Coated cemented carbide members and method of manufacturing the same

Abstract: 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 a component selected from carbides etc. of metals belonging to the groups IVB, VB and VIB of the periodic table and a coating layer (2) 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 (3) is provided on an outermost surface of each insert edge portion (1) of the cemented carbide base material. The coating layer (2) is a single or multiple layer consisting of at least one metal component selected from carbides etc. 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 for serving as a cutting tool.

Description: BACKGROUND OF THE INVENTION 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. 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. EP-A-0 560 212 is directed to a coated cemented carbide having a coating layer on a substrate surface, the substrate surface comprising WC as a hard phase and a hard phase in which a hard phase comprising at least one element selected from the group consisting of carbide, nitride and carbon nitride of Te, coexists with a hard phase comprising at least one element selected from the group consisting of carbides, nitrides, carbon nitrides of Zr and at least one iron family metal forming a binder phase, whereby the coating layer is a single or composite layer comprising an element selected from the group consisting of carbide, nitride, oxide and boride of a metal. US-A-4 828 612 discloses a cemented carbide cutting tool substrate having enhanced surface toughness due to binder enrichment and depletion of aluminum nitride near the peripheral surface. US-A-4 698 266 discloses a coated cemented carbide cutting tool containing WC and metal carbide grains selected from the group TiC, TaC, NbC, HfC and combination thereof. Further, a cobalt bonding phase is provided. The coating comprises one or multiple coating layers. GB-A-2 095 702 discloses another cemented carbide member having a binder einriched surface. The surface can be coated with the refractory oxide, nitride, boride and/or carbide. Cobalt and Nickel are provided as binder phase. 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. These objects are achieved by the coated cemented carbide members and the processes of making the same as defined in the independent claims 1,7 and 20-21 for the Contracting States DE,FR,GB and IT and as defined in the claims 1,8 and 22-23 for the Contracting States ES and SE, respectively. 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 phase. Due to such compositions of the hard phase 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 ("Powder and Powder Metallurgy Vol. 26, No. 6, p. 213). As to the amount of such additive, however, study 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. 2B 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 "2" in each of Figs. 2B and3B. 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. Sample Composition a: Thickness of β Free Layer on Flat Portion (µm) b: Thickness of β Free Layer on Insert Edge Portion (µm) Ratio b/a A WC-4%ZrN-6%Co 40 25 0.63 B WC-8%ZrCN-4%TaC-6%Co 30 20 0.67 C WC-4%HfN-6%Co 40 25 0.63 D WC-2%TiCN-4%TaC-6%Co 25 0 0 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 Sample Flank Wear under Cutting Condition 1 (mm) Chipping Rate under Cutting Condition 2 (%) A 0.185 25 B 0.170 35 C 0.172 22 D 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. Sample Composition a: Thickness of β Free Layer on Flat Portion (µm) b: Thickness of β Free Layer on Insert Edge Portion (µm) Ratio b/a E WC-4%HfC 2%HfCN-6%Co 5 0.5 0.1 F WC-2%ZrC-4%TiN-6%Co 50 70 1.4 G WC-2%ZrCNO-2%HfCNO-6%Co 5 1 0.2 H WC-2%ZrCN-4%NbC-6%Co 4 0.4 0.1 I WC-6%ZrN-6%Co 55 55 1.0 J WC-4%HfC-2%HfCN-6%Co 5 0.4 0.08 K WC-2%ZrC 4%TiN-6%Co 50 75 1.5 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 Cuttinq 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. Sample Flank Wear under Cutting Conditions 3 (mm) Chipping Rate under Cutting Conditions 4 (%) E 0.165 35 F 0.185 10 G 0.172 24 H 0.165 75 I 0.210 10 J 0.163 78 K 0.210 8 D (Comparative Sample) 0.235 80 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 coating 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. Sample Composition a:Thickness of β Free Layer on Flat Portion (µm) b:Thickness of β Free Layer on Insert Edge Portion (µm) Ratio b/a L WC-4%HfN-2%TiC-6%Co 30 40 1.3 M WC-4%TiN-4%TiC-6%Co 25 0 0 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. Sample Flank Wear under Cutting Condition 3 (mm) Chipping Rate (%) L 0.175 20 M 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. Sample a: Thickness of β Free Layer on Flat Portion (µm) b: Thickness of β Free Layer on Insert Edge Portion (µm) Ratio b/a N 40 44 1.1 O 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 tips 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 in 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. Sample Composition a: Thickness of Co Enriched Layer on Flat Portion (µm) b: Thickness of Co Enriched Layer on Insert Edge Portion (µm) Ratio b/a Relative Content of Co in Region of 2 to 50 µm in Depth (to Interior) A1 WC-8%ZrN-6%Co 20 28 1.4 1.5 B1 WC-4%ZrCN-8%TaC-6%Co 5 7 1.4 5.0 C1 WC-16%HfN-6%Co 100 10 0.1 3.5 D1 WC-2%TiCN-4%TaC-6%Co 20 0 0 1.0 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. Sample Flank Wear under Cutting Condition 1 (mm) Chipping Rate under Cutting Condions 2 (%) A1 0.170 45 B1 0.172 30 C1 0.180 22 D1 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. Sample Composition Thickness of Low Hardness Layer on Insert Edge Portion (µm) Hardness of Insert Edge Portion Close to Base Material Surface (kg/mm 2 )X Internal Hardness (kg/mm 2 ) Y Ratio X/Y E1 WC-5%HfC-1%HfCN-6%Co 2 1240 1300 0.95 F1 WC-3%ZrC-3%TiN-6%Co 30 1350 1500 0.9 G1 WC-2%ZrCNO-2%HfCNO-6%Co 20 1300 1550 0.84 H1 W-2%ZrCN-4%NbC-6%Co 5 1350 1480 0.91 I1 WC-6%ZrN-4%TiC-6%Co 50 1020 1700 0.60 J1 WC-4%TiC-4%HfN-6%Co 50 850 1500 0.57 K1 WC-2%TaC 4%TiN-6%Co 0 1350 1600 0.84 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. Sample Flank Wear Under Cutting Conditions 3 (mm) Chipping Rate Under Cutting Conditions 4 (%) E1 0.182 35 F1 0.180 40 G1 0.176 30 H1 0.176 43 I1 0.165 10 J1 0.215 3 K1 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 5B 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 "4" in Figs. 5A and 5B. Sample Composition a:Thickness of Co Enriched Layer on Flat Portion (µm) b:Thickness of Co Enriched Layer on Insert Edge Portion (µm) Ratio b/a Relative Content of Co in Region of 2 to 50 µm in Depth (to Interior) L1 WC-6%HfN-4%TiC-6%Co 30 35 1.2 1.5 M1 WC-6%TiN-4%TiC-6%Co 25 0 0 0.9 L1: Inventive Sample M1: Coventional 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. Sample Flank Wear under Cutting Conditions 3 (mm) Chipping Rate under Cutting Conditions 4 (%) L1 0.175 20 M1 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 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 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. Sample Composition A2, A3 WC-3wt%ZrCN-4wt%NbC-6wt%Co B2 WC-3wt.%ZrCN-4wt%NbC-6wt%Co C2 WC-3wt%HfCN-2wt%TaC-6wt%Co D2 (Conventional Sample) WC-3wt%TiCN-2wt%TaC-6wt%Co 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. Sample Content of Carbo-Nitride of Group 5a Metal in Portion inside Surface Layer Region (to Interior) Content of Carbo-Nitride of Zr of Hf in Portion inside Surface Layer Region (to Interior) Thickness of High Hardness Layer inside Surface Layer Region Maximum Hardness of High Hardness Layer inside Surface Layer Region A2 2.5 Times 1.0 160 1700 B2 1.8 Times 1.0 100 1650 C2 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. Cutting Time: 30 sec. Depth of Cut: 2.0 mm repeated eight times Table 16 shows the results of the aforementioned evaluation tests. Sample Flank Wear (mm) Plastic Deformation (mm) Chipping Rate (%) A2 0.14 0.055 25 A3 0.11 0.054 18 B2 0.16 0.079 20 C2 0.18 0.090 10 D2 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. Inventive Samples No. Wt.% Wt.% Thickness of Layer A ZrC ZrN HfC HfN (ZrHf)C (ZrW)C (HfW)C Co Ni WC 1 0.3 2 Residue 0 2 2 6 Residue 0 3 4 6 Residue 5 4 4.8 6 Residue 5 5 2 6 Residue 15 6 4 6 Residue 30 7 8 6 Residue 50 8 10 6 Residue 10 9 3.5 6.5 6 Residue 10 10 10 5 6 Residue 100 11 8 13 2 Residue 10 12 8.9 13 2 Residue 10 Comparative Samples No. Wt.% Wt.% Thickness of Layer A ZrC ZrN HfC HfN (ZrHf)C (ZrW)C (HfW)C Co Ni WC 13 0.3 1.5 Residue 0 14 11 6 6 Residue 110 15 8 13 3 Residue 10 16 WC-2wt%Co Residue 0 17 WC-2wt%TiN-2wt%TaC-6wt%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 cutting conditions: Cutting Conditions 7 (Wear Resistance Test) Cutting Speed: 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. No. Test 7 (Flank Wear) Test 8 (Chipping Rate) Inventive Samples 1 0.20 mm 60% 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 35 Comparative Samples 13 0.28 95 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 and 32 to 34 shown in Table 19. Samples 26 to 31 are comparative samples having compositions out of the inventive composition range. Inventive Samples No. Wt.% Wt.% Thickness of Layer A (µm) ZrN HfN (ZrHf)C TiC TaC NbC TiN (TiW)CN Co Ni WC 18 0.3 15 10 10 2 Residue 0 19 2 2 6 Residue 15 20 4 2 6 Residue 30 21 4 0.03 6 Residue 35 22 1 1 6 Residue 5 23 8 2 6 Residue 50 24 15 5 6 Residue 100 25 4 2 10 5 Residue 30 Comparative Samples No. Wt.% Wt.% Thickness of Layer A (µm) ZrN HfN (ZrHf)C TiC TaC NbC TiN (TiW)CN Co Ni WC 26 0.3 15 15 5 1.5 Residue 0 27 0.3 26 10 2 Residue 0 28 16 4 6 Residue 110 29 4 2 10 6 Residue 30 30 WC-15wt%TiCN-10w%TaC-10wt%NbC-2wt%Co 6 Residue 0 31 WC-4wt%TiN-2wt%TaC-6wt%Co 13 3 Residue 30 Inventive Examples No. Wt.% Wt.% Thickness of Layer A (Zrw)CN (HfW)CN (TiW)CN TiC (TlHf)C TaC Co Ni WC 32 2.4 3.6 6 Residue 20 33 4.5 2 6 Residue 30 34 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 Cuttinq 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. No. Test 9 (Flank Wear) Test 10 (Chipping Rate) Inventive Samples 18 0.18 mm 60 % 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 42 Comparative Samples 26 0.30 95 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. No. Transverse Rupture Strength at Room Temperature Transverse Rupture Strength at 1000°C Inventive 3 252 kg/mm 2 92 kg/mm 2 Samples 19 216 88 Comparative Samples 17 190 80

Claims: Claims for the following Contracting States : DE, FR, GB, IT A coated cemented carbide member comprising 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 compound selceted from carbides, nitrides, carbo-nitrides and carbonic nitrides of metals belonging to the groups IVB, VB and VIB of the periodic table (deming 1923), wherein said hard phase contains at least one metal compound 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 (3) is provided on an outermost surface of each insert edge portion (1) of said cemented carbide base material, and a coating layer (2) being provided on the surface of said layer (3) which is a single or multiple layer consisting of at least one metal compound selected from the group of carbides, nitrides, carbo-nitrides, oxides and borides of metals belonging to the groups IVB, VB and VIB of the periodic table and aluminum oxide and wherein said layer (3) has a thickness of 5 to 50 µm on a flat portion of each surface forming said insert edge portion (1) and a thickness of 0.1 to 1.4 times said thickness of said flat portion on said insert edge portion (1). A coated cemented carbide member in accordance with claim 1, wherein said hard phase consists of a solid solution of at least one metal compound selected from carbides, nitrides and carbo-nitrides of Zr and/or Hf and at least one metal compound selected from carbides, nitrides and carbo-nitrides of metals belonging to the group VB of the periodic table, and WC. A coated cemented carbide member in accordance with claim 2, wherein a larger amount of said at least one metal compound selected from carbides, nitrides and carbo-nitrides of metals belonging to the group VB of the periodic table forming said hard phase is contained over an internal region of up to 1 to 200 µm in depth from a surface layer region consisting of only WC and an iron family metal as compared with a region inside thereof. A coated cemented carbide member in accordance with claim 2, wherein said at least one metal compound selected from carbides, nitrides and carbo-nitrides of Zr and/or Hf is contained over an internal region of up to 1 to 200 µm in depth from a surface layer region consisting of only WC and an iron family metal in the same weight ratio as that in a region inside thereof while only said at least one metal compound selected from carbides, nitrides and carbo-nitrides of metals belonging to the group VB of the periodic table forming said hard phase is contained over said region in a larger weight ratio than that in said inside region. A coated cemented carbide member in accordance with claim 2, wherein a region having higher hardness than an inside region is provided over a depth of 1 to 200 µm from a surface layer region consisting of only WC and an iron family metal, the maximum hardness of said region being in a range of 1400 to 1900 kg/mm 2 in Vickers hardness with a load of 500 g. A coated cemented carbide member in accordance with claim 2, wherein no η phase is contained in said outermost surface of said insert edge portion (1) in said base material. A coated cemented carbide member comprising a cemented carbide base material containing a binder metal consisting of at least one iron family metal and a hard phase of at least one metal compound selected from carbides, nitrides, carbo-nitrides and carbonic nitrides of metals belonging to the groups IVB, VB and VIB of the periodic table (deming 1923) wherein said hard phase contains at least one metal compound selected from carbides, nitrides, carbo-nitrides and carbonic nitrides of Zr and/or Hf, and WC , a binder phase enriched layer (4) containing a larger amount of said binder metal as compared with the interior is provided on an outermost surface of each insert edge portion (1) of said cemented carbide base material, and a coating layer (2) being provided on the surface of said layer (4) which is a single or multiple layer of at least one metal compound 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, and wherein said binder phase enriched layer (4) has a thickness of 5 to 50 µm on a flat portion of each surface forming said insert edge portion (1) and a thickness of 0.1 to 1.4 times that thickness on said flat portion on said insert edge portion (1). A coated cemented carbide member in accordance with claim 7, wherein the amount of said binder metal contained in a region immediately under said coating layer (2) provided on said insert edge portion (1) in a range of up to 2 to 50 µm in thickness from the surface of said base material is 1.5 to 5 times that of said binder metal contained in the interior in weight ratio. A coated cemented carbide member in accordance with claim 7, wherein a low hardness layer having lower hardness than the interior is provided in a region immediately under said coating layer (2) in a range of up to 2 to 50 µm in depth from the surface of said base material. A coated cemented carbide member in accordance with claim 7, wherein internal hardness of said base material is 1300 to 1700 kg/mm 2 in Vickers hardness with a load of 500 g, and hardness of said low hardness layer provided on said insert edge portion (1) is 0.6 to 0.95 times said internal hardness. A coated cemented carbide member in accordance with claim 7, wherein said hard phase consists of a solid solution of at least one metal compound selected from carbides, nitrides and carbo-nitrides of Zr and/or Hf and at least one metal compound selected from carbides, nitrides and carbo-nitrides of metals belonging to the group VB of the periodic table, and WC. A coated cemented carbide member in accordance with claim 11, wherein a larger amount of said at least one metal compound selected from carbides, nitrides and carbo-nitrides of metals belonging to the group VB of the periodic table forming said hard phase is contained over a region of up to 1 to 200 µm in depth from a surface layer region of said binder phase enriched layer (4) as compared with a region inside thereof. A coated cemented carbide member in accordance with claim 11, wherein said at least one metal compound selected from carbides, nitrides and carbo-nitrides of Zr and/or Hf has the same weight ratio as that in the interior over a region of 1 to 200 µm in depth from a surface layer region of said binder phase enriched layer (4) while only said at least one metal compound selected from carbides, nitrides and carbo-nitrides of metals belonging to the group VB of the periodic table forming said hard phase has a larger weight ratio in said region as compared with that in the interior. A coated cemented carbide member in accordance with claim 11, wherein a region having higher hardness than an inside region is provided over a depth of 1 to 200 µm from a surface layer region of said binder phase enriched layer (4) the maximum hardness of said region being in a range of 1400 to 1900 kg/mm 2 in Vickers hardness with a load of 500 g. A coated cemented carbide member in accordance with claim 11, wherein no η phase is contained in said outermost surface of said insert edge portion (1) in said base material. A coated cemented carbide member in accordance with claim 1 containing WC and one or more iron family metals as binder metals, wherein the cemented carbide base material contains: 0.3 - 15 percent by weight of a hard phase consisting of at least one metal compound selected from a group of nitrides and carbo-nitrides of Zr and/or HF and a solid solution of at least two such metal compounds, 2 - 15 percent by weight of a binder phase consisting of only Co or Co and Ni and a remainder consisting of WC and anavoidable impurities; and a single or multiple layer consisting of one or more metal materials selected from carbides, nitrides, oxides and borides of metals belonging to the groups IVB, VB and VIB of the periodic table and aluminum oxide coating the surface of said cemented carbide base material. A coated cemented carbide member in accordance with claim 16, wherein said hard phase consisting of at least one metal compound 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 compounds disappears or decreases in a region immediately under the coating layer (12) in a range of up to 2 to 100 µm in depth from the surface of the base material. A coated cemented carbide member in accordance with claim 1 containing WC and one or more iron family metals as binder metals, wherein the cemented carbide base material contains: 0.3 to 15 percent by weight of a hard phase consisting of at least one metal compound 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 compounds, 0.03 to 35 percent by weight of a hard phase consisting of at least one metal compound selected from a group of 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 compounds, 2 to 15 percent by weight of a binder phase consisting of only Co,or Co and Ni, and a remainder consisting of WC and unavoidable impurities; and a single or multiple layer consisting of one or more metal compounds 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, being provided on the surface of said cemented carbide base material. A coated cemented carbide member in accordance with claim 18, wherein said hard phase consisting of at least one metal compound 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 compounds and the hard phase consisting of at least one metal compound selected from carbides, nitrides, 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 compounds, disappear or decrease in a region immediately under said coating layer (2) in a range of up to 2 to 100 µm in depth from the surface of the base material. A method of manufacturing the coated cemented carbide member of claims 1 - 6, comprising: a step of sintering powder which consists of a binder metal containing at least one iron family metal, and hard phases of at least one metal compound selected from at least carbides, nitrides, carbo-nitrides and carbonic nitrides of Zr and/or Hf, and WC; a step of grinding or polishing an outermost surface of each insert edge portion for bevelling the same into a chamfered shape or a curved surface shape in a range leaving a layer consisting of only WC and said binder metal (3) or a binder phase enriched layer (4) or a binder phase enriched layer (4) in combination with a low hardness layer on said outermost surface; and a step of forming a coating layer (2) of a single or multiple layer consisting of at least one metal compound selected from carbides, nitrides, carbo-nitrides, oxides and borides of metals belonging to the groups IVB, VB and VIB of the periodic table (deming 1923) and aluminum oxide. A method of manufacturing a coated cemented carbide member in accordance with claims 7 - 15, comprising: a step of sintering powder which consists of a binder metal containing at least one iron family metal and hard phases, at least one metal compound selected from at least carbides, nitrides, carbo-nitrides and carbonic nitrides of Zr and/or Hf, and WC; a step of grinding or polishing an outermost surface of each insert edge portion for bevelling the same into a chamfered shape or a curved surface shape in a range leaving a layer consisting of only WC and said binder metal (3), or a binder phase enriched layer (4) or a low hardness layer in combination with said binder phase enriched layer (4) on said outermost surface; and a step of forming a coating layer (2) of a single or multiple layer consisting of at least one metal compound selected from carbides, nitrides, carbon nitrides, oxides and borides of metals belonging to the groups IVB, VB and VIB of the periodic table (deming 1923) and aluminum oxide. A method of manufacturing a coated cemented carbide member in accordance with claims 20 and 21, wherein at first a step of molding the powder by press molding into a shape with bevelled insert edge portions is included. Claims for the following Contracting States : ES, SE A coated cemented carbide member comprising 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 compound selected from carbides, nitrides, carbo-nitrides and carbonic nitrides of metals belonging to the groups IVB, VB and VIB of the periodic table (deming 1923), wherein said hard phase contains at least one metal compound 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 (3) is provided on an outermost surface of each insert edge portion (1) of said cemented carbide base material, and a coating layer (2) being provided on the surface of said layer (3) which is a single or multiple layer consisting of at least one metal compound selected from the group of carbides, nitrides, carbo-nitrides, oxides and borides of metals belonging to the groups IVB, VB and VIB of the periodic table and aluminum oxide. A coated cemented carbide member in accordance with claim 1, wherein said layer (3) has a thickness of 5 to 50 µm on a flat portion of each surface forming said insert edge portion (1) and a thickness of 0.1 to 1.4 times said thickness on said flat portion on said insert edge portion (1). A coated cemented carbide member in accordance with claim 1, wherein said hard phase consists of a solid solution of at least one metal compound selected from carbides, nitrides and carbo-nitrides of Zr and/or Hf and at least one metal compound selected from carbides, nitrides and carbo-nitrides of metals belonging to thegroup VB of the periodic table, and WC. A coated cemented carbide member in accordance with claim 3, wherein a larger amount of said at least one metal compound selected from carbides, nitrides and carbo-nitrides of metals belonging to the group VB of the periodic table forming said hard phase is contained over an internal region of up to 1 to 200 µm in depth from a surface layer region consisting of only WC and an iron family metal as compared with a region inside thereof. A coated cemented carbide member in accordance with claim 3, wherein said at least one metal compound selected from carbides, nitrides and carbo-nitrides of Zr and/or Hf is contained over an internal region of up to 1 to 200 µm in depth from a surface layer region consisting of only WC and an iron family metal in the same weight ratio as that in a region inside thereof while only said at least one metal compound selected from carbides, nitrides and carbo-nitrides of metals belonging to the group VB of the periodic table forming said hard phase is contained over said region in a larger weight ratio than that in said inside region. A coated cemented carbide member in accordance with claim 3, wherein a region having higher hardness than an inside region is provided over a depth of 1 to 200 µm from a surface layer region consisting of only WC and an iron family metal, the maximum hardness of said region being in a range of 1400 to 1900 kg/mm 2 in Vickers hardness with a load of 500 g. A coated cemented carbide member in accordance with claim 3, wherein no η phase is contained in said outermost surface of said insert edge portion (1) in said base material. A coated cemented carbide member comprising a cemented carbide base material containing a binder metal consisting of at least one iron family metal and a hard phase of at least one metal compound selected from carbides, nitrides, carbo-nitrides and carbonic nitrides of metals belonging to the groups IVB, VB and VIB of the periodic table (deming 1923) wherein said hard phase contains at least one metal compound selected from carbides, nitrides, carbo-nitrides and carbonic nitrides of Zr and/or Hf, and WC , a binder phase enriched layer (4) containing a larger amount of said binder metal as compared with the interior is provided on an outermost surface of each insert edge portion (1) of said cemented carbide base material, and a coating layer (2) being provided on the surface of said layer (4) which is a single or multiple layer of at least one metal compound 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. A coated cemented carbide member in accordance with claim 8, wherein said binder phase enriched layer (4) has a thickness of 5 to 50 µm on a flat portion of each surface forming said insert edge portion (1) and a thickness of 0.1 to 1.4 times that thickness on said flat portion on said insert edge portion (1). A coated cemented carbide member in accordance with claim 8, wherein the amount of said binder metal contained in a region immediately under said coating layer (2) provided on said insert edge portion (1) in a range of up to 2 to 50 µm in thickness from the surface of said base material is 1.5 to 5 times that of said binder metal contained in the interior in weight ratio. A coated cemented carbide member in accordance with claim 8, wherein a low hardness layer having lower hardness than the interior is provided in a region immediately under said coating layer (2) in a range of up to 2 to 50 µm in depth from the surface of said base material. A coated cemented carbide member in accordance with claim 8, wherein internal hardness of said base material is 1300 to 1700 kg/mm 2 in Vickers hardness with a load of 500 g, and hardness of said low hardness layer provided on said insert edge portion (1) is 0.6 to 0.95 times said internal hardness. A coated cemented carbide member in accordance with claim 8, wherein said hard phase consists of a solid solution of at least one metal compound selected from carbides, nitrides and carbo-nitrides of Zr and/or Hf and at least one metal compound selected from carbides, nitrides and carbo-nitrides of metals belonging to the group VB of the periodic table, and WC. A coated cemented carbide member in accordance with claim 13, wherein a larger amount of said at least one metal compound selected from carbides, nitrides and carbo-nitrides of metals belonging to the group VB of the periodic table forming said hard phase is contained over a region of up to 1 to 200 µm in depth from a surface layer region of said binder phase enriched layer (4) as compared with a region inside thereof. A coated cemented carbide member in accordance with claim 13, wherein said at least one metal compound selected from carbides, nitrides and carbo-nitrides of Zr and/or Hf has the same weight ratio as that in the interior over a region of 1 to 200 µm in depth from a surface layer region of said binder phase enriched layer (4) while only said at least one metal compound selected from carbides, nitrides and carbo-nitrides of metals belonging to the group VB of the periodic table forming said hard phase has a larger weight ratio in said region as compared with that in the interior. A coated cemented carbide member in accordance with claim 13, wherein a region having higher hardness than an inside region is provided over a depth of 1 to 200 µm from a surface layer region of said binder phase enriched layer (4) the maximum hardness of said region being in a range of 1400 to 1900 kg/mm 2 in Vickers hardness with a load of 500 g. A coated cemented carbide member in accordance with claim 13, wherein no η phase is contained in said outermost surface of said insert edge portion (1) in said base material. A coated cemented carbide member in accordance with claim 1 containing WC and one or more iron family metals as binder metals, wherein the cemented carbide base material contains: 0.3 - 15 percent by weight of a hard phase consisting of at least one metal compound selected from a group of nitrides and carbo-nitrides of Zr and/or HF and a solid solution of at least two such metal compounds, 2 - 15 percent by weight of a binder phase consisting of only Co or Co and Ni and a remainder consisting of WC and anavoidable impurities; and a single or multiple layer consisting of one or more metal materials selected from carbides, nitrides, oxides and borides of metals belonging to the groups IVB, VB and VIB of the periodic table and aluminum oxide coating the surface of said cemented carbide base material. A coated cemented carbide member in accordance with claim 18, wherein said hard phase consisting of at least one metal compound 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 compounds disappears or decreases in a region immediately under the coating layer (12) in a range of up to 2 to 100 µm in depth from the surface of the base material. A coated cemented carbide member in accordance with claim 1 containing WC and one or more iron family metals as binder metals, wherein the cemented carbide base material contains : 0.3 to 15 percent by weight of a hard phase consisting of at least one metal compound selected from a group of carbides, nitrides and carbo-nitrides of Zr and/or I-If and a solid solution of at least two such metal compounds, 0.03 to 35 percent by weight of a hard phase consisting of at least one metal compound selected from a group of 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 compounds, 2 to 15 percent by weight of a binder phase consisting of only Co,or Co and Ni, and a remainder consisting of WC and unavoidable impurities; and a single or multiple layer consisting of one or more metal compounds 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, being provided on the surface of said cemented carbide base material. A coated cemented carbide member in accordance with claim 20, wherein said hard phase consisting of at least one metal compound 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 compounds and the hard phase consisting of at least one metal compound selected from carbides, nitrides, 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 compounds, disappear or decrease in a region immediately under said coating layer (2) in a range of up to 2 to 100 µm in depth from the surface of the base material. A method of manufacturing the coated cemented carbide member of claims 1- 7, comprising: a step of sintering powder which consists of a binder metal containing at least one iron family metal, and hard phases of at least one metal compound selected from at least carbides, nitrides, carbo-nitrides and carbonic nitrides of Zr and/or Hf, and WC; a step of grinding or polishing all outermost surface of each insert edge portion for bevelling the same into a chamfered shape or a curved surface shape in a range leaving a layer consisting of only WC and said binder metal (3) or a binder phase enriched layer (4) or a binder phase enriched layer (4) in combination with a low hardness layer on said outermost surface; and a step of forming a coating layer (2) of a single or multiple layer consisting of at least one metal compound selected from carbides, nitrides, carbo-nitrides, oxides and borides of metals belonging to the groups IVB, VB and VIB of the periodic table (deming 1923) and aluminum oxide. A method of manufacturing a coated cemented carbide member in accordance with claims 8 - 17, comprising: a step of sintering powder which consists of a binder metal containing at least one iron family metal and hard phases, at least one metal compound selected from at least carbides, nitrides, carbo-nitrides and carbonic nitrides of Zr and/or Hf, and WC; a step of grinding or polishing an outermost surface of each insert edge portion for bevelling the same into a chamfered shape or a curved surface shape in a range leaving a layer consisting of only WC and said binder metal (3), or a binder phase enriched layer (4) or a low hardness layer in combination with said binder phase enriched layer (4) on said outermost surface; and a step of forming a coating layer (2) of a single or multiple layer consisting of at least one metal compound selected from carbides, nitrides, carbon nitrides, oxides and borides of metals belonging to the groups IVB, VB and VIB of the periodic table (deming 1923) and aluminum oxide. A method of manufacturing a coated cemented carbide member in accordance with claims 22 and 23, wherein at first a step of molding the powder by press molding into a shape with bevelled insert edge portions is included.

Inventors: CHUDO MASUO, KOBAYASHI MITSUNORI, NOMURA TOSHIO, UCHINO KATSUYA, CHUDO, MASUO, KOBAYASHI, MITSUNORI, NOMURA, TOSHIO, UCHINO, KATSUYA, Chudo, Masuo, c/o Itami Works of Sumitomo, KOBAYASHI, MITSUNORI, C/O ITAMI WORKS OF SUMITOMO, NOMURA, TOSHIO, C/O ITAMI WORKS OF SUMITOMO, Uchino, Katsuya, c/o Itami Works of Sumitomo
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES, LIMITED
Application year: 1993
Main classification: C23C30
IPC codes: C22C29, C23C30