The present invention relates to a coated cutting tool insert useful for grooving or severing steel components such as steel or stainless steel tubes and bars. The insert is characterized by WC—Co-based cemented carbide substrate having a highly w-alloyed Co-binder phase and a relatively thin coating including an inner layer of ticxNyOz with columnar grains followed by a layer of fine grained κ—Al2O3 and a top layer of TiN.

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Patent
   RE39986
Priority
Jul 09 1998
Filed
Jun 08 2006
Issued
Jan 01 2008
Expiry
Jul 08 2019
Inventors
Piirhonen,…
Assg.orig
Sandvik In…
Assg.curr
Sandvik In…
Entity
Large
Referenced by
1
References
16
Maint.:
EXPIRED
EXAMPLE 1
EXAMPLE 2
EXAMPLE 3
EXAMPLE 4
EXAMPLE 5
10. A method of making a cutting tool insert comprising a WC—Co-based cemented carbide body with a highly w-alloyed binder phase and a CW-ratio of 0.78-0.93, the method comprising coating the body by the steps of:
forming a first innermost layer of ticxNyOz with a CVD-based technique, wherein x+y+z=1, the first layer having a thickness of 0.1-1.5 μm and equiaxed grains with a size <0.5 μm,
forming a second layer of ticxNyOz by a MTCVD-technique, wherein x+y+z=1, the second layer having a thickness of 0.4-3.9 μm and columnar grains with an average diameter of 0.1-5.0 μm,
forming a third layer of a smooth κ-Al2O3 having a thickness of 0.5-5.5 μm, and
forming the layers such that the total thickness of the first and second layers is 0.5-4.0 μm, and the total thickness of all layers is 2.0-6.0 μm.
1. A cutting tool insert comprising:
a cemented carbide body comprising
6-15 weight % Co, 0.2-1.8 weight % cubic carbides of Ti, Ta, Nb or any combination thereof, a highly w-alloyed binder phase with a CW-ratio of 0.78-0.93, and the balance WC; and
a coating comprising
a first innermost layer of ticxNyOz wherein x+y+z=1, the first layer having a thickness of 0.1-1.5 μm and equiaxed grains with size <0.5 μm,
a second layer of ticxNyOz wherein x+y+z=1, the second layer having a thickness of 0.4-3.9 μm, with columnar grains with an average diameter of 0.1-5.0 μm,
a third layer of a smooth fine-grained κ—Al2O3 layer with a thickness of 0.5-5.5 μm, and
a total thickness of the first innermost ticxNyOz and the second ticxNyOz layer is 0.5-4.0 μm, and the total thickness of all layers is 2.0-6.0 μm.
2. The cutting tool insert of claim 1, wherein the body comprises 9-12 weight % Co and a CW ratio of 0.80-0.91.
3. The cutting tool inset of claim 1, wherein in the first layer y>x and z<0.2, and the thickness of the first layer is 0.1-0.6 μm.
4. The cutting tool insert of claim 1, wherein in the second layer z=0, x>0.3 and y>0.3, the second layer has a thickness of 1.5-3.0 μm, with the columnar grains having an average diameter of 0.1-2.0 μm.
5. The cutting tool insert of claim 1, wherein in the third layer the grains of the κ—Al2O3 have a size on the order of 0.5-2.0 μm, and the third layer has a thickness of 0.5-3.0 μm.
6. The cutting tool insert of claim 1, wherein the total thickness of the first and second layers is 1.5-3.5 μm.
7. The cutting tool insert of claim 1, wherein the total thickness of all the layers is 3.0-5.0 μm.
8. The cutting insert of claim 1 further comprising an outermost layer of TiN having a thickness of 0.1-1.0 μm.
9. The cutting insert of claim 8, wherein the outermost TiN-layer has been removed along the cutting edge.
11. The method of claim 10, wherein the step of forming the first layer further comprises providing the first layer with y>x and z<0.2 and a thickness of 0.1-0.6 μm.
12. The method of claim 10 wherein the step of forming the second layer further comprises using acetonitrile as the carbon and nitrogen source and forming the second layer at a temperature of 850-900° C., the step of forming the second layer further comprises providing z=0, x>0.3 and y>0.3, a thickness of 1.5-3.0 μm, and with the columnar grains having an average diameter of 0.1-2.0 μm.
13. The method of claim 10, wherein the third layer is provided with a thickness of 0.5-3.0 μm.
14. The method of claim 10, wherein the method further comprises forming an outer layer of TiN having a thickness of <1 μm.
15. The method of claim 10, wherein the method further comprises providing the first and second layers with a total thickness of 1.5-3.5 μm, and a total thickness of all layers of 3.0-5.0 μm.
16. The method of claim 10 wherein the said cemented carbide body has a cobalt content of 9-12 weight % and 0.4-1.8 weight % cubic carbides of Ta and Nb.
17. The method of claim 10 wherein the cemented carbide body has a cobalt content of 10-11 weight %.
18. The method of claim 17 wherein the cemented carbide body has a CW-ratio of 0.82-0.90.
19. The method of claim 14, wherein the outermost TiN-layer is removed along a cutting edge.
20. The method of claim 19, wherein the outermost TiN-layer is removed by brushing.
0. 21. The cutting tool inset of claim 3, wherein in the second layer z=0, x>0.3 and y>0.3, the second layer has a thickness of 1.5-3.0 μm with the columnar grains having an average diameter of 0.1-2.0 μm.
0. 22. The cutting tool insert of claim 21, wherein in the third layer the grains of the κ-Al2O3 have a size on the order of 0.5-2.0 μm and the third layer has a thickness of 0.5-3.0 μm.
0. 23. The cutting tool insert of claim 22, wherein the total thickness of all the layers is 3.0-5.0 μm.
0. 24. The cutting insert of claim 22 further comprising an outermost layer of TiN having a thickness of 0.1-1.0 μm.
0. 25. The cutting insert of claim 24, wherein the outermost TiN-layer has been removed along the cutting edge.
0. 26. The method of claim 11 wherein the step of forming the second layer further comprises using acetonitrile as the carbon and nitrogen source and forming the second layer at a temperature of 850-900° C., the step of forming the second layer further comprises providing z=0, x>0.3 and y>0.3, a thickness of 1.5-3.0 μm and with the columnar grains having an average diameter of 0.1-2.0 μm.
0. 27. The method of claim 26, wherein the method further comprises forming an outer layer of TiN having a thickness of <1 μm.
0. 28. The method of claim 27, wherein the outermost TiN-layer is removed along a cutting edge.
0. 29. The method of claim 26, wherein the method further comprises providing the first and second layers with a total thickness of 1.5-3.5 μm and a total thickness of all layers of 3.0-5.0 μm.
0. 30. The method of claim 10 wherein the said cemented carbide body has a cobalt content of 9-12 weight % and 0.4-1.8 weight % cubic carbides of Ta and Nb.
0. 31. The method of claim 30 wherein the cemented carbide body has a CW-ratio of 0.82-0.90.
kA/m hAm2/kg and wt % Co is the weight percentage of Co in the cemented carbide. The CW-value is a function of the W content in the Co binder phase. A low CW-value corresponds to a high W-content in the binder phase. According to the present invention improved cutting performance is achieved if the cemented carbide substrate has a CW-ratio of 0.78-0.93.

According to the present invention a parting tool insert is provided with a cemented carbide substrate with a composition of 6-15 wt % Co, preferably 9-12 wt % Co, and most preferably 10-11 wt % Co. The composition further includes 0.2-1.8 wt % cubic carbides, preferably 0.4-1.8 wt % cubic carbides, most preferably 0.5-1.7 wt % cubic carbides, of the metals Ta, Nb and Ti and balance WC. The cemented carbide may also contain other carbides from elements from group IVb, Vb or VIb of the periodic table. The content of Ti is preferably on a level corresponding to a technical impurity. The preferred average grain size of the WC depend on the binder phase content. At a preferred composition of 10-11 wt-% Co, the preferred grain size is 1.5-2.0 μm, most preferably about 1.7 μm. The CW-ratio shall be 0.78-0.93, preferably 0.80-0.91, and most preferably 0.82-0.90. The cemented carbide may contain small amounts, <1 volume %, of ρ-phase (M6C), without any detrimental effect. From the CW-value it follows that no free graphite is allowed in the cemented carbide substrate according to the present embodiment.

The coating comprises a first innermost layer of TiCxNyOz with x+y+z=1, preferably y>x and z<0.2, most preferably y>0.8 and z=0, with equiaxed grains with a size <0.5 μm, and a total thickness <1.5 μm but >0.1 μm, preferably the thickness is 0.1-0.6 μm;

    • a second layer of TiCxNyOz with x+y+z=1, preferably with z=0, x>0.3 and y>0.3, most preferably x>0.5, with a thickness of 0.4-3.9 μm, preferably the thickness is 1.5-3.0 μm, the second layer has columnar grains with an average diameter of <5 μm, preferably 0.1-2.0 μm;
    • the total thickness of the first and second layers is 0.5-4.0 μm, preferably 1.5-3.5 μm. Preferably, the first layer is thinner than the second layer;
    • a third layer of a smooth, fine-grained Al2O3 consisting essentially of the κ-phase having a grain size about 0.5-2 μm. However, the layer may contain small amounts, 1-3 vol-%, of the θ or the α-phases as determined by x-ray diffraction (XRD) measurement. The Al2O3-layer has a thickness of 0.5-5.5 μm, preferably 0.5-3.0 μm;
    • preferably, this Al2O3-layer is followed by a further layer of TiN having a thickness <1 μm, preferably 0.1-0.5 μm thick. The Al2O3 or the TiN layer can be the outermost layer. This outermost layer, whether Al2O3 or TiN, has a surface roughness Rmax<0.4 μm over a length of 10 μm. The TiN-layer, if present, is preferably removed along the cutting edge by a suitable removal technique, such as brushing; and
    • the total thickness of the first, second and third layers is 2-6 μm, preferably 3-5 μm.

According to a method of the invention, a WC—Co-based cemented carbide substrate is made with a highly W-alloyed binder phase with a CW-ratio of 0.78-0.93, preferably 0.80-0.91, and most preferably 0.82-0.90. The content of cubic carbides of the metals Ta, Nb and Ti is 0.2-1.8 wt %, preferably 0.4-1.8 wt %, and most preferably 0.5-1.7 wt %. The substrate further includes 6-15 wt % Co, preferably 9-12 wt % Co, and most preferably 10-11 wt % Co. The WC grain size is 1.5-2.0 μm, most preferably about 1.7 μm, when the Co content is in the 10-11 wt. % range. The body is coated by:

    • a first innermost layer of TiCxNyOz with x+y+z=1, preferably y>x and z<0.2, most preferably y>0.8 and z=0, with equiaxed grains with size <0.5 μm and a total thickness <1.5 μm, preferably >0.1 μm, preferably 0.1-0.6 μm, using known CVD-methods;
    • a second layer of TiCxNyOz with x+y+z=1, preferably with z=0, x>0.3 and y>0.3, most preferably x>0.5, with a thickness of 0.4-3.9 μm, preferably 1.5-3.0 μm, with columnar grains and with an average diameter of about <5 μm, preferably 0.1-2.0 μm, is applied preferably using a MTCVD-technique (e.g.—using acetonitrile as the carbon and nitrogen source for forming the layer in the temperature range of 700-900° C.). The exact conditions, however, depend to a certain extent on the design of the equipment used;
    • the total thickness of the first and second layers is 0.5-4.0 μm, preferably 1.5-3.5 μm. Preferably, the first layer is thinner than the second layer;
    • a third layer of a smooth, fine-grained Al2O3 consisting essentially of the κ-phase having a grain size about 0.5-2.0 μm. The Al2O3-layer has a thickness of 0.5-5.5 μm, preferably 0.5-3.0 μm. Preferably, this Al2O3-layer is followed by a further layer of TiN having a thickness <1 μm, preferably 0.1-0.5 μm thick. The Al2O3 layer can be exposed as the outermost layer. The outermost layer of Al2O3 or TiN has a surface roughness Rmax<0.4 μm over a length of 10.0 μm. The smooth coating surface can be obtained by gently wet-blasting the coating surface with fine grained (400-150 mesh) alumina powder, or by brushing (preferably used when TiN top layer is present) the edges with brushes based on SiC as disclosed in Swedish patent application 9402543-4. The TiN-layer, if present, is preferably removed along the cutting edge; and
    • the total thickness of the first, second and third layers is 2.0-6.0 μm, preferably 3.0-5.0 μm.

As a way of further illustrating the present invention and the advantages thereof, the following examples are given.

EXAMPLE 1

A. A cemented carbide cutting tool insert in style N151.2-300-5E with the composition 10.5 wt-% Co, 1.16 wt-% Ta, 0.28 wt-% Nb and balance WC, with a binder phase highly alloyed with W corresponding to a CW-ratio of 0.87, was coated with an innermost 0.5 μm equiaxed TiC0.05N0.95-layer with a high nitrogen content, corresponding to an estimated C/N ratio of 0.05, followed by a 2.2 μm thick layer of columnar TiCo0.54N0.46 deposited using MT-CVD technique. In subsequent steps during the same coating process a 1.5 μm layer of Al2O3 consisting of pure ic-phase was formed according to procedure disclosed in EP-A-523 021. A thin, 0.5 μm, TiN layer was deposited, during the same cycle, on top of the Al2O3-layer. Hence, the total thickness of all layers is 4.7 μm. The coated insert was brushed by a SiC containing nylon straw brush after coating, removing the outer TiN layer on the edge.

B. A cemented carbide cutting tool insert in style N151.2-300-SE with the composition of 8.0 wt-% Co, no cubic carbides, balance WC and a CW-ratio of 0.94 was prepared. The insert was coated with an innermost 0.5 μm equiaxed TiCN-layer. A 1.5 μm TiN layer was deposited, during the same cycle, on top of the TiCN-layer. No post treatment was applied.

C. A cemented carbide cutting tool insert in style N151.2-300-SE with the composition of 8.0 wt-% Co, no cubic carbides, balance WC and a CW-ratio of 0.94. The insert was coated with an innermost 0.5 μm equiaxed TiCN-layer with a high nitrogen content, corresponding to an estimated C/N ratio of 0.05, followed by a 4.0 μm thick layer of columnar TiCN deposited using MT-CVD technique. In subsequent steps during the same coating process a 1.0 μm layer of Al2O3 consisting of pure K phase was formed according to procedure disclosed in EP-A-523-021. A thin, 0.5 μm TiN layer was deposited, during the same cycle, on top of the Al2O3-layer. The coated insert was brushed by a SiC containing nylon straw brush after coating, removing the outer TiN layer on the edge.

D. A comparative cemented carbide cutting tool insert in style similar to N151.2-300-5E from an external leading cemented carbide producer was selected for comparison. The carbide had a composition of 11.0 wt-% Co, 7.1 wt-% TiC, 12.1 wt-% TaC, 1.3 wt-% NbC, balance WC and a CW-ratio of 0.80. The insert had a coating consisting of 1.1 μm TiN and, outermost, 0.3 μm TiCN layer. Examination in light optical microscope revealed no edge treatment subsequent to coating.

Inserts from A, B and C were compared in a flaking test comprising a facing operation in austenitic stainless steel (SanMac 304L). Feed 0.15 mm/rev, speed 130 m/min and depth of cut varying between 0-2.5 mm.

Number of cuts
before extensive
Insert flaking
A (acc. to invention) 10 
B (outside invention) 5
C (outside invention) 1
D (external grade) 3

EXAMPLE 2

Inserts A, B, C and D from above were tested in a serving test of stainless steel (SS2343) in the form of 12 mm bar stainless steel.

The rotating speed was 1800 rpm, feed varying 0.15-0.02 mm/rev (low feed rate close to centre of bar).

The wear mechanism was flaking combined with nose cracking.

Insert Number of components
A (acc. to invent.) 380
B (outside invention) 180
C (outside invention) 200
D (external grade) 200

EXAMPLE 3

Inserts A (insert style N151.2-400-4E) and D were tested at an end users machine shop in severing of stainless steel tube (SS2343, OD 27 mm, ID 25 mm) with feed 0.05 mm/rev and speed 150 m/min.

Insert D failed due to major chipping of the cutting edge while a very small chipping was seen on insert A.

Insert Number of components
A (acc. to invention) 324
D (external grade) 108

EXAMPLE 4

Inserts A and D were tested at an end users machine shop in parting to centre of an annealed high alloy steel SS2242 with feed 0.15 mmlrev and speed 100 m/min.

Insert D failed due to cracking in the corners while a very small deformation in the corners was seen on insert A.

Insert Number of components
A (acc. to invention) 400
D (external grade) 150

EXAMPLE 5

Inserts A (insert style N151.2-400-4E) and D were tested at an end users machine shop in parting of a steel bar (SS2225, OD 50 mm) with feed 0.06-0.14 mm/rev and speed 180 m/min.

Insert D failed due to chipping of the cutting edge while even flank wear was seen on insert A.

Insert Number of components
A (acc. to invention) 300
D (external grade) 150

While the present invention has been described by reference to the above-described embodiments, certain modifications and variations will be evident to those of ordinary skill in the art. Therefore, the present invention is to limited only the scope and spirit of the appended claims.

INVENTORS:

Piirhonen, Anders, Kullander, Gregor, Reineck, Ingrid, Selinder, Torbjorn

THIS PATENT IS REFERENCED BY THESE PATENTS:
Patent Priority Assignee Title
8080323, Jun 28 2007 KENNAMETAL INC Cutting insert with a wear-resistant coating scheme exhibiting wear indication and method of making the same
THIS PATENT REFERENCES THESE PATENTS:
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