JPH06240401A - Hard sintered material - Google Patents

Abstract

PURPOSE:To inhibit the production of pores and to facilitate densification by forming a hard sintered material from a hard phase having a specified compsn., a metallic bonding phase and a specified 3rd phase. CONSTITUTION:The hard sintered material is formed from a hard phase based on Mo2CrB2, a metallic bonding phase based on one or more among Ni, Fe and Co and one or more kinds of 3rd phases dispersed in the metallic bonding phase and selected among a phase contg. Ta and Cr, a phase incorporating Ti and a phase contg. Cr and oxygen. The hard phase is contained by 30wt.% to.98wt.% and the 3rd phase are contained by 0.3vol.% to <30vol.%. Oxygen is contained in the 3rd phases and Cr and/or Mo allowed to enter into solid soln. in the metallic bonding phase is contained by 5wt.% to <35wt.% each. The objective hard sintered material having satisfactory strength and hardness at high temp. can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has physical properties such as hardness and strength that are equal to or superior to those of existing hard sintered materials such as WC-Co cemented carbides at room temperature. The present invention relates to a hard sintered material that maintains excellent strength and hardness even in a high temperature range of 500 ° C. or higher where strength cannot be maintained by a material or a hard sintered material, and that has good corrosion resistance to molten metals such as aluminum and zinc.

[0002]

2. Description of the Related Art A hard sintered material having a metal as a binder phase is also called cermet, and has excellent hardness of ceramics,
It was expected that a material having both heat resistance and corrosion resistance and excellent toughness that a metal has would be realized, and there was a period of intense research in the past.

However, the hard-sintered materials that have been put into practical use so far are relatively small in number in spite of the large number of combinations. Among the hard sintered materials that have been put into practical use, WC-Co based cemented carbide has good sinterability, it is easy to obtain a material having excellent hardness and strength, and there are also improvements that have been made continuously. Its usage has increased significantly and now forms one large market.

Although WC-Co type cemented carbide is often used under severe operating conditions, it has a weak point of rapidly losing hardness and strength at high temperatures of 500 ° C. or higher. In particular, due to the recent remarkable development of technology, there is an urgent need for hard sintered materials having superior durability under severe conditions.

The applications in which the conventional WC-Co type cemented carbide cannot be used as they are include die-casting materials used at high temperatures, metal working members, machine parts and sliding members. Also, it can be used if it is cooled,
It may be inconvenient to use the cooling.

The presence of a ternary hard compound (crystal) called Mo ₂ CrB ₂ is due to the existence of, for example, Poroshkovaya.
Metallurgya, No. 5 (77), p. 7
9-87, May, 1969, and reports Mo ₂ Ni.
The addition of Cr to a hard sintered material of B ₂ compound boride system is described in 1992 Autumn Meeting of the Japan Institute of Metals, p. 691 and JP-A-62-196353.

It is conceivable from these reports that Mo ₂ CrB ₂ will be compounded with various metals to have high toughness and a hard sintered material will be obtained. However, when actually compounded, a sintered material with considerably high hardness can be obtained, but due to the presence of Cr in the raw material or oxygen that binds to Cr during the pretreatment of the raw material, the sintered material in the sintered body is However, there is a problem in that pores are generated and a product having practical strength cannot be obtained.

The reason why the hard sintered material of this system has a large hardness is that Mo ₂ CrB ₂ which is a main constituent substance has a hard crystal phase. There are no reports of using Mo ₂ CrB ₂ as the hard phase of hard sintered materials.

[0009]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems and suppresses the formation of pores.
It is an object of the present invention to provide a hard sintered material that maintains high strength and hardness even at the above-mentioned high temperatures and has corrosion resistance against molten metal such as aluminum.

[0010]

The present invention has been made to achieve the above-mentioned object, and the hard sintered material of the present invention comprises a hard phase containing Mo ₂ CrB ₂ as a main component, Ni, Fe and A metal binder phase containing at least one selected from Co as a main component, and a phase containing Ta and Cr dispersed in the metal binder phase,
1 selected from a phase containing Ti and a phase containing Cr and oxygen
It is characterized by being composed of three or more kinds of third phases.

[0011] In hard sintered material of the present invention, the hard Ta is being captured portion in a manner to replace the Mo of Mo ₂ CrB ₂ in the hard phase, that the Mo ₂ CrB ₂ according to the present invention mainly The phases are hard phases including those partially substituted with Ta or the like. In addition to Ta being a solid solution in the metal binding phase, Ta forms a third phase dispersed in the metal binding phase as a phase containing Ta and Cr. Further, Ti partially forms a solid solution in the metal binding phase, and forms a third phase dispersed in the metal binding phase as a Ti-containing phase. Oxygen, nitrogen, carbon, etc. are contained in this third phase.

Further, the Mo ₂ CrB referred to in the present invention is
_The hard phase mainly composed of ₂ contains Ni or Fe in a state where Cr is partially substituted with Cr, and the presence of this compound can be confirmed by X-ray diffraction as described later.

The metallic binder phase is composed of Ni, Fe, which are the main components,
Mo, Cr, W, Ta, Ti on Co or these alloys
Alternatively, Nb or the like is formed as a solid solution, and among these solid solution components, W, Ta, Nb, and Cr contribute to the improvement of the high temperature strength of the metal binding phase.

As a starting material for producing a hard phase mainly composed of Mo ₂ CrB ₂ , any compound containing these constituent elements can be used. For example, Mo
B and Ni-Cr alloy, CrB ₂ or CrB and Mo,
It suffices to combine Mo, B and powder raw materials such as a Ni—Cr alloy and mix Mo, Cr, B and the like so as to have a stoichiometric composition.

Further, in order to suppress the generation of pores during sintering and improve the characteristics by making the hard sintered material dense, in the present invention, a Ta-based compound and / or a Ti-based compound, for example, a nitride of Ta or Ti is used. , Boride, hydride, carbide, etc. are added. These added compounds form a third phase during sintering, trap oxygen such as the cause of pores, and suppress the generation of pores. Further, Cr also serves as an oxide and functions to suppress the formation of pores.

In order to produce the hard sintered material of the present invention, for example, the starting materials prepared in a predetermined composition are put in a pot mill using a stainless steel pot and a stainless steel ball, and pulverized and mixed with ethanol as a pulverizing medium. Do at the same time. The slurry-like raw material powder separated from the balls after pulverization is dried under reduced pressure while being heated to obtain a molding powder.

Then, the molding powder is applied to a die press or C
A compact is formed by IP (isostatic press) molding or the like, and is densified at a firing temperature of preferably 1250 ° C. to 1400 ° C. in a vacuum or reduced pressure atmosphere. Here, in order to reliably generate the important third phase for ensuring the physical properties of the material, the rate of temperature increase in the temperature range from 1000 ° C at which the formation of the third phase compound and the hard phase begins to 1200 ° C at which the liquid phase occurs Is preferably as small as 50 ° C./hour or less, or is kept at a constant temperature within this temperature range for 2 hours or more.

Under such firing conditions, a hard sintered material having a small porosity, high hardness and high strength can be easily obtained. Here, crushing and mixing are not limited to pot mills, vibration mills,
Various commonly used crushers such as an attrition mill can be used. Also, ethanol was used as the grinding medium because of its safety and ease of handling, but acetone, hexane, etc. can also be used.

Further, depending on the raw material powder used, it is also possible to carry out dry pulverization and mixing in an atmosphere substituted with argon or nitrogen without using a pulverizing medium. Further, by pressure sintering such as hot pressing or HIP (hot isostatic pressing), it is possible to sinter densely even at a firing temperature of 1250 ° C. or less, and to obtain dense and good physical properties. A sintered body is obtained.

Even if sintering is performed at 1400 ° C. or higher, a sintered body having good physical properties can be obtained, although some deterioration or deformation of physical properties is observed due to growth of crystal grains. Considering the physical properties of the obtained sintered body and the ease of sintering, it is preferably 12
Sintering is performed in the temperature range of 50 to 1400 ° C.

The reaction and densification process at the time of sintering are estimated from the phase diagram and the composition of the compound in the sintering process in the above-mentioned literature, and hard sintering having a metallic binder phase containing Ni as a main component. In the case of a material, it is presumed that sintering proceeds due to the following reactions. Where γ alloy (γ
Phase) is a solid solution of Mo, Cr, Ta and / or Ti and Ni.

[Chemical formula 1] around 1000 ° C: 2MoB + Mo + Ni-Cr
Alloy + Ta compound → Mo ₂ CrB ₂ + Ni + Mo + Cr
+ Ta compound Around 1250 ° C .: Mo ₂ CrB ₂ + Ni + Mo + Cr +
Ta compound → (Mo, Ta) ₂ CrB ₂ + γ alloy + Ta
Phases containing Cr and Cr

As a result of these reactions, the products in the resulting sintered body were examined by X-ray diffractometry to find that Mo ₂ CrB ₂
Hard phase and metal bonded phase (Mo, Cr, Ta, T)
Ni alloy in which i and the like are dissolved) and a phase containing Ta and Cr, T
It can be seen that the hard sintered material has a three-phase structure including one or more third phases selected from the phase containing i and the phase containing Cr and oxygen. The presence of this third phase is easily confirmed by observation with SEM or EPMA, and can also be observed by observation with an optical microscope at a magnification of 500 times or more.

The preferred hard sintered material of the present invention contains the hard phase in an amount of 30% by weight or more and less than 98% by weight. When the amount of the hard phase is less than 30% by weight, the amount of the metal phase is large and the hardness is slightly insufficient, and the physical properties such as hardness and strength at high temperature tend to be deteriorated. When the amount of the hard phase is 98% by weight or more, even if the hardness is high, only a small amount of the metallic phase as the binding phase exists, so that high binding strength cannot be obtained and the sintered body tends to be brittle. Considering the balance of strength including hardness and toughness, the more preferable content of the hard phase is 65 to 95% by weight.

In another preferred hard sintered material of the present invention,
The third phase is contained in an amount of 0.3% by volume or more and less than 30% by volume. If the amount of the third phase dispersed in the metal binding phase is less than 0.3% by volume, the density of the obtained sintered body may be low. vice versa,
Even if the phase containing Ta and Cr is contained in an amount of 30% by volume or more, there is almost no effect of densification and strength improvement, the specific gravity of the sintered body becomes large, and Ta is expensive, so that the material is cost effective. Is less practical. Volume% of this third phase
Can be calculated by taking a photograph of the cut surface of the sintered body with an SEM or an optical microscope and calculating the ratio of the surface area of the third phase appearing on the cut surface. The more preferable content of the third phase is 0.5 to 20 from the physical properties of the obtained sintered body.
% By volume.

[0025] Ta and Ti form a solid solution in the metal binder phase to improve the strength and toughness of the metal binder phase at room temperature and high temperature, and at the same time, they bond with Cr in the metal binder phase and have pores. It is considered that the oxygen, which is the cause of the generation, is trapped to improve the bonding strength between the hard phase and the metal bonding phase, thereby contributing to the densification of the sintered body and the improvement of the physical properties. In addition, the third dispersed in the metallic binder phase
It is considered that the phases make the structure of the sintered body fine and contribute to the improvement of the physical properties of the sintered body.

In another preferred hard sintered material of the present invention,
Oxygen is contained in the third phase. Since the third phase is a compound containing oxygen, generation of pores in the sintered body is suppressed, and a dense hard sintered material having high hardness and strength can be obtained.

In another preferred hard sintered material of the present invention,
Cr and / or Mo which are solid-dissolved in the metal binder phase are 5% by weight or more and less than 35% by weight, respectively. When the amount of Mo and Cr which are solid-solved in the metal binder phase is less than 5% by weight, the solid solution strengthening of the metal binder phase is not sufficient, and the effect of improving the strength and hardness of the hard sintered material cannot be obtained. . On the other hand, 3
When it is solid-soluted in a supersaturated amount of 5% by weight or more, brittle intermetallic compounds are precipitated in the sintered material during cooling after sintering or during practical use, which tends to reduce the strength and toughness of the hard sintered material. The solid solution amount of Mo, Cr, etc. in the metal binding phase can be analyzed by an X-ray microanalyzer or fluorescent X-ray analysis.

[0028]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Example 1 As a starting material, M having a boron content of 10.33% by weight was used.
oB powder (average particle size of about 4 μm) and CrB powder having a boron content of 9% by weight (average particle size of about 10 μm), and a small amount of Mo powder (average particle size of about 3 μm) as a component adjustment for hard phase formation. ) Is added, and carbonyl Ni powder (average particle size of about 1 μm) is used as a raw material for the metal binding phase, and T is used as a Ta source.
An aN powder (average particle size of about 1 μm) was prepared as follows.

That is, powders of MoB, CrB, Mo, Ni and TaN are 29.24% by weight and 16.
71% by weight, 30.45% by weight, 18.83% by weight and 4.77% by weight, each raw material powder was put in a stainless steel pot of a vibration mill, and 24 hours in an ethanol solvent using a stainless steel ball. Was crushed and mixed.

The crushed slurry was put in an evaporator and dried under reduced pressure while heating, and passed through a 140-mesh sieve to obtain a molding powder. This molding powder is put into a die press and pressure of 200 kg / cm ² is applied to 20 mm × 30 mm.
Molded to a shape of × 40mm, and further CIP 1.5to
N / cm ² was pressed to obtain a green compact.

This green compact was placed in an atmosphere furnace at 5 × 10 ^-3 m
Sintered under vacuum of mHg. That is, after holding at 1100 ° C. for 2 hours, sintering was performed at the maximum temperature of 1285 ° C. for 1 hour. The obtained sintered body was cut and processed into a test piece, and the Vickers hardness (H _v ) and the three-point bending strength (the size of the test piece was 3 mm × 4 mm × 30 mm, and the measurement span was 20 mm) were measured. In addition, the structure of the cut surface was observed by an optical microscope and SEM, and the composition was analyzed by X-ray diffraction and EPMA.

H _v at room temperature of the obtained sintered body was 12
50 kg / mm ² , bending strength is 200 kg / mm ² , 8
The bending strength at 00 ° C. was 170 kg / mm ² . In addition, the X-ray shown in FIG.
A line diffraction pattern was obtained. That is, FIG. 1 is an X-ray diffraction diagram showing the crystal composition of one example of the hard sintered material according to the present invention,
The relationship between the diffraction angle 2θ (°) and the diffraction intensity is shown. Mo ₂ Cr
The diffraction peak of the hard phase mainly composed of B ₂ is marked with * in the figure, and the metal-bonded phase containing Ni as a main component is marked with γ.

Further, from the observation of the structure by SEM and an optical microscope and the analysis by EPMA, the sintered body was composed of a hard phase and a metal binding phase (γ phase) and a third phase containing Ta, Cr and oxygen. Confirmed the coexistence of Ta in addition to Mo, Cr and B. Further, it was confirmed that the metal binding phase was composed of Ni, Cr and Ta and a small amount of unavoidable impurities introduced from stainless steel balls and the like.

The amount of the hard phase in the sintered body was calculated as 85% by weight, assuming that all the compounded B form the hard phase mainly composed of Mo ₂ CrB ₂ . The content of the third phase was 5% by volume calculated from the cross-sectional area of the third phase appearing on the cut surface of the sintered body, and C dissolved in the metallic binder phase was dissolved.
The amount of r was 10% by weight and the amount of Ni was 25% by weight.
Since the amount of unavoidable impurities was as small as 1% by weight or less, the composition of the sintered body is shown in the following examples by ignoring this amount.

Examples 2 to 22 and Comparative Examples 1 to 6 The compositions and firing temperatures of other examples are shown in Table 1, their physical properties and constitutions are shown in Table 2, and similarly in Comparative Examples, Tables 3 and 4 are shown. Are summarized below. In addition to the raw material powder used in Example 1, C having an average particle size of the order of 1 μm is used.
r, Co, Fe, Ti, Ni and TiN powders were used.
The conditions of crushing, mixing, drying, molding, etc. were in accordance with Example 1, and the sintering was performed by first holding at 1100 ° C. for 2 hours and then holding at the firing temperature shown in Table 1 for 1 hour to perform sintering. Comparative Examples 6 and 7 are existing WC-Co based cemented carbides.

[0037]

[Table 1]

[0038]

[Table 2]

[0039]

[Table 3]

[0040]

[Table 4]

In the examples shown in Tables 1 and 2, the physical properties at room temperature are almost equal to or superior to those of typical WC-Co cemented carbides (see Comparative Examples 6 and 7). In consideration of the fact that the bending strength at 800 ° C. is hardly reduced, it is understood that the hard sintered material according to the present invention is a practical material having excellent physical properties, especially at high temperatures.

The results of Comparative Examples 1 to 5 show that the flexural strength and hardness levels are relatively low due to the presence of pores and the like. In the examples, the addition of Ta and / or Ti results in a flexural strength. It was clearly improved, and it was judged that this was due to the fact that it was densified with few pores together with the observation result of the structure separately performed.

[0043]

The hard phase mainly composed of Mo ₂ CrB ₂ and N
A hard sintered material composed of a metallic binder phase containing at least one selected from i, Fe and Co as a main component forms pores in the sintered body due to oxygen and the like which are considered to accompany the Cr raw material during sintering. Although it was difficult to densify, by mixing Ta and Ti into the raw material, the third phase such as Ta-Cr compound, Ti compound, and Cr oxide dispersed in the metallic binder phase was formed. It was formed, the generation of pores was suppressed, and the densification was facilitated. Thus, a hard sintered material having a sufficient strength and hardness even at a high temperature of 800 ° C., which is composed of a hard phase mainly composed of Mo ₂ CrB ₂ and a metal bonded phase of an iron group metal, was obtained.

This hard sintered material is remarkably excellent in physical properties in a high temperature range as compared with the conventional WC-Co type cemented carbide and has corrosion resistance against molten metal such as aluminum. For applications where Co-based cemented carbide could not be used, or applications where it could be used but had a short service life, such as mold materials for die casting used at high temperatures, metal working members, machine parts, sliding members, etc. Since it can be preferably used, its industrial utilization effect is great.

[Brief description of drawings]

FIG. 1 is an X-ray diffraction diagram showing an example of a crystal composition of a hard sintered material according to the present invention.

[Explanation of symbols]

*: Diffraction peak of hard phase mainly composed of Mo ₂ CrB ₂ γ: Diffraction peak of metal bonded phase

Claims (6)

[Claims] 1. A hard phase mainly composed of Mo ₂ CrB ₂ and N
i, Fe and Co, a metal bonding phase containing at least one selected from the main components, and Ta and Cr dispersed in the metal bonding phase.
A hard sintered material comprising a phase containing Ti, a phase containing Ti, and one or more third phases selected from a phase containing Cr and oxygen. 2. The hard sintered material according to claim 1, which contains a hard phase in an amount of 30% by weight or more and less than 98% by weight. 3. The hard sintered material according to claim 1, which contains a third phase in an amount of 0.3% by volume or more and less than 30% by volume. 4. The hard sintered material according to claim 1, 2 or 3, wherein oxygen is contained in the third phase. 5. The hard sintered material according to claim 1, wherein the solid solution of Cr and / or Mo in the metallic binder phase is 5% by weight or more and less than 35% by weight, respectively. 6. The hard sintered material according to claim 1, 2, 3, 4, or 5, wherein the metal binder phase has Ni as a main component.