Vanadium carbide hardness

Vanadium carbide (VC) is used to alloy iron to produce high-speed, high-temperature cutting tools for cutting metals and other hard substances. 

Kumashiro Y., Sakuma E., 1980, The Vickers micro-hardness of non-stoichiometric niobium carbide and vanadium carbide single crystals up to 1500°C, J. Mater. Sci., 15, 1321-1324. 

Vanadium carbide is manufactured by the carburization of pure vanadium pentoxide (mostly produced from ammonium vanadate) in vacuum at 1700°C. Vanadium carbide exhibits a high hardness, but its brittleness prevents its wide utilization in cemented carbides. In WC-Co alloys, it is added in quantities of < 1% by weight as a particle growth inhibitor. 

A detailed electron microscopic examination has been made on high purity C-Fe-V alloys with particular reference to the aging behavior prior to the hardness peak in the temperature range of 500-600°C [1966Ray]. Precipitation of vanadium carbide on aging has been studied in a ferritic iron-vanadium alloy containing a small amount of carbon by [1973Hei]. 

HOU] Light microscopy, magnetometry, resistometry, Rockwell hardness (HRC) up to 1000°C, 0.4-16%V, 0.1-3 mass% C, ferrite, austenite, cementite, vanadium carbide... 

There is an interesting phenomenon about a relation between nitrogen solubility and hardness, concerning of atomic vacancy hardness of TiN shows mountain-like curve with maximum value at x = 0.78 [5], This means that the stoichiometric composition does not show maximum hardness. It can be explained that nitrogen atoms on the sublattices select regular replacement, as well as carbon atom in vanadium carbide VCi [6]. Thus, we use TiN hereafter as titanium nitride in place of TiNo,97. 

Vanadium (V). Vanadium contributes to the refinement of the carbide structure and thus improves the forgeability of tool steels. Moreover, vanadium exhibits a strong tendency to form hard carbides (e.g., VC and V C), which improves both the hardness and the wear properties of tool steels. However, an excessive amount of vanadium carbides makes the grinding of the tool steel extremely difficult, imparting a low grindability. 

Niobium in Tool Steels. In the matrix method of tool-steel development, the composition of the heat-treated matrix determines the steel s initial composition. Carbide volume-fraction requirements then are calculated, based upon historical data, and the carbon content is adjusted accordingly. This approach has been used to design new steels in which niobium is substituted for all or part of the vanadium present as carbides in the heat-treated material. Niobium provides dispersion hardening and grain refinement, and forms carbides that are as hard as vanadium, tungsten, and molybdenum carbides. 

The carbides and nitrides of vanadium and titanium crystallize in the same face centered cubic (fee) system, and because of the closeness of their cell parameters (Table 15.1) form solid solutions. These ceramic materials exhibit interesting mechanical, thermal, chemical and conductive properties.1,2 Their high melting point, hardness and wide range of composition have therefore attracted considerable attention in the last decade. Moreover, their good abrasion resistance and low friction also make these ceramics attractive for protective coating applications.3-5 Chemical vapor deposition (CVD) is a commonly used technique for the production of such materials. In the conventional thermally activated process, a mixture of gases is used.6-9 In the case of TiC, TiN, VC and VN, this mixture is... 

Very hard carbides result from strongly heating the oxides with carbon. They are empirically MC and have the NaCl structure. Vanadium also forms V4C3 which has a defect structure, carbon atoms being missing from some of the lattice positions. 

The presence of carbide and nitride precipitates in alloy steels can have a beneficial effect on the mechanical properties of the steels concerned. How-ever, the amounts, morphology and distribution of the precipitated phases must be carefully controlled in order to achieve the properties required. Because the presence of hard precipitates in a steel during hot-rolling operations can result in damage both to the rollers and to the steel, it is important that information be available on the ranges of temperature and composition in which precipitated phases are stable. For this reason, and also to achieve desired precipitation characteristics using the minimum amounts of expensive precipitating elements such as niobium, titanium, vanadium, etc., it is helpful to cany out prior calculations of the stability of precipitates in steels of different compositions. 

Most of these are carbon-manganese-molybdenum alloys with small additions of chromium and/or nickel plus vanadium or niobium. Vanadium or niobium acts as a carbide stabilizer and grain refiner, improving both elevated temperature strength and notch ductility. An exception is Fortiweld (MOBO 45 is the same steel), which is a boron-treated 1/2% molybdenum steel. This alloy is the cheapest of the group, but has hardly been used for reactors in the U.K., possible because its impact properties in thick sections are not so attractive as alternative steels. 

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