Metallurgical Terms and Definitions

Aecm , Ae1 , Ae3 , Ae4:
The temperatures of phase changes at equilibrium.

Age Hardening:
Hardening by aging (heat treatment) usually after rapid cooling or cold working.

Age Softening:
Spontaneous decrease of strength and hardness that takes place at room
temperature in certain strain hardened alloys, especially those of aluminum.

Alloying Element:
An element added to and remaining in a metal that changes structure and
properties.

Annealing:
A generic term denoting a treatment consisting of heating to and holding at a suitable temperature followed by cooling at a suitable rate, used primarily to soften metallic materials, but also to simultaneously produce desired changes in other properties or in microstructure. The purpose of such changes may be, but is not confined to:improvement of machinability, facilitation of cold work, improvement of mechanical or electrical properties, and /or increase in stability of dimensions. When the term is used unqualifiedly, full annealing is implied. When applied only for the relief of stress, the process is properly call stress relieving or stress-relief annealing.
Apparent Density:
(1) The weight per unit volume of a powder, in contrast to the weight per unit volume of the individual particles. (2) The weight per unit volume of a porous solid,where the unit volume is determined from external dimensions of the mass. Apparent density is always less than the true density of the material itself.

Austenite:
A solid solution of one or more elements in face-centered cubic iron (gamma iron).
Unless otherwise designated (such as nickel austenite), the solute is generally assumed to be carbon.

Bainite:
The combination of ferrite and cementite from the austenitic state at temperature below the pearlitic range where it is difficult for carbon to diffuse into pearlite. The structure appears to be feathery in appearance and/or needle-like.

Bend Test:
A test for determining relative ductility of metal that is to be formed (usually sheet, strip, plate, or wire) and for determining soundness and toughness of metal (after welding, for example). The specimen is usually bent over a specified diameter through a specified angle for a specified number of cycles.

Brinell Hardness Number (HB):
A number related to the applied load and to the surface area of the permanent impression made by a ball indenter.

Brinell Hardness Test:
A test for determining the hardness of a material by forcing a hard steel or carbide ball of specified diameter (typically 10mm) into it under a specified load. The result is expressed as the Brinell Hardness Number.

Brittleness:
The tendency of a material to fracture without first undergoing significant plastic deformation. Contrast with ductility.

Carbon Equivalent:
(1) For cast iron, an empirical relationship of the total carbon, silicon, and phosphorus contents expressed by the formula:
CE= %C+0.3(%Si) + 0.33 (%P)
-0.027 (%Mn) + 0.4 (%S)
(2) For rating of weldability:
CE= C+ Mn + Ni + Cu + Cr + Mo + V
6 15 15 5 5 5

Carbonitriding:
A case hardening process in which a suitable ferrous material is heated above the lower transformation temperature in a gaseous atmosphere of such composition as to cause simultaneous absorption of carbon and nitrogen by the surface and , by diffusion,create a concentration gradient. The heat-treating process is completed by cooling at a rate that produces the desired properties in the workpiece.

Carburizing:
Absorption and diffusion of carbon into solid ferrous alloys by heating, to a temperature usually above Ac3, in contact with a suitable carbonaceous material. A form of case hardening that produces a carbon gradient extending inward from the surface, enabling the surface layer to be hardened either by quenching directly from the carburizing
temperature or by cooling to room temperature, then reaustenitizing and quenching.

Case:
In heat treating, that portion of a ferrous alloy, extending inward from the surface, whose composition has been altered during case hardening. Typically considered to be the portion of an alloy (a) whose composition has been measurably altered from the original composition, (b) that appears light when etched, or (c) that has a higher hardness value
than the core. Contrast with core.

Case Hardening:
A generic term covering several processed applicable to steel that change the chemical composition of the surface layer by absorption of carbon, nitrogen, or a mixture of the two and, by diffusion, create a concentration gradient. The processes commonly used are carburizing and quench hardening; cyaniding; nitriding; and carbonitriding. The use of the applicable specific process name is preferred.

Cementite:
A hard (800HV), brittle compound of iron and carbon, known chemically as iron carbide and having the approximate chemical formula Fe3C. It is characterized by an orthorhombic crystal structure. When it occurs as a phase in steel, the chemical composition will be altered by the presence of manganese and other carbide-forming elements. The highest cementite contents are observed in white cast irons, which are used in applications where high wear resistance is required.

Cold Working:
Deforming metal plastically under conditions of temperature and strain rate that induce strain hardening. Usually, but not necessarily, conducted at room temperature. Contrast with hot working.

Compression Test:
A method for assessing the ability of a material to withstand compressive loads. Analyses of structural behavior or metal forming require knowledge of compression stress-strain properties.

Compressive Strength:
The maximum compressive stress that a material is capable of developing, based on original area of cross section.

Compressive Stress:
A stress that causes an elastic body to deform (shorten) in the direction of the applied load. Contrast with tensile stress.

Defect:
(1) A discontinuity whose size, shape, orientation, or location makes it detrimental to the useful service of the part in which it occurs. (2) A discontinuity or discontinuities which by nature or accumulated effect (for example, total crack length) render a part or product unable to meet minimum applicable acceptance standards or specifications.

Die Casting:
(1) A casting made in a die. (2) A casting process in which molten metal is forced under high pressure into the cavity of a metal mold.
Metallurgical Terms and Definitions

Discontinuity:
(1) Any interruption in the normal physical structure or configuration of a part, such as cracks, laps, seams, inclusions, or porosity. A discontinuity may or may not affect the utility of the part. (2) An interruption of the typical structure of a weldment, such as a lack of homogeneity in the mechanical, metallurgical, or physical characteristics of the material or weldment. A discontinuity is not necessarily a defect.

Elasticity:
The property of a material by virtue of which deformation caused by stress
disappears upon removal of the stress.

Elongation:
A term used in mechanical testing to describe the amount of extension of a test
piece when stressed.

Engineering Strain:
A term sometimes used for average linear strain or conventional strain in order to
differentiate if from true strain. In tension testing it is calculated by dividing the change in the gage length by the original gage length.

Engineering Stress:
A term sometimes used for conventional stress in order to differentiate it from true
stress. In tension testing, it is calculated by dividing the breaking load applied to the specimen by the original cross-sectional area of the specimen.

Etching:
Subjecting the surface of a metal to preferential chemical or electrolytic attack in
order to reveal structural details for metallographic examination.

Exstensometer:
An instrument for measuring changes in length over a given gage length caused by
application or removal of a force. Commonly used in tension testing.

Extrusion:
The conversion of an ingot or billet into lengths of uniform cross section by forcing metal to flow plastically through a die orifice.

Failure:
A general term used to imply that a part in service (a) has become completely
inoperable, (b) is still operable but incapable of satisfactorily performing its intended function, or (c) has deteriorated seriously, to the point that it has become unreliable or unsafe for continued use.

Fatigue:
The phenomenon leading to fracture under repeated or fluctuating stresses having
a maximum value less than the ultimate tensile strength of the material.

Fatigue Failure:
Failure that occurs when a specimen undergoing fatigue completely fractures into
two parts of which has softened or been otherwise significantly reduced in stiffness by thermal heating or cracking.

Ferrite:
A solid solution of one or more elements in body-centered cubic iron (alpha iron).

Ferrous:
Metallic materials in which the principal component is iron.

Flowlines:
(1) Texture showing the direction of metal flow during hot or cold working. Flow
lines can often be revealed by etching the surface or a section of a metal part. (2) In mechanical metallurgy, paths followed by minute volumes of metal during deformation.

Fluorescent Penetrant Inspection:
Inspection using a fluorescent liquid that will penetrate any surface opening; after
the surface has been wiped clean, the location of any surface flaws may be detected by the fluorescence, under ultraviolet light, of back-seepage of the fluid.

Formability:
The ease with which a metal can be shaped through plastic deformation.
Evaluation of the formability of a metal involves measurement of strength, ductility, and the amount of deformation required to cause fracture.

Forming:
(1) Making a change, with the exception of shearing or blanking, in the shape or
contour of a metal part without intentionally altering its thickness. (2) The plastic deformation of a billet or a blanked sheet between tools (dies) to obtain the final configuration. Metalforming processes are typically classified as bulk forming and sheet forming. Also referred to as metalworking.

Fractography:
Descriptive treatment of fracture of materials, with specific reference to
photographs of the fracture surface.

Fracture:
The irregular surface produced when a piece of metal is broken.
Gage:
(1) The thickness of sheet or the diameter of wire. The various standards are
arbitrary and differ with regard to ferrous and nonferrous products as well as sheet and wire.
(2) An aid for visual inspection that enables an inspector to determine more reliably whether the size or contour of a formed part meets dimensional requirements.
(3) An instrument used to measure thickness or length.

Gage Length:
The original length of that portion of the specimen over which strain, change of
length and other characteristics are measured.

Grain:
An individual crystal in a polycrystalline material; it may or may not contain
twinned regions and subgrains.

Grain Boundary:
A narrow zone in a metal or ceramic corresponding to the transition from one
crystallographic orientation to another, thus separating one grain from another; the atoms in each grain are arranged in an orderly pattern.

Grain Growth:
(1) An increase in the average size of the grains in polycrystalline material, usually as a result of heating at elevated temperature.
(2) In polycrystalline materials, a phenomenon occurring fairly close below the melting point in which the larger grains grow still larger while the smallest ones gradually diminish and disappear.

Grain Size:
For metals, a measure of the areas or volumes of grains in a polycrystalline
material, usually expressed as an average when the individual sizes are fairly uniform. In metals containing two or more phases, grain size refers to that of the matrix unless otherwise specified. Grain size is reported in terms of number of grains per unit area or volume, in terms of average diameter, or as a grain-size number derived from area measurements.

Granular Fracture:
A type of irregular surface produced when metal is broken that is characterized by
a rough, grainlike appearance, rather than a smooth or fibrous one.

Hardenability:
The relative ability of a ferrous alloy to form martensite when quenched from a
temperature above the upper critical temperature.

Hardening:
Increasing hardness of metals by suitable treatment, usually involving heating and
cooling.

Hardness:
A measure of the resistance of a material to surface indentation or abrasion; may
be thought of as a function of the stress required to produce some specified type of
surface deformation.

Heat Treatment:
Heating and cooling a solid metal or alloy in such a way as to obtain desired
conditions or properties.

High Strength Low Alloy (HSLA) Steels:
Steels designed to provide better mechanical properties and/or greater resistance
to atmospheric corrosion than conventional carbon steels.

Hot Working:
The plastic deformation of metal at such a temperature and strain rate that
recrystallization takes place simultaneously with the deformation, thus avoiding any strain

hardening
Also referred to as hot forging and hot forming.

Hydrogen Embrittlement:
A process resulting in a decrease of the toughness or ductility of a metal due to the presence of atomic hydrogen. Hydrogen embrittlement has been recognized classically as being of two types. The first, known as internal hydrogen embrittlement, occurs when the hydrogen enters molten metal which becomes supersaturated with hydrogen immediately after solidification. The second type, environmental hydrogen embrittlement, results from hydrogen being absorbed by solid metals. This can occur during elevated-temperature
thermal treatments and in service during electroplating, contact with maintenance
chemicals, corrosion reactions, cathodic protection, and operating in high-pressure
hydrogen.

Impact Test:
A test for determining the energy absorbed in fracturing a test piece at high
velocity, as distinct from static test.

Impregnation:
(1) Treatment of porous castings with a sealing medium to stop pressure leaks.
(2) The process of filling the pores of a sintered compact, usually with a liquid such as a lubricant.
(3) The process of mixing particles of a non-metallic substance in a cemented carbide matrix, as in diamond-impregnated tools.

Inclusion:
A physical and mechanical discontinuity occurring within a material or part, usually
consisting of solid, encapsulated foreign material.

Induction Hardening:
A surface-hardening process in which only the surface layer of a suitable ferrous
workpiece is heated by electromagnetic induction to above the upper critical temperature and immediately quenched.

Insert:
(1) A part formed from a second material, usually a metal, which is placed in the
molds and appears as an integral structural part of the final casting. (2) A removable portion of a die or mold.

Intergranular:
Between crystals or grains. Also called intercrystalline.

Intergranular Cracking:
Cracking or fracturing that occurs between the grains or crystals in a
polycrystalline aggregate. Also called intercrystalline cracking.

Investment Casting:
(1) Casting metal into a mold produced by surrounding, or investing, an
expendable pattern with a refractory slurry coating that sets at room temperature, after which the wax or plastic pattern is removed through the us of heat prior to filling the mold with liquid metal.
(2) A part made by the investment casting process.

Killed Steel:
Steel treated with a strong deoxidizing agent such as silicon or aluminum in order
to reduce the oxygen content to such a level that no reaction occurs between carbon and oxygen during solidification.

Knoop Hardness Number (HK):
A number related to the applied load and to the projected area of the permanent
impression made by a rhombic-based pyramidal diamond indenter having included edge
angles of 172o 30’ and 130o 0’ computed from the equation:
HK= ____P____
0.07028d2
where P is applied load, kgf; and d is the long diagonal of the impression, mm. In
reporting Knoop hardness numbers, the test load is stated.

Knoop Hardness Test:
An indentation hardness test using calibrated machines to force a rhombic-based
pyramidal diamond indenter having specified edge angles, under specified conditions, into the surface of the material under test and to measure the long diagonal after removal of the load.

Low Alloy Steels:
A category of ferrous materials that exhibit mechanical properties superior to plain
carbon steels as the result of additions of such alloying elements as nickel, chromium, and molybdenum.

Machinability:
The relative ease of machining a metal.

Martensite:
Is cooling rapidly from the austenitic state to temperature below 550oF, the
resultant structure appears to have fine accucular or needle-like appearance. The structure is highly stressed and supersaturated with carbon.

Mechanical Metallurgy:
The science and technology dealing with the behavior of metals when subjected to
applied forces; often considered to be restricted to plastic working or shaping of metals.

Mechanical Properties:
The properties of a material that reveal its elastic and inelastic behavior when force
is applied, thereby indicating its suitability for mechanical applications; for example, modulus of elasticity, tensile strength, elongation, hardness, and fatigue limit.

Metallograph:
An optical instrument designed for visual observation and photomicrography of
prepared surfaces of opaque materials at magnifications of 25 to approximately 2000x.

Metallography:
The study of the structure of metals and alloys by various methods, especially by
optical and electron microscopy.

Metallurgy:
The science and technology of metals and alloys. Process metallurgy is concerned
with the extraction of metals from their ores and with refining of metals; physical
metallurgy, with physical and mechanical properties of metals as affected by composition, processing, and environmental conditions; and mechanical metallurgy, with the response of metals to applied forces.

Microhardness:
The hardness of a material as determined by forcing an indenter such as Vickers or
Knoop indenter into the surface of a material under very light load; usually, the
indentations are so small that they must be measured with a microscope.

Microhardness Test:
A microindentation hardness test using a calibrated machine to force a diamond
indenter of specific geometry, under a test load of 1 to 1000 gram-force, into the surface of the test material and to measure the diagonal or diagonals optically.

Modulus of Elasticity (E):
The measure of rigidity or stiffness of a material; the ratio of stress, below the
proportional limit, to the corresponding strain.

Morphology:
The characteristic shape, form, or surface texture or contours of the crystals,
grains, or particles of (or in) a material, generally on a microscopic scale.

Mounting:
A means by which a specimen for metallographic examination may be held during
preparation of a section surface. The specimen can be embedded in plastic or secured
mechanically in clamps.

Necking:
(1) The reduction of the cross-sectional area of a material in a localized area by
uniaxial tension or by stretching.
(2) The reduction of the diameter of a portion of the length of a cylindrical shell or tube.

Nitriding:
Introducing nitrogen into the surface layer of a solid ferrous alloy by holding at a
suitable temperature (below Ac1 for ferritic steels) in contact with a nitrogenous material, usually ammonia or molten cyanide of appropriate composition. Quenching is not required to produce a hard case.

Nitrocarburizing:
Any of several processes in which both nitrogen and carbon are absorbed into the
surface layers of a ferrous material at temperatures below the lower critical temperature and, by diffusion, create a concentration gradient. Nitrocarburizing is performed primarily to provide an antiscuffing surface layer and to improve fatigue resistance.

Oxidation:
(1) A reaction in which there is an increase in valence resulting from a loss of
electrons. Contrast with reduction.
(2) A corrosion reaction in which the corroded metal forms an oxide; usually applied to reaction with a gas containing elemental oxygen, such as air.
(3) A chemical reaction in which one substance is changed to another by oxygen combination with the substance. Much of the dross from holding and melting furnaces is the result of oxidation of the alloy held in the furnace.

Pearlite:
A metastable lamellar aggregate of ferrite and cementite resulting from the
transformation of austenite at temperatures above the bainite range.

Permanent Set:
The deformation remaining after a specimen has been stressed a prescribed amount
in tension, compression, or shear for a specified time period and released for a specified time period.

Phosphating:
Forming an adherent phosphate coating on a metal by immersion in a suitable
aqueous phosphate solution.

Physical Metallurgy:
The science and technology dealing with the properties of metals and alloys, and of
the effects of composition, processing, and environment on these properties.

Plastic Deformation:
The permanent (inelastic) distortion of materials under applied stresses that strain
the material beyond its elastic limit.

Plasticity:
The property of a material which allows it to be repeatedly deformed without
rupture when acted upon by a force sufficient to cause deformation and which allows it to retain its shape after the applied force has been removed.

Plastic Strain Ratio (r-value):
In formability testing of metals, the ratio of the true width strain to the true
thickness strain in a sheet tensile, r = ew et. A formability parameter that relates to drawing, it is also known as the anisotropy factor. A high r-value indicated a material with good drawing properties.

Plug:
(1) A rod or mandrel over which a pierced tube is forces.
(2) A rod or mandrel
that fills a tube as it is drawn through a die.
(3) A punch or mandrel over which a cup is drawn.
(4) A protruding portion of a die impression for forming a corresponding recess in the forging.
(5) A false bottom in a die.

Polishing:
(1) A surface-finishing process for ceramics and metals utilizing successive grades
of abrasive.
(2) Smoothing metal surfaces, often to a high luster, by rubbing the surface with a fine abrasive, usually contained in a cloth or other soft lap. Results in microscopic flow of some surface metal together with actual removal of a small amount of surface
metal.
(3) Removal of material by the action of abrasive grains carried to the work by a flexible support, generally either a wheel or a coated abrasive belt. (4) A mechanical, chemical, or electrolytic process or combination thereof used to prepare a smooth, reflective surface suitable for microstructural examination that is free of artifacts or damage introduced during prior sectioning or grinding.

Polycrystalline:
Pertaining to a solid comprised of many crystals or crystallites, intimately bonded
together. May be homogeneous (one substance) or heterogeneous (two or more crystal
types or compositions).

Porosity:
(1) Fine holes or pores within a solid; the amount of these pores is expressed as a
percentage of the total volume of the solid.
(2) Cavity-type discontinuities in weldments formed by gas entrapment during solidification.
(3) A characteristic of being porous, with voids or pores resulting from trapped air or shrinkage in a casting.

Powder Metallurgy:
The technology and art of producing metal powders and utilizing metal powders
for production of massive materials and shaped objects.

Powder Metallurgy Part:
A shaped object that has been formed from metal powders and sintered by heating
below the melting point of the major constituent. A structural or mechanical component made by the powder metallurgy process.

Preheating:
Heating before some further thermal or mechanical treatment. For tool steel,
heating to an intermediate temperature immediately before final austenizing. For some nonferrous alloys, heating to a high temperature for a long time, in order to homogenize the structure before working. In powder metallurgy, an early stage in the sintering procedure when, in a continuous furnace, lubricant or binder burnoff occurs without atmosphere protection prior to actual sintering in the protective atmosphere of the high heat chamber.

Quenching:
Rapid cooling of metals (often steels) from a suitable elevated temperature. This
generally is accomplished by immersion in water, oil, polymer solution, or salt, although forced air is sometimes used.

Quenching Crack:
Fracture of a metal during quenching from elevated temperature. Most frequently
observed in hardened carbon steel, alloy steel, or tool steel parts of high hardness and low toughness. Cracks often emanate from fillets, holes, corners, or other stress raisers and result from high stresses due to the volume changes accompanying transformation to
martensite.

Recarburize:
(1) To increase the carbon content of molten cast iron or steel by adding
carbonaceous material, high-carbon pig iron, or a high-carbon alloy. (2) To carburize a metal part to return surface carbon lost in processing; also known as carbon restoration.

Recrystallization:
(1) The formation of a new, strain-free grain structure from that existing in coldworked
metal, usually accomplished by heating.
(2) The change from one crystal structure
to another, as occurs on heating or cooling through a critical temperature. (3) A process, usually physical, by which one crystal species is grown at the expense of another or at the expense of others of the same substance but smaller in size.

Residual Stress:
(1) The stress existing in a body at rest, in equilibrium, at uniform temperature, and not subjected to external forces. Often caused by the forming or thermal processing curing process.
(2) An internal stress not depending on external forces resulting from such factors as cold working, phase changes, or temperature gradients.
(3) Stress present in a body that is free of external forces or thermal gradients. (4) Stress remaining in a structure or member as a result of thermal or mechanical treatment or both. Stress arises in fusion welding primarily because the weld metal contracts on cooling from the solidus to room temperature.

Rockwell Hardness Test:
An indentation hardness test using a calibrated machine that utilizes the depth of
indentation, under constant load, as a measure of hardness.

Rockwell Superficial Hardness Test:
The same test as used to determine the Rockwell hardness number except that
smaller minor and major loads are used. In Rockwell testing, the minor load is 10kgf, and the major load is 60, 100, or 150 kgf. In superficial Rockwell testing, the minor load is 3kgf, and major loads are 15, 30, or 45 kgf. In both tests, the indenter may be either a diamond cone or a steel ball, depending principally on the characteristics of the material being tested.

Roughness:
(1) Relatively finely spaced surface irregularities, the heights, widths, and
directions of which establish the predominant surface pattern. (2) The microscopic peakto-
valley distances of surface protuberances and depressions.

Segregation:
(1) Nonuniform distribution of alloying elements, impurities, or microphases in
metals and alloys.
(2) A casting defect involving a concentration of alloying elements at specific regions, usually as a result of the primary crystallization of one phase with the subsequent concentration of other elements in the remaining liquid. Microsegregation refers to normal segregation on a microscopic scale in which material richer in an alloying element freezes in successive layers on the dendrites (coring) and in constituent network. Macrosegregation refers to gross differences in concentration (for example, from one area of a casting to another). Shear Bands:
(1) Bands of very high shear strain that are observed during rolling of sheet metal.
During rolling, these form at approximately 35o to the rolling plane, parallel to the transverse direction. They are independent of grain orientation and at high strain rates traverse the entire thickness of the rolled sheet. (2) Highly localized deformation zones in metals that are observed at very high strain rates, such as those produced by high velocity (100 to 3600 m/s, or 330 to 11,800 ft/s) projectile impacts or explosive rupture.

Shore Hardness:
A measure of the resistance of material to indentation by a spring-loaded indenter
during Sceleroscope hardness testing. The higher the number, the greater the resistance. Normally used for rubber materials.

Solidification:
The change in state from liquid to solid upon cooling through the melting
temperature or melting range.

Spheroidite:
A structure of global carbide in a matrix of soft ferrite.

Steel:
An iron-base alloy, malleable in some temperature ranges as initially cast,
containing manganese, usually carbon, and often other alloying elements. In carbon steel and low-alloy steel, the maximum carbon is about 2.0%; in high-alloy steel, about 2.5%.
The dividing line between low-alloy and high-alloy steels is generally regarded as being at about 5% metallic alloying elements.

Steel is said to be differentiated from two general classes of “irons”: the cast irons, on the high-carbon side, and the relatively pure irons such as ingot iron, carbonyl iron, and electrolytic iron, on the low-carbon side. In some steels containing extremely low carbon, the manganese content is the principal differentiating factor, steel usually containing at least 0.25% and ingot iron considerably less.

Strain Hardening:
An increase in hardness and strength of metals caused by plastic deformation at
temperatures below the re-crystallization range. Also known as work hardening.

Stress Relieving:
Heating to a suitable temperature, holding long enough to reduce residual stresses,
and then cooling slowly enough to minimize the development of new residual stresses.

Structure:
As applies to a crystal, the shape and size of the unit cell and the location of all
atoms within the unit cell. As applied to microstructure, the size, shape, and arrangement of phases.

Swage:
(1) The operation of reducing or changing the cross-section area of stock by the
fast impact of revolving dies. (2) The tapering of bar, rod, wire, or tubing by forging, hammering, or squeezing; reducing a section by progressively tapering lengthwise until the entire section attains the smaller dimension of the taper.

Tensile Strength:
In tensile testing, the ratio of maximum load to original cross-sectional area. Also
called ultimate strength.

Tensile Stress:
A stress that causes two parts of an elastic body, on either side of a typical stress plane, to pull apart.

Tension:
The force or load that produces elongation.

Tension Testing:
A method of determining the behavior of materials subjected to uniaxial loading,
which tends to stretch the material. A longitudinal specimen of known length and
diameter is gripped at both ends and stretched at a slow, controlled rate until rupture occurs. Also known as tensile testing.
Torsion:
(1) A twisting deformation of a solid or tubular body about an axis in which lines
that were initially parallel to the axis become helices. (2) A twisting action resulting in shear stresses and strains.

Transformation Temperature:
The temperature at which a change in phase occurs. This term is sometimes used
to denote the limiting temperature of a transformation range. The following symbols are used for irons and steel:

Accm. In hypereutectoid steel, the temperature at which a solution of cementite in austenite is completed during heating.
Ac1. The temperature at which austenite begins to form during heating.

Ac3. The temperature at which transformation of ferrite to austenite is completed during
heating.

Ac4. The temperature at which austenite transforms to delta ferrite during heating.
Aecm , Ae1 , Ae3 , Ae4. The temperatures of phase changes at equilibrium.
Arcm. In hypereutectoid steel, the temperature at which precipitation of cementite starts during cooling.

Ar1. The temperature at which transformation of austenite to ferrite or to ferrite plus
cementite is completed during cooling.
Ar3. The temperature at which austenite begins to transform to ferrite during cooling.

Ar4. The temperature at which delta ferrite transforms to austenite during cooling.
Ar-. The temperature at which transformation of austenite to pearlite starts during
cooling.

Mf. The temperature at which transformation of austenite to martensite is completed
during cooling.

Ms (or Ar.). The temperature at which transformation of austenite to martensite starts during cooling.

Note: All these changes, except formation of martensite, occur at lower temperatures
during cooling than during heating, and depend on the rate of change of temperature.

Transgranular:
Through or across crystals or grains. Also called intracrystalline or
transcrystalline.

Transition Phase:
A nonequilibrium state that appears in a chemical system in the course of
transformation between two equilibrium states.
Transverse Direction:
Literally, “across,” usually signifying a direction or plane perpendicular to the
direction of working. In rolled plate or sheet, the direction across the width is often called long transverse: the direction through the thickness, short transverse.

True Strain:
(1) The ratio of the change in dimension, resulting from a given load increment, to
the magnitude of the dimension immediately prior to applying the load increment. (2) In a body subjected to axial force, the natural logarithm of the ratio of the gage length at the moment of observation to the original gage length. Also known as natural strain.

True Stress:
The value obtained by dividing the load applied to a member at a given instant by
the cross-sectional area over which it acts.

Ultimate Strength:
The maximum stress (tensile, compressive, or shear) a material can sustain without
fracture; determined by dividing maximum load by the original cross-sectional area of the specimen. Also known as nominal strength or maximum strength.

Ultimate Tensile Strength:
The ultimate or final (highest) stress sustained by a specimen in a tension test.
Upset:
(1) The localized increase in cross-sectional area of a workpiece or weldment
resulting from the application of pressure during mechanical fabrication or welding.
(2) That portion of a welding cycle during which the cross-sectional area is increased by the application of pressure.
(3) Bulk deformation resulting from the application of pressure in welding. The upset may be measured as a percent increase in interfacial area, a reduction in length, or a percent reduction in thickness (for lap joints).

Upsetting:
The working of metal so that the cross-sectional area of a portion or all of the
stock is increased.

Vickers Hardness Number (HV):
A number related to the applied load and the surface area of the permanent
impression made by a square-based pyramidal diamond indenter having included face
angles of 136o, computed form:
HV= 2P sin a/2 = 1.8544P
d2 d2 where P is applied load (kgf), d is mean diagonal of the impression (mm), and is the face angle of the indenter (136o).

Vicker Hardness Test:
A microindentation hardness test employing a 136o diamond pyramid indenter
(Vickers) and variable load, enabling the use of one hardness scale for all ranges of hardness-from very soft lead to tungsten carbide. Also known as diamond pyramid
hardness test.

Weldability:
A Specific or relative measure of the ability of a material to be welded under a
given set of conditions. Implicit in this definition is the ability of the completed weldment to fulfill all functions for which the part was designed.

Yield:
(1) Evidence of plastic deformation in structural materials. Also known as plastic
flow or creep.
(2) The ratio of the number of acceptable items produced in a production run to the total number that were attempted to be produced.
(3) Comparison of casting weight to the total weight of metal poured into the mold.

Yield Point:
The first stress in a material, usually less than the maximum attainable stress, at
which an increase in strain occurs without an increase in stress. Only certain materialsthose which exhibit a localized, heterogeneous type of transition from elastic to plastic deformation-produce a yield point. If there is a decrease in stress after yielding, a distinction may be made between upper and lower yield points. The load at which a sudden drop in the flow curve occurs is called the upper yield point. The constant load shown on the flow curve is the lower yield point.

Yield Strength:
The stress at which a material exhibits a specified deviation from proportionality of stress and strain. An offset of 0.2% is used for many materials, particularly metals.

Yield Stress:
The stress level of highly ductile materials at which large strains take place without further increase in stress.

Youngs Modulus:
A term used synonymously with modulus of elasticity. The ratio of tensile or
compressive stresses to the resulting strain.