JPS62107055A - Surface treatment of iron alloy material - Google Patents

Abstract

PURPOSE:To provide a surface layer having excellent adhesiveness by subjecting an iron alloy material subjected to a nitriding treatment and hafnium material to a low-temp. heating treatment by using a treating agent consisting of the chloride, fluoride, etc., of specific metals to diffuse hafnium into the surface of the iron alloy. CONSTITUTION:A round bar test piece (6mm diameter and 30mm length) is subjected to the salt bath nitriding treatment. A vessel contg. the treating agent is heated to form a fused salt bath. After the powder of hafnium is added into such salt bath, the bar test piece is immersed therein and is subjected to the heating treatment at <=700 deg.C and is then taken out to form the carbonitride layer of hafnium on the surface of the bar test piece. >=1 kinds are selected from the respective groups of the chloride, fluoride, borofluoride, oxide, bromide, etc., of alkali metals or alkaline earth metals, and halogenated ammonium salt are selected as the treating material. The dense layer of which the surface layer has the high adhesiveness to the base material is thus formed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention forms a hafnium (Hf) nitride or carbonitride layer on the surface of iron alloy materials such as molds, jigs, and machine parts. This invention relates to a surface treatment method.

[Conventional technology]

When the surface of an iron alloy material is coated with a surface layer consisting of hafnium carbide, nitride, or carbonitride.

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, 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 plasma CVD (chemical vapor deposition) using hafnium halide, etc. (e.g. , JP-A-55-65357, JP-A-55-164072). In these methods, the Ac1 transformation point of iron is approximately 70
Since the treatment is carried out at a temperature below 0°C, it does not cause heat distortion to the base material of the iron alloy material (although a surface layer can be formed, the formed surface layer has good throwing power and adhesion). It's difficult to get things.

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.

[Problem that the invention seeks to solve]

The present invention solves the above-mentioned conventional problems, and achieves high adhesion of iron alloy materials to the base material by efficient heat treatment at low temperatures using extremely simple equipment, without causing distortion to the base material. The superior hafnium nitride removal process seeks to provide a method for forming a carbonitride surface layer.

[Means for solving problems]

The present invention applies nitriding treatment to form a nitride layer of iron/nitrogen or iron/carbon/nitrogen on the surface of the iron alloy material, and then combines the iron alloy material with the hafnium material.

Chlorides of alkali metals or alkaline earth metals.

Borofluoride, fluoride, oxide, bromide, iodide.

One or more of carbonates, nitrates, borates,
or/and ammonium halide salts.

Hafnium nitride or carbonitride is formed on the surface of the iron alloy material by heat treatment at 700°C or lower 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. This is a method for surface treatment of iron alloy materials, which is characterized by forming a surface layer made of metal.

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, two alloy steel, cast iron, or a sintered alloy, or it may be one containing very little 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 that is formed, the carbon content of the surface layer may be increased by carburizing or the like prior to nitriding (or carburizing may be carried out during nitriding.
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) onto the surface of an iron alloy material to form a nitride layer. This nitride layer is
It consists 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. In addition,
Directly below the nitride layer is a solid solution layer (diffusion layer) of nitrogen in iron.
is formed. 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-mentioned compounds include chlorides such as 1lfC14°HfBr4,
Examples include bromides. 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.

Examples of the treatment agent include chlorides, fluorides, boron fluorides, and oxides of alkali metals or alkaline earth metals.

One of bromide, iodide, carbonate, nitrate, or borate
It consists of one or both of an alkali metal or alkaline earth metal compound consisting of a species or two or more kinds, and/or 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 21 LiC
l + NaF + KF.

LiF, KBF4. NazCO3, LiCO3, K
Examples include CO3, NaN0z, NazO, etc., and one or more of these are used. In addition, halogenated ammonium salts include NH4Cl, Nt(
nBr+ N1)4. r , N1)41, etc., and metal halides include Crl z + CrB
r3 + VCI3 + T iFa.

Examples include TiBra+FeCl3, and one or more of these may be used.

Therefore, as the treatment agent, only the alkali metal or alkaline earth metal compound, or only one or both of the ammonium halide salt and the metal halide may be used.

The above-mentioned alkali metal or alkaline earth metal compound and one or both of an ammonium halide salt and a metal halide may be used.

Note that when using a compound containing Ti or Cr, 1)
There is a possibility that a surface layer containing Ti and Cr is formed simultaneously with f.

Further, when a hafnium halide such as l1fC14 is used as a processing 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 is a chloride or fluoride of an alkali metal or alkaline earth metal among the processing agents.

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. In addition, 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 CaClz. Furthermore, for reasons such as adjusting the viscosity of the molten salt bath, AhO:i+ZrO
An oxide such as No. 2 or a cyanide compound such as NaCN may be added.

The hafnium material is immersed in the molten salt bath.

This is to dissolve hafnium into the molten bath salt.

The method of immersing the hafnium material is to add the material in powder form (preferably 200 meshes or less) or thin plate form to a molten bath, or to electrolyze by immersing the material in the form of a rod or plate in a molten bath as an anode. There are methods such as anodic dissolution of hafnium. 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 molten salt 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 0.1
~0.8 A/crA 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 bath, 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, and in a state in which hafnium is infused, an iron alloy material is immersed in the molten salt bath as a cathode, and electrolytic treatment is performed. 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 the hafnium material as an anode and the iron alloy material as a cathode in a molten salt bath of a 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 the iron alloy material is 2A/cut or less, practically 0.05-1, OA
/cot is appropriate.

Incidentally, both the molten salt immersion method and the molten salt electrolysis method described above can be carried out either in the air atmosphere or in a protective gas (Nz, Ar, etc.).

Next, the powder method involves coexisting the processing agent with a mixed powder of a hafnium material and an iron alloy material.

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. 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 the iron alloy material and the above mixed powder in a non-contact state within 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 agent used in the powder method is an alkali metal or alkaline earth metal chloride monofluoride or bromide.

One or more of iodides, boron fluorides, and/or ammonium halide salts.

It consists of metal halides or both. In addition, in the case of fluidized bed among powder methods.

The metal halide mentioned above is one that sublimes or evaporates at a temperature below the heat treatment temperature (VCI: ++FeCl3.Ti
F4. VF: l+ TiBra, etc.) is 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's for a reason.

The mixing ratio of the processing agent and the hafnium material is preferably in a range in which the processing agent is contained in an amount of 0.5 to 20% by weight (hereinafter referred to as % by weight) relative to the hafnium material. Outside this range, it becomes difficult to continuously form a 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 treatment agent and hafnium material should be determined according to JISlk when using the burial method, paste method, or non-contact method.
It is sufficient to pass through a sieve of 1OO. Whether it is coarser or finer than this, there is no particular effect.

Further, when carrying out a fluidized bed method, particles having a particle size in the range of 60 to 350 mesh are preferred. If it is coarser than 60 mesh, a large amount of gas is required to fluidize the mixed powder,
Moreover, surface layer formation is difficult to proceed. On the other hand, when the mesh 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-mentioned 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, inert powder such as alumina (Alz(h)) can be added.Furthermore, some combinations of hafnium materials and processing agents have poor surface layer formation effects.In such cases, conventional active A known halide is added as an agent.

The effect of forming a surface layer can be enhanced. The amount of these additives added can be arbitrarily selected depending on the purpose.

Below, the embedding method is a specific example of the powder method described above.

The paste method, non-contact method, and fluidized bed method will be explained in detail.

In the burying method, a mixed powder of a treatment agent and a hafnium material is placed in a certain container, and the iron alloy material to be treated is buried in the powder.3 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. Note that a layer of inert powder such as alumina or metal powder such as iron-boron powder may be provided at the opening of the container to prevent outside air from entering.

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. The paste of this mixed powder is usually coated on the surface of the iron alloy material to a thickness of 1) 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 coating 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.

A refractory material such as alumina is added to the mixed powder to prevent the mixed powder from forming a lump during fluidization, and the iron alloy material and the powder are placed in the furnace, and a fluidizing gas is introduced to form the powder. This creates a fluidized bed state. When heat treatment is performed using this method, an extremely smooth surface layer can be obtained, and the temperature distribution of the fluidized bed is uniform, so
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/ca for handling purposes.
! A range of is good.

The heating temperature of the above heat treatment is 700° C. or lower. By processing in a temperature range of 700° C. or lower, 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 treatment is performed at a temperature lower than 450° C., the rate of formation of a surface layer consisting of dihafnium nitride or carbonitride is very slow. In practice, the high temperature tempering temperature of die steel,
A temperature of 520 to 600°C, which is the tempering temperature of structural steel, 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.

[Effect]

The formation mechanism of the surface layer made of hafnium nitride or carbonitride according to the present invention is not clear.

Judging by the inventors from microanalyzer analysis and the relationship between processing time and thickness, the following is believed to be the case. The following explanation is about the mechanism of forming a hafnium carbonitride layer (the following m, n, o,
p represents a number).

First, by performing nitriding treatment on the iron alloy 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, resulting in Fe
A nitride layer is formed in the form m (C+N) fi. Further, directly below this nitride layer, a solid solution of nitrogen (Fe
-N shape) is also formed.

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 in pes+(c,N)n is substituted with Ilf, and the nitride layer is (Hf, Fe). (
C, N) changes to 9. When all of the PeJClN)n layer changes to ()If,Fe)o(C,N), there is no further growth of the (Hf,Fe)o(C1N)p layer. Note + atr + Fe) O(CI N) 1)
In the layer, the surface has more Ilf, and the closer it is to the base metal, the more F
There tends to be a lot of e. Therefore, depending on the conditions, the surface F
The amount of e is so small that it may be appropriate to express it as Hf, (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 Pen CC+ N)
The n layer is (Hf, Fe). (C9N) (Hf, Pe) on the surface side until it changes to p. There is a surface layer consisting of two layers: a (C9N) p layer and a Few (CIN) n layer on the base material side. The thickness of this surface layer is approximately equal to the thickness of the initial Few(C1N)n layer.

Furthermore, in the case of forming a surface layer made of hafnium nitride, the mechanism for forming one surface layer 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 the formation of a surface layer using this mechanism and thus having such a treatment time-thickness relationship has not been known so far. Not yet.

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 (FeJClN) and the n layer thickness (Hf, Fe) are determined.

The total thickness of the (C,N)p layer thickness) was not affected by the heat treatment time. On the other hand, when heat treatment is performed at a high temperature such as 1000° C. (curve Sl), as the heat treatment time becomes longer, the surface layer thickness also increases as in general diffusion treatment.

In addition, in practical use, all iron, carbon, and nitrogen nitride layers (Hf
,Re). There is no need to change it to a (C,N)p layer.

Even in the state where two layers coexist, all (Iff, Fe)
.

The state may be changed to a (C,N)p layer (the same applies to the case where the iron/nitrogen nitride layer is changed to a surface layer made of hafnium nitride).

〔Effect of the invention〕

According to the present invention, after forming an iron-nitrogen or iron-carbon-nitrogen nitride layer, hafnium diffusion treatment is performed at a low temperature of 700°C or less using the above-mentioned specific treatment agent. An excellent surface layer of hafnium nitride or carbonitride can be formed on the material.

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

5. Also, since the layer according to the present invention is formed by diffusion, it is possible to form PV without any diffusion reaction even though it is processed at low temperature.
Unlike the carbide layer and nitride layer formed by D, it has excellent adhesion to the base material and can form a dense surface layer. Moreover, the thickness of the formed layer is practically sufficient.

In addition, 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. I can do it.

〔Example〕

Two aspects of the present invention will be described in detail below. Note that % means weight %.

Example 1 A JIS-3KH51 round bar specimen having a diameter of 61 m and a length of 30 mm was immersed in a salt bath at 0° C. for 2 hours to undergo salt bath nitriding treatment. Next, a heat-resistant steel container containing a mixture of 52 mol% of CaC1z and 148 mol% of NaC was heated in an electric furnace in the atmosphere to form a molten salt bath at 550°C.
00 mesh hafnium metal powder was added at 20% to the molten salt bath.

The nitrided specimens were placed in this 550°C molten salt bath.
After soaking for 25 hours, it was 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. Note that the horizontal axis in FIG. 1 is the 1z square 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 lhr is the total thickness of the nitride layer and the hafnium carbonitride layer. (The thickness of only the hafnium 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 3 μm.

In addition, a micrograph (magnification: 400 times) of the cross-sectional structure of the surface layer formed by immersion treatment for 8 hours is shown in FIG. 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. Further, in analysis using an X-ray microanalyzer, N and C were found in the surface layer along with Hf, as shown in FIG. Analysis from the surface showed that about 50% ilf was present. Furthermore, in X-ray diffraction, a diffraction line corresponding to HfN was observed. The surface layer formed by this is (Hf
.

It was confirmed that it was a hafnium carbonitride layer consisting of Fe) (N, C).

Also, for comparison, JIS nitrided by the same process as above.
-3KH51 specimens were immersed in a molten salt bath heated to 1025°C and treated, resulting in the formation of a hafnium carbonitride layer with the thickness shown by curve S1 in Figure 1. . As is clear from this comparative example, the immersion time is long (
However, in the present invention, the total surface layer thickness does not increase even if the immersion time becomes longer.

Therefore, it has become clear that the formation mechanism of the carbonitride layer of the present invention is different from that of the comparative example of the Tsutsuyoshi treatment.

Example 2゜A JIS-345C specimen (diameter 7n) was prepared in the same manner as in Example 1.
n, length 50 mm) was subjected to salt bath nitriding treatment.

Next, CaC1z + NaC1 having the same composition as in Example 1
A molten salt bath was prepared, and 1,200 mesh of hafnium metal powder was added in an amount of 20% 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 treated by 4-hour immersion, we found that a surface layer with a thickness of approximately 6 μm was formed, as shown in the micrograph of the cross-sectional structure of the surface layer (1000x magnification) in Figure 4. was. According to the results of X-ray diffraction and XvA microanalyzer analysis shown in Figure 5, this surface layer consists of (Iff, Fe) (N,
C) a hafnium carbonitride layer consisting of force 9'
It was slighted.

Example 3. - An industrial pure iron specimen (carbon content 0.03% or less) measuring 8 mm in diameter and 351 mm in length was subjected to ion nitriding treatment at 550'C for 4 hours.

Next, CaCl2 + NaCl with the same composition as in Example 1
+A hafnium metal molten salt bath was prepared. 600 yen for this bath
℃ and immersed the specimen in the bath for 8 hours.

Thereafter, it was taken out of the bath and cooled in oil.

The formed surface layer can be seen in the micrograph of the cross-sectional structure shown in Figure 6 (
As shown in the graph (magnification: 400 times), the layer thickness was about IO μm, which is the same as the thickness of the nitride layer when subjected to ion nitriding. Furthermore, from the results of the X-ray microanalyzer analysis shown in FIG. 7, about 40% of Hf as well as N and C were observed in the surface layer. In addition, from the results of X-ray diffraction, diffraction lines of HfN were observed,
The formed surface layer was confirmed to be a hafnium carbonitride layer consisting of (Hf, Fe) (C, N).

Example 4゜ Cylindrical JIS with outer diameter φ10, inner diameter φ6, length 25
The -348C specimen was subjected to gas nitrocarburizing treatment at 570°C for 6 hours.

Next, a molten salt bath of CaCl2 + NaCl with the same composition as in Example 1 was prepared, and in this bath, 3% A1) a3 powder (-320 mesh) and 20%
of hafnium metal powder (-200 mesh) was added. The molten salt bath was brought to 550°C.

The specimens were immersed for 9 hours and 25 hours, respectively, and then taken out of the bath and cooled in oil.

When we measured the roundness of these two types of specimens, we found that
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 circularity of the specimen when immersed in a molten salt bath at a temperature of 850°C (immersion time: 4 hours) was approximately 20 μm, which is approximately three times that of the specimen treated with the present invention. It was also big.

When the sample 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.

Furthermore, analysis using X-ray diffraction and an X-ray microanalyzer confirmed that the layer was a carbonitride layer of hafnium.

Example 5 A JIS-3KDII specimen (diameter: 6 mm, length: 30 mm) was subjected to ion nitriding treatment at 550° C. for 3 hours.

Next, a molten salt bath of CaCl2 + NaCl with the same composition as in Example 1 was prepared in a graphite container, and a
Insert a plate-shaped hafnium metal plate consisting of a dragon x 35 cranes x 3 cranes, and use this as the anode and the graphite container as the cathode.

Electricity was applied for about 17 hours at an anode current density of 0.8 A/cal.

By 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 the treated specimen was cut and the surface layer was observed, the thickness of the formed surface layer was approximately 5 μm, as shown in the micrograph of the cross-sectional structure in FIG. 8 (400x magnification). In addition, when investigated by X%1 microanalyzer analysis, 2
In addition to Ilf and N, C was also observed in the surface layer, and the third surface layer was confirmed to be a hafnium carbonitride layer.

Example 6 A JIS-345C specimen measuring approximately 7 mm in diameter and 50 mm in length was nitrided in a salt bath at 570°C for 1 hour.

Next, a graphite container containing a mixture of 50 mol% KP and 50 mol% LiF was heated to 580°C in an electric furnace in the atmosphere to prepare a molten salt bath, and 1100 mesh hafnium metal powder was added to this bath. 25% was added to the molten salt bath.

The nitrided specimen was immersed in this 580°C bath, and the cathode current density was 0.05 using this as a cathode and the graphite container as an anode.
A/I performed electrolysis by applying electricity myself for 8 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 surface layer 1 was approximately 6 μm thick.
It was confirmed that it consists of Fe) (C,N). In addition, analysis results from the surface show that in addition to approximately 45% Hf, N and C
was confirmed.

Example 7 A JIS 5KH51 specimen was subjected to salt bath nitriding treatment in the same manner as in Example 1.

Next, LtzCO3 45%, Co, 25%,
A heat-resistant steel container containing a mixture of 30% NazCO3 is heated to 550°C in an atmospheric furnace to prepare a molten salt bath, and 1200 mesosh of hafnium metal powder is added to the bath at 30% of the molten salt bath. % added. After thoroughly stirring this bath, the specimen was kept immersed in this 550° C. bath for 4 hours.

The sample was taken out of the bath and cooled in oil, and the formed surface layer was analyzed by cross-sectional structure observation and an X-ray microanalyzer. The first surface layer was about 4 μm thick, and the layer contained about 40% of the surface layer. In addition to Hf, N and C were recognized. Also,
When examined by X-ray diffraction, the diffraction lines matched well with those of )lfN, and therefore the surface layer was.

It was confirmed that it consists of (Iff, Fe) (C, N).

Example 8 A JIS-3K4 specimen of 8 cranes in diameter x 30 dragons in length was heated to 570℃.
, 150 minutes.

Next, 1100 mesh of hafnium metal 90% and potassium borofluoride (KBF4.) were placed in a stainless steel container.
The above sample was embedded in a mixed powder consisting of 10%. Further, to prevent oxidation, the mixed powder was coated with 1100 mesh of ferroboron powder to a thickness of 3 to 4N. 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, Iff, N, and C were found in the first surface layer, and approximately 20% Hf was found in the analysis results from the second surface, indicating that this layer was , which was confirmed to be a carbonitride layer of hafnium.

Example 9 Al2O2 (-80 mesos) 60%, hafnium metal (-100 mesos) 38.8%, NIl, CI (-
A mixed powder consisting of 1.2% (80 mesh) was placed in a fluidized bed furnace, and argon gas was introduced from the bottom of the furnace (flow rate in the furnace was 200 cm/min, pressure at the furnace inlet was 1.5 kg/min).
cnl) to bring the mixed powder into a fluid state. In this fluidized bed furnace, JIS
Charge SK4 rod (diameter 7mm, length 50μl) and heat to 600℃.
The mixture was heat-treated for 8 hours.

When the formed surface layer was analyzed with an X-ray microanalyzer, the first surface layer was composed of Hf, N, and C, and the second surface analysis detected about 25% Ilf.

It was confirmed that it was a carbonitride layer of hafnium.

Example 1 A JIS 5KH51 specimen with a diameter of 6.5 mm and a length of 401 layers was subjected to salt bath nitriding treatment in the same manner as in Example 1.

Next, 52 mol% of CaC1z and 148 mol% of NaC
The mixture was placed in a heat-resistant steel container and heated in an electric furnace in the atmosphere for 57
Prepare a molten salt bath by heating to 0°C, and add 120% to this bath.
0 mesh hafnium metal powder was added in an amount of 25% based on the total amount of the molten salt bath. After the specimen was immersed in this 570° C. bath for 8 hours, it was taken out and cooled in oil.

When the formed surface layer was examined by X-ray diffraction and X-ray microanalyzer analysis, one surface layer was (Iff, F
e) It was confirmed that it was a hafnium carbonitride layer consisting of (C,N).

Next, the above hafnium carbonitride-coated specimen (sample C) was dry-tested using a Fabry tester using gas carburized and quenched JIS-3CM415 as a mating material under a load of 400 k.
g, rotation speed 30Orpm, wear rate Q, 1m/sec,
A friction test was conducted under the condition that the test time was 4 min. For comparison, a friction test was also conducted on a JIS-5KH51 specimen (sample ms2) that had not been subjected to the above-mentioned nitriding treatment or heat treatment, and a 5KH51 specimen that had been subjected to only nitriding treatment (sample Nl53).

The results of the above friction test are shown in the table. In addition, sample disease S2.
In S3, there were clear burn-in scratches, whereas in sample NIC, only small damage was observed.

From this, it can be seen that the surface layer formed according to the present invention is superior in terms of wear resistance and seizure resistance as compared to that of the comparative example.

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. FIGS. 4, 6, and 8 show Examples 1, 2, and 3, respectively.
5 shows a micrograph showing the cross-sectional structure of the surface layer formed by the treatment of the present invention, and FIGS. 3, 5, and 7 show the iron alloy material treated according to the present invention in Example 1.2.3, respectively. It is a figure which shows the X-ray microanalyzer analysis result of the surface part of.

Claims (8)

[Claims] (1) After performing nitriding treatment to form an iron/nitrogen or iron/carbon/nitrogen nitride layer on the surface of the iron alloy material, the iron alloy material, hafnium material, and alkali metal or alkaline earth metal Chloride, fluoride, boron fluoride, oxide,
One of bromide, iodide, carbonate, nitrate, or borate
heat-treating at 700° C. or lower to diffuse hafnium onto the surface of the above-mentioned iron alloy material. A method for surface treatment of an iron alloy material, characterized in that a surface layer consisting of hafnium nitride or carbonitride is formed on the surface of the iron alloy material. (2) The method for surface treatment of an iron alloy material according to claim (1), wherein the hafnium material comprises one or more of hafnium metal, hafnium alloy, and hafnium compound. (3) 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. Surface treatment of the iron alloy material according to claim (1) Method. (4) The heat treatment is performed by melting the treatment agent and electrolytically treating the iron alloy material as a cathode in a molten salt bath in which the hafnium material is immersed.
) The method for surface treatment of iron alloy materials described in section 2. (5) The method for 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 for 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 iron alloy 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. Material surface treatment method. (8) The heat treatment is performed on the surface of the iron alloy material according to claim (1), which is performed by making a mixed powder of the treatment agent and the hafnium material into a fluid state and placing the iron alloy material therein. Processing method.