CN104889379B

CN104889379B - Metal powder for powder metallurgy, composite, granulated powder, and sintered body

Info

Publication number: CN104889379B
Application number: CN201510091555.6A
Authority: CN
Inventors: 田村贵之; 中村英文
Original assignee: Seiko Epson Corp
Current assignee: Seiko Epson Corp
Priority date: 2014-03-04
Filing date: 2015-02-28
Publication date: 2020-03-03
Anticipated expiration: 2035-02-28
Also published as: CN104889379A; JP6354592B2; US20150252459A1; JP2015180767A

Abstract

The present invention relates to a metal powder for powder metallurgy, a composite, a granulated powder, and a sintered body. The metal powder for powder metallurgy is characterized in that Fe is a main component; contains 15 to 26 mass% of Cr; ni is contained in a proportion of 7 to 22 mass%; si is contained in a proportion of 0.3 to 1.2 mass%; contains 0.005-0.3 mass% of C; zr in a proportion of 0.01 to 0.5 mass%; and Nb in a proportion of 0.01 to 0.5 mass%. In addition, it preferably has an austenitic crystal structure.

Description

Metal powder for powder metallurgy, composite, granulated powder, and sintered body

Technical Field

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

Background

In the powder metallurgy method, a composition containing 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 production process of such a sintered body, a diffusion phenomenon of atoms occurs between the particles of the metal powder, whereby the compact gradually densifies and sintering is completed.

For example, patent document 1 proposes a metal powder for powder metallurgy containing Zr and Si, and the remainder being composed of at least one element selected from the group consisting of Fe, Co, and Ni, and an unavoidable element. According to such a metal powder for powder metallurgy, the sinterability is improved by the action of Zr, and a sintered body with high density can be easily produced.

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

However, depending on the use of the sintered body, further densification may be required. In this case, the sintered body is further subjected to an additional treatment such as Hot Isostatic Pressing (HIP) treatment to achieve high density, but the amount of work is significantly increased and the cost is inevitably high.

Accordingly, there is an increasing desire to realize a metal powder that can produce a sintered body of high density without applying additional processing.

Prior art documents

Patent document

Patent document 1: japanese patent laid-open No. 2012-87416

Disclosure of Invention

The purpose of the present invention is to provide a metal powder for powder metallurgy, a composite, and a granulated powder, which can produce a sintered body having a high density, and a sintered body having a high density produced using the metal powder for powder metallurgy.

The above object is achieved by the present invention described below.

The metal powder for powder metallurgy of the present invention is characterized in that Fe is a main component; contains 15 to 26 mass% of Cr; ni is contained in a proportion of 7 to 22 mass%; si is contained in a proportion of 0.3 to 1.2 mass%; contains 0.005-0.3 mass% of C; zr in a proportion of 0.01 to 0.5 mass%; and Nb in a proportion of 0.01 to 0.5 mass%.

This makes it possible to optimize the alloy composition and to promote densification of the metal powder for powder metallurgy during sintering. As a result, a metal powder for powder metallurgy that can produce a sintered body having a high density can be obtained without applying an additional treatment.

The metal powder for powder metallurgy of the present invention preferably has an austenitic crystal structure.

This can impart high corrosion resistance and high elongation to the sintered body to be produced. That is, a metal powder for powder metallurgy that can produce a sintered body having high corrosion resistance and high elongation in spite of high density can be obtained.

In the metal powder for powder metallurgy of the present invention, the ratio Zr/Nb of the Zr content to the Nb content is preferably 0.3 to 3.

Thus, when the metal powder for powder metallurgy is sintered, the timing shift between the precipitation of the Nb carbide and the precipitation of the Zr carbide can be optimized. As a result, the pores remaining in the molded body can be sequentially swept from the inside and discharged, and therefore, the pores generated in the sintered body can be minimized. Therefore, a metal powder for powder metallurgy which can produce a sintered body having a high density and excellent sintered body characteristics can be obtained.

In the metal powder for powder metallurgy of the present invention, the total of the Zr content and the Nb content is preferably 0.05 mass% or more and 0.6 mass% or less.

This makes it possible to produce a sintered body which is required to have a high density and is sufficient.

The metal powder for powder metallurgy according to the present invention more preferably contains Mo in a proportion of 1 mass% to 5 mass%.

This can prevent a significant decrease in the density of the sintered body to be produced, and can further enhance the corrosion resistance of the sintered body.

In the metal powder for powder metallurgy of the present invention, the average particle diameter is preferably 0.5 μm or more and 3.0 μm or less.

This makes it possible to produce a sintered body having a particularly high density and excellent mechanical properties, because the number of voids remaining in the sintered body is extremely small.

The composite of the present invention is characterized by containing: the metal powder for powder metallurgy of the present invention; and a binder for binding the particles of the metal powder for powder metallurgy to each other.

This makes it possible to obtain a composite that can produce a sintered body having a high density.

The granulated powder of the present invention is formed by granulating the metal powder for powder metallurgy of the present invention.

This can provide a granulated powder which can produce a sintered body having a high density.

The sintered body of the present invention is obtained by sintering a metal powder for powder metallurgy, the main component of which is Fe; contains 15 to 26 mass% of Cr; ni is contained in a proportion of 7 to 22 mass%; si is contained in a proportion of 0.3 to 1.2 mass%; contains 0.005-0.3 mass% of C; zr in a proportion of 0.01 to 0.5 mass%; and Nb in a proportion of 0.01 to 0.5 mass%.

Thus, a high-density sintered body can be obtained without applying additional processing.

The sintered body of the present invention preferably includes a first region in the form of particles and having a relatively high content of silicon oxide; and a second region having a relatively lower silicon oxide content than the first region.

This can reduce the oxide concentration in the crystal interior, suppress significant growth of crystal grains, and obtain a sintered body having a high density and excellent mechanical properties.

Detailed Description

The metal powder, composite, granulated powder and sintered body for powder metallurgy according to the present invention will be described in detail below.

Metal powder for powder metallurgy

First, the metal powder for powder metallurgy of the present invention will be explained.

In powder metallurgy, a composition containing a metal powder for powder metallurgy and a binder is formed 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 produced in a near-net shape (a shape close to a final shape) as compared with other metallurgical techniques.

As a metal powder for powder metallurgy used in powder metallurgy, conventionally, attempts have been made to achieve a high density of a sintered body to be produced by appropriately changing the composition thereof. However, since the sintered body is likely to have voids, it is necessary to achieve a further high density of the sintered body in order to obtain the same mechanical properties as those of the ingot.

Therefore, conventionally, the obtained sintered body is subjected to additional treatment such as hot isostatic pressing (HIP treatment) to increase the density. However, such additional processing is accompanied by a large amount of effort and cost, and therefore, it is an obstacle to the expansion of the use of the sintered body.

In view of the above-described problems, the present inventors have made extensive studies on conditions for obtaining a sintered body having a high density without applying additional treatment. As a result, the present inventors have found a composition capable of achieving a high density of a sintered body by optimizing the composition of an alloy constituting the metal powder, and have completed the present invention.

Specifically, the metal powder for powder metallurgy of the present invention is a metal powder comprising: contains 15 to 26 mass% of Cr; ni is contained in a proportion of 7 to 22 mass%; si is contained in a proportion of 0.3 to 1.2 mass%; contains 0.005-0.3 mass% of C; zr in a proportion of 0.01 to 0.5 mass%; nb is contained in a proportion of 0.01 to 0.5 mass%; the remainder is made up of Fe and other elements. Such a metal powder can optimize the alloy composition, and can particularly improve densification during sintering. As a result, a high-density sintered body can be produced without applying additional processing.

Further, by increasing the density of the sintered body, a sintered body having excellent mechanical properties can be obtained. Such a sintered body can be widely used for applications such as machine parts and structural parts to which an external force (load) is applied.

The alloy composition of the metal powder for powder metallurgy according to the present invention will be described in further detail below. In the following description, the metal powder for powder metallurgy is sometimes simply referred to as "metal powder".

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

The content of Cr in the metal powder is 15 mass% to 26 mass%, preferably 15.5 mass% to 25 mass%, more preferably 16 mass% to 21 mass%, and still more preferably 16 mass% to 20 mass%. If the content of Cr is less than the lower limit, the corrosion resistance of the sintered body produced will be insufficient depending on the overall composition. On the other hand, if the Cr content exceeds the upper limit, the sinterability decreases depending on the overall composition, and it becomes difficult to increase the density of the sintered body.

Further, a more preferable range of the Cr content is defined according to the Ni and Mo content described later. For example, when the content of Ni is 7 mass% or more and 22 mass% or less and the content of Mo is less than 1.2 mass%, the content of Cr is more preferably 18 mass% or more and 20 mass% or less. On the other hand, when the content of Ni is 10 mass% or more and 22 mass% or less, and the content of Mo is 1.2 mass% or more and 5 mass% or less, the content of Cr is more preferably 16 mass% or more and less than 18 mass%.

Ni is an element that similarly imparts corrosion resistance and heat resistance to the sintered body produced.

The content of Ni in the metal powder is 7 mass% to 22 mass%, preferably 7.5 mass% to 17 mass%, and more preferably 8 mass% to 15 mass%. By setting the Ni content within the above range, a sintered body excellent in long-term mechanical properties can be obtained.

When the content of Ni is less than the lower limit, corrosion resistance and heat resistance of the sintered body to be produced may not be sufficiently improved depending on the overall composition, while when the content of Ni exceeds the upper limit, corrosion resistance and heat resistance may be rather lowered.

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

The content of Si in the metal powder is 0.3 mass% or more and 1.2 mass% or less, preferably 0.4 mass% or more and 1 mass% or less, and more preferably 0.5 mass% or more and 0.9 mass% or less. If the content of Si is less than the lower limit, the effect of adding Si becomes insufficient depending on the overall composition, and therefore the corrosion resistance and mechanical properties of the sintered body to be produced are lowered. On the other hand, if the content of Si exceeds the above upper limit, the total composition will increase too much Si, which in turn will decrease the corrosion resistance and mechanical properties.

C (carbon) can particularly improve sinterability by using Zr and Nb described later in combination. Specifically, Zr and Nb are bonded to C to form carbides such as ZrC and NbC. The Zrc and NbC carbides are dispersed and precipitated, thereby producing an effect of preventing significant growth of crystal grains. Although the clear reason why such an effect can be obtained is not clear, one reason for this is that the dispersed precipitates become obstacles and inhibit the remarkable growth of crystal grains, and thus the variation in the size of crystal grains can be suppressed. This makes it difficult to form voids in the sintered body and prevents the expansion of crystal grains, thereby obtaining a sintered body having high density and high mechanical properties.

The content of C in the metal powder is 0.005 mass% or more and 0.3 mass% or less, preferably 0.008 mass% or more and 0.15 mass% or less, and more preferably 0.01 mass% or more and 0.08 mass% or less. If the content of C is less than the lower limit, crystal grains tend to grow depending on the composition of the whole body, and the mechanical properties of the sintered body become insufficient. On the other hand, if the content of C exceeds the above upper limit, the total composition will increase too much C, which in turn will decrease the sinterability.

Zr (zirconium) forms a solid solution with Fe to form a low melting point phase, but the low melting point phase causes rapid atomic diffusion at the time of sintering of the metal powder. Then, the atomic diffusion becomes a driving force to rapidly contract the inter-particle distance of the metal powder, and a neck is formed between the particles. As a result, the compact is densified and rapidly sintered.

On the other hand, the atomic radius of Zr is slightly larger than that of Fe. Specifically, the atomic radius of Fe is about 0.117nm, and the atomic radius of Zr is about 0.145 nm. Therefore, although Zr is in solid solution with Fe, it is not in solid solution completely, and a part of Zr is Zr carbide such as ZrC or ZrO₂Etc. Zr oxide (below)Collectively referred to as "Zr carbides") precipitate. And it is considered that the precipitated Zr carbide and the like inhibit the remarkable growth of the crystal grains when the metal powder is sintered. As a result, as described above, voids are less likely to be formed in the sintered body, and the expansion of crystal grains is prevented, whereby a sintered body having high density and high mechanical properties can be obtained.

As described in detail later, the precipitated Zr carbide or the like promotes the accumulation of silicon oxide at the grain boundaries, and as a result, the sintering is promoted and the density is increased while the expansion of the crystal grains is suppressed.

Further, Zr is a ferrite-forming element, and therefore precipitates a body-centered cubic lattice phase. This body-centered cubic lattice phase is superior in sinterability to other crystal lattice phases, and therefore contributes to the densification of the sintered body.

In addition, Zr functions as a deoxidizer for removing oxygen contained as an oxide in the metal powder. This can reduce the oxygen content, which causes a reduction in sinterability, and can further increase the density of the sintered body.

The content of Zr in the metal powder is 0.01 mass% or more and 0.5 mass% or less, preferably 0.03 mass% or more and 0.2 mass% or less, and more preferably 0.05 mass% or more and 0.1 mass% or less. If the Zr content is less than the lower limit, the effect of adding Zr becomes insufficient depending on the overall composition, and therefore, the density of the sintered body to be produced becomes insufficient. On the other hand, if the Zr content exceeds the upper limit, the proportion of carbide becomes too high due to too much Zr in the entire composition, which adversely impairs high density.

Nb (niobium) also has a slightly larger atomic radius than Fe but a slightly smaller atomic radius than Zr. Specifically, the atomic radius of Fe is about 0.117nm, and the atomic radius of Nb is about 0.134 nm. Therefore, a part of Nb is Nb carbide such as NbC or Nb₂O₅And Nb oxide (hereinafter collectively referred to as "Nb carbide") is precipitated. Therefore, it is considered that Zr carbide and the like are precipitated separately from Nb carbide and the like at the time of sintering, and these precipitates inhibit the remarkable growth of crystal grains and promote the deposition of silicon oxide at grain boundariesAnd (6) accumulating.

On the other hand, such precipitation of Zr carbide and Nb carbide starts in a lower temperature region than the precipitation of Nb carbide and the like. Although the reason is not clear, it is considered that the difference in atomic radius between Zr and Nb is related to the difference. Further, it is estimated that the timing of the effect of precipitation of Nb carbide or the like and the effect of precipitation of Zr carbide or the like are different when the metal powder is sintered, depending on the temperature range of carbide precipitation. It is considered that the occurrence of variation in the timing of carbide precipitation suppresses the formation of voids and a dense sintered body can be obtained. That is, it is considered that the presence of both Nb carbide and Zr carbide can increase the density and suppress the expansion of crystal grains.

The Nb content in the metal powder is 0.01 mass% or more and 0.5 mass% or less, preferably 0.03 mass% or more and 0.2 mass% or less, and more preferably 0.05 mass% or more and 0.1 mass% or less. If the content of Nb is less than the lower limit, the effect of adding Nb is insufficient depending on the overall composition, and therefore the density of the sintered body to be produced becomes insufficient. On the other hand, if the Nb content exceeds the upper limit, the Nb content becomes too high depending on the overall composition, so that the carbide ratio becomes too high, and conversely, the density is increased at a loss.

When the ratio of the Zr content to the Nb content is Zr/Nb, the Zr/Nb content is preferably 0.3 to 3, and more preferably 0.5 to 2. By setting Zr/Nb within the above range, it is possible to optimize the timing of precipitation of Nb carbides and the like and precipitation of Zr carbides and the like. In this way, the cavities remaining in the compact can be sequentially swept out and discharged from the inside, and therefore the cavities 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 high density and excellent mechanical properties can be obtained.

As described above, the total content of Zr and Nb is preferably 0.05 mass% to 0.6 mass%, more preferably 0.10 mass% to 0.48 mass%, and still more preferably 0.12 mass% to 0.24 mass%. By setting the total of the Zr content and the Nb content within the above range, it becomes necessary and sufficient to increase the density of the sintered body to be produced.

When the ratio of the total of the Zr content and the Nb content to the Si content is (Zr + Nb)/Si, (Zr + Nb)/Si is preferably 0.1 to 0.7, more preferably 0.15 to 0.6, and further preferably 0.2 to 0.5. By setting (Zr + Nb)/Si within the above range, the decrease in toughness and the like at the time of addition of Si is sufficiently compensated by the addition of Zr and Nb. As a result, a metal powder which can produce a sintered body having excellent mechanical properties such as toughness and excellent corrosion resistance due to Si can be obtained in spite of its high density.

Further, it is considered that by adding an appropriate amount of Zr and Nb, the above-described Zr carbide and the above-described Nb carbide become "nuclei" at grain boundaries in the sintered body, and silicon oxide is accumulated. By the accumulation of silicon oxide at the grain boundaries, the oxide concentration inside the crystal is reduced, and therefore, the promotion of sintering is achieved. As a result, it is considered that densification of the sintered body is further promoted.

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

Further, as described above, the accumulated silicon oxide is likely to be located at the triple point of the grain boundary, and thus tends to be formed into a granular shape. Therefore, in the sintered body, the first region in which the granular shape is formed and the content of silicon oxide is relatively high and the second region in which the content of silicon oxide is relatively lower than that in the first region are easily formed. Due to the presence of the first region, as described above, it is possible to achieve a reduction in the oxide concentration inside the crystal and suppress a significant growth of crystal grains.

When qualitative and quantitative analysis is performed by an electron beam microanalyzer (EPMA) in each of the first region and the second region, O (oxygen) becomes a main element in the first region, and Fe becomes a main element in the second region. As described above, the first region exists mainly at the grain boundary, and the second region exists inside the crystal. Therefore, when the content ratio of Fe is compared with the content ratio of O and Si in the first region, the content ratio of Fe is larger than the sum of the content ratios of O and Si. On the other hand, in the second region, the sum of the contents of both elements, i.e., O and Si, is absolutely smaller than the content of Fe. From this, it was found that the accumulation of Si and O was achieved 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 and 10000 times or less the Fe content. The content of Si in the first region is preferably 3 times or more and 10000 times or less of the content of Si in the second region.

Further, at least one of the Zr content and the Nb content satisfies the relationship of the first region > the second region, although the composition ratio may vary. The following is thus shown: in the first region, the Zr carbide and the Nb carbide become nuclei for silicon carbide accumulation. Specifically, the Zr content in the first region is preferably 3 times or more and 10000 times or less the Zr content in the second region. Similarly, the Nb content in the first region is preferably 3 times or more and 10000 times or less the Nb content in the second region.

In addition, the accumulation of silicon oxide as described above is considered to be one cause of the densification of the sintered body. Therefore, it is considered that even in the case of the sintered body having a high density achieved by the present invention, silicon oxide may not be accumulated depending on the composition ratio.

The diameters of the first regions forming the granular shape vary depending on the Si content in the entire sintered body, but are all approximately 0.5 μm to 15 μm, and preferably approximately 1 μm to 10 μm. This can suppress a decrease in mechanical properties of the sintered body due to the accumulation of silicon oxide, and can sufficiently promote densification of the sintered body.

The diameter of the first region can be determined as an average value of diameters (circle equivalent diameters) of circles having the same area as the area of the first region determined by the shade in an electron micrograph of a cross section of the sintered body. In the averaging, 10 or more measurement values are used.

When the ratio of the total of the Zr content and the Nb content to the C content is (Zr + Nb)/C, (Zr + Nb)/C is preferably 1 to 16, more preferably 2 to 13, and further preferably 3 to 10. 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 an increase in density due to the addition of Zr and Nb. As a result, a metal powder capable of producing a sintered body excellent in mechanical properties such as tensile strength and toughness can be obtained.

The metal powder for powder metallurgy of the present invention may contain, in addition to these elements, at least one of Mn, Mo, Cu, N, and S as necessary. In addition, these elements are also inevitably contained in some cases.

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

The content of Mn in the metal powder is not particularly limited, but is preferably 0.01 mass% or more and 3 mass% or less, and more preferably 0.05 mass% or more and 1 mass% or less. By setting the Mn content within the above range, a sintered body having high density and excellent mechanical properties can be obtained.

When the content of Mn is less than the lower limit, the corrosion resistance and mechanical properties of the sintered body to be produced may not be sufficiently improved depending on the overall composition, while when the content of Mn exceeds the upper limit, the corrosion resistance and mechanical properties may be rather lowered.

Mo is an element that enhances the corrosion resistance of the produced sintered body.

The content of Mo in the metal powder is not particularly limited, but is preferably 1 mass% or more and 5 mass% or less, more preferably 1.2 mass% or more and 4 mass% or less, and further preferably 2 mass% or more and 3 mass% or less. By setting the content of Mo within the above range, the corrosion resistance of the sintered body can be further enhanced without causing a significant decrease in the density of the sintered body to be produced.

Cu is an element that enhances the corrosion resistance of the sintered body to be produced.

The content of Cu in the metal powder is not particularly limited, but is preferably 5 mass% or less, and more preferably 1 mass% or more and 4 mass% or less. By setting the Cu content within the above range, the corrosion resistance of the sintered body can be further enhanced without causing a significant decrease in the density of the sintered body to be produced.

N is an element for improving mechanical properties such as yield strength of the sintered body to be produced.

The content of N in the metal powder is not particularly limited, but is preferably 0.03 mass% to 1 mass%, more preferably 0.08 mass% to 0.3 mass%, and still more preferably 0.1 mass% to 0.25 mass%. By setting the content of N within the above range, mechanical properties such as yield strength of the sintered body can be further improved without causing a significant decrease in density of the sintered body to be produced.

In addition, in the case of producing the metal powder to which N is added, for example, a method of using a raw material after nitriding, a method of introducing nitrogen gas into a molten metal, a method of subjecting the produced metal powder to nitriding treatment, and the like are used.

S is an element for improving the machinability of the sintered body to be produced.

The content of S in the metal powder is not particularly limited, but is preferably 0.5% by mass or less, and more preferably 0.01% by mass or more and 0.3% by mass or less. By setting the S content within the above range, the cutting performance of the produced sintered body can be further improved without causing a significant decrease in the density of the produced sintered body.

In addition, V, W, Co, B, Ti, Se, Te, Pd, Al, and the like may be added to the metal powder for powder metallurgy of the present invention. In this case, the content of each of these elements is not particularly limited, but is preferably less than 0.1% by mass, and even if the total content is less than 0.2% by mass. In addition, these elements are also inevitably contained in some cases.

The metal powder for powder metallurgy of the present invention may contain impurities. Examples of the impurities include all elements except for Fe, Cr, Ni, Si, C, Zr, Nb, Mn, Mo, Cu, N, S, V, W, Co, B, Ti, Se, Te, Pd, and Al, and specifically include Li, Be, Na, Mg, P, K, Ca, Sc, Zn, Ga, Ge, Y, Ag, In, Sn, Sb, Hf, Ta, Os, Ir, Pt, Au, and Bi. The amount of these impurities is preferably set so that each element has a smaller content than each of Fe, Cr, Ni, Si, C, Zr, and Nb. The amount of these impurities mixed is preferably set to less than 0.03 mass%, more preferably less than 0.02 mass%, of each element. The total amount is preferably less than 0.3% by mass, and more preferably less than 0.2% by mass. In addition, if the content ratio of these elements is within the above range, the effect is not hindered as described above, and therefore, these elements can be intentionally added.

On the other hand, although O (oxygen) may be intentionally added or inevitably mixed, the amount thereof is preferably about 0.8% by mass or less, more preferably about 0.5% by mass or less. By absorbing the amount of oxygen in the metal powder to such an extent, the sinterability becomes high, and a sintered body having a high density and excellent mechanical properties can be obtained. The lower limit is not particularly set, but is preferably 0.03 mass% or more from the viewpoint of ease of mass production and the like.

Fe is a component (main component) having the highest content in the alloy constituting the metal powder for powder metallurgy of the present invention, and has a large influence on the characteristics of the sintered body. The content of Fe is not particularly limited, but is preferably 50 mass% or more.

The composition ratio of the metal powder for powder metallurgy can be determined by, for example, iron and copper atom absorption spectrometry defined in JIS G1257 (2000), iron and copper ICP emission spectrometry defined in JIS G1258 (2007), iron and steel spark discharge emission spectrometry defined in JIS G1253 (2002), iron and steel X-ray fluorescence spectrometry defined in JIS G1256 (1997), weight, titration, absorptiometry defined in JIS G1211 to G1237, and the like. Specifically, there are mentioned, for example, a solid emission spectrum analyzer (spark discharge emission spectrum analyzer, model: SPECTROLA, type: LAVMB08A) manufactured by Spikek corporation and an ICP apparatus (CIROS120 type) manufactured by Rigaku (Co., Ltd.).

JIS G1211 to G1237 are as follows.

Method for determining iron and steel-carbon in JIS G1211 (2011)

JIS G1212 (1997) method for determining iron and steel-silicon

JIS G1213 (2001) method for determining manganese in iron and steel

JIS G1214 (1998) method for determining iron and steel-phosphorus

JIS G1215 (2010) method for determining iron and steel-sulfur content

JIS G1216 (1997) method for determining iron and steel-nickel content

JIS G1217 (2005) method for determining iron and steel-chromium

JIS G1218 (1999) method for determining iron and steel-molybdenum

JIS G1219 (1997) method for determining iron and steel-copper

JIS G1220 (1994) method for determining the quantity of iron and steel-tungsten

JIS G1221 (1998) method for quantifying iron and steel-vanadium

JIS G1222 (1999) method for determining iron and steel-cobalt

JIS G1223 (1997) method for determining iron and steel-titanium

JIS G1224 (2001) method for determining aluminum in iron and steel

JIS G1225 (2006) method for determining iron and Steel-arsenic

JIS G1226 (1994) method for determining iron and steel-tin

JIS G1227 (1999) method for determining boron in iron and steel

JIS G1228 (2006) method for determining iron and steel-nitrogen

JIS G1229 (1994) Steel-lead quantitative method

Method for determining zirconium in JIS G1232 (1980) steel

JIS G1233 (1994) steel-selenium quantitative method

Method for quantifying tellurium in JIS G1234 (1981) steel

Method for determining amount of antimony in iron and steel according to JIS G1235 (1981)

Method for quantifying tantalum in JIS G1236 (1992) steel

JIS G1237 (1997) method for determining iron and steel-niobium

In particular, when C (carbon) and S (sulfur) are specified, oxygen flow combustion (high-frequency induction furnace combustion) -infrared absorption method defined in JIS G1211 (2011) is also used. Specifically, there is mentioned a carbon/sulfur analyzer CS-200 manufactured by LECO.

In addition, when N (nitrogen gas) and O (oxygen gas) are specified, in particular, a method for determining nitrogen in iron and steel specified in JIS G1228 (2006) and a method for determining oxygen in a metal material specified in JIS Z2613 (2006) are also used. Specifically, there may be mentioned an oxygen/nitrogen analyzer TC-300/EF-300 manufactured by LECO.

In addition, the metal powder for powder metallurgy of the present invention preferably has an austenitic crystal structure. The austenitic crystal structure imparts high corrosion resistance and high elongation to the sintered body. Therefore, the metal powder for powder metallurgy having such a crystal structure can produce a sintered body having high corrosion resistance and high elongation in spite of its high density.

Whether or not the powder metallurgy metal powder has an austenitic crystal structure can be determined by, for example, an X-ray diffraction method.

The average particle diameter 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 diameter, since the number of pores remaining in the sintered body is extremely small, a sintered body having particularly high density and excellent mechanical properties can be produced.

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

When the average particle size of the metal powder for powder metallurgy is less than the lower limit, the formability may be reduced and the sintered density may be reduced in the case of a shape which is difficult to form, and when the average particle size exceeds the upper limit, the gaps between particles during forming may become large, and the sintered density may eventually be reduced.

The particle size distribution of the metal powder for powder metallurgy is preferably as narrow as possible. Specifically, if the average particle diameter of the metal powder for powder metallurgy is within the above range, the maximum particle diameter is preferably 200 μm or less, more preferably 150 μm or less. By controlling the maximum particle diameter of the metal powder for powder metallurgy within the above range, the particle size distribution of the metal powder for powder metallurgy can be made narrower, and higher density of the sintered body can be achieved.

The maximum particle size is a particle size at which the cumulative amount becomes 99.9% from the smaller diameter side in the cumulative particle size distribution on a mass basis obtained by the laser diffraction method.

When the short diameter and the long diameter of the particles of the metal powder for powder metallurgy are S [ mu ] m and L [ mu ] m, the average value of the aspect ratio defined by S/L is preferably from about 0.4 to 1, and more preferably from about 0.7 to 1. Since the metal powder for powder metallurgy having such an aspect ratio has a shape relatively close to a spherical shape, the filling ratio at the time of molding is improved. As a result, the density of the sintered body can be increased.

The long diameter is a maximum length that can be obtained in a projection image of the particle, and the short diameter is a maximum length that can be obtained in a direction orthogonal to the long diameter. The average aspect ratio is determined as an average value of the aspect ratios of 100 or more particles.

In addition, the tap density of the metal powder for powder metallurgy of the present invention is preferably 3.5g/cm³Above, more preferably 4g/cm³The above. When the metal powder for powder metallurgy has such a high tap density, the filling property between particles becomes particularly high when a compact is obtained. Thus, a particularly dense sintered body can be obtained in the end.

The specific surface area of the metal powder for powder metallurgy of the present invention is not particularly limited, but is preferably 0.1m²A value of at least one per gram, more preferably 0.2m²More than g. In the case of such a metal powder for powder metallurgy having a large specific surface area, the activity (surface energy) of the surface is high, and therefore, sintering can be easily performed even with a small amount of energy applied. Due to the fact thatIn this case, when the molded body is sintered, a difference in sintering speed between the inside and the outside of the molded body is less likely to occur, and it is possible to suppress a decrease in sintering density due to the remaining pores on the inside.

Method for producing sintered body

Next, a method for producing a sintered body using the metal powder for powder metallurgy of the present invention will be described.

The method for manufacturing a sintered body comprises: a preparing a composition for preparing a sintered body; b a molding step for producing a molded body; a degreasing step of applying a degreasing treatment; and D a firing step of firing. Next, the respective steps will be explained in order.

A composition preparation procedure

First, the metal powder for powder metallurgy of the present invention and a binder are prepared and kneaded by a kneader to obtain a kneaded product (composition).

In the kneaded mixture (embodiment of the composite of the present invention), the powder metallurgy metal powder is uniformly dispersed.

The metal powder for powder metallurgy of the present invention is produced by various powdering methods such as an atomization method (e.g., a water atomization method, a gas atomization method, a high-speed rotating water stream atomization method, etc.), a reduction method, a carbonyl method, a pulverization method, and the like.

Among them, the metal powder for powder metallurgy of the present invention is preferably produced by an atomization method, and more preferably produced by a water atomization method or a high-speed rotating water stream atomization method. The atomization method is a method of producing metal powder by causing molten metal (metal solution) to collide with a fluid (liquid or gas) injected at high speed to pulverize the molten metal and cool it. By producing the metal powder for powder metallurgy by such an atomization method, extremely fine powder can be efficiently produced. In addition, the particle shape of the obtained powder is close to spherical due to the action of surface tension. Therefore, a high filling rate can be obtained during molding. That is, a powder capable of producing a sintered body having a high density can be obtained.

In addition, as the atomization method, when a water atomization method is used, water is sprayed to the molten metal (hereinafter, referred to as "atomized water")The pressure of (A) is not particularly limited, but is preferably from about 75MPa to 120MPa (750 kgf/cm)²Above 1200kgf/cm²Below), more preferably from about 90MPa to 120MPa (900 kgf/cm)²Above 1200kgf/cm²Below).

The water temperature of the atomized water is not particularly limited, and is preferably about 1 ℃ to 20 ℃.

The atomized water is often sprayed in a conical shape having a vertex on the falling path of the molten metal and decreasing in outer diameter downward. At this time, the vertex angle θ of the cone formed by the atomized water is preferably about 10 ° to 40 °, and more preferably about 15 ° to 35 °. This enables the metal powder for powder metallurgy having the above composition to be reliably produced.

In addition, according to the water atomization method (particularly, the high-speed rotating water stream atomization method), it is possible to cool the molten metal particularly quickly. Therefore, high-quality powder can be obtained in a wide range of alloy compositions.

Further, the cooling rate in cooling the molten metal in the atomization method is preferably 1 × 10⁴More preferably 1X 10℃/s or higher⁵The temperature is higher than the second temperature. By such rapid cooling, a homogeneous metal powder for powder metallurgy can be obtained. As a result, a high-quality sintered body can be obtained.

The metal powder for powder metallurgy thus obtained may be classified as necessary. Examples of the classification method include dry classification such as screen classification, inertia classification and centrifugal classification, and wet classification such as sedimentation classification.

On the other hand, examples of the binder include polyolefins such as polyethylene, polypropylene, ethylene-vinyl acetate copolymers, acrylic resins such as polymethyl methacrylate and polybutyl methacrylate, styrene resins such as polystyrene, polyesters such as polyvinyl chloride, polyvinylidene chloride, polyamides, polyethylene terephthalate and polybutylene terephthalate, polyethers, polyvinyl alcohol, polyvinylpyrrolidone, copolymers of these, and various organic binders such as various waxes, paraffins, higher fatty acids (e.g., stearic acid), higher alcohols, higher fatty acid esters, and higher fatty acid amides, and one or more of these may be used in combination.

The content of the binder is preferably about 2 to 20 mass%, more preferably about 5 to 10 mass%, of the whole kneaded material. When the content of the binder is within the above range, a molded article having good moldability can be formed, the density can be increased, and the stability of the shape of the molded article can be particularly improved. In addition, this can optimize the large difference between the molded body and the degreased body, so-called shrinkage rate, and prevent the reduction in dimensional accuracy of the finally obtained sintered body. That is, a sintered body having high density and high dimensional accuracy can be obtained.

In addition, a plasticizer may be added to the kneaded mixture as needed. Examples of the plasticizer include phthalates (e.g., DOP, DEP, DBP), adipates, trimellitates, and sebacates, and one or more of these plasticizers can be used in combination.

In addition to the metal powder for powder metallurgy, a binder and a plasticizer, various additives such as a lubricant, an antioxidant, a degreasing accelerator and a surfactant may be added to the kneaded mixture as needed.

The kneading conditions vary depending on various conditions such as the metal composition of the metal powder for powder metallurgy to be used, the particle size, the composition of the binder, and the amounts of these components, and the kneading temperature can be set to about 50 ℃ to 200 ℃ inclusive, and the kneading time can be set to about 15 minutes to 210 minutes inclusive, as an example.

Further, the kneaded mixture is granulated (agglomerated) as necessary. The particle diameter of the particles is, for example, about 1mm to 15 mm.

Further, according to the molding method described later, instead of the kneaded product, granulated powder can be produced. The kneaded product and granulated powder of these are examples of the composition to be supplied to the molding step described later.

An embodiment of the granulated powder of the present invention is obtained by applying a granulation treatment to the metal powder for powder metallurgy of the present invention and bonding a plurality of metal particles to each other with a binder.

Examples of the binder used for the production of the granulated powder include polyolefins such as polyethylene, polypropylene, ethylene-vinyl acetate copolymers, acrylic resins such as polymethyl methacrylate and polybutyl methacrylate, styrene resins such as polystyrene, polyesters such as polyvinyl chloride, polyvinylidene chloride, polyamides, polyethylene terephthalate and polybutylene terephthalate, polyethers, polyvinyl alcohol, various resins such as polyvinylpyrrolidone and these copolymers, various types of organic binders such as waxes, paraffins, higher fatty acids (e.g., stearic acid), higher alcohols, higher fatty acid esters and higher fatty acid amides, and one or more of these may be used in combination.

Among them, polyvinyl alcohol or polyvinyl pyrrolidone is preferably contained as the binder. These binder components have high cohesiveness, and therefore, even a small amount thereof can form granulated powder with high efficiency. Further, since the thermal decomposition property is high, the decomposition and removal can be surely performed in a short time at the time of degreasing and firing.

The content of the binder is preferably about 0.2 to 10 mass%, more preferably about 0.3 to 5 mass%, and still more preferably 0.3 to 2 mass% of the entire granulated powder. When the content of the binder is within the above range, very large particles can be granulated, a large amount of non-granulated metal particles can be suppressed from remaining, and granulated powder can be efficiently formed. Further, the moldability is improved, and therefore, the stability of the shape of the molded article can be particularly improved. Further, by setting the content of the binder within the above range, the difference between the sizes of the compact and the degreased body, so-called shrinkage, can be optimized, and a reduction in dimensional accuracy of the finally obtained sintered body can be prevented.

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

On the other hand, examples of the granulation treatment include a spray drying method, a rotary granulation method, a fluidized bed granulation method, a rotary fluidized granulation method, and the like.

In the granulation treatment, a solvent for dissolving the binder is used as necessary. Examples of such a solvent include water, an inorganic solvent such as carbon tetrachloride, a ketone solvent, an alcohol solvent, an ether solvent, a cellosolve solvent, an aliphatic hydrocarbon solvent, an aromatic heterocyclic compound solvent, an amide solvent, a halogen compound solvent, an ester solvent, an amine solvent, a nitrile solvent, a nitro solvent, and an organic solvent such as an acetaldehyde solvent, and one or a mixture of two or more selected from these solvents can be used.

The average particle diameter of the granulated powder is not particularly limited, but is preferably from about 10 μm to 200 μm, more preferably from about 20 μm to 100 μm, and still more preferably from about 25 μm to 60 μm. The granulated powder having such a particle diameter has good fluidity and can reflect the shape of the molding die more faithfully.

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

B Process of Forming

Next, the kneaded product or granulated powder is molded to produce a molded body having the same shape as the target sintered body.

The method for producing the molded article (Molding method) is not particularly limited, and various Molding methods such as powder compaction (compression Molding), Metal powder Injection Molding (MIM) and extrusion Molding can be used.

Among them, the molding conditions in the powder compacting method vary depending on various conditions such as the composition and particle size of the metal powder for powder metallurgy to be used, the composition of the binder, and the amounts of these components, and the molding pressure is preferably 200MPa to 1000MPa (2 t/cm)²Above 10t/cm²Below) degree.

The molding conditions in the metal powder injection molding method vary depending on various conditionsHowever, the material temperature is preferably about 80 ℃ to 210 ℃ inclusive, and the injection pressure is preferably about 50MPa to 500MPa (0.5 t/cm)²Above 5t/cm²Below).

The molding conditions in the extrusion molding method vary depending on various conditions, but the material temperature is preferably from about 80 ℃ to 210 ℃ inclusive, and the extrusion pressure is preferably from about 50MPa to 500MPa inclusive (0.5 t/cm)²Above 5t/cm²Below).

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

The shape and size of the molded article to be produced are determined by predicting the shrinkage of the molded article in the subsequent degreasing step and firing step.

C degreasing step

Next, the obtained molded body was subjected to degreasing treatment (binder removal treatment) to obtain a degreased body.

Specifically, the binder is decomposed by heating the molded body, and the binder is removed from the molded body, thereby completing the degreasing treatment.

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.

In the case of using the method of heating the molded article, the heating conditions of the molded article are slightly different depending on the composition and the amount of the binder, but the temperature is preferably about 100 ℃ to 750 ℃ and 0.1 hour to 20 hours, more preferably 150 ℃ to 600 ℃ and 0.5 hour to 15 hours. Thereby, the molded body can be degreased as necessary and sufficiently without sintering the molded body. As a result, a large amount of binder component can be reliably prevented from remaining inside the degreased body.

The gas atmosphere when the molded body is heated is not particularly limited, and examples thereof include a reducing gas atmosphere such as hydrogen, an inert gas atmosphere such as nitrogen or argon, an oxidizing gas atmosphere such as the atmosphere, and a reduced-pressure gas atmosphere obtained by reducing the pressure of these gases.

On the other hand, examples of the gas for decomposing the binder include ozone gas and the like.

In addition, in such a degreasing step, by separately performing a plurality of steps (steps) under different degreasing conditions, the binder in the molded body can be decomposed and removed more quickly without remaining in the molded body.

Further, the degreased body may be subjected to machining such as cutting, polishing, or cutting, as necessary. Since the degreased body has relatively low hardness and large plasticity, the shape of the degreased body can be prevented from being deformed, and the degreased body can be easily machined. By such machining, a sintered body with high dimensional accuracy can be obtained easily in the end.

D firing Process

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 diffuses at the interfaces between the particles, and sintering is completed. At this time, the degreased body is rapidly sintered by the mechanism described above. As a result, a compact and high-density sintered body can be obtained as a whole.

The firing temperature varies depending on the composition, particle size, and the like of the metal powder for powder metallurgy used for producing the compact and the degreased body, but is, for example, approximately 980 ℃ to 1330 ℃. Further, it is preferably about 1050 ℃ to 1260 ℃ inclusive.

The firing time is 0.2 hours to 7 hours, preferably about 1 hour to 6 hours.

In the firing step, the firing temperature and a firing gas atmosphere described later may be changed in the middle of the firing step.

By setting the firing conditions within such a range, the entire degreased body can be sufficiently sintered while preventing excessive sintering and excessive expansion of the crystal structure. As a result, a sintered body having a high density and particularly excellent mechanical properties can be obtained.

Further, since the firing temperature is relatively low, the heating temperature can be easily controlled to be constant by the firing furnace, and therefore, the temperature of the degreased body can be easily controlled to be constant. As a result, a more homogeneous sintered body can be produced.

Further, since the firing temperature as described above is a firing temperature that can be sufficiently realized by a general firing furnace, an inexpensive firing furnace can be used, and the running cost can be suppressed. In other words, if the firing temperature exceeds the above firing temperature, an expensive firing furnace using a special heat-resistant material is required, and the running cost may increase.

Although the gas atmosphere during firing is not particularly limited, in view of preventing significant oxidation of the metal powder, it is preferable to use a reducing gas atmosphere such as hydrogen, an inert gas atmosphere such as argon, or a reduced-pressure gas atmosphere obtained by reducing the pressure of these gas atmospheres.

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, degreasing, and sintering has a higher relative density than a sintered body obtained by sintering a conventional metal powder. Therefore, according to the present invention, it is possible to realize a sintered body having a high density which cannot be achieved without applying the additional treatment such as the HIP treatment.

Specifically, according to the present invention, although the composition of the metal powder for powder metallurgy is slightly different, as an example, an improvement of the relative density of 2% or more can be expected as compared with the conventional art.

As a result, the relative density of the obtained sintered body can desirably be 97% or more (preferably 98% or more, and more preferably 98.5% or more), as an example. A sintered body having a relative density in such a range, although having a shape infinitely close to a target shape by utilizing a powder metallurgy technique, can be applied to various machine parts and structural parts with almost no post-processing since it has excellent mechanical properties comparable to an ingot.

Further, the tensile strength and 0.2% proof stress of a sintered body produced by molding a composition containing the metal powder for powder metallurgy of the present invention and a binder, degreasing, and sintering are higher than those of a sintered body sintered similarly using a conventional metal powder. This is presumably because the mechanical properties of the sintered body produced by optimizing the alloy composition improve the sinterability of the metal powder.

The surface of the sintered body produced as described above has high hardness. Specifically, the vickers hardness of the surface is desirably 140 to 500 as an example, although the composition of the metal powder for powder metallurgy is slightly different. Further, it is preferably 150 to 400. A sintered body having such hardness has particularly high durability.

In addition, although the sintered body has a sufficiently high density and mechanical properties without being subjected to additional treatment, various additional treatments may be applied in order to achieve higher density and improve mechanical properties.

The additional treatment may be an additional treatment for increasing the density, such as the HIP treatment described above, or may be various quenching treatments, various cryogenic treatments, various tempering treatments, or the like. These additional processes may be performed alone or in combination of a plurality of them.

In the above-described firing step and various additional treatments, light elements in the metal powder (in the sintered body) are exhibited, and the composition of the finally obtained sintered body may be slightly changed from the composition in the metal powder.

For example, the content of C in the final sintered body may vary within a range of 5% to 100% (preferably within a range of 30% to 100%) of the content of the metal powder for powder metallurgy, although the content varies depending on the process conditions and the treatment conditions.

Similarly, O may vary depending on the process conditions and the treatment conditions, but the content of O in the final sintered body may vary within a range of 1% to 50% (preferably within a range of 3% to 50%).

On the other hand, as described above, the produced sintered body can be subjected to the HIP treatment in one cycle of the additional treatment as needed, but the effect may not be sufficiently exhibited even if the HIP treatment is performed. Although the HIP treatment can achieve a higher density of the sintered body, the density of the sintered body obtained in the present invention is sufficiently increased already at the end of the firing step. Therefore, even if the HIP treatment is further performed, it is difficult to further increase the density.

Further, since the object to be treated needs to be pressurized by the pressure medium in the HIP treatment, the object to be treated may be contaminated, the composition and physical properties of the object to be treated may unexpectedly change due to contamination, and the object to be treated may discolor due to contamination. In addition, there is also a possibility that: the residual stress is generated or increased in the object to be processed by the pressurization, and the residual stress is released with time, thereby causing a problem of deformation or a reduction in dimensional accuracy.

In contrast, according to the present invention, since a sintered body having a sufficiently high density can be produced without applying such a HIP treatment, a sintered body having a high density and a high strength can be obtained as in the case of applying the HIP treatment. Further, such sintered body is less likely to be contaminated, discolored, unexpectedly changed in composition and physical properties, and the problems of deformation and reduction in dimensional accuracy are less likely to occur. 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, since the sintered body produced in the present invention requires almost no additional treatment for improving mechanical properties, the composition and crystal structure are easily uniform throughout the sintered body. Therefore, the structure is highly isotropic and excellent in durability against loads from all directions regardless of the shape.

It has been confirmed that in the sintered body thus manufactured, the porosity in the vicinity of the surface is relatively smaller than that in the interior. Although the reason for this is not clear, it is possible to cite that the sintering reaction proceeds more easily in the vicinity of the surface than in the interior of the compact by adding Zr and Nb.

Specifically, when the porosity in the vicinity of the surface of the sintered body is a1 and the porosity in the interior of the sintered body is a2, a2-a1 is preferably 0.5% to 10%, more preferably 1% to 5%. A sintered body having A2-A1 in such a range has a necessary and sufficient mechanical strength, and the surface can be easily flattened. That is, by polishing the surface of the sintered body, a surface having high mirror surface properties can be obtained.

Such a highly specular sintered body not only has high mechanical strength but also has excellent aesthetic properties. Therefore, this sintered body is also suitable for use in applications requiring a beautiful appearance.

The porosity a1 in the vicinity of the surface of the sintered body is a porosity in a range of 25 μm in the center radius at a position at a depth of 50 μm from the surface in the cross section of the sintered body. The porosity a2 in the sintered body is a porosity in a range of 25 μm in the center radius at a position at a depth of 300 μm from the surface in the cross section of the sintered body. These porosity ratios are values obtained by observing the cross section of the sintered body with a scanning electron microscope, and dividing the area of the pores present in the above-mentioned range by the area in the above-mentioned range.

The metal powder, composite, granulated powder and sintered body for powder metallurgy according to the present invention have been described above based on preferred embodiments, but the present invention is not limited thereto.

Further, the sintered body of the present invention is used for all structural parts such as automobile parts, bicycle parts, railway vehicle parts, ship parts, aircraft parts, transportation equipment parts such as parts of space vehicles (e.g., robots, etc.), computer parts, electronic equipment parts such as parts of mobile phone terminals, mechanical parts such as refrigerators, washing machines, air conditioners, machine parts such as machine tools, semiconductor manufacturing apparatuses, plant equipment parts such as nuclear power plants, thermal power plants, hydroelectric power plants, oil refineries, chemical complexes, watch parts, tableware, jewelry, ornaments such as spectacle frames, and the like.

Examples

Next, examples of the present invention will be explained.

1. Production of sintered body

(sample No.1)

1. First, metal powders having compositions shown in table 1, which were produced by a water atomization method, were prepared. The metal powder had an average particle diameter of 4.05 μm and a tap density of 4.20g/cm³The specific surface area is 0.23m²/g。

The compositions of the powders shown in table 1 were identified and quantified by inductively coupled plasma atomic emission spectrometry (ICP method). In the ICP analysis, an ICP apparatus (CIROS120 type) manufactured by Rigaku (ltd.) was used. For identification and quantification of C, a carbon/sulfur analyzer (CS-200) manufactured by LECO was used. Further, an oxygen/nitrogen analyzer (TC-300/EF-300) manufactured by LECO was used for the identification and quantification of O.

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

3. Then, the mixed raw materials were kneaded in a kneader to obtain a composite.

4. Next, the composite was molded by an injection molding machine under the molding conditions shown below to produce a molded article.

Molding conditions

Material temperature: 150 ℃ C

Injection pressure: 11MPa (110 kgf/cm)²)

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

Conditions of degreasing

Degreasing temperature: 500 deg.C

Degreasing time: 1 hour (holding time at degreasing temperature)

Degreasing gas atmosphere: atmosphere of nitrogen

6. Next, the degreased body obtained was fired under the firing conditions shown below. Thus, a sintered body was obtained. The sintered body had a cylindrical shape with a diameter of 10mm and a thickness of 5 mm.

Firing conditions

Firing temperature: 1150 deg.C

And (3) sintering time: 3 hours (holding time at firing temperature)

Firing gas atmosphere: argon atmosphere

(sample No.2 to 30)

Sintered bodies were obtained in the same manner as in the method for producing the sintered body of sample No.1, except that the composition of the metal powder for powder metallurgy was changed as shown in Table 1. Further, the sintered body of sample No.30 was subjected to HIP treatment under the following conditions after firing. The sintered bodies of sample nos. 18 to 20 were obtained using metal powders produced by a gas atomization method. In addition, the remarks column in table 1 indicates "gas".

HIP treatment conditions

Heating temperature: 1100 deg.C

Heating time: 2 hours

Pressurizing force: 100MPa

TABLE 1

In table 1, the sintered body of each sample No. corresponds to "example" of the present invention, and does not correspond to "comparative example" of the present invention.

Although each sintered body contains a trace amount of impurities, the description thereof is omitted in table 1.

(sample No.31 to 48)

Sintered bodies were obtained in the same manner as in the method for producing the sintered body of sample No.1, except that the composition of the metal powder for powder metallurgy was changed as shown in Table 2. Further, the sintered body of sample No.48 was subjected to HIP treatment under the following conditions after firing. Further, sintered bodies of sample Nos. 41 to 43 were obtained using metal powders produced by a gas atomization method. In addition, the remarks column in table 2 indicates "gas".

HIP treatment conditions

Heating temperature: 1100 deg.C

Heating time: 2 hours

Pressurizing force: 100MPa

TABLE 2

In table 2, the sintered body of each sample No. corresponds to "example" of the present invention, and does not correspond to "comparative example" of the present invention.

Although each sintered body contains a small amount of impurities, the description thereof is omitted in table 2.

(sample No.49 to 66)

Sintered bodies were obtained in the same manner as in the method for producing the sintered body of sample No.1, except that the composition of the metal powder for powder metallurgy was changed as shown in Table 3. Further, the sintered body of sample No.66 was subjected to HIP treatment under the following conditions after firing. The sintered bodies of sample nos. 59 to 61 were obtained using metal powders produced by a gas atomization method. In addition, the remarks column in table 3 indicates "gas".

HIP treatment conditions

Heating temperature: 1100 deg.C

Heating time: 2 hours

Pressurizing force: 100MPa

TABLE 3

In table 3, the sintered body of each sample No. corresponds to "example" of the present invention, and does not correspond to "comparative example" of the present invention.

Although each sintered body contains a small amount of impurities, table 3 does not show them.

(sample No.67)

1. First, as in the case of sample No.1, metal powders having compositions shown in table 4 were produced by a water atomization method.

2. Next, the metal powder is granulated by a spray drying method. The binder used at this time was polyvinyl alcohol, and the amount used was 1 part by mass relative to 100 parts by mass of the metal powder. In addition, 50 parts by mass of a solvent (ion-exchanged water) was used for the polyvinyl alcohol 1 part by mass. Thus, a granulated powder having an average particle size of 50 μm was obtained.

3. Then, the granulated powder was subjected to powder compaction under the following compaction conditions. In addition, a press molding machine was used for the molding. The shape of the molded article produced was a 20mm square cube.

Molding conditions

Material temperature: 90 deg.C

Forming pressure: 600MPa (6 t/cm)²)

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

Conditions of degreasing

Degreasing temperature: 450 deg.C

Degreasing time: 2 hours (holding time at degreasing temperature)

Degreasing gas atmosphere: atmosphere of nitrogen

5. Next, the degreased body obtained was fired under firing conditions shown below. Thus, a sintered body was obtained.

Firing conditions

Firing temperature: 1150 deg.C

And (3) sintering time: 3 hours (holding time at firing temperature)

Firing gas atmosphere: argon atmosphere

(sample No.68 to 87)

Sintered bodies were obtained in the same manner as in sample No.67, except that the composition of the metal powder for powder metallurgy and the like were changed as shown in Table 4. Further, the sintered body of sample No.87 was subjected to HIP treatment under the following conditions after firing.

HIP treatment conditions

Heating temperature: 1100 deg.C

Heating time: 2 hours

Pressurizing force: 100MPa

TABLE 4

In table 4, the metal powder and sintered body for powder metallurgy of each sample No. corresponds to "example" of the present invention, and does not correspond to "comparative example" of the present invention.

2. Evaluation of sintered body

2.1 evaluation of relative Density

The sintered density of each sample No. sintered body was measured based on the method for measuring the density of a sintered metal material specified in JIS Z2501 (2000), and the relative density of each sintered body was calculated with reference to the true density of a metal powder for powder metallurgy used for producing each sintered body.

The measurement results are shown in tables 5 to 8.

2.2 evaluation of dimensional hardness

Dimensional hardness was measured for the sintered body of each sample No. based on the test method of dimensional hardness test specified in JIS Z2244 (2009).

2.3 evaluation of tensile Strength, 0.2% yield Strength and elongation

The tensile strength, 0.2% yield strength and elongation of the sintered body of each sample No. were measured in accordance with the metal material tensile test method specified in JIS Z2241 (2011).

The measured physical property values were evaluated according to the following evaluation criteria.

Evaluation criteria for tensile Strength (tables 5 and 8)

A: the sintered body has a tensile strength of 520MPa or more

B: the sintered body has a tensile strength of 510MPa or more and less than 520MPa

C: the sintered body has a tensile strength of 500MPa or more and less than 510MPa

D: the sintered body has a tensile strength of 490MPa or more and less than 500MPa

E: the sintered body has a tensile strength of 480MPa or more and less than 490MPa

F: the sintered body has a tensile strength of less than 480MPa

Evaluation criteria for tensile Strength (tables 6 and 7)

A: the sintered body has a tensile strength of 560MPa or more

B: the sintered body has a tensile strength of 550MPa or more and less than 560MPa

C: the sintered body has a tensile strength of 540MPa or more and less than 550MPa

D: the sintered body has a tensile strength of 530MPa or more and less than 540MPa

E: the sintered body has a tensile strength of 520MPa or more and less than 530MPa

F: the sintered body has a tensile strength of less than 520MPa

Evaluation criteria for 0.2% yield Strength (tables 5 and 8)

A: the 0.2% yield strength of the sintered body is 195MPa or more

B: the 0.2% yield strength of the sintered body is 190MPa or more and less than 195MPa

C: the sintered body has a 0.2% yield strength of 185MPa or more and less than 190MPa

D: the 0.2% yield strength of the sintered body is 180MPa or more and less than 185MPa

E: the 0.2% yield strength of the sintered body is 175MPa or more and less than 180MPa

F: the 0.2% yield strength of the sintered body is less than 175MPa

Evaluation criteria for 0.2% yield Strength (tables 6 and 7)

A: the 0.2% yield strength of the sintered body is 225MPa or more

B: the 0.2% yield strength of the sintered body is 220MPa or more and less than 225MPa

C: the 0.2% yield strength of the sintered body is 215MPa or more and less than 220MPa

D: the 0.2% yield strength of the sintered body is 210MPa or more and less than 215MPa

E: the 0.2% yield strength of the sintered body is 205MPa or more and less than 210MPa

F: the 0.2% yield strength of the sintered body is less than 205MPa

Evaluation criteria for elongation

A: the sintered body has an elongation of 48% or more

B: the sintered body has an elongation of 46% or more and less than 48%

C: the sintered body has an elongation of 44% or more and less than 46%

D: the sintered body has an elongation of 42% or more and less than 44%

E: the elongation of the sintered body is 40% or more and less than 42%

F: the elongation of the sintered body is less than 40%

The evaluation results are shown in tables 5 to 8. As described above, the evaluation criteria in tables 5 and 8 are different from those in tables 6 and 7 depending on the physical property values.

TABLE 5

TABLE 6

TABLE 7

TABLE 8

As is clear from tables 5 to 8, the sintered bodies corresponding to the examples have higher relative density and dimensional hardness than the sintered bodies corresponding to the comparative examples (except for the sintered bodies subjected to the HIP treatment). In addition, significant differences in the properties of tensile strength, 0.2% yield strength and elongation were also confirmed.

On the other hand, it was confirmed that all the physical property values of the sintered body corresponding to the examples and the sintered body subjected to HIP treatment were equivalent.

2.4 Cross-sectional observation of the sintered body by Scanning Electron Microscope (SEM)

An observation image was obtained by a scanning electron microscope (JXA-8500F, manufactured by Nippon electronics Co., Ltd.) on a cross section of the sintered body corresponding to the example. The acceleration voltage during imaging was 15kV, and the magnification was 1 ten thousand times.

As a result of observation, a granular region (first region) having a dark color and a region (second region) having a light color and located at a position surrounding the first region were confirmed in the cross section of each sintered body. Therefore, the average value of the circle-equivalent diameters of the first region is about 2 μm to 8 μm in any sintered body.

Then, qualitative and quantitative analysis of the observation area was performed by an electron beam microanalyzer. As a result, in the first region, the sum of the Si content and the O content is 2.5 times to 3.5 times the Fe content. The content of Si in the first region is 14 times or more the content of Si in the second region. The content of Zr in the first region is 3 times or more the content of Zr in the second region.

From the above, it was confirmed that in the sintered body corresponding to the example, silicon oxide was accumulated with Zr carbide or the like as a core.

From this, it was confirmed that, according to the present invention, the same high density and excellent mechanical properties as those of the sintered body subjected to the HIP treatment can be imparted to the sintered body without applying an additional treatment such as the HIP treatment to achieve high density.

Further, it was confirmed from the crystal structure analysis by X-ray diffraction that all of the sintered bodies corresponding to the examples had a structure mainly of an austenite crystal structure.

Claims

1. A sintered body characterized in that a sintered body,

is prepared by sintering metal powder for powder metallurgy,

in the metal powder for powder metallurgy, in the case of the metal powder,

fe as the main component;

contains 15 to 26 mass% of Cr;

ni is contained in a proportion of 7 to 22 mass%;

si is contained in a proportion of 0.3 to 1.2 mass%;

contains 0.005-0.3 mass% of C;

zr in a proportion of 0.01 to 0.5 mass%; and

contains 0.01 to 0.5 mass% of Nb,

the ratio of Zr/Nb to Nb content is 0.3 to 3,

the total of the Zr content and the Nb content is 0.12 to 0.24 mass%,

the sintered body includes:

a first region which is granular and has a relatively high silicon oxide content; and

a second region having a relatively low silicon oxide content compared with the first region,

in the first region, the sum of the Si content and the O content is 1.5 times to 10000 times the Fe content,

the content of Si, Zr, and Nb in the first region is 3 times to 10000 times greater than the content of Si, Zr, and Nb in the second region.

2. The sintered body according to claim 1,

the metal powder for powder metallurgy has an austenitic crystal structure.

3. The sintered body according to claim 1 or 2,

the metal powder for powder metallurgy further contains Mo in a proportion of 1 to 5 mass%.

4. The sintered body according to claim 1 or 2,

the sintered body has an average particle diameter of 0.5 to 30 [ mu ] m.

5. The sintered body according to claim 1 or 2,

the ratio (Zr + Nb)/Si of the total of the Zr content and the Nb content to the Si content of the metal powder for powder metallurgy is 0.1 to 0.7.

6. The sintered body according to claim 1 or 2,

the ratio (Zr + Nb)/C of the total of the Zr content and the Nb content to the C content of the metal powder for powder metallurgy is 1 to 16.

7. The sintered body according to claim 1 or 2,

the content of Mn in the metal powder for powder metallurgy is 0.01-3 mass%.

8. The sintered body according to claim 1 or 2,

the content of Mo in the metal powder for powder metallurgy is 1 to 5 mass%.

9. The sintered body according to claim 1 or 2,

the metal powder for powder metallurgy has a Cu content of 1 to 5 mass%.

10. The sintered body according to claim 1 or 2,

the content of N in the metal powder for powder metallurgy is 0.03 to 1 mass%.

11. The sintered body according to claim 1 or 2,

the content of S in the metal powder for powder metallurgy is 0.01-0.5 mass%.

12. The sintered body according to claim 1 or 2,

the metal powder for powder metallurgy has a V, W, Co, B, Ti, Se, Te, Pd and Al content of less than 0.1 mass% and a total content of less than 0.2 mass%.

13. The sintered body according to claim 1 or 2,

the content of O in the metal powder for powder metallurgy is 0.03 to 0.8 mass%.