Fatigue - The tendency for a metal to break under conditions of repeated cyclic stressing below the ultimate tensile strength.

Fatigue Limit - See ''Endurance Limit".

Fatigue Test - Highly polished samples are subjected to stress while bending, which results in a reversal of stress for every complete revolution. The stress is reduced on each succeeding sample until the maximum stress a sample will sustain for ten million reversals has been reached. Since experience justifies the assumption that if steel can withstand ten million reversals, it can withstand such stress indefinitely. This stress is reported as the fatigue limit.

Fiber Stress - Unit stress at a certain point when the overall section stress is not uniform.

Fin - Protuberances resulting from the improper squeezing of steel during rolling. Also see ''Flash".

Finished Steel - Which is ready for the market without any further work or treatment such as wire, bars, sheets, rails, plates, etc. Blooms, billets, slabs, and wire rods are termed semi-finished.

Finishing Temperature -Temperature at which hot mechanical working of metal is completed.

Firebox Quality - Quality of plates for use in pressure vessels which will be exposed to fire or heat and the resulting thermal and mechanical stresses.

Flakes - An internal steel fracture with a bright, scaly appearance.

Flame Annealing - The direct application of a high-temperature flame to a steel surface for the purpose of removing stresses and softening metal. Commonly used to remove stresses from welds.

Flame Cutting - Commonly denotes the producing of shapes from flat steel with single or multiple torch setups. Torches may be guided by hand, mechanically or by an electric eye.

Flame Hardening - In this method of hardening, the surface layer of a medium or high carbon steel is heated by a high-temperature torch and then quenched.

Flange Quality - Quality of plates for use in pressure vessels which are not exposed to fire or radiant heat. Special manufacturing, testing and marking are required.

Flash - A thin fin of metal formed at the sides of a die forging or sometimes a rolled bar where a small portion of the metal is forced out between the edges of the forging dies or the rolls.

Flash Point - Ignition point - usually applied to oils.

Forging - A piece of metal which has been shaped or formed, while hot, by forging with a hammer (hand or power), in a press, or by a drop hammer.

Forging Quality - Semi-finished steel produced for applications involving forging require manufacturing control for chemical composition, deoxidization mold practice, pouring, rolling, discard, cooling surface preparation, testing and inspection. Purchaser's method of fabrication and end use is a vital consideration in producing steel to this broad definition.

Forging Stresses - Stresses resulting from forging or from cooling from the forging temperature.

Fracture - The surface of a break in metal.

Fracture Test - Breaking metal to determine structure or physical condition by examining the fracture.

Free Machining - A term used to describe a metal which may be machined with less power at relatively high speed without the development of excessive heat and from which the chips will break off easily leaving a smooth surface. Free machining steel has internal friction reduced by the alteration of the chemical composition through the modification of the carbon, manganese, sulphur or selenium content or by addition of lead.

Full Annealing - Heating to above the critical temperature range followed by slow cooling through the range, producing maximum softness.

Full Hardness - Usually the hardness of heat-treated steel after quenching and before tempering.