Hard alloy cutting tool

Abstract

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

Description

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

[0002] Cemented carbides based on WC with a cobalt binder have been known in the art for nearly a century. Other metals known as binder metals in cemented carbides are iron and nickel, however, cobalt is by far the most used.

[0003] Due to the environmental and health impacts of cobalt, there has been an ongoing effort to find an alternative binder for it. However, it is difficult to replace or limit the amount of cobalt without negatively affecting the material properties. For cutting tools, the substrate properties are important for the overall performance of the tool, and even small changes in the composition may have an adverse effect on the performance.

[0004] For cemented carbides with a Co binder, it is difficult to change the relationship between toughness and hardness. For example, it is impossible to increase toughness without reducing hardness, and vice versa.

[0005] Iron is a known binder element, but it is generally not preferred because it is considered to have a negative impact on the toughness of cemented carbides. Pure iron binders tend to form brittle phases (i.e., martensite, Fe carbides, etc.). In addition, in standard production, it is difficult to achieve carbon control to produce a microstructure without defects ((W,Me)C subcarbide or graphite precipitates).

[0006] An object of the present invention is to be able to manufacture a cemented carbide having an alternative binder phase, which has equal or improved properties compared to a cemented carbide with a Co binder.

[0007] Another object of the present invention is to obtain a cemented carbide that can change its hardness while substantially maintaining its toughness.

[0008] Another object of the present invention is to obtain a cemented carbide with minimal grain growth of WC grains during sintering. Summary of the Invention

[0009] The present invention relates to a cutting tool, which comprises a cemented carbide substrate, wherein the cemented carbide comprises: a hard phase containing WC; a mixed carbide phase; and a metal binder, wherein the cemented carbide comprises the elements V, Cr, Ni and Fe in amounts such that:

[0010] - the weight fraction of V / (V + Cr + Ni + Fe) is between 0.0030 and 0.050,

[0011] - weight fraction Cr / (V+Cr+Ni+Fe) between 0.010 and 0.040,

[0012] - weight fraction Ni / (V+Cr+Ni+Fe) is between 0.020 and less than 0.050,

[0013] - The weight fraction Fe / (V+Cr+Ni+Fe) is between 0.86 and 0.967.

[0014] The cemented carbide according to the present invention has the advantage that the hardness can be changed while substantially maintaining the toughness.

[0015] Another advantage is that the WC grain size can be controlled since grain growth is minimal during sintering, which is due in part to the strong grain growth inhibition effect of vanadium.

[0016] The cemented carbide according to the present invention comprises WC, a mixed carbide phase and a metal binder, wherein the mixed carbide phase will be formed during sintering. The exact composition of the mixed carbide phase is not completely known, but can be described as a carbide phase with a specific stoichiometry different from the conventional γ phase, depending on the amount and type of elements present in the cemented carbide. Upon analysis, the mixed carbide phase has a crystal structure similar to the η phase, however, the η phase usually contains a large amount of binder metal. The mixed carbide phase contains a small amount of Fe, see the EDX analysis in the examples. More specifically, the phase can be (V, W) x C y One or more of these elements in a phase with an atomic ratio V:W of 3:1 to 3:2.

[0017] Most of the added V will be found in the mixed carbide phase in the final cemented carbide together with small amounts of added Cr and W from WC.The metallic binder may also contain smaller amounts of other elements present in the cemented carbide which will inevitably dissolve in the metallic binder during sintering.

[0018] In one embodiment of the invention, the total amount of the elements Fe, Cr and Ni in the metal binder is at least 90% by weight of the binder, preferably at least 95% by weight of the binder. The binder may also contain other elements, such as W present in the cemented carbide, which are dissolved in the binder during sintering.

[0019] The amount of metallic binder in the cemented carbide is preferably between 3 and 20% by weight of the cemented carbide, more preferably between 5 and 15% by weight.One way to determine the amount of metallic binder is by image analysis or by chemical analysis of the cemented carbide composition.

[0020] The cemented carbide contains V in an amount such that the weight fraction V / (V + Cr + Ni + Fe) is between 0.0030 and 0.050, preferably between 0.010 and 0.030, and more preferably between 0.015 and 0.020. If the V content is too low, WC grain growth during sintering will increase; if the V content is too high, the toughness of the cemented carbide will rapidly decrease, resulting in embrittlement at the WC interface.

[0021] The cemented carbide contains Cr in an amount 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 solution strengthening effect of Cr in Fe will decrease, resulting in a low hardness-toughness combination; if the Cr content is too high, Cr carbide precipitates will form at the grain boundaries of the cemented carbide, deteriorating the material properties.

[0022] The cemented carbide contains Ni in an amount 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, and more preferably between 0.020 and 0.030. If the Ni content is too low, the binder of the cemented carbide will exhibit lower ductility, resulting in fragilization of the composite material; if the Ni content is too high, the strength and temperature stability against heat exposure of the cemented carbide will decrease.

[0023] 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.

[0024] In one embodiment of the present invention, except for inevitable impurities, the cemented carbide does not contain other components other than W, C, Fe, Ni, Cr, and V. This means that no other elements are added as raw materials.

[0025] The cemented carbide may be substantially free of Co, which herein means that Co is not added as a raw material and Co exists in the cemented carbide at the level of impurities, preferably less than 1 wt%, and more preferably less than 0.5 wt%. Usually, a small amount of Co is detected because some manufacturing equipment (such as milling bodies) contains Co-containing cemented carbide and the contribution to the overall composition may be small.

[0026] The hard phase contains at least 50 wt% of WC. The average grain size of WC is suitably between 0.2 and 10 μm, preferably between 0.2 and 5 μm. For example, the average grain size of WC can be measured by using the mean linear intercept method on SEM / LOM images.

[0027] In one embodiment of the present invention, the cemented carbide may further contain other components common in the field of cemented carbides, such as one or more carbides, carbonitrides or nitrides of Ti, Ta and Nb. Then, the elements from these carbides will inevitably dissolve in the binder during sintering.

[0028] 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.

[0029] In one embodiment of the present invention, the cemented carbide substrate is provided with a wear-resistant PVD coating, and the PVD coating is preferably a nitride, oxide, carbide or a mixture thereof of one or more elements selected from Groups 4, 5 and 6 of the periodic table, and optionally has Al and / or Si.

[0030] In yet another embodiment of the present invention, the cemented carbide substrate is provided with a wear-resistant CVD coating.

[0031] In yet another embodiment of the present invention, the cemented carbide substrate is provided with a wear-resistant CVD coating, and the CVD coating comprises several layers and is preferably at least a carbonitride layer and an Al2O3 layer.

[0032] The cutting tool herein refers to a cutting tool insert, end mill or drill bit.

[0033] The present invention also relates to a method for manufacturing the above-mentioned cutting tool, and the cutting tool comprises the cemented carbide substrate as described above. The method comprises the following steps:

[0034] - Providing WC powder,

[0035] - Providing a powder containing elements V, Fe, Ni and Cr,

[0036] - Providing a milling liquid,

[0037] - Grinding, drying, pressing and sintering the powder into a cemented carbide.

[0038] The raw material containing elements V, Fe, Ni and Cr can be added as pure metals, alloys of two or more metals, or as their carbides, nitrides or carbonitrides. The addition amount of the raw material should be such that the binder phase will have the composition as described above after sintering.

[0039] In one embodiment of the present invention, the powder is VC, Cr3C2, Fe and Ni.

[0040] The average grain size of the WC powder used is preferably 0.2 - 10 μm, more preferably 0.2 - 5 μm (FSSS).

[0041] Any liquid commonly used as a grinding fluid in conventional cemented carbide manufacturing can be used. The grinding fluid is preferably water, an alcohol, or an organic solvent, more preferably water or a mixture of water and an alcohol, and most preferably a mixture of water and ethanol. The properties of the slurry depend on the amount of grinding fluid added. Since drying the slurry requires energy, the amount of liquid should be minimized to keep costs low. However, enough liquid needs to be added to achieve a pumpable slurry and avoid system blockages. Additionally, other compounds commonly known in the art can be added to the slurry, such as dispersants, pH regulators, etc.

[0042] An organic binder is also optionally added to the slurry to facilitate granulation during subsequent spray drying operations and also as a pressing agent for any subsequent pressing and sintering operations. The organic binder can be any binder commonly used in the art. For example, the organic binder can be paraffin wax, polyethylene glycol (PEG), long-chain fatty acids, etc. Based on the total volume of the dried powder, the amount of the organic binder is suitably between 15 and 25 volume %, and the amount of the organic binder is not included in the total volume of the dried powder.

[0043] The slurry containing the powder forming the hard phase, the powder forming the binder phase, and possibly the organic binder is suitably mixed by performing a grinding operation in a ball mill or an attritor mill. The grinding is suitably carried out by first forming a slurry containing the metal binder powder, the first and second powder portions, and possibly the organic binder. Then the slurry is suitably ground in a ball mill or an attritor mill to obtain a homogeneous slurry blend.

[0044] The slurry containing the powdered material mixed with the organic liquid and possibly the organic binder is atomized through a suitable nozzle in a drying tower, where the small droplets are instantaneously dried by a stream of hot gas (e.g., in a stream of nitrogen) to form agglomerated particles. For small-scale experiments, other drying methods can also be used, such as tray drying.

[0045] Subsequently, a green body is formed from the dried powder / particles by a pressing operation (such as uniaxial pressing, multi-axial pressing, etc.).

[0046] Subsequently, the green body formed from the powder / particles manufactured according to the present invention is sintered according to any conventional sintering method, such as vacuum sintering, sinter-HIP, spark plasma sintering, gas pressure sintering (GPS), etc.

[0047] In one embodiment of the present invention, the sintering temperature is between 1350 and 1550 °C.

[0048] In one embodiment of the present invention, the sintering process is HIP sintering carried out at a temperature between 1350 and 1550 °C and at a pressure of at least 40 bar, preferably between 40 and 80 bar.

[0049] In one embodiment of the present invention, the cemented carbide substrate is provided with a coating.

[0050] In one embodiment of the present invention, the cemented carbide substrate manufactured as described above is provided with a wear-resistant coating using CVD or PVD technology.

[0051] In one embodiment of the present invention, the cemented carbide substrate is provided with a wear-resistant PVD coating, and the PVD coating is preferably a nitride, oxide, carbide or mixture thereof of one or more elements selected from Groups 4, 5 and 6 of the Periodic Table of Elements, and optionally has Al and / or Si.

[0052] In one embodiment of the present invention, a CVD coating is deposited, and the CVD coating 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, may also be deposited.

[0053] Additional treatments can also be performed on the coating, such as brushing, sandblasting, etc.

[0054] The present invention also discloses a cemented carbide cutting tool manufactured according to the above method. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 A comparison graph of the hardness and toughness (K1C) values of the cemented carbide (solid circles) according to the present invention and the cemented carbide with Co binder collected from literature data (hollow circles) is described.

[0056] Figure 2 Shows Figure 1 A close-up of the area within the dashed line in

[0057] Figure 3 Shows the relationship between the K1c difference (ΔK1c) and V added to the binder at three different sintering temperatures from Example 2 (the numbers represent the sample numbers from Table 2).

[0058] Figure 4 Shows the XRD diffraction patterns of cemented carbides with different V contents, where the peaks of the mixed carbide phase marked as A are clearly visible. The peaks marked as B are the peaks of WC.

[0059] Figure 5Shows a SEM-EDX image of the microstructure of the cemented carbide according to the present invention, showing a layered structure of all elements, in which mixed carbide (1), WC grains (2) and binder phase (3) are shown.

[0060] Figure 6 Shows the same part of the microstructure as in Figure 6 in the SEM-EDX image, in which tungsten is highlighted, 1 is the mixed carbide, 2 is the WC grain, and 3 is the binder phase.

[0061] Figure 7 Shows the same part of the microstructure as in Figure 6 in the SEM-EDX image, in which iron is highlighted, 2 is the WC grain, and 3 is the binder phase.

[0062] Figure 8 Shows the same part of the microstructure as in Figure 6 in the SEM-EDX image, in which vanadium is highlighted, 1 is the mixed carbide phase.

[0063] Example 1

[0064] The cemented carbide is prepared from the following raw materials: Cr3C2, VC, Ni and Fe, in amounts such that the composition of the total powder (excluding WC) is: 91 wt% Fe, 3.5 wt% Ni, 1.4 wt% Cr and 4.0 wt% V. The addition of carbon black is at most 0.4% by weight of the mixture, more specifically, between 0.15% and 0.4%. The average particle size of the WC powder is 0.83 μm (FSSS). The amount of V+Cr+Ni+Fe in the cemented carbide is changed according to Table 1. The raw material powders are ground in a ball mill for 8 hours together with an organic binder (PEG at 2% by weight based on the total powder weight) and a grinding liquid (water / alcohol) to form a slurry, which is dried and ground in an agate mortar to obtain a powder blend. The powder is pressed into a green body. The green body is sintered in a HIP (hot isostatic pressing) furnace, where the maximum sintering temperature is 1450 °C, the sintering time is 1 hour of vacuum sintering at 40 mbar, followed by a high-pressure step of 50 bar for 15 minutes to reduce the porosity of the sample.

[0065] After grinding and polishing, the toughness (K1C) and hardness (HV30) of the sintered body are measured. HV30 is measured according to ASTM B294. The fracture toughness K1C is measured according to the Shetty method.

[0066]

[0067] To compare the results in Table 1 with those of cemented carbides with Co binder, the hardness and toughness (K1C) values from Table 1 were plotted together with those of cemented carbides with pure Co metal as binder based on literature data, see Figure 1 and 2 . The data from Table 1 were fitted according to a linear model fitted to the data in the range of HV30 between 1600 and 2200 and K1C between 5 and 12. The range and the model are shown as a dashed box and a solid line on the graph. The results obtained for different binder contents in the present invention are shown as solid circles in the same range.

[0068] As Figure 1 and 2 can be seen, the hardness and toughness properties of the cemented carbides according to the present invention are in the same range as those of the cemented carbides with Co binder.

[0069] Example 2

[0070] Using the same raw materials as in Example 1, powders with different V contents were prepared in the same manner according to the composition in Table 2. The samples were sintered in a HIP furnace at 3 different temperatures (1410, 1450 and 1500 °C), see Table 2. The sintering time was 60 minutes of vacuum sintering at 40 mbar at the highest temperature, followed by 15 minutes of high pressure sintering at 50 bar.

[0071] The K1C and hardness of the samples were analyzed in the same manner as in Example 1. To evaluate the effect of different V contents, the difference (ΔK1c) between the measured K1c and the calculated K1c was evaluated for V added to the binder phase, see Table 2. The ΔK1c value is the difference between the measured K1c and the K1c value calculated according to a linear model fitted to a subset of the literature data of the selected WC-Co cemented carbides (shown in Figure 1 ):

[0072] K1c_calculated = 15.22 - 0.003527 × HV.

[0073]

[0074] Figure 3 For the three sintering temperatures, the relationship between V content and ΔK1c was plotted, and it can be clearly seen that the properties obtained at the V content according to the present invention are the best (the numbers represent the sample numbers from Table 2).

[0075] Example 3

[0076] The sample from Example 2 was analyzed using XRD. The sample was prepared by bakelite casting, grinding, and polishing. XRD measurements were performed on a Bruker Discover D8 diffractometer with a Davinci design, equipped with a lμS microfocus source (CuK α radiation, λ = 1.5418 Å), a Våntec-500 area detector, and a ¼ Eulerian cradle. The X-ray source was operated at 50 kV and 1 mA. The sample was mounted on a sample holder with tape. All experiments were performed using a collimator size of 1.0 mm in diameter. The measurements were made on the polished side of the blade being measured. The data were collected in the 2θ range of 10 o -140 o .

[0077] The XRD data were analyzed using the software DIFFRAC EVA (Bruker) and High Score Plus (Malvern Panalytical).

[0078] In Figure 4 , the XRD diffraction pattern is shown, where the peaks of WC are marked, and the peaks of three mixed carbide phases are also shown. The XRD diffraction patterns of the samples with different V contents clearly show that as the V content increases, the peaks indicating the mixed carbides increase.

[0079] Example 4

[0080] Three samples according to the present invention were analyzed by SEM-EDX (energy-dispersive X-ray spectroscopy) using a Zeiss Supra 40 electron microscope with AZtec software (from Oxford Instruments) to perform elemental mapping and compositional analysis at selected points of the mixed carbide phase. The acceleration voltage was 10 kV and the working distance was 8.5 mm. Specifically, the mixed carbide phase was studied.

[0081] The samples were Invention 5 (from Table 1) and two other samples according to the present invention, Invention 9 and Invention 10. Invention 9 and Invention 10 were made in the same manner as in Example 1, where Invention 9 and Invention 10 contained 7.7 wt% and 16.5 wt% of the same Fe-V-Ni-Cr mixture as in Example 1, respectively. Invention 9 used the same WC raw material as in Example 1, but the WC raw material had a particle size of 7.15 μm (FSSS).

[0082] Specifically, the mixed carbide phase was studied.

[0083] In Figures 5-8In [the figure], the EDX image of Invention 10 is shown, in which V, Fe, and W are highlighted. It can be seen that the mixed carbide phase contains a large amount of V and W, but contains a small amount of Fe (invisible in the image). It can also be seen that the binder contains a large amount of Fe but almost no V.

[0084] Analyzing the average composition of the mixed carbide phase gives the composition in weight %, as shown in Table 3:

[0085]

[0086] As can be seen from Table 3, the mixed carbide phase mainly contains W, C, and V, but only contains small amounts of Fe, Ni, and Cr.

Claims

1. A cutting tool, the cutting tool comprising a cemented carbide substrate, wherein the cemented carbide comprises: a hard phase comprising WC; a mixed carbide phase; and a metallic binder, wherein the cemented carbide comprises 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, - the weight fraction Fe / (V + Cr + Ni + Fe) is between 0.86 and 0.

967.

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

3. The cutting tool according to claim 1, wherein the total amount of the elements Fe, Cr and Ni in the metallic binder is at least 90 wt% of the binder.

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

040.

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

030.

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

045.

7. The cutting tool according to any one of the preceding claims, wherein the cutting tool further comprises a coating.

8. A method of manufacturing a cutting tool according to any one of claims 1 - 7, the cutting tool comprising a cemented carbide substrate, wherein the method comprises the following steps: - providing WC powder, - providing a powder comprising the elements V, Fe, Ni and Cr, - providing a grinding fluid, - grinding, drying, pressing and sintering the powders into a cemented carbide.

9. The method of manufacturing a cutting tool according to claim 8, wherein the sintering is carried out at a sintering temperature between 1350 °C and 1550 °C and at a pressure of at least 40 bar.

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