The present invention relates to a method of making a cemented carbide comprising wc, 6-12 wt. % Co and 0.1-0.7 wt. % Cr, wherein the wc-grains are coated with Cr prior to mixing and no milling takes place during the mixing step. As a result a cemented carbide with improved properties is obtained.
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1. A method of manufacturing a cemented-carbide powder, comprising the steps of:
(i) coating a hard constituent powder comprising wc with a coating selected from the group consisting of Cr and Cr+Co to form a coated hard constituent powder;
(ii) wet-mixing, without milling, the coated wc-powder with binder metal and pressing agent, to form a wet-mixed powder; and
(iii) drying said wet-mixed powder to form a dried cemented carbide powder;
(iv) pressing the dried cemented carbide powder to form a shaped body; and
(v) sintering the shaped body,
wherein the dried cemented carbide powder has a CW-ratio of 0.8 to 1.0, where the CW-ratio is defined as
CW-ratio=Ms/(wt. % Co*0.0161) where Ms is the saturation magnetization of the sintered cemented carbide body in hAm2/kg and wt % Co is the weight percentage of Co in the cemented carbide.
2. The method of
3. The method of
4. The method of
5. The method of
6. The method of
7. The method of
0. 9. The method of
(iv) pressing the dried cemented carbide powder to form a shaped body; and
(v) sintering the shaped body.
0. 10. The method according to
CW-ratio=Ms/(wt. % Co * 0.0161) wherein Ms is the saturation magnetization of the sintered cemented carbide body in kA/m and wt % Co is the weight percentage of Co in the cemented carbide.
12. A cutting insert made by the method of
0. 13. The method of
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The sintered inserts according to the invention are used coated or uncoated, preferably coated with conventional PVD (TiCN+TiN) or PVD (TiN).
According to the method of the present invention coated WC-powder with submicron grain size distribution is wet mixed without milling with binder metal and pressing agent, dried preferably by spray drying, pressed to inserts and sintered.
WC-powder with grain size distribution according to the invention with coarse grains tails greater than 1.5 μm having been eliminated can be prepared by milling and sieving such as in a jetmill-classifier. It is an important feature of the invention that the milling takes place without milling i.e. there should be no change in grain size or grain size distribution as a result of the mixing.
According to the method of the present invention the submicron hard constituents, after careful deagglomeration are coated with a grain growth inhibitor metal such as Cr, V, Mo, W, preferably Cr using methods disclosed in U.S. Pat. No. 5,993,730 and, optionally, an iron group binder metal, preferably Co, using methods disclosed in patent U.S. Pat. No. 5,529,804. In such case the cemented carbide powder obtained from the above method includes Cr-coated, or optionally Cr+Co coated, WC, possibly with further additions of Co-powder in order to obtain the desired final composition.
The following examples are given to illustrate various aspects of the invention.
Cemented carbide tool inserts of the type N151.2-400-4E, an insert for parting, with a composition having WC, 0.4 wt. % Cr, and 10 wt. % Co, with a grain size of 0.8 μm, were produced according to the invention. Chromium and cobalt coated WC with 0.44 weight % Cr and 2.0 weight % Co, prepared according to U.S. Pat. Nos. 5,993,730 and 5,529,804 was mixed with additional amounts of Co to obtain the desired material composition. The mixing was carried out in ethanol (0.25 fluid per kg cemented carbide powder) for 2 hours in a laboratory mixer and the batch size was 10 kg. Furthermore, 2 wt. % lubricant, was added to the slurry. The carbon content was adjusted with carbon black to a binder phase alloyed with W to obtain a CW-ratio of 0.85. After spray drying, the inserts were pressed and sintered according to standard practice and dense structures with porosity A00 and hardness HV3=1550 were obtained.
Cemented carbide tool inserts of the type N151.2-400-4E were produced in the same way as in Example 1 but from chromium and cobalt coated WC having 0.22 weight % Cr, 2.0 weight % Co and with a final powder composition of WC of 0.2 weight % Cr and 10.0 weight % Co. The same physical properties (porosity A00; HV3=1550) as in Example 1 were obtained.
Cemented carbide tool inserts of the type N151.2-400-4E were produced in the same way as in Example 1 but from chromium coated WC having 0.44 weight % Cr and with a final powder composition of the WC of 0.4 weight % Cr and 10.0 weight % Co. The same physical properties (porosity A00; HV3=1550) as in Example 1 were obtained.
Cemented carbide tool inserts of the type N151.2-400-4E were produced in the same way as in Example 1 but from chromium coated WC having 0.22 weight % Cr and with a final powder composition of WC, 0.2 weight % Cr and 10.0 weight % Co. The same physical properties (porosity A00; HV3=1550) as in Example 1 were obtained.
Cemented carbide standard tool inserts of the type N151.2-400-4E were produced with the same chemical composition, average grain size of WC and CW ratio as in Example 1 but from powder manufactured with a conventional ball milling technique. The same physical properties (porosity A00; HV3=1550) as in Example 1 were obtained.
Cemented carbide standard tool inserts of the type N151.2-400-4E were produced with the same chemical composition, average grain size of WC and CW-ratio as in Example 1 but from powder manufactured with the a conventional ball milling technique and with the powder composition WC, 0.2 weight % Cr and 10.0 weight % Co. Initial abnormal grain growth and reduction in hardness compared to Example 1 (porosity A00; HV3=1500) were obtained.
Sintered inserts from Examples 1-4 and Comparative Examples 1 and 2 were treated in a standard PVD (TiCN+TiN) coating process with all inserts charged in the same coating batch.
Coated inserts according to the invention from Examples 1-4 were compared in toughness behaviour against coated reference inserts from Comparative Examples 1 and 2 in a technological parting test.
The test data were:
Operation:
Parting off 3 mm thick discs from a bar
Material:
SS1672, diameter 46 mm
Cutting data:
Speed = 150 m/min
Feed = 0.33 mm/rev
diameter
46-8 mm
Feed = 0.05 mm/rev
diameter
8-4 mm
Feed = 0.03 mm/rev
diameter
4-0 mm
Number of subtests (edges):
3
Evaluation of toughness:
Number of cuts before fracture
Results
Example
No. of cuts
1
220
2
270
3
210
4
280
Comp. 1 (prior art)
180
Comp. 2 (prior art)
160
As clearly demonstrated by the above comparative data, cemented carbide bodies formed consistent with the principles of the present invention possess unexpectedly superior properties when compared to conventional materials.
The foregoing has described the principles, preferred embodiments and modes of operation of the present invention. However, the invention should not be construed as being limited to the particular embodiments discussed. Thus, the above-described embodiments should be regarded as illustrative rather than restrictive, and it should be appreciated that variations may be made in those embodiments by those skilled in the art without departing from the scope of the present invention as defined by the following claims.
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