A
Absorbing. Thermo mechanical treatment of steel in the metastable austenitic condition below the recrystallization temperature followed by quenching to obtain martensite and/or bainite.
Acm, A.,A3, A4. Same as Aecm, Ael, Ae3, and Ae4.
ACem, ACt, AC3, AC4. Defined under transformation temperature.
Acicular ferrite. A highly sub structured nonequiaxed ferrite that forms upon continuous cooling by a mixed diffusion and shear mode of transformation that begins at a temperature transformation range for upper bainite. It is distinguished from bainite in that it has a limited amount of carbon available; thus, there is only a small amount of carbide present.
Aecm, Aet, Ae3, AC4. Defined under transformation temperature.
Aerated bath nitriding. A type of liquid nitriding in which air is pumped through the molten bath creating agitation and increased chemical activity.
Age hardening. Hardening by aging, usually after rapid cooling or cold working. See also aging.
Age softening. Spontaneous decrease of strength and hardness that takes place at room temperature in certain strain hardened alloys, especially those of aluminum.
Aging. A change in the properties of certain metals and alloys that occurs at ambient or moderately elevated temperatures after hot working or a heat treatment (quench aging in ferrous alloys, natural or artificial aging in ferrous and nonferrous alloys) or after a cold working operation (strain aging). The change in properties is often, but not always, due to a phase change (precipitation), but never involves a change in chemical composition of the metal or alloy. See also age hardening, artificial aging, interrupted aging, natural aging, over aging, precipitation hardening, precipitation heat treatment, progressive aging, quench aging, step aging, and strain aging.
Air-hardening steel. A steel containing sufficient carbon and other alloying elements to harden fully during cooling in air or other gaseous mediums from a temperature above its transformation range. The terms should be restricted to steels that are capable of being hardened by cooling in air in fairly large sections, about 2 in. (50 mm) or more in diameter. Same as self-hardening steel.
Air quenching. Quenching of a product by forced air, e.g. ventilators
Allotropy. A near synonym for polymorphism. Allotropy is generally restricted to describing polymorphic behaviour in elements, terminal phases, and alloys whose behaviour closely parallels that of the predominant constituent element.
Alloy cast iron. A cast iron containing more than 3% alloy content. Alloy cast irons may be a type of ductile cast iron, gray cast iron, or white cast iron.
Alloy steel. Steel containing specified quantities of alloying elements (other than carbon and the commonly accepted amounts of manganese, copper, silicon, sulphur, and phosphorus) within the limits recognized for constructional alloy steels, added to effect changes in mechanical or physical properties.
Alpha ferrite. See ferrite.
Annealing. A generic term denoting a treatment, consisting of heating to and holding at a suitable temperature followed by cooling at a suitable rate, used primarily to soften metallic materials, but also to simultaneously produce desired changes in other properties or in microstructure. The purpose of such changes may be, but is not confined to: improvement of machinability, facilitation of cold work, improvement of mechanical or electrical properties, and/or increase in stability of dimensions. When the term is used without qualification, full annealing is implied. When applied only for the relief of stress, the process IS properly called stress relieving or stress-relief annealing. In ferrous alloys, annealing usually is done above the upper critical temperature, but the time-temperature cycles vary widely in both maximum temperatures attained and in cooling rate employed, depending on composition, material condition, and results desired. When applicable. The following commercial process names should be used: black annealing, blue annealing, box annealing, bright annealing, cycle annealing, flame annealing, full annealing, graphitizing, intercritical annealing, isothermal annealing, malleablizing, order hardening, process annealing, quench annealing, spheroidizing, and sub critical annealing.
Annealing carbon. Fine, apparently amorphous carbon particles formed in white cast iron and certain steels during prolonged annealing. Also called temper carbon.
Annealing twin. A twin form in a crystal during recrystallization.
Anneal to temper. A final partial anneal that softens a cold worked nonferrous alloy to a specified level of hardness or tensile strength.
Arcm, Art, An, Ar4, Ar', Ar". Defined under transformation temperature.
Artificial aging. Aging above room temperature. See also aging. Compare with natural aging.
As-quenched condition. Condition of an alloy during the time immediately following quenching and before the mechanical properties have been significantly altered by precipitation hardening
Athermal transformation. A reaction that proceeds without benefit of thermal fluctuations; that is, thermal activation is not required. In contrast, a reaction that occurs at constant temperature is an isothermal transformation; thermal activation is necessary in this case and the reaction proceeds as a function of time.
Austempering. A heat treatment for ferrous alloys in which a part is quenched from the austenitizing temperature at a rate fast enough to avoid formation of ferrite or pearlite and then held at a temperature just above Ms until transformation to bainite is complete. Although designated as bainite in both austempered steel and austempered ductile iron (ADI), austempered steel consists of two phase mixtures containing ferrite and carbide, while austempered ductile iron consists of two phase mixtures containing ferrite and austenite.
Austenite. A solid solution of one or more elements in face-centered cubic iron. Unless otherwise designated (such as nickel austenite), the solute is generally assumed to be carbon.
Austenitic grain size. The size attained by the grains of steel when heated to the austenitic region; may be revealed by appropriate etching of cross sections after cooling to room temperature.
Austenitizing. Forming austenite by heating a ferrous alloy into the transformation range (partial austenitizing) or above the transformation range (complete austenitizing). When used without qualification, the term implies complete austenitizing.