Glossary of Terms

The Performance Metals Glossary of Terms is designed to help you find the meanings of some of the terms used in the metal industry. Just click on a letter below to view the corresponding definitions. If you find that a term is not listed, please Contact Us.

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Air Frame Tubing: This tubing is produced for aircraft structural parts. It is made to special surface quality, mechanical properties and other characteristics required by Military Specifications (MIL-T-...), SAE Aeronautical Materials Specifications (AMS...), and the American Society for Testing Materials (ASTM...).
Aging: In a metal or alloy, a change in properties that generally occurs slowly at room temperature and more rapidly at higher temperature
Air-Hardening Steel: A steel containing sufficient carbon and other alloying elements to harden fully during cooling in air or other gaseous mediums from a temperature above its transformation range. The term should be restricted to steels that are capable of being hardened by cooling in air in fairly large sections, about 2" or more in diameter. Same as self-hardening steel.
Aircraft Quality: Steel which has a special cleanliness rating determined by magnetic particle testing. The terms "Aircraft Quality" and "Magnaflux Quality" are considered synonymous.
Alclad: Composite sheet produced by bonding either corrosion-resistant aluminum alloy or aluminum of high purity to base metal of structurally stronger aluminum alloy.
Alloy Steel: Steel containing significant quantities of alloying elements (other than carbon and the commonly accepted amounts of manganese, silicon, sulfur, and phosphorus) added to effect changes in the mechanical or physical properties.
Annealing (see also Heat Treatment): Heating to and holding a suitable temperature and then cooling at a suitable rate, for such purposes as reducing hardness, improving machinability, facilitating cold working, producing a desired microstructure, or obtaining desired mechanical, physical, or other properties. When applicable, the following more specific terms should be used: black annealing, blue annealing, box annealing, bright annealing, flame annealing, graphitizing, intermediate annealing, isothermal annealing, malleablizing, process annealing, quench annealing, recrystallization annealing and spheroidizing. When applied to ferrous alloys, the term "annealing", without qualification, implies full annealing. When applied to nonferrous alloys, the term "annealing" implies a heat treatment designed to soften a cold worked structure by recrystallization or subsequent grain growth or to soften an age-hardened alloy by causing a nearly complete precipitation of the second phase in relatively coarse form. Any process of annealing will usually reduce stresses, but if the treatment is applied for the sole purpose of such relief, it should be designated stress relieving.

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. The specimen is usually bent over a specified diameter through a specified angle for a specified number of cycles.
Bevel: An angular cut in the ID or OD of a tube end.
Billet: A solid semifinished round or square product that has been hot worked by forging, rolling, or extrusion. An iron or steel billet has minimum width or thickness of 11/2" and the cross-sectional area varies from 21/4 to 36 sq. in. For nonferrous metals, it may also be a casting suitable for finished or semi-finished rolling or for extrusion. As used in the manufacture of seamless tubes, it is a round bar with dimensions and other characteristics suitable for piercing into tubing.
Broken Surface: A surface having innumerable minute cracks running normal to the direction of working.
Bright Annealing: Annealing in a protective medium to prevent discoloration of the bright surface.
Brinell Hardness Test: A test for determining the hardness of a material by forcing a hard steel or carbide ball of specified diameter into it under a specified load.

Carbon Steel

Steel containing carbon up to about 2% and only residual quantities of other elements except those added for deoxidation, with silicon usually limited to 0.60% and manganese to about 1.65%. Also termed "plain carbon steel", "ordinary steel", and "straight carbon steel".

Case Hardening

Hardening a ferrous alloy so that the outer portion, or case, is made substantially harder than the inner portion, or core. Typical processes used for case hardening are carburizing, cyaniding, carbonitriding, nitriding, induction hardening, and flame hardening.

Clad Metal

A composite metal containing two or three layers that have been bonded together. The bonding may have been accomplished by corolling, welding, casting, heavy chemical deposition, or heavy electroplating.

Cold Drawing

A process in which tube is drawn at room temperature through a die and over a mandrel to achieve its final size and to provide better surface finish, closer tolerances, lighter walls, smaller diameters, longer lengths, or a different combination of mechanical properties from those possible through hot finishing or direct welding.

Chamfer

A beveled surface to eliminate an otherwise sharp corner.
A relieved angular cutting edge at a tooth corner.

Cold Working

Permanent strain produced by an external force in a metal below its recrystallization temperature.

Charpy Impact Test

(Also see Impact Testing.) A pendulum-type single-blow impact test in which the specimen, usually notched, is supported at both ends as a simple beam and broken by a falling pendulum. The energy absorbed, as determined by the subsequent rise of the pendulum, is a measure of impact strength or notch toughness.

Corrosion

Chemical or electrochemical deterioration of a metal or alloy.

Corrosion Embrittlement

The severe loss of ductility of a metal resulting from corrosive attack, usually intergranular and often not visually apparent.

Corrosion Fatigue

Effect of the application of repeated or fluctuating stresses in a corrosive environment characterized by shorter life than would be encountered as a result of either the repeated or fluctuating stresses alone or the corrosive environment alone.

Corrosion Resistance

The ability to resist attack of corrosion.

Drawing

Forming recessed parts by forcing the plastic flow of metal in dies.
Reducing the cross section of wire or tube by pulling it through a die.
A misnomer for tempering.

Density

The mass-per-unit volume of a substance, usually expressed in the metals industry in pounds per cubic inch.

Dimension (OD)

Outside Diameter. Specified in inches and fractions of an inch

Dimension (ID)

Inside Diameter. Specified in the same units as the OD.

Dimension (Mean Diameter)

The average of two measurements of the diameter taken at right angles to each other.

Dimension (Wall)

Wall thickness or gauge. Specified in either fractions or decimals of an inch or by a "wire gauge" number. In the United States, the most common gauge used for tube is the Birmingham iron gauge, designated "B.W.G.".

Ductility

The ability of a material to deform plastically without fracturing, being measured by elongation or reduction of area in a tensile test, by height of cupping in an Erichsen test, or by other means

Elongation: The amount of permanent stretch, usually referring to a measurement of a specimen after fracture in a tensile test. It is expressed as a percentage of the original gauge length.
Electric Resistance Welded Steel Tube: Tube made from strip, sheet or bands by electric resistance heating and pressure, the strip being part of the electrical circuit. The electric current, which may be introduced into the strip through electrodes or by induction, generates the welding heat through the electrical resistance of the strip.
Electric Resistance Welded Steel Tube (As-Drawn): Tube that is unheat-treated and cold drawn, and has a scale-free, cold drawn surface.

Fatigue: The phenomenon leading to fracture under repeated or fluctuating stresses having a maximum value less than the tensile strength of the material. Fatigue fractures are progressive, beginning as minute cracks that grow under the action of the fluctuating stress.
Flare Test: A test applied to tube, involving a tapered expansion over a cone. Similar to pin-expansion test.
Fracture Strength: As usually related to the tensile test, fracture strength or true breaking strength is defined as the load on the specimen at the time of fracture.
Free Machining: Pertains to the machining characteristics of an alloy to which an ingredient has been introduced to give small broken chips, lower power consumption, better surface finish, and longer tool life; among such additions are sulfur or lead to steel, lead to brass, lead and bismuth to aluminum, and sulfur or selenium to stainless steel.
Full Annealing: (Also see Heat Treatment.) Annealing a ferrous alloy by austenitizing and then cooling slowly through the transformation range. The austenitizing temperature to hypoeutectoid steel is usually above Ac3; and for hypereutectoid steel, usually between Ac1 and Accm.

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. Grain sizes are reported in terms of grains per unit area or volume, average diameter, or as a grain-size number derived from area measurements.
Grain Size (Apparent Ferrite Grain Size): The average of the size of the ferrite grains as microscopically viewed in the normalized or annealed condition.
Grain Size (Austenitic Grain Size): Usually measured by the McQuaid-Ehn method, it represents the austenitic grain size of a material at a prescribed temperature above the upper critical, frequently 1700° F. For austenitic stainless steels the grain size does not change upon cooling and is that observed microscopically at room temperature.
Gun Drill: A drill, usually with one or more flutes and with coolant passages through the drill body, used for deep-hole drilling.

Heat Treatment of Steel (Normalize): A process which consists of heating to a temperature approximately 100° F above the upper critical temperature (above 1650° F) and cooling in still air at room temperature. Normalizing is utilized to obtain moderate ncreases in hardness in medium carbon steels or to alter the weld microstructure in lower carbon steels.
Hardenability: In a ferrous alloy, the property that determines the depth and distribution of hardness induced by cooling from a suitable elevated temperature. The hardness can vary with the cooling rate.
Hardening: Increasing the hardness by suitable treatment, usually involving heating and cooling
Hardness: A measure of the degree of a material's resistance to indentation. It is usually determined by measuring resistance to penetration, by such tests as Brinell, Rockwell, and Vickers.
Heat Treatment of Steel: A combination of heating and cooling operations applied to a metal or alloy in the solid state to obtain desired conditions or properties. Heating for the sole purpose of hot working is excluded from the meaning of this definition.
Heat Treatment of Aluminium: Aluminium alloys are divided into two distinct groups based upon their reaction to thermal treatment. Heat-treatable tube alloys (2000, 6000 and 7000 series) can be strengthened by thermal treatment and subjected to repeated heat treatment cycles without harmful effects. Non-heat-treatable tube alloys (1000, 3000 and 5000 series) can be strengthened only by cold working.

Impact Test: A test to determine the behavior of materials when subjected to high rates of loading, usually in bending, tension, or torsion. The quantity measured is the energy absorbed in breaking the specimen by a single blow, as in the Charpy or Izod tests.
Induction Hardening: Quench hardening in which the heat is generated by electrical induction.

Jominy Test: (also see End-Quench Hardenability Test) Hardenability test performed usually on alloy steels to determine depth and degree of hardness resulting from a standard end quenching method with cold water.

Killed Steel: Steel deoxidized 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.

Laminations: Metal defects with separation or weakness generally aligned parallel to the worked surface of the metal. May be the result of pipe, blisters, seams, inclusions, or segregation elongated and made directional by working. Lamination defects may also occur in metal-powder compacts.

Machinability

The relative ease of machining a metal.

Mandrel

A device used to retain the cavity in hollow metal products during working.
A metal bar around which other metal may be cast, bent, formed or shaped.

Minimum all

Any wall having tolerances specified all on the plus side.

Modulus of Elasticity

A measure of the rigidity of metal. Ratio of stress, within proportional limit, to corresponding strain. Specifically, the modulus obtained in tension or compression is Young's modulus, stretch modulus or modulus of extensibility; the modulus obtained in torsion or shear is modulus of rigidity, shear modulus or modulus of torsion; the modulus covering the ratio of the mean normal stress to the change in volume per unit volume is the bulk modulus. The tangent modulus and secant modulus are not restricted within the proportional limit; the former is the slope of the stress-strain curve at a specified point; the latter is the slope of a line from the origin to a specified point on the stress-strain curve. Also called "elastic modulus" and "coefficient of elasticity".

Mechanical Properties

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

Mechanical Tubing

Used for a variety of mechanical and structural purposes, as opposed to pressure tubing, which is used to contain or conduct fluids or gases under pressure. It may be hot finished or cold drawn. It is commonly manufactured to consumer specifications covering chemical analysis and mechanical properties.

Metric System of Measurements

In the metric system of measurements, the principal unit for length is the meter(metre); the principal unit for volume, the liter (litre); and the principal unit for weight, the gram. The following prefixes are used for subdivisions and multiples: milli = 1/1000; centi = 1/100; deci = 1/10; deca = 10; hecto = 100; kilo = 1000. In abbreviations, the subdivisions are frequently used with a smaller letter and the multiples with a capital letter, although this practice is not universally followed everywhere the metric system is used. All the multiples and the subdivisions are not used commercially. Those ordinarily used for length are kilometer, meter, centimeter, and millimeter; for area, square meter, square centimeter and square millimeter; for volume, cubic meter, cubic decimeter (liter), cubic centimeter, and cubic millimeter. The most commonly used weights are the kilogram and gram. The metric system was legalized in the United States by an Act of Congress in 1866.

Normalizing: Heating a ferrous alloy to a suitable temperature above the transformation range and then cooling in air to a temperature substantially below the transformation range.
Non-Destructive Testing: Methods of detecting without destroying or permanently changing the material being tested. Test methods include ultrasonic, eddy current, flux leakage, magnetic particle, liquid, penetrant and X-ray.
Nitriding: Introducing nitrogen into a solid ferrous alloy by holding at a suitable temperature (below Ar1 for ferritic steels) in contact with a nitrogenous material, usually ammonia of molten cyanide of appropriate composition. Quenching is not required to produce a hard case.

Ovality: The difference between the maximum and minimum outside diameters of any one cross section of a tube. It is a measure of deviation from roundness.
Overaging: Aging under conditions of time and temperature greater than those required to obtain maximum change in a certain property, so that the property is altered in the direction of the initial value. See Aging
Oxidation: In its simplest terms, oxidation means the combination of any substance with oxygen. Scale developed during heat treatment is a form of oxidation.

Pitting Corrosion

Non-uniform corrosion usually forming small cavities in the metal surface.

Physical Properties

The properties, other than mechanical properties, that pertain to the physics of a material; for example, density, electrical conductivity, heat conductivity, thermal expansion.

Piercing

A seamless tubemaking method in which a hot billet is gripped and rotated by rolls or cones and directed over a piercer point which is held on the end of a mandrel bar.

Pipe

The central cavity formed by contraction in metal, especially ingots, during solidification.
The defect in wrought or case products resulting from such a cavity.
An extrusion defect due to the oxidized surface of the billet flowing toward the center of the rod at the back end.
A tubular metal product, cast or wrought.

Pitting

Forming small sharp cavities in a metal surface by nonuniform electro-deposition or by corrosion.

Preheating

Heating before some further thermal or mechanical treatment. For tool steel, heating to an intermediate temperature immediately before austenitizing. For some nonferrous alloys, heating to a high temperature for a long time, in order to homogenize the structure before working.

Quench Hardening: Hardening a ferrous alloy by austenitizing and then cooling rapidly enough so that some or all of the austenite transforms to martensite. The austenitizing temperature for hypoeutectoid steels is usually above Ac3 and for hypereutectoid steels usually between Ac1 and Accm.

Random Length: Tube produced to a permissible variation in length. (Frequently seven feet.)
Reduction of Area: Machining without regard to finish, usually to be followed by a subsequent operation.
Rough Machining: Machining without regard to finish, usually to be followed by a subsequent operation.

Shear Strength: The stress required to produce fracture in the plane of cross section, the conditions of loading being such that the directions of force and of resistance are parallel and opposite, although their paths are offset a specified minimum amount.
Seam: On the surface of metal, an unwelded fold or lap which appears as a crack, usually resulting from a defect obtained in casting or in working.
Specification: A document defining the measurements, tests, and other requirements to which a product must conform: typically covering chemistry, mechanical properties, tolerances, finish, reports, marking and packaging.
Stainless Steel: Steel containing 10.5% or more chromium. Other elements may be added (e.g., nickel, molybdenum) to achieve special properties.
Steel: An iron-base alloy, malleable in some temperature range 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 to be differentiated from two general classes of "irons": the cast irons, 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%; ingot iron contains considerably less.
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.
Superficial Rockwell Hardness Test: Form of Rockwell hardness test using relatively light loads which produce minimum penetration. Used for determining surface hardness or hardness of thin sections or small parts, or where large hardness impression might be harmful.

Tensile Strength: In tensile testing, the ratio of maximum load to original cross-sectional area. Also called ultimate strength.
Tolerance: Permissible variation.
Toughness: Ability of a metal to absorb energy and deform plastically before fracturing. It is usually measured by the energy absorbed in a notch-impact test, but the area under the stress-strain curve in tensile testing is also a measure of toughness.

Ultimate Strength: The maximum conventional stress, tensile, compressive, or shear, that a material can withstand.

Vickers Hardness Test: See Hardness

Work Hardening: Hardness developed in metal as a result of cold working. See Cold Working.

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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 metals exhibit a yield point. If there is a decrease in stress after yielding, a distinction may be made between upper and lower yield points.
Yield Strength: The stress at which a material exhibits a specified deviation from proportionality of stress. An offset of 0.2% is used for many metals.

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