STAINLESS STEEL is a term used in a broad sense, par ticularly in America, to cover all "rustless steels" (q.v.) or iron alloys designed to resist atmospheric corrosion, attack by organic solutions, hot or cold acids or chemicals, or scaling at elevated temperatures. In the restricted sense the term applies as a trade name to cutlery steels containing not more than 0.70% carbon and from 9 to 16% of chromium patented in 1916 by the Engligh metallurgist Brearley. Chromium is the principal alloying element in most stainless metals (in the broad sense used above). Stain less or rustless iron contains less than 0.1o% carbon and usually from 12 to 18% chromium, the balance being iron. It is inher ently stainless to atmospheric corrosion, resists most acids and chemicals fairly well, and can be fabricated and worked cold like mild steel. Most of the possible iron-carbon-chromium com pounds up to 3% carbon and 6o% chromium have been patented, in addition to the Brearley patent noted above, and many of them containing more than 20% chromium, either in the form of forgings or castings, are non-scaling. Chromium steels containing considerable nickel, for instance 18% chromium and 8% nickel, are non-rusting and are austenitic (q.v.) in structure, very tough,
may be hardened by cold work, and are being widely adopted by industry as an "all purpose" alloy (semi-noble). Addition of silicon improves the resistance to scaling of this and plain chro mium steels (gas engine valves, for instance, contain 8% chro mium and 3% silicon). Other alloying elements are also used for special purposes. Superior resistance to hot or cold hydrochloric acid (until recently unobtainable by any but the noble metals) is given by an alloy of 20% iron, 20% molybdenum and 6o% nickel. Alloys based on 35% nickel, 15% chromium, 5o% iron make strong, tough, and scale resistant parts for furnaces.
While the entire field of iron-carbon-chromium-nickel-silicon alloys is so big that the surface has barely been scratched, to say nothing of possible additions of tungsten, molybdenum, cobalt, copper, manganese, and aluminium, enough is known of the prop erties of various stainless alloys so that small pieces or large equipment which will corrode or scale no faster than 0.02 in. per year can now be furnished for nearly all commercial liquids or in dustrial atmospheres. (E. E. T.)