Coated Cutting Tools

Abstract

The present invention relates to a coated cutting tool including a cemented carbide body and a wear-resistant coating thereof, wherein the cemented carbide consists of WC particles and η-phase particles embedded in a metal binder, the metal binder containing Co and Cr, the Co content in the cemented carbide being 6-12 wt %, the η-phase content in the metal binder being 4-5 vol %, and the average particle size of the η-phase particles being 1-5 μm, and wherein the Cr / Co ratio in the cemented carbide is 1.0-2.5%.

Description

[Technical Field]

[0001] The present invention relates to a coated cutting tool, wherein the cutting tool is PVD coated and the substrate is a cemented carbide, the cemented carbide comprising WC, Co, η-phase particles, and Cr. [Background technology]

[0002] Cutting tools for metal cutting often consist of a cemented carbide substrate with a wear-resistant coating. Cutting tools for milling operations also need to have high wear resistance, high edge line toughness, and high hardness at high temperatures. In milling applications, one of the wear mechanisms of cutting tools is the formation of comb cracks. Milling cutting tools are subjected to cycles of heating and cooling, which can expand and contract the surface of the tool and cause the formation of comb cracks along the cutting edge.

[0003] Comb crack resistance can be addressed by adjusting the compressive stress of the PVD layer. Wear evaluation during milling of gray cast iron has been studied, and it has been found that when comb cracks occur in cutting applications, they attack the binder extensively. When the binder is attacked, the wear of the cutting tool progresses rapidly, for example, to the point where the coating separates, and the cutting edge of the cutting tool is at an increased risk of blade breakage.

[0004] WO2017108610 discloses a cemented carbide containing finely dispersed η phase that exhibits increased resistance to comb cracking.

[0005] It is an object of the present invention to provide a milling cutting insert with enhanced comb crack resistance, as well as sufficient toughness and wear resistance, particularly in ISO-K milling applications, such as milling cast iron. Summary of the Invention

[0006] At least one of the above mentioned objects is achieved by a cutting tool according to claim 1. Preferred embodiments are disclosed in the dependent claims.

[0007] The present invention relates to a coated cutting tool including a cemented carbide body and a coating thereof, wherein the cemented carbide consists of WC particles and η-phase particles in a metal binder, the metal binder containing Co and Cr, the Co content in the cemented carbide being 6 to 12 wt%, preferably 6 to 10 wt%, more preferably 7 to 8 wt%, the η-phase content in the cemented carbide being 4 to 5 vol%, and the average particle size of the η-phase particles being 1 to 5 μm, preferably 2 to 4 μm, more preferably 2 to 3 μm, and wherein the Cr / Co ratio in the cemented carbide is 1.0 to 2.5%, preferably 1.5 to 2.5%.

[0008] It has been found that the composition of the cemented carbide described in this invention can improve the chemical resistance of the metal binder while maintaining the toughness and hardness of the cemented carbide.

[0009] The cutting tools disclosed herein may be, for example, inserts or end mills designed for milling applications.

[0010] The cemented carbide of the present invention comprises WC and η-phase particles embedded in a metallic binder, the metallic binder comprising Co and Cr, and also W, which is dissolved into the metallic binder from the WC particles during sintering of the cemented carbide.

[0011] By cutting tool coating is meant herein a coating deposited on a cemented carbide substrate to increase the wear resistance of the cutting tool, which can be, for example, a coating deposited by physical vapor deposition (PVD).

[0012] The Co content in the cemented carbide of the present invention is preferably 6-12 wt% Co. If the Co content is lower than 6 wt%, the cutting tool loses toughness properties. On the other hand, if the Co content is higher than 12 wt%, the cutting tool loses comb crack resistance. A Co content higher than 12 wt% also makes the cutting tool more sensitive to chemical attack by the coolant used in milling applications and the workpiece material during cutting.

[0013] The η-phase content in the cemented carbide of the present invention is 4-5% by volume. If the η-phase content is higher than 5% by volume, most of the Co content in the metal binder is consumed by the η-phase particles, which makes the cemented carbide too brittle. If the η-phase content is lower than 4% by volume, there is an increased risk that the η-phase particles will form clusters, which are brittle unlike well-distributed η-particles.

[0014] The Cr content in the cemented carbide of the present invention is such that Cr (wt%) / Co (wt%) is 1.0-2.5%. Surprisingly, it has been found that this content of Cr in the cemented carbide improves cutting tool properties. When Cr is added to the cemented carbide, the η phase particles contain Cr and the η phase is composed of (W, Co, Cr). x C. Cr also exists in solid solution in the metallic binder phase containing Co. Cr also acts as a grain growth inhibitor during sintering, limiting the continued growth and coarsening of WC grains. If the Cr content is too low, Cr still influences WC grain growth, but the solid solution is limited. If the Cr content is too high, the cemented carbide becomes too hard and too brittle for ISO-K milling applications. Cemented carbides with Cr contents in the weight ratio range Cr / Co 1.0-2.5% are highly strengthened due to the solid solution effect. Co improves work hardening properties, improves high-temperature hardness, and improves chemical resistance, such as corrosion resistance.

[0015] The cemented carbide according to the present invention has a low carbon content, which results in the formation of η-phase particles. This results in a cemented carbide having both a W content in the binder and η-phase particles. The η-phase is defined herein as Me, where Me is selected from W, Co, and Cr. 12 and MeC, whereby carbide is (W,Co,Cr)C and / or (W,Co,Cr) 12 It could also be C.

[0016] In the present invention, the cemented carbide contains finely dispersed eta-phase particles. The eta-phase particles may exist as very large, brittle, unwanted particles, typically larger than 50 μm or even larger than 100 μm, which are not part of the present invention. The eta-phase particles of the present invention have an average particle size of 1 to 5 μm, and these particles are uniformly distributed within the metal binder of the cemented carbide. The finely dispersed eta-phase particles of the present invention are formed during the sintering process, and the carbon deficiency and equilibration temperature must be controlled during the process to achieve the claimed eta-phase appearance and content. The substoichiometric carbon content difference between obtaining unwanted large clumps of eta phase and obtaining finely distributed eta phase is a target and can be very small. Approaching that limit requires monitoring the microstructure to ensure the avoidance of unwanted large clumps. Carefully adjusting the carbon content and then monitoring the results in terms of the resulting microstructure is a procedure known to those skilled in the art.

[0017] In one embodiment of the present invention, the cemented carbide comprises 75 to 91% by volume of WC, preferably 80 to 87% by volume of WC.

[0018] In one embodiment of the present invention, the content, i.e., area fraction, of eta-phase particles in the portion of the substrate close to the surface of the substrate corresponds to the content in the innermost portion of the substrate. In one embodiment of the present invention, the distribution of eta-phase is constant throughout the cemented carbide substrate, i.e., the cemented carbide does not contain any gradient of eta-phase or regions free of eta-phase, as in, for example, US 4,843,039. The distribution of eta-phase is preferably as uniform as possible.

[0019] In one embodiment of the present invention, the WC grain size in the cemented carbide is 0.6 to 0.8 μm.

[0020] In one embodiment of the invention, the cemented carbide consists of WC and eta-phase particles in a metallic binder consisting of Co and Cr, with some W dissolved in the metallic binder. W will inevitably dissolve in the metallic binder during sintering, and the exact amount will depend on several things, such as the overall composition of the cemented carbide, the exact carbon content, etc.

[0021] In one embodiment of the invention, the coating is a PVD coating.

[0022] In one embodiment of the present invention, the coating thickness is 2.5 to 4.5 μm.

[0023] In one embodiment of the invention, the coating is multilayered having at least one layer of TiAlN and at least one layer of Al2O3.

[0024] In one embodiment of the present invention, the Al2O3 is nanocrystalline γ-Al2O3, and the Ti:Al ratio in TiAlN is 33:67.

[0025] In one embodiment of the present invention, the coating comprises an outermost layer of metallic Al as a wear indicating layer, preferably with a layer thickness of 30 to 100 nm.

[0026] In one embodiment of the invention, the coating consists of the sub-layers TiAlN / γ-Al2O3 / TiAlN / γ-Al2O3 / TiAlN / γ-Al2O3 / TiAlN / Al.

[0027] In one embodiment of the present invention, the cutting tool is a milling insert.

[0028] In one embodiment of the present invention, the cutting tool is subjected to shot peening.

[0029] method The cemented carbide of the present invention is made according to standard cemented carbide manufacturing methods, using the steps of milling, drying, pressing, and sintering.

[0030] The carbon content needs to be adjusted during the production of the cemented carbide to achieve the correct eta phase content.

[0031] The formation of uniformly or finely distributed eta-phase particles according to the present invention is achieved by carefully controlling the carbon content during the manufacture of the cemented carbide. The cemented carbide in the present invention is made with a sub-stoichiometric carbon content within a certain range. Sub-stoichiometric carbon is a measure of the carbon content relative to the stoichiometric carbon content. Sub-stoichiometric content is a good measure to use because it is independent of other parameters such as binder phase content, other carbides, etc.

[0032] Suitably the carbon content is between -0.30 and -0.16 wt% sub-stoichiometric carbon, preferably between -0.28 and -0.17 wt% sub-stoichiometric carbon.

[0033] The stoichiometric carbon content is calculated by assuming that the carbides in the cemented carbide are perfectly stoichiometric, e.g., the atomic ratio W:C is assumed to be 1:1. If other carbide-forming elements, e.g., Cr, are present in the cemented carbide, the corresponding carbide Cr3C2 is also assumed to be stoichiometric.

[0034] The stoichiometric carbon content in a sintered cemented carbide, e.g., consisting of Co and WC, can be calculated either based on the amount of added WC raw material in the powder, assuming an atomic ratio W:C of 1:1, or from measuring e.g. W in the sintered material and then calculating the stoichiometric carbon content from the measured content, assuming an atomic ratio W:C of 1:1.

[0035] This means that the term sub-stoichiometric carbon, as used herein, is the total carbon content in the cemented carbide as determined by chemical analysis minus the calculated stoichiometric carbon content based on WC and possible other carbides present in the cemented carbide.

[0036] [Carbon content]=[Stoichiometric carbon content]+[Substoichiometric carbon content]

[0037] As an example, if the stoichiometric carbon content for a particular cemented carbide is 5.60 wt. % and the cemented carbide is made with a carbon content of 5.30 wt. %, the sub-stoichiometric carbon content would be −0.30 wt. %.

[0038] It is important that the carbon content is measured in the sintered cemented carbide because some of the carbon is lost during sintering, for example due to the formation of CO. The exact amount of carbon lost depends on the particular sintering furnace and sintering process. Thus, the powder will have a slight excess of carbon compared to what is desired in the sintered cemented carbide.

[0039] The Co and Cr content in cemented carbides can be measured by chemical analysis by XRF (X-ray fluorescence) using a Panalytical Axios Max Advanced instrument. The values ​​obtained are the total Cr and / or Co content in both the binder, the η-phase grains, and the grain boundaries.

[0040] The carbon content in the sintered cemented carbide or powder can be measured by a LECO WC-600 instrument.

[0041] The amount of η phase in the cemented carbide was determined by image analysis of an optical microscope (LOM) using the software Image J with the "automatic" setting. The image magnifications were 1000X and 2000X, and two measurements were taken at each magnification. The values ​​in Table 2 are the average values. Therefore, the values ​​in the table are the averages from the total of two measurements for each image, which is four image analyses performed on two images. The area percentage in the image is considered to correspond to the volume percentage in the cemented carbide. The volume percentage of WC can be determined in the same way as the volume percentage of the η phase.

[0042] The average grain size of the eta-phase and WC grains can be measured by the average line intercept of the LOM images at 1000x or 2000x magnification.

[0043] The coating thickness was measured on a smooth cross section of the SEM image.

[0044] The hardness and toughness of the cemented carbide were measured using Vickers indentation.

[0045] Embodiments of the present invention will now be described with reference to the accompanying drawings. [Brief explanation of the drawings]

[0046] [Figure 1] FIG. 1 shows a schematic diagram of one embodiment of a cutting tool (1), which is a milling insert having an inclined surface (2), a side surface (3), and a cutting edge (4) therebetween. [Figure 2] FIG. 1 shows a schematic diagram of one embodiment of a cutting tool (1), which is a turning insert having an inclined surface (2), a side surface (3), and a cutting edge (4) therebetween. [Figure 3]1 is a view showing a cross section of an LOM (optical optical microscope) of a cemented carbide containing Cr and containing η-phase particles (black), WC particles (gray), and a metal binder (white), which is the base material of invention 1. FIG. [Figure 4] FIG. 1 shows an LOM cross section of a cemented carbide containing η-phase particles (black), WC particles (gray), and a metal binder (white) but no Cr, which is the substrate of Comparative 1. [Figure 5] FIG. 1 is a diagram showing an LOM cross section of a WC / Co cemented carbide containing no η-phase particles and no Cr, which is the base material of Reference 1. [Example]

[0047] Exemplary embodiments of the present invention will now be disclosed in more detail and compared to a reference embodiment. Coated cutting tools (inserts) were manufactured, analyzed and evaluated in cutting tests.

[0048] Base material Cemented carbide substrates were manufactured. Three different compositions were prepared. Invention 1 was a cemented carbide containing η-phase particles and Cr, Comparative 1 was a cemented carbide containing η-phase particles but no Cr, and Reference 1 was a cemented carbide composed of WC and metallic Co.

[0049] The cemented carbide was prepared from the raw powders according to Table 1. Table 1 Powder composition The TIFF2025540405000002.tif40170 powder was ball milled with a grinding fluid (water / ethanol in a 9 / 91 ratio) and an organic binder, 2 wt. % PEG. The amount of PEG is not included in the dry powder weights shown in Table 1. After milling, the slurry was pan-dried. The dried mass was then pressed into green bodies. The green bodies were sintered at 1410 °C in Ar and CO at 40 mbar.

[0050] The amount of η-phase was determined by image analysis of an optical microscope (LOM) using the software Image J with the "automatic" setting. The image magnifications were 1000X and 2000X, and two measurements were taken at each magnification. The values ​​in Table 3 are the average values. Therefore, the values ​​in the table are the average from the total of two measurements for each image, which is four image analyses performed on two images.

[0051] The stoichiometric carbon content in the sintered cemented carbide was calculated by first measuring the total carbon content in the sintered cemented carbide using a LECO WC-600 instrument; for this analysis, the sample was crushed before analysis. The accuracy of the values ​​is ±0.01 wt%. The W, Co, and Cr contents are measured by XRF (X-ray fluorescence) using a Panalytical Axios Max Advanced instrument. The amounts of cobalt, chromium, and carbon are subtracted from the total weight of the sample to obtain the W content, which is used to calculate the stoichiometric carbon content, assuming WC has a 1:1 ratio.

[0052] Subtracting the stoichiometric carbon content from the total carbon measured by the LECO WC-600 instrument gives the substoichiometric carbon value. As can be seen in Table 2, the substoichiometric carbon value in the sintered material is different from that in the powder. This is because some of the carbon reacts with oxygen during sintering and escapes as CO or CO2, which reduces the total final C content of the cemented carbide.

[0053] The carbon in the powder was adjusted to achieve the desired microstructure in the sintered cemented carbide. The measured carbon content in the powder and sintered cemented carbide substrate is shown in Table 2. Table 2 Carbon content in powders and cemented carbides TIFF2025540405000003.tif48170

[0054] The compositions of the sintered cemented carbide substrates are shown in Table 3. The η-phase content and average particle size of the η-phase particles were measured according to the methods disclosed above. The distribution of η-phase particles in both the cemented carbides of Inventive 1 and Comparative 1 was continuous throughout, and no gradient in the η-phase content was observed. No γ-phase particles, very large η-phase particles, or graphite were observed in the cemented carbides. Table 3 Base material composition TIFF2025540405000004.tif48170η forms in the Invention 1 and Comparative samples at the expense of approximately 1.4 wt. % Co, so that the 6% Co in Reference 1 corresponds to Invention 1 and Comparative 1 samples containing η phase particles.

[0055] The area fractions of WC, η-phase particles, and metal binder in the cemented carbides were investigated by LOM and SEM. The volume fractions are shown in Table 4. Table 4 Volume ratio in cemented carbide TIFF2025540405000005.tif40170

[0056] Hardness and toughness were measured according to the methods disclosed above, and the obtained values ​​are shown in Table 5. Table 5 Hardness and toughness TIFF2025540405000006.tif40170 The inventive sample, Inventive 1, exhibited both higher hardness and higher toughness compared to both the reference sample, Reference 1, and the comparative sample, Comparative 1.

[0057] coating All sintered cemented carbide substrates were coated in a PVD process with a wear-resistant PVD coating. The coating equipment used to deposit the PVD coating of the present invention was approximately 1 m 3 The chamber size was a Hauzer HTC1000 (IHI Hauzer Techno Coating BV, Netherlands).

[0058] The thickness of the deposited layer was measured on the side of the insert.

[0059] The PVD coating included the following layers starting from the substrate:

[0060] The first inner layer is 2 μm thick and made of TiAlN with an Al:Ti ratio of 67:33. The crystal structure is mainly cubic, with only a small amount of hexagonal AlN phase present.

[0061] Then a layer of nanocrystalline γ-Al2O3 with a thickness of 0.5 μm.

[0062] On the γ-Al2O3 layer, a 0.7 μm thick multilayer was deposited, consisting of the layer sequence TiAlN / γ-Al2O3 / TiAlN / γ-Al2O3. TiAlN has an Al:Ti atomic ratio of 67:33. All four layers have approximately the same layer thickness, i.e., about 0.175 μm each.

[0063] Then, a layer of TiAlN with a thickness of 0.6 μm and an atomic ratio of Al:Ti of 67:33.

[0064] Finally, an outer metallic color layer of aluminum, approximately 50 nm thick, is deposited, which is thick enough to give the surface a "silver-like" color. This top layer can be used, for example, to blast the beveled surface of a cutting tool.

[0065] The total thickness of the PVD coating was 3.8 μm as measured on the side of the cutting tool.

[0066] Post-processing Some of the PVD-coated substrates were subjected to a dry blasting process, and these samples are designated with the suffix SP. Dry blasting was performed in a commercial dry blasting machine using commercially available zirconia beads. The beads had a diameter of 70–125 μm. The blasting pressure was 5.3 bar, and the belt speed was 150 mm / min. The dry blasting process affects the toughness properties of the cutting tool.

[0067] Performance Test Test 1 Coated cutting tools with geometry P2808.1 were tested in rough milling operations with workpiece material GG25 / GJL250 cast iron (ISO K). Cutting speed v c is 200 m / min, feeding speed f z is 0.25mm / tooth, the number of teeth z in the cutter is 1, and the axial depth of cutting a p is 3 mm, and the radial depth of cutting a e The wear width of the cutting tool bevel was detected by optical measurement of the main cutting edge at specified intervals in the milling distance. The average results of the maximum wear at a milling distance of 5600 mm for two parallel cutting tests for each type of specimen are shown in Table 6. Table 6 TIFF2025540405000007.tif63170*Same test conditions as Invention 1 and Reference 1 but using a different batch of processed material, which may affect the results.

[0068] Test 2 Coated cutting tools with insert geometry SNMX120512-D27 were tested in rough milling operations with GG25 / GJL250 cast iron (ISO K) workpiece material. Cutting speed v c is 220 m / min, and the feed rate f z is 0.36 mm / tooth, the number of teeth z in the cutter is 8, and the axial depth of cutting a p is 3 mm, and the radial depth of cutting a e The cutting depth was up to 60 mm. No cutting fluid was used. Tool life criteria were set at increasing power consumption and decreasing smoothness progression. Machining continued until the end of the life criteria was reached. The average results of the four parallel cutting tests for each specimen type are shown in Table 7. Table 7 TIFF2025540405000008.tif33170

[0069] Test 3 Coated cutting tools with geometry ADGT1606PERD56 were tested in finish milling operations with workpiece material GGG50 / GJS50014 medium grade cast iron (ISO K). Cutting speed v c is 360 m / min, and the feed rate f z is 0.2 mm / tooth, the number of teeth z in the cutter is 6, and the axial depth of cutting a p is 0.3 mm, and the radial depth of cutting a e The wear depth was up to 55 mm. A water-miscible cutting fluid was used. Machining lasted for 80 minutes. After machining, the maximum width of wear on the cutting tool bevel was detected by optical measurement of the main cutting edge. The average results of six parallel cutting tests for each specimen type are shown in Table 8. Table 8 TIFF2025540405000009.tif25170

[0070] Test 4 Coated cutting tools of the geometry SDMW09T320A57 were tested in rough milling operations with Sibodur 700 high ductility spheroidal cast iron (ISO K) workpiece material. Cutting speed v c is 87 m / min, and the feed rate f z is 0.15mm / tooth, the number of teeth z in the cutter is 3, and the axial depth of cutting a p is 69 mm, the radial depth of cutting a e The cutting depth was 60 mm. A water-miscible cutting fluid was used. The tool life criterion was set at an absolute power consumption greater than 15 kW. Machining continued until the end of the life criterion was reached. The average results of the four parallel cutting tests for each specimen type are shown in Table 9. Table 9 TIFF2025540405000010.tif25170

[0071] While the present invention has been described in connection with various exemplary embodiments, it should be understood that the invention should not be limited to the disclosed exemplary embodiments, but rather is intended to cover various modifications and equivalent arrangements within the scope of the appended claims.

Claims

1. 1. A coated cutting tool comprising a cemented carbide body and a coating thereof, wherein the cemented carbide comprises WC particles, η-phase particles, and a metal binder, the metal binder comprising Co and Cr, the Co content in the cemented carbide being 6 to 12 wt %, preferably 6 to 10 wt %, more preferably 7 to 8 wt %, the η-phase content being 4 to 5 vol %, and the average grain size of the η-phase particles being 1 to 5 μm, preferably 2 to 4 μm, more preferably 2 to 3 μm, and wherein the Cr / Co ratio in the cemented carbide is 1.0 to 2.5%.

2. 2. The coated cutting tool of claim 1, wherein the Cr / Co ratio in the cemented carbide is 1.5-2.5%.

3. 3. The coated cutting tool of claim 1, wherein the content of eta phase in the portion of the substrate adjacent to the surface of the substrate matches the content of eta phase in the innermost portion of the substrate.

4. The coated cutting tool according to any one of claims 1 to 3, wherein the WC grain size in the cemented carbide is 0.6 to 0.8 μm.

5. 5. The coated cutting tool of claim 1, wherein the cemented carbide consists of WC and eta phase particles in a metallic binder of Co and Cr, with some W dissolved in the metallic binder.

6. 6. The coated cutting tool of claim 1, wherein the coating is a PVD coating.

7. A coated cutting tool according to any one of claims 1 to 6, wherein the coating thickness is 2.5 to 4.5 µm.

8. The coating comprises at least one layer of TiAlN and Al ２ O ３ 8. The coated cutting tool of claim 1, wherein the cutting tool is multi-layered, having at least one layer of

9. Al ２ O ３ is nanocrystalline γ-Al ２ O ３ and / or the Ti:Al ratio in the TiAlN is 33:

67.

10. A coated cutting tool according to any one of claims 1 to 9, wherein the coating comprises an outermost layer of metallic Al as a wear indicating layer, preferably with a layer thickness of 30 to 100 nm.

11. The coating has a sub-layer TiAlN / γ-Al ２ O ３ / TiAlN / γ-Al ２ O ３ / TiAlN / γ-Al ２ O ３ 11. The coated cutting tool of claim 1, consisting of TiAlN / Al.

12. 12. The coated cutting tool of any one of claims 1 to 11, wherein the cutting tool is a milling insert.

13. 13. The coated cutting tool of any one of claims 1 to 12, wherein the cutting tool has been subjected to shot peening.

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