Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
1999-07-15
2001-01-30
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C075S010250, C148S321000, C148S324000, C148S333000, C148S334000, C148S442000, C148S905000, C407S119000, C427S250000, C428S636000, C428S660000, C428S908800, C428S932000, C428S938000
Reexamination Certificate
active
06180266
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to cutting tools such as hobbing cutters, end mills and so on having cutting edges made of high speed tool steels.
2. Description of the Related Art
High speed tool steels and cemented carbides are used as typical conventional cutting tool materials of cutting tools such as hobbing cutters, end mills and so on.
High speed tool steels for cutting tools containing more than 2% of Vanadium (V) are exploited as cutting tool materials having a high hardness, wear resistance and a high heat resistance.
Cemented carbides, on the other hand, are very hard and exhibit both excellent wear resistance and high heat resistance. However, because of the cemented carbides are frangible and of high material costs as well as high machining costs, and further, the cemented carbides have inferior in both grindability and anti-shock resistance compared with the high speed tool steels, the cemented carbides are not presently in wide practical use as cutting tool materials for reasons of a lack of credibility in quality and high material costs as well as high machining costs. Therefore most hobbing cutters which perform interrupted cuttings are made of high speed tool steels, and only small parts thereof are made of cemented carbides.
High speed tool steels for use for such cutting tools usually contain more than 2% of Vanadium (V) to enlarge the carbide grain size of hard MC-type carbide grains mainly consisting of Vanadium alloys. However, conventional high speed tool steels produced by melting which contain more than 3% of V, result that the more amount of V increase, the more become liable to generate crystallized coarse or elongated angled MC-type carbide grains, deteriorating both grindability as well as toughness, and become liable to cause a problem of a chipping or fracture of the tool cutting edge starting from one of the MC-type carbide grains.
Also, conventional high speed tool steels produced by sintering powder disclosed, for instance, in U.S. Pat. No. 5,252,119, are liable to generate too fine grain particles of MC-type carbides which result insufficient toughness causing a problem of quick or large wear of the cutting edge and shorten tool life despite of using high cost materials.
In wet-cutting of hobs using cutting oil, although the whole surfaces of the hob cutting edges are initially coated with Ti- or Ti-alloy ceramic coating films, after re-ground of the hob cutting edges are performed, the coating films deposited on the cutting faces, or rake faces, are removed away, and there are required both heat- and wear-resistances of the high speed tool steel materials themselves of the hobs.
On the other hand, in dry-cutting of hobs performed without the supply of cutting oil, the hob materials must have high hardness, sufficient toughness to resist shocks by interrupt cuttings of hobs and heat resistance. In addition, the surfaces of the cutting edges must deposit coating films having wear-, heat-, and acid-resistances as well as lubricative properties to prevent wear, chipping and fracture thereof. Further, the hob materials are required to have a good affinity with the above coating films.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a cutting tool having a cutting edge made of a high speed tool steel having high a wear resistance, a sufficient toughness to resist a shock by interrupt cutting of the cutting tool and a heat resistance to prevent wear, chipping and fracture thereof.
Other object of the present invention is to provide a cutting tool having a cutting edge made of a high speed tool steel having a good affinity with the coating films.
Another object of the present invention is to provide a cutting tool which is adapted for both wet-cutting using cutting oil as well as dry-cutting performed without the supply of cutting oil.
These and other object are performed by providing a cutting tool having a cutting edge made of a high speed tool steel consisting essentially of by weight C:0.6 to 1.8%, Si:1.2% max, Mn:0.5% max, Cr:3.5 to 5.0%, Mo:10% max, W:21% max, V:2 to 4% and Co:4 to 9%; or alternately, V:4 to 6% and Co:7 to 10%; the balance being Fe and incidental impurities, and the steel of the cutting edge comprising MC-type carbide grains which mainly comprise vanadium carbide grains each having a maximum equal value diameter of a circle ranging substantially 5 to 14 &mgr;m, which equal value diameter of the circle being a diameter of any one of a circle being converted to the circle having the same cross sectional area as that of a cross sectional area of any one of the MC-type carbide grains, and the MC-type carbide grains having an equal value diameter of a circle ranging substantially 5 to 14 &mgr;m have a ratio between short and long diameters ranging over substantially 0.3, wherein the ratio between short and long diameters is a value obtained by dividing a short diameter of any one of the MC-type carbide grains by a long diameter of the same.
By such an arrangement of the present invention, the cutting tool having the cutting edge made of the high speed tool steel exhibits a very high wear resistance, sufficient toughness to resist the shock caused by interrupt cutting of the cutting tool and heat resistance thereby preventing wear, chipping and fracture thereof. Also, the cutting tool exhibits a very high heat resistance to withstand the heat generated in a dry cutting of steel materials performed without a supply of cutting oil which is expected an increasingly wide use hereafter.
Preferably, the MC-type carbide grains having an equal value diameter of a circle ranging substantially 5 to 14 &mgr;m have a ratio of cross sectional area ranging substantially 3 to 8%, wherein the ratio of cross sectional area is a ratio dividing a total sum of the cross sectional areas of the MC-type carbide grains by a total cross sectional plane area being cut away and measured along a plane substantially parallel to a forgoing or rolling axis of the steel.
Further preferably, a surface of the cutting edge has at least one or more of layer of Ti- and/or Ti-alloy coating film applied by PVD to more increase both wear and anti-chipping resistance.
More preferably, the high speed tool steel is produced by subjecting a repeated or doubled electro-slag melting process to adjust the grain size of the MC-type carbide grains under conditions; preventing an entry of O
2
and N
2
gases into melting steel, at melting speed: 400 to 800 kg/h, and keeping a ratio of a diameter of an ingot divided by an electrode diameter to be kept in a range of from 1.2 to 1.7.
As a result of applicants's actual experiences using cutting tools such as solid hobs and end mils both made of high speed tool steels, they recognized in order to obtain a high speed tool steel having high heat- and wear resistances, sufficient toughness to resist the shock caused by interrupt cutting of the cutting tools, and further, to prevent wear, chipping and fracture thereof, it is essential to restrict adequately a maximum equal value diameter of a circle of the MC-type carbide grains so that the grains have a maximum equal value diameter of a circle ranging substantially 5 to 14 &mgr;m, and further to restrict a ratio between short and long diameters which is a value obtained by dividing a short diameter of any one of the MC-type carbide grains by a long diameter of the same as large as possible so that each MC-type carbide grain having an equal value diameter of a circle ranging substantially 5 to 14 &mgr;m has a near spherical shape.
Also, it is essential to restrict adequately a ratio of total sum of the cross sectional areas of MC-type carbide grains having an equal value diameter of a circle ranging substantially 5 to 14 &mgr;m with respect to a total cross sectional plane area being cut away and measured along a plane substantially parallel to a forgoing or rolling axis of the steel. These are reasons applicants proposed restriction of elements of the present invention.
The plane substantially parallel to
Amano Hirokuni
Asakura Syunichi
Nakagawa Kiyoshi
Shimatani Yuji
Frank Robert J.
Jennings Leo J.
Jones Deborah
Koehler Robert R.
Nachi-Fujikoshi Corp
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