Specialized metallurgical processes – compositions for use therei – Compositions – Consolidated metal powder compositions
Reexamination Certificate
2001-11-26
2002-10-15
Mai, Ngoclan (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Compositions
Consolidated metal powder compositions
C075S236000, C075S238000, C075S244000, C419S048000
Reexamination Certificate
active
06464747
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention elates to a sintered cermet material which can be effectively use in tools for machining special work pieces, end a method for producing such cermet material. The sintered cermet material of the present invention is in particular suited for machining high class cast iron such as niresist cast iron and austempered spheroidal graphite cast iron, as well a normal cast irons including spheroidal graphite cast iron and flaky graphite cast iron. The products are especially adapted for an efficient machining at a high feeding rate.
2. Technical Background
The technical background will be explained with reference to cutting tools for machining high class cast iron such as niresist cast iron and austempered spheroidal graphite cast iron. Niresist (Ni-Resist) cast iron is a nickel-chromium-copper austenitic cast iron, in which graphite is distributed in an austenite matrix. Niresist cast iron is excellent in resistance against wear, heat and corrosion, in relation to normal cast irons, and accordingly is widely used as a material for various machine parts which are demanded both hot strength and wear resistance as employed in corrosive circumstances. In particular, recent remarkable improvements in automotive has made performance of motor vehicles have made niresist cast iron principal material for the primary parts of motor vehicles. On the other hand, in an austempered spheroidal graphite cast iron, which is obtained by heat-treating spheroidal graphite cast iron, graphite particles exist in bainite and austenite phases. For this type of cast iron reference is made to JIS G 5503 FCAD 1000-5. Austempered spheroidal graphite, with such high tensile strength and excellent wear resistance over common cast irons, has become a promising material for mechanical parts to be used in aggressive circumstances. It surely is going to be a good material for the construction of motor vehicles, which are now under pressure of reduction in body size and weight.
In order to shape high class cast iron such as these niresist cast iron and austempered spheroidal graphite cast iron into final configuration and dimensions of the basic important parts, normally, the high class cast iron has been frequently required to be subjected to s cutting work after cast. Cutting tools for cutting high class cast iron such as these niresist cast iron and austempered spheroidal graphite cast iron must have the performance that such high class cast iron can be cut rapidly with a required cutting accuracy without waste. If tip ends of cutting tools are worn out or fractured upon chipping or like operations, there occur folding and burr in cut surfaces of high class cast iron such as these niresist cast iron and austempered spheroidal graphite cast iron, and consequently required dimensional accuracy and surface roughness cannot be obtained, resulting in products that cannot be shipped.
For these reasons, when the tip ends of the cutting tools are worn out or fractured, the cutting tools must be immediately replaced. The replacement of cutting tools decreases the productivity. Therefore, the number of replacements must be reduced to its minimum For this reason, the development of cutting tools that have long tool life and are inexpensive has been earnestly demanded. TiCN sintered cermet materials disclosed is publications of Japanese unexamined patent applications Nos. Sho 62-280362 and Sho 62-278265, for example, have been proposed as materials for cutting tools capable of overcoming these problems.
High class cast iron such as these niresist cast iron and austempered spheroidal graphite cast iron (hereinafter referred to as ADI) exhibits high hardness, and is excellent in wear resistance, as compared with normal spheroidal graphite cast iron, and in ADI, the austenite structure is transformed to martensite due to stress generated upon cutting the work, and consequently the hardness of the structure itself increases remarkably during the cutting work in addition such high class tact iron generates heat vigorously during the cutting work. as compared with the case of normal spheroidal graphite cast iron. Furthermore, where the high class cast iron castings have a roughened as-cast surface, which needs to be cut first. Upon cutting these coarse casting surfaces, interrupted cuts which cause vibration may occur. Accordingly, cutting tools have been required to exhibit toughness endurable against these interrupted cuts.
As described above, the cutting tools for machining high class cast iron are required to have a wear resistance adequate for the hard high class cast iron, heat resistance causing no thermal degradation (decrease in hardness) due to heat upon cutting, and toughness (fracture resistance) enduring the interrupted cuts which occur upon cutting casting surfaces. The TiC sintered cermet materials disclosed in the above-described publications, however, are particularly low in heat resistance so that the hardness thereof decreases due to beat upon cutting, and consequently the wear resistance is decreased. This results in that the cutting tools must be replaced frequently.
In order to improve only the wear resistance (hardness), cutting tools, each containing cBN and diamond, may be used. These cutting tools, however, are low in toughness, and consequently, may be fractured during cutting works.
As described above, conventionally, there have been used no cutting tools exhibiting the wear resistance, heat resistance and fracture resistance, which are all inquired to cut high class cast iron such as niresist cast iron and austempered spheroidal graphic cast iron, and accordingly the extension of the tool life, which has been desired as cutting tools, has not been able to be effected.
SUMMARY OF THE INVENTION
It is one object of the present invention to provide sintered cermet materials capable of composing inexpensive tools such as cutting tools, which exhibit excellent heat resistance, wear resistance and fracture resistance, and have long life time, and a method for producing such sintered cermet materials.
It is another object of the present invention to provide sintered cermet materials capable of composing inexpensive cutting tools, each having long tool lift, which can cut metal work pieces composed of not only normal cast iron such as spheroidal graphite cast iron and flake graphite cast iron but also high class cast iron such as niresist cast iron and austempered spheroidal graphite cast iron, inclusive of casting surfaces thereof under severe conditions such as a high speed cutting, heavy cutting, and interrupted cutting, and a method for producing such sintered cermet materials, especially where the present invention is applied to cutting tools as typical tools.
The present inventors have continued to develop sintered cermet materials for cutting tools and a method for producing such sintered cermet materials over many years. As a result, they have found that by preparing a mixed powder containing powders of TiCN, Si
3
N
4
, Al
2
O
3
, CrxN (x=1-2.7) and ZrN, at least one powder of W and WC, and at least one metal powder selected from the group consisting Co, Ni, Ta and Mo, and by sintering the prepared mixed powder ,the above-described objects can be achieved, and, based on this finding, they have completed the present invention
The reason why the above-described objects can be achieved has not been sufficiently clarified, but can be estimated as follows: By preparing a mixed powder containing .powders of TiCN, Si
3
N
4
, Al
2
O
3
, CrxN (x=1-2.7) and ZrN, at least one powder of W and WC, and at least one metal powder selected from the group consisting of Co, Ni, Ta and Mo, and sintering the prepared mixed powder to compose a sintered cermet material, the crystal structure has a structure varied from TiCN, Si
3
N
4
, Al
2
O
3
, CrxN (x=1-2.7) as starting raw materials, and this new phase contributes to the improvement of the quality of the material upon cutting or other operations. Where the sintered cermet mater
Enya Yasuhiro
Gotoh Kenji
Hosomi Satoru
Aisin Seiki Kabushiki Kaisha
Mai Ngoclan
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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