Surface-coated carbide alloy cutting tool

Details Surface-coated carbide alloy cutting tool Surface-coated carbide alloy cutting tool

2004-03-18

2004-12-28

Turner, Archene (Department: 1775)

Stock material or miscellaneous articles

Structurally defined web or sheet

Including components having same physical characteristic in...

C051S307000, C051S309000, C407S119000, C428S336000, C428S697000, C428S698000, C428S699000, C428S701000, C428S702000

Reexamination Certificate

active

06835446

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cutting tool made of a surface-coated cemented carbide alloy (hereinafter referred to as a coated cemented carbide tool) whose cutting edge portion exerts an excellent heat-resistant plastic deformability when various types of steel and cast iron are cut under high-speed cutting conditions accompanied with high heat generation.
2. Description of the Related Art
There has conventionally been known a coated cemented carbide tool comprising, on the surface of a substrate made of a tungsten carbide (hereinafter referred to as WC)-based cemented carbide alloy (hereinafter referred to as a cemented carbide substrate), a hard coating layer composed of the following layers (a) to (c) deposited thereon:
(a) a Ti compound layer, as a lower layer, formed by chemical vapor deposition (hereinafter referred to as “CVD”) and/or physical vapor deposition (hereinafter referred to as “PVD”) which has an average thickness of 3 to 20 &mgr;m and is made of one layer or a plurality of two or more layers among a layer of carbide of Ti (hereinafter referred to as TiC), a layer of nitride of Ti (hereinafter referred to as TiN), a layer of carbonitride of Ti (hereinafter referred to as TiCN), a layer of carboxide of Ti (hereinafter referred to as TiCO) and a layer of carbonitroxide of Ti (hereinafter referred to as TiCNO);
(b) an aluminum oxide (hereinafter referred to as Al
2
O
3
) layer, as an upper layer formed by CVD which has an average thickness of 3 to 15 &mgr;m and has an &agr;-type crystal structure; and
(c) if necessary, a TiN layer having an average thickness of 0.5 to 2 &mgr;m, as a surface layer, is deposited on the upper layer for the purpose of identification of the cutting edges before and after cutting operations because of its golden color tone. Also, it has been known that this coated cemented carbide tool may be used for both continuous and interrupted cutting operations of various types of steel and cast iron.
Also, it has been known that the Ti compound layer and the Al
2
O
3
layer, which constitute the hard coating layer of the coated cemented carbide tool described above, generally have a granular crystal structure and, as described in Japanese Patent Application, First Publication No. Hei 6-8010, and Japanese Patent Application, First Publication No. Hei 7-328808, the TiCN layer constituting the Ti compound layer is formed by CVD at a moderate temperature within a range from 700 to 950° C. using a mixed gas containing an organic carbonitride as a reaction gas in a conventional CVD apparatus, thereby providing the layer with a crystal structure grown longitudinally for the purpose of improving the toughness of the layer itself.
With recent increases in demands for labor saving and energy saving as well as cost reduction in cutting operations, cutting operations tend to be conducted at high speed, along with the development of high performance cutting machines. When a conventional coated cemented carbide tool is used in continuous cutting or interrupted cutting of various types of steel and cast iron under normal conditions, no problem arise. However, when the coated cemented carbide tool is used in a high-speed cutting operation, thermoplastic deformation, which can cause abnormal wear at the cutting edge portion, is liable to occur due to high heat generated during the cutting operation. As a result, the process of wear is accelerated and failure occurs within a relatively short time.
SUMMARY OF THE INVENTION
From aforementioned point of view, the present inventors have studied about the conventional coated cemented carbide tool in order to develop a coated cemented carbide tool, which exerts an excellent thermoplastic deformation resistance during high-speed cutting operations, thus yielding the following results (1) to (3).
(1) When the Ti compound layer, as a lower layer, is formed on the surface of a cemented carbide substrate under normal deposition conditions and an Al
2
O
3
layer having a &kgr;- or &thgr;-type crystal structure is formed also under normal deposition conditions and then the resulting material is subjected to a heat treatment in this state, preferably, in an Ar atmosphere under the conditions of a temperature of 1000° C. or higher for a predetermined time, the &kgr;- or &thgr;-type crystal structure is converted into an &agr;-crystal structure. As a result, cracks formed during the heat transformation are uniformly dispersed and distributed in the resulting heat transformed &agr;-type Al
2
O
3
layer and the heat transformed &agr;-type Al
2
O
3
layer operates as a heat-insulating layer for high heat generated during high-speed cutting operations due to an action of a large number of cracks which are present in the heat transformed &agr;-type Al
2
O
3
layer, and also suppresses high heat from being transferred to the cemented carbide substrate. Consequently, thermoplastic deformation of the cutting edge portion is markedly suppressed and the occurrence of abnormal wear is prevented, and therefore the cutting edge portion exhibits a normal wear pattern, thus enabling cutting operations for a long period.
(2) In a coated cemented carbide tool comprising a hard coating layer composed of the heat transformed &agr;-type Al
2
O
3
layer, as an intermediate layer, and an &agr;-type Al
2
O
3
layer, as an upper layer, deposited on the surface of the intermediate layer also under normal deposition conditions, some portion of the deposited Al
2
O
3
sufficiently enters into cracks formed during the heat transformation at the interface with the heat transformed &agr;-type Al
2
O
3
layer, thereby making it possible to maintain the cracks formed during the heat transformation in a markedly stable state, thus enabling a cutting operation for a long period without causing chipping even if high-speed cutting is conducted under the interrupted conditions.
(3) In the heat transformed &agr;-type Al
2
O
3
layer formed by heat transformation of the &kgr;-type Al
2
O
3
layer, since the basal plane of the hexagonal crystal of the respective crystals constituting the layer exhibits a unique orientation, which is generally in parallel with the film growth surface, such that the film itself has excellent wear resistance, the layer exhibits excellent cutting performances, along with the heat-insulating effect of the film.
The present invention has been completed based on the results described above and provides a coated cemented carbide tool, which exerts an excellent thermoplastic deformation resistance during the high-speed cutting operation, the cutting tool comprising, on the surface of a cemented carbide substrate, a hard coating layer including the following layers (a) to (c) or (a) to (d):
(a) a Ti compound layer, as a lower layer, which has an average thickness of 0.5 to 20 &mgr;m, preferably 3 to 15 &mgr;m, and more preferably 5 to 10 &mgr;m, and is made of one layer or a plurality of two or more layers formed by vapor deposition process, among a TiC layer, a TiN layer, a TiCN layer, a TiCO layer and a TiCNO layer;
(b) a heat transformed &agr;-type Al
2
O
3
layer, as an intermediate layer, which has an average thickness of 1 to 25 &mgr;m, preferably 3 to 15 &mgr;m, and more preferably 5 to 10 &mgr;m, formed by heat transformation of a vapor deposited &kgr;- or &thgr;-type Al
2
O
3
layer;
(c) an Al
2
O
3
layer, as an upper layer, formed by vapor deposition process which has an average thickness of 0.3 to 10 &mgr;m, preferably 0.5 to 5 &mgr;m, and more preferably 0.5 to 2 &mgr;m, and an &agr;-type crystal structure; and
(d) if necessary, at least one layer of TiN, TiC or TiCN, as a surface layer (d), formed by vapor deposition process which has an average thickness of 0.1 to 5 &mgr;m, preferably 0.3 to 4 &mgr;m, and more preferably 0.5 to 2 &mgr;m.
The Al
2
O
3
layer having the heat transformed &agr;-type crystal structure preferably has a structure in which cracks formed during the heat transformation are uniformly dispersed and distributed.
The average thickness of each const

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