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Glossary of MinSE


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C

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When carburising steel, it is the ratio of the vapour pressure of carbon in austenite to the vapour pressure of graphite (the reference state) for any given temperature.
Hungary flag Karbon reakcióképesség
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A laser in which the active medium comprises a mixture of 10% CO2 , 30% N2 and 60% He. CO2 laser light haa a wavelength of 10.6 µm. For laser alloying and transformation hardening, carbon dioxide lasers are typically rated in the range of 1 to 3 kW and can deliver a maximum power denisty ≈106 to 109 W/cm2 to the surface. For further information see LASER.
Hungary flag Széndioxid (CO2) lézer
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The amount of nascent carbon available at the surface for solution in austenite during carburising. Often expressed in wt-% in relation to the Fe-C system. Depending on the media employed, the carbon may or may not be in equilibrium with the surface. Measures of carbon potential can be gained from dew point determination, infra-red gas analysis or oxygen sensing. Also see gas carburising, infra-red gas analysis and zirconium oxygen sensor.
Hungary flag Karbonpotenciál
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Carbon concentration as a function of depth below the surface.
Hungary flag Karbon eloszlás
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Thermochemical diffusion treatment involving the enrichment of a surface with carbon. It is mostly applied to low carbon (0.12-0.18 wt-%) steels, but non-ferrous metals, like titanium can also be hardened through carburising, but the mechanism of hardening in that example is quite different. Nowadays, carburising is mostly carried out using gaseous, fluidized bed or plasma media, although in some technologically less developed countries, salt bath, paste and pack methods are still widely used. This comment is reserved in part for large volume industrial operations and excludes small workshops and other engineering businesses where pack carburising is frequently justifiable given their very small turnover of work; in such cases, investment in major capital equipment is clearly unjustified. Steels are generally carburised between 850 and 1050°C, whilst in the austenitic state; this stage is followed by an oil or gas quench (to ambient temperature) which causes the formation of martensite. Subsequently, the carburised steels are tempered at approximately 150 to 200°C, to obviate case embrittlement. The carbon content of the steel core is sufficiently low (0.12-0.18wt-%C) to retain relatively high toughness, even in the as-quenched state. Specified case depths vary depending upon the application loading, but are generally deeper than those attained by nitriding, reaching a maximum of approximately 2mm. Carburising, like nitriding, improves rolling contact fatigue endurance since the volume expansion accompanying the hardening step, places the carburised case in a state of residual compressive stress. The majority of drive shafts and gears used in automobiles are carburised. It is probably the singular most important surface engineering technology used in the automotive vehicle sector. See gaseous carburising, pack carburising, plasma carburising, salt bath carburising and vacuum carburising. With regard to process control, it is very important to achieve the correct carbon content in the carburised case (≈0.8 wt-%) otherwise excessive retained austenite will result. See retained austenite.
Hungary flag Cementálás/karbonizálás
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The surface zone that has received a change in alloying content after a given thermochemical diffusion method, such as nitriding or carburising.
Hungary flag Réteg
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Strictly speaking this is the depth of diffusional penetration by, for example, carbon after carburising or nitrogen after nitriding. However, within the heat treatment sector, a number of definitions of case depth have emerged; some have become formalised by appropriate standards authorities, like ASTM, DIN and SIS. In the USA, case depth is frequently defined as that portion of the treated zone which has a hardness above 50 Rockwell C. The most precise measurements employ the microhardness technique with Vickers or Knoop diamond indenters. In this instance, case depth is frequently defined as the depth of case with a hardness that is at least 50 kg/mm2 above that of the core.
Hungary flag Réteg mélység
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A general term meaning carburising, carbonitriding or induction hardening.
Hungary flag Kéregedzés
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The erosion of a surface caused by the collapse of vacuum bubbles formed in a fluid. A condition which frequently affects ship propellers and impellers.
Hungary flag Kimaródás
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(i) An obsolete term denoting carburising; (ii) A general term used to denote any surface diffusion method that results in the formation of a surface layer containing interstitial or intermetallic ccompounds. See diffusion coating and diffusion metallizing.
Hungary flag Cementálás

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