By Daniel Maragni
Stainless steel is an iron-carbon alloy 'containing more than 4% and less than 30% chromium, as well as small amounts of nickel, manganese, and other elements. A fairly recent discovery, it enters the metallurgical scene around the turn of the century with one of the first U.S. patents being held by J. Baur in 1819 for chromium type steel used for bars in prisons.
Between the years 1900 and 1915 many basic principles of stainless steels were being examined and derived in the United States and Europe, and were a direct result of more advanced and methodical metallurgic studies. Critical chromium content, the nature of corrosion resistance, and the role of carbon as an alloying element all were determined at this time.
Since them two major discoveries stand out from the general contributions to stainless steel metallurgy. The first was the substitution of manganese for nickel as an alloying element, which occurred during World War II when nickel was in short supply and resulted in a higher strength alloy. The second occurred about ten years later and introduced a precipitation-hardening alloy which has terrific strength at high operating temperatures.
Stainless Steel exhibits two major characteristics which endear it to industry, architecture and science - corrosion resistance and high yield strength. Corrosion resistance, a function of increased chromium content, is due to the ability of the metal to form a tight, adherent surface film almost immediately upon exposure to air. This film, probably an iron chromium oxide, resists a variety of industrial gases and chemicals, and is self-renewing if punctured or scratched. Strength, which varies according to composition and structure of the steel, can stand 30,000 psi to more than 250,000 psi at room temperature, and can be maintained from 2000°F to near absolute zero.
Stainless steels are typed according to their internal metallographic structure and their characteristics are determined by the proportions of alloying elements and their subsequent treatment. A full range of physical properties are possible, from the very tough and impact-resistant austenitic steels to the extremely hard and brittle martensitic ones. All the stainless steels can be worked by conventional means. They can be cut, cast, machined; cold formed, hot formed, and joined using soldering, brazing and welding. But due to the extremely refined manufacturing techniques and the need for more powerful machinery and slower working time, stainless steel production costs tend to be very high.
Stainless steel is extremely versatile and can serve both decorative and functional purposes. Perhaps the first and most obvious decorative / functional use of stainless steel was in architecture. Stainless steel's particular ability to resist the ravages of the atmosphere was exploited by architects who timidly began using is only for trim, but soon expanded its use to exterior decorative facings. Early examples of architectural stainless steel include the Empire State building and the Chrysler building which have endured the corrosive atmosphere of New York City for many years with very little ill effect.
The field of industrial design also has been successful in utilizing this versatile metal. Mass-produced stainless steel furniture for office and home, and stainless tableware Virtually cover the world. Artists and craftsman also have been quick to realize the advantages of a medium which will take a variety of forms and finishes, and is practically indestructible. From large-scale sculpture to small items of personal jewelry, stainless steel has been adapted to express a full range of aesthetic values.
Stainless steel is a metal of the future; new alloys and applications of it are being discovered everyday. Its extreme versatility and desirable physical characteristics no doubt will favor its increasing use, and only time will reveal the full extent of its functional and decorative potential.