JP2018083967A - Iron-based sintered material and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dense and high rigidity iron-based sintered material.SOLUTION: Provided is an iron-based sintered material made of a sintered compact in which compound grains are dispersed into an iron-based matrix. At least a part of the compound grains is made of a nitrogen compound including Ti and/or V and N. The sintered compact includes C by 1.5 to 10%, N by 0.4 to 3% and Ti and/or V by 2.5 to 36% with the whole thereof as 100 mass% (simply referred as%). Its relative density can reach 93% or higher and its Young's modulus can reach 165 GPa or higher. The iron-based sintered material can be obtained, e.g., by sintering a molded body made of raw material powder obtained by mixing iron-based powder, TiC powder or VC powder and Gr powder at 1,140°C or higher in a nitrogen atmosphere. It is considered that the densification of the sintered compact is generated by the promotion of the generation of an Fe-C based liquid phase together with Gr or the like by isolated C owing to reaction of TiC or VC with N.SELECTED DRAWING: Figure 1A

Description

  The present invention relates to an iron-based sintered material that can be densified or highly rigid and a method for producing the same.

  A member ("iron-based sintered material" or simply "sintered material") obtained by sintering a compact of a raw material powder (mixed powder) containing iron (Fe) as a main component is often used. If an iron-based sintered material is used, even a member having a complicated shape can be obtained in a state close to the shape of the final product (so-called near net shape), so that manufacturing costs can be reduced by reducing processing costs and improving yield.

  By the way, in order to improve the mechanical characteristics of the iron-based sintered material, the composition of the raw material powder, the molding pressure, the sintering conditions, and the like are adjusted as appropriate. However, since an iron-based sintered material as it is generally sintered contains fine pores, the density or rigidity (Young's modulus) is often inferior to that of molten steel.

  Under such circumstances, proposals for obtaining high-rigidity steel by methods other than melting have been made, and for example, there are descriptions related to the following patent documents.

JP 2002-60885 A

  Patent Document 1 proposes a hot extruded material (high-rigidity steel) made of Fe-Cr-V powder (raw material powder) atomized in a nitrogen gas atmosphere. This hot extruded material is a particle-dispersed iron-based alloy in which VN particles are dispersed in an Fe—Cr matrix, and exhibits a high Young's modulus.

  However, the high-rigidity steel as disclosed in Patent Document 1 is only obtained as a hot-extrusion material, and cannot reduce the processing cost and improve the yield due to the near net shape. Moreover, the raw material powder of Patent Document 1 is a material in which highly rigid VN is distributed in advance on the particle surface, and it is difficult to obtain a high-density molded body or sintered body by a conventional sintering method or the like.

  The present invention has been made in view of such circumstances, and an object thereof is to provide an iron-based sintered material that can be densified or increased in rigidity by an entirely different approach, and a method for producing the same. .

  As a result of diligent research to solve the above-mentioned problems, the present inventor reacted with nitrogen during sintering to promote the appearance of a Fe-C liquid phase, thereby increasing the density. It was newly found out that a sintered body can be obtained. By developing this discovery, the present invention described below has been completed.

《Method for producing iron-based sintered material》
(1) The method for producing an iron-based sintered material according to the present invention comprises an iron-based sintered material comprising a sintering step of heating a raw material powder compact in which compound powder is mixed with iron-based powder to form a sintered body. It is a manufacturing method, Comprising: At least one part of the said compound powder consists of a carbon compound containing Ti and / or V,
The raw material powder comprises 100% by mass (simply referred to as “%”) of the raw material powder as a whole, and contains 1.5 to 10% of C and 2.5 to 36% of Ti and / or V in total, A sintering process is a process of heating the said molded object at the sintering temperature of 1140-1350 degreeC in the sintering atmosphere containing nitrogen.

  According to the manufacturing method of the present invention, it is possible to obtain a sufficiently dense sintered body by one molding and sintering without performing hot forging or the like. Moreover, the shape change accompanying the dimensional shrinkage during sintering is isotropic. Therefore, according to the present invention, even if the member has a complicated shape, it is possible to achieve both high density and high rigidity and reduction in manufacturing cost by the near net shape.

The reason why at least a dense iron-based sintered material can be obtained by the production method of the present invention is considered as follows. The molded body according to the present invention contains Ti or V carbon compounds (particles) in the constituent particles. This carbon compound can be at least partially converted into a more stable nitrogen compound when contacted with N or N ₂ in a high temperature environment during sintering. At that time, C liberated from the carbon compound reacts with Fe present around the carbon compound and promotes the appearance of the Fe—C liquid phase. It is considered that a dense sintered body can be obtained in the present invention by the appearance of a relatively large number of Fe—C liquid phases.

  However, as a result of earnest research by the present inventors, the types of carbon compounds that can achieve both the above-described near net shaping and densification / high rigidity are limited, and preferred carbon compounds are Ti and And / or V carbon compounds. The present invention is epoch-making in that it has found such a carbon compound and has completed a method for producing an iron-based sintered material that can achieve both shape maintenance and densification using the carbon compound.

(2) By the way, the carbon compound that contributes to the generation of the above-described Fe—C-based liquid phase (also simply referred to as (Ti, V) C) is supplied as a compound powder different from the iron-based powder, It is also possible to supply the iron-based powder itself or another alloy powder. Further, N that contributes to the generation of the Fe—C-based liquid phase is supplied from the outside (sintered atmosphere) of the molded body in a gas state (N ₂ ), or in the molded body as a nitrogen compound or an N-containing alloy. It is also possible to supply from the inside. Therefore, the combination of the (Ti, V) C and N supply sources is not limited to the combination described above ((Ti, V) C source: compound powder, N source: nitrogen-containing atmosphere). A combination is also possible.

(I) First, the present invention is a method for producing an iron-based sintered material, comprising a sintering step of heating a raw material powder compact in which compound powder is mixed with iron-based powder to form a sintered body, wherein the compound At least a part of the powder is composed of a carbon compound containing Ti and / or V. The raw material powder further contains a nitrogen source powder, and the total raw material powder is 100%, and C is 1.5 to 10%. Ti and / or V in a total of 2.5 to 36%, and the sintering step is a method for producing an iron-based sintered material, which is a step of heating the molded body at a sintering temperature of 1140 to 1350 ° C. Good.

  The production method of the present invention is a case where the (Ti, V) C source is a compound powder and the N source is a nitrogen source powder. In this case, since N is supplied as a part of the raw material powder, the sintering step can be performed in a vacuum atmosphere or an inert gas atmosphere such as Ar. Of course, the sintering atmosphere may be a nitrogen-containing atmosphere.

(Ii) Moreover, this invention is a manufacturing method of the iron-based sintered material provided with the sintering process which heats the molded object of the raw material powder containing iron-based powder, and makes it a sintered compact, Comprising: Ti and / or V and C, and the raw material powder includes 100% of the raw material powder as a whole, C includes 1.5 to 10%, and Ti and / or V in total 2.5 to 36%, The sintering step may be a method for producing an iron-based sintered material, which is a step of heating the compact at a sintering temperature of 1140 to 1350 ° C. in a sintering atmosphere containing nitrogen.

  The production method of the present invention is a case where the (Ti, V) C source is an iron-based powder and the N source is a nitrogen-containing atmosphere. In this case, it is not always necessary to add the compound powder as the (Ti, V) C source. The iron-based powder containing the (Ti, V) C source itself may be a main iron source powder or an alloy powder added separately to the iron source powder.

(Iii) Further, the present invention is a method for producing an iron-based sintered material, comprising a sintering step of heating a raw material powder compact containing iron-based powder to form a sintered body, wherein the iron-based powder comprises: Ti and / or V and C are included, and the raw material powder further includes a nitrogen source powder, the total raw material powder is 100%, C is 1.5 to 10%, and Ti and / or V in total Including 2.5 to 36%, the sintering step may be a method for producing an iron-based sintered material, which is a step of heating the compact at a sintering temperature of 1140 to 1350 ° C.

  The production method of the present invention is a case where the (Ti, V) C source is an iron-based powder and the N source is a nitrogen source powder. In this case, a compound powder serving as a (Ti, V) C source and a nitrogen-containing atmosphere (sintering atmosphere) are not necessarily required.

《Iron-based sintered material》
(1) The present invention is not limited to the manufacturing method described above, and can be grasped as a densified iron-based sintered material. That is, the present invention provides an iron-based sintered material comprising a sintered body in which compound particles are dispersed in an iron-based matrix, wherein at least a part of the compound particles includes Ti and / or V and N. The sintered body comprises 100% by mass (simply referred to as “%”) of the entire sintered body, C is 1.5 to 10%, N is 0.4 to 3%, Ti and / or with containing 2.5 to 36% of V in total, true density ([rho ₀₎ bulk density for ([rho) relative density (ρ / ρ ₀₎ is the ratio of 93% or more iron-based sintered material But you can.

(2) The compound particles composed of nitrogen compounds dispersed in the iron-based matrix according to the present invention are originally supplied as a raw material, and the carbon compound supplied as a raw material reacts with N during the sintering process. May be generated. All of the carbon compound supplied as a raw material may be changed to a nitrogen compound, or a part thereof may remain in the sintered body without being changed. In the latter case, the compound particles dispersed in the iron-based matrix are, in addition to nitrogen compound particles, for example, carbon compound particles made of any one or more of titanium carbide, titanium carbonitride, vanadium carbide, or vanadium carbonitride. Will be included.

(3) Since the sintered body according to the present invention is dense as described above, the relative density can be 93% or more, 95% or more, 97% or more, 98% or more, or even 99% or more.

  The sintered body according to the present invention can also exhibit high rigidity (Young's modulus). For example, the sintered body according to the present invention can have a Young's modulus of 165 GPa or more, 170 GPa or more, 180 GPa or more, 200 GPa or more, or 210 GPa or more, depending on the composition, density, and the like of the sintered body.

<Others>
(1) “Relative density” as used herein is the ratio (ρ / ρ ₀ × 100%) of the bulk density (ρ) to the true density (ρ ₀ ). The bulk density (ρ) may be calculated from the actually measured size and mass of the sample, or may be obtained by the Archimedes method if the sample shape is complicated and it is difficult to measure the size.

If the composition of the raw material powder (mixed powder) at the time of manufacture is known, it is calculated from the blended mass (Wi) and true density (specific gravity / literature value or catalog value) of each powder (elementary powder) used for the preparation. The pore free density (PFD) is the true density (ρ ₀ ). The PFD of an existing iron-based sintered material (sintered body) can be obtained by the Archimedes method using a sample that has been made a pore-free state by hot forging or the like.

In addition, when the pore-free density (PFD) calculated from the blending ratio of known raw material powders is used, if the sintered body absorbs N ₂ from the outside (sintering atmosphere) and increases in weight, the relative density Can slightly exceed 100%. However, it is usually an error level.

(2) “Young's modulus” as used herein is measured by the ultrasonic pulse method.

(3) The “particle size” of the powder in the present specification is specified by sieving or an average particle size. The classification using a sieve is specified in accordance with JIS Z 8801. For example, “a μm or less (−a μm)” means a powder having passed through a sieve having a nominal opening of a μm. The “average particle diameter” is specified from the median diameter (D50) based on the particle size distribution measurement by a laser diffraction particle size distribution analyzer.

(4) In addition to Fe, C, N, Ti, V, Mo, Cr, etc., the iron-based sintered material according to the present invention contains a small amount of modifying elements (Si, Mn, Cu, Ni, Co, Nb, W). , P, B, etc.) and inevitable impurities. The iron-based sintered material according to the present invention is not limited to a sintered member close to the final shape of the product, and may be a material such as an ingot shape, a rod shape, a tubular shape, or a plate shape.

(5) Unless otherwise specified, “x to y” in this specification includes a lower limit value x and an upper limit value y. A range such as “a to b” can be newly established with any numerical value included in various numerical values or numerical ranges described in the present specification as a new lower limit value or upper limit value.

It is a graph which shows the relationship between the amount of TiC and relative density. It is a graph which shows the relationship between VC amount and relative density. It is a graph which shows the relationship between the weight change before and behind sintering, and the amount of N in a sintered compact. It is a graph which shows the relationship between the amount of Gr when a TiC powder is mix | blended, and a relative density. It is a graph which shows the relationship between the amount of Gr when a TiC powder is mix | blended, and Young's modulus. It is a graph which shows the relationship between the amount of Gr when a VC powder is mix | blended, and a relative density. It is a graph which shows the relationship between the amount of Gr when a VC powder is mix | blended, and Young's modulus. It is a graph which shows the influence of the sintering temperature which has on the relationship between VC amount and relative density. It is a graph which shows the influence of the sintering temperature which has on the relationship between VC amount and Young's modulus. It is a graph which shows the influence of the iron-base powder on the relationship between the amount of TiC and relative density. It is a graph which shows the influence of the iron base powder on the relationship between the amount of TiC and Young's modulus. It is a graph which shows the influence of the iron-base powder on the relationship between VC amount and relative density. It is a graph which shows the influence of the iron base powder on the relationship between VC amount and Young's modulus. The Si ₃ N ₄ powder added to the raw material powder is a graph showing the relationship between the TiC content and the relative density when sintering in a vacuum atmosphere. It is a graph showing the relationship between the Si ₃ N ₄ content and relative density when sintering in a vacuum atmosphere. It is a graph which shows the relationship between the amount of Si ₃ N ₄ and Young's modulus when sintered in a vacuum atmosphere. It is a graph which shows the influence of sintering atmosphere on the relationship between TiC amount and relative density when using SKH57 (iron-based powder). It is a graph which shows the influence of a sintering atmosphere which has on the relationship between the amount of TiC when using SKH57, and Young's modulus. It is a graph which shows the influence of the shaping | molding pressure on the relationship between the amount of TiC and relative density when using SKH57. It is a graph which shows the influence of the shaping | molding pressure which has on the relationship between the amount of TiC when using SKH57, and Young's modulus. It is a graph which shows the relationship between each compound amount when a various compound powder is mix | blended with SKH57, and a relative density. It is a graph which shows the relationship between each compound amount when a various compound powder is mix | blended with SKH57, and Young's modulus. It is an EPMA image which shows distribution of each element in the metal structure which concerns on sample B12 (TiC addition). It is an EPMA image which shows distribution of each element in the metal structure which concerns on sample B31 (VC addition).

  One or two or more components arbitrarily selected from the present specification may be added to each component of the present invention described above. Components related to the manufacturing method can also be components related to the iron-based sintered material. Which embodiment is the best depends on the target, required performance, and the like.

<Raw material powder>
(1) The raw material powder according to the present invention as a whole contains at least a part of Ti, including at least Fe as a main component, Ti and / or V (simply expressed as “Ti / V”), and C. / V and C include powder in the same particle. As long as this is satisfied, the raw material powder may be only one kind of iron-based powder, or may be a mixed powder in which two or more kinds of powders are mixed. The mixed powder may be composed of only two or more types of iron-based powders, or may be composed of one or more types of iron-based powders and another type of one or more additional powders. Examples of additive powders other than iron-based powders include compound powders, alloy powders, and carbon source powders (eg, graphite powder). The compound powder and the alloy powder may be an alloy element source for improving various characteristics (strength, ductility, corrosion resistance, etc.) of the N source and the sintered body in addition to the (Ti, V) C source.

(2) The iron-based powder is made of pure iron or an iron alloy. The iron alloy may contain Cr, Mo, etc. in addition to C and Ti / V. Mo and Cr contribute to the improvement of the strength and toughness of the sintered material (matrix). Mo and Cr are 100% by mass (simply referred to as “%”) as a whole of the raw material powder, for example, 0.2 to 4%, further 0.7 to 2.5%, and 0.5 to 5% in total. Furthermore, it is preferable in it being 1-3%. The particle size of the iron-based powder is preferably 300 μm or less, and more preferably 250 μm or less.

(3) Examples of the (Ti, V) C source powder added to the iron-based powder include Ti / V carbon compound powder. Specifically, it is carbide powder or carbonitride powder such as TiC, VC, TiC-TiN.

  For example, Ti is 2.5 to 35%, 3.5 to 30%, more preferably 5 to 20%, and V is 4.5 to 25%, 5.5 to 20%. Is 7 to 15%, and the total Ti / V is preferably 2.5 to 36%, 5 to 30%, and more preferably 8 to 20%. C is preferably 1.5% to 10%, 2% to 9%, 2.5% to 8%, and more preferably 3% to 6%, assuming that the entire raw material powder is 100%. If these elements are too small, the density of the sintered body cannot be increased. If the elements are too large, the cost of raw materials becomes high, and the amount of TiC and VC particles to be produced increases, resulting in embrittlement and reduced strength properties (particularly ductility).

  When TiC powder is used as the (Ti, V) C source powder, the entire raw material powder is 100%, for example, 3 to 43%, 5 to 30%, or 7 to 25% of TiC powder may be blended. If VC powder is used, the entire raw material powder may be 100%, for example, 6 to 30%, 7 to 25%, or 8 to 20% of VC powder may be blended.

  C is preferably supplied separately from (Ti, V) C source powder, iron-based powder, etc., or as graphite (Gr) powder. The graphite powder contributes to densification of the sintered body by increasing the amount of Fe—C liquid phase generated in cooperation with (Ti, V) C. The graphite powder may be blended, for example, 0.2 to 2.0%, 0.5 to 1.4%, and further 0.7 to 1.1%, with the entire raw material powder being 100%. In particular, when added together with TiC powder, 0.7 to 1.4%, and when added together with VC powder, 0.5 to 1.1% may be blended.

When the molded body is sintered at least in a non-nitrogen atmosphere, an N source powder to be added to the iron-based powder is required. The N source powder is preferably one that releases N during sintering and changes (Ti, V) C to (Ti, V) N. An example of such N source powder is silicon nitride (Si ₃ N ₄ ) powder. In addition to the N source powder, the raw material powder according to the present invention may contain a compound powder containing N, an alloy powder, or the like. For example, a powder that is stable in the sintering temperature range and does not contribute significantly to densification, such as TiN powder, may be blended in the raw material powder, which can contribute to increasing the rigidity of the sintered body.

<Molding process>
The molding pressure at the time of obtaining a molded body from a raw material powder having a desired composition is preferably in the range of, for example, 300 to 1200 MPa, 350 to 900 MPa, or even 390 to 600 MPa. According to the present invention, a dense sintered body can be obtained even when the molding pressure is relatively low. However, if the molding pressure is too small, the dimensional change of the sintered body relative to the molded body increases. Excessive molding pressure lacks industrial productivity.

  The molding pressure is preferably adjusted so that the relative density of the molded body is 60 to 92%, more preferably 65 to 90%. In particular, when nitrogen is introduced into the molded body from the outside (nitrogen-containing atmosphere), if the density of the molded body becomes excessive, nitrogen is not introduced into the molded body, making it difficult to densify the sintered body.

  The forming process may be cold forming (room temperature forming) or warm forming. The lubrication between the raw material powder and the mold may be performed by an internal lubricant blended in the raw material powder or by mold lubrication. When performing mold lubrication, it is preferable to use a mold lubrication warm pressure molding method (refer to Japanese Patent No. 3309970 for details).

<< Sintering process >>
(1) The sintering temperature at which the compact is sintered is preferably 1140 to 1350 ° C., 1175 to 1300 ° C., or 1225 to 1280 ° C. at which an Fe—C liquid phase can be generated. If the sintering temperature is too low, the sintered body cannot be sufficiently densified, or it takes a long time to densify the sintered body. When the sintering temperature is excessive, the energy cost increases and the shape collapses. Incidentally, the eutectic point of Fe—C (binary system) is 1147 ° C.

  The sintering time for heating the molded body at the above sintering temperature is preferably 0.2 to 3 hours, and more preferably 0.4 to 1.5 hours. When the sintering time is too short, the sintered body is not sufficiently densified, and the sintering itself is insufficient. If the sintering time is excessive, the productivity is lowered. Although the sintering time is adjusted according to the sintering temperature, in the case of the present invention, a dense sintered body can be obtained in a relatively short sintering time unless the sintering temperature is low. Conversely, even when the sintering temperature is low, a dense sintered body can be obtained by increasing the sintering time.

In the sintering step according to the present invention, the sintering atmosphere can be a vacuum atmosphere or an inert gas atmosphere. However, when the sintering atmosphere is a nitrogen-containing atmosphere, the sintered body can be efficiently densified. In this nitrogen-containing atmosphere, for example, the N ₂ gas pressure (including partial pressure) is preferably 0.5 to 1000 kPa, and more preferably 2 to 300 kPa. If the gas pressure is too low, nitrogen cannot be sufficiently introduced into the molded body, and an excessive gas pressure causes an increase in production cost.

(2) When nitrogen is introduced into the molded body from the outside, it is preferable to perform a preliminary step of exposing the molded body in a nitrogen-containing atmosphere below the sintering temperature before heating the molded body at the sintering temperature described above. Thereby, nitrogen can be sufficiently introduced into the molded body, and the sintered body can be efficiently densified.

  Although the preliminary process can be performed independently of the sintering process, it is efficient to perform the preliminary process while heating the compact in the sintering furnace to the sintering temperature. For example, the preliminary process may be held in the molded body in a nitrogen-containing atmosphere at a constant temperature lower than the sintering temperature, or may be combined in a heating process that reaches the sintering temperature. In the former case, for example, the temperature of the nitrogen-containing atmosphere is preferably 800 to 1120 ° C, and more preferably 1000 to 1100 ° C. In the latter case, it is preferable to lower the rate of temperature rise to the sintering temperature than usual. For example, the temperature increase rate may be 5 to 30 ° C./min. Note that the gas pressure in the nitrogen-containing atmosphere may be changed before and after the sintering temperature (preliminary process and sintering process).

(3) The sintering step preferably includes a cooling step for forcibly cooling the heated sintered body. Thereby, the coarsening etc. of the metal structure of a sintered compact can be suppressed, and the improvement of the mechanical characteristic can be aimed at by extension. Note that the forced cooling can be performed, for example, by introducing a refrigerant gas (N ₂ , Ar, etc.) into the furnace.

《Iron-based sintered material》
Since the iron-based sintered material of the present invention is densified and has a high density, it exhibits excellent mechanical properties (rigidity, strength, etc.). In particular, since the iron-based sintered material of the present invention includes a hard (high rigidity) compound (nitrogen compounds such as TiN and VN, carbon compounds such as TiC and VC), it has a high Young's modulus corresponding to its density. Demonstrate. In the iron-based sintered material of the present invention, since (Ti, V) C changes to (Ti, V) N and densification is achieved, the entire sintered body is 100% by mass (simply referred to as “%”). .), N is contained in an amount of 0.4 to 3%, 0.5 to 2.5%, and further 0.8 to 2%. However, the presence form of N contained in the sintered body according to the present invention is not limited to (Ti, V) N.

  The iron-based sintered material of the present invention is suitable for various members that require high rigidity, particularly for members that have a relatively complicated shape and can reduce production costs by a near net shape. For example, the iron-based sintered material of the present invention is preferably used for engine parts (for example, connecting rods) for automobiles, transmission parts, chassis parts, suspension parts, various shafts, pulleys, and the like.

  Manufacture samples (molded body and sintered body) with various changes in raw material powder composition, molding pressure, sintering conditions (atmosphere, temperature), etc., and measure their relative density, dimensional change, weight change, Young's modulus, etc. did. Based on these, the content of the present invention will be described more specifically.

<Production of sample>
[Raw material powder]
(1) Iron-based powder First, the following four types of iron-based powders were prepared.
(i) Pure Fe powder
(ASC100.29 / specific gravity: 7.86 g / cm ³ manufactured by Höganäs AB),
(ii) Fe-Mo alloy powder: Fe-1.5% Mo
(Astaloy Mo manufactured by Höganäs AB / specific gravity: 7.86 g / cm ³ ),
(iii) Fe-Cr alloy powder: Fe-1.5% Cr-0.2% Mo
(Astaloy CrL / specific gravity: 7.82 g / cm ³ manufactured by Höganäs AB),
(iv) SKH57 powder: Fe—1.3% C—0.34% Si—0.34% Mn—4% Cr—3.5% Mo—9.9% W—3.3% V—10% Co
(JIS high-speed tool steel / specific gravity: 8.26 g / cm ³ )

  SKH57 powder had an average particle size of 11 μm, and other iron-based powders had a particle size of −212 μm, and all powders were used as received. The composition (%) of each powder means a mass ratio (the same applies hereinafter). The blending ratio and content composition of the raw material powder described later are also mass ratios.

(2) Compound powder Next, the following five types of compound powder were prepared.
(i) TiC powder: Ti-19.8% C
(Average particle diameter: 1.6 μm / specific gravity: 4.93 g / cm ³ )
(ii) VC powder: V-16.9% C
(Average particle diameter: 1.4 μm / specific gravity: 5.43 g / cm ³ )
(iii) TiC-TiN powder: Ti-9.9% C-10.7% N
(Average particle diameter: 1.4 μm / specific gravity: 5.19 g / cm ³ )
(iv) TiN powder: Ti-21.9% N
(Average particle diameter: 1.3 μm / specific gravity: 5.44 g / cm ³ )
(v) Si ₃ N ₄ powder: Si-40% N
(Average particle diameter: 3.2 μm / specific gravity: 3.44 g / cm ³ )
Si ₃ N ₄ powder is manufactured by Denka Co., Ltd., and other compound powders are manufactured by Nippon Shin Metal Co., Ltd.

(3) Further, graphite (Gr) powder: JCPB (average particle diameter: 5.1 μm / specific gravity: 2.25 g / cm ³ ) manufactured by Nippon Graphite Industry Co., Ltd. was also prepared.

[Mixing process]
Except for the case where only one kind of iron-based powder was used, each powder weighed to a desired blending ratio was mixed for 3 minutes in a mortar, and further rotated and mixed for 30 minutes by a ball mill. The mixed powder thus obtained was used as a raw material powder.

[Molding process]
A raw material powder was pressure-molded by a mold lubrication warm pressure molding method (see Japanese Patent No. 3309970) to produce a compact (φ14 × 10 mm). The molding pressure was either 392 MPa, 588 MPa or 784 MPa.

[Sintering process]
(1) Each compact was sintered in a batch-type sintering furnace. The sintering atmosphere was a vacuum atmosphere (1-5 × 10 ⁻² Pa) or a nitrogen (N ₂ ) atmosphere. The nitrogen atmosphere was configured by introducing a certain amount (5 liters / minute) of nitrogen gas into the furnace and adjusting the gas pressure to 100 to 102 kPa.

The sintering temperature was either 1250 ° C, 1200 ° C or 1150 ° C. The soaking time (sintering time) for maintaining the sintering temperature was 30 minutes (0.5 hours). The sintered body in a heated state after the sintering time passed was sprayed with a refrigerant (gas) and rapidly cooled to about 60 ° C. (cooling rate: about 90 ° C./min) (cooling step). At this time, Ar was used as a refrigerant when sintered in a vacuum atmosphere, and N ₂ was used as a refrigerant when sintered in a nitrogen atmosphere.

(2) When sintering in a nitrogen atmosphere, a preliminary process was performed before performing the above-described sintering process. The preliminary process is performed by holding the molded body in the above-described sintering furnace in a nitrogen atmosphere and holding at a constant temperature (1100 ° C.) during the temperature rising process up to the sintering temperature for a certain time (30 minutes). It was.

<Measurement>
(1) density, weight change, dimensional change,
For the compact and sintered body of each sample, first, the dimensions and weight were measured, and the changes in bulk density (ρ), dimensions before and after sintering (height, diameter), and weight were determined.

Based on the bulk density (ρ) and the true density (ρ ₀ ), the relative density of each sample was calculated. For the true density (ρ ₀ ), a pore-free density (PFD) calculated based on the blend composition and specific gravity of each powder was used.

  Further, the difference between the dimensions after sintering minus the dimensions before sintering (dimensions of the molded body) was divided by the dimensions before sintering to obtain the dimensional change rate before and after sintering. The rate of dimensional change was calculated for both height and diameter.

  Furthermore, the weight change rate before and after sintering was determined by dividing the difference obtained by subtracting the weight before sintering (weight of the compact) from the weight after sintering by the weight before sintering.

(2) Young's modulus The Young's modulus of the sintered body (test piece) according to each sample was determined by an ultrasonic pulse method. Specifically, the Young's modulus was calculated from the propagation speed of the longitudinal wave and the transverse wave propagating through the test piece by using the longitudinal wave and transverse wave vibrators to propagate the ultrasonic pulse.

(3) N amount About some samples, N amount (mass%) contained in a sintered compact was measured. The measurement was carried out using an oxygen / nitrogen analyzer (EMGA-650, manufactured by Horiba, Ltd.) by an inert gas melting-thermal conductivity method.

<< Observation >>
For some samples (No. B12, B31), the distribution of each element contained in the sintered body (metal structure) was measured using a field emission electron beam microanalyzer (FE-EPMA / JXA-8500F manufactured by JEOL Ltd.). Analyzed with

<Evaluation>
The production conditions and characteristics of each sample are summarized in Tables 1 to 6. Moreover, the graph which put together the characteristic etc. of each sample was shown to each FIG. Based on these, the features of the present invention will be specifically described below. In addition, the containing composition shown to each table | surface converts and shows the mass ratio of C, Ti, V, or N contained in raw material powder based on the composition and mixture ratio of each powder.

(1) Influence of sintering atmosphere and carbide amount (TiC amount, VC amount) Samples with various changes in the blending ratio of compound powder (TiC powder or VC powder) and Gr powder with pure Fe powder as iron-based powder, The results are shown in Table 1 and Tables 2A and 2B (both are simply referred to as “Table 2”). Table 1 shows each sample sintered in a vacuum atmosphere, and Table 2 shows each sample sintered in a nitrogen atmosphere.

  FIG. 1A shows the relationship between the mixing ratio of TiC powder (simply referred to as “TiC amount”) and the relative density for each sample in which the mixing ratio of Gr powder (simply referred to as “Gr amount”) is 1.2%. FIG. 1B shows the relationship between the blending ratio of VC powder (simply referred to as “VC amount”) and the relative density for each sample with Gr powder: 0.8%. 1A and 1B (both are simply referred to as “FIG. 1”) also show the relative density of the molded body. Hereinafter, unless otherwise specified, the relative density of the sintered body is simply referred to as “relative density”.

  First, as is apparent from FIG. 1, when a molded body in which TiC powder or VC powder is mixed in raw material powder is sintered in a nitrogen atmosphere, the relative density of the sintered body is substantially proportional to the TiC amount or the VC amount. It was found that it increased. Incidentally, it was also found that when sintered in a vacuum atmosphere, the relative density of the sintered body was almost the same as the relative density of the molded body and hardly increased.

  Next, for each sample (TiC powder blend, Gr amount: 1.2%) sintered in a nitrogen atmosphere, the weight change rate (ΔW) before and after sintering and the mass of nitrogen contained in the sintered body The relationship with the ratio (simply referred to as “N amount”) is shown in FIG. As is apparent from FIG. 2, it was found that the increase in the N amount is substantially proportional to the increase in the weight in the sintered body. Furthermore, considering the decrease in weight when sintered in a vacuum atmosphere: about 0.2%, the amount of N contained in the sintered body sintered in a nitrogen atmosphere is approximately ΔW + 0.2. Can be estimated.

  In some of the samples shown in each table, the relative density of the sintered body is over 100%. The main reason is considered to depend on the increment of N occluded from the outside (nitrogen atmosphere) (the same applies hereinafter).

(2) Effect of Gr Amount Based on the respective samples shown in Table 2, the relationship between the amount of Gr blended in the raw material powder and the relative density or Young's modulus of the sintered body is shown in FIGS. 3A and 3B (both of them are simply referred to as “FIG. 3”) are cases where TiC powder is blended in the raw material powder, and FIGS. 4A and 4B (both of them are simply referred to as “FIG. 4”) are raw materials. This is a case where VC powder is blended in the powder.

  As is apparent from FIGS. 3 and 4, it was found that the relative density and Young's modulus can be sufficiently improved by blending the Gr powder in the raw material powder even if the TiC amount and the VC amount are small. In other words, even if the amount of Gr is small, the relative density and the Young's modulus can be sufficiently improved if the amount of TiC and the amount of VC increase. Therefore, it can be said that the total amount of C is preferably within the range defined by the present invention in order to achieve densification or high rigidity of the sintered body.

(3) Influence of sintering temperature Table 3 shows samples in which the temperature at which a compact formed of a raw material powder containing pure Fe powder, VC powder and Gr powder was sintered in a nitrogen atmosphere was changed. Based on the samples shown in Table 2B and Table 3, the relationship between the VC amount and the relative density or Young's modulus is shown in FIGS. 5A and 5B (both are simply referred to as “FIG. 5”).

  As is clear from FIG. 5, it was found that when the sintering temperature is increased, a sufficiently high relative density and Young's modulus can be realized in a short sintering process even if the amount of VC is small. However, it was also found that sufficient relative density and Young's modulus can be obtained when the amount of VC increases even at a low sintering temperature. From this, it can be said that even when the sintering temperature is low and the amount of VC is small, for example, if the sintering time is set appropriately, the relative density and the Young's modulus can be sufficiently increased.

(4) Effect of iron-based powder Table 4 shows samples in which the type of iron-based powder was changed. Based on each sample shown in Table 2 and Table 4, the influence of the iron-based powder on the relationship between the TiC amount or VC amount and the relative density or Young's modulus is shown in FIGS. 6A and 6B (both are simply referred to as “FIG. 6”) are cases where TiC powder is blended in the raw material powder, and FIGS. 7A and 7B (both are simply referred to as “FIG. 7”) are raw materials. This is a case where VC powder is blended in the powder.

  As is apparent from FIGS. 6 and 7, when the Fe—Cr alloy powder is used, there is a tendency to be slightly densified. Basically, the influence of the type of iron-based powder is small, and any iron-based powder. It has been found that densification and high rigidity can be achieved even when using.

(5) Influence of N source A sample obtained by sintering a molded body made of a raw material powder containing Si ₃ N ₄ powder (N source powder) in addition to pure Fe powder, TiC powder and Gr powder in a vacuum atmosphere is shown. This is shown in FIG. FIG. 8 shows the relationship between the TiC content and the relative density when the mixing ratio of the Si ₃ N ₄ powder (simply referred to as “Si ₃ N ₄ content”) is constant. Further, the relationship between the amount of Si ₃ N ₄ and the relative density or Young's modulus when the TiC amount is constant is shown in FIGS. 9A and 9B (both are simply referred to as “FIG. 9”).

  As is apparent from FIGS. 8 and 9, if there is an appropriate amount of N source in the molded body, even when sintered in a vacuum atmosphere, as in the case of sintering in a nitrogen atmosphere, densification and high It was found that rigidity could be achieved.

(6) Influence of pre-alloying Table 6A, Table 6A shows each sample in which V and C are pre-alloyed with SKH57 as an iron-based powder, and various types and amounts of compound powder, molding pressure, and sintering atmosphere are changed. 6B (both are simply referred to as “Table 6”).

  First, for each sample sintered in a vacuum atmosphere or a nitrogen atmosphere, the relationship between the amount of TiC and the relative density or Young's modulus is shown in FIGS. 10A and 10B (both are simply referred to as “FIG. 10”). As is clear from FIG. 10, it was found that when SKH57 was used for sintering in a vacuum atmosphere, the relative density and Young's modulus decreased as the amount of TiC increased. On the other hand, when sintered in a nitrogen atmosphere, even if the amount of TiC is increased to about 40% by mass, a high relative density of almost 100% can be stably obtained, and the Young's modulus can be increased almost in proportion to the amount of TiC. all right.

  Next, for each sample obtained by sintering compacts having different molding pressures in a nitrogen atmosphere, the relationship between the amount of TiC and the relative density or Young's modulus is simply referred to as “FIG. 11”. )Pointing out toungue. As is clear from FIG. 11, it was found that the relationship between the TiC amount and the relative density or Young's modulus described above was maintained even when the molding pressure was changed.

By the way, as is clear when comparing sample F1 and sample F4 shown in Table 6A, even when the raw material powder does not contain any compound powder and is only iron-based powder (SKH57), by sintering in a nitrogen atmosphere, The relative density was about 2% and the weight change rate was about 0.8% higher than when sintered in a vacuum atmosphere. From this, it can be said that N ₂ in the nitrogen atmosphere also reacts with VC contained in the iron-based particles prealloyed to densify the sintered body.

  Furthermore, for each sample obtained by sintering a molded body made of a raw material powder containing a Ti-based compound powder other than TiC (TiC-TiN powder or TiN powder) in a nitrogen atmosphere, the compounding ratio of these compounds (simply referred to as “compound amount”) .) And the relative density or Young's modulus are shown in FIGS. 12A and 12B (both are simply referred to as “FIG. 12”). As is clear from FIG. 12, it can be seen that even when a TiC—TiN powder or TiN powder is blended in addition to the TiC powder, a high relative density can be obtained and the Young's modulus can be increased. However, it was also found that the compound powder having a higher C content is easier to achieve densification and higher rigidity of the sintered body.

(7) Metal structure The result of observing each sintered body of the sample B12 containing TiC and the sample B31 containing VC by FE-EPMA is shown in FIG. 13A and FIG. 13B (both are simply referred to as “FIG. 13”). .) Respectively. As is clear from FIG. 13, it was found that the TiC or VC distribution and the N distribution coincided. From these results, part of the carbide that was present in the raw material powder changed to nitride, carbonitride, or a mixture of them, and the Fe-C liquid phase appeared and the sintered body became dense. It can be said that it was done.

  As described above, it has been confirmed by the evaluation, analysis, and the like based on a large number of samples that the iron-based sintered material can be densified and highly rigid within the range defined in the present invention.

Claims (12)

A method for producing an iron-based sintered material comprising a sintering step of heating a raw material powder compact in which compound powder is mixed with iron-based powder into a sintered body,
At least a part of the compound powder is composed of a carbon compound containing Ti and / or V,
The raw material powder includes 100% by mass (hereinafter simply referred to as “%”) of the raw material powder, C includes 1.5 to 10%, and Ti and / or V in total 2.5 to 36%,
The said sintering process is a manufacturing method of the iron-based sintered material which is a process of heating the said molded object at the sintering temperature of 1140-1350 degreeC in the sintering atmosphere containing nitrogen. A method for producing an iron-based sintered material comprising a sintering step of heating a raw material powder compact in which compound powder is mixed with iron-based powder into a sintered body,
At least a part of the compound powder is composed of a carbon compound containing Ti and / or V,
The raw material powder further contains a nitrogen source powder, the total raw material powder is 100%, C is 1.5 to 10%, and Ti and / or V is 2.5 to 36% in total,
The said sintering process is a manufacturing method of the iron-based sintered material which is a process of heating the said molded object at the sintering temperature of 1140-1350 degreeC.   The method for producing an iron-based sintered material according to claim 1, wherein the carbon compound is at least one of titanium carbide, titanium carbonitride, vanadium carbide, and vanadium carbonitride. A method for producing an iron-based sintered material comprising a sintering step of heating a compact of a raw material powder containing iron-based powder to form a sintered body,
The iron-based powder includes Ti and / or V and C,
The raw material powder includes 100% of the raw material powder as a whole, 1.5 to 10% of C, and 2.5 to 36% of Ti and / or V in total,
The said sintering process is a manufacturing method of the iron-based sintered material which is a process of heating the said molded object at the sintering temperature of 1140-1350 degreeC in the sintering atmosphere containing nitrogen. A method for producing an iron-based sintered material comprising a sintering step of heating a compact of a raw material powder containing iron-based powder to form a sintered body,
The iron-based powder includes Ti and / or V and C,
The raw material powder further contains a nitrogen source powder, the total raw material powder is 100%, C is 1.5 to 10%, and Ti and / or V is 2.5 to 36% in total,
The said sintering process is a manufacturing method of the iron-based sintered material which is a process of heating the said molded object at the sintering temperature of 1140-1350 degreeC.   The method for producing an iron-based sintered material according to any one of claims 1 to 5, wherein the raw material powder further contains graphite powder.   The said sintering process is a process which makes the sintering time which heats the said molded object at the said sintering temperature 0.2 to 3 hours, Manufacture of the iron-based sintered material in any one of Claims 1-6 Method.   The said sintering process is a manufacturing method of the iron-based sintered material in any one of Claims 1-7 provided with the preliminary | backup process which exposes the said molded object in nitrogen-containing atmosphere below the said sintering temperature.   The said molded object is a manufacturing method of the iron-based sintered material in any one of Claims 1-8 formed by press-molding the said raw material powder at 300-1200 MPa. An iron-based sintered material comprising a sintered body in which compound particles are dispersed in an iron-based matrix,
At least a part of the compound particles comprises a nitrogen compound containing Ti and / or V and N,
The sintered body is 100% by mass (simply referred to as “%”), and C is 1.5 to 10%, N is 0.4 to 3%, Ti and / or V. together with containing 2.5 to 36% in total, the true density ([rho ₀₎ iron-based sintered material relative density is the ratio of bulk density _{(ρ) (ρ / ρ 0} ) is 93% or more relative to.   The iron-based sintered material according to claim 10, wherein the sintered body has a Young's modulus of 165 GPa or more.   The iron-based sintered material according to claim 10 or 11, wherein the compound particles further include carbon compound particles made of at least one of titanium carbide, titanium carbonitride, vanadium carbide, and vanadium carbonitride.