Bonded phase reinforced wear-resistant cemented carbide

Abstract

To provide cemented carbide with excellent wear resistance. [Solution] The cemented carbide contains 56.000 to 95.997 wt% of the total cemented carbide, consisting of a hard phase made of tungsten carbide (WC) with an average grain size of 0.20 to 2.0 μm; 3.000 to 20.0000 wt% of the total cemented carbide, consisting of a binder phase containing at least one of cobalt (Co) or nickel (Ni); and 0.003 to 4.000 wt% of the total cemented carbide, with a weight ratio of "molybdenum (Mo) / (Mo + binder phase)" of 0.250 to 0.500, and containing less Mo than the binder phase, and the total of the hard phase, binder phase, Cr3C2, and Mo is 100 wt%.

Description

Technical Field

[0001] This invention relates to a binder phase strengthened wear-resistant cemented carbide.

Background Art

[0002] Cemented carbides are widely used as tools for cutting or machining metal materials such as steel, cast steel, manganese steel, stainless steel (for example, micro drills), punching dies, drawing dies (for example, dies for steel cord wire drawing or plugs), extrusion dies, nozzles, molding dies, etc., and as mechanical parts resistant to wear.

[0003] One of the characteristics required for cemented carbides used in the above-mentioned tools and mechanical parts is "wear (low) resistance (difficult to wear away)". Approaches to improving wear resistance include hardening the material to reduce the amount of wear, making the surface such that friction hardly occurs, i.e., having a small coefficient of friction, and adding a lubricating component.

[0004] In order to harden the material and reduce the amount of wear, cemented carbides having a high-hardness tungsten carbide (WC) with a fine average particle size as a hard phase are widely used. Cemented carbides containing WC with a small average particle size are hard and have improved wear resistance.

[0005] The manufacturing process of cemented carbide includes a sintering process in which a compressed powder is heated to a temperature below the melting point of the elements in its composition to densify it. It is known that WC undergoes grain growth during sintering, resulting in an increase in grain size. Since WC grain growth leads to a decrease in the hardness of cemented carbide, it is common practice to add metal carbides to suppress WC grain growth in order to obtain a hard cemented carbide by inhibiting grain growth, in addition to WC and a binder material to bond WC particles (e.g., cobalt (Co)). Currently, vanadium carbide (VC), which is highly effective in suppressing WC grain growth, is often added. Cemented carbide obtained by sintering with the addition of VC maintains a smaller WC grain size and exhibits improved hardness compared to cemented carbide obtained by sintering without the addition of VC. The suppression of WC grain growth by VC is thought to be because VC precipitates on the WC particles, inhibiting their growth.

[0006] While the addition of VC improves the hardness and wear resistance of cemented carbide, the precipitation of VC on WC particles reduces the strength of the interface between WC particles and the bonding phase, such as Co (WC / Co interface), leading to a tendency for WC particles to detach prematurely from the cemented carbide. This can cause premature detachment of WC particles when cemented carbide tools are used continuously as wear-resistant tools, shortening the tool's lifespan. In other words, while new cemented carbide tools have good wear resistance, they cannot maintain this wear resistance over a long period after use.

[0007] As mentioned above, in addition to hardening the material (the cemented carbide itself), another approach to improving wear resistance is to create a surface that is less prone to friction, i.e., has a low coefficient of friction. Reducing the coefficient of friction on the surface of cemented carbide also improves its wear resistance and extends the life of the tool.

[0008] Patent Document 1 discloses a cemented carbide alloy with improved wear resistance achieved by adding a small amount of molybdenum carbide (Mo2C) or molybdenum (Mo). Mo is known as a lubricant, and it is believed that the cemented carbide alloy in Patent Document 1 improves its wear resistance by reducing the coefficient of friction on its surface through the addition of Mo or Mo2C. However, if the amount of Mo or Mo2C added is too small, the hardness may decrease compared to VC-added cemented carbide alloys, resulting in inferior wear resistance.

[0009] Patent Document 2 relates to "a cemented carbide and cermet composition having a high-entropy alloy (HEA) bonding phase, a related manufacturing method for cemented carbide and cermet having a high-entropy alloy (HEA) bonding phase, and a cutting tool incorporating a cemented carbide and cermet composition" (

[0001] ). It discloses a cemented carbide containing a ceramic hard phase (for example, niobium carbide and tungsten carbide (

[0014] , Table 1 in

[0101] )) present in an amount of 70 wt% to 93 wt% of the total weight of the cemented carbide composition, and a high-entropy alloy (HEA) bonding phase present in an amount of 7 wt% to 30 wt% of the total weight of the cemented carbide composition, and containing one or more of nickel, molybdenum, cobalt, iron, and chromium (for example,

[0012] ). Reference Document 2 also discloses a cemented carbide containing molybdenum (Mo) as a bonding phase, but there is no discussion whatsoever regarding the amount of Mo added. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Unexamined Patent Publication No. 147842 / 1983 [Patent Document 2] U.S. Patent Application Publication No. 2024 / 0384377 Specification [Overview of the project] [Problems that the invention aims to solve]

[0011] The objective of this invention is to provide a bond phase-reinforced wear-resistant cemented carbide alloy that exhibits excellent hardness and long-term wear resistance, and more specifically, has hardness comparable to that of VC-added cemented carbide alloys, while also exhibiting low wear over the long term. [Means for solving the problem]

[0012] The bonded phase-reinforced wear-resistant cemented carbide according to this invention contains 56,000 to 95,997 wt% of the total cemented carbide of a hard phase consisting of tungsten carbide (WC) with an average grain size of 0.20 to 2.0 μm, 3,000 to 20,000 wt% of the total cemented carbide of a bonded phase containing at least one of cobalt (Co) and nickel (Ni), and 0.003 to 4,000 wt% of the total cemented carbide of chromium carbide (Cr3C2), with a weight ratio of "molybdenum (Mo) / (Mo + bonded phase)" of 0.250 to 0.500, and containing less Mo than the above bonded phase, and the total of the above hard phase, bonded phase, Cr3C2, and Mo is 100 wt%. It goes without saying that unavoidable impurities, that is, substances that are present in the raw materials or inevitably introduced during the manufacturing process, and which are inherently unwanted, may be present in cemented carbide because they are present in trace amounts and do not affect the characteristics of the product, and are therefore tolerated.

[0013] The bond phase-reinforced wear-resistant cemented carbide provided by this invention is a cemented carbide with added molybdenum (Mo) (hereinafter referred to as Mo-added cemented carbide), containing Mo / (Mo + bond phase) in a weight ratio of 0.250 to 0.500. Since Mo is dissolved in the bond phase containing at least one of Co and Ni during sintering, the amount of Mo is less than the amount of bond phase. In this invention, the amount of Mo is defined by the ratio of Mo that occupies the bond phase in which Mo is dissolved (referred to as the reinforced bond phase). As described above, the bond phase itself is present in an amount of 3.000 to 20.000 wt% of the total cemented carbide. When the binder phase is present at its lower limit of 3,000 wt%, the lower limit of Mo is 1,000 wt%, and when the binder phase is present at its upper limit of 20,000 wt%, the upper limit of Mo is 20,000 wt%. Therefore, the binder phase-enhanced wear-resistant cemented carbide of this invention includes Mo in the range of 1,000 wt% or more and less than 20,000 wt%.

[0014] The bonding phase may be elemental Co or elemental Ni, or it may contain both Co and Ni. It may also contain metals other than Co and Ni, such as iron (Fe).

[0015] The bonded-phase-reinforced wear-resistant cemented carbide according to this invention has been confirmed to maintain wear resistance over a longer period of time when used continuously, compared to VC-added cemented carbide with added vanadium carbide (VC). It is believed that the premature shedding of WC particles that occurs in VC-added cemented carbide, and the resulting decrease in wear resistance after long-term use, is less likely to occur in the bonded-phase-reinforced wear-resistant cemented carbide according to this invention. The bonded-phase-reinforced wear-resistant cemented carbide according to this invention can be suitably used in tools and machine parts that are used over a long period of time.

[0016] It is thought that by not adding VC, which exhibits a good grain growth inhibitory effect of WC, cemented carbide containing large grain sizes of WC can be produced, resulting in cemented carbide with inferior HRA (hardness). However, it has been found that by solid-solving Mo in a predetermined proportion into the binder phase, cemented carbide with HRA (hardness) equivalent to that of VC-added cemented carbide can be produced. Mo is known to exhibit a grain growth inhibitory effect similar to VC, but it is also known to be inferior to that of VC. Therefore, it is thought that the reason why Mo-added cemented carbide, in which Mo is added instead of VC, can exhibit hardness equivalent to that of VC-added cemented carbide is that the binder phase becomes harder due to the solid-solving of Mo, and as a result, the overall HRA (hardness) of the cemented carbide becomes similar to that of VC-added cemented carbide. It has also been found that Mo-added cemented carbide may have a lower coefficient of friction compared to VC-added cemented carbide. This invention provides a binder-phase-enhanced wear-resistant cemented carbide in which the binder phase is hard (binder-phase-enhanced type) and the coefficient of friction is low (wear-resistant).

[0017] It was confirmed that the coefficient of friction of cemented carbide tends to improve as the amount of Mo dissolved in the binder phase increases. However, it was also confirmed that if the amount of Mo dissolved in the binder phase is too high, the flexural strength of the cemented carbide may decrease. From this perspective, the upper limit for the amount of Mo is set at 0.500 by weight ratio of the binder phase in which Mo is dissolved (reinforced binder phase) (Mo / (Mo+binder phase) is less than 0.500).

[0018] As mentioned above, if the amount of Mo dissolved in the binder phase is small, it becomes difficult to achieve the desired properties (especially hardness) of VC-added cemented carbide. To facilitate the advantageous effects of VC-added cemented carbide, the lower limit of the Mo amount is set at 0.250 by weight ratio of the binder phase in which Mo is dissolved (reinforcement binder phase) (Mo / (Mo+ binder phase) is 0.250 or higher).

[0019] The basic function (action) of the bonding phase (reinforcing bonding phase) is to bind (bind) the hard phase. Considering that the bonding phase reliably binds the hard phase (prevents the hard phase from falling off), preferably, the lower limit of the bonding phase is set to 8.000 wt%. When there is an amount of the bonding phase of about 8.000 wt%, it becomes easier to increase or decrease the amount of Mo dissolved in the bonding phase.

[0020] In one embodiment, it further contains 0.003 to 4.000 wt% of titanium carbonitride (Ti(C,N)) with respect to the entire cemented carbide, and the total of the hard phase, the bonding phase, the Cr3C2, the Mo, and the Ti(C,N) is 100 wt%. It has been confirmed that further adding Ti(C,N) achieves a further improvement in the wear resistance of the cemented carbide. A relatively small amount of addition of Ti(C,N) to the entire cemented carbide is sufficient, specifically 0.003 to 4.000 wt% equivalent to Cr3C2.

[0021] Preferably, the Ti(C,N) is produced by carbonitriding titanium oxide (TiO2) during sintering. When producing the cemented carbide, instead of using Ti(C,N) itself as a starting material, TiO2 is used as a starting material and carbonitrided during sintering to obtain fine Ti(C,N). The addition of fine Ti(C,N) is considered to contribute to the improvement of the wear resistance of the cemented carbide.

Brief Description of the Drawings

[0022] [Figure 1] It is a flowchart showing an example of the manufacturing process of a cemented carbide tool. [Figure 2] (A) shows a schematic diagram of the worn surface of a VC-added cemented carbide, and (B) shows an enlarged cross-sectional schematic diagram along the B-B line of (A). [Figure 3] (A) shows a schematic diagram of the worn surface of a Mo-added cemented carbide, and (B) shows an enlarged cross-sectional schematic diagram along the B-B line of (A). [Figure 4](A) shows a schematic diagram of the worn surface of a Mo-added cemented carbide further added with Ti(C,N), and (B) shows an enlarged cross-sectional schematic diagram along the B-B line of (A). [Figure 5] It is a graph showing the relationship between HRA (hardness) and the friction coefficient for each of a plurality of samples shown in Table 1. [Figure 6] It is a graph showing the relationship between the Mo / (Mo + Co) weight ratio and the friction coefficient for each of a plurality of samples shown in Table 1. [Figure 7] It is a graph showing the relationship between the Mo / (Mo + Co) weight ratio and the average wear width for each of a plurality of samples shown in Table 1. [Figure 8] It is a graph showing the relationship between the number of moldings and the mold wear amount for each of the VC-added cemented carbide and the Mo-added cemented carbide.

Mode for Carrying Out the Invention

[0023] The cemented carbide according to an embodiment of this invention is a first phase composed of tungsten carbide (WC) (hereinafter, referred to as "WC phase" or comprehensively as "hard phase"), and a second phase containing at least one of cobalt (Co) or nickel (Ni) (hereinafter, referred to as "bonding phase"), which is a second phase in which molybdenum (Mo) is dissolved in the bonding phase (hereinafter, the bonding phase in which Mo is dissolved is referred to as "strengthened bonding phase"), and chromium carbide (Cr3C2) (hereinafter, also referred to as "grain growth inhibiting phase"), and is a so-called WC-based cemented carbide. Embodiments of this invention also provide a cemented carbide further added with titanium carbonitride (Ti(C,N)) as will be described later.

[0024] (1) Content of hard phase (WC phase) The cemented carbide contains WC phase in an amount of 56.000 wt% to 95.997 wt% of the total cemented carbide. If the WC phase is less than 56.000 wt%, the proportion of the binder phase increases relatively, which can make it difficult to control the grain growth of the WC phase (see below for details on WC phase grain growth). By including 56.000 wt% or more of the WC phase, the grain growth of the WC phase is effectively suppressed, and the average grain size of the WC after sintering can be maintained at a relatively small diameter (2.0 μm or less). Furthermore, if the WC phase exceeds 95.997 wt%, the proportion of the binder phase decreases relatively, and the flexural strength of the cemented carbide decreases. By keeping the WC phase at 95.997 wt% or less, the flexural strength of the cemented carbide can be ensured to be above a predetermined value. The proportion of the WC phase to the total cemented carbide is adjusted by the amount of WC raw material powder added.

[0025] (2) Content of the binding phase The binding phase is used to bind WC particles together.

[0026] The bonding phase contains cobalt (Co). Nickel (Ni) can be used instead of Co, or both Co and Ni may be used. Iron (Fe) can also be added. The bonding phase is a metal whose main components are these metallic elements (containing 50.0 wt% or more of the total bonding phase).

[0027] If the binder phase content of the cemented carbide is less than 3,000 wt% of the total cemented carbide, the flexural strength of the cemented carbide decreases, and if it exceeds 20,000 wt%, the hardness of the cemented carbide decreases. From these perspectives, the binder phase content of cemented carbide is set to be between 3,000 wt% and 20,000 wt%. The ratio of the binder phase to the total cemented carbide can also be adjusted by changing the amount of raw material powder added.

[0028] (3) Content of grain growth inhibiting phase (chromium carbide (Cr3C2)) The grain growth inhibiting phase is used to suppress grain growth in the WC phase, and Cr3C2, which also contributes to improving the hardness and oxidation resistance of the binder phase, is used. The Cr3C2 content in the cemented carbide is set to 0.003 wt% to 4.000 wt%, and preferably the upper limit is the amount that can be completely dissolved in the binder phase. The reason for including the grain growth inhibiting phase is, as mentioned above, to suppress grain growth in the WC phase and maintain the WC phase as a fine-grained material. Grain growth in the WC phase is a phenomenon in which WC phase dissolved in the binder phase during sintering precipitates onto other WC phases, growing into particles with a larger diameter. It is thought that the presence of Cr3C2 around the WC phase reduces the precipitation of the WC phase, thereby suppressing grain growth of the WC phase.

[0029] (4) Molybdenum (Mo) content Mo is used to reduce the coefficient of friction of cemented carbide, thereby improving its wear resistance and extending its wear resistance over a long period, as explained below. Mo dissolves into the binder phase, improving its hardness as well (strengthened binder phase). The appropriate weight ratio of Mo to the total binder phase in which Mo is dissolved (referred to as the "strengthened binder phase") is 0.250 or more and less than 0.500 (for example, "Mo / (Mo+Co)"). (Details will be described later.) The amount of Mo is less than that of the binder phase, and preferably limited to the amount that is completely dissolved in the binder phase (for example, Co).

[0030] (5) Ti(C,N) content By adding titanium carbonitride (Ti(C,N)) to the aforementioned hard phase (WC phase), reinforcing bonding phase (e.g., Co+Mo), and grain growth inhibiting phase (Cr3C2), wear resistance can be improved compared to cemented carbide without added Ti(C,N). Ti(C,N) exists in a point-like manner at the interface between the hard phase and the reinforcing bonding phase, which is thought to make it difficult for the hard phase to grow (size increase), resulting in further improvement of wear resistance. Even a small amount of Ti(C,N) contributes to improved wear resistance. Conversely, the addition of a large amount of Ti(C,N) causes aggregation of Ti(C,N), leading to a decrease in flexural strength. An appropriate content is similar to that of Cr3C2, that is, approximately 0.003 wt% to 4.000 wt%.

[0031] As mentioned above, both Cr3C2 and Ti(C,N) exert a growth-inhibiting effect on the hard phase, but they differ in that Cr3C2 dissolves in the bonded phase (reinforced bonded phase), while Ti(C,N) does not dissolve in the bonded phase (reinforced bonded phase) and exists as grains at the interface between the hard phase and the reinforced bonded phase.

[0032] This document outlines the manufacturing process of cemented carbide tools using cemented carbide alloys. Figure 1 is a flowchart showing an example of the cemented carbide tool manufacturing process. Here, we will explain an example using a metal with cobalt (Co) as the main component as the bonding phase. We will also use the cemented carbide alloy containing Ti(C,N) mentioned above as an example.

[0033] A predetermined amount of raw material powders of tungsten carbide (WC) 11, cobalt (Co) 12, chromium carbide (Cr3C2) 13, metallic molybdenum (Mo) 14, titanium oxide (TiO2) 15, and carbon (C) 16 are placed in a cylindrical container, and a number of small diameter balls made of cemented carbide are also placed in the cylindrical container, and the cylindrical container is rotated. The raw material powders are crushed and mixed inside the container (step 21) (ball mill). To enhance the crushing effect and prevent oxidation of the powders, organic solvents such as acetone, alcohol, and hexane are also placed in the cylindrical container, causing the raw material powders to become a slurry (mud-like) inside the cylindrical container. An attritor may be used for crushing and mixing the raw material powders.

[0034] The pulverized and mixed slurry-like raw material powder is then dried by methods such as spray drying or mixer drying, thereby removing the organic solvent from the raw material powder (Step 22).

[0035] The pulverized and mixed raw material powder, from which the organic solvent has been removed, is pressed (compressed) by methods such as mold molding, rubber mold molding, or extrusion molding, and molded into a predetermined shape (step 23).

[0036] The molded product is sintered in a heating furnace under a nitrogen atmosphere (step 24).

[0037] The pulverized and mixed raw material powder contains C16, and the heating furnace operates under a nitrogen atmosphere. Therefore, TiO215, one of the raw material powders, is carbonitrided in the heating furnace to produce Ti(C,N). Compared to using Ti(C,N) itself as a raw material powder, this method allows for finer particle size of Ti(C,N).

[0038] By sintering the molded product at a predetermined temperature, a cemented carbide is obtained in which WC11 forms the hard phase and Co12 and Mo14 dissolved in it form the reinforcing bonding phase. Cr3C213 dissolves in the reinforcing bonding phase and suppresses grain growth of WC11 as described above. Ti(C,N) does not dissolve in the reinforcing bonding phase but exists as granules in a point-like manner at the interface between WC11 and the reinforcing bonding phase, thereby suppressing grain growth of WC11.

[0039] Carbide alloys can contain very small pores. To remove these pores, HIP (Hot Isostatic Pressing) is performed (Step 25). For example, argon gas at a gas pressure of 5 to 100 MPa is applied, which removes the pores.

[0040] Finally, through shaping, coating, etc., cemented carbide tools (wear-resistant tools, cutting tools, machining tools, etc.) are manufactured using cemented carbide (Step 26). Machine parts made of cemented carbide can be manufactured in the same way.

[0041] Figures 2 to 4 schematically and exaggeratedly show the wear surface of a cemented carbide alloy in which WC11 is the hard phase and Co12 is the binder phase. In Figures 2 to 4, (B) is a partially enlarged schematic cross-sectional view along the BB line in (A).

[0042] Figure 2 is a schematic diagram of a cemented carbide alloy doped with vanadium carbide (VC). VC precipitates on the hard WC1 and WC2 (the precipitated VC is schematically shown by thick lines), and it is thought that this VC precipitation suppresses grain growth in WC1 and WC2. In Figure 2(B), the depressions on the surface (wear surface) of Co12 schematically show how some of the Co12 is removed by wear. VC precipitates around WC, but it is removed at the wear surface.

[0043] Figure 3 is a schematic diagram of a cemented carbide alloy with molybdenum (Mo) added. Mo also has a grain growth inhibiting effect on WC1 and WC2, but not to the same extent as VC. Therefore, cemented carbides with larger grain sizes of WC are produced compared to VC-added cemented carbides. Generally, the hardness (HRA) of cemented carbides improves as the grain size of WC decreases, and cemented carbides with larger grain sizes tend to be less hard. However, it has been found that by adding an appropriate amount of Mo, cemented carbides with hardness equivalent to that of VC-added cemented carbides can be produced (test results will be described later). The reason why Mo-added cemented carbides (Figure 3), in which Mo is added instead of VC, can exhibit hardness equivalent to that of VC-added cemented carbides (Figure 2) is thought to be that the bond phase hardens due to solid solution of Mo (Co + Mo) (reinforced bond phase), and as a result, the overall HRA (hardness) of the cemented carbide becomes similar to that of VC-added cemented carbides.

[0044] Figure 4 is a schematic diagram of a cemented carbide alloy with added Ti(C,N) in addition to Mo. It is thought that the presence of Ti(C,N) as points between WC1 and WC2 (at the interface between WC1 or WC2 and the reinforcing bonding phase (Co+Mo)) makes it difficult for grain growth to occur in adjacent WC1 and WC2.

[0045] Table 1 shows the hardness (HRA) and average bending strength (kgf / mm²) of cemented carbide samples (No. 1 to No. 18) containing tungsten carbide (WC) 11, chromium carbide (Cr3C2) 13, and cobalt (Co) 12, as well as one of vanadium carbide (VC), molybdenum (Mo) 14, or titanium carbonitride (Ti(C,N)). 2 The results of the measurement of friction coefficient and average wear width (mm) are shown. Samples No. 1-5, No. 6-12, and No. 13-18 have different Co12 contents (8.0wt%, 10wt%, and 12.0wt%, respectively). Samples No. 1, No. 6, and No. 13 are VC-added cemented carbide without Mo (VC-added cemented carbide), samples No. 2, No. 7, No. 8, and No. 14 have neither Mo nor VC added, and samples No. 3-5, No. 9-12, and No. 15-18 have Mo added without VC, with different amounts of Mo (Mo-added cemented carbide). Samples No. 8 and No. 12 have Ti(C,N) added (No. 8 has neither Mo nor VC added, and No. 12 has Mo added). The average particle size (0.5μm) of WC11 is consistent for all samples. The Cr3C213 content is uniformly set at 0.2 wt% for No. 8 and No. 12, and 1.0 wt% for all others.

[0046] [Table 1]

[0047] Hardness (HRA) was measured according to the TAS standard "Rockwell Scale A Test Method for Hard Materials" (TAS 0051:2021). Folding strength was measured according to the TAS standard "Folding Strength Test Method for Hard Materials" (TAS 0050:2021). The coefficient of friction and average wear width were measured according to the JIS standard "Abrasion Test Method for Fine Ceramics by Ball-on-Disk Method" (JIS R 1613:2010). Table 1 also shows the "Mo / (Mo+Co)" value, which indicates the weight ratio of Mo14 to the reinforcing binder phase.

[0048] Figure 5 shows the measurement results from Table 1 in a graph with HRA (hardness) on the horizontal axis and the coefficient of friction on the vertical axis. The dashed line represents the approximate straight line for each plot of Mo-added cemented carbide samples No. 3 to No. 5, which have a Co12 content of 8 wt% (hereinafter also referred to as 8% Co). The dashed line represents the approximate straight line for each plot of Mo-added cemented carbide samples No. 9 to No. 12, which have a Co12 content of 10 wt% (hereinafter also referred to as 10% Co). The solid line represents the approximate straight line for each plot of Mo-added cemented carbide samples No. 15 to No. 18, which have a Co12 content of 12 wt% (hereinafter also referred to as 12% Co).

[0049] Samples No. 1 and No. 2 (8% Co), No. 6 and No. 7 (10% Co), and No. 13 and No. 14 (12% Co) differ in whether or not VC is added (lower numbers indicate VC added, higher numbers indicate no VC added) (see Table 1). It can be seen that the VC-added samples (No. 1, No. 6, No. 13) (VC-added cemented carbide) show a significant improvement in HRA (hardness) compared to the VC-free samples (No. 2, No. 7, No. 14). Furthermore, the higher the Co content of the sample, the greater the improvement in HRA (hardness) due to the addition of VC. In addition, the friction coefficient of the VC-added samples is somewhat lower than that of the VC-free samples. In other words, the addition of VC greatly contributes to both the improvement in hardness and the reduction in the friction coefficient of cemented carbide, i.e., the improvement in wear resistance. The significant improvement in hardness, in particular, is thought to be because, as mentioned above, WC11 grain growth occurred during sintering in the VC-free sample, whereas in the VC-added sample, WC11 grain growth was effectively suppressed by VC. Cr3C213 also has an effect of suppressing WC11 grain growth, but it is thought that the addition of VC is particularly effective in suppressing WC grain growth.

[0050] Focusing on samples No. 1 to No. 5 containing 8% Co, a comparison was made between sample No. 1, a VC-added cemented carbide with 0.50 wt% VC added, and sample No. 3, a Mo-added cemented carbide with 1.00 wt% Mo added instead of VC. The coefficient of friction was almost the same, but the HRA (hardness) of No. 1 was considerably higher. When the amount of Mo added was increased to 3.00 wt% (sample No. 4), both the HRA (hardness) and the coefficient of friction improved considerably compared to sample No. 3. When the amount of Mo added was further increased to 5.00 wt% (sample No. 5), the coefficient of friction improved even more compared to sample No. 4, and the HRA (hardness) was almost the same as sample No. 4. Referring to Table 1, the average wear width of sample No. 1, a VC-added cemented carbide, was 0.230 mm, while the average wear widths of samples No. 4 and No. 5, which are Mo-added cemented carbides with Mo added instead of VC, were 0.190 mm and 0.180 mm, respectively. This shows that samples No. 4 and No. 5, with Mo added amounts of 3.00 wt% and 5.0 wt%, respectively, exhibit improved wear resistance compared to sample No. 1, a VC-added cemented carbide. Sample No. 3, a Mo-added cemented carbide with a Mo added amount of 1.0 wt%, did not show improved wear resistance compared to sample No. 1, a VC-added cemented carbide.

[0051] Focusing on the 10%Co samples No. 6 to No. 11, the coefficient of friction of sample No. 8, a Mo-added cemented carbide with 1.00 wt% Mo added instead of VC, is almost the same as that of sample No. 6, a VC-added cemented carbide with 0.5 wt% VC added. However, the HRA (hardness) of sample No. 6 is considerably higher. Nevertheless, increasing the amount of Mo added (No. 10, No. 11) greatly improves the coefficient of friction. Referring to Table 1, the average wear width of sample No. 6, a VC-added cemented carbide, is 0.240 mm, while the average wear widths of samples No. 10 and No. 11, which are Mo-added cemented carbides, are 0.230 mm and 0.160 mm, respectively. This shows that samples No. 10 and No. 11, which are Mo-added cemented carbides, have improved wear resistance compared to sample No. 6, a VC-added cemented carbide.

[0052] The same was true for samples No. 13 to No. 18, which contained 12% Co; by adding Mo instead of VC and further increasing the amount of Mo added, the wear resistance was improved.

[0053] We examined samples No. 8 and No. 12, which had Ti(C,N) added. Sample No. 8, which had neither VC nor Mo added, showed improved hardness and friction coefficient compared to sample No. 7, and a significant increase in average bending strength, resulting in a narrower average wear width. Comparing sample No. 12, which had both Mo and Ti(C,N) added, with sample No. 8, both hardness and friction coefficient improved (average bending strength slightly decreased), and the average wear width was narrower. Furthermore, comparing sample No. 11, which had Mo added but no Ti(C,N), with sample No. 12, sample No. 12 showed improved hardness and a narrower average wear width than sample No. 11, indicating that the addition of Ti(C,N) contributes to improved wear resistance.

[0054] Referring to Figure 5, among the 8%Co (dotted line), 10%Co (single dotted line), and 12%Co (solid line) samples, the 10%Co (single dotted line) and 12%Co (solid line) samples all commonly showed an increase in HRA (hardness) as the amount of Mo added increased. For the 8%Co (dotted line), increasing the amount of Mo added from 3.0 wt% to 5.0 wt% did not result in an increase in HRA (hardness) (Sample No. 4 and Sample No. 5). Considering that Mo does not easily precipitate on the surface of WC, meaning that the grain growth inhibitory effect of WC is not as strong as that of VC, the reason why the HRA (hardness) of the cemented carbide increased with the addition of Mo is thought to be that the solid solution of Mo in the Co bonding phase hardened the bonding phase, which contributed to the improvement in the HRA (hardness) of the cemented carbide (reinforced bonding phase). Furthermore, the fact that no increase in HRA (hardness) was observed when the amount of Mo added to 8% Co (dotted line) was increased from 3.0 wt% to 5.0 wt% suggests that the amount of Co-bonding phase was small, and the Mo dissolved in the Co-bonding phase became saturated at around 3.0 wt% addition.

[0055] In any case, it was found that the average wear width, one of the indicators of wear resistance determined by the HRA (hardness) and friction coefficient of cemented carbide, can be made equivalent to that of VC-added cemented carbide by adding a small amount of Cr3C2, which functions as a grain growth inhibiting phase, and adding a predetermined amount or more of Mo, even without adding VC, which exhibits a good grain growth inhibiting effect. Furthermore, it was found that by adding the amount of binder phase necessary to sufficiently solid dissolve the predetermined amount or more of Mo without saturating it, the wear resistance exceeds that of VC-added cemented carbide. It was also found that the greater the amount of binder phase, the greater the effect of lowering the friction coefficient, and the easier it is to obtain a Mo-added cemented carbide with excellent wear resistance.

[0056] Figure 6 shows the measurement results from Table 1 as a graph with the Mo / (Mo+Co) weight ratio on the horizontal axis and the coefficient of friction on the vertical axis (samples No. 3, 4, 5, 9, 10, 11, 12, 15, 16, 17, and 18, which contain Mo, are plotted).

[0057] It can be seen that the lower the amount of Mo (Mo / (Mo+Co)) in the reinforcing bonding phase, the higher the coefficient of friction, and the higher the amount of Mo in the reinforcing bonding phase, the lower the coefficient of friction tends to be. The lower the coefficient of friction, the better the wear resistance of the cemented carbide. As mentioned above, considering that a Mo-added cemented carbide, which has been prepared by adding a small amount of Cr3C2 that functions as a grain growth inhibiting phase, adding more than a predetermined amount of Mo, and adding the amount of bonding phase necessary to ensure sufficient solid solution without saturating the Mo above the predetermined amount, possesses a hardness comparable to that of a VC-added cemented carbide, it can be considered that a Mo-added cemented carbide has a surface with lower frictional force compared to a VC-added cemented carbide.

[0058] Figure 7 shows the measurement results from Table 1 as a graph with the Mo / (Mo+Co) weight ratio on the horizontal axis and the average wear width (mm) on the vertical axis (samples No. 3, 4, 5, 9, 10, 11, 12, 15, 16, 17, and 18, which contain Mo, are plotted).

[0059] Similar to the coefficient of friction, the average wear width, which represents the degree of wear resistance of cemented carbide, tends to narrow (i.e., become less prone to wear) as the amount of Mo occupying the reinforcing bonding phase increases.

[0060] Table 1 and Figures 5-7 show that when the content of the binder phase (Co) is relatively high (10 wt% or more), even with a Mo content of around 1.0 wt%, a Mo-added cemented carbide with superior wear resistance compared to VC-added cemented carbide can be obtained. When the amount of the binder phase (Co) is relatively low (a lower limit of around 3.00 wt% is considered), a low Mo content results in a Mo-added cemented carbide with inferior hardness and wear resistance compared to VC-added cemented carbide (No. 3 in Table 1 has inferior hardness and friction coefficient compared to No. 1), but increasing the Mo content yields a Mo-added cemented carbide with superior wear resistance compared to VC-added cemented carbide (No. 4 and No. 5 in Table 1 have improved wear resistance compared to No. 1). To achieve properties almost equivalent to a 0.5 wt% VC-added cemented carbide even with a Co content at the lower limit of Mo-added cemented carbide, the Mo / (Mo+Co) weight ratio needs to be 0.250 or higher. By setting the Mo / (Mo+Co) weight ratio to 0.250 or higher, it is possible to obtain a cemented carbide with hardness and wear resistance equivalent to or improved compared to VC-added cemented carbide.

[0061] While increasing the Mo / (Mo+Co) weight ratio improves wear resistance, it also leads to a decrease in average flexural strength (for example, No. 9 and No. 10 in Table 1). Considering that Mo-added cemented carbide is used as a tool and machine part, a decrease in average flexural strength is undesirable, and it is considered appropriate to limit the Mo / (Mo+Co) weight ratio to around 0.500.

[0062] Figure 8 is a graph comparing the relationship between the number of molded products and the amount of mold wear, obtained by fabricating two molds using VC-added cemented carbide (Sample No. 6) and Mo-added cemented carbide (Sample No. 11), and molding a large number of molded products using each of the two molds.

[0063] While VC-added cemented carbide had a slightly higher HRA (hardness) than Mo-added cemented carbide, a relatively rapid increase in wear was observed in the VC-added cemented carbide mold when molding a large number of molded products (continuous mold use over a long period). Referring to Figure 8, it can be seen that the VC-added cemented carbide mold (indicated by the triangle mark) shows a sharp increase in wear when the number of molded products exceeds 100,000. It is thought that the VC-added cemented carbide mold experienced detachment of WC particles due to its use in molding a large number of molded products, which caused the rapid increase in wear. On the other hand, no rapid increase in wear was observed in the Mo-added cemented carbide mold (indicated by the black circle mark) even when used to mold more than 100,000 molded products. This indicates that Mo-added cemented carbide exhibits less wear over the long term compared to VC-added cemented carbide.

[0064] Mo-added cemented carbides have a particularly low coefficient of friction, which reduces friction and suppresses heat generation. Therefore, they are suitable for applications in sliding parts and cutting tools that tend to generate heat. Furthermore, since molybdenum (Mo) has a low affinity for copper (Cu) and can suppress reactions with copper, they are also suitable for applications in tools and industrial cutting tools that come into contact with copper.

[0065] In the above-described embodiment, an example using Co12 as the bonding phase was explained, but it is thought that the same results can be obtained by using nickel (Ni) instead of Co12. [Explanation of symbols]

[0066] 11 Tungsten Carbide (WC) 12 Cobalt (Co) 13. Chromium carbide (Cr3C2) 14 Molybdenum (Mo)

Claims

1. The cemented carbide contains a hard phase consisting of tungsten carbide (WC) with an average grain size of 0.20 to 2.0 μm in an amount of 56.000 to 95.997 wt% of the total cemented carbide. The cemented carbide contains a bonding phase comprising at least one of cobalt (Co) and nickel (Ni) in an amount of 3,000 to 20,000 wt% relative to the entire cemented carbide. Chromium carbide (Cr ３ C ２ ) contains 0.003 to 4.000 wt% of the total cemented carbide, In terms of weight ratio, the "molybdenum (Mo) / (Mo+ bonded phase)" is 0.250 to 0.500, and it contains less Mo than the above bonded phase. The above hard phase, the above binding phase, and the above Cr ３ C ２ And the sum of the above Mo is 100 wt%, Bonding phase-reinforced wear-resistant cemented carbide.

2. The cemented carbide further contains 0.003 to 4.000 wt% titanium carbonitride (Ti(C,N)) relative to the total cemented carbide. The above hard phase, the above binding phase, and the above Cr ３ C ２ And the sum of the above Mo and the above Ti(C,N) is 100 wt%, The bonded phase-reinforced wear-resistant cemented carbide according to claim 1.

3. The above Ti(C,N) is titanium oxide (TiO ２ It is produced by carbonitriding during sintering. The bonded phase-enhanced wear-resistant cemented carbide according to claim 2.

4. The lower limit of the above-mentioned bound phase is 8.000 wt%. The bonded phase-reinforced wear-resistant cemented carbide according to claim 1.

5. A tool or machine part made of a bonded phase-reinforced wear-resistant cemented carbide according to any one of claims 1 to 4.

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