Fatigue

The phenomenon leading to fracture under repeated or fluctuating stresses having a maximum value less than the yield strength of the material. Fatigue fractures are progressive, beginning as minute cracks that propagate under the action of the fluctuating stress.

Fatigue Strength

Highest value of stress that a material can withstand for a given number of cycles.

Ferrite

A metallurgical phase of iron in which metallic alloying elements are in solid solution, but carbon is essentially insoluble. Ferrite is virtually absent in quenched martensitic and austenitic stainless steels, but its presence characterizes ferritic stainless steels. Annealed martensitic steels contain ferrite and carbide.

Ferritic

Grade of steel containing in excess of about 12% chromium and used in a condition in which their micro-structure consists of ferrite plus carbides.

Ferritic Stainless Steel

Straight Chromium non-hardenable class of stainless steel alloys with Chromium ranging from 10.5 to 30% and Carbon under .20% A term used to identify certain high-chromium content, stainless steels, such as Types 409, 430, 434, 430, 439, 442, and 446. These steels are essentially non-hardenable by heat treatment and only slightly hardenable by cold work.

Ferroalloy

An iron-bearing product, not within the range of those called steels, which contains a considerable amount of one or more alloying elements, such as manganese, silicon, phosphorus, vanadium, chromium, ferromanganese, ferrophosphorus, ferrosilicon, and ferrovanadium. The chief use of these alloys is for making additions of their respective alloying elements to molten steel.

Ferrochrome

A finishing material which contains about 70% chromium. It is used when it is desired to add chromium to steel.

Ferromanganese

A product of the blast furnace, containing, besides iron, 78 to 82% of manganese and some silicon, phosphorus, sulphur and carbon. It is used as a deoxidizer and for the introduction of manganese into steel.

Fin

A defect extending from end to end of a bar or other rolled section caused by the spreading of the steel into the clearance of the rolls, thus producing a thin overfill. If rolled in another pass, a fin usually becomes a lap.

Finishes:

  • Hrap No. 1.  Hot-rolled, annealed, and descaled.
  • Bright-annealed. Is a bright cold-rolled highly reflective finish abstained by final annealing in a controlled atmosphere furnace.
  • Temper-rolled. The finish of products resulting from cold-working the annealed and descaled or bright-annealed product sufficiently to obtain mechanical properties higher than those normally obtained. Appearance will vary depending upon the amount of cold work required and the alloy

Fish eyes

Areas on a fractured steel surface having a characteristic white crystalline appearance.

Fishscale

A scaly appearance in a porcelain enamel coating in which the evolution of hydrogen from the base metal. Individual scales are usually small, but have been observed up to 25 mm (1 in.) or more in diameter. The scales are somewhat like blisters that have cracked part way around the perimeter but still remain attached to the coating around the rest of the perimeter; if detached completely, it is one form of pop-off.

Flakes

Short discontinuous internal fissures in ferrous metals attributed to stresses produced by localized transformation and decreased solubility of hydrogen during cooling after hot-working. In a fractured surface, flakes appear as bright silvery areas; on an etched surface thay appear as short discontinuous cracks. Also called shatter cracks and snowflakes.

Flame Hardening

A process of hardening a ferrous alloy by heating it above the transformation range by means of a high-temperature flame, and then cooling as required. Flare Test

Flash Welding

A resistance butt-welding process in which the weld is produced over the entire abutting surface by pressure and heat, the heat being produced by electric arcs between the members being welded.

Flatness

Measure of variance from a flat surface. On cold-rolled strip flatness variance is measured: 1) across the width (i.e. crossbow) and 2) along the length (i.e. edge wave). Crossbow allowable variance is expressed in thousandths of an inch maximum per inch of width (i.e. commercial flatness is .020″ P.I.W.). Edge wave is calculated knowing the length of a typical wave and the height of that wave; the wave-controlling condition is then stated by the formula of wave height divided by twice the wave length times 100 being less than a stated percentage (i.e. w/21 x 100 < 6%).

Flow Lines

(1) Texture showing the direction of metal flow during hot or cold working. Flow lines often can be revealed by etching the surface or a section of a metal part. (2) In mechanical metallurgy, paths followed by volume elements of metal during deformation.

Flow Stress

The shear stress required to cause plastic deformation of solid metals.

Flux

(1) In refining, a material used to remove undesirable substances as a molten mixture. It may also be used as a protective covering for molten metal. (2) In welding, a material used to prevent the formation of, or to dissolve and facilitate the removal of, oxides and other undesirable substances.

Flying Shear

A shear which severs steel as the piece continues to move. In continuous mills, the piece being rolled cannot be stopped for the shearing operation, so the shear knives must move with it until it is severed

Foil

Metal in any form less than 0.006 in. in thickness.

Forging

(1) As a noun; a metal product which gas been formed by hammering or pressing. (2) As a verb; forming hot metal into the desired shape by means of hammering or pressing.

Four-High Mill

See Reversing Mill.

Fractography

Descriptive treatment of fracture, especially in metal, with specific reference to photography of the fracture surface.

Fracture Test

Breaking a specimen and examining the fractured surface with the unaided eye or with a low-power microscope to determine such things as composition, grain size, case depth, soundness, and presence of defects.

Free Machining

Pertains to the machining characteristics of an alloy to which one or more ingredients have been introduced to produce small broken chips, low power consumption, better surface finish or longer tool life.

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