Stainless steel is an iron-based alloy with elevated chromium content. In accordance with international standards steel is classified as “stainless steel” if its chemical composition has a minimum chromium content of 10.5%. Stainless steel, which is often also alloyed with further elements such as nickel and molybdenum, is a well-established material allowing a wide range of end uses, especially if superior corrosion resistance and aesthetic demands are in focus.
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One fundamental characteristic of stainless steel is described by means of corrosion resistance in aggressive environments. The presence of the alloying element chromium ensures the formation of a chromium-rich layer, the passive layer. This film is insoluble, compact and protects the material against corrosive atmospheres.
Its passivation occurs naturally and spontaneously in an oxidizing atmosphere when exposed to air or in an aqueous solution. If the stainless steel surface gets scratched or damaged mechanically in other ways the passive layer forms spontaneously again, ensuring the protection against corrosive media is restored immediately. The passive layer is extremely thin and transparent. It gives stainless steel its typical grey-silver metal finish. Other surface finishes are also common, e.g. the mirror-like “bright annealed” finish or ground and brushed finishes for decorative applications.
The presence of chromium also ensures resistance against harmful localized forms of corrosion such as pitting and crevice corrosion while the presence of the alloying element molybdenum in combination with chromium delivers even better results. Stainless steel is an extraordinary material with numerous applications today and more to come in the future. Growth in its consumption is higher than for most other materials used. Stainless steel is 100% recyclable (production is always based on scrap and not on iron ore), hygienic, durable and accompanies us in all phases of our daily lives.