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La
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Chemical symbol for Lanthanum. |
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Lap
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A defect appearing as a seam on a rolled bar. Laps are rolled over
pieces of material that arise when a bar is given a pass through the
rolls after a sharp overfill or fin has been formed, causing the
protrusion to be rolled into the surface of the product. The
presence of oxides usually prevents the lap welding to the original
bar surface, so that in subsequent cold working it is carried
through as a longitudinal crack. |
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Latent Heat
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Thermal energy absorbed or released when a substance undergoes a
phase change. |
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L-D Process
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An oxygen steel making process named after the towns in Austria,
Linz and Donawitz, where it was first developed. It is a modified
Bessemer process, steel is produced in a solid bottom converter by
injection of oxygen into the molten iron bath from a water cooled
lance inserted through the converter mouth. Present day BOS (basic
oxygen steelmaking) plants are developments of the L- D Process. |
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Leaded Steels
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When added to steel, lead does not go into solution but exists in a
very finely divided state along the grain boundaries. It greatly
assists machinability as it acts as a lubricant between the steel
and the tool face. Lead is normally added in amounts between
0.15-0.35% and when combined with similar amounts of sulfur,
optimum machinability is attained as in such steel as BS 970 230M07
Pb. |
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Li
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Chemical symbol for Lithium. |
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Limiting Range of Stress
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The greatest range of stress that a metal can withstand for an
indefinite number of cycles without failure. If exceeded, the metal
fractures after a certain number of cycles, which decrease as the
range of stress increases. |
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Limiting Ruling Section
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The maximum diameter of cross section of a bar or component in which
certain specified mechanical properties are achieved after heat
treatment. |
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Limits
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A term used to determine a minimum and maximum. In a mechanism, it
should denote the minimum and maximum sizes for each part, between
which the parts will function properly in conjunction with each
other and outside of which they will not. The words "limits" and
"tolerances" are often interchanged, "tolerance" represents the
difference between the minimum and maximum limits. |
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Limits of Proportionality
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The stress (load divided by original area of cross section of the
test piece) at which the strain (elongation per unit of gauge
length) ceases to be proportional to the corresponding stress. It is
usually determined from a load-elongation diagram, obtained by
plotting extensometer readings and is the stress at which the
load-elongation line ceases to be straight. |
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Liquid Carburising
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A widely used method of case-hardening steel that eliminates scaling
and the tendency to decarburization and results in clean components.
Sodium cyanide is the common media for this process, usually heated
within the range of 900-930°C. It is advisable to pre-heat the
components in neutral salts to avoid a temperature drop resulting
from immersing cold components into the cyanide. After carburizing,
either single quench hardening or refining and hardening and
tempering is carried out. |
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Liquid Penetrant Inspection
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A type of nondestructive inspection that locates discontinuities
that are open to the surface of a metal by first allowing a
penetrating dye or fluorescent liquid to infiltrate the
discontinuity, removing the excess penetrant, and then applying a
developing agent that causes the penetrant to seep back out of the
discontinuity and register as an indication. Liquid penetrant
inspection is suitable for both ferrous and nonferrous materials,
but is limited to the detection of open surface discontinuities in
nonporous solids. |
