Terminology relating to corrosion resistant metals, performance, properties, testing and microstructure
ABRASIVE – Small particles of material that are propelled at high velocity to impact a surface during abrasive blast cleaning.
ABRASIVE BLAST CLEANING – Cleaning and roughening of a surface produced by the high-velocity impact of an abrasive that is propelled by the discharge of pressurized fluid from a blast nozzle or by a mechanical device such as a centrifugal blasting wheel. (Also referred to as Abrasive Blasting.)
ACID – A substance which releases hydrogen ions when dissolved in water. Most acids will dissolve the common metals and will react with a base to form a neutral salt and water.
ACTIVE – The negative direction of electrode potential. (2) A state of a metal that is corroding without significant influence of reaction product.
ALKALI – A group of water soluble mineral compounds, usually considered to have moderate strengths as bases (as opposed to the caustic or strongly basic hydroxides, although this differentiation is not always made). In general, the term is applied to bicarbonate and carbonate compounds when they are present in the water or solution.
AMPHOTERIC METAL – A metal that is susceptible to corrosion in both acid and alkaline environments.
ANAEROBIC – Free of air or un-combined oxygen.
ANION – A negatively charged ion that migrates through the electrolyte toward the anode under the influence of a potential gradient.
ANODE – The electrode of an electrochemical cell at which oxidation occurs. Electrons flow away from the anode in the external circuit. Corrosion usually occurs and metal ions enter the solution at the anode.
ANODE CORROSION EFFICIENCY – The ratio of the actual corrosion (mass loss) of an anode to the theoretical corrosion (mass loss) calculated from the quantity of electricity that has passed between the anode and cathode using Faraday’s law.
ANODIC INHIBITOR – A chemical substance that prevents or reduces the rate of the anodic or oxidation reaction.
ANODIC POLARIZATION – The change of the electrode potential in the noble (positive) direction caused by current across the electrode/electrolyte interface. [See Polarization.]
ANODIC PROTECTION – Polarization to a more oxidizing potential to achieve a reduced corrosion rate by the promotion of passivity.
ANTIFOULING – Preventing fouling.
ATMOSPHERIC CORRISION – The gradual degradation or alteration of a material by contact with substances present in the atmosphere, such as oxygen, carbon dioxide, water vapour, and sulphur and chlorine compounds.
AUSTENITIC STEEL – A steel whose microstructure at room temperature consists predominantly of austenite.
BARRIER COATING – (1) A coating that has a high resistance to permeation of liquids and/or gases. (2) A coating that is applied over a previously coated surface to prevent damage to the underlying coating during subsequent handling
BEACH MARKS – The characteristic markings on the fracture surfaces produced by fatigue crack propagation (also known as clamshell marks, conchoidal marks, and arrest marks).
BRITTLE FRACTURE – Fracture with little or no plastic deformation.
CARBON STEEL – (1) Alloy of carbon and iron containing up to 2% carbon and up to 1.65% manganese and residual quantities of other elements, except those intentionally added in specific quantities for de-oxidation (usually silicon and/or aluminium). (2) An iron-based alloy containing carbon (usually less than 2.0%) and manganese (usually not less than 0.25%) with no specified minimum quantity for any alloying element other than manganese, silicon, and copper, and that contains only an incidental amount of any element other than carbon, silicon, manganese, copper, sulphur, and phosphorus.
CARBURIZING – The absorption and diffusion of carbon into iron or an iron-based alloy in contact with a suitable carbonaceous environment at elevated temperature.
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 are carburizing, cyaniding, carbo-nitriding, nitriding, induction hardening, and flame hardening.
CASTING – Metal that is obtained at or near its finished shape by the solidification of molten metal in a mold.
CATHODE – The electrode of an electrochemical cell at which reduction is the principal reaction. Electrons flow toward the cathode in the external circuit.
CATHODIC CORROSION – Corrosion resulting from a cathodic condition of a structure, usually caused by the reaction of an amphoteric metal with the alkaline products of electrolysis.
CATHODIC INHIBITOR – A chemical substance that prevents or reduces the rate of the cathodic or reduction reaction.
CATHODIC POLARIZATION – The change of the electrode potential in the active (negative) direction caused by current across the electrode/electrolyte interface.
CATHODIC PROTECTION – A technique to reduce the corrosion of a metal surface by making that surface the cathode of an electrochemical cell.
CATION – A positively charged ion that migrates through the electrolyte toward the cathode under the influence of a potential gradient.
CAVITATION – The formation and rapid collapse of cavities or bubbles within a liquid which often results in damage to a material at the solid/liquid interface under conditions of severe turbulent flow.
CEMENTITE – Microstructural constituent of steels composed of iron carbide (Fe3C).
CEMENTATION – The introduction of one or more elements into the surface layer of a metal by diffusion at high temperature. (Examples of cementation include carburizing [introduction of carbon], nitriding [introduction of nitrogen], and chromizing [introduction of chromium].)
CHEVRON PATTERN – A V-shaped pattern on a fatigue or brittle-fracture surface. The pattern can also be one of straight radial lines on cylindrical specimens.
CHLORIDE STRESS CORROSION CRACKING – Cracking of a metal under the combined action of tensile stress and corrosion in the presence of chlorides and an electrolyte (usually water).
COLD WORKING – Deforming metal plastically under conditions of temperature and strain rate that induce strain hardening, usually, but not necessarily, conducted at room temperature.
COMPRESSIVE STRENGTH – The maximum compressive stress a material is capable of withstanding without fracture or excessive flattening based on the load applied to its original cross-sectional area.
CONDUCTIVITY – (1) A measure of the ability of a material to conduct an electric charge. It is the reciprocal of resistivity. (2) The current transferred across a material (e.g., coating) per unit potential gradient.
CORROSION – The deterioration of a material, usually a metal, that results from a reaction with its environment.
CORROSION FATIGUE – Fatigue-type cracking of metal caused by 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 stress alone or the corrosive environment alone.
CORROSION INHIBITOR – A chemical substance or combination of substances that, when present in the environment, prevents or reduces corrosion.
CORROSION POTENTIAL (Ecorr) -The potential of a corroding surface in an electrolyte relative to a reference electrode under open-circuit conditions (also known as rest potential, open-circuit potential, or freely corroding potential).
CORROSION RATE – The rate at which corrosion proceeds.
CORROSION RESISTANCE – Ability of a material, usually a metal, to withstand corrosion in a given system.
CORROSIVENESS – The tendency of an environment to cause corrosion.
CREEP – Time-dependent strain occurring under stress.
CREEP STRENGTH – That stress which, when applied to a material at a specific elevated temperature, will cause a specified amount of elongation.
CREVICE CORROSION – Localized corrosion of a metal surface at, or immediately adjacent to, an area that is shielded from full exposure to the environment because of close proximity of the metal to the surface of another material.
CRITICAL HUMIDITY – The relative humidity above which the atmospheric corrosion rate of some metals increases sharply.
CRITICAL PITTING POTENTIAL (EP, EPP) – The lowest value of oxidizing potential (voltage) at which pits nucleate and grow. The value depends on the test method used.
CURRENT – (1) A flow of electric charge. (2) The amount of electric charge flowing past a specified circuit point per unit time, measured in the direction of net transport of positive charges. (In a metallic conductor, this is the opposite direction of the electron flow.)
CURRENT DENSITY – The current to or from a unit area of an electrode surface.
DEALLOYING – The selective corrosion of one or more components of a solid solution alloy
DENDRITE – A crystal that has a treelike branching pattern, being most evident in cast metals, slowly cooled through the solidification range.
DEPOSIT ATTACK – Corrosion occurring under or around a discontinuous deposit on a metallic surface (also known as poultice corrosion).
DEZINCIFICATION – A corrosion phenomenon resulting in the selective removal of zinc from copper-zinc alloys. (This phenomenon is one of the more common forms of de-alloying.)
DIFFERENTIAL AERATION CELL – An electrochemical cell, the electromotive force of which is due to a difference in air (oxygen) concentration at one electrode as compared with that at another electrode of the same material.
DISSIMILAR METALS – Different metals that could form an anode-cathode relationship in an electrolyte when connected by a metallic path.
DUCTILITY – The ability of a material to withstand significant plastic deformation prior to fracture. (It is often measured by the elongation or reduction in the cross-sectional area of a tensile test specimen.)
DUPLEX STAINLESS STEEL – Stainless steel whose microstructure at room temperature consists primarily of a mixture of austenite and ferrite (also called austenitic/ferritic stainless steel).
ELASTIC DEFORMATION – Changes of dimensions of a material upon the application of a stress within the elastic range. Following the release of an elastic stress, the material returns to its original dimensions without any permanent deformation.
ELASTIC LIMIT – The maximum stress to which a material may be subjected without retention of any permanent deformation after the stress is removed.
ELASTICITY – The property of a material that allows it to recover its original dimensions following deformation by a stress below its elastic limit.
Electric Arc Furnace – An economical method of steelmaking that is energized by an electric arc flowing between two bottom electrodes. Furnace charges consist of purchased scrap.
ELECTRICAL ISOLATION – The condition of being electrically separated from other metallic structures or the environment.
ELECTROCHEMICAL CELL – A system consisting of an anode and a cathode immersed in an electrolyte so as to create an electrical circuit. The anode and cathode may be different metals or dissimilar areas on the same metal surface.
ELECTRODE – A conductor used to establish contact with an electrolyte and through which current is transferred to or from an electrolyte.
ELECTRODE POTENTIAL – The potential of an electrode in an electrolyte as measured against a reference electrode. (The electrode potential does not include any resistance losses in potential in either the electrolyte or the external circuit. It represents the reversible work to move a unit of charge from the electrode surface through the electrolyte to the reference electrode.)
ELECTROLYTE – A chemical substance containing ions that migrate in an electric field.
EMBRITTLEMENT – Loss of ductility of a material resulting from a chemical or physical change.
ENVIRONMENT – The surroundings or conditions (physical, chemical, mechanical) in which a material exists.
ENVIRONMENTAL CRACKING – Brittle fracture of a normally ductile material in which the corrosive effect of the environment is a causative factor.
The following terms have been used in the past in connection with environmental cracking but are now obsolete and should not be used:
EROSION – The progressive loss of material from a solid surface due to mechanical interaction between that surface and a fluid, a multicomponent fluid, or solid particles carried with the fluid.
EROSION-CORROSION – A conjoint action involving corrosion and erosion in the presence of a moving corrosive fluid or a material moving through the fluid, leading to accelerated loss of material.
ETCH – A roughened surface produced by chemical, electrochemical or mechanical means. To dissolve unevenly a part of the surface of a material to highlight microstructure in metallography.
EXFOLIATION CORROSION – Localized subsurface corrosion in zones parallel to the surface that result in thin layers of un-corroded metal resembling the pages of a book.
FATIGUE – The phenomenon leading to fracture of a material under repeated or fluctuating stresses having a maximum value less than the tensile strength of the material.
FATIGUE STRENGTH – The maximum stress that can be sustained for a specified number of cycles without failure.
FERRITE – The body-centred cubic crystalline phase of iron-based alloys.
FERRITIC STEEL – A steel whose microstructure at room temperature consists predominantly of ferrite.
FILIFORM CORROSION – Corrosion that occurs under a coating in the form of randomly distributed thread-like filaments.
FOULING – An accumulation of deposits. This includes accumulation and growth of marine organisms on a submerged metal surface and the accumulation of deposits (usually inorganic) on heat exchanger tubing.
FRACTURE MECHANICS – A quantitative analysis for evaluating structural reliability in terms of applied stress, crack length, and specimen geometry.
FREE MACHINING – 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.
FRETTING CORROSION – Deterioration at the interface of two contacting surfaces under load which is accelerated by their relative motion.
GALVANIC ANODE – A metal that provides sacrificial protection to another metal that is more noble when electrically coupled in an electrolyte. This type of anode is the electron source in one type of cathodic protection.
GALVANIC CORROSION – Accelerated corrosion of a metal because of an electrical contact with a more noble metal or non-metallic conductor in a corrosive electrolyte.
GALVANIC COUPLE – A pair of dissimilar conductors, commonly metals, in electrical contact in an electrolyte.
GALVANIC CURRENT – The electric current between metals or conductive non-metals in a galvanic couple.
GALVANIC SERIES – A list of metals and alloys arranged according to their corrosion potentials in a given environment.
GENERAL CORROSION – Corrosion that is distributed more or less uniformly over the surface of a material.
GRAIN – An individual crystal in a solid metal or alloy in which the atoms are arranged in an orderly pattern.
GRAIN BOUNDARY – The irregular junction of two adjacent grains in a metal.
GRAPHITISATION – The formation of graphite in iron or steel, usually from decomposition of iron carbide at elevated temperatures. [Should not be used as a term to describe graphitic corrosion.]
HARDNESS – Resistance of metal to plastic deformation, usually by indention.
HEAT-AFFECTED ZONE – That portion of the base metal that is not melted during brazing, cutting, or welding, but whose microstructure and properties are altered by the heat of these processes.
HEAT TREATMENT – Heating and cooling a solid metal or alloy in such a way as to obtain desired properties. Heating for the sole purpose of hot working is not considered heat treatment.
HIGH-TEMPERATURE HYDROGEN ATTACK – A loss of strength and ductility of steel by high-temperature reaction of absorbed hydrogen with carbides in the steel, resulting in decarburization and internal fissuring.
HOT WORKING – Deforming metal plastically at such a temperature and strain rate that recrystallization takes place simultaneously with the deformation, thus avoiding any strain hardening.
HYDROGEN BLISTERING – The formation of subsurface planar cavities, called hydrogen blisters, in a metal resulting from excessive internal hydrogen pressure. Growth of near-surface blisters in low-strength metals usually results in surface bulges.
HYDROGEN EMBRITTLEMENT – A loss of ductility of a metal resulting from absorption of hydrogen.
HYDROGEN-INDUCED CRACKING – Stepwise internal cracks that connect adjacent hydrogen blisters on different planes in the metal, or to the metal surface (also known as stepwise cracking).
HYDROGEN STRESS CRACKING – Cracking that results from the presence of hydrogen in a metal in combination with tensile stress. It occurs most frequently with high-strength alloys.
IMPACT RESISTANCE – Ability of a material to resist deformation from impact.
IMPINGEMENT CORROSION – A form of erosion-corrosion generally associated with the local impingement of a high-velocity, flowing fluid against a solid surface.
INCLUSION – A non-metallic phase such as an oxide, sulphide, or silicate particle in a metal.
INTERDENDRITIC CORROSION – Corrosive attack of cast metals that progresses preferentially along paths between dendrites.
INTERGRANULAR CORROSION – Preferential corrosion at or along the grain boundaries of a metal (also known as intercrystalline corrosion).
INTERGRANULAR STRESS CORROSION CRACKING – Stress corrosion cracking in which the cracking occurs along grain boundaries.
INTERNAL OXIDATION – The formation of isolated particles of oxidation products beneath the metal surface.
ION – An electrically charged atom or group of atoms.
IRON ROT – Deterioration of wood in contact with iron-based alloys.
KNIFE-LINE ATTACK – Intergranular corrosion of an alloy along a line adjoining or in contact with a weld after heating into the sensitization temperature range.
LINING – A coating or layer of sheet material adhered to or in intimate contact with the interior surface of a container used to protect the container against corrosion by its contents and/or to protect the contents of the container from contamination by the container material.
LIQUID METAL CRACKING – Cracking of a metal caused by contact with a liquid metal.
LOW-ALLOY STEEL – Steel with a total alloying element content of less than approximately 5%, but more than specified for carbon steel.
LOW-CARBON STEEL – Steel having less than 0.30% carbon and no intentional alloying additions.
MARTENSITE – A hard supersaturated solid solution of carbon in iron characterized by an acicular (needle-like) microstructure.
MARTENSITIC STEEL – Steel in which a microstructure of martensite can be attained by quenching at a cooling rate fast enough to avoid the formation of other microstructures.
METALLISING – The coating of a surface with a thin metal layer by spraying, hot dipping, or vacuum deposition.
MICROSTRUCTURE – The structure of a prepared surface of a metal as revealed by a microscope at a magnification exceeding 25x.
MILL SCALE – The oxide layer formed during hot fabrication or heat treatment of metals.
MODULUS OF ELASTICITY – A measure of the stiffness or rigidity of a material. It is actually the ratio of stress to strain in the elastic region of a material. If determined by a tension or compression test, it is also called Young’s Modulus or the coefficient of elasticity.
NITRIDING – Case hardening process in which nitrogen is introduced into the surface of metallic materials (most commonly ferrous alloys). Typical processes include, but are not limited to, liquid nitriding, gas nitriding, and ion or plasma nitriding.)
NOBLE – The positive direction of electrode potential, thus resembling noble metals such as gold and platinum.
NOBLE METAL – (1) A metal that occurs commonly in nature in the free state. (2) A metal or alloy whose corrosion products are formed with a small negative or a positive free-energy change.
NOBLE POTENTIAL – A potential more cathodic (positive) than the standard hydrogen potential.
NORMALISING – Heating a ferrous alloy to a suitable temperature above the transformation range (austenitising), holding at temperature for a suitable time, and then cooling in still air to a temperature substantially below the transformation range.
NOTCH PROPAGATION – The increase in depth or length of a cut, nick, or scratch in a material when the material is stressed.
OPEN-CIRCUIT POTENTIAL – The potential of an electrode measured with respect to a reference electrode or another electrode in the absence of current.
OXIDATION – (1) Loss of electrons by a constituent of a chemical reaction. (2) Corrosion of a metal that is exposed to an oxidising gas at elevated temperatures.
PASSIVATION – A reduction of the anodic reaction rate of an electrode involved in corrosion.
PASSIVE – (1) The positive direction of electrode potential. (2) A state of a metal in which a surface reaction product causes a marked decrease in the corrosion rate relative to that in the absence of the product.
PATINA – A thin layer of corrosion product, usually green, that forms on the surface of metals such as copper and copper-based alloys exposed to the atmosphere.
pH – The negative logarithm of the hydrogen ion activity written as: pH = –log10 (aH+), where aH+ = hydrogen ion activity = the molar concentration of hydrogen ions multiplied by the mean ion-activity coefficient.
PICKLING – (1) Treating a metal in a chemical bath to remove scale and oxides (e.g., rust) from the surface. (2) Complete removal of rust and mill scale by acid pickling, duplex pickling, or electrolytic pickling.
PITTING – Localized corrosion of a metal surface that is confined to a small area and takes the form of cavities called pits.
PITTING FACTOR – The ratio of the depth of the deepest pit resulting from corrosion divided by the average penetration as calculated from mass loss.
PLASTIC DEFORMATION – Permanent deformation caused by stressing beyond the elastic limit.
PLASTICITY – The ability of a material to deform permanently (non-elastically) without fracturing.
POSTWELD HEAT TREATMENT – Heating and cooling a weldment in such a way as to obtain desired properties.
PRECIPITATION HARDENING – Hardening caused by the precipitation of a constituent from a supersaturated solid solution.
QUENCHING – Rapid cooling in the heat treating of metals, the step of cooling metals rapidly in order to obtain desired properties; most commonly accomplished by immersing the metal in oil or water.
REDUCTION – Gain of electrons by a constituent of a chemical reaction.
REFERENCE ELECTRODE – An electrode whose open-circuit potential is constant under similar conditions of measurement, which is used for measuring the relative potentials of other electrodes.
RELATIVE HUMIDITY – The ratio, expressed as a percentage, of the amount of water vapour present in a given volume of air at a given temperature to the amount required to saturate the air at that temperature.
RESIDUAL STRESS – Stress present in a component free of external forces or thermal gradients.
RESISTIVITY – (1) The resistance per unit length of a substance with uniform cross section. (2) A measure of the ability of an electrolyte (e.g., soil) to resist the flow of electric charge (e.g., cathodic protection current). Resistivity data are used to design a ground bed for a cathodic protection system.
RISER – (1) That section of pipeline extending from the ocean floor up to an offshore platform. (2) The vertical tube in a steam generator convection bank that circulates water and steam upward.
RUST – Corrosion product consisting of various iron oxides and hydrated iron oxides. (This term properly applies only to iron and ferrous alloys.)
RUST BLOOM – Discoloration indicating the beginning of rusting.
SACRIFICIAL PROTECTION – Reduction of corrosion of a metal in an electrolyte by galvanically coupling it to a more anodic metal (a form of cathodic protection).
SCALING – (1) The formation at high temperatures of thick corrosion-product layers on a metal surface. (2) The deposition of water-insoluble constituents on a metal surface.
SENSITISING HEAT TREATMENT – A heat treatment, whether accidental, intentional, or incidental (as during welding), that causes precipitation of constituents (usually carbides) at grain boundaries, often causing the alloy to become susceptible to intergranular corrosion or intergranular stress corrosion cracking.
SHOT PEENING – Inducing compressive stresses in the surface layer of a material by bombarding it with a selected medium (usually steel shot) under controlled conditions.
SIGMA PHASE – An extremely brittle Fe-Cr phase that can form at elevated temperatures in Fe-Cr-Ni and Ni-Cr-Fe alloys.
SLIP – A deformation process involving shear motion of a specific set of crystallographic planes.
SLOW STRAIN RATE TECHNIQUE – An experimental technique for evaluating susceptibility to environmental cracking. It involves pulling the specimen to failure in uniaxial tension at a controlled slow strain rate while the specimen is in the test environment and examining the specimen for evidence of environmental cracking.
SOLUTION HEAT TREATMENT – Heating a metal to a suitable temperature and holding at that temperature long enough for one or more constituents to enter into solid solution, then cooling rapidly enough to retain the constituents in solution.
SOUR GAS – A gaseous environment containing hydrogen sulphide and carbon dioxide in hydrocarbon reservoirs. Prolonged exposure to sour gas can lead to hydrogen damage, sulphide-stress cracking, and/or stress-corrosion cracking in ferrous alloys.
SPALLING – The spontaneous chipping, fragmentation, or separation of a surface or surface coating.
STAINLESS STEEL – Steel containing 10.5% or more chromium, possibly with other elements added to secure special properties.
STANDARD ELECTRODE POTENTIAL – The reversible potential for an electrode process when all products and reactions are at unit activity on a scale in which the potential for the standard hydrogen reference electrode is zero.
STRESS CORROSION CRACKING – Cracking of a material produced by the combined action of corrosion and tensile stress (residual or applied).
STRESS RELIEVING (THERMAL) – Heating a metal to a suitable temperature, holding at that temperature long enough to reduce residual stresses, and then cooling slowly enough to minimize the development of new residual stresses.
SULPHIDATION – The reaction of a metal or alloy with a sulphur-containing species to produce a sulphur compound that forms on or beneath the surface of the metal or alloy.
SULPHIDE STRESS CRACKING – Cracking of a metal under the combined action of tensile stress and corrosion in the presence of water and hydrogen sulphide (a form of hydrogen stress cracking).
SUPER DUPLEX STAINLESS STEEL – Stainless steel whose microstructure at room temperature consists primarily of a mixture of austenite and ferrite (also called austenitic/ferritic stainless steel), with a chromium content typically >25%.
TARNISH – Surface discoloration of a metal resulting from formation of a film of corrosion product.
TEMPERING – Heat treatment by heating to a temperature below the lower critical temperature for the purpose of decreasing the hardness and increasing the toughness of hardened steel, hardened cast iron, and sometimes normalized steel.
TENSILE STRENGTH – In tensile testing, the ratio of maximum load to original cross-sectional area nb. also called ultimate tensile strength.
TENSILE STRESS – A stress that causes two parts of an elastic body, on either side of a typical stress plane, to pull apart.
TENSION – The force or load that produces elongation.
THERMAL SPRAYING – A group of processes by which finely divided metallic or non-metallic materials are deposited in a molten or semi-molten condition to form a coating.
UNIFORM CORRISION – Corrosion that proceeds at about the same rate over a metal surface.
ULTIMATE STRENGTH – The maximum stress that a material can sustain.
VACUUM DEGASSING – A process by which the amount of carbon in the steel is reduced by exposing liquid steel to a very low vacuum environment. Carbon combines in the process with oxygen to form carbon monoxide, which is removed in the process. The result is a steel that contains lower levels of carbon and thus, has higher formability.
WELD DECAY – Intergranular corrosion, usually of stainless steel or certain nickel-base alloys, that occurs as the result of sensitization in the heat-affected zone during the welding operation.
WELD METAL – That portion of a weldment that has been molten during welding.
WORKING ELECTRODE – The test or specimen electrode in an electrochemical cell.
WROUGHT – Metal in the solid condition that is formed to a desired shape by working (rolling, extruding, forging, etc.), usually at an elevated temperature.
YIELD POINT – The stress on a material at which the first significant permanent or plastic deformation occurs without an increase in stress. In some materials, particularly annealed low-carbon steels, there is a well-defined yield point from the straight line defining the modulus of elasticity.
YIELD STRENGTH – The stress at which a material exhibits a specified deviation from the proportionality of stress to strain. The deviation is expressed in terms of strain by either the offset method (usually at a strain of 0.2%) or the total-extension-under-load method (usually at a strain of 0.5%).