ACID STEEL - Steel melted in a furnace that has an acid bottom and lining and under a slag that is dominantly siliceous.

AGE HARDENING - A process of aging that increases hardness and strength and ordinarily decreases ductility. Age hardening usually follows rapid cooling or cold working.

AGING - Change in a metal by which its structure recovers from an unstable condition produced by quenching or by cold working such as cold reduction. The change in structure is marked by changes in physical properties. Aging which takes place slowly at room temperature may be accelerated by slight increase in temperature. See strain aging.

AIR HARDENING STEEL - An alloy steel that is hardened by cooling in air from a tempera?ture higher than the transformation range. Also called self-hardening steel.

ALLOY - A substance that has metallic properties and is composed of two or more chemical elements of which at least one is a metal.

ALLOY STEEL - Steel containing significant quantities of alloying elements (other than carbon and the commonly accepted amounts of manga?nese, silicon, sulfur and phosphorus) added to effect changes in the mechanical or physical properties.

ALLOYING ELEMENT - Chemical elements constituting an alloy; in steels, usually lim?ited to the metallic elements added to modify the properties of steel.

ANNEALING - A process involving heating and cooling, usually applied to induce softening. The term also refers to treatments intended to alter mechanical or physical properties, produce a definite microstructure. or remove gases. When applicable, the follow?ing more specific terms should be used: black annealing, blue annealing, box annealing, bright annealing, full annealing, graphitizing, isothermal annealing, malleablizing, process annealing, spheroidizing, stabilizing annealing. Definitions of some of these are given in their alphabetical positions in this glossary. When applied to ferrous alloys, the term annealing, without qualifications, implies full annealing. Any process of annealing will usually reduce stresses, but if the treatment is applied for the sole purpose of such relief, it should be designated as stress relieving

ARTIFICIAL AGING - An aging treatment above room temperature.

AUSTEMPERING - A trade name for a patented heat treating process that consists in quenching a ferrous alloy from a temperature above the transformation range, in a medium having a rate of heat abstrac?tion sufficiently high to prevent the formation of high-tempera?ture transformation products; and in maintaining the alloy, until transformation is complete, at a temperature below that of pearlite formation and above that of martensite formation.