Stainless Steel Pipe Fittings

Composition of surface oxidation skin of stainless steel plate

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The deformation resistance of the stainless steel plate is very high. It is very easy to stick to the mould when drawing the stainless steel plate, which leads to the scratch on the stainless steel plate. In order to ensure that the drawing process can be carried out smoothly, it is necessary to make proper surface treatment for stainless steel plates, including surface oxide coating and surface coating.
The composition of the oxide sheet on the surface of the stainless steel plate is very complex, which is influenced by the alloy elements in the stainless steel composition. Therefore, it is necessary to understand the properties of the common elements and their oxides in the stainless steel plate.
According to the order of influence from large to small, chromium and its oxides and chromium metals are stable in nitric acid, alkali, carbonate solution and organic acid, but they are easy to dissolve in hydrochloric acid and hot concentrated sulfuric acid. The common chrome oxide mainly include chromium oxide, chromium oxide and chromium oxide chromium oxide three, which is very unstable in the air will be oxidized to form Cr2O3.
Chromic oxide is a kind of green insoluble material, basically insoluble in acid solution. Three chromium oxide is chromic anhydride can dissolve in sulfuric acid and nitric acid solution.
In addition to nickel and its oxides, nickel metals are basically insoluble in sulfuric acid and hydrochloric acid, only in nitric acid. The oxide of nickel mainly consists of two kinds of nickel oxide and three oxidation of two nickel. The former is dissolved in hydrochloric acid and sulfuric acid, and the latter is very dense and insoluble in sulphuric acid.
Then, manganese and its oxide, manganese metal can be dissolved in acid, manganese oxide more common, there are MnO, Mn2O3, MnO2, Mn3O4, Mn2O7. Low valence oxide is alkaline, manganese dioxide is two, and high valence oxide is anhydride. Because the oxide skin on the surface of the stainless steel plate is a low price manganese, it can be dissolved in acid.
The oxide of silicon is mainly silica, which can only act with hydrofluoric acid, and it will dissolve in hot alkali solution to form the corresponding silicate.
The alloy element molybdenum in stainless steel does not interact with hydrochloric acid and dilute sulfuric acid, but it will only be dissolved in nitric acid and hot sulfuric acid. The oxide is MoO3, it can dissolve in acid and alkali.
Titanium is always stable at room temperature and can resist corrosion. It is easy to form compounds with oxygen and nitrogen at high temperature, namely titanium dioxide and titanium nitride. The former will be dissolved in sulfuric acid and alkali.
Stainless steel plate surface oxidation in the skin of main component of chromic oxide and nickel oxide form they are chrome spinel and nickel spinel. The oxide scale is dense and thin, and is firmly combined with stainless steel substrate. It is difficult to remove simple acid pickling. It is usually removed with alkali leaching and mixed acid washing.
Source: China Stainless Steel Plate Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)

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Stainless Steel

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