Metallurgical Terms
E
E.
Symbol for Modulus of Elasticity and Damping.
Elastic Limit
The highest stress that can be applied to a metal without producing a
measurable amount of plastic (i.e. permanent) deformation. Usually assumed to
coincide with the limit of proportionality.
Elasticity
The tendency of a body to return to its original size and shape, after
having been stretched, compressed or deformed. The ratio of the stress called
into play in the body by the action of the deforming forces to the strain or
change in dimensions or shape is called the coefficient or modulus of
elasticity.
Electric Steel
Steel made by one of the electric processes where the heat required for
melting the steel is provided either by an electric are, usually made to pass
between the metal itself and a carbon electrode, i.e., the are process, or by
eddy currents induced by a high frequency current. In each process the furnace
lining may be either acid or basic.
Electrolytic Polishing
An anodic treatment carried out in various electrolytes over a range of
temperature and current density producing a brightly reflecting surface. Very
useful for producing a bright smooth surface on intricate components, and for
preparing laboratory specimens for microscopical examination.
Electron Microscope
An instrument for the examination of structures, the details of which are
too fine to be resolved by the use of either visible or ultra-violet light. A
stream of electrons and an electromagnetic field replace the light rays and
optical lenses of the ordinary microscope.
Electron Probe Micro Analyzer
An instrument which uses an extremely fine beam of electrons to examine the
polished surface of metals. The electrons excite x radiation characteristics of
the elements present thus permitting the analysis of small phases such as
non-metallic inclusions and carbide particles.
Electroslag Melting. (ElectroAux Melting)
A re-melting process in which an electrode is melted by the heat generated
in a conducting slag contained in water cooled mould. Molten metal passes
through the slag to form an ingot. Some refining of the metal can be achieved by
choosing slag of appropriate composition, but the ingot is of approximately the
same composition as the electrode. (See also Welding).
Elongation
(a) The total extension produced in a tensile test and determined after
fracture by holding the pieces of a fractured tensile test piece together and
measuring between pop marks applied before starting the test. It is a measure of
ductility and is expressed as a percentage of the original gauge length, which
should also be given. The international standard gauge length is 5•65√ So, where
So is the crosssectional area of the test piece.
(b) The extension produced, for example, in rolling.
End Quench Test
See Jominy Test)
Endurance Limit
In fatigue testing, the value of the applied alternating stress which will
produce fracture after a given number of reversals. (Cf: Fatigue Limit).
Energiser
A substance added to carburiring mixtures to accelerate the carbon case
hardening process. The energizers most generally used are barium or sodium
carbonates whose action is similar to a catalyst. It is believed that the
energizer provides carbon dioxide, which in turn reacts with incandescent carbon
to form an additional supply of carbon monoxide.
Equiaxed Crystals
Crystals whose axes are approximately equal. They form in the centre of an
ingot where the temperature gradient is not steep enough for marked directional
crystallization to take place.
Equilibrium Diagram. (Constitutional Diagram)
A diagram constructed from thermal and other data showing the limits of
temperature and composition within which the different constituents and phases
of the alloy system in question are stable. From this, the changes of structure
and the composition of the constituents in equilibrium at any specified
temperature can be determined.
Erichsen Test
A cupping test, using a tool with a spherical end of 20mm diameter to deform
the test sheet, which is held between annular jaws of 27mm internal diameter.
The tool is pressed into the metal until a crack appears in the cup, and the
depth of cup in mm at this instant is taken as a measure of the ductility of the
metal and is known as the Erichsen number.
Etching
A process of revealing the structure of metal by selective chemical attack
of the structure. This is rendered possible by the differently orientated
crystals having different rates of solution in the etching reagents.
Etching Pits
Small cavities formed on the surface of metals during etching.
Eutectic
A mixture of definite composition, consisting of two or more constituents,
which solidify simultaneously out of the liquid at a minimum freezing point.
This point occurs at the intersection of two descending liquidus curves in a
binary system or three descending liquidus curves in a ternary system.
Eutectic Change
The transformation from the liquid to the solid state in a eutectic alloy.
It involves the simultaneous crystallization of two constituents in a binary
system and of three in a ternary system.
Eutectic Point
The point in the binary or ternary constitutional diagram indicating the
composition of the eutectic alloy, or mixture of minerals, and the temperature
at which it solidifies.
Eutectic Structure
The characteristic arrangement of the constituents in a eutectic resulting
from their simultaneous crystallization from the melt.
Eutectoid
A mixture of two or more constituents which forms simultaneously on cooling
from a solid solution and transforms again on heating, e.g., pearlite. The
essential difference between the eutectic and a eutectoid is that the eutectoid
is formed from the melt whereas the eutectoid is formed from a solid.
Eutectoid Steel
Steel having the same composition as the eutectoid point in the iron-carbon
system (0•83 % carbon), and which, therefore, with suitable cooling conditions,
consists entirely of pearlite at temperatures below 710˚C.
Exfoliation
(See Spaling)
Extensometer
An instrument for measuring minute extensions of 'the test piece during a
tensile test. This is necessary when determining the Limit of Proportionality or
Proof Stress.
Extrusion
The application to a relatively massive billet or blank, of sufficient
pressure to cause the metal to flow through a restricted orifice, thereby
forming a greatly elongated section. In hot extrusion, the metal is above its
re-crystallization temperature and thus continuously re-crystallizes and is not
work hardened during the process. In cold extrusion, the metal does not reach
the temperature of recrystallization and may, therefore, be considerably work
hardened by the process. In the production of seamless tubes a hot billet is
forced to flow through a die over a mandrel positioned centrally in the die.