JP7618329B1 - Sintered alloys and dies - Google Patents

Abstract

A sintered alloy characterized in that it forms a solid solution phase consisting of at least one metal element selected from the group consisting of Ti, Ta, Nb and V, and at least one of C and _N , and that it contains 38 to 95 volume % of said compound phase, with 80 volume % or more of the compound phase having an NaCl type structure and a _Cr3C2 phase.

Description

The present invention relates to a sintered alloy and a mold made of a sintered alloy.

Materials used for molds for various optical lenses include SUS420J2, ultrafine-grained cemented carbide, and binderless cemented carbide, but when precision in shape is required, such as for molds for aspherical lenses, binderless cemented carbide, which has a small thermal expansion coefficient, is used.

On the other hand, a variety of materials are being used as lens materials, and lens materials with a higher thermal expansion coefficient than conventional materials are being used. Mold materials with a high thermal expansion coefficient may also be used when molding shapes that are difficult to mold using the thermal expansion coefficient of conventional mold materials.

Patent No. 2574426 (Patent Document 1) discloses an optical element molding die used in press molding of glass optical elements, in which at least the portion of the die that comes into contact with the glass has a composition of (a) 65.7 to 92.9 wt % tungsten, 24.0 to 0.8 wt % titanium, 10.3 to 6.3 wt % carbon, and the remainder unavoidable impurities, and (b) a two-phase mixed structure in which the first phase is a tungsten carbide phase and the second phase is a solid solution complex carbide phase of titanium and tungsten in a NaCl-type crystal.

Japanese Patent No. 6049978 (Patent Document 2) discloses a sintered alloy for molding dies with a large thermal expansion coefficient that is advantageous for molding glass materials with a large thermal expansion coefficient, and has _{a Cr3C2 -} NbC-Ni composition containing 20 mass% to 40 mass% NbC, 0.3 mass% to 10 mass% _Ni , unavoidable impurities, and the remainder being Cr3C2. This sintered alloy for molding dies with a large thermal expansion coefficient not only enables molding of materials with a large thermal expansion coefficient, but also enables molding of materials with shapes that are difficult to mold with conventional materials.

Patent No. 7351582 (Patent Document 3) improves the oxidation resistance of the sintered alloy for molding dies, which has a large thermal expansion coefficient, thereby extending the life of the dies and improving the quality of the molded products.

Patent No. 2574426 Patent No. 6049978 Patent No. 7351582

In recent years, as the variety of products to be molded has increased, molding materials with various thermal expansion coefficients have been proposed, and there are an increasing number of opportunities to mold unusual shapes that have never been seen before. In order to accommodate these applications, it is necessary to provide molding dies with an appropriate thermal expansion coefficient.

The present invention relates to a lens molding die material that can obtain any required thermal expansion coefficient and can also be imparted with properties such as specularity, thermal conductivity, strength, and oxidation resistance as required.

That is, the inventors discovered that a sintered alloy that forms a solid solution phase containing at least one metal element selected from Ti, Ta, Nb and V, and at least one of C and N, and that contains a compound phase (hereinafter also referred to as an "MC phase") having an NaCl-type structure at least 80 volume % of which is a _{Cr3C2 phase} and a WC phase has a thermal expansion coefficient of approximately 10.3 MK ^-1 _for the _Cr3C2 phase and a thermal expansion coefficient of approximately 4.2 to 5.0 MK ^-1 for the WC phase, and is therefore suitable as a molding die material that has any thermal expansion coefficient between the thermal expansion coefficient of conventional binderless cemented carbide, which is 4 to 5 MK ^-1 , and the thermal expansion coefficient of the materials in Patent Documents 2 and 3, which is approximately 9 MK ^-1 , and can be imparted with properties such as specularity, thermal conductivity, strength, and oxidation resistance as necessary, and thus arrived at the present invention.

That is, the sintered alloy according to the first embodiment of the present invention forms a solid solution phase consisting of at least one metal element selected from the group consisting of Ti, Ta, Nb, and V, and at least one of C and N, and 80 volume % or more of the sintered alloy is composed of a compound phase having a NaCl type structure and a _{Cr3C2 phase} ;
The composition is characterized in that the compound phase is contained in an amount of 38 to 95% by volume.

The sintered alloy according to the second embodiment of the present invention forms a solid solution phase consisting of at least one metal element selected from the group consisting of Ti, Ta, Nb, and V, at least one of W and Mo, and at least one of C and N, and is composed of a compound phase having a NaCl type structure and a Cr3C2 phase, with 80 volume % or more of the solid solution phase being composed of the compound phase having a NaCl type structure and the _{Cr3C2 phase} ,
The compound phase is contained at 38 to 95% by volume,
The compound phase is characterized in that at least one of W and Mo is dissolved in the compound phase in an amount of 0.1 to 45 atomic % based on the total amount of metal elements in the compound phase.

The sintered alloy according to the third embodiment of the present invention forms a solid solution phase consisting of at least one metal element selected from the group consisting of Ti, Ta, Nb, and V, and at least one of C and N, and is composed of a compound phase having a NaCl type structure of 80 volume % or more, a binder phase consisting of at least one of Ni, Co, and Fe, and a _{Cr3C2 phase} ;
The composition is characterized in that the compound phase is contained in an amount of 38 to 95% by volume, and the binder phase is contained in an amount of 8.2% by volume or less.

The sintered alloy according to the fourth embodiment of the present invention forms a solid solution phase consisting of at least one metal element selected from the group consisting of Ti, Ta, Nb, and V, at least one of W and Mo, and at least one of C and N, and is composed of a compound phase having a NaCl type structure of 80 volume % or more, a binder phase consisting of at least one of Ni, Co, and Fe, and a _{Cr3C2 phase} ;
The compound phase is contained in an amount of 38 to 95% by volume, and the binder phase is contained in an amount of 8.2% by volume or less,
The compound phase is characterized in that at least one of W and Mo is dissolved in the compound phase in an amount of 0.1 to 45 atomic % based on the total amount of metal elements in the compound phase.

The sintered alloy according to the fifth embodiment of the present invention forms a solid solution phase consisting of at least one metal element selected from the group consisting of Ti, Ta, Nb, and V, and at least one of C and N, and is composed of a compound phase having a NaCl type structure of 80 volume % or more, a binder phase consisting of at least one of Ni, Co, and Fe, and a WC phase;
The composition is characterized in that it contains the compound phase in an amount of 8 to 95% by volume and the binder phase in an amount of 2.0% by volume or less.

The sintered alloy according to the sixth embodiment of the present invention forms a solid solution phase consisting of at least one metal element selected from the group consisting of Ti, Ta, Nb, and V, at least one of W and Mo, and at least one of C and N, and is composed of a compound phase having a NaCl type structure of 80 volume % or more, a binder phase consisting of at least one of Ni, Co, and Fe, and a WC phase;
The compound phase is contained in an amount of 8 to 95% by volume, and the binder phase is contained in an amount of 2.0% by volume or less,
The compound phase is characterized in that at least one of W and Mo is dissolved in the compound phase in an amount of 0.1 to 45 atomic % based on the total amount of metal elements in the compound phase.

The sintered alloy according to the seventh embodiment of the present invention comprises a WC phase and _{a Cr3C2} phase,
The steel is characterized in that it contains the Cr ₃ C ₂ phase in an amount of 10 to 90 volume %.

The sintered alloy according to the eighth embodiment of the present invention comprises a WC phase, a binder phase comprising at least one of Ni, Co and Fe, and a _{Cr3C2 phase} ;
The steel is characterized in that it contains 10 to 90 volume % of the Cr ₃ C ₂ phase and 2.0 volume % or less of the binder phase.

The sintered alloy according to the ninth embodiment of the present invention is characterized in that it forms a solid solution phase consisting of at least one metal element selected from the group consisting of Ti, Ta, Nb and V, and at least one of C and N, and that 80 volume % or more of the solid solution phase consists of a compound phase having a NaCl type structure, a WC phase, and a _{Cr3C2 phase} .

The sintered alloy according to the tenth embodiment of the present invention forms a solid solution phase consisting of at least one metal element selected from the group consisting of Ti, Ta, Nb, and V, at least one of W and Mo, and at least one of C and N, and is composed of a compound phase having a NaCl type structure, a WC phase, and a _Cr3C2 phase, with 80 volume % or more of the compound phase being composed of the NaCl type structure, WC phase, and _Cr3C2 phase,
The compound phase is characterized in that at least one of W and Mo is dissolved in the compound phase in an amount of 0.1 to 45 atomic % based on the total amount of metal elements in the compound phase.

The sintered alloy according to the eleventh embodiment of the present invention forms a solid solution phase consisting of at least one metal element selected from the group consisting of Ti, Ta, Nb, and V, and at least one of C and N, and is composed of a compound phase having a NaCl structure of 80 volume % or more, a binder phase consisting of at least one of Ni, Co, and Fe, a WC phase, and a _{Cr3C2 phase} ;
The binder phase is contained in an amount of 2.0% by volume or less.

The sintered alloy according to the twelfth embodiment of the present invention forms a solid solution phase consisting of at least one metal element selected from the group consisting of Ti, Ta, Nb, and V, at least one of W and Mo, and at least one of C and N, and is composed of a compound phase having a NaCl structure of 80 volume % or more, a binder phase consisting of at least one of Ni, Co, and Fe, a WC phase, and _{a Cr3C2} phase;
The binder phase contains 2.0% by volume or less,
The compound phase is characterized in that at least one of W and Mo is dissolved in the compound phase in an amount of 0.1 to 45 atomic % based on the total amount of metal elements in the compound phase.

In the ninth to twelfth embodiments, it is preferable that the compound phase is contained in an amount of 10 to 90 volume percent.

In the ninth to twelfth embodiments, the volume ratio of the content of the Cr ₃ C ₂ phase to the content of the WC phase is preferably 0.125 to 8.

It is preferable that the grain size of the WC phase is 0.1 to 2.5 μm.

In the first to twelfth embodiments, it is preferable that the material is sintered by hot pressing.

A mold according to one embodiment of the present invention is characterized in that it is made of the above-mentioned sintered alloy.

According to the present invention, it is possible to obtain a lens molding die material that can obtain any required thermal expansion coefficient and can also be endowed with properties such as specularity, thermal conductivity, strength, and oxidation resistance as required.

[1] First embodiment The sintered alloy according to the first embodiment of the present invention is characterized in that it forms a solid solution phase consisting of at least one metal element selected from the group consisting of Ti, Ta, Nb and V, and at least one of C and N, and that it is composed of a compound phase having a NaCl type structure (hereinafter also referred to as "MC phase") and a _{Cr3C2 phase} , with the MC phase being 38 to 95 volume %.

The MC phase is a carbide, carbonitride, nitride, or solid solution of at least one of the metal elements Ti, Ta, Nb, and V (including the case where it is composed of a single compound), and has a NaCl type structure. By including an MC phase containing at least one of Ti, Ta, Nb, and V and having a NaCl type structure, the oxidation resistance of the sintered alloy is improved. In particular, by including Ti in the MC phase, particularly excellent oxidation resistance is obtained. The MC phase may be a solid solution phase containing Ti in addition to Ta, Nb, or V. In that case, the content of Ti is preferably 10 to 90 mol%, more preferably 40 to 80 mol%, of the amount of metal elements contained in the MC phase. The MC phase is preferably a carbide or carbonitride. Among Ti, Ta, Nb, and V, Ti carbide has high hardness, so when there is a lot of Ti in the MC phase, the material has excellent wear resistance, but it also tends to be hard and brittle, so it may be difficult to obtain a mirror finish. In such cases, it is better to add less Ti. The inclusion of V improves the adhesion resistance of the die. The MC phase may be a solid solution phase containing at least one of the metal elements Ti, Ta, and Nb, and further containing V. In addition, when it is desired to prevent the components Ti, Ta, Nb, and V from being mixed into the processed material, the amount of the element can be adjusted to be small. In addition, oxygen and boron may be further included, and Zr, Hf, and Cr may be further included.

The sintered alloy (MC- _{Cr3C2 alloy} ) according to the first embodiment is easy to obtain a sintered alloy with a thermal expansion coefficient of about 7 to 9 MK ^-1 , and is excellent in oxidation resistance. By making the MC phase content 38 to 95% by volume, the target thermal expansion coefficient of about 7 to 9 MK ^-1 can be obtained. When the MC phase content exceeds 95% by volume, the MC phase structure is prone to grain growth, making it difficult to obtain a mirror finish of the sintered alloy. When the MC phase content is less than 38% by volume, it is difficult to obtain a thermal expansion coefficient smaller than about 9 MK ^-1 . The MC phase content is preferably 40 to 90% by volume, more preferably 45 to 85% by volume.

The MC phase may have at least one of W and Mo dissolved in it at 0.1 to 45 atomic % relative to the total amount of metal elements in the MC phase. WC and Mo ₂ C have a hexagonal crystal structure when used alone, but when dissolved in the MC phase, the grain growth of the MC phase can be suppressed while maintaining the NaCl-type crystal structure, and the oxidation resistance can be further improved. In this case, the rigidity, hardness, thermal expansion coefficient, etc. of the alloy can be changed by changing the content of W or Mo, so that a composition that gives the alloy the desired characteristics depending on the application can be selected, and the ease of mirror finishing and wear resistance can be adjusted by changing the hardness of the alloy. A small amount of W or Mo may be dissolved in it within the range of 0.1 to 43 atomic % so as to improve the oxidation resistance while maintaining the NaCl-type crystal structure. In order to obtain appropriate rigidity, hardness, and thermal expansion coefficient, it is more preferable that at least one of W and Mo is dissolved in it at 5 to 43 atomic %, and even more preferable that it is dissolved in it at 10 to 40 atomic % relative to the total amount of metal elements in the MC phase.

Here, the MC phase having a NaCl-type crystal structure means that 80% or more by volume of the MC phase has a NaCl-type crystal structure. In other words, in addition to the NaCl-type crystal structure, the MC phase may contain small amounts of crystals, oxides, borides, etc. having a hexagonal structure, and when the MC phase contains multiple metal elements, it may contain an MC phase having a core-rim structure in addition to a solid solution having a NaCl-type crystal structure. The MC phase may also be composed of multiple types of phases with different compositions.

The _{Cr3C2 phase} has a high thermal expansion coefficient of 10.3 MK ^-1 and a hardness close to 1300 HV, so the inclusion of the _{Cr3C2 phase} increases the thermal expansion coefficient of the sintered alloy, making it easier to achieve a mirror finish and improving the specularity. In addition, the sintered alloy contains the _{Cr3C2 phase} and does not contain any hard phases other than the MC phase with a NaCl structure that has excellent oxidation resistance, resulting in a synergistic effect that allows the excellent specularity to be maintained for a long period of time.

When a phase consisting of chromium compounds other than _Cr3C2 , such as the _{Cr23C6 phase} or the _{Cr7C3 phase ,} is formed, the thermal expansion coefficient decreases in proportion to the content. In addition, since it is more brittle than the _{Cr3C2 phase} , it is more likely to cause problems as a tool. The _{Cr3C2 phase} may contain a _small amount of _chromium compounds other than _{Cr3C2 ,} such as _Cr23C6 or _Cr7C3 , and here, the " _{Cr3C2 phase} " means that 80 volume % or more of the chromium compounds is the _{Cr3C2 phase} .

The atomic ratio of the amount of light elements such as C and N contained in the MC phase to the amount of metal elements contained in the MC phase is preferably 0.8 or more. If the atomic ratio of the amount of light elements is smaller than 0.8, the sintered alloy is not sufficiently densified, and if the ratio is even smaller, compound phases other than the MC phase with a Cr ₃ C ₂ phase or NaCl type structure are likely to occur, making it impossible to obtain high oxidation resistance. The atomic ratio of metal elements to light elements is calculated by subtracting the amount of carbon in the Cr ₃ C ₂ phase calculated from the amount of carbon in the Cr ₃ C ₂ raw material powder used and the addition ratio from the amount of alloy carbon in the sintered body, and calculating the atomic ratio from the remaining components, or by directly analyzing the MC phase with EDS. The atomic ratio of the amount of light elements such as C and N contained in the MC phase to the amount of metal elements contained in the MC phase is preferably 1.0 or less. If the atomic ratio of the amount of light elements is larger than that, free carbon is likely to be generated in the alloy.

The grain size of the MC phase is preferably 0.1 to 6 μm. The grain size of the MC phase is the diameter of a circle having the same area as the cross-sectional area of the MC phase in any cross section of the sintered alloy. To make the grain size of the MC phase less than 0.1 μm, the raw powder must be finely milled, which increases costs and also deteriorates the moldability of the powder. If the grain size of the MC phase is larger than 6 μm, the specularity decreases, which may cause problems when used in a mold. The grain size of the MC phase can be determined by photographing the cross section of the sintered alloy with a scanning electron microscope (SEM) and using image analysis software from the resulting SEM photograph. The grain size of the MC phase is more preferably 0.5 to 3 μm.

The grain size of the _{Cr3C2 phase} is preferably 9μm or less. If the grain size of _{the Cr3C2} phase exceeds 9μm, the specularity may decrease. The grain size of _{the Cr3C2} phase can be determined in the same manner as the grain size of the MC phase. The grain size of _{the Cr3C2} phase is more preferably 0.5 to 7μm.

The sintered alloy according to the first embodiment of the present invention may further contain a metal phase consisting of at least one of Ni, Co, and Fe. By containing the metal phase, the desired thermal expansion coefficient and toughness can be obtained. The content of the metal phase is preferably 8.2% by volume or less. By containing Ni as the metal phase, the sinterability and toughness can be improved. Co and Fe increase the strength of the sintered alloy at room temperature and high temperatures. In addition, Fe can be obtained relatively inexpensively. The content of each element can be selected to obtain the required characteristics depending on the use of the tool. If the content of the metal phase exceeds 8.2% by volume, the surface roughness Ra after finishing becomes rough, and the tool deformation resistance during use at high temperatures decreases. It is more preferable that the content of the metal phase is 8% by volume or less.

[2] Second embodiment The sintered alloy according to the second embodiment of the present invention is characterized in that it forms a solid solution phase consisting of at least one metal element selected from the group consisting of Ti, Ta, Nb and V, and at least one of C and N, and is composed of a compound phase (hereinafter also referred to as "MC phase") having an NaCl type structure of 80% or more by volume, a binder phase consisting of at least one of Ni, Co and Fe, and a WC phase, and contains 8 to 95% by volume of the MC phase and 2.0% by volume or less of the binder phase.

The sintered alloy (MC-WC alloy) according to the second embodiment is easy to obtain a sintered alloy with a thermal expansion coefficient of about 5 to 7 MK ^-1 . The MC phase may be the same as that of the first embodiment. If the MC phase is less than 8 volume %, the required thermal expansion coefficient is not obtained, and the oxidation resistance is also reduced. If the MC phase is more than 95 volume %, the structure is prone to grain growth, making it difficult to obtain a mirror finish, and the strength is also reduced. The content of the MC phase is preferably 10 to 92 volume %, more preferably 12 to 90 volume %.

The sintered alloy according to the second embodiment contains 2.0% by volume or less of a metal phase consisting of at least one of Ni, Co, and Fe, so that the sinterability is improved and the sintering temperature can be lowered. In addition, since a small amount of metal component is present between each particle, the growth due to the coalescence of particles can be suppressed, so that a fine grain structure is easily obtained and the specularity and strength are improved. Furthermore, the desired toughness can be obtained, and defects due to chipping during use of the tool are unlikely to occur. In addition, as in the first embodiment, the content of each element can be selected to obtain the characteristics required depending on the use of the tool. If the content of the metal phase exceeds 2.0% by volume, the tool deformation resistance during use at high temperatures decreases. The content of the metal phase is preferably 1.5% by volume or less, and more preferably 1% by volume or less.

The grain size of the WC phase is preferably 0.1 to 2.5 μm. The grain size of the WC phase can be determined in the same manner as the grain size of the MC phase. By adjusting the WC grain size to the range of 0.1 to 2.5 μm, an MC-WC alloy with a fine grain structure can be obtained, resulting in high specularity. On the other hand, since it contains a WC phase, the oxidation resistance is somewhat inferior to that of the first embodiment. The grain size of the WC phase is more preferably 0.11 to 2.0 μm, even more preferably 0.12 to 1.5 μm, even more preferably 0.13 to 1.0 μm, and particularly preferably 0.14 to 0.7 μm.

In the MC phase of the sintered alloy according to the second embodiment, as in the first embodiment, at least one of W and Mo may be dissolved in a solid solution of 0.1 to 45 atomic % relative to the total amount of metal elements in the MC phase. A small amount of W or Mo, about 0.1 to 43 atomic %, may be dissolved in the solid solution to improve oxidation resistance while maintaining a NaCl-type crystal structure. In order to obtain appropriate rigidity, hardness, and thermal expansion coefficient, it is more preferable that at least one of W and Mo is dissolved in a solid solution of 5 to 43 atomic %, and even more preferable that it is dissolved in a solid solution of 10 to 40 atomic %, relative to the total amount of metal elements in the MC phase. As light elements, oxygen and boron may be included. As metal elements, Zr, Hf, and Cr may be included.

[3] Third embodiment The sintered alloy according to the third embodiment of the present invention is characterized in that it comprises a WC phase and a Cr ₃ C ₂ phase, and contains 10 to 90 volume % of the Cr ₃ C ₂ phase.

The sintered alloy (Cr ₃ C ₂ -WC alloy) according to the third embodiment can obtain a wide range of thermal expansion coefficients by changing the ratio of each phase, and has a wide range of thermal expansion coefficients of about 5 to 9 MK ^-1 by making the content of the Cr ₃ C ₂ phase 10 to 90 volume %. In addition, the thermal conductivity tends to be high compared to other alloy systems with similar thermal expansion coefficients. The _{Cr 3} C ₂ phase may be the same as that of the first embodiment. When the content of _{the Cr 3} C ₂ phase exceeds 90 volume %, the Cr ₃ C ₂ phase is prone to grain growth and it is difficult to obtain a mirror finish. When the content of the Cr ₃ C ₂ phase is less than 10 volume %, the oxidation resistance tends to be poor. The content of the _{Cr 3} C ₂ phase is preferably 15 to 85 volume %, more preferably 20 to 80 volume %. When the WC phase ratio is high, the oxidation resistance is somewhat poor, but the toughness and strength are excellent.

The grain size of the alloy structure can be easily adjusted by selecting the mixed grinding conditions and the raw material of the WC phase, and for example, an ultrafine grain alloy can be obtained, so that a _Cr3C2 - _WC alloy with good specularity can be easily obtained. The grain size of the WC phase may be the same as that of the second embodiment. As a result, a fine grain _Cr3C2 - _WC alloy can be obtained, so that a high specularity can be obtained.

In the sintered alloy according to the third embodiment, if the sinterability of the alloy is insufficient, the sintered alloy may contain 2.0 vol. % or less of a metal phase consisting of at least one of Ni, Co, and Fe. This makes it possible to obtain the desired toughness, and defects due to chipping during use of the tool are less likely to occur. In addition, since the sinterability is also increased, the sintering temperature can be lowered, and grain growth is also suppressed, so that specularity and strength tend to be increased. As in the first embodiment, the content of each element can be selected to obtain the characteristics required depending on the use of the tool. If the content of the metal phase exceeds 2.0 vol. %, the tool deformation resistance during use at high temperatures decreases. The content of the metal phase is preferably 1.5 vol. % or less, and more preferably 1 vol. % or less.

[4] Fourth embodiment The sintered alloy according to the fourth embodiment of the present invention is characterized in that it forms a solid solution phase consisting of at least one metal element selected from the group consisting of Ti, Ta, Nb and V, and at least one of C and N, and that 80 volume % or more of the solid solution phase consists of a compound phase having a NaCl type structure (hereinafter also referred to as "MC phase"), a WC phase, and _{a Cr3C2} phase.

In the MC-Cr ₃ C ₂ alloy or MC-WC alloy of the present invention, when an intermediate thermal expansion coefficient of about 7 MK ^-1 is to be obtained, it is possible to increase the ratio of the MC phase, but the increase in the ratio of the MC phase tends to cause coarsening of the MC phase, which tends to cause problems such as a decrease in specularity and strength. For this reason, by making an MC-Cr ₃ C ₂ -WC alloy in which the three phases of the MC phase, the Cr ₃ C ₂ phase, and the WC phase coexist, it is possible to prevent the coarsening of the structure. The MC phase, the Cr ₃ C ₂ phase, and the WC phase may be the same as those in the first to third embodiments.

The sintered alloy (MC- _{Cr3C2 -} WC alloy) according to the fourth embodiment preferably contains 10 to 90 volume % of the MC phase. If the MC phase is less than 10 volume %, the oxidation resistance decreases. If the MC phase is more than 90 volume %, the structure is prone to grain growth, making it difficult to obtain a mirror finish and reducing strength. The MC phase content is preferably 20 to 90 volume %, more preferably 40 to 85 volume %. If the WC phase ratio is increased, the oxidation resistance tends to decrease, but it is easy to obtain a small thermal expansion coefficient, a large thermal conductivity, and high toughness. If the MC phase ratio is increased, the oxidation resistance increases and it is easy to obtain a medium thermal expansion coefficient, improving sinterability.

The volume ratio of the _Cr3C2 phase content to the WC _phase content is preferably 0.125 to 8. If the volume ratio of the _Cr3C2 phase content to the _WC phase content is less than 0.125, the oxidation resistance tends to be low, and if it exceeds 8, the specularity tends to be low. The volume ratio of the _Cr3C2 phase content to the _WC phase content is preferably 0.15 to 6.6, and more preferably 0.2 to 5.

Increasing the _{Cr3C2 phase} ratio improves oxidation resistance and makes it easier to obtain a large thermal expansion coefficient. When the MC phase amount is 10 volume percent and the volume ratio of the _{Cr3C2 phase} to the WC phase is 0.125 to 8, a thermal expansion coefficient of about 6 to 9 MK ^-1 can be obtained. Similarly, when the MC phase amount is 90 volume percent, a thermal expansion coefficient of about 6.5 to 7.5 MK ^-1 can be obtained.

The sintered alloy according to the fourth embodiment can obtain the required thermal expansion coefficient and required characteristics by changing the ratios as necessary. Although an alloy with a thermal expansion coefficient of about 7 MK ^-1 can be obtained with a _Cr3C2 - _WC alloy, it is better to select an MC- _Cr3C2 - _WC alloy when oxidation resistance is particularly important, and a _Cr3C2 - _WC alloy when thermal conductivity is to be increased.

The sintered alloy according to the fourth embodiment may contain 2.0 vol. % or less of a metal phase consisting of at least one of Ni, Co, and Fe when alloy strength is required or when the sinterability of the alloy is insufficient. If the content is more than 2.0 vol. %, the wear resistance may be poor. The content of the metal phase is preferably 1.5 vol. % or less, and more preferably 1 vol. % or less.

In the MC phase of the sintered alloy according to the fourth embodiment, as in the first embodiment, at least one of W and Mo may be dissolved in a solid solution of 0.1 to 45 atomic % relative to the total amount of metal elements in the MC phase. Small amounts of W and Mo, about 0.1 to 43 atomic %, may be dissolved in the MC phase to improve oxidation resistance while maintaining a NaCl-type crystal structure. In order to obtain appropriate rigidity, hardness, and thermal expansion coefficient, it is more preferable that at least one of W and Mo is dissolved in a solid solution of 5 to 43 atomic %, and even more preferable that it is dissolved in a solid solution of 10 to 40 atomic %, relative to the total amount of metal elements in the MC phase.

Lens molding dies using the sintered alloy of the present invention may be coated with a hard film coating such as DLC, or a metal film coating such as platinum. Not limited to lens molding dies, various coatings may be applied to members and tools using the sintered alloy of the present invention in order to maximize the features of the present invention.

[5] Manufacturing method of sintered alloy The sintered alloy of the present invention can be obtained by normal sintering, hot press sintering, etc. That is, a predetermined amount of powder is weighed, wet mixed, crushed, dried, and then pressure molded in a die to obtain a powder compact. This powder compact can be cut or ground to obtain the required shape, or the powder compact can be pre-sintered and then machined to obtain the required shape. Also, the powder can be filled into a mold of a predetermined shape and hot press sintered to obtain the required shape. In the case of normal sintering, the powder compact can be sintered in a vacuum or in an inert gas atmosphere such as nitrogen or argon at a sintering temperature of 1300 to 1540°C.

HIP treatment may be further performed after sintering. This will reduce the pores that occur during sintering. The temperature of the HIP treatment can be set appropriately depending on the composition of the sintered alloy, but it may be a temperature below the sintering temperature. If the temperature is higher than the sintering temperature, Cr carbides and other particles will grow into grains, resulting in a decrease in strength. HIP treatment can also be used to adjust the grain size of the structure.

Regardless of the amount of metallic phase, either normal sintering or hot press sintering may be used. When using hot press sintering, the sintering temperature can be lowered to make it easier to obtain a fine grain structure. When the amount of metallic phase is small and it is difficult to obtain a dense alloy by normal sintering, sintering by hot press may be used. In this case, the metallic phase content is preferably 0 to 2.0% by volume, and more preferably 0 to 1% by volume. By hot press sintering a sintered alloy that does not contain any metallic phase or contains a small amount of metallic phase, it becomes a dense alloy and the specularity can be further improved, resulting in a sintered alloy that is suitable for use as a mold.

There are no particular limitations on the hot press as long as it is generally capable of forming a sintered alloy, but the sintering conditions are preferably a vacuum or an inert gas atmosphere such as nitrogen or argon, a pressure of 20 to 100 MPa, and a sintering temperature of 1200 to 1500°C. Devices other than hot presses, such as electric current sintering, may also be used.

[6] Molds and other uses The sintered alloy of the present invention can be suitably used as a material for molds, particularly molds for lens molding, and in order to mold parts without problems, a mold material having an optimal thermal expansion coefficient within the range of about 5 to 9 MK ^-1 can be selected in consideration of the thermal expansion coefficient of the lens material and the shape of the molded part. In addition, the sintered alloy can be suitably used when a mold for molding parts requires a thermal expansion coefficient larger than that of ordinary cemented carbide or binderless cemented carbide and excellent oxidation resistance, and can be suitably used for members, tools, etc. that require a high thermal expansion coefficient, high wear resistance, and excellent oxidation resistance.

The present invention will be described in further detail with reference to the inventions, but is not limited thereto.

Example 1
The raw material _powders used were _Cr3C2 (2.4μm), Ni (2.3μm), Co (1.4μm), Fe (2.9μm), TaC (1.6μm), NbC (1.6μm), TiC (1.6μm), Ti( _C0.5 , _N0.5 ) (2.1μm), TaN (2.0μm), Nb( _C0.7N0.3 ) ( _2.5μm ), WC (0.8μm), _Mo2C (3.1μm), and various solid solution powders shown in Table 1. The solid solution powders were prepared by wet mixing carbides, nitrides, and carbonitrides to obtain the compositions shown in Table 1, subjecting the mixture to a solid solution treatment in a high-temperature furnace, and then pulverizing and sieving the mixture to obtain raw material powders (1.3-3.1μm).

For samples containing a small amount of metallic phase components, powders that had been pre-ground by wet grinding metallic powder and other powders were used, while samples containing 4% or more by volume of metallic phase components were used as is without pre-grinding. Depending on the sample, C powder was also added to reduce oxides contained in the powder and adjust the amount of carbon.

Sintering was performed by normal sintering or hot press sintering under an inert gas atmosphere of nitrogen or argon, and the obtained sintered body was subjected to HIP treatment to produce sintered alloys of invention products 1 to 20 and comparison products 1 to 5. In normal sintering, the sintering temperature was 1400°C to 1540°C, the pressure was 40 kPa to 90 kPa, and the sintering atmosphere was _N2 or Ar. In hot press sintering (invention products 6, 7, 8, 11, 12, 15, 17, 19, 20), the sintering temperature was 1200°C to 1650°C, and the sintering atmosphere was Ar. For the sintered alloys of invention products 1 to 20 and comparison products 1 to 5 that contain MC phase, the compound ratio constituting the MC phase was obtained. The obtained results are shown in Table 2. The compound ratio constituting the MC phase listed in Table 2 was calculated by converting it to each compound, taking into account the compound ratio at the time of blending and the carbon and nitrogen amounts of the sintered alloy.

The obtained samples were examined for flexural strength, hardness, thermal expansion coefficient, high-temperature oxidation resistance, thermal conductivity, and surface roughness using the following methods. The results are shown in Table 3 together with the overall evaluation.

(Transverse strength)
The flexural strength (MPa) of the sintered alloys of the invention products 1 to 20 and the comparison products 1 to 5 was determined by flexural strength measurement (three-point bending test) according to the method of JIS B4104.

(Rockwell hardness HRA)
The Vickers hardness (HRA) of the sintered alloys of the invention products 1 to 20 and the comparison products 1 to 5 was measured by the Rockwell A hardness test method for CIS027B sintered alloys.

(Thermal expansion coefficient RT-700℃)
The sintered alloys of invention products 1 to 20 and comparison products 1 to 5 were heated from room temperature to 700° C. using a vertical thermal dilatometer, and the thermal expansion coefficient RT-700° C. (MK ^-1 ) was measured.

(Oxidation resistance 700℃)
The sintered alloys of invention products 1 to 20 and comparison products 1 to 5 were heated in air at 700° C. for 30 minutes, and the oxidation weight gain (oxidation weight per unit area) (g/m ² ) was determined.

(Thermal Conductivity)
The thermal conductivity of the sintered alloys of the invention products 1 to 20 and the comparison products 1 to 5 was determined by a laser flash method thermal constant measuring device.

(surface roughness after finishing Ra)
The sintered alloys of the invention products 1 to 20 and the comparison products 1 to 5 were mirror-finished using diamond slurry, and the surface roughness Ra (nm) was measured.

(evaluation)
Molds were made using the sintered alloys of invention products 1-20 and comparison products 1-5, and glass lenses were repeatedly molded to evaluate the molds based on the number of times they were used and the specularity of the molded surface after repeated use. If they could be used a specified number of times or more and still maintained good specularity, they were marked with an ◎, if they could be used a specified number of times or more, they were marked with an ○, if they could be used up to the specified number of times, they were marked with a △, and if they could not be used up to the specified number of times, they were marked with an ×.

As can be seen from Table 3, inventions 1 to 20 have various required thermal expansion coefficients in the range of 4.9 to 9.2 MK ^-1 , and are excellent in necessary properties such as specularity, thermal conductivity, strength, and oxidation resistance. That is, the MC-Cr ₃ C ₂ alloy has excellent oxidation resistance, the MC-WC alloy has excellent strength and specularity, and the Cr ₃ C ₂ -WC alloy has excellent specularity and high thermal conductivity, and it was found that the MC-Cr ₃ C ₂ -WC alloy can suppress the grain growth of the phase, thereby improving specularity and strength. In addition, in order to improve oxidation resistance, Mo and/or W may be dissolved in a solid solution of 0.1 to 45 atomic % relative to the total amount of metal elements in the MC phase. The thermal expansion coefficient of the MC phase can be changed by changing the amount of W.

In the comparative example 1, the MC-Cr ₃ C ₂ alloy contained a large amount of MC phase at 97 volume percent, which caused grain growth of the MC phase, resulting in poor surface roughness. In the comparative example 2, the MC-WC alloy contained a small amount of MC phase at 3.0 volume percent, which caused a low thermal expansion coefficient of 4.7 MK ^-1 , which meant that the required thermal expansion coefficient could not be obtained, and the oxidation resistance was also poor. In the comparative example 3, which contained only the MC phase, grain growth of the MC phase occurred, resulting in poor surface roughness. In the comparative example 4, the Cr ₃ C ₂ -WC alloy contained a large amount of Cr ₃ C ₂ phase at 96 volume percent, which meant that the thermal expansion coefficient was high at 10.1 MK ^-1 , which meant that the required thermal expansion coefficient could not be obtained, and the Cr ₃ C ₂ phase grew grains, resulting in poor surface roughness. In the comparative example 5, the Cr ₃ C ₂ -WC alloy contained a small amount of Cr ₃ C ₂ phase at 5.7 volume percent, resulting in poor oxidation resistance.

Claims (18)

A solid solution phase is formed consisting of at least one metal element selected from Ti, Ta, Nb and V (wherein Ta or Nb is contained as an essential element, or at least one of Ti, Ta and Nb further contains V) and at least one of C and N, and 80% by volume or more of the solid solution phase is composed of a compound phase having a NaCl type structure and a _{Cr3C2 phase} ;
A sintered alloy containing the compound phase in an amount of 38 to 95% by volume. A solid solution phase is formed consisting of at least one metal element selected from Ti, Ta, Nb and V (wherein Ta or Nb is contained as an essential element, or at least one of Ti, Ta and Nb further contains V) , at least one of W and Mo, and at least one of C and N, and 80 volume % or more of the solid solution phase is composed of a compound phase having a NaCl type structure and _{a Cr3C2} phase,
The compound phase is contained at 38 to 95% by volume,
The sintered alloy is characterized in that the compound phase contains 0.1 to 45 atomic % of at least one of W and Mo in solid solution relative to the total amount of metal elements in the compound phase. A solid solution phase is formed of at least one metal element selected from Ti, Ta, Nb and V (wherein Ta or Nb is contained as an essential element, or at least one of Ti, Ta and Nb further contains V) and at least one of C and N, and 80% by volume or more of the compound phase has a NaCl type structure, a binder phase selected from at least one of Ni, Co and Fe, and a _Cr3C2 phase _;
A sintered alloy containing 38 to 95 volume % of said compound phase and 8.2 volume % or less of said binder phase. A solid solution phase is formed consisting of at least one metal element selected from Ti, Ta, Nb and V (wherein Ta or Nb is contained as an essential element, or at least one of Ti, Ta and Nb further contains V) , at least one of W and Mo, and at least one of C and N, and 80 volume % or more of the compound phase has a NaCl type structure, a binder phase consisting of at least one of Ni, Co and Fe, and a _{Cr3C2 phase} ;
The compound phase is contained in an amount of 38 to 95% by volume, and the binder phase is contained in an amount of 8.2% by volume or less,
The sintered alloy is characterized in that the compound phase contains 0.1 to 45 atomic % of at least one of W and Mo in solid solution relative to the total amount of metal elements in the compound phase. A solid solution phase is formed of at least one metal element selected from Ti, Ta, Nb and V (wherein Ta or Nb is contained as an essential element, or at least one of Ti, Ta and Nb further contains V) and at least one of C and N, and the solid solution phase is composed of a compound phase having an NaCl type structure of 80 volume % or more, a binder phase selected from at least one of Ni, Co and Fe, and a WC phase;
A sintered alloy containing 8 to 95 volume % of said compound phase and 2.0 volume % or less of said binder phase. A solid solution phase is formed of at least one metal element selected from Ti, Ta, Nb and V (wherein Ta or Nb is contained as an essential element, or at least one of Ti, Ta and Nb further contains V) , at least one of W and Mo, and at least one of C and N, and the solid solution phase is composed of 80 volume % or more of a compound phase having a NaCl type structure, a binder phase selected from at least one of Ni, Co and Fe, and a WC phase;
The compound phase is contained in an amount of 8 to 95% by volume, and the binder phase is contained in an amount of 2.0% by volume or less,
The sintered alloy is characterized in that the compound phase contains 0.1 to 45 atomic % of at least one of W and Mo in solid solution relative to the total amount of metal elements in the compound phase. It consists of WC phase and _{Cr3C2 phase} ,
A sintered alloy containing 10 to 50 volume % of the Cr ₃ C ₂ phase. It is composed of a WC phase, a binder phase consisting of at least one of Ni, Co, and Fe, and a _{Cr3C2 phase} ,
A sintered alloy comprising said Cr ₃ C ₂ phase in an amount of 10 to 50 volume % and said binder phase in an amount of 2.0 volume % or less. A sintered alloy characterized in that it forms a solid solution phase consisting of at least one metal element selected from Ti, Ta, Nb and V (wherein Ta or Nb is contained as an essential element, or at least one of Ti, Ta and Nb further contains V) and at least one of C and N, and in that 80 volume % or more of the sintered alloy is composed of a compound phase having a NaCl type structure, a WC phase, and a _{Cr3C2 phase} . A solid solution phase is formed consisting of at least one metal element selected from Ti, Ta, Nb and V (wherein Ta or Nb is contained as an essential element, or at least one of Ti, Ta and Nb further contains V) , at least one of W and Mo, and at least one of C and N, and 80 volume % or more of the solid solution phase is composed of a compound phase having a NaCl type structure, a WC phase, and a _{Cr3C2 phase} ;
The compound phase is contained in an amount of 10 to 90% by volume,
The sintered alloy is characterized in that the compound phase contains 0.1 to 45 atomic % of at least one of W and Mo in solid solution relative to the total amount of metal elements in the compound phase. A solid solution phase is formed consisting of at least one metal element selected from Ti, Ta, Nb and V (wherein Ta or Nb is contained as an essential element, or at least one of Ti, Ta and Nb further contains V) and at least one of C and N, and the solid solution phase is composed of a compound phase having a NaCl type structure of which 80 volume % or more, a binder phase consisting of at least one of Ni, Co and Fe, a WC phase, and _{a Cr3C2} phase;
The compound phase is contained in an amount of 10 to 90% by volume,
A sintered alloy comprising the binder phase in an amount of 2.0 volume % or less. A solid solution phase is formed consisting of at least one metal element selected from Ti, Ta, Nb and V (wherein Ta or Nb is contained as an essential element, or at least one of Ti, Ta and Nb further contains V) , at least one of W and Mo, and at least one of C and N, and the solid solution phase is composed of 80 volume % or more of a compound phase having a NaCl type structure, a binder phase consisting of at least one of Ni, Co and Fe, a WC phase, and a _{Cr3C2 phase} ;
The compound phase is contained in an amount of 10 to 90% by volume, and the binder phase is contained in an amount of 2.0% by volume or less,
The sintered alloy is characterized in that the compound phase contains 0.1 to 45 atomic % of at least one of W and Mo in solid solution relative to the total amount of metal elements in the compound phase. 10. The sintered alloy according to claim 9, characterized in that the compound phase is contained in an amount of 10 to 90% by volume. 13. The sintered alloy according to claim 9, wherein the volume ratio of the content of said Cr ₃ C ₂ phase to the content of said WC phase is 0.125-8. A sintered alloy according to any one of claims 7 to 12, characterized in that the grain size of the WC phase is 0.1 to 2.5 μm. A mold made of the sintered alloy of any one of claims 1 to 12. WC phase and Cr ₃ C ₂ It consists of phases,
The Cr ₃ C ₂ A hot forming die comprising a sintered alloy containing 10 to 90 volume % (but excluding 65 to 90 volume %) of a sintered phase. A WC phase, a binder phase consisting of at least one of Ni, Co, and Fe, and Cr ₃ C ₂ It consists of phases,
The Cr ₃ C ₂ 1. A hot-molding die comprising a sintered alloy containing 10 to 90 volume % (but excluding 65 to 90 volume %) of a binder phase and 2.0 volume % or less of said binder phase.