Patent Application
20080050186
It has now surprisingly been found that a hard cubic carbide containing cemented carbide substrate combined with a relatively thin PVD-coating in combination with a special edge treatment giving a sharp edge greatly improves the edge line security, and wear resistance in addition to good resistance against plastic deformation resulting in increased tool life and surface quality on the workpiece surfaces when milling in hardened steels and hard cast irons with hardness more than about 45 HRC.
The substrate comprises a cemented carbide with a hardness of from about 1700 HV3 to about 2000 HV3, preferably with the composition from about 5.4 to about 6.3 wt-% Co, preferably from about 5.7 to about 6.1 wt-% Co, from about 0.7 to about 1.0 wt-% Ta+Nb, preferably from about 0.6 to about 0.95 wt-% Ta+Nb, most preferably from about 0.7 to about 0.9 wt-% Ta+Nb, and from about 5.0 to about 7.0 wt-% Ti, preferably from about 5.5 to about 6.5 wt-% Ti, most preferably from about 6.0 to about 6.4 wt-% Ti, added as TaC, NbC and TiC or mixtures of these, and balance WC with as sintered Hc-value of from about 20 to about 26, preferably from about 21 to about 25, kA/m.
The cobalt binder phase is alloyed with W giving the invented cemented carbide cutting insert its desired properties. W in the binder phase influences the magnetic properties of cobalt and can hence be related to a value, CW-ratio, defined as
CW-ratio=magnetic-% Co/wt-% Co
where magnetic-% Co is the weight percentage of magnetic Co and wt-% Co is the weight percentage of Co in the cemented carbide.
The CW-ratio varies between 1 and about 0.75 dependent on the degree of W-alloying. Lower CW-ratios correspond to higher W and CW=1 corresponds practically to an absence of W in the binder phase. The cemented carbide body according to the invention has a CW-ratio from about 0.75 to about 0.95, preferably from about 0.78 to about 0.90.
The uncoated substrates have a 10° angle and 0.2 mm wide negative chamfer giving an edge sharpness of 0(sharp) to about 40 μm.
The coating comprises a homogeneous AlxTi1-xN-layer with x=from about 0.6 to about 0.67, preferably x=about 0.62. The total thickness of the layer is more than about 1 μm, preferably more than about 1.8 μm, but less than about 3.8 μm, preferably less than about 3.0 μm. Both the composition and the thickness are determined on the flank face 1 mm from the nose radius and 200 μm from the cutting edge.
The present invention also relates to a method of making a coated cutting tool insert consisting of a cemented carbide substrate and a coating. The cemented carbide substrate has before coating a 10° angle and 0.2 mm wide negative chamfer giving an edge sharpness of 0(sharp) to about 40 μm and is made using conventional powder metallurgical techniques milling, pressing and sintering.
The substrate comprises a cemented carbide with a hardness of from about 1700 HV3 to about 2000 HV3, preferably with the composition from about 5.4 to about 6.3 wt-% Co, preferably from about 5.7 to about 6.1 wt-% Co, from about 0.7 to about 1.0 wt-% Ta+Nb, preferably from about 0.6 to about 0.95 wt-% Ta+Nb, most preferably from about 0.7 to about 0.9 wt-% Ta+Nb, and from about 5.0 to about 7.0 wt-% Ti, preferably from about 5.5 to about 6.5 wt-% Ti, most preferably from about 6.0 to about 6.4 wt-% Ti, added as TaC, NbC and TiC or mixtures of these, and balance WC with as sintered Hc-value of from about 20 to about 26, preferably from about 21 to about 25 kA/m.
After conventional post sintering treatment a coating comprising AlxTi1-xN with x=from about 0.6 to about 0.67, preferably x=about 0.62 is deposited by cathodic arc evaporation using a target material consisting of TiAl-alloy of suitable composition, in an N2 gas atmosphere. The total thickness of the coating is more than about 1 μm, preferably more than about 1.8 μm, but less than about 3.8 μm, preferably less than about 3.0 μm.
The present invention also relates to the use of the insert described above for milling in hard steels, tool steels, hardened steels and hard cast irons with hardness more than about 45 HRC at a cutting speed of from about 50 to about 180 m/min and a feed of from about 0.1 to about 0.4 mm/rev.
The invention is additionally illustrated in connection with the following examples, which are to be considered as illustrative of the present invention. It should be understood, however, that the invention is not limited to the specific details of the examples.
A. Cemented carbide milling inserts in accordance with the invention with the composition 5.90 wt-% Co, 0.56 wt-% Ta, 0.35 wt-% Nb, 6.16 wt-% Ti added as TaC, NbC and TiC and balance WC with as sintered Hc-value of 23 kA/m and with a binder phase alloyed with W corresponding to a CW-ratio of 0.86 were coated with a 2.9 μm homogeneous Al0.62Ti0.38N-PVD-layer by cathodic arc evaporation using a target material consisting of a Ti33Al67-alloy. The arc evaporation was performed in an N2 gas atmosphere.
B. (Reference) Commercial cemented carbide milling inserts with the composition of 3.70 wt-% Co, 1.43 wt-% Ta, 0.42 wt-% Nb and balance WC and with an Hc-value of 23 kA/m and a CW-ratio of 0.9. The inserts were coated with a 2.9 μm (Ti,Al)N PVD-coating as in A.
Inserts from A and B were tested in turning of a cast steel.
Criteria for replacing inserts: edge line chipping and/or risk of insert breakage.
Results:
Inserts from A and B were tested in milling of a cast steel.
Criteria for replacing inserts: edge line chipping and/or risk of insert breakage.
Results:
Although the present invention has been described in connection with preferred embodiments thereof, it will be appreciated by those skilled in the art that additions, deletions, modifications, and substitutions not specifically described may be made without department from the spirit and scope of the invention as defined in the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0601759-4 | Aug 2006 | SE | national |
