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stainless steel:see steelsteel,
alloy of iron, carbon, and small proportions of other elements. Iron contains impurities in the form of silicon, phosphorus, sulfur, and manganese; steelmaking involves the removal of these impurities, known as slag, and the addition of desirable alloying elements.
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complex alloyed steel that is resistant to corrosion under atmospheric conditions and in aggressive media. The main alloying element in stainless steels is chromium (12–20 percent). Stainless steels also contain elements that accompany iron in its alloys (carbon, silicon, manganese, sulfur, and phosphorus), as well as elements introduced into steel for the purpose of imparting to it the required physical and mechanical properties and corrosion resistance (nickel, manganese, titanium, niobium, cobalt, and molybdenum). The corrosion resistance of steel increases with increasing chromium content. Alloys containing more than 12 percent Cr are stainless under ordinary conditions and in weakly aggressive media; steels containing more than 17 percent Cr are corrosion-resistant even in more aggressive oxidative and other media, particularly nitric acid (up to 50 percent).
The corrosion resistance of stainless steels is explained by the formation of an extremely thin protective film, consisting of oxides or other insoluble compounds, at the interface between the chromium-containing alloy and the medium. The homogeneity of the metal, the condition of its surface, and the lack of a tendency toward intercrystalline corrosion are of great importance in this case. Excessively high stresses in parts and equipment give rise to corrosion cracking in a variety of aggressive media (especially media containing chlorides) and sometimes lead to failure. Complex alloyed stainless steels and alloys with a higher nickel content and additives of molybdenum, copper, and silicon in various combinations are corrosion-resistant in strong acids (sulfuric, hydrochloric, hydrofluoric, and phosphoric acids and their mixtures). In such cases, a particular type of stainless steel is selected for each specific set of conditions (temperature and concentration of the medium).
Stainless steels are divided into chromium, chrome-nickel, and chrome-manganese-nickel steels (more than 100 grades) in terms of chemical composition. In terms of structure, martensitic, semi-ferritic, and ferritic types are distinguished. Polished chromium stainless steels of the martensitic type have the highest corrosion resistance. Chromium stainless steels are used to make valves in hydraulic presses, turbine blades, equipment for cracking plants, cutting tools, springs, and household articles.
Chrome-nickel and chrome-manganese-nickel stainless steels are divided into austenitic, austenitic-ferritic, austenitic-marten-sitic, and austenitic-carbide types. Austenitic stainless steels are subdivided into those that are susceptible to intercrystalline corrosion and the “stabilized” types, which contain additives of titanium and niobium. A sharp reduction in susceptibility of stainless steels to intercrystalline corrosion is also achieved by a decrease in the carbon content to 0.03 percent. Stabilized austenitic stainless steels are used in the production of welding equipment used in aggressive media (in this case, heat treatment is not required after welding). These types of steel are used as heat-resistant materials in the production of articles exposed to temperatures of 550°-800°C. Steels susceptible to intercrystalline corrosion usually undergo heat treatment after welding (parts welded by spot or seam welding do not require heat treatment). Chrome-nickel and chrome-manganese-nickel stainless steels are widely used in industry and by consumers. Structural elements under high loads that operate at high temperatures (up to 550°C) are made from martensitic-aging steels of the austenitic-martensitic type, which have relatively high strength (cr* = 1200–1500 meganewtons per sq m, or 120–150 kilograms-force per sq mm), great toughness, and good weldability. Stainless steels are used in both wrought and cast form.
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Khimushin, F. F. Nerzhaveiushchie stall 2nd ed. Moscow, 1967.
Materialy v mashinostroenii: Spravochnik, vol. 3. Moscow, 1968.
Babakov, A. A., and M. V. Pridantsev. Korrozionnostoikie stali i splavy. Moscow, 1971.
Potak, Ia. M. Vysokoprochnye stali. Moscow, 1972.
F. F. KHIMUSHIN