Metallurgical Terms
F
F
Chemical Symbol for Fluorine
Face Centred Cubic Lattice
An arrangement of atoms in crystals in which the atomic centres are disposed
in space in such a way that they may be supposed to be situated at the corners
and the middle of the faces of a set of cubic cells, i.e., the lattice possesses
half an atom in the middle of each face of the cubic lattice, the corners each
sharing one atom with seven other cubes. Thus, each unit cell contains four
atoms.
Fatigue
The effect on a metal of repeated cycles of stress. Fracture results from
the development of a crack which progresses across the section, with repeated
stress. (See also Fatigue Limit and Corrosion Fatigue).
Fatigue Limit
The maximum value of the applied alternating stress which a test piece can
withstand indefinitely. (Cf. Endurance Limit).
Fatigue Range
The maximum range of stress which a metal will withstand indefinitely. When
the maximum stress in tension equals that in compression, the fatigue range is
twice the fatigue limit. The mean stress, i.e., half the range, must be stated
to define the fatigue conditions.
Fe
Chemical symbol for Iron from Latin Ferrum
Feeder Head (Hot Top) (Sinkhead)
A refractory lining inserted in, or superimposed on the top of, a cast iron
ingot mould. Its function is to keep the head of the ingot molten so that when
the lower portion freezes the contraction cavity which forms can be filled. The
term feeder head may also be applied to the upper part of the ingot which feeds
the contraction cavity. The efficiency of the head may be improved by using
insulating refractory, or incorporating exothermic material in it. Exothermic or
insulating powder may also be put on top of the molten metal in the head or an
electric are may be struck to keep the steel molten.
Ferrite
A term once restricted to pure alpha iron but now extended to include any
solid solutions of which alpha or delta iron, as distinct from gamma iron, is
the solvent. Alpha ferrite forms from the gamma, austenitic phase, in slowly
cooled hypo-eutectoid steels. It may contain, in solid solution, many of the
special elements, e.g., up to 30% chromium, or 15% silicon, but very little
carbon, i.e., less than 0 •03 %. Pure iron consists of 100% ferrite and ferrite
is the principal constituent in low carbon steels.
Ferritic Steel
The term is generally applied to high chromium steels whose structure
consists largely of ferrite and are incapable of being completely
re-crystallized by heat treatment, because they form very little austenite on
heating.
Ferro Alloys
A term used for alloys of iron with another metal such as chromium,
manganese, silicon, tungsten, molybdenum or vanadium. These alloys are used as a
means of introducing the alloying element into steel or cast iron, or as
deoxidizers. Ferro alloys are produced by electric smelting or by reduction with
aluminium, and exception being high carbon ferro manganese which is normally
produced in blast furnaces.
Ferro Manganese
The form in which manganese isgenerally used in the steel industry. The
ordii~ary qualities contain 70 to 80 % manganese and about 7 % carbon.
Spiegeleisen may contain from 12 to 30 % manganese and about 5 % carbon. These
alloys are produced in small blast furnaces of standard type except that they
are often fitted with special cooling devices, owing to the high temperatures
involved in the reduction of manganese oxides. Low carbon ferro manganese is an
electric furnace product and is available in several grades, of which the
highest quality may contain as much as 90 % manganese with a maximum carbon
content of O •07 %.
Fettling
(a) The removal of adherent sand from castings by hammering, shot-blasting,
tumbling or hydro blast.
(b) Repairing the bed of an open hearth furnace.
Fibre
(See Flow Lines)
Fibrous Fracture
(See Fracture)
Fin
(See Flash)
Firecracks.
(a) Cracks found, for example, on the surface of rolls of hot rolling mills,
or metallic bodies which have been subjected to repeated heating and cooling.
(b) (Chill Cracks). Marks on the surface of a hot rolled product which appear
periodically, having been produced by a crack or cracks on the surface of the
roll.
Fish Scale Fracture
A fracture showing coarse facets, found in tool steels which have been
re-hardened without intermediate annealing.
Flakes (Hair Line Cracks, Snow Flakes)
Fine internal fissures which may be found lying in various directions in the
interior of steel. They occur most frequently in large alloy steel sections but
may also be found in carbon steels. Flakes in the heads of rails are known as
Shatter Cracks. They are caused by hydrogen in the steel and may be prevented by
appropriate heat treatment or by casting in a vacuum.
Flaking
(See Spalling)
Flame Hardening (Shorterizing)
A method for local hardening in which the steel is heated by a mechanically
operated oxyacetylene blowpipe which traverses the object to be hardened at a
predetermined rate. Quenching is often carried out by a jet of water which
follows immediately behind and is likewise mechanically controlled. The hardened
layer may vary in depth from a mere skin to 6mm, according to the material being
treated.
Flame Plating
A surface hardening process in which hard particles projected at high
velocity become bonded to a metal surface.
Flash (Fin)
(a) The metal that is in excess of that required to fill the final
impression in a pair of forging dies and is exuded as a thin plate at the
parting line between the dies.
(b) A thin fin of metal formed at the mould joint or parting in a casting due to
the cope and drag not matching properly.
(c) In pressure welding, the metal squeezed out of a joint made by the
resistance-welding process.
Flash Butt Welding
(See Welding)
Flow Forming
An operation similar to spinning in which the deformation of the blank is
done automatically under hydraulic pressure.
Flow Lines (Fibre)
(a) The appearance revealed by etching hot-worked steel and caused by local
differences in composition, and inclusions, drawn out in the direction of
working. Flow lines are significant since the fibre habit results in directional
properties.
(b) Striations visible on etching cold-worked steels. They are caused by local
electrolytic differences of potential produced by the varying degrees of local
distortion, and indicate the principal directions in which movement of the metal
has taken place.
Flux Density
(See Magnetic Flux Density)
Forge Welding
(See Welding)
Forging
(a) Working metal parts to a finished shape by means of hammering or
pressing after the material has been rendered plastic by heating to a high
temperature. Forging may be by hammer forging, press forging and drop forging or
stamping. Hammer forging is carried out by steam or pneumatic hammers and
deformation is brought about by a number of sharp successive blows of short
duration. Press forging is done by hydraulic presses and the deforming pressure
is applied for longer periods.
(b) The product of the forging operation. (See also Drop Forging).
Fracture
The type of surface found on breaking a piece of steel. A nomenclature has
been adopted to describe certain types. Crystalline is bright and glittering,
failure having developed along the cleavage planes of the individual crystals.
Such a fracture is typical for a brittle material. In fibrous or woody fracture,
the appearance is due to the elongation of the individual grains and this may be
accentuated by the presence of slag or by a banded structure; it is grey and
dull in appearance and is characteristic of a ductile but non-homogeneous
material such as wrought iron. A silky fracture has a very smooth, fine, dull
grain and usually occurs in a highly ductile material such as mild steel. A
vitrious fracture characterizes a fine grained non-ductile material. A tough
fracture refers to a ductile material where failure occurs only after
considerable deformation, whilst in a brittle fracture metal fails by cleavage
with little or no plastic deformation.
Fracture Toughness
The ability of a material containing a defect to withstand stress without
fracture. The limiting value known as plane strain fracture toughness (K1c) is a
measure of the resistance of material containing a crack of specified dimensions
to withstand a given set of loading conditions without fracturing in a brittle
manner.
Free Cutting Steels
Steels to which special additions have been made to promote machinability.
Sulphur, lead or selenium are added for this purpose.
Fretting
This takes place when two solids pressed together repeatedly move a very
small amount in relation to one another; Very small particles of the solids
become detached and form debris which is frequently in the form of an oxide. The
resulting damage is some tines called fretting corrosion. Fretting often
initiates fatigue failure.
Full Annealing
A softening process in which the steel is heated to and held for a suitable
length of time at a temperature, which for hypo-eutectoid steel is above the
transformation range, and for hyper-eutectoid steel within the transformation
range, followed by slow cooling to 600˚C or below.
Fusion Welding
(See Welding)