Manufacturing method of sintered body

Abstract

To provide a method for producing a sintered body that can prevent the surface of the sintered body being oxidized with simple equipment.SOLUTION: A method for producing a sintered body includes a step for sintering a molding disposed on a belt in a belt furnace in a state where a cover disposed on the belt is put on the molding, the molding made from powder containing silicon element and iron element.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a sintered body. [Background technology]

[0002] A known method for producing sintered bodies is powder metallurgy, which involves filling a metal powder as raw material into a mold to produce a compact, followed by heat treatment and sintering the metal powder. Powder metallurgy is suitable for mass production of products of the same shape, and has been adopted as a method for producing sintered bodies of various shapes and materials. For example, Patent Document 1 describes the production of sintered parts by heat treating a compact formed from an alloy powder composition containing an alloy powder made of austenitic stainless steel.

[0003] Furthermore, Patent Document 2 describes a method for producing a sintered soft magnetic member by compacting an Fe alloy powder containing silicon and iron elements into a desired shape and sintering the resulting compact. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-37735 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-060830 Summary of the Invention [Problem to be solved by the invention]

[0005] When a sintered body is produced by powder metallurgy, if the surface of the sintered body is oxidized, it becomes impossible to perform a surface treatment such as a chemical conversion treatment on the sintered body in a later step, and there is a problem that the oxidized portion must be polished, cut, or the like in order to perform the surface treatment. In particular, as described in Patent Document 2, when a compact made from an Fe alloy powder containing silicon is heat-treated, there is a problem that the surface of the sintered body is easily oxidized.

[0006] Therefore, it is preferable to heat treat the molded body in an environment where the supply of oxygen to the molded body is suppressed, such as an inert gas atmosphere, a reduced pressure atmosphere, etc. However, since this makes the sintering equipment complicated and large, it is desirable to suppress the surface oxidation of the sintered body using simple equipment.

[0007] In view of the above circumstances, an object of the present disclosure is to provide a method for producing a sintered body that can suppress surface oxidation of the sintered body using simple equipment. [Means for solving the problem]

[0008] Specific means for solving the above problems include the following aspects. <1> A method for producing a sintered body, comprising a step of sintering a compact formed from a powder containing silicon and iron elements, the compact being placed on a belt in a belt furnace and covered with a cover placed on the belt. <2> The powder contains 1.5 mass % to 6.5 mass % of the silicon element, with the remainder being iron element and unavoidable impurities. <1> A method for producing the sintered body according to claim 1. <3> A method for producing a sintered body, comprising a step of sintering a compact, the compact being formed from a powder containing a component having an oxide formation energy of -300 kJ / mol or less, and placed on a belt in a belt furnace, while the compact is covered with a cover. <4> The content of the component in the powder is 1.5% by mass to 6.5% by mass. <3> A method for producing the sintered body according to claim 1. <5> The cover is made of ceramic or carbon. <1> ~ <4> 1. A method for producing a sintered body according to any one of the above. <6> The method further comprises the step of forming a coating on the surface of the sintered body obtained by sintering the green body. <1> ~ <5> 1. A method for producing a sintered body according to any one of the above. <7> The volume of the cover is 200% to 50,000% of the volume of the molded body. <1> ~ <6> 1. A method for producing a sintered body according to any one of the above. [Effects of the Invention]

[0009] According to the present disclosure, it is possible to provide a method for producing a sintered body that can suppress surface oxidation of the sintered body using simple equipment. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram for explaining a method for producing a sintered body according to the present disclosure. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments for carrying out the present invention will be described in detail. However, the present invention is not limited to the following embodiments. In the following embodiments, components (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and do not limit the present invention.

[0012] In the present disclosure, the term "process" includes not only a process that is independent of other processes, but also a process that cannot be clearly distinguished from other processes as long as the purpose of the process is achieved.

[0013] In the present disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in this disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples.

[0014] [Method for producing the sintered body according to the first embodiment] Regarding the method for producing a sintered body according to the present disclosure, a first embodiment of the method for producing a sintered body will be described. The method for producing a sintered body of the present disclosure includes a step of sintering a molded body formed from a powder containing silicon and iron elements, which is placed on a belt in a belt furnace, while the molded body is covered with a cover placed on the belt (hereinafter also referred to as the "sintering step").

[0015] In the manufacturing method of the present disclosure, a molded body formed from a powder containing silicon and iron elements is sintered while covered with a cover. This prevents surface oxidation of the resulting sintered body without the need for an environment that suppresses oxygen supply to the molded body, such as an inert gas atmosphere or a reduced-pressure atmosphere, during heat treatment of the molded body. Therefore, surface oxidation of the sintered body can be prevented using simple equipment without increasing the size or complexity of the equipment. Furthermore, because surface oxidation of the sintered body can be prevented by simple measures in a belt furnace, the manufacturing method of the present disclosure provides excellent productivity for sintered bodies.

[0016] Since silicon has a low oxide formation energy, it is thought that a molded body formed from a powder containing silicon and iron is prone to surface oxidation when heated. On the other hand, the manufacturing method of the present disclosure makes it possible to obtain a sintered body with reduced surface oxidation from this molded body using simple equipment.

[0017] Furthermore, in the manufacturing method of the present disclosure, oxidation of the sintered body is suppressed, and therefore the magnetic properties of the manufactured sintered body tend to be excellent.

[0018] <Sintering process> The manufacturing method of the present disclosure includes a sintering step in which a compact placed on a belt in a belt furnace is sintered while the compact is covered with a cover placed on the belt. Details of the belt furnace, compact, cover, etc. used in the sintering step, as well as details of the sintering conditions, etc. will be described below.

[0019] (belt furnace) The manufacturing method of the present disclosure uses a belt furnace equipped with a belt for transporting the compact and a heat treatment means for sintering the compact. The belt furnace can sinter the compact placed on the belt in a stationary or transported state. The belt may be a mesh belt. The configuration of the heat treatment device is not particularly limited, and a device with a general configuration can be used.

[0020] In the manufacturing method disclosed herein, the molded body is sintered while covered with a cover, and the supply of oxygen to the molded body is suppressed during heat treatment of the molded body, so the belt furnace may be an open furnace in which the inside of the furnace is not isolated from the outside air.

[0021] (Molded body) The molded body to be sintered in the manufacturing method of the present disclosure is molded from a powder containing silicon and iron. The method for obtaining the molded body from the powder is not particularly limited, and examples include a method in which the powder is filled into a mold and pressed. When filling the mold with the powder, the powder may be mixed with a lubricant, resin, etc.

[0022] The powder containing silicon and iron is not particularly limited, and may include, for example, an Fe alloy powder containing silicon and iron, or a mixed powder of Si powder containing silicon and Fe powder containing at least iron.

[0023] The powder containing silicon and iron may contain elements other than silicon and iron. The other elements are not particularly limited and include metal elements such as Al, Ni, Pb, Cu, Cr, Ti, Au, Ag, Co, Mg, Wo, Mo, Ta, and Nd, and non-metal elements such as P. The other elements may be one type or two or more types.

[0024] The powder containing elemental silicon and elemental iron preferably contains 1.5 mass % to 6.5 mass % of elemental silicon, with the remainder being elemental iron and unavoidable impurities. Furthermore, the powder containing silicon and iron preferably contains 1.5 mass % to 6.5 mass % silicon, no other elements or 2 mass % or less of other elements, with the remainder being iron and unavoidable impurities.

[0025] The particle size of the powder containing elemental silicon and elemental iron is not particularly limited, and may be, for example, in the range of 1 μm to 150 μm. In the present disclosure, particle size refers to the volume average particle size (D50) measured by a laser diffraction / scattering method.

[0026] When the powder containing silicon and iron elements includes the above-mentioned Fe alloy powder, Si powder, Fe powder, etc., the particle size of the Fe alloy powder may be in the range of 75 μm to 150 μm, the particle size of the Si powder may be in the range of 1 μm to 45 μm, and the particle size of the Fe powder may be in the range of 75 μm to 150 μm.

[0027] The shape of the compact may be adjusted appropriately depending on the sintered body to be produced, and examples thereof include the shapes of electronic parts, machine parts, automobile parts, etc.

[0028] (cover) In the manufacturing method of the present disclosure, the molded body placed on the belt is sintered while being covered with a cover. The shape, material, etc. of the cover are not particularly limited as long as it can cover the molded body placed on the belt. For example, the cover may be an open box-shaped member.

[0029] The cover is preferably made of ceramic or carbon from the viewpoint of heat resistance. Examples of ceramic include alumina, silica, zirconia, earthenware, and porcelain.

[0030] The volume of the cover is preferably 200% to 50,000% of the volume of the molded body in order to suitably cover the molded body and suitably suppress surface oxidation of the sintered body, and more preferably 500% to 2,500% in terms of productivity.

[0031] (Sintering conditions) The sintering conditions for sintering the compact are not particularly limited. The temperature for the heat treatment is not particularly limited and can be set depending on the size of the compact, the type of powder, etc. For example, the temperature may be in the range where the maximum temperature inside the belt furnace reaches 1100°C to 1200°C. The heat treatment time is not particularly limited and can be set depending on the size of the compact, the type of powder, etc. For example, the time required for the temperature inside the belt furnace to reach 1100° C. or higher may be in the range of 10 to 120 minutes.

[0032] The sintered body after the heat treatment is preferably cooled while covered with a tray in order to suitably suppress oxidation of the surface of the sintered body.

[0033] In the manufacturing method of the present disclosure, a plate-like member may be placed on a belt, and a molded body may be placed on the belt via the plate-like member. This plate-like member may also be a member for adjusting the shrinkage rate of the molded body (hereinafter also referred to as a "shrinkage rate adjusting member"). In this way, the volumetric shrinkage rate of the powder contained in the molded body when sintered is adjusted by the shrinkage rate adjusting member on which the molded body is placed. Therefore, even if the shrinkage rate of the molded body varies depending on the location, a sintered body with excellent dimensional accuracy can be obtained.

[0034] When the shape of a compact is asymmetrical from top to bottom, placing a shrinkage rate adjusting member on the belt can effectively improve the dimensional accuracy of the sintered body. Furthermore, in order to more effectively improve the dimensional accuracy of the sintered body obtained by heat-treating the compact, it is preferable that the shape of the compact be such that the area a of surface A, which is in contact with the shrinkage rate adjusting member, is larger than the area b of surface B, which is opposite surface A (a > b). When a compact with a shape that satisfies the relationship a > b is placed on a shrinkage rate adjusting member and sintered, the shrinkage of surface A, which is in contact with the shrinkage rate adjusting member, is relatively suppressed. This reduces the difference in the shrinkage rate of the compact between surface A and surface B, resulting in a product with excellent dimensional accuracy.

[0035] When the shape of the molded body satisfies the relationship a>b, the ratio of a to b is not particularly limited. For example, the value of a / b may be in the range of 1.1 to 5.

[0036] The method for adjusting the shrinkage rate of a molded article using a shrinkage rate adjusting member is not particularly limited. For example, the shrinkage rate may be adjusted by adjusting the surface roughness of the region where the shrinkage rate adjusting member contacts the molded article. For example, the surface roughness may be adjusted by forming scratches, protrusions, or the like on the surface of the shrinkage rate adjusting member, roughening it by etching, or the like.

[0037] The material of the shrinkage rate adjusting member is not particularly limited as long as it has heat resistance to the temperature of the heat treatment, and examples thereof include the material of the cover described above.

[0038] In the manufacturing method of the present disclosure, when the belt in the belt furnace is a mesh belt, it is preferable to place a plate-like member on the belt and place the molded body and cover on the plate-like member, which prevents oxygen from being supplied into the cover through the mesh belt when sintering the molded body, and thus effectively prevents surface oxidation of the sintered body.

[0039] For example, as shown in FIG. 1, it is preferable to place a plate-like member 3 on a mesh belt 1, and then place a molded body 4 and a cover 2 on the plate-like member 3, and then sinter the molded body 4 in this state.

[0040] The cooled sintered body may be subjected to post-treatments as needed, such as polishing, cutting, and the film-forming process in the film-forming step described below.

[0041] <Film formation process> The manufacturing method of the present disclosure may include a coating formation step in which a coating is formed on the surface of a sintered body obtained by sintering a compact. In the manufacturing method of the present disclosure, since surface oxidation of the sintered body is suppressed, a coating can be suitably formed on the surface of the sintered body without undergoing a step of removing the oxide coating by polishing, cutting, or the like.

[0042] In the coating formation step, a coating containing elemental phosphorus may be formed on the surface of the sintered body, which tends to improve the corrosion resistance of the sintered body under harsh conditions such as high temperature and high humidity. In the film forming step, the film may be formed by steam treatment (for example, black dyeing), zinc chromate treatment, electroless plating treatment, or the like.

[0043] Whether or not a coating containing elemental phosphorus is present on the surface of the sintered body can be determined by whether or not elemental phosphorus is present on the surface of the sintered body, specifically by a known method such as elemental analysis.

[0044] The method for forming a coating containing elemental phosphorus on the surface of the sintered body is not particularly limited, and may be, for example, a phosphate coating method, which is one of the chemical conversion treatments for sintered bodies. In the phosphate coating method, a sintered body is immersed in a liquid containing phosphate, and heated as necessary, whereby a coating can be formed on the surface of the sintered body by the phosphate coating method.

[0045] When a coating is formed on the surface of a sintered body by the phosphate coating method, the type of phosphate to be used is not particularly limited, and one or more types may be selected from manganese phosphate, zinc phosphate, calcium phosphate, etc.

[0046] The phosphorus-containing coating may contain an element contained in the phosphate used to form the coating, such as at least one element selected from the group consisting of manganese, zinc, and calcium.

[0047] The sintered body after the coating formation step may be subjected to post-treatments such as polishing, cutting, chemical conversion treatment, etc., as required.

[0048] [Method for producing sintered body according to the second embodiment] Next, a second embodiment of the method for producing a sintered body according to the present disclosure will be described. The method for producing a sintered body according to the present disclosure includes a step of sintering a molded body, which is formed from a powder containing a component whose oxide formation energy is -300 kJ / mol or less and placed on a belt in a belt furnace, while the molded body is covered with a cover. Below, the conditions that differ from those in the first embodiment of the method for producing a sintered body will be described, and a description of similar conditions will be omitted.

[0049] In the manufacturing method of the present disclosure, a molded body formed from a powder containing a component with an oxide formation energy of -300 kJ / mol or less (hereinafter also referred to as the "specific component") is sintered while covered with a cover. This makes it possible to suppress surface oxidation of the sintered body obtained without the need for an environment that suppresses the supply of oxygen to the molded body during heat treatment, such as an inert gas atmosphere or a reduced-pressure atmosphere. Therefore, surface oxidation of the sintered body can be suppressed using simple equipment without making the equipment complex or large.

[0050] The specific component preferably has an oxide formation energy of −300 kJ / mol or less, more preferably −550 kJ / mol or less, and may have an oxide formation energy of −1000 kJ / mol or more.

[0051] Specific components include silicon element (oxide formation energy: 650 kJ / mol) and titanium element (oxide formation energy: 750 kJ / mol).

[0052] The content of the specific component in the powder is preferably 1.5% by mass to 6.5% by mass. The powder containing the specific component may also contain iron element, the other elements mentioned above, and the like. [Example]

[0053] The above-described embodiment will be described in more detail below based on examples, but the present disclosure is not limited to the following examples.

[0054] Example 1 Powder having the composition shown below was filled into a mold and pressed to produce a cylindrical compact. (Powder composition) Fe...97.65% by mass Si...2 mass% P...0.35 mass%

[0055] An alumina plate was placed on the belt of a belt furnace that did not isolate the inside from the outside air, and the compact and cover (cover material: alumina) were placed on the alumina plate so that the cover covered the compact. The covered compact was then subjected to heat treatment (maximum temperature reached: 1160°C, time to reach 1100°C or higher: 30 minutes), and after the heat treatment, the sintered compact was cooled while still covered with the cover, and after cooling, the sintered compact was removed from the cover.

[0056] <Comparative Example 2> An alumina plate was placed on the belt of a belt furnace that did not isolate the inside from the outside air, and a molded body obtained in the same manner as in Example 1 was placed on the alumina plate. A sintered body was obtained in the same manner as in Example 1, except that the molded body was not covered with a cover.

[0057] (Elemental analysis of sintered body surface) The sintered bodies obtained in Example 1 and Comparative Example 1 were subjected to elemental analysis of the surfaces by energy dispersive X-ray spectroscopy (EDX). The amount of oxygen atoms on the surface of the sintered body in Example 1 was 4.5 mass %, while the amount of oxygen atoms on the surface of the sintered body in Comparative Example 1 was 31.4 mass %. This means that oxidation of the surface of the sintered body in Example 1 was more suppressed than in Comparative Example 1.

[0058] (Film formation treatment) When the sintered bodies of Example 1 and Comparative Example 1 were immersed in an aqueous solution of manganese phosphate (concentration: 30 to 50 (total acidity), 80°C to 100°C), a coating containing phosphorus was observed in the sintered body of Example 1, but no coating containing phosphorus was observed in the sintered body of Comparative Example 1.

[0059] (Compared to pusher furnace) The power consumption and production efficiency were compared between the case where a sintered body was produced by placing an alumina plate on the belt of a belt furnace as in Example 1 and the case where a sintered body was produced using a pusher furnace. In the method for producing a sintered body in Example 1, the amount of electricity per input amount of compact was approximately 30% to 40% lower than in the method for producing a sintered body using a pusher furnace. Furthermore, in the method for producing a sintered body in Example 1, the time required to produce a sintered body from the prepared green body was about half that required in the method for producing a sintered body using a pusher furnace. When using a pusher furnace, much time was required for stacking, setting up trays, etc.

[0060] As a result, compared to heat treatment of a molded body using, for example, a pusher furnace in an environment where the supply of oxygen to the molded body is suppressed, such as an inert gas atmosphere or a reduced pressure atmosphere, in Example 1, it is possible to suppress surface oxidation of the sintered body at low cost using simple equipment, with low energy consumption, and by improving manufacturing efficiency, etc. [Explanation of symbols]

[0061] 1... mesh belt, 2... cover, 3... plate-like member, 4... molded body

Claims

1. A plate-like member (excluding porous plate-like members) is placed on the belt in the belt furnace to adjust the shrinkage rate of the molded body. ) is arranged on the belt, and a molded body formed from a powder containing silicon and iron elements is arranged on the belt via the plate-like member, and the molded body is sintered in a state where the molded body is covered with a cover arranged on the belt, A method for producing a sintered body, wherein the area a of the surface A of the compact that contacts the plate-like member is larger than the area b of the surface B opposite to surface A.

2. 2. The method for producing a sintered body according to claim 1, wherein the powder contains 1.5 to 6.5 mass % of the silicon element, with the remainder consisting of iron element and unavoidable impurities.

3. 3. The method for producing a sintered body according to claim 1, wherein the cover is made of ceramic or carbon.

4. A method for manufacturing a sintered body described in any one of claims 1 to 3, wherein the plate-like member is an alumina plate.

5. The method for producing a sintered body according to any one of claims 1 to 4, further comprising the step of forming a coating on the surface of the sintered body obtained by sintering the green body.

6. The method for producing a sintered body according to any one of claims 1 to 5, wherein the volume of the cover is 200% to 50,000% of the volume of the compact.

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