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| Tellurium (Te) |
| Like selenium it is used, usually in conjunction with lead, to improve the machinability of steel. |
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| Temper |
| A term which is used in a number of different contexts: (i) A heat treatment carried out below the lower critical temperature to reduce the hardness and increase the toughness of steels that have been hardened by their transformation to martensite. (ii) In tool steels, the term is sometimes used, inadvisedly so, to denote the carbon content of the steel. (iii) To grade the degree of hardness achieved by cold working of both non-ferrous metals and of low-carbon e.g. hard, half-hard, quarter-hard etc. |
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| Temper Brittleness |
| A term used to describe a loss in toughness which can sometimes occur when a steel with a martensitic microstructure is tempered. It occurs only in alloy steels, which contain certain impurity elements, and which have either been tempered and then slowly cooled through, or used in, an embrittling temperature range. |
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| Temper Colours |
| The colour of the thin oxide film that develops on a steel surface when the steel is tempered. The colour, which can range from a light straw to a deep purple, depends on the film thickness and so is dependent on both the time and temperature of the tempering. It is used to judge tempering temperatures when more accurate methods are not available. |
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| Temper Rolling |
| This is a finishing light cold rolling reduction applied to cold-reduced and annealed low-carbon steel sheet to achieve one or more of the following: suppression of the yield point, increase in strength and hardness, improvement in flatness, attainment of a specific finish. In the case of metallic-coated steel sheet it may also be for the elimination and correction of flaws in the coating. |
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| Tempering |
| A heat treatment in which steel hardened by transformation to martensite, is heated to a temperature below the lower critical temperature in order to decrease hardness and improve toughness. |
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| Tensile Strength |
| This value is normally obtained from a tensile test and is then the maximum load applied to the tensile test specimen before it fractures, divided by the original cross-sectional area of the gauge length. It is also known as the maximum stress or ultimate tensile strength. |
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| Tensile Test |
| A test in which a specimen of a standardised geometry is gripped at both ends and stretched at a slow controlled rate by axial loading until rupture occurs. The test provides information on the strength and ductility of the material tested. (See BS EN 10002-1: 1990). |
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| Thermo-mechanically Controlled Rolling (TMCR) |
| Thermo-mechanically rolling: This is the conventional hot rolling process as a result of which, in combination with the chemical composition of the material, the prescribed mechanical properties are obtained in the as-rolled condition. Controlled Rolling involves a lower than normal finish rolling temperature and creates a fine grain size and an excellent combination of strength and toughness, without the need for subsequent heat treatment. Normalised rolling: By carefully selected chemical composition and finishing and coiling temperature a set of prescribed mechanical properties is obtained which will still be achievable after the product has itself been normalised, i.e. at >900C. |
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| Tin |
| A corrosion protective coating for steel as in tinplate used in the packaging industry. An undesirable element in steel as it can give rise to hot shortness and to temper brittleness. |
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| Tolerances |
| The permissible deviation in specified nominal dimensions, or in other characteristics, of a piece of material or a part. |
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| Tool Steel |
| A generic term covering a whole range of both carbon and alloy steels commonly used to make tools. This therefore includes steels used to make cutting tools, press tools, dies, moulds for both plastics and die-casting, hand-tools, in fact any tool used to shape metals or other materials. |
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| Torsional Strength |
| The resistance of a material to deformation when it is subjected to torque. |
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| Toughness |
| A measure of the ability of a material to absorb energy and deform plastically before it fractures. It is proportional to the total area under the stress-strain curve, plotted from zero stress to fracture for the material. It is nominally determined for a metal from the energy absorbed in an impact test. More sophisticated fracture toughness tests are also available to determine the susceptibily of a steel to a crack or defect and to determine critical crack size. |
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| Transformation Range |
| The range of temperature within which austenite forms when a steel is being heated up or within which austenite transforms when a steel is being cooled down. |
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| Transformation Temperature |
| The temperature at which a change in phase occurs. |
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| Transition Temperature |
| An arbitrarily defined temperature lying within the temperature range in which the fracture of notched steel impact. |
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| Transverse Test |
| A test made perpendicular to the principle direction in which the metal has been worked. |
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| TTT Curve |
| An abbreviation for the Time-Temperature-Transformation curve. This is determined by dilatometer studies and are used to identify the phases that will be present after specific thermal treatments. They may be for isothermal of continuous cooling conditions. |
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| Tufftriding |
| A process of low temperature (550-570C), surface hardening of steel through immersion in a bath of molten cyanide-based salt. The resulting shallow nitrogen-enriched surface layer on the steel gives improvements in wear behaviour and in corrosion resistance. |
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| Tungsten |
| Forms very hard stable carbides in steel, so is often found in tool steels, up to 1.5-2.5%. Much larger additions, 18% or more, can be found in some high speed steels. |
