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Metal Glossary



The process of rubbing, grinding, or wearing away by friction.

Acid Steel

Steel melted in a furnace with an acid bottom and lining and under a slag containing an excess of an acid substance such as silica.


The change a passive surface of a metal undergoes to become a chemically active state. Contrast with passivation.


In a metal or alloy, a change in properties that generally occurs slowly at room temperature and more rapidly at higher temperatures.

Air – Hardening Steel

A steel containing sufficient carbon in other alloying elements to harden fully during cooling in air or other gaseous mediums form 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 two inches or more in diameter. Same as self-hardening steel.


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, sulphur, and phosphorus) added to affect changes in the mechanical or physical properties.


Forming an aluminum or aluminum alloy coating on a metal by hot dipping, hot spraying, or diffusion.


Heating to and holding at a suitable temperature and then cooling at a suitable rate, for such purposes as reducing hardness, improving machine ability, facilitating cold working, producing a desire, micro structure, 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, recrystallizing annealing and spheroidizing. When applied to ferrous alloys, the term “ annealing “ , without qualification, implies full annealing. when applied to non ferrous alloys, the term “annealing” implies a heat treatment designed to soften a cold worked structure by recrystallizing or subsequent grain growth or to soften an age-harden alloy by causing a nearly complete precipitation of the second phase in relatively course form. Any process or annealing will usually reduce stresses , but if the treatment is applied the sole purpose of such relief, it should be designated stress relieving.

Atomic-Hydrogen Welding

Arc welding with heat from and arc between two tungsten or other suitable electrodes in a hydrogen atmosphere. The use of pressure and filler metal is optional.


Quenching a ferrous alloy from a temperature above the transformation range, in a medium having a rate of heat abstraction high enough to prevent the formation of high-temperature transformation products, and then holding the alloy, until transformation is complete, as a temperature below that of pearlite formation and above that of all martensite formation.


A solid solution of one or more elements in face-centered cubic iron.


Forming austenite by heating a ferrous alloy into the transformation range (partial austenitizing) or above the transformation range (complete austenitizing).


A decomposition product of austenite consisting of an aggregate of ferrite and carbide. In general, it forms at temperatures lower than those where very fine pearlite forms and higher than that where martensite begins to form on cooling. Its appearance is feathery if formed in the upper part of the temperature range; acicular, resembling tempered martensite, if formed in the lower part.

Banded Structure

A segregated structure of nearly parallel bands aligned in the direction of working.


The decarburized layer just beneath the scale that results from heating steel in an oxidizing atmosphere.

Basic Steel

Steel melted in a furnace with a basic bottom and lining and under a slag containing an excess of a basic substance such as a magnesia or lime.

Bearing Load

A compressive load supported by a member, usually a tube or a collar, along a line where contact is made with a pin, rivet, axle, or shaft.

Bearing Strength

The maximum bearing load at failure divided by the effective bearing area. In a pinned or riveted joint, the effective area is calculated as the product of the diameter of the hole and the thickness of the bearing member.

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.

Bent Radius

The inside radius of a bent section.

Bessemer Process

A process for making steel by blowing air through molten pig iron contained in a refractory lined vessel so as to remove by oxidation most of the carbon, silicon, and manganese.


A solid semi-finished round or square product that has been hot worked by forging, rolling or extrusion. An iron or steel billet has a minimum width or thickness of 1 1/2 in. and the cross-sectional area varies from 2 1/4 to 36 sq. in. For non-ferrous metals, it may also be a casting suitable for finished or semi-finished rolling or for extrusion.


A defect in metal, on or near the surface, resulting from the expansion of gas in a subsurface zone. Very small blisters are called “pinheads” or “pepper blisters”.


A semi-finished hot rolled product, rectangular in cross section, produced on a blooming mill for iron and steel, the width is not more than twice the thickness, and the cross-sectional area is usually not less than 36 sq. in. Iron and steel blooms are sometimes made by forging.

Blue Annealing

Heating hot rolled ferrous sheet in an open furnace to a temperature within the transformation range and then cooling in air in order to soften the metal. The transformation of a bluish oxide on the surface is incidental.

Blue Brittleness

Brittlenesss exhibited by some steels after being heated to some temperature within the range of 300° to 650°F, and more especially if the steel is worked at the elevated temperature. Killed steels are virtually free of this kind of brittleness.


Subjecting the scale-free surface of a ferrous alloy to the action of air, stream, or other agents at a suitable temperature, thus forming a thin blue film of oxide and improving the appearance and resistance to corrosion. NOTE: This term is ordinarily applied to sheet, strip, or finished parts. It is used also to denote the heating of springs after fabrication in order to improve their properties.

Box Annealing

Annealing a metal or alloy in a sealed container under conditions that minimize oxidization. In box annealing a ferrous alloy, the charge is usually heated slowly to a temperature below the transformation range, but sometimes above or within it, and then cooled slowly; this process is also called “close annealing” or “pot annealing”.

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.

Brittle Fracture

Fracture with little or no plastic deformation.


(1) Permanently damaging a metal or alloy by heating to cause either incipient melting or intergranular oxidation. See overheating. (2) In grinding getting the work hot enough to cause discoloration or to change the microstructure by tempering or hardening.


Smoothing surfaces through frictional contact between the work and some hard pieces of material such as hardened metal balls.


(1) Deviation from edge straightness usually referring to the greatest deviation of side edge from a straight line. (2) Sometimes used to denote crown in rolls where the center diameter has been increased to compensate for deflection caused by the rolling pressure.


A dished distortion in a flat or nearly flat surface sometimes referred to as “oil canning”.

Capped Steel

Semikilled steel cast in a bottle-top mold and covered with a cap fitting into the neck of the mold. The cap causes the top metal to solidify. Pressure is built up in the sealed-in molten metal and results in a surface condition much like that of rimmed steel.

Carbon Steel

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


Introducing carbon and nitrogen into a solid ferrous alloy by holding above Ac1 in an atmosphere that contains suitable gases such as hydrocarbons, carbon monoxide, and ammonia. The carbonitrided alloy is usually quench hardened.


Introducing carbon into a solid ferrous alloy by holding above Ac1 in contact with a suitable carbonaceous material, which may be a solid, liquid, or gas. The carburized alloy is usually quench hardened.

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.


A 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.

Centrifugal Casting

A casting made by pouring metal into a mold that is rotated or revolved.

Ceramic Tools

Cutting tools made from fused, sintered, or cemented metallic oxides.


(1) A beveled surface to eliminate an otherwise sharp corner. (2) A relieved angular cutting edge at tooth corner.

Charpy Test

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.

Chemical Milling

Removing metal stock by controlled selective chemical etching.

Chromadizing (Chromodizing, Chromatizing)

Forming an acid surface to improve paint adhesion on aluminum or aluminum alloys, mainly aircraft skins, by treatment with a solution of chromic acid.


A surface treatment at elevated temperature, generally carried out in pack, vapor, or salt bath, in which an alloy is formed by the inward diffusion of chromium into the base metal.

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.

Coil Breaks

Creases or ridges across a metal sheet transverse to the direction of coiling, occasionally occurring when the metal has been coiled hot and uncoiled cold.

Cold Short

A condition of brittleness existing in some metals at temperatures below the recrystallization temperature.

Cold Shut

(1) A discontinuity that appears on the surface of cast metal as a result of two streams of liquid meeting and failing to unite. (2) A portion of the surface of a forging that is separated, in part, from the main body of metal oxide.

Cold Work

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

Compressive Strength

The maximum compressive stress that a material is capable of developing based on original area of cross section. In the case of a material which fails in compression by shattering fracture, the compressive strength has a very definite value. In the case of materials which do not fail in compression by a shattering fracture, the value obtained for compressive strength is an arbitrary value depending upon the degree of distortion that is regarded as indicating complete failure of the material.

Continuous Casting

A casting technique in which an ingot, billet, tube, or other shape is continuously solidified while it is being poured, so that its length is not determined by mold dimensions.

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.

Covered Electrode

A filler-metal electrode, used in arc welding, consisting of a metal core wire with a relatively thick covering which provides protection for the molten metal from the atmosphere, improves the properties of the weld metal and stabilizes the arc. The covering is usually mineral or metal powders mixed with cellulose or other binder.


Time-dependent strain occurring under stress. The creep strain occurring at the diminishing rate is called primary creep; that occurring at a minimum and almost constant rate, secondary creep; that occurring at an accelerating rate, tertiary creep.

Creep Limit

(1) The maximum stress that will cause less then a specified quantity of creep in a given time. (2) The maximum nominal stress under which the creep strain rate decreases continuously with time under constant load and at a constant temperature. Sometimes used synonymously with creep strength.

Creep Strength

(1) The constant nominal stress that will cause a specified quantity of creep in a given time at a constant temperature. (2) The constant nominal stress that will cause a specified creep rate at a constant temperature.

Crevice Erosion

A type of concentration-cell corrosion; corrosion of a metal that is caused by the concentration of dissolved salts, metal ions, oxygen, or other gases, and such, in crevices or pockets remote from the principal fluid stream, with a resultant building up of differential cells that ultimately cause deep pitting.

Critical Cooling Rate

The minimum rate of continuous cooling just sufficient to prevent undesired transformations. For steel, the slowest rate at which it can be cooled from above the upper critical temperature to prevent the decomposition of austenite at any temperature above the Ms.

Critical Point

(1) The temperature or pressure at which a change in crystal structure phase, or physical properties occurs. Same as a transformation temperature. (2) In an equilibrium diagram, that specific value of composition, temperature and pressure, or combinations thereof, at which the phases of a heterogeneous systems are in equilibrium.

Cross Rolling

The rolling of a sheet so that the direction of rolling changed about 90° from the direction of the previous rolling.


A counter on a sheet or roll where the thickness of diameter increases from edge to center.

Cutting Speed

The linear or peripheral speed of relative motion between the tool and workpiece in the principal direction of cutting.


Introducing carbon and nitrogen into a solid ferrous alloy by holding above Ac1 in contact with molten cyanide or suitable composition. The cyanided alloy is usually quench hardened.

DC (Direct Chill) Casting

A continuous method of making ingots or billets for sheet or extrusion by pouring the metal into a short mold. The base of the mold is a platform that is gradually lowered while the metal solidifies, the frozen shell of metal acting as a retainer for the liquid metal below the wall of the mold. The ingot is usually cooled by the impingement of water directly on the mold or on the walls of the solid metal as it is lowered. The length of the ingot is limited by the depth to which the platform can be lowered: therefore, it is often called semicontinuous casting.


The loss of carbon from the surface of the ferrous alloy as a result of heating in a medium that reacts with the carbon at the surface.


(1) Forming recessed parts by forcing the plastic flow of metal in dies. (2) Reducing the cross section of wire or tubing by pulling it through a die. (3) A misnomer of tempering.

Drop Forging

A forging made with a drop hammer.

Drop Hammer

A forging hammer that depends on gravity for its force.


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.

Duralumin (obsolete)

A term formerly applied to the class of age-hardened aluminum copper alloys containing manganese, magnesium, or silicon.


The formation of scallops (ears) around the top edge of a drawn part caused by differences in the directional properties of the sheet metal used.

Eddy-Current Testing

Nondestructive testing method in which eddy-current flow is induced in the test object. Changes in the flow caused by variations in the object are reflected into a nearby coil or coils for subsequent analysis by suitable instrumentation and techniques.

Elastic Limit

The maximum stress to which a material may be subjected without any permanent strain remaining upon complete release of stress.


In tensile testing, the increase in gauge length, measured after fracture of the specimen within the gauge length, usually expressed as a percentage of the original gauge length.

Endurance Limit

Same as fatigue limit.


The phenomenon leading to fracture under repeated or fluctuating stresses having a maximum of value less than the tensile strength of the material. Fatigue fractures are progressive, beginning as minute cracks that grow under the action of fluctuating stress.

Fatigue Life

The number of cycles of stress that can be sustained prior to failure for a stated test condition.

Fatigue Limit

The maximum stress below which a material can presumably endure an infinite number of stress cycles. If the stress is not completely reversed, the value of the mean stress, the minimum stress or the stress ratio should be stated.

Fatigue Strength

The maximum stress that can be sustained for a specified number of cycles without failure, the stress being completely reversed within each cycle unless otherwise stated.


A solid solution of one or more elements in body-centered cubic iron. Unless otherwise designated (for instance, chromium ferrite), the solute is generally assumed to be carbon. On some equilibrium diagrams there are two ferrite regions separated by an austenite area. The lower area is alpha ferrite; the upper, delta ferrite. If there is no designation, alpha ferrite is assumed.

Ferrite Banding

Parallel bands of free ferrite aligned in the direction of working. Sometimes referred to as ferrite streaks.

Fiber Stress

Local stress through a small area (a point of line) on a section where the stress is not uniform, as in a beam under a bending load.


Short, discontinuous internal fissures in ferrous metals attributed to stresses produced by localized transformations and decreased solubility of hydrogen during cooling after hot working. In a fractured surface, flakes appear as bright silvery areas; on an etched surface they appear as short discontinuous cracks. Also called “shatter cracks” and “snowflakes”.

Flame Annealing

Annealing in which the heat is applied directly by a flame.

Flame Hardening

Quench hardening in which the heat is applied directly by a flame.


(1) In forging, the excess metal forced between the upper and lower dies. (2) In die casting, the fin of metal which results from leakage between the mating die surfaces. (3) In resistance butt welding, a fin formed perpendicular to the direction of applied pressure.

Flash Welding

A resistance butt welding process in which the weld is produced over the entire abutting surface by pressure and heat, the heat being produced by electric arcs between the members being welded.


Metal in sheet form less then 0.006" in thickness.


Plastically deforming metal, usually hot, into desired shapes with compressive force, with or without dies.

Fracture Test

Breaking a specimen and examining the fractured surface with the unaided eye or with a low-power microscope to determine such things as composition, grain size, case depth, soundness, and presence of defects.

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

Annealing a ferrous alloy by austenitizing and then cooling slowly through the transformation range. The ausenitizing temperature to hypoeutectoid steel is usually above Ac3; and for hypereutectoid steel, usually between Ac1 and Accm.


Developing a condition on the rubbing surface of one or both mating parts where excessive friction between high spots results in localized welding with substantial spalling and a further roughening of the surface.

Galvanic Corrosion

Corrosion associated with the current of a galvanic cell consisting of two dissimilar conductors in an electrolyte or two similar conductors in dissimilar electrolytes. Where the two dissimilar metals are in contact, the resulting action is referred to as “couple action”.

Grain Size

(1) For metals, a measure of the areas or volumes of grains in a polycyrstalline 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.

Granular Fracture

A type of irregular surface produced when metal is broken, that is characterized by a rough, grain-like appearance as differentiated from a smooth silky, fibrous, type. It can be sub-classified into transgranular and intergranular forms. This type of fracture is frequently called crystalline fracture, but the inference that the metal has crystallized is not justified.


Annealing a ferrous alloy in such a way that some or all of the carbon is precipitated as graphite.

Gray Cast Iron

A cast iron that gives a gray fracture due to the presence of flake graphite. Often called gray iron.

Grinding Cracks

Shallow cracks formed in the surface of relatively hard materials because of excessive grinding heat or the high sensitivity of the material.

Gun Drill

A drill, usually with one or more flutes and coolant passages through the drill body, used for deep hole drilling.

Hammer Forging

Forging in which the work is deformed by repeated blows. Compare with press forging.

Hard Chromium

Chromium deposited for engineering purposes, such as increasing the wear resistance of sliding metal surfaces, rather than as a decorative coating. It is usually applied directly to basis metal and customarily thicker than a decorative deposit.


In a ferrous alloy, the property that determines the depth and distribution of hardness induced by quenching.


Increasing the hardness by suitable treatment, usually involving heating and cooling.

Heat-Affected Zone

That portion of the base metal which was not melted during brazing, cutting, or welding, but whose microstructure and physical properties were altered by the heat.


Holding at high temperature to eliminate or decrease chemical segregation by diffusion.


Removing stock generally on the internal cylindrical surface of a workpiece with an abrasive stick mounted in a holder.

Hot Shortness

Brittleness in metal in the hot forming range.

Hot Top

(1) A reservoir thermally insulated or heated, to hold molten metal on top of a mold to feed the ingot or casting as it contracts on solidifying to avoid having “pipe” or voids.

Immersed Scanning

In ultrasonics, a planned, systematic movement of the beam relative to the object being inspected, the search unit being coupled to this object through a column of liquid. In most cases the object and the search unit are submerged in water.

Impact Energy (Impact Value)

The amount of energy required to fracture a material, usually measured by means of an Izod or Charpy test. The type of specimen and testing conditions affect the values and therefore should be specified.

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 braking the specimen by a single blow, as in the Charpy or Izod test.


Nonmetallic materials in a solid metallic matrix.

Induction Hardening

Quench hardening in which the heat is generated by electrical induction.

Inert-Gas Shielded-Arc Welding

Arc welding in an inert gas such as argon or helium.

Ingot Iron

Commercially pure open-hearth iron.

Investment Casting

(1) Casting metal into a mold produced by surrounding (investing) an expendable pattern with a refractory slurry that sets at room temperature after which the wax, plastic, or frozen mercury pattern is removed through the use of heat. Also called precision casting, or lost-wax process. (2) A casting made by the process.

Izod Test

A pendulum type of single blow impact test in which the specimen, usually notched, is fixed at one end and broken by a falling pendulum. The energy absorbed, as measured by a subsequent rise of the pendulum, is a measure of impact strength or notch toughness.

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.


A load of 1000 lbs.


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.


A surface defect, appearing as a seam, caused by folding over hot metal, fins, or sharp corners and then rolling or forging them into a surface, but not welding them.

Light Metal

One of the low-density metals such as aluminum, magnesium, titanium, beryllium, or their alloys.

Longitudinal Direction

The principal direction of flow in worked metal.

Low-Hydrogen Electrode

A covered arc welding electrode that provides an atmosphere around the arc and molten weld metal which is low in hydrogen.


The relative ease in machining a metal.

Machinability Index

A relative measure of the machinability of an engineering material under specified standard conditions.

Magnetic-Particle Inspection

A nondestructive method of inspection for determining the existence and extent of possible defects in ferromagnetic materials. Finely divided magnetic particles, applied to the magnetized part, are attached to and outline the pattern of any magnetic-leakage fields created by discontinuities.


Quenching an austenitized ferrous alloy in a medium at a temperature in the upper part of the martensite range, or slightly above that range, and holding that in the medium until the temperature throughout the alloy is substantially uniform. The alloy is then allowed to cool in the air through the martensite range.


(1) In an alloy, a metastable transitional structure intermediate between two allotropic modifications whose abilities to dissolve a given solute differ considerably, the high-temperature phase having the greater solubility. The amount of the high temperature phase transformed to martensite depends to a large extent upon the temperature attained in cooling, there being a rather distinct beginning temperature. (2) A metastable phase of steel, formed by a transformation of austenite below the Ms (or Ar”) temperature. It is an interstitial supersaturated solid solution of carbon in iron having a body-centered tetragonal lattice. Its microstructure is characterized by an acicular, or needle-like, pattern.

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.

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”.


Introducing nitrogen into a solid ferrous alloy by holding at a suitable temperature (below Ac1 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.


Heating a ferrous alloy to a suitable temperature above the transformation range and then cooling in the air to a temperature substantially below the transformation range.

Open-Hearth Furnace

A reverberatory melting furnace with a shallow hearth and a low roof. The flame passes over the charge in the hearth, causing the charge to be heated both by direct flame and radiation from the roof and sidewalls of the furnace. In ferrous industry, the furnace is regenerative.

Orange Peel

A pebble-grain surface which develops in forming of metals having coarse grains.


Heating a metal or alloy to such a high temperature that its properties are impaired. When the original properties cannot be restored by further heat treating, by mechanical working, or by combination of working and heat treating, the overheating is know as burning.

Oxygen-Free Copper

Electrolytic copper free from cuprous oxide, produced without the use of residual metallic or metalloidal deoxidizers.

Pancake Forging

quickly with a minimum of tooling. It usually requires considerable machining to attain the finish size.


A lamellar aggregate of ferrit and cementite, often occurring in steel and case iron.


Mechanical working of metal by hammer blows or shot impingement.

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.


Removing surface oxides from metals by chemical or electrochemical reaction.

Pig Iron

(1) High-carbon iron made by reduction of iron ore in the blast furnace. (2) Cast iron in the form of pigs.


(1) The central cavity formed by contraction in metal, especially ingots, during solidification. (2) The defect in wrought or cast products resulting from such a cavity. (3) An extrusion defect due to the oxidized surface of the billet flowing towards the center of the rod at the back end. (4) A tubular metal product, cast or wrought.


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


Producing a smooth surface finish on metal by rapid succession of blows delivered by highly polished dies or by a hammer designed for the purpose, or by rolling in a planishing mill.


Heating weldments immediately after welding, for tempering, for stress relieving, or for providing a controlled rate of cooling to prevent formation of a hard or brittle structure.

Precipitation Hardening

Hardening caused by the precipitation of a constituent from a supersaturated solid solution.


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.

Press Forging

Forging metal, usually hot, between dies in a press.


Metal products, principally sheet and plate, of the highest quality and free from visible defects.

Process Annealing

In the sheet and wire industries, heating a ferrous alloy to a temperature close to, but below, the lower limit of the transformation range and then cooling in order to soften the alloy for further cold working.

Proof Stress

(1) The stress that will cause a specified small permanent set in a material. (2) A specified level of stress to be applied to a member or structure to indicate its ability to withstand service loads.

Proportional Limit

The maximum stress at which strain remains directly proportional to stress.

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.


(1) The change from one crystal structure to another, as occurs on heating or cooling through a critical temperature. (2) The formation of a new, strain-free grain structure from that existing in cold worked metal, usually accomplished by heating.

Recyrstallization Temperature

The approximate minimum temperature at which complete recrystallization of a cold worked metal occurs within a specified time.

Reduction of Area

(1) Commonly, the difference , expressed as a percentage of original area, between the original cross-sectional area of a test tensile specimen and the minimum cross sectional area measured after complete separation. (2) The difference, expressed as a percentage of original area, between original cross-sectional area and that straining the specimen.

Refractory Metal

A metal having an extremely high melting point. In the board sense, it refers to metals having melting points above the range of iron, cobalt, and nickel.

Residual Stress

Stress present in a body that is free of external forces or thermal gradients.

Rimmed Steel

A low-carbon steel containing sufficient iron oxide to give a continuous evolution of carbon monoxide while the ingot is solidifying, resulting in a case or rim of metal virtually free of voids. Sheet and strip products made from the ingot have very good surface quality.

Roller Leveling

Leveling by passing flat stock through a machine having a series of small diameter staggered rolls.

Rough Machining

Machining without regard to finish, usually to be followed by a subsequent operation.


A defect consisting of a flat volume of metal joined to a casting through a small area. It is usually set in a depression, a flat side being separated from the metal of the casting proper by a thin layer of sand.


Forming a thick layer of oxidation products on metals at high temperatures.

Scalped Extrusion Ingot

A cast, solid, or hollow extrusion ingot which has been machined on the outside surface.


Cutting surface areas of metal objects, ordinarily by using a gas torch. The operation permits surface defects to be cut from ingots, billets, or the edges of plate that is to be beveled for butt welding.


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.<

Secondary Hardening

Tempering certain alloy steels at certain temperatures so that the resulting hardness is greater than that obtained by tempering the same steel at some lower temperature for the same time.


Non-uniform distribution of alloying elements, impurities or microphases.

Semikilled Steel

Steel that is completely deoxided and contains sufficient dissolved oxygen to react with the carbon to form carbon monoxide to offset solidification shrinkage.

Sendzimir Mill

A mill having two work rolls of 1 to 2 1/2-in. diam. each, backed up by two rolls twice that diameter and each of these backed up by bearings on a shaft mounted eccentrically so that rotating it increases the pressure between bearings and back up rolls.

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.

Shell Molding

Forming a mold from thermosetting resin-bonded sand mixtures brought in contact with preheated (300° to 500°F) metal patterns, resulting in a form shell with a cavity corresponding to the outline of the pattern. Also called “Croning Process”.

Shielded-Arc Welding

Arc welding in which the arc and the weld metal are protected by a gaseous atmosphere, the products of decomposition of the electrode covering, or a blanket of fusible flux.


A form of brittleness in metal. It is designed as “cold”, “hot”, and ”red”, to indicate the temperature range in which the brittleness occurs.


Diffusing silicon into solid metal, usually steel, at an elevated temperature.


A piece or strip of metal produced to a suitable thickness, width, and edge configuration, from which pipe or tubing is made.

Slack Quenching

The process of hardening steel by quenching from the austenitizing temperature at a rate slower that the critical cooling rate for the particular steel resulting in incomplete hardening and the formation of one or more transformation products in addition to or instead of martensite.

Solid Solution

A single solid homogeneous crystalline phase containing two or more chemical species.

Solution Heat Treatment

Heating an alloy to a suitable temperature, holding at that temperature long enough to allow one or more constituents to enter solid solution, and then cooling rapidly enough to hold the constituents in solution. The alloy is left in a supersaturated, unstable state, and may subsequently exhibit quench aging.


The cracking and flaking of particles out of a surface.


Heating and cooling to produce a spheroidal or globular form of carbide in steel. Spheroidizing methods frequently used are: 1 Prolonged holding at a temperature just below Ae1. 2 Heating and cooling alternately between temperatures that are just below Ae1. 3 Heating to a temperature above Ae1 or Ae3 and then cooling very slowly in the furnace or holding at a temperature just below Ae1. 4 Cooling at a suitable rate from the minimum temperature at which all carbide is dissolved to prevent the reformation of a carbide network, and then reheating in accordance with methods 1 or 2 above. (Applicable to hypereutectoid steel containing a carbide network.)

Spot Welding

Welding of lapped parts in which fusion is confined to a relatively small circular area. It is generally resistance welding, but may also be gas-shielded tungsten-arc, gas-shielded metal-arc, or submerged-arc welding.

Stabilizing Treatment

Any treatment intended to stabilize the structure of an alloy of the dimensions of a part. (1) Heating austenitic stainless steels that contain titanium, columbium, or tantalum to a suitable temperature below that of a full anneal in order to inactivate the maximum amount of carbon by precipitation as a carbide of titanium, columbium, or tantalum. (2) Transforming retained austenite in parts made from tool steel. (3) Precipitating a constituent from a nonferrous solid solution to improve the workability, to decrease the tendency of certain alloys to age harden at room temperature, or to obtain dimensional stability.


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 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, 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%; ingot iron contains considerably less.

Sterling Silver

A silver alloy containing at least 95.2% Ag, the remainder being unspecified but usually copper.


A measure of the change in the size or shape of a body, referred to its original size or shape. “Linear Strain” is the change per unit length of a linear dimension. “True Strain” (or “natural strain”) is the natural logarithm of the ratio of the length at the moment of observation to the original gauge length. “Conventional strain” is the linear strain referred to the original gauge length. “Shearing strain” (or “shear strain”) is the change in angle (expressed in radians) between two lines originally at right angles. When the term strain is used alone it usually refers to the linear strain in the direction of the applied stress.


Force per unit area, often thought as force acting through a small area within a plane. It can be divided into components, normal and parallel to the plane, called “normal stress” and “shear stress”, respectively. “True stress” denotes the stress where force and area measured at the same time. “Conventional stress”, as applied to tension and compression tests, is force divided by the original area. “Nominal stress” is the stress computed by simple elasticity formulas, ignoring stress raisers and disregarding plastic flow; in a notch bond test, for example, it is bending moment divided by minimum section modulus.

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.

Stress-Corrosion Cracking

Failure by cracking under combined action or corrosion and stress, either external (applied) or internal (residual). Cracking may be either intergranular, or transgranular, depends on metal and corrosive medium.

Stress-Rupture Test

A tension test performed at constant temperature, the load being held at such a level as to cause rupture. Also known as “creep-rupture test”.

Stretcher Leveling

Leveling where a piece of metal is gripped at each end and subjected to a stress higher than its yield strength to remove wrap and distortion. Sometimes called patent leveling.

Stretcher Straightening

A process for straightening rod, tubing, and shapes by the application of tension at the ends of the stock. The products are elongated a definite amount to remove warpage.

Stretcher Strains

Elongated markings that appear on the surface of some materials when deformed just past the yield point. These markings lie approximately parallel to the direction of maximum shear stress and the result of localized yielding. Same as Luders lines.


An alloy developed for very high temperature service where relatively high stresses (tensile, thermal, vibratory, and shock) are encountered and where oxidation resistance is frequently required.

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.

Tack Welds

Small scattered welds made to hold parts of a weldment in proper alignment while the final welds are being made.


(1) In heat treatment, reheating hardened steel or hardened cast iron to some temperature below the eutectoid temperature for the purpose of decreasing the hardness and increasing toughness. The process also is sometimes applied to normalized steel. (2) In tool steels, “temper” is sometimes used, but unadvisedly, to denote the carbon content. (3) In nonferrous alloys and in some ferrous alloys (steels that cannot be hardened by heat treatment), the hardness and strength produced by mechanical or thermal treatment, or both, and characterized by a certain structure, mechanical properties, or reduction in area during cold working.

Temper Brittleness

Brittleness that results when certain steels are held within, or are cooled slowly, through a certain range of temperature below the transformation range. The brittleness is revealed by notched-bar impact tests at or below room temperature.


Reheating a quench-hardened or normalized ferrous alloy to a temperature below the transformation range and then cooling at any rate desired.

Tensile Strength

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


A twisting action resulting in shear stresses and strains.


Ability of a metal to absorbed 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.

Transformation Ranges (Transformation Temperature)

Those ranges of temperature within which austenite forms during heating and transform during cooling. The two ranges are distinct, sometimes overlapping but never coinciding. The limiting temperatures of the ranges depend on the composition of the alloy and on the rate of change of temperature, particularly during cooling.

Transition Temperature

(1) An arbitrarily defined temperature within the temperature range in which metal fracture characteristics determined usually by notched tests are changing rapidly such as from primarily fibrous (shear) to primarily crystalline (cleavage) fracture. Commonly used definitions are (transition temperature for 50% cleavage fracture”, “10-ft-lb transition temperature”, and “transition temperature for half maximum energy”. (2) Sometimes also used to denote the arbitrarily defined temperature in a range in which the ductility changes rapidly with temperature.


Literally, “across”, usually signifying a direction or plane perpendicular to the direction of working.


A type of boring where an annular cut is made into a solid material with the coincidental formation of a plug or solid cylinder.

Ultimate Strength

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

Ultrasonic Frequency

A frequency, associated with elastic waves, that is greater than the highest audible frequency, generally regarded as being higher that 15 kc per sec.

Ultrasonic Waves

Waves of ultrasonic frequency. They include longitudinal, transverse, surface, and standing waves.

Universal Mill

A rolling mill in which rolls with a vertical axis roll the edges of the metal stock between some of the passes through the horizontal rolls.

Vacuum Melting

Melting in a vacuum to prevent contamination from air, as well as to remove gases already dissolved in the metal; the solidification may also be carried out in a vacuum or at low pressure.

Wrought Iron

A commercial iron consisting of slag (iron silicate) fibers entrained in a ferrite matrix.

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 and strain. An offset of 0.2% is used for many metals.

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