|Publication number||USRE40005 E1|
|Application number||US 11/449,887|
|Publication date||Jan 15, 2008|
|Filing date||Jun 9, 2006|
|Priority date||Sep 6, 1996|
|Publication number||11449887, 449887, US RE40005 E1, US RE40005E1, US-E1-RE40005, USRE40005 E1, USRE40005E1|
|Inventors||Asa Kutscher, Kenneth Westergren, Björn Ljungberg, Anders Lenander|
|Original Assignee||Sandvik Intellectual Property Ab|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (15), Non-Patent Citations (2), Referenced by (2), Classifications (21), Legal Events (1)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present application is a reissue of U.S. Pat. No. 5,945,207, which claims the benefit of priority to Swedish Application No. 9603264-4 filed Sep. 6, 1996.
The present invention relates to a coated cutting tool (cemented carbide insert) particularly useful for the machining of cast iron parts by turning.
Cast iron materials may be divided into two main categories, grey cast iron and nodular cast iron. Cast iron materials typically often have an outer layer of cast skin, which may contain various inclusions of sand, rust and other impurities and also a surface zone which is decarburized and contains a larger amount of ferrite than the rest of the material.
The wear when machining grey cast iron materials with Al2O3-coated cutting tools is dominated by chemical, abrasive and so-called adhesive wear. In order to protect the cutting tool against chemical wear, it is desirable to use as thick Al2O3 layers as possible. This is contradicted by the properties regarding adhesive wear that this type of layer generally possesses. Adhesive wear occurs when fragments or individual grains of the layer are pulled away from the cutting edge by the work piece chip formed. The surface zone with high amounts of ferrite particularly puts severe demands on the adhesive properties of the coating and in combination with the inclusions in the cast skin on the work piece, causes notch wear at the depth of cut on the main cutting edge.
Another feature in the machining of grey cast iron is its sensitivity to excessive amounts of Co binder phase in the interface between the cemented carbide cutting insert and the coating. Excessive amounts of Co binder phase deteriorate the adhesion between coating and cemented carbide and lead to flaking of the coating during machining.
Swedish Application 9502640-7 (which corresponds to U.S. Ser. No. 08/675,034, our reference 024444-233) discloses a coated cutting insert tool of a cemented carbide body of a composition 5-11 weight % Co, <10 weight %, preferably 1.5-7.5 weight %, cubic carbides of the metals Ti, Ta and/or Nb and balance WC, especially suited for machining of low alloyed steel components by turning.
It is an object of this invention to avoid or alleviate the problems of the prior art.
It is further an object of this invention to provide a coated cutting tool particularly useful for the machining of cast iron parts by turning.
In one aspect of the invention there is provided a cutting tool insert comprising a coating and a cemented carbide body, said cemented carbide body comprising WC, 5-10 weight % Co and <0.5 weight % cubic carbides of metals from groups IVb, Vb, or VIb of the periodic table with a highly W-alloyed binder phase having a CW-ratio of 0.8-0.9 and a surface composition of the cemented carbide body being well-defined, the amount of Co on the surface being within −4 weight % to +4 weight % of the nominal Co content of the body and said coating comprising:
In another aspect of the invention there is provided a method of making a cutting insert comprising a cemented carbide body and a coating wherein a WC-Co-based cemented carbide body is sintered, said sintering including a cooling step which at least to below 1200° C. is performed in a hydrogen atmosphere of pressure 0.4-0.9 bar and thereafter coating said sintered body with
The Figure is a micrograph in 2000× magnification of a coated insert according to the present invention in which
It has surprisingly been found that by combining the following features: a cemented carbide body with a highly W-alloyed binder phase, a low content of cubic carbides and a well-defined surface composition resulting from a specific sintering process, a columnar TiCxNyOz layer, a textured α-Al2O3 layer, a TiN layer, fulfilling the demands of easy identification of used edges, and a post-treatment of the coating cutting edge by brushing, an excellent cutting tool for machining of cast iron materials, especially grey cast iron, can be obtained.
According to the present invention, a cutting tool insert is provided with a cemented carbide body of a composition 5-10 weight % Co, preferably 5-8 weight % Co, <2 weight %, preferably <0.5 weight %, most preferably 0 weight % cubic carbides of the metals Ti, Ta and/or Nb and balance WC. The grain size of the WC is in the range of 1-2.5 μm. The cobalt binder phase is highly alloyed with W. The content of W in the binder phase can be expressed as the
CW-ratio=Ms/(weight % Co×0.0161),
It has now been found according to the present invention that improved cutting performance is achieved, if the cemented carbide body has a CW-ratio of 0.75-0.93, preferably 0.80-0.90. The cemented carbide body may contain small amounts, <1 volume %, of eta phase (M6C), without any detrimental effect.
The surface composition of the cemented carbide insert is well-defined and the amount of Co on the surface is within −4 weight % to +4 weight % of the nominal content.
Alternatively, the cemented carbide according to the present invention consists of WC and Co and has an about 100-350 μm wide, preferably 150-300 μm wide, binder phase depleted surface zone in which the binder phase content increases continuously and in a non-step-wise manner without maximum up to the nominal content of the binder phase in the inner portion of the cemented carbide body. The average binder phase content in a 50 μm surface zone is 25%-75%, preferably 40%-60%, of the nominal binder phase content.
The coating comprises
a layer of TiCxNyOz, with x+y+z=1, with z<0.5, preferably x>y, most preferably x>0.5 and 0.1<z<0.4, with a thickness of 0.1-2 μm and with equiaxed or needle-like grains with size <0.5 μm, this layer being the same as or different from the innermost layer;
In order to obtain a smooth cutting edge line suitable for machining, the edge of the coated insert is subjected to a brushing treatment giving a surface roughness Rmax≦0.4 μm over a length of 10 μm according to the method described in Swedish Application No. 9402543-4 (which corresponds to U.S. Ser. No. 08/497,934, our reference 024444-144). This treatment removes the top layer of TiCxNyOz along the cutting edge line. It is also within the scope of this invention that the surface might be smoothed by a wet blasting treatment.
Furthermore, as disclosed in U.S. Pat. No. 5,654,035 or Swedish Applications 9304283-6 (which corresponds to U.S. Ser. No. 08/348,084, our reference 024444-092) or 9400089-0 (which corresponds to U.S. Ser. No. 08/366,107, our reference 024444-093), the α-Al2O3 layer has a preferred crystal growth orientation in either the (104)-, (012)- or (110)-direction, preferably in the (012)-direction, as determined by X-ray Diffraction (XRD) measurements. A Texture Coefficient (TC) can be defined as:
TC for the set of (012), (104) or (110) crystal plans should be larger than 1.3, preferably larger than 1.5.
According to the method of the present invention, a WC-Co-based cemented carbide body having a highly W-alloyed binder phase with a CW-ratio of 0.75-0.93, preferably 0.8-0.9, is subjected to a conventional sintering process and removing the surface cobalt by etching as disclosed in U.S. Pat. No. 5,380,408. Alternatively, for cemented carbide consisting of WC and Co cooling at least to below 1200° C. may be performed in a hydrogen atmosphere of pressure 0.4-0.9 bar as disclosed in Swedish Application 9602750-3 (which corresponds to International Application No. PCT/SE97/01231).
The insert is coated with
The edge line of the inserts in smoothed, e.g., by brushing the edges based on, e.g., SiC, as disclosed in Swedish Application 9402543-4.
When a TiCxNyOz layer with z>0 is desired, CO2 and/or CO are/is added to the reaction gas mixture.
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.
Inserts are made as follows:
The inserts are tested in a facing operation. The workpiece material is nodular cast iron, SS717. The workpiece shape causes intermittent cutting conditions during each revolution. Cutting speed is 250 m/min, feed 0.10 mm/rev and cutting depth is 2.0 mm. The operation is performed using coolant.
This type of operation typically causes severe flaking of the coating. The coating is torn off the insert in fragments. The wear can be measured as the part of the edge line on which the coating has flaked off compared to the total length of the edge line used in the cutting operation.
% of Edge Line with Flaking
Inserts of type A, B, D and E in Example 1 above are tested in an intermittent cutting operation in grey cast iron, SS0125. The cutting conditions put high demands on the flaking resistance of the coating as well as the chemical and abrasive wear resistance of the coating. The shaping of the work piece is such that for each revolution, two entrances in the work piece will be made giving intermittent cutting conditions. Cutting speed is 300 m/min, cutting feed is 0.25 mm/rev and cutting depth is 2.0 mm. The machining is made without using any coolant.
Number of Passes Before
the Edge Was Worn Out
The same cutting conditions is used as in Example 2 with inserts of type A, B, C, D and F from the same batches as in Example 1. In this test, coolant is used during machining.
Number of Passes
State of the Edge
minor chipping of edge line
not worn out
undamaged edge line
not worn out
fracture in cutting edge
insert worn out
fracture in cutting edge
insert worn out
fracture in cutting edge
insert worn out
Cemented carbide inserts of type A, B and G in Example 1 are tested in a turning test that causes deformation of the cutting edge leading to flaking of the coating and enhanced wear of the insert. The test is performed in a nodular cast iron SS0737 and for a certain combination of feed and cutting depth in a longitudinal turning operation, the highest possible cutting rate before deformation of the cemented carbide occurs is sought.
Highest Possible Cutting Speed
The principles, preferred embodiments and modes of operation of the present invention have been described in the foregoing specification. The invention which is intended to be protected herein, however, is not to be construed as limited to the particular forms disclosed, since these are to be regarded as illustrative rather than restrictive. Variations and changes may be made by those skilled in the art without departing from the spirit of the invention.
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|Citing Patent||Filing date||Publication date||Applicant||Title|
|US8080323||Mar 28, 2008||Dec 20, 2011||Kennametal Inc.||Cutting insert with a wear-resistant coating scheme exhibiting wear indication and method of making the same|
|US20070283554 *||May 4, 2007||Dec 13, 2007||Sandvik Intellectual Property Ab||Cutting tool insert|
|U.S. Classification||428/216, 428/698, 51/309, 51/307, 428/469, 428/323, 428/336, 428/472, 428/701, 407/119, 428/702, 428/212, 428/325|
|Cooperative Classification||Y10T428/265, Y10T428/24942, Y10T407/27, Y10T428/24975, Y10T428/25, Y10T428/252, C23C16/30|