JP7013948B2 - Base material and cutting tools - Google Patents

Description

The present invention relates to a substrate and a cutting tool.

As a product that requires high hardness, for example, there is a cutting tool. Cemented carbide is used as a hard material used in such products.

Here, cutting tools and the like are often exposed to high temperatures, and at high temperatures, wear of the cemented carbide is accelerated, and it may not be possible to achieve the life of the desired length of the product. Therefore, cemented carbide used for cutting tools and the like is required to have wear resistance at high temperatures.

In order to impart wear resistance at high temperatures to a cutting tool, for example, Patent Document 1 (Japanese Unexamined Patent Publication No. 9-125229) has a technique for forming a coating film having excellent wear resistance at high temperatures on a substrate. It has been disclosed. However, recently, there is an increasing need for machining difficult-to-cut materials such as heat-resistant alloys, and improvement in cutting speed is also required, and cutting tools are being used in higher temperature environments. Even with a cutting tool coated with a coating as disclosed in Patent Document 1, if the coating is worn or destroyed by use in a higher temperature environment and the base material is exposed, the wear resistance sharply decreases. Resulting in. Therefore, it is desired to further improve the wear resistance of the base material itself at high temperatures.

By using a sintered body (cemented carbide) containing a material having excellent high temperature resistance such as Al ₂ O ₃ and an intermetallic compound phase containing Al as the material of the base material of the cutting tool, the base material of the cutting tool itself The wear resistance at high temperatures can be improved (see, for example, Patent Document 2 (Japanese Unexamined Patent Publication No. 2014-208888)).

Japanese Unexamined Patent Publication No. 9-125229 Japanese Unexamined Patent Publication No. 2014-208888

However, cutting tools are also required to have fracture resistance. Here, the cemented carbide containing Al ₂ O ₃ has extremely high heat resistance (wear resistance at high temperature), but the fracture resistance is not sufficient. On the other hand, the cemented carbide containing the intermetallic compound phase containing Al has a certain degree of fracture resistance, but does not have extremely high heat resistance (wear resistance at high temperature) as _high as _Al2O3 .

Therefore, an object of the present disclosure is to provide a base material made of cemented carbide having extremely high heat resistance (wear resistance at high temperature) and improved fracture resistance, and a cutting tool provided with the same. Is.

The substrate according to one aspect of the present invention is made of a cemented carbide having a first hard phase, a second hard phase and a bonded phase. The first hard phase is made up of WC particles and the second hard phase is made up of Al ₂ O ₃ . The bound phase comprises at least one metal selected from Co and Ni. The base material has a surface layer that does not contain the second hard phase on its surface, and the thickness a of the surface layer and the thickness b of the base material satisfy 0.01 ≦ 2a / b ≦ 0.50.

The cutting tool according to the uniform state of the present disclosure includes the above-mentioned base material.

According to the above, it is possible to provide a base material made of cemented carbide having extremely high heat resistance (wear resistance at high temperature) and improved fracture resistance, and a cutting tool provided with the same.

[Explanation of Embodiment of the present invention]
First, embodiments of the present invention will be listed and described.

In this specification, the notation in the form of "A to B" means the upper and lower limits of the range (that is, A or more and B or less), and there is no description of the unit in A and the unit is described only in B. , The unit of A and the unit of B are the same.

[1] The substrate according to one aspect of the present disclosure is made of a cemented carbide having a first hard phase, a second hard phase and a bonded phase. The first hard phase is made up of WC particles and the second hard phase is made up of Al ₂ O ₃ . The bound phase comprises at least one metal selected from Co and Ni. The base material has a surface layer that does not contain the second hard phase on its surface, and the thickness a of the surface layer and the thickness b of the base material satisfy 0.01 ≦ 2a / b ≦ 0.50. The base material has improved wear resistance and fracture resistance at high temperatures.

[2] The bonded phase preferably contains an Al bonded phase containing at least one metal selected from Co and Ni, Al and C. At this time, in an arbitrary cross section of the base material, the area ratio c of the Al-bonded phase occupying the area of the surface layer and the area ratio d of the Al-bonded phase occupying the area inside the base material other than the surface layer are c. It is preferable that / d ≧ 1.0 is satisfied. Since the Al-bonded phase is excellent in plastic deformation resistance at high temperature, deformation of the cutting edge of the base material can be suppressed by increasing the ratio of the Al-bonded phase in the surface layer, and the wear resistance of the base material is further improved. Because.

[3] The Al-bonded phase preferably further contains W. This is because the solid solution of W in the Al-bonded phase increases the high-temperature hardness of the Al-bonded phase and further improves the wear resistance at high temperatures.

[4] The superhard alloy is at least one metal selected from the group consisting of Group 4 elements, Group 5 elements and Group 6 elements of the Periodic Table, and at least one selected from the group consisting of C, N, O and B. It is preferable to further contain a third hard phase composed of a compound with the element of the above, or a solid solution thereof (however, excluding WC). By including the third hard phase, the cemented carbide maintains the wear resistance at high temperature, suppresses the generation of cracks due to thermal or mechanical impact, and has oxidation resistance and resistance to the work material. This is because the reactivity is further improved.

[5] The cutting tool according to the present disclosure includes a base material made of the above-mentioned cemented carbide. By using a base material made of the above-mentioned cemented carbide having improved wear resistance and fracture resistance at high temperatures, it is possible to extend the life of the cutting tool.

[6] The cutting tool preferably has a coating on at least a part of the surface of the base material. By providing the coating film, the wear resistance of the cutting tool is further improved, and the life of the cutting tool can be further extended.

[Details of Embodiments of the present disclosure]
Hereinafter, embodiments of the present disclosure (hereinafter referred to as “the present embodiment”) will be described. However, the following description does not limit this disclosure. Further, when a compound or the like is represented by a chemical formula in the present specification, it is intended to include all conventionally known atomic ratios when the atomic ratio is not particularly limited, and is not necessarily limited to those in the stoichiometric range.

<Base material>
The substrate according to this embodiment is made of a cemented carbide having a first hard phase, a second hard phase and a bonded phase. The cemented carbide may contain components other than these as long as they are contained. The first hard phase is made up of WC particles and the second hard phase is made up of Al ₂ O ₃ . The bound phase comprises at least one metal selected from Co and Ni. For example, the first hard phase is composed of an aggregate of a plurality of particles, and the bonded phase is scattered in the first hard phase as particles.

The substrate has a surface layer on its surface that does not contain a second hard phase. A second hard phase having excellent wear resistance at high temperature but poor toughness due to low toughness exists inside the base material, and a surface layer not containing the second hard phase exists on the surface of the base material. Therefore, it is possible to achieve both the chipping resistance of the base material and the wear resistance at high temperatures. The base material may have at least a part of its surface covered with a surface layer, and the entire surface of the base material may be covered with a surface layer.

Further, in the base material, the thickness a of the surface layer and the thickness b of the base material satisfy 0.01 ≦ 2a / b ≦ 0.50. The thickness a of the surface layer means the length of the surface layer in a direction perpendicular to the main surface of the base material (a surface having a larger area than other surfaces). Further, the thickness b of the base material is the length of the base material in the direction perpendicular to the main surface of the base material. When 2a / b <0.01, the effect of improving the fracture resistance of the base material by the surface layer cannot be sufficiently exhibited. On the other hand, when 2a / b> 0.50, the effect of improving the wear resistance of the base material at high temperature by the second hard phase inside the base material cannot be sufficiently obtained. A and b preferably satisfy 0.07 <2a / b <0.15. This is because the effect of improving the chipping resistance of the base material by the surface layer and the effect of improving the wear resistance of the base material at high temperature by the second hard phase inside the base material can be obtained in a well-balanced manner. The surface layer is a layer that does not contain the second hard phase (Al ₂ O ₃ ), but if the particle size of the second hard phase is sufficiently smaller than the thickness of the surface layer, for example, any surface layer is included. In the vertical cross section (cross section perpendicular to the main surface of the base material), the distance from the main surface of the base material to the center of gravity of the second hard phase closest to the main surface of the base material (in the direction perpendicular to the main surface of the base material). As a distance), the thickness a of the surface layer can be approximately measured. Further, when the thickness of the base material is not uniform within the main surface of the base material (for example, when the main surface of the base material has irregularities), the thickness b of the base material is the position where the thickness of the base material is the thinnest. Refers to the thickness of the base material. Further, when the base material has surface layers on both main surfaces in the thickness direction, the thickness a of the surface layer means the thickness of the surface layer on one main surface side. “2a / b” means (2a) / b, that is, the quotient of 2a divided by b.

In a cemented carbide having a hard phase (first hard phase and second hard phase) and a bonded phase used in the present disclosure, the bonded phase is not a metal Co but a heat resistant alloy (Co-based superalloy, Ni-based superalloy, etc.). ). Heat-resistant alloys are materials used in parts used at high temperatures, such as jet engines and gas turbines, and have excellent heat resistance. Further, the cemented carbide contains Al ₂ O ₃ (second hard particles) having higher heat resistance than WC (first hard particles). As a result, the high-temperature hardness of the cemented carbide itself (base material itself) is improved.

The first hard phase and the bonded phase are preferably contained in a dispersed state in the cemented carbide. This improves the wear resistance of the cemented carbide (base material) at high temperatures. Further, both the first hard phase and the bonded phase are contained in a state of being dispersed in the cemented carbide together with the γ phase, which is a matrix phase made of at least one metal selected from the group consisting of Co and Ni. Is preferable. This makes it possible to obtain a base material having both high temperature hardness and fracture resistance. It is more preferable that both the first hard phase and the bonded phase are contained in the cemented carbide in a uniformly dispersed state. Here, the dispersed state means that the first hard phase and the bonded phase are in contact with each other and exist in the cemented carbide in a state where the contact between the phases of the same type is relatively small.

The bonded phase preferably contains an Al bonded phase containing at least one metal selected from Co and Ni, Al and C. This is because the high temperature hardness of the bonded phase is improved by the solid solution strengthening. At this time, in an arbitrary cross section of the base material, the area ratio c of the Al-bonded phase occupying the area of the surface layer and the area ratio d of the Al-bonded phase occupying the area inside the base material other than the surface layer are c /. It is preferable to satisfy d ≧ 1.0. Since the Al-bonded phase is excellent in plastic deformation resistance at high temperature, deformation of the cutting edge of the base material can be suppressed by increasing the ratio of the Al-bonded phase in the surface layer, and the wear resistance of the base material is further improved. Because. c and d preferably satisfy c / d> 1.5. This is because a higher plastic deformation suppressing effect can be obtained.

The Al-bonded phase preferably further contains W. This is because the solid solution of W in the Al-bonded phase increases the high-temperature hardness of the Al-bonded phase and further improves the wear resistance at high temperatures.

The superhard alloy comprises at least one metal selected from the group consisting of Group 4 elements, Group 5 elements and Group 6 elements of the Periodic Table, and at least one element selected from the group consisting of C, N, O and B. It is preferable to further contain a third hard phase composed of the compound of the above or a solid solution thereof (excluding WC). By including the third hard phase, it is possible to impart effects such as improvement of oxidation resistance and reactivity resistance and suppression of crack generation due to impact on the base material to the base material.

Periodic Table As at least one metal selected from the group consisting of Group 4 elements, Group 5 elements and Group 6 elements, for example, titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium Examples thereof include (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), and tungsten (W). Examples of the compound include TiWC, TiWCN, NbWC, TaMoWC, TaNbWC, TiC, NbC, TaC, ZrC, ZrCN, VC, TaNbC, TiN and TiCN.

The average particle size of the first hard phase is preferably 0.1 μm or more and 10 μm or less, and more preferably 0.5 μm or more and 3.0 μm or less. In this range, a cemented carbide having sufficient hardness and being dense can be obtained.

The average particle size of the second hard phase is preferably 0.05 μm or more and 2.0 μm or less, and more preferably 0.1 μm or more and 0.5 μm or less. In this range, it is expected that the wear resistance and the fracture resistance of the base material at high temperature will be further improved. If the average particle size is too small, the wear resistance at high temperature may decrease, and if the average particle size is too large, the fracture resistance may decrease.

The average particle size of the third hard phase is preferably 0.1 μm or more and 5 μm or less, and more preferably 0.3 μm or more and 1.0 μm or less. In this range, a dense cemented carbide can be obtained.

The amount of the second hard phase inside the substrate is preferably 0.01% or more and 10% or less, and more preferably 0.1% or more and 4% or less in terms of area ratio. In this range, wear resistance and fracture resistance at high temperatures can be further improved. If the second hard phase is too small, the wear resistance at high temperature may be lowered, and if it is too large, the fracture resistance may be lowered.

Further, the cemented carbide (base material) of the present embodiment may contain unavoidable impurities (B, N, O, etc.) as long as the effects of the present disclosure are not impaired. Further, the cemented carbide of the present embodiment may contain an abnormal layer called a free carbon or an η phase in its structure.

<Physical property evaluation method for cemented carbide>
The cemented carbide constituting the base material contains a hard phase (first hard phase, second hard phase and third hard phase) and a bonded phase (including an Al bonded phase), and a hard phase (first hard phase). Content (area ratio) of phase, second hard phase and third hard phase) and bonded phase, average particle size of hard phase (first hard phase, second hard phase and third hard phase), composition of bonded phase Etc. can be confirmed as follows.

First, a sample containing an arbitrary cross section of the base material is prepared. A focused ion beam device, a cross-section polisher device, or the like can be used to prepare the cross section. Next, the processed cross section is imaged with a SEM (Scanning Electron Microscope) at a magnification of 10000 to obtain an electronic image for 10 fields of view. Next, element mapping is performed for a predetermined region (12 μm × 9 μm) in each electronic image using the attached EPMA (Electron Probe Micro-Analysis) or EDX (Energy Dispersive X-ray spectroscopy).

Based on the obtained element mapping, the region containing WC is designated as the first hard phase, the region containing Al and O is designated as the second hard phase, the region does not contain WC, and is selected from the group consisting of Ni and Co. A region containing at least one of these elements is referred to as a binding phase, and a region containing Al and C among the binding phases is referred to as an Al binding phase. This makes it possible to confirm in which portion the hard phase (first hard phase and second hard phase) and the bonded phase are contained in the cemented carbide. In addition, the composition of the bound phase can be obtained from the element mapping. Depending on the sintering conditions, there may be pores in addition to the hard phase and the bonded phase.

The area ratio of the Al-bonded phase in the base material and the area ratio of the hard phase inside the base material are preferably determined by using image analysis software (“Mac-View I”, manufactured by Mountech Co., Ltd.). The area ratio c of the Al-bonded phase in the area of the surface layer is the ratio of the Al-bonded phase in the total area of the visual field of any surface layer 1 photographed by SEM in the cross section of the base material. The area ratio d of the Al-bonded phase in the area inside the base material is the ratio of the Al-bonded phase in the total area of one visual field inside any base material photographed by SEM in the cross section of the base material. The value is an average value of the ratios obtained for 10 visual fields. One field of view is, for example, a square having a length of 20 μm and a width of 20 μm.

Furthermore, using image analysis software (“Mac-View I”, manufactured by Mountech Co., Ltd.), the average particle diameter (Heywood diameter: particles of the first hard phase, the second hard phase, and the third hard phase present in the substrate). The average value of the diameters of virtual circles having the same area as the area) is calculated. Each value is an average value of the results analyzed in 10 fields of view.

The composition of the compound particles constituting the hard phase (first hard phase, second hard phase and third hard phase) and the ratios (% by mass) of WC, Al ₂ O ₃ and the compound particles are super hard. It can be confirmed by crushing the alloy, determining the content ratio of each element in the crushed product by ICP emission spectroscopic analysis method, and calculating the composition ratio of each component based on this.

The content ratio of WC particles in the cemented carbide is relatively high, and therefore, there are many regions where the WC particles are adjacent to each other. Adjacent WC particles can be distinguished from each other by the result of element mapping and the backscattered electron image obtained from the SEM image. This is because in the backscattered electron image, a color difference (shading) due to a difference in the crystal orientation of each WC particle is observed.

The thickness a of the surface layer of the base material is not particularly limited as long as the presence of the second hard phase is recognized, but for example, an arbitrary cross section of the base material is photographed with an optical microscope or SEM, and the cross section thereof It can be measured as the length of the surface layer in the direction perpendicular to the main surface of the substrate. The surface layer is a layer that does not contain the second hard phase (Al ₂ O ₃ ), but if the particle size of the second hard phase is sufficiently smaller than the thickness of the surface layer, for example, in the above-mentioned photographed cross section, for example. The thickness a of the surface layer can be approximately measured as the distance from the main surface of the base material to the center of gravity of the second hard phase closest to the main surface of the base material (distance in the direction perpendicular to the main surface of the base material). As the value, the average value of the values measured at three or more places can be adopted.

<Manufacturing of base material made of cemented carbide>
The base material of the present embodiment comprises a cemented carbide manufactured by a manufacturing method including a step of producing a bonded phase powder, a step of mixing raw material powder, a molding step, a sintering step, and a cooling step described in detail below.

In the sintering step, the maximum temperature of sintering is 1300 ° C to 1800 ° C, and when the temperature of sintering is 1200 ° C or higher, it is 0.5 kPa to 10 kPa in an inert gas atmosphere, and the keep time is It is preferably 0.5 to 2 hours. Further, in the cooling step, it is preferable that the temperature is cooled from the maximum temperature to 1300 ° C. at a rate of, for example, 1 ° C./min, and the gas partial pressure at that time is 5 kPa or more. Hereinafter, each step will be described in detail.

(Preparation process of bonded phase powder)
First, at least one metal selected from the group consisting of Co and Ni, and Al are used as raw materials, and an intermetallic compound phase is prepared by atomization, arc dissolution, plasma treatment, or the like.

The obtained intermetallic compound phase is pulverized by, for example, a bead mill, a ball mill, a jet mill, or the like to obtain a bonded phase powder. In addition to the above, W, V, Ti, Nb, Ta, B, C and the like may be added when preparing the bonded phase powder. The average particle size of the bonded phase powder is preferably 0.3 to 3 μm. Examples of the beads or balls used in the bead mill or ball mill include beads or balls made of alumina, silicon nitride, or cemented carbide having a particle size of 0.1 to 3 mm, and examples of the dispersion medium include ethanol, acetone, and liquid nitrogen. Can be mentioned. The processing time by the bead mill or the ball mill is, for example, 30 minutes to 200 hours. The slurry obtained by the bead mill or the ball mill is dried in an inert gas or in vacuum to obtain a bound phase powder. When a jet mill is used as another method, the supply gas is an inert gas. Examples of the inert gas include argon and nitrogen.

(Mixing process of raw material powder)
Next, the obtained bonded phase powder and the separately prepared WC particle powder are mixed by an attritor, a ball mill, a mortar or the like. At this time, an appropriate amount of C is added in consideration of the amount of C contained in the bound phase. From the viewpoint of controlling the mass of the Al-bonded phase, Co, Ni powder, or both may be added.

The mixing is carried out in an open state to the atmosphere. This allows oxygen to be incorporated into the mixture. From the viewpoint of uniformly dispersing Al ₂ O ₃ in the cemented carbide, the mixing time is preferably 6 to 20 hours.

Examples of the ball used in the ball mill include balls made of alumina, silicon nitride or cemented carbide having a diameter of 3 mm, and examples of the dispersion medium include ethanol, acetone and liquid nitrogen. The processing time by the ball mill is, for example, 3 to 20 hours. A mixed powder can be obtained by, for example, drying the slurry obtained by mixing in the air.

In order to form the second hard phase, instead of directly adding the Al ₂ O ₃ powder, the mixing step of the raw material powder is performed in an atmospheric atmosphere, and oxygen in the atmosphere is adsorbed on the raw material powder during sintering. Al ₂ O ₃ is formed. This is because it is necessary to control the formation of Al ₂ O ₃ in order to prepare a surface layer that does not contain the second hard phase. A sufficient amount of oxygen can be adsorbed on the mixed powder by mixing in the air for 1 hour or more regardless of the device.

When the raw material powder containing Al is mixed in the air for 1 hour or more, the amount of oxygen adsorbed on the mixed powder becomes more than the amount required for all of Al to form Al ₂ O ₃ . Oxygen that was not used for the formation of Al ₂ O ₃ is combined with carbon contained in the mixed powder and released as a gas to the outside of the cemented carbide during the sintering process. In addition, a part of oxygen is used to form an oxide with a metal other than Al.

Among the raw material powders constituting the cemented carbide, the WC particles are preferably 30% by mass or more and 95% by mass or less, and more preferably 80% by mass or more and 95% by mass or less.

Of the raw material powders constituting the cemented carbide, the total of Co particles, Ni particles and (Co, Ni) _{(1-xy) Al xWy} is preferably 1% by mass or more and 30% by mass or less. More preferably, it is 1% by mass or more and 15% by mass or less. x represents the elemental ratio of Al, preferably satisfying 5 ≦ x ≦ 30, and more preferably 10 ≦ x ≦ 25. If x is too small, the second hard phase and the Al-bonded phase may not be sufficiently formed, and if x is too large, the second hard phase and the Al-bonded phase are excessively formed, and the fracture resistance is lowered. there is a possibility. When x is in the above range, the wear resistance of the cemented carbide (base material) at high temperature is further improved. y represents the elemental ratio of W, preferably satisfying 0 ≦ y ≦ 10. W contributes to the ratio of the second hard phase and the Al-bonded phase inside the cemented carbide, and when y is large, the area ratio of the Al-bonded phase increases and the area ratio of the second hard phase decreases. When y is in the above range, the hardness of the Al-bonded phase increases due to the solid solution of W in the Al-bonded phase, and the wear resistance at high temperature is further improved. If y is too large, the formation of the second hard phase may be insufficient.

Further, among the raw material powders constituting the cemented carbide, the total amount of the compounds constituting the third hard phase is preferably 65% by mass or less, more preferably 15% by mass or less. When the raw material powder is in the above range, the cemented carbide can secure sufficient denseness and maintain a good balance between hardness and toughness of the cemented carbide (base material).

(Molding process)
The obtained mixed powder is placed in, for example, a cemented carbide mold (Ta capsule or the like) and pressed to obtain a pressure molded product. The molding method is not particularly limited as long as it is a general condition. The press pressure is preferably 10 MPa to 16 GPa, for example 100 MPa.

(Incinerator process)
Next, the pressure molded body is sintered. Sintering is preferably performed by taking a sufficient time after the appearance of the liquid phase of the bonded phase. The maximum temperature for sintering is preferably 1300 to 1800 ° C. The keep time at the maximum temperature is, for example, 0.5 to 2 hours. By setting the maximum temperature in the above range, the average particle diameter of the hard phase (first hard phase, second hard phase and third hard phase) can be set in a desired range. As a result, the first hard phase and the bonded phase are densely sintered, and fine Al ₂ O ₃ is deposited inside the cemented carbide, so that wear resistance and fracture resistance at higher temperatures are improved. Cemented carbide can be obtained.

When the sintering temperature is 1200 ° C. or higher, the gas partial pressure is preferably 0.5 kPa or higher and 10 kPa or lower in an atmosphere of an inert gas (for example, _N2 or Ar). Since cemented carbide is usually sintered in vacuum, oxygen release is promoted and a surface layer is excessively formed. In the present embodiment, when the above-mentioned gas partial pressure is applied under the atmosphere of an inert gas when the sintering is kept at the maximum temperature, the release of oxygen in the cemented carbide is suppressed, so that 0.01 ≦ A substrate satisfying 2a / b ≦ 0.50 can be obtained. At this time, the higher the gas partial pressure, the more oxygen stays in the cemented carbide, the smaller the thickness a of the surface layer, and the lower the gas partial pressure, the larger the amount of oxygen released and the larger a.

(Cooling process)
The cooling step is a step of cooling the sintered body after the sintering is completed. From the maximum temperature to 1300 ° C, it is preferable to cool at a rate of 1 ° C / min. When the maximum temperature is less than 1400 ° C, 100 ° C from the maximum temperature to "maximum temperature minus 100 ° C" is cooled at a rate of, for example, 1 ° C / min. The partial pressure of the gas during cooling is preferably 5 kPa or more, more preferably 50 kPa or more in an inert gas atmosphere.

The partial pressure of the gas during cooling affects the area ratio of the Al-bonded phase inside the substrate. In the surface layer that does not form Al ₂ O ₃ , Al stays in the bonded phase to form the Al bonded phase, so that the area ratio c of the Al bonded phase to the area of the surface layer is the area inside the substrate. It is expected to be larger than the area ratio d of the Al-bonded phase that occupies. However, if the partial pressure of the gas during cooling is low, Al in the Al-bonded phase of the surface layer without oxygen to be bonded moves into the cemented carbide through the liquid phase, so that c becomes small and plastic deformation resistance is reduced. There is a risk that the sex will deteriorate. When the partial pressure of the gas during cooling is in the above range, the diffusion movement of Al in the surface layer can be suppressed, so that c can be kept large and c / d can be satisfied.

Whether Al forms Al ₂ O ₃ or an Al-bonded phase depends on the amount of Al and C in the compounding composition and the sintering conditions. In the present invention, we have found a technique for forming a surface layer containing no Al ₂ O ₃ depending on the sintering conditions. When the above sintering conditions are not satisfied, the surface layer may not be formed at all or may be excessively formed.

<Cutting tool>
The cutting tool according to this embodiment includes the above-mentioned base material. By using a base material made of the above-mentioned cemented carbide having improved wear resistance and fracture resistance at high temperatures, it is possible to extend the life of the cutting tool. The cutting tools include drills, end mills, replaceable cutting tips for drills, replaceable cutting tips for end mills, replaceable cutting tips for milling, replaceable cutting tips for turning, metal saws, and gear cutting tools. , Reamers, taps, etc. can be exemplified.

<Coating>
Further, a coating film may be provided on at least a part of the surface of the base material. By providing the coating film, the wear resistance of the cutting tool is further improved, and the life of the cutting tool can be further extended. It is also possible to impart the characteristics of the coating in the cutting tool.

As the coating film, it is preferable to use a coating film having a coefficient of thermal expansion of 7 × 10 ^-6 / K or more and 9 × 10 ^-6 / K or less. As the composition of the coating film, a nitride or carbonitride of one or more metals selected from the group consisting of Ti, Al, Cr, Si, Hf, Zr, Mo, Nb, Ta, V and W is preferable.

Further, the coating film preferably has an oxidation resistance of 1000 ° C. or higher. Here, "having an oxidation resistance of 1000 ° C. or higher" means that the coating layer is evaluated in the atmosphere by a thermal analysis-differential thermal analysis (TG / DTA: Thermogravimetry / Differential Thermal Analysis) device. It means that the temperature at which the weight increase occurs is 1000 ° C. or higher. Preferable examples of the composition constituting such an oxidation-resistant coating layer include AlTiSiN, AlCrN, TiZrSiN, CrTaN, HfWSiN, CrAlN and the like.

The coating film as described above can be formed by either a physical vapor deposition (PVD) method or a chemical vapor deposition (CVD) method. When the film is formed by the CVD method, it is easy to obtain a film having excellent adhesion to the substrate. Examples of the CVD method include a thermal CVD method. When the film is formed by the PVD method, compressive residual stress is applied, and its toughness can be easily increased. The cathode arc ion plating method can also be used in that the adhesion between the coating film and the cemented carbide (base material) is significantly improved.

The coating film in the cutting tool according to the present embodiment is preferably coated on and in the vicinity of the cutting edge portion of the substrate, and may be coated on the entire surface of the substrate. Further, the hard film may be a single layer or a multilayer. The thickness of the hard film is preferably 1 μm or more and 20 μm or less, and more preferably 1.5 μm or more and 15 μm or less.

Hereinafter, the present disclosure will be described in more detail with reference to examples, but the present disclosure is not limited thereto.

<Examples 1 to 22>
First, the metal powder represented by the composition of ₍ Co, Ni) _(1-xy) Al _xWy shown in Table 1 was mixed, and an intermetallic compound phase was prepared by an atomizing method. The obtained intermetallic compound phase was pulverized by a bead mill using a cemented carbide ball having a particle size of 1 μm. The obtained slurry was dried in vacuum to obtain a bound phase powder.

The obtained bonded phase powder, hard particles (WC particles and third hard phase compound particles), Co particles and Ni particles, and C powder, together with a ball made of cemented carbide having a diameter of 3.5 mm and ethanol, are added to the atmosphere. It was put into an open type attritor and mixed for 8 hours. The obtained slurry was dried in the air to obtain a mixed powder. The ratio of each raw material and the composition (compound type) of the third hard phase compound particles when the amount of the raw material powder other than the C powder is 100% by mass are as shown in Table 1. The blending amount of the C powder is 0.2% by mass with respect to the amount of the raw material powder other than the C powder.

The mixed powder was filled in a mold made of cemented carbide and pressed at a pressure of 100 MPa to obtain a pressure molded product.

This pressure-molded body was sintered under the sintering conditions shown in Table 2 to obtain a base material made of cemented carbide. The keeping time of the maximum temperature (sintering temperature) at this time was set to 1 hour.

Examples 1 to 10 have the same composition but different sintering conditions. Examples 15-19 include a third hard phase containing the compounds listed in Table 1.

<Comparative Examples 101 to 105>
A bound phase powder containing no Al or a bound phase powder having an extremely high or low Al content was used. The composition and sintering conditions of the mixed powder were as shown in Tables 1 and 2. Other than that, a base material made of cemented carbide was prepared in the same manner as in the examples.

<Comparative Examples 106 to 111>
Using raw material powders with the same composition, sintering was performed by methods with different sintering conditions such as sintering temperature and gas partial pressure. The composition and sintering conditions of the mixed powder were as shown in Tables 1 and 2. Other than that, a base material made of cemented carbide was prepared in the same manner as in the examples.

Table 1 shows the characteristics of each raw material powder used in the production (blending amount (mass%) of each raw material powder and composition of each component), which is the above-mentioned method for the sintered body after production. It was in agreement with the result analyzed by the ICP emission spectroscopic analysis method.

(Evaluation of physical properties of base material)
The cemented carbide constituting the base material contains a hard phase (first hard phase, second hard phase and third hard phase) and a bonded phase (alloy powder), and a hard phase (first hard phase, first hard phase, first). 2 Hard phase and 3rd hard phase) and the content (area ratio) of the bonded phase, the average particle size of the hard phase (1st hard phase, 2nd hard phase and 3rd hard phase), composition of the bonded phase, etc. It was measured in the same manner as the method described in the above embodiment. Table 2 shows the average particle size of the hard phase and the area ratio of the second hard phase inside the substrate.

The thickness a of the surface layer of the base material and the thickness b of the base material were measured in the same manner as described in the above-described embodiment, and 2a / b was determined. The area ratio c of the Al-bonded phase in the area of the surface layer and the area ratio d of the Al-bonded phase in the area inside the substrate were also measured in the same manner as described in the above-described embodiment, and c /. I asked for d. These results are shown in Table 2.

(Cutting test)
The obtained substrate was subjected to a flat surface polishing treatment to prepare a throw-away tip having an SNG432 shape, and evaluated by turning.

A fracture resistance test was conducted under the conditions shown in Table 3, and the number of impacts until the cutting edge was fractured was examined. The larger the value, the better the fracture resistance. The test results are shown in Table 5.

A wear resistance test was performed under the conditions shown in Table 4, and the cutting time up to a flank wear of 0.2 mm was investigated. The larger the value, the better the wear resistance. The test results are shown in Table 5.

As shown in Table 2, Examples 1 to 22 satisfy 0.01 ≦ 2a / b ≦ 0.5. From the results in Table 5, in Examples 1 to 22, the number of impacts until the cutting edge is broken and the cutting time up to the flank wear of 0.2 mm are larger than those in the comparative example in which 0.01 ≦ 2a / b ≦ 0.5 are not satisfied. Both show high levels, and it can be seen that both fracture resistance and wear resistance are improved.

From the results of Examples 15 to 19, it can be seen that when the base material contains the third hard phase, the cutting time up to the flank wear of 0.2 mm is longer and the wear resistance is improved.

From the results of Example 7, the cutting tool is used when 0.07 <2a / b <0.15 and c / d> 1.5 are satisfied among Examples 1 to 14 in which the amounts of the bonded phases are the same. It can be seen that the wear resistance and the fracture resistance of the are the most improved.

From the results of Examples 21 and 22, it can be seen that the wear resistance and fracture resistance of the cutting tool are further improved when the average particle size of the second hard phase is 0.05 μm or more and 2.0 μm or less. If the average particle size is too small, the wear resistance at high temperature is lowered, and if the average particle size is too large, the fracture resistance is likely to be lowered.

Further, from the results of Examples 21 and 22, when the amount of the second hard phase inside the base material is 0.01% or more and 10% or less in terms of area ratio, the wear resistance and fracture resistance of the cutting tool are improved. It turns out to be more improved. If the second hard phase is too small, the wear resistance at high temperature is lowered, and if it is too large, the fracture resistance is likely to be lowered.

In Examples 1 to 14, the amount of the bonded phase (total of Co powder, Ni powder and bonded phase powder) is the same as that of Comparative Examples 101, 102 and 104 to 110, but 0.01 ≦ 2a / b ≦ 0. It can be seen that the wear resistance is improved while satisfying 5 and maintaining a high fracture resistance.

In Examples 15 to 19, the amount of the bonded phase (total of Co powder, Ni powder and bonded phase powder) is the same as that of Comparative Example 103, but 0.01 ≦ 2a / b ≦ 0.5 is satisfied. It can be seen that the wear resistance is improved while maintaining the fracture resistance.

Comparative Examples 101 to 103 containing no Al do not contain the second hard phase and have low wear resistance. In Comparative Example 103, the first hard phase is finer than in Comparative Examples 101 and 102, and the cemented carbide has high hardness and low toughness, so that the wear resistance is slightly higher. Comparative Example 104 having a low Al content does not satisfy 0.01 ≦ 2a / b ≦ 0.5, and no improvement in wear resistance and fracture resistance is observed. Further, Comparative Example 105 having a high Al content does not have a surface layer that does not contain the second hard phase, and the fracture resistance is lowered.

Comparative Examples 106 to 111 have the same bonded phase composition as in Examples 1 to 14, but the sintering conditions are different and 0.01 ≦ 2a / b ≦ 0.5 are not satisfied. In these comparative examples, no improvement in wear resistance is observed, or a significant decrease in fracture resistance is observed, and both improvement in fracture resistance and wear resistance cannot be achieved at the same time.

The embodiments and examples disclosed this time should be considered to be exemplary in all respects and not restrictive. The scope of the present invention is shown by the scope of claims rather than the embodiments described above, and is intended to include the meaning equivalent to the scope of claims and all modifications within the scope.

Claims (6)

A substrate made of a cemented carbide having a first hard phase, a second hard phase and a bonded phase.
The first hard phase consists of WC particles.
The second hard phase is made of Al ₂ O ₃ .
The average particle size of the second hard phase is 0.04 μm or more and 2.10 μm or less.
The bonded phase comprises an Al bonded phase containing at least one metal selected from Co and Ni, Al and C.
The base material has a surface layer containing the first hard phase and the bonded phase on the surface and does not contain the second hard phase, and the thickness a of the surface layer and the thickness b of the base material are 0 . .04 ≤ 2a / b ≤ 0.50 ,
Among the raw material powders constituting the cemented carbide, the WC particles are 30% by mass or more and 95% by mass or less.
The amount of the second hard phase inside the base material other than the surface layer is 0.01% or more and 11.08% or less in terms of area ratio . In an arbitrary cross section of the base material, the area ratio c of the Al-bonded phase occupying the area of the surface layer and the area ratio d of the Al-bonded phase occupying the area inside the base material other than the surface layer are , C / d ≧ 1.0, according to claim 1. The base material according to claim 1 or 2, wherein the Al-bonded phase further contains W. Periodic Table A compound of at least one metal selected from the group consisting of Group 4 elements, Group 5 elements and Group 6 elements and at least one element selected from the group consisting of C, N, O and B, or a compound. The base material according to any one of claims 1 to 3, further comprising a third hard phase composed of the solid solution. A cutting tool comprising the substrate according to any one of claims 1 to 4. The cutting tool according to claim 5, wherein a coating is provided on at least a part of the surface of the base material.