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 to 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 cutting tools has been improved in recent years. The cutting efficiency is determined 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 the 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 group or family metal in a larger amount than that in the interior, a layer (.beta. 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 .beta. free layer is formed particularly in each cornered insert edge portion 1, while the thickness of the as-formed .beta. 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 known chemical vapor deposition is applied as a coating method in such a coated cemented carbide, a fragile .eta. phase is formed in the cornered insert edge portion 1 by reaction with carbon forming the base material during formation of the coating layer. Thus, chipping resistance is lowered and the coating layer fails with the .eta. phase portion, to increase the progress of wear.
In order to improve the 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 when used under high cutting speed conditions due to a high temperature applied thereto, although the 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.