Cutting tools

Abstract

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

Description

Technical Field

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

[0002] In the field of cutting tool technology for metalworking, CVD coating is a well-known method for enhancing tool wear resistance. CVD coatings are typically made from ceramic materials such as TiN, TiC, Ti(C,N), and Al2O3.

[0003] EP2791387 discloses a cutting tool coated with a fine-grained titanium carbonitride layer. This coating advantageously exhibits high resistance to spalling during turning and high-speed cutting of ductile iron. The columnar MTCVD Ti(C,N) layer is described as having an average grain width of 0.05–0.4 μm.

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

[0005] One object of the present invention is to provide a coated cutting tool with improved wear resistance in metal cutting applications. A further object is to improve its wear 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 wear and flank wear when turning steel and hardened steel.

[0006] At least one of these objectives is achieved by a coated cutting tool as described in item 1.

[0007] Preferred implementation methods are listed in the dependent items.

[0008] This disclosure relates to a cutting tool for metal cutting, wherein the cutting tool comprises a substrate at least partially coated with a 3-30 μm coating, the substrate being made of cemented carbide, cermet, or ceramic, the coating comprising more than one layer, wherein at least one layer is a Ti(C,N) layer with a thickness of 3-25 μm, wherein the Ti(C,N) layer is composed of columnar grains, wherein

[0009] The average grain size D of the Ti(C,N) layer was measured by X-ray diffraction using CuKα radiation. 422 At that time, the grain size D 422 The full width at half maximum (FWHM) of peak (422) is calculated using the Scherrer formula:

[0010]

[0011] Where D 422 λ is the average grain size of the Ti(C,N) grains in the Ti(C,N) layer; K is the shape factor, set to 0.9 here; λ is the wavelength of CuKα1 radiation, set to 0.9 here. B 422 It is the FWHM value of the reflection (422); and θ is the Bragg angle, where D 422 ≥25nm and ≤35nm.

[0012] Surprisingly, cutting tools with very fine-grained Ti(C,N) layers exhibited remarkably high wear resistance in metal cutting applications, such as turning high-alloy steels. It is believed that the combination of high crystallinity and columnar grains with numerous grain boundaries contributes to this high wear resistance.

[0013] In one embodiment of the invention, when measured using CuKα radiation and θ-2θ scanning, the at least one Ti(C,N) layer exhibits an X-ray diffraction pattern, wherein TC(hkl) is defined according to the Harris formula:

[0014]

[0015] Where I(hkl) is the intensity (integral area) of the measured (hkl) reflection, I0(hkl) is the standard intensity according to the ICDD PDF card No. 42-1489, n is the number of reflections, and the reflections used in the calculation are (1 1 1), (2 0 0), (2 20), (3 1 1), (3 3 1), (4 2 0), and (4 2 2), where TC(422)≥3.

[0016] In one embodiment of the invention, the thickness of the at least one Ti(C,N) layer is 6-25 μm and exhibits an X-ray diffraction pattern, wherein TC(422)≥4.

[0017] In one embodiment of the invention, the thickness of the at least one Ti(C,N) layer is 4.5-25 μm, and it exhibits an X-ray diffraction pattern, with TC(422) being the highest and TC(311) being the second highest. In another embodiment of the invention, the C / (C+N) ratio in the Ti(C,N) layer is 50% to 70%, preferably 55% to 65%. An advantage of this composition is that the Ti(C,N) layer exhibits high chemical stability.

[0018] In one embodiment of the invention, the coating comprises an innermost TiN layer.

[0019] In one embodiment of the present invention, the Ti(C,N) layer is the outermost layer of the coating.

[0020] The present invention also relates to the use of the above-mentioned cutting tools in metal cutting.

[0021] In one embodiment of the invention, the cutting tool is used for metal cutting of high alloy steel, hardened steel, cast iron or stainless steel, preferably for metal cutting of high alloy steel.

[0022] In one embodiment of the invention, the cutting tool is a drill bit, a milling insert, or a turning insert, preferably a turning insert.

[0023] Post-treatments can be applied to the coated cutting tools described herein, such as any combination of sandblasting, brushing, or shot peening. Sandblasting post-treatment can be, for example, wet or dry sandblasting using alumina particles.

[0024] Other objects and features of the invention will become apparent from the following definitions and embodiments considered in conjunction with the accompanying drawings. Attached Figure Description

[0025] Embodiments of the present invention will be described with reference to the accompanying drawings, wherein:

[0026] Figure 1 A scanning electron microscope (SEM) image of a cross-section of sample A, which serves as an example of the coating of the present invention, is shown.

[0027] Figure 2 A scanning electron microscope (SEM) image of a cross section of sample B, which serves as an example of a reference coating, is shown.

[0028] Figure 3 A scanning electron microscope (SEM) image of a cross section of sample C, which serves as an example of a reference coating, is shown.

[0029] Figure 4 A scanning electron microscope (SEM) image of the outer surface of sample A, which serves as an example of the coating of the present invention, is shown.

[0030] Figure 5 A scanning electron microscope (SEM) image of the outer surface of sample B, which serves as an example of a reference coating, is shown.

[0031] Figure 6 A scanning electron microscope (SEM) image of the outer surface of sample C, which serves as an example of a reference coating, is shown.

[0032] Figure 7The TKD (transmission Kikuchi diffraction) mapping of a planar image in the Ti(C,N) layer of sample A is shown. The planar image is approximately 6 μm from the substrate-coating interface.

[0033] Figure 8 The TKD (transmission Kikuchi diffraction) mapping of a planar image in the Ti(C,N) layer of sample B is shown. The planar image is approximately 6 μm from the substrate-coating interface.

[0034] Figure 9 The TKD (transmission Kikuchi diffraction) mapping of a planar image in the Ti(C,N) layer of sample C is shown. The planar image is approximately 6 μm from the substrate-coating interface.

[0035] Figure 10 Bright-field images of a planar view of the Ti(C,N) layer in sample A, obtained by transmission electron microscopy (TEM), are shown. The planar view is approximately 6 μm from the substrate-coating interface.

[0036] Figure 11 Bright-field images of a planar view of the Ti(C,N) layer in sample B, obtained by transmission electron microscopy (TEM), are shown. The planar view is approximately 6 μm from the substrate-coating interface.

[0037] Figure 12 Bright-field images of a planar view within the Ti(C,N) layer of sample C, obtained through transmission electron microscopy (TEM) analysis, are shown. The planar view is approximately 6 μm from the substrate-coating interface.

[0038] definition

[0039] The term "cutting tool" as used herein is intended to refer to cutting tools suitable for metal cutting applications, such as inserts, end mills, or drills. Applications may include, for example, turning, milling, or drilling of metals such as steel.

[0040] method

[0041] XRD

[0042] To investigate the texture or orientation and average grain size of the layer, 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 in a sample holder, ensuring that the flank face of the sample was parallel to a reference surface of the sample holder and at an appropriate height. Cu-Kα radiation was used for measurements, with a voltage of 45 kV and a current of 40 mA. A 1 / 2-degree anti-scattering slit and a 1 / 4-degree diverging slit were used. The diffraction intensity of the coated cutting tool was measured within a 2θ range of 20° to 140°, i.e., within an incident angle θ range of 10° to 70°. Data analysis was performed using PANalytical's X'Pert HighScore Plus software, including background fitting, Cu-Kα2 stripping, and profile fitting.

[0043] The grain size of the layer was calculated using the integral peak full width at half maximum (FWHM) of the graphical fitting curve obtained from PANalytical's X'Pert HighScore Plus software, according to the Scherrer formula (Eq1) (Birkholz, 2006).

[0044] The average grain size D is calculated from the full width at half maximum (FWHM) of peak (422) according to the following Scherrer formula. 422 :

[0045]

[0046] Where D 422 λ is the average grain size of the Ti(C,N); K is the shape factor, set to 0.9 here; λ is the wavelength of CuKα1 radiation, set to 0.9 here. B is the FWHM value of the (422) reflection; and θ is the Bragg angle, i.e., the angle of incidence.

[0047] β is the line width at FWHM (in radians) after subtracting the instrumental width (0.00174533 radians), and θ is the angle of incidence. The Gaussian approximation (Eq2) (Birkholz, 2006) is used for calculating the width after subtracting the instrumental width.

[0048] β=√((FWHM 表观 ) 2 -(FWHM 仪器 ) 2 )

[0049] Where β is the actual widening (in radians) used for grain size calculation, FWHM 表观 It is the measurement of the widening (in radius), FWHM仪器 It is an increase in instrument width (in radians).

[0050] The texture or orientation of the layer is defined based on an X-ray diffraction pattern, measured using CuKα radiation and θ-2θ scanning, wherein TC(hkl) is defined according to the following Harris formula:

[0051]

[0052] Where I(hkl) is the intensity (integral area) of the measured (hkl) reflection, I0(hkl) is the standard intensity according to the ICDD PDF card No. 42-1489, n is the number of reflections, and the reflections used in the calculation are (1 1 1), (2 0 0), (2 20), (3 1 1), (3 3 1), (4 2 0) and (4 2 2).

[0053] Since other layers that may exist above the Ti(C,N) layer will affect the X-ray intensity entering the Ti(C,N) layer and leaving the entire coating, these need to be corrected for, taking into account the linear absorption coefficients of the corresponding compounds in the layers. Alternatively, the other layers above the Ti(C,N) monolayer can be removed by methods that substantially do not affect the XRD measurements, such as chemical etching.

[0054] It should be noted that peak overlap is a phenomenon that can occur in X-ray diffraction analysis of coatings containing, for example, multiple crystalline layers and / or coatings deposited on a matrix containing a crystalline phase, and this needs to be considered and compensated for by those skilled in the art. It should also be noted that, for example, WC in the matrix may have diffraction peaks close to the relevant peaks of this invention.

[0055] Elemental analysis was performed using a JEOL JXA-8530F electron microprobe analysis system equipped with a wavelength dispersive spectroscopy (WDS) instrument to determine... Figure 1 , 2 The C / (C+N) ratio of the Ti(C,N) layer presented in Figure 3 was compared with that of the Ti(C,N) layer. The analysis of the Ti(C,N) layer was performed on a polished cross-section of the rake face. For each type of Ti(C,N) layer, three samples were analyzed at 10 points at 50 μm intervals, along a straight line parallel to the substrate surface, at a distance of 4–6 μm from the interface between the substrate and the TiN layer. Data were obtained using 10 kV, 29 nA, and a Ti(C,N) reference with a composition of 10.22 wt% C, 10.68 wt% N, 78.86 wt% Ti, and 0.24 wt% O. Example

[0056] Exemplary embodiments of the present invention will now be disclosed in more detail and compared with reference embodiments. Coated cutting tools (blades) are manufactured and analyzed and evaluated in cutting tests.

[0057] The cemented carbide substrate was manufactured using conventional processes including grinding, mixing, spray drying, pressing, and sintering. The sintered substrate was CVD coated in an Ionbond-type radial CVD reactor of size 530, capable of accommodating 10,000 half-inch cutting inserts. The substrate was placed on a plate, and samples for further testing and analysis 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 (inserts) is CNMG-120408-PM. The cemented carbide composition is 7.2 wt% Co, 2.9 wt% TaC, 0.5 wt% NbC, 1.9 wt% TiC, 0.4 wt% TiN, and the balance WC.

[0058] CVD deposition

[0059] In a process at 400 mbar and 885 °C, a first innermost layer of TiN, approximately 0.2 μm thick, was deposited on all substrates. A gas mixture of 48.8 vol% H2, 48.8 vol% N2, and 2.4 vol% TiCl4 was used. Subsequently, a Ti(C,N) layer was deposited as disclosed below.

[0060] 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 the balance H2.

[0061] 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 the balance H2.

[0062] On sample C, a Ti(C,N) layer was deposited in two steps: an inner Ti(C,N) layer and an outer Ti(C,N) layer. The inner Ti(C,N) layer was deposited for 10 minutes at 55 mbar and 885 °C in a gas mixture of 3.0 vol% TiCl4, 0.45 vol% CH3CN, 37.6 vol% N2, and the balance H2. The outer Ti(C,N) layer 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 the balance H2.

[0063] Coating analysis

[0064] The layer thickness was measured on the rake face of the cutting tool sample using an optical microscope. The layer thickness of the coating on sample AC is shown in Table 1.

[0065] Table 1. Layer Thickness

[0066] sample Layer thickness TiN [μm] Layer thickness Ti(C,N) [μm] A 0.2 9.3 B 0.2 8.3 C 0.2 9.0

[0067] The grain size of the Ti(C,N) layer was analyzed by X-ray diffraction, as disclosed above, with peak 422 analyzed. The C / (C+N) ratio of the Ti(C,N) layer was analyzed using electron microprobe analysis, as disclosed above. The obtained grain sizes and carbon contents of samples A, B, and C are presented in Table 2.

[0068] Table 2. Grain size and carbon content

[0069] sample Grain size [nm] The C / (C+N) ratio in Ti(C,N) A 33 60.3％ B 37 59.5％ C >67* 55.8％

[0070] *Uncorrected Scherrer is used because there is no peak broadening caused by small grain size.

[0071] As disclosed above, X-ray diffraction was used to analyze the orientation of the Ti(C,N) layer. The results are presented in Table 3.

[0072] Table 3. Texture Coefficient

[0073] sample TC(111) TC(200) TC(220) TC(311) TC(331) TC(420) TC(422) A 0.31 0.01 0.20 1.58 0.64 0.18 4.08 B 0.38 0.01 0.06 1.71 0.37 0.14 4.33 C 0.41 0.01 0.07 1.98 0.41 0.16 3.96

[0074] The grain size of the Ti(C,N) in the samples was also investigated using TEM images of planar views of the Ti(C,N) layer. First, cross-sections of each sample were prepared using a mid-cutting blade, followed by polishing. Then, using a lift-out technique, FIB (Focused Ion Beam) flakes were extracted from the Ti(C,N) coating parallel to the substrate surface at approximately 6 μm from the coating-substrate interface. The flakes were thinned using an ion beam until electronic transparency was achieved. Bright-field scanning TEM images were obtained on a Thermo Fisher Scientific Titan transmission electron microscope operating at 300 kV. TKD (Transmission Kikuchi Diffraction) maps were collected using an Oxford Aztec system mounted on a Thermo Fisher Scientific Helios FIB-SEM. IPF (Inverse Poleogram) maps with grain boundary coverage were generated using Aztec Crystal software. Bright-field images are shown below. Figure 10-12 As shown in the image. (TKD image as shown) Figure 7-9 As shown in the figure, a grain size distribution is present in all samples. It can also be seen that the Ti(C,N) in sample A exhibits smaller grains compared to the Ti(C,N) in sample B.

[0075] Cutting Test 1

[0076] The cutting tool was tested in longitudinal turning operations on SS2310 (a high-alloy steel) workpiece material. Cutting speed V c The feed rate is 125 m / min, and the feed rate is f. n The cutting speed is 0.072 mm / revolution, and the cutting depth is a. p The cutting edge is 2mm thick, and a water-miscible cutting fluid is used. Machining continues until the end-of-life criteria are met. One cutting edge of each tool is evaluated.

[0077] The tool life standard is set as follows: primary or secondary flank wear >0.3mm or crater area >0.2mm. 2 Once any one of these criteria is met, the sample is considered to have reached its lifespan. The results of the cutting tests are presented in Table 4.

[0078] Table 4. Results of Cutting Test 1

[0079] sample Lifespan (minutes) Standard lifespan A 84 Secondary flank wear B 52 Secondary flank wear C 40 Primary back face wear

[0080] As shown in Table 4, compared with samples B and C, sample A exhibits unexpectedly high wear resistance and has nearly twice the lifespan.

[0081] Cutting Test 2

[0082] The cutting tool was also tested in intermittent end-face turning operations on 100*100mm square bars of SS1672 steel. Cutting speed V c The feed rate is 250 m / min, and the feed rate is f. n The cutting depth a is 0.1 mm / revolution. p The cutting edge is 2.5mm, and a water-miscible cutting fluid is used. Machining continues until the end-of-life criteria are met. One cutting edge of each tool is evaluated.

[0083] When evaluating tool wear, the percentage of damage along the contact length where the main cutting edge contacts the workpiece material is measured. The tool life criterion is set at ≥40% damage, such that the substrate is exposed along the main cutting edge in the area in contact with the workpiece material. Tool wear is measured every three cycles, i.e., after three facing passes. Once the criterion is met, the tool life is considered reached. To calculate the final tool life at 40% damage, a simple interpolation is performed between the damage before and after reaching 40%. Table 5 presents the average results of four parallel cutting tests for each type of sample. Occasionally, cutting edge breakage was observed, and these were removed from the results. Only samples showing continuous wear are included here, thus reflecting the coating's contribution to tool life.

[0084] Table 5. Results of Cutting Test 2

[0085] sample Lifespan [cycle] A 24.2 B 15.7 C 7.2

[0086] While the invention has been described in conjunction with various exemplary embodiments, it should be understood that the invention is not limited to the disclosed exemplary embodiments, but rather is intended to cover various modifications and equivalent arrangements as indicated in the appended claims. Furthermore, it should be recognized that, as a general matter of design choice, any disclosed form or embodiment of the invention can be incorporated into any other disclosed, described, or suggested form or embodiment. Therefore, its intent is limited to what is indicated by the scope of the appended claims.

Claims

1. A cutting tool for metal cutting, wherein the cutting tool comprises a substrate at least partially coated with a 3-30 µm coating, the substrate being made of cemented carbide, cermet, or ceramic, the coating comprising one or more layers, wherein the coating comprises at least one Ti(C,N) layer having a thickness of 3-25 µm, wherein the Ti(C,N) layer is composed of columnar grains, wherein The average grain size D of the Ti(C,N) layer was measured by X-ray diffraction using CuKα radiation. 422 At that time, the grain size D 422 The full width at half maximum (FWHM) of peak (422) is calculated using the Scherrer formula: Where D 422 λ is the average grain size of Ti(C,N) grains in the Ti(C,N) layer; K is the shape factor, set to 0.9 here; λ is the wavelength of CuKα1 radiation, set to 1.5405 Å here; B 422 It is the FWHM value of the reflection (422); and θ is the Bragg angle. Where D 422 ≥25 nm and ≤35 nm The C / (C+N) ratio in the Ti(C,N) layer is 50% to 70%. The coating described herein comprises an innermost TiN layer.

2. The cutting tool according to claim 1, wherein the Ti(C,N) layer has a thickness of 4.5-25 µm and exhibits an X-ray diffraction pattern when measured using CuKα radiation and θ-2θ scanning, wherein TC(hkl) is defined according to the Harris formula: Where I(hkl) is the intensity (integral area) of the measured (hkl) reflection, I0(hkl) is the standard intensity according to the ICDD PDF card No. 42-1489, n is the number of reflections, and the reflections used in the calculation are (1 1 1), (2 0 0), (2 2 0), (3 11), (3 3 1), (4 2 0), and (4 2 2), where TC(422)≥3.

3. The cutting tool according to claim 2, wherein the thickness of the Ti(C,N) layer is 6-25 µm and TC(422)≥4.

4. The cutting tool according to claim 2 or 3, wherein the Ti(C,N) layer exhibits an X-ray diffraction pattern, wherein TC(422) is the highest and TC(311) is the second highest.

5. The cutting tool according to any one of claims 1 to 3, wherein the C / (C+N) ratio in the Ti(C,N) layer is 55% to 65%.

6. The cutting tool according to any one of claims 1 to 3, wherein the Ti(C,N) layer is the outermost layer of the coating.

7. The cutting tool according to any one of claims 1 to 3, wherein the cutting tool is a drill bit, a milling insert, or a turning insert.

8. Use of the cutting tool according to any one of the preceding claims in metal cutting.

9. Use of the cutting tool according to claim 8 in metal cutting of high alloy steel, hardened steel, cast iron or stainless steel.

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