Cutting tools

Abstract

The present invention relates to a cutting tool comprising a cemented carbide substrate containing WC and 2 to 20 wt% of a Ni-based metal binder, wherein the cemented carbide contains Ni and Cr such that the Cr / Ni weight ratio is between 0.06 and 0.20, the cemented carbide contains 1 to 10 volume% of an eta phase, the average particle size of the eta phase particles is between 0.1 and 10 μm, and the cemented carbide does not contain a gamma phase. The cutting tool according to the present invention exhibits maintenance or improvement of properties compared to cemented carbide having a Co binder.

Description

Technical Field

[0001] The present invention relates to a cutting tool comprising a cemented carbide substrate and a metal binder containing an eta phase, Ni and Cr. The present invention also relates to a method for manufacturing a cutting tool.

Background Art

[0002] Tungsten carbide (WC)-based cemented carbides using a cobalt binder have been known in the art for about 100 years. Other metals known as binder metals for cemented carbides include iron and nickel, but cobalt is the most widely used.

[0003] Since cobalt has an adverse effect on the environment and health, research is underway to find a substitute binder for cobalt. However, it is difficult to replace cobalt or limit its usage without adversely affecting the material properties. In cutting tools, the properties of the substrate are important for the performance of the entire tool, and even a slight change in composition can potentially have an adverse effect on performance.

[0004] Nickel is suitable for the production of cemented carbides because it provides good wettability with WC. Nickel also exhibits excellent performance under oxidation and corrosion conditions compared to WC-Co cemented carbides. The main drawback of Ni-based cemented carbides is their low mechanical strength. One of the reasons is that the stacking fault energy of Ni is higher than that of Co, so the work hardening of Ni remains moderate compared to Co.

[0005] It has been particularly difficult to find a cemented carbide using an alternative binder with acceptable edge toughness.

Brief Description of the Drawings

[0006] [Figure 1] Figure showing the effect (calculated as delta) on toughness and hardness depending on different Cr addition amounts and the presence or absence of the gamma phase

Mode for Carrying Out the Invention

[0007] The object of the present invention is to provide a cemented carbide using an alternative binder phase that has properties equivalent to or improved to those of a substrate using a Co binder.

[0008] Furthermore, an object of the present invention is to provide a cemented carbide using an alternative binder phase that has cutting performance equivalent to or improved to that of a substrate using a Co binder. [Overview of the Initiative]

[0009] The present invention relates to a cutting tool comprising a cemented carbide substrate containing WC and 2 to 20% by weight of a Ni-based metal binder. The cemented carbide contains Ni and Cr such that the Cr / Ni weight ratio is between 0.06 and 0.20, and the cemented carbide contains 1 to 10% by volume of eta phase, with an average particle size of the eta phase between 0.1 and 10 μm. The cemented carbide does not contain gamma phase.

[0010] The cemented carbide according to the present invention does not contain a gamma phase. The gamma phase (also called the cubic system) is formed during sintering when one or more gamma phase-forming elements are present, such as Ti, Ta, Nb, Zr, V, Hf, and Mo, and is represented by the general formula (W,X)(C,N) or (W,X)(C), where X is one or more of the gamma phase-forming elements.

[0011] In this specification, a cemented carbide that does not contain a gamma phase means that the gamma phase cannot be observed in the microstructure of a LOM image at a magnification of 500x or more.

[0012] A cemented carbide that does not contain a gamma phase means that when gamma phase-forming elements such as Ti, Ta, Nb, Zr, V, Hf, and Mo are added, the content of these elements in the binder is kept below their solubility so that a gamma phase does not form. The presence of a gamma phase in the microstructure is undesirable because it leads to brittleness.

[0013] In one embodiment of the present invention, the total content of gamma phase-forming elements such as Ti, Ta, Nb, Zr, V, Hf, and Mo is preferably less than 1 atomic percent in the binder and more preferably less than 0.5 atomic percent in the binder phase of the cemented carbide.

[0014] In one embodiment of the present invention, the amount of gamma phase-forming elements such as Ti, Ta, Nb, Zr, V, Hf, and Mo is at the impurity level; that is, raw materials containing gamma phase-forming elements such as Ti, Ta, Nb, Zr, V, Hf, and Mo are not used in the production of cemented carbide according to the present invention.

[0015] The cemented carbide according to the present invention contains an eta phase. When the total carbon content falls below a certain value, an eta phase is formed in the cemented carbide.

[0016] Ni-based metal binders include Ni and Cr, and the metal binder is present in an amount between 2 and 20% by weight of the sintered body, preferably between 5 and 12% by weight. In this specification, Ni-based metal binder means that the binder contains more than 70% by weight of Ni. The binder also includes other elements that inevitably dissolve in the binder during sintering. Such elements include, for example, W and C derived from WC.

[0017] In one embodiment of the present invention, the total amount of Ni, Cr, and W in the binder is at least 98% by weight.

[0018] Cr is a commonly added element in cemented carbides, but the amount of Cr that can be added is usually limited by the solubility of Cr in the metal binder. If the amount of Cr exceeds the solubility in the binder, brittle carbides such as Cr7C3 precipitate in the microstructure, reducing the mechanical properties of the cemented carbide.

[0019] However, the upper limit of the amount of Cr added according to the present invention, i.e., the upper limit of the amount of Cr7C3 formed, can be higher than that of conventional cemented carbides that do not contain an eta phase, because an eta phase is present in the microstructure. Cr becomes part of the eta phase, and therefore, a larger amount of Cr can be added to the cemented carbide without forming brittle Cr7C3 carbides.

[0020] Cr can be added up to the limit where Cr7C3 is formed, but for practical reasons, it is not advisable to get too close to that limit. Appropriately, Cr is added so that the Cr / Ni weight ratio is between 0.06 and 0.20, preferably between 0.10 and 0.18.

[0021] Adding chromium (Cr) in these amounts to cemented carbides is beneficial because it contributes to the refinement of the microstructure and promotes the formation of the fine-grained eta phase. Higher Cr content also promotes the strengthening of the solid solution in the binder, resulting in increased hardness without reducing toughness. If the Cr content falls below the set range, hardness and other mechanical properties become insufficient.

[0022] The cemented carbide according to the present invention has a WC grain size between 0.1 and 12 μm, preferably between 0.4 and 9 μm, as measured, for example, by image analysis.

[0023] In this specification, cemented carbide means that the cemented carbide contains at least 50% by weight of WC.

[0024] The cemented carbide according to the present invention is essentially Co-free. This means that no Co powder is added as described herein. However, if the same manufacturing equipment as that used for Co-containing cemented carbide is used, and / or if the grinding ball medium is made of Co-containing cemented carbide, small amounts of Co may be present due to contaminants. As described herein, essentially Co-free means that the cemented carbide contains less than 1% by weight of Co, preferably less than 0.5% by weight. The Co content can be analyzed using conventional chemical analysis.

[0025] In one embodiment of the present invention, the cemented carbide contains Ru such that the weight ratio of Ru / (Ru + Ni) is between 0.05 and 0.20. By adding Ru, the ability of the binder to dissolve elements such as W can be enhanced. Most of the Ru dissolves in the Ni-based binder.

[0026] In one embodiment of the present invention, the cemented carbide insert is provided with a wear-resistant CVD (Chemical Vapor Deposition) or PVD (Physical Vapor Deposition) coating.

[0027] Additional treatments known in the art, such as brushing and blasting, can also be applied to the coating.

[0028] As used herein, the cutting tool means a tool such as an insert, an end mill, or a drill.

[0029] In one embodiment of the present invention, the cutting tool is an insert, preferably a milling insert.

[0030] In one embodiment of the present invention, the cemented carbide substrate is used for milling cast iron, steel, HRSA alloy, or Ti alloy.

[0031] In one embodiment of the present invention, the cemented carbide does not contain a gamma phase, contains WC and a Ni-based metal binder of 2 to 20% by weight, the cemented carbide contains Cr such that the weight ratio of Cr / Ni is between 0.06 and 0.20, the cemented carbide contains an eta phase in an amount between 1 and 10% by volume, and the eta phase particles have an average particle size between 0.1 and 10 μm. The cemented carbide does not contain elements other than W, C, Ni, and Cr, and the balance is inevitable impurities.

[0032] In one embodiment of the present invention, the cemented carbide contains WC and 8-12 wt% of a Ni-based metallic binder, without a gamma phase, and the cemented carbide contains Cr such that the Cr / Ni weight ratio is between 0.14 and 0.18. The cemented carbide further contains an amount between 1.5 and 5 volume% of an eta phase, and the eta phase particles have an average grain size between 0.5 and 3 μm. The cemented carbide contains no elements other than W, C, Ni, and Cr, and the remainder is unavoidable impurities.

[0033] In one embodiment of the present invention, the cemented carbide does not contain a gamma phase and contains WC and 2 to 20 wt% of a Ni-based metal binder, the cemented carbide contains Cr such that the Cr / Ni weight ratio is between 0.06 and 0.20 and Ru such that the Ru / (Ru+Ni) weight ratio is between 0.05 and 0.2, the cemented carbide contains an amount of eta phase between 1 and 10 volume%, and the eta phase particles have an average grain size between 0.1 and 10 μm. The cemented carbide does not contain elements other than W, C, Ni, and Cr, and the remainder is unavoidable impurities.

[0034] The present invention also relates to a method for manufacturing a cutting tool comprising the above-mentioned cemented carbide substrate. The method is as follows: - To provide WC powder, - To provide (one or more) powders containing Cr and Ni to form a binder phase, to form a powder blend. - To provide a grinding liquid, - To obtain cemented carbide by crushing, drying, pressurizing, and sintering powder. This includes each step, where, W and / or W2C are The cemented carbide, after sintering, contains 1 to 10 volume percent of the eta phase, and the average grain size of the eta phase is between 0.1 and 10 μm. It is added to the powder blend in such an amount.

[0035] The amount and distribution of the eta phase are controlled by the carbon content in the cemented carbide. To adjust the carbon content so that the desired eta phase is formed, one or more of W and W2C are added to the powder blend to create a carbon deficiency.

[0036] In one embodiment of the present invention, one or more powders of W and W2C are pre-ground before being added to the other raw materials.

[0037] The exact amounts of W and W2C depend on the composition of the other raw materials.

[0038] Normally, some carbon is lost during sintering due to the presence of oxygen. Oxygen reacts with carbon during sintering, releasing as CO or CO2, and therefore the carbon balance changes, requiring adjustment of the amount of one or more of W and W2C added. The exact amount of carbon lost during sintering depends on the raw materials and manufacturing techniques used, and it is the responsibility of those skilled in the art to adjust the amount of W and / or W2C added so that the desired amount and particle size of the eta phase in the sintered material are achieved.

[0039] In one embodiment of the present invention, the amount of WC added is between 80 and 98% by weight based on the dry powder weight. The particle size (FSSS) of the WC powder is appropriately between 0.1 and 12 μm, preferably between 0.4 and 9 μm.

[0040] The (one or more) powders forming the binder phase may be one or more of Ni, NiCr alloys, and Cr3C2. The (one or more) powders forming the binder phase are added such that the amount of metal binder is between 2 and 20% by weight, preferably 5 and 12% by weight, based on the dry powder weight.

[0041] In one embodiment of the present invention, grain growth can be suppressed, for example, by adding small amounts of elements such as Ti, Ta, Nb, Zr, V, Hf, and Mo, which are normally considered gamma phase-forming elements, for example, as carbides / nitrides. However, the amount of these elements must be low enough to almost completely avoid the formation of the gamma phase.

[0042] In one embodiment of the present invention, no raw materials containing gamma phase-forming elements such as Ti, Ta, Nb, Zr, V, Hf, and Mo are added during the production of the cemented carbide according to the present invention. If these elements were present in the sintered cemented carbide, the amount would be at the impurity level.

[0043] Any liquid commonly used as a grinding liquid in conventional cemented carbide manufacturing can be used. The grinding liquid is preferably water, alcohol, or an organic solvent, more preferably water, or a mixture of water and alcohol, and most preferably a mixture of water and ethanol. The properties of the slurry depend on the amount of grinding liquid added. Since energy is required to dry the slurry, the amount of liquid should be kept to a minimum to reduce costs. However, a sufficient amount of liquid needs to be added to achieve a slurry that can be pumped and to prevent system clogging. Additionally, other compounds commonly known in the art, such as dispersants and pH adjusters, can be added to the slurry.

[0044] An organic binder may be optionally added to the slurry to promote granulation during the subsequent spray-drying operation and to function as a pressurizing agent for the subsequent pressurizing and sintering operations. The organic binder can be any binder commonly used in the art. Examples of organic binders include paraffin, polyethylene glycol (PEG), and long-chain fatty acids. The amount of organic binder is appropriately between 15 and 25 volume percent based on the total volume of the dry powder, and the amount of organic binder is not included in the total volume of the dry powder.

[0045] A slurry containing a powder that forms a hard component, a powder that forms a binder phase, and optionally an organic binder, can be mixed by grinding in either a ball mill or an attritor mill. The slurry is then properly ground in a ball mill or attritor mill to obtain a homogeneous slurry blend.

[0046] The slurry, a mixture of powdered material and, optionally, an organic binder, is atomized through a suitable nozzle in a drying tower, where the small droplets are instantly dried by a high-temperature gas stream, such as a nitrogen stream, to form aggregated granules. For small-scale experiments, other drying methods, such as bread drying, can also be used.

[0047] Unsintered bodies are formed from dried powder / granules by pressing operations such as uniaxial presses and multiaxial presses.

[0048] An unsintered body formed from powder / granules manufactured according to the present invention is subsequently sintered according to any conventional sintering method such as vacuum sintering, sintering HIP (high static pressure), discharge plasma sintering, or gas pressure sintering (GPS).

[0049] The sintering temperature is typically between 1300 and 1580°C, preferably between 1350 and 1470°C.

[0050] In one embodiment of the present invention, the sintering process includes a sintering HIP step carried out at a temperature between 1350 and 1550°C and a pressure of at least 40 bar, preferably between 40 and 80 bar. Typically, an inert argon atmosphere is used during the HIP step without the intentional addition of CO or H2. However, residual amounts of other gases (H2O, CO, CO2) may form in situ during the sintering process.

[0051] In yet another embodiment of the present invention, the cemented carbide insert is coated with a wear-resistant CVD or PVD coating. [Examples]

[0052] Example 1 Samples were prepared to investigate the effects of different Cr addition amounts and TiC addition (for gamma phase formation). Raw material powders according to Table 1 (the remainder being WC with a particle size of 0.81-0.87 μm (FSSS)) were ground in a ball mill for 10 hours with an organic binder (2% by weight of PEG based on the total weight of the powder) and a grinding solution (water / ethanol) to form a slurry. This slurry was dried and ground in an agate mortar to obtain a powder blend. The powder was pressure-molded to obtain an unsintered body. The unsintered body was sintered in a HIP (hot isostatic) furnace (the maximum sintering temperature was 1410°C, and the sintering time was 1 hour at 40 mbar vacuum sintering), and then a high-pressure sintering step of 15 minutes at 50 bar of Ar was performed to reduce the porosity of the sample. The average cooling rate was 1.6°C / min from 1410 to 1100°C and 6.6°C / min from 1100 to 100°C. TIFF2026516881000002.tif82170

[0053] After grinding and polishing, the toughness (K1C) and hardness (HV30) of the sintered body were measured. HV30 was measured in accordance with ISO 6507:2018. Fracture toughness (K1C) was measured in accordance with ISO 28079.

[0054] The volume fraction and particle size of the Eta phase were determined by image analysis using the "Analyze particles" function of ImageJ software with the "include holes" and "0-Infinity" filter settings. When measuring the Eta phase, the "exclude on edges" option for Ferret size was additionally enabled in the "Analyze particles" function. Before measurement, color LOM images were converted to 8-bit grayscale images using automatic thresholding. The images used for analysis were LOM images at a magnification of 1000x, and images between 10 and 12 were processed. The values ​​in Table 2 are the average values. The average particle size of the Eta phase is given as the minimum Ferret particle size. Examination of the LOM images of the samples revealed a finely dispersed Eta phase in all samples, and the gamma phase was clearly observed in the comparison sample. The results are given in Table 2. TIFF2026516881000003.tif88170

[0055] The data in Table 2 is also shown in Figure 1, illustrating the effects of different Cr addition amounts (x-axis) and the presence or absence of the gamma phase.

[0056] In Figure 1, the toughness and hardness values ​​are recalculated on the "delta" (y-axis). For cemented carbides containing Co as a binder, it is possible to obtain a baseline plot of hardness against toughness (K1C) from literature data. "Delta" is the value calculated from the distance from that baseline to the experimentally measured values ​​of HV and KIC.

[0057] The delta value should be as close to zero (or greater than zero) as possible. Delta is as follows: TIFF2026516881000004.tif10170

[0058] Here, ΔHV and ΔKIC are measured values ​​(HV, KIC) and calculated values ​​(HV calc KIC calc It is the difference between ΔHV and ΔKIC, and the coefficient I is -1 when ΔHV and ΔKIC are negative values, and +1 when ΔHV and ΔKIC are positive values. TIFF2026516881000005.tif32170

[0059] In the formula, a, b, and c are constants determined by substituting experimentally measured HV and KIC values ​​into Equation 4: a = 2,670,000, b = 4,590, c = 1,240.

[0060] Figure 1 clearly shows that when an amount of TiC sufficient to form a gamma phase is added, the delta value decreases compared to the corresponding cemented carbide that does not contain a gamma phase.

[0061] Example 2 A cemented carbide insert with geometric shape R390-11T308M-PM was manufactured using the raw materials given in Table 3. The remainder was WC with a grain size (FSSS) of 0.81 to 0.87 μm. TIFF2026516881000006.tif28170

[0062] The raw material powder was ground together with an organic binder (2% by weight of PEG based on the total weight of the powder) and a grinding solution (water / ethanol) in a Netzsch Labstar bead mill at an efficiency of 1-2 kWh to form a slurry. This slurry was dried and ground in an agate mortar to obtain a powder blend. The powder was pressure-molded to obtain an unsintered body.

[0063] The unsintered body was sintered in a HIP (Hot Isostatic Pressurization) furnace (the maximum sintering temperature was 1410°C, and the sintering time was 1 hour under vacuum sintering at 40 mbar). Subsequently, a high-pressure sintering step was performed with 50 bar of Ar for 15 minutes to reduce the porosity of the sample. The average cooling rate was 1.6°C / min from 1410°C to 1100°C and 6.6°C / min from 1100°C to 100°C.

[0064] The insert was coated with PVD.

[0065] In this specification, these inserts will be referred to as Invention 6 (Ti-free) and Comparative Example 9 (Ti-added).

[0066] Similar to the sample in Example 1, the sintered body was ground and polished, and then the toughness (K1C), hardness (HV30), and volume % and average particle size (minimum ferret diameter) of the eta phase were measured.

[0067] The total carbon content in the sintered material is measured using a LECO CS-844. Approximately 0.2 grams of a pre-weighed sample is burned in a stream of purified oxygen using RF induction heating. The carbon in the sample is oxidized to carbon dioxide (CO2), which is then removed by oxygen carriers through a heated dust filter, a dry reagent, and a non-dispersive infrared (NDIR) cell.

[0068] The results are given in Table 4. TIFF2026516881000007.tif37170

[0069] Example 3 For comparison, a cemented carbide insert (containing 10 wt% Co, 0.39 wt% Cr, and the remainder WC) with the same shape as the inserts of Invention 6 and Comparative Example 9 was manufactured. WC powder with an average particle size (FSSS) of 0.81 to 0.87 μm was used. This cemented carbide was manufactured by a standard method, namely, by grinding, spray drying, pressure molding, and sintering. This cemented carbide insert was coated with the same PVD coating as the insert according to the present invention. Hereinafter, this insert will be referred to as Comparative Example 10.

[0070] Practical Example 1 In this milling test, the coated cemented carbide insert according to the present invention (Invention 6) is compared with an insert having a gamma phase (Comparative Example 9) and an insert having Co as a binder (Comparative Example 10) (both having the same shape as R390-11T308M-PM). This test was performed using Toolox 33 tool steel under dry conditions with the following cutting parameters: Vc: 250(m / min) Fz: 0.20 (mm) ap: 2.0(mm) ae: 49.0 (mm) Time required per cut: 0.29 minutes The criterion for tool life was chipping on the flank (mm) ≥ 0.50.

[0071] The results are shown in Table 5, and tool life is the average of four tests. TIFF2026516881000008.tif33170

[0072] As shown in Table 5, the insert according to the present invention exhibited performance equivalent to that of the corresponding insert having Co as a binder.

[0073] As shown in Table 5, the insert according to the present invention showed slightly better performance than the corresponding insert having Co as a binder.

[0074] Practical Example 2 This milling test compares a coated cemented carbide insert according to the present invention (Invention 6) with an insert using Co as a binder (Comparative Example 10) (both having the same geometric shape as R390-11T308M-PM). This test was performed using steel Dievar under dry conditions with the following cutting parameters: Vc: 215(m / min) Fz: 0.15 (mm) ap: 3.0(mm) ae: 12.0 (mm) Time required per cut: 0.04 minutes The criterion for tool life was a chip width (mm) ≥ 0.50 along the edge line.

[0075] The results are shown in Table 6, and tool life is the average of 8 tests. TIFF2026516881000009.tif22170

[0076] As shown in Table 6, the insert according to the present invention exhibited significantly better performance than the corresponding insert having Co as a binder.

Claims

1. A cutting tool comprising a cemented carbide base material containing WC and 2 to 20% by weight of a Ni-based metal binder, wherein the cemented carbide is Ni and Cr such that the Cr / Ni weight ratio is between 0.06 and 0.20 including and The cemented carbide contains 1 to 10 volume percent of the eta phase, and the average grain size of the eta phase is between 0.1 and 10 μm, and The cemented carbide does not contain a gamma phase. cutting tools.

2. The cutting tool according to claim 1, wherein the weight ratio between Cr and Ni is between 0.10 and 0.

18.

3. A cutting tool according to claim 1 or 2, which is essentially free of Co.

4. A cutting tool according to any one of claims 1 to 3, wherein the cemented carbide contains an amount of eta phase between 1 and 7 volume percent.

5. A cutting tool according to any one of claims 1 to 4, wherein the cemented carbide contains an amount of eta phase between 1.5 and 5 volume percent.

6. A cutting tool according to any one of claims 1 to 5, wherein the cemented carbide includes an eta phase having an average grain size between 0.5 and 3 μm.

7. A cutting tool according to any one of claims 1 to 6, wherein the cemented carbide contains Ru such that the weight ratio of Ru / (Ru+Ni) is between 0.05 and 0.

20.

8. A cutting tool according to any one of claims 1 to 7, wherein the cutting tool is provided with a coating.

9. A method for manufacturing a cutting tool comprising a cemented carbide substrate according to any one of claims 1 to 8, - To provide WC powder, - To form a powder blend, provide (one or more) powders containing Cr and Ni to form a binder phase. - To provide a grinding liquid, - To obtain cemented carbide, the powder is crushed, dried, pressurized, and sintered. Includes, W and / or W ２ C is, The cemented carbide is added to the powder blend in an amount such that it contains 1 to 10 volume percent of the eta phase, and the average particle size of the eta phase is between 0.1 and 10 μm. method.

10. A method for manufacturing a cutting tool comprising a cemented carbide substrate according to claim 9, comprising a sintering HIP step carried out at a temperature between 1350 and 1550°C and a pressure of at least 40 bar, preferably between 40 and 80 bar.

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