Metallurgical Terms
T
Ta
Chemical symbol for tantalum
Tandem Mill
An arrangement of rolling mill stands, one behind the other, where the work
is in more than one stand at the same time.
Te
Chemical symbol for tellurium
Temper
(a) The operation of tempering.
(b) The degree of hardness left in a steel after quenching and tempering.
(c) The amount of carbon present in a tool steel, e.g., razor temper 1•5% C,
file temper 1•3% C, die temper 0•75% C.
(d) The percentage increase in length of a sheet after cold rolling.
(e) The degree of hardness of cold rolled low carbon steel strip as controlled
by heat treatment and cold deformation. Strip is produced in a series of tempers
from full hard or hard temper (in the U.S.A. No. 1 temper), which is the most
heavily cold rolled condition, to soft or dead soft (No.5 temper U.S.A.) which
is the annealed condition.
(f) The moisture content of sand at which any certain maximum physical test
value is obtained.
(g) (verb) The process of mixing sand with sufficient water or other liquid to
develop its moulding properties. (See also Tempering).
Temper Brittleness
The loss in notched-bar impact resistance found in some medium- or low-alloy
steels when they are tempered within the temperature range of 350˚C to 600˚C or
slowly cooled from a higher tempering temperature. It is revealed by the
notched-bar impact test, but not by the tensile test.
Temper Colours
The colour of the oxide layer which forms on heating bright steel at
temperatures of the order of 200˚C to 400˚C. It is sometimes used as an
indication of the temperature when tempering hardened tool steel, the colours
changing wit increase of temperature. Approximate temperatures for plain carbon
steels are:
Light Straw 210˚C
Straw 225˚C
Dark Straw 240˚C
Yellow Brown 255˚C
Red Brown 265˚C
Purple 273˚C
Violet 285˚C
Cornflower Blue 29S˚C
Pale Blue 310˚C
Grey 330˚C
The above temperatures apply to normal tempering times, but the formation of the
oxide film, like the tempering operation itself, is affected to some extent by
time, and tempering for an excessively long period, even at a temperature as low
as 220˚C, would eventually produce a temper colour which would pass from straw,-
through brown to purple. Higher temperatures are required to obtain the same
colours in the corrosion and heat-resisting steels.
Temper Rolling
(See Skin Pass)
Tempering
(a) The process of heating hardened normalized or mechanically worked steel
at some temperature below the transformation range, and holding suitable time at
that temperature. The object of tempering is to decrease the hardness and to
increase the toughness. (See also Stess relieving).
(b) Preparing the clay intended for the production of crucibles by treading it
with the bare feet. (See also Temper).
Tensile Strength
(Maximum Stress) (Ultimate Tensile Stress) The highest load applied in
breaking, a tensile test piece divided by the original cross-sectional area of
the test piece.
Tensile Test
A test in which specimens are subjected to an increasing tensile force until
they fracture. A stress-strain curve may be plotted and the limit of
proportionality, proof stress, yield point, tensile strength, elongation and
reduction of area determined.
Terne Plate
Steel sheet coated with a tin-lead alloy, the coating being carried out by
the hot dip process.
Thermal Equilibrium Diagram
(See Phase Diagram)
Thermal Expansion
(See Coefficient of Expansion)
Thermal Hysteresis
(See Transformation Range)
Thermocouple
A device for measuring temperature in which two dissimilar conductors have a
common junction where they make perfect electrical and thermal contact with each
other. If the temperature of the common junction differs from that of the free
ends an electron motive force is developed in the system of a magnitude which is
dependent on the temperature difference.
Thomas Process
The name used on the Continent for the basic Bessemer process. (See Bessemer
process).
Ti
Chemical symbol for titanium
Time Temperature Transformation Curve (TTT Curve)
An isothermal transformation diagram showing the time which austenite takes
to transform isothermally at various temperatures between Ag and the
commencement of martensite formation (Ms). It is sometimes known as an S-Curve,
so called because for some steels, e.g., plain carbon steels, it represents a
letter S in shape. The information given is useful in heat treatment practice,
particularly for interrupted quenching, martempering and austempering.
Time Yield
(See Hatfield Time Yield)
Tough Fracture
(See Fracture)
Transformation Range
The temperature range within which austenite forms and ferrite or carbide
progressively dissolves while ferrous alloys are being heated. Also the
temperature range within which austenite decomposes to form ferrite and carbide
on cooling. The range is lower on cooling than on heating, this phenomenon is
known as thermal hysteresis. The temperatures are influenced by composition and
the rate of heating or cooling.
Transformation Temperature
The temperature at which a change in phase occurs or the limiting
temperature of a transformation range. For ferrous alloys these limiting
temperatures, or critical points, are known by symbols: Ac (c=chauffage or
heating) and Ar (r = refroidissement or cooling)
Accm: In hyper-eutectoid steel the temperature at which solution of carbide in
austenite is complete.
Arcm: The temperature at which carbide starts to precipitate on cooling.
Ac1: The temperature at which austenite begins to form on heating.
Ar1: The temperature at which the transformation of austenite to ferrite and
carbide is complete on cooling.
Ac3: The temperature at which transformation of alpha ferrite to austenite is
complete.
Ar3: The temperature at which austenite starts to transform to alpha ferrite on
cooling.
Ac4: The temperature at which austenite transforms to delta ferrite on heating.
Ar4: The temperature at which delta ferrite transforms to austenite,
Ms: The highest temperature at which martensite forms on cooling.
Mf: The temperature at which martensite formation is complete on cooling.
The martensite change is not reversible and is not affected by the rate of
cooling. All the other changes occur at lower temperatures on cooling than on
heating and depend on the rate of change of temperature.
Transition Temperature
The temperature at which a transition from ductile to brittle fracture takes
place in steel. It is commonly determined by making a series of Charpy impact
tests at various temperatures; the transition temperature is usually taken as
the point where 50% of the fracture surface shows cleavage. There are other
methods of assessing the transition temperature, e.g., by bend tests, and each
method gives a different value.
Transverse Test
(a) A test applied to cast iron in which a bar is supported at its ends and
loaded in the centre of the span until fracture occurs.
(b) A test taken at right angles to the principal direction of rolling or
forging.
Troosite
An obsolete term for upper bainite.
Tropenas Converter
A small, tilting, side-blown converter with a row of tuyeres on one side
which direct the blast on to the surface of the metal thus refining it. The
blast is often enriched with oxygen.
TTT Curve
An abbreviation of Time Temperature Transformation Curve.
Tufftriding
A nitrogen surface hardening process giving a softer case than conventional
nitriding.
Tuyere (Twyer)
A nozzle through which air is blown into a blast furnace or cupola. It is
usually made of copper and kept cool by circulating water. The term may be
applied to nozzles through which air is blown into other types of furnaces.
Twinning
Well-defined bands in crystals in which the orientation of the atoms in the
crystal lattice is the mirror image of that of the remainder of the crystals. It
may be a result of heat treatment following cold-work, as in the austenitic 18/8
stainless steels.
Twyer
(See Tuyere)