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Dead Soft
|
A temper of nonferrous alloys and some ferrous alloys corresponding
to the condition of minimum hardness and tensile strength produced
by full annealing. |
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Decalescence
|
A term used in reference to the absorption of heat without a
corresponding increase in temperature, when steel is heated through
the critical points (phase changes). |
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Decarburization
|
The loss of carbon from the surface of steel as a result of heating
in a carbon weak atmosphere. During the rolling of steel hot
surfaces are exposed to the decarburizing effects of oxygen in the
atmosphere and as a result the surface is depleted of carbon. In
steels where the components are to be subsequently heat treated it
is necessary to remove the decarburized surface by machining. |
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Delta Iron
|
When pure or practically carbon-free iron is cooled from above its
melting point it solidifies at about 1535șC as delta iron having a
body-centered cubic lattice structure, which persists down to about
1400șC. On further cooling it undergoes an allotropic change to
gamma iron which has a face-centered cubic lattice and is
non-magnetic. |
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Dendrite
|
A crystal that has a treelike branching pattern most evident in cast
metals slowly cooled through the solidification range. |
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Deoxidation
|
Elements such as silicon and aluminum when added to molten steel
react to form stable oxides and reduce the amount of dissolved
oxygen. The solubility of oxygen in steel is reduced as temperature
is lowered during solidification and the excess oxygen combines to
form carbon monoxide. If the molten metal is not deoxidized the
effervescence produced by the evolution of carbon monoxide during
solidification would result in blow holes and porosity. Steel
treated in this way is termed, "Killed Steel". |
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Descaling
|
It is necessary to remove the scale from hot rolled bars or coil
before bright drawing. This is normally carried out by shot blasting
or pickling in acid. Other methods of descaling steel products
include sand blasting, flame descaling and tumbling. |
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Deseaming
|
A process of burning out defective areas on the surface of ingots,
blooms or billets. The condition of the surface is such that it can
then be rolled or forged into a satisfactory product. |
|
Dew Point
|
The temperature and pressure at which a gas begins to condense to a
liquid. |
|
Dew Point Analyzer
|
An atmosphere monitoring device that measures the partial pressure
of water vapor in an atmosphere. |
|
Diamond Pyramid Hardness Test
|
This test, more commonly known as the Vickers test, finds greater
use in the laboratory than the workshop. It employs a pyramid shaped
diamond with an included angle of 136° which is impressed into the
specimen using loads of 5 to 120 kg making a small square
impression. This test is used for finished or polished components
because the impression can be very small. The diamond pyramid
hardness number is obtained from a calculation based on measuring
the diagonals of the impressions in the steel. |
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Die
|
The term die is most commonly used in tooling, i.e. press tools
"punch and die" but there are many other types of die, e.g. thread
cutting dies, forming dies, forging dies, die-casting dies, etc. The
term when applied to steel often refers to drawing dies through
which hot rolled wire and bar are drawn to produce the finish and
dimensional accuracy that is required for bright steel. |
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Direct Quenching
|
(1) Quenching carburized parts directly from the carburizing
operation. (2) Also used for quenching pearlitic malleable parts
directly from the malleablizing operation. |
|
Direct-Fired Tunnel-Type Furnace
|
A continuous-type furnace where the work is conveyed through a
tunnel-type heating zone, and the parts are hung on hooks or
fixtures to minimize distortion. |
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Dislocation
|
A discontinuity in the crystal lattice of a metal. The movement of
dislocations under stress may be used to explain slip, creep,
plastic yielding, etc. |
|
Dissociation
|
The chemical breakdown of a compound into simpler compounds or
elements. One of the most common examples is the dissociation of
ammonia (NH3) into nitrogen and hydrogen. |
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Dolomite
|
A natural carbonate of calcium and magnesium generally used as a
flux in blast furnaces. |
|
Double Aging
|
Employment of two different aging treatments to control the type of
precipitate formed from a supersaturated matrix in order to obtain
the desired properties. The first aging treatment, sometimes
referred to as intermediate of stabilizing, is usually carried out
at higher temperature than the second. |
|
Double Tempering
|
A treatment in which a quench-hardened ferrous metal is subjected to
two complete tempering cycles, usually at substantially the same
temperature, for the purpose of ensuring completion of the tempering
reaction and promoting stability of the resulting microstructure. |
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Drawing
|
The process of pulling metal wire, rods, or bars through a die with
the effect of altering the size, finish and mechanical properties.
In the USA, it is a term used for tempering. |
|
Drop Forging
|
An operation in which a metal shape is formed by forcing hot metal
into impressions formed in solid blocks of hardened alloy steel, the
forging dies. The dies are made in halves, one attached to the
rising and falling block of the drop forge and the other to the
stationary anvil. Drop forgings are widely used in the automotive
industry for crankshafts, stub-axles, gears, etc. |
|
Ductile Cast Iron
|
A cast iron that has been treated while molten with an element such
as magnesium or cerium to induce the formation of free graphite
nodules or spherulites, which imparts a measurable degree of
ductility to the cast metal. Also known as nodular cast iron,
spherulitic graphite cast iron and SG iron. |
|
Ductile Fracture
|
Fracture characterized by tearing of metal accompanied by
appreciable gross plastic deformation and expenditure of
considerable energy. Contrast with brittle fracture. |
|
Ductility
|
The property of metal which permits it to be reduced in cross
sectional area without fracture. In a tensile test, ductile metals
show considerable elongation eventually failing by necking, with
consequent rapid increase in local stresses. Measured by elongation
or reduction of area in a tensile test, by height of cupping in an
Erichsen test or by other means. |
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Dye Penetrant Inspection
|
A method for detecting surface porosity or cracks in metal. The part
to be inspected is cleaned and coated with a dye which penetrates
any flaws that may be present. The surface is wiped clean and coated
with a white powder. The powder absorbs the dye held in the defects
indicating their location. |
