Steel Metals Glossary

Age Hardening — Hardening by aging, usually after rapid cooling or cold working. Hardening is a result of a precipitation process, often submicroscopic, which occurs when a super-saturated solid solution is naturally aged at atmospheric temperatures or artificially aged in some specific range of elevated temperature. Aging occurs more rapidly at higher temperatures. Synonymous with precipitation hardening.

Air Frame Tubing — This stainless steel tubing is produced for aircraft structural parts. This tubing is made to special surface quality, mechanical properties, and other characteristics required by Military Specifications (MIL-T- . . . .) and SAE Aeronautical Materials Specifications (AMS . . .).

Air Hardening — Heating a suitable grade of steel with high hardenability above the critical temperature range and then cooling in air for the purpose of hardening.

Aircraft Quality — Is a steel which has a special cleanliness rating determined by magnetic particle testing. The terms “Aircraft Quality” and “Magnaflux Quality” are considered synonymous.

Alloy Steel — All steels contain carbon and small amounts of silicon, sulfur, manganese, and phosphorus. Steels which contain intentional additions of elements other than these, or in which silicon and manganese are present in large amounts for the express purpose of improving or altering any of the physical or mechanical properties of the steel, are termed alloy steels.

Annealing — Annealing is a heat treatment process which usually involves a relatively slow cooling after holding the material for some time at the annealing temperature. The purpose of the annealing treatment may include the following: (a) to induce softness; (b) to remove internal stresses; (c) to refine the grain size; (d) to modify physical and/or mechanical properties; (e) to produce a definite microstructure; (f) to improve machinability. It is generally desirable to use more specific terms in describing the heat treatment to be used, e.g., finish anneal, or full anneal.

Austenitic Stainless Steel— Low carbon, iron-chromium-nickel stainless alloys containing more than 16 percent chromium, with sufficient nickel to provide an austenitic structure at normal temperatures. These alloys cannot be hardened by heat treatment, but can be hardened by cold working. They are normally non-magnetic, but can be slightly magnetic depending upon composition and amount of cold working.

Average Wall — A tube whose wall thickness is permitted to range over or under the specified nominal wall measurement within certain defined tolerances.

Bearing Quality Steels — Steels suitable for use in balls, rollers, and races of high quality anti-friction bearings.

Billet — As used in the manufacture of seamless tubes, a round bar with dimensions and other characteristics suitable for piercing into tubing.

Bloom — A semi-finished piece of steel, resulting from the rolling or forging of an ingot. A bloom is square or not more than twice as wide as thick, and usually not less than 36 square inch in cross-sectional area.

Borescope — An optical device used for inspecting under low magnification the inside surface of tubes.

Bright Anneal — Carried out in a controlled furnace atmosphere, so that surface oxidation is reduced to a minimum and the tube surface remains relatively bright.

Brinell Hardness — A measure of the degree of a material’s resistance to indentation. It is usually determined by measuring resistance to penetration.

Camber — The amount of curvature or deviation from exact straightness over any specified length of tubing.

Capped Steel — Semi-killed steel which has characteristics similar to those of rimmed steels but to a degree intermediate between rimmed and killed steel. The capping operation limits the time of gas evolution and prevents the formation of an excessive number of gas voids within the ingot.

Carbide Precipitation — The phenomenon of carbides coming out of a solid solution, occurring in stainless steel when heated into the range of 800-1600 degrees Fahrenheit.

Carbon Steel — A steel consisting of essentially iron, carbon, manganese, and silicon. Carbon steel has no minimum content required for aluminum, chromium, cobalt, columbium, molybdenum, nickel, titanium, tungsten, vanadium, zirconium, or any other element added to obtain alloying effect. Small quantities of certain residual elements are considered incidental.

Carburizing — Adding carbon to the surface of iron-base alloys by heating the metal below its melting point in contact with carbonaceous solids, liquids, or gases. Desired hardness and toughness properties are developed in the high carbon “case” by quenching and tempering.

Case Hardening — A heat treatment in which the surface (case) of an iron-base alloy is made harder than the interior (core). Any of the following methods may be employed: flame hardening, induction hardening, carburizing, cyaniding, or nitriding.

Check Analysis — An analysis of the metal after it has been rolled or forged into semi-finished or finished forms. It is not a check on the ladle analysis, but is a check against the chemistry ordered.

Cleanup — The amount of metal removal required to obtain desired dimensions and complete removal of inherent surface imperfections.

Coefficient of Thermal Expansion — A physical property value representing the change in length per unit length, the change in area per unit area or the change in volume per unit volume per one degree increase in temperature.

Cold Drawing — A process in which tubing 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.

Cold Reduction — The reduction of sectional dimensions of a tube by any of a number of types of cold-working operations.

Cold Rolled Tube — ERW tubing exhibiting the surface of cold rolled strip.

Cold Sinking — Similar to cold drawing, except that the tube is drawn through a die, but without an internal mandrel. Usually used only for making heavy wall or small tubing where drawing over a mandrel is impractical. Only outside diameter is closely controlled.

Cold Working — Permanent plastic deformation of a metal below its recrystallization temperature.

Conditioning — The removal of surface defects (seams, laps, pits, etc.) from steel. Conditioning is usually done when the steel is in semi-finished condition (bloom, billet, slab). It may be accomplished, after an inspection, by chipping, scarfing, grinding, or machining.

Corrosion — Chemical or electrochemical deterioration of a metal or alloy.

Creep Strength — The constant nominal stress that will cause a specified quantity of creep in a given time at a constant temperature. It is a measure of a tube’s ability to withstand prolonged stress or load without significant continuous deformation. In steels, it is an important factor only at elevated temperatures.

Crown — Crown, in plates, sheet, or strips, is characterized by a greater thickness in the middle than at the edges. It may be caused by a deflecting (bending) of the rolls or by worn rolls.

Cut Length — Refers to tubing ordered to a specified length and permitting a tolerance of a standardized fraction of an inch over but nothing under the specified length.

Cyaniding — A process in which an iron-base alloy is heated in contact with a cyanide salt so that the surface absorbs carbon and nitrogen. Cyaniding is followed by quenching and tempering to produce a case with a desired combination of hardness and toughness.

Dead Soft — A heat treatment applied to achieve maximum softness and ductility.

Decarburization — The loss of carbon from the surface of an iron-base alloy as the result of heating in an environment which removes the carbon. In medium or high carbon steels, decarburization leads to a pronounced lowering of the fatigue limit.

Density — The mass per unit volume of a substance, usually expressed in the tubing industry in pounds per cubic inch.

Drawing — Synonymous with TEMPERING, which is preferable.Drawn cold drawn tubing and has a scale free cold drawn surface.

Ductility — The ability of a tube to deform plastically. Frequently, elongation during tensile testing is used as a measurement of this property.

Dye Penetrant Inspection — Non-destructive test employing dye or fluorescent chemical and sometimes black light to detect surface defects.

Eccentricity — The displacement of the I.D. of the tube with respect to its O.D. Eccentricity results in the variation of wall thickness normal to seamless tubing.

Eddy Current — Non-destructive testing method using eddy current flow for the purpose of recognizing a discontinuity in the piece being tested.

Elastic Limit — A measure of the maximum stress that may be applied to a tube without leaving a permanent deformation or strain after the stress is released.

Electric Furnace Process — One of the common methods used for melting and refining stainless and some alloy steels. It involves the use of electric power as the sole source of heat, thereby preventing contamination of the steel by impurities in the fuel as in other melting processes.

Electric Resistance Welded Tubing — Tubing made from strip 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.

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 gage length.

Endurance Limit — The maximum stress below which a material can presumably endure an infinite number of stress cycles.

Etch Test — Exposure of a specimen to acid attack for the purpose of disclosing the presence of foreign matter, defects, segregation, pattern, or flow lines.

Extrusion — Production process in which steel is forced by compression through a die into solids (round or special shape) or through a die and over a mandrel to form a tubular shape.

Ferritic Stainless Steel — The designation used for certain straight chromium steels which exhibit microstructures consisting mainly of ferrite at ordinary temperatures. Ferritic stainless steels are divided into two classifications: hardenable, and non-hardenable. When rapidly cooled from elevated temperatures the non-hardenable grades (ferritic) have a ferritic microstructure. The hardenable grades (martensitic) will exhibit a martensitic microstructure when rapidly cooled.

Finish — In the steel industry, refers to the type of surface condition desired or existing in the finished product.

Finish Anneal — Heating of cold-worked tubing to a temperature below the lower critical, usually 950 degrees F. Generally this treatment will relieve peak stresses without altering hardness to any extent.

Finish Machine Size — Normally specified in terms of the maximum machined O.D. and the minimum machined I.D. as applied to tubular parts. Finish machine size represents the size of the part as it comes from the final machining operation. From this size the tube mill can calculate a tube size which will be guaranteed to cleanup upon machining.

Flame Hardening — A process of heating the surface layer of an iron-base alloy above the transformation temperature range by means of the flame of a high temperature torch, followed by quenching.

Flanged End — In a flanged end, the tube has been belled or expanded and a flange turned over until the wall of the tube end is at right angles to the wall of the tube.

Flash-In Tubing — Welded tubing which still retains the I.D. bead or flash formed during the welding operation. It can be furnished in either the as-welded, sunk, or heat-treated condition.

Flash-Removed — Welded tubing from which the I.D. flash formed during the welding operation has been removed by some mechanical method. It can be furnished in either the as-welded, sunk, or heat-treated condition.

Forging — Used as a general term to describe the rolling, pressing, or hammering of steel which displaces the metal under compression by a locally applied force, usually at hot working temperatures.

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.

Full Anneal — Heating to a temperature above the upper critical and slow cooling below the lower critical.

Gages, Gauges — A measurement of thickness There are various standard gages such as United States Standard Gage (USS), Galvanized Sheet Gage (GSG), Birmingham Wire Gage (BWG).

Grain Size — A measure of the size of individual metallic crystals usually expressed as an average. Grain size is reported as a number in accordance with procedures described in ASTM grain size specifications. Apparent Ferrite Grain Size is the average of the size of the ferrite grains as microscopically viewed in the normalized or annealed condition. Austenitic Grain Size, which is usually measured by the McQuaid-Ehn method, represents the austenitic grain size of a material at a prescribed temperature above the upper critical, frequently 1700 degrees F. For austenitic stainless steels the grain size does not change upon cooling and is that observed microscopically at room temperature.

Gun Metal Finish — Welded tubing normalized, annealed, or stress relieved in a controlled atmosphere furnace which exhibits a gun metal finish.

Hardenability — The property in steel that determines the depth and distribution of hardness induced by cooling from a suitable elevated temperature. The hardness can vary with the cooling rate.

Hardness — A measure of the degree of a material’s resistance to indentation. It is usually determined by measuring resistance to penetration.

Heat Treatment — 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.

Hot Finished Seamless Stainlss Tubing — Tubing produced by rotary piercing, extrusion, and other hot working processes without subsequent cold finishing operations.

Hot Rolled Tube — ERW tubing exhibiting the pickled surface of hot rolled strip.

Hot Rolled ERW Tubing — As welded electric resistance welded tubing made from hot rolled strip or sheet.

Hot Shortness (Red Shortness) — A condition encountered in some metals wherein ductility is lessened at hot working temperatures.

Hot Working — The mechanical working of metal above the recrystallization temperature.

Huey Test — A corrosion test for stainless steels. The weight loss per unit area is measured after each of five 48-hour boils in 65 percent nitric acid. The test results are calculated to and reported as the average corrosive rate of the five boils in inches per month (ipm) corrosion rates. The test is used to determine the suitability of a material for nitric acid service. Since most of the weight loss is due to intergranular attach, the Huey test is commonly used as an indication of the resistance of a stainless steel to intergranular corrosion.

Hydrostatic Test — A test in which a liquid, usually water, under pressure, is used internally to detect and locate leaks in a tube of a fabricated structure.

Impact Testing — There are several methods of determining the toughness of a steel, but the Izod and Charpy notched-bar tests are used quite widely. In both tests, the samples are cooled or heated to the desired test temperature, then struck once with a pendulum which fractures the specimen. The energy required to fracture the specimen, the impact strength, is measured in foot-pounds.

Inclusions — particles of nonmetallic impurities, usually oxides, sulphides, silicates, which are mechanically held in metals and alloys during solidification.

Ingot Mold — A mold in which ingots are cast. Molds may be circular, square, or rectangular in shape, with walls of various thickness. Some molds are of larger cross section at the bottom; others are larger at the top.

Integral Finned Tubing — Tubing with raised surface fins formed from the wall of the tube itself.

Intergranular Corrosion — A type of electrochemical corrosion that progresses preferentially along the grain boundaries of an alloy, usually because the grain boundary regions contain material anodic to the central regions of the grain.

Internal Soundness — Refers to condition of inside of material — lack of defects, pipe, segregation, non-uniformity of composition.

Isothermal Anneal — Austenitizing an heat treatable alloy and cooling to and holding at a temperature at which austenite transforms to a relatively soft ferrite-carbide aggregate.

Jominy 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 an agent such as silicon or aluminum to reduce the free oxygen content so that no harmful reaction occurs between carbon and oxygen during solidification.

Ladle — A large vessel into which molten steel or molten slag is received and handled.

Ladle Analysis — Chemical analysis obtained from a sample taken during the pouring of the steel.

Laminations — Defects resulting from the presence of blisters, seams, or foreign inclusions aligned parallel to the worked surface of a metal.

Lap — A surface defect caused from folding the surface of an ingot, bloom, or bar during hot rolling operations and then rolling or forging the fold into the surface.

Machinability — A measure of the relative ease with which steel may be machined.

Machining — The deliberate removal of metal by one or more of several processes.

Macroetch — A testing procedure for locating and identifying porosity, pipes, bursts, unsoundness, inclusions, segregations, carburization, flow lines from hot working, etc. Surface of the test piece should be reasonably smooth or even polished. After applying a suitable etching solution, the structure developed by the action of the reagent may be observed with a microscope.

Magnaflux Test — This test is conducted by suitably magnetizing the material and applying a prepared wet or dry magnetic powder of fluid which adheres to it along lines of flux leakage. It shows the existence of surface and slightly subsurface non-uniformities.

Malleability — The property that determines the ease of deforming a metal when the material is subjected to rolling or hammering. The more malleable metals can be hammered or rolled into thin sheet more easily than others.

Mandrel — (1) A device used to retain the cavity in hollow metal products during working. (2) A metal bar around which other metal may be cast, bent, formed, or shaped.

Maraging — A process of improving the mechanical strength of certain ferrous alloys. The name was derived from two hardening reactions: martensite and aging. The maraging strengthening mechanism is based on the age hardening (precipitation hardening) of extra-low carbon martensite.

Martensite — A constituent in quenched steel formed without diffusion and only during rapid cooling below the martensitic start (Ms) temperature. Martensite is the hardest of the transformation products of austenite.

Maximum and Minimum — The dimensions resulting after applying the proper tolerances to the nominal dimensions.

McQuaid-Ehn Test — A special test for revealing the austenitic grain size of ferritic steels when the steel is heated to 1700 degrees F. and carburized. There are eight standard McQuaid-Ehn grain sizes — sizes 5 to 8 are considered fine grain and sizes under 5 are considered coarse grain.

Mechanical Properties — Those properties of a material that reveal the elastic and in-elastic reaction when force is applied, or that involve the relationship between stress and strain — for example, the modulus of elasticity hardness, tensile strength, and fatigue limit. These properties have often been referred to as “physical properties”, but the term “mechanical properties” is correct.

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.

Medium Anneal — Subjecting tubing to a subcritical temperature to obtain specific mechanical properties.

Metallography — The science dealing with the constitution and structure of metals and alloys as revealed by the unaided eye or by such tools as low powered magnification, optical microscope, electron microscope, and diffraction or X-ray techniques.

Metric System of Measurements — In the metric system of measurements, the principal unit for length is the meter; the principal unit for volume, the liter; and the principal unit for weight, the gram. The following prefixes are used for sub-divisions and multiples: milli = 1/1000; centi = 1/100; deci = 1/10; deca = 10; hecto = 100; kilo = 1000. In abbreviations, the sub-divisions 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 sub-divisions 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.

Microcleanliness — Refers to the extent of quality of nonmetallic inclusions observed by examination under a microscope.

Micro-Etch — Micro-etching is used for the examination of a sample under a microscope. Etching solutions tend to reveal structural details because of preferential chemical attack on the polished surface.

Minimum Wall— Any wall having tolerances specified all on the plus side. Generally, the lightest wall permitted within specified tolerances. A “minimum wall tube” is one whose wall thickness is not permitted to fall below the specified nominal measurement.

Modulus of Elasticity — The ratio of stress applied to a material and the resulting strain occurring at the stresses below the elastic limit.

Moment of Inertia — Also known as the “Second Moment” relates to the product of a distance squared multiplied by an area. “I” is always positive and has the dimension of length to the fourth power. It is widely used in engineering equations to calculate bending stress and maximum allowable loads as well as other important values.

Nitriding — A process of case hardening in which a ferrous alloy, usually of special composition, is heated in an atmosphere of cracked ammonia or in contact with nitrogenous material to produce surface hardening without quenching by the absorption of nitrogen, Nitriding is normally conducted in a range from 900 degrees to 1000 degrees F.

Nominal — The theoretical or stated value of the O.D., I.D., or wall dimension as specified by the customer.

Non-Destructive Testing — Methods of detecting defects without destroying or permanently changing the material being tested. Test methods include ultrasonic, eddy current, magnetic particle, liquid, penetrant, and X-ray.

Normalize — Normalizing is a process which consists of heating to a temperature approximately 100 degrees F. above the upper critical temperature and cooling in still air.

Notch Brittleness — Susceptibility of a material to brittle fracture at points of stress concentration.

Notch Sensitivity — A measure of the reduction in strength of a metal caused by the presence of stress concentration.

O.D. — Outside Diameter. Specified in inches and fractions of an inch, or inches and decimals of an inch.

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.

Oxidation — In its simplest terms, oxidation means the combination of any substance with oxygen. Scale developed during heat treatment is a form of oxidation.

Oxide — A compound consisting of oxygen and one or more metallic elements.

Passivate — The changing of the chemically active surface of a metal to a much less active state by the application of the proper chemical treatment or by applying an induced electrical current and voltage for cathodic or anodic protection from corrosion. An example of chemically passivating stainless steel would be to immerse stainless in a hot solution of approximately 10 to 20 percent by volume nitric acid and water.

Photomicrograph — A photographic reproduction of an object magnified more than ten times used to show microstructure characteristics of steel.

Physical Properties — Those properties not specifically related to reaction to external forces. These include such properties as density, electrical resistance, coefficient of thermal conductivity.

Pickled — Tubing has had the scale from hot fabrication or heat treatment removed by one of several types of acid solutions.

Pickling — Use of solutions, usually acids to remove surface oxides from a tube may also be used to produce a desired surface finish.

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.

Porosity — Unsoundness caused in cast metals by the presence of blowholes or shrinkage cavities.

Porthole Drawn — To produce structural aluminum pipe and tube. A conventional extrusion press is used with special dies called porthole or bridge dies. These dies are made with a fixed mandrel that is part of the die and held in place by a bridge. The aluminum is extruded around the bridge and is fused or “pressure welded” back together as it passes out through the orifice of the die.

Pressure Tubing — Tubing produced for the purpose of containing or conducting fluids or gases under pressure.

Profilometer — An instrument used for measuring surface finish. The vertical movements of a stylus as it traverses the surface are amplified electromagnetically and recorded (or indicated) as the surface roughness.

Proof Stress — The load per square inch of the original cross-sectional area which, when removed, has caused a permanent elongation not exceeding a defined amount (usually 0.0001 inch per inch of gage length). A test of this type is more commonly used in Europe than in this country, where it largely has been replaced by yield strength measurements.

Pyrometer — An instrument of any of various types used for measuring temperatures.

Quenching — A process of rapid cooling from an elevated temperature, by contact with liquids or gases.

Radius of Gyration — This is square root of the Moment of Inertia divided by the area of the section you are interested in. It is useful for comparative purposes to evaluate various sizes and sections, but is generally not used in engineering equations. Radius of Gyration has units of length.

Random Length — Tubing produced to a permissible variation in length. (Frequently seven feet.)

Recrystallization — The reversion of distorted cold worked microstructure to a new, strain-free structure during annealing.

Reduction of Area — A measure of ductility determined in a tensile test. It is the maximum reduction, at the fracture, of the cross section area of a specimen, as compared with its original cross section area.

Rimmed Steel — A steel which forms a relatively clean outer layer (rim) during solidification. Sheet and strip made from such steel has good surface quality and is frequently used for ERW tubing.

Rockwell Hardness — A measure of the degree of a material’s resistance to indentation. It is usually determined by measuring resistance to penetration.

Roto-Rock (Tube Reducing or Rockrite) — A method of cold finishing tubing in which a machine rolls or rocks a split die over a tube. The tube is supported on the inside by a tapered mandrel.

Seam — A tight but unwelded imperfection on the surface of a wrought metal product.

Section Modulus — The ratio I/c is called the Section Modulus. “I” is the Moment of Inertia and “c” relates to the outer dimension of a section. Section Modulus is normally designated “Z”. It is quantity used in formulas when determining the size beam or tube to be used to withstand a designated maximum stress. The units of Section Modulus are inches to the third power.

Segregation — Nonuniform distribution of alloying elements, impurities, or microphases.

Semi-Killed Steel — Steel that is incompletely deoxidized to permit the evolution of carbon monoxide, thereby offsetting solidification shrinkage.

Sensitization — Sensitization of stainless steel is defined as a susceptibility to preferential grain boundary attack. Material which exhibits grain boundary carbide precipitation may or may not be sensitized.

Soak — To hold an ingot, slab, bloom, billet, or other piece of steel in a hot furnace, pit, or chamber to secure uniform temperature.

Soaking Pit — A furnace or pit for the heating of ingots of steel to make their temperature uniform prior to rolling or forging.

Soft Anneal — A high temperature stress relieving anneal usually performed in the temperature range of 1250 to 1350 degrees F. This anneal reduces hardness and strength of a cold worked steel to achieve near maximum softness.

Solution Anneal— Heating steel into a temperature range wherein certain elements or compounds dissolve, followed by cooling at a rate sufficient to maintain these elements in solution at room temperature. The expression is normally applied to stainless and other special steels.

Special Smooth I.D. — A cold drawn tube in which special attention is paid to the internal surface. Depth of pits and scores in I.D. are guaranteed to be below published maximum depths. Microinch finish is guaranteed in ERW tubes.

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.

Spheroidizing Anneal — A general term which refers to heat treatments that promote spheroidal or globular forms of carbide in carbon or alloy steels.

Spinning — A type of forming (hot or cold) which involves rotating a tube at high speed against fixed or rolling tools for the purpose of altering shape, size, etc.

Stabilizing Anneal — A treatment applied to austenitic stainless steels wherein carbides of various forms are deliberately precipitated. Sufficient additional time is provided at the elevated temperature to diffuse chromium into the areas adjacent to the carbides (usually grain boundaries). This treatment is intended to lessen the chance of intergranular corrosion.

Stress Corrosion Cracking — Cracking of metals under combined action of temperature, corrosion, and stress. The stress can be either applied or residual. Austenitic stainless steels are especially susceptible to cracking in chloride containing environments.

Stress Relieving — A heat treatment which reduces internal residual stresses that have been induced in metals by casting, quenching, welding, cold working, etc. The metal is soaked at a suitable temperature for a sufficient time to allow readjustment of stresses. The temperature of stress relieving is always below the transformation range. Finish anneal, medium anneal, and soft anneal (sub-critical) describe specific types of stress relief anneals.

Strip — A flat-rolled steel product which serves as the raw material for welded tubing.

Sunk or Sink Drawn — Tubing drawn through a die with no inside mandrel to control I.D. or wall thickness.

Swaged — A mechanical reduction of the cross sectional area of a metal, performed hot or cold by forging, pressing, or hammering.

Tempering — Reheating quenched or normalized steel to a temperature below the transformation range (lower critical) followed by any desired rate of cooling.

Tensile Strength — The maximum load per square inch of original cross sectional area carried during a tension test to failure of the specimen. This term is preferred over the formerly-used ultimate strength.

Thermal Conductivity — A measure of the ease with which heat is transmitted through a material.

Toughness — A measure of ability to absorb energy and deform plastically before fracturing.

Transformation Temperature — The temperature at which a change in phase occurs in steels. The term is sometimes used to denote the limiting temperature of a transformation range.

Transverse Tension Test — A tension test for evaluating mechanical properties of a material in a direction transverse to that of rolling.

Turning — A method for removing the surface from a work piece by bringing the cutting edge of a tool against it while the piece or tool is rotated.

Ultrasonic Testing — The method of detecting defects in tubes or welds by passing high frequency sound waves into a material then monitoring and evaluating the reflected signals.

Upsetting — A metal-working operation similar to forging, generally used to thicken the ends of tubes prior to threading.

Wall — Wall Thickness or Gage. Specified in either fractions or decimals of an inch or by a “wire gage” number. In the United States, the most common gage used for tubing is the “Birmingham” iron wire gage, designated “B.W.G.”.

Work Hardening — Hardness developed in metal as a result of cold working. See cold working.

Yield Point — The first stress in a material measured as load per unit of original cross sectional area at which an increase in strain occurs without an increase in stress.

Yield Strength — The stress at which a material exhibits a specified deviation from proportionality of stress and strain. An offset of 0.2 percent is most frequently used