Cutting Tools

Abstract

The present invention relates to a cutting tool for metal cutting comprising a substrate at least partially coated with a 3-30 μm coating, said substrate being cemented carbide, cermet or ceramic, said coating comprising one or more layers, at least one layer being a Ti(C,N)-layer having a thickness of 3-25 μm, said Ti(C,N)-layer being composed of columnar grains with an average grain size of ≧25 nm and ≦35 nm.

Description

[Technical field]

[0001] The present invention relates to a coated cutting tool comprising a substrate and a coating, the coating comprising a Ti(C,N) layer having an average grain size between 25 nm and 35 nm. [Background technology]

[0002] In the art of cutting tools for metalworking, the use of CVD coatings is a well-known method to increase the wear resistance of tools. CVD coatings of ceramic materials such as TiN, TiC, Ti(C,N) and Al2O3 are commonly used.

[0003] EP 2 791 387 discloses a coated cutting tool with a fine-grained titanium carbonitride layer. The coating is advantageous in that it exhibits high resistance to spalling during turning and high speed cutting of nodular cast iron. A columnar MTCVD Ti(C,N) layer with an average grain width of 0.05-0.4 μm is described.

[0004] There is a continuing need to find cutting tool coatings that can extend the life of cutting tools and / or withstand higher cutting speeds than known cutting tool coatings. Summary of the Invention

[0005] It is an object of the present invention to provide a coated cutting tool having improved resistance to wear in metal cutting applications. A further object is to improve its resistance during turning operations, particularly when turning steel and hardened steel. A further object is to provide a wear resistant coating that provides high resistance to crater and flank wear when turning steel and hardened steel.

[0006] At least one of these objects is achieved by a coated cutting tool according to claim 1.

[0007] Preferred embodiments are recited in the dependent claims.

[0008] The present disclosure relates to a cutting tool for metal cutting comprising a substrate at least partially coated with a 3-30 μm coating, the substrate being a cemented carbide, a cermet or a ceramic, the coating comprising one or more layers, at least one layer being a Ti(C,N) layer having a thickness of 3-25 μm, the Ti(C,N) layer being composed of columnar grains, the average grain size D422 and grain size D423 of the Ti(C,N) layer measured by X-ray diffraction with CuKα radiation, 422 is calculated from the full width at half maximum (FWHM) of the (422) peak according to the Scherrer formula: TIFF2024514959000002.tif14170[where, D 422 is the average grain size of the Ti(C,N) grains in the Ti(C,N) layer, K is the shape factor, set here to 0.9, λ is the wavelength of the CuKα1 line, set here to 1.5405 Å, and B 422 is the FWHM value of the (422) reflection, θ is the Bragg angle, and D 422 for cutting tools ≧25 nm and ≦35 nm.

[0009] Surprisingly, it has been found that cutting tools with a very fine-grained Ti(C,N) layer exhibit very high resistance to wear when used in metal cutting applications such as turning in high alloy steels. It is believed that the combination of crystallinity and columnar grains with a large amount of grain boundaries contributes to the high wear resistance.

[0010] In one embodiment of the invention, the at least one Ti(C,N) layer exhibits an X-ray diffraction pattern measured using CuKα radiation and a θ-2θ scan, where TC(hkl) is defined according to the Harris equation: TIFF2024514959000003.tif23170 [where I(hkl) is the measured intensity (integrated area) of the (hkl) reflection, I0(hkl) is the standard intensity according to ICDD PDF-Card No. 42-1489, n is the number of reflections, the reflections used in the calculation are (111), (200), (220), (311), (331), (420) and (422), and TC(422) is ≥ 3].

[0011] In one embodiment of the invention, the at least one Ti(C,N) layer has a thickness of 6-25 μm and exhibits an X-ray diffraction pattern with a TC(422) of 4 or greater.

[0012] In one embodiment of the invention, said at least one Ti(C,N) layer has a thickness of 4.5-25 μm and exhibits an X-ray diffraction pattern with the highest TC(422) and the second highest TC(311). In one embodiment of the invention, the C / (C+N) ratio in the Ti(C,N) layer is 50%-70%, preferably 55%-65%. This composition is advantageous in that this Ti(C,N) layer exhibits high chemical stability.

[0013] In one embodiment of the present invention, the coating includes an innermost layer of TiN.

[0014] In one embodiment of the present invention, the Ti(C,N) layer is the outermost layer of the coating.

[0015] The present invention also relates to the use of the above-mentioned cutting tool in metal cutting.

[0016] In one embodiment of the invention the cutting tool is used for metal cutting in high alloy steel, hardened steel, cast iron or stainless steel, preferably for metal cutting in high alloy steel.

[0017] In one embodiment of the present invention, the cutting tool is a drill, a milling insert or a turning insert, preferably a turning insert.

[0018] The coated cutting tools described herein may be subjected to post-treatments such as blasting, brushing or shot peening in any combination. The post-blasting treatment may be wet blasting or dry blasting, for example using alumina particles.

[0019] Further objects and features of the present invention will become apparent from the following definitions and examples considered in conjunction with the accompanying drawings.

[0020] Embodiments of the present invention will now be described with reference to the accompanying drawings. [Brief description of the drawings]

[0021] [Figure 1] 1 shows a scanning electron microscope (SEM) image of a cross section of an example of a coating of the present invention, Sample A. [Diagram 2] 1 shows a scanning electron microscope (SEM) image of a cross section of an example of a reference coating, sample B. [Diagram 3] 1 shows a scanning electron microscope (SEM) image of a cross section of an example of a reference coating, sample C. [Figure 4] 1 shows a scanning electron microscope (SEM) image of the exterior surface of an example of a coating of the present invention, Sample A. [Diagram 5] 1 shows a scanning electron microscope (SEM) image of the exterior surface of a reference coating example, Sample B. [Figure 6] 1 shows a scanning electron microscope (SEM) image of the exterior surface of an example of a reference coating, Sample C. [Figure 7] This shows a TKD (Transmission Kikuchi Diffraction) map of the top view in the Ti(C,N) layer of sample A. The top view is at a distance of about 6 μm from the substrate-coating interface. [Figure 8] This shows a TKD (Transmission Kikuchi Diffraction) map of the top view in the Ti(C,N) layer of sample B. The top view is at a distance of about 6 μm from the substrate-coating interface. [Figure 9] Figure 1 shows a TKD (Transmission Kikuchi Diffraction) map of the top view in the Ti(C,N) layer of sample C. The top view is at a distance of about 6 μm from the substrate-coating interface. [Figure 10] FIG. 1 shows a bright field image of a transmission electron microscope (TEM) analysis of a top view in the Ti(C,N) layer of sample A. The top view is at a distance of about 6 μm from the substrate-coating interface. [Figure 11] FIG. 1 shows a bright field image of a transmission electron microscope (TEM) analysis of a top view in the Ti(C,N) layer of sample B. The top view is at a distance of about 6 μm from the substrate-coating interface. [Figure 12]FIG. 1 shows a bright field image of a transmission electron microscope (TEM) analysis of a top view in the Ti(C,N) layer of sample C. The top view is at a distance of about 6 μm from the substrate-coating interface. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] definition The term "cutting tool" is intended in this specification to denote a cutting tool suitable for metal cutting applications, such as an insert, an end mill or a drill. The field of application may be, for example, turning, milling or drilling in metals such as steel.

[0023] method XRD To investigate the texture or orientation of the layers and also the average grain size, X-ray diffraction (XRD) was performed on the flank face using a PANalytical CubiX3 diffractometer equipped with a PIXcel detector. The coated cutting tool was mounted on the sample holder ensuring that the flank face of the specimen was parallel to the reference plane of the sample holder and also at the appropriate height. Cu-Kα radiation was used for the measurements at a voltage of 45 kV and a current of 40 mA. 1 / 2 degree anti-scatter slits and 1 / 4 degree divergence slits were used. The diffraction intensity from the coated cutting tool was measured over a 2θ range of 20°-140°, i.e., an incidence angle θ range of 10-70°. Data analysis including background fitting of the data, Cu-Kα2 stripping and profile fitting was performed using PANalytical's X'Pert HighScore Plus software.

[0024] The integrated peak full width at half maximum of the profile fitted curve obtained from PANalytical's X'Pert HighScore Plus software was used to calculate the grain size of the layer according to Scherrer's equation (Eq. 1) (Birkholz, 2006).

[0025] Average particle size D 422is calculated from the full width at half maximum (FWHM) of the (422) peak according to the Scherrer formula: TIFF2024514959000004.tif14170[where D 422 is the average grain size of Ti(C,N), K is the shape factor, set here as 0.9, λ is the wavelength of the CuKα line, set here as 1.5405 Å, B is the FWHM value of the (422) reflection, and θ is the Bragg angle, i.e., the angle of incidence.

[0026] β is the line broadening at FWHM (in radians) after subtraction of instrumental broadening (0.00174533 radians) and θ is the angle of incidence. A Gaussian approximation was used to calculate the broadening with subtraction of instrumental broadening (Equation 2) (Birkholz, 2006): β=√((FWHM obs ) 2 -(FWHM ins ) 2 ) where β is the actual broadening (in radians) used in the particle size calculation and FWHM obs is the measured broadening (in radians) and FWHM ins is the instrumental broadening (in radians)].

[0027] The texture or orientation of the layers was defined based on the X-ray diffraction patterns measured using CuKα radiation and θ-2θ scan, and TC(hkl) was defined based on the Harris equation: TIFF2024514959000005.tif24170 [where I(hkl) is the measured intensity (integrated area) of the (hkl) reflection, I0(hkl) is the standard intensity according to ICDD PDF-Card No. 42-1489, n is the number of reflections, and the reflections used in the calculation are (111), (200), (220), (311), (331), (420) and (422)].

[0028] Possible further layers on top of the Ti(C,N)-layer affect the X-ray intensity entering the Ti(C,N)-layer and exiting the entire coating, so these must be corrected taking into account the linear absorption coefficients of the respective compounds in the layers. Alternatively, further layers on top of the Ti(C,N)-monolayer can be removed by methods that do not substantially affect the XRD measurement results, e.g. chemical etching.

[0029] It should be noted that peak overlap is a possible phenomenon in X-ray diffraction analysis of coatings, for example comprising several crystalline layers and / or deposited on substrates comprising crystalline phases, which must be taken into account and corrected for by the skilled person. It should also be noted that for example WC in the substrate may have diffraction peaks in the vicinity of the relevant peaks of the present invention.

[0030] Elemental analysis is carried out by electron microprobe analysis using a JEOL electron microprobe JXA-8530F equipped with a wavelength dispersive spectrometer (WDS) to measure the C / (C+N) ratio of the Ti(C,N) layers represented in Figures 1, 2 and 3. The analysis of the Ti(C,N) layers was carried out on the polished cross-sections of the rake face. For each type of Ti(C,N) layer, three samples were analyzed at 10 points, with an interval of 50 μm along a straight line parallel to the substrate surface and at a distance of 4-6 μm from the contact surface between the substrate and the TiN layer. The data were acquired using 10 kV, 29 nA, and a Ti(C,N) standard with a composition of 10.22 wt% C, 10.68 wt% N, 78.86 wt% Ti and 0.24 wt% O. EXAMPLES

[0031] Exemplary embodiments of the present invention will now be disclosed in more detail and in comparison with a reference embodiment.Coated cutting tools (inserts) were manufactured, analyzed and evaluated in cutting tests.

[0032] The cemented carbide substrates were manufactured using conventional processes including grinding, mixing, spray drying, compacting and sintering. The sintered substrates were CVD coated in an Ionbond Type size 530 radial CVD reactor capable of accommodating 10,000 half-inch size cutting inserts. The substrates were placed on a plate and samples to be further tested and analyzed were selected from the center of the chamber and along half the radius of the plate. The ISO-type geometry of the cemented carbide substrate (insert) was CNMG-120408-PM. The composition of the cemented carbide was 7.2 wt% Co, 2.9 wt% TaC, 0.5 wt% NbC, 1.9 wt% TiC, 0.4 wt% TiN and balance WC.

[0033] CVD deposition A first innermost coating of about 0.2 μm TiN was deposited on all substrates in a process at 400 mbar and 885° C. A gas mixture of 48.8 vol. % H2, 48.8 vol. % N2, and 2.4 vol. % TiCl4 was used. A Ti(C,N) layer was then deposited as disclosed below.

[0034] On sample A, a Ti(C,N) layer was deposited in one step at 80 mbar and 870 °C in a gas mixture of 2.95 vol. % TiCl4, 0.45 vol. % CH3CN and balance H2.

[0035] On sample B, a Ti(C,N) layer was deposited in one step at 80 mbar and 830 °C in a gas mixture of 2.95 vol. % TiCl4, 0.45 vol. % CH3CN and balance H2.

[0036] On sample C, the Ti(C,N) layer was deposited in two steps, inner Ti(C,N) and outer Ti(C,N). The inner Ti(C,N) was deposited for 10 min at 55 mbar and 885 °C in a gas mixture of 3.0 vol.% TiCl4, 0.45 vol.% CH3CN, 37.6 vol.% N2 and balance H2. The outer Ti(C,N) was deposited at 55 mbar and 885 °C in a gas mixture of 7.8 vol.% N2, 7.8 vol.% HCl, 2.4 vol.% TiCl4, 0.65 vol.% CH3CN and balance H2.

[0037] Coverage Analysis The layer thickness was measured on the rake face of the cutting tool samples using an optical microscope. The layer thicknesses of the coatings for samples A to C are shown in Table 1. TIFF2024514959000006.tif50170

[0038] The grain size of the Ti(C,N) layer was analyzed by X-ray diffraction by analyzing the 422 peak as disclosed above. The C / (C+N) ratio of the Ti(C,N) layer was analyzed using electron microprobe analysis as disclosed above. The resulting grain size and carbon content of samples A, B and C are presented in Table 2. TIFF2024514959000007.tif56170

[0039] The orientation of the Ti(C,N) layer was analyzed using X-ray diffraction as disclosed above, and the results are shown in Table 3. TIFF2024514959000008.tif42170

[0040] The grain size of Ti(C,N) in the samples was also examined by TEM images of the top view of the Ti(C,N) layer. First, a cross section of each sample was prepared by cutting the insert in the middle and then polishing the cross section. Then, a FIB (focused ion beam) lamella was removed from the Ti(C,N) coating, parallel to the substrate surface, approximately 6 μm from the coating-substrate interface, using a lift-out technique. The lamella was thinned using an ion beam until electron transparency was achieved. Bright-field scanning TEM images were acquired on a ThermoFisherScientific Titan transmission electron microscope operating at 300 kV. TKD (transmission Kikuchi diffraction) maps were collected by an Oxford Aztec system installed on a ThermoFisherScientific Helios FIB-SEM. IPF (inverse pole figure) maps with grain boundary overlay were produced by AztecCrystal software. Bright-field images are shown in Figures 10-12. TKD images are shown in Figures 7-9. It can be seen that there is a distribution of particle size in all samples. It can also be seen that the Ti(C,N) in sample A shows smaller particles than the Ti(C,N) in sample B.

[0041] Cutting test 1 The cutting tools were tested in a longitudinal turning operation on a workpiece of SS2310, a high alloy steel. c is 125m / min, and the feed, f n is 0.072 mm / revolution, and the cutting depth, a p The cutting edge was 2 mm and a water-miscible cutting fluid was used. Machining was continued until the end of life time criterion was reached. One cutting edge per cutting tool was evaluated.

[0042] Tool life criteria are >0.3mm for primary or secondary flank wear or >0.2mm for crater area 2 When any of these criteria was met, the specimen was considered to have reached its end of life. The results of the cutting tests are shown in Table 4. TIFF2024514959000009.tif42170

[0043] As can be seen in Table 4, sample A unexpectedly exhibits high wear resistance, nearly doubling the life span of samples B and C.

[0044] Cutting test 2 The cutting tool was also tested in an intermittent face turning operation on a 100x100mm square workpiece of SS1672 steel. c is 250m / min, and the feed, f n is 0.1mm / revolution, and the cutting depth, a p The cutting edge diameter was 2.5 mm and a water-miscible cutting fluid was used. Machining was continued until the end-of-life criteria was reached. One cutting edge per cutting tool was evaluated.

[0045] During the evaluation of tool wear, the % of damage of the first edge was measured along the contact length where the first edge was in contact with the workpiece. The tool life criterion was set as more than 40% damage as the substrate was exposed along the first edge in the contact area with the workpiece. Tool wear was measured every 3 cycles, i.e. after 3 facing passes. As soon as the criterion was met, the tool life was considered to be reached. To calculate the final tool life at 40% damage, a simple interpolation was made between before and after 40% damage was reached. The average results of 4 parallel cutting tests per specimen type are presented in Table 5. Occasionally, cutting edge fractures were observed and these were excluded from the results. Only specimens showing continuous wear, thereby reflecting the contribution to tool life from the coating, are included here. TIFF2024514959000010.tif41170

[0046] Although the present invention has been described in connection with various exemplary embodiments, it should be understood that the present invention is not limited to the disclosed exemplary embodiments, but rather is intended to include various modifications and equivalent arrangements within the scope of the appended claims. Moreover, it should be recognized that any disclosed form or embodiment of the present invention can be incorporated into any other disclosed or described or suggested form or embodiment as a general design modification. It is therefore intended to be limited only as indicated by the scope of the appended claims attached hereto.

Claims

1. A cutting tool for metal cutting comprising a substrate at least partially coated with a 3-30 μm coating, said substrate being a hard metal, a cermet or a ceramic, said coating comprising one or more layers, at least one layer being a Ti(C,N) layer having a thickness of 3-25 μm, said Ti(C,N) layer being composed of columnar grains, The average grain size D of the Ti(C,N) layer measured by X-ray diffraction using CuKα radiation ４２２ , particle size D ４２２ But Scherrer's formula [In the formula, D ４２２ is the average grain size of the Ti(C,N) grains in the Ti(C,N) layer, K is a shape factor, set here as 0.9, and λ is the CuKα value, set here as 1.5405 Å. １ is the wavelength of the line, and B ４２２ is the FWHM value of the (422) reflection, θ is the Bragg angle, and D ４２２ is ≧25 nm and ≦35 nm. (422) A cutting tool for metal cutting, calculated from the full width at half maximum (FWHM) of the peak according to

2. The at least one Ti(C,N) layer having a thickness of 4.5 to 25 μm exhibits an X-ray diffraction pattern measured using CuKα radiation and θ-2θ scan, where TC(hkl) is defined according to the Harris equation: where I(hkl) is the measured intensity (integrated area) of the (hkl) reflection, and I ０ (hkl) are standard intensities according to ICDD PDF-Card No. 42-1489, n is the number of reflections, the reflections used in the calculation are (111), (200), (220), (311), (331), (420) and (422), and TC(422) is ≧3], a cutting tool according to claim 1.

3. 3. The cutting tool of claim 2, wherein the at least one Ti(C,N) layer has a thickness of 6-25 μm and a TC(422) of ≧4.

4. 3. The cutting tool of claim 2, wherein the at least one Ti(C,N) layer exhibits an X-ray diffraction pattern having a highest TC(422) and a second highest TC(311).

5. The cutting tool according to claim 1, wherein the C / (C+N) ratio in the Ti(C,N) layer is between 50% and 70%, preferably between 55% and 65%.

6. The cutting tool of claim 1 , wherein the coating comprises an innermost layer of TiN.

7. The cutting tool of claim 1 , wherein the Ti(C,N) layer is the outermost layer of the coating.

8. The cutting tool according to claim 1 , which is a drill, a milling insert or a turning insert, preferably a turning insert.

9. Use of a cutting tool according to any one of claims 1 to 8 in metal cutting.

10. 10. Use of a cutting tool according to claim 9 in metal cutting in high alloy steel, hardened steel, cast iron or stainless steel, preferably for metal cutting in high alloy steel.

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