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| Calcium (Ca) |
| Aluminium - killed steel, while in the ladle prior to being cast, often has calcium, in the form of calcium silicide, injected into the liquid bath. The addition of calcium lowers the level of the remaining oxygen and sulphur contents of the steel and modifies the residual inclusion composition and shape. This has the effect of improving the cleanliness, castability, machinability and of reducing the anisotropy of toughness and ductility of the steel. |
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| Carbides |
| Carbides are chemical compounds comprising carbon and either single metallic elements, or more complex combinations of more than one metallic element. The simplest example is iron carbide which is always present in steels. Provided carbides are present in the correct form, ie with regard to size and dispersion, they are beneficial. Carbides of iron, chromium, molybdenum are formed in quenched and tempered steels and help create the required combination of strength and toughness. Particular use is made of carbides, (or the more complex carbonitrides, which include nitrogen) in high strength low alloy (HSLA) microalloyed steels. A proportion of the increased strength of these materials is due to the effects which eg niobium carbide precipitates have on the structure of the product. The composition, size and distribution of carbides has a significant effect on steel properties. |
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| Carbon - Manganese Steels |
| Carbon-manganese steels refers to a family of medium to high strength steels which through a combination of correct selection of chemical composition and hot mill processing parameters produces products with enhanced formability and toughness. |
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| Carbon (C) |
| An essential alloying addition in steel. As the carbon content of steel increases so does the strength and hardness. To optimise the ductility and toughness for a given strength level the steel would be quenched and tempered. The majority of carbon would then be in the form of fine carbides. Carbon besides increasing the strength and hardness also increases hardenability (q.v.). In general, the higher the carbon content, the greater the care required in welding. (See Carbon Equivalent.) |
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| Carbon Equivalent |
| A key parameter (CEV) in assessing the weldability of a steel. The higher the value, the greater the care needed, especially with regard to pre- and post- heat treatment. Cev = C + Mn + Cr + Mo + V + Ni + Cu 6 5 15 |
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| Carbon Steel |
| A non alloy steel generally with a carbon content greater than 0.25%, in which the amount of carbon present is the major factor in determining its mechanical properties. |
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| Carbonitriding |
| A thermochemical method of surface hardening a steel in which the steel is heated into the austenitic region and carbon and nitrogen diffused into the steel surface, following which, the steel is quenched. |
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| Carburising |
| A thermochemical process in which steel is heated into the austenitic region in a carbon-rich atmosphere, so causing carbon to diffuse into the steel surface. The carburised steel product is then quenched. |
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| Case-Hardening |
| A process in which the surface (case) of the steel is hardened and the interior (core) of the steel is left unchanged. A number of different techniques are available for achieving this objective. |
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| Cast Iron |
| Cast Iron differs from steel in that is has a much higher carbon content, 2.0-4.5%, in combination with amounts of silicon, manganese, phosphorus and sulphur as determined by the type of cast iron, and the end use. |
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| Cementite |
| This is the name given to the compound of iron and carbon, Fe3C (iron carbide) which is a microstructural constituent found in many steels. It is very hard and brittle. |
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| Charpy Test |
| A test used to determine the degree of toughness of a steel. A standard Charpy test specimen is 10mm square in cross-section, 55mm long and has a V-notch mechined in it at mid-length. The specimen is supported in a machine in which it is fractured by a swinging pendulum. The energy absorbed in fracturing the specimen in Joules (J) is read from a scale on the instrument, and is a measure of the toughness of the steel being tested. (See BS EN 10045-1: 1990). Charpy tests are usually conducted over a range of temperatures in order to determine the ductile-brittle transition temperature of a steel. |
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| Chromium (Cr) |
| Added to increase the hardenability of steel. A strong carbide former, so is present in quenched and tempered engineering steels, up to 3.5%, ball bearing steel, 1-1.5%, tool steels, (up to 12% in cold-working die steel) and in creep and heat resisting steels. When steels contain 11% or more of chromium they are termed stainless because of their corrosion resistance which is due to the thin passive chromium-rich oxide film which forms on the steel surface. |
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| Clean Steel |
| A clean steel is one with a low and controlled content of non-metallic (oxide and sulphide) inclusions in order to maximise ductility, toughness, fatigue resistance, formability and isotropy of properties. |
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| CNC |
| Computer Numerically Controlled. |
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| Cobalt (Co) |
| An alloying element used in super high speed steels, maraging steels, alloys for permanent magnets and in high temperature resistant alloys for use in jet engines. |
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| Coefficient of Expansion |
| The value of the ratio of the dimensional change (length, area, volume) of a material to the change in temperature that has caused it. |
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| Cold Drawing |
| A process in which steel, in the form for example of bar, rod, tube, section or wire, is reduced in cross-sectional area and so increased in length by being pulled through a die. Initially, the steel is at room temperature but the reduction process may cause a noticeable increase in the temperature of the drawn steel. Cold drawing increases strength but reduces ductility and toughness. |
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| Cold Reduced |
| See 'Cold Rolled'. |
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| Cold Rolled |
| The term cold rolled is used to describe materials which have been rolled at a temperature below the recrystallisation temperature. As a result of cold rolling the product is extremely hard, and in the great majority of cases it is necessary to anneal it before it has any commercial value. The product so produced is characterised by a good surface and enhanced thickness tolerances. Such a product is also referred to as 'cold reduced'. |
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| Cold Working |
| Changing the shape of a piece of steel, at a temperature which is below the recrystallisation temperature, ie by plastic deformation, eg by rolling, forging, extrusion, drawing, spinning, machining etc. |
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| Continuous Casting |
| A method of producing long lengths of solid steel of simple cross-sectional shape, such as slab, bloom or billet by pouring liquid steel from a ladle, via a tundish, into the top of a water-cooled metal mould of short length which is faced with a copper alloy. The solidifying product is continuously withdrawn from the bottom of the mould, and cut to length prior to further processing. |
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| Controlled Atmosphere |
| A type of atmosphere, eg a mixture of nitrogen and hydrogen, which is used in a heat treatment furnace to prevent unwanted reactions such as oxidation or decarburisation occurring to the work piece. |
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| Core |
| The centre, as opposed to the surface layers, of a piece of steel, eg a coil, bar or component. |
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| Corrosion Fatigue |
| Fatigue accelerated by simultaneous attack from a corrosive environment. |
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| Creep |
| Time dependent plastic deformation. It is a serious design consideration when metals are operating under stress at high temperatures; creep rate is markedly temperature dependent. Creep tests involve the determination of the strain-time curve for the steel under constant stress and constant temperature conditions. |
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| Critical Cooling Rate |
| The minimum rate of cooling which will produce a fully martensitic microstructure in a steel when it is cooled from austenitic condition to room temperature. As the alloy content and carbon content of steel is increased the critical cooling rate of the steel decreases. |
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| Critical Temperature |
| The temperature at which a phase change occurs in steel. The exact value of this temperature depends on the particular phase change occurring eg austenite to ferrite or cementite or the reverse, on the chemical composition of the steel, on whether the steel is being heated or cooled and on the rate of heating or cooling. |
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| Crystalline Fracture |
| When this type of fracture occurs in a steel it will have a shiny appearance as the fracture path in each grain has followed a cleavage plane so producing in each grain a flat reflective surface. |
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| CTCD |
| Inspection technique on formed material. |
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| Cyanide Hardening |
| A surface hardening treatment in which a low-carbon steel is immersed in a bath of molten cyanide-based salt causing carbon and nitrogen to diffuse into the steel surface so enabling a hardened case to be produced on the steel when it is quenched from the salt bath. |
