Sintered alloy and mold

Abstract

A sintered alloy comprising a compound phase and a Cr3C2 phase, the compound phase containing a solid solution phase comprising at least one metal element selected from Ti, Ta, Nb and V and at least one metal element selected from C and N, and having a NaCl-type structure at least 80 vol% or more, the content of the compound phase being 38 vol% to 95 vol%.

Description

Technical Field

[0001] The present invention relates to sintered alloys and molds made from the sintered alloys. Background Technology

[0002] SUS420J2, ultrafine cemented carbide, and binderless cemented carbide have been used as materials for molds used to mold various optical lenses. For molds requiring high shape accuracy, such as those for aspherical lenses, binderless cemented carbide with a low coefficient of thermal expansion is used.

[0003] On the other hand, various materials are being used as lens materials. When using lens materials with a higher coefficient of thermal expansion compared to conventional materials, and when molding shapes that are difficult to mold using molds with a coefficient of thermal expansion of conventional mold materials, mold materials with a high coefficient of thermal expansion are sometimes used.

[0004] JP 2574426 B (Patent Document 1) discloses an optical element molding die for pressure molding glass optical elements, wherein at least the portion of the die in contact with the glass has: (a) a composition consisting of 65.7% to 92.9% wt% tungsten, 24.0% to 0.8% wt% titanium, 10.3% to 6.3% wt% carbon and the balance being unavoidable impurities, and (b) a two-phase mixed structure consisting of a tungsten carbide phase (first phase) and a solid solution composite carbide phase of titanium and tungsten having NaCl-type crystals (second phase).

[0005] JP 6049978 B (Patent Document 2) discloses a sintered alloy for molds with a high coefficient of thermal expansion, which is advantageous for molding glass materials with a high coefficient of thermal expansion. The alloy has a Cr3C2-NbC-Ni composition, comprising 20% ​​to 40% by mass of NbC, 0.3% to 10% by mass of Ni, unavoidable impurities, and the balance Cr3C2. This sintered alloy for molds with a high coefficient of thermal expansion not only enables the molding of materials with a high coefficient of thermal expansion but also enables the molding of materials with shapes that are difficult to mold using molds made from conventional materials.

[0006] JP 7351582 B (Patent Document 3) discloses a sintered alloy and a mold made from the sintered alloy, wherein the sintered alloy improves the oxidation resistance of the sintered alloy used in molds with a high coefficient of thermal expansion, thereby extending the life of the mold and improving the quality of the molded product.

[0007] Existing technical documents

[0008] Patent Document 1: JP 2574426 B

[0009] Patent Document 2: JP 6049978 B

[0010] Patent Document 3: JP 7351582 B

[0011] Purpose of the invention

[0012] In recent years, with the diversification of molded products, mold materials with various coefficients of thermal expansion have been proposed, and there is an increasing demand for molding special shapes that are not conventionally available. To meet these applications, it is essential to provide a mold with a suitable coefficient of thermal expansion. Summary of the Invention

[0013] This invention relates to a lens molding die material, which can obtain the desired coefficient of thermal expansion at will, and can be endowed with properties such as mirror properties, thermal conductivity, strength and oxidation resistance as needed.

[0014] In other words, the inventors have discovered that sintered alloys containing two or more hard phases selected from a compound phase (the compound phase comprising at least one metallic element selected from Ti, Ta, Nb, and V, and at least one of C and N, and having a NaCl-type structure of 80% by volume or more) (hereinafter also referred to as the "MC phase"), a Cr3C2 phase, and a WC phase are suitable as mold materials, said mold materials having a 4 to 5 MK [structure / performance] of conventional binderless cemented carbides. -1 The coefficient of thermal expansion is approximately 9 MK, similar to the materials in patent documents 2 and 3. -1 The coefficients of thermal expansion are arbitrary between those of the Cr3C2 phase, since the coefficient of thermal expansion of the Cr3C2 phase is approximately 10.3 MK. -1 Furthermore, the thermal expansion coefficient of the WC phase is approximately 4.2 to 5.0 MK. -1 Furthermore, the mold material can be endowed with properties such as mirror finish, thermal conductivity, strength, and oxidation resistance as needed. This invention has been completed based on such findings.

[0015] Specifically, the sintered alloy according to the first embodiment of the present invention is composed of a compound phase and a Cr3C2 phase, wherein the compound phase comprises a solid solution phase consisting of at least one metallic element selected from Ti, Ta, Nb, and V, and at least one of C and N, and has a NaCl-type structure of more than 80% by volume.

[0016] The content of the compound phase is from 38% to 95% by volume.

[0017] The sintered alloy according to a second embodiment of the present invention comprises a compound phase and a Cr3C2 phase, wherein the compound phase comprises a solid solution phase consisting of at least one metallic element selected from Ti, Ta, Nb, and V, at least one selected from W and Mo, and at least one selected from C and N, and has a NaCl-type structure of more than 80% by volume.

[0018] The content of the compound phase is from 38% to 95% by volume, and

[0019] Relative to the total amount of metal elements in the compound phase, at least one of W and Mo is dissolved in the compound phase in amounts ranging from 0.1 atomic% to 45 atomic%.

[0020] The sintered alloy according to a third embodiment of the present invention comprises a compound phase, a binder phase, and a Cr3C2 phase. The compound phase comprises a solid solution phase consisting of at least one metallic element selected from Ti, Ta, Nb, and V, and at least one of C and N, and has a NaCl-type structure of at least 80% by volume. The binder phase consists of at least one of Ni, Co, and Fe.

[0021] The content of the compound phase is from 38% to 95% by volume, and

[0022] The content of the binder phase is less than 8.2% by volume.

[0023] The sintered alloy according to a fourth embodiment of the present invention comprises a compound phase, a binder phase, and a Cr3C2 phase. The compound phase comprises a solid solution phase consisting of at least one metallic element selected from Ti, Ta, Nb, and V, at least one from W and Mo, and at least one from C and N, and has a NaCl-type structure of at least 80% by volume. The binder phase consists of at least one from Ni, Co, and Fe.

[0024] The content of the compound phase is from 38% to 95% by volume.

[0025] The content of the binder phase is less than 8.2% by volume, and

[0026] Relative to the total amount of metal elements in the compound phase, at least one of W and Mo is dissolved in the compound phase in amounts ranging from 0.1 atomic% to 45 atomic%.

[0027] The sintered alloy according to a fifth embodiment of the present invention comprises a compound phase, a binder phase, and a WC phase. The compound phase comprises a solid solution phase consisting of at least one metallic element selected from Ti, Ta, Nb, and V, and at least one of C and N, and has a NaCl-type structure of more than 80% by volume. The binder phase consists of at least one of Ni, Co, and Fe.

[0028] The content of the compound phase is from 8% to 95% by volume, and

[0029] The content of the binder phase is less than 2.0% by volume.

[0030] The sintered alloy according to a sixth embodiment of the present invention comprises a compound phase, a binder phase, and a WC phase. The compound phase comprises a solid solution phase consisting of at least one metallic element selected from Ti, Ta, Nb, and V, at least one from W and Mo, and at least one from C and N, and has a NaCl-type structure of at least 80% by volume. The binder phase consists of at least one from Ni, Co, and Fe.

[0031] The content of the compound phase is from 8% to 95% by volume, and

[0032] The content of the binder phase is less than 2.0% by volume.

[0033] Relative to the total amount of metal elements in the compound phase, at least one of W and Mo is dissolved in the compound phase in amounts ranging from 0.1 atomic% to 45 atomic%.

[0034] The sintered alloy according to the seventh embodiment of the present invention is composed of a WC phase and a Cr3C2 phase.

[0035] The content of the Cr3C2 phase is from 10% to 90% by volume.

[0036] The sintered alloy according to the eighth embodiment of the present invention is composed of a WC phase, a binder phase, and a Cr3C2 phase, wherein the binder phase is composed of at least one of Ni, Co, and Fe.

[0037] The content of the Cr3C2 phase is from 10% to 90% by volume, and

[0038] The content of the binder phase is less than 2.0% by volume.

[0039] According to the ninth embodiment of the present invention, the sintered alloy is composed of a compound phase, a WC phase and a Cr3C2 phase, wherein the compound phase comprises a solid solution phase consisting of at least one metallic element selected from Ti, Ta, Nb and V and at least one of C and N, and has a NaCl-type structure of more than 80% by volume.

[0040] The sintered alloy according to the tenth embodiment of the present invention is composed of a compound phase, a WC phase, and a Cr3C2 phase. The compound phase comprises a solid solution phase consisting of at least one metallic element selected from Ti, Ta, Nb, and V, at least one from W and Mo, and at least one from C and N, and has a NaCl-type structure of more than 80% by volume.

[0041] Relative to the total amount of metal elements in the compound phase, at least one of W and Mo is dissolved in the compound phase in amounts ranging from 0.1 atomic% to 45 atomic%.

[0042] The sintered alloy according to the eleventh embodiment of the present invention comprises a compound phase, a binder phase, a WC phase, and a Cr3C2 phase. The compound phase comprises a solid solution phase consisting of at least one metallic element selected from Ti, Ta, Nb, and V, and at least one of C and N, and has a NaCl-type structure of at least 80% by volume. The binder phase consists of at least one of Ni, Co, and Fe.

[0043] The content of the binder phase is less than 2.0% by volume.

[0044] The sintered alloy according to the twelfth embodiment of the present invention comprises a compound phase, a binder phase, a WC phase, and a Cr3C2 phase. The compound phase comprises a solid solution phase consisting of at least one metallic element selected from Ti, Ta, Nb, and V, at least one from W and Mo, and at least one from C and N, and has a NaCl-type structure of at least 80% by volume. The binder phase consists of at least one from Ni, Co, and Fe.

[0045] The content of the binder phase is less than 2.0% by volume.

[0046] Relative to the total amount of metal elements in the compound phase, at least one of W and Mo is dissolved in the compound phase in amounts ranging from 0.1 atomic% to 45 atomic%.

[0047] In the ninth to twelfth embodiments, the content of the compound phase is preferably from 10% to 90% by volume.

[0048] In the ninth to twelfth embodiments, the volume ratio of the Cr3C2 phase content to the WC phase content is preferably 0.125 to 8.

[0049] The particle size of the WC phase is preferably 0.1 to 2.5 μm.

[0050] In the first to twelfth embodiments, sintering is preferably carried out by hot pressing.

[0051] The mold according to the first embodiment of the present invention is made of the above-described sintered alloy.

[0052] Invention Effects

[0053] According to the present invention, a lens molding die material can be obtained, which can obtain any desired coefficient of thermal expansion and can be endowed with properties such as mirror properties, thermal conductivity, strength and oxidation resistance as needed. Detailed Implementation

[0054] [1] First Implementation Scheme

[0055] The sintered alloy according to a first embodiment of the invention is composed of a compound phase (also referred to below as the "MC phase") and a Cr3C2 phase, wherein the compound phase comprises a solid solution phase consisting of at least one metallic element selected from Ti, Ta, Nb and V and at least one of C and N, and has a NaCl-type structure of more than 80% by volume, and the content of the compound phase is from 38% to 95% by volume.

[0056] The MC phase is a carbide, carbonitride, nitride, or solid solution (including those composed of a single compound) of at least one metallic element selected from Ti, Ta, Nb, and V, and has a NaCl-type structure. Because the sintered alloy contains this 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, when the MC phase contains Ti, particularly excellent oxidation resistance is obtained. The MC phase can be a solid solution phase containing Ti in addition to Ta, Nb, or V. In this case, the Ti content is preferably 10 mol% to 90 mol% relative to the amount of metallic element contained in the MC phase, and more preferably 40 mol% to 80 mol%. Preferably, the MC phase is a carbide or carbonitride. Among Ti, Ta, Nb, and V, Ti carbides have high hardness; therefore, when the MC phase contains a large amount of Ti, it becomes a material with excellent wear resistance, but it also tends to become hard and brittle, making it difficult to obtain a mirror finish. Therefore, reducing the amount of Ti added is better in this case. The inclusion of V improves the mold's anti-adhesion properties. The MC phase can be a solid solution phase containing V in addition to at least one metallic element selected from Ti, Ta, and Nb. Furthermore, if it is necessary to avoid the inclusion of components from Ti, Ta, Nb, and V into the material to be processed, this can be adjusted by reducing the content of these elements. In addition, it can contain oxygen and boron, and may also contain Zr, Hf, and Cr.

[0057] The sintered alloy (MC-Cr3C2 alloy) according to the first embodiment readily achieves a coefficient of thermal expansion of approximately 7 to 9 MK. -1 It is a sintered alloy with excellent oxidation resistance. By setting the MC phase content to 38% to 95% vol%, approximately 7 to 9 MK can be obtained. -1 The target coefficient of thermal expansion. When the MC phase content exceeds 95% by volume, the MC phase structure is prone to grain growth, and it is difficult to obtain the mirror finish of the sintered alloy. When the MC phase content is below 38% by volume, it is difficult to obtain a coefficient of thermal expansion of less than approximately 9 MK. -1The coefficient of thermal expansion. The content of MC phase is preferably 40% to 90% by volume, and more preferably 45% to 85% by volume.

[0058] At least one of W and Mo, ranging from 0.1 atomic% to 45 atomic% relative to the total amount of metallic elements in the MC phase, can be dissolved in the MC phase. While WC and Mo₂C themselves have hexagonal crystal structures, when dissolved in the MC phase, the MC phase retains a NaCl-type crystal structure and inhibits grain growth, thereby further improving oxidation resistance. Since the stiffness, hardness, and coefficient of thermal expansion of the alloy can be controlled by changing the content of W and Mo, the composition can be chosen to achieve the desired properties depending on the application, and the ease of mirror finishing and wear resistance can be adjusted by changing the hardness of the alloy. Small amounts of W or Mo can be dissolved in the range of 0.1 atomic% to 43 atomic% to improve oxidation resistance while maintaining the NaCl-type crystal structure. More preferably, at least one of W and Mo, ranging from 5 atomic% to 43 atomic% relative to the total amount of metallic elements in the MC phase, and even more preferably, at least 10 atomic% to 40 atomic% relative to the total amount of metallic elements in the MC phase, can be dissolved in the MC phase.

[0059] Here, "MC phase with NaCl-type crystal structure" means that more than 80% by volume of the MC phase has a NaCl-type crystal structure. That is, in addition to the NaCl-type crystal structure, it can also contain small amounts of hexagonal crystals, oxides, borides, etc. Furthermore, when the MC phase contains multiple metal elements, besides a solid solution with a NaCl-type crystal structure, it can also contain MC phases with a core-edge structure. In addition, the MC phase can be composed of multiple types of phases with different compositions.

[0060] Because the Cr3C2 phase has 10.3 MK -1 Due to its high coefficient of thermal expansion and hardness approaching 1300 HV, when the sintered alloy contains the Cr3C2 phase, the coefficient of thermal expansion increases, making mirror finishing easier and improving the mirror finish. Furthermore, because the sintered alloy contains the Cr3C2 phase and does not contain any hard phases other than the NaCl-type MC phase with excellent oxidation resistance, it achieves a synergistic effect of maintaining excellent mirror finish over a long period.

[0061] When a phase composed of chromium compounds other than Cr3C2 is formed, such as Cr... 23 When C6 or Cr7C3 phases are present, the coefficient of thermal expansion decreases proportionally to the content. Furthermore, because they are more brittle than Cr3C2 phases, they are more prone to causing defects when used as tools. If chromium compounds other than Cr3C2, such as Cr... 23If the amounts of C6 and Cr7C3 are relatively small, then the Cr3C2 phase may contain these chromium compounds; here, "Cr3C2 phase" means that more than 80% by volume of chromium compounds are in the Cr3C2 phase.

[0062] The atomic ratio of light elements such as C and N in the MC phase to the amount of metallic elements in the MC phase is preferably 0.8 or higher. When the atomic ratio of light elements is less than 0.8, the densification of the sintered alloy will be insufficient. If the ratio is even lower, compound phases other than the Cr3C2 phase and the MC phase with a NaCl-type structure are easily formed, thus making it impossible to obtain high oxidation resistance. The atomic ratio of metallic elements to light elements is determined by subtracting the amount of carbon in the Cr3C2 phase calculated from the amount of carbon in the Cr3C2 raw material powder used and the addition ratio from the total carbon content of the sintered body, and then calculating the atomic ratio from the remaining components, or by directly performing EDS analysis on the MC phase. The atomic ratio of light elements such as C and N in the MC phase to the amount of metallic elements in the MC phase is preferably 1.0 or lower. When the atomic ratio of light elements is greater than this value, free carbon is easily formed in the alloy.

[0063] The particle size of the MC phase is preferably 0.1 to 6 μm. The particle size of the MC phase is defined as the diameter of a circle having an area equal to the cross-sectional area of ​​the MC phase in any cross-section of the sintered alloy. Setting the particle size of the MC phase to less than 0.1 μm requires refining the raw material powder, which increases cost and also worsens the powder's formability. When the particle size of the MC phase is greater than 6 μm, the mirror finish decreases, which may cause defects when used in molds. The particle size of the MC phase can be determined by taking images of the cross-section of the sintered alloy using a scanning electron microscope (SEM) and analyzing the obtained SEM images using image analysis software. The particle size of the MC phase is more preferably 0.5 to 3 μm.

[0064] Ideally, the particle size of the Cr3C2 phase is below 9 μm. When the particle size of the Cr3C2 phase exceeds 9 μm, the specular properties may decrease. The particle size of the Cr3C2 phase can be determined in the same manner as the particle size of the MC phase. The specular properties of the Cr3C2 phase are more preferably 0.5 to 7 μm.

[0065] The sintered alloy according to the first embodiment of the present invention may further contain a metallic phase composed of at least one of Ni, Co, and Fe. When the sintered alloy contains a metallic phase, the desired coefficient of thermal expansion and toughness can be obtained. The content of the metallic phase is preferably 8.2 vol% or less. When the sintered alloy contains Ni as a metallic phase, sinterability and toughness can be improved. Co and Fe increase the strength of the sintered alloy at room temperature and high temperature. In addition, Fe is relatively inexpensive to obtain. The content of each element can be selected according to the intended use of the tool to obtain the desired properties. When the content of the metallic phase exceeds 8.2 vol%, the surface roughness Ra after finishing becomes coarser, and the resistance to tool deformation during high-temperature use decreases. The content of the metallic phase is more preferably 8 vol% or less.

[0066] [2] Second Implementation Plan

[0067] The sintered alloy according to a second embodiment of the present invention comprises a compound phase (also referred to below as the "MC phase"), a binder phase, and a WC phase. The compound phase comprises a solid solution phase consisting of at least one metallic element selected from Ti, Ta, Nb, and V, and at least one of C and N, and has a NaCl-type structure of 80% by volume or more. The binder phase consists of at least one of Ni, Co, and Fe. The content of the compound phase is from 8% to 95% by volume, and the content of the binder phase is less than 2.0% by volume.

[0068] The sintered alloy (MC-WC alloy) according to the second embodiment readily achieves a coefficient of thermal expansion of approximately 5 to 7 MK. -1 The sintered alloy. The MC phase can be the same as in the first embodiment. When the MC phase content is less than 8 vol%, the desired coefficient of thermal expansion cannot be obtained, and the oxidation resistance is also reduced. In addition, when the MC phase content exceeds 95 vol%, the structure is prone to grain growth, making it difficult to obtain a mirror finish, and the strength is also reduced. The MC phase content is preferably from 10 vol% to 92 vol%, and more preferably from 12 vol% to 90 vol%.

[0069] Since the sintered alloy according to the second embodiment contains less than 2.0 vol% of a metallic phase composed of at least one of Ni, Co, and Fe, sinterability is improved, thereby enabling a lower sintering temperature. Furthermore, because a small amount of metallic component is inserted between the particles, growth due to particle aggregation is suppressed, making it easier to obtain a fine structure and improving mirror finish and strength. In addition, the desired toughness can be obtained, and defects caused by spalling during tool use are less likely to occur. Also, as in the first embodiment, the content of each element can be selected according to the intended use of the tool to obtain the desired properties. When the content of the metallic phase exceeds 2.0 vol%, the resistance to tool deformation during high-temperature use decreases. The content of the metallic phase is preferably 1.5 vol% or less, and more preferably 1 vol% or less.

[0070] The particle size of the WC phase is preferably 0.1 to 2.5 μm. The particle size of the WC phase can be determined in the same manner as the particle size of the MC phase. By adjusting the WC particle size to the range of 0.1 to 2.5 μm, an MC-WC alloy with a fine structure is obtained, thus achieving high mirror finish. On the other hand, because it contains the WC phase, its oxidation resistance is slightly inferior to that of the first embodiment. The particle 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.

[0071] Similar to the first embodiment, the MC phase of the sintered alloy according to the second embodiment may have at least 0.1 atomic% to 45 atomic% of W and Mo dissolved in solid solution relative to the total amount of metal elements in the MC phase. A small amount of W or Mo, from about 0.1 atomic% to 43 atomic%, may be dissolved in solid solution to improve oxidation resistance while maintaining the NaCl-type crystal structure. More preferably, at least 5 atomic% to 43 atomic% of W and Mo may be dissolved in solid solution relative to the total amount of metal elements in the MC phase, and even more preferably, 10 atomic% to 40 atomic% may be dissolved in solid solution to obtain suitable stiffness, hardness, and coefficient of thermal expansion. The sintered alloy may contain oxygen and boron as light elements. The sintered alloy may contain Zr, Hf, and Cr as metal elements.

[0072] [3] Third Implementation Plan

[0073] According to the third embodiment of the present invention, the sintered alloy is composed of a WC phase and a Cr3C2 phase, wherein the content of the Cr3C2 phase is 10% to 90% by volume.

[0074] The sintered alloy (Cr3C2-WC alloy) according to the third embodiment can obtain a wide range of coefficients of thermal expansion by changing the ratio of each phase, and by setting the content of the Cr3C2 phase to 10% to 90% by volume, it has a coefficient of thermal expansion of about 5 to 9 MK. -1 It has a wide range of coefficients of thermal expansion. Furthermore, compared to other alloy systems with similar coefficients of thermal expansion, it tends to have higher thermal conductivity. The Cr3C2 phase can be the same as in the first embodiment. When the Cr3C2 phase content exceeds 90 vol%, grain growth of the Cr3C2 phase is likely to occur, and a mirror finish is difficult to achieve. When the Cr3C2 phase content is less than 10 vol%, oxidation resistance tends to be poor. The Cr3C2 phase content is preferably 15 vol% to 85 vol%, and more preferably 20 vol% to 80 vol%. When the WC phase ratio is high, oxidation resistance is slightly worse, but toughness and strength are excellent.

[0075] The particle size of the alloy structure can be easily adjusted by the mixing and grinding conditions and the selection of the raw materials for the WC phase, and, for example, ultrafine alloys can be obtained, thereby making it easy to obtain Cr3C2-WC alloys with good mirror finish. The particle size of the WC phase can be the same as in the second embodiment. As a result, a microfine Cr3C2-WC alloy is obtained, thus achieving high mirror finish.

[0076] When the sinterability of the alloy is insufficient, the sintered alloy according to the third embodiment may contain 2.0 vol% or less of a metallic phase composed of at least one of Ni, Co, and Fe. As a result, the desired toughness can be obtained, and defects due to spalling during tool use are less likely to occur. In addition, since the sinterability is improved, the sintering temperature can be lowered, and since grain growth is also suppressed, the mirror finish and strength tend to be improved. As in the first embodiment, the content of each element can be selected according to the target use of the tool to obtain the desired properties. When the content of the metallic phase exceeds 2.0 vol%, the resistance to tool deformation during high-temperature use decreases. The content of the metallic phase is preferably 1.5 vol% or less, and more preferably 1 vol% or less.

[0077] [4] Fourth Implementation Plan

[0078] The sintered alloy according to the fourth embodiment of the present invention is composed of a compound phase (also referred to below as the "MC phase"), a WC phase and a Cr3C2 phase, wherein the compound phase comprises a solid solution phase consisting of at least one metallic element selected from Ti, Ta, Nb and V and at least one of C and N, and has a NaCl-type structure of more than 80% by volume.

[0079] In the MC-Cr3C2 alloy or MC-WC alloy of the present invention, when attempting to obtain approximately 7 MK -1When considering the intermediate coefficient of thermal expansion, increasing the ratio of the MC phase is conceivable. However, as the ratio of the MC phase increases, coarsening of the MC phase easily occurs, and simultaneously, disadvantages such as reduced mirror finish and strength also tend to arise. Therefore, by making it an MC-Cr3C2-WC alloy in which the MC, Cr3C2, and WC phases coexist, structural coarsening can be prevented. The MC, Cr3C2, and WC phases can each be the same as in the first to third embodiments.

[0080] The sintered alloy (MC-Cr3C2-WC alloy) according to the fourth embodiment preferably contains 10 vol% to 90 vol% of the MC phase. When the MC phase content is below 10 vol%, the oxidation resistance decreases. Furthermore, when the MC phase content exceeds 90 vol%, grain growth easily occurs in the structure, making it difficult to achieve a mirror finish and reducing strength. The MC phase content is preferably 20 vol% to 90 vol%, and more preferably 40 vol% to 85 vol%. Increasing the WC phase ratio tends to decrease oxidation resistance, but it easily yields a low coefficient of thermal expansion and higher thermal conductivity and toughness. Increasing the MC phase ratio improves oxidation resistance, facilitates obtaining a moderate coefficient of thermal expansion, and improves sinterability.

[0081] Preferably, the volume ratio of the Cr3C2 phase to the WC phase is 0.125 to 8. When the volume ratio of the Cr3C2 phase to the WC phase is less than 0.125, the antioxidant properties tend to be lower, and when it exceeds 8, the mirror finish tends to be lower. The volume ratio of the Cr3C2 phase to the WC phase is preferably 0.15 to 6.6, and more preferably 0.2 to 5.

[0082] Increasing the proportion of the Cr3C2 phase improves antioxidant properties and facilitates the attainment of a high coefficient of thermal expansion. When the amount of the MC phase is 10% by volume and the volume ratio of the Cr3C2 phase to the WC phase is 0.125 to 8, approximately 6 to 9 MK can be obtained. -1 The coefficient of thermal expansion. Similarly, when the amount of MC phase is 90% by volume, a coefficient of thermal expansion of approximately 6.5 to 7.5 MK can be obtained. -1 The coefficient of thermal expansion.

[0083] The sintered alloy according to the fourth embodiment can achieve the necessary coefficient of thermal expansion and necessary properties by changing the ratios as needed. Note that a coefficient of thermal expansion of approximately 7 MK can be obtained using a Cr3C2-WC alloy. -1 While alloys are generally acceptable, MC-Cr3C2-WC alloy should be chosen when oxidation resistance is particularly important, and Cr3C2-WC alloy should be chosen when improved thermal conductivity is required.

[0084] When alloy strength is required or when the sinterability of the alloy is insufficient, the sintered alloy according to the fourth embodiment may contain 2.0 vol% or less of a metallic phase composed of at least one of Ni, Co, and Fe. When it exceeds 2.0 vol%, the wear resistance may be poor. The content of the metallic phase is preferably 1.5 vol% or less, and more preferably 1 vol% or less.

[0085] Similar to the first embodiment, the MC phase of the sintered alloy according to the fourth embodiment may have at least 0.1 atomic% to 45 atomic% of W and Mo dissolved in solid solution relative to the total amount of metal elements in the MC phase. A small amount of W or Mo, from about 0.1 atomic% to 43 atomic%, may be dissolved in solid solution to improve oxidation resistance while maintaining the NaCl-type crystal structure. More preferably, to obtain suitable stiffness, hardness, and coefficient of thermal expansion, at least 5 atomic% to 43 atomic% of W and Mo may be dissolved in solid solution relative to the total amount of metal elements in the MC phase, and even more preferably, 10 atomic% to 40 atomic% may be dissolved in solid solution relative to the total amount of metal elements in the MC phase.

[0086] Lens molding dies using the sintered alloy of the present invention can be coated with a hard film such as DLC, or a metal film such as platinum. To maximize the features of the present invention, various coatings can be applied not only to the lens molding dies, but also to various components or tools using the sintered alloy of the present invention.

[0087] [5] Preparation method of sintered alloys

[0088] The sintered alloy of the present invention is obtained by conventional sintering, hot pressing sintering, etc. That is, a predetermined amount of powder is weighed, wet-mixed and ground, dried, and then pressed into a mold to obtain a powder compact. This powder compact can be cut or ground into the desired shape, or the powder compact can be pre-sintered and then machined to obtain the predetermined shape. Alternatively, the powder can be filled into a mold of a predetermined shape and hot-pressed to obtain the predetermined shape. In the case of conventional sintering, the sintered alloy is obtained by sintering the powder compact in a vacuum or in an inert atmosphere such as nitrogen or argon at a sintering temperature of 1300 to 1540°C.

[0089] After sintering, a further HIP (Hybrid Intercalation-Insulation) treatment can be performed. This reduces the porosity generated during sintering. The HIP treatment temperature can be appropriately set according to the composition of the sintered alloy, but it can be equal to or lower than the sintering temperature. This is because if the temperature is higher than the sintering temperature, Cr carbides and other materials will undergo grain growth, resulting in reduced strength. The grain size can also be adjusted through HIP treatment.

[0090] Regardless of the amount of metallic phase, either conventional sintering or hot pressing sintering can be used. When using hot pressing sintering, a fine structure can be obtained by lowering the sintering temperature. When the amount of metallic phase is small and it is difficult to obtain a dense alloy by conventional sintering, hot pressing sintering can be performed. 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 pressing sintering sintered alloys containing no metallic phase or a small amount of metallic phase, a dense alloy is obtained, and the mirror finish can be further improved, thus obtaining sintered alloys suitable for use as molds.

[0091] There are no particular restrictions on hot pressing, as long as it roughly forms a sintered alloy. However, it is preferred to sinter in a vacuum or under an inert atmosphere such as nitrogen or argon at a pressure of 20 to 100 MPa and a sintering temperature of 1200 to 1500 °C. Alternatively, equipment other than a hot press, such as electric current sintering, can be used.

[0092] [6] Molds and other applications

[0093] The sintered alloy of the present invention is suitable for use as a material for molds, particularly for lens molding, and, in order to mold defect-free parts, considering the coefficient of thermal expansion of the lens material and the shape of the molded portion, a material with a thermal expansion coefficient of about 5 to 9 mk can be selected. -1 The invention identifies the optimal coefficient of thermal expansion for mold materials within a given range. Furthermore, the invention is not limited to this; it is suitable for use when molds for molded parts require a higher coefficient of thermal expansion or superior oxidation resistance compared to conventional cemented carbide or binder-free cemented carbide. The invention is also suitable for components or tools requiring high coefficients of thermal expansion, high wear resistance, and excellent oxidation resistance.

[0094] Example

[0095] The invention will be described in more detail by way of the invention itself, but the invention is not limited thereto.

[0096] Example 1

[0097] The raw material powders used were 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), and Ti(C) 0.5 N 0.5 ) (2.1 μm), TaN (2.0 μm), Nb(C 0.7 N 0.3Solid solution powders (1.3 to 3.1 μm) were prepared by blending carbides, nitrides and carbonitrides having the compositions shown in Table 1, wet mixing, solid solution treatment in a high-temperature furnace, followed by pulverization and sieving.

[0098] Table 1

[0099]

[0100] For samples containing a small amount of metallic phase components, powders pre-crushed by wet milling of the metallic powder and other powders are used. For powders containing more than 4% by volume of metallic phase components, they are used as is without pre-crushing. Additionally, depending on the sample, carbon powder is added to reduce oxides contained in the powder or to adjust the carbon content.

[0101] Sintering was performed in an inert atmosphere of nitrogen or argon, either by conventional sintering or hot-pressing, and the resulting sintered bodies were subjected to HIP treatment to prepare sintered alloys of Inventions 1 to 20 and Comparative Examples 1 to 5. In conventional sintering, the sintering temperature was set to 1400°C to 1540°C, the pressure to 40 kPa to 90 kPa, and the sintering atmosphere to N2 or Ar. In hot-pressing sintering (Inventions 6, 7, 8, 11, 12, 15, 17, 19, 20), the sintering temperature was set to 1200°C to 1650°C, and the sintering atmosphere to Ar. For those Inventions 1 to 20 and Comparative Examples 1 to 5 containing the MC phase, the ratio of compounds constituting the MC phase was determined. The results are shown in Table 2. The ratio of compounds constituting the MC phase described in Table 2 was determined by converting them to individual compounds while taking into account the compound ratios during mixing and the carbon and nitrogen content of the sintered alloys.

[0102] Table 2

[0103]

[0104] The transverse fracture strength, hardness, coefficient of thermal expansion, high-temperature oxidation resistance, thermal conductivity, and surface roughness of the obtained samples were determined by the following methods. The results, along with their comprehensive evaluation, are shown in Table 3.

[0105] (Transverse tensile strength)

[0106] The transverse fracture strength (MPa) of the sintered alloys of Inventions 1 to 20 and Comparative Examples 1 to 5 was determined by transverse fracture strength measurement (3-point bending test) according to the method of JIS B4104.

[0107] (Rockwell Hardness HRA)

[0108] The Vickers hardness (HRA) of the sintered alloys of Inventions 1 to 20 and Comparative Examples 1 to 5 was measured by the CIS 027B Rockwell Hardness A Test Method for Sintered Alloys.

[0109] (Coefficient of thermal expansion RT-700℃)

[0110] The sintered alloys of inventions 1 to 20 and comparative examples 1 to 5 were heated from room temperature to 700°C using a vertical dilatometer, and the coefficient of thermal expansion RT-700°C (MK) was measured. -1 ).

[0111] (Antioxidant value at 700℃)

[0112] The sintered alloys of inventions 1 to 20 and comparatives 1 to 5 were heated at 700°C for 30 minutes in an atmosphere to determine the oxidation weight increment (oxidation weight per unit area) (g / m²). 2 ).

[0113] (thermal conductivity)

[0114] The thermal conductivity of the sintered alloys of Inventions 1 to 20 and Comparative Examples 1 to 5 was determined by a laser flash thermal constant measuring device.

[0115] (Surface roughness Ra after finishing)

[0116] The surface roughness Ra (nm) of the sintered alloys of Inventions 1 to 20 and Comparative Examples 1 to 5 after mirror finishing using diamond slurry was determined.

[0117] (evaluate)

[0118] Glass lenses were repeatedly molded using sintered alloy forming molds of Inventions 1 to 20 and Comparative Examples 1 to 5, and the molds were evaluated based on the number of repetitions and the mirror finish of the molded surfaces after repeated use. A mold was rated "Excellent" if it could be used more than a predetermined number of times while still maintaining good mirror finish, "Good" if it could be used more than a predetermined number of times, "Average" if it could be used up to a predetermined number of times, and "Poor" if it could not be used up to a predetermined number of times.

[0119] Table 3

[0120]

[0121] As can be seen from Table 3, inventions 1 to 20 have the required mass of 4.9 to 9.2 MK. -1It exhibits a wide range of coefficients of thermal expansion and excels in essential properties such as mirror finish, thermal conductivity, strength, and oxidation resistance. Specifically, MC-Cr3C2 alloys are found to possess excellent oxidation resistance, MC-WC alloys to have excellent strength and mirror finish, and Cr3C2-WC alloys to possess excellent mirror finish and high thermal conductivity. Furthermore, MC-Cr3C2-WC alloys suppress grain growth in each phase, thereby improving mirror finish and strength. Additionally, to improve oxidation resistance, 0.1 atomic% to 45 atomic% of Mo and / or W can be dissolved relative to the total amount of metal elements in the MC phase. By changing the amount of W, the coefficient of thermal expansion of the MC phase can be altered.

[0122] Comparative sample 1 has a high MC phase content of 97 vol% in the MC-Cr3C2 alloy, thus the MC phase undergoes grain growth, and its surface roughness is particularly poor. Comparative sample 2 has a low MC phase content of 3.0 vol% in the MC-WC alloy, therefore its coefficient of thermal expansion is lower at 4.7 MK. -1 The required coefficient of thermal expansion could not be obtained, and the oxidation resistance was also poor. Comparative sample 3 contained only the MC phase, so the MC phase underwent grain growth, resulting in poor surface roughness. Comparative sample 4 had a high Cr3C2 phase content of 96% by volume in the Cr3C2-WC alloy, thus resulting in a higher coefficient of thermal expansion of 10.1 MK. -1 The required coefficient of thermal expansion cannot be obtained, and the Cr3C2 phase undergoes grain growth, resulting in poor surface roughness. Comparative sample 5 has a low Cr3C2 phase content of 5.7 vol% in the Cr3C2-WC alloy, thus exhibiting poor oxidation resistance.

Claims

1. A sintered alloy comprising a compound phase and a Cr3C2 phase, wherein the compound phase comprises a solid solution phase consisting of at least one metallic element selected from Ti, Ta, Nb, and V, and at least one of C and N, and has a NaCl-type structure of more than 80% by volume. The content of the compound phase is from 38% to 95% by volume.

2. A sintered alloy comprising a compound phase and a Cr3C2 phase, wherein the compound phase comprises a solid solution phase consisting of at least one metallic element selected from Ti, Ta, Nb, and V, at least one from W and Mo, and at least one from C and N, and has a NaCl-type structure of more than 80% by volume. The content of the compound phase is from 38% to 95% by volume, and Relative to the total amount of metal elements in the compound phase, at least one of W and Mo is dissolved in the compound phase in amounts ranging from 0.1 atomic% to 45 atomic%.

3. A sintered alloy comprising a compound phase, a binder phase, and a Cr3C2 phase, wherein the compound phase comprises a solid solution phase consisting of at least one metallic element selected from Ti, Ta, Nb, and V, and at least one of C and N, and has a NaCl-type structure of at least 80% by volume; and the binder phase consists of at least one of Ni, Co, and Fe. The content of the compound phase is from 38% to 95% by volume, and The content of the binder phase is less than 8.2% by volume.

4. A sintered alloy comprising a compound phase, a binder phase, and a Cr3C2 phase, wherein the compound phase comprises a solid solution phase consisting of at least one metallic element selected from Ti, Ta, Nb, and V, at least one from W and Mo, and at least one from C and N, and has a NaCl-type structure of more than 80% by volume; and the binder phase consists of at least one from Ni, Co, and Fe. The content of the compound phase is from 38% to 95% by volume. The content of the binder phase is less than 8.2% by volume, and Relative to the total amount of metal elements in the compound phase, at least one of W and Mo is dissolved in the compound phase in amounts ranging from 0.1 atomic% to 45 atomic%.

5. A sintered alloy comprising a compound phase, a binder phase, and a WC phase, wherein the compound phase comprises a solid solution phase consisting of at least one metallic element selected from Ti, Ta, Nb, and V, and at least one of C and N, and has a NaCl-type structure of at least 80% by volume; and the binder phase consists of at least one of Ni, Co, and Fe. The content of the compound phase is from 8% to 95% by volume, and The content of the binder phase is less than 2.0% by volume.

6. A sintered alloy comprising a compound phase, a binder phase, and a WC phase, wherein the compound phase comprises a solid solution phase consisting of at least one metallic element selected from Ti, Ta, Nb, and V, at least one from W and Mo, and at least one from C and N, and has a NaCl-type structure of more than 80% by volume; and the binder phase consists of at least one from Ni, Co, and Fe. The content of the compound phase is from 8% to 95% by volume, and The content of the binder phase is less than 2.0% by volume. Relative to the total amount of metal elements in the compound phase, at least one of W and Mo is dissolved in the compound phase in amounts ranging from 0.1 atomic% to 45 atomic%.

7. A sintered alloy composed of WC phase and Cr3C2 phase, The content of the Cr3C2 phase is from 10% to 90% by volume.

8. A sintered alloy comprising a WC phase, a binder phase, and a Cr3C2 phase, wherein the binder phase is composed of at least one selected from Ni, Co, and Fe. The content of the Cr3C2 phase is from 10% to 90% by volume, and The content of the binder phase is less than 2.0% by volume.

9. A sintered alloy comprising a compound phase, a WC phase and a Cr3C2 phase, wherein the compound phase comprises a solid solution phase consisting of at least one metallic element selected from Ti, Ta, Nb and V and at least one of C and N, and has a NaCl-type structure of more than 80% by volume.

10. A sintered alloy comprising a compound phase, a WC phase, and a Cr3C2 phase, wherein the compound phase comprises a solid solution phase consisting of at least one metallic element selected from Ti, Ta, Nb, and V, at least one from W and Mo, and at least one from C and N, and has a NaCl-type structure of more than 80% by volume. Relative to the total amount of metal elements in the compound phase, at least one of W and Mo is dissolved in the compound phase in amounts ranging from 0.1 atomic% to 45 atomic%.

11. A sintered alloy comprising a compound phase, a binder phase, a WC phase, and a Cr3C2 phase, wherein the compound phase comprises a solid solution phase consisting of at least one metallic element selected from Ti, Ta, Nb, and V, and at least one of C and N, and has a NaCl-type structure of at least 80% by volume; and the binder phase consists of at least one of Ni, Co, and Fe. The content of the binder phase is less than 2.0% by volume.

12. A sintered alloy comprising a compound phase, a binder phase, a WC phase, and a Cr3C2 phase, wherein the compound phase comprises a solid solution phase consisting of at least one metallic element selected from Ti, Ta, Nb, and V, at least one from W and Mo, and at least one from C and N, and has a NaCl-type structure of more than 80% by volume; and the binder phase consists of at least one from Ni, Co, and Fe. The content of the binder phase is less than 2.0% by volume. Relative to the total amount of metal elements in the compound phase, at least one of W and Mo is dissolved in the compound phase in amounts ranging from 0.1 atomic% to 45 atomic%.

13. The sintered alloy according to any one of claims 9 to 12, wherein the content of the compound phase is from 10% to 90% by volume.

14. The sintered alloy according to any one of claims 9 to 13, wherein the volume ratio of the Cr3C2 phase content to the WC phase content is 0.125 to 8.

15. The sintered alloy according to any one of claims 7 to 14, wherein the particle size of the WC phase is 0.1 to 2.5 μm.

16. The sintered alloy according to any one of claims 1 to 12, wherein the sintered alloy is sintered by hot pressing.

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

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