Patent Application
20080166192
The present invention relates to coated cemented carbide inserts with a binder phase enriched surface zone particularly useful for heavy roughing turning operations of very large steel components with improved edge security and wear resistance in combination with extremely good plastic deformation resistance.
For turning of steel materials, both stainless and normal steels, coated cemented carbide inserts are widely used, especially CVD-coated inserts with a binder phase enriched cemented carbide body.
Through the binder phase enriched surface zone, an extension of the application area is obtained. The far most commonly used type is a cemented carbide body with a from about 10 to about 30 μm thick surface zone that is essentially free from cubic phase and moderately enriched in binder phase. Examples are U.S. Pat. No. 4,277,283, U.S. Pat. No. 4,610,931, U.S. Pat. No. 4,830,283 and U.S. Pat. No. 5,106,674.
Another type of binder phase enriched cemented carbide inserts is the so called stratified type, which is accomplished using a powder with very carefully controlled carbon content and a sintering process with controlled cooling. This type has a surface zone from about 15 to about 45 μm thick, which is more strongly enriched in binder phase by several thin stratified layers of binder phase essentially parallel to the outer surface. In large scale production, the carbon control is difficult and the stratified binder phase enrichment is rarely used in practice.
EP-A-603143 discloses a cemented carbide with a binder phase enriched surface zone, said cemented carbide containing WC and cubic phases in a binder phase in which the binder phase enriched surface zone has an outer part essentially free of cubic phase and an inner part containing cubic phase and stratified binder phase layers. It is thus a combination of the abovementioned two types of binder phase enrichments.
Heavy duty machining operations to which the invention relates are characterized by the use of relatively high forces to shape workpieces both by non-cutting and cutting processes. Such operations include non-cutting shaping processes such as extruding, rolling, drawing and ironing and cutting processes such as punching, shearing, and broaching, as well as high force drilling, grinding, milling and turning processes. Characteristic of heavy duty machining operations, work done on the workpiece together with friction between the tool and workpiece generate sufficient heat to distort the workpiece and cause high rates of tool wear.
One example of a heavy duty application is heavy roughing turning operations of very large steel components such as drive shafts for ships and shafts for wind power plants which can be up to 20 m long and up to 1.5 m in diameter, where large cutting inserts are used with iC greater than or equal to about 19 mm, iC is the diameter of the inscribed circle of the insert, and a thickness of greater than or equal to about 6 mm. The demands on the cutting inserts are extremely high as the forged shafts often are oval and have forged skin and inclusions in the surface (oxide scale). With the ovality, the depth of cut (DOC) may be zero occasionally during the cutting operation. The steel type may be low alloyed or carbon steel, e.g., tough hardened steel. Furthermore, the cutting data is extreme with feed rates up to about 2.5 mm and depths of cut up to about 30 mm. This together puts very high demands on toughness behaviour, resistance to plastic deformation and wear resistance on the cutting tool insert.
It is an object of the present invention to provide a cutting tool insert particularly useful for heavy duty applications such as heavy roughing turning operations of very large steel components.
It is a further object of the present invention to provide a cutting tool insert with improved edge security, wear resistance in combination with extremely good plastic deformation resistance.
In one embodiment of the invention, there is provided a coated cutting tool insert comprising a cemented carbide insert body with a stratified binder phase enriched surface zone and a coating wherein the stratified binder phase enriched surface zone has a binder phase content having a maximum of from about 1.5 to about 4 times the nominal binder phase content and is from about 15 to about 45 μm thick whereby the stratified binder phase enriched surface zone as well as an about 100 to about 300 μm thick zone underneath it contain no free graphite, i.e., correspond to a C-porosity of C00 and with a C-porosity in the inner central part of the cemented carbide body of from about C06 to about C08, and the inserts are large with an iC, inscribed circle diameter, of greater than or equal to about 19 mm, and a thickness of greater than or equal to about 6 mm.
In another embodiment of the invention, there is provided a method of making a coated cutting tool insert comprising a cemented carbide insert body with a stratified binder phase enriched surface zone and a coating comprising providing a cemented carbide insert body with an inscribed circle diameter of greater than or equal to about 19 mm, and a thickness of greater than or equal to about 6 mm, with a carbon content corresponding to a C-porosity in the inner central part of the cemented carbide insert body of from about C06 to about C08, and a Hc-value of from about 9.0 to about 13.5, the stratified binder phase enriched surface zone is from about 15 to about 45 μm thick and the binder phase content of the binder phase enriched surface zone has a maximum of from about 1.5 to about 4 times the nominal binder phase content made by sintering a presintered or compacted body with, for formation of stratified layers, an optimum amount of carbon in an inert atmosphere or in vacuum, for about 15 to about 180 min at from about 1380 to about 1520° C., followed by slow cooling, from about 20 to about 100° C./h, through the solidification region, from about 1300 to about 1220° C.
In still another embodiment of the present invention, there is provided the use of the insert described above for heavy duty machining applications of very large components of steel, at a cutting speed in the range of from about 25 to about 100 m/min, feed rates in the range of from about 1 to about 2.5 mm and depth of cut from about 0 to about 30 mm, depth of cut=0 due the ovality of the work pieces.
It has now surprisingly been found that cutting tool inserts showing improved properties with respect to the different demands prevailing at the above mentioned cutting operations can be obtained with cutting tool inserts comprising: a cemented carbide body with a stratified binder phase enriched surface zone partly depleted in cubic phase and with a well balanced carbon content giving a well defined content of free carbon, graphite, in the inner part of the cemented carbide body, preferably in combination with a columnar TiCxNy-layer and a post treated α-Al2O3 top layer.
According to the present invention, a coated cutting tool insert is provided comprising a cemented carbide with a binder phase with a very low W-content and with a stratified binder phase enriched surface zone partly depleted in cubic phase and a coating preferably comprising a columnar TiCxNy-layer and a post treated α-Al2O3 top layer. The inserts are large with an iC of greater than or equal to about 19 mm, preferably from about 30 to about 60 mm and a thickness of greater than or equal to about 6 mm, preferably from about 9 to about 20 mm.
The cemented carbide has a composition of from about 5 to about 10, preferably from about 5.5 to about 8, most preferably from about 6 to about 7, wt-% Co, from about 5 to about 12, preferably from about 7 to about 10, most preferably from about 8 to about 9, wt-% cubic carbides or carbonitrides of the metals from group IVA and VA, preferably Ti, Ta and Nb, and preferably with a Ti-content of from about 1.0 to about 4.0 wt-%, most preferably from about 1.5 to about 3.0 wt-%, and balance WC, preferably from about 80 to about 88 wt-% WC. The nitrogen content is less than about 0.1, preferably from about 0.02 to about 0.1, most preferably from about 0.04 to about 0.07, wt-% and the carbon content is adjusted to correspond to a C-porosity in the inner central part of the cemented carbide body of from about C06 to about C08, preferably about C08. The stratified binder phase enriched surface zone is from about 15 to about 45, preferably from about 20 to about 40, most preferably from about 25 to about 35, μm thick, preferably with an outer part essentially free from cubic phase. The thickness of this outer part is from about 25 to about 50, preferably from about 30 to about 45, % of the total thickness of the stratified binder phase enriched surface zone. The binder phase content of the binder phase enriched surface zone has a maximum of from about 1.5 to about 4, preferably from about 2 to about 3, times the nominal binder phase content. Further, the stratified binder phase enriched surface zone as well as an about from about 100 to about 300 μm thick zone underneath it contain no free graphite, i.e., corresponds to a C-porosity of C00. The Hc-value is from about 9 to about 13.5, preferably from about from about 10 to about 12, kA/m.
The cobalt binder phase is alloyed to a very low amount of tungsten (W). 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 can vary between 1 and about 0.75 dependent on the degree of alloying. A lower CW-ratio corresponds to a higher W content and a CW-ratio=1 corresponds practically to an absence of W in the binder phase.
According to the present invention, the improved cutting performance is enhanced if:
The present invention also relates to a method of making coated cutting tool inserts having a cemented carbide body with a composition of from about 5 to about 10, preferably from about 5.5 to about 8, most preferably from about 6 to about 7 wt-% Co, from about 6 to about 11, preferably from about 7 to about 10, most preferably from about 8 to about 9 wt-% cubic carbides or carbonitrides of the metals from group IV and V, preferably Ti, Ta and Nb, and preferably with a Ti-content of from about 1 to about 4 wt-%, most preferably from about 1.5 to about 3 wt-%, and balance WC, preferably from about 80 to about 88 wt-% WC. The nitrogen content is less than about 0.1, preferably from about 0.02 to about 0.10, most preferably from about 0.04 to about 0.07, wt-% and the carbon content is adjusted to correspond to a C-porosity in the inner central part of the cemented carbide body of from about C06 to about C08, preferably about C08.
Production of cemented carbides according to the invention is most favorably done by sintering a presintered or compacted body containing nitrogen and, for formation of stratified layers, an optimum amount of carbon (which can be determined by the skilled artisan) in an inert atmosphere or in vacuum, for about 15 to about 180 min at from about 1380 to about 1520° C., followed by slow cooling, from about 20 to about 100° C./h, preferably from about 40 to about 70° C./h, through the solidification region, from about 1300 to about 1220° C., preferably from about 1290 to about 1240° C. The sintering conditions are adjusted to obtain an Hc-value in the range of from about 9 to about 13.5, preferably from about 10 to about 12, kA/m. The CW-ratio should be about 0.96-1, preferably within about 0.98-1, most preferably within about 0.99-1. The stratified binder phase enriched surface zone is from about 15 to about 45, preferably from about 20 to about 40, most preferably from about 25 to about 35, μm thick preferably with an outer part essentially free from cubic phase. The thickness of this outer part is from about 25 to about 50, preferably from about 30 to about 45, % of the total thickness of the stratified binder phase enriched surface zone. The binder phase content of the binder phase enriched surface zone has a maximum of from about 1.5 to about 4, preferably from about 2 to about 3, times the nominal binder phase content. Prior to the coating, the inserts are treated to an edge radius of from about 35 to about 95, preferably from about 40 to about 60, μm and surface cleaned using electrochemical or blasting methods.
The inserts are provided with a coating comprising:
The present invention also relates to the use of cutting tool inserts as described above for heavy duty machining applications such as heavy roughing turning operations of very large components of steel, preferably of carbon steel or low alloyed steel, e.g., tough hardened steel, such as drive shafts for ships and shafts for wind power plants which can be as large as 20 m long and up to about 1.5 m in diameter using large cutting inserts with an iC of greater than or equal to about 19 mm, preferably from about 30 to about 60 mm and a thickness of greater than or equal to about 6 mm, preferably from about 9 to about 20 mm at a cutting speed of in the range of from about 25 to about 100, preferably from about 25 to about 75 m/min, feed rates in the range of from about 1 to about 2.5 mm and depth of cut from 0 to about 30 mm, depth of cut=0 due to the ovality of the work pieces, preferably from about 3 to about 30 mm.
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.
From a powder mixture with the composition 2.2 weight-% TiC, 0.5 weight-% TiCN, giving an N-content of 0.05 wt-%, 3.6 weight-% TaC, 2.4 weight-% NbC, 6.5 weight-% Co and rest WC with 0.25 weight-% overstoichiometric carbon content, turning inserts SCMT380932 with iC=38 mm and thickness=9.5 mm were pressed. The inserts were sintered in H2 up to 450° C. for dewaxing and further in vacuum to 1350° C. and subsequently in a protective atmosphere of 40 mbar Ar for 1 h at 1450° C. The cooling was performed with a well controlled temperature decrease of 60° C./h within the temperature interval 1290 to 1240° C. in the same protective atmosphere. After that the cooling continued as normal furnace cooling with maintained protective atmosphere.
The sintered inserts had a binder phase enriched surface zone. The outer part of this surface zone was moderately binder phase enriched, essentially free of cubic phase and with a weakly developed statified binder phase structure, and had a thickness of 15 μm. Inside this outer part, there was a 20 μm thick zone containing cubic phase and with a strong cobalt enrichment as a stratified binder phase structure. The maximum cobalt-content in this part was 17 weight-% as an average over a distance of 100 μm parallel to the surface. The measurement was done using line scan in a micro-probe analyser equipped with wavelength dispersive spectrometer (WDS). Further below this part there was a zone about 150-200 μm thick with essentially nominal content of cubic phase and binder phase but without graphite. In the inner part of the insert graphite was present corresponding to a C-porosity of C08. The Hc-value was 11.5 and the CW-ratio was 0.99.
The inserts were edge rounded using a brushing method to a radius of 50 μm and surface cleaned by an electrochemical method and then coated with a first 0.5 μm thick TiCxNy-layer with a high nitrogen content corresponding to an x-value of about 0.05, followed by a second 8 μm thick TiCxNy-layer, with an x-value of about 0.55 and with a columnar grain structure using MTCVD-technique (temperature 850-885° C. and CH3CN as the carbon/nitrogen source). In subsequent steps during the same coating cycle a third 1 μm thick Ti(C,O)-layer was deposited followed by a fourth 7 μm thick layer of α-Al2O3 and a 1 μm thick top layer of TiN.
The inserts were finally wet blasted on the rake face with alumina grit in order to remove the top TiN-layer and to produce a smooth surface finish of the exposed Al2O3-layer of Ra=0.2 μm over a length of 10 μm.
Inserts from Example 1 were tested at a customer producing shafts for wind power plants and compared to commercially available inserts suitable for this type of operation and in the same insert style as in Example 1, see table 1 (prior art).
The inserts were tested in a heavy roughing longitudinal turning operation of a forged shaft with diameter 800 mm and 8 m in length in steel SS2244.
Cutting speed: 37 m/min
Feed rate: 1.8 mm/rev
Depth of cut: 4-30 mm (sometimes 0, due to ovality)
No coolant
The tool life of the insert according to invention (Example 1) was 115 min compared to 55 min and 38 min for ref A and ref B, respectively. The wear type was mainly flank wear for the insert according to the invention, plastic deformation and breakage for ref A, and plastic deformation for ref B.
From Example 2 it is evident that the insert according to the invention gives superior performance due a very good combination of edge toughness and plastic deformation resistance.
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 |
|---|---|---|---|
| 0602815-3 | Dec 2006 | SE | national |
