WO2021106233A1

WO2021106233A1 - Metal component and method for producing same

Info

Publication number: WO2021106233A1
Application number: PCT/JP2020/005455
Authority: WO
Inventors: 尚男冨士川; 渡辺　崇則; 宏之渡邊; 博貴宮下
Original assignee: エア・ウォーターＮｖ株式会社
Priority date: 2019-11-26
Filing date: 2020-02-13
Publication date: 2021-06-03
Also published as: CN114585768A

Abstract

Provided is a metal component having a surface layer that is resistant to heat/corrosion and wear, the surface layer having high durability with respect to repeated thermal stress.　The present invention comprises a parent material that is an iron-based metal or a nickel-based metal, and a surface improvement layer formed on the surface of the parent material. The surface improvement layer is configured so as to include a chromium compound layer that is present on the surface side, and a deposition layer that is present between the chromium compound layer and the parent material, the deposition layer being such that the chromium compound is deposited in a parent-material metal constituting the parent material.　The thermal expansion coefficients of these layers increases sequentially from the surface toward a deep section such that the thermal expansion coefficient of the chromium compound layer is less than that of the deposition layer, which in turn is less than that of the parent material. Specifically, the difference in thermal expansion coefficient between each of the layers is low. This makes it possible to raise the durability of the surface layer with respect to repeated thermal stress and to maintain the characteristics of heat/corrosion resistance and wear resistance of the surface layer. There are many environments and applications in which the present invention can be used.

Description

Metal products and their manufacturing methods

The present invention relates to a metal product and a method for manufacturing the same.

Technology is being made to form a surface layer made of chromium nitride on the surface of the iron-based metal and improve the wear resistance, oxidation resistance, corrosion resistance, etc. of the iron-based metal. Regarding such a technique, the applicant has developed the technique shown in Patent Document 1 below. In addition, the applicant has grasped the following Patent Document 2 as prior art related to the related technology.

Japanese Unexamined Patent Publication No. 2016-74948 Japanese Unexamined Patent Publication No. 2011-122190

The above-mentioned Patent Document 1 is intended to form a surface layer made of chromium carbonitride by subjecting an iron alloy material to a nitriding treatment in advance and then a chromasing treatment.

The above-mentioned Patent Document 1 has the following description.
[0020]
The metal surface modification method according to claim 1 prepares a base material which is an iron-based metal or a nickel-based metal. The surface of iron-based metals and nickel-based metals is covered with an oxide film or a passivation film. The presence of an oxide film or a passivation film on the surface generally tends to hinder the diffusion and permeation of nitrogen atoms. The nitriding treatment is performed in which the base material is heated and held in an atmosphere containing a nitriding source gas. By this nitriding treatment, nitrogen atoms are diffused and permeated on the surface of the base material activated by the halogenation treatment. Then, the nitrided base material is subjected to a chromaze treatment in which the nitrided base material is present in a powder containing metallic chromium powder and is heated and held at a temperature of 850 to 1200 ° C. By this chromium treatment, chromium atoms are diffused and permeated into the surface layer portion where nitrogen atoms are diffused and permeated, and a surface modification layer is formed.
[0087]
5 (a) and 5 (b) show the elemental distribution of the surface modification layer formed in the examples. The measurement was carried out by measuring the concentration distribution of the material cross section by EPMA (X-ray microanalyzer).
FIG. 5A is a surface modification layer formed by subjecting the SUS304 base material to a fluorine treatment, a soft nitriding treatment, and a chromaze treatment. The soft nitriding treatment was performed at 570 ° C. for 2 hours.
FIG. 5B is a surface modification layer formed by subjecting the SUS304 base material to a fluorine treatment, a nitriding treatment, and a chromaze treatment. The nitriding treatment was performed at 570 ° C. for 30 minutes.
In each case, a layer having a high concentration of Cr and N and a low concentration of Fe is formed at a thickness of about 50 μm on the surface side. This can be regarded as a chromium nitride layer. The chromium nitride layer is chromium about 82 wt%, nitrogen about 11% by weight, can be identified as a Cr 2 _N. Further, at a thickness of about 60 μm on the lower side thereof, a layer having a low nitrogen concentration and a high Fe and Cr concentration is formed. This can be seen as a chromium-enriched layer in which chromium is diffused and permeated into the base material.

In Patent Document 2, when a carbide coating layer is formed on an iron-based base material, an intermediate layer composed of a composite carbide of an element to be coated and iron of the base material is formed, and thermal expansion of the base material and the coating layer is performed. This is an attempt to prevent cracking of the coating layer due to a coefficient difference.

The above-mentioned Patent Document 2 has the following description.
[0007]
Taking the Cr film as an example, the sliding member of the present invention is characterized in that the steel member is coated with a chromium carbide layer via an intermediate layer composed of a composite carbide (Fe, Cr) C of iron and chromium. And. This layer structure is shown in FIG. 1 (a). As shown in FIG. 1A, cracking of the coating film can be prevented.
[0009]
Further, the present invention is a method for manufacturing a sliding member in which a chromium carbide layer is coated on a steel material portion via an intermediate layer composed of a composite carbide (Fe, Cr) C of iron and chromium by diffusion permeation treatment, and the steel material structure is It is characterized by containing cementite in advance and performing diffusion permeation treatment in the austenite + cementite region on the Fe—C system state diagram. When the structure of the surface of the steel member is in the state of austenite + cementite, Fe ₃ C is stably present in the austenite + cementite region. Therefore, Cr is supplied from the outside to _{react with Fe 3} C, as shown in FIG. An intermediate layer made of (Fe, Cr) C can be reliably formed on the surface of the steel member.

In the metal product obtained by the technique of Patent Document 1, an austenitic metal is subjected to a nitriding treatment and then a chromaze treatment. This forms a surface layer of Cr 2 _N layer, a chromium-concentrated layer of the inside. Furthermore, there is a base material inside it.
The Cr ₂ N layer is ceramic, the thermal expansion coefficient of 9 × ^{10 -6} / ℃ and small. Thermal expansion coefficient of austenitic base material for most present inside is 17 × 10 -6 ^/ ℃, becomes about twice as compared with the Cr 2 _N layer. Further, nitrogen is substantially not present in the chromium-enriched layer. Therefore, the coefficient of thermal expansion of the chromium-enriched layer is not significantly different from the coefficient of thermal expansion of the austenitic base metal. Thus, the Cr 2 _N layer is the outermost layer, in between the chromium-concentrated layer and the base material which exists as a lower layer, the thermal expansion coefficient is largely different divergence. In such a layer structure, for example when used at a high temperature of at least 1000 ° C., a thermal stress caused by repeated heating and cooling, which may cause peeling or cracking of the Cr 2 _N layer. For this reason, conventional metal products have restrictions on the environment in which they can be used and their uses.

The iron-based sliding member obtained by the technique of Patent Document 2 is subjected to diffusion permeation treatment of Cr or the like using an iron-based material containing cementite as a steel material structure in advance as a base material. As a result, a carbide layer on the surface layer and an intermediate layer made of a composite carbide of iron and Cr or the like are formed inside the carbide layer. Furthermore, there is a base material inside it.
In this method, the base material needs to be an iron-based material containing cementite in advance, that is, containing 0.6% by weight or more of carbon. Therefore, the intermediate layer cannot be formed with a material having high corrosion resistance, for example, stainless steel or heat-resistant steel, which has a low carbon content. Therefore, there is a problem that it cannot be applied to an environment or an application in which corrosion resistance is also required.
Further, the compound precipitated in the intermediate layer is a carbide such as a Cr-based carbide, and is more easily decomposed when heated to a high temperature as compared with a Cr-based nitride or the like. Therefore, there is also a problem that the performance tends to deteriorate when used in a high temperature environment.

The present invention has been made to solve the above problems, and provides a metal product having the following object and a method for producing the same.
Provided are a metal product having a heat-resistant / corrosion-resistant and wear-resistant surface layer having high resistance to repeated thermal stress, and a method for producing the same.

The metal product according to claim 1 adopts the following configuration in order to achieve the above object.
A base material which is an iron-based metal or a nickel-based metal and a surface modification layer formed on the surface of the base material are provided.
The surface modification layer is
The chromium compound layer existing on the surface side and
It is formed between the chromium compound layer and the base metal, and includes a precipitation layer in which the chromium compound is precipitated in the base metal constituting the base metal.

The metal product according to claim 2 adopts the following configuration in addition to the configuration according to claim 1.
The closer the precipitation layer is to the chromium compound layer on the surface side, the larger the precipitation amount of the chromium compound.

The metal product according to claim 3 adopts the following configuration in addition to the configuration according to claim 1 or 2.
The base material is any one of stainless steel, heat-resistant steel, and nickel-based alloy having a carbon concentration of 0.6% by weight or less, and the chromium compound is a chromium nitride.

The method for producing a metal product according to claim 4 employs the following configuration in order to achieve the above object.
For base metal that is iron-based metal or nickel-based metal
Nitriding treatment is performed to heat and hold the base metal in an atmosphere containing a nitriding source gas.
By performing a chromaze treatment in which the above-mentioned nitriding base material is present in a powder containing metallic chromium powder and heat-held.
On the surface of the above base material,
The chromium compound layer existing on the surface side and
A surface-modified layer exists between the chromium compound layer and the base metal, and is formed by including a precipitation layer in which the chromium compound is precipitated in the base metal constituting the base metal.

As the method for producing a metal product according to claim 5, in addition to the configuration according to claim 4, the following configuration is adopted.
The nitriding treatment produces a nitriding layer having a thickness of at least 1.5 times or more the thickness of the chromium compound layer contained in the finally formed surface modification layer.

As the method for producing a metal product according to claim 6, in addition to the configuration according to claim 5, the following configuration is adopted.
In the chromaze treatment, the nitriding layer produced by the nitriding treatment is subjected to a time to reach a predetermined thickness.

The metal product according to claim 1 includes a base material which is an iron-based metal or a nickel-based metal, and a surface modification layer formed on the surface of the base material. The surface modification layer includes a chromium compound layer existing on the surface side and a precipitation layer existing between the chromium compound layer and the base material. That is, a precipitation layer exists between the chromium compound layer, which is a hard ceramic layer, and the base material, which is an iron-based or nickel-based metal. The precipitation layer is formed by precipitating a chromium compound in the base metal constituting the base material.
Therefore, the coefficient of thermal expansion of each layer gradually increases from the surface to the deep part, with the chromium compound layer <precipitation layer <base material. Therefore, the difference in the coefficient of thermal expansion between the layers is smaller than that in the prior art in which the coefficient of thermal expansion greatly deviates between the chromium compound layer on the surface, the chromium-concentrated layer, and the base material. As a result, the surface layer has higher resistance to repeated thermal stress than before, and the heat resistance, corrosion resistance, and wear resistance of the surface layer can be maintained. The environment and applications that can be used are wider than before.

In the metal product according to claim 2, the closer the precipitation layer is to the chromium compound layer on the surface side, the larger the precipitation amount of the chromium compound.
As a result, the coefficient of thermal expansion of the precipitation layer gradually increases from the surface to the deep part. Therefore, the coefficient of thermal expansion changes continuously rather than stepwise from the chromium compound layer on the surface side to the base material. As a result, the surface layer has higher resistance to repeated thermal stress than before, and the heat resistance, corrosion resistance, and wear resistance of the surface layer can be maintained. The environment and applications that can be used are wider than before.

The metal product according to claim 3 is any one of stainless steel, heat-resistant steel, and nickel-based alloy having a carbon concentration of 0.6% by weight or less as the base material.
By forming a surface modification layer containing two layers, a chromium compound layer and a precipitation layer, on such a base material, a metal product having excellent properties can be obtained. Stainless steels, heat-resistant steels, and nickel-based alloys having a carbon concentration of 0.6% by weight or less do not contain high concentrations of carbon such that cementite is present in the base material. Therefore, it is not possible to form an intermediate layer made of a carbide layer on the surface layer and a composite carbide of iron and Cr or the like inside the carbide layer only by performing the diffusion permeation treatment of chromium. For example, by performing nitriding treatment to diffuse and permeate nitrogen atoms, and then performing diffusion permeation treatment of chromium, a chromium nitride layer is formed as a chromium compound layer on the surface, and the difference in coefficient of thermal expansion between the base material and the like is formed. It is possible to form a precipitation layer in which chromium nitride is precipitated in the base metal in order to alleviate the above.
This metal product has extremely high hardness, excellent heat resistance and corrosion resistance, and exhibits excellent performance in environments such as high-temperature oxidation, high-temperature corrosion, erosion, and cavitation. In addition, the above metal products exhibit excellent performance in an acid / alkali environment, a neutral environment, and a corrosive environment such as chloride such as seawater. Then, the metal product can be applied to parts that require heat resistance and wear resistance in a turbocharger, for example, in the case of automobile parts. Further, for example, in a mold used for die casting of aluminum, magnesium, zinc, etc., it prevents melting damage to the alloy and maintains excellent performance. In addition, it can be applied to many parts such as blade materials, valve materials, pump materials, etc. in the environment such as chemical industry, thermal power generation, and alternative energy. Further, it can be applied to materials and parts used in an acid / alkali environment, a neutral environment, and a corrosive environment such as chloride such as seawater.

The method for producing a metal product according to claim 4 is to perform a nitriding treatment on a base material which is an iron-based metal or a nickel-based metal by heating and holding the base material in an atmosphere containing a nitride source gas, and containing metallic chromium powder. Chromize treatment is performed in which the above-mentioned nitriding base material is present in the powder and is heated and held. As a result, a surface modification layer is formed on the surface of the base material. The surface modification layer is made to include a chromium compound layer existing on the surface side and a precipitation layer existing between the chromium compound layer and the base material. The precipitation layer has a structure in which a chromium compound is precipitated in the base metal metal constituting the base material.
Therefore, the coefficient of thermal expansion of each layer gradually increases from the surface to the deep part, with the chromium compound layer <precipitation layer <base material. Therefore, the difference in the coefficient of thermal expansion between the layers is smaller than that in the prior art in which the coefficient of thermal expansion greatly deviates between the chromium compound layer on the surface, the chromium-concentrated layer, and the base material. As a result, the surface layer has higher resistance to repeated thermal stress than before, and the heat resistance, corrosion resistance, and wear resistance of the surface layer can be maintained. The environment and applications that can be used are wider than before.

The method for producing a metal product according to claim 5 is a nitride layer having a thickness of at least 1.5 times or more the thickness of the chromium compound layer contained in the surface-modified layer finally formed by the nitriding treatment. To generate.
Thereby, the precipitation layer as described above can be surely formed.

In the method for producing a metal product according to claim 6, the chromaze treatment is carried out for a period of time during which the nitriding layer produced by the nitriding treatment has a predetermined thickness.
Thereby, the precipitation layer as described above can be surely formed.

It is a schematic diagram explaining the difference between a conventional product and this invention. It is a diagram which shows the element distribution state of the surface modification layer, (A) is Comparative Example 1, and (B) is Example 1. It is a cross-sectional photomicrograph of a surface layer portion, (A) is Comparative Example 1, and (B) is Example 1. It is a diagram which shows the cross-sectional hardness distribution of Comparative Example 1 and Example 1. FIG. It is an appearance observation photograph after a shot blast test, (A) is Comparative Example 1, and (B) is Example 1. It is an appearance observation photograph after the heating and cooling repeated test, (A) is Comparative Example 1, and (B) is Example 1. It is a cross-sectional micrograph of the surface layer part of Example 2. It is a diagram which shows the element distribution state of the surface modification layer of Example 2. It is an appearance observation photograph after a shot blast test using SUS329J4L which is a duplex stainless steel as a base material. It is an appearance observation photograph after repeated heating and cooling test using SUS329J4L which is a duplex stainless steel as a base material.

Next, a mode for carrying out the present invention will be described.

◆ is a ceramic layer Cr 2 _N layer Background of development surface, chromium-concentrated layer of the inside and a base material alloy layer at the interface of the ceramic layer and the alloy layer, the thermal expansion coefficient is deviated Is the root of the problem. That is, the chromium rich layer of the alloy layer present between the Cr 2 _N layer and the base material, there is no nitrogen. For this reason, the coefficient of thermal expansion at the above-mentioned layer interface deviates, and the resistance to repeated thermal stress is not sufficient.

Therefore, the alloy layer interposed between the Cr 2 _N layer and the base material, was recalled that precipitating chromium compound is a ceramic. That is, between the Cr 2 _N layer and the base material, to form a layer of the thermal expansion coefficient of the medium between the ceramic layer and the alloy layer. As a result, the dissociation of the coefficient of thermal expansion at the layer interface described above is alleviated, and the problem is solved.

Further, as the chromium compound, it is preferable to precipitate a chromium nitride instead of a carbide such as a chromium carbide. Nitride has a higher decomposition temperature than carbide and is hard to decompose even at high temperature when heated, so the performance to alleviate the deviation of the coefficient of thermal expansion of the precipitated layer does not deteriorate when used in a high temperature environment. Because it is effective.

FIG. 1 is a schematic view illustrating the difference between the above-mentioned conventional product and the present invention. (A) is a conventional product, and (B) is an invention of the present application.
As shown in FIG. 1 (A), conventional products, thermal expansion coefficient of the Cr 2 _N layer and chromium-concentrated layer (high-chrome alloy layer) is greatly different. Nitrogen does not exist in the chromium-enriched layer of the alloy layer, and the coefficient of thermal expansion deviates at the layer interface.
As shown in FIG. 1 (B), the present invention is, in the deposition layer is present nitrogen, toward the base material via deposition layer from Cr 2 _N layer (Cr 2 _N deposition layer), thermal expansion coefficient gradually Has changed to. The deviation of the coefficient of thermal expansion at the layer interface is alleviated.
In the diagram of the coefficient of thermal expansion in FIG. 1, the coefficient of thermal expansion increases toward the bottom of the vertical axis.

◆ Metal Product The metal product of the present embodiment includes a base material which is an iron-based metal or a nickel-based metal, and a surface modification layer formed on the surface of the base material.

[Base material]
An iron-based metal or a nickel-based metal is used as the base metal metal constituting the base metal.

As the iron-based metal, various steel materials and iron-based alloys can be used. Examples of the steel materials and iron-based alloys include carbon steel, alloy steel, nickel chrome steel, nickel chrome molybdenum steel, chrome steel, chrome molybdenum steel, manganese steel, tool steel, stainless steel, heat resistant steel, nitrided steel, and skin. Various steel types such as hardened steel can be applied.

A nickel-based alloy can be used as the nickel-based metal. As the nickel-based alloy, for example, an alloy having a nickel content of 50% by weight or more can be used. Specifically, nickel-copper type (Monel), nickel-chromium type (Inconel), nickel-molybdenum type (Hastelloy) and the like can be used.

As the base metal, it is particularly preferable to use any one of stainless steel, heat-resistant steel, and nickel-based alloy having a carbon concentration of 0.6% by weight or less. For example, ferritic stainless steels such as SUS410L and SUS430, martensitic stainless steels such as SUS410 and SUS420J2, two-phase stainless steels such as SUS821L1, SUS323L and SUS329J31, SUS329J3L, SUS329J4L and SUS327L1, SUS304, SUS316 and SUS310. Ferritic stainless steels such as SUH21 and SUH409, martensitic heat resistant steels such as SUH3 and SUH11, austenitic heat resistant steels such as SUH35 and SUH660, heat resistant cast steels such as SCH21 and SCH22, and nickel groups such as ALLOY625 and ALLOY800H. An alloy or the like can be preferably used.

Such a stainless steel, heat-resistant steel, and nickel-based alloy having high corrosion resistance that does not contain cementite in the base material are subjected to, for example, nitriding treatment to diffuse and permeate nitrogen atoms, and then chromium diffusion and permeation treatment. In order to form a chromium nitride layer as a chromium compound layer on the surface and alleviate the difference in thermal expansion coefficient between the base metal and the base metal, it is possible to form a precipitation layer in which chromium nitride is precipitated in the base metal. ..

[Surface modified layer]
The surface modification layer is composed of a chromium compound layer existing on the surface side and a precipitation layer existing between the chromium compound layer and the base material.

As will be described later, the surface modification layer can be formed on the surface of the base material by subjecting the base material to a nitriding treatment and a chromaze treatment. At this time, if necessary, a halogenation treatment is performed before the nitriding treatment.

[Chromium compound layer]
The chromium compound layer is formed by combining the nitrogen atoms of the nitride layer formed on the surface of the base metal by the above-mentioned nitriding treatment and the chromium atoms that have penetrated into the above-mentioned nitride layer by the above-mentioned chromizing treatment. The nitrided layer is an iron nitride layer on the surface and a nitrogen diffusion layer in the deep part thereof. The iron nitride layer on the surface may not be formed depending on conditions such as nitriding treatment.

Chromium compound constituting the chromium compound layer is preferably a Cr 2 _N. The chromium compound layer can be formed to a thickness of about 5 to 50 μm from the viewpoint of performance and economy.

[Precipitation layer]
The precipitation layer is formed by precipitating a chromium compound in the base metal metal constituting the base material.

The precipitation layer is formed by invading the nitrogen diffusion layer in which nitrogen atoms are diffused in the base metal by the above-mentioned nitriding treatment by the above-mentioned chromium treatment. That is, the chromium atom that has penetrated deeper than the chromium compound layer forms a chromium compound with the nitrogen atom existing in the nitrogen diffusion layer and precipitates. Since it is on the deeper side than the surface, the nitrogen atom concentration in the nitrogen diffusion layer is low, and the chromium compound does not form a layer as in the above-mentioned chromium compound layer, but the particulate chromium compound is precipitated.

By allowing the precipitation layer to exist between the chromium compound layer and the base material, the coefficient of thermal expansion of each layer increases sequentially from the surface to the deep part with the chromium compound layer <precipitation layer <base material. Therefore, the difference in the coefficient of thermal expansion between the layers becomes small. This increases the resistance of the surface layer to repeated thermal stresses.

It is preferable that the closer the precipitation layer is to the chromium compound layer on the surface side, the larger the precipitation amount of the chromium compound. In other words, it is preferable that the closer the precipitation layer is to the base material in the deep part, the smaller the precipitation amount of the chromium compound is.

Further, the chromium compound is preferably a chromium nitride, not a carbide such as a chromium carbide. Nitride has a higher decomposition temperature than carbide and is less likely to decompose even at high temperatures when heated, so the performance of mitigating the deviation of the coefficient of thermal expansion of the precipitated layer is less likely to deteriorate when used in a high temperature environment. Because.

That is, the nitrogen concentration of the precipitation layer is higher as it is closer to the chromium compound layer on the surface side, and is lower as it is closer to the base material in the deep part. By doing so, the coefficient of thermal expansion of the precipitation layer gradually increases from the surface toward the deep part. Therefore, the coefficient of thermal expansion between each layer gradually increases from the surface chromium compound layer toward the deep base material. This makes the surface layer more resistant to repeated thermal stresses. That is, peeling and cracking can be prevented by absorbing the strain generated by the thermal stress.

From the viewpoint of performance and economy, the precipitation layer can be formed to have a thickness of about 5 to 100 μm at a portion where the nitrogen concentration is 5 atomic% or more. A more preferable range of the thickness of the precipitation layer is 8 to 50 μm. Nitrogen infiltrated by nitriding treatment, not all is consumed to form the chromium compound layer surface (Cr 2 _N layer), a nitrogen concentration of nitrogen in the portion to be the deposition layer is 5 atom% or more The purpose is to leave it. As a result, nitrogen is combined with Cr whose concentration decreases toward the inside, Cr ₂ N whose precipitation amount decreases toward the inside is formed, and the precipitation layer of the present invention is formed. In such a precipitation layer, the hardness gradually decreases toward the inside.

[Effect of Embodiment]
The metal product of the above embodiment has the following effects.

The metal product of the present embodiment includes a base material which is an iron-based metal or a nickel-based metal, and a surface modification layer formed on the surface of the base material. The surface modification layer includes a chromium compound layer existing on the surface side and a precipitation layer existing between the chromium compound layer and the base material. That is, a precipitation layer exists between the chromium compound layer, which is a hard ceramic layer, and the base material, which is an iron-based or nickel-based metal. The precipitation layer is formed by precipitating a chromium compound in the base metal constituting the base material.
Therefore, the coefficient of thermal expansion of each layer gradually increases from the surface to the deep part, with the chromium compound layer <precipitation layer <base material. Therefore, the difference in the coefficient of thermal expansion between the layers is smaller than that in the prior art in which the coefficient of thermal expansion greatly deviates between the chromium compound layer on the surface, the chromium-concentrated layer, and the base material. As a result, the surface layer has higher resistance to repeated thermal stress than before, and the heat resistance, corrosion resistance, and wear resistance of the surface layer can be maintained. The environment and applications that can be used are wider than before.

In the metal product of the present embodiment, the closer the precipitation layer is to the chromium compound layer on the surface side, the larger the precipitation amount of the chromium compound.
As a result, the coefficient of thermal expansion of the precipitation layer gradually increases from the surface to the deep part. Therefore, the coefficient of thermal expansion changes continuously rather than stepwise from the chromium compound layer on the surface side to the base material. As a result, the surface layer has higher resistance to repeated thermal stress than before, and the heat resistance, corrosion resistance, and wear resistance of the surface layer can be maintained. The environment and applications that can be used are wider than before.

In the metal product of the present embodiment, the base material is any one of stainless steel, heat-resistant steel, and nickel-based alloy having a carbon concentration of 0.6% by weight or less.
By forming a surface modification layer containing two layers, a chromium compound layer and a precipitation layer, on such a base material, a metal product having excellent properties can be obtained. Stainless steels, heat-resistant steels, and nickel-based alloys having a carbon concentration of 0.6% by weight or less do not contain high concentrations of carbon such that cementite is present in the base material. Therefore, it is not possible to form an intermediate layer made of a carbide layer on the surface layer and a composite carbide of iron and Cr or the like inside the carbide layer only by performing the diffusion permeation treatment of chromium. For example, by performing nitriding treatment to diffuse and permeate nitrogen atoms, and then performing diffusion permeation treatment of chromium, a chromium nitride layer is formed as a chromium compound layer on the surface, and the difference in coefficient of thermal expansion between the base material and the like is formed. It is possible to form a precipitation layer in which chromium nitride is precipitated in the base metal in order to alleviate the above.
This metal product has extremely high hardness, excellent heat resistance and corrosion resistance, and exhibits excellent performance in environments such as high-temperature oxidation, high-temperature corrosion, erosion, and cavitation. In addition, the above metal products exhibit excellent performance in an acid / alkali environment, a neutral environment, and a corrosive environment such as chloride such as seawater. Then, the metal product can be applied to parts that require heat resistance and wear resistance in a turbocharger, for example, in the case of automobile parts. Further, for example, in a mold used for die casting of aluminum, magnesium, zinc, etc., it prevents melting damage to the alloy and maintains excellent performance. In addition, it can be applied to many parts such as blade materials, valve materials, pump materials, etc. in the environment such as chemical industry, thermal power generation, and alternative energy. Further, it can be applied to materials and parts used in an acid / alkali environment, a neutral environment, and a corrosive environment such as chloride such as seawater.

◆ Manufacturing Method of Metal Product In the manufacturing method of the metal product of the present embodiment, the base metal, which is an iron-based metal or a nickel-based metal, is subjected to nitriding treatment and chromaze treatment.
In the nitriding treatment, the base metal is heated and held in an atmosphere containing a nitriding source gas.
In the chromaze treatment, the nitrided base material is present in a powder containing metallic chromium powder and is heated and held.

Further, in the method for producing a metal product of the present embodiment, a halogenation treatment can be performed prior to the nitriding treatment.

[Halogenation treatment]
The halogenation treatment is performed by heating and holding the base metal in an atmosphere gas containing halogen using a heating furnace capable of controlling the atmosphere.

As the halogen used for the atmosphere gas, for example, _{a halogen gas such as F 2} , Cl ₂ , HCl, NF ₃ or a halide gas can be used.

As the atmospheric gas, a mixed gas containing 0.5 to 20% by volume of halogen and the balance being nitrogen gas, hydrogen gas, an inert gas or the like can be used.

The halogenation treatment activates the surface by heating and holding the base material at 200 to 550 ° C. for about 10 minutes to 3 hours in the atmospheric gas.

〔Nitriding treatment〕
In the nitriding treatment, if necessary, the halogenated base material is heated and held in an atmosphere containing a nitriding source gas.

As the nitriding treatment, any method of gas nitriding treatment, gas nitrocarburizing treatment, salt bath nitriding treatment, vacuum nitriding treatment, and ion nitriding (plasma nitriding) treatment can be applied.

The gas nitriding / gas nitrocarburizing is performed in an atmosphere of nitriding or soft nitriding, that is, in an atmosphere in which NH ₃ is used as a nitrogen source and N ₂ , CO, CO ₂ , H _{2 and the} like are mixed as necessary. This can be done by heating and holding the base metal that has been halogenated.

The salt bath nitriding can be performed by heating and holding the base metal in a salt bath containing cyanide or cyanic acid as a main component.

In ion nitriding (plasma nitriding), a glow discharge is generated by applying a DC voltage of several hundred volts with the furnace body as the anode and the object to be treated as the cathode in a nitrogen mixed gas atmosphere of 0.1 to 10 Pa. The ionized gas component is accelerated at high speed to collide with the surface of the object to be treated, which is heated and nitriding is promoted by a sputtering action or the like.

The heating temperature and holding time can be appropriately determined according to the nitriding method to be adopted and the characteristics of the target surface modification layer. For example, it can be heated and held at a predetermined temperature within the range of 350 to 900 ° C. (preferably 350 to 650 ° C.) for a predetermined time.

By the above nitriding treatment, a nitrogen diffusion layer having a high nitrogen concentration is formed on the surface layer portion of the base material. After that, by performing the chromium treatment, the chromium atom that diffuses and permeates by the chromium treatment and the nitrogen atom existing in the nitrogen diffusion layer are bonded to form a chromium nitride layer as a chromium compound layer.
When the soft nitriding treatment is performed as the above nitriding treatment, a carbon dioxide diffusion layer having a high nitrogen concentration and a high carbon concentration is formed on the surface layer portion of the base material. After that, by performing the chromium treatment, the chromium atom that diffuses and permeates by the chromium treatment is bonded to the nitrogen atom and the carbon atom existing in the carbon dioxide diffusion layer, and a chromium nitride layer is formed as a chromium compound layer.

In the metal surface modification method of the present embodiment, it is preferable to form a diffusion layer in which nitrogen is diffused at a nitrogen concentration of 10 atomic% or more and a thickness of 5 μm or more by the above nitriding treatment.

After the above nitriding treatment and before the chromaizing treatment, a treatment for normalizing the surface can be performed if necessary. As the normalization process, for example, a process such as shot peening or a barrel can be adopted.

The nitriding treatment, the chromium compound layer (Cr 2 _N layer) of at least 1.5 times or more the nitride layer having a thickness in the thickness of which is contained in the surface-modified layer which is finally formed (compound layer + diffusion layer There is) to generate.

[Chromaize processing]
In the chromaze treatment, the nitrided base material is present in a powder containing metallic chromium powder and is heated and held. By the chromium treatment, chromium atoms are diffused and permeated from the surface of the base metal after the nitriding treatment.

The chromaze treatment is performed only for a time when the nitriding layer (compound layer + diffusion layer) generated by the nitriding treatment has a predetermined thickness.
Thus, it is possible to form a deposition layer having a slope gradient of N and Cr in the inner side of the Cr 2 _N layer.

The chromaze treatment can be performed by the powder packing method. The powder pack method is
This is performed by burying the base metal that has been subjected to the nitriding treatment in the treatment agent powder filled in the heat-resistant case, placing the heat-resistant case in an atmosphere furnace, and heating and holding the heat-resistant case while flowing a gas for promoting the reaction. By doing so, the chromium atoms are treated so as to diffuse and permeate from the surface of the base metal after the nitriding treatment.

As the treatment agent powder, a metal chromium powder or an iron-chromium alloy powder, an Al ₂ O ₃ powder for preventing sintering, and a powder agent to which a small amount _{of NH 4} Cl or NH ₄ F for promoting a reaction is added are used. Can be done.

As the gas for promoting the reaction, H ₂ or Ar can be used.

Heat holding is held at a predetermined temperature within the range of 850 to 1200 ° C. (preferably 900 to 1200 ° C.) for a predetermined time. By doing so, chromium atoms are diffused and permeated from the surface of the base metal after the nitriding treatment to form a surface modification layer.

[Surface modified layer]
In the method for producing a metal product of the present embodiment, a surface modification layer is formed on the surface of the base material by subjecting the above-mentioned base material to a nitriding treatment and a chromaze treatment.
As described above, the surface modification layer includes a chromium compound layer existing on the surface side and a precipitation layer existing between the chromium compound layer and the base material. The precipitation layer is formed by precipitating a chromium compound in the base metal constituting the base material.

Chromium compounds to form the chromium compound layer is preferably a Cr 2 _N. Here, the precipitation layer inside the _{Cr 2} N layer can be rephrased as the inclined structure layer of _{Cr 2 N.} Such a precipitated layer is thermodynamically not high enough to form _{Cr 2 N in layers.} However, there is a nitrogen concentration enough to precipitate partially Cr 2 _N. Also, if go further inward, amount of precipitation of Cr 2 _N decreases as the nitrogen concentration decreases. Finally, the nitrogen concentration becomes such that _{Cr 2 N cannot be precipitated.} In this manner, the deposition layer is than an inclined deposition layer of Cr 2 _N. Moreover, the Cr 2 _N is higher decomposition temperature than carbides, for difficult to decompose at high temperatures when heated, deterioration in performance to mitigate the divergence of the thermal expansion coefficient of the deposited layer when used in a high temperature environment This is because it is difficult to do.

[Effect of Embodiment]
The method for producing a metal product of the above embodiment has the following effects.

In the method for producing a metal product of the present embodiment, a base material which is an iron-based metal or a nickel-based metal is subjected to a nitriding treatment in which the base material is heated and held in an atmosphere containing a nitride source gas, and a powder containing metal chromium powder is performed. Chromize treatment is performed in which the above-mentioned nitriding base material is present and held by heating. As a result, a surface modification layer is formed on the surface of the base material. The surface modification layer is made to include a chromium compound layer existing on the surface side and a precipitation layer existing between the chromium compound layer and the base material. The precipitation layer has a structure in which a chromium compound is precipitated in the base metal metal constituting the base material.
Therefore, the coefficient of thermal expansion of each layer gradually increases from the surface to the deep part, with the chromium compound layer <precipitation layer <base material. Therefore, the difference in the coefficient of thermal expansion between the layers is smaller than that in the prior art in which the coefficient of thermal expansion greatly deviates between the chromium compound layer on the surface, the chromium-concentrated layer, and the base material. As a result, the surface layer has higher resistance to repeated thermal stress than before, and the heat resistance, corrosion resistance, and wear resistance of the surface layer can be maintained. The environment and applications that can be used are wider than before.

Next, the examples will be described together with the comparative examples.

[Comparative Example 1]
FIG. 2A shows the elemental distribution of the surface modified layer formed by subjecting the SUS304 base material to fluorine treatment, nitriding treatment and chromaze treatment under the following conditions.
◎ Fluorine treatment Atmosphere: Fluorine-based gas (NF ₃ : 10 vol% + N ₂ : 90 vol%)
Temperature: 300 ° C
Time: 15 minutes ◎ Nitriding treatment Atmosphere: NH ₃ : 50 vol% + N ₂ : 50 vol%
Temperature: 570 ° C
Time: 30 minutes ◎ Chromize treatment Treatment agent: Powdered Cr or Fe-Cr alloy to which a required amount _{of Al 2} O ₃ _{for preventing sintering is added and a small amount of NH 4} Cl for reaction promotion is added. Air flow: Hydrogen Or argon airflow Temperature: 1050 ° C
Time: 10 hours

[Example 1]
FIG. 2B shows the elemental distribution of the surface modified layer formed by subjecting the SUS310S base material to a fluorine treatment, a nitriding treatment, and a chromaze treatment under the following conditions.
◎ Fluorine treatment Atmosphere: Fluorine-based gas (NF ₃ : 10 vol% + N ₂ : 90 vol%)
Temperature: 400 ° C
Time: 60 minutes ◎ Nitriding treatment Atmosphere: NH ₃ : H ₂ : N ₂ = 30:20:50
Temperature: 590 ° C
Time: 20 hours ◎ Chromize treatment Treatment agent: Metal Cr grains or Fe-Cr alloy grains + Al ₂ O ₃ for anti-sintering + Small amount NH ₄ Cl for reaction promotion
Airflow: Hydrogen or Argon Temperature: 1050 ° C
Time: 2 hours

In each case, a layer having a high concentration of Cr and N and a low concentration of Fe is formed at a thickness of about 10 to 20 μm on the surface side. This can be regarded as a chromium nitride layer. The chromium nitride layer contains about 80% by weight of chromium and about 10% by weight of nitrogen as measured by the weight concentration ratio shown in FIG. 2 (A). Further, in the measurement of the atomic number concentration ratio in FIG. 2B, chromium is about 60 atomic% and nitrogen is about 30 atomic%. This allows identified as Cr ₂ N. Further, a layer having a high concentration of Fe and Cr is formed at a thickness of about 10 to 60 μm on the lower side thereof. This is a chromium-enriched layer in which chromium is diffused and permeated into the base material. The surface in FIG. 2A is the position where Cr and N rise.

Comparative Example 1 is nitrogen in the high Cr concentration layer underlying the Cr 2 _N layer has not been detected, are not substantially nitrogen present.
Example 1 above, under the Cr 2 _N layer, a layer of graded composition of Cr concentration and N concentration decreases gradually exists. The layer having this inclined composition is the precipitation layer of the present invention.

FIG. 3A is a cross-sectional micrograph of the surface layer portion of Comparative Example 1.
FIG. 3B is a cross-sectional micrograph of the surface layer portion of Example 1 above.
Comparative Example 1, Cr 2 _N layer on the surface, the interface of the high-Cr diffusion layer and the base material are clearly observed.
Example 1, the interface of the deposited layer and the base material with Cr 2 _N layer and under it, not clearly observed as compared to Comparative Example 1.

FIG. 4 shows the results of measuring the cross-sectional hardness of Comparative Example 1 and Example 1.

In Comparative Example 1, the hardness is as high as MHv1500 or more at about 10 μm from the surface, but the hardness is sharply lowered to about MHv500 or less at a depth of 20 μm or more from the surface. Nitrogen is not substantially present in this portion, substantially free even precipitation of Cr 2 _N.

In Example 1, a layer having a high hardness of about 20 μm is present from the surface, and a hardness gradient layer is formed in which the hardness gradually decreases from about MHv1400 to about MHv500 or less toward the base material side. That is, about 20 μm from the surface is a chromium compound layer having the hardness of the chromium compound layer, and a portion having a depth of about 50 μm or more from the surface is the base material layer having the hardness of the base material. It is a hardness gradient layer between the material layers, but the hardness gradually decreases.

In the hardness gradient layer, the chromium concentration and the nitrogen concentration are gradually decreased. At least 5 atomic% or more nitrogen atoms is combine with chromium Cr 2 _N by Kuromaizu process performed at 850 ° C. or higher. Therefore, under the Cr 2 _N layer, a layer of chromium concentration and the nitrogen concentration decreases gradually is formed. This layer is a deposition layer of the present invention that Cr 2 _N is the precipitation amount toward the base material side dispersed precipitates is gradually reduced.

Next, a test was conducted in which an impact force by shot blasting (glass powder: 0.4 MPa) was applied to the surfaces of Comparative Example 1 and Example 1.

FIG. 5A is an appearance observation photograph of Comparative Example 1 after shot blasting was performed for 10 seconds.
FIG. 5B is an appearance observation photograph of Example 1 after shot blasting was performed for 30 seconds.
On the surface of Comparative Example 1, a large number of peelings caused by the impact of shot blasting occurred in the portions indicated by some arrows as an example.
No such peeling or cracking occurred on the surface of Example 1.

Further, a test was carried out in which heating and cooling from 1000 ° C. to room temperature were repeated 100 times.
FIG. 6A is an appearance observation photograph of Comparative Example 1.
FIG. 6B is an appearance observation photograph of Example 1.
On the surface of Comparative Example 1, in addition to a large number of peelings occurring in the portions indicated by some arrows as an example, cracks such as the circled portions also occurred.
No such peeling or cracking occurred on the surface of Example 1.

[Example 2]
As Example 2, SUS329J4L, which is a duplex stainless steel, was used as a base material and subjected to fluorine treatment, nitriding treatment and chromaze treatment under the following conditions.
◎ Fluorine treatment Atmosphere: Fluorine-based gas (NF ₃ : 10 vol% + N ₂ : 90 vol%)
Temperature: 400 ° C
Time: 60 minutes ◎ Nitriding treatment Atmosphere: NH ₃ : H ₂ : N ₂ = 30:20:50
Temperature: 590 ° C
Time: 20 hours ◎ Chromize treatment Treatment agent: Metal Cr grains or Fe-Cr alloy grains + Al ₂ O ₃ for anti-sintering + Small amount NH ₄ Cl for reaction promotion
Airflow: Hydrogen or Argon Temperature: 1050 ° C
Time: 5 hours

FIG. 7 is a cross-sectional micrograph of the surface layer portion of Example 2.
Example 2 also, on the inner side of the Cr 2 _N layer have increases and N concentration, the austenite phase is stabilized, precipitation of the σ layer is not observed.

FIG. 8 is a diagram showing the element distribution state of the surface modification layer of Example 2.
Example 2 also, be graded composition region is formed as going inside the Cr 2 _N layer clearly seen.

If the two-phase stainless steel such as SUS329J4L, in the conventional processing techniques, sigma layer is deposited on the high-Cr alloy layer of the inner surface layer of Cr ₂ N layer. Therefore, the corrosion resistance when the has occurred peeling the Cr 2 _N layer is a danger of degradation is concerned.

In Example 2, it can be seen that the SUS329J4L ferritic stainless steel has a structure in which precipitation of the σ phase is suppressed and peeling is difficult.
FIG. 9 is an appearance observation photograph after performing a shot blast test (glass powder: 0.4 MPa × 30 seconds) in Example 2 above.
FIG. 10 is an appearance observation photograph after performing a test in which heating and cooling from 1000 ° C. to room temperature is repeated 100 times in Example 2.
In this case as well, no peeling or cracking occurred.

Table 1 below shows the treatment conditions, the thickness of each treatment layer, and the presence or absence of peeling or cracking in Examples 1 to 8 and Comparative Examples 1 to 4. The atmosphere of the fluorinated treatment is a fluorine-based gas (NF ₃ : 10 vol% + N ₂ : 90 vol%), and the atmosphere of the nitriding treatment is NH ₃ : H ₂ : N ₂ = 30:20: It is 50, and the comparative example is NH ₃ : N ₂ = 50:50.

For deposit thickness shown in Table 1, although the interface of the deposited layer and the base material in the underlying Cr ₂ N layer is not clear in the present invention, the hardness of Cr ₂ N layer becomes MHv1400 or more, MHv1400 since following MHv500 more regions of Cr 2 _N is in the dispersed precipitated hardness is increased hardness gradient layer, to identify the thickness of MHv500 ~ 1400 from a cross-sectional hardness measurement results, expressed as the deposition layer thickness It was done. In the comparative example, although the precipitation layer of the present invention does not exist, the thickness of MHv500 to 1400 is similarly specified and described from the cross-sectional hardness measurement result.

Further, as shown in Table 1, in Examples 1 to 8, the thickness of the nitrided layer (compound layer + diffusion layer) formed by the nitriding treatment is the surface modified layer finally formed. it is at least 1.5 times the thickness of the thickness of the chromium compound layer (Cr 2 _N layer) contained. On the other hand, in Comparative Examples 1-4, nitride layer thickness formed by the nitriding treatment, is 1.5 times or less the thickness of the finally formed by the chromium compound layer (Cr 2 _N layer).

By providing a graded composition of summary Cr 2 _N between the Cr 2 _N layer and the base material ◆, as shown in FIG. 1, absorbing the difference in thermal expansion coefficients of the interface between the Cr 2 _N layer and the base material However, the generated thermal stress is reduced.
From the above, it is clear that the treatment of the present application has significantly improved resistance to peeling and cracking due to thermal stress and impact force.

Modification Examples Although the particularly preferable embodiments of the present invention have been described above, the present invention is not limited to the embodiments shown, and can be modified into various embodiments, and the present invention is various modifications. The purpose is to include an example.

Claims

A base material which is an iron-based metal or a nickel-based metal and a surface modification layer formed on the surface of the base material are provided.
The surface modification layer is
The chromium compound layer existing on the surface side and
A metal product that exists between the chromium compound layer and the base metal, and is composed of a precipitation layer in which a chromium compound is precipitated in the base metal constituting the base metal.
The metal product according to claim 1, wherein the deposition amount of the chromium compound increases as the precipitation layer is closer to the chromium compound layer on the surface side.
The metal product according to claim 1 or 2, wherein the base material is any of stainless steel, heat-resistant steel, and nickel-based alloy having a carbon concentration of 0.6% by weight or less, and the chromium compound is a chromium nitride. ..
For base metal that is iron-based metal or nickel-based metal
Nitriding treatment is performed to heat and hold the base metal in an atmosphere containing a nitriding source gas.
By performing a chromaze treatment in which the above-mentioned nitriding base material is present in a powder containing metallic chromium powder and heat-held.
On the surface of the above base material,
The chromium compound layer existing on the surface side and
It is characterized by forming a surface modification layer that exists between the chromium compound layer and the base metal and is composed of a precipitation layer in which a chromium compound is precipitated in the base metal constituting the base metal. The manufacturing method of metal products.
The production of the metal product according to claim 4, wherein the nitriding treatment produces a nitriding layer having a thickness of at least 1.5 times or more the thickness of the chromium compound layer contained in the finally formed surface modification layer. Method.
The method for producing a metal product according to claim 5, wherein the chromaze treatment is performed for a time during which the nitriding layer produced by the nitriding treatment reaches a predetermined thickness.