Grade for cast iron

Details Grade for cast iron Grade for cast iron

1998-12-09

2001-06-26

Turner, Archene (Department: 1775)

Stock material or miscellaneous articles

Structurally defined web or sheet

Including components having same physical characteristic in...

C428S212000, C428S323000, C428S325000, C428S336000, C428S697000, C428S698000, C428S699000, C428S701000, C428S702000

Reexamination Certificate

active

06251508

ABSTRACT:

BACKGROUND OF THE INVENTION
In U.S. Pat. No. 5,137,774, the increased performance of &agr;-Al
2
O
3
as compared to &kgr;-Al
2
O
3
as a coating on a cemented carbide insert when turning cast iron was shown. In addition, in U.S. Pat. Nos. 5,635,247 and 5,700,569 as well as U.S. Pat. No. 6,015,614 there are shown various alumina-coated cemented carbide inserts in which the alumina is deposited on a Ti(C,N) layer or multilayers. However, in tests as conducted by the present inventor, it was noticed that the adhesion of an &agr;-Al
2
O
3
layer to the underlying TiCN layer as well as the adhesion of the TiCN layer to the cemented carbide substrate was often unsatisfactory when the insert was used in the turning of cast iron. The coating failed due to edge chipping which resulted in accelerated wear.
The main reasons for edge chipping have been identified by the present inventor from these tests to be the weak substrate-coating adhesion as well as the weak bond between TiCN and &agr;-Al
2
O
3
.
In one study of the TiC-cemented carbide interface of a 6 &mgr;m thick CVD-deposited TiC layer by Vuorinen et al., “
TEM Study of Microstructure and Crystallography at the TiC/Cemented Carbide Interface”, Science of Hard Materials,
1983, pp. 433-447, it was found by transmission electron microscopy (TEM) that the TiC layer is composed of two regions. Close to the substrate and extending to a thickness of 1.5-2 &mgr;m is a layer of fine, equiaxed TiC grains. Above that is a layer of larger (typically 2-4 &mgr;m) grains of TiC.
In another study published in
Thin Solid Films,
232 (1993) pp. 73-82, Vuorinen et al., entitled “
Interfacial Characterization of Chemically Vapour Deposited Titanium Carbide on Cemented Carbide”,
TiC coatings were CVD-deposited on cemented carbide substrates under non-carburizing conditions. In the absence of &eegr;-carbide, it was found that the TiC nucleated and grew epitaxially on both {0001}- and {10{overscore (1)}0}- WC planes.
Because of the increased performance in turning cast iron which is obtained when using a coated cemented carbide insert having an outer layer of &agr;-Al
2
O
3
, the search for acceptable inserts has continued.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of this invention to avoid or alleviate the problems of the prior art.
It is further an object of this invention to provide a coated cemented carbide insert having an alumina outer layer useful in the turning of cast iron with acceptable life.
In one aspect of the invention there is provided a coated cemented carbide body comprising a coated cemented carbide substrate, a multilayer Ti(C,N) intermediate layer and an Al
2
O
3
outer layer wherein the Ti(C,N) intermediate layer comprises a first, inner layer of columnar grained Ti(C,N) and a second, outer layer of equiaxed grained Ti(C,N).
In another aspect of the invention there is provided a coated cemented carbide body comprising a cemented carbide substrate having a series of sequential layers thereon, said layers in order from the substrate being:
(a) a bonding layer having a thickness of up to 1 &mgr;m selected from the group consisting of TiC, TiN and Ti(C,N);
(b) a multilayer TiCN layer comprising a first, inner layer of columnar grained Ti(C,N) having a grain width (W) of 0.1-0.5 times the layer thickness and a length (L) of 0.5-0.8 times the total layer thickness and a second, outer layer of equiaxed grains having a grain size of from 0.2 to 1.0 &mgr;m, the total thickness of the Ti(C,N) layer being from 3 to 5 &mgr;m when used for milling and from 5 to 10 &mgr;m when used for turning;
(c) a layer of (TiAl)(CO) having a thickness of from about 0.5 to 3 &mgr;m;
(d) an &agr;-Al
2
O
3
layer having a thickness of from about 4 to 10 &mgr;m; and
(e) an outer layer of about 1 &mgr;m or less thickness of TiN.


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Vuorinen et al., “TEM Study of Microstructure and Crystallography at the TiC/Cemented Carbide Interface”,Science of Hard Materials, 1983, pp. 433-447 (No Month).
Vuorinen et al., “Interfacial Characterization of Chemically Vapour Deposited Titanium Carbide on Cemented Carbide”,Thin Solid Films, 232 (1993) pp. 73-82 (No Month).

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