After being discovered in 1912, stainless steels, or simply stainless steel, were studied more in-depth to make it possible to use a material that would be more resistant to the inconvenient corrosion of common steels, forming metal alloys from two main chemical elements: iron and chromium. In addition to having greater resistance to corrosion (rust), these alloys, widely used in the industry, could give rise to products with various characteristics.
Among the various types of stainless steel, the following stand out:
Martensitic: these are essentially chromium alloys. They are ferromagnetic, hardenable by heat treatments, and generally resistant to corrosion in less aggressive environments. The chromium content ranges from 10.5 to 18%, and the carbon content must not exceed 1.2%. The combination of carbon and chromium can increase wear resistance, as in the case of knife blades. Other elements can be added to improve corrosion resistance, toughness, and machinability. Examples include steels 410 and 420.
Austenitic: these are non-magnetic steels and can only be hardened by cold working. They generally have excellent cryogenic properties and good resistance to high temperatures. The chromium content usually varies from 16 to 26%; nickel and manganese can be up to 15%. Molybdenum, copper, silicon, aluminum, titanium, and niobium can be added to impart certain characteristics such as oxidation resistance. Sulfur can be added to certain grades to improve machinability. Examples include steels 304, 304L, 316, and 316L.
Ferritic: the chromium content in these steels usually ranges from 10.5 to 30%. Some grades may contain molybdenum, silicon, aluminum, titanium, and niobium to provide specific characteristics. Sulfur can be added, as in the case of martensitic steels, to improve machinability. Ferritic alloys are ferromagnetic, meaning they are attracted to magnets. They may exhibit good ductility and formability, but at high temperatures, the strengths are relatively low compared to austenitic grades. Toughness can be slightly limited at low temperatures. Examples include steels 409, 430, 439, and 441.
With so many varieties, various myths arise. One of them claims that magnets do not attract stainless steel, and if they do, the steel is impure. However, as mentioned earlier, this is not true. All stainless steels from the ferritic and martensitic families, for example, are magnetic. Whether or not a magnet attracts stainless steel does not determine the purity of the material but rather distinguishes its chemical composition.
Since it is a metal alloy and not a metal composed of a single chemical element, it is not possible to say whether stainless steel is pure or not. After all, stainless steels can be produced from various combinations of elements. It is in the complexity of chemical compositions that the highest-quality stainless steel is produced, ensuring excellent properties according to the application and conditions of use of the final product, considering quality, strength, and durability.
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