Abstract:
A coated cemented carbide member includes a cemented carbide base material containing a binder metal of at least one iron family metal and a hard phase, and a coating layer provided on the surface of the cemented carbide base material. The hard phase contains at least one metal component selected from carbides, nitrides, carbo-nitrides and carbonic nitrides of Zr and/or Hf and WC. A layer consisting of only WC and an, iron family metal or a binder phase enriched layer or a low hardness layer is provided on an outermost surface of each insert edge portion of the cemented carbide base material. The coating layer is a single or multiple layer consisting of at least one metal component selected from carbides, nitrides, carbo-nitrides, oxides and borides of metals belonging to the groups IVB, VB and VIB of the periodic table. Due to this structure, it is possible to improve chipping resistance with no deterioration of wear resistance in the coated cemented carbide member to be used, for example, as a cutting tool.

Description:
This application is a continuation of Ser. No. 08/361,030 filed Dec. 21, 1994 now U.S. Pat. No. 5,643,658 which is a continuation of Ser. No. 08/039,976 filed Mar. 30, 1993 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a coated cemented carbide member which is applied to a cutting tool or the like and a method of manufacturing the same, and more particularly, it relates to a coated cemented carbide member which is excellent in toughness and wear resistance and a method of manufacturing the same. 
     2. Description of the Background Art 
     A coated cemented carbide member, which comprises a cemented carbide base material and a coating layer of titanium carbide or the like vapor-deposited on its surface, is generally applied to a cutting tool of high efficiency for cutting a steel material, a casting or the like, due to toughness of the base material and wear resistance of the surface. 
     Cutting efficiency of such a cutting tool is improved in recent years. The cutting efficiency is decided by the product of a cutting speed (V) and an amount of feed (f). When the cutting speed V is increased, the tool life is rapidly reduced. Therefore, improvement of the cutting efficiency is attained by increasing the amount of feed f. In order to improve the cutting efficiency by increasing the amount of feed f it is necessary to prepare a base material of the cutting tool from a tough material which can withstand high cutting stress. 
     In order to improve cutting characteristics of a cutting tool by implementing inconsistent characteristics of wear resistance and chipping resistance, various proposals have been made in general. For example, there have been proposed cemented carbide base materials which are provided on outermost surfaces thereof with a layer (enriched layer) containing an iron family metal in a larger amount than that in the interior, a layer (β free layer) consisting of only WC and a binder metal, and a region (low hardness layer) having lower hardness as compared with the interior, in order to improve wear resistance and chipping resistance. 
     In an insert shown in FIG. 1, however, absolutely no β free layer is formed particularly in each cornered insert edge portion 1, while the thickness of the as-formed β free layer is extremely reduced in a peripheral portion of such a corner. Further, the insert edge portion 1 has higher hardness than the interior due to reduction of a binder phase and increase of a hard phase, and hence it is impossible to attain sufficient wear resistance and chipping resistance. When generally employed chemical vapor deposition is applied to a coating method in such a coated cemented carbide, a fragile η phase is caused in the cornered insert edge portion 1 by reaction with carbon forming the base material in formation of the coating layer. Thus, chipping resistance is lowered and the coating layer falls with the η phase portion, to cause progress of wear. 
     In order to improve strength of a cemented carbide, there is a method of increasing the amount of the binder phase contained in the cemented carbide. In this case, however, plastic deformation is caused in the insert under a high cutting speed condition due to a high temperature applied thereto, although toughness is improved by such increase of the amount of the binder phase. 
     On the other hand, there is a method of increasing the amounts of additives such as Ti and Ta in the cemented carbide to improve heat resistance, thereby improving the tool life. In this case, however, strength of the cemented carbide is extremely reduced. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a coated cemented carbide member which is remarkably improved in chipping resistance with no deterioration of wear resistance. 
     Another object of the present invention is to provide a coated cemented carbide member having both of wear resistance and toughness in cutting work of high efficiency. 
     According to a first aspect of the present invention, a coated cemented carbide member comprises a cemented carbide base material, containing a binder metal of at least one iron-family metal and a hard phase of at least one metal component selected from carbides, nitrides, carbo-nitrides and carbonic nitrides of metals belonging to the groups IVB, VB and VIB of the periodic table, and a coating layer provided on its surface. The hard phase contains at least one element selected from carbides, nitrides, carbo-nitrides and carbonic nitrides of Zr and/or Hf, and WC. Each insert edge portion of this cemented carbide member is provided-on its outermost surface with a layer consisting of only WC and an iron family metal. The coating layer is formed by a single or multiple layer which consists of at least one material selected from carbides, nitrides, carbo-nitrides, oxides and borides of metals belonging to the groups IVB, VB and VIB of the periodic table and aluminum oxide. 
     According to this structure, a β free layer is also formed on the insert edge portion, whereby it is possible to improve chipping resistance of the cemented carbide member with no deterioration of wear resistance. 
     In a preferred embodiment of the inventive coated cemented carbide member, the layer, provided on the surface of the base material, consisting of only WC and an iron family metal has a thickness of 5 to 50 μm in each flat portion forming each insert edge portion and 0.1 to 1.4 times that of the flat portion in the insert edge portion. 
     While the coated cemented carbide member according to the first aspect of the present invention has the layer consisting of only WC and an iron family metal on the outermost surface of each insert edge portion, a coated cemented carbide member according to a second aspect of the present invention is characterized in that each insert edge portion of a base material is provided on its outermost surface with an enriched layer of a binder phase containing a larger amount of a binder metal as compared with the interior. As to the remaining structure, this coated cemented carbide member is similar to that according to the first aspect of the present invention. 
     Also according to this structure, it is possible to improve chipping resistance with no deterioration of wear resistance since an enriched layer and a low hardness layer are formed on a cornered portion such as an insert edge portion. 
     In a preferred embodiment of this coated cemented carbide member, the thickness of the enriched layer is 5 to 100 μm in a flat portion of each surface forming each insert edge portion and 0.1 to 1.4 times that in the flat portion in the insert edge portion. If this multiplying factor is less than 0.1 times, chipping resistance is disadvantageously deteriorated to the same degree as that of a conventional cemented carbide member having no enriched layer, although excellent wear resistance is maintained. If the multiplying factor exceeds 1.4 times, on the other hand, wear resistance is disadvantageously deteriorated although chipping resistance is remarkably improved as compared with the prior art. Further, an amount of the iron family metal contained in a portion of the insert edge portion immediately under the coating layer in a range of up to 2 to 50 μm in depth from the surface of the base material is preferably 1.5 to 5 times that in the interior in weight ratio. If this multiplying factor is less than 1.5 times, sufficient improvement of chipping resistance cannot be attained although excellent wear resistance is maintained. If the multiplying factor exceeds 5 times, on the other hand, wear resistance is disadvantageously deteriorated although chipping resistance is improved. 
     It is also possible to improve chipping resistance with no deterioration of wear resistance by forming a low hardness layer having lower hardness than the interior in the portion immediately under the coating layer in the range of up to 2 to 50 μm from the surface of the base material. 
     It is preferable that internal hardness of the coated cemented carbide base material is 1300 to 1700 kg/mm 2  in Vickers hardness (Hv) with a load of 500 g, and hardness of the low hardness layer which is formed on the insert edge portion is 0.6 to 0.95 times the internal hardness. If this multiplying factor is less than 0.6 times the internal hardness, a tendency of deterioration in wear resistance is observed. If the multiplying factor exceeds 0.95 times, on the other hand, improvement of chipping resistance is reduced. 
     In the coated cemented carbide member according to the first or second aspect of the present invention, it is possible to further improve wear resistance and plastic deformation resistance in the structure having a β free layer, a binder phase enriched layer or a low hardness layer on the outermost surface of the base material including each insert edge portion when the hard phase contains at least one metal component selected from carbides, nitrides and carbo-nitrides of Zr and/or Hf and a solid solution of at least one metal component selected from carbides, nitrides and carbo-nitrides of metals belonging to the group VB of the periodic table as well as WC. 
     This is because a region having higher hardness than the interior is defined in a range of up to 1 to 200 μm in depth from the region of the surface layer, i.e., β free type layer or the binder phase enriched layer, due to employment of such a composition, thereby improving plastic deformation resistance. Such improvement of plastic deformation resistance is caused since the amount of at least one metal component selected from carbides, nitrides and carbo-nitrides of metals, having high hardness, belonging to the group VB of the periodic table is increased in the range of up to 1 to 200 μm in depth from the region of the surface layer of the base material as compared with the interior. 
     Such a hard region defined in immediately under the region of surface layer of the base material is preferably 1 to 200 μm in thickness. No particular improvement is recognized if the thickness is less than 1 μm, while a tendency of insufficient chipping resistance is recognized if the thickness exceeds 200 μm, although effects are improved as to wear resistance and plastic deformation resistance. 
     The maximum hardness of such a hard region is preferably in a range of 1400 to 1900 kg/mm 2  in Vickers hardness (Hv) with a load of 500 g. If the maximum hardness is in a range of less than 1400 kg/mm 2 , a tendency of insufficient wear resistance and plastic deformation resistance is recognized although an effect as to chipping resistance is improved. If the maximum hardness is in a range exceeding 1900 kg/mm 2 , on the other hand, a tendency of insufficient chipping resistance is recognized although effects as to wear resistance and plastic deformation resistance are improved. 
     The coated cemented carbide according to the first or second aspect of the present invention is manufactured by the following method: First, a coated cemented carbide base material is sintered and thereafter each edge portion of the base material is polished for bevelling in a range for leaving a β free layer, an enriched layer or a low hardness layer, or the coated cemented carbide base material is so sintered that each edge portion of the base material is previously bevelled by die pressing in the aforementioned range. The bevelling includes chamfering and curving of the edge portion. 
     In order to adjust the thickness of each insert edge portion of the coated cemented carbide member while leaving a β free layer, an enriched layer or a low hardness layer on the edge portion, there is a method of employing powder which is prepared by changing the total amount of at least one material selected from carbides, nitrides, carbo-nitrides and carbonic nitrides of Zr and/or Hf in a hard phase and holding the same in a vacuum or a constant nitrogen pressure in a temperature range of 1350° to 1500° C. 
     Further, it is possible to bevel each insert edge portion of the as-obtained sintered body by brushing with ceramic grains such as alumina grains or GC abrasive grains, honing by barrel polishing or grinding, thereby adjusting the ratio of a thickness of a β free layer, an enriched layer or a low hardness layer to that of the layer in each portion excluding the edge portion. It is also possible to form a β free layer, an enriched layer or a low hardness layer on each insert edge portion by employing powder having a composition similar to the above, previously forming the powder into a shape having a bevelled insert edge portion by die pressing and sintering the same in a similar method. 
     Thereafter a coating layer is formed on such a base material of cemented carbide. This coating layer is a single or multiple layer of at least one metal component selected from carbides, nitrides, carbo-nitrides, oxides and borides of metals belonging to the groups IVB, VB and VIB of the periodic table and aluminum oxide, which is formed by ordinary chemical or physical vapor deposition. Due to this coating layer, it is possible to improve wear resistance and chipping resistance in high-speed cutting in a balanced manner. 
     In a more preferred embodiment of the coated cemented carbide member according to the first or second aspect of the present invention, a structure having no η phase on an outermost surface of a base material in each insert edge portion is combined with a structure having a β free layer, a binder phase enriched layer or a low hardness layer on the outermost surface of the base material including such an insert edge portion. Due to this structure, it is possible to further improve wear resistance and chipping resistance. Since no fragile η phase is contained in the insert edge portion, on which a η layer is most easily precipitated in ordinary chemical vapor deposition, it is possible to prevent deterioration of insert strength caused by brittleness of the η phase thereby improving chipping resistance, while it is also possible to prevent such a phenomenon that the coating layer falls with the fragile η phase in cutting work to progress wear, thereby improving wear resistance. 
     As to manufacturing of such a structure containing no η phase in the insert edge portion on the outermost surface of the base material, there is a method of forming a first coating layer which is in direct contact with the base material by physical vapor deposition or chemical vapor deposition employing a raw material requiring a smaller amount of carbon supply from the base material as compared with conventional chemical vapor deposition using methane as a carbon source. Considering the degree of adhesion (peeling resistance) with respect to the base material, it is particularly effective to employ acetonitrile as a carbide and nitride source for forming the coating layer in a temperature range of at least 900° C. by MT-CVD (moderate temperature-chemical vapor deposition). 
     According to a third aspect of the present invention, a coated cemented carbide member has the following structure in a cemented carbide containing binder metals of WC and one or more iron family metals: 
     The cemented carbide contains 0.3 to 15 percent by weight of a hard phase consisting of at least one metal component selected from a group of carbides, nitrides and carbo-nitrides of Zr and/or Hf and a solid solution of at least two such metal components. The cemented carbide further contains 2 to 15 percent by weight of only Co or Co and Ni as a binder phase. The cemented carbide contains tungsten carbide and unavoidable impurities in addition to the hard phase and the binder chase. 
     Due to such compositions of the hard chase and the binder phase, it is possible to improve wear resistance and chipping resistance of a tool in a well-balanced manner under high speed and high feed rate cutting conditions. In ordinary cutting work of a steel material or a casting, the temperature at the insert of the tool is increased to several 100° to 1000° C., leading to remarkable reduction in strength and hardness of the cemented carbide forming the tool. When a carbide of Zr or Hf and the like are added to the cemented carbide within the range of the present invention, strength of the cemented carbide is improved not only at the room temperature but in a high temperature range as compared with a conventional cemented carbide containing only a carbide of Ti, Ta or Nb etc., while it is possible to maintain high hardness under a high temperature. A cemented carbide containing a carbide of Zr or Hf and the like in the range of the present invention has relatively low hardness at the room temperature as compared with the prior art, while its hardness exceeds that of the prior art at a high temperature around a cutting temperature. Thus, the inventive cemented carbide is improved in hardness under a high temperature as compared with a conventional cemented carbide of the same composition containing the same amounts of a carbide and the like, whereby it is possible to maintain excellent wear resistance while improving toughness of the cemented carbide by reducing the amount of the hard phase and increasing that of the binder phase as compared with the prior art. 
     Further, the surface of the cemented carbide base material having such a structure is provided with the single or multiple coating layer consisting of one or more metal components selected from carbides, nitrides, oxides and borides of metals belonging to the groups IVB, VB and VIB of the periodic table and aluminum oxide. 
     Due to provision of such a coating layer, wear resistance is ensured on the surface of the cemented carbide. Such a coating layer is formed by ordinary chemical or physical vapor deposition. 
     If the amount of the hard phase consisting of at least one metal component selected from a group of carbides, nitrides and carbo-nitrides of Zr and/or Hf and a solid solution of at least two such metal components is less than 0.3 percent by weight, no sufficient effects are attained as to improvement cemented carbide strength and hardness in a high temperature range and no-sufficient effect of improvement in tool life can be attained in cutting in a high temperature range or at a high speed. If the amount exceeds 15 percent by weight, on the other hand, strength of the cemented carbide is extremely reduced with insufficient toughness, leading to reduction of the tool life. 
     If the amount of the binder phase is less than 2 percent by weight, the tool life cannot be improved due to reduction in sintering property of the cemented carbide. If the amount exceeds 15 percent by weight, on the other hand, the tool life cannot be improved due to reduction in plastic deformation resistance. 
     Zr and/or Hf can be previously added to a metal in the form of a carbide in which W is dissolved, or a carbo-nitride. Also when a carbo-nitride of Zr forms a solid solution with Hf, it is possible to attain a similar effect. 
     It is generally known possible to improve strength of a WC-Co cemented carbide by adding Zr and/or Hf etc. thereto (&#34;Powder and Powder Metallurgy&#34; Vol. 26, No. 6, p. 213). As to the amount of such additive, however, studs has generally been made only in relation to a small amount of not more than 5 mol percent with respect to 10 percent of Co forming a binder phase (not more than 0.9 percent by weight in the case of ZrC and not more than 1.6 percent by weight in the case of HfC in the cemented carbide). According to the present invention, at least 5 mol percent of such additive is added with respect to a binder phase. The inventors have made study as to a region containing a larger amount of such additive as compared with the prior art, to find that employment of a cemented carbide having a composition of this region has an effect in improvement of a tool life for the first time. 
     According to a preferred embodiment of this coated cemented carbide member, a hard phase consisting at least one metal component selected from a group of carbides, nitrides and carbo-nitrides of Zr and/or Hf and a solid solution of at least two such metal components disappears or decreases in a region immediately under the coating layer in a range of up to 2 to 100 μm in depth from the surface of the cemented carbide base material. 
     Toughness of the cemented carbide surface can be improved by such a structure, while toughness of the overall cemented carbide can be further improved by combination with the aforementioned composition in its interior. It is well known that a carbide of Ti etc. disappears from a cemented carbide surface by employment of a carbide or a carbo-nitride of Ti (Transactions of the Japan Institute of Metals, Vol. 45, No. 1, p. 90, for example). In a conventional tool of such a structure, however, the carbide and the like still remain in each insert edge portion of the tool. When a carbide or a carbo-nitride of Zr or Hf is added to the cemented carbide in the inventive coated cemented carbide member, on the other hand, the carbide or carbo-nitride disappears or decreases also in each insert edge portion. Due to this structure, it is possible to extremely improve toughness of an insert of a tool as compared with the prior art. If the layer in which a hard phase of Zr or Hf disappears or decreases is less than 2 μm in thickness from the surface of the base material, however, no effect is attained as to toughness of the surface. If the thickness exceeds 100 μm, on the other hand, wear resistance is reduced. Thus, the thickness of the layer is preferably in a range of 5 to 50 μm. 
     It is possible to control the thickness of the layer in which the hard phase disappears or decreases by adding a hard phase of Zr and/or Hf as a carbide, a nitride or a carbo-nitride, heating/holding the mixture in a vacuum or under a constant nitrogen pressure in a temperature range of 1350° to 1500° C. and controlling the holding time and the degree of vacuum or the nitrogen pressure. 
     A coated cemented carbide member according to a fourth aspect of the present invention is similar in composition to that according to the third aspect. In addition to the aforementioned hard phase, this coated cemented carbide member further-contains 0.03 to 35 percent by weight of another-hard phase consisting of at least one metal component selected from carbides, nitrides and carbo-nitrides of metals, excluding Zr and Hf, belonging to the groups IVB, VB and VIB of the periodic table and a solid solution of at least two such metal components. 
     The coated cemented carbide member of such a structure has the following characteristics: 
     It is possible to improve toughness of a cemented carbide containing a carbide of Zr or Hf and the like by increasing the amount of a binder phase as compared with a conventional cemented carbide, since such a cemented carbide has high strength and hardness under a high temperature. However, this cemented carbide exhibits low hardness under a low temperature. When the cemented carbide contains only a hard phase of a carbide of Zr or Hf and the like, therefore, wear resistance may be insufficient under cutting conditions causing no increase of a temperature at the insert. In order to compensate for such insufficiency of wear resistance under such conditions, a carbide having high hardness selected from those of metals, excluding Zr and Hf, belonging to the groups IVB, VB and VIB of the periodic table and the like are added to the cemented carbide in addition to the carbide of Zr or Hf and the like, so that it is possible to maintain excellent hardness under a low temperature. If the amount of the carbide selected from those of metals, excluding Zr and Hf, belonging to the groups IVB, VB and VIB of the periodic table is less than 0.03 percent by weight, however, no effect is attained as to improvement of hardness. If the amount exceeds 35 percent by weight, on the other hand, hardness is excessively increased to cause chipping, leading to reduction in tool life. 
     Other reasons for restriction of numerical values of the hard phase and a binder phase are similar to those for the aforementioned coated cemented carbide member according to the third aspect of the present invention. 
     Also in the coated cemented carbide member according to the fourth aspect of the present invention, the hard phase preferably disappears or decreases in a region immediately under the coating layer in a range of up to 2 to 100 μm in depth from the base material surface, similarly to the coated cemented carbide member according to the third aspect. The reason for this is identical to that described above with reference to the preferred embodiment of the coated cemented carbide member according to the third aspect of the present invention, and the thickness of such a layer is also preferably in a range of 5 to 50 μm. 
     In order to control this thickness, it is possible to apply a method which is similar to that described above with reference to the coated cemented carbide member according to the third aspect of the present invention. 
     The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view showing the shape of an insert of CNMG120408 under the ISO standards; 
     FIG. 2A is a structural photograph showing a section in an insert edge portion of a coated cemented carbide member according to Example 1 of the present invention, and FIG. 2B is a model diagram thereof; 
     FIG. 3A is a structural photograph showing a section in an insert edge portion of a conventional coated cemented carbide member, and FIG. 3B is a model diagram thereof; 
     FIG. 4A is a model diagram showing a section in an insert edge portion of a coated cemented carbide member according to another Example of the present invention, and FIG. 4B is a model diagram showing a section in an insert edge portion of a comparative member for that shown in FIG. 4A; 
     FIG. 5A is a model diagram showing a section in an insert edge portion of a coated cemented carbide member according to still another Example of the present invention, and FIG. 5B is a model diagram showing a section in an insert edge portion of a comparative member for that shown in FIG. 5A; and 
     FIG. 6 is a graph showing relations between Vickers hardness levels and temperatures of two types of coated cemented carbide members according to further Example of the present invention and a conventional coated cemented carbide member. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Examples of the present invention are now described. 
     EXAMPLE 1 
     Grade powder materials having compositions A to D (wt. %) shown in Table 1 were formed into tips each having a shape of CNMG120408 under ISO standards (see FIG. 1), heated to a temperature of 1450° C. in a vacuum and held at this temperature for 1 hour, and thereafter cooled. Then insert edge portions 1 of the as-obtained sintered bodies were honed with a brush employing GC abrasive grains, to be provided with curved surfaces. Thereafter the sintered bodies serving as base materials were coated with inner layers of a carbide, a nitride and a carbo-nitride of Ti having thicknesses of 7 μm in total and outer layers of aluminum oxide having thicknesses of 1 μm. 
     As to these samples, sectional structures in the insert edge portions 1 shown in FIG. 1 were analyzed to obtain the following results: 
     FIGS. 2A and 2B show such a sectional structure in the sample A, while FIGS. 3A and 3B show that in the sample D. FIGS. 2A and 3A are structural photographs, and FIGS. 23 and 3B are model diagrams thereof respectively. The coating layer comprising the inner layer and the outer layer is indicated as a single layer with a reference number &#34;2&#34; in each of FIGS. 2B and 3B. It is understood from the model diagrams shown in FIGS. 2B and 3B that the insert edge portion 1 was also provided with a β free layer 3 in the sample A, while that of the sample D was provided with no such β free layer. Table 1 also shows thicknesses a of β free layers provided on flat portions of the respective samples, thicknesses b of those provided on insert edge portions (as to a and b, refer to FIG. 2B) and ratios b/a therebetween. 
     
                       TABLE 1______________________________________            a: Thickness of                        b: Thickness of β            β Free Layer on                        Free Layer onSam-             Flat Portion                        Insert Edge Portion                                   Ratiople  Composition (μm)     (μm)    b/a______________________________________A    WC-4% ZrN-  40          25         0.636% CoB    WC-8% ZrCN- 30          20         0.674% TaC-6% CoC    WC-4% HfN-  40          25         0.636% CoD    WC-2% TiCN- 25           0         04% TaC-6% Co______________________________________ A to C: Inventive Samples D: Comparative Sample 
    
     The samples A to D were subjected to evaluation of cutting performance. Cutting conditions for the evaluation tests and the results thereof are as follows: 
     Cutting Conditions 1 (Wear Resistance Test) 
     Cutting Speed: 300 m/min. 
     Workpiece: SCM415 
     Feed Rate: 0.4 mm/rev. 
     Cutting Time: 30 min. 
     Depth of Cut: 2.0 mm 
     Cutting Oil: water-soluble 
     Cutting Conditions 2 (Chipping Resistance Test) 
     Cutting Speed: 100 m/min. 
     Workpiece: SCM435 (four-grooved material) 
     Feed Rate: 0.2 to 0.4 mm/rev. 
     Cutting Time: 30 sec. 
     Depth of Cut: 2.0 mm repeated eight times 
     
                       TABLE 2______________________________________      Flank Wear under                   Chipping Rate under      Cutting Condition 1                   Cutting Condition 2Sample     (mm)         (%)______________________________________A          0.185        25B          0.170        35C          0.172        22D          0.225        80______________________________________ 
    
     As clearly understood from the above test results, the sample D having no β free layer in each insert edge portion 1 was inferior to the other samples in both of flank wear and chipping rate. 
     EXAMPLE 2 
     Grade powder materials having compositions E to K (wt. %) shown in Table 3 were employed to form coated cemented carbide samples. Shapes of tips, sintering conditions, honing conditions for insert edge portions 1 and thicknesses of coating layers 2 were similar to those in Example 1. Table 3 also shows thicknesses of β free layers provided on flat portions and the insert edge portions (a and b) in the respective samples and ratios (b/a) therebetween. 
     
                       TABLE 3______________________________________            a: Thickness of                        b: Thickness of β            β Free Layer on                        Free Layer onSam-             Flat Portion                        Insert Edge Portion                                   Ratiople  Composition (μm)     (μm)    b/a______________________________________E    WC-4% HfC-  5           0.5        0.12% HfCN-6% CoF    WC-2% ZrC-  50          70         1.44% TiN-6% CoG    WC-2% ZrCNO-            5           1          0.22% HfCNO-6% CoH    WC-2% ZrCN- 4           0.4        0.14% NbC-6% CoI    WC-6% ZrN-  55          55         1.06% CoJ    WC-4% HfC-  5           0.4         0.082% HfCN-6% CoK    WC-2% ZrC   50          75         1.54% TiN-6% Co______________________________________ E to K: Inventive Samples 
    
     The above samples E to K were subjected to evaluation of cutting performance. Cutting conditions for the evaluation tests are as follows: 
     Cutting Conditions 3 (Wear Resistance Test) 
     Cutting Speed: 220 m/min. 
     Workpiece: SCM435 
     Feed Rate: 0.4 mm/rev. 
     Cutting Time: 20 min. 
     Depth of Cut: 2.0 mm 
     Cutting Oil: water-soluble 
     Cutting Conditions 4 (Chipping Resistance Test) 
     Cutting Speed: 100 m/min. 
     Workpiece: SCM 435 (four-grooved material) 
     Feed Rate: 0.2 to 0.4 mm/rev. 
     Cutting Time: 30 sec. 
     Depth of Cut: 2.0 mm repeated eight times 
     Table 4 shows the results of the evaluation tests. 
     
                       TABLE 4______________________________________      Flank Wear under                   Chipping Rate under      Cutting Conditions                   Cutting Conditions 4Sample     3 (mm)       (%)______________________________________E          0.165        35F          0.185        10G          0.172        24H          0.165        75I          0.210        10J          0.163        78K          0.210         8D          0.235        80(ComparativeSample)______________________________________ 
    
     As understood from the above test results, the inventive samples E to K were improved in balance between wear resistance and chipping resistance as compared with the comparative sample D having no β free layer 3 on each insert edge portion 1. The chipping rate was slightly increased in the sample H since the β free layers 3 were relatively small in thickness on both of the flat and insert edge portions, while that of the sample J was also slightly increased since the β free layer 3 provided on each insert edge portion 1 was slightly smaller in thickness than that provided on each flat portion. On the other hand, wear resistance was slightly deteriorated in the sample I since the β free layers 3 were relatively large in thickness on both of the flat and edge portions, while that of the sample K was also slightly deteriorated since the β free layer provided on each insert edge portion 1 was large in thickness. However, these inventive samples H to K were also sufficiently improved in balance between wear resistance and chipping resistance as compared with the comparative sample D. 
     EXAMPLE 3 
     Grade powder materials having compositions (wt. %) shown in Table 5 were previously formed to have curved surfaces in insert edge portions 1 by die pressing and sintered so that boating layers 2 were then provided on base material surfaces of the as-formed sintered bodies, to form coated cemented carbide samples. Shapes of the tips, sintering conditions, and compositions and thicknesses of the coating layers 2 were similar to those of Examples 1 and 2. Table 5 also shows thicknesses of β free layers 3 provided on flat and insert edge portions (a and b) of samples L and M and ratios (b/a) therebetween. 
     
                       TABLE 5______________________________________            a: Thickness of                        b: Thickness of β            β Free Layer on                        Free Layer onSam-             Flat Portion                        Insert Edge Portion                                   Ratiople  Composition (μm)     (μm)    b/a______________________________________L    WC-4% HfN-  30          40         1.32% TiC-6% CoM    WC-4% TiN-  25           0         04% TiC-6% Co______________________________________ L: Inventive sample M: Comparative sample 
    
     These samples L and M were also subjected to evaluation of cutting performance. Cutting conditions for the evaluation tests were similar to the cutting conditions 3 and 4 of Example 2. Table 6 shows the results of the evaluation tests. 
     
                       TABLE 6______________________________________      Flank Wear under      Cutting Condition 3                   Chipping RateSample     (mm)         (%)______________________________________L          0.175        20M          0.180        90______________________________________ 
    
     As understood from the results of evaluation shown in Table 6, the samples L and M were equivalent in wear resistance to each other. However, it was confirmed that the sample M was extremely inferior in chipping rate to the sample L. The sample M was deteriorated in chipping rate since its hard phase contained no metal component selected from carbides, nitrides, carbo-nitrides, of Zr and/or Hf. 
     EXAMPLE 4 
     Grade powder having a composition of WC - 2% ZrN - 4% TiC - 6% Co was employed to form a tip having the shape of CNMG120408 under ISO standards by previously chamfering each insert edge portion 1 at an angle of 25° in a size of 0.1 mm as viewed from a rake face side by die pressing. Thereafter this tip was heated in a vacuum and held at a temperature of 1400° C. for 1 hour, to form a sintered body. Similarly to Examples 1, 2 and 3, the sintered body serving as a base material was provided with coating layers 2, to form a sample N. 
     Grade powder of the same composition as the above was formed into a tip having the shape of CNMG120408 under ISO standards, sintered under the same conditions as the sample N, and thereafter each insert edge portion 1 of this sintered body was ground to be chamfered similarly to the above. The sintered body serving as a base material was provided with coating layers 2 similarly to the above, to prepare a sample O. 
     FIGS. 4A and 4B typically illustrate sections in insert edge portions 1 of the samples N and O respectively. Table 7 shows thicknesses of β free layers provided on flat portions and insert edge portions (a and b) of the samples N and O and ratios (b/a) therebetween 
     
                       TABLE 7______________________________________   a: Thickness of                 b: Thickness of β   β Free Layer on                 Free Layer on   Flat Portion  Insert Edge Portion                              RatioSample  (μm)       (μm)      b/a______________________________________N       40            44           1.1O       40             0           0______________________________________ 
    
     It is understood from FIGS. 4A and 4B that the insert edge portion 1 of the sample N was provided with a β free layer 3 while that of the sample O was provided with no such β free layer 3. 
     It has been proved by the results of the evaluation tests in Examples 1 to 4 that the following conditions are desirable in order to improve chipping resistance with no deterioration of wear resistance: 
     (1) The hard phase contains at least one metal component selected from carbides, nitrides, carbo-nitrides and carbonic nitrides of Zr and/or Hf. 
     (2) The β free layer has a thickness of 5 to 50 μm on each flat portion forming each insert edge portion. 
     (3) The β free layer provided on each insert edge portion has a thickness of 0.1 to 1.4 times that on each flat portion, i.e., a thickness of 0.5 to 70 μm. 
     Further Examples of the present invention are now described. 
     EXAMPLE 5 
     Grade powder materials having compositions (wt. %) shown in Table 8 were formed into tins each having the shape of CNMG120408 under ISO standards (see FIG. 1), and thereafter these compacts were heated to 1450° C. in a vacuum and held at the temperature for 1 hour, to form sintered bodies. Then insert edge portions 1 of these sintered bodies were honed with a brush employing GC abrasive grains. Thereafter the sintered bodies serving as base materials were coated with inner layers of a carbide, a nitride and a carbo-nitride of Ti having thicknesses of 7 μm in total and outer layers of aluminum oxide,. Table 8 shows thicknesses a of binder phase enriched layers 4 provided on flat portions, thicknesses b of the binder phase enriched layers 4 provided on insert edge portions 1, ratios b/a therebetween and relative weight ratios of Co contained an the interiors in regions immediately under the coating layers 2 in ranges of up to 2 to 50 μm in depth from the base material surfaces. Samples A1 to C1 are inventive samples, and a sample D1 is a conventional sample. 
     
                       TABLE 8______________________________________             a:       b:           Relative             Thickness                      Thickness    Content of             of Co    of Co        Co in             Enriched Enriched     Region of             Layer on Layer on     2 to 50 μm             Flat     Insert Edge  in Depth             Portion  Portion Ratio                                   (toSample Composition (μm)  (μm) b/a  Interior)______________________________________A1    WC-8% ZrN-  20       28      1.4  1.5 6% CoB1    WC-4% ZrCN- 5        7       1.4  5.0 8% TaC-6% CoC1    WC-16% HfN- 100      10      0.1  3.5 6% CoD1    WC-2% TiCN- 20       0       0    1.0 4% TaC-6% Co______________________________________ A1 to C1: Inventive Samples D1: Conventional Sample 
    
     The respective samples were subjected to evaluation of cutting performance under conditions similar to the cutting conditions 1 and 2 in Example 1. Table 9 shows the results of the evaluation tests. 
     
                       TABLE 9______________________________________      Flank Wear under                   Chipping Rate under      Cutting Condition 1                   Cutting Conditions 2Sample     (mm)         (%)______________________________________A1         0.170        45B1         0.172        30C1         0.180        22D1         0.225        80______________________________________ 
    
     As clearly understood from the above results of evaluation, it was confirmed that the samples A1 to C1 were slightly superior in wear resistance and remarkably superior in chipping resistance to the sample D1 having no binder phase enriched layer on each insert edge portion 1. 
     EXAMPLE 6 
     Grade powder materials having compositions (wt. %) shown in Table 10 were employed to form coated cemented carbide samples. Shapes of the tips, sintering conditions, honing conditions for insert edge portions 1, and compositions and thicknesses of coating layers 2 were similar to those in Example 1. 
     Table 10 also shows thicknesses of low hardness layers provided on insert edge portions 1 of the respective samples, levels of hardness in the vicinity of the cemented carbide base material surfaces (insert edge portions 1) and the interiors thereof, and ratios therebetween. 
     
                                           TABLE 10__________________________________________________________________________        Thickness               Hardness of        of Low Insert Edge        Hardness               Portion Close        Layer on               to Base        Insert Edge               Material                       Internal        Portion               Surface Hardness                              RatioSample    Composition        (μm)               (kg/mm.sup.2)X                       (kg/mm.sup.2)Y                              X/Y__________________________________________________________________________E1  WC-5% HfC-        2      1240    1300   0.95    1% HfCN-6% CoF1  WC-3% ZrC-        30     1350    1500   0.9    3% TiN-6% CoG1  WC-2% ZrCNO-        20     1300    1550   0.84    2% HfCNO-    6% CoH1  W-2% ZrCN-        5      1350    1480   0.91    4% NbC-6% CoI1  WC-6% ZrN-        50     1020    1700   0.60    4% TiC-6% CoJ1  WC-4% TiC-        50     850     1500   0.57    4% HfN-6% CoK1  WC-2% TaC        0      1350    1600   0.84    4% TiN-6% Co__________________________________________________________________________ E1 to J1: Inventive Samples K1: Comparative Samples 
    
     The respective samples were subjected to evaluation of cutting performance under conditions similar to the cutting conditions 3 and 4 in Example 2. Table 11 shows the results of the evaluation tests. 
     
                       TABLE 11______________________________________      Flank Wear Under                   Chipping Rate Under      Cutting Conditions                   Cutting Conditions 4Sample     3 (mm)       (%)______________________________________E1         0.182        35F1         0.180        40G1         0.176        30H1         0.176        43I1         0.165        10J1         0.215         3K1         0.172        85______________________________________ 
    
     As understood from the above results of evaluation, the samples E1 to J1 have better balance between wear resistance and chipping resistance. The sample J1 is a little bit insufficient in wear resistance, however, from the viewpoint of the balance between wear resistance and chipping resistance, the sample J1 is better than sample K1 which has no low hardness layer on each insert edge portion 1. 
     EXAMPLE 7 
     Grade powder materials having compositions (wt. %) shown in Table 12 were previously formed to have chamfered insert edge portions 1 by die pressing sintered and provided with coating layers 2, to prepare coated cemented carbide samples. Shapes of the tips, sintering conditions, and compositions and thicknesses of the coating layers 2 were similar to those in Examples 6 and 7. Table 12 also shows thicknesses a of enriched layers provided on flat portions of samples L1 and M1, thicknesses b of the binder phase enriched layers provided on insert edge portions 1, ratios b/a therebetween, and relative weight ratios of Co with respect to the interiors in regions immediately under the coating layers 2 in ranges of up to 2 to 50 μm in depth from the base material surfaces. FIGS. 5A and 53 typically illustrate sections of the insert edge portions of the samples L1 and M1 respectively. The portions correspond to the binder phase enriched layers and/or low hardness layers are indicated with a reference number &#34;4&#34; in FIGS. 5A and 5B. 
     
                       TABLE 12______________________________________                                   Relative            a: Thickness                      b: Thickness Content of            of Co     of Co        Co in            Enriched  Enriched     Region of            Layer on  Layer on     2 to 50 μm            Flat      Insert Edge  in DepthSam-             Portion   Portion Ratio                                   (tople  Composition (μm)   (μm) b/a  Interior)______________________________________L1   WC-6% HfN-  30        35      1.2  1.54% TiC-6% CoM1   WC-6% TiN-  25         0      0    0.94% TiC-6% Co______________________________________ L1: Inventive Sample M1: Conventional Sample 
    
     These samples L1 and M1 were also subjected to evaluation of cutting performance under conditions similar to the cutting conditions 3 and 4 in Example 2. Table 13 shows the results of the evaluation tests. 
     
                       TABLE 13______________________________________      Flank Wear under                   Chipping Rate under      Cutting Conditions                   Cutting Conditions 4Sample     3 (mm)       (%)______________________________________L1         0.175        20M1         0.178        75______________________________________ 
    
     It is understood from the above results of evaluation that the samples L1 and M1 were substantially equivalent in wear resistance to each other, while it was confirmed that the sample M1 was extremely inferior in chipping rate to the sample L1. This is because a hard phase of the sample M1 contained no metal component selected from carbides, nitrides, carbo-nitrides, Zr and/or Hf. 
     It was proved from the results of the evaluation tests in Examples 5 to 7 that the following conditions are desirable in order to improve chipping resistance with no deterioration of wear resistance: 
     (1) The hard phase contains at least one metal component selected from carbides, nitrides, carbo-nitrides and carbonic nitrides of Zr and/or Hf. 
     (2) The binder phase enriched layer or the low hardness layer has a thickness of 5 to 100 μm on each flat portion forming each insert edge portion. 
     (3) The binder phase enriched layer or the low hardness layer provided on each insert edge portion has a thickness of 0.1 to 1.4 times that on the flat portion, i.e., a thickness of 0.5 to 140 μm. 
     (4) The amount of the iron family metal contained in the region immediately under the coating layer in a range of up to 2 to 50 μm in depth from the base material surface is 1.5 to 5 times that in the interior in weight ratio. 
     (5) Internal hardness of the cemented carbide is 1300 to 1700 kg/mm 2  in Vickers hardness with a load of 500 g, and that of the low hardness layer provided on each insert edge portion is 0.6 to 0.95 times the internal hardness. 
     Further Examples of the present invention are now described. 
     EXAMPLE 8 
     Samples having compositions shown in Table 14 were formed into tips each having the shape of CNMG120408 under ISO standards, and thereafter held in a vacuum at 1450° C. for 1 hour to be sintered. Thereafter insert edge portions 1 of the sintered bodies were honed with a brush employing GC abrasive grains, to have curved surfaces. The as-formed sintered bodies sensing as base materials were coated with inner layers of a carbide, a nitride and a carbo-nitride of Ti having thicknesses of 7 μm in total and outer layers of aluminum oxide of 1 μm in thickness. 
     A base material having the same composition as that of the sample A2 was coated with an inner layer of TiCl 4 , CH 3  CN and H 2  having a thickness of 7 μm by MT-CVD at 950° C. and thereafter coated with an outer layer of aluminum oxide of 1 μm in thickness, to prepare a sample A3. 
     
                       TABLE 14______________________________________Sample      Composition______________________________________A2, A3      WC-3 wt % ZrCN-4 wt % NbC-6 wt % CoB2          WC-3 wt. % ZrCN-4 wt % NbC-6 wt % CoC2          WC-3 wt % HfCN-2 wt % TaC-6 wt % CoD2          WC-3 wt % TiCN-2 wt % TaC-6 wt % Co(ConventionalSample)______________________________________ 
    
     The aforementioned samples were analyzed to find that η phases were precipitated on insert edge portions 1 of the samples A2, B2 and C2 in thicknesses of 0.5 to 2 μm while no such η phase was precipitated on each insert edge portion 1 of the sample A3. 
     Each sample had a β free layer 3, a binder phase enriched layer 4 and a low hardness layer 4 of the same thicknesses. Such thicknesses were 20 μm in the samples A2 and A3, 25 μm in the sample B2 and 30 μm in the sample C2 respectively. Table 15 shows the amounts and hardness levels of metals belonging to the group 5a of the periodic table contained in portions inside surface layer regions of these samples. 
     
                       TABLE 15______________________________________                               Maximum  Content of Content of Thickness                               Hardness of  Carbo-Nitride             Carbo-Nitride                        of High                               High  of Group 5a             of Zr of Hf                        Hardness                               Hardness  Metal in   in Portion Layer  Layer  Portion inside             inside     inside inside  Surface Layer             Surface Layer                        Surface                               Surface  Region (to Region (to Layer  LayerSample Interior)  Interior)  Region Region______________________________________A2     2.5 Times  1.0        160    1700B2     1.8 Times  1.0        100    1650C2     1.2 Times  1.05        40    1550______________________________________ 
    
     The aforementioned samples, including the conventional sample D2 for comparison, were subjected to evaluation of cutting performance under the following conditions: 
     Cutting Conditions 5 (Wear Resistance and Plastic Deformation Resistance Tests) 
     Cutting Speed: 150 m/min. 
     Workpiece: SK5 
     Feed Rate: 0.7 mm/rev. 
     Cutting Time: 5 min. 
     Depth of Cut: 2.0 mm 
     Cutting Oil: water-soluble 
     Cutting Conditions 6 (Chipping Resistance Test) 
     Cutting Speed: 100 m/min. 
     Workpiece: SCM435 
     Feed Rate: 0.2 to 0.4 mm/rev. 
     Chatting Time: 30 sec. 
     Depth of Cut: 2.0 mm repeated eight times 
     Table 16 shows the results of the aforementioned evaluation tests. 
     
                       TABLE 16______________________________________   Flank       Plastic      ChippingSample  Wear (mm)   Deformation (mm)                            Rate (%)______________________________________A2      0.14        0.055        25A3      0.11        0.054        18B2      0.16        0.079        20C2      0.18        0.090        10D2      0.28        0.145        90______________________________________ 
    
     It is understood from the above results of evaluation that the inventive samples A2, B2 and C2 were extremely superior to the comparative sample D2 not only in wear resistance and plastic deformation resistance but in chipping resistance. Further, the sample A3 was further superior to the sample A2 in wear resistance and chipping resistance. This is conceivably because each insert edge portion 1 of the sample A3 was provided with no η phase. 
     EXAMPLE 9 
     Raw powder materials were prepared from WC of 4 μm in grain size, ZrC of 1 to 2 μm in grain size, ZrN, HfC, HfN, (Zr, Hf)C (in a composition of 50 mol % ZrC), (Zr, W)C (in a composition of 90 mol % ZrC), (Hf, W)C (in a composition of 90 mol % HfC), Co and Ni respectively. These raw powder materials were wet-blended with each other to form grade powder materials having compositions shown in Table 17. The grade powder materials were press-molded into tips each having the shape of CNMG120408 under ISO standards, and thereafter heated in an H 2  atmosphere to a temperature of 1000° to 1450° C. at a rate of 5° C./min. The tips were then held in a vacuum at 1450° C. for 1 hour, and cooled. 
     
                                           TABLE 17__________________________________________________________________________Wt. %                      Wt. %    ThicknessNo.   ZrC ZrN    HfC       HfN          (ZrHf)C              (ZrW)C                  (HfW)C                      Co Ni                           WC  of Layer A__________________________________________________________________________Inventive Samples1  0.3                     2    Residue                                02  2                       6    Residue                                03  4                       6    Residue                                54                  4.8     6    Residue                                55     2                    6    Residue                               156     4                    6    Residue                               307     8                    6    Residue                               508              10          6    Residue                               109  3.5   6.5               6    Residue                               1010    10    5              6    Residue                               10011       8                 13 2 Residue                               1012                     8.9 13 2 Residue                               10Comparative Samples13 0.3                       1.5                           Residue                                014    11    6              6    Residue                               11015       8                 13 3 Residue                                016 WC-2 wt % Co                 Residue                                017 WC-2 wt % TiN-2 wt % TaC-6 wt % Co                           Residue                               20__________________________________________________________________________ 
    
     Then the as-formed sintered bodies serving as base materials were subjected to cutting edge processing, and coated with inner layers of TiC having thicknesses of 5 μm and outer layers of aluminum oxide having thicknesses of 1 μm, to be subjected to cutting tests under the following ting conditions: 
     Cutting Conditions 7 (Wear Resistance Test) 
     Cutting Steed: 350 m/min. 
     Workpiece: SCM415 
     Feed Rate: 0.5 mm/rev. 
     Cutting Time: 20 min. 
     Depth of Cut: 2.0 mm 
     Cutting Conditions 8 (Toughness Test) 
     Cutting Speed: 100 m/min. 
     Workpiece: SCM435 (four-grooved material) 
     Feed Rate: 0.20 to 0.40 mm/rev. 
     Cutting Time: 30 sec. 
     Depth of Cut: 2.0 mm repeated eight times 
     Table 18 shows the results of the cutting tests. These samples included those having hard phase disappearance layers on base material surfaces and those having no such layers. Such hard phase disappearance layers are expressed as layers A. Thicknesses of such layers A are shown in the rightmost column of Table 17. 
     
                       TABLE 18______________________________________           Test 7    Test 8   No.     (Flank Wear)                     (Chipping Rate)______________________________________Inventive 1         0.20 mm    60%Samples   2         0.24      45     3         0.22      40     4         0.21      36     5         0.25      24     6         0.23      18     7         0.21      10     8         0.16      43     9         0.17      47     10        0.24      60     11        0.25      40     12        0.23      35Comparative     13        0.28      95Samples   14        0.28      80     15        0.30      20     16        0.21      80     17        0.24      75______________________________________ 
    
     EXAMPLE 10 
     Raw powder materials were prepared from WC of 4 μm in grain size, ZrN of 1 to 2 μm in grain size, HfN, (Zr, Hf)C (in a composition of 50 mol % ZrC), TiC, TiN, TaC, NbC, (Ti, W)CN (in a composition of 30 wt. % TiC and 25 wt. % TiN with a remainder of WC), (Hf, W)CN (in a composition of 90 mol % HfCN with a remainder of WC), (Ti, Hf)C (in a composition of 50 mol % TiC), Co and Ni respectively to form grade powder materials having compositions shown in Table 19, similarly to Example 9. These grade powder materials were press-molded into tips each having the shape of CNMG120408 under ISO standards, and thereafter heated in an H 2  atmosphere to a temperature of 1000° to 1450° C. at a rate of 5° C./min. The tips were held in a vacuum at 1450° C. for 1 hour, and thereafter cooled. Then the as-formed sintered bodies serving as base materials were subjected to cutting edge processing, and coated with inner layers of TiC having thicknesses of 5 μm and outer layers of aluminum oxide having thicknesses of 1 μm by ordinary CVD, to form inventive samples 18 to 25 shown in Table 19. Samples 26 to 34 are comparative samples having compositions out of the inventive composition range. 
     
                                           TABLE 19__________________________________________________________________________Inventive Samples                                  ThicknessWt. %                         Wt. %    of Layer ANo.   ZrN HfN    (ZrHf)C        TiC           TaC              NbC                 TiN                    (TiW)CN                         Co Ni                              WC  (μm)__________________________________________________________________________18       0.3 15 10 10         2    Residue                                   019 2         2                6    Residue                                  1520    4         2             6    Residue                                  3021 4                  0.03    6    Residue                                  3522    1      1                6    Residue                                   523 8            2             6    Residue                                  5024       15              5    6    Residue                                  10025    4         2             10 5 Residue                                  30__________________________________________________________________________Comparative Samples                                  ThicknessWt. %                         Wt. %    of Layer ANo.   ZrN HfN    (ZrHf)C        TiC           TaC              NbC                 TiN                    (TiW)CN                         Co Ni                              WC  (μm)__________________________________________________________________________26       0.3 15 15 5            1.5                              Residue                                   027       0.3 26 10            2    Residue                                   028       16              4    6    Residue                                  11029    4          2            10 6 Residue                                  3030 WC-15 wt % TiCN-1 wt % TaC-10 wt % NbC-2 wt % Co                         6    Residue                                   0   WC-4 wt % TiN-2 wt % TaC-6 wt % Co                         13 3 Residue                                  30__________________________________________________________________________Wt. %                          Wt. %   ThicknessNo.   (Zrw)CN   (HfW)CN        (TiW)CN              TiC                 (T1Hf)C                      TaC Co                            Ni                              WC  of Layer A__________________________________________________________________________26 2.4       3.6               6   Residue                                  2027      4.5                2   6   Residue                                  3028                 0.7                 1.3      6   Residue                                   5__________________________________________________________________________ 
    
     The respective samples shown in Table 19 were subjected to wear resistance and toughness tests under the following cutting conditions: 
     Cutting Conditions 9 (Wear Resistance Test) 
     Cutting Speed: 160 m/min. 
     Workpiece: SCM415 
     Feed Rate: 0.5 mm/rev. 
     Cutting Time: 40 min. 
     Depth of Cut: 1.5 mm 
     Cutting Conditions 10 (Toughness Test) 
     Cutting Speed: 100 m/min. 
     Workpiece: SCM435 (four-grooved material) 
     Feed Rate: 0.15 to 0.25 mm/rev. 
     Cutting Time: 30 sec. 
     Depth of Cut: 2.0 mm repeated eight times 
     Table 20 shows the results of the evaluation tests. 
     
                       TABLE 20______________________________________           Test 9    Test 10   No.     (Flank Wear)                     (Chipping Rate)______________________________________Inventive 18        0.18 mm    60%Samples   19        0.20      35     20        0.21      25     21        0.22      28     22        0.24      48     23        0.20      22     24        0.24      14     25        0.24      35     32        0.20      32     33        0.20      22     34        0.23      42Comparative     26        0.30      95Samples   27        0.17      74     28        0.28      45     29        0.28      33     30        0.24      90     31        0.28      88______________________________________ 
    
     EXAMPLE 11 
     The samples Nos. 3 and 19 shown in Tables 17 and 19 according to Examples 9 and 10 were subjected to measurement of transverse rupture strength under the room temperature and a high temperature and high-temperature hardness. The hardness levels were measured under loads of 5 kg. Table 21 and FIG. 6 show the results, with the results of the comparative sample 17 in Table 17. It is understood from these results that the inventive samples 3 and 19 were superior to the comparative sample 17 in transverse rupture strength and hardness under high temperatures. 
     
                       TABLE 21______________________________________         Transverse Rupture                       Transverse         Strength at Room                       Rupture Strength   No.   Temperature   at 1000° C.______________________________________Inventive  3      252 kg/mm.sup.2                           92 kg/mm.sup.2Samples   19      216           88Comparative     17      190           80Samples______________________________________ 
    
     The following Table 22 lists all of the above samples that have a hard phase consisting of WC and at least one of carbides, nitrides, carbonitrides or carbonic nitrides of HF and/or Zr and solid solutions thereof, and that have a surface layer flat portion thickness (a) in the range from 5 μm to 100 μm and a ratio of the edge portion thickness to the flat portion thickness (b/a) in the range from 0.1 to 1.4. Table 22 recites the composition, flat portion thickness (a), the thickness ratio (b/a), and the cutting test results for each sample as reported above. The cutting test results are for above cutting conditions 2 or 4, whereby a &#34;0&#34; symbol indicates a chipping rate of not more than 50% and a Δ symbol indicates a chipping rate of more than 50%. Table 22 also shows the total percentage content (W) of nitrides, carbonitrides, and carbonic nitrides of Zr and/or Hf relative to the total composition, and the weight ratio of Zr and Hf relative to the amount of binder phase ((Zr+Hf)/Co) in each sample. 
     
                                           TABLE 22__________________________________________________________________________                              Cutting              w   a           TestSample    Composition    (wt. %)                  (μm)                     b/a                        (Zr + Hf)/Co                              Results__________________________________________________________________________Table 1    WC-4% ZrN-6% Co              4   40 0.63                        0.58  ◯Table 1    WC-4% HfN-6% Co              4   40 0.63                        0.62  ◯CTable 3    WC-4% HfC-2% HfCN-6% Co               6! 2                  5  0.1                        0.94  ◯ETable 3    WC-2% ZrCNO-2% HfCNO-              4   5  0.2                        0.60  ◯G   6% CoTable 3    WC-6% ZrN-6% Co              6   55 1.0                        0.87  ◯ITable 8    WC-8% ZrN-6% Co              8   20 1.4                        1.16  ◯A1Table 8    WC-16% HfN-6% Co              16  100                     0.1                        2.47  ◯C1Table 3    WC-2% ZrCN-2% NbC-6% Co              2   4  0.1                        0.29  ΔH*Table 3    WC-4% HfC-2% HfCN-6% Co               6! 2                  5  0.08                        0.94  ΔJ*__________________________________________________________________________ *comparative samples; underlined value is out of inventive range-. 
    
     Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.