Coated cutting tool

Abstract

The present invention relates to a coated cutting tool comprising a coating and a cemented carbide substrate where the cemented carbide comprises WC and a Ni-based metal binder wherein the metal binder comprises Ni, Fe and Cr so that the weight ratio N i / (Ni+Fe) is between 0.68 and 0.8; and the Cr content in the cemented carbide is such that the weight ratio Cr / (Cr+Ni+Fe) is between 0.03 and 0.12, and wherein the coating has a thickness of between 2 and 25 μm.

Description

[0001] Coated cutting tool

[0002] The present invention relates to a coated cutting tool comprising a cemented carbide substrate wherein the substrate has a Ni-based metal binder comprising Ni, Fe and Cr.

[0003] Background

[0004] The market of cutting tools for chip forming metal cutting operations is dominated by CVD (Chemical Vapor Deposition) and PVD (Physical Vapor Deposition) coated cemented carbides wherein the cemented carbide usually is made of WC in a metallic binder of Co.

[0005] In recent years, efforts to replace Co has been done due its hazardous properties and the fact that Co is considered to be a Critical Raw Material. This have led to an increased activity to develop binders either with a reduced amount of cobalt or completely cobalt free. Despite this, metal binders with a reduced amount of Co or even without Co are still rare or non-existing in the products on the market. There are several reasons for this, one is that it is difficult to achieve substrate properties that can match those for cemented carbide with cobalt binders. Upscaling the production of these new cemented carbides are also challenging.

[0006] Other reasons are that, when replacing Co, it can lead to difficulties using well known coating technologies, post treatments etc. Especially during chemical vapor deposition, which is performed using reactive gases at high temperature, since interactions occur between the gas phase and the cemented carbide.

[0007] Among the alternative metal binders a mixture of Ni and Fe is a promising candidate, due to its mechanical properties. A relatively high Ni / Fe ratio is to be preferred when looking at the mechanical properties of the cemented carbide. However, such high Ni content can cause deterioration of e.g. a CVD coating (chemical vapor deposition) since Ni will diffuse into the coating in such amounts so that the coating is deteriorated. Lowering the Ni content in the metal binder can help maintaining the coating properties but will lower properties such as toughness and hardness of the substrate.

[0008] Cr is a known additive for cemented carbides and can be beneficial to control the grain growth of the WC grains as well as increased corrosion resistance. However, when Co binder is used, Cr additions to the substrate composition can also affect a CVD coating negatively.

[0009] It is an object of the present invention to provide a coated cutting tool for metal cutting having a cemented carbide substrate with a Ni-based binder having a performance equal to, or improved, compared to when Co is used as binder.

[0010] Detailed description of the present invention

[0011] The present invention relates to a coated cutting tool comprising a coating and a cemented carbide substrate where the cemented carbide comprises WC and a Ni-based metal binder. The metal binder comprises Ni, Fe and Cr so that the weight ratio Ni / (Ni+Fe) in the cemented carbide is between 0.68 and 0.8; and the Cr content in the cemented carbide is such that the weight ratio Cr / (Cr+N i+Fe) is between 0.03 and 0.12 and wherein the coating has a thickness of between 2 and 25 pm.

[0012] By cemented carbide is herein meant that at least 50 wt% of the hard phase, is WC. By hard phase is herein meant all phases except the metal binder phase.

[0013] The Ni-based metal binder comprises mainly Ni, Fe and Cr and by that is herein meant that at least 90 wt% of the binder consists of Ni, Fe and Cr. By Ni-based binder is herein meant that the binder contains at least 60 wt% Ni.

[0014] The metal binder is present in an amount of 2 to 20 wt% of the sintered cemented carbide, preferably between 5 to 12 wt% of the sintered cemented carbide. Although, the main elements in the binder are Ni, Fe and Cr but as is well known in the art of cemented carbide manufacturing, other elements e.g. W from the WC, will be present in the metal binder since they are inevitably dissolved in the metal binder during sintering. If other common additives, such as cubic carbides etc. are added, elements such as Ti, Nb, Ta, V etc. can also be found on the metal binder.

[0015] The cemented carbide according to the present invention comprises Ni and Fe is such amounts that the weight ratio N i / (N i+Fe) is between 0.68 and 0.8, preferably between 0.70 and 0.74, more preferably between 0.71 and 0.74. If the Ni content is too high, there is a risk that it will degrade any coating deposited onto the substrate with regard to microstructure features (grain size, grain morphology, crystal orientation) and hence physical and mechanical properties are completely lost. If the Ni content is too low, the mechanical properties of the substrate such as hardness and toughness, will not suffice and the overall performance of the cutting tool will be inferior.

[0016] Cr is a common addition in cemented carbides but the amount of Cr that can be added is usually limited by the solubility of Cr in the metal binder. If the amount of Cr exceeds the solubility in the binder, a brittle carbide, Cr?C3, is precipitated in the microstructure and the mechanical properties of the cemented carbide will deteriorate.

[0017] Cr is be added up to the limit where Cr?Cs is formed, however, for practical reasons it is not suitable to be too close to that limit. Suitably the weight fraction Cr / (Cr+Ni+Fe) is between 0.03 and 0.12, preferably between 0.035 and 0.095.

[0018] If the amount of Cr is too low, the hardness and other mechanical properties will not suffice.

[0019] The cemented carbide according to the present invention is essentially free from Co. By that is herein meant that no Co powder is added. Co can however be present in smaller amounts due to contamination if the same manufacturing equipment is used as for Co containing cemented carbides and / or if the milling ball media is made of Co containing cemented carbide. By essentially free from Co is herein meant that the cemented carbide comprises less than 1 wt% Co, preferably less than 0.5wt %. The Co content is measured according to standard practice when doing chemical analysis on cemented carbides.

[0020] The cemented carbide according to the present invention can have any average WC grain size known for cutting tools. Preferably the average WC grain size is between 0.1 and 12 pm, more preferably between 0.4 and 9 pm as measured by the linear intercept method. The specific average WC grain size is however chosen depending on the specific cutting application.

[0021] The carbon content in the sintered cemented carbide should be selected so that neither eta phase nor free graphite is present in the cemented carbide microstructure after sintering. If the carbon content is too low, eta phase can form. If the carbon content is too high, graphite can form in the material. Methods for adjusting the carbon balance to achieve this is well known to a person skilled in the art of making cemented carbides. In one embodiment of the present invention, the cemented carbide comprises gamma phase, sometimes also called cubic phase. Gamma phase is formed during sintering if one or more gamma phase forming elements, e.g. Ti, Ta, Nb, Zr, V, Mo, Cr, Hf are present and can be written with the general formula (W,X)(C,N) or (W,X)(C) where X can be one or more gamma phase forming elements The amount of gamma phase is suitably from 1 to 20 vol%, preferably from 2 to 7 vol%. This can be measured in different ways preferably by making an image analysis, e.g. by using Image J, on either a Light Optical Microscope (LOM) image or a Scanning Electron Microscope (SEM) micrograph of a cross section of the substrate to calculate the average fraction of gamma phase. When the cemented carbide is provided with a gradient in the surface zone, the amount of gamma phase as given herein is measured in the bulk.

[0022] In one embodiment of the present invention, when the cemented carbide comprises gamma phase, the cemented carbide can comprise a binder phase enriched surface zone free from gamma phase.

[0023] The thickness of the surface zone is suitably from 5 to 35 pm. The thickness is measured between the surface of the substrate and the border between the gamma phase containing bulk and the surface zone which is depleted from gamma phase. In a SEM or LOM image this border is easy to identify since it is quite distinct. The measurements of the thickness of the surface zone should preferably be done on a flat surface, preferably on the flank face, not too close to the cutting edge. By that is herein meant that the measurements should be performed at least 0.3 mm from the cutting edge.

[0024] By binder enriched is herein meant that the binder phase content in the surface zone is at least 1.3 times the binder phase content in the bulk. The binder phase content in the surface zone is suitably measured at a depth of half the total thickness / depth of the surface zone. By bulk is herein defined as the area that is not the surface zone. All measurements performed on the bulk should be performed at an area not too close to the surface zone. By that is herein meant that any measurements done to the microstructure of the bulk should be performed at a depth of at least 200 pm from the surface.

[0025] By depleted of gamma phase is herein meant that the surface zone contains no, or very few gamma phase particles, i.e. less than 0.5 area%. In one embodiment of the present invention the coating is a CVD coating.

[0026] In one embodiment of the present invention the coating comprises one or more layers selected from TiN, TiCN, AITiN, ZrCN, TiB2, AI2O3, or multilayers comprising 01-AI2O3 and / or K-AI2O3.

[0027] In one embodiment of the present invention the coating comprises an inner TiN layer, preferably the thickness of the TiN layer is 0.3-1 pm.

[0028] In one embodiment of the present invention the coating comprises a TiCN layer, preferably the thickness of the TiCN layer is 6-12 pm.

[0029] In one embodiment of the present invention the TiCN layer exhibits a texture coefficient TC(hkl), as measured by X-ray diffraction using CuKa radiation and 0-20 scan, defined according to Harris formula (1), where l(hkl) is the measured intensity (integrated area) of the (hkl) reflection, lo(hkl) is the standard intensity according to ICDD's PDF-card No 42-1489, n is the number of reflections, reflections used in the calculation are (1 1 1), (2 00), (2 2 0), (3 1 1), (3 3 1), (4 2 0), (4 2 2) and (5 1 1), wherein TC(4 2 2) is > 4.

[0030] In one embodiment of the present invention the coating comprises a a- AI2O3 layer, preferably the thickness of the a- AI2O3 layer is 4-8 pm.

[0031] In one embodiment of the present invention the 01-AI2O3 layer exhibits a texture coefficient TC(hkl), as measured by X-ray diffraction using CuKa radiation and 0-20 scan, defined according to Harris formula (1) where l(hkl) is the measured intensity (integrated area) of the (hkl) reflection, lo(hkl) is the standard intensity according to ICDD's PDF-card No. 00-010-0173, n is the number of reflections used in the calculation, and where the (hkl) reflections used are (1 04), (1 1 0), (1 1 3), (024), (1 1 6), (2 1 4), (3 00) and (00 12) characterized in that TC(0 0 12) > 6, preferably > 7. In one embodiment of the present invention the coated cutting tool comprises a substrate comprising WC and Ni-based metal binder where the weight ratio Ni / (Ni+Fe) is between 0.70 and 0.72; and the Cr content in the cemented carbide is such that the weight ratio Cr / (Cr+Ni+Fe) is between 0.075 and 0.095.

[0032] In one embodiment of the present invention the coated cutting tool comprises a substrate comprising WC and Ni-based metal binder where the weight ratio N i / (N i+Fe) is between 0.70 and 0.72; and the Cr content in the cemented carbide is such that the weight ratio Cr / (Cr+Ni+Fe) is between 0.035 and 0.05.

[0033] In one embodiment of the present invention the coated cutting tool comprises a substrate comprising WC and Ni-based metal binder where the weight ratio N i / (N i+Fe) is between 0.73 and 0.75; and the Cr content in the cemented carbide is such that the weight ratio Cr / (Cr+Ni+Fe) is between 0.075 and 0.095.

[0034] In one embodiment of the present invention the coated cutting tool comprises a substrate comprising WC and Ni-based metal binder where the weight ratio N i / (N i+Fe) is between 0.73 and 0.75; and the Cr content in the cemented carbide is such that the weight ratio Cr / (Cr+Ni+Fe) is between 0.035 and 0.05.

[0035] In one embodiment of the present invention the coated cutting tool comprises a substrate comprising WC and Ni-based metal binder where the weight ratio N i / (N i+Fe) is between 0.73 and 0.75, and the Cr content in the cemented carbide is such that the weight ratio Cr / (Cr+Ni+Fe) is between 0.045 and 0.065.

[0036] In one embodiment of the present invention the coated cutting tool comprises a substrate comprising WC and Ni-based metal binder where the weight ratio N i / (N i+Fe) is between 0.73 and 0.75; and the Cr content in the cemented carbide is such that the weight ratio Cr / (Cr+Ni+Fe) is between 0.065 and 0.075.

[0037] By cutting tool is herein meant an insert, end mill or drill.

[0038] In one embodiment of the present invention, the cutting tool is an insert, preferably a turning insert.

[0039] In one embodiment of the present invention, the cemented carbide substrate is used for turning in steel. The present invention also relates to a method of making a cutting tool according to the above.

[0040] The method comprises the following steps:

[0041] - providing a WC powder;

[0042] - providing powder(s) comprising the elements Fe, Ni and Cr

[0043] - mixing the powders with a milling liquid to form a slurry, drying said slurry into granules,

[0044] - pressing and sintering said granules into a sintered cemented carbide substrate; depositing a coating onto said substrate using chemical vapor deposition at a deposition temperature of at least 800°C.

[0045] The raw materials comprising the elements Fe, Ni and Cr can be added as pure metals, alloys of two or more metals or as carbides, nitrides or carbonitrides thereof. The raw materials should be added in such amounts so that the binder phase, after sintering will have the composition as has been described above.

[0046] In one embodiment of the present invention, the powders are 3C2, Fe and Ni.

[0047] The WC powder used with an average grain size of preferably 0.2-10 pm, more preferably 0.2-5 pm (FSSS).

[0048] In one embodiment of the present invention, when a gamma phase is desired, powders comprising one or more of carbides, nitrides or carbonitrides of one or more of Ti, Ta, Nb, Zr, V, Mo, Cr and Hf are added to form the gamma phase during sintering. In the case where a binder phase enriched surface zone free from gamma phase is desired, at least one of the gamma phase forming powders is a nitride or carbonitride.

[0049] Any liquid commonly used as a milling liquid in conventional cemented carbide manufacturing can be used. The milling liquid is preferably water, alcohol or an organic solvent, more preferably water or a water and alcohol mixture and most preferably a water and ethanol mixture. The properties of the slurry are dependent on the amount of milling liquid added. Since the drying of the slurry requires energy, the amount of liquid should be minimized to keep costs down. However, enough liquid needs to be added to achieve a pumpable slurry and avoid clogging of the system. Also, other compounds commonly known in the art can be added to the slurry e.g. dispersion agents, pH-adjusters etc. An organic binder is also optionally added to the slurry in order to facilitate the granulation during the following spray drying operation but also to function as a pressing agent for any following pressing and sintering operations. The organic binder can be any binder commonly used in the art. The organic binder can e.g. be paraffin, polyethylene glycol (PEG), long chain fatty acids etc. The amount of organic binder is suitably between 15 and 25 vol% based on the total dry powder volume, the amount of organic binder is not included in the total dry powder volume.

[0050] The slurry comprising powders forming hard constituents and powders forming the binder phase, and possibly an organic binder is suitably mixed by a milling operation, either in a ball mill or attritor mill. The milling is suitably made by first forming a slurry comprising metal binder powder, the first and second powder fraction, and possibly an organic binder. Then the slurry is suitably milled in a ball mill or attritor mill to obtain a homogenous slurry blend.

[0051] The slurry containing the powdered materials mixed with the organic liquid and possibly the organic binder is atomized through an appropriate nozzle in the drying tower where the small drops are instantaneously dried by a stream of hot gas, for instance in a stream of nitrogen, to form agglomerated granules. For small scale experiments, also other drying methods can be used, e.g. pan drying.

[0052] Green bodies are subsequently formed from the dried powders / granules by a pressing operation such as uniaxial pressing, multiaxial pressing etc.

[0053] The green bodies formed from the powders / granules made according to the present invention, is subsequently sintered according to any conventional sintering methods e.g. vacuum sintering, Sinter HIP, spark plasma sintering, gas pressure sintering (GPS) etc.

[0054] In one embodiment of the present invention, the sintering temperature is between 1350 and 1550°C.

[0055] In one embodiment of the present invention, the sintering process comprises a sinter

[0056] HIP step performed at a temperature of between 1350 and 1550°C, and a pressure of at least 40 Bar, preferably between 40 and 80 Bar. Drawings

[0057] Figure 1 shows a SEM image of a top surface of the AI2O3 layer of Invention 1.

[0058] Figure 2 shows a SEM image of a cross section of the substrate / coating interface of Invention 1 showing the innermost TiN layer and the TiCN layer.

[0059] Figure 3 shows a SEM image of a top surface of the AI2O3 layer of Invention 3.

[0060] Figure 4 shows a SEM image of a cross section of the substrate / coating interface of Invention 3 showing the innermost TiN layer and the TiCN layer.

[0061] Figure 5 shows a SEM image of a top surface of the AI2O3 layer of Invention 4.

[0062] Figure 6 shows a SEM image of a cross section of the substrate / coating interface of Invention 4 showing the innermost TiN layer and the TiCN layer.

[0063] Figure 7 shows a SEM image of a top surface of the AI2O3 layer of Invention 5.

[0064] Figure 8 shows a SEM image of a cross section of the substrate / coating interface of Invention 5 showing the innermost TiN layer and the TiCN layer.

[0065] Figure 9 shows a SEM image of a top surface of the AI2O3 layer of Invention 6.

[0066] Figure 10 shows a SEM image of a cross section of the substrate / coating interface of Invention 6 showing the innermost TiN layer and the TiCN layer.

[0067] Figure 11 shows a SEM image of a top surface of the AI2O3 layer of Comparative 1.

[0068] Figure 12 shows a SEM image of a cross section of the substrate / coating interface of Comparative 1 showing the innermost TiN layer and the TiCN layer.

[0069] Figure 13 shows a SEM image of a top surface of the AI2O3 layer of Comparative 2.

[0070] Figure 14 shows a SEM image of a top surface of the AI2O3 layer of Comparative 3.

[0071] Example 1

[0072] Squared cemented carbide substrates were manufactured from the powder compositions given in Table 1. Table 1

[0073] The WC powder had an average particle size (FSSS) of 0.8 pm. Adjustment of the carbon balance by adding carbon was done to avoid eta and graphite formation. The raw material powders were milled in a ball mill for 8 h together with an organic binder (2 wt% PEG based on total powder weight) and a milling liquid (water / ethanol) to form a slurry which was dried and milled in agate mortar to obtain a powder blend. The powder was pressed into green bodies. The green bodies were sintered in a HIP (hot isostatic pressure) furnace where maximum sintering temperature was 1450°C and sintering time was 1 h at 40 mbar vacuum sintering followed by 15 min 50 bar high-pressure step to reduce porosity of the samples.

[0074] After sintering, one side of the cemented carbide substrate was polished before the coating process.

[0075] For comparison, a commercial substrate having Co as a binder was also coated with the CVD coating. This sample is herein denoted Comparative 3.

[0076] The sintered substrates were then coated with a CVD coating deposited in a radial lonbond Bernex TM type CVD equipment 530 size 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. CVD coatings were deposited on the above presented cemented carbide compositions and a summary of the layers is given in Table 2.

[0077] Table 2. The layers of the deposited coating

[0078] Before starting the CVD deposition, the CVD chamber was heated up to reach 885 °C. A pre-heating step was performed at 200mbar and in 100 vol% N2 from room temperature up to 600 °C, and from 600 °C up to 885 °C in 100 vol% H2.

[0079] The substrates were first coated with an about 0.4 pm thick TiN-layer at 885 °C. Thereafter an approximately 8 pm TiCN layer was deposited by employing the well- known MTCVD technique using TiCI4, CH3CN, N2, HCI and H2 at 885 °C. The volume ratio of TiC / CHsCN in an initial part of the MTCVD deposition of the TiCN layer was 6.6, followed by a period using a ratio of TiC / CHsCN of 3.7. The details of the TiN and the TiCN deposition are shown in Table 3.

[0080] Table 3. MTCVD of TiN and TiCN

[0081] After the deposition of the TiCN outer layer the temperature was increased from 885°C to 1000°C in an atmosphere of 75 vol% H2 and 25 vol% N2. An about 1 thick bonding layer was deposited at 1000°C on top of the MTCVD TiCN layer by a process consisting of four separate reaction steps. First a HTCVD TiCN step using TiC , CH4, N2, HCI and H2 at 400 mbar, then a second step (TiCNO-1) using TiCk, CH3CN, CO, N2 and H2 at 70 mbar, then a third step (TiCNO-2) using TiCk, CH3CN, CO, N2 and H2 at 70 mbar and finally a fourth step (TiN) using TiCk, N2 and H2 at 70 mbar. During the third deposition step some of the gases were continuously changed as indicated by a first start level and a second stop level presented in Table 4. Prior to the start of the subsequent AI2O3 nucleation, the bonding layer was oxidized for 4 minutes in a mixture of CO2, CO, N2 and H2.

[0082] The details of the bonding layer deposition are shown in Table 4.

[0083] Table 4. Bonding layer deposition

[0084] The 01-AI2O3 layer was deposited at 1000°C and 55 mbar in two steps. The first step using 1.2 vol-% AIC , 4.7 vol-% CO2, 1.8 vol-% HCI and balance H2 giving about 0.1 pm a- AI2O3 and a second step using 1.16 % AICk, 4.65 % CO2, 2.91 % HCI, 0.58 % H2S and balance H2 giving a total 01-AI2O3 layer thickness of about 5 pm. In order to investigate the texture of the layer(s) X-ray diffraction was conducted on the polished and sintered side of the coated substrates using a Xpert-Pro, Malvern Panalytical diffractometer system equipped with a X'Celerator detector type. The coated substrates were mounted in sample holders to ensure that the surface of the coated substrates was parallel to the reference surface of the sample holder and also that the surface of the coated substrate was at appropriate height. Cu-Ka radiation source (1.54A) was used for the measurements, with a voltage of 45 kV and a current of 40 mA. A 0.04 radian sol ler slit was used for the incident beam path. For the diffracted beam a 1 / 16 degree divergent was used. The Beta-filter Nickel had a thickness of 0.020 mm. The diffracted intensity from the coated cutting tool was measured in the range 15° to 140° 20, i.e. over an incident angle 0 range from 10 to 70°.

[0085] The data analysis, including background subtraction, Cu-Ka2 stripping and profile fitting of the data, was done using PANalytical's X'Pert HighScore Plus software. A general description of the fitting is made in the following. The output (integrated peak areas for the profile fitted curve) from this program was then used to calculate the texture coefficients of the layer by comparing the ratio of the measured intensity data to the standard intensity data according to a PDF-card of 01-AI2O3, using the Harris formula (1) as disclosed below. Since the layer is finitely thick the relative intensities of a pair of peaks at different 20 angles are different than they are for bulk samples, due to the differences in path length through the layer. 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, when calculating the TC values.

[0086] Since possible further layers above the 01-AI2O3 layer will affect the X-ray intensities entering the 01-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. 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.

[0087] In order to investigate the texture of the 01-AI2O3 layer X-ray diffraction was conducted using CuKaradiation and texture coefficients TC (h k I) for different growth directions of the columnar grains of the 01-AI2O3 layer were calculated according to Harris formula (1), where I ( h k I) = measured (integrated area) intensity of the (h k I) reflection, I o(h k l)=standard intensity according to ICDD's PDF-card no 00-010-0173, n=number of reflections to be used in the calculation. In this case the (h k I) reflections used are: (104), (1 10), (1 1 3), (0 24), (1 1 6), (2 14), (3 00) and (00 12).

[0088] The texture coefficients TC (hkl) for different growth directions of the columnar grains of the TiCN layer were calculated according to Harris formula (1) as disclosed earlier, where l(hkl) is the measured (integrated area) intensity of the (hkl) reflection, IO(hkl) is the standard intensity according to ICDD's PDF-card no 42-1489, n is the number of reflections to be used in the calculation. In this case the (hkl) reflections used are (1 1 1), (2 00), (2 2 0), (3 1 1), (3 3 1), (42 0) and (42 2).

[0089] 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. An overlap of peaks from the 01-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 invention.

[0090] XRD was used to analyse the TC values of the 01-AI2O3 and the TiCN in accordance with the method as disclosed above. The results from the XRD are presented in Table 5.

[0091] Table 5. XRD results

[0092] The coating quality deposited in the CVD process above described was determined by analyzing both the outer surface and morphology of AI2O3 and the interface between substrate and the first TiN layer. Unevenness of AI2O3 surface can be result from growth of coarse grains and correlates with the formation of intermetallic phases such as N isTi formed at the interface between the substrate and the coating.

[0093] For this investigation, a Carl Zeiss AG-Supra 40SEM (Scanning Electron Microscope) type was used at 3500X magnification in order to detect surface roughness on outer surface AI2O3. The results of the analyses are shown in Table 6. When the unevenness of the AI2O3 was difficult to determine the interface between the substrate and coating was analyzed to collect the correct information regarding coating quality. Cross section images were mainly focused at the interface between the substrate and the first TiN layer to determine if diffusion of binder elements had disturbed the growth of the coating. For this investigation, the SEM was used at 1200X magnification (see figures 2, 4, 6, 8 and 10). Table 6. Coating evaluation

[0094] As can be seen in Table 5 and 6 the samples according to the invention, i.e. Invention 1-6 shows a CVD coating with equal properties, both texture coefficients and visual appearance (see e.g. figures 1-10) as the CVD coating deposited onto a substrate having Co as binder, see figure 14. The comparative samples, Comparative 1 and 2, have CVD coatings that is clearly affected by the substrate composition, specifically the visual appearance is deteriorated which is shown in Figures 11 and 13 (top view of the AI2O3 of Comparative 1 and 2) where the unevenness is clearly visible. Figure 12 shows a cross section of the coating of Comparative 2, where it can be seen that the AI2O3 layer is less columnar compared to the Invention (e.g. Figures 2, 4, 6, 8 and 10). In Figure 12 it can also be seen that the coating contains some pores.

[0095] Example 2

[0096] Cutting tool inserts according to the invention were manufactured from the powder compositions given in Table 7 where the balance was a WC powder with an average particle size (FSSS) of 4.2 pm. Adjustment of the carbon balance by adding carbon was done according to standard practice to avoid eta and graphite formation. The aimed carbon content was to be close to graphite formation, i.e. with a small excess of carbon. In the (Ta,Nb)C raw material the weight ratio Ta / Nb was 3.4 and for the (Ti,W)C raw material the weight ratio Ti / W was 0.84. The raw material powders were milled in a ball mill for 32 h together with an organic binder (2 wt% PEG based on total powder weight) and a milling liquid (water / ethanol) to form a slurry which was spray dried to obtain a powder blend. The powder was pressed into green bodies. The green bodies were sintered at a temperature of 1480°C for 1 h at 40 mbar vacuum sintering.

[0097] Table ?

[0098] After sintering the cemented carbide inserts contained a gamma phase in the bulk and had a surface zone free from gamma phase with a thickness of 14 and 18 pm for Invention 7 and 8 respectively.

[0099] The substrates according to the invention were then coated with a CVD coating according to the process as described in Example 1.

[0100] Two different substrates having Co as binder were also coated in the same process. The compositions of the comparative substrates are given in Table 8 where the balance was WC. The aim is to achieve the same substrate composition as for Invention 7 and 8 but where the only difference being the binder composition.

[0101] Table 8 The cemented carbide inserts contained gamma phase in the bulk in about the same amount as for the inventive samples and had a surface zone free from gamma phase with a thickness of about 22 pm for both Comparative 4 and 5.

[0102] The coating parameters for all the samples are shown in Table 9.

[0103] Table 9

[0104] Performance testing

[0105] Test 1

[0106] The coated inserts from Example 2 were tested in a turning operation in cast steel (Impax supreme) at the following cutting conditions: f = 0.7 mm / rev ap= 2 mm

[0107] T = 30 s

[0108] Vc= 120 m / min The results from the test can be seen in Table 10.

[0109] Table 10 As can be seen in Table 10, the inserts having a composition according to the present invention have considerably less plastic deformation compared to the comparative inserts having a Co binder.

[0110] Test 2

[0111] The coated inserts from Example 2 were tested in a face turning operation in cast steel (Impax supreme) at the following cutting conditions:

[0112] Vc=170 m / min f = 0.35 mm / rev ap= 2 mm

[0113] Tool life criterion was flank wear VBB=0.3 mm.

[0114] Two inserts of each type were tested and the result shown in Table 11 is an average of those two tests.

[0115] Table 11

[0116] As can be seen in Table 11, the inserts having a composition according to the present invention have a considerably longer tool life compared to the comparative inserts having a Co binder.

[0117] Test 3

[0118] The coated inserts from Example 2 were tested in a turning operation in a medium carbon steel C45, at the following cutting conditions: Vc= 250 m / min f = 0.3 mm / rev ap= 2 mm

[0119] The inserts were tested both with and without cooling. Tool life criterion was either flank wear VBB=0.2 mm or a crater area more than 0.2 mm2.

[0120] The results from the tests are shown in Table 12.

[0121] Table 12

[0122] As can be seen in Table 12, the inserts having a composition according to the present invention have a considerably longer tool life compared to the comparative inserts having a Co binder.

Claims

Claims1. A coated cutting tool comprising a coating and a cemented carbide substrate where the cemented carbide comprises WC and 2 to 20 wt% of a Ni-based metal binder, wherein the metal binder comprises Ni, Fe and Cr so that the weight ratio Ni / (N i+Fe) in the cemented carbide is between 0.68 and 0.8; and the Cr content in the cemented carbide is such that the weight ratio Cr / (Cr+Ni+Fe) is between 0.03 and 0.12; wherein the coating has a thickness of between 2 and 25 pm.

2. A coated cutting tool according to claim 1 wherein the weight ratio Ni / (N i+Fe) is between 0.7 and 0.74; and the Cr content in the cemented carbide is such that the weight ratio Cr / (Cr+Ni+Fe) is between 0.035 and 0.095.

3. A coated cutting tool according to any of the preceding claims wherein the cemented carbide is essentially free from Co.

4. A coated cutting tool according to any of the preceding claims wherein the metal binder consists of more than 90 wt% of Ni, Fe and Cr.

5. A coated cutting tool according to any of the preceding claims wherein the cemented carbide comprises between 1 and 20 vol% gamma phase.

6. A coated cutting tool according to claim 6 wherein the cemented carbide comprises a binder phase enriched surface zone free from gamma phase where the surface zone has a thickness of between 5 and 35 pm.

7. A coated cutting tool according to any of the preceding claims wherein the coating is a CVD coating.

8. A coated cutting tool according to any of the preceding claims, wherein the coating comprises one or more layers selected from TiN, TiCN, AITiN, ZrCN, TiB2, AI2O3, or multilayers comprising 01-AI2O3 and / or K-AI2O3.

9. A coated cutting tool according to any of the preceding claims, wherein the coating comprises an inner TiN layer, preferably the thickness of the TiN layer is 0.3-1 pm.

10. A coated cutting tool according to any of the preceding claims, wherein the coating comprises a TiCN layer, preferably the thickness of the TiCN layer is 6-12 pm.

11. The coated cutting tool of claim 10, wherein the TiCN layer exhibits a texture coefficient TC(hkl), as measured by X-ray diffraction using CuKa radiation and 0-20 scan, definedaccording to Harris formula (1)where l(hkl) is the measured intensity (integrated area) of the (hkl) reflection, lo(hkl) is the standard intensity according to ICDD's PDF-card No 42-1489, n is the number of reflections, reflections used in the calculation are (1 1 1), (2 0 0), (2 2 0), (3 1 1), (3 3 1), (4 2 0), (4 2 2) and (5 1 1), wherein TC(4 2 2) is > 4.

12. A coated cutting tool according to any of the preceding claims, wherein the coating comprises a a- AI2O3 layer, preferably the thickness of the a- AI2O3 layer is 4-8 pm.

13. The coated cutting tool of claim 12, wherein the 01-AI2O3 layer exhibits a texture coefficient TC(hkl), as measured by X-ray diffraction using CuKa radiation and 0-20 scan, defined according to Harris formula (1) where l(hkl) is the measured intensity (integrated area) of the (hkl) reflection, lo(hkl) is the standard intensity according to ICDD's PDF-card No. 00-010-0173, n is the number of reflections used in the calculation, and where the (hkl) reflections used are (1 04), (1 1 0), (1 1 3), (024), (1 1 6), (2 1 4), (3 0 0) and (0 0 12) characterized in that TC(0 0 12) > 6, preferably > 7.

14. A method of making a coated cutting tool according to any of claims 1-13 comprising the steps of:- providing a WC powder;- providing powder(s) comprising the elements Fe, Ni and Cr- mixing the powders with a milling liquid to form a slurry, drying said slurry into granules,- pressing and sintering said granules into a sintered cemented carbide substrate,- depositing a coating onto said substrate using chemical vapor deposition at a deposition temperature of at least 800°C.

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