Classifications

• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
  • C04B35/56—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbides or oxycarbides
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C29/00—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides
  • C22C29/02—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides
  • C22C29/04—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides based on carbonitrides
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C29/00—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides
  • C22C29/02—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides
  • C22C29/06—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides based on carbides, but not containing other metal compounds
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C29/00—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides
  • C22C29/02—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides
  • C22C29/06—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides based on carbides, but not containing other metal compounds
  • C22C29/08—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides based on carbides, but not containing other metal compounds based on tungsten carbide
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C29/00—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides
  • C22C29/02—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides
  • C22C29/06—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides based on carbides, but not containing other metal compounds
  • C22C29/10—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides based on carbides, but not containing other metal compounds based on titanium carbide

Definitions

• the present invention relates to sintered alloys and molds made of sintered alloys.
• SUS420J2 ultrafine-grained cemented carbide, binderless cemented carbide, etc. have been used as materials for molds used in molding various optical lenses, but when high geometric precision is required, such as for molds for aspherical lenses, binderless cemented carbide, which has a low thermal expansion coefficient, is used.
• lens materials are being used as lens materials, and lens materials with higher thermal expansion coefficients than conventional materials are being used, and mold materials with higher thermal expansion coefficients are sometimes used when molding shapes that are difficult to mold using the thermal expansion coefficients of conventional mold materials.
• Patent Document 1 discloses an optical element molding die used in press molding of glass optical elements, in which at least the portion of the die that comes into contact with the glass has a composition of (a) 65.7 to 92.9 wt% tungsten, 24.0 to 0.8 wt% titanium, 10.3 to 6.3 wt% carbon, and the remainder unavoidable impurities, and (b) a two-phase mixed structure in which the first phase is a tungsten carbide phase and the second phase is a solid solution complex carbide phase of titanium and tungsten in the form of an NaCl-type crystal.
• Patent Document 2 discloses a sintered alloy for forming dies with a high thermal expansion coefficient that is advantageous for forming glass materials with a high thermal expansion coefficient, having a Cr3C2 - NbC-Ni composition containing 20 mass% to 40 mass% NbC, 0.3 mass% to 10 mass% Ni, unavoidable impurities, and the remainder being Cr3C2 .
• This sintered alloy for forming dies with a high thermal expansion coefficient not only enables the forming of materials with a high thermal expansion coefficient, but also enables the forming of materials with shapes that are difficult to form with conventional materials.
• Patent Document 3 improves the oxidation resistance of the sintered alloy for molding dies, which has a high thermal expansion coefficient, thereby extending the life of the dies and improving the quality of the molded products.
• the present invention relates to a lens molding die material that can be used to obtain any desired thermal expansion coefficient and can also be given properties such as specularity, thermal conductivity, strength, and oxidation resistance as needed.
• a sintered alloy that forms a solid solution phase containing at least one metal element selected from Ti, Ta, Nb, and V, and at least one of C and N, and that contains two or more hard phases selected from a compound phase (hereinafter also referred to as an "MC phase") having an NaCl-type structure, Cr3C2 phase , and WC phase, has a thermal expansion coefficient of approximately 10.3 MK -1 for the Cr3C2 phase and a thermal expansion coefficient of approximately 4.2 to 5.0 MK -1 for the WC phase, and therefore has any thermal expansion coefficient between the thermal expansion coefficient of 4 to 5 MK -1 of conventional binderless cemented carbide and the thermal expansion coefficient of approximately 9 MK -1 of the materials in Patent Documents 2 and 3, and is suitable as a molding die material that can be imparted with properties such as specularity, thermal conductivity, strength, and oxidation resistance as needed, and thus arrived at the present invention.
• the sintered alloy according to the first embodiment of the present invention forms a solid solution phase consisting of at least one metal element selected from Ti, Ta, Nb, and V and at least one of C and N, and 80% by volume or more of the sintered alloy is composed of a compound phase having an NaCl-type structure and a Cr3C2 phase;
• the composition is characterized in that it contains the compound phase in an amount of 38 to 95% by volume.
• the sintered alloy according to the second embodiment of the present invention forms a solid solution phase consisting of at least one metal element selected from the group consisting of Ti, Ta, Nb, and V, at least one of W and Mo, and at least one of C and N, and 80% by volume or more of the sintered alloy is composed of a compound phase having an NaCl-type structure and a Cr3C2 phase;
• the compound phase is contained in an amount of 38 to 95% by volume,
• the compound phase is characterized in that at least one of W and Mo is dissolved in a solid solution in an amount of 0.1 to 45 atomic % relative to the total amount of metal elements in the compound phase.
• a sintered alloy according to a third embodiment of the present invention forms a solid solution phase consisting of at least one metal element selected from the group consisting of Ti, Ta, Nb, and V, and at least one of C and N, and is composed of a compound phase having an NaCl structure of 80% or more by volume, a binder phase consisting of at least one of Ni, Co, and Fe, and a Cr3C2 phase ;
• the composition is characterized in that it contains 38 to 95% by volume of the compound phase and 8.2% by volume or less of the binder phase.
• a sintered alloy according to a fourth embodiment of the present invention forms a solid solution phase consisting of at least one metal element selected from the group consisting of Ti, Ta, Nb, and V, at least one of W and Mo, and at least one of C and N, and is composed of a compound phase having an NaCl-type structure of 80% by volume or more, a binder phase consisting of at least one of Ni, Co, and Fe, and a Cr3C2 phase ;
• the compound phase is contained in an amount of 38 to 95% by volume, and the binder phase is contained in an amount of 8.2% by volume or less,
• the compound phase is characterized in that at least one of W and Mo is dissolved in a solid solution in an amount of 0.1 to 45 atomic % relative to the total amount of metal elements in the compound phase.
• a sintered alloy according to a fifth embodiment of the present invention 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% by volume or more, a binder phase consisting of at least one of Ni, Co, and Fe, and a WC phase;
• the composition is characterized in that it contains 8 to 95% by volume of the compound phase and 2.0% by volume or less of the binder phase.
• a sintered alloy according to a sixth embodiment of the present invention forms a solid solution phase consisting of at least one metal element selected from the group consisting of Ti, Ta, Nb, and V, at least one of W and Mo, and at least one of C and N, and is composed of a compound phase having an NaCl-type structure of 80% by volume or more, a binder phase consisting of at least one of Ni, Co, and Fe, and a WC phase;
• the compound phase is contained in an amount of 8 to 95% by volume, and the binder phase is contained in an amount of 2.0% by volume or less,
• the compound phase is characterized in that at least one of W and Mo is dissolved in a solid solution in an amount of 0.1 to 45 atomic % relative to the total amount of metal elements in the compound phase.
• a sintered alloy according to a seventh embodiment of the present invention comprises a WC phase and a Cr3C2 phase, The alloy is characterized by containing 10 to 90 volume % of the Cr 3 C 2 phase.
• the sintered alloy according to the eighth embodiment of the present invention comprises a WC phase, a binder phase comprising at least one of Ni, Co and Fe, and a Cr3C2 phase,
• the alloy is characterized in that it contains 10 to 90% by volume of the Cr 3 C 2 phase and 2.0% by volume or less of the binder phase.
• the sintered alloy according to the ninth embodiment of the present invention is characterized in that it forms a solid solution phase consisting of at least one metal element selected from the group consisting of Ti, Ta, Nb, and V, and at least one of C and N, and that 80% or more by volume of the solid solution phase is composed of a compound phase having an NaCl-type structure, a WC phase, and a Cr3C2 phase.
• 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 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 80% by volume or more of the sintered alloy is composed of a compound phase having an NaCl-type structure, a WC phase, and a Cr3C2 phase ;
• the compound phase is characterized in that at least one of W and Mo is dissolved in a solid solution in an amount of 0.1 to 45 atomic % relative to the total amount of metal elements in the compound phase.
• a sintered alloy according to an eleventh embodiment of the present invention 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 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 ;
• the binder phase is contained in an amount of 2.0% by volume or less.
• a sintered alloy according to a twelfth 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 composed of a compound phase having an NaCl 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 ;
• the binder phase contains 2.0% by volume or less
• the compound phase is characterized in that at least one of W and Mo is dissolved in a solid solution in an amount of 0.1 to 45 atomic % relative to the total amount of metal elements in the compound phase.
• the compound phase is preferably contained at 10 to 90 volume %.
• the volume ratio of the content of the Cr 3 C 2 phase to the content of the WC phase is preferably 0.125 to 8.
• the particle size of the WC phase is preferably 0.1 to 2.5 ⁇ m.
• the sintering be performed by hot pressing.
• a mold according to one embodiment of the present invention is characterized by being made from the above-mentioned sintered alloy.
• the present invention provides a lens molding die material that can be used to obtain any desired thermal expansion coefficient and can also be given properties such as specularity, thermal conductivity, strength, and oxidation resistance as needed.
• 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 being contained in an amount of 38 to 95 volume %.
• MC phase compound phase having an NaCl-type structure and a Cr3C2 phase
• the MC phase is a carbide, carbonitride, nitride, or solid solution of at least one of the metallic elements Ti, Ta, Nb, and V (including cases where it consists of 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.
• the inclusion of Ti in the MC phase provides particularly excellent oxidation resistance.
• the MC phase may also be a solid solution phase containing Ti in addition to Ta, Nb, or V.
• the Ti content is preferably 10 to 90 mol%, and more preferably 40 to 80 mol%, of the metallic elements contained in the MC phase.
• the MC phase is preferably a carbide or carbonitride.
• 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 achieve 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 of the metallic elements Ti, Ta, and Nb.
• the amount of that element can be reduced.
• oxygen and boron may be further included, and Zr, Hf, and Cr may also be further included.
• the sintered alloy (MC- Cr3C2 alloy ) according to the first embodiment is easy to obtain a sintered alloy with a thermal expansion coefficient of about 7 to 9 MK -1 , and also has excellent oxidation resistance.
• the target thermal expansion coefficient of about 7 to 9 MK -1 can be obtained.
• the MC phase content exceeds 95 volume %, the MC phase structure is prone to grain growth, making it difficult to obtain a mirror finish in the sintered alloy.
• the MC phase content is less than 38 volume %, it is difficult to obtain a thermal expansion coefficient of less than about 9 MK -1 .
• the MC phase content is preferably 40 to 90 volume %, more preferably 45 to 85 volume %.
• the MC phase may contain at least one of W and Mo dissolved in it at 0.1 to 45 atomic % relative to the total amount of metal elements in the MC phase.
• W and Mo2C have a hexagonal crystal structure when dissolved alone, but when dissolved in the MC phase, they can maintain the NaCl-type crystal structure while suppressing grain growth of the MC phase and further improving oxidation resistance.
• the rigidity, hardness, thermal expansion coefficient, etc. of the alloy can be adjusted, allowing for the selection of a composition that achieves the desired properties depending on the application.
• the hardness of the alloy can be adjusted to adjust the ease of mirror finishing and wear resistance.
• W or Mo may be dissolved in the range of 0.1 to 43 atomic % to improve oxidation resistance while maintaining the NaCl-type crystal structure.
• the MC phase having an NaCl-type crystal structure means that 80% or more by volume of the MC phase has an NaCl-type crystal structure.
• it may also contain small amounts of crystals, oxides, borides, etc. with a hexagonal crystal structure, and when the MC phase contains multiple metal elements, it may also contain an MC phase with a core-rim structure in addition to a solid solution with an NaCl-type crystal structure.
• the MC phase may be composed of multiple types of phases with different compositions.
• the Cr3C2 phase has a high thermal expansion coefficient of 10.3 MK -1 and a hardness of nearly 1300 HV, so the inclusion of the Cr3C2 phase increases the thermal expansion coefficient of the sintered alloy, making it easier to achieve a mirror finish and improving the specularity. Furthermore, the sintered alloy contains the Cr3C2 phase and does not contain any hard phases other than the MC phase with an 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.
• the Cr3C2 phase may contain small amounts of chromium compounds other than Cr3C2 , such as Cr23C6 or Cr7C3 .
• Cr3C2 phase refers to a chromium compound in which 80 volume % or more of the chromium compounds are the Cr3C2 phase .
• the atomic ratio of the amount of light elements, such as C and N, contained in the MC phase to the amount of metal elements contained in the MC phase is preferably 0.8 or higher. If the atomic ratio of the light elements is less than 0.8, the sintered alloy will not be sufficiently densified. If the ratio is even lower, compound phases other than the MC phase, such as the Cr3C2 phase and NaCl-type structure, will likely form, making it difficult to achieve high oxidation resistance.
• the atomic ratio of metal elements to light elements can be calculated by subtracting the amount of carbon in the Cr3C2 phase, calculated from the carbon content and addition ratio of the Cr3C2 raw powder used, from the amount of alloy carbon in 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 the amount of light elements, such as C and N, contained in the MC phase to the amount of metal elements contained in the MC phase is preferably 1.0 or lower. If the atomic ratio of the light elements is higher, free carbon is more likely to form in the alloy.
• the grain size of the MC phase is preferably 0.1 to 6 ⁇ m.
• the grain size of the MC phase is the diameter of a circle with 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 ⁇ m, the raw material powder must be refined, which increases costs and also worsens the moldability of the powder. If the grain size of the MC phase is larger than 6 ⁇ m, 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. A grain size of the MC phase of 0.5 to 3 ⁇ m is more preferable.
• the grain size of the Cr3C2 phase is preferably 9 ⁇ m or less. If the grain size of the Cr3C2 phase exceeds 9 ⁇ m, 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 ⁇ m.
• the sintered alloy according to the first embodiment of the present invention may further contain a metallic phase consisting of at least one of Ni, Co, and Fe.
• a metallic phase allows for the desired thermal expansion coefficient and toughness to be obtained.
• the metallic phase content is preferably 8.2% by volume or less.
• Ni as a metallic phase improves sinterability and toughness.
• Co and Fe increase the strength of the sintered alloy at room temperature and high temperatures. Fe is also 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 metallic phase content exceeds 8.2% by volume, the surface roughness Ra after finishing will be high, and tool deformation resistance during use at high temperatures will be reduced. It is more preferable that the metallic phase content be 8% by volume or less.
• 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.
• MC phase compound phase
• the sintered alloy (MC-WC alloy) according to the second embodiment is easy to obtain with a thermal expansion coefficient of approximately 5 to 7 MK -1 .
• 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.
• the sintered alloy according to the second embodiment contains 2.0% by volume or less of a metallic phase consisting of at least one of Ni, Co, and Fe, which improves sinterability and allows for lower sintering temperatures. Furthermore, the presence of trace amounts of metallic components between each particle suppresses particle growth due to coalescence, making it easier to obtain a fine-grained structure and improving specularity and strength. Furthermore, the desired toughness can be achieved, making it less likely for defects due to chipping to occur during tool use. As with the first embodiment, the content of each element can be selected to obtain the properties required depending on the intended use of the tool. If the metallic phase content exceeds 2.0% by volume, tool deformation resistance during use at high temperatures decreases. The metallic phase content is preferably 1.5% by volume or less, and more preferably 1% by volume or less.
• the grain size of the WC phase is preferably 0.1 to 2.5 ⁇ m.
• the grain size of the WC phase can be determined in the same way as the grain size of the MC phase.
• the grain size of the WC phase is more preferably 0.11 to 2.0 ⁇ m, even more preferably 0.12 to 1.5 ⁇ m, even more preferably 0.13 to 1.0 ⁇ m, and particularly preferably 0.14 to 0.7 ⁇ m.
• At least one of W and Mo may be dissolved in a solid solution at 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.
• Light elements may include oxygen and boron.
• Metal elements may include Zr, Hf, and Cr.
• a sintered alloy according to a third embodiment of the present invention is characterized by comprising a WC phase and a Cr 3 C 2 phase, and containing 10 to 90 volume % of the Cr 3 C 2 phase.
• the sintered alloy ( Cr3C2 -WC alloy) according to the third embodiment can achieve a wide range of thermal expansion coefficients by varying the ratio of each phase.
• the Cr3C2 phase content By setting the Cr3C2 phase content to 10 to 90 volume %, the alloy has a wide range of thermal expansion coefficients, approximately 5 to 9 MK -1 . Furthermore, the alloy tends to have a higher thermal conductivity compared to other alloy systems with similar thermal expansion coefficients.
• the Cr3C2 phase may be the same as that of the first embodiment. When the Cr3C2 phase content exceeds 90 volume %, the Cr3C2 phase is prone to grain growth, making it difficult to achieve a mirror finish. When the Cr3C2 phase content is less than 10 volume %, oxidation resistance tends to be poor.
• the Cr3C2 phase content is preferably 15 to 85 volume %, more preferably 20 to 80 volume %. When the WC phase ratio is high, oxidation resistance is somewhat poor, but toughness and strength are excellent.
• the grain size of the alloy structure can be easily adjusted by selecting the mixed grinding conditions and the raw material of the WC phase, and 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, which in turn provides high specularity.
• 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 the desired toughness to be achieved, making the tool less susceptible to defects due to chipping during use. Furthermore, the increased sinterability allows for a lower sintering temperature, and grain growth is suppressed, which tends to improve specularity and strength.
• the content of each element can be selected to obtain the properties required for the tool's intended use. If the metallic phase content exceeds 2.0 vol. %, the tool's resistance to deformation during use at high temperatures decreases.
• the metallic phase content is preferably 1.5 vol. % or less, and more preferably 1 vol. % or less.
• 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.
• MC phase compound phase
• MC- Cr3C2 alloy and MC-WC alloy of the present invention increasing the proportion of the MC phase is considered when attempting to obtain an intermediate thermal expansion coefficient of approximately 7 MK -1 .
• 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 using an MC- Cr3C2 - WC alloy in which the MC phase, Cr3C2 phase , and WC phase coexist, coarsening of the structure can be prevented.
• the MC phase, Cr3C2 phase , and WC phase may each be the same as in the first to third embodiments.
• the sintered alloy (MC- Cr3C2 - WC alloy) according to the fourth embodiment preferably contains 10 to 90 volume % of the MC phase. If the MC phase is less than 10 volume %, 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 %. If the WC phase ratio is increased, oxidation resistance tends to decrease, but a small thermal expansion coefficient is easily obtained, and it is easy to obtain a large thermal conductivity and high toughness. If the MC phase ratio is increased, oxidation resistance is increased and a moderate thermal expansion coefficient is easily obtained, improving sinterability.
• the volume ratio of the Cr3C2 phase content to the WC phase content is preferably 0.125 to 8. If the volume ratio of the Cr3C2 phase content to the WC phase content is less than 0.125, the oxidation resistance tends to be low, and if it exceeds 8, the specularity tends to be low.
• the volume ratio of the Cr3C2 phase content to the WC phase content is preferably 0.15 to 6.6, and more preferably 0.2 to 5.
• Increasing the Cr3C2 phase ratio improves oxidation resistance and makes it easier to obtain a large thermal expansion coefficient.
• the MC phase amount is 10% by volume and the volume ratio of the Cr3C2 phase to the WC phase is 0.125 to 8, a thermal expansion coefficient of about 6 to 9 MK -1 can be obtained.
• the MC phase amount is 90% by volume, a thermal expansion coefficient of about 6.5 to 7.5 MK -1 can be obtained.
• the sintered alloy according to the fourth embodiment can obtain the required thermal expansion coefficient and properties by changing the ratios as needed.
• a Cr3C2 - WC alloy can also be obtained with a thermal expansion coefficient of about 7MK -1 , it is better to select an MC- Cr3C2 - WC alloy when oxidation resistance is particularly important, and a Cr3C2 - WC alloy when high thermal conductivity is desired.
• the sintered alloy according to the fourth embodiment may contain up to 2.0% by volume 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% by volume, wear resistance may be poor.
• the metal phase content is preferably up to 1.5% by volume, and more preferably up to 1% by volume.
• At least one of W and Mo may be dissolved in a solid solution at 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.
• Lens molding dies made 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.
• a hard film such as DLC
• a metal film such as platinum.
• Various coatings may be applied not only to lens molding dies, but also to components and tools made using the sintered alloy of the present invention in order to maximize the features of the present invention.
• 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.
• HIP treatment can also be performed after sintering. This can reduce pores that occur during sintering.
• the HIP treatment temperature can be set appropriately depending on the composition of the sintered alloy, but it can also be a temperature below the sintering temperature. If the temperature is higher than the sintering temperature, chromium carbides and other particles will grow into grains, resulting in a decrease in strength. HIP treatment can also be used to adjust the grain size of the structure.
• Either normal sintering or hot press sintering can be used regardless of the amount of metallic phase.
• the sintering temperature can be lowered to make it easier to obtain a fine-grained structure.
• hot press sintering can also be used.
• 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 creates a dense alloy, which can further improve specularity and therefore produces a sintered alloy that is suitable for use as a mold.
• Hot pressing is not particularly limited as long as it generally forms a sintered alloy, but sintering conditions are preferably carried out in a vacuum or in an inert gas atmosphere such as nitrogen or argon, at a pressure of 20 to 100 MPa and a sintering temperature of 1200 to 1500°C. It is also possible to use equipment other than hot pressing, such as electric current sintering.
• the sintered alloy of the present invention can be suitably used as a material for molds, particularly molds for molding lenses, and in order to mold parts without any defects, a mold material having an optimum thermal expansion coefficient within a range of approximately 5 to 9 MK -1 can be selected taking into consideration the thermal expansion coefficient of the lens material and the shape of the molded part. Furthermore, without being limited to this, the sintered alloy can be suitably used when a mold for molding parts requires a higher thermal expansion coefficient and superior oxidation resistance than ordinary cemented carbide or binderless cemented carbide, and can be suitably used for components, tools, etc. that require a high thermal expansion coefficient, high wear resistance, and excellent oxidation resistance.
• Example 1 The raw material powders used were Cr3C2 (2.4 ⁇ m), Ni (2.3 ⁇ m), Co (1.4 ⁇ m), Fe (2.9 ⁇ m), TaC (1.6 ⁇ m), NbC (1.6 ⁇ m), TiC (1.6 ⁇ m), Ti( C0.5 , N0.5 ) (2.1 ⁇ m), TaN ( 2.0 ⁇ m), Nb(C0.7N0.3 ) (2.5 ⁇ m), WC (0.8 ⁇ m), Mo2C (3.1 ⁇ m), and various solid solution powders listed in Table 1.
• 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 mixture to a solid solution treatment in a high-temperature furnace. The resulting powder was then crushed and sieved to obtain the raw material powder (1.3-3.1 ⁇ m).
• pre-ground powders made by wet grinding metal powder and other powders were used, while samples containing 4% or more by volume of metallic phase components were used as is without pre-grinding.
• C powder was also added to reduce oxides contained in the powder and adjust the amount of carbon.
• Sintering was performed using conventional sintering or hot-press sintering under an inert gas atmosphere of nitrogen or argon, followed by HIP treatment to produce sintered alloys (Invention Products 1-20 and Comparative Products 1-5).
• the sintering temperature was 1400°C to 1540°C
• the pressure was 40 kPa to 90 kPa
• the sintering atmosphere was N2 or Ar.
• hot-press sintering Invention Products 6, 7, 8, 11, 12, 15, 17, 19, and 20
• the sintering temperature was 1200°C to 1650°C
• the sintering atmosphere was Ar.
• 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.
• Thermal expansion coefficient RT-700°C The sintered alloys of invention products 1 to 20 and comparison products 1 to 5 were heated from room temperature to 700°C using a vertical dilatometer, and the thermal expansion coefficient RT-700°C (MK -1 ) was measured.
• thermo 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.
• 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 a ⁇ ; if they could be used a predetermined number of times or more, they were marked with a ⁇ ; if they could be used up to the predetermined number of times, they were marked with a ⁇ ; if they could not be used up to the predetermined number of times, they were marked with an ⁇ .
• Inventions 1 to 20 possessed the required thermal expansion coefficients in the range of 4.9 to 9.2 MK -1 , while also possessing the necessary properties, such as specularity, thermal conductivity, strength, and oxidation resistance.
• the MC- Cr3C2 alloy exhibited excellent oxidation resistance
• the MC-WC alloy exhibited excellent strength and specularity
• the Cr3C2 - WC alloy exhibited excellent specularity and high thermal conductivity.
• the MC-Cr3C2 - WC alloy suppressed phase grain growth, thereby enhancing specularity and strength.
• 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.
• the MC- Cr3C2 alloy contained a high MC phase content of 97 volume percent, which caused grain growth of the MC phase, resulting in poor surface roughness.
• the MC-WC alloy contained a low MC phase content of 3.0 volume percent, resulting in a low thermal expansion coefficient of 4.7 MK -1 , which did not achieve the required thermal expansion coefficient, and also poor oxidation resistance.
• the MC phase contained only the MC phase, which caused grain growth of the MC phase, resulting in poor surface roughness.
• the Cr3C2 - WC alloy contained a high Cr3C2 phase content of 96 volume percent, which caused a high thermal expansion coefficient of 10.1 MK -1 , which did not achieve the required thermal expansion coefficient, and also caused grain growth of the Cr3C2 phase, resulting in poor surface roughness.
• the Cr3C2 - WC alloy contained a low Cr3C2 phase content of 5.7 volume percent, resulting in poor oxidation resistance.

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