Metal treatment – Stock – Cobalt base
Reexamination Certificate
2000-11-15
2004-05-11
King, Roy (Department: 1742)
Metal treatment
Stock
Cobalt base
C420S435000, C420S436000, C407S119000
Reexamination Certificate
active
06733603
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention is directed to alloys for industrial cutting tools, especially the variety of tools known as cutting inserts, where enhanced resistance to abrasion and corrosion, especially in acidic environments of a reducing nature, are required, as well as toughness. One particular application relates to cutting optical fibers, where corrosive chlorides are present; another particular application relates to cutting wood in secondary operations such as furniture manufacture, where abrasive glues and the like are present.
Heretofore industrial cutting tool inserts have been made from a variety of materials including tool steels as well as sintered tungsten carbide materials. When cutting is done in a corrosive medium, highly alloyed, corrosion-resistant materials are required to prevent the cutting edge from deteriorating. One commercially available alloy, Stellite 6K, is often used in such environments. This alloy is cobalt based with a hardness of HRC 44-47 in the fully annealed condition. Because this alloy is made by hot rolling, it also possesses a high toughness. This alloy has been selected for industrial cutting tool applications due to its combination of hardness and toughness in addition to its corrosion resistance. One disadvantage of Stellite 6K has been its susceptibility to attack in strongly corrosive media and also under certain abrasive conditions.
Sintered tungsten carbide materials have often been selected over Stellite 6K in severe abrasive conditions. If corrosion is involved as well, a commercially available cobalt based alloy called Tangtung G is chosen. A cutting tool made of Tangtung G is produced by chill casting. No wrought version of this alloy is commercially available. A wrought microstructure is preferred over a cast microstructure in high performance cutting tools.
SUMMARY OF THE INVENTION
Among the objects of this invention, therefore, are to provide an alloy for industrial cutting tools which has enhanced corrosion resistance in strongly corrosive media; to provide such an alloy having enhanced abrasion resistance; to provide such an alloy having a wrought microstructure; to provide such an alloy having resistance to acidic environments of a reducing nature; and to provide such an alloy which avoids internal additions of tungsten.
Briefly, therefore, the invention is directed to a cobalt-based alloy for forming industrial cutting tool inserts, the alloy having a wrought microstructure, improved resistance to corrosion and abrasive wear and comprising from about 3% to about 15% by weight Mo and no more than 1% by weight W.
The invention is also directed to a cobalt-based alloy for forming industrial cutting tools for use in acidic environments of a reducing nature, the alloy having a wrought microstructure and consisting essentially of, by approximate weight percent:
C
0.5-2.5
Cr
25-35
Mo
3-15
W
no more than 1
Ta + Nb + V + Ti
up to 6
Mn + Si + Ni + Fe
no more than 10
Co
Balance.
In another aspect the invention is directed to a cobalt-based alloy for forming industrial cutting tool inserts for cutting optical fibers, the alloy having a wrought microstructure, enhanced resistance to chloride corrosion, and consisting essentially of, by approximate weight percent:
C
0.5-2.5
Cr
25-35
Mo
3-15
W
no more than 1
Ta + Nb + V + Ti
up to 6
Mn + Si + Ni + Fe
no more than 10
Co
Balance
with the microstructure being characterized by banding and occasional twinning, with grains having a grain size larger than 20 microns constituting at least 20% of the alloy's volume and with grains having a grain size smaller than 5 microns constituting at least 20% of the alloy's volume.
The invention is also directed to industrial cutting tool inserts constructed from the foregoing alloys.
Other objects and features of the invention will be in part apparent and in part pointed out hereinafter.
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Davis et al, editors, “Nickel, Cobalt, and Their Alloys”, 2000, ASM International, pp. 347, 354, 362, 363, 365.*
Eric Stephenson, Circular Saws, Jan. 1972, pp. 76-77 and 95-111.
McKee Bradley
Purvis Ian
Wu James B. C.
Deloro Stellite Company Inc.
King Roy
Senniger Powers Leavitt & Roedel
Wilkins, III Harry D.
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