The present invention relates to a method of making a cemented carbide body with a bimodal grain size distribution by powder metallurgical methods including wet mixing, without milling, of wc-powders with different grain size distributions with binder metal and pressing agent, drying, pressing and sintering. The grains of the wc-powders are classified in at least two groups, a group of smaller grains and a group of larger grains. According to the method of the present invention, the grains of the group of smaller grains are precoated with a growth inhibitor with or without binder metal.
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1. A method of making a cemented carbide body with a bimodal grain size distribution comprising the steps of:
(i) wet mixing, without milling, wc-powders with a binder metal and a pressing agent, the wc powders comprising smaller grains precoated with a grain growth inhibitor, and larger grains;
(ii) drying the mixture of step (i);
(iii) pressing the dried mixture to form a pressed body; and
(iv) sintering the pressed body.
19. A method of making a cemented carbide body comprising the steps of:
(i) providing a wc powder, the wc powder comprises a group of fine wc grains and a group of course coarse wc grains;
(ii) precoating the fine wc grains with a grain growth inhibitor;
(iii) precoating the course coarse wc grains with a binder metal;
(iv) wet mixing, without milling, the precoated fine wc grains, the precoated course coarse wc grains, additional binder metal and a pressing agent;
(v) drying the mixture of step (iv);
(vi) pressing the dried mixture to form a pressed body; and
(vii) sintering the pressed body.
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CW-ratio=Ms/(wt-% Co*0.0161) where Ms is the measured saturation magnetization of the sintered body in κA/m hAm2/kg and wt-% Co is the weight percentage of Co in the cemented carbide is 0.82-1.0.
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A cemented carbide body with the composition, in addition to WC, of 10 wt-% Co, and 0.3 wt-% Cr3C2 were produced according to the invention. Cobalt-coated WC with an average grain size of 4.2 μm, WC-3 wt-% Co, prepared in accordance with U.S. Pat. No. 5,505,902 and chromium coated WC with an average grain size of 0.8 μm, WC-0.43 wt-% Cr, prepared in accordance with 970378-6 was carefully deagglomerated in a laboratory jetmill equipment, and mixed with additional amounts of Co to obtain the desired material composition. The coated WC-particles consisted of 40 wt-% of the particles with the average grain size of 4.2 μm and 60 wt-% of the particles with the average grain size of 0.8 μm, giving a bimodal grain size distribution. The mixing was carried out in an ethanol and water solution (0.25 liter fluid per kg of cemented carbide powder) for 2 hours in a laboratory mixer and the batch size was 10 kg. Furthermore, 2 weight-% lubricant was added to the slurry. The carbon content was adjusted with carbon black to render a binder phase alloyed with W corresponding to a CW-ratio of 0.89. After spray drying, the inserts were pressed and sintered according to standard practice and a dense bimodal structure with no porosity having an extremely low amount of grain growth was obtained.
A cemented carbide body with the composition, in addition to WC, of 10 wt-% Co, and 0.3 wt-%-Cr3C2 were produced according to the invention. Cobalt-coated WC with an average grain size of 4.2 μm, WC-3 wt-% Co, prepared in accordance with U.S. Pat. No. 5,505,902 and chromium-cobalt coated WC with an average grain size of 0.8 μAm, WC-0.43 wt-% Cr-2 wt-% Co, prepared in accordance with 9703738-6 was carefully deagglomerated in a laboratory jetmill equipment, and mixed with additional amounts of Co to obtain the desired material composition. The coated WC-particles consisted of 40 wt-% of the particles with the average grain size of 4.2 μm and 60 wt-% of the particles with the average grain size of 0.8 μm, giving a bimodal grain size distribution. The mixing was carried out in an ethanol and water solution (0.25 liter fluid per kg cemented carbide powder) for 2 hours in a laboratory mixer and the batch size was 10 kg. Furthermore, 2 weight-% lubricant was added to the slurry. The carbon content was adjusted with carbon black to a binder phase alloyed with W corresponding to a CW-ratio of 0.89. After spray drying, the inserts were pressed and sintered according to standard practice and a dense bimodal structure identical to Example 1 and with no porosity and having an extremely low amount of grain growth was obtained.
A cemented carbide body with the composition, in addition to WC, of 10 wt-% Co, 0.2 wt-% VC were produced according to the invention. Cobalt-coated WC with an average grain size of 4.2 μm, WC-3 wt-% Co, prepared in accordance with U.S. Pat. No. 5,505,902 and vanadium coated WC with an average grain size of 0.8 μm, WC-0.28 wt-% V, prepared in accordance with 9703738-6 was carefully deagglomerated in a laboratory jetmill equipment, and mixed with additional amounts of Co to obtain the desired material composition. The coated WC-particles consisted of 40.0 wt-% of the particles with the average grain size of 4.2 μm and 60 wt-% of the particles with the average grain size of 0.8 μm, giving a bimodal grain size distribution. The mixing was carried out in an ethanol and water solution (0.25 liter fluid per kg cemented carbide powder) for 2 hours in a laboratory mixer and the batch size was 10 kg. Furthermore, 2 weight-% lubricant was added to the slurry. The carbon content was adjusted with carbon black to a binder phase alloyed with W corresponding to a CW-ratio of 0.89. After spray drying, the inserts were pressed and sintered according to standard practice and a dense bimodal structure identical to Example 1 and with no porosity having an extremely low amount of grain growth was obtained.
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