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How is the corrosion resistance of stainless steel coils achieved
source：www.p-t7.com | Release time：2025年11月10日1、 Core principle: Formation and function of passivation film
The substrate of stainless steel coils contains a high proportion of chromium (usually ≥ 10.5%). When chromium is in air or in contact with media such as water and oxygen, it quickly reacts with oxygen to form a very thin (3-5nm) chromium oxide (Cr ? O3) passivation film on the surface.
This passivation film has a dense structure and good continuity, which can completely cover the surface of the substrate and act like a "protective film" to isolate the contact between corrosive media (such as acid, alkali, salt, and moisture) and internal metals, preventing the dissolution of metal ions and thus avoiding corrosion.
The passivation film has self-healing properties. If it is damaged due to mechanical friction, minor scratches, etc., as long as there is oxygen or water in the environment, the chromium in the substrate will quickly oxidize again, forming a complete passivation film and continuing to play a protective role.
2、 Strengthening of Corrosion Resistance by Alloy Composition
Chromium is the fundamental core element, and the higher the content (such as 316L containing chromium ≥ 16%), the stronger the stability and density of the passivation film, and the better the corrosion resistance.
The addition of nickel (such as 304 containing 8% -10.5% nickel) can enhance the toughness and intergranular corrosion resistance of the passivation film, while improving the processing performance of stainless steel.
The addition of molybdenum (such as 316L containing 2% -3% molybdenum) can enhance the stability of the passivation film in chloride ion environments (such as seawater, salt spray, acid-base solutions), greatly improving its resistance to pitting and crevice corrosion.
The appropriate addition of nitrogen element can further enhance the density of the passivation film, while improving the strength of stainless steel and balancing corrosion resistance and mechanical properties.
3、 Production process ensures corrosion resistance
Smelting process: Refining techniques (such as AOD, VOD) are used to reduce the content of impurities such as carbon and sulfur, avoid impurities damaging the continuity of the passivation film, and reduce corrosion hazards.
Surface treatment: Acid pickling and passivation treatment after cold rolling (removing oxide scale and iron pollution generated during the rolling process) can promote the formation of a uniform passivation film; Surface states such as 2B and BA are optimized through rolling and annealing processes to ensure surface smoothness and reduce gaps and defects caused by corrosive media adhesion.
Subsequent processing control: Avoid surface scratches and oil residue during the production process, prevent local passivation film damage or inability to form, and ensure overall corrosion resistance consistency.
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