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| A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z |
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| Machinability |
| A term used to describe the ease with which a metal can be machined. |
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| Macrostructure |
| The structure of metals as seen when viewed with the naked eye or at low magnification. |
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| Magnetic Crack Detection |
| Also known as magnetic particle inspection. This is a non-destructive method of detecting surface and sub-surface discontinuities, (cracks, porosity etc.), in ferromagnetic materials. Finely divided magnetic particles, applied to the magnetised material, are attracted to, and outline the pattern of any magnetic leakage fields and so reveal the presence of the discontinuity which created the leakage. |
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| Malleability |
| The characteristic of metals which permits them to be deformed plastically by compressive forces without fracture. |
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| Manganese (Mn) |
| A most useful additive to steels. Mild deoxidiser. Combines with sulphur and so decreases the chance of the steel suffering from hot shortness. Improves the toughness of ferrite-pearlite steels. Improves hardenability. Hadfield's manganese steel, which is characterised by its great resistance to wear, contains around 13% Mn. It is used in some grades of austenitic stainless steel to replace the more expensive nickel as it is an austenite stabiliser. |
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| Maraging Steels |
| Maraging steels are a family of high nickel alloy steels i.e. typically not less than 18%, which are characterised by extremely high strength and toughness. Nickel is one of a group of possible additions to steel which encourages the formation of austenite, as opposed to forming carbides. Because of this, under the correct conditions high strength can be conferred by the transformation of austenite into martensitic type structures. The merit of maraging steels is that this change brought about as a result of a simple heat treatment, a consequence of which is that the problems of distortion normally associated with high temperature heat treatments are avoided. A typical heat treatment might involve heating to 820C followed by air cooling (which avoids the distortion which would be associated with a faster rate cooling). The process is completed by ageing at a temperature in the range 450-510C. |
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| Martempering |
| A heat transformation procedure in which an austenitised steel is quenched to a temperature just above MS, the martensite start temperature, at a rate fast enough to avoid the formation of ferrite, pearlite or bainite. The steel is then held at this temperature for long enough to achieve temperature uniformity without transformation and then cooled to room temperature. The process is employed to minimise the chance of quench cracking or distortion occurring. |
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| Martensite |
| A microstructural form found in steel when it has been cooled from its austenitic state to room temperature at a greater than the critical cooling rate of the steel. It is a metastable solid solution with a body-centred tetragonal structure and its hardness depends primarily upon the carbon content of the steel. |
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| Mass Effect |
| A term used to emphasise the effect of section size on the rate at which a steel can be cooled through its austenitic transformation, and hence the effect of section size on the microstructure and mechanical properties that can be produced in a steel of a particular chemistry when cooled in this manner. |
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| Maximum Stress |
| When used in relation to the tensile testing of a metal the value of the maximum stress is obtained by dividing the maximum load to which the test piece is subject to by the original cross-sectional area of the specimens gauge length. |
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| McQuaid-Ehn Grain Size Test |
| A method for determining the re-formed parent austenite grain size of steels, primarily intended for case-hardening, so is mainly used on carbon and alloy steels containing up to approximately 0.25% carbon. In the test, samples of the steel are carburised under standard conditions and the austenite grain size is revealed by the network of cementite which forms on their boundaries during slow cooling. |
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| Melting Point |
| The temperature at which a solid begins to melt. |
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| Micron |
| A unit of length. It is 1 x 10-6m (0.001mm). |
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| Microstructure |
| The internal structure of a material revealed when a sample is polished, etched and viewed under a microscope. |
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| Mild Steels |
| A description generally taken to mean a non-alloy steel with a maximum carbon content of about 0.25%. |
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| Mill margin |
| Material allowed between mill supplied size & final cut size to allow cutting operations. |
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| Modulus of Elasticity |
| The ratio of the stress applied to the metal to the strain which the stress produces, when the metal is behaving in an elastic manner. If the stress occurs from tensile loading conditions the ratio, the modulus elasticity, is known as Young's modulus (E). It is a measure of the stiffness of the metal. |
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| Molybdenum (Mo) |
| A strong carbide forming alloying element in steel. Produces a pronounced secondary hardening effect and so is present in hot working tool steels and is used as a partial replacement for tungsten in certain grades of high speed steel. Greatly improves hardenability (of the elements commonly added for this purpose only vanadium has a stronger effect), and reduces temper embrittlement, so is often used in quenched and tempered engineering steels. Used in conjunction with Cr and V in creep resistant steels. Up to 5% can be present in maraging steels. Added to stainless steels to promote resistance to pitting and crevice corrosion attack. |
