JP6274530B2 - Metal substrate surface treatment method - Google Patents

Description

  The present invention relates to a surface treatment method for a metal substrate. In particular, the present invention relates to a surface treatment method for performing calorizing treatment on a metal substrate in an air atmosphere.

  Surface treatment is performed in order to impart new characteristics (abrasion resistance, heat resistance, corrosion resistance, etc.) to the metal substrate or to improve the surface characteristics. As one of such surface treatments, calorizing treatment for forming an aluminum diffusion layer on the surface of the Fe-based material is performed (for example, see Patent Documents 1 and 2).

In the calorizing treatment, an object to be treated (Fe-based material) is embedded in a mixed powder of Fe—Al alloy powder and ammonium chloride powder and heated to about 900 to 1050 ° C. By heating, Al and Cl react to generate AlCl ₃ vapor, which comes into contact with the surface of the object to be processed, and the Fe and Al of the object to be processed are replaced, and Al diffuses into the object to be processed. To do. As a result, an aluminum diffusion layer made of an Fe—Al alloy is formed. Since this Fe—Al alloy is excellent in wear resistance, heat resistance, oxidation resistance, and the like, such excellent characteristics can be imparted to the workpiece.

JP 2007-17029 A JP 2000-141012 A

  However, in the calorizing process, the container filled with the object to be processed and the mixed powder is sealed or semi-sealed and heat-treated in a reducing atmosphere or in a vacuum. Therefore, there is a problem that the cost is high because the container sealing process, the atmosphere adjustment at the time of heating, and the like are required.

  The reason why the container is sealed or semi-sealed and heat treatment is performed in a reducing atmosphere or vacuum is to prevent oxidation of the Fe-Al alloy powder in the object to be processed and the mixed powder and solidification of the mixed powder.

  In the calorizing process, if the object to be processed and the Fe—Al alloy powder are oxidized, it is difficult to form an aluminum diffusion layer and it is difficult to modify the surface of the object to be processed. Further, when the mixed powder is solidified, there is a problem that it is difficult to recover the object to be processed embedded in the mixed powder.

  The present invention has been made in view of the above circumstances, and a low-cost surface treatment method for a metal substrate that can sufficiently form an aluminum diffusion layer on a metal substrate that is an object to be processed even when the calorizing treatment is performed in an air atmosphere. The purpose is to provide in.

  Since the treatment agent (mixed powder of Fe-Al alloy powder and ammonium chloride powder) used for the calorizing treatment is powdery, there are voids between the particles, so to speak, it is in a porous state. Therefore, when such a treatment agent in a porous state is oxidized, it is considered that it is oxidized in a porous state (where voids exist). On the other hand, if the oxidation of the treatment agent proceeds excessively, it is considered that the particles adhere to each other and the entire treatment agent is solidified.

  However, when the present inventors heat a container filled with an object to be processed and a processing agent in an air atmosphere, surprisingly, only the surface of the powdered processing agent is oxidized in the initial stage of heating, resulting in a dense structure. It was found that a thick film was formed.

  This dense film is formed at the interface between the treatment agent and the atmosphere, and blocks the entry of the atmosphere into the treatment agent. In other words, at least the object to be processed and the treatment agent present in the vicinity thereof are sealed by the film. As a result, it has been found that the object to be processed (metal base material) and the processing agent embedded in the processing agent are not oxidized by oxygen in the atmosphere, and can be calorized even in an air atmosphere. Obtained.

  The present invention has been made by solving the above problems based on such knowledge.

That is, the aspect of the present invention is
(1) A preparation step of preparing a container in which a metal base material contains Fe-Al alloy powder and ammonium chloride powder and is embedded in a treatment agent not containing alumina powder and filled inside the container;
A calorizing treatment step of heating the container and forming an aluminum diffusion layer on a surface layer portion of the metal substrate,
The calorizing treatment step is performed in an air atmosphere, and before forming the aluminum diffusion layer, a dense film is formed at the interface between the treatment agent and the air, and the metal substrate surface treatment method is characterized in that It is.
(2) The metal substrate surface treatment method according to (1), wherein the dense film contains alumina obtained by a reaction between aluminum contained in the treatment agent and oxygen in the atmosphere. .
(3) In the calorizing treatment, the metal substrate surface treatment method according to (1) or (2), wherein a maximum temperature during heating is in a range of 650 to 1000 ° C.
(4) The metal substrate according to any one of (1) to (3), wherein in the preparation step, the container filled with the metal base material and the treatment agent is sealed or semi-sealed. This is a surface treatment method for a material.
(5) The metal substrate surface treatment method according to any one of (1) to (4), wherein the container is a casing of a heating furnace.
(6) The metal substrate surface treatment method according to any one of (1) to (4), wherein the container is a crucible.
(7) If the total amount of the treatment agent is 100% by mass, the proportion of the Fe—Al alloy powder is 85 to 99.9% by mass, according to any one of (1) to (6) This is a surface treatment method for a metal substrate.
(8) The surface treatment method for a metal substrate according to any one of (1) to (7), wherein the metal substrate is an Fe-based material.

  ADVANTAGE OF THE INVENTION According to this invention, even if it performs calorizing processing in air | atmosphere atmosphere, the surface treatment method of the metal base material which can fully form an aluminum diffusion layer in the metal base material which is a to-be-processed object can be provided at low cost. .

FIG. 1 is a schematic diagram for explaining a method of filling a container with a workpiece and a treatment agent in the surface treatment method according to the present embodiment. FIG. 2 is an enlarged view of a portion II in FIG. 1 and is a schematic diagram for explaining a mechanism by which a dense film is formed on the surface of the treatment agent. FIG. 3 is a schematic diagram for explaining a place where a dense film is formed when a horizontal heating furnace is used as a container in the surface treatment method according to the present embodiment. FIG. 4 is a schematic diagram for explaining a method of filling an object to be processed and a processing agent into a container when a horizontal heating furnace is used as the container in the surface treatment method according to the present embodiment. FIG. 5 is a metal micrograph and SEM photograph of a sample cross section according to an example of the present invention. FIG. 6 is a metal micrograph and SEM photograph of a sample cross section according to an example of the present invention.

Hereinafter, the present invention will be described in detail in the following order based on embodiments shown in the drawings.
1. 1. Surface treatment method of metal substrate 1-1 Preparatory step 1-2 Calorizing treatment step 1-3 Metal substrate after surface treatment Effect of the present embodiment 3. Modified example

(1. Surface treatment method of metal substrate)
In the metal substrate surface treatment method according to the present embodiment, a calorizing treatment is performed in an air atmosphere on a metal substrate made of an Fe-based material. Hereinafter, the surface treatment method will be specifically described.

(1-1 Preparation process)
First, a metal substrate that is an object to be calorized is prepared. The metal substrate is composed of an Fe-based material or a Ni-based material, and in this embodiment, the metal substrate is an Fe-based material. The Fe-based material may be composed of Fe and inevitable impurities, or may be a material mainly composed of Fe. In addition to Fe, the Fe-based material may contain known alloy elements such as C, Cr, and Ni. Moreover, the metal base material 1 has various shapes according to the use for which the metal base material is used, and is not particularly limited.

Subsequently, as shown in FIG. 1, the prepared metal substrate 1 is used as a container so as to be embedded in a treatment agent 5 having a mixed powder of Fe—Al alloy powder and ammonium chloride (NH ₄ Cl) powder. Is filled in the casing 10 (core tube) of the heating furnace. “Embed the metal substrate in the treatment agent” means that the metal substrate 1 is treated with the treatment agent 5 so that the entire surface of the metal substrate 1 is covered with the treatment agent 5 in the housing 10. This means placing it inside. The volume ratio occupied by the processing agent and the object to be processed with respect to the inside of the filling container is not particularly limited as long as the volume occupied by the atmosphere is secured to some extent.

  The material of the container may be any material that is less likely to be oxidized than the Fe—Al alloy, but various materials can be used because the Fe—Al alloy easily reacts with oxygen. For example, an Fe-based material may be used. In addition, since a processing agent expand | swells at the time of the calorizing process mentioned later, it is preferable that it is a material which has the intensity | strength of the grade which is not damaged by the expansion | swelling. In this embodiment, it is preferable to be comprised from oxide ceramics, and the alumina, mullite, etc. which are used as a refractory material are illustrated.

  In this embodiment, after filling the metal base material 1 and the treatment agent 5, the opening of the housing 10 is closed with glass wool 20 or the like to make the inside of the housing 10 semi-sealed. The “semi-sealed state” refers to a state in which airtightness is maintained so that the temperature inside the housing can be kept uniform by heating in the calorizing process. By adopting such a semi-sealed state, air circulation between the outside of the housing and the inside of the housing is also restricted to some extent. As a result, the supply of oxygen to the inside of the casing is limited, and excessive oxidation of the surface of the treatment agent is unlikely to occur, which is preferable. Such a semi-sealed state can also be realized by placing a lid on the opening of the housing 10.

  The inside of the housing may be sealed. However, since the sealing process is costly, it is preferable that the housing be in a semi-sealed state that can be easily realized by using simpler means. Note that when the inside of the housing is sealed, the inside does not need to be in a vacuum state, and the housing may be sealed in the presence of the atmosphere. As will be described later, rather, a certain amount of oxygen needs to be present inside the housing.

In the present embodiment, the treatment agent only needs to have at least Fe—Al alloy powder and ammonium chloride (NH ₄ Cl) powder. As long as the effects of the present invention can be obtained, powders other than these powders may be included. However, when alumina powder is added, a dense film is not formed on the surface of the treatment agent as described later. The agent preferably does not contain alumina powder, and consists only of Fe—Al alloy powder and ammonium chloride (NH ₄ Cl) powder.

  Moreover, when the total mass of the whole processing agent is 100% by mass, the proportion of the Fe—Al alloy powder is preferably 85 to 99.9% by mass. By setting it in such a range, as will be described later, in the atmosphere during heating, a dense film can be formed on the surface of the treatment agent to the extent that the contact with the atmosphere inside the treatment agent and the object to be treated can be blocked it can.

  Furthermore, the proportion of Al in the Fe—Al alloy in the Fe—Al alloy powder may be a known proportion, and an example is a range of 10 to 90 mass%. By setting it as such a range, Al can be diffused efficiently.

(1-2 Calorizing treatment process)
Subsequently, the heating furnace filled with the metal substrate 1 and the treatment agent 5 is heated to perform calorizing treatment. At this time, the atmosphere inside the heating furnace is not adjusted and is set to an air atmosphere.

  As the heating proceeds, as shown in FIG. 2, Al in the Fe—Al alloy powder contained in the treatment agent 5 reacts with oxygen in the atmosphere 70 at the interface I between the treatment agent 5 and the atmosphere 70. At the interface I, an alumina film 5a having a predetermined thickness is formed. The alumina film 5a is formed as a dense oxide film so as to cover the entire interface.

  Specifically, the surface of the treatment agent powder having voids between particles is oxidized by oxygen in the atmosphere 70, and a dense oxide film 5a is formed on the entire interface I. That is, a portion that was porous to the extent that the atmosphere 70 can be circulated before the surface oxidation is dense enough to prevent the atmosphere 70 from entering the treatment agent 5 after the surface oxidation. It changes to 5a.

  By forming such a dense film 5a, a portion inside the dense film 5a becomes a sealed space cut off from the atmosphere 70. Since this sealed space is filled with the object to be processed and the processing agent present in the vicinity thereof, a normal calorizing process is performed as the heating proceeds. That is, Al diffuses in the surface layer portion of the object to be processed (metal base material) to form an aluminum diffusion layer.

  Although the detailed reason why the alumina film is formed as a dense film only on the surface of the treatment agent is unknown, it is considered that the Fe—Al alloy easily reacts with oxygen, the amount of oxygen in the container, and the like.

  The heating furnace is preferably a vertical type. That is, it is preferable that the opening of the heating furnace is in the vertical direction. As shown in FIG. 3, when the heating furnace is a horizontal type, since the opening is in the horizontal direction, the alumina film 5a is formed on the opening and the upper part of the heating furnace, so that the object to be processed is more than the case of the vertical type. This is because it becomes difficult to take out 1.

  In the present embodiment, the heating rate during heating is preferably in the range of 4 to 20 ° C./min until less than 500 ° C., and 500 ° C. or more is in the range of 1 to 18 ° C./min. It is preferable.

  In addition, the maximum temperature during heating is preferably 650 ° C. or higher, and more preferably 880 ° C. or higher, in order to sufficiently diffuse Al into the metal substrate. Further, from the viewpoint of preventing cracks generated in the formed aluminum diffusion layer, the maximum temperature during heating is preferably 1000 ° C. or less, and more preferably 900 ° C. or less.

  Furthermore, the holding time at the maximum temperature is preferably 6 hours or more and 20 hours or less in order to sufficiently diffuse Al into the metal substrate.

  Hold at maximum temperature for a predetermined time and then cool. From the viewpoint of preventing cracks generated in the aluminum diffusion layer, the cooling may be natural cooling or slow cooling. After cooling, the metal base material (object to be processed) subjected to calorizing treatment is taken out from the heating furnace. At this time, since the alumina film is formed on the surface of the treatment agent, it is removed. The treatment agent (mixed powder of Fe—Al alloy powder and ammonium chloride powder) inside the alumina film maintains a powder form and is not in a solidified state in which the powder particles are fixed to each other.

  Therefore, the metal substrate embedded in the treatment agent can be easily taken out despite the calorizing treatment in the air atmosphere. Furthermore, since the treatment agent after the calorizing treatment can be recovered as a powder, the treatment agent can be reused as a treatment agent for the calorizing treatment. By reusing the treatment agent, the cost required for the calorizing treatment can be further reduced.

(1-3 metal substrate after surface treatment)
As for the metal base material obtained by said surface treatment method, the aluminum diffusion layer is formed in the surface layer part. Since this aluminum diffusion layer is a layer formed by substituting a part of the metal element (for example, Fe) existing in the surface layer portion of the metal base material with Al, it is integrated with the metal base material. ing.

  The thickness of the aluminum diffusion layer may be measured based on a contrast difference between the metal substrate and the aluminum diffusion layer observed by an optical microscope or an electron microscope, or based on a predetermined element distribution measured by EPMA or the like. You may measure. Since the thickness of the aluminum diffusion layer substantially depends on the calorizing treatment conditions, the thickness may be controlled by changing the treatment conditions according to desired characteristics. In this embodiment, the thickness of the aluminum diffusion layer is about several μm to 100 μm.

  Further, the aluminum diffusion layer may be further observed as two layers of a surface layer and an intermediate layer in the direction (depth direction) from the aluminum diffusion layer toward the metal substrate. Both the surface layer and the intermediate layer are layers formed by diffusing Al. The difference between the surface layer and the intermediate layer is due to the difference in the degree of Al diffusion, the difference in crystal structure, and the like. Specifically, both layers are mainly composed of an Fe-Al alloy (intermetallic compound, solid solution, etc.), and the surface layer has a large amount of Al and is almost constant in the depth direction. In the intermediate layer, the abundance of Al decreases toward the metal substrate side. That is, in the depth direction, the abundance of Al tends to gradually decrease, and the aluminum diffusion layer has a gradient composition.

  The hardness of the intermediate layer indicates a value between the hardness of the surface layer and the hardness of the metal substrate, and the thermal expansion coefficient also indicates a value between the thermal expansion coefficient of the surface layer and the thermal expansion coefficient of the metal substrate. . Therefore, the intermediate layer can serve as a buffer between the surface layer and the metal substrate, and suppresses the occurrence of cracks due to the difference in hardness and thermal expansion coefficient between the surface layer and the metal substrate. Can do.

  In this embodiment, since the aluminum diffusion layer is an Fe—Al alloy, the hardness is higher than that of the metal base material as the base material, and the metal base material has excellent wear resistance. Further, in a high temperature environment, it reacts with oxygen in the atmosphere to form alumina on the surface of the aluminum diffusion layer, thereby providing excellent heat resistance and oxidation resistance to the metal substrate.

  Furthermore, when the aluminum diffusion layer has an intermediate layer, generation of cracks in the surface layer can be suppressed, and peeling of the surface layer can be suppressed.

(2. Effects of this embodiment)
In this embodiment, by heating a heating furnace filled with a metal base material to be processed and a processing agent, the surface of the processing agent is oxidized at the interface between the processing agent and the atmosphere, and dense alumina is obtained. A film is formed. Since the alumina film once formed blocks the entry of air, oxygen does not reach the object to be processed and the treatment agent disposed inside the alumina film. Therefore, the treatment object and the treatment agent present in the vicinity thereof are not oxidized, and Al is sufficiently diffused in the surface layer portion of the treatment object (metal substrate) even when the calorizing treatment is performed in the air atmosphere. be able to. As a result, it is possible to obtain a metal base material modified so that the surface layer portion has good wear resistance, heat resistance, oxidation resistance, and the like.

  In addition, unlike the conventional calorizing treatment, it is not necessary to adjust the atmosphere to a neutral or reducing atmosphere, and since it can be performed in the air, the apparatus and process for adjusting the atmosphere can be omitted. As a result, the cost required for the surface treatment of the metal substrate can be reduced.

  Furthermore, if the alumina film is removed when the workpiece is taken out after the calorizing treatment, the treatment agent is maintained in powder form without solidifying inside the alumina membrane, so that the workpiece can be easily taken out. Can do. Further, if the alumina film is removed, most of the treatment agent used for the calorizing treatment can be recovered as a powder as before the treatment, and can be reused as the treatment agent for the next calorizing treatment.

As described above, the effect of such an invention is to oxidize the surface of the powder in which voids exist between particles and to adopt a technique that cannot be easily conceived to form a dense film, Can be obtained. For example, by incorporating an alumina powder in the treatment agent, calorizing treated if, at temperatures calorizing process is performed, since the alumina powder is not sintered in dense state, as described above, the atmospheric intrusion It is impossible to form a film as dense as possible.

(3. Modified examples)
In the above-described embodiment, the object to be processed and the processing agent are filled into the casing (core tube) of the heating furnace, and the calorizing process is performed. The calorizing treatment may be carried out by placing it on the surface. The method of filling the crucible with the object to be processed and the treatment agent, the treatment agent to be used, etc. may be the same as in the above embodiment. “Crucible” refers to a container-like member configured to be filled with an object to be processed and a processing agent.

  When the heating furnace is a horizontal type, it is preferable to perform a calorizing treatment using a crucible as shown in FIG. 4 in order to facilitate removal of the object to be processed.

  In the above embodiment, calorizing treatment was performed in an air atmosphere, but by controlling the size of the container, the amount of the treatment agent, etc., the calorizing treatment is performed even in an atmosphere having a higher oxygen partial pressure than in the air atmosphere. It is considered possible.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the embodiment mentioned above at all, and can be variously modified within the range which does not deviate from the summary of this invention.

  Hereinafter, the present invention will be described based on further detailed examples, but the present invention is not limited to these examples.

  In the examples, a pipe made of SUS310S (outer diameter 27.2 mm × inner diameter 13.2 mm × length 10 mm) was used as the metal substrate. This metal substrate was placed in a vertical heating furnace together with the treatment agent. The inside of the heating furnace was filled with a treatment agent to a height of 180 mm, and a metal substrate was fixed and buried at a position where the height was 90 mm. The filling volume of the treatment agent and the object to be treated was about 80% with respect to the volume inside the heating furnace. Glass wool was disposed in the opening of the heating furnace. As a result, air was present inside the heating furnace, and the inside of the heating furnace was in a semi-sealed state by glass wool.

  As the treating agent, a mixed powder of 99.5% by mass of Fe—Al alloy powder and 0.5% by mass of ammonium chloride powder was used. Moreover, Al in the Fe—Al alloy powder was 50 mass%.

  Subsequently, the metal substrate was heated and calorized in an air atmosphere. The calorizing treatment conditions were 8 ° C./min until reaching 500 ° C., the rate of temperature increase from 500 ° C. to the maximum temperature was 3.75 ° C./min, and the maximum temperature and holding time are shown in Table 1. The cooling conditions were natural cooling.

  After the calorizing treatment, when the glass wool arranged at the opening of the heating furnace was removed, it was confirmed that the surface of the treatment agent was covered with a white film. The white film was removed, and the metal base material (SUS310S pipe) after the calorizing treatment was taken out of the heating furnace, and a sample was prepared as follows. First, the pipe was cut into an annular shape, the exposed cross section was cut into a fan shape, and the cross section was embedded in resin. This was polished and acid cleaned to prepare a sample.

  In addition, when the white film | membrane removed at the time of taking out was grind | pulverized and X-ray diffraction was performed, the peak resulting from an alumina was observed and it has confirmed that the said white film | membrane was comprised from the alumina.

  About the obtained sample, using a metal microscope (LV-100 manufactured by Nikon) and a scanning electron microscope (TM-300 manufactured by Hitachi High-Technology), a portion corresponding to the outer surface of the pipe and the vicinity thereof The thickness of the surface layer and the intermediate layer was measured based on the contrast difference in the observed image. The observation images are shown in FIGS. 5 and 6, and the thickness measurement results are shown in Table 1.

  Furthermore, about the surface layer, the intermediate | middle layer, and the metal base material part, micro Vickers hardness was measured using the microhardness tester (Akashi Seisakusho HM-124). The results are shown in Table 1.

  5 and 6, it was confirmed that the surface layer 1a as the aluminum diffusion layer was formed when the maximum temperature was 650 to 950 ° C. In particular, when the temperature was 750 to 950 ° C., it was confirmed that two layers of the surface layer 1a and the intermediate layer 1b as the aluminum diffusion layer were formed. Further, from Table 1, the Vickers hardness of the surface layer 1a and the intermediate layer 1b is higher than the Vickers hardness of the base material 1c, and the Vickers hardness of the intermediate layer 1b is equal to the Vickers hardness of the surface layer 1a and SUS310S (base material 1c). It was confirmed that it was between Vickers hardness. Therefore, it is considered that the occurrence of cracks in the surface layer 1a can be suppressed by the presence of the intermediate layer.

  In the surface treatment method according to the present invention, as described above, the calorizing treatment can be performed in an air atmosphere. Therefore, it is not necessary to use a device for adjusting the atmosphere, a vacuum device, or the like, and calorizing treatment can be performed at low cost. Further, since the treatment agent used for the calorizing treatment does not solidify after the treatment and can be recovered in a powder form, the treatment agent can be reused and the calorizing treatment can be performed at a lower cost.

1 ... Metal substrate (object to be treated)
DESCRIPTION OF SYMBOLS 1a ... Surface layer 1b ... Intermediate layer 1c ... Base material 5 ... Treatment agent 5a ... Dense film (alumina film)
DESCRIPTION OF SYMBOLS 10 ... Container or heating furnace housing | casing 20 ... Glass wool 30 ... Heat generating body 40 ... Crucible 41 ... Lid 70 ... Air | atmosphere

Claims (8)

A preparatory step of preparing a container in which the metal base material contains Fe-Al alloy powder and ammonium chloride powder and is embedded in a treatment agent not containing alumina powder and filled inside the container;
A calorizing treatment step of heating the container and forming an aluminum diffusion layer on a surface layer portion of the metal substrate,
The calorizing treatment step is performed in an air atmosphere, and before forming the aluminum diffusion layer, a dense film is formed at the interface between the treatment agent and the air, and the metal substrate surface treatment method is characterized in that .   The surface treatment method for a metal substrate according to claim 1, wherein the dense film includes alumina obtained by a reaction between aluminum contained in the treatment agent and oxygen in the atmosphere.   3. The surface treatment method for a metal substrate according to claim 1, wherein in the calorizing treatment, a maximum temperature during heating is in a range of 650 to 1000 ° C. 3.   The surface of the metal substrate according to any one of claims 1 to 3, wherein in the preparation step, the container filled with the metal substrate and the processing agent is sealed or semi-sealed. Processing method.   The surface treatment method for a metal substrate according to any one of claims 1 to 4, wherein the container is a casing of a heating furnace.   The surface treatment method for a metal substrate according to any one of claims 1 to 4, wherein the container is a crucible.   The metal according to any one of claims 1 to 6, wherein a ratio of the Fe-Al alloy powder is 85 to 99.9 mass% when a total amount of the treatment agents is 100 mass%. A substrate surface treatment method.   The surface treatment method for a metal substrate according to any one of claims 1 to 7, wherein the metal substrate is an Fe-based material.