JP6667264B2 - Manufacturing method of high-rigidity iron-based sintered alloy - Google Patents

Description

  The present invention relates to a high-rigidity iron-based sintered alloy capable of achieving both high rigidity (high Young's modulus) and low cost of structural members and the like at a high level, and a method for producing the same.

  The structural member is required not only to be not damaged but also to have desired deformation characteristics and vibration characteristics. For this reason, it is often preferable that the metal material used for the structural member has high strength and high Young's modulus. From such a viewpoint, steel materials are used for many structural members.

  The strength of the steel material can be easily changed by controlling the structure or adjusting the composition by heat treatment or the like. However, since the Young's modulus is a physical property value, the Young's modulus of the steel material is usually 190 to 210 GPa regardless of its composition or metal structure. The degree is almost constant.

  However, in order to reduce the size and weight of various members and to improve the performance of mechanical devices (eg, engines and the like), there is a tendency to require a steel material with a further increased Young's modulus (referred to as “high-rigidity steel” as appropriate). The description related to such high-rigidity steel is found in, for example, the following patent documents. In the present specification, an iron-based material that does not contain carbon (C) is also appropriately referred to as “steel” for convenience.

Japanese Patent No. 3314505 Japanese Patent No. 3898387 JP 2002-47527 A JP-A-5-239504 Japanese Patent No. 3478930

Patent Literatures 1 to 3 propose high-rigidity steels in which titanium diboride particles (TiB ₂ particles) are dispersed in an iron-based matrix. The patent document 4 proposes a high-rigidity steel dispersed with ceramic particles other than TiB ₂ particles in a stainless matrix.

  However, in these patent documents, a desired high Young's modulus is achieved by subjecting a sintered body to hot working such as hot extrusion or hot upsetting, or HIP treatment, and densification. are doing. When hot working or the like is performed, the cost is increased due to an increase in man-hours, and the original advantage of the sintering method of reducing the manufacturing cost of a member by using a sintered body having a final shape as it is is hindered.

Patent Document 5 proposes a high-rigidity steel in which TiB ₂ particles and the like are crystallized or precipitated in an iron-based matrix by a smelting method. In order to perform such a smelting method, a special melting apparatus capable of heating to a high temperature of 2000 to 2600 ° C. is required, and equipment costs increase. In addition, since the thus obtained high-rigidity steel is usually a bulk or a casting having a small degree of freedom in shape, it is necessary to reduce the manufacturing cost of structural members by a (near) net shape such as a sintering method. It is difficult.

The present invention has been made in view of such circumstances, and even when a relatively large amount of high-rigidity particles (TiB ₂ particles) are contained, the sintered body is not necessarily densified by hot working or the like. An object of the present invention is to provide an iron-based sintered alloy exhibiting a sufficiently high Young's modulus even as it is, and a method for producing the same.

The present inventors have conducted extensive research to solve this problem, a result of repeated trial and error, the Zr with TiB ₂ particles are present in small amounts, even without performing hot working, etc., TiB ₂ particles in the iron-based matrix It has been newly found that a finely dispersed and dense sintered body can be obtained. By developing these results, the present invention described below has been completed.

《High-rigidity iron-based sintered alloy》
(1) A high-rigidity iron-based sintered alloy according to the present invention is a high-rigidity iron-based sintered alloy in which high-rigidity particles having a higher Young's modulus than the matrix are dispersed in a matrix made of iron (Fe) or an iron alloy. Wherein the high-rigidity particles include titanium diboride (TiB ₂ ) particles occupying 10 to 50% by volume with the entire high-rigidity iron-based sintered alloy being 100% by volume. % Of zirconium (Zr).

(2) When the high-rigidity iron-based sintered alloy of the present invention (hereinafter, simply referred to as “sintered alloy”) contains an appropriate amount of Zr and contains a large amount of TiB ₂ particles (for example, 10% by volume or more). However, the TiB ₂ particles are homogeneously dispersed in the matrix, resulting in a dense metal structure with very few voids and the like. Thus, the sintered alloy of the present invention has a high density without being densified by hot working or the like, and has a high Young's modulus (almost in accordance with the composite rule) in accordance with the abundance ratio of TiB ₂ particles. Can be demonstrated.

Moreover, the TiB ₂ particles have extremely high thermal (mechanical) stability, and do not react with the matrix during sintering to generate an excessive liquid phase. For this reason, the sintered body according to the present invention maintains the shape (shape before sintering) of the formed body almost as it is, even if the shaped body may be reduced in a similar manner with respect to the formed body, and maintains shape retention and dimensional change. Excellent predictability. Therefore, when the sintered alloy of the present invention is used, in addition to the above-mentioned omission of hot working and the like, it is also possible to greatly reduce machining and the like by (near) net shape. And higher manufacturing cost can be achieved at the same time.

Although of course, TiB ₂ particles (specific gravity 4.3~4.7g / cm ³⁾ is a lower density than Fe (specific gravity 7.8~7.9g / cm ³⁾ which is a main constituent element of the matrix since a hard sintered alloy is lightweight and high strength in accordance with the TiB ₂ particle amount.

(3) The reason why the sintered alloy of the present invention exhibits such excellent characteristics is not always clear, but is considered as follows at present. Although the TiB ₂ particles have excellent thermal stability as described above, during sintering, B slightly released from the surface of the TiB ₂ particles reacts with Fe of the matrix in the vicinity (grain boundary) thereof, When the sintering temperature is equal to or higher than the eutectic point of Fe-B (about 1140 ° C.), a liquid phase may be generated at the grain boundaries.

However, since the TiB ₂ particles are originally excellent in thermal stability, the liquid phase generated at such a grain boundary is small, and the wettability between the TiB ₂ particles and the liquid phase generated at the grain boundary is poor. Therefore, when TiB ₂ particle amount which is contained or formulation is increased, TiB ₂ not liquid phase is sufficiently penetrate like to aggregate portion of the particles, voids may remain in the aggregation portion of the TiB ₂ particles. As a result, as the amount of TiB ₂ particles increases, the relative density of the sintered body decreases, and as the relative density decreases, the Young's modulus also decreases.

But the reason is not clear, when the Zr even a small amount of the sintered alloy is present, Zr was greatly improved wettability with the liquid phase arising in the TiB ₂ particles and a grain boundary, the aggregation portion of the TiB ₂ particles The liquid phase is easy to penetrate the pores. This reduces the vacancies aggregate portion of TiB ₂ particles, relative density and thus the Young's modulus of the sintered body also increases. Thus, even when the content of the TiB ₂ particles is increased, the sintered alloy of the present invention has a high Young's modulus according to the content of the TiB ₂ particles without being subjected to hot forging or the like, and remains sintered. It is considered that the expression has started.

As described above, in the sintered alloy according to the present invention, the simple rule is not simply governed by the compound rule (combination rule) that the Young's modulus is improved in accordance with the amount (volume%) of the high-rigidity particles. Gold's Young's modulus also shows a strong correlation with its relative density. Therefore, in order to increase the rigidity of the sintered alloy, it is essential to contain (blend) a high rigidity particle amount according to a desired Young's modulus and to secure a high relative density. Therefore, the sintered alloy of the present invention has a relative density (ρ / ρ ₀ × 100%), which is a ratio of a bulk density (ρ) to a true density (ρ ₀ ), of 96% or more, 97% or more, and even 98% or more. It is preferred that there be.

《Manufacturing method of high rigidity iron-based sintered alloy》
(1) The present invention can be understood as a method for producing a high-rigidity iron-based sintered alloy as described below. That is, the present invention provides a molding step of obtaining a molded product obtained by press-molding a mixed powder obtained by mixing an iron-based powder made of iron or an iron alloy, a highly rigid powder containing titanium diboride particles, and a zirconium source powder, And a sintering step of obtaining a high-rigidity iron-based sintered alloy comprising the sintered body. Further, the present invention can be understood as a high-rigidity iron-based sintered alloy obtained by the above-described manufacturing method independently of the above-described sintered alloy.

(2) Based on this manufacturing method, the above-described high-rigidity iron-based sintered alloy can be understood as follows. That rigid iron-based sintered alloy of the present invention, pressure to the mixed powder of the high rigidity powder and the zirconium source powder containing iron-based powder and the TiB ₂ particles made of an iron-based particles are particles of iron or an iron alloy A high-rigidity iron-based sintered alloy comprising a sintered body obtained by sintering a pressed compact, wherein the high-rigidity powder is 10 to 50% by volume when the entire mixed powder is 100% by volume. by weight of TiB ₂ particles, wherein the zirconium source powder is characterized in that it comprises 0.1 to 3 wt% of Zr when the entire powder excluding the high-rigidity powder from the mixed powder is 100 mass% It may be something.

Furthermore rigid iron-based sintered alloy of the present invention, pressure to the mixed powder of the high rigidity powder and the zirconium source powder containing iron-based powder and the TiB ₂ particles made of an iron-based particles are particles of iron or an iron alloy A high-rigidity iron-based sintered alloy made of a sintered body obtained by sintering a pressed compact, wherein the high-rigidity powder is 5 to 35% by mass when the entire mixed powder is 100% by mass. , 10 to 30% by mass, more preferably 15 to 25% by mass, and the zirconium source powder is 0.2 to 4% by mass, 0.4 to 2.5% by mass when the whole mixed powder is 100% by mass. %, Or 0.7 to 1.5% by mass.

  At this time, the iron-based powder is Mo of 0.2 to 4% by mass, more preferably 0.4 to 2.5% by mass, and 0.5 to 6% by mass, and more preferably 1. to 100% by mass of the entire iron-based powder. An iron alloy powder containing at least one of 5 to 4% by mass of Cr is preferable.

  Preferably, the sintered body is heated at a sintering temperature or higher at which a liquid phase is formed at at least a part of the grain boundary between the iron-based particles and the boride particles.

《Other》
(1) The volume ratio (vol%) referred to in the present specification is calculated based on a pore-free volume (PFV) excluding pores (Pore), unless otherwise specified. For example, “with the entire sintered alloy as 100% by volume” means that the volume (PFV) obtained by removing the pores (Pore) contained therein from the apparent volume (bulk volume) of the sintered alloy is 100 volumes. It means as%.

The term “relative density” as used in the present specification refers to the ratio (ρ / ρ ₀ × 100) of the bulk density (ρ) of the sintered body (molded body) to the true density (ρ ₀ ) of the sintered body (also the molded body). %). At this time, the bulk density (ρ) is calculated from the actually measured dimensions and mass of a test piece for measurement (for example, a cylindrical test piece having a reference size of φ14 × 10 mm). The true density (ρ ₀ ) is obtained by dividing the actually measured mass by the volume (PFV) obtained by removing holes from the test piece (pore-free density: PFD).

  When manufacturing a sintered alloy, the volume (Vi = Wi / Di) occupied by each raw material powder is determined from the blended mass (Wi) of each raw material powder and its true density (Di: literature value or catalog value), The sum of the respective volumes (ΣVi) was the total volume of the mixed powder, and this was defined as the pore-free volume (PFV: ΣVi) of the sintered alloy. In addition, the compounding mass (Wi) of each raw material powder is an actually measured value.

By using this pore-free volume (PFV: ΔVi), the volume ratio of TiB ₂ particles in the sintered alloy or the volume ratio of high-rigidity powder (particularly TiB ₂ particles) in the mixed powder, and further, the relative density can be easily calculated. . For example, by dividing the volume (Vt = Wt / Dt) of TiB ₂ particles (powder) determined from the blended mass (Wt) and its true density (Dt) by the pore-free volume (ΣVi), The volume ratio of TiB ₂ particles (powder) in the mixed powder can be calculated (Vt / ΣVi × 100%).

(2) The "Young's modulus" referred to in this specification is measured by an ultrasonic pulse method on a cylindrical measurement test piece (φ14 × 10 mm).

(3) The “average particle size” of the powder referred to in the present specification is specified by a median diameter (D50) based on a particle size distribution measurement using a laser diffraction type particle size distribution analyzer. The particle size of the powder is specified by sieving. For example, a powder consisting of particles that have passed through a sieve with a nominal opening of a μm has a particle size expressed as “−a μm”. The classification using a sieve conforms to JIS Z8801.

(4) The high-rigidity particles according to the present invention are entirely or mostly composed of TiB ₂ particles, but are different from the particles having a high Young's modulus, such as carbide particles, nitride particles, oxide particles and TiB _2. May be contained in a small amount.

  The matrix according to the present invention depends on the composition of the high-rigidity particles, but in addition to Fe, Mo, Cr, Cu, Ni, etc., a small amount of modifying elements (Mn, Si, V, Co, Ti, Nb, W, P, B, etc.) and unavoidable impurities. The modifying element makes it possible to improve the strength, toughness, ductility, dimensional stability, and the like of the high-rigidity iron-based sintered alloy.

(5) Regardless of the form, the sintered alloy of the present invention may be, for example, a material such as an ingot, a rod, a tube, or a plate, or a final product or a member similar thereto. However, the sintered body according to the present invention exhibits high density, high Young's modulus, high strength and the like even when sintered, and at least the shape before sintering (the shape of the molded body) is maintained at least similarly. Therefore, it is preferable that the sintered alloy of the present invention is a sintered member (structural member or the like) that can utilize the (near) net shape because both high rigidity and low cost can be achieved at a high level.

(6) The mechanical properties such as Young's modulus, strength and elongation (toughness) exhibited by the high-rigidity iron-based sintered alloy of the present invention are determined by the type and composition of each raw material powder, molding conditions (molding method, molding pressure, etc.). , Sintering conditions (temperature, time, atmosphere, etc.), etc., it is difficult to specify all of them. To put it bluntly, the high-rigidity iron-based sintered alloy of the present invention preferably has a Young's modulus of 230 GPa or more, more preferably 250 GPa or more.

(7) Unless otherwise specified, “x to y” in this specification includes the lower limit x and the upper limit y. A range such as “ab” may be newly set as a new lower limit or upper limit using various numerical values or numerical values included in the numerical range described in the present specification. Unless otherwise specified, a matrix other than the highly rigid particles (particularly TiB ₂ particles) is considered as a matrix.

4 is a graph showing the relationship between the amount of TiB ₂ particles and the relative density of a sintered body when no auxiliary agent is added. It is a graph showing the TiB ₂ particles amounts and sintered Young's modulus of the relationship at that time. It is the bar graph which compared the relative density of the sintered compact which added the auxiliary agent (1 mass%) which consists of various borides. It is a bar graph which compared Young's modulus of those sintered compacts. It is the bar graph which compared the relative density of the sintered compact which added the auxiliary agent (1 mass%) which consists of various carbides. It is a bar graph which compared Young's modulus of those sintered compacts. It is the bar graph which compared the relative density of the sintered compact which added the auxiliary agent (1 mass%) which consists of an oxide or a nitride. It is a bar graph which compared Young's modulus of those sintered compacts. It is a graph showing the relationship between the relative density of the added amount and the sintered body aid (ZrB ₂ or ZrC). 4 is a graph showing the relationship between the amount of the additive and the Young's modulus of the sintered body. 4 is a graph showing the relationship between the amount of the additive and the tensile strength of the sintered body. 4 is a graph showing the relationship between the amount of the additive and the elongation of the sintered body. Aid: is a graph showing the relationship between the relative density of TiB ₂ particle amount and the sintered body (ZrB 2 ₁ wt%) upon addition of. It is a graph showing the TiB ₂ particles amounts and sintered Young's modulus of the relationship at that time. 4 is a graph showing a relationship between a sintering temperature and a relative density of a sintered body. 4 is a graph showing a relationship between a sintering temperature and a Young's modulus of a sintered body. 4 is a graph showing a relationship between a sintering temperature and a tensile strength of a sintered body. It is a graph which shows the relationship between sintering temperature and elongation of a sintered compact. Aids: a different metallographic photograph of each sintered body having a sintering temperature of (ZrB 2 ₁ wt%) upon addition of. It is a metallographic structure photograph of each sintered compact from which sintering temperature differs when an auxiliary agent is not added. Is a graph showing the relationship between the relative density of TiB ₂ particle amount and the sintered body when the addition of Cu powder. It is a graph showing the TiB ₂ particles amounts and sintered Young's modulus of the relationship at that time. It is a graph showing the tensile strength of the relationship of TiB ₂ particle amount and the sintered body at that time. 4 is a graph showing the relationship between the amount of TiB ₂ particles and the elongation of a sintered body at that time. 4 is a graph showing a relationship between a molding pressure and a relative density of a sintered body when a sample is manufactured using a Cr-based iron-based powder. It is a graph which shows the relationship between the molding pressure at that time and the Young's modulus of a sintered compact. It is a graph which shows the relationship between the compacting pressure at the time of adding Ni powder, and the relative density of a compact. It is a graph which shows the relationship between the molding pressure and the relative density of a sintered compact. 4 is a graph showing the relationship between the molding pressure and the Young's modulus of the sintered body.

  The contents described in this specification can apply not only to the high-rigidity iron-based sintered alloy of the present invention, but also to a method of manufacturing the same. A component related to a manufacturing method can be a component related to a product if understood as a product-by-process claim. One or more components arbitrarily selected from the present specification can be added to the components of the present invention described above. Which embodiment is best depends on the target, required performance, and the like.

"matrix"
The matrix constituting the sintered alloy of the present invention may be pure iron, but is preferably made of an iron alloy containing various alloy elements in order to increase the rigidity and the strength. Each alloy element may be dissolved in Fe or form a compound with Fe or another element to precipitate. Such alloy elements include, for example, molybdenum (Mo), chromium (Cr), copper (Cu), nickel (Ni), and the like. It is preferable that at least one of them is contained in a matrix in an appropriate amount. Each alloy element may be supplied as a single powder or may be supplied as an alloy powder (such as an iron alloy powder).

Mo and Cr are elements that improve the strength and toughness of the sintered alloy (matrix). If these elements are too small, there is no effect, and if they are too large, the toughness of the sintered alloy decreases. Mo is preferably contained in an amount of 0.1 to 3% by mass (simply represented by "%"), 0.3 to 2.5%, and more preferably 0.5 to 2%. It is preferable that Cr be contained in an amount of 0.3 to 5%, 1 to 4%, and more preferably 2 to 3.5%. In particular, when both Cr and Mo are contained, the total thereof is preferably 2 to 5%, more preferably 2.5 to 4%. Cu is also an element for improving the strength of the sintered alloy, and is preferably contained in an amount of 0.3 to 5%, 1 to 4%, and more preferably 1.5 to 3%. Further, Ni is an element that densifies the sintered alloy to improve its relative density or Young's modulus, and preferably contains 0.3 to 3%, more preferably 0.5 to 2%. Although Ni alone promotes the densification of the sintered alloy containing TiB ₂ particles, the effect is particularly great when coexisting with Zr. The composition of the alloy element described in this specification is a mass ratio when the entire matrix is 100% by mass, unless otherwise specified.

《High-rigidity particles》
The high rigidity particles are particles having a larger Young's modulus than the iron-based matrix, and include borides (TiB ₂ , FeB, MoB, Cr ₂ B, NbB ₂ , VB ₂ , HfB ₂ , ZrB _2, etc.) and carbides (ZrC, _{TiC, VC, Mo 2 C,} NbC , etc.), nitrides (ZrN, etc.), such as an oxide _(ZrO 2, TiO _2, etc.), may be used particles composed of a variety of ceramics. However, TiB ₂ particles are the most excellent as highly rigid particles that are stable in an iron-based matrix even at high temperatures and exhibit a stable high Young's modulus.

In the sintered alloy of the present invention therefore, the entire 100 vol%, TiB ₂ particles 10 to 50 vol%, when 20 to 40% by volume further comprises 25-35% by volume preferred. TiB ₂ particles are too small becomes insufficient high Young's modulus of the sintered alloy, is a TiB ₂ particles excessive, lowered elongation of the sintered alloy (toughness) is large, unfavorably becomes difficult to mold itself. The high-rigidity particles according to the present invention may be only TiB ₂ particles, or may contain a small amount of the above-mentioned other types of ceramic particles.

"Production method"
(1) Raw Material Powder The raw material powder according to the present invention includes an iron-based powder and an optional alloy element source powder, a zirconium source powder, and a TiB ₂ powder mixed so as to form a matrix having the above-described desired composition. It is composed of a mixed powder obtained by mixing a high-rigidity powder containing particles.

  As the iron-based powder, for example, iron alloy powder such as pure iron powder, Fe- (1-2%) Mo, Fe- (1-5%) Cr- (0.1-0.8%) Mo is used. preferable.

  In addition, as the alloy element source powder, in addition to the above-described iron-based powder, an iron alloy powder having a different composition from that of the iron-based powder (which may contain Cr or Mo), a copper source powder made of pure copper, a copper alloy, a copper compound, or the like is used. Can be.

  If the average particle diameter (median diameter: D50) of these iron-based powders and alloy element source powders is 1 to 20 μm, and more preferably 5 to 15 μm, or they are classified to −45 μm by sieving, they have high steel properties. It is preferable because it is excellent in dispersibility of particles and density improvement by sintering.

The high-rigidity powder may be only the TiB ₂ powder as described above, or may include another type of high-rigidity powder. It is preferable that the high rigidity powder has an average particle size (D50) of 0.5 to 5 μm, and more preferably 1 to 4 μm, because of excellent moldability and handleability.

  The zirconium source powder is preferably made of any one or more of the aforementioned Zr boride powder, carbide powder, oxide powder and nitride powder. The zirconium source powder preferably has an average particle size (D50) of 0.5 to 5 μm, and more preferably 1 to 4 μm, because of excellent moldability and handleability.

(2) Molding Step The molding step is a step of obtaining a molded body by pressing a mixed powder obtained by mixing the above-mentioned various powders into a desired composition. The molding pressure may be, for example, in the range of 350 to 1500 MPa, 600 to 1350 MPa, and more preferably 800 to 1200 MPa. If the molding pressure is too low, the density of the formed body and thus the sintered body will be insufficient, and if the molding pressure is too large, the life of the mold will decrease and the equipment cost will increase, which is not preferable. In the case of the present invention, a sufficiently high-density sintered body can be obtained by mixing the zirconium source powder and selecting the sintering temperature without increasing the molding pressure too much.

  The forming step may be cold forming (room temperature forming) or warm forming. Further, the lubrication between the mixed powder and the mold may be performed by mixing an internal lubricant with the mixed powder, or may be performed by mold lubrication. When performing mold lubrication, it is preferable to use a mold lubrication warm press forming method (for details, see Japanese Patent No. 3309970).

(3) Sintering step The sintering step is a step of heating a molded body to obtain a sintered body. The sintering temperature and sintering time are appropriately selected in consideration of the desired properties, productivity, etc. of the sintered alloy, but if they are too large, the energy cost increases, and if they are too small, the relative density and the Young's modulus are sufficient. Cannot be secured. In particular, the sintering temperature is preferably 1140 ° C. or higher at which a liquid phase occurs between the iron-based particles and the highly rigid particles (TiB ₂ particles). Therefore, the sintering temperature is preferably, for example, 1140 ° C to 1350 ° C, 1180 ° to 1300 ° C, and more preferably 1200 ° to 1280 ° C. The sintering time (time for maintaining the above sintering temperature) is preferably, for example, 0.1 to 3 hours, and more preferably 0.1 to 1 hour. The sintering process is performed in an oxidation preventing atmosphere such as a vacuum atmosphere, an argon gas atmosphere (atmospheric pressure or higher), an argon gas partial atmosphere (an argon gas atmosphere reduced in pressure (for example, 0.5 to 2 kPa) with respect to the atmospheric pressure). It is preferred that this be done.

(4) Others In the case of the present invention, the cooling step (especially the cooling rate) after the sintering step is not necessarily required. However, it is preferable that the cooling rate after heating in the sintering step is high, because the coarsening of the metal structure of the sintered body can be suppressed.

《Iron-based sintered alloy members》
By using the sintered alloy of the present invention, it is possible to easily increase the rigidity of various members, to improve the mechanical characteristics (strength, etc.) and vibration characteristics of the members, and to reduce the weight and thickness of the members and to increase the degree of freedom in designing. It becomes possible. The sintered alloy of the present invention may be used in any applications, for example, engine parts (for example, connecting rods) for automobiles, transmission parts, chassis parts, suspension parts, various shafts and pulleys, and acoustic parts. It is preferably used as a material or a product close to the final shape.

  A large number of samples (iron-based sintered alloys) with various changes in the type (composition, particle size, etc.), composition, molding conditions, sintering conditions, etc. of the raw material powders are manufactured, and the measurement, structure observation and evaluation of these samples are performed. Was. Through these, the contents of the present invention will be described more specifically.

《Production of sample》
(1) Raw Material Powder As a raw material powder, an iron-based powder, a TiB ₂ powder which is a high rigidity powder, an auxiliary powder (a Zr source powder or the like), and an alloy element source powder were prepared. In addition, the component composition of each powder was simply represented by “%”, with the whole of each powder being 100% by mass. The particle size (particle size) of each powder is specified by the method described above.

  Examples of the iron-based powder include Fe-1.5% Mo powder (average particle size: 12 μm) or Fe-3% Cr-0.5% Mo powder (average particle diameter), which is a low alloy steel fine powder manufactured by Epson Atmix Co. (Particle size: 11 μm). These iron-based powders are the main raw material powders constituting the matrix (the remainder other than the auxiliary powder and the alloy element source powder).

The TiB ₂ powder, Nippon Metal Co., Ltd. of _TiB 2 -N (average particle size: 2.9 .mu.m) was used. Any of the following was used as the auxiliary powder. The ZrO ₂ powder, TiO ₂ powder and ZrN powder were manufactured by Kojundo Chemical Co., Ltd., and the other boride powders were manufactured by Nippon Shinkin Co., Ltd. FeB powder (Fe-17.2% B / particle size: -63 μm / product number: Fe-B H1), MoB powder (Mo-10.2% B / average particle size: 4.1 μm / product number: MoB-O), CrB powder (Cr-28.4% B / average particle size: 5.7 μm / product number: CrB ₂ -O), NbB ₂ powder (Nb-18.5 B% / average particle size: 2.1 μm / product number: NbB ₂₎ -O), VB ₂ powder (V-28.4B% / average particle size: 3.9 .mu.m / part: VB ₂ -O), HfB ₂ powder (Hf-10.4B% / average particle size: 3.9 .mu.m / Product number: HfB ₂ -O), ZrB ₂ powder (Zr-18.8 B% / average particle size: 3.3 μm / product number: ZrB ₂ -O), ZrC powder (Zr-11.2 C% / average particle size: 2) 0.7 μm / product number: ZrC-O), TiC powder (Ti-19.7 C% / average particle size: 1.8 μm / product number: TiC), VC powder (V-16.7 C% / average particle size: 1.4 μm) / Part No. VC), MoC ₂ powder (Mo-5.9C% / average particle size: 1.7 [mu] m / Part: Mo ₂ C), NbC powder (Nb-11.4C% / average particle size: 1.1 .mu.m / Part: NbC ), ZrO ₂ powder (purity 98% / average particle diameter: about 1 μm), TiO ₂ powder (purity 99.9% / average particle diameter: about 2 μm), ZrN powder (purity 98% / average particle diameter: 3 μm).

  As the alloy element source powder, pure Cu powder (CE-25, manufactured by Fukuda Metal Foil & Powder Co., Ltd./average particle size: 63 μm or less), which is a copper source powder, was used.

(2) Mixed powder The compounded powder obtained by weighing each of the raw material powders described above in the proportions (compounding amounts) shown in Tables 1 to 9 was mixed in a mortar for 3 minutes, and further rotated and mixed in a ball mill for 30 minutes to obtain various mixed powders. (Mixing step). In addition, the composition was shown as 100% by mass or 100% by volume of the whole mixed powder. As described above, the blending volume (Vi) of each raw material powder is calculated based on each blending mass and specific gravity (published value or indicated value), and the total (ΣVi) of the blending volume (Vi) of each raw material powder is calculated. ) Was taken as the volume of the whole mixed powder.

(3) Molding Step Two kinds of molds having different cavity shapes were prepared, and each mixed powder was molded under pressure by the mold lubrication warm pressure molding method described above. At this time, the mold was heated to 150 ° C. (molding temperature) by a band heater. A 1% solution of lithium stearate (LiSt) solution (higher fatty acid-based lubricant) dispersed in water was applied to the inner peripheral surface of the heated mold. The molding pressure was adjusted in the range of 392 to 1176 MPa as shown in each table, but the molding pressure was 784 MPa unless otherwise specified. In addition, for the mold lubrication warm press forming method, reference was made to the description in Japanese Patent No. 3309970 and the like.

  In this way, two types of molded articles were obtained, which were a cylindrical test specimen (φ14 × 10 mm) and a flat tensile test specimen (approximately 55 × 20 × 3 mm).

(4) Sintering step Each molded body is heated in a vacuum atmosphere (about 1 to 5 × 10 ^-2 Pa · A) using a batch type sintering furnace (PVSGgr 20/20 manufactured by Shimadzu Mectem Co., Ltd.). Sintered. The sintering temperature was adjusted in the range of 900 to 1300 ° C. as shown in each table, but the sintering temperature was 1250 ° C. unless otherwise specified. The soaking time (sintering time) for maintaining the sintering temperature was 30 minutes.

The sintered body in the heated state after sintering was furnace-cooled (slowly cooled) to 900 ° C. and then rapidly cooled to 900 ° C. to 60 ° C. by blowing N ₂ gas (cooling step). The cooling rate during the rapid cooling was about 70 ° C./min (1.2 ° C./sec).

<< Measurement / Observation >>
(1) Density, density change, dimensional change,
The dimensions and weight before and after sintering were measured using the measurement test piece for each sample, and the bulk density (GD) and relative density (%) of the compact and the bulk density (S. D.), relative density (%), and dimensional change before and after sintering (ΔT: thickness change, ΔD: diameter change). In addition, the dimensional change rate was obtained by dividing the difference obtained by subtracting the dimension before sintering from the dimension after sintering by the dimension before sintering. The results thus obtained are summarized in each table.

(2) Young's modulus, tensile strength and (breaking) elongation Ultrasonic pulses are propagated through a sintered columnar measuring test piece of each sample using longitudinal and transverse wave transducers, The Young's modulus was calculated from the propagation speed of the longitudinal wave and the transverse wave propagating in the test piece (ultrasonic pulse method). The results thus obtained are summarized in each table.

  Further, a tensile test was performed with an autograph (Shimadzu Corporation), and the strength (tensile strength) and elongation until each test piece was broken were measured. The test speed at this time was 2.0 mm / min. The results thus obtained are summarized in each table.

(3) Structure observation The metal structure of some samples was observed using a scanning electron microscope (SEM). This observation was performed after embedding a cut piece taken from the test piece into a resin and mirror-polishing the surface thereof. Details of the metal structure will be described later.

《Evaluation》
Along with various evaluation items, representative samples were extracted from the sample groups shown in each table, and their characteristics were shown in graphs (each figure) and compared. Based on these, the features of the sintered alloy of the present invention will be specifically described.

(1) Relative Density and Young's Modulus The characteristics of each sample manufactured using only iron-based powder and TiB ₂ powder without blending the auxiliary powder are shown in Table 1 and FIG. 1A and FIG. (Referred to as “FIG. 1”).

As is clear from these, the relative density of the sintered body and its Young's modulus are clearly correlated, and it was found that as the relative density increases, the Young's modulus of the sintered body also increases. For this reason, even if the amount of TiB ₂ particles is simply increased, it is difficult to increase the rigidity of the sintered alloy according to the so-called compounding rule (composite rule) unless the relative density of the sintered body increases. It became clear. When the auxiliary powder is not added and the TiB ₂ particle amount exceeds 20 to 25%, the Young's modulus of the iron-based sintered alloy cannot be increased even if high pressure molding is performed. It was also found that the rate tended to decrease.

(2) In addition to the type of iron-based powder and TiB ₂ powder auxiliary agent, and Tables 2-4 the characteristics of each sample was prepared using the powdery mixture was added various aids powders, FIG 2A~-4B It was shown to. In each of the samples, the TiB ₂ powder was blended so that the volume ratio of the TiB ₂ particles in the sintered alloy was 30% by volume, and the amount of each auxiliary powder was 1% by mass. All the samples shown in each figure were manufactured at a molding pressure of 784 MPa and a sintering temperature of 1250 ° C. The same applies to the following points unless otherwise specified.

2A and 2B (FIG. 2A and FIG. 2B), a sintered alloy (sample 143) in which TiB ₂ particles: 30% by volume without adding the auxiliary powder had a relative density of about 91% and a Young's modulus of about 200 GPa. As is clear from both figures, the sintered alloy to which the auxiliary powder composed of boride was added, except for the case where NbB ₂ powder was added, all of which had a relative density and a relative density. It was found that the Young's modulus increased. In particular, it was found that when zirconium boride (ZrB ₂ ) powder was added, the relative density was significantly increased to 98% or more and the Young's modulus to 275 GPa or more.

This tendency is evident from FIGS. 3A and 3B (both are simply referred to as “FIG. 3”) and FIGS. 4A and 4B (both are simply referred to as “FIG. 4”). The same was true when (ZrC) powder, zirconium oxide (ZrO ₂ ) powder or zirconium nitride (ZrN powder) was added. As described above, the presence of Zr in the sintered alloy (matrix) ensures that the relative density and Young's modulus of the sintered alloy are improved in accordance with the amount of TiB ₂ particles even when the amount of TiB ₂ particles is large. It is clear that it will be obtained. In addition, Zr can be added in various forms, but when a Zr compound is used, it is apparent that the relative density and Young's modulus of the sintered alloy can be easily improved in the order of ZrB ₂ >ZrC>ZrN> ZrO _2. became.

(3) Amounts of Additives (ZrB ₂ and ZrC) The amounts of ZrB ₂ and ZrC, which are particularly effective for improving the relative density and Young's modulus of the sintered alloy containing a large amount of TiB ₂ particles, are varied. Tables 5A and 5B (together, simply referred to as “Table 5”) and FIGS. 5A to 5D (together, simply referred to as “FIG. 5”) are shown in Tables 5A and 5B. Indicated. As is clear from these, even when a very small amount of the auxiliary agent (ZrB ₂ or ZrC) is added, all of the relative density, Young's modulus, tensile strength and elongation of the sintered body are rapidly improved. . However, such a tendency is remarkable when the additive amount of the auxiliary agent is 1% by mass or less (elongation is 0.5% by mass or less), and even if the auxiliary agent is added more (more than 1% by mass), It was also found that each characteristic could be saturated. It has also been found that, when the auxiliary is added excessively (more than 2% by mass), the tensile strength of the sintered alloy is reduced.

(4) Compounding amount of TiB ₂ particles The amount of the ZrB ₂ powder was set to 0.5% by mass, 1% by mass or 2% by mass, and the mixing amount of the TiB ₂ particles and the molding pressure were variously changed. The characteristics are shown in Tables 6A to 6C (each table is simply referred to as “Table 6”) and FIGS. 6A and 6B (each figure is simply referred to as “FIG. 6”). FIG. 6 shows a case where the amount of ZrB ₂ powder added was 1% by mass.

As is clear from these, when the auxiliary agent (ZrB ₂ ) is added, the relative density of the sintered body can be increased to 97% or more without high-pressure molding if the amount of TiB ₂ particles is up to about 30% by volume. Further, it can be set to 98%, and it has become clear that the Young's modulus almost conforms to the compound rule. In addition, if high-pressure molding (1000 MPa or more) is performed, a high relative density can be secured even when the amount of TiB ₂ particles is 40% by volume or more, and a very high-rigidity sintered alloy having a Young's modulus of 320 GPa or more is obtained. I was able to do it. However, the TiB ₂ particles amount is more than 60 vol%, making itself specimens by die molding was difficult.

(5) Influence of sintering temperature The characteristics of each sample manufactured by changing the sintering temperature variously when the ZrB ₂ powder was added (1% by mass) and when it was not added were shown in Table 7 and FIG. To FIG. 7D (the figures are collectively referred to simply as “FIG. 7”).

As is evident from these, it was clarified that the relative density, Young's modulus and tensile strength of the sintered body rapidly increased by setting the sintering temperature to 1140 ° C. or higher. And it became clear that when the ZrB ₂ powder was added, all the characteristics were greatly improved. Particularly tensile strength, was found to significantly higher by the addition of ZrB ₂ powder.

(6) Metal structure FIGS. 8A and 8B (simply a combination of both figures) show a metal structure photograph of each sample (sintered body) having a different sintering temperature between the case where ZrB ₂ powder was added and the case where ZrB ₂ powder was not added. FIG. 8). During each photograph, a Kohai portion TiB ₂ particles are Awahai unit matrix, the black part is the residual vacancy.

As is clear from FIG. 8, in the metal structure of the sample in which the sintering temperature was 1100 ° C., pores (black portions) remained in the agglomerated portion of TiB ₂ particles regardless of the presence or absence of the addition of ZrB ₂ powder. It became a state. However, in the metal structure of the sample having a sintering temperature of 1150 ° C. or higher, the distribution state of residual air particles greatly differs depending on whether or not ZrB ₂ powder is added.

That is, it was found that when the ZrB ₂ powder was added, the residual vacancies in the aggregated portion of the TiB ₂ particles were significantly reduced as the sintering temperature was increased, and the densification was promoted. On the other hand, when the ZrB ₂ powder was not added, unless the sintering temperature was 1300 ° C. or higher, a large amount of pores remained even when the sintering temperature was increased.

As can be seen by comparing Table 7 and FIG. 8, it can be said that the relative density of the sintered body and the Young's modulus are greatly correlated. From these facts, it is considered that by adding ZrB ₂ powder, densification was promoted at a sintering temperature of 1150 ° C. or higher, and a high Young's modulus was obtained.

(7) Addition of Cu powder Regarding the case where Cu powder (2% by mass) was added to the iron-based powder as the alloying element source powder and the case where Cu powder was not added, each was manufactured by changing the blending amount of TiB ₂ particles in various ways. The characteristics of the sample are shown in Table 8 and FIGS. 9A to 9D (each figure is simply referred to as “FIG. 9”). FIG. 9 also shows the characteristics of a sample to which no Cu powder was added and a sample to which no ZrB ₂ powder was further added.

As is clear from FIG. 9, when the Cu powder is added, the relative density and the Young's modulus of the sintered body hardly change, but the tensile strength of the sintered body is largely improved and its elongation tends to be reduced. It was confirmed that. Furthermore, when the blending amount of the TiB ₂ particles was 30% by volume or more, it was also clarified that the addition of the Cu powder did not affect the elongation of the sintered body. Therefore, it was confirmed that when the blending amount of the TiB ₂ particles is 25 vol% or more, and more preferably 30 vol% or more, the addition of Cu powder not only increases the rigidity but also increases the strength.

(8) Composition of iron-based powder Table 9 shows the characteristics of each sample manufactured by changing the molding pressure using an iron-based powder containing Cr, and FIG. 10A and FIG. "). FIG. 10 also shows the characteristics of a sample in which the same iron-based powder was used and ZrB ₂ powder was not added. As is clear from FIG. 10, it was confirmed that the same tendency as in the case of the Mo-based low alloy steel powder was obtained even when the iron-based powder was a Cr-based low alloy steel powder.

(9) Addition of Ni powder As an alloy element source powder (or a kind of auxiliary powder), a sample in which Ni powder (1% by mass) was added to an iron-based powder and a sample in which Ni powder was not added were manufactured, and their characteristics were measured. The results are shown in Table 10 and FIGS. 11A to 11C (the drawings are collectively referred to simply as “FIG. 10”). In producing these samples, Fe-1.5% Mo powder was used for the iron-based powder, the above-mentioned TiB ₂ powder was used for the high-rigidity powder, and carbonyl Ni powder (manufactured by Inco / average particle size: 3.9 μm) was used for the Ni powder. ) Was used. The forming step, the sintering step, and the measurement of the sample were performed as described above. However, for cooling after sintering, the furnace was cooled (slowly cooled) to 1000 ° C. and then rapidly cooled by blowing N ₂ gas from 1000 ° C. (cooling step). Table 10 and FIG. 11 also show the characteristics of samples to which neither ZrB ₂ powder nor Ni powder was added.

First, as is clear from FIG. 11A, the relative density of the molded body increases almost in proportion to the molding pressure regardless of the composition of the mixed powder. However, as is clear from FIGS. 11B and 11C, when Ni powder alone is added, the relative density and Young's modulus of the sintered body are significantly increased even when the molding pressure is lower than when no Ni powder is added. Was. Then, it was found that when Ni powder was added together with ZrB ₂ powder, the relative density and Young's modulus of the sintered body were remarkably improved even when the molding pressure was low, at least as high as when the molding pressure was high. Therefore, it has been clarified that by adding Ni powder in addition to ZrB ₂ powder, a sintered alloy having a sufficiently high relative density or Young's modulus can be obtained even in a region where the molding pressure is low.

(10) Dimensional change As is clear from the dimensional change rate (ΔT) in the thickness direction and the dimensional change rate (ΔD) in the radial direction of each sample shown in Tables 1 to 10, the auxiliary powder containing Zr was used. When added, the sintered body of each sample was slightly reduced with respect to the compact, but the difference between ΔT and ΔD was small. From this, it was confirmed that, even when the relative density and the Young's modulus of each sintered body increased, the shape of the formed body was maintained similarly.

Claims (9)

A molding step of pressing a mixed powder obtained by mixing an iron-based powder made of iron or an iron alloy, a highly rigid powder containing TiB ₂ particles, and a zirconium source powder at 350 to 1500 MPa to obtain a molded body;
A sintering step of heating the molded body at 1140 to 1350 ° C. to obtain a sintered body,
The TiB ₂ particles include 10 to 50% by volume when the entire mixture powder is 100% by volume,
The zirconium source powder contains 0.1 to 3% by mass of Zr when the entire powder obtained by removing the high-rigidity powder from the mixed powder is 100% by mass,
A method for producing a high-rigidity iron-based sintered alloy comprising a sintered body and a high-rigidity iron-based sintered alloy having a Young's modulus of 230 GPa or more. 2. The sintered body according to claim 1, wherein the sintered body is heated at a sintering temperature or higher at which a liquid phase is formed at at least a part of a grain boundary between the iron-based powder particles and the boride particles including at least the TiB ₂ particles. For manufacturing high-rigidity iron-based sintered alloys. The method for producing a high-rigidity iron-based sintered alloy according to claim 1 or 2, wherein the sintering step is a step of setting a sintering temperature to 1180 to 1300 ° C.   The method for producing a high-rigidity iron-based sintered alloy according to any one of claims 1 to 3, wherein the zirconium source powder comprises at least one of a boride, a carbide, an oxide, and a nitride of zirconium.   The method for producing a high-rigidity iron-based sintered alloy according to any one of claims 1 to 4, wherein the iron-based powder is made of an iron alloy containing molybdenum (Mo) and / or chromium (Cr).   The method for producing a high-rigidity iron-based sintered alloy according to any one of claims 1 to 5, wherein the mixed powder further includes a copper source powder. The high-rigidity powder is contained in an amount of 5 to 35% by mass when the entire mixed powder is 100% by mass,
The method for producing a high-rigidity iron-based sintered alloy according to any one of claims 1 to 6, wherein the zirconium source powder is contained in an amount of 0.2 to 4% by mass when the entire mixed powder is taken as 100% by mass.   The iron-based powder is an iron alloy powder containing at least one of 0.2 to 4% by mass of Mo and 0.5 to 6% by mass of Cr, assuming that the entire iron-based powder is 100% by mass. Item 6. A method for producing a high-rigidity iron-based sintered alloy according to Item 5. 9. The sintered body according to claim 1, wherein a relative density (ρ / ρ ₀ × 100%), which is a ratio of a bulk density (ρ) to a true density (ρ ₀ ), is 96% or more. Manufacturing method of high-rigidity iron-based sintered alloy.