Sintered Member and Method for Producing Sintered Member

The present disclosure relates to a sintered member and a method of manufacturing a sintered member.

The present application claims priority from Japanese Patent Application No. 2022-071901 filed on Apr. 25, 2022, the entire contents of which are incorporated herein by reference.

A method of manufacturing a sintered member in PTL 1 includes the step of subjecting a raw material powder to press-forming to produce a green compact, the step of forming a hole in the green compact, and the step of sintering the green compact having the hole formed therein. The raw material powder contains iron powder, copper powder, carbon powder, and ethylenebisstearamide.

The sintered member of the present disclosure is

The sintered member manufacturing method of the present disclosure includes:

There is a demand for manufacturing a sintered member having a hole with a large depth relative to its diameter or having a groove with a large depth relative to its width.

One object of the present disclosure is to provide a sintered member having a hole with a large depth relative to its diameter or having a groove with a large depth relative to its width. Another object of the present disclosure is to provide a method of manufacturing the sintered member.

The sintered member of the present disclosure has a hole with a large depth relative to its diameter or has a groove with a large depth relative to its width. The sintered member manufacturing method of the present disclosure can manufacture the sintered member of the present disclosure.

First, embodiments of the present disclosure will be enumerated and described.

The sintered member has the hole with a large depth relative to its diameter or the groove with a large depth relative to its width.

The sintered member composed of pure iron or an iron alloy has the hole with a large depth relative to its diameter or the groove with a large depth relative to its width.

The sintered member composed of stainless steel has the hole with a large depth relative to its diameter or the groove with a large depth relative to its width.

In the above sintered member manufacturing method, the raw material powder containing the lubricant having a melting point of 150° C. or lower is pressed, and this allows the lubricant to easily spread into spaces between the particles of the green compact produced. Since the lubricant has been spread into the spaces between the particles in the green compact, the hole can be formed by drilling the green compact, and the groove can be formed by grooving the green compact. The relative density of the green compact is the same as the relative density of the workpiece. Since the relative density of the green compact produced is 95% or more, the amount of shrinkage when the workpiece is sintered is very small. Therefore, the dimensions of the hole and the groove in the workpiece are maintained and are substantially the same as the dimensions of the hole and the groove in the sintered member. With the sintered member manufacturing method described above, a sintered member having a hole with a large depth relative to its diameter or having a groove with a large depth relative to its width can be produced.

By pressing the raw material powder, the lubricant can easily and widely spread into the spaces between the particles in the green compact.

Embodiments of the present disclosure will be described based on the drawings. In the drawings, the same numerals denote components with the same names. The dimensions of members shown in the drawings are for the purpose of clarity of description, and these dimensions do not necessarily represent the actual dimensional relations.

Referring to, a sintered memberin an embodiment will be described. The sintered memberis composed of a metal. One feature of the sintered memberin the present embodiment is that the sintered memberhas a high relative density and has at least one of a holehaving a specific size and a groovehaving a specific size.

The material of the sintered memberis a metal. The metal is, for example, pure iron, an iron alloy, or a nonferrous metal.

The pure iron is iron with a purity of 99% or more. Specifically, the pure iron is a material with an iron (Fe) content of 99% by mass or more.

The iron alloy is an alloy containing an additive element with the balance being iron (Fe) and unavoidable impurities. In the iron alloy, the content of Fe is highest. The additive element contained in the iron alloy is, for example, at least one element selected from the group consisting of nickel (Ni), copper (Cu), chromium (Cr), molybdenum (Mo), manganese (Mn), carbon (C), silicon (Si), aluminum (Al), phosphorus (P), boron (B), nitrogen (N), and cobalt (Co). Specific examples of the iron alloy include stainless steel, Fe—C-based alloys, Fe—Cu—Ni—Mo-based alloys, Fe—Ni—Mo—Mn-based alloys, Fe—P-based alloys, Fe—Cu-based alloys, Fe—Cu—C-based alloys, Fe—Cu—Mo-based alloys. Fe—Ni—Mo—Cu—C-based alloys. Fe—Ni—Cu-based alloys, Fe—Ni—Mo—C-based alloys, Fe—Ni—Cr-based alloys, Fe—Ni—Mo—Cr-based alloys, Fe—Cr-based alloys. Fe—Mo—Cr-based alloys, Fe—Cr—C-based alloys, Fe—Ni—C-based alloys, and Fe—Mo—Mn—Cr—C-based alloys. Examples of the stainless steel include austinite stainless steel. Examples of the austenite stainless steel include SUS304 and SUS304L.

The nonferrous metal is, for example, copper, a copper alloy, aluminum, or an aluminum alloy.

The composition of the sintered membercan be checked by analyzing the composition by ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometry).

The relative density of the sintered memberis 95% or more. The sintered memberhaving a relative density of 95% or more has good mechanical properties such as strength. The relative density of the sintered membermay be 96% or more, particularly 97% or more. No particular limitation is imposed on the upper limit of the relative density of the sintered member, and the upper limit can be appropriately selected so long as the sintered membercan be manufactured. The relative density of the sintered membermay be, for example, 99.9% or lower. Specifically, the relative density of the sintered membermay be 95% to 99.9%, 96% to 99.9%, particularly 97% to 99.9%.

The relative density of the sintered memberis the ratio (%) of the actual density of the sintered memberto the true density of the sintered member. Specifically, the relative density of the sintered memberis determined as [(actual density of sintered member)/(true density of sintered member)×100]. The actual density of the sintered membercan be determined by immersing the sintered memberin oil to impregnate the sintered memberwith the oil and computing [oil-impregnated density (mass of sintered memberbefore impregnation with oil)/(mass of sintered memberafter impregnation with oil)]. The oil-impregnated density is defined as (mass of sintered memberafter impregnation with oil/volume of sintered memberafter impregnation with oil). Specifically, the actual density of the sintered membercan be determined as (mass of sintered memberbefore impregnation with oil/volume of sintered memberafter impregnation with oil). The volume of the sintered memberafter impregnation with the oil can be measured typically by a liquid displacement method. The true density of the sintered memberis a theoretical density determined from the composition of the sintered memberon the assumption that the sintered membercontains no voids.

The holeis a through hole or a blind hole. The blind hole has a bottom. No particular limitation is imposed on the number of holes, and the number can be appropriately selected. When the number of holesis two or more, the holesmay include both a through hole and a blind hole. The holehas a substantially uniform diameter in a direction along the depth of the hole.

The diameter x(mm) and depth y(mm) of the holesatisfy the following requirements (a1) to (a7). The details of the requirements will be described in Test Example 1 with reference to.

The upper limit of the depth y(mm) of the holerelative to the diameter x(mm) depends on, for example, the limit of the diameter of the tool and the limit of its length or the limit of the size of the green compact during its manufacturing process. For example, in a commonly used commercial drill used to form the hole, the ratio L/D of the flute length L (mm) of the drill to the diameter D (mm) of the drill is about 20 or less or about 30 or less. The limit of the ratio LD depends on the diameter D and the material of the tool but is said to be 40 or less or 50 or less, even for special drills used to drill particularly deep holes. For example, the upper limit of the depth yof the holerelative to the diameter xis at least 50 times the diameter xin all the requirements (a1) to (a7). It is considered that the depth of the holeformed by a method of manufacturing the sintered member in the present embodiment described later can be larger than the depth of a hole that can be formed using a drill with L/D=50, which is the manufacturing limit of the drill.

No particular limitation is imposed on the number of grooves, and the number of groovescan be appropriately selected. The groovehas a substantially uniform width in a direction along the depth of the groove.

The width x(mm) and depth y(mm) of the groovesatisfy the following requirements (b1) to (b3). The details of the requirements will be described in Test Example 2 with reference to.

The upper limit of the depth y(mm) of the grooverelative to the width x(mm) depends on, for example, the limit of the width of the tool or the limit of the size of the green compact during its manufacturing process.

The sintered membermay have both the holeand the groove, although their illustration is omitted.

A sintered member manufacturing method according to an embodiment includes: step A of preparing a raw material powder; step B of producing a green compact; step C of producing a workpiece; and step D of sintering the workpiece. One feature of the sintered member manufacturing method is that the specific raw material powder is prepared in step A and at least one of the specific hole and groove is formed in step C. With the sintered member manufacturing method according to the embodiment, the sintered memberdescribed above is manufactured.

In step A, the raw material powder containing a metal powder and a lubricant is prepared. The raw material powder contains no organic binder. The metal powder is, for example, a ferrous powder or a nonferrous powder.

The ferrous powder is one powder selected from the group consisting of a pure iron powder, a first iron alloy powder, a first powder mixture, a second powder mixture, a third powder mixture, and a fourth powder mixture. The pure iron included in the pure iron powder has a purity of 99% or more as described above. The first iron alloy included in the first iron alloy powder is the iron alloy described above. The first powder mixture is composed of the pure iron powder and an alloying element powder. The alloying element powder is a powder of an element used to produce the iron alloy in step D. The alloying element is an additive element of the above-described iron alloy. When the sintered membermanufactured is composed of an iron alloy containing a plurality of additive elements, the alloying element powder contains a plurality of additive element powders. The second powder mixture is composed of a second iron alloy powder and a carbon powder. Examples of the second iron alloy contained in the second iron alloy powder include Fe—Cu-based alloys, Fe—Ni—Mo—Cu-based alloys, Fe—Ni—Mo-based alloys, Fe—Cr-based alloys, Fe—Ni-based alloys, and Fe—Mo—Mn—Cr-based alloys. The third powder mixture is composed of the pure iron powder, the alloying element powder, and the first iron alloy powder. The fourth powder mixture is composed of the pure iron powder, the alloying element powder, the second iron alloy powder, and a carbon powder.

The nonferrous powder is a copper powder, a copper alloy powder, an aluminum powder, or an aluminum alloy powder.

The lubricant spreads into the spaces between a plurality of particles under the processing heat generated when the raw material powder is pressed in step B. Such a lubricant has a melting point of 150° C. or lower. The melting point of the lubricant may be 110° C. or lower, particularly 85° C. or lower. The melting point of the lubricant is, for example, 50° C. or higher. Specifically, the melting point of the lubricant may be 50° C. to 150° C., 55° C. to 110° C., particularly 60° C. to 85° C. Specific examples of the lubricant include stearic acid, erucic acid amide, and stearic acid amide. These lubricants can easily and widely spread into the spaces between the plurality of particles under the processing heat in step B.

The content of the lubricant contained in the raw material powder is, for example, 0.025% by mass to 0.2% by mass. When the content is 0.025% by mass or more, the lubricant can easily and widely spread into the spaces between the plurality of particles under the processing heat in step B. Therefore, at least one of the hole and the groove can be easily formed in step C. In particular, a plurality of holes and/or a plurality of grooves can be easily formed using the same tool. When the above content is 0.2% by mass or lower, a dense green compact can be easily formed in step B. Moreover, volume shrinkage due to loss of the lubricant when the workpiece is sintered in step D can be reduced, and a high-density sintered member with high dimensional accuracy can be easily manufactured. The content may be 0.04% by mass to 0.18% by mass. The content is a value when the total amount of the raw material powder is set to 100% by mass.

In step B, the raw material powder is pressed to produce a green compact having a relative density of 95% or more. The relative density may be 97% or more, particularly 98% or more. The relative density of the green compact is determined as [(actual density of green compact/true density of green compact)×100]. The meaning of the actual density of the green compact is the same as the meaning of the actual density of the sintered member described above. The meaning of the true density of the green compact is the same as the true density of the sintered member described above. No particular limitation is imposed on the shape of the green compact, and the shape can be appropriately selected. The shape of the green compact is, for example, columnar or tubular. The green compact is produced using an appropriate die that can be used to form any of the above shapes.

The molding pressure is set such that the green compact formed has a relative density of 95% or more and that heat allowing the lubricant to spread into the spaces between the particles is generated. Specifically, in this step, the processing heat during molding allows the lubricant to spread. To allow the lubricant to spread, the die is not heated by a heater. The molding pressure is, for example, 1560 MPa or more. The higher the molding pressure, the higher the relative density of the green compact produced. The molding pressure may be 1660 MPa or more, 1760 MPa or more, particularly 1860 MPa, and 1960 MPa or more. The upper limit of the molding pressure is not specifically set.

In step C, the green compact is subjected to at least one cutting process selected from hole drilling and grooving, and a workpiece having at least one of a hole and a groove is thereby produced. The relations between the diameter xand depth yof the formed hole are within the ranges described above. The relations between the width xand depth yof the formed groove are within the ranges described above. Since the lubricant has been spread into the spaces between the particles of the green compact, at least one of the hole and groove satisfying the above ranges can be formed. A drill is one example of the tool used to form the hole. The drilling may be performed under wet conditions with internal or external lubrication, which depends on the diameter of the drill. Examples of the tool used to form the groove include dicing blades, metal saws, and grooving tools.

In step D, the workpiece is sintered. By sintering the workpiece, the sintered memberis manufactured. As a result of the sintering, the workpiece shrinks. The relative density of the workpiece is the same as the relative density of the green compact. Specifically, the workpiece has a high relative density. Therefore, the amount of shrinkage of the workpiece due to sintering is very small. In this case, the relative density of the sintered memberis more than or equal to the relative density of the workpiece. Specifically, the relative density of the sintered memberis 95% or more. The dimensions of the hole and groove in the workpiece are maintained and are substantially the same as the dimensions of the holeand the groovein the sintered member. The sintering conditions can be appropriately selected according to the composition of the raw material powder. The sintering temperature is, for example, 1100° C. to 1400° C. and may be 1200° C. to 1300° C. The sintering time is, for example, 15 minutes to 150 minutes and may be 20 minutes to 60 minutes. Well-known sintering conditions may be applied.

The sintered member manufacturing method may further include at least one step selected from step α of subjecting the sintered memberto heat treatment and step β of subjecting the sintered memberto finishing processing.

In step α, the sintered memberis subjected to carburizing and quenching and then to tempering. The mechanical properties, particularly hardness and toughness, of the sintered memberare likely to be improved through step α.

In step β, the surface roughness of the sintered memberis reduced, and the dimensions of the sintered memberare adjusted to its design dimensions. Examples of the finishing processing include surface polishing of the sintered member.