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| Lap |
| The presence of an area of 'double skin' on the surface of a wrought steel product, e.g. on a section of rolled bar. The most common cause of this type of defect is from excess material being squeezed out into the roll collar during a roll pass so forming a fin on either side of the product. On turning the steel for the next pass the fins are then rolled back into the steel surface so producing laps. |
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| Laser Cutting and Welding |
| Laser cutting is a process in which a laser beam is used to cut e.g. blanks from a sheet of metal. Because of the intense and highly localised nature of a laser beam, a high degree of precision can be achieved. Provided the material being cut is of adequate quality, the risk of distortion is greatly reduced. The cut is much cleaner than one produced by any other means. Laser welding is the reverse of cutting; in this case the intense heat of a laser beam is being used to execute a precision weld of high quality. |
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| L-D Process |
| A process of making steel in which oxygen is blown from a water-cooled lance onto a bath, consisting mainly of blast furnace iron, in a large refactory lined tillable vessel. The process is named after the two towns in Austria, Linz and Donawitz, from where it originates but is now more commonly known as Basic Oxygen Steelmaking (BOS) or the Basic Oxygen Furnace (BOF). |
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| Leaded Steels |
| Steels to which lead, in amounts between 0.15-0.35%, has been added, usually in conjunction with sulphur, to improve the machinability of the product. |
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| Limit of Proportionality |
| The maximum level of stress which a metal can withstand and still obey Hooke's Law, i.e. it is the point on the stress-strain which any increase in stress will cause a deviation from linearity. In practice, this means a permanent set. |
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| Limiting Ruling Section |
| The maximum diameter bar size for which a stated set of mechanical properties can be obtained for a particular steel composition after a given quench and temper heat treatment. |
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| Liquid Carburising |
| A treatment in which carbon is diffused into the surface of steel, in order to harden it, through immersion of the state in a bath of molten sodium cyanide-based salt. |
