SE1051204A1 - Cermet - Google Patents

Abstract

En kermet tillhandahålles som är lämplig som en komponent för ettskärverktyg med utmärkt brottbeständighet och som har förmågan att skäraett arbetsstycke för att bilda en högkvalitativ bearbetad yta av arbetsstycket,och ett belagt kermetverktyg. Kermeten innehåller hårda faser sammansattaav en förening, såsom karbonitrid av en metall vald från metallerna igrupperna 4, 5 och 6 i det periodiska systemet, och en bindemedelsfashuvudsakligen sammansatt av järngruppsmetall, de hårda faserna binds tillvarandra med bindemedelsfasen. Kermeten innehåller de hårda fasernabildade av fyra typer av kom med olika sammansättningar och morfologier;således har kermeten hög nötningsbeständighet, är utmärkt i termer avbrottmotstånd och kallsvetsningsmotstånd, och tillhandahållertillfredsställande kvalitet av en bearbetad yta. En första hård fas 1 bildas avkorn med en enfas sammansatt av Ti(C,N). Den andra hårda fasen 2 bildasav korn med en kärna-bård-struktur innehållande en kärna 2a sammansatt avTi(C,N) och en bård 2b som helt täcker kärnan 2a. Den tredje hårda fasen 3bildas av korn med en kärna-bård-struktur som innehåller en kärna och enbård och som är sammansatt av en komplex fast karbonitridlösninginnehållande Ti och W, kärnan 3a med en högre W-koncentration än den ibården 3b. Den fjärde hårda fasen 4 bildas av korn med en enfassammansatt av en komplex fast karbonitridlösning innehållande Ti.

Description

having main hard phases cornposed of tungsten carbide (WC). Thus, sudden fracture occurs easily, so that a stable tool life is not obtained. In recent years, in cutting work, it has been desired to further improve the quality of a maehined surface of a Workpiece and to improve low resistance to fracture, Which is a drawback of cermet tools, to obtain a stable tool life.

[0005] Known cermets including hard phases formed of grains having a single-phase structure that does not have a rim have low wettability with a binder phase and thus have inferior resistance to fracture.

[0006] For known cermets including hard phases formed of grains having a core-rim structure, cracks propagate easily along boundaries between cores and rirns, thus reducing the resistance to fracture. In particular, when cores are fine, it is difficult to inhibit the propagation of cracks and thus to improve the resistance to fracture.

[0007] Accordingly, it is an object of the present invention to provide a cermet which has excellent resistance to fracture and which is suitable as a material for a cutting tool capable of cutting a workpiece so as to form a high-quality machined surface of the workpiece. It is another object of the present invention to provide a coated cermet tool containing a substrate composed of the cermet.

Means for Solving Problem

[0008] The inventors have found that in the case Where a hard phase is present in a cermet in a specific range and Where four types of grains having different compositions and morphologies are present as grains constituting the hard phase, the cermet has high wear resistance and significantly improved resistance to fracture and welding resistance.

Furthermore, improvement in welding resistance and so forth also improves the surface quality of a workpiece. The present invention specifies the hard phase content and the four types of grains constituting the hard phase on the basis of the findings described above.

[0009] A cermet of the present invention includes hard phases composed of one or more compounds selected from the group consisting of earbides, nitrides, carbonitrides, and solid solutions of metals in groups 4, 5, and 6 of the periodic table, and a binder phase mainly composed of an iron group element, the hard phases being bonded to each other with the binder phase. The cermet contains 70% by mass to 97% by mass of the hard ' phases and the remainder being substantially formed of the binder phase. Furthermore, the hard phases of the cermet include a first hard phase, a second hard phase, a third hard phase, and a fourth hard phase described below.

The first hard phase is a hard phase which has a single phase composed of only titanium carbonitride (Ti(C,N)) or is a hard phase in Which Ti(C,N) is partially covered With a complex carbonitride solid solution containing titanium (Ti) and one or more metals selected from metals (provided that Ti is excluded) in groups 4, 5, and 6 of the periodic table.

The second hard phase is a hard phase having a core-rim structure including a core and a rim that entirely covers the core. The core is composed of Ti(C,N). The rim is composed of a complex carbonitride solid solution containing Ti and one or more metals selected from metals (provided that Ti is excluded) in groups 4, 5, and 6 of the periodic table.

The third hard phase is a hard phase having a core-rim structure that includes a core and a rim entirely covering the core. The core and the rim contain the same elements and are composed of complex carbonitride solid solutions containing at least Ti and W. The core has a higher tungsten concentration than the tungsten concentration in the rim.

The fourth hard phase is a hard phase having a single-phase structure composed of a complex carbonitride solid solution containing Ti and one or more metals selected from metals (provided that Ti is excluded) in groups 4, 5, and 6 of the periodic table.

[0010] In the cerrnet of the present invention, the incorporation of a specific amount of the hard phases and the coexistence of the first hard phase, the second hard phase, the third hard phase, and the fourth hard phase servings as the hard phases enables the cerniet to have the functions of the first hard phase to the fourth hard phase. Specifically, for the cermet of the present invention, the presence of the high-hardness hard phase results in excellent wear resistance. Furthermore, the presence of the hard phase having excellent wettability with the binder phase allows the cermet to maintain satisfactory Wettability with the binder phase and to have microstructures in which the binder phase is uniformly present. The uniformization of the microstructures improves the wear resistance and the resistance to fracture. Moreover, for the cermet of the present invention, the presence of the hard phase having excellent thermal properties improves the thermal conductivity, thereby inhibiting thermal cracking and improving the welding resistance. As described above, the cermet of the present invention has excellent wear resistance and improves the resistance to fracture and the welding resistance. Thus, a cutting tool composed of the cermet of the present invention is not easily worn or fractured, stabilizing and extending the tool life. Furthermore, satisfactory welding resistance makes it possible to provide a fine machined surface, improving the quality of the machined surface of a workpiece.

The present invention Will be described in more detail below.

[0011] <> The cermet of the present invention contains 70% by mass to 97% by mass of the hard phases and the remainder being substantially formed of the binder phase and incidental impurities. Examplcs of the incidental impurities include oxygen and metal elements in a concentration on the order of parts per million contained in raw materials and mixed in the production process.

[0012] <> [Composition] Each of the hard phases contains a compound of at least one metal element selected from metals in groups 4, 5, and 6 of the periodic table and at least one element selected from carbon (C) and nitrogen (N). In other words, each of the hard phases contains at least one selected from carbides, nitrides, carbonitrides, and solid solutions of the metal elements described above. In particular, the cermet of the present invention is a Ti(C,N)- based cermet containing at least a carbonitride solid solution that contains a titanium carbonitride (Ti(C,N)) and titanium (Ti). lf the proportion of the hard phases exceeds 97% by mass, the resistance to fracture is significantly reduced due to an excessively low binder phase content. If the proportion of the hard phases is less than 70% by mass, the hardness is significantly reduced due to an excessively high binder phase content, thereby reducing the wear resistance. The proportion of the hard phases is more preferably in the range of 80% by mass to 90% by mass.

[0013] The hard phases include four types of hard phases: the first hard phase, the second hard phase, the third hard phase, and the fourth hard phase, Which have different compositions and morphologies. Specifically, the hard phases include a Ti(C,N)-based hard phase, a Ti-containing hard phase having another composition, a hard phase having a single-phase structure, and a hard phase having a core-rim structure. The present states of the four types of hard phases described above can be easily discriminated by the light and shade of a photomicrograph taken with a scanning electron microscope (SBM).

[0014] (First Hard Phase) The first hard phase is formed of grains having a single-phase structure substantially composed of Ti(C,N) alone or is formed of grains in Which Ti(C,N) is partially covered With a complex carbonitride solid solution containing Ti and one or more metals selected from metals, other than Ti, in groups 4, 5, and 6 of the periodic table, i.e., in which Ti(C,N) is not entirely covered with the complex carbonitride solid solution. The first hard phase has a high Ti content compared with the third hard phase and the fourth hard phase described below, so that the first hard phase has high hardness and low reactivity with steel generally used for a workpiece. Thus, the presence of the first hard phase in the cermet particularly results in improvement in wear resistance and welding resistance.

[0015] (Second Hard Phase) The second hard phase is formed of grains having a core-rim structure including a core and a rim that entirely covers the core, the core being substantially composed of Ti(C,N) (Ti(C,N) accounts for 95% or more, in atomic percent, of the entire core), and the rim that entirely covers the core being composed of a complex carbonitride solid solution containing Ti and at least one metal selected from metals, other than Ti, in groups 4, 5, and 6 of the periodic table. Specific examples of the composition of the rim include (Ti,W,Mo)(C,N), (Ti,W,Nb)(C,N), (Ti,W,Mo,Nb)(C,N), and (Ti,W,Mo,Nb,Zr)(C,N).

Unlike the first hard phase, the secondhard phase has the rim Which entirely covers the core and Which has satisfactory Wettability with the binder phase, thus inhibiting the occurrence of pores in the cermet to lead to uniform microstructures and a stable hardness.

The uniforrnization of the microstructures results in further improvement in toughness such as resistance to fracture. Hence, the presence of the second hard phase in the cermet provides the stable effects of, in particular, Wear resistance and resistance to fracture.

[0016] (Third Hard Phase) The third hard phase is formed of grains having a core-rim structure that includes a core and a rim Which contain the same elements and which are composed of complex carbonitride solid solutions containing at least titanium and tungsten. Furthermore, the core of the grains has a higher tungsten concentration than that in the rim. Specific examples of the composition include (Ti,W)(C,N), (Ti,W,Mo)(C,N), (Ti,W,Nb)(C,N), and (Ti,W,Mo,Nb)(C,N). The third hard phase has a higher W content than those of the first hard phase and the second hard phase and thus has improved thermal conductivity With the high hardness maintained. This improves the thermostability, the heat crack resistance properties, the resistance to fracture, and the resistance to plastic deformation. [001 7] (Fourth Hard Phase) The fourth hard phase is formed of grains having a single-phase structure composed of a complex carbonitride solid solution containing Ti and at least one metal selected from metals, other than Ti, in groups 4, 5, and 6 of the periodic table. Unlike the third hard phase, the grains do not have a distinct boundary between a core and a rim. All the grains have a uniform composition. A typical example of a metal other than Ti contained in the fourth hard phase is W. Specific examples of the composition of the fourth hard phase include (Ti,W)(C,N), (Ti,W,Mo)(C,N), (Ti,W,Nb)(C,N), and (Ti,W,Mo,Nb)(C,N). ln particular, in the case where the fourth hard phase contains W, unlike the third hard phase, the concentration of W is not significantly changed (W is not localized), i.e., W is uniformly distributed throughout the fourth hard phase. Thus, the presence of the fourth hard phase in the cermet results in only a slight reduction in hardness but results in uniform hardness, so that crack propagation does not easily occur in the hard phases. Furthermore, the coefficient of thermal conductivity is increased, thus leading to improvements in heat crack resistance properties and resistance to fracture.

[0018] In the case Where the hard phases are substantially constituted by only the first hard phase and the second hard phase, it is difficult to improve the resistance to fracture. In the case Where the hard phases are substantially constituted by only the first hard phase and the third hard phase, pores are liable to be formed due to poor Wettability with the binder phase, thus leading to low resistance to fracture. ln the case where the hard phases are substantially constituted by only the first hard phase and the fourth hard phase, pores are also liable to be formed due to poor wettability with the binder phase, thus leading to insufficient hardness and low resistance to fracture.

[0019] In the case where the hard phases are substantially constituted by only the second hard phase and the third hard phase, it is difficult to inhibit the propagation of cracks along boundaries between cores and rims, which is a problem in the related art, so that desired resistance to fracture is not provided. In the case where the hard phases are substantially constituted by only the second hard phase and the fourth hard phase, the resistance to fracture is not improved.

[0020] In the case where the hard phases are substantially constituted by the first hard phase, the second hard phase, and the third hard phase and do not contain the fourth hard phase, the proportion of the third hard phase containing W is relatively increased. A high W content is liable to cause the reaction of W With a workpiece (in particular, steel) during cutting. Thus, welding occurs easily, leading to the deterioration of a machined surface of the workpiece. That is, the presence of the fourth hard phase in addition to the first hard phase, the second hard phase, and the third hard phase results in excellent quality (glossiness) of a machined surface of a workpiece and makes it possible to stably maintain the excellent quality.

[0021] In the case where the hard phases are substantially constituted by the first hard phase, the second hard phase, and the fourth hard phase and do not contain the third hard phase, although the coefficient of therrnal conductivity is increased, the hardness is reduced. This is liable to cause the propagation of cracks, thus leading to a high incidence of fracture. That is, the presence of the third hard phase in addition to the first hard phase, the second hard phase, and the fourth hard phase results in a further increase in the coefficient of therrnal conductivity to inhibit therrnal cracking and the propagation of cracks, thus effectively improving the resistance to fracture.

[0022] In the case Where the hard phases are substantially constituted by the second hard phase, the third hard phase, and the fourth hard phase and do not contain the first hard phase, it is difficult to obtain the effect of improving the Wear resistance and the Welding resistance, which is the effect resulting from the presence of the first hard phase. In particular, a machined surface of a workpiece has low glossiness.

[0023] In the case where the hard phases are substantially constituted by the first hard phase, the third hard phase, and the fourth hard phase and do not contain the second hard phase, in other words, in the case Where a Ti(C,N)-based hard phase, which is a main component of the hard phases in the cermet, is the first hard phase alone, the wettability With the binder phase is extremely degraded to easily form pores as described above, thus leading to the deterioration in mechanical properties.

[0024] ln the cermet of the present invention, the coexistence of, in particular, the third hard phase and the fourth hard phase in addition to the first hard phase and the second hard phase results in the inhibition of the reaction With steel With therrnostability maintained.

Hence, a cutting tool containing a substrate composed of the cermet of the present inventiori has improved resistance to thermoplastic deformation, improved resistance to thermal cracking, and improved Welding resistance, thus improving the quality of a machined surface of a Workpiece.

[0025] [Grain Size] The hard phases are preferably formed of a mixture of coarse grains and fine grains, in particular, formed of fine grains each having a size of l um or less and coarse grains each having a size of more than l um and 3 um or less. Furthermore, with respect to the total area of the hard phases, 60% to 90% of the hard phases are formed of the coarse grains, and the remainder of the hard phases are formed of the fine grains. Moreover, preferably, the coarse grains are formed of the first hard phase, the second hard phase, the third hard phase, and fourth hard phase, and the fine grains are substantially formed of the first hard phase and the second hard phase.

[0026] For such microstructures formed of the grains with different sizes, the fine grains are present so as to fill gaps between the coarse grains, irnproving the hardness and the fracture toughness. Since each of the coarse grains has a size exceeding 1 pm and each of the fine grains has a size of l pm or less, sufficiently large gaps are provided between the coarse grains, so that the fine grains can be present in the gaps. As a result, the effects of improving the hardness and the fracture toughness described above are provided.

Furthermore, since each of the coarse grains has a size of 3 pm or less, an excessive amount of the binder phase is not present between the grains, thus preventing reductions in hardness and fracture toughness due to the presence of a large binder-phase pool. Each of the fine grains particularly preferably has a size of 0.1 pm to 0.8 pm.

[0027] The area proportion of the coarse grains is 60% or more. That is, an appropriate amount of the coarse grains is present, thus sufficiently providing the effect of inhibiting the propagation of cracks and enhaneing the toughness. Furthermore, the area proportion of the coarse grains is 90% or less. Thus, the fine grains are sufficiently present in gaps between the coarse grains, improvirig the hardness and inhibiting the propagation of cracks.

Moreover, the presence of an appropriate amount of the fine grains results in a reduction in the surface roughness of the uppermost surface of the cermet, providing excellent cutting performance. More preferably, the area proportion of the coarse grains is in the range of 70% to 85%. ln addition, with respect to the total area of the fine grains, 80% or more, preferably 90% or more, and more preferably substantially all of the fine grains are formed of the first hard phase and the second hard phase. Thus, high-hardness fine Ti(C,N) is sufficiently present, enhancing the wear resistance. Methods for determining the grain size, the area, and the area proportion specified in the present invention will be described below.

[0028] The size and area proportions of the grains constituting the hard phases are adjusted by, for example, adjusting the size and amounts of raw material powders added and production conditions (eg, grinding time and sintering conditions). A longer grinding time tends to lead to finer grains constituting the hard phases in the cennet. A higher sintering temperature tends to lead to coarser grains constituting the hard phases in the 10 cermet. Even if the grinding time is prolonged to form a finer powder, a higher sintering temperature may result in grain growth to form coarse grains constituting the hard phases.

[0029] With respect to the total area of the hard phases, in the case that the area proportion of the first hard phase having a grain size of more than 1 um and 3 pm or less (coarse grains) is denoted by S1 and the area proportion of the second hard phase having a grain size of more than l um and 3 um or less (coarse grains) is denoted by S2, (S1 + S2) is preferably in the range of 0.1 to 0.5. In the case Where (S1 + S2) is 0.1 or more, welding of the cermet to a Workpiece does not occur easily. This inhibits the occurrence of a minute tear on a surface of a workpiece, improving the quality of a inachined surface of the Workpiece. Furthermore, improvement in welding resistance results in a reduction in Wear, improving the Wear resistance of tools. In the case where (S1 + S2) is 0.5 or less, a reduction in toughness due to an increase in hardness is inhibited, so that fracture and chipping are less prone to occur. More preferably, (S1 + S2) is in the range of 0.3 to 0.5. [003 0] In the case that the area proportion of the third hard phase having a grain size of more than 1 pm and 3 um or less (coarse grains) is denoted by S3 and the area proportion of the fourth hard phase having a grain size of more than 1 pm and 3 um or less (coarse grains) is denoted by S4, When Sl/(Sl + S2) is in the range of 0.1 to 0.4 and S3/(S3 + S4) is in the range of 0.4 to 0.9, a better balance between Wear resistance and resistance to fracture is provided. Furthermore, the surface gloss of a workpiece is further improved.

More preferably, S1/(S1 + S2) is in the range of 0.3 to 0.4, and S3/(S3 + S4) is in the range of 0.7 to 0.9. [003 1] In the case that the area of the first hard phase having a grain size of l um or less (fine grains) is denoted by SS1 and the area of the second hard phase having a grain size of 1 pm or less (fine grains) is denoted by SS2, SS1/(SS1 + SS2) is preferably in the range of 0.5 to 0.9. When SSl/(SSl + SS2) is 0.5 or more, the area ofthe fine first hard phase is larger than that of the second hard phase. This leads to significant improvement in wear resistance. When SSl/(SSl + SS2) is 0.9 or less, the proportion of the first hard phase among the fine hard phases is not excessively large. This suppresses a possible reduction in hardness due to the fact that the presence of an excess amount of the fine first hard phase ll causes a reduction in Wettability and that the reduction in wettability causes the formation of micropores. More preferably, SSl/(SSl + S82) is in the range of 0.55 to 0.7.

[0032] The proportion of the total area of the third hard phase and the fourth hard phase is preferably more than 40% With respect to the total area (hard phases + binder phase) of the cermet. In this case, stable thermal properties are obtained, improving the resistance to thermal cracking and resistance to fracture. In particular, most of the third and fourth hard phases are preferably formed of coarse grains. [003 3] <> The binder phase is composed of at least one metal, serving as a main component, selected from iron group elements of cobalt (Co), iron (Fe), and nickel (Ni). In the case where the binder phase consists substantially of one or more metals selected from the iron group metals described above, the one or more metals are defined as the "main component".

Altematively, in the case Where an alloy (solid solution) composed of the one or more metals selected from the iron group metals described above and an element included in the hard phases described above is contained in an arnount of 0.1% by mass to 20% by mass with respect to the total mass of the binder phase, i.e., in the case Where 80% by mass or more of the binder phase is composed of the one or more iron group metals, the one or more iron group metals are defined as the "main component". In the case where the binder phase contains an element included in the hard phases, the toughness tends to be improved by solution hardening, thus enhancing the resistance to fracture. Furthermore, in the case Where at least one of Co and Ni serves as the main component (80% by mass or more of the total mass of the binder phase), the binder phase has high Wettability With the hard phases and excellent corrosion resistance. In this case, the cermet is more suitable for use in cutting tools.

[0034] In the case Where the binder phase contains both Ni and Co, in particular, in the case Where the mass ratio of Ni to Co present in the binder phase (the ratio of the mass of Ni to the mass of Co) is denoted by Ni/Co, Ni/Co is preferably .in the range of 0.7 to 1.5.

When Ni/Co is in the range of 0.7 to 1.5, it is possible to inhibit a reduction in wettability to maintain high toughness and to inhibit a reduction in hardness to maintain high strength. 12 Partieularly preferably, Ni/Co is in the range of 0.8 to 1.2. Ni/Co can be adjusted by, for example, adjusting the amounts of a Co powder and a Ni powder added as raw materials. [003 5] [Additional Containable Element] The cermet of the present invention may contain molybdenum (Mo). In the case Where Mo is contained, in particular, the second hard phase tends to be easily formed.

Thus, the wettability between the hard phases and the binder phase is enhanced, so that the binder phase is sufficiently present around the grains constituting the hard phases, thereby improving the toughness. The Mo content is preferably in the range of 0.01 % by mass to 2.0% by mass. A Mo content of 0.01% by mass or more results in improvements in the wettability, hardness, and toughness of the entire cermet, as described above. A Mo content of 2.0% by mass or less results in suppression of the fact that the first hard phase is difficult to form and that the amounts of the second hard phase and the third hard phase are increased. It is thus possible to inhibit the propagation of cracks along boundaries between cores and rims, which is a problem in the related art, so that desired resistance to fracture is provided. More preferably, the Mo content is in the range of 05% by mass to 1.5% by mass. Mo may not be contained. [003 6] <> The cermet with the foregoing structure according to the present invention includes the four types of hard phases as described above and thus is excellent in terms of resistance to fracture and Welding resistance as well as wear resistance. So, the cermet is suitably used as a substrate material for a cutting tool (cermet tool) that will provide a satisfactory maehined surface. [003 7] <> The substrate may include a hard coating that covers at least part of a surface of the substrate. The hard coating is preferably arranged at least on and near the edge. The hard coating may be arranged over the entire surfaces of the substrate. The hard coating may be formed of a single layer or multiple layers. The hard coating preferably has a total thickness of 1 to 20 um. Regarding a method for producing the hard coating, a 13 chemical vapor deposition method (CVD method), such as a thermal CVD method, or a physical vapor deposition method (PVD method), such as an arc ion plating method, may be employed. [003 8] The hard coating is composed of a compound of one or more elements selected from the group consisting of alurninum (Al), Silicon (Si), and metals in groups 4, 5, and 6 of the periodic table with one or more elements selected from the group consisting of carbon (C), nitrogen (N), oxygen (O), and boron (B). That is, the hard coating is composed of one or more substances selected from the group consisting of cubic boron nitride (cBN), diamond, diamond-like carbon (DLC), and compounds of carbides, nitrides, oxides, borides, and solid solutions of the above-described elements such as metals.

Specific examples of the substances include Ti(C,N), Al2O3, (Ti,Al)N, TiN, TiC, (Al,Cr)N.

[0039] Cermets are typically produced through the steps of the preparation of raw materials, the grinding and mixing of the raw materials, molding, and sintering. The cermet of the present invention can be produced by using raw material powders described below and adjusting the grinding and mixing time and sintering conditions.

[0040] <> A powder of a compound of at least one metal selected from metals in groups 4, 5, and 6 of the periodic table with at least one element selected from carbon (C) and nitrogen (N), and a powder, typically an iron group metal powder, to be formed into the binder phase are used as raw materials. The use of a fine powder and a relatively coarse powder as these powders has a tendency to lead to the cermet having the hard phases formed of mixed grains of the coarse and fine grains, as described above. The particle size of the powders may be appropriately selected in view of the size of grains constituting the hard phases. [004l] To form the first hard phase and the second hard phase, for example, a Ti(C,N) powder is used. Regarding the Ti(C,N) powder, hitherto, Ti(C,N) powders have been produced from sponge Ti serving as a starting material. ln particular, the use of a Ti(C,N) l4 powder produced from TiOZ serving as a starting material has a tendency to form the fine first hard phase. Furthermore, as described above, the additional use of a Mo-containing compound powder has a tendency to form the second hard phase. To form the third hard phase, a W-containing powder, such as a WC powder, is used. To form the fourth hard phase, a powder of a compound containing Ti and a metal selected from metals, other than Ti, in groups 4, 5, and 6 of the periodic table, for example, a (Ti,W)(C,N) powder, is used.

The use of this compound powder has a tendency to form grains constituting the fourth hard phase, i.e., the grains having a single-phase structure in which Ti forms a uniform solid solution with a metal selected from metals, other than Ti, in groups 4, 5, and 6 of the periodic table.

[0042] <> A longer grinding time results in a finer powder and has a tendency to form the fine hard-phase grains in the cermet. However, an excessively long grinding time can cause reaggregation or difficulty in forrning a compound serving as a nucleus because of excessively small size. The grinding and mixing time is preferably in the range of 12 hours to 36 hours.

[0043] <> An excessively high sintering temperature can cause the growth of grains constituting the hard phases, which is liable to lead to a large number of coarse grains in the cermet. ln particular, an excessively high sintering temperature can cause difficulty in forming grains constituting the fourth hard phase. Thus, the sintering temperature is preferably in the range of l400°C to 1600°C. Furthermore, in the sintering step, a molded article that has been heated for a predetermined time is preferably cooled in vacuum or an inert gas atmosphere, such as argon (Ar). ln the case of the inert gas atmosphere, in particular, a relatively low pressure of 665 Pa to 6650 Pa is preferably used. ln addition, a higher cooling rate of, for example, 10 °C/min or more has a tendency to form the fourth hard phase.

Effect of the invention

[0044] A coated cermet tool of the present invention has excellent wear resistance and 15 resistance to fracture and is capable of cutting a workpiece so as to form a high-quality machined surface of the workpiece. A cermet of the present invention is suitably usable as a component of the tool.

Brief Description of Drawings

[0045] [Figl] Fig.l is a schematic explanatory drawing of four types of hard phases present in a cermet of the present invention.

Description of Embodiments

[0046] A cutting tool composed of a cermet was produced. The composition and microstructures of the cermet and the cutting performance of the cutting tool were investigated.

[0047] The cutting tool was produced as follows. Raw material powders described below Were prepared. (1) Ti(C,N) powder with average particle size of 0.7 um A Ti(C,N) powder is a powder produced from TiOg as a starting material. The C/N ratio is 1/ 1. (2) Ti(C,N) powder with average particle size of 0.8 um and Ti(C,N) powder with average particle size of 3.0 um Each of the Ti(C,N) powders is a powder produced from sponge Ti serving as a starting material. The C/N ratio is l/l. ln Table I, these Ti(C,N) powders are expressed as "s-TiCN". (3) (Ti,W)(C,N) powder with average particle size of 2.8 um A (Ti,W)(C,N) powder is a powder in which a Ti(C,N) powder forrns a solid solution with W. The C/N ratio is l/l. (4) WC powder, NbC powder, TaC powder, MozC powder, Ni powder, and Co powder with average particle size of 0.5 to 3.0 um These powders are cornmercially available.

The prepared raw material powders were weighed and mixed in such a manner that compositions (% by mass) shown in Table I were achieved, forming powders 1 to 12. 16

[0048] [Table I] Compositions of raw material powder (% by mass) i 1 10 10 20 25 10 10 0 1 7 7 2 20 20 10 15 10 10 0 1 6 8 3 10 5 20 20 20 10 0 1 7 7 4 20 15 10 10 20 10 0 1 6 8 5 10 5, 15 20 25 10 0 1 7 7 6 20 15 5 10 25 10 0 1 8 0 7 0 30 10 15 20 10 0 1 7 7 ~8 10 10 20 25 10 5 5 1 7 7 9 20 10 0 25 20 10 0 1 7 7 10 20 20 25 0 10 10 0 1 7 7 11 20 10 15 30 0 10 0 1 7 7 12 0 10 25 40 0 10 0 1 7 7

[0049] The prepared powders were charged into a Stainless-steel pot together With an acetone solvent and cemented carbide balls. The rnixture was ground and mixed (wet process). Table II shows raw material powders used to produce samples and grinding and mixing time (hour). After grinding and mixing, the mixture was dried to provide a mixed powder. A small amount of paraffin was added to the resulting mixed powder. Press forming was performed with a mold at 98 MPa to produce a molded compact with the geometry CNMG 120408.

[0050] 17 [Tabie 111 Sam le Powder Gfindifišäfid' ' ' . content Nå Nu (goiüirglg time šdzïdïietrilonšs Nl/CO by mass) 1 6 36 B 0. 73 0. 94 2 I 6 24 B 0. 72 0. 94 3 i 2 12 Å l. 31 0. 93 4 2 i 12 C 1. 29 0. 93 6 1 24 Å 0. 96 0. 94 6 3 24 Å 0. 96 0. 95 7 4 36 Å 1. 34 0. 93 8 8 24 C 0. 96 0. 92 9 3 36 C 0. 96 0. 94 10 05 36 Å 0. 97 0. 93 11 4 36 C 1. 29 0. 93 12 4 36 B 1. 29 0. 93 13 5 24 Å 0. 96 0. 94 14 2 36 Å 1. 29 0. 94 15 6 36 C 0. 96 0. 93 16 2 24 B 0. 97 0. 93 17 6 12 C 0. 74 0. 93 18 6 36 Å 0. 72 0. 96 19 9 36 B 0. 97 0. 93 100 7 12 C 0. 96 0. 93 101 9 36 Å 0. 96 0. 92 102 ll 36 B 0. 97 - 0. 93 103 10 12 Ål 0. 96 0. 93 104 12 36 Å 0. 96 0. 94 105 10 36 Å 0. 97 0. 94

[0051] After each of the molded compacts Was heated to 450°C to remove paraffin, the resulting cornpacts Were heated from room temperature to 1250°C in vacuum. The subsequent sintering (including a Cooling step) Was performed under conditions shown in Table III to form a sintered compact.

[0052] [Table III] 18 Sintering conditions _ Sintering Holding .

Condition Atmøgsanïenc Pressure temperature time aprïgslàgegre Pressure (Pa) (°C) (min ) (Pa) A NZ 133 _ 1500 60 Vacuum -~ B NZ 1330 1420 40 Vacuum _ C N, 399 1550 60 Ar 665

[0053] Any section of each of the resulting sintered compacts was formed. The section was observed With a scanning electron microscope (SEM) at a magnification of ><5000.

The results demonstrate that for each sintered compact, at least one type of grain selected from a black grain, a grain in which the black grain was partially covered with a gray region (hereinafter, the two grains are collectively referred to as a "single black grain"), a grain in which the black grain was entirely covered with the gray region (hereinafter, the grain is referred to as a "black-core double grain"), a grain in Which a white grain was entirely covered with a gray region (hereinafter, the grain is referred to as a "white-core double grain"), and a gray grain (hereinafter, the grain is referred to as a "gray grain") was observed in the observation field of view. In each of sintered compact samples 1 to 19, as illustrated in Figure, the four types of grains were observed: the single black grain (first hard phase l), the black-core double grain (second hard phase 2), the white-core double grain (third hard phase 3), and the gray grain (fourth hard phase 4). The first hard phase 1 is formed of only the black grain or the black grain partially covered with the gray region (rim lb). In the second hard phase 2, a core 2a appears black, and a rim 2b appears gray. ln the third hard phase 3, a core 3a appears white, and a rim 3b appears gray. A binder phase 10 is present between the grains. In contrast, in each of sintered compact samples 100 to 105, at least one of the single black grain, the black-core double grain, the White- core double grain, and the gray grain was not observed.

[0054] TEM-EDX analysis of compositions of the grains described above showed that the single black grain was composed of Ti(C,N); in the black-core double grain, the core was composed of Ti(C,N) and the rim covering the core was composed of a complex 19 carbonitride solid solution containing Ti and one or more metals selected from W, Nb, Ta, and Mo; in the white~core double grain was a complex carbonitride solid solution containing Ti and one or more metals selected from W, Nb, Ta, and Mo, and the core had a higher W concentration than that in the rim covering the core; and the gray grain was composed of a complex carbonitride solid solution Ti and one or more metals selected from W, Nb, Ta, and Mo. Furthermore, the gray grain did not have a distinct boundary between a core and a rim. The components of the hard phases can be analyzed by, for example, EPMA, X-ray fluorescence analysis, ICP-AES as well as TEM-EDX analysis.

[0055] The binder phase Was present between the grains. TEM-EDX analysis showed that the binder phase was substantially composed of Co and Ni. Among samples, some binder phases contained approximately several percent by mass of the constituent elements of the hard phases in the form of a solid solution. Analysis of the binder phase showed that the sintered compact had a Co content substantially equal to the amount of the raw material Co powder fed and that the Ni content of the sintered compact tended to be reduced by about 0.2% to about 03%, as compared with the amount of the raw material Ni powder fed. Thus, the hard phase content of each sample (sintered compact) is substantially equal to an amount (about 86% by mass) obtained by subtraction of the amounts of the Co powder and the Ni powder used as raw materials. Furthermore, the mass ratio of Ni to Co, i.e., Ni/Co, present in the binder phase was determined. Table II shows the results. Moreover, the Mo content (% by mass) of each sample (sintered compact) was investigated by ICP analysis. Table II also shows the results.

[0056] The size of all grains of each sample (sintered compact) present in the observation field of view was determined on the basis of the SEM observation images (><5000) of the sections. The Martin's diameter (the length of a chord bisecting the proj ected area of a grain when the grain is projected onto a plane from a certain direction) was used as the grain size. Specifically, a photomicrograph of the section of each sintered compact was used, and the length of a chord bisecting the area of a grain present in the photomicrograph was defined as the grain size. Regarding a grain having a core-rim structure, the diameter of a region including the rim was defined as the grain size. The results demonstrated that in any sample, grains each having a size of more than 3 um were little observed and that 20 the hard phases Were substantially formed of the grains each having a size of 3 pm or less.

[0057] The area of each of the grains Was determined using the grain size (the Martins diameter described above) determined from the observation images (><5000) of the sections.

In each of the first hard phase, the second hard phase, the third hard phase, and the fourth hard phase, the total area of grains having a size of more than 1 pm and 3 pm or less (hereinafter, these total areas are referred to as a "coarse-grain area (l)", a "coarse-grain area (2)", a "coarse-grain area (3)", and a "coarse-grain area (4)") was determined. In the first hard phase, the total area of grains each having a size of l um or less (hereinafter, the total area is referred to as a "fine-grain area (l )“) was determined. In the second hard phase, the total area of grains each having a size of 1 um or less (hereinafter, the total area is referred to as a"f1ne-grain area (2)") was determined. The sum of the coarse-grain area (1), the coarse-grain area (2), the coarse-grain area (3), the coarse-grain area (4), the fine- grain area (I), and the fine-grain area (2) was defined as the total area of the hard phases.

Table IV shows the proportion of the sum of the coarse-grain areas (l) to (4) with respect to the total area of the hard phases, i.e., the area proportion of the coarse grains "coarse grains/all hard phases" (%). Furthermore, Table IV shows the area proportion of each of the coarse-grain area (1), the coarse-grain area (2), the coarse-grain area (3), the coarse- grain area (4), the fine-grain area (1), and the fine-grain area (2) with respect to the total area of the hard phases. With respect to the total area of the hard phases, the area proportion of the coarse-grain area (l) was denoted by Sl, the area proportion of the coarse-grain area (2) was denoted by S2, the area proportion of the coarse-grain area (3) Was denoted by S3, and the area proportion of the coarse-grain area (4) Was denoted by S4.

In this case, (Sl + S2), Sl/(Sl + S2), and S3/(S3 + S4) were determined. Table IV shows the results. Furthermore, in the case that the fine-grain area (l) was denoted by SSl and the fine-grain area (2) Was denoted by SS2, SSI/(SSl + SS2) and the area proportion of the total area of the third hard phase and the fourth hard phase with respect to the area of the entire cermet (the hard phases + binder phase) (here, the area of an observation image in the field of view), ie., (third + fourth)/(entire cermet), were determined. Table IV also shows the results. In any of samples including the third hard phase or the fourth hard phase, grains constituting the third hard phase or grains constituting the fourth hard phase each had a size of more than about l um. Grains each having a size of l um or less and 21 constitutíng the third hard phase or the fourth hard phase were little observed.

[0058] [Table IV] 22 oo oo .o oo .o oo .o o .o oo o oo o o oo oo ooo oo oo .o oo .o 8 .o oo .o oo oo o oo oo o o ooo oo oo .o oo .o oo .o oo .o oo o oo oo oo o oo ooo oo oo .o oo .o oo .o oo .o oo oo o oo o oo oo. ooo oo oo .o oo .o oo .o oo .o oo oo oo o o oo oo ooo oo oo .o oo .o oo .o oo .o oo oo oo oo oo o o ooo oo oo .o oo .o oo .o oo .o oo o oo o oo oo oo oo oo oo .o oo .o oo .o oo .o oo o oo oo oo o oo oo oo oo .o oo .o oo .o o .o oo oo oo oo o oo o oo oo oo .o oo .o oo .o oo .o oo o oo oo oo oo oo oo oo oo .o oo .o oo .o oo .o oo oo oo oo o oo o oo oo oo .o oo .o oo .o oo .o oo o oo oo oo oo oo oo oo oo .o oo .o oo .o oo .o oo o oo oo oo oo oo oo oo oo .o oo .o oo .o oo .o oo o oo oo oo oo oo oo oo oo .o oo .o oo .o oo .o oo o oo oo oo oo oo oo oo oo .o oo .o oo .o oo .o oo oo oo oo o oo oo oo oo oo .o oo .o oo .o oo .o oo oo oo oo o oo oo o oo oo .o oo .o oo .o oo .o oo oo oo oo oo oo oo o oo oo .o oo .o oo .o oo .o oo oo oo oo oo oo oo o oo oo .o oo .o oo .o oo .o oo oo oo oo oo oo oo o oo oo .o oo .o oo .o oo .o oo oo oo oo oo oo oo o oo oo .o oo .o oo .o oo .o oo oo oo oo oo oo oo o oo oo .o oo .o oo .o oo .o oo oo oo oo oo o oo o oo oo .o oo .o oo .o oo .o oo oo oo o oo o oo o oo oo .o oo .o oo .o oo .o oo oo oo o oo o oo o ooooon Éooo 23% oooošowowoooou ëoošomfiooo ñooowooflooowooo m5 ocommwooooo wowowooowwouooo os owwoono ooošoooooooo ooooooooooooo oooooooooo oooooooooo ooooo ošmoowoowoooo .ooo om o woowo ošeo ošw .ošeo ošo .oz \^Loï_3om+wo_;o.v oooooom oouoooo US oo uoooofoøo oo u oooošo mwmna wow; Ucoomw mwmcm nom; wwofi mÉEmw oootâooo ä: š :oíoooooo ooå 23 [005 9] Surfaces of the resulting sintered compacts Were subj ected to surface grinding treatment and edging treatment, producing a cutting insert (cutting tool), provided With a breaker, with the geometry CNMG 120408. Cutting tests (turning tests in all cases) were performed with the resulting cutting inserts under conditions shown in Table V described below to evaluate the wear resistance, resistance to fracture, and the surface roughness of the machined surfaces. Table VI shows the results. measured according to JlS B 0601(200l).

[0060] [Table v] The surface roughness Ra was Wear resistance test Fracture resistance test Workpiece I SCM435 Surface roughness test of machined surface Workpiece I SCM415 with four slot grooves Workpi ece 2 SCM415 Cutt i ne Speed : 300m/ min Cuttingl sueecl I 250mIn/mín Cuttíng speed I IOOmm/min Cut: 1.0mm Cut: 1. 5111111 cut: 1. Omni Feed I Û. l-Smm/Tev.

Feedï 0. 15mm/I6V.

Feed: 0. 15mm/rev.

Cutting oil: used Cutting oil: used Cutting oil: used Cutting time : 30min Eva l uat i on : wear amount (ntm) of t* I ank face after Iapse of cuttíng time Evaluation: number of repetitlons at time of fracture (times) Cutting time I 30min Evaluation: surface roughness Ra [oøei] [Tabie V1] 24 Sampm Wear resistance test Fiactufe resistance Suffaße Fouëhness No. (mm) test (time-ß) rest Rairim) 1 0.16 7694 1.34 2 0.14 6982 1.2 3 0.13 8352 1.1 0 4 0.12 8006 1.1 5 0.105 8350 0.8 6 0.09 9860 0.9 7 0.08 9003 0.8 8 0.09 8344 0.9 9 0.08 10312 0.7 10 0.11 8634 0.8 11 0.13 7983 1.2 12 0.12 8693 1.3 13 0.12 8560 1.2 14 0.11 5970 1.1 15 0.15 7543 0.9 16 0.13 5880 0.75 17 0.16 7330 1.2 18 0.17 6580 1.4 19 0.14 6230 1.3 100 0.31 4005 2.1 101 0.23 3653 1.5 102 0.19 1 4210 1.2 103 0.32 4998 2 104 0.15 3991 1.3 105 0.28 2980 1.9

[0062] Table VI shows that samples 1 to 19 each including all of the first hard phase, the second hard phase, the third hard phase. and the fourth hard phase had excellent wear resistance and excellent resistance to fracture compared With samples 100 to 105 in which any one of the four types described above was absent. Furthermore, each of samples l to 19 provided a small surface roughness Ra and a high-quality machined surface of the xvorkpiece.

[0063] 25 Among samples 1 to 19, in particular, for samples having an area proportion of the coarse grains of 60% to 90%, the hardness and fracture toughness tend to be improved, further enhancing the Wear resistance and resistance to fracture. Furthermore, among samples 1 to 19, in particular, for samples in Which (S1 + S2) is in the range of 0.] to 0.5 and samples in Which Sl/(Sl + S2) is in the range of 0.1 to 0.4 and S3/(S3 + S4) is in the range of 0.4 to 0.9, the surface roughness Ra tends to be further reduced, resulting in excellent surface quality. Among samples 1 to 19, in particular, samples in Which SSl/(SSl + SS2) is in the range of 0.5 to 0.9 tend to have further enhanced wear resistance.

In addition, among samples 1 to 19, in particular, samples in Which (third + fourth)/(entire cermet) is more than 40% has excellent toughness.

[0064] (Ti,Al)N coatings (thickness: 4 pm) Were formed by an arc ion plating method on the surfaces of the cutting inserts of samples 1 to 19, forming coated inserts. The wear resistance test Was performed under test conditions shown in Table V. The results demonstrated that all samples had excellent Wear resistance compared with the samples Without the hard coatings.

[0065] The foregoing embodiments may be appropriately modified without departing from the scope of the present invention. The present invention is not limited to the configurations described above. For exarnple, the compositions and average particle size of the raw material powders, the present states of the grains of the hard phases, and the composition and thickness of the hard coating may be appropriately changed.

Industrial Applicability

[0066] The cermet of the present invention is suitably usable as a material for a cutting tool.

The coated cermet tool of the present invention is suitably usable for turning, milling, and, in particular, cutting of steel.

Reference Signs List

[0067] l first hard phase, lb rim, 2 second hard phase, 2a, 3a core, 2b, 3b rim, 3 third hard phase, 4 fourth hard phase, 10 binder phase i

Claims (9)

26 CLAIMS

1. l. A cermet comprising hard phases composed of one or more compounds selected from the group consisting of carbides, nitrides, carbonitrides, and solid solutions of metals in groups 4, S, and 6 of the periodic table; and a binder phase mainly composed of an iron group element, the hard phases being bonded to each other with the binder phase, the cermet containing 70% by mass to 97% by mass of the hard phases and the remainder being substantially formed of the binder phase, the hard phases including a first hard phase, a second hard phase, a third hard phase, and a fourth hard phase, Wherein the first hard phase is a hard phase Which has a single phase composed of only titanium carbonitride or Which has a single-phase structure in Which titanium carbonitride is partially covered With a complex carbonitride solid solution containing titanium and one or more metals selected from metals (provided that titanium is excluded) in groups 4, 5, and 6 of the periodic table, the second hard phase is a hard phase having a core-rim structure including a core and a rim that entirely covers the core, the core being composed of titanium carbonitride, and the rim being composed of a complex carbonitride solid solution containing titanium and one or more metals selected from metals (provided that titanium is excluded) in groups 4, 5, and 6 of the periodic table, the third hard phase is a hard phase having a core-rim structure that includes a core and a rim entirely covering the core, the core and the rim containing the same elements and being composed of complex carbonitride solid solutions containing at least titanium and tungsten, and the core having a higher tungsten concentration than the tungsten concentration in the rim, and the fourth hard phase is a hard phase having a single-phase structure composed of a complex carbonitride solid solution containing titanium and one or more metals selected from metals (provided that titanium is excluded) in groups 4, S, and 6 of the periodic table.

2. The cermet according to Claim 1, wherein With respect to the total area of the hard phases, 60% to 90% of the hard phases are formed of coarse grains each having a size of more than l um and 3 um or less, and the remainder of the hard phases are formed of fine grains each having a size of 1.0 um or less, Wherein the coarse grains are formed of the first hard phase, the second hard phase, 27 the third hard phase, and fourth hard phase, and the fine grains are substantially formed of the first hard phase and the second hard phase.

3. The cermet according to Claim 2, Wherein With respect to the total area of the hard phases, in the case that the area proportion of the first hard phase formed of the coarse grains is denoted by S1 and the area proportion of the second hard phase formed of the coarse grains is denoted by S2, (S1 + S2) is in the range of 0.1 to 0.5.

4. The cermet according to Claim 2 or 3, Wherein with respect to the total area of the hard phases, in the case that the area proportion of the first hard phase formed of the coarse grains is denoted by S1, the area proportion of the second hard phase formed of the coarse grains is denoted by S2, the area proportion of the third hard phase formed of the coarse grains is denoted by S3, and the area proportion of the fourth hard phase formed of the coarse grains is denoted by S4, S1/(S1 + S2) is in the range of 0.1 to 0.4, and S3/(S3 + S4) is in the range of 0.4 to 0.9.

5. The cermet according to any one of Claims 2 to 4, Wherein, in the case that the area of the first hard phase having a grain size of 1.0 pm or less is denoted by SS1 and the area of the second hard phase having a grain size of 1.0 pm or less is denoted by SS2, SS1/(SS1 + SS2) is in the range of 0.5 to 0.9.

6. The cermet according to any one of Claims 1 to 5, Wherein the proportion of the total area of the third hard phase and the fourth hard phase is more than 40% With respect to the total area of the cermet.

7. The cermet according to any one of Claims 1 to 6, Wherein the cermet contains nickel (Ni) and cobalt (Co) in the binder phase, and Wherein, in the case that the mass ratio of Ni to Co present in the binder phase is denoted by Ni/Co, Ni/Co is in the range of 0.7 to 1.5.

8. The cerrnet according to any one of Claims 1 to 7, Wherein the cermet contains 0,01% by mass to 2.0% by mass molybdenum.

9. A coated cennet tool cornprising a substrate composed of the cermet according to any one of Claims 1 to 8 and a hard coating that covers at least part of a surface of the substrate.