Molybdenum carbides hardness

CARBmES - INDUSTRIAL HARD CARBIDES] (Vol 4) h-molybdenum carbide [12011-97-1]... 

The four most important carbides for the production of hard metals are tungsten carbide [12070-12-17, WC, titanium carbide [12070-08-5] TiC, tantalum carbide [12070-06-3J, TaC, and niobium carbide [12069-94-2] NbC. The binary and ternary soHd solutions of these carbides such as WC—TiC and WC—TiC—TaC (NbC) are also of great importance. Chromium carbide (3 2) [12012-39-0], molybdenum carbide [12011-97-1], MoC, and... 

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. 

Molybdenum Carbides.—The carbide, MojC, may be obtained by heating molybdenum dioxide with carbon or with calcium carbide in an electric furnace. The product shows a brilliant, white, crystalline fracture, cleaves readily, and has a density of 8-9. If a mixture of fused molybdenum, carbon, and excess of aluminium is heated in the electric furnace, the carbide, MoC, is obtained as a grey crystalline powder, of density 8-40 at 20° C., and of hardness 7 to 8. It burns readily in fluorine, forming carbon tetrafluoride and molybdenum... 

Molybdenum carbide will hardly be stable in a plug-flow reactor [450], because the carbide will be oxidised at the inlet. The molybdemun... 

Presently, the majority of cermets are of titanium caibonitride base (with possible additions of M02C, WC, TaC, etc.) and Ni-Mo binder (with possible additions of Co, Al, etc.). The optimization of the hard phase and a careful control of the composition of the binder have given rise to significant improvements in the toughness and in the resistance to plastic deformation. The resultant microstractures are complex, with one or more hard phases with composite gradients (for example core of grain in titanium caibonitride and rim enriched with molybdenum carbide). 

Iron carbide (3 1), Fe C mol wt 179.56 carbon 6.69 wt % density 7.64 g/cm mp 1650°C is obtained from high carbon iron melts as a dark gray air-sensitive powder by anodic isolation with hydrochloric acid. In the microstmcture of steels, cementite appears in the form of etch-resistant grain borders, needles, or lamellae. Fe C powder cannot be sintered with binder metals to produce cemented carbides because Fe C reacts with the binder phase. The hard components in alloy steels, such as chromium steels, are double carbides of the formulas (Cr,Fe)23Cg, (Fe,Cr)2C3, or (Fe,Cr)3C2, that derive from the binary chromium carbides, and can also contain tungsten or molybdenum. These double carbides are related to Tj-carbides, ternary compounds of the general formula M M C where M = iron metal M = refractory transition metal. 

Tantalum Carbide, TaC, has been prepared by heating a mixture of tantalum pentoxide and carbon in a molybdenum boat at 1260° C. in a stream of hydrogen,2 or by the action of hydrogen and carbon monoxide on tantalum pentachloride. It is a dark grey or black substance which is insoluble in all acids, and bums to the pentoxide when powdered and heated in air. Density—13 96. It melts with decomposition at 4100° abs., which is probably the highest melting-point yet recorded for a chemical compound. Its hardness coefficient fees between 9 and 10. It is a good conductor of electricity.4 For its crystal structure see reference cited.5... 

Of the different molybdenum-carbon phases only dimolybdenum carbide P-M02C has any industrial importance. It is manufactured by reacting molyb-denum(VI) oxide or metallic molybdenum with carbon black at 1350 to 1800°C in carbon tube short circuit furnaces under hydrogen atmospheres. Due to its low hardness the use of M02C is virtually limited to TiC-Mo2C-Ni cutting materials. 

The metal nitrides of the transition metals of the subgroups of the IVth, Vth and Vlth groups are very similar to the corresponding carbides in their. structures (interstitial compounds of the MN type) and their properties such as hardness, melting point and electrical conductivity (see Table 5.6-3). Tungsten and molybdenum nitrides are exceptions with different structures and decompose with nitrogen loss above 800°C. 

The problem of poor adhesion to the substrate may be mitigated by the choice of an appropriate material. Especially metals with the ability to form carbides are suitable for this purpose. However, carbide formation alone is not sufficient to obtain films rehably adhering to the respective substrate. Films deposited on molybdenum, for instance, tend toward spontaneous delamination upon stress. Hence the film should be sought to bear the least possible stress to achieve good adhesion. The so-called stress is a quantity hard to assess for being influenced by a multitude of parameters Hke the thickness of the film, problems related to the grain boundaries, lattice mismatch, and thermal strain. 

CHRONIC HEALTH RISKS (Molybdenum and insoluble molybdenum and insoluble compounds) based upon animal experiments, accumulation of molybdenum dust in the lungs, spleen, and heart, showed a decrease of DNA and RNA in the kidneys, spleen, and liver exposure to molybdenum dust from alloys or carbides caused "hard-metal lung disease" in humans. (Soluble molybdenum compounds) repeated exposure to soluble molybdenum compounds, based on animals data, suggests an association with the gout can cause anemia in animals exposure to molybdenum trioxide (M0O3), over a period of 3-7 years, has caused pneumoconiosis in workers. 

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. 

Tungsten carbide (WC), the hard phase, together with cobalt (Co), the binder phase, forms the basic cemented carbide structure from which other types of cemented carbide have been developed. In addition to the straight tungsten carbide - cobalt compositions - cemented carbide may contain varying proportions of titanium carbide (TiC), tantalum carbide (TaC), and niobium carbide (NbC). These carbides are mutually soluble and can also dissolve a high proportion of tungsten carbide. Also, cemented carbides are produced which have the cobalt binder phase alloyed with, or completely replaced by, other metals such as iron (Fe), chromium (Cr), nickel (Ni), molybdenum (Mo), or alloys of these elements. 

Abrasive tool wear is also increased by the alloying elements chrome, molybdenum, and mngsten (Cr, Mo, W), which aU tend to form hard carbides in steels with greater carbon contents. These carbides plough into the surface of the cutting tool, which eventually results in shorter tool life. 

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