min, and a pressure of 1.5 Kg/cm ² at the furnace inlet) to bring the mixed powder into a fluid state. A JIS SK4 rod (diameter 7 mm, length 50 mm) that had been nitrided in a salt bath in the same manner as in Example 1 was placed in this fluidized bed furnace and heated at 600° C. for 16 hours.

When the formed surface layer was analyzed with an X-ray microanalyzer, it was found that the surface layer was composed of Cr, N, and C, as shown in Figure 11, and the surface layer was composed of Cr, N, and C.
40% Cr was detected, and the X-ray diffraction results showed that
The layer was (Cr,
Fe) (C, N).

Example 11 570 JIS/SKD61 specimens with a diameter of 7 mm and a length of 50 mm
Salt bath nitriding treatment was performed at ℃ for 4 hours.

Next, Al ₂ O ₃ (-80 mesh) 58.8%, pure chromium (-100 mesh) 40%, NH ₄ Cl (-80 mesh)
A mixed powder consisting of 1.2% was placed in a fluidized bed furnace and argon gas was introduced from the bottom of the furnace (flow rate 200cm/min,
The mixed powder was brought into a fluid state under a pressure of 1.5 Kg/cm ² ). The above SKD61 specimen was charged into this fluidized bed furnace,
Heat treatment was performed by holding at 600°C for 16 hours.

When the formed surface layer was analyzed using an X-ray microanalyzer, it was found that the surface layer was composed of Cr, N, and C, as shown in Figure 12.
60% Cr was detected. According to the results of X-ray diffraction
The layer was (Cr,
Fe) ₂ (C,N) was confirmed.

Example 12 A JIS S45C specimen with a diameter of 6.5 mm and a length of 40 mm was subjected to salt bath nitriding treatment in the same manner as in Example 1.

Next, a mixture of 52 mol% CaCl ₂ and 48 mol% NaCl was placed in a heat-resistant steel container and heated to 600°C in an electric furnace in the atmosphere.
Adjust the molten salt bath by heating to
200 meshes of pure chromium powder was added at 25% to the total amount of the molten salt bath. After immersing the specimen in this 600°C bath for 8 hours, it was taken out and cooled in oil.

When the formed surface layer was examined by X-ray diffraction, it was found that
A diffraction line corresponding to (Cr, Fe) ₂ (C, N) + (Cr, Fe) (C, N) was observed, and it was confirmed that the surface layer was a chromium carbonitride layer.

Next, the above chromium carbonitride coated specimen (sample No. C)
For this, the gas carburized and quenched JIS/SCM415 was used as a mating material, and the test was carried out dry and under load using a fabrication tester.
A friction test was conducted under the conditions of 200 kg, rotation speed 300 rpm, and friction speed 0.1 m/sec. For comparison, JIS/S45C without the above nitriding treatment or combustible treatment is shown.
Specimen (sample No. S2) and S45C with only nitriding treatment
A friction test was also conducted on the specimen (sample No. S3).

The specimen of sample No. S2 was seized in a test time of about 3 seconds, and showed a wear amount of about 90 mg/cm ² . Also sample No.S
Test piece No. 3 did not seize during the 3 minute test time, but showed a large amount of wear of about 35 mg/cm ² .

On the other hand, with sample No. C according to the present invention, almost no amount of wear was observed after a test time of 3 minutes.
No signs of burn-in were observed.

In addition, JIS/S45C specimens were immersed in a molten salt bath at a high temperature of 900°C for 3 hours to coat a vanadium carbide (VC) layer with a thickness of approximately 3 μm, or chemical vapor deposition was performed at 850°C for 4 hours. Approximately 7μm by CVD method
Friction tests were also carried out on JIS S45C specimens coated with a carbonitride layer of titanium made of Ti (C, N). There was a lot of wear. From this, it can be seen that the surface layer formed according to the present invention is not inferior in terms of wear resistance and seizure resistance compared to the surface layer formed by immersion in a molten salt bath at high temperature or CVD.

[Brief explanation of drawings]

FIG. 1 is a diagram showing changes in the layer thickness of the surface layer formed in Example 1 with respect to immersion time, and FIG.
Figures 4 and 6 are examples 1, 2, and 3, respectively.
Micrographs (400x) showing the cross-sectional structure of the surface layer formed by the treatment of the present invention, FIGS. 3, 5, 7, 8, 9, 10, 1
1 and 12 show Examples 1 to 4, respectively.
7, 8, 10, and 11 are diagrams showing the results of X-ray microanalyzer analysis of the surface portion of the iron alloy material treated according to the present invention.

Claims (1)

[Claims] 1. After performing nitriding treatment to form a nitride layer of iron/nitrogen or iron/carbon/nitrogen on the surface of the iron alloy material, the iron alloy material, the chromium material, and the alkali metal or alkaline earth Chlorides, fluorides, boron fluorides, oxides, bromides, iodides, carbonates of similar metals,
The chromium is heated at 680°C or lower in the presence of a treatment agent consisting of one or more of nitrates, borates, ammonium halides, and/or metal halides to remove chromium from the above-mentioned iron alloy material. It is characterized by forming a surface layer on the surface of the iron alloy material, which is made of chromium nitride or carbonitride and has a thickness within the range of the thickness of the nitride layer, by diffusing it onto the surface. Surface treatment method for iron alloy materials. 2 The above chromium materials include pure chromium, chromium alloy,
The method for surface treatment of an iron alloy material according to claim 1, which comprises one or more chromium compounds. 3. The method of surface treatment of an iron alloy material according to claim 1, wherein the heat treatment is performed by immersing the chromium material and the iron alloy material in a molten bath containing the treatment agent. 4 The heat treatment melts the processing agent,
Claim 1: Performed by electrolytic treatment using an iron alloy material as a cathode in a molten bath immersed in a chromium material.
A method for surface treatment of iron alloy materials as described in . 5. The method of surface treatment of an iron alloy material according to claim 1, wherein the heat treatment is performed by embedding the iron alloy material in a mixed powder of the treatment agent and the chromium material. 6. The method of surface treatment of iron alloy material according to claim 1, wherein the heat treatment is performed by applying a paste of mixed powder of the treatment agent and chromium material to the iron alloy material. 7. The surface treatment of the iron alloy material according to claim 1, wherein the heat treatment is performed by placing the mixed powder of the treatment agent and the chromium material in a fixed space with the iron alloy material in a non-contact state. Method. 8. The method of surface treatment of an iron alloy material according to claim 1, wherein the heat treatment is carried out by bringing the mixed powder of the treatment agent and the chromium material into a fluid state and placing the iron alloy material therein.