The corrosion resistance of stainless steel is essentially dependent on the chromium content.
Passivation is the process by which stainless steel will form a thin, good adhesive and resistant chromium oxide layer (10-20 A) spontaneously or specifically. As a result the surface gets passive and corrosion resistant.
The following proceedings can reduce the corrosion resistance of stainless steel:
- The improper use of grinding wheels,
- Contact with mild steel or chrome steel,
- Contact with acid or alkali in such a big quantity that is not consistent with the data of the material specification,
- Laser cutting,
The mechanical operation on stainless steel might damage the ability for corrosion resistance because the stability of the surface can be affected by the processing. The surface can be polluted, its structure can change or stresses can arise in the material. Therefore it is necessary to pickle and passivate the particles after machining. The properly cured surface becomes fully resistant again according to the specifications of the raw material and regains its decorative metallic appearance.
The passivation is the chemical treatment of stainless steel surface. The passivation process involves the fully immersion of the parts in a passivation bath. Large parts can be effectively pickeled with pickling gel.
In all cases, the first step of the passivation process is cleaning and degreasing in order to prepare the machined or fabricated parts for passivation. After applying the pickling paste the gel must be left to work 30 minutes to days (depending on temperature and steel grade). After the self-passivation happened the pickling residues can be removed by using a high pressure water jet.
In order to protect our environment it is necessary to treat and neutralise the waste water according to the Hungarian low as the final step of the process. If it is not possible to manage it in the company the waste water must be delivered to a specialist for waste water neutralisation.
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