| Acicular Ferrite | A highly substructed nonequaixed ferrite formed upon continuous cooling by a mixed diffusion and shear mode of transformation that begins at a temperature slightly higher than the transformation temperature range for upper bainite in that it has a limited amount of carbon available; thus, there is only a small amount of carbide present. |
| Acid Embrittlement | A form of hydrogen embrittlement that may be induced in some metals by acid treatment. |
| Acid Steel | Steel produced in a furnace with an acid lining, i.e. consisting of a siliceous refractory and under a siliceous slag. With an acid slag, carbon, silicon and manganese only are removed so that the pig iron must not contain sulfur and phosphorus in percentages exceeding those permissible for the specification being made. Most steel manufactured today is in furnaces with basic linings. |
| Age Hardening | Hardening by aging, usually after rapid cooling or cold working. |
| Age Softening | Spontaneous decrease of strength and hardness that takes place at room temperature in certain strain-hardened alloys, especially those of aluminum. |
| Aging | Aging is a structural change, usually by precipitation, that occurs in some alloys after a preliminary heat treatment or cold working operation. Aging may take place in some alloys at room temperature in moderate time (days) or in others may be done in shorter time at furnace temperatures. Over-aging may be done at a temperature above normal to produce some desirable modification of physical properties. |
| Air-Hardening Steel | An alloy steel which will form martensite and develop a high hardness when cooled in air from its proper hardening temperature. Sometimes referred to as self- hardening steel. A steel that becomes fully hardened when cooled in air from above its critical point and does not require rapid quenching by oil or water. The risk of distortion is greatly reduced by air hardening. High Speed Steel was one of the earliest examples of this type of steel. |
| Allotropy | The property possessed by certain elements to exist in two or more distinct forms that are chemically identical but have different physical properties. In the case of iron the crystal structure has one form at room temperature and another at high temperature. When heated above 910°C the atomic structure changes from body centered cubic to face centered cubic but reverts again when cooled. The allotropy of iron modifies the solubility of carbon, and it is because of this that steel can be hardened. |
| Alloy Steel | A steel to which one or more alloying elements other than carbon have been deliberately added (e.g. chromium, nickel, molybdenum) to achieve a particular physical property. |
| Alpha Iron | The body centered cubic form of iron which, in pure iron, exists up to 910°C. |
| Aluminizing | Forming a corrosion and oxidation-resistant coating on a metal by coating with aluminum and usually diffusing to form an aluminum-rich alloy. |
| Anneal to Temper | A final partial anneal that softens a cold worked nonferrous alloy to a specified level of hardness or tensile strength. |
| Annealing | Heating steel to, and holding at a suitable temperature, followed by relatively slow cooling. The purpose of annealing may be to remove stresses, to soften the steel, to improve machinability, to improve cold working properties, to obtain a desired structure. The annealing process usually involves allowing the steel to cool slowly in the furnace. |
| Annealing, Finish | A sub-critical annealing treatment applied to cold-worked low-or medium-carbon steel. Finish annealing, which is a compromise treatment, lowers residual stresses, thereby minimizing the risk of distortion in machining while retaining most of the benefits to machinability contributed by cold working. |
| Annealing, Intermediate | Annealing wrought metals at one or more stages during manufacture and before final treatment. |
| Annealing, Partial | An imprecise term used to denote a treatment given to cold-worked material to reduce their strength to a controlled level or to affect stress relief. To be meaningful, the type of material, the degree of cold work, and the time-temperature schedule must be stated. |
| Arc Furnace | A steel melting furnace in which heat is generated by an arc between graphite electrodes and the metal. Both carbon and alloy steels are produced in electric arc furnaces and scrap rather than molten metal is used as the base material. Furnaces with capacities up to 200 tons are now in use. |
| Atmosphere | The gaseous environment in which the metal being treated is heated for processing. Atmospheres are used to protect from chemical change or to alter the surface chemistry of steel through the addition or removal of carbon, nitrogen, hydrogen, and oxygen and to add certain metallic elements as chromium, silicon, sulfur, etc. |
| Austempering | Quenching from a temperature above the transformation range to a temperature above the upper limit of martensite formation, and holding at this temperature until the austenite is completely transformed to the desired intermediate structure, for the purpose of conferring certain mechanical properties. |
| Austenite | This is the name for any solid solution in which gamma iron is the solvent. It is a phase in steel where it consists of face-centered cubic iron with carbon in solid solution. It is non-magnetic and unstable at room temperature. Austenite is a structure name and means nothing as to composition. It is the structure from which all quenching heat treatments must start. |
| 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. |
| Austenitic Steels | Steels containing high percentages of certain alloying elements such as manganese and nickel which are austenitic at room temperature and cannot be hardened by normal heat-treatment but do work harden. They are also non-magnetic. Typical examples of austenitic steels include the 18/8 stainless steels and 14% manganese steel. |
| 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. |
| Austenitizing Temperature | The temperature at which a steel is substantially all austenite. |
