Cutting tool

Abstract

The present invention relates to a cutting tool comprising a substrate of a cemented carbide comprising WC grains, eta phase grains, Cr and Co, wherein Co is present in an amount ranging from 6 to 16 wt%, wherein the weight ratio of Cr to Co ranges from 0.01 to 0.05, wherein the eta phase 5 content ranges from 1 to 15 vol%, wherein the sub-stoichiometric carbon content ranges from -0.30 to -0.60 wt%, wherein the coercivity Hc in the cemented carbide ranges from 9.0 to 11.5 kA / m, wherein all wt% and vol% values are based on the total weight or volume of the cemented carbide; and a coating adhered to the substrate.

Description

[0001] Cutting tool

[0002] The present invention relates to a cutting tool comprising a coated cemented carbide-based substrate.

[0003] Background of the invention

[0004] Cemented carbide-based substrates are well-known for use in coated cutting tools for metal machining applications. As an example, it is known to incorporate ruthenium (Ru) in the Co binder phase of the cemented carbide. This results in a cemented carbide substrate with an improved resistance to thermal cracking and reduction of propagation of cracks into the substrate during metal machining processes. The high temperature wear resistance properties of such a cemented carbide composition may thus be improved. Ru is a rare and expensive raw material which is complicated to recycle. It is therefore an objective to provide an alternative to Ru-alloyed cemented carbides. Also, it is an objective to extend the service life and thus further improve the wear resistance of cutting tools, in particular with respect to flank wear resistance. The present invention intends to provide such a cutting tool.

[0005] The invention

[0006] The present invention relates to a cutting tool comprising a substrate of a cemented carbide comprising WC grains, eta phase grains, Cr and Co, wherein Co is present in an amount ranging from 6 to 16 wt%, wherein the weight ratio of Cr to Co ranges from 0.01 to 0.05, wherein the eta phase content ranges from 1 to 15 vol%, and wherein the sub-stoichiometric carbon content ranges from -0.30 to -0.60 wt%, wherein the coercivity Hcin the cemented carbide ranges from 9.0 to 11 .5 kA / m, wherein all wt% and vol% values are based on the total weight or volume of the cemented carbide; and a coating adhered to the substrate.

[0007] According to one embodiment, the weight ratio of Cr to Co ranges from 0.02 to 0.04 or from 0.025 to 0.035 or from 0.026 to 0.035 or from 0.027 to 0.035 or from 0.028 to 0.035 or from 0.029 to 0.032.

[0008] According to one embodiment, the eta phase content ranges from 1 .5 to 14 vol% or 2 to 14 vol% or 2.5 to 13 vol% or 2.6 to 13 vol%

[0009] According to one embodiment, Co is present in an amount ranging from 8 to 14 wt% or preferably 9 to 11.5 wt%. According to one embodiment, the WC grain size >1 .00 m, preferably >1.01 pm or >1 .02 pm or >1 .03 pm or >1 .04 pm or >1 .05 pm.

[0010] According to one embodiment, the WC grain size < 1 .20 pm.

[0011] According to one embodiment, the sub-stoichiometric carbon content ranges from -0.31 to - 0.55 wt% or from -0.31 to -0.50 wt%, preferably from -0.32 to -0.50 wt%.

[0012] According to one embodiment, the substrate has a content of titanium up to 0.003 wt%.

[0013] According to one embodiment, the coating comprises a nano-multilayer of alternating layers of a first nanolayer being Tii.xAlxN, 0.5<x<0.65, and a second nanolayer being Tii.ySiyN, 0.06<y<0.21.

[0014] According to one embodiment, the coating comprises a layer of a-AI2O3.

[0015] According to one embodiment, the coating comprises a layer of (Tii-XAIX)N, wherein x ranges from 0.50 to 0.75.

[0016] According to one embodiment, the coating comprises a layer of K-AI2O3.

[0017] According to one embodiment, the coercivity Hcin the cemented carbide ranges from preferably from 9.0 to 11 kA / m or 9.5 to 10.5 kA / m or 9.5 to 10.4 kA / m or 9.5 to 10.3 kA / m or 9.5 to 10.2 kA / m or 9.5 to 10.1 kA / m or 9.5 to 10.0 kA / m. According to one embodiment, the coercivity Hcin the cemented carbide ranges from 9.5 to 11.5 or 9.5 to 11.

[0018] According to one embodiment, the substrate is coated with at least one coating layer, which preferably has been deposited by means of CVD or PVD processes.

[0019] A too high Co content generally decreases the hardness of the substrate. This may render the cemented carbide less effective in applications requiring high wear resistance. A too high Co content may also reduce the abrasive wear resistance of the cemented carbide making it less durable in demanding environments.

[0020] A too low Co content can make the material more brittle and prone to cracking under stress which may result in poor densification, higher porosity and lower mechanical strength.

[0021] Cr acts as a grain growth inhibitor. Without sufficient Cr, tungsten carbide (WC) grains can grow excessively during sintering leading to a coarser microstructure. This can reduce the hardness and wear resistance of the substrate. An insufficient amount of Cr can thus negatively impact the overall mechanical properties, such as toughness and strength. The material may become less durable and more prone to failure under stress. If the Cr content is too high, the Cr will have a strong affinity for carbon resulting in the formation of brittle Cr rich carbides. This can adversely affect the hardness and toughness of the cemented carbides. High concentrations of Cr can also decrease the fracture toughness making the material prone to cracking under stress.

[0022] According to one embodiment, the average grain size of the eta phase grains ranges from 0.1 to 10 pm, preferably from 2 to 4.5 pm.

[0023] By “eta phase” is herein meant carbides selected from Me^C and Me6C where Me is one or more metals selected from W and the binder phase metal or metals.

[0024] The sub-stoichiometric carbon content is a measure of the carbon content in relation to the stoichiometric value of carbon. The stoichiometric carbon content is calculated by assuming that the WC is completely stoichiometric, i.e. that the atomic ratio W:C is 1 :1. Since other carbide-forming elements are present, also their carbides are assumed to be stoichiometric in the corresponding calculations.

[0025] This means that the term sub-stoichiometric carbon content, SCC, as used herein is the total carbon content (in wt%) determined from chemical analysis, preferably by means of a LECO CS844 instrument, minus the calculated stoichiometric carbon content (in wt%) based on the WC and possible further carbides present in the cemented carbide.

[0026] As an example, if the stoichiometric carbon content for a particular cemented carbide is 5.60 wt%, and the same cemented carbide would be made, but with a carbon content of 5.30 wt%, the sub-stoichiometric carbon would be -0.30 wt%.

[0027] To achieve the correct carbon content in the final sintered cemented carbide manufacturing, W and / or W2C is added in amounts resulting in a sub-stoichiometric carbon content, SCC, in the sintered cemented carbide as further specified herein.

[0028] The cemented carbide has a low carbon content resulting in the formation of an eta phase. This will result in a cemented carbide having both a W content in the metal binder and in the eta phase grains. The eta phase formed is, however, not present as large grains or agglomerates but as fine and well-distributed grains. The desired form of the eta phase is provided by controlling the carbon balance carefully during the manufacturing process.

[0029] If the carbon content in the sintered cemented carbide is too low, i.e. lower than -0.60 wt% sub-stoichiometric carbon content, the amount of eta phase becomes too large and the particle size increases considerably whereby the cemented carbide is rendered brittle. On the other hand, if the carbon content is > -0.30 wt% sub-stoichiometric carbon content but still in the eta phase-forming region, the formed eta phase may become unevenly distributed in the form of large agglomerates resulting in a toughness decrease of the cemented carbide. According to one embodiment, the cemented carbide comprises from 65 to 95 vol% WC, for example from 70 to 90 vol% WC, preferably from 75 to 85 vol% WC. According to one embodiment, the average WC grain size in the cemented carbide is > 1 .00 pm such as > 1 .01 pm or > 1 .02 pm or > 1 .03 urn. According to one embodiment, the average WC grain size is < 1.20 pm such as < 1.19 pm or < 1.18 pm or < 1.17 pm. The particle size of the WC powder used is selected to provide a desired WC grain size in the cemented carbide while taking into account the effects of all components in the raw material powder mixture and the milling procedure used. The particle size (FSSS) of the WC powder prior to milling suitably ranges from 0.5 to 11 pm such as from 9 to 11 pm.

[0030] To obtain the desired carbon content in the sintered cemented carbide, W and W2C are preferably admixed prior to sintering.

[0031] The carbon content in the sintered cemented carbide is measured since some of the carbon will be lost during the sintering process due to the formation of e.g. CO2. The exact amount of carbon lost depends on the sintering furnace and the sintering process. The admixed powder shall thus have a small excess of carbon compared to what is aimed for in the sintered cemented carbide.

[0032] By the term finely dispersed eta phase is meant the cemented carbide microstructure does not contain more than 8 clusters or eta phase grains larger than 15 pm, i.e. a maximum Feret diameter larger than 15 pm, within an area of 1 mm2in a light optical microscope image at 200 times magnification.

[0033] According to one embodiment, the eta phase is homogeneously distributed throughout the whole cemented carbide substrate whereby no eta phase gradients or eta phase-free zones exist in the cemented carbide as further disclosed in US 4,843,039.

[0034] According to one embodiment, the substrate of the cutting tool is free from titanium (Ti), tantalum (Ta), vanadium (V) and niobium (Nb). By free from titanium, tantalum, vanadium or niobium is meant the substrate may only contain impurity levels up to 0.003 wt% or up to 0.002 wt% or up to 0.001 wt% for each of the elements.

[0035] According to one embodiment, the substrate of the cutting tool is free from ruthenium (Ru). By free from ruthenium is meant the substrate may only contain impurity levels up to 0.001 wt% such as up to 0.0001 wt%.

[0036] According to one embodiment, the cemented carbide comprises WC grains, eta phase grains, Cr and Co, wherein Co is present in an amount ranging from 8 to 15 wt%, wherein the Cr / Co weight ratio ranges from 0.026 to 0.05, wherein the eta phase content ranges from 2.6 to 13 vol%, wherein the sub-stoichiometric carbon content ranges from -0.31 to -0.50 wt%, and wherein the coercivity Hcof the cemented carbide ranges from 9.5 to 10 kA / m, wherein all wt% and vol% values are based on the total weight or volume of the cemented carbide; and wherein the substrate is coated with at least one coating layer.

[0037] According to one embodiment, a coating comprising one or more layers comprising at least one layer of a-AI2O3is deposited on the substrate. Preferably, the coating has a thickness ranging from 1 to 20 pm. Preferably, the coating is deposited by chemical vapour deposition (CVD). The a-AI2O3layer preferably exhibits an X-ray diffraction (XRD) pattern as measured by means of CuKa radiation and 9-29 scan, wherein the texture coefficient TC(hkl) is defined according to Harris formula wherein the (h k I) reflections used are (1 0 4), (1 1 0), (1 1 3), (0 2 4), (1 1 6), (2 1 4), (3 0 0) and (00 12), wherein l(h k l) = measured intensity (integrated peak area) of the (h k l) reflection; lo(h k l)= standard intensity according to ICDD's PDF-card No. 00-10-0173, and wherein n= number of reflections used in the calculation (in this case 8 reflections), and wherein 1<TC(0 2 4) <4 and 3<TC(0 0 12)<6.

[0038] The a-AI2O3layer is preferably deposited by thermal CVD. Alternatively other CVD deposition processes can be used. These options apply also for any further layers as disclosed below.

[0039] The a-AI2O3layer preferably comprises crystalline grains. Grains of the a-AI2O3layer comprising (0 0 1) planes in parallel with the substrate surface will hereinafter be referred to as (0 0 1) oriented grains. Grains of the a-AI2O3layer comprising (0 1 2) planes in parallel with the substrate surface will be referred to as (0 1 2) oriented grains.

[0040] According to one embodiment, the a- AI2O3layer comprises a mixture of (00 1) oriented grains and (0 1 2) oriented grains whereby the (0 0 1) oriented grains may contribute to high crater wear resistance and the (0 1 2) oriented grains may contribute to high resistance against cracking and flaking of the coating when the cutting edges are exposed to plastic deformation.

[0041] A means to express preferred texture is to calculate a texture coefficient TC (h k I) using the Harris formula (1) on the basis of a defined set of XRD reflections measured on the respective sample. The intensities of the XRD reflections are standardized using a JCPDF-card indicating the intensities of the XRD reflections of the same material, i.e. the a- AI2O3, but with random orientation, such as in a powder of the material. A texture coefficient TC (h k I) > 1 of a layer of a crystalline material is an indication that the grains of the crystalline material are oriented with their (h k I) crystallographic plane parallel to the substrate surface more frequently than in a random distribution. The texture coefficient TC (0 0 12) is used herein to indicate preferred crystal growth with the (0 0 1) plane parallel to the substrate surface. The (0 0 1) crystallographic plane is parallel to the (0 0 6) and (0 0 12) crystallographic planes in the a- AI2O3crystallographic system. In a corresponding way, the (0 1 2) crystallographic plane is parallel to the (0 2 4) crystallographic plane in the a-AI2O3crystallographic system.

[0042] According to one embodiment, said a-AI2O3layer exhibits texture coefficients 1<TC(0 2 4)<3 and 3.5<TC(0 0 12)<5.5. According to one embodiment, said a-AI2O3layer exhibits texture coefficients 1 ,5<TC(0 2 4)<2.5 and 4<TC(0 0 12)<5.

[0043] According to one embodiment, the third strongest TC(h k I) of said a-AI2O3layer is TC(1 1 0). According to one embodiment, the sum of the TC(0 0 12) and TC(0 2 4) for said a-AI2O3layer is >6.5.

[0044] According to one embodiment, the a-AI2O3layer comprises columnar grains. Preferably the a- AI2O3layer comprises columnar grains of {00 1 } and {0 1 2} orientation respectively throughout the total thickness of the a-AI2O3layer.

[0045] According to one embodiment, the a-AI2O3layer comprises columnar a-AI2O3layer grains, wherein the average width of said columnar grains ranges from 0.5 to 2 pm as measured along a line parallel to the surface of the substrate in the middle of said a-AI2O3layer.

[0046] According to one embodiment, the average thickness of the a-AI2O3layer ranges from 2 to 10 pm or from 3 to 7 pm.

[0047] According to one embodiment, the coating further comprises a layer of one or more of TiN, TiCN, TiC, TiCO, and TiCNO.

[0048] According to one embodiment, the coating comprises layers in the following order counted from the surface of the substrate: TiN, TiCN, TiCNO and a-AI2O3.

[0049] According to one embodiment, the coating comprises an outermost wear-indicating colour layer, for example a TiN layer. The coating comprising at least the a-AI2O3layer and the production thereof is further disclosed in EP3478874.

[0050] According to one embodiment, a coating comprising at least a layer of K-AI2O3is deposited on the substrate. Preferably, the K-AI2O3is deposited by chemical vapor deposition (CVD). Preferably, a x-scan from -80° to 80° over the (0 0 6) reflection of said K-AI2O3layer shows the strongest peak centered around 0°. The K-AI2O3layer is typically deposited by thermal CVD. Alternatively, other CVD deposition processes can be used. This also applies to any further layers of the coating as disclosed below.

[0051] The FWHM (Full Width Half Maximum) of said peak is preferably <25° such as <20°, more preferably <18° wherein the FWHM is the width of the peak at half its maximum height. Generally, the narrower the peak, the more well-textured or well-oriented the layer.

[0052] The cutting tool of the present invention preferably comprises a K-AI2O3layer comprising a high fraction of {0 0 1} planes in parallel with the surface of the substrate.

[0053] According to one embodiment, the strongest peak of the K-AI2O3layer in an X-ray diffractogram from 15° to 140° is the (0 0 2) reflection. The second strongest peak may preferably be from the (0 0 4) reflection. The third strongest peak may preferably be from the (0 0 6) reflection.

[0054] According to one embodiment, the average thickness of the K-AI2O3layer ranges from 1 to 20 pm such as from 2 to 10 pm, preferably from 3 to 7 pm.

[0055] According to one embodiment, the coating comprising the K-AI2O3layer further comprises an a-AI2O3layer located between said K-AI2O3layer and the substrate. The a-AI2O3layer is preferably a layer with a high fraction of {0 0 1} planes in parallel with the surface of the substrate. Preferably, the fraction of {0 0 1} planes in parallel with the surface of the substrate are dominating. A {0 0 I} texture in said a-AI2O3layer can be utilized to form a strong {0 0 1} texture in a subsequent K-AI2O3layer. According to one embodiment, said a-AI2O3layer exhibits an x-scan from -80° to 80° over the (0 0 12) reflection of said a-AI2O3layer that shows the strongest peak centered around 0°, wherein the FWHM of said peak is <25°, preferably <20°, more preferably <18°.

[0056] According to one embodiment, the thickness of said a-AI2O3layer ranges from 0.5 to 2 pm, preferably from 0.7 to 1 pm.

[0057] According to one embodiment of the present invention, the coating further comprises one or more layers of TiN, TiCN, TiC, TiCO, TiAICO and TiCNO.

[0058] According to one embodiment, a TiCN layer is located between said a-AI2O3layer and the substrate. The TiCN layer is preferably columnar. The TiCN layer is preferably a layer with a high fraction of {2 1 1}, {3 1 1} and {1 1 1} planes in parallel with the surface of the substrate. Preferably, the fraction of {2 1 1}, {3 1 1} and {1 1 1} planes in parallel with the surface of the substrate are dominating, i.e. the intensities of the reflection from these planes are of the highest intensity in an XRD diffractogram. This texture in said TiCN layer can be utilized to form a strong {0 0 1} texture in a subsequent a-AI2O3layer. According to one embodiment, said a-AI2O3layer and said K-AI2O3layer are separated by one or several layers of TiN, TiC, TiCN, TiCO, TiAICO, TiCNO, preferably TiN, TiC and / or TiCN, most preferably TiN. The layer(s) separating said a-AI2O3layer and said K-AI2O3layer are preferably {1 1 1} textured. According to one embodiment, the K-AI2O3layer is in direct contact with a {1 1 1} textured TiN layer.

[0059] According to one embodiment, the thickness of said layer(s) of one or more of TiN, TiC, TiCN, TiCO, TiCNO, TiAICO located between said a- AI2O3layer and said K- AI2O3layer is < 0.5 pm, preferably between 0.02 pm and 0.5 pm, more preferably < 0.4 pm or < 0.3 pm or < 0.2 pm.

[0060] According to one embodiment, the coating comprises layers in the following order as seen from the surface of the substrate: TiN, TiCN, TiCNO, a-AI2O3, TiN and K- AI2O3. According to one embodiment, the coating comprises an outermost wear indicating colour layer such as TiN. The coating comprising the K-AI2O3layer and the preparation thereof is further disclosed in EP3263739.

[0061] According to one embodiment, the substrate is coated with a coating comprising at least a layer of (Tii.xAlx)N, where x ranges from 0.50 to 0.75, preferably from 0.60 to 0.70, most preferably from 0.60 to 0.67. The crystal structure of the (Tii.xAlx)N layer is preferably of NaCI type. The total thickness of the layer is preferably from 1 to 5 pm, more preferably from 1 to 4 pm or from 1 to 3 pm or from 1 to 2 pm, wherein the thickness is measured in the middle of the flank face. The layer is preferably strongly textured in the (200)-direction, with a texture coefficient TC(200) of about 1 .6 to 2.1 .

[0062] The texture coefficient (TC) is defined as follows: where l(hkl)=intensity of the (hkl) reflection

[0063] Io (hkl)=standard intensity according to JCPDS card no 38-1420 n=number of reflections used in the calculation; and the (hkl) reflections used are: (111), (200), and (220).

[0064] According to one embodiment, the compressive stress of the (Tii.xAlx)N layer ranges from 0.5 to 10 GPa, preferably from 1 to 6 GPa, more preferably from 3 to 5 GPa. The method used to grow the (T _XAIX)N layer is preferably based on arc evaporation of an alloyed cathode or composite cathode whereby the Ti+AI cathode composition preferably is from 25 to 50 atomic% Ti, preferably from 30 to 40 atomic% Ti, most preferably from 33 to 35 atomic% Ti.

[0065] Before the coating procedure is initiated, the substrate surface is preferably cleaned by applying an ion etching in an Ar atmosphere or in a mixture of Ar and H2. The evaporation current is preferably from 50 to 200 A depending on the cathode size and the cathode material. When using cathodes of about 63 mm in diameter during the evaporation, the current is preferably from 60 to 100 A. The substrate bias is preferably from -20 to -50 V. The deposition temperature is preferably from 400 to 700°C. According to one embodiment, the (Tii-xAlx)N layer is grown in an Ar+N2atmosphere consisting of from 0 to 50 vol% Ar, preferably from 0 to 20 vol% Ar at a total pressure from 1 .0 to 7.0 Pa, preferably from 3.0 to 5.5 Pa.

[0066] According to one embodiment, on top of the (Tii.xAlx)N layer, a TiN layer is deposited. Preferably the TiN layer has a thickness ranging from 0.1 to 0.5 pm such as from 0.1 to 0.3 pm. The TiN layer is preferably deposited by means of arc evaporation.

[0067] According to one embodiment, the coating comprising at least a layer of (Tii.xAlx)N has a thickness ranging from 1 to 5 pm, preferably 1 to 4 pm. The preparation of the coating is further described in US8034438.

[0068] According to one embodiment, a coating comprising at least a nano-multilayer of alternating layers is coated on the substrate, preferably a nano-multilayer wherein the first nanolayer is (Tii-xAlx)N, wherein 0.35<x<0.70, and the second nanolayer is Tii.ySiyN, wherein 0.05<y<0.25, wherein a sequence of one first nanolayer and one second nanolayer forms a layer period, wherein the average layer period thickness in the nano-multilayer preferably is <50 nm. The average layer period thickness of the nano-multilayer preferably ranges from 2 to 15 nm, more preferably from 3 to 6 nm.

[0069] Preferably, with respect to the first nanolayer (Tii.xAlx)N: 0.45<x<0.70, more preferably 0.55<x<0.70 or 0.60<x<0.70.

[0070] Preferably, with respect to the second nanolayer Tii.ySiyN: 0.06<y<0.23, more preferably 0.06<y<0.21 , and most preferably 0.08<y<0.16.

[0071] According to one embodiment, the average column width of the nano-multilayer is from 5 to 100 nm, or from 10 to 70 nm, or from 25 to 70 nm. The thickness of the nano-multilayer is preferably from about 0.5 to about 10 pm, more preferably from about 0.5 to about 5 pm, and most preferably from about 1 to about 3 pm.

[0072] The nano-multilayer is preferably deposited by means of cathodic arc evaporation.

[0073] According to one embodiment, the substrate is in addition to the nano-multilayer of alternating layers further coated with a layer of TiN, (Ti,AI)N or (Cr,AI)N, preferably (Ti,AI)N located between the substrate and the nano-multilayer, preferably as an innermost layer of the coating. If the (Ti,AI)N layer is deposited on the substrate, (Ti,AI)N which may be indicated as Tii.zAlzN, it suitably has a composition wherein 0.35<z<0.70, preferably 0.45<z<0.70, most preferably 0.55<z<0.70 or 0.60<z<0.70. According to a preferred embodiment, the Ti-AI relation in the (Ti,AI)N layer is the same as the Ti-AI relation in the first nanolayer of the nano-multilayer. The thickness of the (Ti,AI)N layer preferably ranges from about 0.1 to about 2 pm, more preferably from about 0.3 to about 1 .5 pm, such as from about 0.3 to about 1 pm.

[0074] According to one embodiment, the coating further comprises a top layer of (Ti,Si)N. The (Ti,Si)N expressed as Tii.vSivN is suitably composed such that 0.06<v<0.23, or 0.06<v<0.16, or 0.06<v<0.12. In a preferred embodiment, the Ti-Si relation in the top layer of (Ti,Si)N is the same as the Ti-Si relation in the second nanolayer of the nano-multilayer. The thickness of this top layer can be from about 0.02 to about 0.5 pm, preferably from about 0.05 to about 0.2 pm.

[0075] According to one preferred embodiment, the coating deposited on the substrate comprises a nano-multilayer of alternating layers of a first nanolayer being Tii.xAlxN, 0.5<x<0.65, and a second nanolayer being Tii.ySiyN, 0.06<y<0.21 , wherein the average layer period thickness of the nano-multilayer preferably ranges from 3 to 15 nm, wherein the average column width in the nano-multilayer preferably is from 25 to 70 nm, and wherein the thickness of the nanomultilayer preferably is from about 1 to about 3 pm. Preferably, an innermost layer of (Ti,AI)N is deposited on the substrate in between the substrate and the nano-multilayer. Preferably, the (Ti,AI)N layer has a thickness ranging about 0.5 to 1.5 pm. The preparation of the coating comprising the nano-multilayer is further disclosed in WO2010 / 140958. The cutting tool suitably is an insert or an end mill for machining metals including machining operations such as milling, turning or drilling.

[0076] Detailed description of the figures

[0077] Figure 1 shows a SEM image of a fine-dispersed eta phase according to the invention. Definitions and Methods

[0078] Eta phase content

[0079] The amount of eta phase in the cemented carbide was determined by image analysis of LOM (light optical microscope) using the software Image J using the “Analyze particles” function with “exclude on edges” and the “O-Infinity” filter settings. Prior to the measurements, colour LOM images were converted into 8-bit black and white images using Automatic threshold setup. The magnifications of the images were 1000X. At least five measurements were done and the values in table 2 represents an average value thereof. The value presented in table 2 is thus an average from a total of at least five image analyses performed on at least five images with one measurement on each image. The area fraction in the image is assumed to correspond to the volume fraction in the cemented carbide. The volume fraction of the WC can be determined in the same way as the eta phase volume fraction.

[0080] Eta phase grain size

[0081] The average grain size of the eta phase grains is herein defined as the average value of the maximum feret diameter of the eta phase grains. This value was determined herein by image analysis on a light optical microscope (LOM) image using the software Image J using the “Analyze particles and the “0- Infinity” filter settings. The Feret size option “exclude on edges” was activated in the “Analyze particles” function. Prior to the measurements, colour LOM images were converted into 8-bit black and white images using Automatic threshold setup. The images used for the analysis were LOM images with a magnification of 1000X and at least 5 images were processed and maximum Feret diameters were obtained for each image and an overall average value of the maximum Feret diameter was calculated.

[0082] WC grain size determination

[0083] The average grain size of the WC, d, is herein determined from the value of the magnetic coercivity. The relationship between coercivity and grain size of WC is described, e.g., in Roebuck et al., Measurement Good Practice No. 20, National Physical Laboratory, ISSN 1368-6550, November 1999, Revised February 2009, Section 3.4.3, pages 19-20. For the purposes of this application the grain size of the WC, d, is determined according to formula (8) on page 20 in the above-mentioned reference:

[0084] K=(Ci+diWCo)+ (c2+d2Wco) / d. Re-arranging the formula: d = (c2+d2WCo) / (K-(ci+diWCo)), wherein d= WC grain size of the cemented carbide body, K= coercivity of the cemented carbide body in kA / m, herein measured according to standard DIN IEC 60404-7, WCo= wt% Co in the cemented carbide body, Ci = 1.44, c2= 12.47, di = 0.04, and d2= -0.37.

[0085] S-value

[0086] The dissolved amount (wt%) of tungsten (W) in the binder phase may be expressed as the S-value. S= o16.1 x 100 [%], where o is the measured magnetic moment (MM) of the binder phase in pT m3kg~1. The S-value depends on the content of W in the binder phase and increases with a decreasing tungsten content. The dissolution of W in the binder phase, i.e. the S-value, depends on the carbon content in the carbides and the degree of carbon saturation in the powder.

[0087] Laver thickness

[0088] The thickness of the coating layers is measured by SEM (scanning electron microscope) according to methods well-known to the skilled person.

[0089] Examples

[0090] Cemented carbide compositions were prepared by mixing raw material powders containing tungsten carbide (WC), cobalt (Co) powder, chromium carbide (Cr3C2) and metallic tungsten powder (W) as set out in table 1 (Inventions 1a, 1 b, 2a, 2b). Also comparatives compositions 3a and 3b were prepared. In addition, a PVD-coated reference insert (Ref) was prepared by mixing elements including ruthenium as set out in table 1 . 2 powder batches were manufactured, one for preparation of PVD coatings and one for preparation of CVD coatings. Table 1

[0091] Cpis the total carbon content in the powder mixture (weighed quantity of carbon). Csis the total carbon content in the sintered cemented carbide composition as measured with a LECO CS844 instrument. The WC powder according to the invention had a Fischer method (FSSS) particle size of 9.80 to 10.80 pm.

[0092] The powders of the powder mixtures were milled in a ball mill together with a milling liquid (with 87 wt% ethanol) and an organic binder (2 wt% PEG). The amount of PEG was not taken into consideration when calculating the dry powder weights presented in Table 1. After milling, the slurries formed were dried in a spray dryer and thereafter pressed into green bodies inserts in a pressing operation at about 172 MPa. The powder batches were milled in 1 kg or 4 kg batches and spray dried in a lab spray dryer. The green bodies were sintered in vacuum for 60 minutes at a temperature of 1410°C and 30 minutes at a temperature of 1470 °C (for subsequent CVD coating) and 1470 °C (for subsequent PVD coating) respectively.

[0093] The average content of the eta phase was determined by the method described herein. An average value from 5 images is shown in Table 2. The average grain size of the eta grains was determined by the method as described herein. An average value from 5 images is shown in Table 2.

[0094] Also the sub-stoichiometric carbon content as set out in table 2 was determined in accordance with the methods disclosed herein after sintering. The eta phase grains in the samples containing eta phase were evenly distributed throughout the whole substrate. No gradient in the eta phase content was observed in the samples. No large eta phase grains or graphite were found in the cemented carbide.

[0095] The area fraction of the WC, the eta phase grains and the metallic binder of the cemented carbides were studied in LOM and in SEM (Scanning Electron Microscope). Further details of the cemented carbide sintered at 1470 °C are also presented in Table 2 including the density, the coercivity and the degree of magnetic moment (S).

[0096] Table 2

[0097] PVD coating

[0098] The sintered variants from batch 1 for subsequent PVD coating were subjected to grinding and edge treatment prior to PVD coating. Also, prior to coating deposition occurred, the inserts were ultrasonically cleaned in standard industrial cleaning liquids. The PVD coating deposition was performed in an Oerlikon Balzers Domino Kila Flex PVD machine with four cathodic arc flanges. Three flanges, each of which equipped with four 63 mm cathodes, were used in the deposition process. Before the deposition started, the system was pumped down to high vacuum (< 8 x 105mbar) and preheated to about 600°C whereby the inserts were subjected to Ar ion etching.

[0099] The PVD coating deposition was made in two steps. In the first step, a bottom layer was deposited from two arc flanges equipped with Tio.33Alo.67 cathodes. The process was run at arc currents of 60 A for all 8 cathodes, a substrate bias potential of -30 V, an atmosphere of 4 Pa N2, and a temperature of about 450°C. Deposition was carried out to obtain a layer thickness of about 0.5 pm at 3-fold rotation of the inserts at a rotational speed of 3 rpm. The resulting Tii.xAlxN layer was measured to have an Al content of about x=0.62, a NaCI-type cubic crystal structure, and columnar-shaped grains.

[0100] In the second step, a nano-laminated layer was deposited from two arc flanges, one equipped with Tio.33Alo.67 cathodes and one with Tio9Sio 1 cathodes. The process was run at arc currents of 60 A for all 8 cathodes, a substrate bias potential of -30 V, an atmosphere of 4 Pa N2, and a temperature of about 450°C. The nano-laminated layer of alternating Tii.xAlxN and Tii.ySiyN sublayers was formed by rotation of the inserts in front of the two arc flanges. Based on EDX measurement of the average chemical composition of the nano-laminated layer and the bottom layer, the approximate compositions of the sublayers were estimated to correspond to x=0.62 and y=0.07. XRD and SEM showed that the nano-laminated layer had a NaCI-type cubic structure and columnar grains. The layer was grown to a thickness of about 2 pm resulting in a total coating thickness of about 2.5 pm, as measured in the middle of the flank face of the inserts.

[0101] Subsequent to the PVD coating deposition, the coated inserts were subjected to shotpeening and blasting to provide a SEEX1204AFTN-M14 geometry.

[0102] CVD coating

[0103] Three sintered variants from the batch 2 were prepared by plan grinding, form grinding, edge treatment, and wash prior to CVD coating.

[0104] To perform the CVD coating procedure, the substrates were first coated with an approximately 0.1 pm thick TiN from TiCI4, N2, and H2at 860 °C and 600 mbar. Then an approximately 5 pm thick TiCN by employing the well-known MTCVD technique using TiCI4, CH3CN, N2and H2at 860 °C and 60 mbar was coated on the TiN layer. The volume ratio of TiCI4 / CH3CN in an initial part of the MTCVD deposition of the TiCN layer was 9.1 , followed by a period using a ratio of TiCI4 / CH3CN of 2.5.

[0105] On top of the MTCVD TiCN layer, an approximately 1 pm thick bonding layer was deposited at 1000 °C using a process consisting of four separate steps: First an HTCVD TiN using TiCI4, N2, HCI, and H2at 400 mbar, then a second step (TiCNO-1) using TiCI4, CH3CN, CO, N2, HCI, and H2at 60 mbar, then a third step (TiCNO-2) using TiCI4, CO, N2, and H2at 60 mbar, and finally a fourth step (TiN) using TiCI4, N2, and H2at 60 mbar. Prior to initiating subsequent AI2O3nucleation, the bonding layer was oxidized for five minutes in a mixture of CO2, CO, N2, and H2at 60 mbar. On top of the bonding layer, an a- AI2O3layer was deposited at 1000 °C in three steps: the first step using 1 .7 vol% AICI3, 2.9 vol% CO2, 1.6 vol% HCI, balance H2at 60 mbar resulting in approximately a 0.1 thick pm a- AI2O3and a second step using 1 .6 vol% AICI3, 4.5 vol% CO2, 2.2 vol% HCI, 0.6 vol% H2S, and balance H2at 60 mbar and a third step using 1 .6 vol% AICI3, 6.2 vol% CO2, 1 .9 vol% HCI, 0.1 vol% H2S, and balance H2at 150 mbar resulting in a total thickness of an a-AI2O3layer of approximately 4 pm.

[0106] Subsequent to the CVD coating, the inserts were subjected to shot peening and blasting to provide a geometry SEEX1204AFTN-M14 geometry.

[0107] Table 3 shows Hv10 and Hv30 hardness values as well as K1C fracture toughness values of the invention samples 1a, 1 b, 2a and 2b and comparative samples 3a and 3b as well as Hv10 for the reference (Ref). The indicated measured hardness and fracture toughness values for the PVD and CVD samples are mean values of the measurements (which were very similar for the PVD and CVD coated samples). As can be noted, the hardness levels Hv10 were on the same level as the reference (Ref) thus indicating a similar hardness were obtained for the inventive samples which did not contain any ruthenium in the substrates.

[0108] Table 3

[0109] Cutting test

[0110] A Face milling test was carried out and the flank wear was measured on the SEEX1204 AFTN-M14 inserts. However, the dominating wear mode on the flank was comb cracks, which resulted in chipping towards the end of the tool life. The test was performed without cutting fluid. The cutting data as presented in table 4 were specifically chosen to induce comb cracks on the inserts. Four cutting edges from two inserts (2x2) were utilized and the process was then repeated. The material of the workpiece was SS2244.

[0111] Table 4

[0112] PVD coated inserts

[0113] Table 5 shows the flank wear of the PVD coated inserts after 6.25, 12.5 and 18.75 minutes for invention samples (with different carbon content in their respective powder mixtures) sintered at 1470°C as well as the flank wear of the reference.

[0114] Table 5

[0115] As can be noted from table 5, the flank wear is more limited for all invention samples than comparative 3a and reference at any time.

[0116] CVD coated inserts

[0117] Tables 6a and 6b show the flank wear of the CVD coated inserts after 6.25, 12.5 and 18.75 minutes for invention samples 1 b and 2b and comparative 3b with a varying degree of carbon added to the powder mixture prior to sintering at 1470°C (table 6a) and 1410°C (table 6b) respectively.

[0118] Table 6a As can be noted from table 6a, a lower flank wear was obtained for invention samples 1 b and 2b compared to comparative 3b after 50 minutes in use.

[0119] Table 6b As can be noted from table 6b, a lower flank wear was obtained for inventions 1 b and 2b than comparative 3b after 50 minutes in use.

Claims

Claims1. Cutting tool comprising a substrate of a cemented carbide comprising WC grains, eta phase grains, Cr and Co, wherein Co is present in an amount ranging from 6 to 16 wt%, wherein the weight ratio of Cr to Co ranges from 0.01 to 0.05, wherein the eta phase content ranges from 1 to 15 vol%, and wherein the sub-stoichiometric carbon content ranges from -0.30 to -0.60 wt%, wherein the coercivity Hcin the cemented carbide ranges from 9.0 to11.5 kA / m, wherein all wt% and vol% values are based on the total weight or volume of the cemented carbide; and a coating adhered to the substrate.

2. Cutting tool according to claim 1 , wherein weight ratio of Cr to Co ranges from 0.02 to 0.04.

3. Cutting tool according to claim 1 or 2, wherein the weight ratio of Cr to Co ranges from 0.026 to 0.035.

4. Cutting tool according to any one of claims 1 to 3, wherein the eta phase content ranges from 2.6 to 13 vol%.

5. Cutting tool according to any one of claims 1 to 4, wherein Co is present in an amount ranging from 8 to 14 wt%.

6. Cutting tool according to any one of claims 1 to 5, wherein the coercivity Hcis9.5 to 11.5.

7. Cutting tool according to any one of claims 1 to 6, wherein the coercivity Hcis9.5 to 11.

8. Cutting tool according to any one of claims 1 to 7, wherein the WC grain size >1.00 pm, preferably >1.01 pm or >1.02 pm or >1.03 pm or >1.04 pm or >1.05 pm.

9. Cutting tool according to any one of claims 1 to 8, wherein the WC grain size < 1.20 pm.

10. Cutting tool according to any one of claims 1 to 9, wherein the sub- stoichiometric carbon content ranges from -0.31 to -0.50 wt%.11 . Cutting tool according to any one of claims 1 to 10, wherein the substrate has a content of titanium up to 0.003 wt%.

12. Cutting tool according to any one of claims 1 to 11 , wherein the coating comprises a nano-multilayer of alternating layers of a first nanolayer being Tii. xAlxN, 0.5<x<0.65, and a second nanolayer being Tii.ySiyN, 0.06<y<0.21.

13. Cutting tool according to any one of claims 1 to 11 , wherein the coating comprises a layer of a-AI2O3.

14. Cutting tool according to any one of claims 1 to 11 , wherein the coating comprises a layer of (Tii.xAIX)N, wherein x ranges from 0.50 to 0.75.

15. Cutting tool according to any one of claims 1 to 11 , wherein the coating comprises a layer of K-AI2O3.

Images