Acid-resistant stainless steel 
 Acid two. Arrived in the air can be called out of stainless steel corrosion; strong in a variety of aggressive media can arrive out of steel called acid corrosion of steel. Stainless steel is not necessarily acid, and acid-resistant stainless steel is generally good performance there. Such steel is mainly chromium, nickel and other alloying elements, and also contains a small amount of molybdenum, vanadium, copper, manganese, nitrogen or other elements. Chromium content, some as high as 25% (13% chromium content in the following steel, corrosion not only in the case is strong corrosion), the nickel content of up to 20%. Type of steel is mainly used to manufacture chemical equipment, medical equipment, food industry equipment and other requirements such as stainless steel device. 

 History 
 Stainless steel metallurgy in the history of the invention is a significant achievement. Early 20th century, Audigier (LBGuillet) 1904 ~ 1906 and Portevin (AMPortevin) in 1909 ~ 1911 in France; Giessen (W. Giesen) in 1907 ~ 1909 in the United Kingdom found that the iron - chromium and iron - chromium - nickel alloy corrosion resistance. Monotype Scholz (P. Monnartz) in 1908 - made in Germany in 1911 and passivated stainless steel in many theoretical point of view. The inventor of stainless steel for industrial use: with Cr12 ~ 13% of the martensitic stainless steel is Bridget Hurley (H. Brearley) 1912 ~ 1913 in England; with Cr14 ~ 16%, C0.07 ~ 0.15% of the ferrite Stainless steel is the Dan Qi Zeng (C. Dantsizen) 1911 ~ 1914 in the United States; with C <1%, Cr15 ~ 40%, Ni <20% of the austenitic stainless steel is Maurer (E. Maurer) and Shite Lao Sri Lanka (B. Strauss) 1912 ~ 1914 in Germany. On this basis, followed by the development of the famous "18-8" stainless steel (C ~ 0.1%, Cr ~ 18%, Ni ~ 8%). In the martensitic, ferritic and austenitic stainless steel three types have emerged after the 1930s invented the austenitic - ferritic duplex stainless steel. 1940s to 1950s, martensitic and precipitation hardening semi-austenitic stainless steel and nickel saving Cr-Mn-Ni-N and other stainless steel and carbon content of less than 0.03% of the ultra-low carbon stainless steel also started production. 60 years later there maraging steel, TRIP (transformation inducedplasticity, see thermomechanical treatment) stainless steel and carbon, nitrogen, less than 150ppm total high-purity ferritic stainless steel. The late 1970s, the world annual production of over 10 million tons steel, stainless steel production in some countries about its total steel production of about 1%. China in 1952 and started trial production of a large number of stainless steel, 45 to 70 years has been finalized grades. 

 The role of alloying elements 
 Stainless steel is the most important technical requirements for corrosion resistance, suitable mechanical properties, good cold, thermal processing and welding process performance. Corrosion resistance of chromium stainless steel to obtain the basic elements. When the chromium content in steel up to 12%, the steel in oxidizing medium corrosion resistance mutations of the rise. At this point the steel surface to form a thin, dense chromium oxide film, prevent the continued erosion of the metal matrix is ??(see metal corrosion). In addition to chromium, the steel also contains other elements, some are added as the main ingredient, and some are residual impurities; its impact below.