A cutting tool

Abstract

The present invention relates to a cutting tool comprising a substrate (1) at least partially coated with a coating, said substrate (1) is of cemented carbide or cermet, said coating comprise one or more layers, wherein at least one layer is a κ-Al2O3 layer (3) with a thickness of 3-6 µm, wherein the κ-Al2O3 layer (3) is composed of grains and wherein a grain width is the width of the grain in a direction parallel to the substrate (1) surface, and wherein the average grain width (db) of the κ-Al2O3 grains is measured along a line at a position corresponding to 80% of the thickness of the κ-Al2O3 layer (3) and wherein the average grain width (da) of the κ-Al2O3 grains as measured along a line at 1 µm from the innermost κ-Al2O3 interface, characterized in that the ratio db / da is between 1.45 and 2.00.

Description

[0001] A CUTTING TOOL

[0002] TECHNICAL FIELD

[0003] The present invention relates to a coated cutting tool. The cutting tool is CVD coated and the substrate is a cemented carbide or cermet and the CVD coating comprises a layer of TiCN and a layer of K-AI2O3.

[0004] BACKGROUND

[0005] In the technical area of cutting tools for metal machining, the usage of CVD coatings is a well-known method to enhance the wear resistance of the tool. CVD coatings that are commonly used are coatings such as TiN, TiC, TiCN and AI2O3.

[0006] The wear resistance of an AI2O3 coating is influenced by the crystal structure and the most commonly used are K- and a-ALOs -coatings. The wear properties in machining operations typically differ between a-ALOs coatings and K-AhOs-coatings and therefore their respective application area may also differ.

[0007] EP0753602 A1 discloses a cutting tool comprising a K-AI2O3 coating with a preferred crystal growth orientation, resulting in a {210} texture, which tool exhibits increased wear properties in machining of ball bearing steel.

[0008] It is an object of the present invention to provide a cutting tool with increased lifetime in metal cutting. It is also an object of the present invention to provide a cutting tool with high resistance to flank wear and chipping during metal cutting in steel.

[0009] DESCRIPTION OF THE INVENTION

[0010] 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.

[0011] The present invention relates to a cutting tool comprising a substrate at least partially coated with a coating, said substrate is of cemented carbide or cermet, said coating comprise one or more layers, wherein at least one layer is a K-AI2O3 layer with a thickness of 3-6 pm, wherein the K-AI2O3 layer is composed of grains and wherein a grain width is the width of the grain in a direction parallel to the substrate surface, and wherein the average grain width db of the K-AI2O3 grains is measured along a line at a position corresponding to 80% of the thickness of the K-AI2O3 layer and wherein the average grain width daof the K-AI2O3 grains is measured along a line at a distance of 1 pm from the innermost K-AI2O3 interface, characterized in that the ratio db / dais between 1 .45 and 2.00.

[0012] In one embodiment of the present invention the ratio db / dais between 1.48 and 1.80.

[0013] With the coating of the present invention an intense wet blasting process can be applied to the coating and as a result thereof the application areas for the K-AI2O3 coating is extended.

[0014] It was surprisingly found that a cutting tool provided with a coating comprising a K-AI2O3 layer with grains that fulfills the above-described ratio showed an increased resistance to blasting and an increased resistance to flank wear in milling of stainless steel.

[0015] A K-AI2O3 layer with a thickness thinner than 3 pm is disadvantageous as it limits wear resistance and a thicker K-AI2O3 layer than 6 pm is disadvantageous as it will widen the cutting tool edge radius.

[0016] In one embodiment, the substrate of the coated cutting tool consists of cemented carbide comprising 7-14 wt% Co, for example 11-13 wt% Co, and 0.5 - 0.8 wt% Cr and balance WC.

[0017] The cutting tool is suitably an indexable cutting insert, such as a cutting insert for milling, a cutting insert for turning, or a cutting insert for drilling. Alternatively, the cutting tool is suitably a drill or an endmill.

[0018] The cutting tool comprises a rake face and a flank face and a cutting edge in between.

[0019] In one embodiment of the present invention the residual stress as measured with XRD in the K-AI2O3 layer is between -0.6 GPa and -2.0 GPa, preferably between -1.0 GPa and -1.5 GPa.

[0020] In one embodiment of the present invention the average grain width db of the K-AI2O3 grains as measured along a line extending parallel with the surface of the substrate and at a position corresponding to 80% of the thickness of the K-AI2O3 layer is between 0.6 pm and 0.8 pm, preferably between 0.65 pm and 0.70 pm. By a position corresponding to 80% of the thickness of the K-AI2O3 layer is herein meant as seen in a direction from the surface of the substrate towards the outer surface of the coating, i.e in the growth direction of the K- AI2O3 layer. A position corresponding to 80% of the thickness of the K-AI2O3 layer is a position relatively close to the outermost surface of the of the K-AI2O3 layer. In one embodiment of the present invention the average grain width daof the K-AI2O3 grains as measured along a line extending parallel with the surface of the substrate and at a distance of 1 pm from the innermost K-AI2O3 interface is between 0.4 pm and 0.5 pm, preferably between 0.40 pm and 0.45 pm. The innermost K-AI2O3 interface is the lowermost interface of the K-AI2O3 layer, typically an interface with a bonding layer.

[0021] In one embodiment of the present invention the thickness of the K-AI2O3 layer is between 4 pm and 5 pm.

[0022] In one embodiment of the present invention the coating comprises a TiCN layer between the substrate and the K-AI2O3 layer, preferably the thickness of the TiCN layer is between 1.5 and 2.5 pm.

[0023] In one embodiment of the present invention the coating comprises an innermost TiN layer, preferably the thickness of the innermost TiN layer is between 0.3 and 0.6 pm.

[0024] In one embodiment of the present invention the coating comprises a bonding layer between the TiCN layer and the K-AI2O3 layer, preferably said bonding layer is one or more of TiCO, TiCNO, AITiCO, AITiCNO, more preferably the thickness of the bonding layer is between 1.5 and 2.5 pm.

[0025] In one embodiment of the present invention the surface roughness, Ra, of substrate at the rake face, as measured in an SEM cross section is between 0.05 pm and 0.2 pm, preferably between 0.15 pm and 0.2 pm. An Rawithin the range of between 0.05 pm and 0.2 pm has shown to be advantageous in providing a wear resistant coated cutting tool.

[0026] In one embodiment of the present invention, the K-AI2O3 layer exhibits a texture coefficient TC(hkl), as measured by X-ray diffraction using Cu Ka radiation and 0-20 scan, defined according to Harris formula:

[0027] TC(hkl)=v72^2] ( lothkl)F1) LnZ_|n=i / 0(hfcOj where l(hkl) is the measured integrated area intensity of the (hkl) reflection, lo(hkl) is the standard intensity wherein lo(1 1 1) = 105, lo(O 1 3) = 5026, lo(1 2 2) = 10000, lo(1 1 3) = 1116, l0(2 0 0) = 795, l0(2 0 1) = 1342, l0(0 0 4) = 291 , l0(0 4 0) = 387, l0(0 1 5) = 429 and lo(2 0 4) = 1312, n is the number of reflections used in the calculation, where the (hkl) reflections used are (1 1 1), (0 1 3), (1 2 2), (1 1 3), (2 0 0), (2 0 1), (0 0 4), (0 4 0), (0 1 5) and (2 0 4), wherein TC(0 0 4) + TC(0 1 5) 2== 6, preferably 2= 7, more preferably 2= 8. In one embodiment of the present invention the TiCN layer exhibits a texture coefficient TC(hkl), as measured by X-ray diffraction using Cu Ka radiation and 0-20 scan, defined according to Harris formula (F1) where l(hkl) is the measured intensity (integrated area) of the (hkl) reflection, lo(hkl) is the standard intensity wherein lo(1 1 1) = 7871 , lo(2 O O) = 10000, lo(2 2 0) = 5369, l0(3 1 1) = 2550, l0(3 3 1) = 1128, l0(4 2 0) = 2366, l0(4 2 2) = 2479, and lo(5 1 1) = 1427, n is the number of reflections used in the calculation, and where the (hkl) reflections used are (1 1 1), (2 0 0), (2 2 0), (3 1 1),(3 3 1), (4 2 0), (4 2 2), (5 1 1), wherein TC(4 2 2)^=3, preferably 2? 4, more preferably 2? 5.

[0028] In one embodiment of the present invention the cutting tool comprises a 0.3 - 0.5 pm innermost TiN layer, a 1.5 - 2.5 pm TiCN layer, a 1 .5-2.5 pm AITiCNO bonding layer and a 3-6 pm K-AI2O3 layer.

[0029] Still other objects and features of the present invention will become apparent from the following definitions and examples considered in conjunction with the accompanying drawings.

[0030] METHODS

[0031] Grain width measurement

[0032] The average grain width of the K-AI2O3 grains has been determined at 80 % of the layer thickness, i.e. 20 % from the top surface of the layer, (db) and at 1 pm above the lower interface (da). A grain intercept method was used wherein an average grain width is determined from the grain width measurements of the grains along a line of 25 pm in length on a SEM image. An image of a fractured cross-section was collected on a coated insert on the rake face using a Zeiss Ultra scanning electron microscope, equipped with InLens and SE2 detectors, operating at 2 kV at working distances between 3 and 4 mm at 10 000X magnification, creating images of about 35 pm by 27 pm of the coating cross section. The lines used in the measurement were 25 pm long in the SEM image and parallel with the surface of the substrate.

[0033] Thickness measurement

[0034] The coating layer thicknesses were measured on fractured cross-sections of the coated inserts. The SEM images were created using a Zeiss Ultra scanning electron microscope, equipped with InLens and SE2 detectors. The microscope was operating at 2 kV at a working distance of between 3 and 4 mm and at 10 000X magnification, creating images of about 35 pm by 27 pm. The rake face of the coated cutting tools were studied. Surface roughness measurement

[0035] A surface roughness value for the surface of the substrate on the rake face of the cutting tool was evaluated from SEM images taken from a fractured cross-section. The method used here was performed as follows:

[0036] A fractured cross-section was collected on a coated insert using a Zeiss Ultra scanning electron microscope, equipped with InLens and SE2 detectors, operating at 2 kV at working distances between 3 and 4 mm at 10 000X magnification, creating images of, about 35 pm by 27 pm, of the interface of the cross-section between the substrate and the coating. After identification of the interface the image was digitalized using the Digitizer tool in Origin 2018b (b9.5.5.409) by OriginLab and an Ravalue was calculated as follows:

[0037] The image was imported using the Origin tool Digitizer. Axes were defined in accordance with the scale in the image. Individual points on the interface between substrate and coating were collected at about 0.5 pm average interval, shorter intervals for curved and longer intervals for straighter features, thus creating a surface roughness profile. A linear leastsquares were fitted to the obtained profile. The obtained linear least-squares line was subtracted from the individual data points on the profile, ensuring that eventual image rotation would not affect the evaluation. An Ravalue was the calculated using the formula where n = number of points used on the profile and y; is the distance, in pm, between the point i and the least-squares line.

[0038] X-ray diffraction measurement

[0039] Texture coefficient values, TC(hkl), were measured using XRD with CuKa radiation on rake faces on coated cutting tools by using a Bruker D8 Advance diffractometer, running a Cu tube at 40 kV and 40 mA, equipped with a LynxEye XE-T detector, operating in 0-20 mode. The diffractometer was equipped with fixed beam optics: on the primary side a 2.3° Soller slit and a 0.6 mm divergence slit, on the secondary side an anti-scatter slit of 8 mm followed by a 2.5° Soller slit and a 0.5 mm Ni filter. Diffraction patterns were recorded in the range 18° to 143° in steps of 0.05° in 20 for a total measurement time of about 5 min. The coated cutting tools were mounted in sample holders to ensure that the measured sample surface was parallel to the reference surface of the sample holder and also at the appropriate height.

[0040] The data analysis was made using whole-pattern fitting with the Le Bail method using the Bruker TOPAS 5 program. The output, i.e. the integrated peak areas for the profile fitted curve, from this program were, after corrections described below, then used to calculate the texture coefficients of the layers by comparing the ratio of the measured intensity data to the reference intensities for the layers of TiCN and K-AI2O3 using the Harris formula (F1) as disclosed above.

[0041] The measured intensities were thin film corrected due to differences in relative intensities of the peaks scattered by the layers at different 20 angles are different compared to for bulk samples, due to the differences in path length through the layer(s). Therefore, thin film correction was applied to the extracted integrated peak area intensities for the profile fitted curve, taken into account also the linear absorption coefficient of layer(s), when calculating the TC values. Since possible further layers above, for example, the K-AI2O3 layer will affect the X-ray intensities entering the K-AI2O3 layer and exiting the whole coating, corrections need to be made for these as well, taken into account the linear absorption coefficient for the respective compound in a layer. The same applies for X-ray diffraction measurements of a TiCN layer if the TiCN layer is located below, for example, an K-AI2O3 layer. Alternatively, a further layer, such as TiN, above an alumina layer can be removed by a method that does not substantially influence the XRD measurement results, e.g. chemical etching.

[0042] In order to investigate the texture of the K-AI2O3 layer X-ray diffraction was conducted using CuKa radiation and texture coefficients TC (hkl) for different growth directions of the grains of the K-AI2O3 layerwere calculated according to the Harris formula (F1) as disclosed above, where l(hkl) equals the measured integrated area intensity of the (hkl) reflection with corresponding reference intensity lo(hkl). In this case the (hkl) reflections and their corresponding reference intensities used were: lo(1 1 1) = 105, lo(O 1 3) = 5026, lo(1 2 2) = 10000, l0(1 1 3) = 1116, l0(2 0 0) = 795, l0(2 0 1) = 1342, l0(0 0 4) = 291 , l0(0 4 0) = 387, lo(O 1 5) = 429 and lo(204) = 1312. The measured integrated peak area is thin film corrected and corrected for any further layers above i.e. on top of the K-AI2O3 layer before said ratio is calculated.

[0043] The texture coefficients TC (hkl) for different growth directions of the columnar grains of the TiCN layer were calculated according to the Harris formula (F1) as disclosed above, where l(hkl) equals the measured integrated area intensity of the (hkl) reflection with corresponding reference intensity lo(hkl). In this case the (hkl) reflections and their corresponding reference intensities used were: lo(1 1 1) = 7871 , lo(2 0 0) = 10000, lo(2 2 0) = 5369, l0(3 1 1) = 2550, l0(3 3 1) = 1128, l0(42 0) = 2366, l0(42 2) = 2479, and l0(5 1 1) = 1427. The reflexes (5 1 1) and (3 3 3) are completely overlapped and the intensity of the (5 1 1) peak was therefore calculated from the sum of the intensities for (5 1 1) and (3 3 3), which is the measured one. This correction was performed as follows. I (5 1 1) was set to the sum of integrated peak areas for (5 1 1) and (3 3 3), followed by a subtraction of a calculated value for the (3 3 3) reflex, lc(33 3), using the relation of the reference intensities of intensities for the (1 1 1) and (3 3 3) reflexes: lc(33 3) = 1(1 1 1) * l0(33 3) / 10(1 1 1). The value used for lo(33 3) = 476. The measured integrated peak area is thin film corrected and corrected for any further layers above, for example the kAhCh layer, before said ratio is calculated.

[0044] It is to be noted that peak overlap is a phenomenon that can occur in X-ray diffraction analysis of coatings comprising for example several crystalline layers and / or that are deposited on a substrate comprising crystalline phases, and this has to be considered and compensated for by the skilled person conducting the analysis. A peak overlap of peaks from the K-AI2O3 layer with peaks from the TiCN layer might influence measurement and needs to be considered. It is also to be noted that for example WC in the substrate can have diffraction peaks close to the relevant peaks of the present coating.

[0045] Residual stress measurements

[0046] The residual stress of the K-AI2O3 layer was evaluated on the rake face of an CNMG12 insert by the sin2\ method using the elastic constants 391 GPa and 0.24 for Young’s modulus and Poisson’s ratio, respectively, and the K-AI2O3 (1 2 2) lattice spacings as determined by x-ray diffraction (XRD). The (1 2 2) peak position was determined at 2 (p angles (0 and 180°) and 6\| / angles (corresponding to sin2v values of 0.225, 0.315, 0.405, 0.495, 0.585, and 0.675). The instrumental angles were selected so that the penetration depth, T, was kept constant at 2 pm through-out the measurements, following the method outlined by Kumar, II. Welzel, E.J. Mittemeijer, J. Appl. Cryst. (2006) 39, 633-646. A linear absorption coefficient of 12300 rrr1was used when calculating the penetration depth in AI2O3.

[0047] The coated cutting tools were mounted in sample holders to ensure that the measured sample surface was parallel to the reference surface of the sample holder and also at the appropriate height. The measurements were made on a Bruker D8 Discover instrument using point focus Cu Ka radiation. On the primary side, the instrument was equipped with a polycapillary optic and a 2 mm pin hole. On the secondary side an equatorial Soller slit was used together with a Bruker LynxEye-XET detector operated in 0D mode. The peak fitting was done using the software Bruker Topas5 and Pseudo-Voigt peak functions after which the lattice spacings, d, were calculated and the stress evaluated.

[0048] BRIEF DESCRIPTION OF DRAWINGS

[0049] Embodiments of the invention will be described with reference to the accompanying drawings.

[0050] Fig. 1 is a SEM image of a fractured cross-section of the coating in sample A (Invention), wherein the substrate (1), the TiCN layer (2), the K-AI2O3 layer (3) and the outermost surface (4) of the K-AI2O3 layer are indicated.

[0051] Fig. 2 is a SEM image of a fractured cross-section of the coating in sample B (Reference), wherein the substrate (1), the TiCN layer (2), the K-AI2O3 layer (3) and the outermost surface (4) of the K-AI2O3 layer are indicated.

[0052] Fig. 3 is a schematic drawing of a cross section of the inventive coating wherein widening of the K-AI2O3 grains is shown, (Invention), and wherein a TiCN layer (2), a K-AI2O3 layer (3) and an outermost surface (4) of the K-AI2O3 layer are indicated.

[0053] Fig. 4 is a schematic drawing of a cross section of the reference coating wherein the K-AI2O3 grains are columnar, (Reference), and wherein a TiCN layer (2), a K-AI2O3 layer (3) and an outermost surface (4) of the K-AI2O3 layer are indicated.

[0054] Fig. 5 is a SEM image of a cross section of the Reference coating wherein the grey line represents the position of 80% of the K-AI2O3 layer thickness, wherein the substrate (1), the TiCN layer (2), the K-AI2O3 layer (3) and the outermost surface (4) of the K-AI2O3 layer are indicated.

[0055] Fig. 6 is a SEM image of a cross section of the Inventive coating wherein the grey line represents the position of 1 pm from the interface in the K-AI2O3 layer, wherein the substrate (1), the TiCN layer (2), the K-AI2O3 layer (3) and the outermost surface (4) of the K-AI2O3 layer are indicated. Fig. 7 is a SEM image of the top surface of the K-AI2O3 layer of sample A (Invention), wherein the outermost surface (4) of the K-AI2O3 layer is indicated.

[0056] Fig. 8 is a SEM image of the top surface of the K-AI2O3 layer of sample B (Reference), wherein the outermost surface (4) of the K-AI2O3 layer is indicated.

[0057] Fig. 9 is a SEM image of a fractured cross-section of the coating in sample A (Invention) also including close up areas wherein the intercept method is illustrated by indicating a grey line and grain boundaries marked with black lines, wherein the substrate (1), the TiCN layer (2), the K-AI2O3 layer (3) and the outermost surface (4) of the K-AI2O3 layer are indicated.

[0058] EXAMPLES

[0059] Embodiments of the present invention will be disclosed in more detail in connection with the following examples. The examples are to be considered as illustrative and not limiting embodiments. In the following examples coated cutting tools (inserts) were manufactured, analyzed and evaluated in cutting tests. Cutting tools were prepared wherein the cutting tools comprised a substrate (1) of cemented carbide which was coated with a coating comprising a TiCN layer (2) and a K-AI2O3 layer (3). The performance of these were compared to the performance of a commercially available Seco milling grade, MP1501 , provided with a TiCN layer and an 001 oriented a-AhCh layer.

[0060] Substrate

[0061] Cemented carbide substrates of ISO-type XOMX120408TR, was manufactured and having the composition of 12.5 wt-% Co, 0.7 wt-% Cr and balance WC.

[0062] The powder mixture was milled, dried, pressed and sintered at 1470°C. The sintered cemented carbide substrates comprised about 12.5 wt% Co. No free graphite or eta phase was visible in a SEM micrograph of a cross section of the cemented carbide substrates.

[0063] Polishing of the rake face

[0064] All samples were polished on the rake face using a wet brushing process. The equipment used is of model Sinjet IBX12 with a setup consisting of two operations, where the first operation performs a coarse polishing and edge preparation using a brush with a flat SiC 240K grain size bristle. The second operation performs the fine polishing and the brush consists of a Diamond 1000K bristle. The polishing was performed until a surface roughness of 0.05 pm <Ra< 0.2 pm was obtained. After the polishing, a cleaning operation with ultrasonic bath and alkaline solution was used in order to remove any residues from the polishing process.

[0065] CVD deposition

[0066] The coatings in the examples below were deposited in a radial lonbond Bernex model BPXpro 530 L tandem CVD equipment capable of housing 10000 half-inch size cutting inserts. The samples to be tested and analysed further were selected from the middle of the chamber and at a position along half the radius of the plate between the center and the periphery of the plate.

[0067] Prior to the coating depositions every substrate was cleaned in ethanol bath for 30 minutes prior to the depositions.

[0068] The inserts were first coated with a thin approximately 0.4 pm TiN-layer, then with an approximately 2 pm TiCN layer by employing the well-known MTCVD technique using TiCk, CH3CN, N2, and H2 at 860 °C. The volume ratio of TiCk / CHsCN of the MTCVD deposition of the TiCN layer was 3.7 The details of the TiN and the TiCN depositions are shown in Table 1.

[0069] Table 1. MTCVD of TiN and TiCN

[0070] On top of the MTCVD TiCN layer was a 2 pm thick bonding layer deposited at 1020 °C by a process consisting of five separate reaction steps. First a HTCVD TiN-1 step using TiCk, N2, and H2 at 200 mbar, then a second step (HTCVD TiC-1) using TiCk, CH4, and H2 at 80 mbar, then a third step (HTCVD TiN-2) using TiCk, HCI, N2 and H2 at 500 mbar, a fourth step (HT TiCN-1) using TiCk, CH4, HCI, N2 and H2 at 60 mbar and finally a fifth step (HT TiCNO-1) using TiCk, HCI, CO, N2 and H2 at 60 mbar. Prior to the start of the subsequent K-AI2O3 nucleation, the bonding layer was exposed for 33 minutes in an atmosphere of H2 at 45-55 mbar. The details of the bonding layer deposition are shown in Table 2. Table 2. Bonding layer deposition

[0071] An K-AI2O3 layer was deposited on top of the bonding layer, first AICI3 was flushed over the surface in the AICh-1 step. On the inventive sample A the K-AI2O3 layer deposition included three different process steps (AI2O3-I, AI2O3-2, AI2O3-3) while on the sample B the K-AI2O3 layer deposition included only the first two process steps (AI2O3-I, AI2O3-2), see table 3. The first nucleation step (AI2O3-I) was run equally on both the sample A and sample B, and resulted in about 0.05 pm K-AI2O3. On the inventive sample A the second step (AI2O3-2) resulted in about 2.5 pm K-AI2O3 and the third grain widening step (AI2O3-3) resulted in about 2 pm. The total thickness of the K-AI2O3 layer on the inventive sample A was about 4.5 pm.

[0072] On the reference sample B the second step resulted in about 4.0 pm K-AI2O3. The total thickness of the K-AI2O3 layer on the reference sample B was about 4 pm.

[0073] Table 3. K-AI2O3 deposition steps Shot peening

[0074] The coated cutting tools were then subjected to a shot peening process where the surface was bombarded with a media comprising particles, so called beads, that were non-abrasive and that had a rounded shape. The media was beads of a hard material mainly comprising ZrC>2. The impact or energy from the beads during the shot peening should not be too high since this would increase the risk of damaging the surface and the cutting edge of the cutting tool. Nor should the impact or energy from the beads be too low since the desired technical effect would not be obtained. If the beads are too large the risk of damaging the cutting edge is increased. If the beads are too small the energy and impact transferred from the media to the substrate are less pronounced.

[0075] The shot peening was a dry process whereby the beads were introduced into the path of high pressure air. The shot peening was performed with peening media beads having a diameter of 70-150 pm. The peening pressure was about 5 bar and the distance between the gun nozzle and the surface of the cutting tool insert was about 10 cm. The shot peening was performed perpendicularly to the surface of the cutting tool and the duration per insert was about 1 second.

[0076] Wet blasting

[0077] Following the dry blasting, the coated cutting tools were subjected to a wet blasting process. In this process the cutting tools were subjected to blasting using abrasive grains. Wet blasting is well known in the field of cutting tools and is for example known to introduce residual stresses in coatings of cutting tools.

[0078] The step of wet blasting was performed with a blasting media comprising AI2O3 particles with a diameter of 20-80 pm. The wet blasting was performed perpendicular to the surface of the cutting tool and at a distance between the gun nozzle and the surface of the cutting tool of about 10-20 cm. The blasting pressure was about 1.4-1.8 bar and the duration per insert was about 1 second.

[0079] Coating analyses

[0080] The samples A and B were studied in SEM in cross sections on the rake face. Layer thicknesses are presented in Table 4 Table 4. Layer thicknesses in the samples

[0081] Roughness of substrate on rake face

[0082] The roughness of the substrates at the rake face was measured and the average value of Ra was about 0.18 pm for both samples.

[0083] Grain widening

[0084] The width of the grains in the K-AI2O3 layer was studied in a cross sectional SEM image of the coating on the rake face. The average widths of the K-AI2O3 grains were studied both at 1 pm from the bonding layer (da) and at a position of 80% of the K-AI2O3 total layer thickness (db), in the present case at a position about 3.6 pm from the bonding layer. An average of 4 parallel measurements is presented in table 5.

[0085] Table 5 Grain width in K-AI2O3 layer

[0086] Textu re coeff i ci e nts The texture coefficients were analyzed by X-ray diffraction with the method disclosed above.

[0087] All the calculated TC values are presented in Tables 6 and 7. Table 6. Texture coefficients of the TiCN-layer of Invention A and Reference B.

[0088] Table 7. Texture coefficients of the K-AhCh-layer of Invention A and Reference B. Performance testing - Blasting test

[0089] The cutting tools were evaluated after wet blasting post treatments and the degree of wear from the blasting was studied.

[0090] The samples A and B were subjected to a gentle wet blasting process, blasting G, using a blasting media of AI2O3 particles of a diameter of 20-80 pm mixed with water. The blasting was performed at a distance of 20 cm and for 1 second duration per insert and with a blasting pressure of about 1.4 bar. The samples treated with this gentle blasting were then called sample AG and sample BG.

[0091] The samples A and B were subjected to a strong wet blasting process, blasting S, using a blasting media of AI2O3 particles of a diameter of 20-80 pm mixed with water. The blasting was performed at a distance of 10 cm for 1 second duration per insert and with a blasting pressure of about 1.8 bar. The samples treated with this strong blasting were then called sample AS and sample BS.

[0092] The blasted cutting tools were inspected in a light optical microscope. On the strong blasted reference sample, sample BS, the oxide layer was removed and the coating was destroyed at the edges. The strong blasted inventive sample, sample AS, still had the oxide layer present at the edges. The result of the visual inspection is presented in Table 8.

[0093] Table 8. Blasting evaluation

[0094] The sample A did resist the stronger wet blasting process without the oxide being removed from the cutting edge. Sample A can thus be treated to achieve a higher compressive residual stress and this is advantageous in higher resistance to wear in metal cutting applications.

[0095] Residuals stress

[0096] The residual stresses in the K-AI2O3 layers were measured for samples A and B with the method disclosed above. The stress state was evaluated before post treatment (As- deposited) on samples A and B and after post-treatment (Shot-Peened and Wet blasted) on samples AS and BG, see table 9. Sample AS exhibited significant compressive stress in the K-AI2O3 layer after the post- treatment operations. Table 9. Measured residual stress state in K-AI2O3 layer for the samples before and after post treatment.

[0097] Performance testing - Cutting test

[0098] Coated cutting tools, sample AS and sample BG, of the ISO type XOMX120408TR were shot peened and wet blasted and evaluated in a cutting test. The reference sample BG was wet blasted using the blasting G described above and the inventive sample AS was wet blasted with the blasting S.

[0099] In this cutting test also a reference sample, sample C, was included in the evaluation. Sample C is a commercially available milling grade from Seco, MP2501, of the ISO type XOMX120408TR. Details of sample C are presented below:

[0100] The composition of the substrate of sample C is the same as for the samples A and B disclosed above. The roughness of the substrates at the rake face was measured and the average value of Ra was about 0.18 pm.

[0101] The coating of sample C comprises the following layers, listed starting from the substrate: 0.4 pm TiN, 4 pm TiCN, 0.6 pm AITiCNO bonding layer, 3.5 pm a-ALOa layer and 0.05 pm outermost Cr color layer. Total coating thickness is thus 8.55 pm.

[0102] Texture coefficients of the TiCN layer of the sample C are: TC(1 1 1)=0.05, TC(2 0 0)=0.04, TC(2 2 0)=1.18, TC(3 1 1)=2.02, TC(3 3 1)=1.30, TC(4 2 0)=0.48, TC(4 2 2)=2.70 and TC(5 1 1)=0.22 as measured by X-ray diffraction as disclosed above. Texture coefficients of the a-AhCh layer of the sample C are: TC(1 0 4)=0.02, TC(1 1 0)=0.01 , TC(1 1 3)=0.00, TC(0 2 4)=0.01 , TC(1 1 6)=0.03, TC(0 1 8)=0.28, TC(0 3 0)=0.01 , TC(0 2 10)=0.33, TC(0 0 12)=7.77, TC(0 1 14)=1.53 and TC(0 0 12)+TC(0 1 14)=9.3 as measured by X-ray diffraction using Cu Ka radiation and 0-20 scan, defined according to Harris formula (F1), where l(hkl) is the measured integrated area intensity of the (hkl) reflection, lo(hkl) is the standard intensity wherein Io (1 04)=9681 , Io (1 1 0)=4562, Io (1 1 3)=9742, l0(0 2 4)=5055, l0(1 1 6)=10000, l0(0 1 8)=761 , l0(0 3 0)=6168, Io (0 2 10)=852, Io (0 0 12)=204, Io (0 1 14)=598, n is the number of reflections used in the calculation, where the (hkl) reflections used are the ones listed.

[0103] Residual stress in a-AhCh layer of sample C, as measured in a corresponding way as disclosed above, using the peak (1 1 6) is: -0.92 GPa.

[0104] The coated cutting tools AS, BG and C were tested in a linear side radial milling operation in M2 stainless steel (SS2333) using the following cutting data;

[0105] Milling cutter: R220.69-0063-12-6AN

[0106] Cutting speed vc: 100 m / min

[0107] Cutting feed, fz: 0.2 mm / tooth

[0108] Depth of cut, ap: 3 mm

[0109] Radial depth of cut, ae: 12.6 mm

[0110] Length per pass: 300 mm

[0111] Length of overhang of workpiece: 200 mm

[0112] Lifetime criterion: Flank wear > 0.3 mm

[0113] The machining was performed using a coolant emulsion of 6% at pressure 40 Bar. Three cutting edges per cutting tool were evaluated. All edges in all variants were run in identical manner and stopped when flank wear reached 0.3 pm observed by using a light optical microscope with respect to visible wear of coating on the clearance side in the nose section of the inserts below the area of contact with the work piece material. The results are presented in Table 10.

[0114] Table 10. Cutting test results

[0115] As can be seen in Table 10. the inventive sample AS shows a prolonged lifetime compared to reference samples BG and C.

[0116] While the invention has been described in connection with various exemplary embodiments, it is to be understood that the invention is not to be limited to the disclosed exemplary embodiments; on the contrary, it is intended to cover various modifications and equivalent arrangements within the appended claims.

Claims

CLAIMS1. A cutting tool comprising a substrate (1) at least partially coated with a coating, said substrate (1) is of cemented carbide or cermet, said coating comprising one or more layers, wherein at least one layer is a K-AI2O3 layer (3) with a thickness of 3-6 pm, wherein the K-AI2O3 layer (3) is composed of grains and wherein a grain width is the width of the grain in a direction parallel to the substrate (1) surface, and wherein the average grain width db of the K-AI2O3 grains is measured along a line at a position corresponding to 80% of the thickness of the K-AI2O3 layer (3) and wherein the average grain width daof the K-AI2O3 grains is measured along a line at a distance of 1 pm from the innermost K-AI2O3 interface, characterized in that the ratio db / dais between 1 .45 and 2.00.

2. The cutting tool according to claim 1 , wherein the ratio db / dais between 1.48 and 1.80.

3. The cutting tool in accordance with any of the preceding claims, wherein the residual stress as measured with XRD in the K-AI2O3 layer is between -0.6 GPa and -2.0 GPa.

4. The cutting tool in accordance with any of the preceding claims, wherein the average grain width db of the K-AI2O3 grains as measured along a line at a position corresponding to 80% of the thickness of the K-AI2O3 layer (3) is between 0.6 pm and 0.8 pm.

5. The cutting tool in accordance with any of the preceding claims, wherein the thickness of the K-AI2O3 layer (3) is between 4 pm and 5 pm.

6. The cutting tool in accordance with any of the preceding claims, wherein the coating comprises a TiCN layer (2) between the substrate (1) and the K-AI2O3 layer (3).

7. The cutting tool in accordance with claim 6 wherein the thickness of the TiCN layer (2) is between 1.5 pm and 2.5 pm.

8. The cutting tool in accordance with any of the preceding claims, wherein the coating comprises an innermost TiN layer.

9. The cutting tool in accordance with claim 8, wherein the thickness of the innermost TiN layer is between 0.3 pm and 0.6 pm.

10. The cutting tool in accordance with any of claims 6-7, wherein the coating comprises a bonding layer between the TiCN layer (2) and the K-AI2O3 layer (3), preferably said bonding layer is one or more of TiCO, TiCNO, AITiCO or AITiCNO.

11. The cutting tool in accordance with claim 10, wherein the thickness of the bonding layer is between 1.5 pm and 2.5 pm.

12. The cutting tool in accordance with any of the preceding claims, wherein the surface roughness, Ra, of the substrate (1) at the rake face, as measured in an SEM cross section, is between 0.05 pm and 0.2 pm, preferably between 0.15 pm and 0.2 pm.

13. The cutting tool in accordance with any of the preceding claims, wherein said K -AI2O3 layer (3) exhibits a texture coefficient TC(hkl), as measured by X-ray diffraction using Cu Ka radiation and 0-20 scan, defined according to Harris formula:TC(hkl)=2^2](F1) v7lothkl) LnZ_|n=i / 0(hfcOj where l(hkl) is the measured intensity (integrated area) of the (hkl) reflection, lo(hkl) is the standard intensity wherein lo(1 1 1) = 105, lo(O 1 3) = 5026, lo(1 2 2) = 10000, lo(1 1 3) = 1116, l0(2 0 0) = 795, l0(2 0 1) = 1342, l0(0 0 4) = 291 , l0(0 4 0) = 387, l0(0 1 5) = 429 and lo(2 0 4) = 1312, n is the number of reflections used in the calculation, where the (hkl) reflections used are (1 1 1), (0 1 3), (1 2 2), (1 1 3), (2 0 0), (2 0 1), (0 0 4), (0 4 0), (0 1 5) and (2 0 4), wherein TC(0 0 4) + TC(0 1 5)6, preferably7, more preferably14. The cutting tool of any of the claims 6-13, wherein said TiCN layer (2) exhibits a texture coefficient TC(hkl), as measured by X-ray diffraction using Cu Ka radiation and 0-20 scan, defined according to Harris formula (F1) where l(hkl) is the measured intensity (integrated area) of the (hkl) reflection, lo(hkl) is the standard intensity wherein lo(1 1 1) = 7871 , l0(2 0 0) = 10000, l0(2 2 0) = 5369, l0(3 1 1) = 2550, l0(33 1) = 1128, l0(42 0) = 2366, lo(4 2 2) = 2479, and lo(5 1 1) = 1427, n is the number of reflections used in the calculation, and where the (hkl) reflections used are (1 1 1), (2 0 0), (2 2 0), (3 1 1), (3 3 1) (4 2 0), (4 2 2), (5 1 1), wherein TC(4 2 2)^=3, preferably 3 , more preferably ^5.

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