Cutters – for shaping – Comprising tool of specific chemical composition
Reexamination Certificate
1999-02-24
2001-05-29
Wellington, A. L. (Department: 3722)
Cutters, for shaping
Comprising tool of specific chemical composition
C407S118000
Reexamination Certificate
active
06238148
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
1. Industrial Field of the Invention
The present invention relates to a cemented carbide cutting tool made of a tungsten carbide-based alloy having high chipping resistance (hereinafter referred to as a “cemented carbide cutting tool”), and more specifically, relates to a cemented carbide cutting tool having a sharp cutting edge and maintaining high cutting characteristics for long service life when used as an end mill having an intermittent cutting mode and when cutting is performed under heavy cutting conditions such as at high feed rate and high cutting depth.
2. Description of the Related Art
For example, Japanese Patent Application Laid-Open No. 3-43113 discloses a conventional cemented carbide cutting tool made of a tungsten carbide-based cemented carbide alloy (hereinafter referred to as a “cemented carbide alloy”) composed of 8 to 13 percent by weight of Co and 0.1 to 3 percent by weight of Cr as constituents for forming a binding phase, the balance being tungsten carbide (hereinafter referred to as “WC”) as a constituent for forming a dispersing phase, and incidental impurities, in which the rate of the dispersing phase to the total of the dispersing phase and the binding phase is in a range of 72 to 90 percent by area and the average particle diameter is 1 &mgr;m or less according to measurement of an electron microscopic texture. Since the cemented carbide cutting tool has high toughness and high strength, it is known that the tool is used in practice as an end mill requiring such properties.
3. Problems to be solved by the Invention
In recent years, labor and energy saving for cutting tools has been eagerly awaited, and requirement for these cutting tools is towards heavy cutting conditions such as at high feed rate and high cutting depth. When the above conventional cemented carbide cutting tool is applied to an end mill used in an intermittent cutting mode under heavy cutting conditions, chipping (fine fracture) of the cutting edge occurs and thus the life is running out within a relatively short period.
MEANS FOR SOLVING THE PROBLEMS
The present inventors have directed their attention to the above conventional cemented carbide cutting tool, have researched to improve chipping resistance, and have discovered the following. When using a powdered composite of WC and Co which is made by adding a distilled water containing dissolved cobalt nitrate as a Co source to a mixture of powdered tungsten oxide and powdered carbon in a predetermined ratio in place of powdered WC and powdered Co as raw powdered materials, followed by mixing and drying, and then performing, for example, reduction at 1,050° C. for 30 minutes in a nitrogen atmosphere and carbonization at 1,000° C. for 60 minutes in a hydrogen atmosphere, the dispersing phase of the cemented carbide alloy constituting the resulting cemented carbide cutting tool is composed of ultra-fine particles of a Co-based alloy having a particle diameter of 100 nm or less dispersed in a matrix. Thus, in the cemented carbide cutting tool, the constituents for forming a binding phase which includes major parts of a binding phase between the dispersing phases in the cemented carbide alloy becomes finer and more homogeneous compared to conventional cemented carbide cutting tools having the same content of the constituents for forming the binding phase in the alloy. Based on recognition, in which a finer and more homogeneous distribution causes decreased thermal conductivity, the thermal conductivity was measured. This cemented carbide alloy for cutting tools has a thermal conductivity of 0.2 to 0.6 J/cm·sec·° C. compared to 0.7 to 1.0 J/cm·sec·° C. of a conventional cemented carbide alloy, and thus has superior chipping resistance when it is applied to an end mill used in intermittent cutting mode.
The present invention has been completed by the above, and is characterized by a cemented carbide cutting tool made of a tungsten carbide-based alloy having high chipping resistance comprising:
8 to 13 percent by weight of Co and 0.1 to 3 percent by weight of Cr as constituents for forming a binding phase, the balance being tungsten carbide as a constituent for forming a dispersing phase and incidental impurities, the rate of the dispersing phase to the total of the dispersing phase and the binding phase being in a range of 72 to 90 percent by area and the average particle diameter being 1 &mgr;m or less according to measurement of an electron microscopic texture;
wherein the dispersing phase of the cemented carbide cutting tool made of a tungsten carbide-based alloy comprises a dispersing phase composed of ultra-fine particles dispersed in a matrix and having a particle diameter of 100 nm or less, and the ultra-fine particles comprise a Co based alloy.
The Co content is limited to 8 to 13 percent by weight in the cemented carbide alloy constituting the cemented carbide cutting tool of the present invention, because sufficient toughness is not achieved at a content of less than 8 percent by weight whereas abrasion resistance steeply decreases at a content of higher than 13 percent by weight. The Cr content is also limited to 0.1 to 3 percent by weight, because the grain growth of the dispersing phase is insufficiently suppressed and thus the average diameter of the dispersing phase cannot be reduced to 1 &mgr;m or less at a content of less than 0.1 percent by weight, whereas toughness significantly decreases at a content of higher than 3 percent by weight. Furthermore, high toughness is not achieved when the average particle diameter of the dispersing phase is larger than 1 &mgr;m. As a result, Cr must be contained in an amount of 0.1 percent by weight or more while the average particle diameter of the powdered composite is maintained to 1 &mgr;m or less, in order to control the average particle diameter of the dispersing phase to 1 &mgr;m or less.
The diameter and the density of ultra-fine particles dispersed in WC are controlled by adjusting the average diameters of the powdered tungsten oxide and carbon which are used and by adjusting the conditions for reduction and carbonization. Since hardness and abrasion resistance unavoidably decrease if ultra-fine particles having a particle diameter higher than 100 nm are present in such a case, the diameter of the ultra-fine particles is limited to 100 nm or less.
The rate of the dispersing phase to the total of the dispersing phase and the binding phase is limited to a range of 72 to 90 percent by area, because desired abrasion resistance is not achieved at a rate of less than 72 percent whereas strength of the cemented carbide alloy decreased at a rate of higher than 90%.
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Akiyama Kazuhiro
Okada Kazuki
Taniuchi Toshiyuki
Ergenbright Erica
Mitsubishi Materials Corporation
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Wellington A. L.
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