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Tarnish does not always result from the sole effects of oxygen in the air. For example, silver needs hydrogen sulfide to tarnish, although it may tarnish with oxygen over time. It often appears as a dull, gray or black film or coating over metal. Tarnish is a surface phenomenon that is self-limiting, unlike rust. Only the top few layers of the ...
Stainless steel, also known as inox, corrosion-resistant steel (CRES), and rustless steel, is an alloy of iron that is resistant to rusting and corrosion. It contains iron with chromium and other elements such as molybdenum , carbon , nickel and nitrogen depending on its specific use and cost.
Rust scale forming and flaking off from a steel bar heated to its forging temperature of 1200°C. Rapid oxidation occurs when heated steel is exposed to air. Rust is a general name for a complex of oxides and hydroxides of iron, [4] which occur when iron or some alloys that contain iron are exposed to oxygen and moisture for a long period of ...
Stainless steel can pose special corrosion challenges, since its passivating behavior relies on the presence of a major alloying component (chromium, at least 11.5%). Because of the elevated temperatures of welding and heat treatment, chromium carbides can form in the grain boundaries of stainless alloys.
Black oxide or blackening is a conversion coating for ferrous materials, stainless steel, copper and copper based alloys, zinc, powdered metals, and silver solder. [1] It is used to add mild corrosion resistance, for appearance, and to minimize light reflection. [ 2 ]
A #7 finish is produced by polishing with a 280–320 grit belt or wheel and sisal buffing with a cut and color compound. This is a semi-bright finish that will still have some polishing lines but they will be very dull. Carbon steel and iron are commonly polished to a #7 finish before chrome plating.
Silicon-based polishing pads or a diamond solution can be used in the polishing process. Polishing stainless steel can also increase its sanitary benefits. The removal of oxidization (tarnish) from metal objects is accomplished using a metal polish or tarnish remover; this is also called polishing.
In general, crevice corrosion is of greatest concern for materials which are normally passive metals, like stainless steel or aluminum. Crevice corrosion tends to be of greatest significance to components built of highly corrosion-resistant superalloys and operating with the purest -available water chemistry.