This so-called self-quenching eliminates the need for quenching with water. Since carburizing is a diffusion-controlled process, the carburization times can be reduced with higher temperatures, but at the same time the risk of coarse grain formation increases. After quenching, tempering takes place again at low temperatures. The disadvantage, however, is the simultaneously decreasing toughness or embrittlement of the steel, which can lead to unforeseeable material failure. Shallow cases only 0.002 - 0.005", and deep cases, up to 0.350" have been specified and readily achieved. In the medium frequency range from 1 kHz to about 10 kHz, hardening depth of about 5 to 1 mm can be achieved. Examples include firing pins and rifle bolt faces, or engine camshafts. Carburising with a carburising medium (e.g. Flame hardening is also generally inferior to induction hardening and laser hardening in terms of accuracy (adjustment of the hardening depth). Viele übersetzte Beispielsätze mit "case hardening" – Deutsch-Englisch Wörterbuch und Suchmaschine für Millionen von Deutsch-Übersetzungen. Due to the relatively bulky arrangement of the nozzles, flame hardening is limited, especially for small components with complex geometries. On low carbon steel parts (1213, 12L14, 1117, 8620, etc.) Case-hardened steel combines extreme hardness and extreme toughness, something which is not readily matched by homogeneous alloys since hard steel alone tends to be brittle. Typically, effective case depth is the preferred specified case depth … It is also important to distinguish between total case depth and effective case depth. Hardened steel parts are typically used in rotating applications where high wear resistance and strength is required. Case hardening produces a hard and wear-resistent edge area and a tough core. Why does laser hardening not require quenching with water? Small items may be case-hardened by repeated heating with a torch and quenching in a carbon rich medium, such as the commercial products Kasenit / Casenite or "Cherry Red". The carburized section will have a carbon content high enough that it can be hardened again through flame or induction hardening. During nitriding, the alloyed steel is exposed to a nitrogenous environment at temperatures of about 500 °C. Case hardening may be defined as a process for hardening a ferrous material in such a manner that the surface layer, known as the case, is substantially harder than the remaining material, known as the core. This austenitized state at about 750 °C is then quenched to achieve the desired martensite formation in the surface layer. Since alloying elements generally reduce the critical cooling rate, deeper surface layers can be hardened with high-alloy steels. These very large eddy currents of up to several thousand amperes per square millimeter lead to heating of the workpiece. The major drawback of cyaniding is that cyanide salts are poisonous. This so-called core hardening temperature is then used for quenching. In the high-frequency range of up to several megahertz, even hardening depth of only a few tenths of a millimeter can be achieved. Early iron smelting made use of bloomeries which produced two layers of metal: one with a very low carbon content which is worked into wrought iron, and one with a high carbon outer layer. Typical uses are for the shackle of a lock, where the outer layer is hardened to be file resistant, and mechanical gears, where hard gear mesh surfaces are needed to maintain a long service life while toughness is required to maintain durability and resistance to catastrophic failure. Case hardening to a maximum depth of .032" (.8mm) takes four hours at 1600°F. after a slow cooling from the reheated state (single and double quench hardening) or. Laser hardening is particularly suitable for areas that are very difficult to access, such as Under the critical temperature the workpiece's microstructure does not convert to an austenitic phase, but stays in the ferritic phase, which is why it is called ferritic nitrocarburization. (In some cases, the depth … The carbon can come from a solid, liquid or gaseous source; if it comes from a solid source the process is called pack carburizing. Direct hardening is a special case hardening process. Specified case depth should have a tolerance of .005 min. At a utility frequency of 50 Hz, hardening depth in the range of 20 mm to 10 mm can be achieved. Subsequent tempering is not usual for flame hardening! The surface of the specimen to … In laser hardening, a laser beam with a very high specific power (about factor 10 compared to induction hardening) is guided over the workpiece surface to be austenitized. specify case depth and hardness that is required. What are the characteristics of surface-hardened workpieces? However, due to the high temperatures, a coarse needle-like microstructure in the surface layer is to be expected during core hardening. The thickness of the hardened layer is referred to as the case depth. In addition, no (toxic) exhaust gases are produced during induction hardening compared to flame hardening. During gas carburizing, the component is exposed to a carbon-containing atmosphere. Case hardening improves both the wear resistance and the fatigue strength of parts under dynamic and/or thermal stresses. Depending on the application, different surface hardening methods have developed. Destructive material testing & non-destructive testing (NDT), Fundamental equation of planetary gears (Willis equation). Carbon is infused with the metal at a depth specific per application. Single quench hardening specifically influences the properties of the surface (surface hardening) or the core (core hardening)! In these cases, the surfaces requiring the hardness may be hardened selectively, leaving the bulk of the part in its original tough state. This requires a high design tooling effort in advance so that induction hardening is economical, especially in automated production lines with high batch sizes. With flame hardening, burner flames are moved over the workpiece and quenched with water nozzles! The part is heated to 871–954 °C (1600–1750 °F) in a bath of sodium cyanide and then is quenched and rinsed, in water or oil, to remove any residual cyanide. This is particularly economical in mass production. Both carbon and alloy steels are suitable for case-hardening; typically mild steels are used, with low carbon content, usually less than 0.3% (see plain-carbon steel for more information). The frequencies to be adjusted therefore depend on the thicknesses of the hardness layers to be achieved. It is less complex than hardening and tempering. Liquid carburizing involves placing parts in a bath of a molten carbon-containing material, often a metal cyanide; gas carburizing involves placing the parts in a furnace maintained with a methane-rich interior. Typical hardening depths with laser hardening are in the range of 0.1 mm to 2 mm. The workpiece … Steels without carbon can’t be hard During carburizing the carbon content is increased and now you get a hard surface and a tough core. Above all, the increase in fatigue strength makes case hardening very interesting for dynamically stressed components such as gears or drive shafts. The traditional method of applying the carbon to the surface of the iron involved packing the iron in a mixture of ground bone and charcoal or a combination of leather, hooves, salt and urine, all inside a well-sealed box. case hardening depth [DIN ISO 15787:2010] Einsatzhärtungstiefe-Härtetiefe {f} [Abk. Bone contains some carbonates but is mainly calcium phosphate (as hydroxylapatite). 3), the desired case profile, and cost. Another advantage of induction hardening is the more even heating of the surface, provided the inductor is optimally adapted to the workpiece. 12L14 is not considered a "case hardening" steel according to the Jorgensen Steel Book. Larger surface layers have to be scanned line by line with the laser. In direct hardening, the heated steel is quenched directly from the carburized state! Another common application of case-hardening is on screws, particularly self-drilling screws. [1] The wrought iron, with nearly no carbon in it, was very malleable and ductile but not very hard. While the surface hardness increases strongly due to the nitrides formed, the properties of the component core remain unaffected, as the nitrides only form on the surface. This also significantly reduces the risk of hardening distortion. The nitrides formed on the surface also lead to stresses in the material. What is the primary objective of nitriding? The carbon then diffuses into the surface layer, where it leads to an enrichment of the carbon content to a hardenable level of about 0.8 % carbon, while the core remains low in carbon. Fine grain steels are also suitable for this direct hardening process, which is explained in more detail in the following section. The steel darkens significantly, and shows a mottled pattern of black, blue, and purple caused by the various compounds formed from impurities in the bone and charcoal. A high-frequency alternating current is generated in a copper tool electrode (“primary coil”) which is adapted to the shape of the workpiece to be hardened. The nitride layer also improves corrosion resistance. Normally the hardness of case after hardening and low temperature tempering is 58 to 64 HRC (VPN 570-690). The extra strength that comes from case hardening your steel produces a tough outer layer (called the case) while keeping the inner core (case depth) soft enough to absorb shock. Case hardening a gearbox components creates a hard outer-shell and a pliable inner layer. [2] 1.) The material is then quenched to adjust the core properties. Direct hardening is always suitable when steels do not tend to coarse grain formation and therefore single or double quench hardening is not necessary. Scaling and hardening distortion are less than with flame hardening! There are several methods of case hardening for gears, including vacuum carburizing, atmosphere carburizing, and induction hardening. However, crankshafts or camshafts are usually also surface-hardened after quenching and tempering. At 1450°F the case is only .005" (.13mm) after 1 hour but .016" (.4mm) at 1600°F after the same time. Case hardness is defined as the outer surface that has been made harder than the interior, or core. Carbonitriding is a special type of case hardening. Other techniques are also used in modern carburizing, such as heating in a carbon-rich atmosphere. The surface hardening processes explained so far all have in common that the hard surface layer is achieved by a martensitic microstructure. Case-hardening or surface hardening is the process of hardening the surface of a metal object while allowing the metal deeper underneath to remain soft, thus forming a thin layer of harder metal (called the "case") at the surface. Case hardening is a simple method of hardening steel. With double quench hardening, first the desired properties of the core are adapted (core hardening) and then those of the surface (surface hardening)! In such cases nitride hardening (nitriding) can provide a remedy, which does not require any microstructural transformation. This significantly reduces the already low hardness distortion and scaling. The nitrogen atoms diffuse into the surface of the steel and combine there with present alloying elements such as aluminium, chromium, molybdenum, vanadium and titanium to form hard and wear-resistant nitrides. After carburizing, the workpiece is first cooled slowly and then reheated to core hardening temperature or cooled to core hardening temperature immediately after carburizing. This paper explains why case hardening is benefi-cial; the risks involved and compares the methods for calculat-ing and specifying case depth … Flame or induction hardening are processes in which the surface of the steel is heated very rapidly to high temperatures (by direct application of an oxy-gas flame, or by induction heating) then cooled rapidly, generally using water; this creates a "case" of martensite on the surface. In principle, the hardening temperature can also be selected so that the core is specifically austenitized. In addition, long heating times lead to increased scaling, which usually requires special postprocessing. Toothed wheels are typical cases where surface hardening is used. Übersetzung für "case hardening depth" im Englisch-Deutsch Wörterbuch dictindustry - mit Forum und Beispielen. In addition, it is possible to carburize workpieces in powdered carbon granulate. The fact that heat is mainly generated on the surface rather than inside the material is due to another physical phenomenon, the so-called skin effect. As long as your consent is not given, no ads will be displayed. In the early days, the steel was practically placed in a “case” of glowing coke. In cases where only very low hardening depths are achieved, quenching can also take place without water by the relatively cool material core (self-quenching). This forms a thin surface layer of higher carbon steel, with the carbon content gradually decreasing deeper from the surface. 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