Patent Application
20090169315
This application claims priority to Swedish Application No. 0702865-7 filed Dec. 27, 2007, the entire disclosure of which is incorporated herein by reference.
This invention relates to coated cemented carbide cutting tool inserts. More specifically, the invention relates to coated cemented carbide cutting tool inserts for milling applications in which a combination of high wear resistance and good toughness properties are required.
During milling of various materials with coated cemented carbide cutting tools, the cutting edges are regarded as being worn according to different wear mechanisms. Wear types such as chemical wear, abrasive wear and adhesive wear, are rarely encountered in a pure state, and complex wear patterns are often the result. The domination of any of the wear mechanisms is determined by the application, and is dependent on properties of the machined material, applied cutting parameters and the properties of the tool material. In general, it is very difficult to improve all tool properties simultaneously, and particularly, edge toughness and wear resistance are difficult to combine, and commercial cemented carbide grades have usually been optimised with respect to one or few of the above mentioned wear types, and have consequently been optimised for specific application areas.
U.S. Pat. No. 6,062,776 discloses a coated cutting insert particularly useful for milling of low and medium alloyed steels and stainless steels with raw surfaces such as cast skin, forged skin, hot or cold rolled skin or pre-machined surfaces under unstable conditions. The insert is characterised by a WC—Co cemented carbide with a low content of cubic carbides and a rather low W-alloyed binder phase and a coating including an innermost layer of TiCxNyOz with columnar grains and a top layer of TiN and an inner layer of κ-Al2O3.
U.S. Pat. No. 6,177,178 describes a coated milling insert particularly useful for milling in low and medium alloyed steels with or without raw surface zones during wet or dry conditions. The insert is characterised by a WC—Co cemented carbide with a low content of cubic carbides and a highly W-alloyed binder phase and a coating including an inner layer of TiCxNyOz with columnar grains, an inner layer of κ-Al2O3 and, preferably, a top layer of TiN.
U.S. Pat. No. 6,250,855 discloses a coated milling insert for wet or dry milling of stainless steels of different composition and microstructure. The coated WC—Co based cemented carbide inserts includes a specific composition range of WC—Co without any additions of cubic carbides, a low W-alloyed Co binder and a hard and wear resistant coating including a multilayered structure of sub-layers of the composition (TixAl1-x)N.
EP 1103635 provides a cutting tool insert particularly useful for wet and dry milling of low and medium alloyed steels and stainless steels as well as for turning of stainless steels. The cutting tool is comprised of a cobalt cemented carbide substrate with a multi-layer refractory coating thereon. The substrate has a cobalt content of 9.0-10.9 wt % and contains 1.0-2.0 wt % TaC/NbC. The coating consists of an MTCVD TiCxNyOz layer and a multi-layer coating being composed of κ-Al2O3 and TiCxNyOz layers.
EP 1493845 relates to a coated cemented carbide insert (cutting tool), particularly useful for milling of stainless steels and super alloys but also milling of steels in toughness demanding applications. The cutting tool insert is characterised by a cemented carbide body comprising WC, NbC and TaC, a W-alloyed Co binder phase, and a coating comprising an innermost layer of TiCxNyOz with equiaxed grains, a layer of TiCxNyOz with columnar grains and a layer of α-Al2O3.
EP 1352697 provides coated cemented carbide inserts (cutting tool), particularly useful for milling at high cutting speeds in steels and milling in hardened steels. The inserts are characterized by a WC—Co cemented carbide containing NbC and TaC and a W-alloyed binder phase and a coating including a first, innermost layer of TiCxNyOz with equiaxed grains, a layer of TiCxNyOz with columnar grains and at least one layer of Al2O3 consisting essentially of the κ-phase.
EP 1026271 relates to a coated cemented carbide insert for turning of steels. The insert has a highly alloyed Co-binder phase, 4-12, preferably 7-10, percent by weight of cubic carbides and a WC grain size of 1-4, preferably 2-3 μm. The binder phase enriched surface zone is of a thickness <20 μm and along a line in the direction from the edge to the centre of the insert the binder phase content increases essentially monotonously until it reaches the bulk composition. The coating of the insert comprises 3-12 μm of columnar TiCN and 2-12 μm of Al2O3.
EP 1348779 relates to a cutting tool insert consisting of a cemented carbide substrate and a coating. The cemented carbide substrate comprises WC, 4-7 wt % cobalt, 6-9 wt % cubic carbide forming metals from the groups IVb and Vb, with a binder phase enriched surface zone with a thickness of >20 μm and the total thickness of the coating being less than 30 μm. Inserts according to the invention exhibit favorable wear resistance and edge strength when turning steel.
EP 1528125 relates to a cutting tool insert for rough turning composed of a cemented carbide and a coating. The cemented carbide substrate comprises WC, 7-12 wt-% Co, 5-11 wt-% cubic carbides of metals from the groups IVb, Vb and VIb with a binder phase enriched surface zone. The tungsten carbide phase has a mean intercept length of 0.7-1.4 μm. The coating comprises at least one α-Al2O3.
US 2008/187775 relates to a turning cutting tool insert comprising a cemented carbide body and a coating. The cemented carbide body comprises WC, 6-7 wt-% Co and 6-10, wt-% cubic carbides of the metals from groups IVb, Vb and VIb of the periodic table, preferably Ti, Nb and Ta, and at least one surface of the cemented carbide body comprises a binder phase enriched surface zone being essentially free from cubic carbides and a coating wherein at least one layer is a 5-7 μm thick α-Al2O3 layer with a (104) texture.
EP 1469101 relates to a coated cemented carbide cutting tool insert particularly useful for turning of cast irons but also low alloyed steels at mediate to high cutting speeds. The cutting tool insert is characterised by a cemented carbide body comprising WC, cubic carbonitrides, a W-alloyed Co binder phase, a surface zone of the cemented carbide body that is binder phase enriched and nearly free of cubic carbonitride phase, and a coating including an innermost layer of TiCxNyOz with equiaxed grains, a layer of TiCxNyOz with columnar grains and at least one layer of Al2O3.
EP 1531187 concerns a coated cemented carbide cutting tool insert particularly useful for turning of cast irons. The cutting tool insert is characterized by a cemented carbide body comprising WC, cubic carbonitrides, a W-alloyed Co binder phase, a surface zone of the cemented carbide body that is binder phase enriched and nearly free of cubic carbonitride phase, and a coating including an innermost layer of TiCxNyOz with equiaxed grains, a layer of TiCxNyOz with columnar grains and at least one layer of Al2O3.
EP 1314790 relates to a cutting tool insert consisting of a cemented carbide substrate and a coating. The cemented carbide substrate comprises 73-93% by weight WC, 4-12% by weight binder phase, and cubic carbide phase with a binder phase enriched surface zone essentially free of cubic carbide phase. The cubic carbide phase comprises of elements from the groups IVb and Vb, with the tantalum content on a level corresponding to a technical impurity. Inserts according to the invention exhibit favourable edge strength and thermal shock resistance.
What is needed is a coated cutting tool with enhanced performance for milling. The invention is directed to these, as well as other, important needs.
Accordingly, the invention is directed to coated cemented carbide cutting tool inserts for milling applications in which a combination of high wear resistance and good toughness properties are required. The insert has a body with a tough Co binder phase, tungsten carbide (WC) and cubic carbonitrides as hard phases and a wear resistant coating comprising an Al2O3 layer. The surface zone of the insert body is of a different elemental composition than that of the bulk, giving the inserts enhanced properties.
In one embodiment, the invention is directed to milling tool inserts, comprising:
a cemented carbide body; and
a coating;
wherein said body comprises:
wherein said body has a mean intercept length of about 0.3-1.0 μm and a surface zone with a thickness of at least about 5 μm, wherein said surface zone is Co enriched and essentially free of cubic carbonitride phase;
wherein said coating comprises at least one Al2O3 layer; and
wherein said Al2O3 layer has a thickness of about 1- 15 μm.
In another embodiment, the invention is directed to methods of making a coated milling tool insert, comprising:
preparing a cemented carbide body using powder metallurgy, milling pressing, and sintering;
wherein said body comprises:
wherein said body has a mean intercept length of about 0.3-1.0 μm and a surface zone with a thickness of at least about 5 μm, wherein said surface zone is Co enriched and essentially free of cubic carbonitride phase; and
depositing a coating using chemical vapor deposition (CVD);
In yet other embodiments, the invention is directed to methods for milling of cast iron, steel, or stainless steel, comprising the step of:
using a cutting tool insert described herein at cutting speeds of about 50-500 m/min, with an average feed per tooth of about 0.08-0.5 mm.
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings:
1. Cemented carbide bulk
2. Cemented carbide surface zone
3. A layer consisting of a cubic carbonitride
4. A layer consisting of Al2O3.
According to the present invention, the milling cutting tool insert has a body with a tough Co binder phase, WC and cubic carbonitrides as hard phases and a wear resistant coating comprising an Al2O3 layer. The surface zone of the insert body is of a different elemental composition than that of the bulk, giving the inserts enhanced properties. More specifically, a coated milling tool insert is provided with a cemented carbide body having a composition of about 7-15, preferably about 8-13, most preferably about 9-12, wt % Co, cubic carbonitride phase and WC and a wear resistant coating comprising at least one layer of Al2O3, preferably of the a-phase, with a thickness of about 1-15 μm. The surface zone of the insert body is of a different elemental composition than that of the bulk, giving the insert enhanced properties. The surface zone has a thickness of at least about 5 μm and is binder phase enriched and essentially free of cubic carbonitride phase.
In a first preferred embodiment, the amount of cubic carbonitrides corresponds to about 1.5-25.0% by weight of the cubic carbonitride-forming elements from groups IVb, Vb, VIb, and combinations thereof of the periodic table, preferably about 3.0-15.0% by weight. The amount of cubic carbonitride phase in the body is provided in terms of the amount of cubic carbonitride-forming elements found in the body, for ease of measurement.
In a second preferred embodiment, the cubic carbonitride-forming elements are titanium, tantalum, niobium, zirconium, hafnium, vanadium, chromium, and combinations thereof.
In a third preferred embodiment, the amount of cubic carbonitrides corresponds to about 1.5-25.0% by weight of the cubic carbonitride forming elements titanium, tantalum, and niobium, preferably about 3.0-15.0% by weight. The weight ratio between tantalum and niobium is within about 0.8-4.5, preferably about 1.2-3.0. The weight ratio between titanium and niobium is about 0.5-7.0, preferably about 1.0-4.0.
In a fourth preferred embodiment, the Co enrichment in the surface zone is within about 1.2-3.0 times the bulk Co content.
In a fifth preferred embodiment, particularly for cast iron applications, the Co content is about 7-10 wt %, preferably about 7-9 wt %.
In a sixth preferred embodiment, particularly for cast iron applications, the Co content is about 7-10 wt %, preferably about 7-9 wt %.
In a seventh preferred embodiment, the hard wear resistant coating comprises a layer of cubic carbonitride in the form of TiCxNyOz and a layer of a metal oxide in the form of Al2O3 with a total coating thickness of about 2-20 μm.
Furthermore, the mean intercept length of the tungsten carbide phase measured on a ground and polished representative cross section is about 0.3-1.0 μm, preferably about 0.4-0.9 μm. The intercept length is measured by means of image analysis on micrographs with a magnification of 10000× and calculated as the average mean value of approximately 1000 intercept lengths.
The present invention also relates to a method of making a coated milling tool comprising:
providing a cemented carbide body having a composition of about 7-15, preferably about 8-13, most preferably about 9-12, wt % Co, cubic carbonitride phase and WC with a mean intercept length of about 0.3-1.0 μm, preferably about 0.4-0.9 μm with a surface zone with a thickness of at least about 5 μm which is binder phase enriched and essentially free of cubic carbonitride phase using conventional powder metallurgical methods, milling pressing and sintering. The desired mean intercept length depends on the grain size of the starting powders and milling and sintering conditions and has to be determined by experiments and
depositing a wear resistant coating comprising at least one layer of Al2O3, preferably of the α-phase, with a thickness of about 1-15 μm using chemical vapor deposition (“CVD”) methods known in the art.
The invention also relates to the use of cutting tool inserts according to the above for milling of cast irons, steels and stainless steels at cutting speeds of about 50-500 m/min, preferably about 75-400 m/min, with an average feed per tooth of about 0.08-0.5 mm, preferably about 0. 1-0.4 mm depending on cutting speed and insert geometry.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are now described. All publications mentioned hereunder are incorporated herein by reference. Unless mentioned otherwise, the techniques employed or contemplated herein are standard methodologies well known to one of ordinary skill in the art. The materials, methods, and examples are illustrative only and not limiting.
The present invention is further defined in the following Examples, in which all parts and percentages are by weight and degrees are Celsius, unless otherwise stated. It should be understood that these examples, while indicating preferred embodiments of the invention, are given by way of illustration only. From the above discussion and these examples, one skilled in the art can ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.
Grade A: A cemented carbide substrate in accordance with the invention with the composition 8 wt % Co, 2.0 wt % Ta, 0.9 wt % Nb, 1.5 wt % Ti, balance W, C and N, was produced by conventional milling of powders, pressing of green compacts and subsequent sintering at 1430° C. Investigation of the microstructure after sintering showed that the mean intercept length of the tungsten carbide phase was 0.62 μm and that the surface zone of the inserts consisted of a 20 μm thick binder phase enriched part nearly free of cubic carbonitride phase. The substrate was coated in accordance with the invention with subsequent layers deposited during the same coating cycle. The first layer was a 0.2 μm thick TiCxNyOz layer with z<0.1 and y>0.6, having equiaxed grains. The second layer was 4 μm of columnar TiCxNyOz deposited at about 850° C. with acetonitrile as carbon and nitrogen source, yielding an approximated carbon to nitrogen ratio x/y=1.5 with z<0.1. A 5 μm thick layer of Al2O3, consisting of the α-phase, was deposited at approximately 1000° C.
Grade B: A cemented carbide substrate in accordance with the invention with the composition 8 wt % Co, 2.0 wt % Ta, 0.9 wt % Nb, 1.5 wt % Ti, 0.25 wt % Cr, balance W, C and N, was produced according to grade A. Investigation of the microstructure after sintering showed that the mean intercept length of the tungsten carbide phase was 0.58 μm and that the surface zone of the inserts consisted of a 22 μm thick binder phase enriched part nearly free of cubic carbonitride phase. The substrate was coated in accordance with Grade A.
Grade C: A cemented carbide substrate in accordance with the invention with the composition 8 wt % Co, 2.0 wt % Ta, 0.9 wt % Nb, 1.0 wt % Ti, 0.3 wt % Zr, balance W, C and N, was produced according to grade A. Investigation of the microstructure after sintering showed that the mean intercept length of the tungsten carbide phase was 0.59 μm and that the surface zone of the inserts consisted of a 23 μm thick binder phase enriched part nearly free of cubic carbonitride phase. The substrate was coated in accordance with Grade A.
Grade D: A cemented carbide substrate in with the composition 8 wt % Co, 1.3 wt % TAC, 0.2 wt % NbC and balance WC. Investigation of the microstructure after sintering showed that the mean intercept length of the tungsten carbide phase was 0.63 μm and that the average phase composition was representative throughout the sintered body. The substrate was coated in accordance with Grade A.
Inserts according to Grade A, B, C, and D were tested in a face milling application where coolant was applied.
The tool life was limited by the combination of flank wear, chipping and thermal cracking. The test shows the improved wear resistance and toughness was achieved with a binder phase enriched surface zone.
Grade E: A cemented carbide substrate in accordance with the invention with the composition 10 wt % Co, 3.0 wt % Ta, 2.0 wt % Nb, 2.0 wt % Ti, balance W, C and N, was produced by conventional milling of powders, pressing of green compacts and subsequent sintering at 1430° C. Investigation of the microstructure after sintering showed that the mean intercept length of the tungsten carbide phase was 0.78 μm and that the surface zone of the inserts consisted of a 20 μm thick binder phase enriched part nearly free of cubic carbonitride phase. The substrate was coated in accordance with the invention with subsequent layers deposited during the same coating cycle. The first layer was a 0.2 μm thick TiCxNyOz layer with z<0.1 and y>0.6, having equiaxed grains. The second layer was 3 μm of columnar TiCxNyOz deposited at about 850° C. with acetonitrile as carbon and nitrogen source, yielding an approximated carbon to nitrogen ratio x/y=1.5 with z<0.1. A 3 μm thick layer of Al2O3, consisting of the α-phase, was deposited at approximately 1000° C.
Grade F: A cemented carbide substrate in accordance with the invention with the composition 10 wt % Co, 3.0 wt % Ta, 2.0 wt % Nb, 1.5 wt % Ti, 0.4 wt % Zr, balance W, C and N, was produced according to grade A. Investigation of the microstructure after sintering showed that the mean intercept length of the tungsten carbide phase was 0.76 μm and that the surface zone of the inserts consisted of a 18 μm thick binder phase enriched part nearly free of cubic carbonitride phase. The substrate was coated in accordance with Grade E.
Grade G: A cemented carbide substrate with the composition 10 wt % Co, 1.3 wt % TaC, 0.2 wt % NbC, and balance WC. Investigation of the microstructure after sintering showed that the mean intercept length of the tungsten carbide phase was 0.80 μm and that the average phase composition was representative throughout the sintered body. The substrate was coated in accordance with Grade F.
Inserts according to Grade E, F, and G were tested in a face milling application of a steel component.
The test was stopped at the same maximum flank wear. There was a smaller tendency for edge chipping on Grade E and F compared with Grade G.
When ranges are used herein for physical properties, such as molecular weight, or chemical properties, such as chemical formulae, all combinations and subcombinations of ranges specific embodiments therein are intended to be included.
The disclosures of each patent, patent application, and publication cited or described in this document are hereby incorporated herein by reference, in their entirety.
Those skilled in the art will appreciate that numerous changes and modifications can be made to the preferred embodiments of the invention and that such changes and modifications can be made without departing from the spirit of the invention. It is, therefore, intended that the appended claims cover all such equivalent variations as fall within the true spirit and scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0702865-7 | Dec 2007 | SE | national |
