Patent Grant
8192793
The present invention relates to coated cemented carbide inserts (cutting tools), particularly useful for wet or dry milling of steels.
When machining low and medium alloyed steels and stainless steels with cemented carbide tools, the cutting edge is worn according to different wear mechanisms, such as chemical wear, abrasive wear, and adhesive wear and by edge chipping caused by cracks formed along the cutting edge. 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 commercial cemented carbide grades have usually been optimized with respect to one or few of the above mentioned wear types, and have consequently been optimized for specific application areas.
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.
WO 97/20083 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 characterized 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.
WO 97/20081 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 characterized 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.
EP 1103635 discloses 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 invented cutting tool is comprised of a cemented carbide body with a coating consisting of an MTCVD Ti(C,N) layer and a multi-layer coating being composed of κ-Al2O3 and TiN or Ti(C,N) layers.
WO 2007/069973 discloses a coated cutting tool insert particularly useful for dry and wet machining, preferably milling, in low and medium alloyed steels, stainless steels, with or without raw surface zones. The insert is characterized by a WC—TaC—NbC—Co cemented carbide with a W alloyed Co-binder phase and a coating including an innermost layer of TiCxNyOz with columnar grains and a top layer at least on the rake face of a smooth α-Al2O3.
What is needed is a coated cutting tool with enhanced performance for milling of steel. The invention is directed to these, as well as other, important needs.
Accordingly, the invention is directed to
The cutting tool insert according to the present invention includes a cemented carbide substrate with a relatively low amount of cubic carbides, with a relatively high binder phase content, that is medium to highly alloyed with W and a fine to medium WC grain size. This substrate is provided with a wear resistant coating comprising an equiaxed TiCxNyOz layer, a columnar TiCxNyOz layer, and at least one α-Al2O3 layer.
In one embodiment, the invention is directed to cutting tool inserts, comprising:
In another embodiment, the invention is directed to methods of making a cutting tool insert comprising a cemented carbide body and a coating, said method comprising:
In yet other embodiments, the invention is directed to methods for wet or dry milling of steel, comprising the step of:
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 body,
2. Innermost TiCxNyOz layer,
3. TiCxNyOz layer with columnar grains and
4. α-Al2O3 layer.
According to the present invention a coated cutting tool insert is provided with a cemented carbide body having a composition of 9.3-10.9 wt-% Co, preferably 9.75-10.7 wt-% Co, most preferably 9.9-10.5 wt-% Co; 0.5-2.5 wt-%, preferably 1.0-2.0 wt-%, most preferably 1.2-1.8 wt-% total amount of the metals Ti, Nb and Ta and balance WC. Ti, Ta, and/or Nb may also be partly or completely replaced by other elements from groups IVb, Vb, or VIb of the periodic table. The content of Ti is preferably on a level corresponding to a technical impurity.
In a preferred embodiment, the ratio between the weight concentrations of Ta and Nb is within 7.0-12.0, preferably 7.6-11.4, most preferably 8.2-10.5.
In an alternative preferred embodiment, the ratio between the weight concentrations of Ta and Nb is within about 1.0-5.0, preferably about 1.5-4.5.
The cobalt binder phase is medium to highly alloyed with tungsten. The content of W in the binder phase may be expressed as the S-value=σ/16.1, where σ is the magnetic moment of the binder phase in μTm3 kg−1. The S-value depends on the content of tungsten in the binder phase and increases with a decreasing tungsten content. Thus, for pure cobalt, or a binder in a cemented carbide that is saturated with carbon, S=1, and for a binder phase that contains W in an amount that corresponds to the borderline to formation of η-phase, S=0.78.
The cemented carbide body has an S-value within the range 0.81-0.95, preferably 0.82-0.93, most preferably 0.85-0.90.
The cemented carbide body has a coercivity (Hc) of 10-15, preferably 11-14, most preferably 11.5-13.5 kA/m.
The coating comprises:
In a preferred embodiment, the Al2O3 layer is strongly textured in the (10
The texture coefficient (TC) for the alumina layer is determined according to the following formula:
where
I(hkil)=measured intensity of the (hkil) reflection
IO(hkil)=standard intensity according to JCPDS card no 46-1212
n=number of reflections used in the calculation
(hkil) reflections used are: (10
Consequently, n=6 and the maximum value of the texture coefficient is 6.
In an alternative embodiment, the Al2O3 layer is strongly textured in the (0006)-direction, with a texture coefficient TC(0006) larger than 1.2, preferably between 1.4 and 4.3.
In another alternative embodiment, the Al2O3 layer is strongly textured in the (1012)-direction, with a texture coefficient TC(1012) larger than 2.5, preferably larger than 3, most preferably larger than 3.5.
In a further alternative embodiment, there is a thin, less than 1 μm thick, TiN top layer on the α-Al2O3 layer.
The present invention also relates to a method of making a cutting insert by powder metallurgical technique, wet milling of powders forming hard constituents and binder phase, compacting the milled mixture to bodies of desired shape and size and sintering, comprising a cemented carbide substrate and a coating. According to the method a substrate is provided with a composition of 9.3-10.9 wt-% Co, preferably 9.75-10.7 wt-% Co, most preferably 9.9-10.5 wt-% Co; 0.5-2.5 wt-%, preferably 1.0-2.0 wt-%, most preferably 1.2-1.8 wt-% total amount of the metals Ti, Nb and Ta and balance WC. Ti, Ta, and/or Nb may also be replaced by other elements from groups IVb, Vb, or VIb of the periodic table. The content of Ti is preferably on a level corresponding to a technical impurity.
In a preferred embodiment, the ratio between the weight concentrations of Ta and Nb is within 7.0-12.0, preferably 7.6-11.4, most preferably 8.2-10.5.
In an alternative preferred embodiment, the ratio between the weight concentrations of Ta and Nb is within 1.0-5.0, preferably 1.5-4.5.
The coercivity depends on the grain size of the starting powders and milling and sintering conditions and has to be determined by experiments. The desired S-value depends on the starting powders and sintering conditions and also has to be determined by experiments.
The layer of TiCxNyOz with 0.7≦x+y+z≦1, preferably with z<0.2, x>0.3 and y>0.2, most preferably x>0.4, having a morphology of columnar grains, is deposited with MTCVD-technique onto the cemented carbide using acetonitrile as the carbon and nitrogen source for forming the layer in the temperature range of 700-950° C.
The innermost TiCxNyOz layer and alumina layers are deposited according to known technique.
In an alternative embodiment, a thin, less than 1 TiN top layer is deposited on the α-Al2O3 layer using known technique.
In a further preferred embodiment, the cutting tool insert as described above is treated after coating with a wet blasting or brushing operation, such that the surface quality of the coated tool is improved.
The invention also relates to the use of cutting tool inserts according to the above for wet or dry milling of steels at cutting speeds of 75-400 m/min, preferably 100-300 m/min, with an average feed per tooth of 0.08-0.5 mm, preferably 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 10.3 wt % Co, 1.35 wt % Ta, 0.15 wt % Nb and balance WC, with a binder phase alloyed with W corresponding to an S-value of 0.87 was produced by conventional milling of the powders, pressing of green compacts and subsequent sintering at 1430° C. The Hc value of the cemented carbide was 12.5 kA/m, indicating a mean intercept length of about 0.7 μm. The substrate was coated with a 0.2 μm thick layer of TiN layer, having equiaxed grains, a 2.9 μm thick layer of columnar TiCxNyOz deposited at 835-850° C. with acetonitrile as carbon and nitrogen source, yielding an approximated carbon to nitrogen ratio x/y=1.5 with z<0.1, and a 3.1 μm thick layer of α-Al2O3 deposited at about 1000° C. X-ray diffraction showed that the α-Al2O3 layer had a TC(1014) of 2.1.
Grade B: A cemented carbide substrate according to Grade A was combined with a 3 μm Ti(C,N) and a 3 μm multi-layer coating of four κ-Al2O3 and five TiN layers.
Grade A and B were tested in a face milling operation in steel.
The test was stopped at the same maximum flank wear. The wear resistance was much improved with the grade according to the invention.
Grade C: A cemented carbide substrate with the composition 13 wt % Co, 1.35 wt % Ta, 0.15 wt % Nb and balance WC, with a binder phase alloyed with W corresponding to an S-value of 0.85 and a Hc value of 14 kA/m was coated in accordance with Grade A.
Grade D: A cemented carbide substrate in with the composition 12 wt % Co, 1.3 wt % Ta, 0.2 wt % Nb and balance WC, with a binder phase alloyed with W corresponding to an S-value of 0.89 and a Hc value of 13 kA/m was coated in accordance with Grade A.
Grades A, C and D were tested in a square shoulder milling operation in steel.
The test was stopped at the same maximum flank wear. The tool life was significantly lower for the grades with higher binder phase content.
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 |
|---|---|---|---|
| 0702045 | Sep 2007 | SE | national |
This application is a division of application Ser. No. 12/208,387 filed on Sep. 11, 2008; which claimed priority to Swedish application 0702045-6 filed Sep. 13, 2007. The entire contents of each of the above-identified applications are hereby incorporated by reference.
| Number | Name | Date | Kind |
|---|---|---|---|
| 5487625 | Ljungberg | Jan 1996 | A |
| 5863640 | Ljungberg | Jan 1999 | A |
| 6177178 | Ostlund | Jan 2001 | B1 |
| 6333098 | Olsson | Dec 2001 | B1 |
| 6337152 | Kukino | Jan 2002 | B1 |
| 6632514 | Sulin | Oct 2003 | B1 |
| 7135221 | Ruppi et al. | Nov 2006 | B2 |
| Number | Date | Country |
|---|---|---|
| 0753603 | Jan 2000 | EP |
| 1103635 | Aug 2004 | EP |
| 1493845 | Jan 2005 | EP |
| 9720081 | Jun 1997 | WO |
| 9720083 | Jun 1997 | WO |
| 2007069973 | Jun 2007 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20120009038 A1 | Jan 2012 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12208387 | Sep 2008 | US |
| Child | 13234400 | US |
