Cutting tool

Abstract

The present invention relates to a cutting tool comprising a cermet-based substrate and a coating, wherein the cermet comprises i) a hard phase comprising Ti(C,N); ii) a binder phase comprising a) Co; and b) Mo; wherein the mole fraction of Mo / (Mo+Co) in the cermet ranges from 0.05 to 0.30; and 10 to 25 vol% of the cermet is comprised of binder phase, wherein at least 75 vol% of the total volume of Mo is present in the binder phase as determined by SEM-EDS, and wherein the coating comprises i) a layer of Ti(C,N), (Ti,Al)N or (Ti,Si)N.

Description

[0001] Cutting tool

[0002] The invention relates to a cutting tool.

[0003] Background of the invention

[0004] Cermets with a hard phase of Ti(C,N) and a binder phase of Co are generally known for use in cutting tools for metal machining, for example in surface finishing applications which involve a low depth of cut. The use of ruthenium and / or rhenium in cermets is likewise known. However, it would be desired to further enhance performance of cutting tools in machining applications, e.g. in applications involving high depths of cut. One objective of the present invention is to impart improved hardness and / or toughness to a cermet, in particular with a minimum of constituents in the cermet. Another objective is to provide a cutting tool with improved toughness while maintaining a relatively high hardness. To provide a long tool life, such as in milling applications, a cutting tool should have high resistance against different types of wear including comb crack resistance. An objective of the invention is also to provide a cutting tool with an extended tool life, for example in more demanding machining operations, such as milling with a high depth of cut. A further objective of the invention is to avoid formation of pools in the binder phase of the cermet, i.e. local aggregations of binder metal and thus uneven distribution of metallic binder in the binder phase which has a negative impact on the tool life. A further objective is to reduce the formation of porosity in the cermet and prevent migration of binder metal to the coating of the cutting tool.

[0005] The invention

[0006] The present invention relates to a cutting tool comprising a cermet-based substrate and a coating, wherein the cermet comprises

[0007] i) a hard phase comprising Ti(C,N);

[0008] ii) a binder phase comprising

[0009] a) Co; and

[0010] b) Mo;

[0011] wherein the mole fraction of Mo / (Mo+Co) in the cermet ranges from 0.05 to 0.30; and 10 to 25 vol% of the cermet is comprised of binder phase, wherein at least 75 vol% ofthe total volume of Mo is present in the binder phase as determined by SEM-EDS, and wherein the coating comprises

[0012] i) a layer of Ti(C,N), (Ti,AI)N or (Ti,Si)N, preferably adhered directly to the substrate.

[0013] According to one embodiment, the layer i) can be adhered to the substrate via one or several binding layers such as TiN.

[0014] According to one embodiment, the coating comprises at least one of

[0015] 1.1) a layer of TiC orTi(C,N) adhered to the Ti(C,N) layer of i) and optionally a TiN layer adhered to the TiC or Ti(C,N) layer

[0016] 1.2) a nano-multilayer of (Ti,AI)N / (Ti,Si)N adhered to the Ti(AI,N) layer of i) and optionally a layer of Ti(AI,N) adhered to the nano-multilayer of (Ti,AI)N / (Ti,Si)N 1.3) a layer of TiN adhered to the Ti(AI,N) layer of i)

[0017] 1.4) a layer of NbN adhered to the Ti(AI,N) layer of i)

[0018] 1.5) a layer of AI2O3 adhered to the Ti(C,N) layer of i).

[0019] The layers i.1 )-i.5) can be adhered directly to the layer i) or via one or several binding layers between layer i) and any one of i.1)-i.5), e.g. via a TiN layer in between.

[0020] According to one embodiment, on top of the layer of TiC of i.1), a TiN layer is deposited. Preferably, the TiN layer has a thickness ranging from 0.1 to 15 pm or 0.1 to 10 pm or 1 to 5 pm, preferably 1 to 4 pm. According to one embodiment the TiN layer thickness ranges from 0.1 to 0.5 pm such as from 0.1 to 0.3 pm.

[0021] According to one embodiment, on top the nano-multilayer of (Ti,AI)N / (Ti,Si)N of i.2), a layer of (Ti,AI)N is adhered. Preferably, the (Ti,AI)N layer has a thickness ranging from 0.5 to 20 pm or 1 to 15 pm or 1 to 10 pm or 1 to 5 pm, preferably 1 to 4 pm.

[0022] According to one embodiment, the coating comprises a first nanolayer of (Ti, Al) N or differently expressed (Tii.xAlx)N, wherein 0.35<x<0.70, and a second nanolayer of (Ti,Si)N or differently expressed Tii.ySiyN, wherein 0.05<y<0.25, wherein a sequence of the first nanolayer and the second nanolayer forms a layer period, wherein the average

[0023] layer period thickness in the nano-multilayer preferably is <50 nm and preferably > 2 nm or > 3 nm or > 5 nm. The average layer period thickness of the nano-multilayer preferably ranges from 2 to 30 nm or 2 to 20 nm or 2 to 15 nm, more preferably from 3 to 6 nm.

[0024] The thickness of the nano-multilayer of (Ti,AI)N / (Ti,Si)N is preferably from about 0.5 to 15 pm or 0.5 to about 10 pm, more preferably from about 0.5 to about 5 pm, and

[0025] most preferably from about 1 to about 3 pm.According to one embodiment, from 12 to 25 or 13 to 23 or 15 to 22 or 16 to 22 or 17 to 22 or 18 to 22 vol% of the cermet is comprised of binder phase.

[0026] If the binder phase content is too low, the cermet will suffer from too low toughness resulting in shorter tool life. If the binder phase content is too high, the hardness will be insufficient. According to one embodiment, the mole fraction of Mo / (Mo+Co) is 0.05 to 0.25, preferably 0.06 to 0.25 or 0.07 to 0.25 or 0.08 to 0.25 or 0.09 to 0.25 or 0.10 to 0.25 or 0.12 to 0.25 or 0.12 to 0.20 or 0.12 to 0.18 or 0.12 to 0.15.

[0027] According to one embodiment, the mole fraction of Mo / (Mo+Co) is 0.10 to 0.30 or 0.11 to 0.30 or 0.12 to 0.30 or 0.13 to 0.30 or 0.14 to 0.30 or 0.15 to 0.30 or 0.16 to 0.30 or 0.20 to 0.30 or 0.21 to 0.29 or 0.22 to 0.28.

[0028] According to one embodiment, at least 85 vol%, preferably at least 95 vol%, and more preferably at least 99 vol% of the total volume of Mo is present in the binder phase as determined by SEM-EDS.

[0029] According to one embodiment, no Re or Ru is comprised in the cermet.

[0030] According to one embodiment, the cermet comprises from 75 to 90 vol%, preferably from 78 to 85 vol% or 78 to 82 vol% of hard phase. According to one embodiment, Ti(C,N) corresponds to TiCxNy, wherein x and y preferably ranges from 0.3 to 0.7, more preferably from 0.4 to 0.6. Preferably, the cermet comprises Ti(C,N) in the hard phase in an amount of at least 80 vol%, preferably at least 85 vol% or at least 90 vol% or at least 95 vol% or at least 99 vol% or 100 vol%. According to one embodiment, the hard phase comprises (Ti, M) (C, N), wherein M is at least one element selected from groups 4 to 6 of the periodic table (apart from Ti). M, if present, is preferably selected from at least one of Ta (tantalum), Nb (niobium), and W (tungsten) in a total amount of up to 10 vol% or up to 5 vol% or up to 1 vol%.

[0031] According to one embodiment, the cermet does not comprise nitrides, oxides or oxynitrides of Al, e.g. Al-based compounds such as AIN, AI2O3, orAION. Presence of such compounds may reduce the toughness which in turn decreases the tool life.

[0032] According to one embodiment, the cermet is provided with a CVD-coating or PVD-coating, most preferably a CVD coating.

[0033] According to one embodiment, the thickness of the Ti(C,N), (Ti,AI)N or (Ti,Si)N of layer i) ranges from 0.5 to 15 pm or 1 to 10 pm or 1 to 5 pm, preferably from 2 to 5 pm or 2 to 4 pm. According to one embodiment, the thickness of the TiC, TiN, NbN or AI2O3 layer of i.1 ), i.3)-i.5) ranges from 0.5 to 15 pm or 1 to 15 pm such as 1 to 10 pm, preferably from 2 to 5 pm.According to one embodiment, the AI2O3 layer may be selected from a layer of a-AhCh or K-AI2O3. Preferably, theAhCh layer is deposited by chemical vapour deposition (CVD). According to one embodiment, an a-AhCh layer comprises columnar a-AhCh layer 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 cermet in the middle of the a-AhCh layer.

[0034] According to one embodiment, the coating comprises layers in the following order counted from the surface of the cermet: TiN, TiCN, TiCNO; and a- AhChor K- AI2O3.

[0035] According to one embodiment, the cutting tool has a Mo content < 6 vol% or < 5 vol% or < 4 vol% and preferably > 2 vol% based on the volume of the cermet-based substrate and a Co content < 17 vol% or < 16 vol% such as < 15 vol% and preferably > 5 vol% or > 10 vol% based on the volume of the cermet-based substrate.

[0036] The invention also relates to the use of the cutting tool for surface finishing and / or metal cutting of stainless steel.

[0037] Description of the drawings

[0038] Figures 1a-1d show EDS phase analysis maps of Co, Mo and Ti (C, N) of composition 1 as further described in the working examples herein:

[0039] Figure 1a shows a SEM micrograph of an analyzed region. The micrograph indicates Ti(C, N) grains (black / dark) and binder phase (grey).

[0040] Figure 1b shows an analyzed EDS map of the Ti (C, N) phase (grey) and the binder phase (black). Figure 1c shows a map of binder phase of Co (grey) and figure 1d shows a map of the Mo in the binder phase (white) that is present in the black (empty) regions in the binder phase of the Co phase (grey) in figure 1c.

[0041] Figure 2 shows an XRD pattern indicating presence of C03M0 in the binder phase.

[0042] Figure 3 shows a SEM-BSE (Backscattered Electron) image of a cross section of composition 1 as further specified in the working examples and the coating layers of Ti(C,N) (1) and a-AI2O3 (2).

[0043] Figure 4 shows a SEM-BSE image of a cross section of a reference cermet (composition 8) and the coating layers of Ti(C,N) (1) and a-AhCh (2). Spalling, abnormal growth of a-AhCh and cracks 6 were observed in the coating when Ni was used as binder.

[0044] Figure 5 shows a LOM (Light Optical Microscopy) image of the bulk of composition 1 (in 5a) where the lighter regions indicate the binder 3 and the darker regions indicate the Ti (C, N)grains 4. Reference composition 4 (in fig.5b) as further specified in the working examples shows lighter regions indicating the binder 3 (consisting mostly of Ni binder pools) and darker grey regions indicating the Ti (C, N) grains 4 and yet further darker grey regions indicating porosity 5.

[0045] Figure 6 shows a HV30-KIC plot for inserts prepared from compositions 1-8. It can be seen the fracture toughness of the references indicated as 4-7 in the plot is lower than the inventive cermets produced according to compositions 1-3 with Co-Mo-based binder. Compositions 1-3 show no porosity or binder pools as opposed to composition 4. The hardness increases as the concentration of Mo in the Co binder increases whilst the fracture toughness decreases. The highest fracture toughness is observed in composition 1 where the Mo content is the lowest (mole fractions: 0.87Co-0.13Mo) and the highest hardness is observed in composition 3 where the Mo content is the highest (mole fractions: 0.75Co-0.25Mo). Compositions 4-6 with Ni-Mo based binder showed both lower hardness andfracture toughness compared to compositions 1-3.

[0046] Figures 7-13 show results of the trials of the references and the inventive inserts as further described in the working examples here below. In figures 7-13, solid arrows indicate comb cracks and dashed arrows indicate intersecting parallel cracks.

[0047] Figures 7a-b show LOM images of reference insert (composition 7) after pass 1 (in 7a) and pass 2 (in 7b) following a milling trial (performed with coolant) as further described in example 3. For all trials, 1 pass corresponded to 4 minutes. The reference insert failed after pass 2 corresponding to a tool life of 8 minutes. The failure was caused by formation of comb cracks due to thermo-mechanical loading and an intersecting parallel crack causing complete block isolation in the localized cutting-edge region.

[0048] Figure 8 shows LOM images of the insert produced from composition 1 according to the invention after each pass which failed after pass 4 (pass 1 in fig.8a and pass 4 in fig.Sd) corresponding to a tool life of 16 minutes (following milling trials of example 3). The failure mechanism was the same as for the reference based on composition 7, i.e. that the Co-Mo binder no longer resisted the formation of comb cracks and parallel cracks. The increase in tool life for the insert based on composition 1 can be attributed to the higher fracture toughness.

[0049] Figures 9a (pass 7) and 9b (pass 8) show LOM images of a CVD coated reference cermet (composition 7). Milling operation was performed under coolant condition. The mechanism offailure was formation of comb cracks, and an intersecting parallel crack caused block isolation at the localized region on the cutting edge.

[0050] Figures 10a (pass 17) and 10b (pass 18) show LOM images of inserts prepared from inventive composition 1 which had been CVD coated. The milling operation was performed under coolant condition. The failure mechanism observed was the same as shown in figure 9. Figures 11a (pass 13) and 11b (pass 16) (based on composition 7) and figures 12a (pass 42) and 12b (pass 44) (invention) show LOM images of CVD-coated cermets (references) tested in dry condition.

[0051] Figure 12 shows an increase in tool life compared to the reference insert (in fig.11) when tested in dry condition.

[0052] Figure 13 shows the milling performance under coolant condition where 13a (pass 1) shows LOM images of the inserts produced from composition 8 that shows premature failure in pass 1 and 13b (pass 2) shows CVD coated inserts of composition 8.

[0053] Example 1

[0054] The preparation of the cermet composition according to the invention followed a standard powder metallurgical route including weighing in and mixing Ti (C0.5, Nos), TiC, Co and Mo (added as pure Mo metal) which subsequently were subjected to ball milling with ethanol and PEG (Polyethylene Glycol) as further detailed in table 1. A lab scale ball mill with 4 kg milling capacity was used. The mill was filled with 0.6 I of ethanol, 6 kg of milling balls and 1504.6 g of raw materials as shown in Table 1. The duration of the ball milling process was 24h.Table 1

[0055]

[0056] A slurry was obtained after the ball milling process which then was spray dried to obtain RTP (Ready-To-Press) powders. These powders were then isostatically pressed into a SEEX1204AFTN-MD18 geometry to obtain a compact green body. The green body was sintered in a Hot Isostatic Pressure (HIP) sintering process at a temperature of 1480°C and a pressure of 30 bar (in Ar atmosphere) during 1 h holding time to achieve fully dense hard substrate samples.

[0057] The sintered substrate samples were grinded and wet-blasted to obtain the desired edge radius of 25 pm using commonly known methods. The obtained substrates were then coated using a CVD (Chemical Vapor Deposition) process to provide a coating of Ti(C, NJ / a-AhOs with a total thickness of 7 pm, wherein a 4 pm Ti(C, N) layer was deposited on the cermet substrate at 800°C and a 3 pm a-AhCh layer was deposited on the Ti(C, N) layer at 1000°C according to well-known methods.

[0058] Table 2 shows the cermet compositions manufactured according to the invention (the weight amounts having been converted to % by volume). In compositions 1-3, Co is added whereas in reference compositions 4-6, Ni is added.

[0059] Table 2

[0060]

[0061] Table 3 shows the mole fraction of Co and Mo in compositions 1-3 and Ni and Mo in compositions 4-6 in the binder in a similar way as in Table 2. Table 3 also shows hardness and fracture toughness of the compositions.

[0062] Table 3

[0063]

[0064] As can be noted from table 3, the hardness and the fracture toughness values of the Cocontaining cermet compositions 1-3 are higher than the corresponding Ni-containing reference cermet compositions 4-6. It was unexpected that the Mo-Co based cermet compositions 1-3 show higher fracture toughness while simultaneously showing higher hardness with respect to the Mo-Ni based cermets 4-6.

[0065] Reference cermet compositions 7 and 8 (both being free of Mo) in table 4 below.

[0066] Table 4

[0067]

[0068] Example 2

[0069] In order to estimate the content of Mo in volume% in the binder phase, the following procedure was utilized with respect to the cermet composition:

[0070] Phase mapping of Ti (C, N), Co and Mo of composition 1 was made using SEM (Zeiss-Ultra) and EDS (Thermo-Fisher Scientific) by the following steps:

[0071] Polished cross sections (8 different cross sections from the same sample) of composition 1 were analyzed in EDS (Energy-Dispersive X-Ray Spectroscopy) at 10KV energy with a working distance of 7-8 mm, i.e. a distance between the objective lens and the sample surface. The maps of each phase were obtained using the Path Finder® software for the EDS with assigned phases of Ti (C, N), Co, Mo and Co-Mo. The spectral imaging feature in the software, combined with the Principal Component Analysis (PCA) function with a large Kernel matrix (17X17) were used to estimate the Mo content (in area%) of each phase. Assuming the obtained Mo content in area percent corresponds to the same Mo content in volume percent, an estimate of Mo in volume% is obtained. With such image analysis, it was seen from the 8 cross sections that the Mo content amounted to 99-100 area% by averaging the area% thereof. Thus, it was estimated 99-100 volume% of Mo was present in the binder phase (see also figure 1).

[0072] Hardness and fracture toughness were measured as set out below:

[0073] Measurements of Vicker’s hardness (Hv) (ISO 6507-1 :2018) with a load of 30 kgF were performed on the polished surfaces of the cermet compositions. The Palmqvist fracture toughness (Kic) (ISO 28079:2009) was measured on the indented surface using the Shetty et al method D.K. Shetty, I.G. Wright, PN. Mincer, A.H. Clauer, Indentation fracture of WC-Co cermets, J Mater Sci 20 (1985) 1873-1882 (htps: / / doi.org / 10.1007 / BF0Q555296):

[0074]

[0075] where Hvis the Vicker’s hardness at 30 kgF load, P is the indentation load and l + l2+ l3+ Z4is the sum of the crack length.

[0076] For each measurement of Hv and K1C, 5 indentations were made at different regions on the polished surface of each sample and their mean was recorded. The results are shown in figure 6.Example 3

[0077] Milling tests were performed on a Bridgeport XR-1270 CNC-mill. The spindle speed rate was up to 12,000 rpm and the spindle power was 30 kW. The workpiece material was a stainless steel of 42CrMo4 (SS2244) which was quenched and tempered to achieve a hardness of 35 HRC. It was pre-milled to remove the oxide skin to obtain final dimensions of 100x98x300 mm (width x height x length). After heat treatment, the workpiece material 42CrMo4 contained tempered martensite and carbides facilitating abrasive wear.

[0078] Up-milling with depths of cut at ap=1 mm, feed rate fz=0.1mm / tooth and cutting speed vc=150m / min were selected respectively. A milling cutter of 100 mm diameter with 10 insert slots was chosen where only two inserts were clamped at the opposite slots in each test. Three inserts and 2 cutting edges in each insert were tested, each in their coated and uncoated versions. The milling operations were performed on the as-sintered and on the as-coated inserts. For the as-sintered inserts, the milling operation was performed only under coolant while for the as-coated inserts, the milling operations were performed both under coolant and in dry conditions. In the up-milling, the highest theoretical chip thickness was attained at the end of the engagement and the highest thermo-mechanical load was observed on exit. Application of coolant was made to promote thermal shock to the inserts which in turn promoted comb cracks.

[0079] The insert performance was evaluated by observing the first visual damage onset on the inserts followed by chipping and the end of the tool life was declared when a catastrophic failure occurred, i.e. when a localized region of the cutting edge was completely chipped off. At vc=150 m / min, each pass was 4 minutes. The inserts were inspected with a light optical microscope after every pass. The inserts after the various passes are illustrated in figures 7-13 described here above. The average tool lives for the “as sintered inserts”, “CVD coated inserts machined with coolant” and “CVD coated inserts dry machined” of the invention and reference are summarized in table 5.Table 5

[0080]

[0081] In view of all samples, a clear improvement in tool life can be noted for the inserts according to the inventive cermets.

Claims

Claims1. Cutting tool comprising a cermet-based substrate and a coating, wherein the cermet comprisesi) a hard phase comprising Ti(C,N);ii) a binder phase comprisinga) Co; andb) Mo;wherein the mole fraction of Mo / (Mo+Co) in the cermet ranges from 0.05 to 0.30; and 10 to 25 vol% of the cermet is comprised of binder phase, wherein at least 75 vol% of the total volume of Mo is present in the binder phase as determined by SEM-EDS, and wherein the coating comprisesi) a layer of Ti(C,N), (Ti,AI)N or (Ti,Si)N.

2. Cutting tool according to claim 1, wherein the coating comprises at least one of 1.1) a layer of TiC orTi(C,N) adhered to the Ti(C,N) layer of i) and optionally a TiN layer adhered to the TiC or Ti(C,N) layer1.2) a nano-multilayer of (Ti,AI)N / (Ti,Si)N adhered to the Ti(AI,N) layer of i) and optionally a layer of Ti(AI,N) adhered to the nano-multilayer of (Ti,AI)N / (Ti,Si)N 1.3) a layer of TiN adhered to the Ti(AI,N) layer of i)1.4) a layer of NbN adhered to the Ti(AI,N) layer of i)1.5) a layer of AI2O3 adhered to the Ti(C,N) layer of i).

3. Cutting tool according to claim 1 or 2, wherein the mole fraction of Mo / (Mo+Co) is 0.05 to 0.25.

4. Cutting tool according to claim 1 or 2, wherein the mole fraction of Mo / (Mo+Co) is 0.10 to 0.30.

5. Cutting tool according to any one of claims 1 to 4, wherein at least 85 vol% of the total volume of Mo is present in the binder phase as determined by SEM-EDS.

6. Cutting tool according to any one of claims 1 to 5, wherein no Re is comprised in the cermet.

7. Cutting tool according to any one of claims 1 to 6, wherein no Ru is comprised in the cermet.

8. Cutting tool according to any one of claims 1 to 7, wherein the cermet comprises 75 to 90 vol% of hard phase.

9. Cutting tool according to any one of claims 1 to 7, wherein the hard phase comprises at least 80 vol% of Ti(C,N).

10. Cutting tool according to any one of claims 1 to 9, wherein no nitride, oxide, or oxynitride of Al is comprised in the cermet.

11. Cutting tool according to any one of claims 1 to 10, wherein the Mo content is < 6 vol% and the Co content < 17 vol% based on the volume of the cermet-based substrate.

12. Use of the cutting tool according to any one of claims 1 to 11 for surface finishing and / or metal cutting of stainless steel.

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