Sintered hard alloy, grinding tool, kneading tool, wear-resistant tool, and die

Abstract

This sintered hard alloy comprises a hard phase mainly composed of NbC and including a first hard phase comprising a carbide that includes at least one kind of group 4-6 element (however, Nb is an essential component) and a second hard phase comprising a boride that includes at least kind of group 4-6 element, and a binder phase containing at least one of Ni, Co and Fe, wherein the sintered hard alloy contains 3-30 vol% of the at least one kind of group 4-6 element (excluding the Nb contained in the first hard phase) with respect to the total amount of the hard phase in terms of the carbide, contains, as a binder component, 4-40 vol% of at least one element among Ni, Co and Fe, and includes 0.3-8% of B in terms of mass ratio with respect to the binder phase component.

Description

Sintered hard alloys, crushing tools, kneading tools, wear-resistant tools and dies

[0001] The present invention relates to a sintered hard alloy, and to a crushing tool, a kneading tool, a wear-resistant tool, and a mold using the same.

[0002] In recent years, ceramics and cemented carbide are often used for wear-resistant parts and molds used in crushing, mixing, and kneading resins and magnetic materials. However, ceramics have low toughness and are prone to chipping due to interference between wear-resistant parts. Screws and other components are large, and when made from cemented carbide, their specific gravity is high, making them heavy. This can cause deflection in cantilever screws, and makes it difficult to increase rotational speed.

[0003] On the other hand, when sintering large parts with cermets, there is a problem that they are prone to cracking during sintering. Therefore, in recent years, there has been a demand for large cermet parts that are lightweight and tough for such wear-resistant parts and dies, and that are less susceptible to sintering cracking.

[0004] NbC, which has a hardness and specific gravity intermediate between WC and TiC, has long been attracting attention as such a material. In recent years, research and development of alloys with NbC as the hard phase has been progressing, but NbC alloys sintered using Ni or Co as a binder phase tend to coarsen, causing a decrease in mechanical properties, and are therefore too weak for use in actual tools and molds, so improvements in strength have been required. In addition, most test specimens are vacuum sintered or prototypes are made using hot pressing or SPS, and no actual commercial products have been reported.

[0005] Non-Patent Document 1 discloses that by using NbC as the main raw material and adding one or more of Mo2C, WC, VC, etc., NbC forms a solid solution phase, and furthermore, grain growth of the NbC solid solution phase can be suppressed, thereby improving mechanical properties such as hardness and toughness. It also discloses that mechanical properties can be improved by changing the type of binder phase. However, strength such as transverse rupture strength is low, and strength improvement has been a challenge.

[0006] Patent Document 1 discloses a composite cylinder with a metal cylindrical body and a layer of a corrosion-resistant, wear-resistant Ni- or Co-based sintered alloy containing 10 to 90 weight percent of one or more types of carbide particles sintered into the inner surface of the cylinder, with at least 30 volume percent of the carbide particles being carbides with a specific gravity of 6.5 to 8.5. In a composite cylinder with a metal cylindrical body and a wear-resistant sintered alloy inner surface, the sintered alloy for the inner surface was replaced with NbC-Ni or the like from WC-Co, eliminating the manufacturing problems associated with the high specific gravity of WC-Co. However, the strength and wear resistance were insufficient, making the cylinder unsuitable for applications requiring these.

[0007] Patent Document 2 discloses a cermet alloy consisting of a hard phase mainly composed of carbides or carbonitrides of transition metal elements of Groups 4a, 5a, and 6a and W-Ni-B compounds, and a binder phase mainly composed of Ni, which can be sintered at high density by reduced or normal pressure and can increase hardness without reducing toughness compared to, for example, TiC-WC-Co alloys. In Example 2, Patent Document 2 discloses a cermet alloy (Sample No. 6) having a raw powder composition of NbC-30 vol% WB-10 vol% Ni. However, since Sample No. 6 in Example 2 contains a large amount of WB (30 vol%), most of the 10 vol% Ni forms a complex boride such as the W2NiB2 phase, and the binder phase remaining in the sintered compact is less than 1 mass%. Therefore, the toughness of the cermet alloy is not high.

[0008] Thus, a major feature of NbC-based alloys is their lower specific gravity compared to WC-based alloys, but there is still room for improvement in terms of strength and wear resistance.

[0009] Patent No. 2527078 Publication JP-A-5-78776

[0010] Hubler and Gradt: Forsch Ingenieurwes, 86(2022), 197-211

[0011] Therefore, an object of the present invention is to provide a sintered hard alloy that is lightweight, strong, and highly tough, and that is resistant to cracking during sintering even in thick-walled products and has excellent grindability, as well as a crushing tool, a kneading tool, a wear-resistant tool, and a mold that use the same.

[0012] Therefore, one embodiment of the sintered hard alloy of the present invention is characterized in that it comprises a hard phase mainly composed of NbC, the hard phase including a first hard phase made of carbide containing at least one element of Groups 4 to 6 of the periodic table (however, Nb is an essential component), and a second hard phase made of boride containing at least one element of Groups 4 to 6 of the periodic table, and a binder phase containing at least one of Ni, Co, and Fe, wherein the at least one element of Groups 4 to 6 of the periodic table (excluding Nb) is contained in an amount of 3 to 30 volume % in terms of carbide relative to the total amount of the hard phase, the binder phase component contains at least one of Ni, Co, and Fe in an amount of 4 to 40 volume %, and the binder phase component contains 0.3 to 8% B in a mass ratio.

[0013] The hard phase preferably contains at least one of W, Mo and V as a metallic element.

[0014] The first hard phase is preferably made of a carbide phase containing Nb and at least one element of Groups 4 to 6 of the periodic table other than Nb.

[0015] The second hard phase preferably further contains at least one of Ni, Co and Fe.

[0016] The second hard phase preferably contains W and / or Mo, and more preferably contains Ni.

[0017] The first hard phase is composed of carbide and / or carbonitride, and the carbon content C C and nitrogen content C N C N / (C C +C N ) < 0.5.

[0018] The first hard phase preferably has an average grain size of 0.3 to 4 μm.

[0019] A crushing tool, a kneading tool, a wear-resistant tool, and a mold according to one embodiment of the present invention are characterized by using the above-mentioned sintered hard alloy.

[0020] According to the present invention, a sintered hard alloy can be obtained that is lightweight, strong, and highly tough, and that is resistant to cracking during sintering even in thick-walled products, and has excellent grindability. This makes it suitable for use in large, wear-resistant components that rotate at high speeds, such as screws and grinding blades, and dramatically improves production efficiency in grinding, mixing, and kneading. For example, it is suitable for applications such as tools and grinding blades for grinding, mixing, and kneading resins and magnetic materials. Because of these similar characteristics, it is also suitable for use in molds and peripheral components for lens molding.

[0021] 1 is an SEM photograph showing a polished cross section of Invention Product 3.

[0022] [1] Sintered hard alloy A sintered hard alloy according to one embodiment of the present invention has a hard phase mainly composed of NbC, and includes a first hard phase made of a carbide containing at least one element of Groups 4 to 6 of the periodic table (however, Nb is an essential component), and a second hard phase made of a boride containing at least one element of Groups 4 to 6 of the periodic table. The hard phase and the binder phase contain at least one of Ni, Co, and Fe, and the hard phase contains at least one element of Groups 4 to 6 of the periodic table (excluding Nb) in an amount of 3 to 30% by volume in terms of carbide relative to the total amount of the hard phase. The binder phase contains at least one of Ni, Co, and Fe in an amount of 4 to 40% by volume, and contains 0.3 to 8% B by mass relative to the binder phase component.

[0023] The hard phase contains NbC as a main component. The hard phase containing NbC as a "main component" means that the content of NbC is greater than the total content of the other contained compounds in terms of volume ratio. The content of NbC is preferably 1.5 to 5 times, and more preferably 2 to 4 times, the total content of the other contained compounds in terms of volume ratio.

[0024] The first hard phase is a carbide phase containing NbC as an essential component and at least one element from Groups 4 to 6 of the periodic table. The first hard phase is preferably a carbide phase containing Nb and at least one element from Groups 4 to 6 of the periodic table other than Nb. The first hard phase is preferably a carbide solid solution phase. By forming a solid solution containing Nb and an element from Groups 4 to 6 of the periodic table other than Nb, wear resistance can be imparted to the first hard phase mainly composed of NbC. The metal element constituting the hard phase preferably contains at least one of W, Mo, and V. The first hard phase also preferably contains at least one of W, Mo, and V.

[0025] The hard phase contains at least one Group 4-6 element (excluding Nb) in an amount of 3 to 30 volume % of the total amount of the hard phase, calculated as carbide. The content of at least one Group 4-6 element (excluding Nb) refers to the total amount of Group 4-6 elements other than Nb contained in the hard phase. If the content of Group 4-6 elements other than Nb contained in the hard phase is less than 3 volume %, the content of Group 4-6 elements other than Nb contained in the first hard phase is insufficient, and the hard phase cannot achieve sufficient wear resistance. Furthermore, if the content of Group 4-6 elements other than Nb contained in the hard phase exceeds 30 volume %, the sintered hard alloy cannot achieve sufficient toughness. The content of Group 4-6 elements other than Nb contained in the hard phase is preferably 5 to 30 volume %, more preferably 6 to 25 volume %, and even more preferably 6 to 20 volume %.

[0026] The average grain size of the first hard phase is preferably 0.3 to 4 μm. The average grain size of the first hard phase is determined by Fulman's formula based on the SEM structure of any cross section of the sintered hard alloy. If the average grain size of the first hard phase is less than 0.3 μm, toughness will decrease and chipping will occur depending on the usage conditions. If the average grain size of the first hard phase is more than 4 μm, strength will be insufficient. The average grain size of the first hard phase is more preferably 0.5 to 3.5 μm, and even more preferably 0.7 to 3 μm.

[0027] The first hard phase may be a carbonitride phase, or may contain both a carbide phase and a carbonitride phase. In this case, the carbon content C Cand nitrogen content C N C N / (C C +C N It is preferable that the relationship of C<0.5 is satisfied. In other words, it is preferable that the amount of carbon contained in the sintered hard alloy is greater than the amount of nitrogen, so that the sinterability is not reduced and the material strength can be maintained. The carbon amount C contained in the sintered hard alloy C and nitrogen content C N C N / (C C +C N ) < 0.3 is more preferable.

[0028] The second hard phase is made of a boride containing at least one element from Groups 4 to 6 of the periodic table. The presence of the second hard phase in the hard phase can refine the grain size of the first hard phase and improve strength. A boride phase containing W and / or Mo is particularly preferable because it has a large grain refinement effect. The presence of a boride phase can also improve the sliding properties of the sintered hard alloy. The average grain size of the second hard phase is preferably about 4 μm or less, more preferably 0.1 to 4 μm, and even more preferably 0.2 to 2 μm.

[0029] The second hard phase is preferably composed of a composite boride X2YB2 (X is at least one of the Group 6 elements of the periodic table, and Y is at least one of Ni, Co, and Fe) containing at least one element of the Group 6 elements of the periodic table, at least one metal element of Ni, Co, and Fe, and boron. This allows the first hard phase to be further refined and improves strength. This is thought to be because the inclusion of at least one metal element of Ni, Co, and Fe suppresses grain growth through a pinning effect, and also because the presence of the composite boride lowers the liquid phase appearance temperature, thereby suppressing solid phase growth. Examples of composite borides include W2NiB2, WNiB, W3CoB3, and NiW2B. 15 etc.

[0030] The sintered hard alloy of the present invention has a binder phase containing at least one of Ni, Co, and Fe, and contains 4 to 40 volume % of at least one of Ni, Co, and Fe as the binder phase component. Here, the binder phase component refers to the Ni, Co, and Fe contained in the sintered hard alloy, and the content of the binder phase component means the total content of Ni, Co, and Fe in the sintered hard alloy, including Ni, Co, and Fe present outside the binder phase. The binder phase component preferably contains 5 to 30 volume %, more preferably 6 to 20 volume %, of at least one of Ni, Co, and Fe. The hard phase component can be solid-solved in the binder phase.

[0031] When a sintered hard alloy contains boron, it forms a composite boride of a Group 6 element with the binder phase components, thereby reducing the binder phase content accordingly. Therefore, if a large amount of composite borides is formed, the hardness of the sintered hard alloy increases, but the toughness and strength decrease. Therefore, the amount of boron contained in the sintered hard alloy is 0.3 to 8% by mass relative to the binder phase components. If the amount is less than 0.3%, a sufficient grain refinement effect cannot be obtained, and if it exceeds 8%, sufficient strength and toughness cannot be obtained. The amount of boron contained in the sintered hard alloy is preferably 0.4 to 7% by mass relative to the binder phase components, more preferably 0.6 to 5%, and even more preferably 0.8 to 4%.

[0032] The sintered hard alloy of the present invention may further contain a fourth phase consisting of an intermetallic compound of binder phase components and Nb. Examples of intermetallic compounds include Ni3Nb, Ni6Nb7, Fe2Nb, Fe7Nb6, Fe2Nb3, Co2Nb, and Co7Nb6. The presence of the fourth phase does not particularly adversely affect the characteristics and performance of the sintered hard alloy at room temperature, but it can suppress a decrease in hardness when the temperature of the usage environment increases. The fourth phase may be contained in an amount of 40% by volume or less, preferably 30% by volume or less, and more preferably 20% by volume or less, based on the total amount of the binder phase and the fourth phase.

[0033] [2] Manufacturing method of sintered hard alloy One example of a manufacturing method of the sintered hard alloy of the present invention is a method in which powders of the constituent particles of the above-mentioned sintered hard alloy are blended, wet mixed and pulverized in an organic solvent, dried, and then a binder such as paraffin is added to the powder, which is then pressed to form a compact, and the compact is sintered to obtain a sintered hard alloy.

[0034] Boron, which is a constituent component of the second hard phase, may be added as boron powder or as a powder of a boride such as TiB2 or WB.

[0035] The compact of the mixed powder may be formed by press molding into a near-finished state (near net shape), or may be machined to give a predetermined shape, or may be machined after preliminary sintering to give a predetermined shape.

[0036] The sintering atmosphere can be a vacuum or an inert gas. When sintering a compact made of a nitrogen-containing mixed powder, nitrogen or a nitrogen-containing mixed gas, or CO gas, can be used. The introduction temperature and gas pressure of these atmospheric gases can be varied depending on the purpose. The heating rate, sintering temperature, and holding time, as well as the temperature and gas pressure along the way, can be selected as desired depending on the purpose, such as debinding, improving sinterability, or improving surface properties.

[0037] The sintering temperature is preferably 1250 to 1500°C, and more preferably 1280 to 1450°C. The normally sintered sintered body may be subjected to HIP treatment. The HIP treatment pressure is preferably 0.5 MPa to 200 MPa. Sintering may be performed by hot press sintering, or by electromagnetic energy assisted sintering such as electric current sintering or SPS sintering. Sinter-HIP may also be used depending on the application.

[0038] [3] Sintered Hard Alloy Members The sintered hard alloy of the present invention is suitable for use in large, high-speed rotating tools such as screws and grinding blades, kneading tools, wear-resistant tools, and dies. Therefore, sintered hard alloy members using the sintered hard alloy of the present invention can exhibit excellent performance when used, for example, as crushing, mixing, or kneading members. Furthermore, the sintered hard alloy of the present invention is not limited to these applications. Because it is less likely to crack during tool use, it can also be used for punching punches, room-temperature, warm, and hot forming dies, extrusion dies, dies, and forging punches. Furthermore, because it is less likely to chip or crack during handling, it is effective for use in peripheral components for lens molding, such as barrel dies for special lenses with a large thermal expansion coefficient.

[0039] The sintered hard alloy member of the present invention is not limited to the wear-resistant tools and components described above, and may also be effective in cutting tools such as insert tips, end mills, and drills. Unlike TiCN-based cermets, the sintered hard alloy of the present invention has grindability almost equivalent to that of WC-based cemented carbide, making it easy to shape even components with complex shapes, and reducing cutting costs. Furthermore, the sintered hard alloy member of the present invention may have a hard coating applied to its surface by DLC or PVD, or, depending on the application, by CVD.

[0040] The present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

[0041] Example 1: NbC (1.6 μm), WC (0.8 μm), VC (2.0 μm), MoC (3.5 μm), TaC (1.8 μm), TiC (1.7 μm), B (0.8 μm), TiB (2.8 μm), WB (4.5 μm), NbB (2.0 μm), Ni (2.4 μm), Co (1.4 μm), and Fe (3.0 μm) were prepared as raw material powders. (The numbers in parentheses are the average particle sizes measured by the Fischer particle size measurement method (FSSS method).) Mixed powders were prepared by wet mixing to have the compositions shown in Table 1, compacted under a pressure of 98 MPa, and sintered at 1300°C (in an Ar atmosphere) to produce Invention Products 1 to 21 and Comparative Products 1 to 3. Invention Product 12 used Nb(C) instead of NbC as the raw material powder. 0.5 N0.5 ) (1.8 μm) was used. The carbon content C C The nitrogen content C N When the oxygen and nitrogen were analyzed using an oxygen and nitrogen analyzer (manufactured by LECO), the relationship between the two was found to be: C N / (C C +C N ) was 0.47.

[0042]

[0043] The constituent phases of Invention Products 1-21 and Comparative Products 1-3 were investigated for the proportion (volume %) of elements from Groups 4 to 6 of the Periodic Table other than Nb among the metal elements constituting the hard phase, calculated as carbides; the proportion (%) of boron (mass %) relative to the binder phase components (mass %); the amount of boron (mass %) contained in the sintered alloy; and the metal elements contained in the boride phase. The metal elements contained in the boride phase were measured by elemental analysis using SEM-EDX. The amount of boron contained in the sintered alloy was measured by ICP atomic emission spectroscopy. The results are shown in Table 2.

[0044] Note *1. A: The content (volume %) of elements from Groups 4 to 6 of the periodic table other than Nb among the metal elements that make up the hard phase, converted into carbide. Note *2. B: The ratio (%) of the boron content (mass %) to the binder phase component content (mass %). Note *3. C: The amount of boron contained in the sintered alloy (mass %). Note *4. D: The metal element contained in the boride phase. Note *5. Primary hard phase. Note *6. Secondary hard phase. Note *7. The primary phase is a carbonitride phase.

[0045] The average grain size, Vickers hardness, and transverse rupture strength of the primary hard phase of each sample were measured. The average grain size of the primary hard phase was determined by the Fulman equation based on the SEM structure of an arbitrary cross section of each sample, the Vickers hardness was measured (HV30) using a Vickers hardness tester, and the transverse rupture strength was measured by a three-point bending test based on JIS R 1601, using the #140 flat-ground surface of each sample as the tensile surface.

[0046] To evaluate the wear resistance (resistance to wear as a tool) of each sample assuming its use in a kneading tool, a rubber wheel test (standard: ASTM G65) was conducted, and the degree of wear was rated from 0 to 5. When the wear amount of Invention Product 1 was 0.9 times or more but less than 1.0 times, it was rated "3," when it was 0.8 times or more but less than 0.9 times, it was rated "4," when it was less than 0.8 times, it was rated "5," when it was 1.0 times or more but less than 1.1 times, it was rated "2," when it was 1.1 times or more but less than 1.2 times, it was rated "1," and when it was 1.2 times or more, it was rated "0."

[0047] To evaluate the chipping resistance (resistance to chipping as a tool; toughness), each sample was surface-ground using a diamond wheel (#140) at 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 of 0 to 5. A chip width of 0.9 to 1.1 times the chip width of Invention Product 3 was evaluated as "4," a chip width less than 0.9 times was evaluated as "5," a chip width of 1.1 to 1.2 times was evaluated as "3," a chip width of 1.2 to 1.3 times was evaluated as "2," a chip width of 1.3 to 1.4 times was evaluated as "1," and a chip width of 1.4 times or more was evaluated as "0." Table 3 shows the evaluation results, as well as the average grain size, Vickers hardness, and transverse rupture strength of the first hard phase of each prototype.

[0048] For comparison, a sample made of powdered high speed steel was prepared as Comparative Sample 4, and similar tests were carried out on the wear resistance and chipping resistance.

[0049] Note *1: Powdered high-speed steel.

[0050] Comparative samples 1 and 2 did not contain a secondary hard phase made of boride, and had a large particle size of the primary hard phase, resulting in low wear resistance and poor chipping resistance due to low transverse rupture strength. Comparative sample 3 had a high boron content and a large amount of the secondary hard phase, resulting in excellent wear resistance, but at the same time, poor chipping resistance due to low transverse rupture strength.

[0051] Comparative product 4 was excellent in chipping resistance and was rated "5", but its wear resistance was 4.5 times that of invention product 3, indicating that it was significantly inferior.

[0052] Next, to evaluate the wear resistance of the sintered hard alloy of the present invention when used in a crushing tool, a stainless steel sample was separately prepared, and using a blasting device, SiC powder (grain size: #500) was collided with the stainless steel sample and Invention Product 3 under conditions of a projection angle of 30°, a projection pressure of 0.6 MPa, and a projection time of 90 seconds. After the wear resistance test, the stainless steel sample had twice the amount of wear compared to Invention Product 3, demonstrating that its wear resistance as a crushing tool was significantly inferior.

[0053] The cross section of the sintered compact of Invention Product 3 was mirror-polished, and the SEM structure (5,000x magnification) was photographed using a scanning electron microscope (Regulus 8100, Hitachi High-Tech Corporation) as shown in Figure 1. At the same time, EDS analysis was performed to analyze the composition of each phase, confirming that the first hard phase (gray phase) is a carbide phase containing Nb, W, Mo, and V, and that the second hard phase (white phase) is a boride phase containing W, Mo, Ni, and Co. Furthermore, the crystal structure was examined using XRD, confirming that the second hard phase is (W,Mo)2(Ni,Co)B2.

[0054] When Inventive Product 3 was used in kneading tools, it had a lifespan five times longer than that of the powder high-speed steel of Comparative Product 4. Furthermore, when used in crushing tools, existing stainless steel tools were subject to significant wear, but Inventive Product 3 had a lifespan twice that of stainless steel tools.

Claims

1. A sintered hard alloy comprising a hard phase mainly composed of NbC, the hard phase including a first hard phase made of carbide containing at least one element from Groups 4 to 6 of the periodic table (however, Nb is an essential element), and a second hard phase made of boride containing at least one element from Groups 4 to 6 of the periodic table, and a binder phase containing at least one of Ni, Co, and Fe, wherein the at least one element from Groups 4 to 6 of the periodic table (excluding Nb) is contained in an amount of 3 to 30 volume % based on the total amount of the hard phase in terms of carbide, and at least one of Ni, Co, and Fe is contained as a binder phase component in an amount of 4 to 40 volume %; and 0.3 to 8 mass % of B based on the binder phase component.

2. A sintered hard alloy according to claim 1, characterized in that the hard phase contains at least one of W, Mo and V as a metallic element.

3. A sintered hard alloy according to claim 1 or 2, characterized in that the first hard phase is a carbide phase containing Nb and at least one element of Groups 4 to 6 of the periodic table other than Nb.

4. A sintered hard alloy according to any one of claims 1 to 3, characterized in that the second hard phase further contains at least one of Ni, Co and Fe.

5. A sintered hard alloy according to claim 4, wherein the second hard phase contains Ni.

6. A sintered hard alloy according to any one of claims 1 to 5, characterized in that the second hard phase contains W and / or Mo.

7. The first hard phase is composed of carbide and / or carbonitride, and the carbon content C C and nitrogen content C N C N / (C C +C N 7. The sintered hard alloy according to claim 1, wherein the relationship of σ<0.5 is satisfied.

8. A sintered hard alloy according to any one of claims 1 to 7, characterized in that the first hard phase has an average grain size of 0.3 to 4 µm.

9. A crushing tool, a kneading tool, a wear-resistant tool or a mold made from the sintered hard alloy according to any one of claims 1 to 8.

Images