Cutting tools

Abstract

The present invention relates to a cutting tool insert with optimal hardness and high toughness for demanding cutting operations in hardened steel and cast iron. The cutting tool comprises a substrate (2) of cemented carbide, the cemented carbide comprising hard constituents tungsten carbide (WC) and a (Co) binder phase (4), chromium (Cr) and at least one further element from the group vanadium (V), niobium (Nb), molybdenum (Mo) and iron (Fe). The cemented carbide further has a Co-content of 3.50-4.20 wt.-% of the cemented carbide, a Cr-content of 0.31-0.38 wt.-% of the cemented carbide, a WC-content of at least 95.22 wt.-% of the cemented carbide, and the cemented carbide has a coercive force of 26-32 kA / m.

Description

[Technical Field]

[0001] The present disclosure relates to cutting tools that are particularly useful for machining hardened steels or superalloys. The present disclosure also relates to methods of making the same. [Background technology]

[0002] Hardened steels cover a wide range of steels and properties and exist in many different conditions depending on the intended use. As-hardened, hardened and tempered, and surface hardened (case hardened, nitrided, etc.) are common conditions covering a range of hardness up to 68 HRC. The purpose of hardening is to improve strength and wear resistance.

[0003] Steels suitable for hardening are medium to high carbon steels, often with alloying additions of Cr, Ni, Mn, and Mo. Other alloying elements are added depending on the purpose. Many of these alloying elements are carbide formers that create hard abrasive particles in the steel, which, in addition to high hardness, further reduce machinability and increase cutting edge wear during machining.

[0004] When cemented carbide cutting tools are used in machining hardened steels, the tools wear through various mechanisms, including abrasive and chemical wear of the cutting edge, chipping, and spallation. Coated cutting tools typically have a thin surface layer of wear-resistant carbide, nitride, carbonitride, and / or oxide compounds formed by various deposition techniques. The coating not only contributes to abrasive wear resistance, but also acts as a heat shield to prevent heat diffusion from the cutting surface to the underlying cemented carbide substrate. High temperatures in the edge region combined with high cutting forces result in increased creep deformation in the surface region of the affected substrate, causing plastic deformation of the cutting edge. Cutting tools for machining hardened steels must have good deformation resistance, wear resistance, and toughness.

[0005] To meet these demands, new cemented carbides with advanced properties are needed to provide cutting tools with cemented carbide bodies that have optimal hardness and high toughness for demanding cutting operations in hardened steel and cast iron.

[0006] One object of the present invention is to provide a cutting tool with high hardness, high toughness and thereby improved cutting performance. DETAILED DESCRIPTION OF THE INVENTION

[0007] definition The terminology used herein is for the purpose of describing particular embodiments of the disclosure only and is not intended to be limiting of the present invention. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0008] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0009] The term "cutting tool" as used herein is intended to denote a cutting tool suitable for cutting by chip removal, such as turning, milling, or drilling. Examples of cutting tools are indexable cutting inserts, solid drills, or end mills.

[0010] The term "substrate" as used herein should be understood as a body onto which a coating can be deposited.

[0011] The term "pressing" as used herein refers to pressing a powder of material, such as tungsten carbide (WC), together with cobalt (Co) between a punch and a die to form a green body. Pressing may be uniaxial or multiaxial.

[0012] It should be noted that when the term "thickness" is used to discuss the thickness of a layer, what is meant is the average thickness of the layer being discussed.

[0013] It should be noted that when the term "particle size" is used to discuss the particle size of a substrate, what is meant is the average particle size of the substrate being discussed.

[0014] invention The present invention relates to a cutting tool comprising a substrate of cemented carbide, the cemented carbide comprising a hard constituent of tungsten carbide (WC) in a metallic binder phase (4) comprising cobalt (Co), the cemented carbide further comprising chromium (Cr) and at least one further element from the group consisting of vanadium (V), niobium (Nb), molybdenum (Mo), and iron (Fe), - Co-content is 3.50~4.20wt% of the cemented carbide; - Cr-content is 0.31~0.38wt% of the cemented carbide; - the WC content is at least 95.22 wt% of the cemented carbide; - Cemented carbide has a coercive force of 26 to 32 kA / m.

[0015] The amount of Co binder phase is between 3.50 and 4.20 wt% of the cemented carbide. If the Co content is less than 3.50 wt%, there is a risk of high porosity and the substrate hardness will be too high, making the substrate brittle, while if the Co content is more than 4.20 wt%, the substrate hardness will be too low.

[0016] The amount of Cr is between 0.31 and 0.38 wt% of the cemented carbide. If the Cr content is less than 0.31 wt%, the inhibiting effect on grain growth will be too low, while if the Cr content is more than 0.38 wt%, there is a risk of undesirable precipitation of Cr-carbides in the microstructure.

[0017] Further additions of elements selected from the group consisting of vanadium (V), niobium (Nb), molybdenum (Mo), and iron (Fe) are made to achieve solid solution hardening and control the grain growth of WC, thereby achieving the desired properties such as coercivity, hardness, toughness, etc.

[0018] In one embodiment of the present invention, the cemented carbide contains 0.008-0.09 wt% V, preferably 0.01-0.09 wt% V, and more preferably 0.01-0.06 wt% V.

[0019] In one embodiment of the present invention, V+Nb is at most 0.12 wt% of the cemented carbide.

[0020] In one embodiment of the present invention, the V+Nb+Mo+Fe content of the cemented carbide is max. 0.2 wt%.

[0021] In one embodiment of the present invention, the cemented carbide has a hardness of 1960-2020 HV30, preferably 1960-2010 HV30.

[0022] In one embodiment of the present invention, the cutting tool has a cutting force of 8.6 to 9.7 MPa. -1 / 2 , preferably 9 to 9.6 MPa -1 / 2 It has a fracture toughness of

[0023] In one embodiment of the present invention, the cutting tool has a coercive force of 27 to 31 kA / m.

[0024] In one embodiment of the present invention, the cutting tool has a Cr-content of the binder phase of 8-10 wt%.

[0025] In one embodiment of the present invention, the cutting tool has a coating, preferably a PVD or CVD coating, most preferably a homogeneous or nanolayer PVD coating with a thickness of 1.5-5 μm.

[0026] In one embodiment of the present invention, the coating comprises a 0.2 - 1 μm thick TiAlN inner layer, a 1 - 4 μm thick nanolaminate of alternating TiAlN / TiSiN layers, and an optional 0.2 - 1 μm outer layer of either TiAlN or TiSiN. The layers of the nanolaminate are about 10 - 40 nm thick. Preferably, the composition of the TiAlN - layer of the coating is (Ti x Al 1-x )N, where 0.5 < x < 0.7, and the composition of the TiSiN - layer is (Ti y Si 1-y )N, where 0.05 < y < 0.25.

[0027] The present invention also relates to a method of making a cutting tool as described above. The method comprises a. preparing a powder composition comprising WC particles having an FSSS average particle size at intervals between 0.76 - 0.90 μm, preferably at intervals between 0.78 - 0.88 μm, most preferably at intervals between 0.79 - 0.85 μm, 3.50 - 4.20 wt% Co, 0.31 - 0.38 wt% Cr, and a raw material powder containing at least one of the following elements: V, Nb, Mo, and Fe , b. wet - milling the powder composition, a polymer molding agent, and a milling liquid to form a slurry, c. spray - drying the slurry to form a granulated product, d. shaping the granulated product into a green body having a desired shape and dimensions, e. sintering the green body to form a sintered body having a volume smaller than that of the green body .

[0028] The raw material powder containing at least one of the following elements V, Nb, Mo, and Fe means, in this specification, carbides, nitrides, carbonitrides, or metallic forms of those elements. Cr is usually added as the carbide powder Cr3C2. However, Cr can also be added as a nitride powder.

[0029] The powder composition is mixed with a polymer molding agent, usually PEG (polyethylene glycol) or wax, and a milling liquid to form a slurry. The milling liquid may be any liquid common in the field of making cemented carbides, and preferably a mixture of water and alcohol is used. The slurry is wet-milled in a mill, for example, in a ball mill or an attritor mill. The type of mill and the duration of the milling process are determined by those skilled in the art.

[0030] The slurry is subjected to a spray drying process to form granules. The granules are then formed into a green body by any of the following techniques: pressure molding, injection molding, and extrusion molding. Preferably, pressure molding is used.

[0031] The green body is then sintered to form a cemented carbide tool. Any sintering technique common in the field of sintering cemented carbides, such as vacuum sintering, HIP, etc., can be used. The sintering temperature is typically between 1300 and 1580 °C, preferably between 1360 and 1450 °C.

[0032] In one embodiment of the present invention, a wear-resistant coating having a thickness exceeding 1.5 μm is deposited on a substrate, and preferably the coating is deposited using PVD or CVD techniques. Most preferably, the cutting tool is provided with a homogeneous or nanolayered PVD coating having a thickness of 1.5 to 5 μm.

[0033] In one embodiment of the present invention, the coating deposited on the substrate is a PVD coating comprising a 0.2 to 1 μm thick TiAlN inner layer, a 1 to 4 μm thick nanolaminate of alternating TiAlN / TiSiN layers, and an optional 0.2 to 1 μm outer layer of either TiAlN or TiSiN. The layers of the nanolaminate are about 10 to 40 nm thick. Preferably, the composition of the TiAlN-layer of the coating is (Ti x Al 1-x )N, 0.5 < x < 0.7, and the composition of the TiSiN-layer is (Ti y Si 1-y)N, 0.05 <y<0.25である。

[0034] method Particle size determination of tungsten carbide powders The particle size of the tungsten carbide powder in the raw material was measured using a Fisher sub sieve sizer (FSSS) in accordance with ASTM B330-20.

[0035] Vickers hardness The hardness is determined by Vickers hardness and a load of 30 kg, HV30. The equipment used was a Future-Tech FV300 hardness tester with a CCD camera and a measuring computer. Five indentations were made and the hardness was calculated using the following formula: TIFF0007824973000001.tif13170P=Load in kilograms-force (kgf) d = average diagonal length of the indentation in mm The hardness is measured using a measuring computer that automatically calculates the hardness according to the above.

[0036] The distance between the indentations is at least three times the diagonal length of the indentations.

[0037] The accuracy of this method is ±2%.

[0038] coercive force Coercivity (Hc) is determined in a coercometer by measuring the reversal field required to completely demagnetize a sample magnetized to saturation. The coercivity of a sample is related to the volume fraction of cobalt (Co) in the sample and the grain size of the carbides in the sample.

[0039] S-value The degree of magnetic saturation can be expressed as an S-value. TIFF0007824973000002.tif9170 In the formula, σ s is μTm 3 kg -1 is the measured magnetic moment (Ma) of the binder phase, expressed as 16.1 μTm3 kg -1 is the magnetic moment of pure cobalt. The S-value depends on the W content in the binder phase and increases with decreasing tungsten content.

[0040] Contraction The shrinkage corresponds to the shrinkage of the pressed body during the sintering process, expressed as a percentage, and is measured in the horizontal plane. For green bodies produced by pressing the body, shrinkage is typically linear, about 17%.

[0041] fracture toughness Fracture toughness is determined using the Palmqvist method, also known as the Palmqvist toughness test, in accordance with ISO 28079:2009. This method determines the fracture toughness of cemented carbides in terms of the critical stress intensity factor, K 1c The fracture toughness is determined by performing a Vickers indentation using a load of 30 kgf and measuring the crack length from the corner of the indentation. Palmqvist fracture toughness, K 1c teeth, TIFF0007824973000003.tif11170, where: HV(N / mm 2 or MPa) is the Vickers hardness, P(N) is the indentation load, T (mm) is the total length of the crack.

[0042] The present invention will now be more closely described by way of a description of various aspects of the invention and with reference to the accompanying drawings. [Brief explanation of the drawings]

[0043] [Figure 1] FIG. 10 compares the tool life of a cutting tool insert according to the present disclosure and a comparative cutting tool insert at a cutting speed of 160 m / s. [Figure 2] 1 is a block diagram of an exemplary method for manufacturing a cutting tool insert, steps A to E of which correspond to steps a to e of claim 12. [Figure 3a-c]10A-10C are photographs of the wear of a cutting tool insert according to the present disclosure during machining testing after 5, 10, and 15 minutes, respectively. [Figure 4a-b] 1A and 1B are photographs of the wear of a comparative cutting tool insert during machining testing after 5 and 10 minutes, respectively. [Example]

[0044] Illustrative embodiments of the present disclosure will be described more fully below and with reference to the drawings. However, the devices and methods disclosed herein may be embodied in many different forms and should not be construed as limited to the aspects set forth herein. Cutting tool inserts were manufactured and analyzed. Some of the inserts were evaluated in cutting tests.

[0045] Manufacturing of cutting inserts Base material A cemented carbide substrate of the SNUN12048 formula was produced for sample AJ. Samples C and J were also produced by the CNMG formula. The substrates were produced from raw powders containing tungsten carbide (WC), cobalt (Co) powder, and chromium carbide (Cr3C2) powder, all according to the compositions shown in Table 1. Some samples also contained at least one additional powder element from the group consisting of vanadium (V), niobium (Nb), molybdenum (Mo), and iron (Fe). The composition ratios of each sample are shown in Table 1. The carbon concentration used in the samples was estimated from a phase diagram of a system of 4 wt% Co, 0.36 wt% Cr, and the remainder WC, and the knowledge that approximately 0.09 wt% C is lost during sintering.

[0046] The WC type used in samples A-H had an average particle size of 0.85 μm as measured by FSSS. For comparative sample J, the WC type had an average particle size of 0.6 μm as measured by FSSS. TIFF0007824973000004.tif72170

[0047] The powder for each sample was milled in a ball mill with a milling fluid and an organic binder, which was polyethylene glycol (PEG). The milling fluid consisted of water and ethanol. The resulting slurry was dried in a spray dryer and then pressed into inserts in a pressing operation at approximately 172 MPa. All powder batches for samples / variants except samples C and J were milled in 1 kg batches and spray dried in a laboratory sprayer. Samples C and J were milled and spray dried in full-scale production. The pressed samples were sintered in vacuum for 30 minutes, followed by 30 minutes at a temperature of approximately 1390°C at 30 Bar Ar pressure.

[0048] Coercive force (Hc), degree of magnetic moment (S), hardness (HV30), strength toughness (K 1C ), (ds), and the shrinkage from pressed powder to sintered powder were measured for the sintered samples. The results are shown in Table 2. TIFF0007824973000005.tif72170

[0049] All sintered samples in Table 2 had a porosity of A00 according to ISO 4499-4:2016(E), i.e. no pores were detected at a magnification of ×100.

[0050] Coating of samples C and J A 2.6 μm thick PVD coating was deposited on the substrate of Sample C and Sample J, and the samples will be referred to as Coated Sample C and Coated Sample J hereafter. The PVD coating has a 0.3 μm TiAlN inner layer adjacent to the substrate, followed by a 2.3 μm thick TiAlN / TiSiN nanolaminate, and a thin outer layer of TiSiN. The nanolaminate layer is approximately 20-40 nm thick. The composition of the TiAlN-layer of the coating is (Ti 0.33 Al 0.67 )N, and the composition of the TiSiN-layer is (Ti 0.90 Si 0.10 )N.

[0051] Cutting test Longitudinal turning was carried out by comparing the performance of coated specimens C and J under the same cutting conditions on hardened steel workpiece material. The chemical composition and mechanical properties of the workpiece material are shown in Tables 1 and 2, respectively. Cutting data used: Cutting speed, v c :160m / min Cutting feed, f: 0.20 mm / revolution Cutting depth: approx. 1mm Coolant was used.

[0052] Workpiece material: Uddeholm Orvar Supreme, reinforced to a hardness of 48 HRC.

[0053] The cutting tools used had the form of CNMG120408 inserts.

[0054] The tool life of the cutting tool inserts was determined by observing the flank wear (W) of the inserts after 5, 10, and 15 minutes of cutting time, see also Table 3 and Figure 1. The test was terminated when the flank wear exceeded a maximum value of 0.2 mm or when the tool broke.

[0055] Three edges of each tool were tested and the results can be seen in Table 3 below. TIFF0007824973000006.tif69170

[0056] 1 shows that the average tool life of the three cutting edges of the cutting tool of the present disclosure at a cutting speed of 160 m / min is at least twice the average tool life of the three cutting edges of the comparative cutting tool. FIG. 1 also shows that the cutting edge with the shortest tool life of the cutting tool of Sample C of the present disclosure is longer than the longest tool life of the comparative cutting tool, Sample J.

[0057] Figures 3a-3c show edge C-2 after 5, 10, and 15 minutes of machining. As can be seen, the edge did not exceed 0.2 mm of flank wear before the control at 15 minutes.

[0058] Figures 4a and 4b show edge J-4 after 5 and 10 minutes of machining, respectively. As can be seen in Figure 4b, the flank was already greater than 0.2 mm in the control after 10 minutes of machining.

[0059] As can be seen from the machining tests, Sample C outperforms Comparative Sample J in turning hardened steel.

[0060] The combination of low cobalt content and coarse WC grain size results in cutting inserts with both improved cutting performance as well as improved properties when sintered and shrunk.

Claims

1. 1. A cutting tool comprising a substrate (2) of cemented carbide, the cemented carbide comprising hard constituents of tungsten carbide (WC) in a metallic binder phase (4) comprising cobalt (Co), the cemented carbide further comprising chromium (Cr) and at least one further element from the group consisting of vanadium (V), niobium (Nb), molybdenum (Mo), and iron (Fe), - the Co-content is between 3.50 and 4.20 wt.% of the cemented carbide, - the Cr content is between 0.31 and 0.38 wt.% of the cemented carbide; - the WC-content is at least 95.22 wt.% of the cemented carbide, - The cemented carbide has a coercive force of 26 to 32 kA / m A cutting tool characterized by:

2. 2. The cutting tool of claim 1, wherein the cemented carbide comprises 0.01 to 0.09 wt % V.

3. 2. The cutting tool of claim 1, wherein V+Nb is a maximum of 0.12 wt% of the cemented carbide.

4. 2. The cutting tool of claim 1, wherein the V+Nb+Mo+Fe content is max 0.2 wt% of the cemented carbide.

5. 5. A cutting tool according to any one of claims 1 to 4, wherein the cemented carbide has a hardness of 1960-2020 HV30.

6. Fracture toughness of 8.6 to 9.7 MPa －１／２ The cutting tool according to any one of claims 1 to 5, wherein

7. 7. The cutting tool according to claim 1, wherein the coercive force is 27 to 31 kA / m.

8. Cutting tool according to any one of the preceding claims, wherein the Cr-content of the binder phase is 8-10 wt%.

9. 9. The cutting tool of claim 1, wherein the coating is deposited on a substrate.

10. 10. The cutting tool of claim 9, wherein the coating is a PVD or CVD coating.

11. A method for manufacturing a cemented carbide cutting tool according to any one of claims 1 to 10, comprising the steps of: (a) WC grains having an FSSS average grain size in the interval 0.76-0.90 μm; 3.50 to 4.20 wt. % Co, 0.31 to 0.38 wt% Cr, and A raw material powder containing at least one of the following elements: V, Nb, Mo, and Fe. providing a powder composition comprising: (b) wet milling the powder composition, the polymeric bulking agent, and the milling fluid to form a slurry; (c) spray drying the slurry to form granules; (d) forming the granulation into a green body of desired shape and size; (e) sintering the green body to form a sintered body having a volume smaller than that of the green body; A method comprising:

12. 12. The method of claim 11, wherein the forming of the green body is performed by any one of pressing, injection molding, and extrusion.

13. - coating the sintered body with a wear-resistant coating having a thickness of more than 1.5 μm The method of claim 12 further comprising:

14. - Coating the sintered body by PVD or CVD 14. The method of claim 13, further comprising:

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