Cutters – for shaping – Comprising tool of specific chemical composition
Reexamination Certificate
1998-10-28
2001-05-15
Tsai, Henry (Department: 3722)
Cutters, for shaping
Comprising tool of specific chemical composition
C407S118000, C075S230000, C428S386000, C051S309000
Reexamination Certificate
active
06231277
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a cermet tool and more particularly to a cermet tool that has excellent thermal crack resistance, while maintaining plastic deformation resistance, wear resistance and a long service life even when it is used for intermittent cutting.
BACKGROUND FOR THE INVENTION
A sintered product referred to herein as a cermet contains, as a hard phase component, a carbide, a nitride, or a carbonitride of Ti which serves as an essential metal component and a Group (
4
a
,
5
a
,
6
a
) metal other than Ti, i.e., V, Cr, Zr, Nb, Mo, Hf, Ta, or W. Such materials have become a mainstream material for cutting tools due to their excellent properties, such as excellent plastic deformation resistance, relative to those of conventional super-hard alloys. In recent years, in order to further enhance fracture resistance, thermal shock resistance, and plastic deformation resistance, it has been proposed to incorporate, Ti carbide into the hard phase, of Ti nitride or Ti carbonitride having high toughness and thermal conductivity, (see, for example, Japanese Patent Publication (kokoku) No. 56-51201.
Furthermore, the Japanese Patent Application Laid-Open (kokai) No. 8-24690 discloses a microcrystalline structure which can enhance wear resistance and fracture resistance of the aforementioned Ti nitride-containing cermet. Namely, there is disclosed a core-shell structure in which the central portion (mainly formed of Ti carbonitride) of the core- containing hard phase of the cermet is formed of rounded block-shaped grains primarily formed of (Ti, M)CN and having an aspect ratio of 1.4 or less. There is also disclosed the structure in which the core-containing hard phase is formed such that a Ti carbonitride phase accounts for 90% or less by volume of the core-containing hard phase. This microcrystalline structure improves fracture resistance of aa tool through an increase in strength, while maintaining wear resistance thereof.
For enhancing the strength and hardness of the cermet, tools which are disclosed in the aforementioned publication, it is advantageous to form the central portion of the core-containing hard phase into a rounded-block shape in the microcrystalline structure. However, toughness in turn decreases, with the result that the thermal crack resistance of the substrate decreases. Thus, the problem of poor service life arises in applications that require high thermal crack resistance, such as intermittent cutting of steel.
Accordingly, an object of the present invention is to provide a cermet tool having excellent thermal crack resistance and a long service life even when the tool is used for intermittent cutting such as intermittent cutting of steel, while maintaining plastic deformation resistance and wear resistance that are advantageous points of cermets and to provide a method for manufacturing the same.
BRIEF SUMMARY OF THE INVENTION
In essence, the present invention contemplates an improved cermet tool wherein the essential portion of the tool is formed of a cermet having a structure which includes a bonding phase and a hard phase. The bonding phase is predominantly formed of Ni or Ni and Co, and the hard phase is predominantly formed of a carbonitride phase containing Ti, which serves as an essential metal component. The hard phase also includes at least one metal (M) which is selected from the group consisting of V, Cr, Zr, Nb, Mo, Hf, Ta, and W and mixtures thereof. In a preferred embodiment of the invention, the cermet comprises
Ni or Ni and Co in a total amount of 4-20 wt. %,
Ti in an amount of 50-60 wt. %,
at least one metal selected from the group of V, Cr, Zr, Nb, Mo, Hf, Ta, and W in a total amount of 30-40 Wt. %,
C (carbon) in an amount of 5-10 wt. %, and
N (nitrogen) in an amount of 3-8 wt. %;
the carbonitride phase contains grains of the Ti carbonitride phase containing a metal component Ti in an amount of 90 wt. % or more with respect to all the metal components of the phase; and a cross-sectional microcrystalline structure of the cermet shows that the “total area of grains of the Ti carbonitride phase having a ration of D
max
/D
min
of 1.5 or more” to the “total area of the hard phase” to be 50% or more. D
max
and D
min
are respectively defined as a maximum diameter and a minimum diameter of grains of the titanium carbonitride phase in the microcrystalline structure.
In the preferred embodiment of the invention the carbonitride phase is predominantly formed of first core-shell grains having a core portion (I) comprising a Ti carbonitride phase which contains Ti in an amount of 90 wt. % or more of the metal components in the phase. It also includes a shell portion (I) which is formed around the core portion (I) and comprises a first (Ti, M) carbonitride phase containing Ti in an amount of 40-60 wt. % of the metal components in the phase and one or more metals selected from V, Cr, Zr, Nb, Mo, Hf, Ta, and W in an amount of 40-60 wt. % of the metal components in the phase. The carbonitride phase also includes second core-shell grains having a core portion (II) comprising an M (metal) carbonitride phase whose metal component includes one or more metals selected from V, Cr, Zr, Nb, Mo, Hf, Ta, and W in an amount of 90 wt. % or more and a shell portion (II) which is formed around the core portion (II). The shell portion II comprises a second (Ti, M) carbonitride phase containing Ti in an amount of 20-30 wt. % of the metal components in the phase and one or more metals selected from V, Cr, Zr, Nb, Mo, Hf, Ta, and W in an amount of 70-80 wt. % of the metal components in the phase. A cross-sectional microcrystalline structure of the cermet shows the ratio of “total area of the core portion (I) having a ratio of D
max
/D
min
of 1.5 or more” to “total area of the first core-shell grains and the second core-shell grains” to be 50% or more.
The invention also contemplates a method for manufacturing a cermet tool. The method includes the step of blending a metal powder predominantly formed of Ni or Ni and Co in an amount of 4-20 parts by weight, a powder of a carbonitride whose metal component includes at least one metal selected from V, Cr, Zr, Nb, Mo, Hf, Ta, and W in an amount of 25-40 parts by weight, and a material selected from the group consisting of Ti carbonitride, Ti nitride and/or Ti carbide or a combination of Ti nitride and Ti carbide in a total amount of 60-75 parts by weight to obtain a mixture of powders forming the mixture of powders. The powders are then formed into a predetermined shape and the resultant compact is fired at 1400-1650° C. During the firing, the temperature is increased or elevated from a first temperature of between 1300-1400° C. i.e., a temperature which is lower than the firing temperature, to the firing temperature at 5-10° C./minute.
In a preferred method for manufacturing a cermet tool according to the invention, the temperature is elevated from a second temperature, which is set at 800° C. or more, to the first temperature of between about 1300-1400° C. at 1-5° C./minute.
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patent: 3971656 (1976-07-01), Rudy
patent: 3994692 (1976-11-01), Rudy
patent: 4049876 (1977-09-01), Yamamoto et al.
patent: 4983212 (1991-01-01), Iyori et al.
patent: 5186739 (1993-02-01), Isobe et al.
patent: 5308376 (1994-05-01), Oskarsson
patent: 5710383 (1998-01-01), Takaoka
patent: 6024776 (2000-02-01), Heinrich et al.
patent: 6057046 (2000-05-01), Tsuda et al.
patent: 7252578 (1995-03-01), None
patent: 7237012 (1995-12-01), None
patent: 8246090 (1996-09-01), None
Abstract for Publication No. 08/246090, published Sep. 24, 1996 (Japio).
Abstract for Publication No. 08/246090, published Sep. 24, 1996 (Derwent).
Dougherty & Troxell
NGK Spark Plug Co. Ltd.
Tsai Henry
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