JP2019218576A - Method for producing iron nitride material - Google Patents

Abstract

To provide a novel method for producing an iron nitride material having a nitride layer containing γ'-N .SOLUTION: The present invention provides a method for producing an iron nitride material having a nitride layer containing γ'-FeN on the surface of an iron base material, the method comprising an electrolysis step for electro-depositing γ'-FeN on the surface of the anode by performing molten salt electrolysis using a cathode and an anode made of an iron base material provided in an electrolytic solution in which nitride ions (N) are dissolved in a molten salt, in the electrolysis step, the temperature of the electrolyte being 240°C. or higher, and the potential applied to the described-above anode being more than 0.6 V and 1.5 V or less on the basis of Li/Li.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for producing an iron nitride material.

Conventionally, rare earth magnets containing rare earth elements such as Nd (neodymium) and Sm (samarium) have been widely used as permanent magnets used for motors, generators and the like. However, although rare earth magnets have excellent magnetic properties, the rare earth element contained in the magnet is a rare element, and therefore, a reduction in the amount used is required. As a substitute for the rare earth magnet, a magnet using an iron nitride material has attracted attention. In particular, α ″ -Fe ₁₆ N ₂ is known as an iron nitride material having a very high saturation magnetization and excellent magnetic properties.

Various methods for forming an iron nitride layer have been studied. For example, a method of permeating and diffusing nitrogen into steel by gas nitriding the steel is well known (for example, see Non-Patent Document 1). .
In addition to the method using gas nitriding, a method of forming an iron nitride layer by a molecular beam epitaxy method (for example, see Non-Patent Document 2) and a method of forming an iron nitride layer by a sputtering method (for example, Non-Patent Document 3) is also known.
In addition, a method using a plating method is also known. For example, Patent Document 1 discloses that a molten salt electrolysis is performed using a steel material as a working electrode in an electrolytic bath of a molten salt containing nitride ions to form a nitride layer. A method is disclosed.

JP 2009-052104 A

Takaaki Umeda Kazuo Miyabe, "Development of Production Technology for Nitriding Process Applying Nitriding Potential Control", KOMATSU TECHNICAL REPORT, 2014, Vol. 60, no. 167, pp17-23 M. Komuro et al. , "Epiaxial growth and magnetic properties of Fe16N2 films with high saturation magnetic flux density (invited), Journal of Pharmaceuticals, 90.degree. 67, no. 9, pp. 5126-5130 M. Takahashi et al. , “Magnetic moment of α ″ -Fe16N2 films (invited)”, Journal of Applied Physics, 1994, vol. 76, No. 10, pp. 6642-6647

The treatment by gas nitriding described in Non-Patent Document 1 is a treatment in which NH ₃ gas is introduced into a furnace and heated to 500 ° C. to 580 ° C. to cause nitrogen to permeate and diffuse into a steel material, and the ε phase (Fe ₃ N ) And a γ ′ phase (Fe ₄ N) are formed, but α ″ -Fe ₁₆ N ₂ cannot be formed. This is because α ″ -Fe ₁₆ N ₂ becomes unstable when the temperature exceeds 250 ° C., and is not considered to be generated by the heat treatment at 500 ° C. to 580 ° C.
Further, since the gas nitriding treatment using NH ₃ gas is a treatment for permeating and diffusing nitrogen into a steel material, it is difficult to avoid generation of Fe ₂ N or ε-Fe ₃ N as nitride. Was.

Further, according to the methods described in Non-Patent Documents 2 and 3, although α ″ -Fe ₁₆ N ₂ can be formed, there is a limit on the growth rate, so that there is a problem that time is required for film formation. In addition, continuous processing is difficult due to the necessity of an environment such as a vacuum, which is not suitable for industrial production.

In the method described in Patent Document 1, a steel material (a steel material containing chromium, basically, a stainless steel) is placed in an electrolytic bath of a molten salt containing nitride ions, and is placed at 415 ° C. or lower, preferably 315 ° C. At the following bath temperature, molten salt electrolysis is performed using steel as a working electrode to form a nitride layer having excellent corrosion resistance. However, there is no description or suggestion of α ″ -Fe ₁₆ N ₂ generation in the formed nitride layer. This is because, in the method described in Patent Document 1, the molten salt electrolysis is performed at 415 ° C. or less, preferably 315 ° C. or less. It is considered that ₁₆ N ₂ cannot be formed.

Therefore, an object of the present invention is to provide a method for efficiently producing an iron nitride material in which a nitride layer containing α ″ -Fe ₁₆ N ₂ uniformly on the surface of an iron base material is provided.

One aspect of the present invention is a method for manufacturing an iron nitride material having a first nitride layer containing γ′-Fe ₄ N on a surface of an iron base material (hereinafter, also referred to as a first manufacturing method). ,
By performing molten salt electrolysis using an anode comprising a cathode and an iron base provided in an electrolytic solution in which nitride ions ( ^N3- ) are dissolved in a molten salt, γ'-Fe _{4 N} has electrolytic step of electrodeposition, the a,
In the above electrolysis step, the present invention relates to a method for producing an iron nitride material, wherein the temperature of the electrolytic solution is 240 ° C. or higher and the potential applied to the anode is more than 0.6 V and 1.5 V or less based on Li ⁺ / Li. .

Another aspect of the present invention is a method for manufacturing an iron nitride material having a second nitride layer containing α ″ -Fe ₁₆ N ₂ on a surface of an iron base material (hereinafter, also referred to as a second manufacturing method). So,
By the first manufacturing method, the steps of manufacturing the first iron nitride having a first nitride layer comprising γ'-Fe 4 _N to the surface,
A first heating step of heating the first iron nitride material at a temperature of 600 ° C. or higher to generate a γ phase on the surface of the iron base material;
Quenching the iron substrate in which the γ phase is generated on the surface, and a quenching step of generating an α ′ phase on the surface of the iron substrate,
A second heating step of heating the iron substrate in which the α ′ phase has been generated on the surface at a temperature of 200 ° C. or lower to precipitate α ″ -Fe ₁₆ N ₂ on the surface of the iron substrate,
And a method for producing an iron nitride material.

According to the present _{invention, α '' - Fe 16 N} 2 can provide a suitable manufacturing method of the iron nitride having a nitride layer containing, in particular, epsilon phase is hardly generated, α '' - Fe ₁₆ It is possible to provide a method for manufacturing an iron nitride material having a nitride layer in which N ₂ is uniformly generated. The present invention also provides a novel method for producing an iron nitride material having a nitride layer containing γ′-Fe ₄ N, which is used for producing an iron nitride material having a nitride layer containing α ″ -Fe ₁₆ N _2. provide.

It is a figure which shows typically the essential process in the 2nd manufacturing method which concerns on embodiment of this invention. It is a figure showing the outline of an example of the electrolysis process in the 1st manufacturing method concerning the embodiment of the present invention. It is a figure showing the outline of an example of the composition of the gas electrode which can be used by the manufacturing method of the iron nitride material concerning the embodiment of the present invention. It is a figure showing the outline of another example of the composition of the gas electrode which can be used by the manufacturing method of the iron nitride material concerning the embodiment of the present invention. It is a figure showing the outline of another example of composition of the gas electrode which can be used by the manufacturing method of the iron nitride material concerning the embodiment of the present invention. It is a figure showing the outline of another example of composition of the gas electrode which can be used by the manufacturing method of the iron nitride material concerning the embodiment of the present invention. 7A and 7B show the results of measurement using an X-ray diffractometer, respectively, and FIG. 7B is an enlarged view of a main part of FIG. 7A. FIG. 3 is a diagram showing a Mossbauer spectrum of a nitride layer provided on the surface of an Fe plate in Example 1. 9 is a table showing the results of analyzing the Mossbauer spectroscopy spectrum shown in FIG. 8.

[Summary of Embodiment of the Invention]
First, the contents of the embodiment of the present invention will be listed and described.
(1) A method for manufacturing an iron nitride material according to an embodiment of the present invention (first manufacturing method) includes:
A method for producing an iron nitride material having a first nitride layer containing γ′-Fe ₄ N on a surface of an iron base material,
By performing molten salt electrolysis using an anode comprising a cathode and an iron base provided in an electrolytic solution in which nitride ions ( ^N3- ) are dissolved in a molten salt, γ'-Fe _{4 N} has electrolytic step of electrodeposition, the a,
In the above electrolytic process, the temperature of the electrolytic solution is 240 ° C. or more, and the potential applied to the anode is more than 0.6 V and 1.5 V or less on the basis of Li ⁺ / Li. is there.

According to the aspect of the invention described in the above (1), the generated phase constituting the first nitride layer can be controlled by the temperature of the electrolytic solution (processing temperature) and the potential applied to the anode. Therefore, it is more suitable for generating the γ ′ phase than the gas nitriding treatment, and easily generates γ′-Fe ₄ N uniformly in the first nitride layer. In addition, control for generating a single phase of γ′-Fe ₄ N is easier than in gas nitriding.
In the present invention, that the γ ′ phase is uniformly generated means that the γ ′ phase is uniformly dispersed in the first nitride layer. Moreover, the single phase of γ'-Fe 4 _N, means that it does not contain an intermetallic compound of iron and nitrogen other than γ'-Fe 4 _N.

Further, in the nitriding treatment by molten salt electrolysis, the nitriding treatment can be performed at a lower temperature and in a shorter time than in the gas nitriding treatment, and the amount of deformation of the iron base material during heating can be reduced. Furthermore, it can contribute to reduction of energy consumption during processing.
Then, the iron nitride material having the first nitride layer containing γ′-Fe ₄ N manufactured in this embodiment is the same as the iron nitride material containing α ″ -Fe ₁₆ N ₂ in the manufacturing method described in (17) described below. It can be suitably used as a material for producing an iron nitride material having a two-nitride layer.

(2) In the method for producing an iron nitride material according to (1), the iron base material preferably has a purity of 99% by mass or more.
As described above, by reducing the amount of impurities in the iron base material and setting the purity of the iron base material to 99% by weight or more, it is possible to suppress generation of a foreign phase other than γ′-Fe ₄ N. In addition, in the quenching step in the production method described in (17) described later, it is possible to maintain the easiness of generating the α ′ phase during quenching.

(3) In the method for producing an iron nitride material according to the above (1), the iron base material preferably has a carbon content of 0.02% by mass or more and 2.14% by mass or less.
Even when an iron base material containing carbon is used as the iron base material, γ′-Fe ₄ N can be generated. In the case of gas nitriding, it is not easy to generate γ'-Fe ₄ N on the surface of an iron base material containing carbon.

(4) In the step of electrolyzing the iron nitride material according to any one of (1) to (3), the temperature of the electrolytic solution is preferably 350 ° C. or more and 450 ° C. or less.
In this case, γ′-Fe ₄ N can be efficiently generated on the surface of the iron base material.
On the other hand, when the temperature of the electrolytic solution is lower than 350 ° C., γ′-Fe ₄ N may be difficult to be generated on the surface of the iron base material, and when the temperature exceeds 450 ° C., the deformation amount of the iron base material is reduced. It can get bigger. In addition, the amount of supplied energy increases.

(5) In the step of electrolyzing the iron nitride material according to any one of (1) to (4), the potential applied to the anode is more than 0.6 V and not more than 0.9 V based on Li ⁺ / Li. Is preferred.
In this case, it is more suitable to form a single phase of γ'-Fe ₄ N on the surface of the iron base material.

(6) In the method for producing an iron nitride material according to any one of (1) to (5), the oxide layer formed on the surface of the iron base material used for the anode may be formed before the electrolysis step. It is preferable to have a pretreatment step for removal.
In this case, it is suitable for producing an iron nitride material having a nitride layer having a small oxygen component.

(7) In the method for producing an iron nitride material according to any one of the above (1) to (6), the molten salt is a halide of an alkali metal, a halide of an alkaline earth metal, or a mixture thereof. Is preferred.
(8) In the method for producing an iron nitride material according to the above (7), the alkali metal halide is an alkali metal bromide, an alkali metal iodide, or a mixture of an alkali metal bromide and an alkali metal iodide. Preferably, it is a mixture.
(9) In the method for producing an iron nitride material according to (7), the alkaline earth metal halide is an alkaline earth metal bromide, an alkaline earth metal iodide, or an alkaline earth metal bromide. And a mixture of iodide of alkaline earth metal.
(10) In the method for producing an iron nitride material according to (7) or (8), the alkali metal is preferably at least one selected from the group consisting of Li, K, and Cs.
(11) In the method for producing an iron nitride material according to (7) or (9), the alkaline earth metal may be at least one selected from the group consisting of Mg, Ca, Sr, and Ba. preferable.
(12) In the method for producing an iron nitride material according to (7), it is preferable that the molten salt is LiBr-KBr-CsBr or LiI-KI-CsI.
(13) In the method for producing an iron nitride material according to any one of (1) to (12), the molten salt contains Li ⁺ , K ^+, and Cs ⁺ , and has a Li ⁺ content of 40 mol% or more, It is preferable that the content of K ^{+ is} 80 mol% or less, the content of K ⁺ is 5 mol% or more and 30 mol% or less, and the content of Cs ⁺ is 10 mol% or more and 40 mol% or less.
According to the aspect of the invention described in any one of the above (7) to (13), the molten salt is formed of a material having a low melting point, which is relatively easily available, and which is easy to handle. Can be.
In particular, the embodiment of any one of the above (10) to (13) is suitable for further forming a molten salt having a lower melting point.

(14) In the method for producing an iron nitride material according to any one of (1) to (13), in the electrolytic step, Li ₃ N is added to the molten salt to dissolve nitride ions (N ³⁻ ). It is preferable to use a prepared electrolyte solution.
In this case, nitride ions ( ^N3- ) can be easily dissolved in the molten salt.

(15) In the method for producing an iron nitride material according to any one of (1) to (14), a nitrogen gas reducing electrode is provided on the molten salt, and a nitrogen gas is supplied to the nitriding gas reducing electrode to perform electrochemical electrochemical treatment. It is preferable to form an electrolytic solution in which the nitride ions (N ³⁻ ) are dissolved by reducing the solution.
In this case, nitride ions ( ^N3- ) can be continuously supplied into the molten salt.

(16) In the method for producing an iron nitride material according to any one of (1) to (15), the first nitride layer is preferably a single phase of γ′-Fe ₄ N.
In this case, in the method for manufacturing an iron nitride material according to any one of (17) to (20) described below, when a second nitride layer containing α ″ -Fe ₁₆ N ₂ is formed, Fe ₂ N or ε- The second nitride layer containing no Fe ₃ N can be suitably manufactured.
The second nitride layer containing α ″ -Fe ₁₆ N ₂ and not containing Fe ₂ N or ε-Fe ₃ N is suitable as a magnetic material having stable performance.

(17) A method for producing an iron nitride material according to another embodiment of the present invention is a method for producing an iron nitride material having a second nitride layer containing α ″ -Fe ₁₆ N ₂ on a surface of an iron base material. (Second manufacturing method),
A step of producing a first iron nitride material having a first nitride layer containing γ′-Fe ₄ N on a surface by the method for producing an iron nitride material according to any one of the above (1) to (16);
A first heating step of heating the first iron nitride material at a temperature of 600 ° C. or higher to generate a γ phase on the surface of the iron base material;
Quenching the iron substrate in which the γ phase is generated on the surface, and a quenching step of generating an α ′ phase on the surface of the iron substrate,
A second heating step of heating the iron substrate in which the α ′ phase has been generated on the surface at a temperature of 200 ° C. or lower to precipitate α ″ -Fe ₁₆ N ₂ on the surface of the iron substrate,
Having.

According to the aspect of the invention described in the above (17), the first surface containing γ′-Fe ₄ N on the surface manufactured by the method for manufacturing an iron nitride material according to any one of the above (1) to (16). The first iron nitride material having a nitride layer is heated at a temperature of 600 ° C. or more to generate a γ phase on the surface of the iron base material. Therefore, a nitride layer containing a γ phase and having very few ε phases can be formed on the surface of the iron base material.
Then, in the production method of this embodiment, the iron base material in which the γ phase has been formed is rapidly cooled, and further subjected to aging treatment. Therefore, it is possible to manufacture an iron nitride material having a second nitride layer in which α ″ -Fe ₁₆ N ₂ is uniformly generated while avoiding the inclusion of Fe ₂ N and ε-Fe ₃ N.
Here, that α ″ -Fe ₁₆ N ₂ is uniformly generated means that α ″ -Fe ₁₆ N ₂ is uniformly dispersed in the second nitride layer.

(18) In the method for producing an iron nitride material according to the above (17), in the second heating step, the iron substrate having the α ′ phase formed on the surface is heated to 100 ° C. or more and 200 ° C. or less, It is preferable to hold for 1 hour or more and 240 hours or less.
Such conditions are suitable for changing the α ′ phase to α ″ -Fe ₁₆ N ₂ .

(19) The method for producing an iron nitride material according to the above (17) or (18), further comprising, after the second heating step, a step of forming an anticorrosion layer on the surface of the second nitride layer. preferable.
In this case, in the manufactured iron nitride material, the anticorrosion layer formed in the above step prevents the second nitride layer from being in contact with the external environment. An iron nitride material that is hardly affected and hardly deteriorated can be provided.

(20) In the method for producing an iron nitride material according to the above (19), the anticorrosion layer is preferably made of iron carbide or iron oxide.
In this case, it is suitable for protecting the second nitride layer from the external environment.

[Details of Embodiment of the Invention]
Specific examples of the embodiments of the present invention will be described below with reference to the drawings as appropriate. It should be noted that the present invention is not limited to these exemplifications, but is indicated by the appended claims, and is intended to include all modifications within the meaning and scope equivalent to the claims. .

The manufacturing method according to the embodiment of the present invention includes a method (first manufacturing method) for manufacturing an iron nitride material (first iron nitride material) having a first nitride layer containing γ′-Fe ₄ N; And a method for producing an iron nitride material having a second nitride layer containing Fe ₁₆ N ₂ (a second production method). Here, the second manufacturing method includes the first manufacturing method, and the second manufacturing method includes the step of forming a nitride film having a first nitride layer containing γ′-Fe ₄ N by the first manufacturing method. This is a manufacturing method in which after the iron material is manufactured, a predetermined heat treatment is performed on the obtained iron nitride material.
Therefore, in the following description of the manufacturing method according to the embodiment of the present invention, the entire second manufacturing method will be described in the order of steps, and the first manufacturing method will also be described.

First, the outline of the second manufacturing method will be described.
FIG. 1 is a view schematically showing essential steps in a second manufacturing method according to the embodiment of the present invention.
In the second manufacturing method, the first nitride layer 12 containing γ′-Fe ₄ N is formed on the surface of the iron base material 11 by molten salt electrolytic nitridation S1. This step corresponds to the first manufacturing method.
Next, the first heat treatment S2 is performed on the iron base material 11 on which the first nitride layer 12 containing γ′-Fe ₄ N is formed, and the nitride layer containing γ phase is formed on the surface of the iron base material 11. 13 is formed. Here, the γ phase can be generated by a phase transformation between γ′-Fe ₄ N and α-Fe.
Next, the iron substrate 11 on which the nitride layer 13 containing the γ phase is formed is quenched S3 to form a nitride layer 14 containing the γ phase and α′-Fe ₈ N on the surface of the iron substrate 11. Form.
Thereafter, a second heat treatment (aging treatment) S4 is performed on the iron base material 11 on which the nitride layer 14 containing the γ phase and the α ′ phase is formed, and the γ phase and α ′ 'to form a _-Fe 16 _{N 2} and the second nitride layer 15 comprising a.
In the above second manufacturing method, an iron nitride material having the second nitride layer 15 containing α ″ -Fe ₁₆ N ₂ is manufactured through such steps.

<Molten salt electrolytic nitriding (first production method)>
In the first manufacturing method, the first nitride layer 12 containing γ′-Fe ₄ N is formed on the surface of the iron base material 11.
In the first manufacturing method, for example, a pretreatment step, an electrolysis step, and an anticorrosion layer forming step are performed in this order. Here, the electrolysis step is an essential step, and the pretreatment step and the anticorrosion layer forming step are optional steps performed as necessary.
FIG. 2 is a diagram schematically illustrating an example of an electrolysis step included in the first manufacturing method according to the embodiment of the present invention.

(Pretreatment step)
This step is a step performed before the electrolysis step, for example, a step of removing an oxide layer formed on the surface of the iron base material used for the anode.
The method of removing the oxide layer formed on the surface of the iron base material is not particularly limited, and examples thereof include a method of removing the oxide layer by dissolving the anode by electrolysis and a method of removing the oxide layer by a chemical.
In order to remove the oxide layer by dissolving the anode, for example, a cathode and an anode made of an iron base material are provided in an electrolytic solution in the same manner as in the electrolysis step described later, and the voltage is 2.0 V or more based on Li ⁺ / Li. By applying the potential of the above to the anode, the oxide layer on the anode surface can be dissolved and removed. Note that, after removing the oxide layer, the electrolysis step described later can be performed by setting the potential to be more than 0.6 V and 1.5 V or less on the basis of Li ⁺ / Li.
The removal of the oxide layer can also be performed by dissolving the oxide layer with an acid-based chemical. As the acid-based chemical, for example, nitric acid, hydrochloric acid, sulfuric acid and the like can be used.

(Electrolysis process)
In this step, an electrolytic solution in which nitride ions ( ^N3- ) are dissolved in a molten salt is used.
-Molten salt-
The molten salt may be any as long as it melts at the temperature at which the present electrolysis step is performed to become a liquid. For example, when the electrolysis step is performed at 350 to 450 ° C., it is preferable to select one that melts at 300 ° C. or lower to become a liquid.
As the molten salt having a relatively low melting temperature and being relatively easily available, for example, a halide of an alkali metal, a halide of an alkaline earth metal, or a mixture thereof is preferable. Generally, a molten salt has a lower melting point when a multi-component salt is used than when a single-component salt is used. Therefore, it is preferable to use a mixture of a plurality of types of salts.
Further, the alkali metal halide is preferably bromide, iodide or a mixture of bromide and iodide. Similarly, the alkaline earth metal halide is also preferably bromide, iodide or a mixture of bromide and iodide. Iodide and bromide salts are preferred because they can be melted at a relatively low temperature and are easy to handle.

  The alkali metal is preferably at least one selected from the group consisting of Li, K and Cs. The alkaline earth metal is preferably at least one selected from the group consisting of Mg, Ca, Sr and Ba. These alkali metal and alkaline earth metal halides can be melted at a relatively low temperature and are relatively easily available.

  From the above viewpoint, the molten salt is preferably, for example, LiBr-CsBr, LiBr-KBr-CsBr, Li-KI, Li-CsI, Li-KI-CsI, or the like. Among them, LiBr-KBr-CsBr and Li-KI-CsI are more preferable.

When the molten salt contains Li ⁺ , K ^+, and Cs ⁺ , the Li ⁺ content is 40 mol% or more and 80 mol% or less, the K ⁺ content is 5 mol% or more, 30 mol% or less, and Cs The content of ⁺ is preferably from 10 mol% to 40 mol%. Thereby, a molten salt having a low melting point can be obtained.
The content of Li ^{+ in} the molten salt is more preferably 45 mol% or more and 75 mol% or less, further preferably 50 mol% or more and 70 mol% or less.
The content of K ^{+ in} the molten salt is more preferably 7 mol% or more and 25 mol% or less, further preferably 9 mol% or more and 20 mol% or less.
The content of Cs ^{+ in} the molten salt is more preferably 15 mol% or more and 35 mol% or less, further preferably 20 mol% or more and 30 mol% or less.

-Formation of nitride ions-
The method for dissolving the nitride ions ( ^N3- ) in the molten salt is not particularly limited. For example, nitride ions can be generated in the molten salt by adding and dissolving Li ₃ N in the molten salt. The addition amount of the nitride ions, for example, Li ₃ concentration of N is 0.1 mol% or more, it may be added to Li ₃ N molten salt such that less 10 mol%. By setting the concentration of Li ₃ N to be 0.1 mol% or more, a sufficient amount of nitride ions for depositing γ′-Fe ₄ N by molten salt electrolysis is generated in the molten salt. Can be. In addition, by setting the concentration of Li ₃ N to 10 mol% or less, it is possible to suppress an increase in the melting point of the molten salt.
From these viewpoints, the addition amount of the Li ₃ N is, Li ₃ concentration of N is 0.2 mol% or more, more preferably to be not more than 5 mol%, 0.5 mol% or more, so as to be 3 mol% or less More preferably,
When γ′-Fe ₄ N starts to be deposited in an electrolysis step described later, nitride ions in the electrolytic solution are consumed, so that a large amount of a nitride layer containing γ′-Fe ₄ N is generated. , Li ₃ N may be appropriately added to the molten salt also in the electrolysis step.

As a method for supplying nitride ions (N ³⁻ ) into the molten salt, a nitrogen gas reducing electrode (hereinafter, also simply referred to as “gas electrode”) is provided on the molten salt to supply a nitrogen gas, and nitrogen is supplied by electricity. A method of dissolving nitride ions in the molten salt by chemical reduction may be employed. The gas electrode may be any electrode that can supply a gas containing nitrogen gas to the electrode surface, and a known electrode can be used. As the gas electrode, a gas electrode having a structure shown in FIGS. 3 to 6 is preferable.

The gas electrode shown in FIG. 3 is a gas electrode provided with a cylindrical electrode member 32 having an internal space serving as a flow path of a gas containing nitrogen gas. When this gas electrode is used, the tubular electrode member 32 may be connected to the cathode side of the power supply via the lead wire 31 and the counter electrode may be connected to the anode side of the power supply to apply a potential to the anode. Then, by supplying a gas containing nitrogen gas to the internal space of the cylindrical electrode member 32, the nitrogen gas is reduced on the surface of the internal space and dissolved in the molten salt as nitride ions ( ^N3- ). it can.

In the gas electrode shown in FIG. 4, a conductive porous member 43 is arranged at the tip of the internal space of the cylindrical electrode member 42.
The porous member 43 may have a large number of communication holes communicating between one surface and the other surface. Since the porous member 43 has the communication hole, the gas supplied to the internal space of the gas electrode can be discharged to the outside of the gas electrode. Further, the communication hole may be, for example, a hole that goes straight from one surface of the porous member 43 toward the other surface, or may be formed by a complicated structure such as a three-dimensional network structure. It may be a hole.
When the gas electrode provided with the porous member 43 at the tip of the internal space is arranged in the molten salt, the inside of the communication hole is filled with the molten salt.
When the gas electrode shown in FIG. 4 is used, the tubular electrode member 42 may be connected to the cathode side of the power supply via the lead wire 41, the counter electrode may be connected to the anode side of the power supply, and the potential may be applied to the anode. Since the porous member 43 is conductive, nitrogen gas is reduced on the surface of the communication hole of the porous member 43 by supplying a gas containing nitrogen gas to the internal space of the gas electrode. Thereby, the nitride ions ( ^N3- ) can be dissolved in the molten salt.

It is desirable that the cylindrical electrode members 32 and 42 and the porous member 43 be made of a material that is inert in the molten salt. Examples of the inert material include platinum, gold, alloys thereof, glassy carbon, graphite, stainless steel, nickel, and nickel-based alloys.
The cylindrical electrode member 42 and the porous member 43 may be made of the same material or may be made of different materials.

The gas electrode shown in FIG. 5 includes an electrode member 53 and a tubular member 52.
The tubular member 52 has an internal space that serves as a flow path for a gas containing nitrogen gas, and the electrode member 53 only needs to be disposed in the internal space of the tubular member 52.
When the gas electrode shown in FIG. 5 is used, the electrode member 53 may be connected to the cathode side of the power supply via the lead wire 51, the counter electrode may be connected to the anode side, and a potential may be applied to the anode. At this time, by supplying a gas containing nitrogen gas to the internal space of the tubular member 52, the nitrogen gas is reduced on the surface of the electrode member 53 and dissolved in the molten salt as nitride ions ( ^N3- ). Can be.

  The gas electrode shown in FIG. 6 is the same as the gas electrode shown in FIG. 5 except that the electrode member is made of a porous body 63 having a skeleton of a three-dimensional network structure. In this case, since the surface area of the electrode is increased, the dissolving efficiency of the nitrogen gas supplied to the space inside the tubular member 62 into the molten salt can be further increased.

The tubular members 52 and 62 do not need to be particularly conductive and may be made of a material that is stable in the molten salt.
On the other hand, it is desirable that the electrode member 53 and the porous body 63 are conductive and made of a material that is inert in the molten salt. Examples of the inert material include platinum, gold, alloys thereof, glassy carbon, graphite, stainless steel, nickel, and nickel-based alloys. Examples of the porous body 63 include a nickel porous body having a skeleton of a three-dimensional network structure.
The gas electrode has higher efficiency as the number of portions forming the three-phase interface between the nitrogen gas, the molten salt, and the current-carrying portion of the gas electrode increases. Therefore, the gas electrodes shown in FIGS. 4 and 6 using the porous member to the conductive portion can be more effectively dissolve the nitride ions (N ^3-) in Torushio.

By supplying a gas containing nitrogen gas using such a gas electrode and reducing the nitrogen gas on the surface of the gas electrode, the nitride ions are dissolved in the molten salt.
The gas supplied to the gas electrode is not limited to nitrogen gas, and may be a mixed gas of a gas that does not affect the molten salt and nitrogen gas. As a gas mixed with the nitrogen gas, for example, an argon (Ar) gas is preferable.
When a mixed gas of nitrogen gas and another gas is supplied to the gas electrode, a gas having a high nitrogen gas concentration is preferable in consideration of the reaction efficiency on the electrode surface. That is, it is desirable to adjust the concentration so that the maximum amount of nitrogen gas that can react with the gas electrode used is supplied.

The flow rate of the gas containing nitrogen gas is preferably a flow rate at which the maximum amount of nitrogen gas that can react at the electrode can be supplied from the viewpoint of increasing the efficiency of generating nitride ions.
When a gas containing nitrogen gas is supplied, unreacted gas discharged from the gas electrode may be collected and circulated so as to supply the gas electrode again.

In this step, the molten salt electrolysis is continuously performed using the electrolytic solution 23. In the molten salt electrolysis, a first nitride layer containing γ′-Fe ₄ N is formed on the surface of the anode 21 by electrodeposition.
In this electrolysis step, as shown in FIG. 2, an anode 21 and a cathode 22 are provided in an electrolytic solution 23, and the anode 21 is connected to the anode side of the power supply 24, and the cathode 22 is connected to the cathode side of the power supply 24. Then, by applying a potential to the anode 21, γ′-Fe ₄ N can be generated on the surface of the anode 21.
Here, the power supply 24 only needs to be capable of controlling the potential, and for example, a potentio-galvanostat or the like can be used.

−Electrolyte−
As the electrolytic solution 23, the above-mentioned electrolytic solution is used.
The temperature of the electrolytic solution 23 is set to 240 ° C. or higher. When the temperature of the electrolytic solution 23 is lower than 240 ° C., it is difficult to generate (deposit) γ′-Fe ₄ N.
The temperature of the electrolytic solution 23 is preferably 350 ° C. or more and 450 ° C. or less. In this case, γ′-Fe ₄ N can be efficiently generated on the surface of the anode 21.

−Anode−
As the anode 21, an iron base material is used.
As the iron substrate, an iron substrate having a purity of 99% by mass or more is preferable. In this case, generation of a different phase other than the γ'-Fe ₄ N phase can be suppressed.
The iron base material preferably has a carbon content of 0.02% by mass or more and 2.14% by mass or less. According to the present electrolysis step, γ′-Fe ₄ N can be produced even when an iron base material containing carbon is used as the iron base material.
The iron base material may further contain Ti, V, Cr, Mn, lanthanoid, Al, Si, and the like. These may contain only one kind or two or more kinds.
The shape of the anode 21 is not particularly limited as long as it can be energized, and may be appropriately selected depending on the purpose, such as a flat plate shape. Further, the anode 21 may be formed by molding iron particles into a plate shape or the like. At this time, the molded body may be porous or dense.

−Cathode−
As the cathode 22, a conductive material that is stable in an electrolytic solution may be used.
As the cathode 22, for example, those made of platinum, gold, an alloy thereof, glassy carbon, graphite, stainless steel, alumina, nickel, a nickel-based alloy, or the like can be preferably used.
As the cathode 22, a gas electrode having the same configuration as the gas electrode described in the generation of nitride ions can be used. By using the above gas electrode, nitride ions can be continuously supplied to the electrolytic solution during molten salt electrolysis.

-Electrolysis conditions-
The potential applied to the anode 21 during the electrolysis of the molten salt may be more than 0.6 V and about 1.5 V or less on the basis of Li ⁺ / Li. By setting the above potential to exceed 0.6 V (vs. Li ⁺ / Li), γ′-Fe ₄ N can be favorably generated on the surface of the iron base material used as the anode 21.
On the other hand, by setting the potential to 1.5 V (vs. Li ⁺ / Li) or less, γ′-Fe ₄ N can be formed without dissolving the iron of the anode 21.
The potential applied to the anode 21 should be more than 0.6 V and 0.9 V or less on the basis of Li ⁺ / Li from the viewpoint that it is suitable for generating a single phase of γ′-Fe ₄ N. More preferably, it is more than 0.6V and 0.8V or less.
Further, when the temperature of the electrolytic solution is 350 ° C. or more and 450 ° C. or less, it is particularly preferable that the potential applied to the anode 21 be 0.65 V or more and 0.75 V or less.

The time for performing the molten salt electrolysis is not particularly limited, and may be a time during which the desired γ′-Fe ₄ N is sufficiently generated.
By performing such a step (first manufacturing method), the first nitride layer containing γ′-Fe ₄ N can be formed on the surface of the iron base material.
The iron substrate having the first nitride layer containing γ′-Fe ₄ N formed on the surface obtained by the first manufacturing method is subsequently subjected to the second nitride layer containing α ″ -Fe ₁₆ N _2. It is used to form a material layer on the surface of an iron substrate.

<First heat treatment>
In this step, the iron base material having the first nitride layer containing γ′-Fe ₄ N formed on the surface (hereinafter, also referred to as the first nitride layer-containing iron base material) manufactured by the first manufacturing method is used. Is heated to 600 ° C. or more, and γ-Fe is generated by the phase transformation between γ′-Fe ₄ N and α-Fe.
The heating temperature in the first heat treatment may be 600 ° C. or higher, and the upper limit is preferably 850 ° C. The reason is that when the heating temperature exceeds 850 ° C., thermal decomposition of the nitride proceeds.
The heating temperature is preferably from 650 to 800 ° C.

The heating time in this step is preferably from 10 to 600 seconds. This is because the reaction of the γ'-Fe 4 _N and alpha-Fe and the heating time is too short, the less the amount of insufficient for gamma-Fe, from γ'-Fe 4 _N and the time is too long This is because the transfer of nitrogen to α-Fe proceeds too much, and the amount of generated γ-Fe decreases.
In this step, since the first nitride layer-containing iron base material manufactured by the first manufacturing method is used, when the heat treatment is performed under the above-described conditions, the ε phase is hardly generated, and the nitride layer , Γ-Fe are easily distributed uniformly.

<Quenching>
In this step, the iron base material having γ-Fe formed on the surface obtained in the first heat treatment is quenched to transform γ-Fe into α ′ phase (α′-Fe ₈ N), Α′-Fe ₈ N is formed on the surface of the substrate.
Here, as the quenching condition, for example, a condition of pouring into oil at −50 to 10 ° C. for 1 to 20 seconds may be adopted.

<Second heat treatment (aging treatment)>
In this step, α′-Fe ₈ N generated on the surface of the iron base material is changed to α ″ -Fe ₁₆ N ₂ by aging treatment. Thereby, α ″ -Fe ₁₆ N ₂ precipitates on the surface of the iron base material.
As the condition of the aging treatment, for example, a condition of maintaining the temperature at 100 ° C. or more and 200 ° C. or less for 1 hour or more and 240 hours or less can be adopted.
Under the conditions of the aging treatment, the temperature is preferably from 120 ° C to 180 ° C, and the time is preferably from 2 hours to 120 hours.
The aging treatment is preferably performed in an inert gas atmosphere such as an argon gas atmosphere.

In the embodiment of the present invention, γ′-Fe ₄ N in the first nitride layer-containing iron substrate can be transformed into α′-Fe ₈ N by the above-described first heat treatment and rapid cooling. .
Further, in the first nitride layer-containing iron base material, when the first nitride phase is a single phase of γ′-Fe ₄ N, α ″ − An iron nitride material containing Fe ₁₆ N ₂ and having a second nitride layer in which Fe ₂ N, ε-Fe ₃ N, and the like are extremely small can be manufactured.

(Corrosion protection layer forming step)
The anticorrosion layer forming step is a step performed after the aging treatment, and is a step of forming an anticorrosion layer on the surface of the second nitride layer containing α ″ -Fe ₁₆ N ₂ formed through the aging treatment. is there.
The anticorrosion layer is preferably made of iron carbide or iron oxide.
When the layer made of iron carbide is formed as the anticorrosion layer, as a method of forming the carbon iron layer, for example, after the above-mentioned aging treatment, a carbon material (liquid hydrocarbon or the like) is applied, and the resultant is applied in an inert atmosphere furnace. A baking method, a method of performing a heat treatment in a CO atmosphere, and the like can be employed.
When a layer made of iron oxide is formed as the anticorrosion layer, for example, the iron nitride material on which the second nitride layer containing α ″ -Fe ₁₆ N ₂ is formed may be oxidized under mild conditions. good.
As a condition of the mild oxidation treatment, for example, a method of forming Fe ₃ O ₄ by heat treatment at about 100 ° C. can be adopted.
As the anticorrosion layer, a chromium nitride layer formed by reacting Cr ions or a layer made of SiO ₂ , Al ₂ O ₃ or the like may be used.

In the production method according to the embodiment of the present invention, the second production method including the first production method is performed by using the iron base material as a starting material, so that Fe ₂ N or ε-Fe ₃ An iron nitride material having the second nitride layer in which α ″ -Fe ₁₆ N ₂ is uniformly generated can be manufactured while avoiding generation of N.
In addition, the manufacturing method according to the embodiment of the present invention can uniformly generate α ″ -Fe ₁₆ N ₂ (especially in the thickness direction of the nitride layer) while avoiding generation of Fe ₂ N and ε-Fe ₃ N. This is significantly superior to the method of forming a nitride layer by using a gas nitriding treatment.

  Next, the present invention will be described in more detail based on examples, but the present invention is not limited to only these examples. The scope of the present invention is defined by the scope of the claims, and includes equivalents and all modifications within the scope of the claims.

[Formation of nitride layer containing γ'-Fe ₄ N]
The molten salt electrolytic nitriding was performed under the conditions of Test Examples 1 to 4 below. The resulting nitride layer was analyzed.
(Test Example 1)
-Electrolysis process-
First, an electrolytic solution was prepared by the following method.
LiBr, KBr and CsBr were mixed at a molar ratio of 56.1: 18.9: 25.0 and heated to 250 ° C. to produce a molten salt. Li ₃ N was added to the molten salt so as to have a concentration of 1.0 mol% to prepare an electrolyte.

Next, molten salt electrolytic nitriding was performed.
The molten salt electrolytic nitriding was performed in a glove box in an Ar flow atmosphere.
A 5 mm × 5 mm × 1 mmt Fe plate was used as the anode, and a glassy carbon rod was used as the cathode. An Al-Li alloy was used as a reference electrode. These were placed in the electrolyte.
The temperature of the electrolyte was 450 ° C.
In this step, the anode and the cathode are connected to a potential galvanostat as a power supply capable of controlling the potential, a potential of 0.7 V is applied to the anode based on Li ⁺ / Li, and the molten salt electrolysis is performed at a constant potential for 3 hours. As a result, an iron nitride material having a nitride layer was manufactured.
Here, a nitride layer was formed on the surface of the Fe plate as the anode.

(Test Example 2)
An iron nitride material having a nitride layer was manufactured in the same manner as in Example 1 except that the temperature of the electrolytic solution was changed to 350 ° C. in Test Example 1.

(Test Example 3)
An iron nitride material having a nitride layer was manufactured in the same manner as in Example 1 except that the temperature of the electrolytic solution was set to 350 ° C. and the potential applied to the anode was set to 0.8 V based on Li ⁺ / Li in Test Example 1.

(Test Example 4)
An iron nitride material having a nitride layer was manufactured in the same manner as in Example 1 except that the temperature of the electrolytic solution was set to 350 ° C. and the potential applied to the anode was set to 1.0 V based on Li ⁺ / Li in Test Example 1.

-Evaluation-
(Analysis of generated phase)
Under all the conditions of Test Examples 1 to 4, formation of a nitride layer was observed on the surface of the Fe plate as the anode.
Thus, the generated phase of the obtained nitride layer was analyzed by an X-ray diffractometer. The results are shown in Table 1. Table 1 also shows the electrolysis conditions.
Here, as an X-ray diffractometer, XRD; Ultima IV, Cu-Kα line, λ = 1.5418 °, 40 kV, 40 mA, manufactured by Rigaku Corporation was used.

As shown in Table 1, only Fe ₄ N was generated by controlling the bath temperature of the molten salt bath and the potential applied to the anode during the electrolysis of the molten salt.

  7A and 7B show the measurement results of the nitride layer manufactured in Test Example 1 using an X-ray diffractometer. In the figure, the spectrum of (i) is the measurement result of Test Example 1. FIG. 7B is an enlarged view of a main part of FIG. 7A.

[Formation of nitride layer containing α ″ -Fe ₁₆ N ₂ ]
Next, the following Example 1 was performed using the iron nitride material having a nitride layer made of Fe ₄ N manufactured in Test Example 1 above.
(Example 1)
-Solution treatment (first heat treatment and rapid cooling)-
The Fe plate of Test Example 1 subjected to the electrolytic treatment was heat-treated under the following conditions.
The temperature was raised to 740 ° C. in an inert atmosphere and maintained for 60 seconds. Thereafter, the heated Fe plate was put into oil kept at -5 ° C, and cooled with oil.
The crystal phase existing on the surface of the Fe plate after the heat treatment was analyzed by X-ray diffraction. As a result, Fe (α phase) and Fe (γ phase) were observed.
Also, a shoulder was observed on the high angle side of the (110) peak of Fe (α phase). Since no corresponding iron nitride crystal phase was found at the peak position of this shoulder, it was considered that this shoulder peak was due to Fe (α phase) in which the lattice was distorted and the lattice constant was shifted. The lattice shift of Fe is presumed to be caused by distortion caused by incorporating N into supersaturation, and indicates the existence of a supersaturated α phase (α ′).
FIGS. 7A and 7B show the measurement results by the X-ray diffractometer measured after quenching in Example 1. FIG. In the figure, the spectrum (ii) is the measurement result after quenching.

-Aging treatment (second heat treatment)-
The Fe plate of Example 1 in which the α ′ phase (α′-Fe ₈ N) was generated by the heat treatment was kept at 150 ° C. for 84 hours in an inert atmosphere.
The crystal phase present on the surface of the Fe plate was analyzed by X-ray diffraction on the Fe plate after the aging treatment. As a result, in addition to Fe (α phase) and Fe (γ phase), signs of a peak of Fe ₁₆ N ₂ were observed. Specifically, a new broad shoulder was observed near 202 diffraction line of α ″ -Fe ₁₆ N ₂ located at 42.7 °.
FIGS. 7A and 7B show the measurement results of the X-ray diffractometer measured during and after the aging treatment in Example 1. FIG. In the figure, the spectrum (iii) is the measurement result during the aging treatment (after holding for 24 hours), and the spectrum (iv) is the measurement result after the aging treatment (after holding for 84 hours).

Further, when the Fe plate after the aging treatment was analyzed in detail by Mossbauer spectroscopy, the presence of Fe ₁₆ N ₂ was clarified.
FIG. 8 is a diagram showing a measurement result (Moessbauer spectral spectrum) of the crystal phase (nitride layer) formed on the surface of the Fe plate in Example 1 by Moessbauer spectroscopic analysis. FIG. 9 is a table showing the analysis results of the Mossbauer spectroscopy spectrum shown in FIG.
The details of the above Mossbauer spectroscopy are as follows.
The Mossbauer spectroscopy was performed using Co-57 and the _He-1% was diffused in Rh matrix _{(CH 3) 3} CH gas flow proportional counter. The measurement temperature was room temperature, and the speed calibration was performed using α-Fe.
The spectrum shown in FIG. 8 is the result of fitting. In addition to one Fe site for each of α-Fe and γ-Fe, α ″ -Fe ₁₆ N ₂ and γ′-Fe ₄ N shown as I, II, and III, respectively. Are separated into spectra of three Fe sites, respectively, and a spectrum that cannot be explained by them is observed at around 0 mms ⁻¹ , which indicates that in γ-Fe, nitrogen atoms occupy adjacent lattices. This is a fit obtained as a spectrum obtained from a 57Fe nucleus in an ultrafine structure (denoted as γ-Fe ′).

As is clear from the results of the above-mentioned Mossbauer spectroscopic analysis, it was clarified that the nitride layer obtained in this example contained Fe ₁₆ N ₂ .
As shown in FIG. 9, the integrated intensity ratio of the sub-spectrum corresponding to each phase of the nitride layer is α-Fe: (γ-Fe + γ-Fe ′): α ″ -Fe ₁₆ N ₂ : γ′-Fe ₄ N = 39.0: 36.1: 12.9: 12.0, and the content of Fe ₁₆ N ₂ contained in the nitride layer in the region of about 100 nm on the surface which is the analysis range of Mossbauer spectroscopy is It was about 13%.
Further, Fe ₂ N and Fe ₃ N were not detected from the nitride layer.

DESCRIPTION OF SYMBOLS 11 Iron base material 12, 13, 14, 15 Nitride layer 21 Anode 22 Cathode 23 Electrolyte solution 24 Power supply 31, 41, 51, 61 Lead wire 32, 42 Cylindrical electrode member 43 Porous member 52, 62 Cylindrical member 53 Electrode member 63 Porous body S1 Molten salt electrolytic nitriding S2 First heat treatment S3 Rapid cooling S4 Second heat treatment

Claims (20)

A method for producing an iron nitride material having a first nitride layer containing γ′-Fe ₄ N on a surface of an iron base material,
The molten salt electrolysis is performed using an anode composed of a cathode and an iron base provided in an electrolytic solution in which nitride ions (N ³⁻ ) are dissolved in a molten salt, whereby γ′-Fe is formed on the surface of the anode. _{4 N} has electrolytic step of electrodeposition, the a,
The method for producing an iron nitride material, wherein in the electrolysis step, the temperature of the electrolytic solution is equal to or higher than 240 ° C, and the potential applied to the anode is higher than 0.6 V and equal to or lower than 1.5 V based on Li ⁺ / Li.   The method for producing an iron nitride material according to claim 1, wherein the iron base material has a purity of 99% by mass or more.   The method for producing an iron nitride material according to claim 1, wherein the iron base material has a carbon content of 0.02% by mass or more and 2.14% by mass or less.   4. The method for producing an iron nitride material according to claim 1, wherein in the electrolysis step, the temperature of the electrolyte is 350 ° C. or more and 450 ° C. or less. 5. 5. The production of the iron nitride material according to claim 1, wherein in the electrolysis step, a potential applied to the anode is greater than 0.6 V and less than or equal to 0.9 V based on Li ⁺ / Li. 6. Method.   The nitriding method according to any one of claims 1 to 5, further comprising a pretreatment step of removing an oxide layer formed on a surface of the iron base material used for the anode before the electrolysis step. Manufacturing method of iron material.   The method for producing an iron nitride material according to any one of claims 1 to 6, wherein the molten salt is a halide of an alkali metal, a halide of an alkaline earth metal, or a mixture thereof.   The method for producing an iron nitride material according to claim 7, wherein the alkali metal halide is an alkali metal bromide, an alkali metal iodide, or a mixture of an alkali metal bromide and an alkali metal iodide.   8. The alkaline earth metal halide is an alkaline earth metal bromide, an alkaline earth metal iodide, or a mixture of an alkaline earth metal bromide and an alkaline earth metal iodide. 3. The method for producing an iron nitride material according to item 1.   The method for producing an iron nitride material according to claim 7 or 8, wherein the alkali metal is at least one selected from the group consisting of Li, K, and Cs.   The method for producing an iron nitride material according to claim 7 or 9, wherein the alkaline earth metal is at least one selected from the group consisting of Mg, Ca, Sr, and Ba.   The method for producing an iron nitride material according to any one of claims 1 to 7, wherein the molten salt is LiBr-KBr-CsBr or LiI-KI-CsI. The molten salt contains Li ⁺ , K ^+, and Cs ⁺ , and has a Li ⁺ content of 40 mol% or more and 80 mol% or less, a K ⁺ content of 5 mol% or more, 30 mol% or less, and a Cs ⁺ content of The method for producing an iron nitride material according to any one of claims 1 to 12, wherein the content is 10 mol% or more and 40 mol% or less. 14. The iron nitride material according to claim 1, wherein the electrolysis step includes adding Li ₃ N to the molten salt to form an electrolyte in which nitride ions (N ³⁻ ) are dissolved. Production method. In the electrolysis step, a nitrogen gas reducing electrode is provided on the molten salt, and a nitrogen gas is supplied to the nitriding gas reducing electrode to perform electrochemical reduction to form an electrolytic solution in which nitride ions (N ³⁻ ) are dissolved. The method for producing an iron nitride material according to any one of claims 1 to 14, wherein the method comprises: It said first nitride layer, γ'-Fe 4 _N producing method of nitrided iron as claimed in any one of claims 15 is a single phase. A method for producing an iron nitride material having a second nitride layer containing α ″ -Fe ₁₆ N ₂ on a surface of an iron base material,
By the method of manufacturing nitride iron according to any one of claims 1 to claim 16, comprising the steps of producing a first iron nitride having a first nitride layer comprising γ'-Fe 4 _N to the surface,
A first heating step of heating the first iron nitride material at a temperature of 600 ° C. or higher to generate a γ phase on the surface of the iron base material;
Quenching the iron base material in which the γ phase is generated on the surface, and a quenching step of generating an α ′ phase on the surface of the iron base material,
A second heating step of heating the iron substrate on which the α ′ phase is generated at a temperature of 200 ° C. or less to precipitate α ″ -Fe ₁₆ N ₂ on the surface of the iron substrate,
A method for producing an iron nitride material, comprising:   The said 2nd heating process heats the iron base material in which the said alpha 'phase was generated in the surface at 100 degrees C or more and 200 degrees C or less, and maintains this heating state for 1 hour or more and 240 hours or less. A method for producing the iron nitride material according to the above.   The method for producing an iron nitride material according to claim 17 or 18, further comprising, after the second heating step, a step of forming an anticorrosion layer on the surface of the second nitride layer.   The method according to claim 19, wherein the anticorrosion layer is made of iron carbide or iron oxide.