Technical Data

Metallurgical Terms

La.

Chemical symbol for lanthanum. 

Lap.

(a) A defect appearing as a seam on the surface of forged or rolled products. It is caused by a portion of the steel being folded over on itself and failing to be welded up on a further rolling or forging. Laps may arise from careless working, defective grooves in rolls or from sharp fins on the ingot (Cƒ. Cold lap).

(b) A piece of soft metal, wood or leather, usually in the form of a rotating disc which is charged with an abrasive or polishing powder.

(c) The extent to which one plate of a lap joint covers the other.

Latent Heat.

Thermal energy expended in changing the state of a body without raising its temperature, e.g., ice to water at 0°C, or water to steam at 100°C, or alpha to gamma iron at the A₃ point.

L-D Process.

A modified Bessemer process where 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. (See Basic Oxygen Process).

Li.

Chemical symbol for lithium.

Lime (CaO).

Added to the bath during steelmaking in order to obtain a slag of the required composition.

Limit of Proportionality.

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. In practice it is determined by inspection of a load-elongation diagram, obtained by plotting extensometer readings, and is the stress at which the load-elongation line ceases to be straight.

Liquid Carburizing,

(See Surface Hardening).

Liquidus.

A line in a binary phase diagram or a surface on a ternary phase diagram, representing the temperatures under equilibrium conditions at which freezing begins during cooling, or melting is completed on heating, i.e., the line or surface above which all the alloys in the system are completely molten.

Lithium.

One of the alkali metals. Lithium-containing gas may be used to form a protective atmosphere in annealing surfaces.

Load-Extension Curve.

A line plotted from the results of a tensile test, with loads as ordinates and elongations of the gauge length as abscissae, thus relating the extension of the material under test to the applied load. (See also Stress Strain Curve).

Lost Wax Process.

(See Precision Casting).