Cemented carbide for cutting tool, and cutting tool comprising same

Abstract

The present invention relates to a cemented carbide for a cutting tool, and a cutting tool comprising same. The cemented carbide for a cutting tool, of the present invention, comprises 86-94.8 wt% of WC, 5-12 wt% of Co and 0.2-2.0 wt% of at least one metal element selected from among V, Cr, Nb and Ta, the SMS value of the cemented carbide obtained by [relation 1] is 40-80%, the fraction of an FCC crystal structured Co phase included in the cemented carbide is 60% or more, and the fraction of a phase having a misorientation angle of 45° or less in the FCC crystal structured Co phase is 58-66%. [Relation 1] SMS = saturation magnetization value of sintered body × 100 / TMS (TMS = 2010 × mass proportion of Co)

Description

Cemented carbide for cutting tools and cutting tools containing the same

[0001] The present invention relates to a cemented carbide for cutting tools and a cutting tool comprising the same.

[0002]

[0003] When machining stainless steel and heat-resistant alloys, which are classified as difficult-to-machine materials, plastic deformation of the tool occurs due to strong cutting resistance and high cutting temperatures. Additionally, severe welding and chip detachment caused by chips damage the edge of the tool, significantly reducing tool life. To address these issues, it is necessary to improve the resistance to plastic deformation and the resistance to chip detachment of the cutting tool.

[0004] Cemented carbide for cutting tools is a composite material consisting of a hard phase of WC and a metal phase of Co, and its mechanical properties basically depend on the WC grain size and the amount of Co. To simultaneously improve the hardness and toughness of cemented carbide, methods to refine WC grains are widely used. When carbides such as VC and Cr3C2 are added to the cemented carbide raw materials as grain growth inhibitors, the growth of WC grains is delayed during sintering. At the same time, as the grain growth inhibitor decomposes and is dissolved in Co, solid solution strengthening occurs, which has the effect of improving resistance to plastic deformation.

[0005] However, when carbides are added during the manufacture of cemented carbide, the Total Carbon (TC) of the sintered cemented carbide increases. Furthermore, during machining, carbon migration occurs due to friction and diffusion between the workpiece and the cutting tool; the more active the carbon migration, the greater the welding. In other words, as the TC increases, there is a problem of increased welding of the cutting tool.

[0006] Since difficult-to-machine materials such as stainless steel, titanium, and Inconel have a lower carbon content compared to steel or cast iron, lowering the TC of the cemented carbide reduces the carbon concentration gradient with the workpiece, thereby reducing carbon migration and improving welding.

[0007] However, when carbide-based grain growth inhibitors are added, TC actually increases significantly; therefore, to solve this, metal elements such as V and Cr can be added to reduce TC. The added metals do not undergo a decomposition process and are immediately dissolved in Co, so the solid solution strengthening effect is greater. They combine with carbon present in Co and exist in the form of carbides at the boundary between WC and Co, thereby inhibiting WC grain growth.

[0008] However, if the TC of the cemented carbide is low, the hardness increases and the toughness decreases, resulting in a disadvantage of reduced chipping resistance and fracture resistance.

[0009]

[0010] The objective of the present invention is to provide a cemented carbide for cutting tools and a cutting tool containing the same, which reduces welding by reducing the amount of Total Carbon (TC) by adding a metal element as a WC grain growth inhibitor, and simultaneously improves the increase in hardness and decrease in toughness of the cemented carbide caused by the addition of the metal element by controlling the fraction of the FCC phase of the binder Co and the fraction of the phase with a grain misorientation angle of 45˚ or less.

[0011] The problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art from the description below.

[0012]

[0013] To achieve the objective of the present invention, the present invention provides a cemented carbide according to (1) to (3) and a cutting tool according to (4).

[0014] (1) A cemented carbide for a cutting tool comprising 86 to 94.8 wt% WC, 5 to 12 wt% Co, and 0.2 to 2.0 wt% of one or more metal elements selected from V, Cr, Nb, and Ta, wherein the SMS value obtained by [Equation 1] below of the cemented carbide is 40 to 80%, the fraction of the phase having an FCC crystal structure of the Co phase included in the cemented carbide is 60% or more, and the fraction of the phase having a misorientation angle of 45˚ or less among the Co phases having the FCC crystal structure is 58 to 66%.

[0015] [Equation 1]

[0016] SMS = Saturation magnetization value of sintered body × 100 / TMS (TMS = 2010 × mass ratio of Co)

[0017] (2) In (1), the cemented carbide is a cemented carbide for cutting tools that has undergone vacuum heat treatment at 500 to 700°C for 2 to 12 hours after sintering.

[0018] (3) A cemented carbide for cutting tools, wherein, in (1), there is no abnormal structure such as an eta (η) phase or free carbon within the cemented carbide structure.

[0019] (4) A cutting tool comprising one or more hard films formed by PVD on a cemented carbide base material of any one of (1) to (3).

[0020]

[0021] The cemented carbide and cutting tool according to the present invention have the following effects.

[0022] Since the cemented carbide according to the present invention has metal elements such as V and Cr added, the TC of the cemented carbide is lowered, and in particular, welding can be increased during machining of difficult-to-machine materials such as stainless steel, titanium, and Inconel, which have a lower carbon content compared to cast iron.

[0023] In addition, when metal elements such as V and Cr are added as grain growth inhibitors, the hardness increases and toughness decreases, which leads to a decline in the chipping resistance and fracture resistance of cutting tools. However, by controlling the FCC phase fraction of the Co phase included in the cemented carbide and simultaneously controlling the misorientation fraction of the Co phase to facilitate slip, the toughness of the cemented carbide can be increased, thereby offsetting the effect of the toughness reduction caused by the addition of metal elements, and thus, chipping resistance and fracture resistance can be improved while reducing welding.

[0024] The effects of the present invention are not limited to those mentioned above, and other unmentioned effects will be clearly understood by a person skilled in the art from the description below.

[0025]

[0026] Figure 1 is an image after a cutting evaluation of a cutting tool made of a cemented carbide according to Example 9 of the present invention and a cemented carbide according to Comparative Example 7.

[0027]

[0028] Embodiments of the present invention are described below with reference to the attached drawings so that those skilled in the art can easily implement them. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0029] In addition, to clearly explain the present invention in the drawings, parts unrelated to the explanation have been omitted, and similar parts throughout the specification have been given similar reference numerals.

[0030] Throughout this specification, when a part is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0031] Terms of degree used in this specification, such as “about,” “substantially,” etc., are used to mean at or near the stated value when inherent manufacturing and material tolerances are presented in the stated meaning, and are used to prevent unscrupulous infringers from unfairly exploiting the disclosure in which precise or absolute values ​​are mentioned to aid in understanding the invention.

[0032] Throughout this specification, the term “combination thereof” included in a Markush-style expression means one or more mixtures or combinations selected from the group consisting of components described in the Markush-style expression, and means including one or more selected from the group consisting of said components. Throughout this specification, the description “A and / or B” means “A or B, or A and B”.

[0033]

[0034] [Cemented Carbide]

[0035] The cemented carbide for a cutting tool according to the present invention comprises 86 to 94.8 wt% of WC, 5 to 12 wt% of Co, and 0.2 to 2.0 wt% of one or more metal elements selected from V, Cr, Nb, and Ta, wherein the SMS value obtained by [Equation 1] below is 40 to 80%, the fraction of the phase having an FCC crystal structure of the Co phase included in the cemented carbide is 60% or more, and the fraction of the phase having a misorientation angle of 45˚ or less among the Co phases formed with the FCC crystal structure is 58 to 66%.

[0036] [Equation 1]

[0037] SMS = Saturation magnetization value of sintered body × 100 / TMS (TMS = 2010 × mass ratio of Co)

[0038]

[0039] The WC (tungsten carbide) included in the cemented carbide of the present invention is a wear-resistant hard phase. If included in an amount of less than 86 weight%, it is difficult to obtain the wear resistance required for cutting tools used for the application of the present invention, and if included in an amount exceeding 94.8 weight%, the hardness increases and the bonding strength may decrease due to a lack of binder metal. Therefore, it is preferable to include it in an amount of 86 to 94.8 weight%.

[0040] Furthermore, when the average grain size of WC is less than 0.1㎛, while there is an improvement in hardness and wear resistance due to grain refinement, brittleness increases, leading to a significant decrease in toughness and fracture resistance. From a manufacturing perspective, ultrafine WC particles do not transmit sufficient pressure during pressing, resulting in a large density gradient within the material. Consequently, this can cause uneven shrinkage during the sintering process, and inter-particle aggregation occurs easily, making it difficult to obtain a uniform microstructure. Conversely, when the average grain size of WC exceeds 12㎛, thermal conductivity increases, which may improve heat crack resistance but decreases hardness; moreover, large WC particles can act as crack initiation points, potentially lowering toughness. Additionally, during the sintering process, liquid Co must spread between WC particles via capillary action to achieve densification; however, due to the wide spaces between the particles, the liquid Co cannot be distributed evenly, which can lead to an increase in porosity. Therefore, the average grain size of WC can be 0.1 to 12 μm, and it is preferable to be 0.4 to 9 μm.

[0041] Considering toughness and thermal conductivity, it is preferable that the binder phase used in the cemented carbide of the present invention be composed of cobalt (Co). In addition, if the content of the binder Co is less than 5 weight%, the bonding strength binding the WC particles, which are the wear-resistant hard phase, decreases and the toughness of the cemented carbide decreases, and if it exceeds 12 weight%, the wear resistance decreases due to a lack of the wear-resistant hard phase, so it is preferable that it be included in an amount of 5 to 12 weight%.

[0042] The present invention may include one or more metal elements selected from V, Cr, Nb, and Ta. The metal element dissolves in Co to produce a solid solution strengthening effect, and at the same time combines with carbon present in Co to form fine carbides at the boundary between WC and Co, thereby inhibiting the grain growth of WC during the sintering process. If the content of the metal element is less than 0.2 wt%, the grain growth inhibition effect is insufficient, and if it is included in excess of 2.0 wt%, excessive grain growth inhibition and solid solution strengthening effects may increase brittleness and reduce toughness, and the TC of the cemented carbide becomes too low, resulting in the formation of the emta phase (Me), which is a brittle material. 12 Since C, Me6C) can be formed, it is preferable to include 0.2 to 2.0 weight%.

[0043] If the SMS obtained by [Equation 1] above is not within the range of 40 to 80%, abnormal structures such as delta phase and free carbon may be generated within the microstructure of the base material, or plastic deformation resistance may not be sufficient, which is undesirable, so it is desirable to maintain the SMS value within the above range.

[0044] When a metal element is added to a cemented carbide, the hardness of the cemented carbide increases and the toughness decreases, resulting in reduced chipping resistance and fracture resistance. In the cemented carbide according to the present invention, the reduction in chipping resistance and fracture resistance caused by the addition of a metal element to the Co phase, which is the binder phase, is suppressed by controlling the slip characteristics through controlling the crystal structure of the Co phase, which is the binder phase, and controlling the misalignment fraction of the grain boundaries. To this end, the fraction of the FCC phase is maintained at 60% or more, while simultaneously maintaining the proportion of low-angle boundaries, where the misalignment ratio between grains formed in the FCC phase is 45° or less, within the range of 58% to 66%. Since chipping resistance decreases when the fraction with a misalignment ratio of 45° or less is less than 58% and plastic deformation resistance decreases when it exceeds 66%, it is preferable that the fraction of low-angle boundaries with a misalignment ratio of 45° or less be 58% to 66%.

[0045] The above cemented carbide may preferably undergo vacuum heat treatment at 500 to 700°C for 2 to 12 hours after the sintering process. Vacuum heat treatment is intended to more stably control the crystal structure of the Co phase and the misalignment angle between grains. Co is in a stable FCC phase at 400 to 500°C or higher, and during heat treatment, as the grains of the Co phase grow, the grain boundary area is reduced and the misalignment angle between grains decreases. Since the FCC fraction of the Co phase and the misalignment angle between grains vary slightly depending on the composition and sintering conditions of the cemented carbide, treatment under the above heat treatment conditions is advantageous for stably achieving an FCC fraction of 60% or more and a low-angle grain boundary fraction of 58 to 66% with a misalignment angle of 45° or less.

[0046] The cemented carbide according to the present invention may be free of abnormal structures, such as the eta (η) phase or free carbon, within its microstructure. Here, 'eta phase' refers to M 12It means a carbide phase having the composition of C and / or M6C, where M may include one or more metals selected from tungsten (W), tantalum (Ta), niobium (Nb) and cobalt (Co).

[0047]

[0048] [Cutting Tool]

[0049] The above cemented carbide may be used as a base material and may further include a hard film formed on its surface by physical vapor deposition (PVD). The hard film may be formed as a single layer or a multilayer structure of two or more layers.

[0050] If the total thickness of the hard film is less than 1㎛ or greater than 25㎛, it may be difficult to achieve the physical properties required for the hard film, so it is preferable that the thickness be 1 to 25㎛, and more preferable that the thickness of the hard film be 10 to 20㎛.

[0051]

[0052] <Example>

[0053] Manufacturing of cemented carbide

[0054] In the example, raw WC powders with an average particle size of 0.8 μm and an average particle size of 2.0 μm were prepared. Additionally, Co powder was prepared as the binder metal, and V, Cr, Ta, and Nb powders were prepared as grain growth inhibitors. The powders prepared in this manner were mixed using a mixing device under the same mixing conditions (10 to 15 hours), pressed with a mold to manufacture an insert, and then subjected to HIP (hot isostatic processing) sintering at 1450°C to manufacture a cemented carbide insert.

[0055] For the comparative example, VC, Cr3C2, and TaNbC powders were used as grain growth inhibitors, and cemented carbide inserts were manufactured in the same manner as the embodiments of the present invention.

[0056] Table 1 below shows the composition of cemented carbide produced according to the embodiments and comparative examples of the present invention.

[0057] Classification Composition (Wet%) WCCoVCrTaNbVCCr3C2TaNbC 0.8㎛ 2.0㎛ Example 1 89-10 1.0------Example 2 89-10 1.0-----Example 3 89-10 1.0----Example 4 89-10 1.0---Example 5 89-10 0.5 0.5-----Example 6 87-12 1.0-----Example 7 87-12 0.5 0.5---Example 8 87.5 12 0.5---- -Example 9-8712-1.0-----Example 10-86.512-1.5-----Comparative Example 189-10----1.0--Comparative Example 289-10-----1.0-Comparative Example 389-10----0.50.5-Comparative Example 487-12-----1.0-Comparative Example 587-12------1.0Comparative Example 6-87.512-----0.5-Comparative Example 7-8712-----1.0-Comparative Example 8-86.512-----1.5-

[0058] Table 2 below shows the results of analyzing the physical properties of cemented carbide alloys manufactured according to the embodiments and comparative examples of the present invention.

[0059] Classification Physical Properties Saturation Magnetization (4πσ) SMS Coercivity (Hc) Hardness (Hv) Tightness (TRS) Example 1 13869% 2671715391 Example 2 13266% 2601694406 Example 3 14874% 2411633384 Example 4 14572% 2431650388 Example 5 13366% 2631648402 Example 6 16970% 2481540386 Example 7 18476% 2441485375 Example 8 19179% 1761424390 Example Example 9 17372%1831498410 Example 10 16066%1971521388 Comparative Example 1 17286%2411678395 Comparative Example 2 16582%2351624421 Comparative Example 3 16884%2371635403 Comparative Example 4 21991%2231506348 Comparative Example 5 20585%2121455330 Comparative Example 6 21887%1611395400 Comparative Example 7 20989%1671428379 Comparative Example 8 20092%1751439359

[0060] As can be seen in Table 2 above, the cemented carbide of the example has lower overall saturation magnetization (4πσ) and SMS compared to the cemented carbide of the comparative example. This is because metal elements such as V, Cr, Ta, and Nb are dissolved in Co, which is a ferromagnetic material, and hinder magnetization by an external magnetic field, thereby lowering the saturation magnetization. Even if metal carbides such as VC, Cr3C2, and TaNbC are added as in the comparative example, the saturation magnetization decreases, but the saturation magnetization and SMS do not decrease significantly due to the low solid solution content.

[0061] Looking at the saturation magnetization of Examples 1 to 4, it can be seen that the saturation magnetization is lower when V and Cr are added compared to Ta and Nb, indicating that V and Cr have higher solid solubility in Co. This phenomenon is consistent regardless of changes in WC particle size and Co content, or the addition of multiple metal elements, as seen in Examples 5, 6, 7, and 9. In Examples 8 to 10, as the Cr content increases, the saturation magnetization and SMS decrease, which is due to the increase in the solid solubility of Cr.

[0062] Meanwhile, the cemented carbide of the example generally has higher coercivity (Hc), hardness, and flexural strength (TRS) compared to the cemented carbide of the comparative example. This is because metal elements such as V, Cr, Ta, and Nb combine with C in the matrix to form fine metal carbides, and these carbides are mostly formed at the WC and Co boundaries, thereby inhibiting the grain growth of WC. Even if metal carbides such as VC, Cr3C2, and TaNbC are added as in the comparative example, the coercivity increases, but the coercivity does not increase significantly due to the low solid solution content. Hardness increases due to the grain refinement effect, and flexural strength also increases due to solid solution strengthening of Co, phase transformation, and changes in grain boundaries.

[0063] Looking at the coercivity and hardness of Examples 1 to 4, it can be seen that the cases with added V and Cr have higher coercivity and hardness compared to Ta and Nb, indicating that V and Cr have a greater grain growth inhibition effect. This phenomenon is observed consistently regardless of changes in WC particle size and Co content, or the addition of multiple metal elements, as seen in Examples 5, 6, 7, and 9. In Examples 8 to 10, coercivity increases as the Cr content increases, which is due to greater grain refinement. However, if grain refinement occurs too much, the hardness may increase excessively, potentially leading to a decrease in flexural strength.

[0064] Table 3 below shows the fraction of the phase having an FCC crystal structure among the Co phases of cemented carbide produced according to the embodiments and comparative examples of the present invention, and the fraction of low-angle grain boundaries in which the misorientation angle between grains is 45° or less.

[0065] Classification Co-FCC Phase Fraction Misorientation Angle 45˚ or Less Low Angle Grain Boundary Fraction Example 1 69% 59% Example 2 72% 62% Example 3 60% 58% Example 4 63% 58% Example 5 72% 60% Example 6 70% 63% Example 7 62% 58% Example 8 66% 59% Example 9 70% 61% Example 10 81% 65% Comparative Example 1 42% 54% Comparative Example 2 48% 57% Comparative Example 3 44% 55% Comparative Example 4 45% 54% Comparative Example 5 42% 52% Comparative Example 6 43% 55% Comparative Example 7 45% 57% Comparative Example 8 50% 60%

[0066] As confirmed in Table 3 above, the cemented carbide of the example has a higher FCC fraction in the Co phase and a higher fraction of low-angle grain boundaries with a misorientation angle of 45° or less compared to the cemented carbide of the comparative example. This is because metallic elements such as V, Cr, Ta, and Nb act as elements that stabilize FCC in the Co phase.

[0067] As in the comparative example, when metal carbides such as VC, Cr3C2, and TaNbC are added, the reason the FCC fraction of Co and the fraction of low-angle grain boundaries with a misorientation angle of 45° or less are low is that the solid solution content is low and the Total Carbon (TC) of the cemented carbide increases. Generally, if the TC is high, the FCC fraction decreases, and consequently, the fraction of low-angle grain boundaries decreases. In other words, the FCC fraction and the fraction of low-angle grain boundaries are in a proportional relationship; the FCC crystal structure is a close-packed structure where each atom is packed as closely as possible, resulting in less space for defects and impurities within the crystal, and minimizes directional differences between grains due to high symmetry. In addition, the FCC crystal structure has high stacking fault energy, such as easy slip and difficulty in twin formation, making defect formation difficult, so the misorientation angle mainly exists at low angles.

[0068]

[0069] Preparation of hard coatings

[0070] A hard film was formed on the surface of a hard substrate made of a cemented carbide alloy manufactured according to the embodiments and comparative examples of the present invention using arc ion plating, which is a physical vapor deposition (PVD) method.

[0071] After wet microblasting and washing with ultrapure water, the base material was dried and mounted along its circumference at a predetermined radial distance from the central axis on a rotary table inside the coating furnace. The initial vacuum pressure inside the coating furnace was 8.5 × 10⁻⁶ -5The pressure was reduced to below Torr, and after heating to 500 to 600°C, a pulse bias voltage of -300 to -200V was applied to a substrate rotating on the rotary table under an Ar gas atmosphere to perform ion bombardment for 30 to 60 minutes. The gas pressure for coating was maintained at 50 mTorr or less or 40 mTorr or less, and a substrate bias voltage of -100 to -20V was applied during coating.

[0072] More specifically, for coating, AlTi alloy targets were combined according to composition and arranged in 2 to 4 faces inside the coating furnace, and one or more hard AlTiN films were deposited under conditions of a bias voltage of -60 to -30V, an arc current of 75 to 150A, N2 as a reaction gas, and a pressure of 10 to 30mTorr. Coating conditions may vary depending on equipment characteristics and conditions.

[0073]

[0074] Cutting performance evaluation

[0075] To evaluate the adhesion resistance, plastic deformation resistance, and fracture resistance of PVD-coated cemented carbide inserts manufactured according to the embodiments and comparative examples of the present invention, milling tests were performed under the following conditions, and the results are shown in Table 4 below.

[0076] (1) Evaluation of austenitic stainless steel

[0077] Workpiece: STS316

[0078] Sample Model Number: LNMX060310R-ML

[0079] Cutting speed: 120 m / min

[0080] Cutting feed: 0.6mm / tooth

[0081] Axial depth: 0.8mm

[0082] Radial depth: 33mm

[0083] When machining austenitic stainless steel, welding and tearing generally occur frequently, and as cracking and chipping easily occur at the insert cutting boundary due to work hardening, the anti-seizure and anti-chip properties of cemented carbide have a significant impact on machining performance.

[0084]

[0085] (2) Evaluation of titanium alloys

[0086] Workpiece: Ti6Al4V

[0087] Sample Model Number: LNMX060310R-ML

[0088] Cutting speed: 60 m / min

[0089] Cutting feed: 0.6mm / tooth

[0090] Axial depth: 0.6mm

[0091] Radial depth: 33mm

[0092] During the machining of titanium alloys, significant plastic deformation occurs at the cutting edge along with wear, which subsequently leads to chipping; consequently, the wear resistance, plastic deformation resistance, and chipping resistance of cemented carbide have a significant impact on cutting performance.

[0093]

[0094] (3) Evaluation of Ni-based heat-resistant alloys

[0095] Workpiece: Inconel718

[0096] Sample Model Number: LNMX060310R-ML

[0097] Cutting speed: 30 m / min

[0098] Cutting feed: 0.5mm / tooth

[0099] Axial depth: 0.6mm

[0100] Radial depth: 33mm

[0101] When machining Ni-based heat-resistant alloys, welding and tearing occur frequently from the beginning, and subsequently progress rapidly to wear, plastic deformation, and fracture; as a result, the resistance to welding, plastic deformation, and fracture of the cemented carbide has a significant impact on the machining performance.

[0102]

[0103] Table 4 below shows the results evaluated under the above cutting tool evaluation conditions.

[0104] Classification STS316 Ti6Al4V Inconel718 Machining Length (mm) Machining Length (mm) Machining Length (mm) Example 1 4,500 3,900 1,200 Example 2 5,400 4,500 1,300 Example 3 5,100 4,500 1,400 Example 4 4,500 3,600 1,400 Example 5 4,800 4,500 1,300 Example 6 6,300 3,900 1,500 Example 7 5,100 3,300 1,600 Example 8 6,900 4 ,200 2,000 Example 9 7,200 4,500 1,800 Example 10 6,000 4,200 1,600 Comparative Example 1 2,700 1,500 700 Comparative Example 2 2,700 2,100 800 Comparative Example 3 3,000 2,100 800 Comparative Example 4 3,300 1,800 900 Comparative Example 5 3,300 1,800 1,000 Comparative Example 6 3,600 3,000 1,200 Comparative Example 7 3,600 3,000 1,200 Comparative Example 8 3,000 2,400 1,100

[0105] As confirmed in Table 4 above, the cemented carbide of the example exhibits superior overall machinability compared to the cemented carbide of the comparative example. This is because the example has higher hardness and flexural strength than the comparative example, as well as a higher fraction of the FCC of the Co phase and a higher fraction of low-angle grain boundaries with a misorientation angle of 45° or less. Although the cemented carbide of the example may exhibit brittleness due to its high hardness, its high toughness in terms of crystal structure offsets this, resulting in excellent wear resistance, resistance to plastic deformation, and resistance to fracture. Furthermore, having a low TC results in a smaller carbon concentration gradient with the workpiece, which reduces carbon migration and thus exhibits excellent resistance to adhesion.

[0106] Accordingly, the cemented carbide according to the present invention can reduce welding by reducing the amount of Total Carbon (TC) by adding a metal element as a WC grain growth inhibitor, while simultaneously improving the increase in hardness and decrease in toughness of the cemented carbide caused by the addition of the metal element by controlling the FCC fraction of the Co phase as a binder and the fraction of the phase with an intergranular misorientation angle of 45° or less, thereby providing excellent cutting performance when machining stainless steel, titanium, and Inconel, which are classified as difficult-to-machine materials.

Claims

1. A cemented carbide alloy for cutting tools comprising 86 to 94.8 wt% WC, 5 to 12 wt% Co, and 0.2 to 2.0 wt% of one or more metal elements selected from V, Cr, Nb, and Ta, The SMS value of the above cemented carbide obtained by the following [Equation 1] is 40 to 80%, and The fraction of the phase having an FCC crystal structure of Co included in the above cemented carbide is 60% or more, and A cemented carbide for cutting tools having a fraction of phases with a misorientation angle of 45˚ or less among the Co phases composed of the above FCC crystal structure, of 58 to 66%. [Equation 1] SMS = Saturation magnetization value of sintered body × 100 / TMS (TMS = 2010 × mass ratio of Co) 2. In Paragraph 1, The above cemented carbide is a cemented carbide for cutting tools that has undergone vacuum heat treatment at 500 to 700°C for 2 to 12 hours after sintering.

3. In Paragraph 1, A cemented carbide for cutting tools that does not have abnormal structures such as an eta (η) phase or free carbon within the above cemented carbide structure.

4. A cutting tool comprising one or more hard films formed by the PVD method on a cemented carbide base material described in any one of claims 1 to 3.

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