Lightweight hard alloy and lightweight hard alloy member

Abstract

Provided is a lightweight hard alloy which is obtained by sintering a mixed powder that contains, as a main component, a titanium compound composed of titanium carbide and / or titanium carbonitride, contains 5-33 mass% of W and / or Mo in terms of carbide, and contains, as a binder phase component, 5-40 mass% of at least one metal selected from the group consisting of Ni, Co, and Fe, and which includes a hard phase having a core-rim structure. In the cross-sectional structure of the lightweight hard alloy observed by using a scanning electron microscope, the average particle diameter of a core phase having a diameter of D90 or more is 0.8-3.3 μm on a number basis in the particle size distribution of the area circle-equivalent diameter of the core phase of the hard phase having a core-rim structure, and the average of the ratio Dmax / Dmin of the minimum length Dmin to the maximum length Dmax of a straight line that connects the contour and the center of gravity of the core phase having a diameter of D90 or more is 2.0 or less.

Description

Lightweight hard alloys and lightweight hard alloy components

[0001] This invention relates to a lightweight hard alloy and a lightweight hard alloy member using the same.

[0002] In recent years, ceramics and cemented carbide have often been used as wear-resistant components for crushing, mixing, and kneading resins and magnetic materials. However, ceramics have low toughness and are prone to chipping due to interference between wear-resistant components. Screws and similar components are large in size, and when made from cemented carbide, their high specific gravity results in heavy components, which can cause deflection in cantilevered screws and limit the rotational speed.

[0003] On the other hand, when sintering large components with cermet, there are problems such as a tendency for them to crack during sintering. Therefore, in recent years, there has been a demand for large cermet components that can achieve both lightweight and high toughness in such wear-resistant components, and that are less prone to sintering cracking.

[0004] Patent Document 1 discloses a highly tough cermet in which needle-shaped precipitates containing W as one of the constituent elements are dispersed in a matrix containing TiC: 5-25 wt%, WC: 25-50 wt%, and Ni+Co: 5-40 wt%. However, because it contains a large amount of WC (25-50 wt%), it results in a heavy tool component.

[0005] Patent Document 2 discloses a high-toughness cermet for cutting tools, which has a bonding phase consisting of one or more metals from the Fe group, a first hard dispersed phase consisting of titanium nitride, and a second hard dispersed phase consisting of solid solution carbonitrides of one or more transition metals from groups 4a, 5a, and 6a of the periodic table, with a carbon-to-nitrogen atomic ratio of nitrogen / (carbon+nitrogen) = 0.01 to 0.3. However, the presence of the titanium nitride phase results in poor grindability, and the high cost of the solid solution carbides poses production problems.

[0006] Cermets, primarily composed of titanium compounds such as TiC and Ti(C,N), combine the toughness of cemented carbide with the lightweight properties of ceramics. TiC and Ti(C,N) exhibit relatively good wettability with Ni and Co, resulting in dense sintered bodies. Furthermore, they contain a metallic bonding phase, giving them higher fracture toughness than ceramics. Additionally, TiC and Ti(C,N) have a lower specific gravity than WC, making cermets lighter than cemented carbide. However, existing cermets do not meet the toughness requirements for wear-resistant components compared to cemented carbide, leading to problems such as chipping during use.

[0007] Non-patent document 1 describes commercially available TiC (average particle size by FSSS method: 1.4 μm), Ti(C 0.7 N 0.3 ) (1.4 μm), Ti(C 0.5 N 0.5 Using ) (1.4 μm), Mo2C (3.6 μm), and Ni (2.5 μm), TiC-, Ti(C 0.7 N 0.3 )-,Ti(C 0.5 N 0.5 The present invention discloses TiC-based and Ti(C,N)-based cermets with a composition of )-19 mass% Mo2C-24 mass% Ni. However, Ti(C,N)-based cermets have the problem of easily generating fine powder when mixed with other powders and being prone to cracking when thick-walled products are sintered.

[0008] Japanese Patent Application Publication No. 3-281752 Patent No. 2674243

[0009] Takayuki Shoji, et al., "Elucidation of the cause of sintering cracking in Ti(C,N)-based cermets and development of prevention methods," Powder and Powder Metallurgy, Vol. 57, No. 8, August 2010, pp. 579-586.

[0010] Therefore, the object of the present invention is to provide a lightweight hard alloy that achieves both weight reduction and high toughness, and also has excellent grindability, and a lightweight hard alloy member that is suitable as a wear-resistant component that rotates, such as a screw or a grinding blade, using the same.

[0011] To address the aforementioned issues, we investigated the causes of the low toughness of TiC-based and Ti(C,N)-based cermets, identified the required factors, and attempted to improve toughness at the same hardness level by designing alloys accordingly.

[0012] First, we re-examined the titanium compound powder, which is the main component. Conventionally, for example, Ti(C,N) powder produced by the heated carbonitride method is widely used. However, when the powder is crushed and classified after carbonitride to adjust to the desired particle size, fine particles tend to be generated. As a result, there are many fine particles at the raw material powder stage used in alloy production, and the amount of fine particles increases further during mixing due to further crushing. Due to the generation of these fine particles, a large amount of fine-grained hard phase is generated in the sintered body structure, while the surrounding structure (rim phase) of the relatively larger-grained hard phase becomes more prone to growth. As a result, it was found that the hard phase / hard phase bonding interface increases, making it easier for cracks to propagate and reducing hardness.

[0013] As a result of various studies to solve these problems, the inventors of the present invention have found that by observing the cross-sectional structure of a lightweight hard alloy obtained with a scanning electron microscope, they can obtain a lightweight hard alloy with excellent toughness and high strength when, in the grain size distribution of the core phase of a hard phase having a core-rim structure, the average grain size of the core phase with a D90 or higher particle size on a number basis is 0.8 to 3.3 μm, and the average ratio Dmax / Dmin of the shortest length Dmin to the longest length Dmax of the straight line connecting the centroid and contour of the core phase with a D90 or higher particle size is 2.0 or less.

[0014] Furthermore, when a titanium compound consisting of titanium carbide and / or titanium carbonitride containing a small amount of oxygen is used as the raw material powder for the lightweight hard alloy, it is less likely to be pulverized by mixing and grinding, and less fine powder is generated. In addition, it was found that the resulting sintered alloy retains a large amount of core phase with excellent wear resistance, and peripheral structures are less likely to form. It was also found that when the ratio of oxygen content in the hard core phase to the oxygen content in the rim phase (core phase oxygen content / rim phase oxygen content) is 0.9 or higher, an alloy with high toughness can be obtained.

[0015] That is, the lightweight hard alloy according to the first embodiment of the present invention is a lightweight hard alloy comprising a hard phase having a core-rim structure, obtained by sintering a mixed powder mainly composed of a titanium compound consisting of titanium carbide and / or titanium carbonitride, containing 5 to 33% by mass of W and / or Mo in terms of carbide, and containing 5 to 40% by mass of at least one selected from the group consisting of Ni, Co and Fe as a binder phase component, wherein, in the cross-sectional structure of the lightweight hard alloy observed with a scanning electron microscope, the average particle size of the core phase of the hard phase having a core-rim structure is 0.8 to 3.3 μm on a number basis in the particle size distribution of the area circle diameter of the core phase, and the average ratio Dmax / Dmin of the shortest length Dmin to the longest length Dmax of the straight line connecting the centroid and contour of the core phase of the D90 or higher is 2.0 or less.

[0016] A lightweight hard alloy according to a second embodiment of the present invention is a lightweight hard alloy comprising a hard phase having a core-rim structure, obtained by sintering a mixed powder mainly composed of a titanium compound consisting of titanium carbide and / or titanium carbonitride, containing 5 to 33% by mass of W and / or Mo in terms of carbide, and containing 5 to 40% by mass of at least one selected from the group consisting of Ni, Co and Fe as a binder phase component, wherein the titanium compound contains 0.7% by mass or more of oxygen, and the ratio of the amount of oxygen in the core phase to the amount of oxygen in the rim phase of the hard phase (core phase oxygen amount / rim phase oxygen amount) is 0.9 or more.

[0017] The titanium compound preferably contains 0.7 to 2.5% by mass of oxygen.

[0018] When the amount of particles with a particle size of 0.8 μm or less contained in the mixed powder is A (volume %), it is preferable that the particle amount A satisfies the following formula (1): A < -1.3X + 53.4 ... (1) or is 20 volume percent or less, with respect to the content X (volume %) of at least one selected from the group consisting of Ni, Co, and Fe contained in the mixed powder.

[0019] Preferably, the mixed powder further contains 8% by mass or less of Cr on a Cr3C2 basis.

[0020] The mixed powder preferably contains 15% by mass or less of elements from groups 4 to 6 of the periodic table other than Ti, W, Mo, and Cr, on a carbide basis.

[0021] A lightweight hard alloy according to a third embodiment of the present invention is a lightweight hard alloy mainly composed of a titanium compound consisting of titanium carbide and / or titanium carbonitride, and including a hard phase having a core-rim structure, characterized in that, in the cross-sectional microstructure of the lightweight hard alloy observed with a scanning electron microscope, the average particle size of the core phase of the hard phase having a core-rim structure is 0.8 to 3.3 μm on a number basis, and the average ratio Dmax / Dmin of the shortest length Dmin to the longest length Dmax of the straight line connecting the centroid and contour of the core phase of D90 or higher is 2.0 or less.

[0022] In this embodiment, it is preferable to sinter a mixed powder containing a titanium compound mainly composed of titanium carbide and / or titanium carbonitride.

[0023] A lightweight hard alloy according to a fourth embodiment of the present invention is a lightweight hard alloy comprising a hard phase having a core-rim structure, obtained by sintering a mixed powder mainly composed of a titanium compound consisting of titanium carbide and / or titanium carbonitride, wherein the titanium compound contains 0.7% by mass or more of oxygen, and the ratio of the amount of oxygen in the core phase to the amount of oxygen in the rim phase of the hard phase (core phase oxygen amount / rim phase oxygen amount) is 0.9 or more.

[0024] The titanium compound preferably contains 0.7 to 2.5% by mass of oxygen.

[0025] It is preferable that the nitrogen content of the titanium compound is 0.7% by mass or more and less than 8% by mass.

[0026] A lightweight hard alloy member according to one embodiment of the present invention is characterized by using the above-mentioned lightweight hard alloy.

[0027] According to the present invention, a lightweight, hard alloy is obtained that achieves both weight reduction and high toughness, is less prone to cracking during sintering even in thick-walled products, and has excellent grindability. As a result, it can be suitably used in wear-resistant components that are large in size and rotate at high speeds, such as screws and grinding blades, and production efficiency in grinding, mixing, and kneading can be dramatically improved. For example, it is suitable for tools and grinding blades for grinding, mixing, and kneading resins and magnetic materials. Also, because it has similar characteristics, it is suitable for molds and peripheral components for lens molding.

[0028] This is a schematic diagram showing a method for measuring the ratio Dmax / Dmin, which is the ratio of the shortest length Dmin to the longest length Dmax of a straight line connecting the centroid and contour of a core phase with a nearly circular cross-section. This is a schematic diagram showing a method for measuring the ratio Dmax / Dmin, which is the ratio of the shortest length Dmin to the longest length Dmax of a straight line connecting the centroid and contour of a core phase with a vertically elongated cross-section. This is an SEM image showing a cross-section of the lightweight hard alloy of Invention 8. This is an SEM image showing a cross-section of the lightweight hard alloy of Invention 13.

[0029] [1] Lightweight hard alloy (1) First embodiment The lightweight hard alloy according to the first embodiment of the present invention is a lightweight hard alloy mainly composed of a titanium compound consisting of titanium carbide and / or titanium carbonitride, and including a hard phase having a core-rim structure, characterized in that, in the cross-sectional structure of the lightweight hard alloy observed with a scanning electron microscope, the average particle size of the core phase of the hard phase having a core-rim structure is 0.8 to 3.3 μm on a number basis, and the average ratio Dmax / Dmin of the shortest length Dmin to the longest length Dmax of the straight line connecting the centroid and contour of the core phase of D90 or higher is 2.0 or less.

[0030] The main component is a titanium compound containing carbon, specifically at least one compound selected from the group consisting of titanium carbide and titanium carbonitride. The total amount of titanium compound may also include up to 5% by mass of titanium nitride. Since titanium compounds containing carbon have high hardness and excellent wear resistance, including them as the main component yields a lightweight, hard alloy with excellent wear resistance.

[0031] Here, "main component" refers to the carbon-containing titanium compound being the largest component by mass ratio among the other components. It is desirable that the mass ratio of the titanium compound to the total amount of other components is greater than 50%, and that the carbon-containing titanium compound is 1.5 to 5 times, and more preferably 2 to 4 times, the total amount of the other components by mass ratio.

[0032] In the particle size distribution of the core phase of the hard phase having a core-rim structure, the average particle size of the core phase with a D90 or higher value, based on the number of particles, is 0.8 to 3.3 μm. If the average particle size of the core phase is less than 0.8 μm, the wear resistance may be slightly inferior depending on the usage conditions. If the average particle size of the core phase is greater than 3.3 μm, the strength will be insufficient. The average particle size of the core phase is preferably 0.9 to 3.0 μm, more preferably 1.0 to 2.8 μm, and even more preferably 1.2 to 2.6 μm. The reason for limiting the average particle size of the core phase to core phases with a D90 or higher value is that the average particle size of the core phase in this range has a significant impact on the wear resistance and strength of the lightweight hard alloy. The influence of the pulverization state of the titanium compound in the mixed powder, which will be described later, is also briefly shown.

[0033] The average grain size of core phases with a D of 90 or higher is determined by taking 10 field-of-view SEM images (5,000x magnification) of any cross-sectional SEM structure of the lightweight hard alloy, processing the images, determining the grain size distribution based on the number of core phases with a diameter of 0.2 μm or more from the diameter obtained by converting the area of ​​each core phase to a circle, and then averaging the grain size of the core phases with a D of 90 or higher. These operations can be performed by analyzing the image using general image analysis software such as Image-Pro Plus. Alternatively, an arbitrary cross-section of the lightweight hard alloy may be engraved, and the analysis may be performed based on the SEM structure of the engraved cross-section. The mixed powder in this embodiment is a mixed powder prepared by using a titanium compound powder with a small amount of fine powder to reduce the crushing strength, and therefore the lightweight hard alloy obtained by sintering such a mixed powder has these structural characteristics.

[0034] The ratio Dmax / Dmin of the shortest length Dmin to the longest length Dmax of the straight line connecting the centroid of the core phase with a D90 or above to the contour is 2.0 or less. Here, the measurement methods of the shortest length Dmin and the longest length Dmax will be described using FIGS. 1 and 2. FIGS. 1 and 2 are schematic diagrams showing cross-sections of hard phases having a core rim structure of a lightweight cemented carbide observed with a scanning electron microscope. The centroid of the core phase among the hard phases having a core rim structure is determined, and among the straight lines connecting the centroid to the contour of the core phase, the shortest length is taken as Dmin and the longest length is taken as Dmax. As shown in FIG. 1, when the core phase is close to a sphere (the cross-section of the core phase is close to a circle), the ratio Dmax / Dmin of the shortest length Dmin to the longest length Dmax is small. As shown in FIG. 2, when the core phase is vertically long (the cross-section of the core phase is vertically long), the ratio Dmax / Dmin of the shortest length Dmin to the longest length Dmax is large.

[0035] It is desirable that 60% or more of the core phases with a D90 or above in the core phase particle size distribution of the hard phase having a core rim structure satisfy the ratio Dmax / Dmin ≤ 2.0. Thereby, a lightweight cemented carbide with excellent toughness and high strength can be obtained. More preferably, 65% or more of the core phase is satisfied, even more preferably 70% or more of the core phase is satisfied, even more preferably 75% or more is satisfied, particularly preferably 80% or more is satisfied, and most preferably 90% is satisfied.

[0036] It is preferable that the average value of the ratio Dmax / Dmin of the core phase in the hard phase having a core rim structure is 2.0 or less. Similar to the average particle size of the core phase, the average value of the ratio Dmax / Dmin is obtained by taking 10 fields of view of an arbitrary cross-section SEM structure (5,000 times) of the lightweight cemented carbide for image processing, converting the area of each core phase into the diameter of a circle, obtaining the particle size distribution based on the number of core phases with a diameter of 0.2 μm or more, and averaging the values of the ratio Dmax / Dmin of each core phase with a D90 or above. It is particularly preferable that 60% or more of the core phases in the hard phase having a core rim structure satisfy the ratio Dmax / Dmin ≤ 2.0 and the average value is 2.0 or less. Thereby, a lightweight cemented carbide with particularly excellent toughness and high strength can be obtained.

[0037] When the average particle size of the core phase is 0.8 to 3.3 μm and the ratio Dmax / Dmin of the shortest length Dmin to the longest length Dmax of the straight line connecting the center of gravity to the contour is 2.0 or less, an alloy with excellent toughness and high strength can be obtained. The ratio Dmax / Dmin is preferably 1.9 or less, more preferably 1.8 or less.

[0038] The number of hard phases having a core-rim structure is preferably 30% or more, more preferably 45% or more, still more preferably 60% or more, and particularly preferably 70% or more based on the total number of hard phases. The number of hard phases is determined as the number of hard phases with a diameter of 0.2 μm or more among the diameters obtained by converting the area of each hard phase into a circle by photographing 10 fields of the SEM structure (5,000 times) of an arbitrary cross-section of the lightweight hard alloy and performing image processing. Among these hard phases with a diameter of 0.2 μm or more, those with an observable core-rim structure are defined as hard phases having a core-rim structure.

[0039] The average particle size of the hard phase is preferably 0.8 to 3.5 μm. The average particle size of the hard phase is determined by the Fullman formula based on the SEM structure of an arbitrary cross-section of the lightweight hard alloy. When the average particle size of the hard phase is less than 0.8 μm, the wear resistance may be slightly inferior depending on the usage conditions. When the average particle size of the hard phase exceeds 3.5 μm, the strength is insufficient. The average particle size of the hard phase is more preferably 0.9 to 3.0 μm, still more preferably 1.1 to 2.8 μm, and particularly preferably 1.3 to 2.6 μm.

[0040] An example of the lightweight hard alloy according to the first embodiment of the present invention is obtained by sintering a mixed powder mainly composed of a titanium compound composed of titanium carbide and / or titanium carbonitride, containing 5 to 33% by mass of WC and / or Mo2C, and containing 5 to 40% by mass of at least one selected from the group consisting of Ni, Co, and Fe as a bonding phase component. In the cross-sectional structure of the lightweight hard alloy observed by a scanning electron microscope, in the particle size distribution of the area circle conversion diameter of the core phase among the hard phases having a core-rim structure, the average particle size of the core phase with D90 or more is 0.8 to 3.3 μm, and the average of the ratio Dmax / Dmin of the shortest length Dmin to the longest length Dmax of the straight line connecting the center of gravity of the core phase with D90 or more to the contour is 2.0 or less.

[0041] The mixed powder contains 5 to 33% by mass of WC and / or Mo2C. If the WC and / or Mo2C content is less than 5% by mass, the surrounding structure may not be sufficiently formed in the hard phase of the lightweight hard alloy, making it difficult to control the particle size and resulting in insufficient strength. On the other hand, if the WC and / or Mo2C content exceeds 33% by mass, the hardness of the lightweight hard alloy may be too high, potentially reducing its toughness. The WC and Mo2C content is preferably 7 to 30% by mass, and more preferably 10 to 26% by mass. The titanium compound consisting of titanium carbide and / or titanium carbonitride, WC, and Mo2C are used as the hard phase constituent particles. The mixed powder may contain only Mo2C. The mass ratio of WC to Mo2C (WC / Mo2C ratio) is preferably 0.11 to 1, more preferably 0.25 to 0.67, and even more preferably 0.25 to 0.43. Furthermore, to improve high-temperature properties such as high-temperature deformation, the WC / Mo2C ratio may be set to 1 to 9, or WC alone, if necessary for the application.

[0042] The mixed powder preferably contains 8% by mass or less of Cr in terms of Cr3C2. This can improve the corrosion resistance of the lightweight hard alloy. If the Cr content exceeds 8% by mass in terms of Cr3C2, the toughness may decrease. The Cr may be added as a carbide or nitride, or as an alloy with Ni or Cr. The Cr content is more preferably 0.1 to 5% by mass in terms of Cr3C2, and more preferably 0.5 to 4% by mass.

[0043] At least a portion of WC, Mo2C, and Cr3C2 may be added as a solid solution with other elemental compounds such as titanium compounds.

[0044] The mixed powder may also contain 15% by mass or less of group 4-6 elements of the periodic table other than Ti, W, Mo, and Cr, in terms of carbides. Furthermore, group 4-6 elements other than Ti, W, Mo, and Cr may be added as solid solutions with other elemental compounds such as titanium compounds. Even when other elements are included in the titanium compound, the core can be identified by the difference in brightness, as in the case of alloys using titanium compounds without other elements, or by using areas with different color tones along the core phase / rim phase boundary as a guide to identify the core shape.

[0045] Adding 0.1 to 3% by mass of Zr (calculated as carbide) to the mixed powder improves wear resistance. Below 0.1% by mass, no effect is observed. Above 3% by mass, there is a risk of reducing sinterability. Zr may be added to the mixed powder as a metal, as a carbide, nitride, oxide, or solid solution compound thereof, or as a solid solution in other compounds such as titanium compounds.

[0046] Preferably, the total amount of Group 4 to 6 elements of the periodic table other than Ti that are solid-solved in the titanium compound is 30% by mass or less in terms of carbides relative to the titanium compound.

[0047] In the lightweight hard alloy of this embodiment, some of the W, Mo, and Cr in WC, Mo2C, and Cr3C2, as well as some of the above-mentioned group 4 to 6 elements, form a periphery of the hard phase as a solid solution with a carbon-containing titanium compound. That is, the hard phase forms a core-rim structure with a periphery surrounding a core mainly composed of a titanium compound. Some of these elements also form a solid solution in the binder phase.

[0048] It is preferable that the nitrogen content of the titanium compound be less than 8% by mass. If the nitrogen content of titanium is 8% by mass or more, while it is effective in improving wear resistance due to the retention of the titanium carbonitride core phase and improving strength and alloy hardness by suppressing grain growth of the hard phase, it also worsens grindability and increases the processing time of wear-resistant members, leading to problems such as decreased productivity and increased costs. Furthermore, it is preferable that the nitrogen content of the titanium compound be 0.7% by mass or more. If the nitrogen content is less than 0.7% by mass, fine powder generation is more likely to occur during mixed grinding compared to cases where the nitrogen content is higher.

[0049] The mixed powder contains 5 to 40% by mass of at least one selected from the group consisting of Ni, Co, and Fe as a binder phase component. If this content is less than 5% by mass, the required strength of the lightweight hard alloy cannot be maintained, and if it exceeds 40% by mass, the required wear resistance cannot be maintained. The content of the binder phase component is preferably 10 to 38% by mass, and more preferably 16 to 36% by mass.

[0050] With respect to the entire mixed powder, as the Co content increases, the alloy hardness tends to increase and the wear resistance tends to improve. However, since the wettability with the hard phase decreases, the sinterability decreases, and cracks tend to progress due to the decrease in the interfacial strength. Therefore, when toughness is emphasized, the Co content should be 9.5 mass% or less.

[0051] It is preferable that the BET value of the mixed powder × the theoretical specific gravity is 38 or less. The BET value is the total surface area per unit weight (1 g) of the mixed powder measured by the BET method, expressed in square meters. It corresponds to the specific surface area (m 2 / g) of the mixed powder. The theoretical specific gravity of the mixed powder is calculated from the specific gravity and composition ratio of each raw material powder used. The BET value of the mixed powder × the theoretical specific gravity is a dimensionless number.

[0052] Here, the significance of the parameter of the BET value × the theoretical specific gravity will be explained. The mixed powder of the lightweight hard alloy of this example contains a titanium compound containing carbon as the main component of the hard phase constituent particles and contains WC and / or Mo2C. The specific gravity of WC is 15.6, and the specific gravity of Mo2C is 9.18. On the other hand, for example, the specific gravity of TiC is 4.92, and there is a large difference in the specific gravity of each component. Therefore, the specific gravity of the mixed powder changes greatly depending on their content ratio. As a result, the amount of powder per unit weight (1 g) also changes, so the BET value cannot fully represent the characteristics of the mixed powder. Therefore, by multiplying the BET value by the theoretical specific gravity of the mixed powder, the specific surface area of the powder per volume when the mixed powder is considered as a dense body is used as an index.

[0053] If the BET value × theoretical specific gravity of the mixed powder exceeds 38, the specific surface area per unit volume of the mixed powder becomes too large, resulting in a large amount of fine powder being present in the mixed powder, or the average particle size of the mixed powder becoming too small. This makes it easier for a fine hard phase to form in the lightweight hard alloy, and the dissolution and reprecipitation of the fine powder also makes it easier for a peripheral structure (rim phase) to form around the hard phase. The peripheral structure has low strength, and as the adhesion of the hard phase increases with the formation of the peripheral structure, the fracture toughness also decreases, resulting in insufficient strength and a tendency to chip. It is more preferable for the BET value × theoretical specific gravity of the mixed powder to be 37 or less, even more preferable to be 36 or less, and particularly preferable to be 35 or less. This suppresses the formation of a low-strength peripheral structure and the increase in the adhesion of the hard phase, resulting in an alloy in which a large amount of the core phase of the titanium compound phase, which has high strength and excellent wear resistance, remains, and a lightweight hard alloy with excellent wear resistance and chip resistance can be obtained when used as a tool. If a mixed powder is obtained in which the average particle size of the hard phase constituting the sintered body of the lightweight hard alloy does not exceed 3.5 μm, there is no lower limit to the BET value × theoretical specific gravity.

[0054] When the amount of particles with a particle size of 0.8 μm or less contained in the mixed powder is A (volume %) (assuming the entire mixed powder is 100 volume%), it is preferable that the particle amount A satisfies the following formula (1): A < -1.3X + 53.4 ... (1) or is 20 volume % or less, relative to the content X (volume %) of at least one selected from the group consisting of Ni, Co, and Fe contained in the mixed powder. The particle size distribution of the mixed powder may be measured using a laser diffraction particle size distribution analyzer. From the obtained particle size distribution of the mixed powder, the amount A of particles with a particle size of 0.8 μm or less is calculated as a volume ratio. When the particle amount A satisfies A < -1.3X + 53.4 or is 20 volume % or less, it becomes difficult for a fine hard phase to form in the lightweight hard alloy structure, and because there is a small amount of fine powder, peripheral structures are less likely to form due to melting and reprecipitation during sintering. It is more preferable that the particle amount A satisfies A < -1.3X + 53.4, and even more preferable that the particle amount A satisfies A ≤ -X + 41.3. The particle amount A may satisfy A < -1.3X + 53.4, or be 20% or less by volume of the total mixed powder. Also, the particle amount A may be 20% or less by volume of the total mixed powder.

[0055] (2) Second Embodiment The lightweight hard alloy according to the second embodiment of the present invention is a lightweight hard alloy comprising a hard phase having a core-rim structure, which is obtained by sintering a mixed powder mainly composed of a titanium compound consisting of titanium carbide and / or titanium carbonitride, wherein the titanium compound contains 0.7% by mass or more of oxygen, and the ratio of the amount of oxygen in the core phase of the hard phase to the amount of oxygen in the rim phase (core phase oxygen amount / rim phase oxygen amount) is 0.9 or more.

[0056] The main component is a titanium compound containing carbon, specifically at least one compound selected from the group consisting of titanium carbide and titanium carbonitride. The total amount of titanium compound may also include up to 5% by mass of titanium nitride. Since titanium compounds containing carbon have high hardness and excellent wear resistance, including them as the main component yields a lightweight, hard alloy with excellent wear resistance.

[0057] Here, "main component" refers to the carbon-containing titanium compound being the largest component by mass ratio among the other components. It is desirable that the mass ratio of the titanium compound to the total amount of other components is greater than 50%, and that the carbon-containing titanium compound is 1.5 to 5 times, and more preferably 2 to 4 times, the total amount of the other components by mass ratio.

[0058] In the second embodiment, the titanium compound in the mixed powder contains 0.7% by mass or more of oxygen. By using titanium compound powder containing 0.7% by mass or more of oxygen, the generation of fine particles from the titanium compound powder is reduced, and the thickness of the rim phase of the hard phase of the resulting lightweight hard alloy can be reduced, thereby increasing its toughness. Furthermore, by including an appropriate amount of oxygen in the titanium compound powder, an effect of suppressing rim phase growth can also be expected.

[0059] In this embodiment, the lightweight hard alloy has a ratio of oxygen content in the core phase to oxygen content in the rim phase of the hard phase (core phase oxygen content / rim phase oxygen content) of 0.9 or more. This configuration can be obtained by using titanium compound powder containing 0.7 mass% or more oxygen. The amount of oxygen dissolved in TiC, WC, Mo2C, and Ni is usually small, around 0.3 mass% or less, but the surface area increases due to mixing and grinding, which increases adsorbed oxygen and thus increases the oxygen content of the mixed powder. When a molded body of this mixed powder is sintered, the rim phase contains a large amount of oxygen due to adsorbed oxygen, so the oxygen content of the rim phase becomes greater than the oxygen content of the core phase (core phase oxygen content / rim phase oxygen content), and the ratio becomes less than 0.9. On the other hand, when a titanium compound containing 0.7 mass% or more oxygen is used as the main component, the core phase, which consists of such a titanium compound phase, has a large amount of oxygen, so the ratio of oxygen content in the core phase to oxygen content in the rim phase of the hard phase (core phase oxygen content / rim phase oxygen content) becomes 0.9 or more. The above ratio is preferably 0.95 or higher, more preferably 1.0 or higher, and even more preferably 1.05 or higher.

[0060] The oxygen content in the titanium compound powder is preferably 0.7 to 2.5% by mass. An oxygen content higher than 2.5% by mass reduces sinterability. The oxygen content in the titanium compound powder is preferably 0.8 to 2.4% by mass, more preferably 1.0 to 2.3% by mass, and even more preferably 1.2 to 2.2% by mass.

[0061] The nitrogen content in the titanium compound powder is preferably 0.7% by mass or more and less than 8% by mass. If the oxygen content is less than 0.7% by mass, fine powder generation is more likely to occur during mixing and grinding compared to when it is not, and if it is 8% by mass or more, the grindability of the sintered alloy will decrease. The nitrogen content in the titanium compound powder may be 0.7 to 2.5% by mass. When the oxygen content in the titanium compound powder is 0.7 to 2.5% by mass and the nitrogen content is 0.7% by mass or more and less than 2.5% by mass, it is particularly difficult to grind even during mixing and grinding, and fine powder is less likely to be generated. As a result, a large amount of core phase with excellent wear resistance remains in the sintered alloy, peripheral structures are less likely to form, and a lightweight, hard alloy with high toughness can be obtained.

[0062] When both the oxygen and nitrogen content is less than 0.7% by mass, fine powder generation is more likely to occur during mixing and grinding compared to cases where the oxygen and nitrogen content is higher. The fact that titanium compounds containing appropriate amounts of oxygen and nitrogen do not generate fine powder during mixing and grinding indicates that the titanium compound itself has high toughness. As a result, as mentioned above, peripheral structures are less likely to form during sintering, more core phase remains, the degree of adhesion between hard phases is reduced, and the toughness of the sintered alloy is increased. At the same time, by setting the ratio of hard phases with a core-rim structure (oxygen content of core phase / oxygen content of rim phase) to 0.9 or higher, the toughness of the core part of the core-rim structure itself is also increased. Therefore, compared to sintered alloys with a ratio less than 0.9, fine chipping is less likely to occur during tool use, and wear resistance is also higher.

[0063] The number of hard phases having a core-rim structure is preferably 25% or more of the total number of hard phases, more preferably 40% or more, even more preferably 55% or more, and particularly preferably 65% ​​or more. The number of hard phases is determined by taking 10 field-of-view images (5,000x magnification) of the SEM structure of any cross-section of the lightweight hard alloy, processing the images, and calculating the number of hard phases with a diameter of 0.2 μm or more from the diameter of each hard phase converted to a circle. Among these hard phases with a diameter of 0.2 μm or more, those in which a core-rim structure can be observed are defined as hard phases having a core-rim structure.

[0064] An example of a lightweight hard alloy according to a second embodiment of the present invention is a lightweight hard alloy comprising a hard phase having a core-rim structure, obtained by sintering a mixed powder mainly composed of a titanium compound consisting of titanium carbide and / or titanium carbonitride, containing 5 to 33% by mass of WC and / or Mo2C, and containing 5 to 40% by mass of at least one selected from the group consisting of Ni, Co, and Fe as a binder phase component, wherein the titanium compound contains 0.7% by mass or more of oxygen, and the ratio of the amount of oxygen in the core phase to the amount of oxygen in the rim phase of the hard phase (core phase oxygen amount / rim phase oxygen amount) is 0.9 or more.

[0065] The composition of the mixed powder used in this embodiment may be the same as that of the embodiment in the first embodiment. Furthermore, explanations of other parts common to the first embodiment will be omitted.

[0066] The lightweight hard alloy according to the second embodiment of the present invention, as in the first embodiment, has a particle size distribution of area-circular diameter of the core phase among the hard phases having a core-rim structure, where the average particle size of the core phases with a D90 or higher particle size is 0.8 to 3.3 μm on a number basis, and the average ratio Dmax / Dmin of the shortest length Dmin to the longest length Dmax of the straight line connecting the centroid and contour of the core phases with a D90 or higher particle size may be 2.0 or less. If the titanium compound in the mixed powder contains 0.7 mass% or more of oxygen, fine powder is less likely to be generated, and a large amount of core phase with excellent wear resistance remains in the sintered alloy, making it easier to obtain a hard phase having the above-mentioned core-rim structure.

[0067] In the second embodiment of the present invention, similar to the first embodiment, it is preferable that the BET value × theoretical specific gravity of the mixed powder is 38 or less. In a lightweight hard alloy containing a hard phase having a core-rim structure, which is obtained by sintering a molded body of a mixed powder mainly composed of a titanium compound consisting of titanium carbide and / or titanium carbonitride, if the titanium compound contains 0.7 mass% oxygen, the ratio of the oxygen content of the core phase to the oxygen content of the rim phase of the hard phase (core phase oxygen content / rim phase oxygen content) is 0.9 or more, and the BET value × theoretical specific gravity of the mixed powder is 38 or less, then it is possible to suppress the formation of a peripheral structure with low strength and an increase in the adhesion of the hard phase, and to obtain a lightweight hard alloy with excellent toughness and high strength.

[0068] [2] Method for producing lightweight hard alloys As an example of a method for producing lightweight hard alloys of the present invention, a lightweight hard alloy can be obtained by blending the powders of the hard phase constituent particles and the binder phase constituent particles described above, wet mixing and grinding them in an organic solvent, drying them, and then press-molding the powder to which a binder such as paraffin has been added to form a molded body, and then sintering the molded body.

[0069] The molded body of the mixed powder may be formed into a shape close to the finished product (near-net shape) by press molding, or it may be further machined to give it a predetermined shape. Alternatively, it may be machined to give it a predetermined shape after pre-sintering.

[0070] The sintering atmosphere can be a vacuum or an inert gas. When sintering a molded body made from a nitrogen-containing powder mixture, nitrogen or a nitrogen-containing gas mixture may be used, or CO gas may be used. The introduction temperature and gas pressure of these atmospheric gases may be varied depending on the purpose. The heating rate, sintering temperature and holding time, as well as the temperature holding and gas pressure during the process, can be arbitrarily selected depending on the purpose, such as degreasing, improving sinterability, adjusting the structure and composition of the surface layer, and improving surface properties.

[0071] Titanium compounds include TiC produced by the Menstrum process, and Ti(C,N) produced by heating and carbiditrating metallic titanium, titanium hydride, and titanium oxide as the main raw materials. In many cases, the particle size range is controlled by crushing and classifying the finished titanium compound. This crushing process generates powder that is much finer than the target particle size. It has been found that the presence of a certain amount of this fine powder in the titanium compound powder is one of the reasons for the low toughness of lightweight hard alloys. To improve the toughness of lightweight hard alloys using this titanium compound powder, the amount of fine powder contained in the mixed powder before sintering should be reduced.

[0072] Therefore, it is necessary to select mixing conditions that do not easily generate fine powder. The conditions must be such that a predetermined average particle size can be obtained even with a short mixing time. For example, in the case of mixing and grinding with a ball mill, mixing conditions such as the ball mill rotation speed, powder amount, solvent amount, ball amount, ball diameter, ball material, and mixing and grinding time can be set, but any of the parameters can be changed, and the specific surface area (m²) of the mixed powder can be changed. 2 It was found that the value obtained by multiplying the theoretical specific gravity (per g) by 38 or less is crucial. Furthermore, in the process of investigating this, it was found that some raw material powders contain fine particles at the raw material stage, as mentioned above, and that fine particles can be removed by various methods such as classification, or that the same effect can be obtained by using titanium compound powder with fewer fine particles.

[0073] The sintering temperature is preferably set to 1330-1450°C to avoid excessive growth of the surrounding microstructure of the hard phase. Depending on the application, sintering may be performed by sinter-HIP, or a conventionally sintered body may be subjected to HIP treatment. Sintering may be performed by hot press sintering, or by electromagnetic energy-assisted sintering such as electrosintering or SPS sintering.

[0074] [3] Lightweight Hard Alloy Components The lightweight hard alloy of the present invention is suitably used for wear-resistant components that are large in size and rotate at high speeds, such as screws and crushing blades. Therefore, lightweight hard alloy components using the lightweight hard alloy of the present invention can exhibit excellent performance when used, for example, as components for crushing, mixing, or kneading. Furthermore, the lightweight hard alloy of the present invention is not limited to these applications, and because it is less prone to cracking during tool use, it can be used in punching punches, molding dies at room temperature, warm, and hot, extrusion dies, molds, and forging punches. In addition, because it is less prone to chipping or cracking during handling, it is effective to use it in peripheral components for lens molding, such as barrel molds for special lenses with a large coefficient of thermal expansion.

[0075] The lightweight, hard alloy components of the present invention are effective not only in wear-resistant tools and components as described above, but also in cutting tools such as insert tips, end mills, and drills. Furthermore, the lightweight, hard alloy components of the present invention may be coated with a hard coating on their surface by DLC or PVD, or, depending on the application, by CVD.

[0076] The present invention will be described in more detail by reference to examples, but the present invention is not limited thereto.

[0077] Example 1: As raw material powders, TiC powder (1.4 μm, 1.5 μm, 1.6 μm, 3.5 μm), Ti(C) 0.7 N 0.3 The following powders were prepared: (Ti,Mo)(C,N) powder (1.6 μm, 1.7 μm), (Ti,Mo)(C,N) powder (1.5 μm), (Ta,Nb)C powder (Ta:Nb=9:1, 2.1 μm), WC powder (0.6 μm), Mo2C powder (3.2 μm), Cr3C2 powder (1.3 μm), Ni powder (2.4 μm), Co powder (1.9 μm), and Fe powder (3.5 μm). The numbers in parentheses indicate the average particle size measured by the Fischer particle size determination method (FSSS method). The (Ti,Mo)(C,N) powder has the composition Ti(C 0.7 N 0.3 The mixed powder was subjected to a solid solution treatment by heat treatment in nitrogen to obtain a solid solution with a concentration of -25 mass% Mo2C, and the resulting solid solution was pulverized and classified (oxygen content 0.51 mass%, nitrogen content 5.56 mass%). The TiC powder and Ti(C) used in this example 0.7 N0.3 The powder contains oxygen and nitrogen in the amounts shown in Table 2. These raw material powders were weighed so that the sintered bodies had the compositions of each sample shown in Table 1.

[0078] TiC powder and Ti(C) 0.7 N 0.3 SEM observation was performed on titanium compound raw material powders, specifically (Ti,Mo)(C,N) powder. Those with relatively few fine particles were classified as "low," while those with a relatively large amount of fine particles, likely due to pulverization and classification, were classified as "high." The results are shown in Table 2.

[0079] The weighed powders were mixed and wet-mixed and ground using a ball mill. For the invention, the mixing and grinding conditions were adjusted while considering the amount of fine powder contained in the titanium compound raw material powder so that the BET value × theoretical specific gravity was 38 or less and the average particle size of the hard phase of the resulting sintered body was within the range of 0.8 to 3.5 μm. The grinding intensity level was set as "2" for normal intensity, "1" for weaker intensity, "3" for stronger intensity, and "4" for grinding intensity stronger than level "3". The grinding levels of the mixed powders for each sample are shown in Table 3.

[0080] The powder, after grinding and mixing, was dried using a vacuum dryer, and the particle size distribution of the resulting mixed powder was measured using an MT3300EXII (Microtrac Bell Co., Ltd.). The amount A of particles with a particle size of 0.8 μm or less was calculated as a volume ratio. The results are shown in Table 3.

[0081] The BET value of the mixed powder was measured using TriStarII3020 (Micromeritics). The theoretical specific gravity of the mixed powder was calculated from the specific gravity and composition ratio of the raw material powders for each sample. Table 3 shows the BET value multiplied by the theoretical specific gravity for each sample.

[0082] A binder is added to the mixed powder, resulting in a 98 N / mm² 2 After compacting the powder into a cylindrical shape with dimensions φ20 × 20 H (mm) under pressure, the material was sintered at a sintering temperature of 1400°C for 1 hour to produce Invention 1 to 16 and Comparative 1 to 4. Test specimens for flexural strength testing were prepared by compacting the powder into a rectangular parallelepiped with dimensions 6 × 11 × 31 (mm) and then using the same method.

[0083] The Vickers hardness of each sample was measured using a Vickers hardness tester HV (294N). The results are shown in Table 4.

[0084] The sintered body of each sample was cut, and the cross-section was mirror-polished. Then, SEM images (magnification: 8,000x) showing the polished cross-section were taken using a Regulus8100 (Hitachi High-Tech Corporation). The average grain size of the hard phase was determined using the SEM images. The average grain size of the hard phase was calculated using Fulman's formula. The results are shown in Table 4.

[0085] Using SEM images (magnification: 5,000x) showing the polished cross-section of the sample described above, the average particle size of the core phase with a D90 or higher particle size was determined based on the number of particles in the particle size distribution of the area-circular diameter of the core phase among the hard phases having a core-rim structure. The obtained results are shown in Table 4.

[0086] The oxygen content of the hard phases (core phase and rim phase) of the lightweight hard alloy was measured using an energy-dispersive X-ray spectrometer, QUANTAX FlatQUAD (manufactured by Bruker), and the ratio of the oxygen content of the core phase to the oxygen content of the rim phase (core phase oxygen content / rim phase oxygen content) was determined. The results are shown in Table 4.

[0087] Using the aforementioned SEM images, the particle size distribution of the core phase in terms of area-circular diameter was determined using Image-Pro Plus. Based on the number of particles, the shortest length Dmin and longest length Dmax of the straight line connecting the centroid and contour of the core phase with a D of 90 or higher were determined, and the average value of the ratio Dmax / Dmin was calculated. The results are shown in Table 4.

[0088] The flexural strength of each sample was measured by a three-point bending test based on JIS R 1601. The fracture toughness value K of each sample was also measured. IC The values ​​were measured and calculated based on JIS R 1607. The results are shown in Table 4.

[0089] To evaluate the wear resistance (resistance to wear as a tool) of each sample, a blasting apparatus was used to impact each sample with SiC powder (particle size: #500) under the conditions of a projection angle of 30°, projection pressure of 0.6 MPa, and projection time of 90 seconds. The magnitude of wear of each sample after blasting was evaluated on a scale from 0 to 5. A value of "4" was assigned when the wear amount of Invention 3 was 0.9 times or more but less than 1.1 times, "5" when it was less than 0.9 times, "3" when it was 1.1 times or more but less than 1.5 times, "2" when it was 1.5 times or more but less than 1.9 times, "1" when it was 1.9 times or more but less than 2.3 times, and "0" when it was 2.3 times or more. The obtained results are shown in Table 4.

[0090] To evaluate the chipping resistance (toughness; resistance to chipping as a tool) of each sample, surface grinding was performed using a diamond wheel grinding wheel (#140) with a cutting depth of 5 μm to create a 20° sharp edge. The size of the chip at the tip of the sharp edge of each sample was evaluated on a scale from 0 to 5. A score of "4" was given when the chip width was 0.9 times or more but less than 1.1 times the chip width of Invention 3, "5" when it was less than 0.9 times, "3" when it was 1.1 times or more but less than 1.2 times, "2" when it was 1.2 times or more but less than 1.3 times, "1" when it was 1.3 times or more but less than 1.4 times, and "0" when it was 1.4 times or more. If the chipping resistance did not meet the evaluation of "1", i.e., the evaluation was "0", the wear resistance evaluation was not performed. If either the wear resistance or chipping resistance evaluation is "0", the tool cannot be used. If the evaluation for each alloy is "1" or higher and the total is "5" or higher, then an alloy that prioritizes either toughness or wear resistance, or an alloy with a good balance of toughness and wear resistance, can be selected depending on the intended use. The results are shown in Table 4.

[0091]

[0092]

[0093]

[0094]

[0095] Inventions 1 to 15 have an average particle size of the core phase with a D of 90 or higher in the range of 0.8 to 3.3 μm, and an average ratio Dmax / Dmin of the core phase with a D of 90 or higher of 2.0 or less, exhibiting excellent wear resistance and chipping resistance, as well as excellent flexural strength, enabling both weight reduction and high toughness.

[0096] Invention 12 uses a titanium compound powder with a low amount of fine particles, so its Dmax / Dmin is 2 or less. However, because the amount of oxygen contained in the powder is low at 0.19 mass%, its overall evaluation of wear resistance and chipping resistance is slightly inferior to that of the other inventions. Similarly, Invention 13 also has a Dmax / Dmin of 2 or less, but because the amount of oxygen contained in the titanium compound powder is less than the specified amount and the amount of fine particles is high, it tends to have inferior chipping resistance and wear resistance, and its overall evaluation is inferior to Inventions 6-10. Invention 16 uses a titanium compound with a low amount of fine particles, but because the mixing and grinding level is strong, the amount of fine particles is high, and its Dmax / Dmin slightly exceeds 2. However, because the amount of oxygen contained in the powder is high at 0.89 mass%, it achieves both wear resistance and chipping resistance. Comparative products 1-3 have a Dmax / Dmin greater than 2, and because the amount of oxygen contained in the powder is low at 0.59 mass%, their overall evaluation of wear resistance and chipping resistance is inferior to that of the other inventions.

[0097] SEM images (15,000x magnification) of arbitrary cross-sections of inventions 8 and 13 were taken. The obtained SEM images are shown in Figures 3 and 4. The oxygen content was determined by performing the aforementioned EDS analysis on the core phase (black, circled area) and rim phase (gray, straight line area) of each SEM image, and based on this, the ratio of the oxygen content of the core phase to the oxygen content of the rim phase of the hard phase of the lightweight hard alloy of inventions 8 and 13 was determined.

[0098] In Invention 8, the ratio of the amount of oxygen in the core phase to the amount of oxygen in the rim phase (core phase oxygen amount / rim phase oxygen amount) of the hard phase was approximately 1.13, whereas in Invention 13, the ratio of the amount of oxygen in the core phase to the amount of oxygen in the rim phase (core phase oxygen amount / rim phase oxygen amount) of the hard phase was approximately 0.69.

Claims

1. A lightweight hard alloy comprising a hard phase having a core-rim structure, obtained by sintering a mixed powder mainly composed of a titanium compound consisting of titanium carbide and / or titanium carbonitride, containing 5 to 33% by mass of W and / or Mo in terms of carbide, and containing 5 to 40% by mass of at least one selected from the group consisting of Ni, Co and Fe as a binder phase component, wherein, in the cross-sectional structure of the lightweight hard alloy observed by a scanning electron microscope, the average particle size of the core phase of the hard phase having a core-rim structure, based on the number of particles, is 0.8 to 3.3 μm, and the average ratio Dmax / Dmin of the shortest length Dmin to the longest length Dmax of the straight line connecting the centroid and contour of the core phase of the D90 or higher core phase is 2.0 or less.

2. A lightweight hard alloy comprising a hard phase having a core-rim structure, obtained by sintering a mixed powder mainly composed of a titanium compound consisting of titanium carbide and / or titanium carbonitride, containing 5 to 33% by mass of W and / or Mo in terms of carbide, and containing 5 to 40% by mass of at least one selected from the group consisting of Ni, Co and Fe as a binder phase component, wherein the titanium compound contains 0.7% by mass or more of oxygen, and the ratio of the amount of oxygen in the core phase to the amount of oxygen in the rim phase of the hard phase (core phase oxygen amount / rim phase oxygen amount) is 0.9 or more.

3. The lightweight hard alloy according to claim 2, characterized in that the titanium compound contains 0.7 to 2.5% by mass of oxygen.

4. When the amount of particles with a particle size of 0.8 μm or less contained in the mixed powder is A (volume %), the amount of particles A satisfies the following formula (1): A < -1.3X + 53.4 ... (1) or is 20 volume percent or less, with respect to the content X (volume %) of at least one element selected from the group consisting of Ni, Co, and Fe contained in the mixed powder. This is the lightweight hard alloy according to any one of claims 1 to 3.

5. The lightweight hard alloy according to any one of claims 1 to 4, characterized in that the mixed powder further contains 8% by mass or less of Cr on a Cr3C2 basis.

6. The lightweight hard alloy according to any one of claims 1 to 4, characterized in that the mixed powder contains 15% by mass or less of elements from groups 4 to 6 of the periodic table other than Ti, W, Mo, and Cr, on a carbide basis.

7. The lightweight hard alloy according to claim 5, characterized in that the mixed powder contains 15% by mass or less of elements from groups 4 to 6 of the periodic table other than Ti, W, Mo, and Cr, on a carbide basis.

8. A lightweight hard alloy comprising a titanium compound consisting mainly of titanium carbide and / or titanium carbonitride, and containing a hard phase having a core-rim structure, characterized in that, in the cross-sectional microstructure of the lightweight hard alloy observed by a scanning electron microscope, the average particle size of the core phase of the hard phase having a core-rim structure is 0.8 to 3.3 μm on a number basis, and the average ratio Dmax / Dmin of the shortest length Dmin to the longest length Dmax of the straight line connecting the centroid and contour of the core phase of the D90 or higher is 2.0 or less.

9. The lightweight hard alloy according to claim 8, characterized by being formed by sintering a mixed powder mainly containing a titanium compound consisting of titanium carbide and / or titanium carbonitride.

10. A lightweight hard alloy comprising a hard phase having a core-rim structure, which is obtained by sintering a mixed powder mainly composed of a titanium compound consisting of titanium carbide and / or titanium carbonitride, wherein the titanium compound contains 0.7% by mass or more of oxygen, and the ratio of the amount of oxygen in the core phase to the amount of oxygen in the rim phase of the hard phase (core phase oxygen amount / rim phase oxygen amount) is 0.9 or more.

11. The lightweight hard alloy according to claim 10, characterized in that the titanium compound contains 0.7 to 2.5% by mass of oxygen.

12. The lightweight hard alloy according to any one of claims 1 to 3 and 8 to 11, characterized in that the nitrogen content of the titanium compound is 0.7% by mass or more and less than 8% by mass.

13. A lightweight hard alloy member using the lightweight hard alloy described in any of claims 1 to 3 and 8 to 11.

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