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Round Head Bolt Passivation

Lid sinds 20 jan 2020
Startgewicht: 50 Kg
Streefgewicht: 45 Kg

The corrosion resistance of stainless steel Round Head Bolt in some environments is related to their passivation performance.  When the steel is in a passivated state, a dense oxide film is formed on the surface of the steel, which blocks the corrosion process and temporarily stops the corrosion.
Chromium is the most basic element in stainless steel, and it is also a necessary element to improve the stability of passivation film of steel.  When the chromium content reaches 12%, the alloy can reach the capability of complete self-passivation.  The self-passivating ability of the alloy determines the corrosion resistance of stainless steel to a certain extent. Therefore, the chromium content in austenitic stainless steel cannot be less than 12%, and the chromium content in SUS304 is less than 12% in the current market.
Nickel is an element to improve the corrosion resistance of steel, especially in non-oxidizing sulfuric acid.  Adding nickel to chromium stainless steel can improve its corrosion resistance in sulfuric acid, acetic acid, oxalic acid and neutral salts (especially sulfate).
Manganese can also improve the corrosion resistance of chromium stainless steel in organic acids such as acetic acid, formic acid and glycolic acid, and is more effective than nickel.
Molybdenum can improve the passivation capability of stainless steel DIN 603 and expand the range of passivation medium, such as the use in hot sulfuric acid, dilute hydrochloric acid, phosphoric acid and organic acid.  Molybdenum-containing passivation film can be formed in stainless steel containing molybdenum, which has high stability in many strongly corrosive media and can also prevent chloride ions from damaging the film.
Silicon can improve the corrosion resistance of steel in hydrochloric acid, sulfuric acid and high concentration nitric acid.  Generally, 2%-4% silicon is added to stainless steel to improve its corrosion resistance in the above medium.