Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C29/00—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides
  • C22C29/02—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides
  • C22C29/06—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides based on carbides, but not containing other metal compounds
  • C22C29/08—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides based on carbides, but not containing other metal compounds based on tungsten carbide
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F5/00—Manufacture of workpieces or articles from metallic powder characterised by the special shape of the product
  • B22F2005/001—Cutting tools, earth boring or grinding tool other than table ware

Definitions

• the present invention relates to a cemented carbide alloy (a WC sintered alloy) for cutting tools, and a cutting tool made of this alloy.
• a cemented carbide alloy a WC sintered 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.
• 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.
• 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.
• 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.
• a cemented carbide alloy for cutting tools in accordance with an embodiment of the present invention comprises:
• the cemented carbide alloy in accordance with the embodiment may satisfy the following condition (1):
• the cemented carbide alloy further comprises 0.5 mass% or less Cr, wherein
• the y phases 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.
• 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.
• 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:
• cemented carbide alloy for cutting tools and the cutting tool made of the alloy in accordance with the present invention will now be described.
• M to N 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.
• 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.
• 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.
• the mean value (( ⁇ a+ ⁇ b+ ⁇ c+ ⁇ d+ ⁇ e)/4) of the standard deviations ⁇ a, ⁇ b, ⁇ c, ⁇ d, and ⁇ e 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.
• 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.
• 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 ⁇ -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.
• the y phases are indicated by reference numerals (3) and (4), and some of the y phases (reference numerals (4)) contain internal ⁇ 1 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 ⁇ m because the cemented carbide alloy for cutting tools has insufficient chipping resistance at an average grain size of less than 1.0 ⁇ m and insufficient plastic deformation resistance at an average grain size exceeding 4.0 ⁇ m.
• 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.
• 20 to 80% of the y phases contain ⁇ 1 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 ⁇ 1 phases enhances plastic deformation resistance and defect resistance.
• C is contained to form carbides and is mainly present in the hard phases, y phases, and ⁇ 1 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 ⁇ 1 phases.
• 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.
• 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 ).
• 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 hard phases should have an average grain size in a range of 0.5 to 4.0 ⁇ m.
• An average grain size of less than 0.5 ⁇ m leads to insufficient chipping resistance when the alloy is used as a cutting tool, while an average grain size exceeding 4.0 ⁇ m 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.
• 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.
• 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 ⁇ m (length) by 25 ⁇ m (width)).
• SEM field emission scanning electron microscope
• the compositions are measured in these fields of view by surface analysis at a beam diameter of 1 ⁇ m with an electron probe micro-analyzer (EPMA), and are averaged to yield the overall composition of the alloy.
• EPMA electron probe micro-analyzer
• the hard phases, y phases, and binder phase are identified by the following measurements:
• 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 .
• 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.
• the y phase is defined as having an internal ⁇ 1 phase. At least 20 y phases are observed for the presence of the ⁇ 1 phase, and the percentage of the number of y phases with internal ⁇ 1 phases to the number of all the y phases examined is calculated.
• 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.
• 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 ⁇ m, Co powder with a Fischer particle diameter of 1.2 ⁇ m, Ni powder with a Fischer particle diameter of 1.3 ⁇ m, Cr 3 C 2 powder with a Fischer particle diameter of 1.0 ⁇ m, (Ti 0.25 Zr 0.25 Nb 0.25 Ta 0.25 )C powder with a Fischer particle diameter of 1.1 ⁇ m, (Ti 0.15 Zr 0.15 Nb 0.35 Ta 0.35 )C powder with a Fischer particle diameter of 1.1 ⁇ m, (Ti 0.35 Zr 0.35 Nb 0.15 Ta 0.15 )C powder with a Fischer particle diameter of 1.1 ⁇ m, TiC powder with a Fischer particle diameter of 1.0 ⁇ m, ZrC powder with a Fischer particle diameter of 1.2 ⁇ m, NbC powder with a Fischer particle diameter of 1.1 ⁇ m, and TaC powder with a Fischer particle diameter of 1.1 ⁇ m.
• 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.
• 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.
• 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 ( ⁇ m) Average of ⁇ a- ⁇ e Percentage of gamma phase with ⁇ 1 phase inside (%) Ci+Ni Ti+Zr+Nb+Ta C Cr W & inevitable impurities Ti a avg Zr b avg Nb c av g Ta d avg W e avg Hard phase ⁇ phase 1 A 1 10.2 9.3 6 0 0.0 Balance 22.2 23. 8 18. 9 23. 3 11. 8 4.
• 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.
• Examples 1 to 5 and Comparative Examples 1' to 5' without coating layer were subjected to Cutting test 1
• 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)
• Cutting test 2 Dry external turning of a round bar (200 mm in diameter) of alloy steel (JIS SUS304)
• 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 ).

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• Mechanical Engineering (AREA)
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• Cutting Tools, Boring Holders, And Turrets (AREA)

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