Sintered body and method of manufacturing the same

Abstract

To provide a sintered body allowed to raise relative density together with reducing the manufacturing cost and a method of manufacturing the same.SOLUTION: A method of manufacturing a sintered body includes: a bottom-wall formed-portion forming step of forming a bottom-wall formed portion 110 by joining a predetermined point of a first material powder layer PL; a sidewall grid forming step of, for second and subsequent layers, forming a sidewall formed portion 120 and a grid formed portion 150 consisting of grid structure continuing to the sidewall formed portion 120, by repeating joining of material powder P toward vertical and horizontal directions from the bottom-wall formed portion 110; and a top-wall formed-portion forming step of forming a top-wall formed portion 130 to cover a top of the sidewall and grid formed portions 120, 150, thereby forming an outer-shell grid formed body 160 enclosing the material powder internally and carrying out a sintering step to sinter a powder formed body 100 consisting of the outer-shell grid formed body 160 and the material powder P.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a sintered body obtained by sintering a powder compact made of metal powder or the like into a three-dimensional object, and a method for producing the same. [Background technology]

[0002] A known additive manufacturing method involves alternately stacking raw powders (metal powders, alloy powders, or ceramic powders) onto a powder bed and bonding each layer of the raw powder into a predetermined shape to ultimately produce a three-dimensional object. One additive manufacturing method is the selective sintering method (Powder Bed Fusion, or PBF method), which repeatedly irradiates the raw powder with a laser beam or electron beam to directly sinter it, thereby bonding the sintered portions together to produce the desired three-dimensional object. Another method is the binder jet method, which prints a binder onto the raw powder to be stacked, forming a powder compact in which the raw powder and binder are bonded, and then sintering the powder compact to produce the three-dimensional object. The binder jet method has seen particularly rapid development and practical application in recent years due to its low equipment, raw material, and process costs and its efficient implementation (see Patent Documents 1 and 2, etc.).

[0003] When sintering a powder compact obtained by the binder jet method, i.e., a laminate of multiple powder layers, the powder compact is sintered to a high density due to solid-state diffusion of the metal powder and bonding of the powder at high temperatures. Normally, the density of a powder compact obtained by the binder jet method is about 50% (4 g / cm) in relative density. 3 ), but sintering increases the relative density to over 95%. Unless this level of sintered density is ensured, it is difficult to obtain industrially sufficient mechanical strength. However, when sintering relatively large parts weighing, for example, 1 kg to 80 kg, to a high density, higher temperature and longer sintering times are required compared to methods such as MIM (metal injection molding), which are used for small parts weighing 100 g or less.

[0004] During sintering, the larger the volume of the powder compact to be sintered, the greater the sintering energy required to achieve high density, resulting in enlarged crystal grains. As seen in Hall-Petch's law, sintered bodies with enlarged crystal grains exhibit reduced impact strength, strength, elongation, reduction of area, yield point, and other key mechanical properties. Therefore, sintered bodies made using the binder jet method require finer sintered structures.

[0005] The energy costs involved in sintering large parts are counter to the current trend towards sustainable technologies. However, the demand for binder jetting to manufacture large parts is increasing, which requires a manufacturing technique that allows for high density with low energy costs.

[0006] Conventional powder metallurgy methods have been said to produce parts weighing around 100g. However, binder jetting has made it possible to manufacture powder compacts of large parts weighing around 30kg. However, during the subsequent sintering process, the volume of the powder compact to be sintered is larger than conventional methods, resulting in greater shrinkage behavior during sintering. For example, there is a large difference in the amount of shrinkage between the surface placed on the setter (base plate) and the free surface. Therefore, to make the amount of shrinkage as uniform as possible, measures are taken, such as placing a buffer material made of the same material as the sintering powder material between the workpiece to be sintered and the ceramic setter. This absorbs the shrinkage at the bottom of the workpiece while reducing the difference in shrinkage between the top and bottom of the workpiece.

[0007] In view of the above circumstances, the present inventors have proposed a method for manufacturing sintered bodies that achieves high density, suppresses crystal grain enlargement, and reduces energy costs, while also reducing deformation associated with shrinkage during sintering of laminates caused by high-temperature sintering, thereby enabling the accurate production of larger sintered parts than conventional methods (Patent Document 3).

[0008] The method for manufacturing a sintered body disclosed in Patent Document 3 includes the steps of forming a powder compact containing a first powder for sintering by a binder jet method, forming a coating layer on the surface of the powder compact containing a second powder for sintering having an average particle size smaller than that of the first powder, performing primary sintering by heating the powder compact having the coating layer on its surface to sinter the coating layer made of the second powder to obtain a primary sintered body, and performing secondary sintering by HIP-treating the primary sintered body at a temperature lower than that used for the primary sintering to sinter the first powder to obtain a secondary sintered body. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-120475 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-522331 [Patent Document 3] Patent No. 7316434 Summary of the Invention [Problem to be solved by the invention]

[0010] Generally, when sintering powder compacts like those mentioned above, the binder burns at around 500°C, leaving behind carbides as combustion residue. After that, when the sintering temperature is reached and sintering begins, the carbides inhibit the growth of necks between the powder particles during the sintering process, causing a decrease in the relative density of the sintered compact.

[0011] The present invention aims to provide a sintered body and a method for manufacturing the same, which can further develop the above-mentioned method for manufacturing a sintered body, thereby simplifying the manufacturing process and reducing manufacturing costs, and further increasing the relative density. [Means for solving the problem]

[0012] In the technology described in Patent Document 3, a second powder is mixed with a resin solution to form a slurry, which is then applied to the surface of a molded body made of a first powder, dried, and sintered to form a high-density outer shell made of the second powder on the surface of the molded body. The inventors of the present invention have intensively studied whether such a series of steps can be simplified, and have come up with the idea of ​​forming an outer shell molded portion by bonding powder together instead of a high-density outer shell. In this case, there is a concern that an outer shell molded portion made solely of powder bonded with a binder may be deformed or damaged during transportation. Therefore, the inventors have further studied means for maintaining the shape of the outer shell molded portion.

[0013] The present invention was made based on the above-mentioned considerations, and is a method for manufacturing a sintered body by a three-dimensional additive manufacturing method in which raw material powder is discharged from a hopper onto a powder bed and supplied while falling naturally, and its surface is pressed to repeatedly stack it as a single raw material powder layer of a predetermined thickness, and each time a single raw material powder layer is formed, a portion of the raw material powder layer is bonded.The method for manufacturing a sintered body includes a bottom wall forming portion forming process in which predetermined portions of the first raw material powder layer are bonded to form a bottom wall forming portion, a side wall lattice forming process in which, from the second layer onwards, raw material powder is repeatedly bonded in the vertical and horizontal directions from the bottom wall forming portion to form a side wall forming portion and a lattice forming portion consisting of a lattice structure continuous with the side wall forming portion, and a top wall forming portion forming process in which a top wall forming portion that covers the side wall forming portion and the top of the lattice forming portion is formed to form an outer lattice forming body inside which the raw material powder is sealed, and a sintering process in which a powder forming body consisting of the outer lattice forming body and the raw material powder is sintered.

[0014] In the present invention, a three-dimensional powder compact is formed from an outer lattice compact and raw material powder. The outer lattice compact has a lattice portion that is continuous with a bottom wall portion, a side wall portion, and a top wall portion (hereinafter collectively referred to as the "outer wall portion"). The lattice portion maintains the shape of the powder compact. When this powder compact is sintered, neck growth occurs between the powder particles in the outer lattice compact, forming a sintered outer lattice portion. Meanwhile, the space outside the lattice portion contains raw material powder and voids. Sintering causes neck growth between the powder particles, shrinking the voids to form pores. Because there are no factors that inhibit neck growth, such as binders, during sintering of the raw material powder, an internal sintered portion with a high relative density can be obtained.

[0015] In this way, the present invention simplifies the process by sintering the outer lattice body and the raw material powder inside it in a single process, and also reduces material costs because no binder is present in the space inside the outer lattice body.

[0016] In the present invention, the binder jet method is preferably used as a molding method for the outer lattice molded body, but is not limited thereto, and any molding method can be used. For example, a three-dimensional additive manufacturing method such as selective laser sintering (SLS) can be used. In either molding method, since only raw material powder and voids exist in the space outside the lattice molded body, an internal sintered portion with a high relative density can be obtained.

[0017] Here, we will explain the effect of using the binder jet method to form the outer lattice compact. In this case, the raw material powder is sealed inside the outer lattice compact, which is made by binding the raw material powder with a binder. When this powder compact is sintered, the binder in the outer lattice compact burns off and disappears, and the raw material powder bonds to each other through neck growth between the powders, forming a sintered outer lattice portion. This sintered outer lattice portion consists of a dense structure containing carbides, which are the combustion residue of the binder, and pores.

[0018] On the other hand, the raw powder in the space outside the lattice molded portion does not contain a binder, so when this powder compact is sintered, neck growth between the powders proceeds unhindered, forming an internal sintered portion. This internal sintered portion consists of a dense structure and pores that do not contain carbides, which are the combustion residue of the binder. Therefore, the relative density of the internal sintered portion is higher than that of the outer sintered portion.

[0019] For example, the relative density of the outer sintered lattice portion is 94 to 97%, while the relative density of the inner sintered portion exceeds 97%. Furthermore, the relative density of the inner sintered portion can exceed 98% or even 99%. Because the outer sintered lattice portion has a relatively low relative density, it can be easily machined. Furthermore, by removing the outer sintered lattice portion, a sintered body consisting only of the inner sintered portion, which has an extremely high relative density, can be obtained.

[0020] In the present invention, the raw material powder is sealed (canned) by the outer lattice compact, so this powder compact can be subjected to HIP treatment as is. HIP treatment can be performed at a heating temperature of 900 to 1100°C and a pressurizing pressure of 80 to 120 MPa. This heating temperature is lower than the temperature used for normal metal sintering, and the raw material powder is subjected to high pressure from the outer lattice compact, resulting in effective compression solidification. This minimizes recrystallization in the internal sintered portion, achieving a density approaching 100%. A heating temperature of 950 to 1000°C for HIP treatment is more preferable. Furthermore, to prevent deformation or damage to the outer hull of the outer lattice compact during HIP treatment, the thickness of the outer hull portion of the outer lattice compact is preferably 100 μm or greater.

[0021] In the present invention, even if the sintered body is relatively large, for example, weighing about 30 kg, the densification achieved by HIP treatment is almost constant. Furthermore, because the HIP treatment compresses and solidifies the body at a relatively low temperature, distortion and deformation caused by different amounts of shrinkage at multiple locations, as occurs with conventional high-temperature sintering, are suppressed. Furthermore, it is now possible to produce irregularly shaped sintered bodies with the same quality as canned sintered bodies, which was previously difficult to achieve with the canning treatment.

[0022] Examples of raw material powders include metal powders and alloy powders, especially steel powder. The raw material powders vary depending on the desired sintered product. For example, if the product is a die, an alloy powder of alloy steel for hot die work, such as SKD61, can be used. If the product is a steel cast, high-tensile carbon steel cast iron, such as SCC material, can be used. Other examples include, but are not limited to, at least one of the metal and alloy powders commonly used in MIM, such as stainless steel and Inconel®, carbonyl iron powder, carbonyl nickel powder, nickel-based alloy powder, cobalt-based alloy powder, copper and copper alloy powder, aluminum and aluminum alloy powder, titanium and titanium alloy powder, magnesium and magnesium alloy powder, and ceramic powder. When using a binder jet molding method, water-atomized powders are suitable.

[0023] Next, the sintered body of the present invention comprises an internal sintered portion made of a sintered body of raw material powder, an external lattice sintered portion consisting of an external sintered portion covering the entire circumference of the internal sintered portion and a lattice sintered portion extending vertically and horizontally from the external sintered portion, the external lattice sintered portion being made of a dense structure and pores containing carbides, which are combustion residues of the binder, and the internal sintered portion being made of a dense structure and pores not containing carbides, which are combustion residues of the binder, and the internal sintered portion has a higher relative density than the external sintered portion.

[0024] When such a sintered body is used to form a gear, the surface of the gear is relatively soft, allowing the gears to fit together well, while the interior of the gear has a high relative density and is strong. Thus, the sintered body of the present invention is suitable for use in parts that come into sliding contact with mating parts, such as gears and guides that guide shafts. [Effects of the Invention]

[0025] According to the present invention, the shape of a powder compact, in which raw material powder is filled inside an outer lattice compact, is maintained, thereby preventing deformation or damage to the powder compact during transportation. Furthermore, a sintered body consisting of an outer lattice sintered portion and an inner sintered portion can be obtained in a single sintering process, thereby simplifying the manufacturing method. Furthermore, the sintered body manufactured in this manner has an inner sintered portion that is free of carbides and has a high relative density, resulting in excellent strength and hardness. [Brief explanation of the drawings]

[0026] [Figure 1] FIG. 1 is a perspective view of a sintered body according to an embodiment of the present invention. [Figure 2] FIG. 2 is a perspective side view of a sintered body according to an embodiment of the present invention. [Figure 3] FIG. 1 is a side view showing a lattice formed in an embodiment of the present invention. [Figure 4] 1A to 1C are diagrams schematically illustrating a process for producing a powder compact by a binder jet method according to an embodiment of the present invention. [Figure 5] 1 is a photograph showing the structure of a sintered body according to an example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a transparent perspective view of a sintered body 200 of the embodiment, and Fig. 2 is a transparent side view. The sintered body 200 has a substantially rectangular parallelepiped shape and includes an outer sintered shell 240 consisting of a bottom wall 210, a side wall 220 extending upward from the entire periphery of the bottom wall 210, and a top wall 230 closing an upper opening of the side wall 220.

[0028] A lattice sintered portion 250 is connected to the inner surface of the outer shell sintered portion 240. Figure 3 shows the lattice units that make up the lattice sintered portion 250. The lattice 251 shown in Figure 3(A) is composed of arms 251a that form a cross in a plane, and arms 251b that extend from the intersection of the arms 251a to the front and back sides perpendicular to the plane of the paper. By forming such lattices 251 so that they are connected vertically and horizontally, a jungle gym-like lattice sintered portion 250 is formed.

[0029] The lattice 252 shown in Figure 3(B) is composed of arms 252a that form a cross in a plane, and arms 252b that extend from the intersection of the arms 252a to the front and back sides inclined relative to the plane of the paper. The arms 252b are perpendicular to each other. By molding such lattices 252 so that they are connected vertically and horizontally, the sintered lattice part 250 shown in Figures 1 and 2 is formed.

[0030] The lattice structure 253 shown in Fig. 3(C) is formed by connecting the arms 252a and 252b of the lattice structure 252 shown in Fig. 3(B) in such a manner that they are inclined to each other, with the arms 253a forming an acute angle (obtuse angle) and the arms 253b also forming an acute angle (obtuse angle). By forming such lattices 253 so that they are connected vertically and horizontally, the lattice structure 250 shown in Figs. 1 and 2 is formed.

[0031] Next, the procedure for forming the sintered body 200 as described above will be described. FIGS. 4A to 4F are schematic diagrams illustrating steps in a method for manufacturing a sintered body according to an embodiment. As shown in FIG. 4A, a printing stage (powder bed) 11 is arranged in a printing casing 10 so that it can be raised and lowered. First, raw material powder P is supplied onto the printing stage 11 by gravity from a hopper 12, and is then evenly spread with a roller 13 as shown in FIG. 4B to form a raw material powder layer PL having a predetermined thickness. The average particle size of the raw material powder is, for example, 3 to 50 μm. Next, as shown in FIG. 4C, a liquid binder B is selectively ejected from an inkjet dispenser 14 onto the stacked raw material powder layers PL. Next, a heater 15 is passed directly above the raw material powder layers PL, and the portions of the raw material powder P that are exposed to the ejected binder B are bonded and hardened. This results in the formation of a bottom wall molding portion 110.

[0032] Next, the printing stage 11 is lowered by the thickness of the raw material powder layer PL, the next raw material powder layer PL is stacked, and binder B is supplied to the edge of the bottom wall molding portion 110, and the raw material powder P is bound and hardened in the same manner as above. At the same time, binder B is supplied to the inside of the edge of the bottom wall molding portion 110, in a portion that will become part of the lattice sintered portion 250, and the raw material powder P is bound and hardened. In this way, the raw material powder P is bound and hardened on the edge and inside of the bottom wall molding portion 110, and the hardened portion is formed to a predetermined thickness to form the side wall molding portion 120 and the lattice molding portion 150, as shown in FIG. 4(D).

[0033] After the side wall molding portion 120 and the lattice molding portion 150 are formed, raw material powder layer PL is laminated on the top surface 121 of the side wall molding portion 120, the lattice molding portion 150 inside the side wall molding portion 120, and the raw material powder layer PL, and as shown in Figure 4(E), binder B is supplied to form the top wall molding portion 130. In this way, an outer shell molding portion 140 consisting of the bottom wall molding portion 110, side wall molding portion 120, and top wall molding portion 130, and the lattice molding portion 150 are formed, and the powder molding body 100 is molded with raw material powder P sealed inside the outer shell molding portion 140 and the lattice molding portion 150. Then, the printing stage 11 is raised while the external powder P is sucked out by the suction nozzle, and the powder molding body 100 is removed.

[0034] Next, the powder compact 100 is subjected to HIP treatment at a relatively low temperature. HIP treatment is performed, for example, at 1150°C, 100 MPa, and 3 hours, resulting in a sintered compact 200 in which the inner sintered section 260 is sealed within the outer lattice sintered section 270, which is made up of the outer sintered section 240 and the lattice sintered section 250 (see FIG. 4(F)). When the powder compact 100 is heated from room temperature during HIP treatment, the binder B contained in the outer lattice compact 160 burns at approximately 500°C, leaving carbides as combustion residue. These carbides inhibit the growth of necks between the powder particles in the outer lattice compact 160, resulting in the formation of relatively large pores in the outer sintered section 240 and the lattice sintered section 250. In contrast, since there is no binder in the raw material powder P inside the outer shell sintered portion 240 and outside the lattice sintered portion 250, neck growth between the powders proceeds unhindered, forming a less porous internal sintered portion 260. Note that the HIP treatment is not limited to the above conditions, and may be performed, for example, at a sintering temperature of about 900 to 1100°C and a pressing pressure of about 80 to 120 MPa for an appropriate amount of time.

[0035] The heating temperature (sintering temperature) of the HIP process is lower than the 1300°C to 1400°C of a normal HIP process. This reduces energy costs and reduces thermal deformation. The internal sintered portion 260 can be sintered at a lower temperature than a normal sintering temperature by compressing and solidifying while receiving uniform pressure from the outer molding portion 140. This minimizes recrystallization of the powder in the internal sintered portion 260 in the raw material powder P, suppressing grain enlargement and achieving a high relative density close to 100%.

[0036] In this HIP treatment, the surface of the internal raw material powder P is airtightly sealed by the outer shell forming part 140, so the high pressure from the HIP treatment acts on the entire raw material powder P as an external pressure without penetrating into the interior of the raw material powder P. As a result, the raw material powder is compressed with the same pressure as the external pressure. And, because the outer shell forming part 140 covers the entire surface, the high pressure during the HIP treatment acts evenly on the entire area of ​​the raw material powder P via the outer shell forming part 140.

[0037] As a result, the raw material powder P is densified to form the internal sintered portion 70, thereby obtaining the sintered body 200 of this embodiment. The amount of shrinkage in the sintered body 200 tends to be uniform throughout. As a result, distortion and deformation caused by different amounts of shrinkage in multiple areas are suppressed. Furthermore, HIP processing can be performed without the need for a buffer material between the powder compact 100 and a ceramic setter on which the powder compact 100 is placed, as in the past. Furthermore, it is now possible to produce irregularly shaped sintered bodies, which were difficult to produce using conventional canning processing, with quality equivalent to that achieved by canning processing.

[0038] Figure 5 is a micrograph showing a partial cross section of the sintered body 200. In Figure 5, the black dots are pores. The black dots are large and numerous in the outer sintered portion, while the black dots are small and few in the inner sintered portion. This shows that the relative density of the inner sintered portion is higher than that of the outer sintered portion. Incidentally, the relative density of the outer sintered portion is 94%, while the relative density of the inner sintered portion exceeds 94%.

[0039] The sintered body 200 having the above-described configuration can be configured as, for example, a gear. The outer sintered portion 240 has a relatively low relative density and is soft, which allows for excellent compatibility between gears. On the other hand, the inner sintered portion 260 has a high relative density and is hard, so by removing the outer sintered portion 240 by machining, a sintered body can be obtained in which the inner sintered portion 260, which has high hardness and strength, is the majority. This sintered body is suitable for use in, for example, press molding dies.

[0040] According to the manufacturing method of the sintered body of the above embodiment, the shape of the powder compact 100 is maintained by the outer lattice compact 160, thereby preventing deformation and damage of the powder compact 100 during transportation. Furthermore, the outer molding portion 140 functions similarly to a can, enabling HIP processing in the next process. Thus, the above embodiment simplifies the manufacturing process and reduces manufacturing costs. Furthermore, the sintered body 200 manufactured in this manner has a two-layer structure consisting of an outer sintered portion 240 with a relatively low relative density and an inner sintered portion 260 with a high relative density, making it suitable for use in parts that come into sliding contact with mating parts, such as gears and guides.

[0041] The present invention is not limited to the above-described embodiment, and various modifications are possible as follows. i) The sintering method is not limited to HIP treatment, and a normal sintering method in which heating is performed in a sintering furnace may also be used.

[0042] ii) As a molding method for the powder compact 100, in addition to the binder jet method, any three-dimensional additive manufacturing method such as selective laser sintering (SLS) can be used.

[0043] iii) Metal powder produced by water atomization is suitable as the raw material powder P. Water-atomized powder has an irregular shape, resulting in a large angle of repose and poor fluidity. As in the above embodiment, when raw material powder P made of metal powder for sintering is supplied and spread by gravity from hopper 12 onto printing stage 11, which is open on all sides, the metal powder is less likely to spread unnecessarily in all directions and forms a single raw material powder layer PL of a predetermined thickness. On the other hand, if metal powder with a nearly spherical shape is used, when leveled with roller 13, the good fluidity of the metal powder may cause some areas to spread too much in all directions, resulting in an uneven thickness. [Industrial Applicability]

[0044] The present invention can be used in industrial fields involving relatively large sintered bodies such as press molding dies. [Explanation of symbols]

[0045] 10...printing casing, 11...printing stage (powder bed), 12...hopper, 13...roller, 14...inkjet dispenser, 15...heater, 100...powder molding body, 110...bottom wall molding portion, 120...side wall molding portion, 130...top wall molding portion, 140...outer shell molding portion, 150...lattice molding portion, 160...outer shell lattice molding body, 200...sintered body, 210...bottom wall portion, 220...side wall portion, 230...top wall portion, 240...outer shell sintered portion, 250...lattice sintered portion, 251, 252, 253...lattice, 251a, 251b, 252a, 252b, 253a...arm, 260...internal sintered portion, 270...outer shell lattice sintered portion, B...binder, G...powder molding body, P...raw material powder, PL...raw material powder layer.

Claims

1. A method for manufacturing a sintered body by a three-dimensional additive manufacturing method, in which raw material powder is supplied onto a powder bed while being discharged from a hopper and allowed to fall naturally, and the surface of the powder is pressed to repeatedly stack one raw material powder layer of a predetermined thickness, and each time one raw material powder layer is formed, a part of the raw material powder layer is bonded, a bottom wall forming portion forming step of joining predetermined portions of the first raw material powder layer to form a bottom wall forming portion; a side wall lattice forming step of repeatedly bonding raw material powder from the bottom wall forming portion in the vertical and horizontal directions from the second layer onward to form a side wall forming portion and a lattice forming portion having a lattice structure continuous with the side wall forming portion; a top wall molding portion molding step of molding a top wall molding portion that covers the tops of the side wall molding portion and the lattice molding portion; an outer lattice compact having the raw material powder sealed therein by the above-mentioned steps; A method for producing a sintered body, which includes a sintering step of sintering a powder compact comprising the outer lattice compact and the raw material powder.

2. 2. The method for producing a sintered body according to claim 1, wherein the sintering step is a HIP treatment.

3. 3. The method for producing a sintered body according to claim 1, wherein after the sintering step, at least a part of the outer sintered portion formed by sintering the outer shell molded body is removed.

4. 3. The method for producing a sintered body according to claim 2, wherein the HIP treatment is carried out at a heating temperature of 900 to 1100° C. and a pressing pressure of 80 to 120 MPa.

5. 3. The method for producing a sintered body according to claim 1, wherein the bottom wall molding portion, the side wall molding portion, and the top wall molding portion have a thickness of 100 [mu]m or more.

6. The sintered body has an internal sintered portion made of a sintered body of raw material powder, an external sintered portion that covers the entire circumference of the internal sintered portion, and an external lattice sintered portion that is continuous with the external sintered portion and extends vertically and horizontally within the internal sintered portion, the external lattice sintered portion being made of a dense structure and pores that contain carbides, which are combustion residues of the binder, and the internal sintered portion being made of a dense structure and pores that do not contain carbides, which are combustion residues of the binder, and the internal sintered portion is a sintered body having a higher relative density than the external sintered portion.

7. 7. The sintered body according to claim 6, wherein the relative density of the outer sintered portion is 94 to 97%, and the relative density of the inner sintered portion is greater than 97%.

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