JP6308073B2 - Metal powder for powder metallurgy, compound, granulated powder and sintered body - Google Patents

Description

  The present invention relates to a metal powder for powder metallurgy, a compound, a granulated powder, and a sintered body.

  In the powder metallurgy method, a composition including a metal powder and a binder is molded into a desired shape to obtain a molded body, and then the molded body is degreased and sintered to produce a sintered body. In the manufacturing process of such a sintered body, an atomic diffusion phenomenon occurs between the particles of the metal powder, and thereby the compact is gradually densified, resulting in sintering.

  For example, Patent Document 1 proposes a metal powder for powder metallurgy that includes at least one selected from the group consisting of Fe, Co, and Ni and unavoidable elements, including Zr and Si. According to such metal powder for powder metallurgy, the sinterability is improved by the action of Zr, and a high-density sintered body can be easily manufactured.

  In recent years, the sintered body thus obtained has been widely used for various machine parts, structural parts, and the like.

  However, depending on the application of the sintered body, further densification may be required. In such a case, the sintered body is further subjected to additional processing such as hot isostatic pressing (HIP processing) to increase the density, but the work man-hour is greatly increased. High cost is inevitable.

  Therefore, there is an increasing expectation for the realization of a metal powder capable of producing a high-density sintered body without performing additional processing.

JP 2012-87416 A

  An object of the present invention is to provide a metal powder for metallurgy, compound and granulated powder capable of producing a high-density sintered body, and a high-density sintered body produced using the metal powder for powder metallurgy. There is.

The above object is achieved by the present invention described below.
The metal powder for powder metallurgy of the present invention is mainly composed of Fe,
Cr is included in a proportion of 10% by mass to 30% by mass,
C is contained at a ratio of 0.15% by mass or more and 1.5% by mass or less,
Si is contained in a ratio of 0.3% by mass or more and 1% by mass or less,
Zr is included in a proportion of 0.01% by mass or more and 0.5% by mass or less,
Nb is included in a proportion of 0.01% by mass or more and 0.5% by mass or less,
Mn and Ni are included in a ratio of 0.05% by mass or more and 1.6% by mass or less in total ,
Mo content is characterized der Rukoto than 0.8 wt%.
The metal powder for powder metallurgy of the present invention is mainly composed of Fe,
Cr is contained in a ratio of 10.5% by mass or more and 20% by mass or less,
C is contained in a proportion of 0.35 mass% to 1.15 mass%,
Si is contained at a ratio of 0.4 mass% or more and 0.85 mass% or less,
Zr is contained in a ratio of 0.03% by mass or more and 0.2% by mass or less,
Nb is contained in a ratio of 0.03% by mass or more and 0.2% by mass or less,
Mn and Ni are included in a ratio of 0.08% by mass to 1.3% by mass in total ,
Mo content is characterized der Rukoto than 0.8 wt%.
The metal powder for powder metallurgy of the present invention is mainly composed of Fe,
Cr is included at a ratio of 11% by mass or more and 18% by mass or less,
C is contained at a ratio of 0.4% by mass or more and 1.1% by mass or less,
Si is contained in a proportion of 0.5% by mass or more and 0.8% by mass or less,
Zr is included at a ratio of 0.05% by mass or more and 0.1% by mass or less,
Nb is included in a proportion of 0.05% by mass or more and 0.1% by mass or less,
Mn and Ni are included in a ratio of 0.1% by mass or more and 1% by mass or less in total ,
Mo content is characterized der Rukoto than 0.8 wt%.

  Thereby, since Zr and Nb are appropriately added, remarkable growth of crystal grains is suppressed at the time of sintering, voids are hardly generated in the sintered body, and enlargement of crystal grains is prevented. A metal powder for powder metallurgy capable of producing a high-density sintered body is obtained.

The powder metallurgy metal powder of the present invention preferably has a crystal structure of martensite.

  The crystal structure of martensitic stainless steel is a body-centered cubic lattice in which C and N are dissolved in a supersaturated state, and thus is slightly distorted as compared with a normal body-centered cubic lattice. For this reason, the metal powder for powder metallurgy having such a crystal structure can produce a sintered body having a high hardness reflecting the distortion of the crystal structure.

In the metal powder for powder metallurgy of the present invention, the ratio Zr / Nb of the content ratio of Zr to the content ratio of Nb is preferably 0.3 or more and 3 or less.
In the metal powder for powder metallurgy of the present invention, the ratio Zr / Nb of the content ratio of Zr to the content ratio of Nb is preferably 0.5 or more and 2 or less.

  As a result, it is possible to optimize a shift in timing at which crystal growth starts between a region having Nb carbide as a nucleus and a region having Zr carbide as a nucleus. As a result, since the voids remaining in the molded body can be sequentially discharged from the inside and discharged, the voids generated in the sintered body can be minimized. Therefore, by setting Zr / Nb within the above range, a metal powder capable of producing a sintered body having a high density and excellent mechanical properties can be obtained.

In the metal powder for powder metallurgy according to the present invention, the total of the Zr content and the Nb content is preferably 0.05% by mass or more and 0.6% by mass or less.
In the metal powder for powder metallurgy of the present invention, it is preferable that the total content of Zr and Nb is 0.1% by mass or more and 0.48% by mass or less.
In the metal powder for powder metallurgy according to the present invention, the total of the Zr content and the Nb content is preferably 0.12% by mass or more and 0.24% by mass or less.
As a result, the density of the sintered body to be manufactured becomes necessary and sufficient.

In the metal powder for powder metallurgy according to the present invention, when the total of the Zr content and the Nb content is (Zr + Nb), the ratio (Zr + Nb) to the Si content (Zr + Nb) / Si is 0.1 or more. It is preferable that it is 0.7 or less.
In the metal powder for powder metallurgy according to the present invention, when the total content of Zr and Nb is (Zr + Nb), the ratio of (Zr + Nb) to Si content (Zr + Nb) / Si is 0.15 or more. It is preferable that it is 0.6 or less.
In the metal powder for powder metallurgy of the present invention, when the total of the Zr content and the Nb content is (Zr + Nb), the ratio (Zr + Nb) to the Si content (Zr + Nb) / Si is 0.17 or more. It is preferable that it is 0.5 or less.

  Thereby, the reduction in toughness when Si is added is sufficiently compensated by the addition of Zr and Nb. As a result, it is possible to obtain a metal powder capable of producing a sintered body having excellent mechanical properties such as toughness and excellent corrosion resistance derived from Si, despite its high density.

In the metal powder for powder metallurgy of the present invention, it is preferable that Mn is contained in a proportion of 0.01% by mass or more and 1.25% by mass or less.
In the metal powder for powder metallurgy according to the present invention, it is preferable that Mn is contained in a proportion of 0.03% by mass or more and 0.3% by mass or less.
In the metal powder for powder metallurgy of the present invention, it is preferable that Mn is contained in a proportion of 0.05% by mass or more and 0.2% by mass or less.
As a result, a sintered body having a high density and excellent mechanical properties can be obtained.

In the metal powder for powder metallurgy according to the present invention, it is preferable that Ni is contained at a ratio of 0.05% by mass or more and 0.6% by mass or less.
In the metal powder for powder metallurgy of the present invention, it is preferable that Ni is contained at a ratio of 0.06 mass% to 0.4 mass%.
In the metal powder for powder metallurgy of the present invention, it is preferable that Ni is contained at a ratio of 0.07% by mass or more and 0.25% by mass or less.
As a result, a sintered body having excellent mechanical properties over a long period of time can be obtained.

  In the metal powder for powder metallurgy of the present invention, the average particle size is preferably 0.5 μm or more and 30 μm or less.

  Thereby, since the void | holes which remain | survive in a sintered compact become very few, the sintered compact which was especially high-density and excellent in the mechanical characteristic can be manufactured.

The compound of the present invention comprises the metal powder for powder metallurgy of the present invention and a binder for binding particles of the metal powder for powder metallurgy.
Thereby, the compound which can manufacture a high-density sintered compact is obtained.

The granulated powder of the present invention is obtained by granulating the metal powder for powder metallurgy of the present invention.
Thereby, the granulated powder which can manufacture a high-density sintered compact is obtained.

The sintered body of the present invention is mainly composed of Fe,
Cr is included in a proportion of 10% by mass to 30% by mass,
C is contained at a ratio of 0.15% by mass or more and 1.5% by mass or less,
Si is contained in a ratio of 0.3% by mass or more and 1% by mass or less,
Zr is included in a proportion of 0.01% by mass or more and 0.5% by mass or less,
Nb is included in a proportion of 0.01% by mass or more and 0.5% by mass or less,
Mn and Ni are included in a ratio of 0.05% by mass or more and 1.6% by mass or less in total ,
Mo content is characterized by being produced by sintering a metal powder for Der Ru powder metallurgy than 0.8 wt%.
The sintered body of the present invention is mainly composed of Fe,
Cr is included in a proportion of 10% by mass to 30% by mass,
C is contained at a ratio of 0.15% by mass or more and 1.5% by mass or less,
Si is contained in a ratio of 0.3% by mass or more and 1% by mass or less,
Zr is included in a proportion of 0.01% by mass or more and 0.5% by mass or less,
Nb is included in a proportion of 0.01% by mass or more and 0.5% by mass or less,
Mn and Ni are included in a ratio of 0.05% by mass or more and 1.6% by mass or less in total ,
Mo content is characterized der Rukoto than 0.8 wt%.
Thereby, a high-density sintered compact is obtained.

  In the sintered body of the present invention, the relative density is preferably 97% or more, and the surface Vickers hardness is preferably 570 or more.

  As a result, despite having a shape that is as close as possible to the target shape, it has excellent mechanical properties comparable to the smelted material, so various machine parts with almost no post-processing And a sintered body applicable to structural parts and the like.

Hereinafter, the metal powder for powder metallurgy, compound, granulated powder and sintered body of the present invention will be described in detail.
[Metal powder for powder metallurgy]
First, the metal powder for powder metallurgy according to the present invention will be described.

  In powder metallurgy, a composition including a metal powder for powder metallurgy and a binder is molded into a desired shape, and then degreased and sintered to obtain a sintered body having a desired shape. Such a powder metallurgy technique has an advantage that a sintered body having a complicated and fine shape can be manufactured with a near net (a shape close to the final shape) as compared with other metallurgical techniques.

  As metal powder for powder metallurgy used for powder metallurgy, attempts have been conventionally made to increase the density of a sintered body produced by appropriately changing the composition. However, since pores are easily formed in the sintered body, it is necessary to further increase the density in order to obtain mechanical properties equivalent to the melted material.

  Therefore, conventionally, the obtained sintered body is further subjected to additional processing such as hot isostatic pressing (HIP processing) to increase the density. However, such additional processing involves a lot of labor and cost, and is an obstacle when expanding the use of the sintered body.

  In view of the above problems, the present inventor has intensively studied the conditions for obtaining a high-density sintered body without performing additional processing. As a result, it has been found that the density of the sintered body can be increased by optimizing the composition of the alloy constituting the metal powder, and the present invention has been completed.

  Specifically, the metal powder for powder metallurgy of the present invention contains Fe as a main component, Cr is contained in a proportion of 10% by mass or more and 30% by mass or less, and C is 0.15% by mass or more and 1.5% by mass. % Is contained in a proportion of 0.3% to 1% by mass, Zr is contained in a proportion of 0.01% to 0.5% by mass, and Nb is 0.00%. It is a metal powder that is contained in a proportion of 01% by mass or more and 0.5% by mass or less, and that Mn and Ni are contained in a proportion of 0.05% by mass or more and 1.6% by mass or less. According to such a metal powder, as a result of optimization of the alloy composition, densification during sintering can be particularly enhanced. As a result, a high-density sintered body can be manufactured without performing additional processing.

  And the sintered compact which was excellent in mechanical characteristics will be obtained by densifying a sintered compact. Such a sintered body can be widely applied to applications in which an external force (load) is applied, such as a machine part or a structural part.

  Hereinafter, the alloy composition of the metal powder for powder metallurgy according to the present invention will be described in more detail. In the following description, the metal powder for powder metallurgy may be simply referred to as “metal powder”.

  Cr (chromium) is an element that imparts corrosion resistance to the sintered body to be produced. By using a metal powder containing Cr, a sintered body that can maintain high mechanical properties over a long period of time can be obtained.

  The Cr content in the metal powder is 10% by mass to 30% by mass, preferably 10.5% by mass to 20% by mass, and more preferably 11% by mass to 18% by mass. The When the Cr content is less than the lower limit, depending on the overall composition, the corrosion resistance of the manufactured sintered body becomes insufficient. On the other hand, if the Cr content exceeds the upper limit, depending on the overall composition, the sinterability may be reduced, making it difficult to increase the density of the sintered body.

  C (carbon) can particularly enhance the sinterability when used in combination with Zr or Nb described later. Specifically, Zr and Nb each combine with C to generate carbides such as ZrC and NbC. The carbides such as ZrC and NbC are dispersed and precipitated, thereby producing an effect of preventing remarkable growth of crystal grains. The clear reason why such an effect is obtained is unknown, but as one of the reasons, the dispersed precipitates become an obstacle and inhibit the remarkable growth of the crystal grains, so that the variation in the size of the crystal grains can be suppressed. It is possible. As a result, voids are less likely to occur in the sintered body, and enlargement of crystal grains is prevented, so that a sintered body having a high density and high mechanical properties can be obtained.

  The content of C in the metal powder is 0.15% by mass or more and 1.5% by mass or less, preferably 0.35% by mass or more and 1.15% by mass or less, more preferably 0.4% by mass. % To 1.1% by mass. If the C content is less than the lower limit, depending on the overall composition, the crystal grains are remarkably easily grown, and the mechanical properties of the sintered body become insufficient. On the other hand, when the C content exceeds the upper limit, C increases excessively depending on the entire composition, and the sinterability deteriorates.

  Si (silicon) is an element that imparts corrosion resistance and high mechanical properties to the sintered body to be produced. By using a metal powder containing Si, a sintered body that can maintain high mechanical properties over a long period of time is obtained. can get.

  The content of Si in the metal powder is 0.3 mass% or more and 0.9 mass% or less, preferably 0.4 mass% or more and 0.85 mass% or less, more preferably 0.5 mass%. % To 0.8% by mass. If the Si content is lower than the lower limit value, the effect of adding Si becomes dilute depending on the overall composition, so that the corrosion resistance and mechanical properties of the sintered body to be manufactured are lowered. On the other hand, when the Si content exceeds the upper limit value, depending on the overall composition, Si becomes too much, and the corrosion resistance and mechanical properties are rather deteriorated.

  Zr (zirconium) dissolves in Fe to form a low melting point phase, and this low melting point phase causes rapid atomic diffusion during sintering of the metal powder. And this atomic diffusion becomes a driving force, and the distance between the particles of the metal powder is rapidly shortened to form a neck between the particles. As a result, densification of the molded body proceeds and sintering is performed quickly.

  On the other hand, the atomic radius of Zr is slightly larger than the atomic radius of Fe. Specifically, the atomic radius of Fe is about 0.117 nm, and the atomic radius of Zr is about 0.145 nm. For this reason, although Zr is dissolved in Fe, it does not reach complete solid solution, and a part of Zr is precipitated as Zr carbide such as ZrC. For this reason, this precipitated Zr carbide inhibits remarkable growth of crystal grains. As a result, as described above, voids are less likely to occur in the sintered body, and the enlargement of crystal grains is prevented, and a sintered body having a high density and high mechanical properties can be obtained.

  In addition, as will be described in detail later, the precipitated Zr carbide promotes the accumulation of silicon oxide at the grain boundaries, and as a result, the sintering is promoted and the density is increased while suppressing the enlargement of the crystal grains. .

  Further, since Zr is a ferrite-forming element, a body-centered cubic lattice phase is precipitated. This body-centered cubic lattice phase is excellent in sinterability compared to other crystal lattice phases, and thus contributes to higher density of the sintered body.

  Zr acts as a deoxidizer that removes oxygen contained in the metal powder as an oxide. For this reason, it is possible to reduce the oxygen content that contributes to a decrease in sinterability, and to further increase the density of the sintered body.

  The content of Zr in the metal powder is 0.01% by mass or more and 0.5% by mass or less, preferably 0.03% by mass or more and 0.2% by mass or less, more preferably 0.05% by mass. % To 0.1% by mass. If the Zr content is less than the lower limit, depending on the overall composition, the effect of adding Zr becomes dilute, so that the density of the sintered body to be manufactured becomes insufficient. On the other hand, if the Zr content exceeds the upper limit, depending on the overall composition, Zr becomes too much, and the densification is impaired.

  Nb (niobium) also has a slightly larger atomic radius than that of Fe, but slightly smaller than that of Zr. Specifically, the atomic radius of Fe is about 0.117 nm, and the atomic radius of Nb is about 0.134 nm. For this reason, some Nb precipitates as Nb carbides such as NbC. Therefore, it is considered that Zr carbide and Nb carbide precipitate during sintering, and these precipitates inhibit remarkable growth of crystal grains and promote accumulation of silicon oxide at the crystal grain boundaries.

  On the other hand, the precipitation of such Zr carbide and Nb carbide starts in the lower temperature region of the precipitation of Zr carbide than the precipitation of Nb carbide. The reason for this is not clear, but it is considered that the difference in atomic radius between Zr and Nb is involved. And it is presumed that when the metal powder is sintered, the timing at which the effect of the precipitation of the Nb carbide and the effect of the precipitation of the Zr carbide are manifested due to the difference in the temperature range in which the carbide precipitates. Thus, it is considered that the generation of vacancies can be suppressed and a dense sintered body can be obtained by shifting the timing of precipitation of carbides. That is, it is considered that the presence of both Nb carbide and Zr carbide makes it possible to suppress the enlargement of crystal grains while achieving high density.

  The Nb content in the metal powder is 0.01% by mass or more and 0.5% by mass or less, preferably 0.03% by mass or more and 0.2% by mass or less, and more preferably 0.05% by mass. % To 0.1% by mass. If the Nb content is less than the lower limit, depending on the overall composition, the effect of adding Nb becomes dilute, so that the density of the sintered body to be manufactured becomes insufficient. On the other hand, if the Nb content exceeds the upper limit, depending on the overall composition, Nb is excessively increased, and the densification is impaired.

  In addition, when the ratio of the content ratio of Zr to the content ratio of Nb is Zr / Nb, Zr / Nb is preferably 0.3 or more and 3 or less, and more preferably 0.5 or more and 2 or less. By setting Zr / Nb within the above range, it is possible to optimize the difference in timing between the precipitation of Nb carbide and the precipitation of Zr carbide. Thereby, since the void | hole remaining in a molded object can be discharged | emitted as it sweeps out sequentially from an inner side, the void | hole produced in a sintered compact can be suppressed to the minimum. Therefore, by setting Zr / Nb within the above range, a metal powder capable of producing a sintered body having a high density and excellent mechanical properties can be obtained.

  The Zr content and the Nb content are as described above, but the total of these is preferably 0.05% by mass or more and 0.6% by mass or less, and 0.10% by mass or more. The content is more preferably 0.48% by mass or less, and further preferably 0.12% by mass or more and 0.24% by mass or less. By setting the total content of Zr and Nb within the above range, it is necessary and sufficient to increase the density of the sintered body to be manufactured.

  When the ratio of the total content of Zr and the content of Nb with respect to the content of Si is (Zr + Nb) / Si, (Zr + Nb) / Si is preferably 0.1 or more and 0.7 or less, It is more preferably 0.15 or more and 0.6 or less, and further preferably 0.17 or more and 0.5 or less. By setting (Zr + Nb) / Si within the above range, the reduction in toughness when Si is added is sufficiently compensated by the addition of Zr and Nb. As a result, it is possible to obtain a metal powder capable of producing a sintered body having excellent mechanical properties such as toughness and excellent corrosion resistance derived from Si, despite its high density.

  In addition, by adding appropriate amounts of Zr and Nb, Zr carbides and Zr oxides as described above, and Nb carbides and Nb oxides as described above (hereinafter, referred to as “crystal grains” in the sintered body). These are collectively referred to as “Zr carbide etc.”) as “nuclei”, and it is considered that silicon oxide accumulates. Since silicon oxide accumulates at the crystal grain boundaries, the oxide concentration inside the crystal decreases, so that sintering is promoted. As a result, it is considered that the densification of the sintered body is further promoted.

  Furthermore, since the precipitated silicon oxide easily moves to the triple point of the grain boundary during the accumulation process, crystal growth at this point is suppressed (pinning effect). As a result, remarkable growth of crystal grains is suppressed, and a sintered body having finer crystals can be obtained. Such a sintered body has particularly high mechanical properties.

  Further, the accumulated silicon oxide tends to be located at the triple point of the grain boundary as described above, and therefore tends to be formed into a granular shape. Therefore, the sintered body has such a granular shape, the first region having a relatively high silicon oxide content, and the second region having a relatively low silicon oxide content than the first region, Is formed. The presence of the first region makes it possible to reduce the oxide concentration inside the crystal and suppress the remarkable growth of crystal grains as described above.

  When qualitative quantitative analysis is performed for each of the first region and the second region using an electron beam microanalyzer (EPMA), O (oxygen) is the main element in the first region, while in the second region, Fe is the main element. As described above, the first region exists mainly at the crystal grain boundary, while the second region exists inside the crystal. Therefore, in the first region, when the sum of the content ratios of the two elements of O and Si and the content ratio of Fe are compared, the sum of the content ratios of the two elements is larger than the content ratio of Fe. On the other hand, in the second region, the sum of the contents of the two elements O and Si is overwhelmingly smaller than the content of Fe. From these facts, it is understood that Si and O are integrated in the first region. Specifically, in the first region, the sum of the Si content and the O content is preferably 1.5 times or more of the Fe content. Moreover, it is preferable that the Si content in the first region is at least three times the Si content in the second region.

  Furthermore, although it may differ depending on the composition ratio, at least one of the content ratio of Zr and the content ratio of Nb satisfies the relationship of first region> second region. This indicates that in the first region, the aforementioned Zr carbide or the like serves as a nucleus when silicon oxide accumulates. Specifically, it is preferable that the Zr content in the first region is at least three times the Zr content in the second region.

  Note that the accumulation of silicon oxide as described above is considered to be one cause of densification of the sintered body. Therefore, even if the sintered body has been densified by the present invention, it is considered that silicon oxide may not be accumulated depending on the composition ratio.

  Moreover, although the diameter of the 1st area | region which makes | forms granularity changes according to Si content rate in the whole sintered compact, it is about 0.05 micrometer or more and 15 micrometers or less, Preferably it is about 0.1 micrometer or more and 10 micrometers or less. Thereby, the densification of a sintered compact can fully be accelerated | stimulated, suppressing the fall of the mechanical characteristic of the sintered compact accompanying accumulating of silicon oxide.

  Note that the diameter of the first region is obtained as an average value of the diameters of circles having the same area as the area of the first region specified from light and shade (circle equivalent diameter) in the electron micrograph of the cross section of the sintered body. it can. When the average value is obtained, 10 or more measured values are used.

  Furthermore, when the total ratio of the Zr content and the Nb content to the C content is (Zr + Nb) / C, the (Zr + Nb) / C is preferably 0.05 or more and 0.7 or less. More preferably, it is 0.1 or more and 0.5 or less, and further preferably 0.13 or more and 0.35 or less. By setting (Zr + Nb) / C within the above range, it is possible to achieve both an increase in hardness and a decrease in toughness when C is added and a high density caused by the addition of Zr and Nb. As a result, a metal powder capable of producing a sintered body having excellent mechanical properties such as tensile strength and toughness can be obtained.

  Mn, like Si, is an element that imparts corrosion resistance and high mechanical properties to the sintered body to be produced.

  The Mn content in the metal powder is preferably 0.01% by mass or more and 1.25% by mass or less, more preferably 0.03% by mass or more and 0.3% by mass or less, and 0.05% by mass. It is more preferable that the content is not less than 0.2% and not more than 0.2% by mass. By setting the Mn content within the above range, a sintered body having a high density and excellent mechanical properties can be obtained.

  If the Mn content is less than the lower limit, depending on the overall composition, the corrosion resistance and mechanical properties of the sintered body to be produced may not be sufficiently improved, whereas the Mn content is If the upper limit is exceeded, corrosion resistance and mechanical properties may be deteriorated.

Ni is also an element that imparts corrosion resistance and heat resistance to the sintered body to be produced.
The Ni content in the metal powder is preferably 0.05% by mass or more and 0.6% by mass or less, more preferably 0.06% by mass or more and 0.4% by mass or less, and 0.07% by mass. % Or more and 0.25% by mass or less is more preferable. By setting the Ni content within the above range, a sintered body having excellent mechanical properties over a long period of time can be obtained.

  If the Ni content is less than the lower limit, depending on the overall composition, the corrosion resistance and heat resistance of the sintered body to be produced may not be sufficiently increased. On the other hand, the Ni content is not limited to the upper limit. If the value is exceeded, corrosion resistance and heat resistance may be deteriorated.

  Further, Mn and Ni are included in a ratio of 0.05% by mass to 1.6% by mass in total. Thereby, the mechanical characteristics of the sintered body can be particularly enhanced. The total of the Mn content and the Ni content is preferably 0.08% by mass to 1.3% by mass, and more preferably 0.1% by mass to 1% by mass. Moreover, Mn and Ni should just be the sum total of the content rate in the said range, and either content rate may be 0.

  The metal powder for powder metallurgy of the present invention may contain at least one of Mo, Pb, S, and Al as necessary, in addition to these elements. In addition, these elements may be inevitably included.

Mo is an element that enhances the corrosion resistance of the sintered body to be produced.
The Mo content in the metal powder is preferably 0.2% by mass or more and 0.8% by mass or less, and more preferably 0.3% by mass or more and 0.6% by mass or less. By setting the Mo content in the above range, the corrosion resistance of the manufactured sintered body can be further enhanced.

Pb is an element that improves the machinability of the sintered body to be produced.
The content of Pb in the metal powder is preferably 0.03% by mass or more and 0.5% by mass or less, and more preferably 0.05% by mass or more and 0.3% by mass or less. By setting the Pb content within the above range, the machinability of the manufactured sintered body can be further increased.

S is an element that enhances the machinability of the sintered body to be produced.
Although the content rate of S in a metal powder is not specifically limited, It is preferable that it is 0.5 mass% or less, and it is more preferable that it is 0.01 mass% or more and 0.3 mass% or less. By setting the S content within the above range, the machinability of the manufactured sintered body can be further improved without causing a significant decrease in the density of the manufactured sintered body.

Al is an element that improves the oxidation resistance of the sintered body to be produced.
Although the content rate of Al in a metal powder is not specifically limited, It is preferable that it is 0.5 mass% or less, and it is more preferable that it is 0.05 mass% or more and 0.3 mass% or less. By setting the Al content within the above range, the oxidation resistance of the manufactured sintered body can be further improved without causing a significant decrease in the density of the manufactured sintered body.

  In addition, the metal powder for powder metallurgy according to the present invention may further contain impurities. Examples of the impurities include all elements other than the above-described Fe, Cr, C, Si, Zr, Nb, Mn, Ni, Mo, Pb, S, and Al. Specifically, for example, Li, Be, B N, Na, Mg, P, K, Ca, Sc, Ti, V, Co, Zn, Ga, Ge, Y, Pd, Ag, In, Sn, Sb, Hf, Ta, W, Os, Ir, Pt , Au, Bi and the like. The amount of these impurities mixed is preferably set so that each element is less than the content of Fe, Cr, C, Si, Zr and Nb. The amount of these impurities mixed is preferably set so that each element is less than 0.03% by mass, and more preferably set to be less than 0.02% by mass. Further, the total amount is preferably less than 0.3% by mass, and more preferably less than 0.2% by mass. In addition, as long as the content rate is in the above range, these elements may be intentionally added because the effects as described above are not inhibited.

  On the other hand, O (oxygen) may be added intentionally or inevitably mixed, but the amount is preferably about 0.8% by mass or less, and about 0.5% by mass or less. More preferably. By keeping the amount of oxygen in the metal powder at this level, the sinterability is increased, and a sintered body having a higher density and excellent mechanical properties can be obtained. The lower limit is not particularly set, but is preferably 0.03% by mass or more from the viewpoint of ease of mass production.

  Moreover, it is preferable that the metal powder for powder metallurgy of this invention does not contain Cu substantially. Although a clear reason is unknown, it is because it was discovered that the effect mentioned above which Zr and Nb bring about may be diluted depending on the whole composition by containing Cu. Specifically, the Cu content is preferably less than 0.02% by mass, and more preferably less than 0.01% by mass.

  Fe is a component (main component) having the highest content in the metal powder for powder metallurgy of the present invention, and greatly affects the characteristics of the sintered body. The content of Fe is 50% by mass or more.

  The composition ratio of the metal powder for powder metallurgy is, for example, an atomic absorption method specified in JIS G 1257, an ICP emission analysis method specified in JIS G 1258, a spark emission analysis method specified in JIS G 1253, or JIS. It can be specified by a fluorescent X-ray analysis method defined in G 1256, a weight, titration, absorptiometry or the like defined in JIS G 1211-G 1237. Specifically, for example, a solid emission spectroscopic analyzer manufactured by SPECTRO (spark emission analyzer, model: SPECTROLAB, type: LAVMB08A) and an ICP apparatus manufactured by Rigaku Corporation (CIROS120 type) can be used.

  Further, when specifying C (carbon) and S (sulfur), in particular, an oxygen stream combustion (high frequency induction furnace combustion) -infrared absorption method defined in JIS G1211 is also used. Specifically, a carbon / sulfur analyzer manufactured by LECO, CS-200 may be mentioned.

  Furthermore, in specifying N (nitrogen) and O (oxygen), in particular, the nitrogen determination method for iron and steel specified in JIS G 1228 and the oxygen determination method for metal materials specified in JIS Z 2613 are also used. Specific examples include an oxygen / nitrogen analyzer manufactured by LECO, TC-300 / EF-300.

  The metal powder for powder metallurgy according to the present invention preferably has a martensitic stainless steel crystal structure. The crystal structure of martensitic stainless steel is a body-centered cubic lattice in which C and N are dissolved in a supersaturated state, and thus is slightly distorted as compared with a normal body-centered cubic lattice. For this reason, the metal powder for powder metallurgy having such a crystal structure can produce a sintered body having a high hardness reflecting the distortion of the crystal structure.

  Note that whether or not the metal powder for powder metallurgy has a martensitic stainless steel crystal structure can be determined by, for example, an X-ray diffraction method.

  The average particle size of the metal powder for powder metallurgy of the present invention is preferably 0.5 μm or more and 30 μm or less, more preferably 1 μm or more and 20 μm or less, and further preferably 2 μm or more and 10 μm or less. By using the metal powder for powder metallurgy having such a particle size, the number of voids remaining in the sintered body is extremely reduced, and thus a sintered body having a particularly high density and excellent mechanical properties can be produced. .

  The average particle size is obtained as the particle size when the cumulative amount is 50% from the small diameter side in the cumulative particle size distribution on a mass basis obtained by the laser diffraction method.

  In addition, when the average particle diameter of the metal powder for powder metallurgy is below the lower limit, in the case of a shape that is difficult to mold, there is a possibility that the moldability is lowered and the sintered density is lowered, and the upper limit is exceeded. Since the gaps between the particles become large during molding, the sintered density may also decrease.

  The particle size distribution of the metal powder for powder metallurgy is preferably as narrow as possible. Specifically, when the average particle size of the metal powder for powder metallurgy is within the above range, the maximum particle size is preferably 200 μm or less, and more preferably 150 μm or less. By controlling the maximum particle size of the metal powder for powder metallurgy within the above range, the particle size distribution of the metal powder for powder metallurgy can be narrowed, and the density of the sintered body can be further increased.

  The maximum particle size refers to the particle size when the cumulative amount is 99.9% from the small diameter side in the cumulative particle size distribution on a mass basis obtained by the laser diffraction method.

  Further, when the short diameter of the metal powder metal powder powder powder is S [μm] and the long diameter is L [μm], the average aspect ratio defined by S / L is about 0.4 or more and 1 or less. It is preferable that it is about 0.7 or more and 1 or less. Since the metal powder for powder metallurgy having such an aspect ratio has a shape that is relatively close to a spherical shape, the filling rate when formed is increased. As a result, the sintered body can be further densified.

  The major axis is the maximum length that can be taken in the projected image of the particle, and the minor axis is the maximum length that can be taken in the direction orthogonal to the maximum length. Moreover, the average value of aspect ratio is calculated | required as an average value of the value of the aspect ratio measured about 100 or more particle | grains.

Moreover, the tap density of the metal powder for powder metallurgy of the present invention is preferably 3.5 g / cm ³ or more, more preferably 4 g / cm ³ or more. When the metal powder for powder metallurgy has such a large tap density, the filling property between the particles is particularly high when obtaining a compact. For this reason, a particularly dense sintered body can be finally obtained.

The specific surface area of the metal powder for powder metallurgy of the present invention is not particularly limited, but is preferably 0.1 m ² / g or more, and more preferably 0.2 m ² / g or more. Thus, if it is a metal powder for powder metallurgy with a large specific surface area, since surface activity (surface energy) will become high, it can sinter easily even if provision of less energy. Therefore, when the molded body is sintered, a difference in sintering speed hardly occurs between the inside and the outside of the molded body, and it is possible to suppress a decrease in the sintered density due to remaining voids on the inside. .

[Method for producing sintered body]
Next, a method for producing a sintered body using such metal powder for powder metallurgy according to the present invention will be described.

  The method for producing a sintered body includes [A] a composition preparation step for preparing a composition for producing a sintered body, [B] a molding step for producing a molded body, and [C] a degreasing step for performing a degreasing treatment. And [D] a firing step for firing. Hereinafter, each process will be described sequentially.

[A] Composition Preparation Step First, the metal powder for powder metallurgy of the present invention and a binder are prepared and kneaded with a kneader to obtain a kneaded product (composition).

In the kneaded product (the embodiment of the compound of the present invention), the metal powder for powder metallurgy is uniformly dispersed.
The metal powder for powder metallurgy of the present invention is produced by various powdering methods such as an atomizing method (for example, a water atomizing method, a gas atomizing method, a high-speed rotating water atomizing method, etc.), a reduction method, a carbonyl method, and a pulverizing method. .

  Among these, the metal powder for powder metallurgy of the present invention is preferably manufactured by an atomizing method, and more preferably manufactured by a water atomizing method or a high-speed rotating water atomizing method. The atomizing method is a method for producing a metal powder by causing molten metal (molten metal) to collide with a fluid (liquid or gas) jetted at high speed, thereby pulverizing and cooling the molten metal. By producing metal powder for powder metallurgy by such an atomizing method, extremely fine powder can be produced efficiently. Moreover, the particle shape of the obtained powder becomes close to a spherical shape due to the effect of surface tension. For this reason, a thing with a high filling rate is obtained when shape | molding. That is, a powder capable of producing a high-density sintered body can be obtained.

In addition, when the water atomizing method is used as the atomizing method, the pressure of water sprayed toward the molten metal (hereinafter referred to as “atomized water”) is not particularly limited, but is preferably 75 MPa or more and 120 MPa or less (750 kgf). / Cm ² or more and 1200 kgf / cm ² or less), more preferably 90 MPa or more and 120 MPa or less (900 kgf / cm ² or more and 1200 kgf / cm ² or less).

  The temperature of the atomized water is not particularly limited, but is preferably about 1 ° C. or higher and 20 ° C. or lower.

  Furthermore, atomized water is often sprayed in a conical shape having an apex on the molten metal drop path and the outer diameter gradually decreasing downward. In this case, the apex angle θ of the cone formed by the atomized water is preferably about 10 ° to 40 °, more preferably about 15 ° to 35 °. Thereby, the metal powder for powder metallurgy having the composition as described above can be reliably produced.

  Moreover, according to the water atomization method (especially high-speed rotation water flow atomization method), a molten metal can be cooled especially rapidly. For this reason, a high quality powder is obtained in a wide alloy composition.

Further, the cooling rate when the molten metal is cooled in the atomizing method is preferably 1 × 10 ⁴ ° C./s or more, and more preferably 1 × 10 ⁵ ° C./s or more. By such rapid cooling, for example, in the case of metal powder for powder metallurgy having a crystal structure of martensitic stainless steel, the ratio of retained austenite can be suppressed, so that a powder with less variation in characteristics can be obtained. As a result, a high-quality sintered body can be obtained.

  In addition, you may classify with respect to the metal powder for powder metallurgy obtained in this way as needed. Examples of classification methods include sieving classification, inertia classification, dry classification such as centrifugal classification, and wet classification such as sedimentation classification.

  On the other hand, examples of the binder include polyolefins such as polyethylene, polypropylene, and ethylene-vinyl acetate copolymers, acrylic resins such as polymethyl methacrylate and polybutyl methacrylate, styrene resins such as polystyrene, polyvinyl chloride, and polyvinylidene chloride. Various resins such as polyesters such as polyamide, polyethylene terephthalate, polybutylene terephthalate, polyether, polyvinyl alcohol, polyvinylpyrrolidone or copolymers thereof, various waxes, paraffin, higher fatty acids (eg stearic acid), higher alcohols, Examples include various organic binders such as higher fatty acid esters and higher fatty acid amides. Among these, one kind or a mixture of two or more kinds can be used.

  Among these, as the binder, those mainly composed of polyolefin are preferable. Polyolefin has a relatively high decomposability with a reducing gas. For this reason, when polyolefin is used as the main component of the binder, the molded product can be reliably degreased in a shorter time.

  Further, the content of the binder is preferably about 2% by mass or more and 20% by mass or less, more preferably about 5% by mass or more and 10% by mass or less of the entire kneaded product. When the content of the binder is within the above range, a molded body can be formed with good moldability, the density can be increased, and the shape stability of the molded body can be made particularly excellent. This also optimizes the difference in size between the molded body and the degreased body, the so-called shrinkage rate, and prevents the dimensional accuracy of the finally obtained sintered body from being lowered. That is, a sintered body with high density and high dimensional accuracy can be obtained.

  Moreover, a plasticizer may be added to the kneaded material as necessary. Examples of the plasticizer include phthalic acid esters (eg, DOP, DEP, DBP), adipic acid esters, trimellitic acid esters, sebacic acid esters, and the like, and one or more of these are mixed. Can be used.

  Furthermore, in addition to the metal powder for powder metallurgy, the binder, and the plasticizer, various additives such as a lubricant, an antioxidant, a degreasing accelerator, and a surfactant are added to the kneaded material as necessary. May be.

  The kneading conditions vary depending on various conditions such as the metal composition and particle size of the metal powder for powder metallurgy used, the composition of the binder, and the blending amount thereof. For example, kneading temperature: 50 ° C. or more and 200 ° C. Or less, kneading time: about 15 minutes or more and 210 minutes or less.

  Further, the kneaded product is formed into pellets (small lumps) as necessary. The particle size of the pellet is, for example, about 1 mm to 15 mm.

Depending on the molding method described later, a granulated powder may be produced instead of the kneaded product.
The granulated powder is obtained by binding a plurality of metal particles with a binder by subjecting the metal powder to a granulation treatment.

  Examples of the binder used in the production of the granulated powder include polyolefins such as polyethylene, polypropylene and ethylene-vinyl acetate copolymer, acrylic resins such as polymethyl methacrylate and polybutyl methacrylate, styrene resins such as polystyrene, Various resins such as polyesters such as vinyl chloride, polyvinylidene chloride, polyamide, polyethylene terephthalate, polybutylene terephthalate, polyether, polyvinyl alcohol, polyvinyl pyrrolidone or copolymers thereof, various waxes, paraffin, higher fatty acids (eg, stearin) Acid), higher alcohols, higher fatty acid esters, higher fatty acid amides, and other organic binders. Among these, one or a mixture of two or more can be used.

  Among these, as a binder, what contains polyvinyl alcohol or polyvinylpyrrolidone is preferable. Since these binder components have high binding properties, a granulated powder can be efficiently formed even in a relatively small amount. In addition, since it has high thermal decomposability, it can be reliably decomposed and removed in a short time during degreasing and firing.

  Further, the content of the binder is preferably about 0.2% by mass or more and 10% by mass or less, more preferably about 0.3% by mass or more and 5% by mass or less of the whole granulated powder. More preferably, it is 3 mass% or more and 2 mass% or less. When the binder content is in the above range, granulated powder is efficiently formed while reliably preventing remarkably large particles from being granulated or remaining ungranulated metal particles. be able to. Moreover, since the moldability is improved, the shape stability of the molded body can be made particularly excellent. In addition, by setting the binder content within the above range, the difference in size between the molded body and the degreased body, the so-called shrinkage rate, is optimized to prevent the dimensional accuracy of the finally obtained sintered body from being lowered. can do.

  Furthermore, various additives, such as a plasticizer, a lubricant, an antioxidant, a degreasing accelerator, and a surfactant, may be added to the granulated powder as necessary.

On the other hand, examples of the granulation treatment include a spray drying (spray drying) method, a rolling granulation method, a fluidized bed granulation method, and a rolling fluidization granulation method.
In the granulation treatment, a solvent that dissolves the binder is used as necessary. Examples of such solvents include water, inorganic solvents such as carbon tetrachloride, ketone solvents, alcohol solvents, ether solvents, cellosolve solvents, aliphatic hydrocarbon solvents, aromatic hydrocarbon solvents, aromatic solvents. Organic solvent such as aromatic heterocyclic compound solvent, amide solvent, halogen compound solvent, ester solvent, amine solvent, nitrile solvent, nitro solvent, aldehyde solvent, and the like. One kind or a mixture of two or more kinds is used.

  The average particle size of the granulated powder is not particularly limited, but is preferably about 10 to 200 μm, more preferably about 20 to 100 μm, and more preferably about 25 to 60 μm. The granulated powder having such a particle size has good fluidity and can more accurately reflect the shape of the mold.

[B] Molding Step Next, the kneaded product or the granulated powder is molded to produce a molded body having the same shape as the intended sintered body.

  The production method (molding method) of the molded body is not particularly limited. For example, various molding methods such as a compacting (compression molding) method, a metal powder injection molding (MIM) method, and an extrusion molding method are used. Can be used.

Among these, the molding conditions in the case of the compacting method vary depending on various conditions such as the composition and particle size of the metal powder for powder metallurgy used, the composition of the binder, and the blending amount thereof, but the molding pressure is 200 MPa or more and 1000 MPa or less. It is preferably about (2 t / cm ² or more and 10 t / cm ² or less).

Further, although the molding conditions in the metal powder injection molding method vary depending on various conditions, the material temperature is about 80 ° C. to 210 ° C., and the injection pressure is 50 MPa to 500 MPa (0.5 t / cm ^{2 to} 5 t / cm ^2). The following is preferable.

In addition, although the molding conditions in the extrusion molding method vary depending on various conditions, the material temperature is about 80 ° C. to 210 ° C., and the extrusion pressure is 50 MPa to 500 MPa (0.5 t / cm ^{2 to} 5 t / cm ² ). It is preferable that it is about.

  The molded body thus obtained is in a state where the binder is uniformly distributed in the gaps between the plurality of particles of the metal powder.

  In addition, the shape dimension of the molded object produced is determined in consideration of the shrinkage | contraction part of the molded object in a subsequent degreasing process and a baking process.

[C] Degreasing process Next, the obtained molded body is subjected to a degreasing treatment (debinding treatment) to obtain a degreased body.

  Specifically, the molded body is heated to decompose the binder, thereby removing the binder from the molded body and performing a degreasing process.

  Examples of the degreasing treatment include a method of heating the molded body, a method of exposing the molded body to a gas that decomposes the binder, and the like.

  When using the method of heating the molded body, the heating condition of the molded body is preferably about 100 ° C. or higher and 750 ° C. or lower × 0.1 hour or longer and 20 hours or shorter, although it varies slightly depending on the composition and blending amount of the binder. 150 ° C. or more and 600 ° C. or less × 0.5 hours or more and 15 hours or less is more preferable. Thereby, degreasing | defatting of a molded object can be performed sufficiently and necessary, without sintering a molded object. As a result, it is possible to reliably prevent a large amount of binder component from remaining inside the degreased body.

  The atmosphere for heating the molded body is not particularly limited, and is a reducing gas atmosphere such as hydrogen, an inert gas atmosphere such as nitrogen or argon, an oxidizing gas atmosphere such as air, or these atmospheres. The reduced pressure atmosphere etc. which reduced pressure is mentioned.

On the other hand, examples of the gas that decomposes the binder include ozone gas.
In addition, such a degreasing process is performed by dividing into a plurality of processes (steps) having different degreasing conditions, so that the binder in the molded body can be decomposed and removed more quickly and not to remain in the molded body. Can do.

  Moreover, you may make it perform machining, such as cutting, grinding | polishing, and cutting | disconnection with respect to a degreased body as needed. Since the degreased body is relatively low in hardness and relatively rich in plasticity, it can be easily machined while preventing the shape of the degreased body from collapsing. According to such machining, a sintered body with high dimensional accuracy can be easily obtained finally.

[D] Firing step The degreased body obtained in the step [C] is fired in a firing furnace to obtain a sintered body.

  By this sintering, the metal powder for powder metallurgy is diffused at the interface between the particles, resulting in sintering. At this time, the degreased body is quickly sintered by the mechanism described above. As a result, an entirely dense and dense sintered body can be obtained.

  The firing temperature varies depending on the composition, particle size and the like of the metal powder for powder metallurgy used for the production of the molded body and the degreased body, but is set to about 980 ° C. or higher and 1330 ° C. or lower as an example. The temperature is preferably about 1050 ° C. or higher and 1260 ° C. or lower.

  The firing time is 0.2 hours or more and 7 hours or less, and preferably 1 hour or more and 6 hours or less.

  In the firing step, the sintering temperature or a firing atmosphere described later may be changed during the firing process.

  By setting the firing conditions in such a range, the entire defatted body can be sufficiently sintered while preventing oversintering due to excessive progress of sintering and enlargement of the crystal structure. As a result, a sintered body having a high density and particularly excellent mechanical properties can be obtained.

  Moreover, since the firing temperature is relatively low, the heating temperature in the firing furnace can be easily controlled, and thus the temperature of the degreased body is also likely to be constant. As a result, a more uniform sintered body can be produced.

  Furthermore, since the firing temperature as described above is a firing temperature that can be sufficiently realized in a general firing furnace, an inexpensive firing furnace can be used and a running cost can be suppressed. In other words, when the firing temperature is exceeded, it is necessary to use an expensive firing furnace using a special heat-resistant material, and the running cost may be increased.

  Further, the atmosphere during firing is not particularly limited, but in consideration of preventing significant oxidation of the metal powder, a reducing gas atmosphere such as hydrogen, an inert gas atmosphere such as argon, or these atmospheres The reduced pressure atmosphere etc. which reduced pressure is preferably used.

  The sintered body thus obtained has a high density and excellent mechanical properties. That is, a sintered body produced by molding a composition containing the metal powder for powder metallurgy of the present invention and a binder and then degreasing and sintering the sintered body is obtained by sintering a conventional metal powder. The relative density is higher than Therefore, according to the present invention, a high-density sintered body that could not be reached without additional processing such as HIP processing can be realized without additional processing.

  Specifically, according to the present invention, although it varies slightly depending on the composition of the metal powder for powder metallurgy, an improvement in relative density of 2% or more can be expected as an example.

  As a result, the relative density of the obtained sintered body can be expected to be 97% or more as an example (preferably 98% or more, more preferably 98.5% or more). A sintered body having a relative density in such a range is excellent in mechanical properties comparable to a smelting material, although it has a shape that is almost as close as the target shape by using powder metallurgy technology. Since it has characteristics, it can be applied to various machine parts and structural parts with little post-processing.

  In addition, the sintered body produced by molding, degreasing and sintering the composition containing the metal powder for powder metallurgy of the present invention and the binder has the conventional tensile strength and 0.2% proof stress. It becomes larger than the tensile strength and 0.2% proof stress of the sintered body similarly sintered using metal powder. This is presumably because the alloy composition was optimized to enhance the sinterability of the metal powder, thereby improving the mechanical properties.

  Further, the sintered body manufactured as described above has a high hardness surface. Specifically, although it varies slightly depending on the composition of the metal powder for powder metallurgy, the surface Vickers hardness is expected to be 570 or more and 1200 or less as an example. Further, it is expected to be preferably 600 or more and 1000 or less. The sintered body having such hardness has particularly high durability.

  Note that the sintered body has a sufficiently high density and mechanical properties without any additional treatment, but various additional treatments are required to further increase the density and improve the mechanical properties. You may make it give.

  As this additional process, for example, an additional process for increasing the density like the HIP process described above may be used, and various quenching processes, various sub-zero processes, various tempering processes, etc. may be used. These additional processes may be performed alone or in combination.

Among these, in the quenching treatment, the sintered body is heated for about 980 ° C. to 1200 ° C. for about 0.2 hours to 3 hours and then rapidly cooled. Thereby, although it changes with compositions of the metal powder for powder metallurgy, the crystal structure of austenite can be changed to the crystal structure of martensite. Therefore, this treatment is suitably used when manufacturing a sintered body including a crystal structure of martensitic stainless steel, for example.
Note that water cooling, oil cooling, or the like is used for rapid cooling in the quenching process.

  The sub-zero treatment is a treatment that does not change to the martensite crystal structure in the quenching treatment, but converts the remaining austenite crystal structure to martensite by cooling. The crystal structure of the remaining austenite often becomes martensite with the passage of time, but at this time, since the volume of the sintered body is changed, the size of the sintered body changes over time. Accompany. Therefore, by performing the sub-zero treatment after the quenching treatment, the crystal structure of the remaining austenite can be forcibly converted into martensite, and the occurrence of a problem of dimensional change with time can be prevented.

For cooling the sintered body, for example, dry ice, carbon dioxide gas, liquid nitrogen or the like is used.
The sub-zero treatment temperature is preferably about 0 ° C. or less, and the time is preferably about 0.2 hours or more and 3 hours or less.

  The tempering process is a process in which the sintered body after the quenching process is heated again at a lower temperature than the quenching process. Thereby, toughness can be provided, reducing the hardness of a sintered compact.

  The temperature of the tempering treatment is preferably about 100 ° C. to 200 ° C., and the time is preferably about 0.3 hours to 5 hours.

  In the above-described firing step and various additional treatments, the light element in the metal powder (in the sintered body) volatilizes, and the composition of the finally obtained sintered body slightly changes from the composition in the metal powder. Sometimes it is.

  For example, although C varies depending on the process conditions and processing conditions, the content in the final sintered body is within the range of 5% to 100% of the content in the metal powder for powder metallurgy (preferably 30). % In the range of not less than 100% and not more than 100%).

  O also varies depending on process conditions and processing conditions, but the content in the final sintered body is in the range of 1% to 50% of the content in the metal powder for powder metallurgy (preferably 3 % In the range of not less than 50% and not more than 50%).

  On the other hand, as described above, the manufactured sintered body may be subjected to the HIP process as part of an additional process performed as necessary. However, even if the HIP process is performed, a sufficient effect may not be exhibited. Many. In the HIP process, the sintered body can be further densified, but the sintered body obtained by the present invention has already been sufficiently densified at the end of the firing step. For this reason, even if the HIP process is further performed, it is difficult to further increase the density.

  In addition, in the HIP process, it is necessary to pressurize the object to be processed through a pressure medium, so that the object to be processed is contaminated, or the composition and physical properties of the object to be processed are unintentionally changed due to the contamination. There is a possibility that the object to be treated may be discolored due to contamination. Further, when the pressure is applied, residual stress is generated or increased in the object to be processed, and as this is released over time, there is a risk of causing problems such as deformation and a decrease in dimensional accuracy.

  On the other hand, according to the present invention, since a sufficiently high density sintered body can be manufactured without performing such HIP treatment, the same high density and high strength as in the case of performing HIP treatment. It is possible to obtain a sintered body that has been made into a uniform shape. Such a sintered body has less contamination, discoloration, unintended composition and change in physical properties, etc., and less defects such as deformation and deterioration of dimensional accuracy. Therefore, according to the present invention, a sintered body having high mechanical strength and dimensional accuracy and excellent durability can be efficiently produced.

  In addition, the sintered body produced according to the present invention requires almost no additional treatment for the purpose of improving mechanical properties, and therefore the composition and crystal structure are likely to be uniform throughout the sintered body. For this reason, structural isotropy is high, and it becomes the thing excellent in the durability with respect to the load from all directions irrespective of a shape.

  As mentioned above, although the metal powder for powder metallurgy, compound, granulated powder, and sintered compact of this invention were demonstrated based on suitable embodiment, this invention is not limited to these.

  In addition, the sintered body of the present invention includes, for example, parts for transportation equipment such as parts for automobiles, parts for bicycles, parts for railway vehicles, parts for ships, parts for aircraft, parts for space transport aircraft (for example, rockets). , Parts for electronic devices such as parts for personal computers, parts for mobile phones, parts for electrical equipment such as refrigerators, washing machines, air conditioners, machine parts such as machine tools and semiconductor manufacturing equipment, nuclear power plants, It is used for plant parts such as thermal power plants, hydroelectric power plants, refineries, chemical complexes, clock parts, metal tableware, jewelry, decorative items such as eyeglass frames, and all structural parts.

Next, examples of the present invention will be described.
1. Manufacture of sintered body with molding by injection molding method (Sample No. 1)
[1] First, a metal powder having the composition shown in Table 1 manufactured by the water atomization method was prepared. The metal powder had an average particle size of 3.86 μm, a tap density of 4.38 g / cm ³ , and a specific surface area of 0.24 m ² / g.

  Moreover, the composition of the powder shown in Table 1 was identified and quantified by inductively coupled high-frequency plasma emission spectrometry (ICP method). For ICP analysis, an ICP device (CIROS120 type) manufactured by Rigaku Corporation was used. Further, a carbon / sulfur analyzer (CS-200) manufactured by LECO was used for identification and quantification of C and S. Further, an oxygen / nitrogen analyzer (TC-300 / EF-300) manufactured by LECO was used for identification and quantification of O.

  [2] Next, the metal powder and a mixture of polypropylene and wax (organic binder) were weighed and mixed so that the mass ratio was 9: 1 to obtain a mixed raw material.

[3] Next, the mixed raw material was kneaded with a kneader to obtain a compound.
[4] Next, this compound was molded by an injection molding machine under the molding conditions shown below to produce a molded body.

<Molding conditions>
-Material temperature: 150 ° C
Injection pressure: 11 MPa (110 kgf / cm ² )

  [5] Next, the obtained molded body was subjected to heat treatment (degreasing treatment) under the following degreasing conditions to obtain a degreased body.

<Degreasing conditions>
・ Degreasing temperature: 450 ° C
・ Degreasing time: 2 hours (holding time at the degreasing temperature)
・ Degreasing atmosphere: Nitrogen atmosphere

  [6] Next, the obtained degreased body was fired under the firing conditions shown below. This obtained the sintered compact. The shape of the sintered body was a cylindrical shape having a diameter of 10 mm and a thickness of 5 mm.

<Baking conditions>
・ Baking temperature: 1150 ° C
-Firing time: 3 hours (holding time at the firing temperature)
・ Baking atmosphere: Argon atmosphere

[7] Next, the obtained sintered body was subjected to quenching treatment under the following conditions.
<Quenching treatment conditions>
-Quenching temperature: 980 ° C
-Quenching time: 4 hours-Quenching atmosphere: Argon atmosphere-Cooling method: Water cooling

  [8] Next, the sintered body subjected to the quenching treatment was subjected to sub-zero treatment under the following conditions.

<Sub-zero treatment conditions>
Sub-zero treatment temperature: -196 ° C
・ Sub zero processing time: 2 hours

  [9] Next, the sintered body subjected to the sub-zero treatment was tempered under the following conditions.

<Tempering treatment conditions>
・ Tempering treatment temperature: 210 ℃
・ Tempering treatment time: 4 hours

(Sample Nos. 2-36)
Except for changing the composition and the like of the metal powder for powder metallurgy as shown in Table 1, each sample No. A sintered body was obtained in the same manner as in the method for producing a sintered body of No. 1. Sample No. The sintered body of Sample No. The sintered body obtained in 35 is further subjected to HIP treatment under the following conditions to increase the density of the sintered body. Sample No. The sintered bodies 28 to 30 were obtained using metal powders produced by the gas atomization method. In Table 1, “gas” is written in the remarks column.

<HIP processing conditions>
・ Heating temperature: 1100 ° C
・ Heating time: 2 hours ・ Pressure: 100 MPa

  In Table 1, each sample No. Among these metal powders for powder metallurgy and sintered bodies, those corresponding to the present invention are referred to as “Examples”, and those not corresponding to the present invention are referred to as “Comparative Examples”.

(Sample No. 37-67)
Except for changing the composition of the metal powder for powder metallurgy as shown in Table 2, each sample No. A sintered body was obtained in the same manner as in the method for producing a sintered body of No. 1. Sample No. The sintered body of No. 67 is sample no. The sintered body obtained in 66 is further subjected to HIP treatment under the following conditions to increase the density of the sintered body. Sample No. The sintered bodies 57 to 59 were obtained using metal powders produced by the gas atomizing method. In Table 2, “gas” is written in the remarks column.

<HIP processing conditions>
・ Heating temperature: 1100 ° C
・ Heating time: 2 hours ・ Pressure: 100 MPa

  In Table 2, each sample No. Among these metal powders for powder metallurgy and sintered bodies, those corresponding to the present invention are referred to as “Examples”, and those not corresponding to the present invention are referred to as “Comparative Examples”.

2. 2. Evaluation of Sintered Body with Molding by Injection Molding Method 2.1 Evaluation of Relative Density In accordance with the method of measuring the density of the sintered metal material specified in JIS Z 2501, the sintered metal was measured and the metal for powder metallurgy used to manufacture each sintered body The relative density of each sintered body was calculated with reference to the true density of the powder.
The calculation results are shown in Tables 3 and 4.

2.2 Evaluation of Vickers hardness The Vickers hardness of the sintered body was measured according to the test method of the Vickers hardness test specified in JIS Z 2244.
The measurement results are shown in Tables 3 and 4.

2.3 Evaluation of tensile strength, 0.2% proof stress and elongation With respect to the sintered body, tensile strength, 0.2% proof stress and elongation were measured according to the metal material tensile test method specified in JIS Z 2241.
And about these measured physical-property values, it evaluated in accordance with the following evaluation criteria.

<Evaluation criteria for tensile strength>
A: The tensile strength of the sintered body is very large (1800 MPa or more).
B: The tensile strength of the sintered body is large (1600 MPa to less than 1800 MPa)
C: Sintered body has a slightly high tensile strength (1400 MPa to less than 1600 MPa)
D: The tensile strength of the sintered body is slightly small (from 1200 MPa to less than 1400 MPa)
E: The tensile strength of the sintered body is small (1000 MPa or more and less than 1200 MPa)
F: The tensile strength of the sintered body is very small (800 MPa or more and less than 1000 MPa)
G: The tensile strength of the sintered body is particularly small (less than 800 MPa)

<Evaluation criteria for 0.2% proof stress>
A: The 0.2% proof stress of the sintered body is very large (1200 MPa or more).
B: The 0.2% yield strength of the sintered body is large (1100 MPa or more and less than 1200 MPa).
C: The 0.2% yield strength of the sintered body is slightly large (1000 MPa or more and less than 1100 MPa)
D: The 0.2% yield strength of the sintered body is slightly small (900 MPa or more and less than 1000 MPa)
E: The 0.2% yield strength of the sintered body is small (800 MPa or more and less than 900 MPa)
F: The 0.2% yield strength of the sintered body is very small (700 MPa or more and less than 800 MPa)
G: The 0.2% proof stress of the sintered body is particularly small (less than 700 MPa)

<Evaluation criteria for elongation>
A: The elongation of the sintered body is very large (7% or more)
B: The elongation of the sintered body is large (from 6% to less than 7%)
C: The elongation of the sintered body is slightly large (5% or more and less than 6%)
D: The elongation of the sintered body is slightly small (4% or more and less than 5%)
E: The elongation of the sintered body is small (from 3% to less than 4%)
F: The elongation of the sintered body is very small (2% or more and less than 3%)
G: The elongation of the sintered body is particularly small (less than 2%)
The above evaluation results are shown in Tables 3 and 4.

  As apparent from Tables 3 and 4, the sintered body obtained in each example had a relative density as compared with the sintered body obtained in each comparative example (excluding those subjected to HIP treatment). It was found to be high and have a high Vickers hardness. It was also recognized that there were significant differences in properties such as tensile strength, 0.2% proof stress and elongation.

3. Manufacture of sintered body with molding by compacting method (Sample No. 68)
[1] First, a metal powder having the composition shown in Table 5 was added to Sample No. As in the case of 1, it was produced by the water atomization method.
[2] Next, the metal powder was granulated by spray drying. The binder used at this time was polyvinyl alcohol, and the amount used was 1 part by mass with respect to 100 parts by mass of the metal powder. Moreover, 50 mass parts solvent (ion-exchange water) was used with respect to 1 mass part of polyvinyl alcohol. This obtained the granulated powder with an average particle diameter of 50 micrometers.

[3] Next, this granulated powder was molded by a press molding machine under the molding conditions shown below to produce a molded body. The shape of the molded body was a 20 mm square cube shape.
<Molding conditions>
・ Material temperature: 90 ℃
Molding pressure: 600 MPa (6 t / cm ² )

[4] Next, the obtained molded body was subjected to heat treatment (degreasing treatment) under the following degreasing conditions to obtain a degreased body.
<Degreasing conditions>
・ Degreasing temperature: 450 ° C
・ Degreasing time: 2 hours (holding time at the degreasing temperature)
・ Degreasing atmosphere: Nitrogen atmosphere

[5] Next, the obtained degreased body was fired under the firing conditions shown below. This obtained the sintered compact.
<Baking conditions>
・ Baking temperature: 1150 ° C
-Firing time: 3 hours (holding time at the firing temperature)
-Firing atmosphere: Argon atmosphere [6] Next, sample no. As in the case of 1, the obtained sintered body was subjected to quenching treatment, sub-zero treatment and tempering treatment.

(Sample No. 69-84)
Except for changing the composition and the like of the metal powder for powder metallurgy as shown in Table 5, each sample No. As in the case of 68, a sintered body was obtained. Sample No. The sintered body of No. 84 is Sample No. The 83 sintered body was further subjected to HIP treatment under the following conditions to increase the density of the sintered body.
<HIP processing conditions>
・ Heating temperature: 1100 ° C
・ Heating time: 2 hours ・ Pressure: 100 MPa

  In Table 5, each sample No. Among these metal powders for powder metallurgy and sintered bodies, those corresponding to the present invention are referred to as “Examples”, and those not corresponding to the present invention are referred to as “Comparative Examples”.

4). 4. Evaluation of sintered body with compaction by compacting method 4.1 Evaluation of relative density In accordance with the method of measuring the density of the sintered metal material specified in JIS Z 2501, the sintered metal was measured and the metal for powder metallurgy used to manufacture each sintered body The relative density of each sintered body was calculated with reference to the true density of the powder.
Table 6 shows the calculation results.

4.2 Evaluation of Vickers hardness The Vickers hardness of the sintered body was measured according to the test method of the Vickers hardness test specified in JIS Z 2244.
Table 6 shows the measurement results.

4.3 Evaluation of tensile strength, 0.2% proof stress and elongation With respect to the sintered body, tensile strength, 0.2% proof stress and elongation were measured according to the metal material tensile test method specified in JIS Z 2241.
And about these measured physical-property values, it evaluated in accordance with the above-mentioned evaluation criteria.
The above evaluation results are shown in Table 6.

  As can be seen from Table 6, the sintered bodies obtained in each Example have a high relative density even if the sintered body is sintered by a compacting method (press molding method), and the Vickers It was recognized that the hardness was also high. Moreover, it was recognized that there was a significant difference from the sintered body obtained in the comparative example with respect to characteristics such as tensile strength, 0.2% proof stress and elongation.

  From the above, in the sintered body formed by sintering the Fe—Cr—C—Si alloy powder, Zr and Nb are added appropriately to increase the density as in the HIP process. It has become clear that higher density and higher hardness can be achieved without additional processing.

  In addition, in the sintered compact which performed the HIP process, the high density and high hardness comparable as the sintered compact obtained in each Example were implement | achieved. Therefore, according to the present invention, it has been clarified that a higher density than the HIP process can be achieved without performing the HIP process.

  Moreover, when the content rate of the impurity in the metal powder for powder metallurgy obtained in each Example was measured, all were less than 0.03 mass%.

  Sample No. When the C content and the O content in the sintered body 1 were measured again, they were 0.75% by mass and 0.02% by mass.

  Sample No. In the sintered body of No. 1, the relative density of the sintered body before performing the quenching treatment, the sub-zero treatment and the tempering treatment (sintered body immediately after sintering) was evaluated in the same manner as in 2.1. A value equivalent to that shown in 3 was obtained.

Claims (24)

Fe is the main component,
Cr is included in a proportion of 10% by mass to 30% by mass,
C is contained at a ratio of 0.15% by mass or more and 1.5% by mass or less,
Si is contained in a ratio of 0.3% by mass or more and 1% by mass or less,
Zr is included in a proportion of 0.01% by mass or more and 0.5% by mass or less,
Nb is included in a proportion of 0.01% by mass or more and 0.5% by mass or less,
Mn and Ni are included in a ratio of 0.05% by mass or more and 1.6% by mass or less in total ,
Powder metallurgy metal powder Mo content is characterized der Rukoto than 0.8 wt%. Fe is the main component,
Cr is contained in a ratio of 10.5% by mass or more and 20% by mass or less,
C is contained in a proportion of 0.35 mass% to 1.15 mass%,
Si is contained at a ratio of 0.4 mass% or more and 0.85 mass% or less,
Zr is contained in a ratio of 0.03% by mass or more and 0.2% by mass or less,
Nb is contained in a ratio of 0.03% by mass or more and 0.2% by mass or less,
Mn and Ni are included in a ratio of 0.08% by mass to 1.3% by mass in total ,
Powder metallurgy metal powder Mo content is characterized der Rukoto than 0.8 wt%. Fe is the main component,
Cr is included at a ratio of 11% by mass or more and 18% by mass or less,
C is contained at a ratio of 0.4% by mass or more and 1.1% by mass or less,
Si is contained in a proportion of 0.5% by mass or more and 0.8% by mass or less,
Zr is included at a ratio of 0.05% by mass or more and 0.1% by mass or less,
Nb is included in a proportion of 0.05% by mass or more and 0.1% by mass or less,
Mn and Ni are included in a ratio of 0.1% by mass or more and 1% by mass or less in total ,
Powder metallurgy metal powder Mo content is characterized der Rukoto than 0.8 wt%.   The metal powder for powder metallurgy according to any one of claims 1 to 3, which has a martensite crystal structure.   The metal powder for powder metallurgy according to any one of claims 1 to 4, wherein a ratio Zr / Nb of a content ratio of Zr to a content ratio of Nb is 0.3 or more and 3 or less.   The metal powder for powder metallurgy according to any one of claims 1 to 4, wherein a ratio Zr / Nb of a content ratio of Zr to a content ratio of Nb is 0.5 or more and 2 or less.   The metal powder for powder metallurgy according to any one of claims 1 to 6, wherein the total content of Zr and Nb is 0.05% by mass or more and 0.6% by mass or less.   The metal powder for powder metallurgy according to any one of claims 1 to 6, wherein the total content of Zr and Nb is 0.1% by mass or more and 0.48% by mass or less.   The metal powder for powder metallurgy according to any one of claims 1 to 6, wherein the total content of Zr and Nb is 0.12% by mass or more and 0.24% by mass or less.   The ratio of (Zr + Nb) to Si content (Zr + Nb) / Si is 0.1 or more and 0.7 or less, where (Zr + Nb) is the sum of the Zr content and the Nb content. 10. The metal powder for powder metallurgy according to any one of 9 above.   The ratio of (Zr + Nb) to Si content (Zr + Nb) / Si is 0.15 or more and 0.6 or less, where (Zr + Nb) is the sum of the Zr content and Nb content. 10. The metal powder for powder metallurgy according to any one of 9 above.   The ratio of (Zr + Nb) to Si content (Zr + Nb) / Si is 0.17 or more and 0.5 or less, where (Zr + Nb) is the sum of the content of Zr and the content of Nb. 10. The metal powder for powder metallurgy according to any one of 9 above.   The metal powder for powder metallurgy according to any one of claims 1 to 12, wherein Mn is contained in a proportion of 0.01 mass% or more and 1.25 mass% or less.   The metal powder for powder metallurgy according to any one of claims 1 to 12, wherein Mn is contained in a proportion of 0.03% by mass to 0.3% by mass.   The metal powder for powder metallurgy according to any one of claims 1 to 12, wherein Mn is contained in a proportion of 0.05 mass% or more and 0.2 mass% or less.   The metal powder for powder metallurgy according to any one of claims 1 to 15, wherein Ni is contained in a proportion of 0.05 mass% or more and 0.6 mass% or less.   The metal powder for powder metallurgy according to any one of claims 1 to 15, wherein Ni is contained in a ratio of 0.06 mass% to 0.4 mass%.   The metal powder for powder metallurgy according to any one of claims 1 to 15, wherein Ni is contained at a ratio of 0.07 mass% or more and 0.25 mass% or less.   The metal powder for powder metallurgy according to any one of claims 1 to 18, wherein the average particle size is 0.5 µm or more and 30 µm or less.   A compound comprising: the metal powder for powder metallurgy according to any one of claims 1 to 19; and a binder that binds particles of the metal powder for powder metallurgy.   A granulated powder obtained by granulating the metal powder for powder metallurgy according to any one of claims 1 to 19. Fe is the main component,
Cr is included in a proportion of 10% by mass to 30% by mass,
C is contained at a ratio of 0.15% by mass or more and 1.5% by mass or less,
Si is contained in a ratio of 0.3% by mass or more and 1% by mass or less,
Zr is included in a proportion of 0.01% by mass or more and 0.5% by mass or less,
Nb is included in a proportion of 0.01% by mass or more and 0.5% by mass or less,
Mn and Ni are included in a ratio of 0.05% by mass or more and 1.6% by mass or less in total ,
Sintered bodies Mo content is characterized by being produced by sintering a metal powder for Der Ru powder metallurgy than 0.8 wt%. Fe is the main component,
Cr is included in a proportion of 10% by mass to 30% by mass,
C is contained at a ratio of 0.15% by mass or more and 1.5% by mass or less,
Si is contained in a ratio of 0.3% by mass or more and 1% by mass or less,
Zr is included in a proportion of 0.01% by mass or more and 0.5% by mass or less,
Nb is included in a proportion of 0.01% by mass or more and 0.5% by mass or less,
Mn and Ni are included in a ratio of 0.05% by mass or more and 1.6% by mass or less in total ,
Sintered bodies Mo content is characterized der Rukoto than 0.8 wt%.   The sintered body according to claim 22 or 23, wherein the relative density is 97% or more and the surface has a Vickers hardness of 570 or more.