![]() ^ Tongbaite: Mineral information, data and localities,.National Institute for Occupational Safety and Health (NIOSH). ^ a b c NIOSH Pocket Guide to Chemical Hazards.Undesired formation of chromium carbides in stainless steel and other alloys can lead to intergranular corrosion. Cr 3C 2 prevents large grains from forming in the composite, which results in a fine-grained structure of superior hardness. The tungsten carbide is combined with other carbides such as titanium carbide, niobium carbide, and chromium carbide and sintered together with a cobalt matrix. The primary constituent in most extremely hard cutting tools is tungsten carbide. ![]() These are prefabricated chromium carbide-coated steel plates, which are meant to be welded onto existing structures or machinery in order to improve performance.Ĭhromium carbide is used as an additive in cutting tools made of cemented carbides, in order to improve hardness by preventing the growth of large grains. After over spraying the coating, the coated part must run through a diffusion heat treatment to reach the best results in matter of coupling strength to the base metal and also in matter of hardness.Īnother technique utilizes chromium carbide in the form of overlay plates. The matrix itself contributes to the corrosion resistance of the coating because both nickel and chromium are corrosion resistant in their metallic form. This layer is essentially its own metal matrix composite, consisting of hard ceramic Cr 3C 2 particles embedded in a nickel-chromium matrix. This mixture is then heated to very high temperatures and sprayed onto the object being coated where it forms a protective layer. Cr 3C 2 powder is mixed with solid nickel-chromium. Chromium carbide is used to coat the surface of another metal in a technique known as thermal spraying. The exothermic reaction is initiated, and the resulting heat propagates the reaction throughout the rest of the sample.Ĭhromium carbide is useful in the surface treatment of metal components. A heated wire, a spark, a laser, or an oven may provide the heat. The blended powder is then pressed into a pellet and placed under an inert atmosphere of argon. In this method the reactants are ground and blended in a ball mill. Īnother method for the synthesis of chromium carbide utilizes chromium oxide, pure aluminum, and graphite in a self-propagating exothermic reaction that proceeds as follows: 3Cr 2O 3 + 6Al + 4C → 2Cr 3C 2 + 3Al 2O 3 Decreasing the percentage of carbon content in the initial mixture results in an increase in the yield of the Cr 7C 3, and Cr 23C 6 forms of chromium carbide. The heat and pressure cause the graphite and metallic chromium to react and form chromium carbide. This pressurized gas applies pressure to the sample from all directions while the oven is heated. Hot isostatic pressing utilizes an inert gas, primarily argon, in a sealed oven. After the components have been ground they are pressed into a pellet and subjected to hot isostatic pressing. ![]() In this type of process metallic chromium and pure carbon in the form of graphite are loaded into a ball mill and ground into a fine powder. ![]() Synthesis of chromium carbide can be achieved through mechanical alloying. For this reason Cr 3C 2 is the primary form of chromium carbide used in surface treatment. Cr 3C 2 is the most durable of the three compositions, and has an orthorhombic crystal structure with a microhardness of 2280 kg/mm 2. Cr 7C 3 has a hexagonal crystal structure and a microhardness of 1336 kg/mm 2. Cr 23C 6 has a cubic crystal structure and a Vickers hardness of 976 kg/mm 2. There are three different crystal structures for chromium carbide corresponding to the three different chemical compositions. Yet another chromium-rich carbide mineral is yarlongite, Cr 4Fe 4NiC 4. The mineral form of the Cr 3C 2 compound is tongbaite. The hardest and most commonly used composition for this purpose is Cr 3C 2. When chromium carbide crystals are integrated into the surface of a metal it improves the wear resistance and corrosion resistance of the metal, and maintains these properties at elevated temperatures. These properties make it useful as an additive to metal alloys. It is also a refractory compound, which means that it retains its strength at high temperatures as well. It is extremely hard and corrosion resistant. At standard conditions it exists as a gray solid. Chromium(II) carbide is a ceramic compound that exists in several chemical compositions: Cr 3C 2, Cr 7C 3, and Cr 23C 6.
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