Sintered alloy and die

Abstract

A solid solution phase composed of at least one metal element among Ti, Ta, Nb, and V and at least one of C and N is formed, 80 vol% or more of which is composed of a compound phase having an NaCl structure and a Cr3C2 phase, and the sintered alloy is characterized by containing 38-95 vol% of the compound phase.

Description

Sintered alloys and molds

[0001] The present invention relates to a sintered alloy and a mold made of the sintered alloy.

[0002] Materials used for molds for various optical lenses include SUS420J2, ultrafine-grained cemented carbide, and binderless cemented carbide. However, when high precision in shape is required, such as for molds for aspherical lenses, binderless cemented carbide, which has a small thermal expansion coefficient, is used.

[0003] On the other hand, a variety of materials are being used as lens materials, and lens materials with larger thermal expansion coefficients than conventional materials are being used. In addition, mold materials with larger thermal expansion coefficients are sometimes used when molding objects with shapes that are difficult to mold using conventional mold materials.

[0004] Japanese 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 double carbide phase of titanium and tungsten in the form of an NaCl-type crystal.

[0005] Patent No. 6049978 (Patent Document 2) describes a steel sheet containing 20 mass% or more and 40 mass% or less of NbC, 0.3 mass% or more and 10 mass% or less of Ni, and unavoidable impurities, with the balance being Cr3C2. r3 The paper discloses a sintered alloy for molding dies with a high thermal expansion coefficient, which has a C2-NbC-Ni composition and is advantageous for molding glass materials with a high thermal expansion coefficient. This sintered alloy for molding dies with a high thermal expansion coefficient not only enables molding of materials with a high thermal expansion coefficient, but also enables molding of materials with shapes that are difficult to mold with conventional materials.

[0006] In Japanese Patent No. 7351582 (Patent Document 3), the oxidation resistance of the sintered alloy for molding dies having a large thermal expansion coefficient is improved, thereby extending the life of the dies and improving the quality of the molded products.

[0007] Patent No. 2574426 Patent No. 6049978 Patent No. 7351582

[0008] In recent years, with the diversification of products to be molded, molding materials with various thermal expansion coefficients have been proposed, and opportunities to mold unique shapes that have not been seen before are increasing. In order to respond to these applications, it is necessary to provide molding dies with appropriate thermal expansion coefficients.

[0009] The present invention relates to a lens molding die material that can obtain any desired thermal expansion coefficient and can also impart properties such as specularity, thermal conductivity, strength, and oxidation resistance as required.

[0010] That is, the present inventors have found that a sintered alloy which 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 which contains 80% by volume or more of a compound phase having an NaCl type structure (hereinafter also referred to as an "MC phase"), a Cr3C2 phase, and a WC phase, and which contains two or more hard phases, has a thermal expansion coefficient of the Cr3C2 phase of 10.3 MK -1 The thermal expansion coefficient of the WC phase is about 4.2 to 5.0 MK -1 Therefore, the thermal expansion coefficient of conventional binderless cemented carbide is 4 to 5 MK. -1 Therefore, the thermal expansion coefficient of the materials in Patent Documents 2 and 3 is 9MK. -1 The inventors have discovered that the material has a thermal expansion coefficient of 1000 to 15000 kJ / cm2 and is suitable as a molding die material that can be imparted with properties such as specularity, thermal conductivity, strength, and oxidation resistance as required, and have arrived at the present invention.

[0011] That is, 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 80% by volume or more of the sintered alloy is composed of a compound phase having an NaCl-type structure and a Cr3C2 phase, and that the sintered alloy contains 38 to 95% by volume of the compound phase.

[0012] A sintered alloy according to a 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, at least one of W and Mo, and at least one of C and N, and is composed of a compound phase having an NaCl-type structure for 80 volume % or more, and a Cr3C2 phase, and contains 38 to 95 volume % of the compound phase, and at least one of W and Mo is solid-solved in the compound phase at a rate of 0.1 to 45 atomic % relative to the total amount of metal elements in the compound phase.

[0013] A sintered alloy according to a third 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 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 Cr3C2 phase, and contains 38 to 95% by volume of the compound phase and 8.2% by volume or less of the binder phase.

[0014] A sintered alloy according to a 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, at least one of W and Mo, and at least one of C and N, and is composed of a compound phase having an 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 containing 38 to 95 volume % and the binder phase containing 8.2 volume % or less, and at least one of W and Mo being solid-solved in the compound phase at a rate of 0.1 to 45 atomic % relative to the total amount of metal elements in the compound phase.

[0015] A sintered alloy according to a fifth embodiment of the present invention is characterized in that it forms a solid solution phase consisting of at least one metal element selected from Ti, Ta, Nb, and V, and at least one of C and N, and is composed of a compound 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 compound phase and 2.0% by volume or less of the binder phase.

[0016] A sintered alloy according to a sixth embodiment of the present invention is characterized in that it comprises a compound phase which forms a solid solution phase consisting of at least one metal element selected from Ti, Ta, Nb, and V, at least one of W and Mo, and at least one of C and N, and in which 80% by volume or more of the compound phase has an NaCl-type structure, a binder phase consisting of at least one of Ni, Co, and Fe, and a WC phase, the compound phase contains 8 to 95% by volume and 2.0% by volume or less of the binder phase, and 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.

[0017] A sintered alloy according to a seventh embodiment of the present invention is characterized in that it comprises a WC phase and a Cr3C2 phase, and contains 10 to 90 volume % of the Cr3C2 phase.

[0018] The sintered alloy according to an eighth embodiment of the present invention comprises a WC phase, a binder phase consisting of at least one of Ni, Co, and Fe, and a Cr3C2 phase, and contains 10 to 90 volume % of the Cr3C2 phase and 2.0 volume % or less of the binder phase.

[0019] 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% by volume or more of the solid solution phase consists of a compound phase having an NaCl-type structure, a WC phase, and a Cr3C2 phase.

[0020] A sintered alloy according to a tenth embodiment of the present invention forms a solid solution phase consisting of at least one metal element selected from Ti, Ta, Nb, and V, at least one of W and Mo, and at least one of C and N, and is characterized in that the sintered alloy comprises a compound phase having an NaCl-type structure of 80 volume % or more, a WC phase, and a Cr3C2 phase, and in which at least one of W and Mo is solid-solved in the compound phase at a rate of 0.1 to 45 atomic % relative to the total amount of metal elements in the compound phase.

[0021] A sintered alloy according to an eleventh 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 having an NaCl-type structure of 80% or more by volume, a binder phase consisting of at least one of Ni, Co, and Fe, a WC phase, and a Cr3C2 phase, and contains the binder phase in an amount of 2.0% by volume or less.

[0022] A sintered alloy according to a twelfth 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, at least one of W and Mo, and at least one of C and N, and is composed of a compound 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, a WC phase, and a Cr3C2 phase, and contains 2.0% or less by volume of the binder phase, and at least one of W and Mo is solid-solved in the compound phase at a rate of 0.1 to 45 atomic % relative to the total amount of metal elements in the compound phase.

[0023] In the ninth to twelfth embodiments, the compound phase is preferably contained in an amount of 10 to 90% by volume.

[0024] In the ninth to twelfth embodiments, the volume ratio of the content of the Cr3C2 phase to the content of the WC phase is preferably 0.125 to 8.

[0025] The grain size of the WC phase is preferably 0.1 to 2.5 μm.

[0026] In the first to twelfth embodiments, the sintered product is preferably sintered by hot pressing.

[0027] A mold according to one embodiment of the present invention is characterized by being made of the above-mentioned sintered alloy.

[0028] According to the present invention, a lens molding die material can be obtained that can obtain any desired thermal expansion coefficient and can also be imparted with properties such as specularity, thermal conductivity, strength, and oxidation resistance as required.

[0029] [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 (hereinafter also referred to as "MC phase") having an NaCl-type structure and a Cr3C2 phase, with the MC phase comprising 38 to 95 volume %.

[0030] 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 a single compound) and has an NaCl-type structure. The inclusion of an MC phase containing at least one of Ti, Ta, Nb, and V and having an NaCl-type structure improves the oxidation resistance of the sintered alloy. In particular, the inclusion of Ti in the MC phase provides particularly excellent oxidation resistance. The MC phase may be a solid solution phase containing Ti in addition to Ta, Nb, or V. In this case, the Ti content is preferably 10 to 90 mol%, more preferably 40 to 80 mol%, of the 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 the MC phase contains a large amount of Ti, the material has excellent wear resistance. However, it also tends to be hard and brittle, making it 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 mold. The MC phase may be a solid solution phase containing V in addition to at least one metal element selected from Ti, Ta, and Nb. Furthermore, if it is desired to prevent the Ti, Ta, Nb, and V components from being mixed into the processed material, the amount of the element can be reduced. Furthermore, oxygen and boron may be further included, and Zr, Hf, and Cr may also be further included.

[0031] The sintered alloy (MC-Cr3C2 alloy) according to the first embodiment has a thermal expansion coefficient of 7 to 9 MK. -1 By setting the MC phase content at 38-95 volume %, it is possible to obtain a sintered alloy with a 7-9MK structure. -1When the MC phase content is more than 95% by volume, the MC phase structure tends to undergo grain growth, making it difficult to obtain a mirror finish in the sintered alloy. When the MC phase content is less than 38% by volume, the 9MK -1 It is difficult to obtain a thermal expansion coefficient smaller than about 100%. The content of the MC phase is preferably 40 to 90% by volume, and more preferably 45 to 85% by volume.

[0032] The MC phase may contain at least one of W and Mo dissolved in it at a concentration of 0.1 to 45 atomic percent relative to the total amount of metal elements in the MC phase. While WC and Mo2C have a hexagonal crystal structure when dissolved alone, their solid solution in the MC phase can further improve oxidation resistance while maintaining the NaCl-type crystal structure and suppressing grain growth in the MC phase. By varying the W or Mo content, the alloy's rigidity, hardness, thermal expansion coefficient, and other properties can be altered, allowing for the selection of a composition that achieves the desired alloy characteristics depending on the application. Furthermore, the alloy's hardness can be adjusted to adjust the ease of mirror finishing and wear resistance. Small amounts of W or Mo may be dissolved in the range of 0.1 to 43 atomic percent to improve oxidation resistance while maintaining the NaCl-type crystal structure. To achieve appropriate rigidity, hardness, and thermal expansion coefficient, it is more preferable for one or more of W and Mo to be dissolved in it at a concentration of 5 to 43 atomic percent relative to the total amount of metal elements in the MC phase, and even more preferable for it to be dissolved at a concentration of 10 to 40 atomic percent.

[0033] 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. with a hexagonal crystal structure. When the MC phase contains multiple metal elements, it may contain an MC phase with a core-rim structure in addition to a solid solution with a NaCl-type crystal structure. Furthermore, the MC phase may be composed of multiple types of phases with different compositions.

[0034] Cr3C2 phase is 10.3 MK -1Since it has a high thermal expansion coefficient and a hardness close to 1300 HV, 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. Furthermore, the sintered alloy contains the Cr3C2 phase and does not contain any hard phases other than the MC phase with a NaCl structure, which has excellent oxidation resistance, resulting in a synergistic effect that allows the maintenance of an even better specularity over a long period of time.

[0035] Cr 23 When a phase consisting of chromium compounds other than Cr3C2, such as the C6 phase or 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. 23 A small amount of chromium compounds other than Cr3C2, such as C6 and Cr7C3, may be contained, and here, "Cr3C2 phase" means that 80% by volume or more of the chromium compounds are Cr3C2 phase.

[0036] The atomic ratio 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 greater. If the atomic ratio of light elements is less than 0.8, the sintered alloy will not be sufficiently densified. Even lower ratios will lead to the formation of compound phases other than the MC phase, such as the Cr3C2 phase and NaCl-type structure, making it difficult to achieve high oxidation resistance. The atomic ratio of metal elements to light elements can be calculated by subtracting the carbon content of the Cr3C2 phase, calculated from the carbon content and addition ratio of the Cr3C2 raw powder used, from the alloy carbon content of the sintered compact, and then calculating the atomic ratio from the remaining components, or by directly analyzing the MC phase using EDS. The atomic ratio 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 light elements is greater than this, free carbon is more likely to form in the alloy.

[0037] 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 achieve a grain size of less than 0.1 μm, the raw material powder must be refined, which increases costs and also deteriorates the moldability of the powder. If the grain size of the MC phase is greater 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.

[0038] The grain size of the Cr3C2 phase is preferably 9 μm or less. If the grain size of the Cr3C2 phase exceeds 9 μm, the specularity may decrease. The grain size of the Cr3C2 phase can be determined in the same way as the grain size of the MC phase. The grain size of the Cr3C2 phase is more preferably 0.5 to 7 μm.

[0039] 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. The inclusion of the metal phase allows for the desired thermal expansion coefficient and toughness to be obtained. The metal phase content is preferably 8.2% by volume or less. The inclusion of Ni as the metal phase improves sinterability and toughness. Co and Fe increase the strength of the sintered alloy at room temperature and high temperatures. Furthermore, Fe is relatively inexpensive. The content of each element can be selected to obtain the required characteristics depending on the intended use of the tool. If the metal phase content exceeds 8.2% by volume, the surface roughness Ra after finishing becomes large, and tool deformation resistance during use at high temperatures decreases. The metal phase content is more preferably 8% by volume or less.

[0040] [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.

[0041] The sintered alloy (MC-WC alloy) according to the second embodiment has a thermal expansion coefficient of 5 to 7 MK. -1 It is easy to obtain a sintered alloy of this level. The MC phase may be the same as in the first embodiment. If the MC phase is less than 8% by volume, the required thermal expansion coefficient cannot be obtained and oxidation resistance also decreases. Furthermore, if the MC phase is more than 95% by 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 10 to 92% by volume, and more preferably 12 to 90% by volume.

[0042] The sintered alloy according to the second embodiment contains 2.0 vol% or less of a metallic phase consisting of at least one of Ni, Co, and Fe. This improves sinterability and allows for lower sintering temperatures. Furthermore, the presence of trace amounts of metallic components between particles suppresses particle growth due to coalescence, facilitating the formation of a fine grain structure and improving specularity and strength. Furthermore, the desired toughness can be achieved, reducing defects due to chipping during tool use. As with the first embodiment, the content of each element can be selected to achieve the desired properties depending on the tool's intended use. If the metallic phase content exceeds 2.0 vol%, tool deformation resistance during high-temperature use decreases. The metallic phase content is preferably 1.5 vol% or less, and more preferably 1 vol% or less.

[0043] 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. However, since the WC phase is included, the oxidation resistance is slightly 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.

[0044] As in the first embodiment, the MC phase of the sintered alloy according to the second embodiment may contain at least one of W and Mo dissolved in a proportion of 0.1 to 45 atomic % relative to the total amount of metal elements in the MC phase. Small amounts of W and Mo, approximately 0.1 to 43 atomic %, may be dissolved to improve oxidation resistance while maintaining the NaCl-type crystal structure. To obtain appropriate rigidity, hardness, and thermal expansion coefficient, it is more preferable that at least one of W and Mo be dissolved in a proportion of 5 to 43 atomic %, and even more preferable that it be dissolved in a proportion of 10 to 40 atomic %, relative to the total amount of metal elements in the MC phase. Light elements may include oxygen and boron. Metal elements may include Zr, Hf, and Cr.

[0045] [3] Third embodiment A sintered alloy according to a third embodiment of the present invention is characterized by comprising a WC phase and a Cr3C2 phase, and containing 10 to 90 volume % of the Cr3C2 phase.

[0046] The sintered alloy (Cr3C2-WC alloy) according to the third embodiment can obtain a wide range of thermal expansion coefficients by changing the ratio of each phase. By setting the content of the Cr3C2 phase to 10 to 90 volume %, the thermal expansion coefficient can be increased to 5 to 9 MK. -1 It has a wide range of thermal expansion coefficients. It also tends to have higher thermal conductivity compared to other alloy systems with similar thermal expansion coefficients. The Cr3C2 phase may be the same as in the first embodiment. When the Cr3C2 phase content exceeds 90% by volume, the Cr3C2 phase is prone to grain growth, making it difficult to obtain a mirror finish. When the Cr3C2 phase content is less than 10% by volume, oxidation resistance tends to be poor. The Cr3C2 phase content is preferably 15 to 85% by volume, and more preferably 20 to 80% by volume. When the WC phase ratio is high, oxidation resistance is somewhat poor, but toughness and strength are excellent.

[0047] 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 an ultrafine grain alloy can be obtained, making it easy to obtain a Cr3C2-WC alloy with good specularity. The grain size of the WC phase may be the same as in the second embodiment. This allows for the production of a fine grain Cr3C2-WC alloy, resulting in high specularity.

[0048] In the third embodiment, if the sinterability of the alloy is insufficient, the sintered alloy may contain 2.0 vol.% or less of a metallic phase consisting of at least one of Ni, Co, and Fe. This allows for the desired toughness to be achieved, reducing the likelihood of chipping during tool use. Furthermore, the increased sinterability allows for a lower sintering temperature, suppressing grain growth and tending to improve specularity and strength. As with the first embodiment, the content of each element can be selected to obtain the desired properties depending on the intended use of the tool. If the metallic phase content exceeds 2.0 vol.%, tool deformation resistance during use at high temperatures decreases. The metallic phase content is preferably 1.5 vol.% or less, more preferably 1 vol.% or less.

[0049] [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% or more by volume of the solid solution phase is composed of a compound phase (hereinafter also referred to as "MC phase") having an NaCl-type structure, a WC phase, and a Cr3C2 phase.

[0050] In the MC-Cr3C2 alloy and MC-WC alloy of the present invention, 7MK -1 When attempting to obtain an intermediate thermal expansion coefficient, it is conceivable to increase the proportion of the MC phase. However, increasing the proportion of the MC phase tends to cause coarsening of the MC phase, which can lead to adverse effects such as a decrease in specularity and strength. Therefore, by forming an MC-Cr3C2-WC alloy in which the MC phase, Cr3C2 phase, and WC phase coexist, it is possible to prevent the coarsening of the structure. The MC phase, Cr3C2 phase, and WC phase may each be the same as in the first to third embodiments.

[0051] 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 %, 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 %, and more preferably 40 to 85 volume %. Increasing the WC phase ratio tends to decrease oxidation resistance, but makes it easier to obtain a small thermal expansion coefficient, a large thermal conductivity, and high toughness. Increasing the MC phase ratio increases oxidation resistance and makes it easier to obtain a moderate thermal expansion coefficient, improving sinterability.

[0052] 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.

[0053] 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 %, and the volume ratio of the Cr3C2 phase to the WC phase is 0.125 to 8, the thermal expansion coefficient is 6 to 9. -1 The thermal expansion coefficient is about 6.5 to 7.5 MK when the MC phase amount is 90 volume %. -1 A thermal expansion coefficient of about 1000 MPa is obtained.

[0054] The sintered alloy according to the fourth embodiment can obtain the required thermal expansion coefficient and properties by changing the ratios as needed. -1 However, when oxidation resistance is particularly important, it is better to select MC-Cr3C2-WC alloy, and when high thermal conductivity is desired, it is better to select Cr3C2-WC alloy.

[0055] 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 exceeds 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.

[0056] As in the first embodiment, the MC phase of the sintered alloy according to the fourth embodiment may contain at least one of W and Mo dissolved in a proportion of 0.1 to 45 atomic % relative to the total amount of metal elements in the MC phase. Small amounts of W and Mo, approximately 0.1 to 43 atomic %, may be dissolved in the MC phase to improve oxidation resistance while maintaining the NaCl-type crystal structure. To obtain appropriate rigidity, hardness, and thermal expansion coefficient, it is more preferable that at least one of W and Mo be dissolved in a proportion of 5 to 43 atomic %, and even more preferable that it be dissolved in a proportion of 10 to 40 atomic %, relative to the total amount of metal elements in the MC phase.

[0057] A lens molding die using the sintered alloy of the present invention may be coated with a hard film such as DLC or a metal film such as platinum. Not only lens molding dies, but also members and tools using the sintered alloy of the present invention may be coated with various types of coatings in order to maximize the features of the present invention.

[0058] [5] Manufacturing Method of Sintered Alloy The sintered alloy of the present invention can be obtained by conventional sintering, hot press sintering, etc. That is, a predetermined amount of powder is weighed, wet mixed, pulverized, dried, and then pressure-molded in a mold to obtain a powder compact. This powder compact can be machined or cut to the required shape, or it can be pre-sintered and then machined to obtain the desired shape. Alternatively, the powder can be filled into a mold of a predetermined shape and hot press sintered to obtain the desired shape. In the case of conventional sintering, the powder compact is sintered in a vacuum or in an inert gas atmosphere such as nitrogen or argon at a sintering temperature of 1300 to 1540°C.

[0059] After sintering, HIP treatment may be further performed. This reduces the pores that occur during sintering. The HIP temperature 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, grain growth of Cr carbides and the like occurs, resulting in a decrease in strength. HIP treatment can also adjust the grain size of the structure.

[0060] Either conventional sintering or hot press sintering can be used regardless of the amount of metallic phase. When using hot press sintering, the sintering temperature can be lowered to make it easier to obtain a fine grain structure. If the amount of metallic phase is small and it is difficult to obtain a dense alloy using conventional sintering, hot press sintering can also 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. Hot press sintering a sintered alloy that contains no metallic phase or a trace amount of metallic phase becomes a dense alloy, which can further improve the specularity and therefore produces a sintered alloy that is suitable for use as a mold.

[0061] The hot press is not particularly limited 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. Alternatively, an apparatus other than a hot press, such as an electric current sintering apparatus, may be used.

[0062] [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. In order to mold parts without defects, the thermal expansion coefficient of the lens material and the shape of the molded parts should be taken into consideration, and the sintered alloy can be used in a range of 5 to 9 MK. -1 It is possible to select a mold material having an optimum thermal expansion coefficient within a certain range. In addition, the present invention is not limited to this, and can be suitably used when a mold for molding a part 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.

[0063] The present invention will be described in more detail with reference to inventive products, but the present invention is not limited thereto.

[0064] Example 1 Raw material powders include Cr3C2 (2.4 μm), Ni (2.3 μm), Co (1.4 μm), Fe (2.9 μm), TaC (1.6 μm), NbC (1.6 μm), TiC (1.6 μm), Ti(C 0.5 ,N 0.5 ) (2.1μm), TaN (2.0μm), Nb(C 0.7 N 0.3 ) (2.5 μm), WC (0.8 μm), Mo2C (3.1 μm), and various solid solution powders listed in Table 1 were used. The solid solution powders were prepared by wet-mixing carbides, nitrides, and carbonitrides to obtain the compositions shown in Table 1, and then subjecting the resulting powders to solid solution treatment in a high-temperature furnace, followed by pulverization and sieving to obtain raw material powders (1.3 to 3.1 μm).

[0065]

[0066] For samples containing small amounts of metallic phase components, pre-ground powders were used, which were obtained by wet grinding metallic powders and other powders, while for samples containing 4% or more of metallic phase components, they were used as is without pre-grounding. Depending on the sample, C powder was added to reduce oxides contained in the powder or to adjust the carbon content.

[0067] Sintering was performed using conventional sintering or hot-press sintering under an inert gas atmosphere of nitrogen or argon, followed by HIP treatment of the resulting sintered bodies to produce sintered alloys (Invention Products 1-20 and Comparative Products 1-5). For conventional 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. For hot-press sintering (Invention Products 6, 7, 8, 11, 12, 15, 17, 19, and 20), the sintering temperature was 1200°C to 1650°C, and the sintering atmosphere was Ar. For sintered alloys (Invention Products 1-20 and Comparative Products 1-5) containing MC phase, the ratio of the compounds constituting the MC phase was determined. The results are shown in Table 2. The ratio of the compounds constituting the MC phase listed in Table 2 was calculated by converting each compound into its respective compound, taking into account the compound ratio at the time of blending and the carbon and nitrogen contents of the sintered alloy.

[0068]

[0069] The obtained samples were examined for transverse rupture strength, hardness, thermal expansion coefficient, high-temperature oxidation resistance, thermal conductivity, and surface roughness by the following methods. The results are shown in Table 3 together with the overall evaluation.

[0070] (Transverse Rupture Strength) The transverse rupture strength (MPa) of the sintered alloys of invention products 1 to 20 and comparison products 1 to 5 was determined by transverse rupture strength measurement (three-point bending test) according to the method of JIS B4104.

[0071] (Rockwell Hardness HRA) The Vickers hardness (HRA) of the sintered alloys of invention products 1 to 20 and comparison products 1 to 5 was measured by the Rockwell A hardness testing method for CIS027B sintered alloys.

[0072] (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℃ using a vertical dilatometer, and the thermal expansion coefficient RT-700℃ (MK -1 ) measurements were carried out.

[0073] (Oxidation resistance at 700°C) 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 sought.

[0074] (Thermal Conductivity) The thermal conductivity of the sintered alloys of invention products 1 to 20 and comparison products 1 to 5 was determined using a laser flash thermal constant measuring device.

[0075] (Surface roughness Ra after finishing) The sintered alloys of invention products 1 to 20 and comparison products 1 to 5 were mirror-finished using diamond slurry, and then the surface roughness Ra (nm) was determined.

[0076] (Evaluation) Molds were made using the sintered alloys of invention products 1 to 20 and comparison products 1 to 5, and glass lenses were repeatedly molded. The molds were evaluated based on the number of repetitions and the specularity of the molded surface after repeated use. If the molds could be used a predetermined number of times or more and still maintained good specularity, they were marked with ◎; if they could be used a predetermined number of times or more, they were marked with ○; if they could be used up to the predetermined number of times, they were marked with △; if they could not be used up to the predetermined number of times, they were marked with ×.

[0077]

[0078] As can be seen from Table 3, inventions 1 to 20 ranged from 4.9 to 9.2 MK. -1 These alloys possessed the various thermal expansion coefficients required within the range of 0.1 to 4.5 atomic percent of the MC phase, while also possessing the necessary properties such as specularity, thermal conductivity, strength, and oxidation resistance. Specifically, the MC-Cr3C2 alloy exhibited excellent oxidation resistance, the MC-WC alloy exhibited excellent strength and specularity, and the Cr3C2-WC alloy exhibited excellent specularity and high thermal conductivity. It was found that the MC-Cr3C2-WC alloy suppressed phase grain growth, thereby enhancing specularity and strength. Furthermore, to improve oxidation resistance, Mo and / or W may be incorporated into the MC phase at a solid solution concentration of 0.1 to 45 atomic percent relative to the total metal elements. The thermal expansion coefficient of the MC phase can be altered by varying the amount of W.

[0079] In Comparative Example 1, the MC-Cr3C2 alloy contained a large amount of MC phase at 97% by volume, which caused the MC phase to grow into grains, resulting in poor surface roughness. In Comparative Example 2, the MC-WC alloy contained a small amount of MC phase at 3.0% by volume, resulting in a thermal expansion coefficient of 4.7 MK. -1 The required thermal expansion coefficient was not obtained and the oxidation resistance was also poor. Comparative product 3 contained only the MC phase, which caused grain growth of the MC phase, resulting in poor surface roughness. Comparative product 4 contained a high Cr3C2 phase content of 96 volume % in the Cr3C2-WC alloy, resulting in a thermal expansion coefficient of 10.1 MK. -1 The required thermal expansion coefficient was not obtained, and the Cr3C2 phase grew into grains, resulting in poor surface roughness. Comparative Example 5 had poor oxidation resistance because the Cr3C2 phase content in the Cr3C2-WC alloy was only 5.7 volume percent.

Claims

1. A sintered alloy characterized by forming a solid solution phase consisting of at least one metal element selected from Ti, Ta, Nb, and V and at least one of C and N, and comprising a compound phase having an NaCl-type structure of 80% or more by volume and a Cr3C2 phase, and containing 38 to 95% by volume of said compound phase.

2. 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, at least one of W and Mo, and at least one of C and N, and that it is composed of a compound phase having an NaCl-type structure for 80% or more by volume, and a Cr3C2 phase, and that it contains 38 to 95% by volume of said compound phase, and that at least one of W and Mo is solid-solved in said compound phase at a rate of 0.1 to 45 atomic % relative to the total amount of metal elements in said compound phase.

3. A sintered alloy that forms a solid solution phase consisting of at least one metal element selected from Ti, Ta, Nb, and V, and at least one of C and N, and that is composed of a compound 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 Cr3C2 phase, and that contains 38 to 95% by volume of the compound phase and 8.2% by volume or less of the binder phase.

4. A sintered alloy comprising a compound phase having a NaCl-type structure of 80% or more by volume, a binder phase consisting of at least one of Ni, Co and Fe, and a Cr3C2 phase, which forms a solid solution phase consisting of at least one metal element selected from Ti, Ta, Nb and V, at least one of W and Mo, and at least one of C and N, and which contains 38 to 95% by volume of said compound phase and 8.2% or less by volume of said binder phase, and wherein at least one of W and Mo is solid-solved in said compound phase at a rate of 0.1 to 45 atomic % relative to the total amount of metal elements in said compound phase.

5. A sintered alloy comprising a compound phase which forms a solid solution phase consisting of at least one metal element selected from Ti, Ta, Nb and V and at least one of C and N, with 80% or more by volume having an NaCl-type structure, a binder phase consisting of at least one of Ni, Co and Fe, and a WC phase, and containing 8 to 95% by volume of said compound phase and 2.0% or less by volume of said binder phase.

6. A sintered alloy comprising a compound phase which forms a solid solution phase consisting of at least one metal element selected from Ti, Ta, Nb and V, at least one of W and Mo, and at least one of C and N, with 80% or more by volume having an NaCl-type structure, a binder phase consisting of at least one of Ni, Co and Fe, and a WC phase, the compound phase containing 8 to 95% by volume and 2.0% or less by volume of the binder phase, and wherein at least one of W and Mo is solid-solved in the compound phase at a rate of 0.1 to 45 atomic % relative to the total amount of metal elements in the compound phase.

7. A sintered alloy comprising a WC phase and a Cr3C2 phase, the Cr3C2 phase being contained in an amount of 10 to 90% by volume.

8. A sintered alloy comprising a WC phase, a binder phase consisting of at least one of Ni, Co, and Fe, and a Cr3C2 phase, the Cr3C2 phase being contained in an amount of 10 to 90% by volume, and the binder phase being contained in an amount of 2.0% by volume or less.

9. A sintered alloy characterized by forming a solid solution phase consisting of at least one metal element selected from Ti, Ta, Nb, and V and at least one of C and N, and characterized in that 80% or more by volume is composed of a compound phase having an NaCl-type structure, a WC phase, and a Cr3C2 phase.

10. A sintered alloy which 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 which is composed of a compound phase having an NaCl-type structure of 80% or more by volume, a WC phase, and a Cr3C2 phase, and in which at least one of W and Mo is solid-solved in the compound phase at a rate of 0.1 to 45 atomic % relative to the total amount of metal elements in the compound phase.

11. A sintered alloy comprising a compound phase having a NaCl-type structure, 80% or more by volume of which 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, a binder phase consisting of at least one of Ni, Co, and Fe, a WC phase, and a Cr3C2 phase, and containing 2.0% or less by volume of said binder phase.

12. A sintered alloy comprising a compound phase having 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, with 80% or more by volume having an NaCl-type structure, a binder phase consisting of at least one of Ni, Co, and Fe, a WC phase, and a Cr3C2 phase, the binder phase being contained in an amount of 2.0% by volume or less, and at least one of W and Mo being solid-solved in the compound phase at a rate of 0.1 to 45 atomic % relative to the total amount of metal elements in the compound phase.

13. A sintered alloy according to any one of claims 9 to 12, characterized in that the compound phase is contained in an amount of 10 to 90% by volume.

14. A sintered alloy according to any one of claims 9 to 13, characterized in that the volume ratio of the content of said Cr3C2 phase to the content of said WC phase is 0.125 to 8.

15. A sintered alloy according to any one of claims 7 to 14, characterized in that the grain size of the WC phase is 0.1 to 2.5 µm.

16. A sintered alloy according to any one of claims 1 to 12, which is sintered by hot pressing.

17. A mold made of the sintered alloy of any one of claims 1 to 16.

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