Metallurgical Terms
W
W
Chemical symbol for tungsten, from Wolfram.
Water Gas
The general name of a mixture of gases obtained by the decomposition of
steam by incandescent carbon. It usually contains from 43-44% carbon monoxide,
48-49%, of hydrogen, 3-4 % of carbon dioxide, and 3-4 % of nitrogen. It is used
for heating and lighting.
Welding
Joining two pieces of metal by heat or pressure or both, with or without
added metal, so that re-crystallization takes place across the joint. Usually
there is local fusion. Heat for the process may be obtained in several different
ways such as:-an oxy-acetylene flame, an electric are which may be struck
between an electrode and the metal to be joined, an electron beam in vacuum, or
a chemical reaction (thermit). Among the more commonly used are processes are
the following:
Metal Arc Welding, where the electrode provides the filler metal and is
usually coated to provide flux.
Shielded Are Welding, which uses a protective atmosphere such as argon or
carbon dioxide, and the electrode, may be of tungsten (TIG-tungsten inert gas)
or consumable, to provide filler metal (MIG-metal inert gas).
Atomic Hydrogen Welding, in which hydrogen passed through an arc struck
between tungsten electrodes atomizes and in recombining supplies the heat for
welding.
Submerged Arc welding, which uses a bare electrode and the arc is
submerged in powdered flux.
Electro slag Welding, uses a consumable electrode but there is no are,
the heat being generated by the electric current passing through a conducting
slag, metal from the electrode forms a molten pool which is contained by water
cooled moulds and the edges of the plates being joined.
In Friction Welding, one component of the weld rotates at high speed and
is pressed against the other. Sufficient heat is generated for welding to occur
in the solid state.
Electron Beam Welding, A stream of electrons is used as the energy
source. The process permits very narrow deep welds to be made at high speed and
since the welding is usually done in vacuum the weld is free from oxides and
nitrides; the process can also be used to make welds in air but then penetration
is less and the weld is not so narrow.
Several welding processes use a combination of pressure and heat generated by
electrical resistance. Some of the commonly used processes are:
Resistance-Butt Welding, where the parts are butted together and the
current flowing through the junction generates sufficient heat for the metal to
be locally upset and welded when pressure is applied; Flash Welding is similar
but some arcing is allowed to take place at the junction.
Spot Welding, generally used to join two sheets which are held between
electrodes and heat generated at the interface between the sheets causes local
welding when pressure is applied.
Stitch Welding, consisting of a series of overlapping spot welds; Seam
Welding, using electrodes in the form of rotating wheels which continuously
apply pressure to the sheets, the current is applied intermittently but a
continuous weld is formed.
Projection Welding, using small projections on one or both components of
the weld to localize the heat and pressure, the projections collapse when the
Held is made.
Stud Welding, where an arc is struck between the stud and the metal to
which it is to be joined, pressure is finally applied to make the joint.
Whiskers
Hair-like growths on metals so thin as to be scarcely visible to the naked eye.
They are very much stronger than the metals from which they form, probably
because they are free from defects.
White Annealing
A process of heating pickled steel at a temperature of about 600"C for the
purpose of eliminating the hydrogen which has entered the steel during the
pickling operation, and thus to remove any tendency to hydrogen embrittlement.
White-Heart Process
(See Cast Iron)
White Iron
(See Cast Iron)
Widmanstatten Structure
A structure resulting when steels are cooled at a critical rate from
extremely high temperatures. It consists of ferrite and pearlite and has a
characteristic cross-hatched appearance due to the ferrite having formed along
certain crystallographic planes.
Wild Steel
(See Rising Steel Ingots)
Wolfram
An alternative name for tungsten.
Woody Fracture
(See Fracture)
Work Hardening
The increase in hardness and strength produced by cold plastic deformation
or mechanical working.
Wrought Iron
A commercial iron which was produced by many different processes, as for
example, puddling,Walloon, Lancashire open hearth, or by a variant of any of
these. The chief characteristic of wrought iron is that the temperatures
employed in its production are too low to render it fluid and its condition is
never more than pasty or semi-fused. Hence it contains an appreciable quantity
of slag. On hammering, the metal granules are elongated and weld together whilst
much of the slag is squeezed out, but some remains intermingled with the iron in
thread-like form. Wrought iron has now been replaced by mild steel.