EP4692393A1 - Cemented carbide for cutting tool and cutting tool using same - Google Patents

Abstract

A cemented carbide alloy for cutting tools comprises a hard phase having an average grain size in a range of 0.5 to 4.0 µm and a y phase having an average grain size in the range of 1.0 to 4.0 µm. The y phases each comprise Ti, Zr, Nb, Ta, and W in percentages a, b, c, d, and e, respectively, where a + b + c + d + e = 100.0, and their average values a_avg, b_avg, c_avg, d_avg, and e_avg, where a_avg + b_avg + c_avg + d_avg + e_avg = 100.0, in all the measured y phases satisfy the relations: 20.0 ≤ a_avg ≤ 30.0, 20.0 ≤ b_{avg ≤} 30.0, 10.0 ≤ c_avg ≤ 20.0, 20.0 ≤ d_avg ≤30.0, and 5.0 ≤ e_avg ≤ 15.0. The average of the respective standard deviations σa σb, σc, σd, and σe, of the percentage a, b, c, d, and e is 0.40 or less.

Description

Technical Field
• The present invention relates to a cemented carbide alloy (a WC sintered alloy) for cutting tools, and a cutting tool made of this alloy. This application claims priority based on Japanese Patent Application No. 2023-056798 filed on March 30, 2023 . The entire description in the Japanese patent applications is hereby incorporated by reference.
Background Art
• Cemented carbide alloys, which have high mechanical strength and thermal fatigue resistance, are used for tools, such as cutting tools, drilling tools, and metal processing tools that undergo high impact forces and severe thermal cycles.
• Meanwhile, the conditions under which tools are used are becoming more and more efficient, and tools are required to be more durable; thus, proposals have been made to improve the aforementioned characteristics for cemented carbide alloys used in tools.
• For example, Patent Literature 1 discloses a cemented carbide alloy containing composite carbide (solid solution) of (Ti, W, Ta, Nb, and Zr), in which Ta is partially replaced with inexpensive Nb and Zr to reduce production cost and to prevent degradation of performance during use for cutting applications.
Citation List Patent Literature
• PTL 1: Chinese Patent Application Unexamined Publication No. 1425787
Summary of Invention Technical Problem
• An object of the present invention, which has been accomplished in view of the aforementioned circumstances and proposals, is to provide a cemented carbide alloy that can produce a cutting tool with high plastic deformation resistance and high chipping resistance of the cutting edge, even during use for cutting stainless steel.
Solution to Problem
• A cemented carbide alloy for cutting tools in accordance with an embodiment of the present invention, comprises:
• 5.0 to 15.0 mass% in total Co and Ni;
• 4.0 to 12.0 mass% in total Ti, Zr, Nb, and Ta;
• 5.4 to 6.5 mass% C; and
• the balance being W and inevitable impurities; wherein
• the alloy comprises hard phases primarily composed of W carbide, a binder phase primarily composed of Co and Ni, and y phases primarily composed of Ti, Zr, Nb, Ta and W carbide,
• the hard phase mainly composed of W carbides has an average grain size in a range of 0.5 to 4.0 µm, and the y phase has an average grain size in the range of 1.0 to 4.0 µm,
• the y phases each comprise Ti, Zr, Nb, Ta, and W in percentages a, b, c, d, and e, respectively, where a + b + c + d + e = 100.0, and their average values a_avg, b_avg, c_avg, d_avg, and e_avg, where a_avg + b_avg + c_avg + d_avg + e_avg = 100.0, in all the measured y phases satisfy the relations: 20.0 ≤ a_avg ≤ 30.0, 20.0 ≤ b_avg ≤ 30.0, 10.0 ≤ c_avg ≤ 20.0, 20.0 ≤ d_avg ≤30.0, and 5.0 ≤ e_avg ≤ 15.0, and
• the average of the standard deviations σa, σb, σc, σd, and σe of the percentages a, b, c, d, and e, respectively, is less than 0.40.
• The cemented carbide alloy in accordance with the embodiment may satisfy the following condition (1):
(1) The cemented carbide alloy further comprises 0.5 mass% or less Cr, wherein
• 20 to 80% of the y phases contain y1 phases in their interiors, where the percentage d of Ta atoms in the y1 phases is at least 8 higher than the average value d_avg.
• A cutting tool in accordance with an embodiment of the present invention includes the aforementioned cemented carbide alloy.
Advantageous Effects of Invention
• The cemented carbide alloy can contribute to production of a cutting tool with high plastic deformation resistance and high chipping resistance of the cutting edge, even during use for cutting stainless steel.
Brief Description of Drawings
• Fig. 1 is a schematic diagram of an exemplary microstructure of the cemented carbide alloy for tools in accordance with the present invention.
• Fig. 2 is an illustration of the method of line analysis.
• Fig. 3 is a schematic diagram of an exemplary plastic deformation of the flank surface of a cutting edge, where the upper drawing is a plan view of the rake face while the lower drawing is a side view of the flank surface.
Description of Embodiments
• The present inventor has made an intensive study to produce a cemented carbide alloy for cutting tools that can achieve the aforementioned object. As a result, the inventor has found that the aforementioned objectives can be achieved after the following conditions hold:
• the average grain sizes of the hard phases and the y phases are controlled to be within a predetermined ranges ; and
• the y phases have a predetermined composition, in detail, the average numbers of atoms of the metal components in the y phases are almost equal within a predetermined range, and the average value of the standard deviations of each metal component between the y phase grains is within a predetermined range.
• The cemented carbide alloy for cutting tools and the cutting tool made of the alloy in accordance with the present invention will now be described.
• Throughout the specification and the claims, the numerical range expressed as "M to N" (where M and N are both numerical values) is synonymous with "M or more and N or less" and the range shall include the numerical values of the upper limit (N) and the lower limit (M); the unit stated only for the upper limit (N) shall also apply to the lower limit (M); and the average means the arithmetic mean unless otherwise specified.
1. Composition and Microstructure of Cemented Carbide Alloy for Cutting Tool
• The composition of the cemented carbide alloy for cutting tools in accordance with the embodiments and the microstructure shown schematically in Fig. 1 will now be described in detail.
(1) Co and Ni
• It is preferred that Co and Ni be contained alone or in combination. The total content of Co and Ni is preferably in a range of 5.0 to 15.0% by mass for the following reasons: A content of less than 5.0% by mass results in insufficient chipping resistance of cutting tools, while a content of more than 15.0% by mass results in a decrease in plastic deformation resistance.
• Co and Ni are mainly present in the binder phase (containing crystal grains having an fcc structure, indicated by reference numeral (1) in Fig. 1) and are the main or principal components of the binder phase, and the sum of Co and Ni atoms accounts for more than 50% by atom of all the components (atoms) in the binder phase.
• The binder phase may contain W and C, which are components of the hard phases, at least one selected from the group consisting of Ti, Zr, Nb, Ta, and W, which are contained in the y phases, Cr, which controls the growth of the hard phases, and inevitable impurities. These elements, if present, are presumed to be in solid solution in the binder phase.
• The identification of the binder phase will be described below.
(2) Ti, Zr, Nb, and Ta
• Ti, Zr, Nb, and Ta are all essential components, and the total content of Ti, Zr, Nb, and Ta should be within a range of 4.0 to 12.0% by mass for the following reasons:
  In the case that these components are used in a cutting tool, plastic deformation resistance is insufficient at less than 4.0% by mass while chipping resistance decreases at more than 12.0% by mass.
• Ti, Zr, Nb, Ta, and W are present in the y phases, where the percentages of Ti, Zr, Nb, Ta, and W atoms in one y phase are a, b, c, d, and e, respectively, where a + b + c + d + e = 100.0, and their average values a_avg, b_avg, c_avg, d_avg, and e_avg, where a_avg + b_avg + c_avg + d_avg + e_avg = 100.0, in all the measured y phases preferably satisfy the relations: 20.0 ≤ a_avg ≤ 30.0, 20.0 ≤ b_avg ≤ 30.0, 10.0 ≤ c_avg ≤ 20.0, 20.0 ≤ d_avg ≤ 30.0, and 5.0 ≤ e_avg ≤ 15.0.
• The following relations hold: $$\mathrm{a}=\left[\mathrm{Ti}\right]/\left(\left[\mathrm{Ti}\right]+\left[\mathrm{Zr}\right]+\left[\mathrm{Nb}\right]+\left[\mathrm{Ta}\right]+\left[\mathrm{W}\right]\right)\times 100$$ $$\mathrm{b}=\left[\mathrm{Zr}\right]/\left(\left[\mathrm{Ti}\right]+\left[\mathrm{Zr}\right]+\left[\mathrm{Nb}\right]+\left[\mathrm{Ta}\right]+\left[\mathrm{W}\right]\right)\times 100$$ $$\mathrm{c}=\left[\mathrm{Nb}\right]/\left(\left[\mathrm{Ti}\right]+\left[\mathrm{Zr}\right]+\left[\mathrm{Nb}\right]+\left[\mathrm{Ta}\right]+\left[\mathrm{W}\right]\right)\times 100$$ $$\mathrm{d}=\left[\mathrm{Ta}\right]/\left(\left[\mathrm{Ti}\right]+\left[\mathrm{Zr}\right]+\left[\mathrm{Nb}\right]+\left[\mathrm{Ta}\right]+\left[\mathrm{W}\right]\right)\times 100$$ $$\mathrm{e}=\left[\mathrm{W}\right]/\left(\left[\mathrm{Ti}\right]+\left[\mathrm{Zr}\right]+\left[\mathrm{Nb}\right]+\left[\mathrm{Ta}\right]+\left[\mathrm{W}\right]\right)\times 100$$
• The mean value ((σa+σb+σc+σd+σe)/4) of the standard deviations σa, _σb, σc, σd, and σe of the percentages a, b, c, d, and e, respectively, is preferably 0.4 or less (although the lower limit may be 0.0, it is about 0.1 in one embodiment of the production described below) for the following reason: an average value exceeding 0.4 leads to decreases in plastic deformation resistance and chipping resistance.
• In other words, the fraction of metal atoms in the y phase should be approximately equal and within a predetermined range in order to achieve high plastic deformation resistance and chipping resistance when the alloy is used as a cutting tool.
(3) _Υ-phase
• These elements, Ti, Zr, Nb, and Ta, are present in the form of carbides (not limited to stoichiometric composition) as the main or principal component of the y phases, indicating that the sum of the carbides of these components accounts for more than 50% by atom of all the components (atoms) constituting the y phases. The _Υ-phase may further contain WC contained in the hard phase, Co and Ni contained in the binder phase and inevitable impurities, in addition to these carbides. In Fig. 1, the y phases are indicated by reference numerals (3) and (4), and some of the y phases (reference numerals (4)) contain internal _Υ1 phases (reference numeral (5)) with different compositions.
• The y phases preferably have an average grain size in a range of 1.0 to 4.0 µm because the cemented carbide alloy for cutting tools has insufficient chipping resistance at an average grain size of less than 1.0 µm and insufficient plastic deformation resistance at an average grain size exceeding 4.0 µm. The average grain diameter of the y phase corresponds to the circle equivalent diameter, i.e., the diameter of a circle having an area equal to the area of the y phase. The measurement of the grain size will be described below.
• It is more preferred that 20 to 80% of the y phases contain _Υ1 phases in their interiors, where the percentage d of Ta atoms that is at least 8 higher than the average value d_avg (the upper limit is 22 in an embodiment of the production described below). The presence of a certain number of y phases containing _Υ1 phases enhances plastic deformation resistance and defect resistance.
(4) C
• C is contained to form carbides and is mainly present in the hard phases, y phases, and _Υ1 phases. The preferred content is 5.4 to 6.5% by mass. Within this content, a sufficient amount of carbide can be formed in the hard phases, y phases, and _Υ1 phases.
(5) Cr
• Cr is an optional component and may be present in an amount of less than 0.5% by mass. In other words, the inclusion of Cr is not essential.
• Cr inhibits the growth of W carbide, which dissolves in Cr, in the hard phases, makes the W carbide finer and the grain size distribution narrower, and improves the toughness and plastic deformation resistance of the cemented carbide alloy. This function is impaired at a Cr content exceeding 0.5% by mass, and thus the Cr and W complex carbide precipitates in the binder phase, which reduces the toughness and may be a starting point of chipping.
(5) W
• W is the main or principal, component of the hard phases, and W carbide (mostly WC but not limited to stoichiometric composition) accounts for more than 50% by atom of all the components (atoms) that make up the hard phased (indicated by reference numeral (2) in Fig. 1).
(6) Hard layer
• The hard phases may contain components of the binder phase, components of the y phases, Cr, and inevitable impurities that are unavoidably mixed in during the manufacturing process. The hard phases have an hcp crystal structure, which is different from the fcc crystal structure of the y phases.
• The identification of the hard phases will be described below.
• The hard phases should have an average grain size in a range of 0.5 to 4.0 µm. An average grain size of less than 0.5 µm leads to insufficient chipping resistance when the alloy is used as a cutting tool, while an average grain size exceeding 4.0 µm leads to a reduction in plastic deformation resistance.
• The average grain diameter of the hard phases corresponds to the circle equivalent diameter, i.e., the diameter of a circle having an area equal to the area of the hard phase, just as mentioned about the y phases. The measurement of the average grain diameter will be described below.
(7) Inevitable impurities
• As mentioned above, the hard phased, y phases, and binder phase may contain impurities that are unavoidably (unintentionally) introduced during the manufacturing process, preferably in an outside amount of 0.3% or less by mass for 100% by mass of the entire cemented carbide alloy.
2. Measurement (1) Determination of the composition of cemented carbide alloy for cutting tool
• The surface or cross section of a cemented carbide alloy for cutting tools is mirror finished in, for example, a focused ion beam (FIB) system or a cross-section polishing (CP) system. The mirror finished surface is then observed, for example, at five fields of view in a magnification of 4000 with a field emission scanning electron microscope (SEM) (the size of one field of view is, for example, a square of 25 µm (length) by 25 µm (width)). The compositions are measured in these fields of view by surface analysis at a beam diameter of 1µm with an electron probe micro-analyzer (EPMA), and are averaged to yield the overall composition of the alloy.
(2) Average percentages of atoms of Ti, Zr, Nb, Ta and W in y phases
• The hard phases, y phases, and binder phase are identified by the following measurements:
1. 1) A rectangular observation field of view of 24 µm (length) by 72 µm (width), for example, is determined on the mirror machined surface for measurement of the composition of the entire cemented carbide alloy for cutting tools. EBSD patterns and EDS data are simultaneously captured with the field emission scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectroscope (EDS) and a backscattered electron diffraction device (EBSD). Although typical EDS and EBSD system is an OIM Data Collection from EDAX/TSL (now AMETEK), any other system is also available. The measurement with a field emission scanning electron microscope (SEM) is performed, for example, at an acceleration voltage of 15 kV and a distance between measuring points of 50 nm (other conditions are also available).
   Examples of the software used to analyze EBSD patterns include TSL's OIM Data Collection version 6 and TSL's OIM Analysis version 7. Any other system is available that can perform similar analysis.
2. 2) The averages of the counted values of Co and Ni detected at all measuring points identified as the fcc and hcp phases from the EBSD pattern analysis are calculated. The measuring points assigned to both the fcc and hcp phases with Co and Ni counted values higher than these averages are defined as belonging to the binder phase. The measuring points assigned to hcp phases that are not defined as belonging to the binder phase are defined as belonging to the hard phases. The remaining measuring points are defined as belonging to the y phases.
3. 3) If the adjacent EBSD measuring points are assigned to the same phase, the interface between those measuring points is defined as the phase interface only in the case that the difference in orientation at these measuring points is 5 degrees or more.
4. 4) The y phases determined in this way is subjected to EPMA line analysis. EPMA line analysis will now be explained with reference to Fig. 2, which illustrates the y phase (4) to be measured as containing an internal _Υ1 phase (5). The y phases (3) not containing the _Υ1 phases shown in Fig. 1 is also the target of the measurement without distinction. The observation field of view is, for example, a rectangle of 24 µm in length and 72 µm in width, and a reference line (6) is drawn in the field of view tangent to the phase interface of the y phase (4) to be measured that is present in the rectangle (although the reference line (6) is horizontal to the field of view in Fig. 2, horizontal is not essential). From this reference line (6), a measuring lines (7) are drawn parallel to the reference line (6) at intervals of one-tenth of the average grain diameter of the y phase (the average grain diameter determined without distinguishing between those with and without _Υ1 phase), which is separately determined as described below.
• The measuring lines (7) are continued to be drawn at the same intervals until they no longer extend through the y phase (4) to be measured. The EPMA line analysis is performed on all the measuring lines (7) in the y phase (4) to be measured at a distance of 50 nm between the measuring points to measure the percentages a, b, c, d and e of Ti, Zr, Nb, Ta and W atoms, respectively. An exemplary EPMA beam diameter is 50 nm. The EPMA line analysis (the exemplary beam diameter is 50 nm) is performed on four different y phases per observation field of view to determine the percentages of Ti, Zr, Nb, Ta and W atoms in the y phase. The percentages of atoms are determined in the same manner for at least five observation fields, and the average values a_avg, b_avg, c_avg, d_avg, and e_avg are calculated by averaging all the measurements of at least 20 y phases. If the number of y phases in one field of view is less than 4, the number of fields of view increases such that the total number of y phases to be measured is at least 20 to determine the average values a_avg, b_avg, c_ave, d_avg, and e_avg.
(3) Average grain diameter of hard and y phases
• During measurement and analysis of the EBSD patterns described above, the average grain diameter is determined for the phases assigned to the hard and y phases. The average grain diameter of these phases is determined as follows: Areas of at least 300 hard phases for each phase type are observed and are used for calculation of diameters of circles having the same areas. These circular equivalent diameters are averaged. Examples of software used to measure average particle size include, but are not limited to, TSL OIM Data Collection version 6 and TSL OIM Analysis version 7.
(4) Percentage of the number of y phases with internal _Υ1 phases
• In the EPMA line analysis involving the measurement of the averaged atomic fractions of Ti, Zr, Nb, Ta, and W in the y phase, if the percentage of the measuring points where the fraction d of Ta atoms is at least 8 higher than its average d_avg is more than 1.4% of all the measuring points in one y phase of interest, the y phase is defined as having an internal _Υ1 phase. At least 20 y phases are observed for the presence of the _Υ1 phase, and the percentage of the number of y phases with internal _Υ1 phases to the number of all the y phases examined is calculated.
3. Production
• The cemented carbide alloy for cutting tools and cutting tools including the cemented carbide alloy can typically be produced as follows:
  Raw powder such as WC powder, Co powder, carbide powder containing Ti, Zr, Nb, and Ta are prepared. The raw powders are wet-mixed, dried, and pressed into a shape of a desired cutting tool. The resulting green compact is held at any temperature between 1440°C and 1470°C for 1 to 3 hours and then cooled to 1200°C for sintering. The sinter may then be held at 1200°C for 0 to 24 hours (0 hours holding means no holding).
• The carbide powder containing Ti, Zr, Nb, and Ta should be such that the cemented carbide alloy for cutting tools contains all of Ti, Zr, Nb, and Ta, and may be a powder mixture of Ti carbide, Zr carbide, Nb carbide, and Ta carbide, or a mixture of composite carbides of two or more selected from the group consisting of Ti, Zr, Nb, and Ta.
Examples
• In Examples, the cemented carbide alloy for tools of the present invention is used as a cutting tool, specifically a turning insert. These examples however should not be construed to limit the present invention.
• The following powders were prepared for sintering: WC powder with a Fischer particle diameter of 1.5 to 6.0 µm, Co powder with a Fischer particle diameter of 1.2 µm, Ni powder with a Fischer particle diameter of 1.3 µm, Cr₃C₂ powder with a Fischer particle diameter of 1.0 µm, (Ti_0.25Zr_0.25Nb_0.25Ta_0.25)C powder with a Fischer particle diameter of 1.1 µm, (Ti_0.15Zr_0.15Nb_0.35Ta_0.35)C powder with a Fischer particle diameter of 1.1 µm, (Ti_0.35Zr_0.35Nb_0.15Ta_0.15)C powder with a Fischer particle diameter of 1.1 µm, TiC powder with a Fischer particle diameter of 1.0µm, ZrC powder with a Fischer particle diameter of 1.2 µm, NbC powder with a Fischer particle diameter of 1.1 µm, and TaC powder with a Fischer particle diameter of 1.1 µm.
• These powders were blended according to the compositions shown in Table 1 to prepare powders for sintering. The blends were then wet-mixed in a ball mill for 72 hours, dried, and pressed under a pressure of 100 MPa to make green compacts.
• These green compacts were then subjected to a liquid-phase sintering (main sintering) process that held the compacts at a predetermined temperature for a predetermined time. In this example, the sintering was performed under the conditions shown in Table 2, i.e., heating to a holding temperature of 1440°C and holding for 2 hours at the holding temperature in a vacuum atmosphere of 0.1 Pa or less, or heating to a holding temperature of 1470°C and holding for 1 hour at the holding temperature. The furnace was then maintained in a vacuum atmosphere of 0.1 Pa or less, cooled to 1200°C at a cooling rate of 1 to 20°C/min, and held at 1200°C for 0 to 20 hours under a vacuum atmosphere of 1 Pa or less (cooling rate and holding time are listed in Table 2). Cemented carbide alloys 1 to 10 (hereafter referred to as Examples 1 to 10) were thereby fabricated as shown in Table 3.
• Comparative cemented carbide alloys 1' to 9' (hereafter referred to as Comparative examples 1' to 9') were also produced for comparison.
• The manufacturing processes involved alloy compositions outside the scope of the invention, holding temperatures of 1360°C and 1470°C, cooling rates exceeding 20°C/min, and/or holding times of 0 to 1 hour at 1200°C, in place of the manufacturing processes of Examples 1 to 10.
• In detail, powders for sintering having the compositions shown in Table 1 are wet-mixed for 72 hours in a ball mill, dried, and pressed under a pressure of 100 MPa to produce green compacts, which were then heated to a holding temperature of 1360°C or 1470°C in a vacuum atmosphere of 0.1 Pa or less under the conditions shown in Table 2, and held at the holding temperature for 1 hour for main sintering. The furnace was further maintained in a vacuum atmosphere of 0.1 Pa or less, cooled to 1200°C at a cooling rate of 70°C/min, and held at 1200°C for 0 to 1 hour to produce alloys of Comparative examples 1' to 9' as shown in Table 4.
• The cross sections of the cemented carbide alloys of Examples 1 to 10 and Comparative Examples 1' to 9' were subjected to measurements described above. The results are listed in Tables 3 and 4. [Table 1]

  Raw material powder	Composition (% by mass)
  	Co	Ni	Cr3C2	(Ti0.25Zr0.25 Nb0.25Ta0.25) C	(Ti0.15Zr0.15 Nb0.35Ta0.35) C	(Ti0.35 Zr0.35 Nb0.15Ta0.15) C	TiC	ZrC	NbC	TaC	WC & inevitable impurities
  A	4.6	5.4	-	10.3	-	-	-	-	-	-	Balance
  B	6.2	5.8	-	-	5.3	3.7	-	-	-	-	Balance
  C	6.0	9.0	-	2.1	2.3	-	-	-	-	-	Balance
  D	5.0	-	0.6	7.6	-	5.9	-	-	-	-	Balance
  E	1.5	5. 5	0.3	2.7	3.0	2.1	-	-	-	-	Balance
  F	1.5	2.5	-	-	-	-	1.2	1.0	1.6	2.0	Balance
  G	9.5	6.5	-	-	-	-	5.8	4.1	3. 3	3.1	Balance
  H	4. 8	6. 2	-	-	-	-	1.4	1.3	0.3	0.6	Balance
  I	-	13.0	0.3	-	-	-	2. 7	2.0	1.0	2.8	Balance
  J	3.5	3.5	0.8	-	-	-	3.0	2.0	2. 7	2.6	Balance

• In Table 1, the symbol "-" indicates that the ingredient was not formulated. [Table 3]

  Examples	Row material powder	Process	Composition (% by mass)					Composition of gamma phase (atomic proportion)					Average grain diameter (µ m)		Average of σ a- σ e	Percentage of gamma phase with γ 1 phase inside (%)
  			Ci+Ni	Ti+Zr+Nb+Ta	C	Cr	W & inevitable impurities	Ti aavg	Zr bavg	Nb cavg	Ta davg	W eavg	Hard phase	γ phase
  1	A	1	10.2	9.3	6 0	0.0	Balance	22.2	23. 8	18. 9	23. 3	11. 8	4. 0	3.2	0.3	0
  2	B	2	11.9	7.9	5.9	0.0	Balance	21.6	25.2	19.9	22.8	10. 5	1.5	2. 0	0.2	20
  3	C	3	14.9	4.0	5.4	0.0	Balance	20. 0	20. 9	15.2	29. 8	14. 1	0.9	4.0	0.1	69
  4	D	4	5.1	12.0	6.5	0.5	Balance	29.8	30. 0	15.1	20. 1	5. 0	2.7	1.8	0.3	66
  5	E	5	7.3	6.8	6.0	0.3	Balance	25.5	25.2	11. 6	25.3	12. 4	2.7	1.1	0.3	47
  6	A	6	10.1	9.3	6.0	0.0	Balance	23. 3	23. 3	19. 8	22.3	11. 3	3.5	3. 1	0.3	0
  7	B	7	12.2	8.1	5.7	0.0	Balance	22.1	24.1	20. 0	23. 3	10. 5	1.2	1.0	0.3	25
  8	C	8	15.0	4.0	5.4	0.0	Balance	20. 2	20. 0	16. 5	30. 0	13. 3	0.5	3.8	0. 1	85
  9	D	9	5.0	12.0	6.5	0.5	Balance	30. 0	29.8	14.0	20. 0	6. 2	1. 8	1.5	0.4	74
  10	E	10	6.8	6.8	6. 1	0.3	Balance	24.8	24.9	10.0	25.3	15. 0	1.7	1.0	0.3	49

• It was confirmed that the contents of inevitable impurities were within the aforementioned favorable range in both the Examples and Comparative Examples. [Table 4]

  Comparative Examples	Row material powder	Process	Composition (% by mass))					Composition of gamma phase (atomic proportion)					Average grain diameter (µm)		Average of σa-σe	Percentage of gamma phase with γ 1 phase inside (%)
  			Ci+Ni	Ti+Zr+Nb+Ta	C	Cr	W & inevitable impurities	Ti aavg	Zr bavg	Nb cavg	Ta davg	W eavg	Hard phase	γ phase
  1'	A	1'	10.2	9.3	5.9	0.0	Balance	22.1	23.9	20.0	23.4	10.6	3.5	3.2	1.1	0
  2'	B	2'	11.9	8.0	5.7	0.0	Balance	21.8	24.9	19.6	23.0	10.7	1.5	2.0	1.0	0
  3'	C	3'	15.0	4.0	5.4	0.0	Balance	20.9	20.6	13.5	30.0	15.0	0.9	3.8	0.8	0
  4'	D	4'	5.1	11.9	6.5	0.5	Balance	29.5	29.8	16.1	20.1	4.5	2.7	1.8	1.2	0
  5'	F	5'	3.8	5.1	6.0	0.0	Balance	18.7	17.4	25.2	31.5	7.2	4.2	4.2	9.4	0
  6'	G	6'	15.8	14.1	6.3	0.0	Balance	30.8	25.3	19.3	20.6	4.0	2.1	2.5	12.8	0
  7'	H	7'	11.1	3.0	5.3	0.0	Balance	32.5	33.9	6.5	15.9	11.2	0.4	0.9	17.3	0
  8'	I	8'	13.2	7.3	5.8	0.3	Balance	26.5	20.0	9.2	30.5	13.8	2.4	2.7	10.9	0
  9'	J	9'	7.0	9.0	6.7	0. 7	Balance	20.0	16.5	20.1	18.8	24.6	3.1	2.7	8.5	0.

• Although no coating layer was formed on the surfaces of Examples 1 to 5 and Comparative Examples 1' to 5', a coating layer with an average total thickness shown in Table 5 was formed on the surface of each of Examples 6 to 10 and Comparative Examples 6' to 9' by CVD.
• Although each coating layer was formed by vapor deposition as a three-layer structure, the number of layers in the structure may be one, two, or four or more layers.
• Although there is no particular restriction on the deposition conditions of the hard coating layer, the chemical vapor deposition conditions of TiN, TiCN, and Al₂O₃ in Examples 6 to 10 and Comparative Examples 6' to 9' were as follows:
[CVD conditions for TiN]
• Reaction gas (% by volume):TiCl₄ 2%, N₂ 30%, H₂ balance
• Reaction pressure: 7 kPa
• Reaction temperature: 1000°C
[CVD conditions for TiCN]
• Reaction gas (% by volume):TiCl₄ 2%, CH₃CN 0.7%, N₂ 10%, H₂ balance
• Reaction pressure: 7 kPa
• Reaction temperature: 900°C
[CVD conditions for Al₂O₃]
• Reaction gas (% by volume): AlCl₃ 2.2%, CO₂ 5.5%, HCl 2.2%, H₂S 0.2%, H₂ balance
• Reaction pressure: 7 kPa
• Reaction temperature: 1000°C
[Table 5]

Type of tool		Type of tool substrate	Type of coating layer (Component (average thickness))	Average total thickness of coating layer (µm)
	6	6	TiN(0.2 µm)/TiCN(5 µm)/Al2O3(2.0 µm)	7.2
	7	7	TiN(0.2 µm)/TiCN(5 µm)/Al2O3(2.0 µm)	7.2
	8	8	TiN(0.2 µm)/TiCN(3 µm)/Al2O3(2.5 µm)	5.7
	9	9	TiN(0.2 µm)/TiCN(3 µm)/Al2O3(2.5 µm)	5.7
	10	10	TiN(0.2 µm) /TiCN(3 µm) /Al2O3 (2.5 µm)	5.7
	6'	6	TiN(0.2 µm)/TiCN(5 µm)/Al2O3(2.0 µm)	7.2
	7'	7	TiN(0.2 µm)/TiCN(5 µm)/Al2O3(2.0 µm)	7.2
	8'	8	TiN(0.2 µm)/TiCN(3 µm) /Al2O3(2.5 µm)	5.7
	9'	9	TiN(0.2 µm)/TiCN(3 µm) /Al2O3(2.5 µm)	5.7

• Examples 1 to 5 and Comparative Examples 1' to 5' without coating layer were subjected to Cutting test 1, and Examples 6 to 10 and Comparative Examples 6' to 9' with coating layer were subjected to Cutting test 2. The plastic deformation of the flank surface of the cutting edge was measured and the state of wear of the cutting edge was observed.
Cutting test 1: Wet external turning of a round bar (200 mm in diameter) of alloy steel (JIS, SUS304)
• Workpiece material: JIS, SUS304
• Cutting rate: 250 m/min
• Depth of cut: 1.8 mm
• Feed: 0.18 mm/rev
• Cutting time: 5 minutes (cutting was interrupted every 20 seconds to observe the cutting edge)
• Wet water-soluble cutting fluid was used.
Cutting test 2: Dry external turning of a round bar (200 mm in diameter) of alloy steel (JIS SUS304)
• Workpiece material: JIS, SUS304
• Cutting rate: 55 m/min
• Depth of cut: 1.1 mm
• Feed: 0.12 mm/rev
• Cutting time: 5 minutes (cutting was interrupted every 20 seconds to observe the cutting edge)
• Wet water soluble cutting fluid is used.
• The amount of plastic deformation of the flank surface of the cutting edge was measured after the end of Cutting tests 1 and 2 (after 5 minutes of the cutting time had elapsed), and the state of wear of the cutting edge was observed. The amount of plastic deformation of the relief surface of the cutting edge is determined as follows: A line segment is drawn on the ridge where the relief surface (9) at the main cutting edge and the rake surface (8) intersect at a position far enough from the cutting edge (10) of the tool; the line segment is elongated to the direction of the cutting edge; and the distance (perpendicular to the elongated line segment) between the elongated line segment (12) and the ridge of the deformed cutting edge measured at the furthest point was defined as the amount of plastic deformation (11) on the flank of the cutting edge. If the amount of plastic deformation of the flank surface was 0.100 mm or more, the state of wear was defined as edge deformation (see Fig. 3).
• The results of Cutting tests 1 and 2 are shown in Tables 6 and 7, respectively. In Tables 6 and 7, the term "defects due to plastic deformation" indicates the results of interruption of cutting every 20 seconds and observation of the cutting edge to confirm the occurrence of defects caused by plastic deformation. Such defects were described as "not measurable" because it was difficult to specify the ridges and it was impossible to measure the amount of plastic deformation. [Table 6]

  Example	Plastic deformation of relief surface (mm)	State of wear	Comparative Example	Plastic deformation of relief surface (mm)	State of wear
  1	0.082	Normal	1'	0.169	Edge deformation and chipping
  2	0.055	Normal	2'	0.144	Edge deformation and chipping
  3	0.056	Normal	3'	0.143	Edge deformation and chipping
  4	0.029	Normal	4'	0.153	Edge deformation and chipping
  5	0.042	Normal	5'	Not measurable	Defects due to plastic deformation

  [Table 7]

  Example	Plastic deformation of relief surface (mm)	State of wear	Comparative Example	Plastic deformation of relief surface (mm)	State of wear
  6	0.078	Normal	6'	Not measurable	Defects due to plastic deformation
  7	0.048	Normal	7'	0.179	Edge deformation and chipping
  8	0.061	Normal	8'	0.165	Edge deformation and chipping
  9	0.023	Normal	9'	Not measurable	Defects due to plastic deformation
  10	0.034	Normal

• As shown in Table 6, which shows the results of Cutting Test 1, and Table 7, which shows the results of Cutting Test 2, all Examples exhibited high toughness and plastic deformation resistance with little plastic deformation of the flank surface, which affects the life, without causing uneven wear or defects, whereas Comparative Examples exhibited large amount of plastic deformation of the tool at the specified cutting time, and did not perform machining to achieve predetermined workpiece dimensions.
• The disclosed embodiments are in all respects illustrative only and are not restrictive; the scope of the invention is indicated by the claims, not the embodiments, and is intended to include all modifications and equivalents within the gist and scope of the claims.
Reference sign list
1. 1 binder phase
2. 2 hard phase
3. 3 y phase
4. 4 y phase containing _Υ1 phase
5. 5 _Υ1 phase
6. 6 reference line
7. 7 measuring line
8. 8 flank surface
9. 9 relief surface of main cutting edge
10. 10 cutting edge
11. 11 amount of plastic deformation of relief surface of cutting edge
12. 12 elongated line segment

Claims (3)

1. A cemented carbide alloy for cutting tools, comprising:

   5.0 to 15.0 mass% in total Co and Ni;

   4.0 to 12.0 mass% in total Ti, Zr, Nb, and Ta;

   5.4 to 6.5 mass% C; and

   the balance being W and inevitable impurities; wherein

   the alloy comprises hard phases primarily composed of W carbide, a binder phase primarily composed of Co and Ni, and y phases primarily composed of Ti, Zr, Nb, Ta and W carbide,

   the hard phase mainly composed of W carbides has an average grain size in a range of 0.5 to 4.0 µm, and the y phase has an average grain size in the range of 1.0 to 4.0 µm,

   the y phases each comprise Ti, Zr, Nb, Ta, and W in percentages a, b, c, d, and e, respectively, where a + b + c + d + e = 100.0, and their average values a_avg, b_avg, c_avg, d_avg, and e_avg, where a_avg + b_avg + c_avg + d_avg + e_avg = 100.0, in all the measured y phases satisfy the relations: 20.0 ≤ a_avg ≤ 30.0, 20.0 ≤ b_avg ≤ 30.0, 10.0 ≤ c_avg ≤ 20.0, 20.0 ≤ d_avg ≤30.0, and 5.0 ≤ e_avg ≤ 15.0, and

   the average of the standard deviations σa, σb, σc, σd, and σe of the percentages a, b, c, d, and e, respectively, is less than 0.40.
2. The cemented carbide alloy for cutting tools set forth in Claim 1, further comprising 0.5 mass% or less Cr, wherein
   20 to 80% of the y phases contain _Υ1 phases in their interiors, where the percentage d of Ta atoms in the _Υ1 phases is at least 8 higher than the average value d_avg.
3. A cutting tool comprising the cemented carbide alloy set forth in Claim 1 or 2.