JPH0447029B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention forms a hafnium (Hf) nitride or carbonitride layer on the surface of iron alloy materials such as molds, jigs, tools, and machine parts. This invention relates to a surface treatment method. [Prior Art] When a surface layer of hafnium carbide, nitride, or carbonitride is coated on the surface of an iron alloy material,
It is well known that various properties of iron alloy materials, such as wear resistance, seizure resistance, oxidation resistance, and corrosion resistance, are improved. Many proposals have been made in recent years regarding methods of coating this surface layer. For example, plasma CVD using hafnium halides, etc.
A method has been proposed in which a surface layer consisting of hafnium carbonitride is formed on the surface of an iron alloy material by a chemical vapor deposition method (for example, JP-A-55-65357; −164072). These methods process at a temperature below approximately 700°C, which is the A _c1 transformation point of iron, so a surface layer can be formed without thermally distorting the base material of the iron alloy material. It is difficult to obtain a surface layer with good throwing power and adhesion. Furthermore, the processing steps are complicated and the equipment is expensive. In addition, efficiency is poor because it must be carried out in hydrogen or reduced pressure. [Problems to be Solved by the Invention] The present invention solves the above-mentioned conventional problems, and efficiently heats the base material at low temperatures using extremely simple equipment, without causing distortion in the base material. The object of the present invention is to provide a method for forming a surface layer made of hafnium nitride or carbonitride that has excellent adhesion to a base material on an iron alloy material. [Means for Solving the Problems] The present invention provides a nitriding treatment to form an iron/nitrogen or iron/carbon/nitrogen nitride layer on the surface of the iron alloy material, and then the iron alloy material and hafnium material and one or more of alkali metal or alkaline earth metal chlorides, borate fluorides, fluorides, oxides, bromides, iodides, carbonates, nitrates, borates, or/and halogens. Nitrogen of hafnium is added to the surface of the iron alloy material by heat treatment at 700°C or below in the presence of a treatment agent consisting of one or both of ammonium oxide salt and metal halide. This is a method for surface treatment of iron alloy materials, characterized by forming a surface layer made of carbonitride or carbonitride. In the present invention, the iron alloy material is a material to be treated on which a hafnium nitride or carbonitride layer is formed. The iron alloy material may be one containing carbon, such as carbon steel, alloy steel, cast steel, sintered alloy, etc., or one containing only a very small amount of carbon, such as pure iron. Furthermore, the greater the carbon content in the iron alloy material, the greater the amount of carbon in the hafnium carbonitride layer formed. 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 hafnium carbonitride layer. The nitriding process is to diffuse nitrogen N into the surface of the iron alloy material to form a nitride layer. 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 the hafnium material, hafnium diffuses into the nitride layer, and a substitution reaction between hafnium and iron in the nitride layer occurs. At this time, if the nitride layer is an iron carbonitride layer, a surface layer consisting of hafnium carbonitride is formed, and if the nitride layer is an iron nitride layer, a surface layer consisting of hafnium nitride is formed. A surface 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 determined 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 hafnium nitride or carbonitride layer formed will be thin, while if it is too deep, the toughness of the iron alloy material may decrease. After the iron alloy material is subjected to the nitriding treatment described above, the iron alloy material and the hafnium material are allowed to coexist and heat treated. This heat treatment diffuses hafnium onto the surface of the iron alloy material to form a surface layer made of its nitride or carbonitride. The above-mentioned hafnium material supplies hafnium to be diffused onto the surface of the iron alloy material, and uses a metal containing hafnium, a hafnium compound, or the like. Examples of the metal include hafnium metal and alloys thereof. The above compounds include:
Examples include chlorides and bromides such as HfCl ₄ and HfBr ₄ . Although one or more of these hafnium materials are used, it is most practical to use hafnium metal. Further, the treatment agent has the function of acting as a medium for hafnium to diffuse onto the surface of the iron alloy material.
The treatment agent is an alkali consisting of one or more of chlorides, fluorides, borate fluorides, oxides, bromides, iodides, carbonates, nitrates, and borates of alkali metals or alkaline earth metals. It consists of a metal or alkaline earth metal compound, and/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 , VCl ₃ , TiF ₄ ,
Examples include TiBr ₄ , FeCl _{3 ,} etc., and one of these
Use one or more species. Therefore, as the treatment agent, only the above-mentioned alkali metal or alkaline earth metal compound, or only one or both of the ammonium halide salt and the metal halide may be used. A compound of a similar metal and one or both of an ammonium halide salt and a metal halide may be used. In addition, when using compounds containing Ti or Cr,
A surface layer containing Ti and Cr may be formed simultaneously with Hf. Furthermore, when a hafnium halide such as HfCl ₄ is used as a treatment agent, it can also be used as the hafnium 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. Further, the powder method includes an embedding method, a paste method, a non-contact method, and a fluidized bed method. These will be explained below. The molten salt immersion method is a method in which the treatment agent is melted to form a molten salt bath, and the hafnium material and the iron alloy material are immersed in the molten salt bath. The processing agent used in this method includes alkali metal or alkaline earth metal chloride, fluoride,
One or more of borofluorides, carbonates, nitrates, oxides, borates, and/or metal halides that do not melt and evaporate at temperatures below the heat treatment temperature are used. Note that in order to improve the melting state, it is desirable to use two or more of the above compounds, such as a combination of NaCl and CaCl ₂ . Furthermore, for purposes such as adjusting the viscosity of the molten salt bath.
Oxides such as Al ₂ O ₃ and ZrO ₂ and cyanide compounds such as NaCN may be added. The purpose of dipping the hafnium material along the molten salt is to infiltrate hafnium into the molten salt. As a means of immersing hafnium material,
The material is in powder form (preferably 200 mesh or less)
Alternatively, there is a method of adding hafnium along the molten salt in the form of a thin plate, or a method of immersing the material in the form of a rod or plate as an anode into the molten salt and electrolyzing it to dissolve hafnium in the anode. Introducing hafnium by anodic melting is advantageous in that hafnium can be infused quickly and work efficiency can be improved, and undissolved hafnium material does not accumulate at the bottom of the bath. be. In this case, as the cathode, a conductive substance inserted into a container along the molten salt or elsewhere is used. Increasing the anode current density during anodic melting increases the infiltration rate, but considering that infiltration occurs even without electrolysis,
Relatively low current densities are sufficient. Practically 0.1
~0.8A/ ^cm2 is suitable. The hafnium dissolved in the bath diffuses onto the surface of the nitride layer formed by the nitriding treatment of the iron alloy material to form a hafnium nitride or carbonitride layer. Note that graphite, steel, or the like is used as the container for the molten salt, but steel is sufficient for practical use. In addition, the molten salt electrolysis method is a method in which a hafnium material is immersed in a bath in which a treatment agent is melted to infiltrate the hafnium, and an iron alloy material is immersed as a cathode along the molten salt to perform electrolytic treatment. It is something.
In this case, the bath container or a separately inserted conductive substance is used as the anode. As the treatment agent, the same one as in the molten salt immersion method may be used, and the means for infiltrating hafnium by immersing the hafnium material in a bath containing the treatment agent may also be the same as in the molten salt immersion method. . Alternatively, electrolytic treatment can be performed by immersing a hafnium material as an anode and an iron alloy material as a cathode along the molten salt of the treatment agent.
In this case, there is an advantage that the anodic dissolution of hafnium 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 0.05~
1.0A/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 either in the air or in a protective gas (N ₂ , Ar, etc.). Next, the powder method means that a mixed powder of the treatment agent and a hafnium material and an iron alloy material coexist,
It is heated. In the powder method, the following methods can be used to coexist a mixed powder of a processing agent and a hafnium material and an iron alloy material. Namely, there are two methods: burying the iron alloy material in the mixed powder, which is generally called the burying method, coating the surface of the iron alloy material with the mixed powder, which is generally called the base method, and the non-contact method. There is a method in which the iron alloy material and the above-mentioned mixed powder are arranged in a non-contact state in a certain space, and a method is generally called a fluidized bed method in which the above-mentioned mixed powder is in a fluidized state to form a fluidized bed. There is a method of inserting ferrous alloy material into the layer. The processing agent used in the above powder method is one or two of alkali metal or alkaline earth metal chlorides, fluorides, bromides, iodides, and boron fluorides.
It consists of one or both of a variety of species and/or a halogenated ammonium salt and a metal halide. In addition, among the powder methods, in the case of a fluidized bed, the metal halide mentioned above is one that sublimates or evaporates at a temperature below the heat treatment temperature (VCl ₃ ,
FeCl ₃ , TiF ₄ , VF ₃ , TiBr _4, etc.) are used. This is because when metal halides that do not sublimate or evaporate at temperatures below the heat treatment temperature are used, the amount of gas generated from the processing agent that contributes to the diffusion of hafnium is reduced, resulting in a thinner layer. It is. The mixing ratio of the processing agent and the hafnium material is 0.5 to 20% by weight (hereinafter referred to as % by weight) relative to the hafnium material.
It is desirable that the processing agent is contained in the range of %). Outside this range, it becomes difficult to form a continuous surface layer consisting of hafnium 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 processing agent and hafnium material may be such that it can pass through a JIS No. 100 sieve when implementing the embedding method, paste method, or non-contact method. As a result, there is no particular effect on whether it is coarse or fine. Further, when carrying out a 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. vice versa
When the powder is finer than 350 mesh, the mixed powder tends to float and becomes difficult to handle. Additives can be added to the mixed powder in addition to the above processing agent and hafnium material. For example, when carrying out a paste method, an adhesive such as dextrin or water glass can be added. Additionally, some types of processing agents tend to solidify easily during heat treatment. In this case, an inert powder such as alumina Al ₂ O ₃ can be added. Furthermore, some combinations of hafnium materials and processing agents have poor surface layer formation effects. In such cases, conventionally known halides as activators are added,
The effect of forming a surface layer can be enhanced. The amount of these additives added can be arbitrarily selected depending on the purpose. The embedding method, paste method, non-contact method, and fluidized bed method, which are specific examples of the powder methods described above, will be explained in detail below. In the burying method, a mixed powder of a treatment agent and a hafnium material is placed in a certain container, the iron alloy material to be treated is embedded in the powder, and the container is placed in a heating furnace or atmosphere furnace in the atmosphere, and the entire container is filled with iron. This is a method of heating alloy materials. In order to prevent outside air from entering the opening of the container, a layer of inert powder such as alumina or metal powder such as iron-boron powder may be provided. The paste method is a method in which an adhesive such as an aqueous dextrin solution, glycerin, water glass, ethylene glycol, and alcohol is added to a mixed powder to form a paste. A paste of this mixed powder is usually applied to the surface of the iron alloy material.
Coated with a thickness of 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 paste layer can be made thinner in a non-oxidizing atmosphere. Furthermore, in this paste method, since the surface layer is formed only on the surface portion covered with the paste, it is possible to form the surface layer 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 the 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 there is no contact between the iron alloy material and the mixed powder. 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 prevent powder from adhering to the surface layer. Gas pressure is 0.5 to 2 kg/
A range of cm ² is good. The heating temperature for the above heat treatment is 700°C or less. By processing at a temperature below 700°C, the base material of the iron alloy material becomes less susceptible to distortion. Further, it is desirable that the lower limit temperature is 450°C. When heat treated at a temperature lower than 450℃,
The formation rate of the surface layer of hafnium nitride or carbonitride is very slow. In practice, the high temperature tempering temperature of die steel is 520, which is the tempering temperature of structural steel.
~650℃ is desirable. As the heat treatment time increases, the hafnium content in the surface layer increases. Therefore, the treatment time is determined depending on the desired hafnium 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 15 μm. [Function] The formation mechanism of the surface layer made of hafnium nitride or carbonitride according to the present invention is not clear, but judging from microanalyzer analysis and the relationship between processing time and thickness, the inventors believe that the following It is thought that it is becoming like this. Note that the following explanation is about the mechanism of forming a hafnium carbonitride layer (m, n, o, and p below each represent a number). First, by nitriding the iron alloy material that 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.
A nitride layer is formed in the form of Fe _n (C,N) _o . A solid solution of nitrogen (in the form of Fe--N) is also formed directly below this nitride layer. Thereafter, by subjecting the iron alloy material to heat treatment, hafnium Hf from the outside is diffused into the nitride layer. This diffusion is a reaction in which Fe and Hf replace Fe _n (C, N) _o , and the nitride layer is (Hf, Fe) _p
(C, N) changes to _p . When all the Fe _n (C, N) _o layers change to (Hf, Fe) _p (C, N) _p , no further (Hf, Fe) _p (C, N) _p layers grow. In addition, in the (Hf, Fe) _p (C, N) _p layer, the surface
There is a tendency for there to be more Hf, and the closer it is to the base metal, the more Fe there is.
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 Hf _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. In addition, until all Fe _n (C, N) _o layers change to (Hf, Fe) _p (C, N) _p , (Hf, Fe) _p (C,
N) There is a surface layer consisting of two layers: _{a p} layer and a Fe _n (C, N) _o layer on the base metal side. The thickness of this surface layer is approximately equal to the thickness of the initial Fe _n (C,N) _o layer. Furthermore, when forming a surface layer made of hafnium 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 700°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 possible. unknown.
In the method of the present invention, as shown in FIG. 1 of Example 1, the surface layer thickness (Fe _n (C, N) _o layer thickness and ( Hf, Fe)
_p (C,N) (total thickness of _p layers) is not affected by heat treatment time. On the other hand, when heat treatment is performed at a high temperature such as 1000° C. (curve S1), as the heat treatment time becomes longer, the surface layer thickness also increases as in general diffusion treatment. In addition, in practice, it is not necessary to change all the iron, carbon, and nitrogen nitride layers to (Hf, Fe) _p (C, N) _p layers. The state in which two layers coexist, or the state in which the entire layer is changed to (Hf, Fe) _p (C, N) _p layer (when changing the iron/nitrogen nitride layer to a surface layer consisting of hafnium nitride), is acceptable. (The same applies to) [Effect of the invention] According to the present invention, iron/nitrogen or iron/carbon/
After forming the nitrogen nitride layer, hafnium diffusion treatment is performed at a low temperature of 700°C or less using the above-mentioned specific treatment agent. A surface layer can be formed. Additionally, since the iron alloy material is heated at a low temperature, distortion is less likely to occur in the material. Furthermore, it has good operability due to low temperature treatment and does not require a large amount of energy. Furthermore, since the layer according to the present invention is formed by diffusion, it has excellent adhesion to the base material, unlike carbide and nitride layers formed by PVD, which do not undergo diffusion reactions, despite being processed at low temperatures. A dense surface layer can be formed. Moreover, the thickness of the formed layer is practically sufficient. Furthermore, the method of forming a surface layer made of hafnium nitride or carbonitride of the present invention can form a layer in a much shorter time than the method of forming a hafnium carbide layer without nitriding. Can be done. [Examples] Examples of the present invention will be described below. Note that % means weight %. Example 1 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 550°C molten salt bath, and -200 mesh of hafenium was added to the bath. 20% metal 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 addition, the horizontal axis of FIG. 1 is set to the 1/2 power of the immersion time. 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 hafnium carbonitride layer. (the thickness of the entire surface layer) (curve B shows the thickness of only the hafnium carbonitride layer). The thickness of the total surface layer was almost the same for different treatment times and was approximately 3 μm. Note that FIG. 2 shows a micrograph (400x magnification) of the cross-sectional structure of the surface layer formed by immersion treatment for 8 hours. The surface layer is a layer with a smooth surface, and the boundary between the layer and the base material is complicated, making it a coating layer with excellent adhesion. Furthermore, as shown in FIG. 3, analysis using an X-ray microanalyzer revealed N and C along with Hf in the surface layer. According to the analysis results from the surface, approximately 50% Hf was present. Furthermore, diffraction lines corresponding to HfN were observed in X-ray diffraction. The surface layer formed from this is
It was confirmed that it was a hafnium carbonitride layer consisting of (Hf, Fe) and (N, C). For comparison, a JIS/SKH51 specimen that had been nitrided in the same manner as above was immersed in a molten salt bath heated to 1025°C and treated.
A hafnium carbonitride layer having a thickness shown by curve S1 in FIG. 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 layer thickness does not increase even if the immersion time increases. Therefore, it has become clear that the formation mechanism of the carbonitride layer of the present invention is different from the formation mechanism of the high-temperature treatment of the comparative example. Example 2 A JIS/S45C specimen (diameter 7
mm, length 50 mm) was subjected to salt bath nitriding treatment. Next, a molten salt bath of CaCl ₂ +NaCl having the same composition as in Example 1 was prepared, and -200 mesh hafnium metal powder was added in an amount of 20% to 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 6 μm was formed, as shown in the micrograph of the cross-sectional structure of the surface layer (1000x magnification) in Figure 4. Ta. X-ray diffraction and X shown in Figure 5
From the results of line microanalyzer analysis, it was confirmed that this surface layer was a hafnium carbonitride layer consisting of (Hf, Fe) and (N, C). Example 3 An industrial pure iron specimen (carbon content: 0.03% or less) having a diameter of 8 mm and a length of 35 mm was subjected to ion nitriding treatment at 550° C. for 4 hours. Next, CaCl ₂ +NaCl with the same composition as in Example 1
+Prepared a hafenium metal molten salt bath. The bath was heated to 600°C, and the specimen was immersed in the bath for 8 hours.
Thereafter, it was taken out of the bath and cooled in oil. The formed surface layer has a layer thickness of about 10μ, which is the same as the thickness of the nitride layer when subjected to ion nitriding, as shown in the micrograph of the cross-sectional structure in Figure 6 (400x magnification).
It was m. Furthermore, from the X-ray microanalyzer analysis results shown in FIG. 7, approximately 40% of Hf, as well as N and C, were observed in the surface layer. Furthermore, from the results of X-ray diffraction, diffraction lines of HfN were observed, and the formed surface layer was confirmed to be a hafnium carbonitride layer consisting of (Hf, Fe) and (C, N). Ta. Example 4 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, CaCl ₂ +NaCl with the same composition as in Example 1
A molten salt bath was prepared, and 3% Al ₂ O ₃ powder (-320 mesh) was added to the bath.
and 20% hafnium metal powder (-200 mesh)
was added. This molten salt bath was heated to 550° C., and the specimens were immersed for 9 hours, and then taken out from the bath and cooled in oil. When the roundness of these two 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 7 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 three times larger than the specimen treated with the present invention. When the specimen treated according to the present invention (immersion temperature 550°C, immersion time 9 hours) was cut and the surface layer was observed, the formed surface layer was approximately 8 μm thick, and was analyzed using an X-ray microanalyzer. As a result, it was confirmed that the layer was a hafnium carbonitride layer. Example 5 JIS/SKD11 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 plate-shaped hafnium metal of 40 mm x 35 mm and 9 mm was inserted into the center of this bath, and this was used as an anode and a graphite container. as a cathode,
Current was applied for about 17 hours at an anode current density of 0.8 A/cm ² .
Due to this anodic dissolution treatment of hafnium, about 7% of hafnium was dissolved into the bath based on the total amount of the salt bath, calculated from the weight loss of the hafnium metal plate. The specimen was immersed in this molten salt bath at 550° C. for 9 hours, then taken out and cooled in oil. When we cut the treated specimen and observed the surface layer, we found that the formed surface layer had a thickness of approximately
It was 5 μm. Further, when examined by X-ray microanalyzer analysis, C was also found in the surface layer in addition to Hf and N, and it was confirmed that the surface layer was a carbonitride layer of hafnium. Example 6 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 to 580°C in an electric furnace in the atmosphere to prepare a molten salt bath, and -100 mesh of Hafenim metal powder was added to this bath. For molten salt bath
Added 25%. The nitrided sample was immersed in this 580° C. bath, and electrolysis was carried out by applying current at a cathode current density of 0.05 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 formed surface layer was analyzed by cross-sectional microstructure observation and an X-ray microanalyzer.
It was confirmed that the diameter was 6 μm and that it was composed of (Hf, Fe) and (C, N). In addition, the analysis results from the surface show that approximately
In addition to 45% Hf, N and C were confirmed. Example 7 A JIS/SKH51 specimen was subjected to salt bath nitriding treatment in the same manner as in Example 1. Next, Li ₂ Co ₃ 45%, K ₂ CO ₃ 25%, Na ₂ CO ₃ 30%
A heat-resistant steel container containing the mixture was heated to 550℃ in an atmospheric furnace to prepare a molten salt bath, and -200 mesh of hafnium metal powder was added to this bath at a rate of 30% of the molten salt bath. did. 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 formed surface layer was analyzed by cross-sectional microstructure observation and an X-ray microanalyzer.
The thickness of the layer was 4 μm, and approximately 40% of Hf as well as N and C were observed in the layer. Furthermore, when examined by X-ray diffraction, the diffraction lines matched well with the diffraction lines of HfN, thus confirming that the surface layer was composed of (Hf, Fe) and (C, N). Example 8 A JIS/SK4 specimen with a diameter of 8 mm and a length of 30 mm was heated at 570°C.
Gas nitrocarburizing treatment was performed for 150 minutes. Next, the specimen was embedded in a -100 mesh powder mixture consisting of 90% hafnium metal and 10% potassium borofluoride (KBF ₄ ), which was placed in a stainless steel container. Furthermore, to prevent oxidation, on top of the mixed powder -
100 meshes of ferroboron powder was coated to a thickness of 3-4 mm. The whole container was heated to 600℃ in an atmospheric furnace.
Heated for 16 hours. 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, it was found that Hf, N,
C was recognized, and the analysis result from the surface shows that it is approximately 20%
of Hf was observed, and this layer was confirmed to be a carbonitride layer of hafnium. Example 9 A mixed powder consisting of 60% Al ₂ O ₃ (-80 mesh), 38.8% hafnium metal (-100 mesh), and 1.2% NH ₄ Cl (-80 mesh) was placed in a fluidized bed furnace.
The mixed powder was brought into a fluid state by argon gas introduced from the lower part of the furnace (flow rate in the furnace 200 cm/min, pressure 1.5 Kg/cm ² at the furnace inlet). A JIS SK4 rod (diameter 7 mm, length 50 mm) which 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 8 hours. When the formed surface layer was analyzed with an X-ray microanalyzer, it was found that the surface layer was composed of Hf, N, and C. Approximately 25% Hf was detected in the surface analysis, indicating that it was a hafnium carbonitride layer. was confirmed. Example 10 A JIS/SKH51 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% _CaCl2 and 48 mol% NaCl was placed in a heat-resistant steel container and heated to 570 mol% in an electric furnace in the atmosphere.
A molten salt bath is prepared by heating to
200 meshes of hafnium metal powder was added at 25% to the total amount of the molten salt bath. After immersing the specimen in this 570°C bath for 8 hours, it was taken out and cooled in oil. When the formed surface layer was analyzed by X-ray diffraction and an X-ray microanalyzer, it was confirmed that the surface layer was a hafnium carbonitride layer consisting of (Hf, Fe) (C, N). Next, the hafnium carbonitride coated specimen (sample no.
Regarding C), gas carburized and quenched JIS
Dry test using SCM415 as a mating material using a Fababilly tester, load 400Kg, rotation speed 300rpm, wear rate 0.1
A friction test was conducted under the conditions of m/sec and test time of 4 minutes. Also, for comparison, a JIS/SKH51 specimen (sample No. S2) that was not subjected to the above nitriding treatment or heat treatment.
and SKH51 specimen with only nitriding treatment (sample No. S3)
A friction test was also conducted on the The results of the above friction test are shown in the table. Also, the sample
Seizure scratches were clearly observed in both Nos. S2 and S3, whereas only small damage was observed in sample No. C. From this, it can be seen that the surface layer formed according to the present invention is superior to that of the comparative example in terms of wear resistance and seizure resistance. 【table】

[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.
4, 6, and 8 are micrographs showing the cross-sectional structure of the surface layer formed by the treatment of the present invention in Examples 1, 2, 3, and 5, respectively.
5, 7 are Examples 1, 2, and 3, respectively.
FIG. 3 is a diagram showing the results of an 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 a nitriding treatment to form an iron/nitrogen or iron/carbon/nitrogen nitride layer on the surface of an iron alloy material, the iron alloy material, a hafnium material, and an alkali metal or alkali One or more of earth metal chlorides, fluorides, boric fluorides, oxides, bromides, iodides, carbonates, nitrates, borates, and/or ammonium halide salts,
Hafnium nitride or carbonitride is formed on the surface of the iron alloy material by heat treatment at 700°C or less in the presence of a treatment agent consisting of one or both of the metal halides and diffusing hafnium onto the surface of the iron alloy material. 1. A method for surface treatment of iron alloy materials, characterized by forming a surface layer consisting of metal. 2 The above hafnium material is one or two of hafnium metal, hafnium alloy, and hafnium compound.
A method for surface treatment of an iron alloy material according to claim 1, which comprises at least one species. 3. The method of surface treatment of an iron alloy material according to claim 1, wherein the heat treatment is performed by immersing the hafnium material and the iron alloy material in a molten salt bath in which the treatment agent is melted. 4. The surface treatment of the iron alloy material according to claim 1, wherein the heat treatment is performed by electrolytic treatment in which the treatment agent is melted and the iron alloy material is used as a cathode in a molten salt bath in which the hafnium material is immersed. Method. 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 hafnium material. 6. The method of surface treatment of an iron alloy material according to claim 1, wherein the heat treatment is performed while a paste of a mixed powder of the treatment agent and the hafnium material is applied to the iron alloy material. 7. The surface 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 hafnium material and the iron alloy material in a fixed space in a non-contact state. Processing method. 8. The heat treatment is carried out by making the mixed powder of the treatment agent and hafnium material into a fluidized state and placing the iron alloy material therein.
A method for surface treatment of iron alloy materials as described in .