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Stainless8/22/2023 ![]() ![]() If the protective layer is damaged, the steel below will start to rust. Although paints or oxidation-resistant metals e.g., zinc, nickel and chromium can be employed for galvanization to ensure the carbon steel surface, this protection is only a film. Unfortunately, the iron oxides formed on ordinary carbon steel keeps oxidizing, causing expanded corrosion and eventually holes. All these metals react with oxygen in the atmosphere and form an oxide film on the surface. Meanwhile, the new varieties such as low-carbon stainless steel, ultra-low carbon stainless steel, and duplex stainless steel are developed to enhance the corrosion resistance. In order to avoid the local corrosions, molybdenum, nitrogen, titanium or niobium will be added to the steel. Stainless steel, when exposed to special environments, will also incur some local corrosion, such as pitting, intergranular corrosion, stress corrosion, galvanic corrosion and so on. ![]() If the passivation film on the surface is damaged, the chromium in the steel will react with the oxygen in the atmosphere to produce new passivation film for continuous protection. Hence, there is one thing in common all stainless steels share, that is, at least 10.5% chromium. Moreover, if the surface is damaged, the exposed steel will react with the atmosphere to self-repair and regenerate the oxide, the "passivation film," for resumed protection. This oxide film is so thin as to only a few microns through the chrome the natural luster of the surface can be seen, hence the stainless steel has a unique surface. As the chromium contained reaches 12%, the stainless steel reacted with the atmosphere will produce a passivation film (Cr2O3) on the surface, a dense chromium-rich oxide that effectively protects the stainless steel surface from further oxidation. The “stainless” property is related to the chromium contained within the steel. Stainless steel, in contrast is corrosion resistant. Ordinary carbon steel reacts with oxygen of the atmosphere to form an oxide film on the metal surface and keeps oxidizing, which results in expanded rust, forming a "thousand-layer Cake" type of corrosion until the rotten wear. Why Stainless Steel is Corrosion Resistance? On the contrary, if the compounds are unstable, volatile or dissolved, not bonding with the metal strongly, the corrosion products will be peeling off layer by layer, like the oxide, hence unable to protect the metal matrix from further corrosion. This behavior is known as "passivation effect." If the compounds produced by the chemical corrosion are stable, not easy to evaporate and dissolve, of dense tissue and binding strongly with metal matrix, the corrosion products will stay attached to the metal surface to form a passivation layer, hence to protect the metal matrix from further corrosion. The chemical corrosion product exists on the metal surface, without any current being generated during the corrosion process. The corrosion is known as chemical corrosion. When metal is exposed to and reacts with the dry gas and nonelectrolyte solution, it will produce corrosion. ![]() British usage of stainless steel and inox steel, ngrams shows little difference between the corpuses, and in both cases inox has nearly no usage compared with stainless steel: Wikipedia includes part of a 1915 New York Times article that refers to "a stainless steel" that is "claimed to be non-rusting, unstainable, and untarishable" which at least partly confutes the "stains less" etymology of stainless steel, which is suggested in the link in the question. For example, after a stainless steel surface is cleaned with steel wool rather than brass wool, it may develop rust stains.Įtymonline gives a 1917 date of origin of the term and says stainless steel is "so called because it is highly resistant to rust or tarnish." Edit: tabulates definitions of stainless steel from a dozen sources, two etymology references, and several audio links. Wikipedia says of stainless steel that stainless steel is "also known as inox steel or inox from French inoxydable".Īs is well known, and mentioned in Wikipedia, stainless steel stains less easily and rusts or corrodes less easily, than ordinary steel, but it is not stain-proof and in some conditions can rust or corrode or give such appearance. ![]()
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