supercarbide cutting tools

Abstract

The present invention relates to a cutting tool comprising a cemented carbide substrate, the cemented carbide comprising a hard phase comprising WC, a mixed carbide phase and a metallic binder, the cemented carbide comprising the elements V, Cr, Ni and Fe in amounts such that: the weight fraction V / (V+Cr+Ni+Fe) is between 0.0030 and 0.050; the weight fraction Cr / (V+Cr+Ni+Fe) is between 0.010 and 0.040; the weight fraction Ni / (V+Cr+Ni+Fe) is between 0.030 and less than 0.050; and the weight fraction Fe / (V+Cr+Ni+Fe) is between 0.86 and 0.967. The cemented carbide according to the invention has toughness and hardness comparable to cemented carbide with a Co-binder.

Description

[Technical Field]

[0001] The present invention relates to a cutting tool comprising a cemented carbide substrate with an Fe-based binder, the cemented carbide further comprising V, Cr, and Ni. The present invention also relates to a method for manufacturing such a cutting tool. [Background technology]

[0002] WC-based hardmetals with cobalt binders have been known in the art for nearly 100 years. Other metals known as binder metals for hardmetals are iron and nickel, but cobalt is by far the most commonly used.

[0003] Due to environmental and health implications, ongoing efforts are being made to find alternative binders to cobalt. However, it is difficult to replace or limit the amount of cobalt without adversely affecting material properties. In cutting tools, the properties of the substrate are critical to the overall performance of the tool, and even small changes in composition can have a detrimental effect on performance.

[0004] For cemented carbides with Co binders, there is a relationship between toughness and hardness that is difficult to alter: for example, it is not possible to improve toughness without decreasing hardness, or vice versa.

[0005] Iron is known as a binder element, but is generally not preferred because it is believed to have a negative effect on the toughness of cemented carbides. Pure iron binders have a tendency to form brittle phases (i.e., martensite, Fe-carbides, etc.). Furthermore, control of carbon to produce a defect-free microstructure (precipitates of (W,Me)C subcarbides and graphite) is difficult to achieve with standard manufacturing.

[0006] The object of the present invention is to be able to produce hardmetals with alternative binder phases that have comparable or improved properties compared to hardmetals with Co binders.

[0007] Another object of the present invention is to provide a cemented carbide whose hardness can be varied while substantially maintaining its toughness.

[0008] Another object of the present invention is to obtain a cemented carbide in which the grain growth of WC grains during sintering is small. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 shows a graph comparing hardness and toughness (K1C) values ​​of a cemented carbide according to the invention (black circles) and a cemented carbide with a Co binder (white circles) collected from literature data. [Figure 2] FIG. 2 is a close-up view of the area enclosed by the dotted line in FIG. 1. [Figure 3] FIG. 1 is a diagram showing the relationship between the K1c difference (ΔK1c) and the amount of V added to the binder at three different sintering temperatures in Example 2 (numbers indicate sample numbers in Table 2). [Figure 4] XRD diffraction patterns of cemented carbides with different V contents, where the peak of the mixed carbide phase marked A is clearly visible. The peak marked B is the peak of WC. [Figure 5] FIG. 1 shows an SEM-EDX image of the microstructure of a cemented carbide according to the invention, showing the layered structure of all elements, with mixed carbides (1), WC grains (2) and binder phase (3) shown. [Figure 6] FIG. 7 shows an SEM-EDX image of the microstructure of the same area as in FIG. 6, with tungsten highlighted, 1 mixed carbides, 2 WC grains, and 3 binder phase. [Figure 7] FIG. 7 shows an SEM-EDX image of the same area as in FIG. 6, with iron highlighted, 2 WC grains, and 3 binder phase. [Figure 8] FIG. 7 shows an SEM-EDX image of the microstructure of the same section as in FIG. 6, with vanadium highlighted and 1 being the mixed carbide phase. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention relates to a cutting tool comprising a cemented carbide substrate, the cemented carbide comprising a hard phase comprising WC, a mixed carbide phase and a metallic binder, the cemented carbide comprising the elements V, Cr, Ni and Fe, - the weight fraction V / (V+Cr+Ni+Fe) is between 0.0030 and 0.050, - the weight fraction Cr / (V+Cr+Ni+Fe) is between 0.010 and 0.040; - the weight fraction Ni / (V+Cr+Ni+Fe) is between 0.020 and less than 0.050, - Weight fraction Fe / (V+Cr+Ni+Fe) is between 0.86 and 0.967 Concerning cutting tools, including in such amounts.

[0011] The cemented carbide according to the present invention has the advantage that its hardness can be changed while its toughness is basically maintained.

[0012] Another advantage is that the grain size of the WC can be controlled, as grain growth during sintering is partially minimized due to the strong grain growth inhibitor effect of vanadium.

[0013] The cemented carbide according to the present invention comprises WC, a mixed carbide phase, and a metal binder, and the mixed carbide phase is formed during sintering. Depending on the amounts of elements present in the cemented carbide, the exact composition of the mixed carbide phase is not completely known, but it can be described as a carbide phase with a specific stoichiometry different from that of the conventional gamma phase. When analyzed, the mixed carbide phase has a similar crystal structure to the eta phase, but the eta phase usually contains a larger amount of the binder metal. The mixed carbide phase also contains a small amount of Fe (see EDX analysis in the Examples). More specifically, (V,W) x C y The phase may be one or more of these elements in an atomic ratio V:W of 3:1 to 3:2.

[0014] Most of the added V is contained in the mixed carbide phase in the final cemented carbide, along with small amounts of Cr and W added from the WC. The metal binder may also contain small amounts of other elements present in the cemented carbide that will inevitably dissolve in the metal binder during sintering.

[0015] In one embodiment of the present invention, the total amount of the elements Fe, Cr and Ni in the metal binder is at least 90 wt% of the binder, preferably at least 95 wt% of the binder. The binder may also contain other elements, for example W present in the cemented carbide, which dissolves in the binder during sintering.

[0016] The amount of metal binder in the cemented carbide is preferably between 3 wt% and 20 wt% of the cemented carbide, more preferably between 5 wt% and 15 wt%. One method for determining the amount of metal binder is by image analysis or chemical analysis of the cemented carbide composition.

[0017] The cemented carbide contains an amount of V such that the weight fraction V / (V+Cr+Ni+Fe) is between 0.0030 and 0.050, preferably between 0.010 and 0.030, more preferably between 0.015 and 0.020. Too low a V content leads to large WC grain growth during sintering, whereas too high a V content leads to a rapid decrease in the toughness of the cemented carbide and embrittlement at the WC interface.

[0018] The cemented carbide contains an amount of Cr such that the weight fraction Cr / (V+Cr+Ni+Fe) is between 0.010 and 0.040, preferably between 0.010 and 0.020. If the Cr content is too low, the solid solution strengthening effect of Cr in Fe will be reduced, resulting in a poor combination of hardness and toughness, while if the Cr content is too high, the cemented carbide will precipitate Cr-carbides at the grain boundaries, deteriorating the properties of the material.

[0019] The cemented carbide contains an amount of Ni such that the weight fraction Ni / (V+Cr+Ni+Fe) is between 0.020 and less than 0.050, preferably between 0.020 and 0.045, more preferably between 0.020 and 0.030. Too low a Ni content reduces the ductility of the cemented carbide binder, leading to embrittlement of the composite, while too high a Ni content reduces the strength of the cemented carbide and its temperature stability to heat exposure.

[0020] The cemented carbide contains Fe in an amount such that the weight fraction Fe / (V+Cr+Ni+Fe) is between 0.860 and 0.967, preferably between 0.910 and 0.960.

[0021] In one embodiment of the present invention, the cemented carbide does not contain any other components than W, C, Fe, Ni, Cr and V, except for unavoidable impurities, which means that no other elements are added as raw materials.

[0022] The cemented carbide may be essentially Co-free, which means herein that Co is not added as a raw material and that Co is present in the cemented carbide at impurity levels, preferably less than 1 wt%, more preferably less than 0.5 wt%. Co is typically found in small amounts, as some manufacturing equipment, such as grinding bodies, may contain Co-containing cemented carbide, which may contribute slightly to the overall composition.

[0023] The hard phase contains at least 50 wt% WC. The average grain size of the WC is suitably between 0.2 μm and 10 μm, preferably between 0.2 μm and 5 μm. The average grain size of the WC can be measured, for example, using the mean line intercept method on SEM / LOM images.

[0024] In one embodiment of the present invention, the cemented carbide may also contain other elements common in the cemented carbide art, such as carbides, carbonitrides or nitrides of one or more of Ti, Ta and Nb, with elements from these carbides then necessarily dissolving in the binder during sintering.

[0025] In one embodiment of the present invention, the cemented carbide substrate is provided with a wear-resistant CVD (chemical vapor deposition) or PVD (physical vapor deposition) coating.

[0026] In one embodiment of the present invention, the cemented carbide substrate is provided with a wear-resistant PVD coating, preferably a nitride, oxide, carbide or mixture thereof of one or more elements selected from groups 4, 5 and 6 of the periodic table, and optionally Al and / or Si.

[0027] In yet another embodiment of the present invention, a cemented carbide substrate is provided with a wear-resistant CVD coating.

[0028] In yet another embodiment of the present invention, a cemented carbide substrate is provided with a wear-resistant CVD coating comprising several layers, preferably at least a carbonitride layer and an Al2O3 layer.

[0029] By cutting tool is meant herein a cutting tool insert, an end mill or a drill.

[0030] The present invention also relates to a method for manufacturing a cutting tool according to the above, comprising the above-mentioned cemented carbide substrate, said method comprising the following steps: - preparing WC powder; - providing a powder containing the elements V, Fe, Ni and Cr; - preparing a milling liquid; - grinding, drying, pressing and sintering the powder to form a cemented carbide; Includes.

[0031] The raw materials containing the elements V, Fe, Ni and Cr can be added as pure metals, alloys of two or more metals, or their carbides, nitrides or carbonitrides. The raw materials are preferably added in amounts such that the binder phase has the composition described above after sintering.

[0032] In one embodiment of the present invention, the powder is VC, Cr3C2, Fe and Ni.

[0033] The average particle size (Fisher subsieve size) of the WC powder used is preferably 0.2 to 10 μm, more preferably 0.2 to 5 μm.

[0034] Any liquid commonly used as a milling liquid in conventional cemented carbide manufacturing can be used. The milling 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 milling liquid added. Because drying the slurry requires energy, the amount of liquid should be minimized to reduce costs. However, sufficient liquid must be added to achieve a pumpable slurry and avoid clogging of the system. Additionally, other compounds commonly known in the art, such as dispersants, pH adjusters, etc., can be added to the slurry.

[0035] An organic binder is also optionally added to the slurry to facilitate granulation during the subsequent spray drying operation, as well as to act as a pressing agent for any subsequent pressing and sintering operations. The organic binder can be any binder commonly used in the art. The organic binder can be, for example, paraffin, polyethylene glycol (PEG), long-chain fatty acids, etc. The amount of organic binder is preferably between 15 vol% and 25 vol% of the total dry powder volume, and the amount of organic binder is not included in the total dry powder volume.

[0036] The powders forming the hard components and the powders forming the binder phase, and optionally a slurry containing an organic binder, are suitably mixed by a grinding operation in a ball mill or attritor mill. The grinding is suitably carried out by first forming a slurry containing the metal binder powder, the first and second powder fractions, and optionally an organic binder. The slurry is then suitably ground in a ball mill or attritor mill to obtain a homogeneous slurry blend.

[0037] A slurry containing powdered material mixed with an organic liquid and optionally an organic binder is atomized through a suitable nozzle in a drying tower where small droplets are instantaneously dried by a stream of hot gas, e.g., nitrogen, to form agglomerated granules. For small scale experiments, other drying methods, such as evaporating dish drying, can also be used.

[0038] The dried powder / granules are then subjected to a pressing operation such as uniaxial pressing or multiaxial pressing to form a green body.

[0039] The green body formed from the powder / granules produced according to the present invention is then sintered according to any conventional sintering method, such as vacuum sintering, sinter HIP, spark plasma sintering, gas pressure sintering (GPS), etc.

[0040] In one embodiment of the present invention, the sintering temperature is between 1350°C and 1550°C.

[0041] In one embodiment of the present invention, the sintering method is sinter-HIP carried out at a temperature between 1350° C. and 1550° C. and at a pressure of at least 40 Bar, preferably between 40 Bar and 80 Bar.

[0042] In one embodiment of the present invention, a coating is applied to a cemented carbide substrate.

[0043] In one embodiment of the present invention, the cemented carbide substrate produced as described above is provided with a wear-resistant coating using CVD or PVD techniques.

[0044] In one embodiment of the present invention, the cemented carbide substrate is provided with a wear-resistant PVD coating, preferably a nitride, oxide, carbide or mixture thereof of one or more elements selected from groups 4, 5 and 6 of the periodic table, and optionally Al and / or Si.

[0045] In one embodiment of the present invention, a CVD coating is deposited that includes a first TiCN layer deposited by MTCVD and a second α-Al2O3 layer deposited by CVD. An optional outermost color layer for wear detection, such as a TiN layer, can also be deposited.

[0046] The coating may also be subjected to additional treatments such as brushing or blasting.

[0047] The present invention also discloses a cemented carbide cutting tool manufactured according to the above method. [Example]

[0048] Example 1 Cemented carbides were prepared from raw materials containing Cr3C2, VC, Ni, and Fe, such that the total powder composition, excluding WC, was 91 wt% Fe, 3.5 wt% Ni, 1.4 wt% Cr, and 4.0 wt% V. Carbon black was added up to 0.4% of the mixture weight, more specifically, between 0.15% and 0.4%. The average particle size (Fisher subsieve size) of the WC powder was 0.83 μm. The amounts of V, Cr, Ni, and Fe in the cemented carbides were varied according to Table 1. The raw powders were ball-milled with an organic binder (2 wt% PEG based on the total powder weight) and a milling solution (water / ethanol) for 8 hours to form a slurry, which was then dried and ground in an agate mortar to obtain a powder blend. The powders were pressed into green bodies, which were then sintered in a hot isostatic pressing (HIP) furnace. The maximum sintering temperature was 1450°C, and the sintering time was 1 hour under vacuum sintering at 40 mbar, followed by a 15 minute high pressure step at 50 bar to reduce the porosity of the samples.

[0049] The toughness (K1C) and hardness (HV30) of the sintered compacts after grinding and polishing were measured. HV30 was measured according to ASTM B294. Fracture toughness (K1C) was measured according to Shetty. TIFF2025541879000002.tif94170

[0050] To compare the results in Table 1 with cemented carbides with Co binders, the hardness and toughness (K1C) values ​​from Table 1 were plotted along with the values ​​for cemented carbides with pure Co metal binder based on literature data (see Figures 1 and 2). The data in Table 1 were fitted to a linear model that was fitted to the data in the ranges of HV30 between 1600 and 2200 and K1C between 5 and 12. The ranges and models are shown on the graphs by dashed boxes and solid lines. The results obtained in this invention with varying binder content are displayed in the same ranges by black circles.

[0051] As can be seen from Figures 1 and 2, the cemented carbide according to the present invention has hardness and toughness properties in the same range as cemented carbide with a Co binder.

[0052] Example 2 Powders with different V contents and compositions according to Table 2 were prepared in a similar manner from the same raw materials as in Example 1. The samples were sintered in a HIP furnace at three different temperatures (1410°C, 1450°C, and 1500°C) (see Table 2). The sintering time was 60 minutes at a maximum vacuum sintering temperature of 40 mbar, followed by 15 minutes at high pressure sintering temperature of 50 bar.

[0053] The samples were analyzed for K1c and hardness in the same manner as in Example 1. To assess the effect of different V contents, the difference between the measured and calculated K1c values ​​(ΔK1c) was evaluated versus the amount of V added to the binder phase (see Table 2). The ΔK1c values ​​are the difference between the measured K1c values ​​and the K1c values ​​calculated from a linear model fitted to a selected subset of literature data for WC-Co cemented carbides (shown in Figure 1). K1c_calculated value = 15.22 - 0.003527 * HV TIFF2025541879000003.tif146170

[0054] In FIG. 3, the V content is plotted against ΔK1c for three sintering temperatures, and it can be clearly seen that the best properties are obtained at the V content according to the invention (the numbers indicate the sample numbers in Table 2).

[0055] Example 3 The samples of Example 2 were analyzed using XRD. The samples were prepared by casting on Bakelite, grinding, and polishing. XRD measurements were performed using a 1 μS Microfocus Source (CuK α The measurements were performed on a Davinci-designed Bruker Discover D8 diffractometer equipped with a 1.0 mm diameter collimator (λ = 1.5418 Å), a Vantec-500 area detector, and a quarter-wave Eulerian cradle. The X-ray source was operated at 50 kV and 1 mA. The samples were attached to the sample holder with adhesive tape. A collimator size of 1.0 mm diameter was used in all experiments. Measurements were performed on the polished surface of the investigated insert. Data were collected over the 2θ range of 10° to 140°.

[0056] The XRD data were analyzed using the software DIFFRAC EVA (Bruker) and High Score Plus (Malvern Panalytical).

[0057] Figure 4 shows the XRD diffractograms in which the WC peaks are marked and three peaks of the mixed carbide phase are also shown. The XRD diffractograms of the samples with different V contents clearly show that the peaks representing the mixed carbides increase with increasing V content.

[0058] Example 4 Three samples according to the present invention were analyzed by SEM-EDX (energy dispersive X-ray spectroscopy) using a Zeiss Supra40 electron microscope equipped with Oxford Instruments' AZtec software to perform elemental mapping and compositional analysis at selected points in the mixed carbide phase. The accelerating voltage was 10 kV and the working distance was 8.5 mm. Specifically, the mixed carbide phase was investigated.

[0059] The samples were Invention 5 (Table 1) and two additional samples according to the invention, Invention 9 and Invention 10. Inventions 9 and 10 were produced in the same manner as Example 1, and Inventions 9 and 10 contained 7.7 wt% and 16.5 wt%, respectively, of the same Fe-V-Ni-Cr mixture as Example 1. Invention 9 used the same WC raw material as Example 1, but with a particle size (Fisher subsieve size) of 7.15 μm.

[0060] Specifically, the mixed carbide phase was investigated.

[0061] 5-8 show EDX images of Inventive Example 10 with V, Fe, and W highlighted, which show that the mixed carbide phase contains large amounts of V and W, but small amounts of Fe (not visible in the images). It can also be seen that the binder contains large amounts of Fe, but very little V.

[0062] The average composition of the mixed carbide phase was analyzed and the composition in weight percentage was as shown in Table 3. TIFF2025541879000004.tif86170

[0063] As can be seen from Table 3, the mixed carbide phase mainly contains W, C and V, with only small amounts of Fe, Ni and Cr.

Claims

1. 1. A cutting tool comprising a cemented carbide substrate, the cemented carbide comprises a hard phase comprising WC, a mixed carbide phase and a metal binder; The cemented carbide contains the elements V, Cr, Ni and Fe, the weight fraction V / (V+Cr+Ni+Fe) is between 0.0030 and 0.050, - weight fraction Cr / (V+Cr+Ni+Fe) between 0.010 and 0.040, the weight fraction Ni / (V+Cr+Ni+Fe) is between 0.030 and less than 0.050, - weight fraction Fe / (V+Cr+Ni+Fe) between 0.86 and 0.967 Including cutting tools in such amounts.

2. 2. The cutting tool of claim 1, wherein the content of the metal binder in the cemented carbide is between 3 wt% and 20 wt%.

3. 10. The cutting tool of claim 1, wherein the total amount of the elements Fe, Cr and Ni in the metal bond is at least 90 wt% of the bond.

4. 4. A cutting tool according to any one of claims 1 to 3, wherein the weight fraction V / (V+Cr+Ni+Fe) is between 0.010 and 0.

040.

5. 5. A cutting tool according to any one of claims 1 to 4, wherein the weight fraction Cr / (V+Cr+Ni+Fe) is between 0.012 and 0.

030.

6. 6. A cutting tool according to any one of claims 1 to 5, wherein the weight fraction Ni / (V+Cr+Ni+Fe) is between 0.02 and 0.

045.

7. The cutting tool of claim 1 , further comprising a coating.

8. The following steps: - providing a WC powder; - providing a powder containing the elements V, Fe, Ni and Cr; - preparing a milling liquid; - grinding, drying, pressing and sintering said powder to form a cemented carbide; A method for producing a cutting tool comprising the cemented carbide substrate of any one of claims 1 to 7, comprising:

9. The method of claim 8, wherein sintering is carried out at a sintering temperature between 1350°C and 1550°C and a pressure of at least 40 Bar.

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