Wild Bill IV
Gold $$ Contributor
Since this thread is about Metallurgy, lets talk Powder Metallurgy!!!
Tungsten Carbide (chemical name: Wolfram Carbide-WC)
The two main methods for manufacturing carbide tooling is CEMENTED and SINTERED PROCESSES!! NOT A THROW IN THE MELTING POT PROCESS!! Tungsten melts at 6192°F and is the most dense metal. Twice as dense as steel!! The graphite would ignite (1,202°F) in the crucible! The main cement (binder, glue) is Cobalt for most cemented carbides tools!!! WC (the product of tungsten carbonization) particles sizes range from 0.5-10 micrometers after the ball mill process!!! Those particles are sieved and graded!!! One of the two powder ingredients, the other is powdered COBALT!!! After sintered (the hot press forming of wafer of the two wet mixed and dried ingredients) the fragile wafers are placed on MOLYBDENUM (the moly in Chrome Moly Steel Alloys) plates are set in a vacuum furnace exceeding the Cobalt melting point (2723°F) plus the latent heat (Cobalt phase change energy) which now will bond (cement) the mix!!!! The wafer is now a CEMENTED CARBIDE!!! Cobalt fills the voids (boundary regions) around the WC particles (the grains)!!! This is the true carbide tool matrix!! Not the WC (tungsten carbide) matrix by itself!!!
Here is one paragraph of cemented carbide tool growth!! The last copy and pasted paragraph sentence says it all. There are several other texts written about this subject!!! This is 2 metallurgist authors of the chapter and a metallurgist editor of the text book!!
POWDER METALLURGY - FUNDAMENTAL AND CASE STUDIES, edited by Lesser A. Dobrzanki, Published 29 March 2017, Copyright 2017
Chapter 12 PROPERTIES AND TESTING OF CEMENTED CARBIDES, written by Antonio Kriz and David Bricin
Section 2, Effects of Grinding on Cemented Carbide Properties
Paragraph 6:
Along with the above-described degradation, the temperature of the cemented carbide increases during grinding. The highest temperature is in the area of contact with the grinding wheel. However, the entire volume of the cemented carbide heats up gradually. The rising temperature of the cemented carbide surface and the interaction with the environment lead to surface oxidation. The fresh oxides are stripped during grinding. Apart from grinding, oxidation of cemented carbide may occur during other machining processes, and the new oxide layer may change the geometry of the cutting tool and impair the machining conditions.
The oxidation on the freshly cut cemented carbide surface doesn't get smaller!!! The tungsten oxide is really hard and will cut through most metals and alloys!! GROWTH MAY OCCUR DUE TO OXIDATION!!!! Oxidation growth can also occur due to impurities and/ or voids at the grain/boundary regions too!!! This creates stresses in the matrix causing micro fractures in the matrix, changing the tool geometry very slight!!! After all, a perfect vacuum does not exist!!!
However, surface oxidation can be slowed or stopped!!! Coating the bare WC tooling surface will create a barrier and stop environment oxidation!!
YES, SOME WC TOOLING WILL BE BARE (machining of really high abrasive cast irons and high carbon content steel alloys), AND OTHERS WILL HAVE SPECIFIC PURPOSED COATINGS!! The uncoated tool may see swelling or growth in time and/or hot cutting (accelerating oxidation)!!! WC and Cobalt mix ratios changes physical properties of the tools themselves!!! Chamber reamers will have added Nickel Steel (Chromeless Stainless Steel) powder Sintered in the mix ratio!!! This will change the Cemented temperature!!!
The proper Google question to ask is: Can cemented carbides swell
Us old timer, tool makers have experienced it, know the answer, and know how to fix it!!!
Tungsten Carbide (chemical name: Wolfram Carbide-WC)
The two main methods for manufacturing carbide tooling is CEMENTED and SINTERED PROCESSES!! NOT A THROW IN THE MELTING POT PROCESS!! Tungsten melts at 6192°F and is the most dense metal. Twice as dense as steel!! The graphite would ignite (1,202°F) in the crucible! The main cement (binder, glue) is Cobalt for most cemented carbides tools!!! WC (the product of tungsten carbonization) particles sizes range from 0.5-10 micrometers after the ball mill process!!! Those particles are sieved and graded!!! One of the two powder ingredients, the other is powdered COBALT!!! After sintered (the hot press forming of wafer of the two wet mixed and dried ingredients) the fragile wafers are placed on MOLYBDENUM (the moly in Chrome Moly Steel Alloys) plates are set in a vacuum furnace exceeding the Cobalt melting point (2723°F) plus the latent heat (Cobalt phase change energy) which now will bond (cement) the mix!!!! The wafer is now a CEMENTED CARBIDE!!! Cobalt fills the voids (boundary regions) around the WC particles (the grains)!!! This is the true carbide tool matrix!! Not the WC (tungsten carbide) matrix by itself!!!
Here is one paragraph of cemented carbide tool growth!! The last copy and pasted paragraph sentence says it all. There are several other texts written about this subject!!! This is 2 metallurgist authors of the chapter and a metallurgist editor of the text book!!
POWDER METALLURGY - FUNDAMENTAL AND CASE STUDIES, edited by Lesser A. Dobrzanki, Published 29 March 2017, Copyright 2017
Chapter 12 PROPERTIES AND TESTING OF CEMENTED CARBIDES, written by Antonio Kriz and David Bricin
Section 2, Effects of Grinding on Cemented Carbide Properties
Paragraph 6:
Along with the above-described degradation, the temperature of the cemented carbide increases during grinding. The highest temperature is in the area of contact with the grinding wheel. However, the entire volume of the cemented carbide heats up gradually. The rising temperature of the cemented carbide surface and the interaction with the environment lead to surface oxidation. The fresh oxides are stripped during grinding. Apart from grinding, oxidation of cemented carbide may occur during other machining processes, and the new oxide layer may change the geometry of the cutting tool and impair the machining conditions.
The oxidation on the freshly cut cemented carbide surface doesn't get smaller!!! The tungsten oxide is really hard and will cut through most metals and alloys!! GROWTH MAY OCCUR DUE TO OXIDATION!!!! Oxidation growth can also occur due to impurities and/ or voids at the grain/boundary regions too!!! This creates stresses in the matrix causing micro fractures in the matrix, changing the tool geometry very slight!!! After all, a perfect vacuum does not exist!!!
However, surface oxidation can be slowed or stopped!!! Coating the bare WC tooling surface will create a barrier and stop environment oxidation!!
YES, SOME WC TOOLING WILL BE BARE (machining of really high abrasive cast irons and high carbon content steel alloys), AND OTHERS WILL HAVE SPECIFIC PURPOSED COATINGS!! The uncoated tool may see swelling or growth in time and/or hot cutting (accelerating oxidation)!!! WC and Cobalt mix ratios changes physical properties of the tools themselves!!! Chamber reamers will have added Nickel Steel (Chromeless Stainless Steel) powder Sintered in the mix ratio!!! This will change the Cemented temperature!!!
The proper Google question to ask is: Can cemented carbides swell
Us old timer, tool makers have experienced it, know the answer, and know how to fix it!!!
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