Several influencing factors of stainless steel rusting

When rust spots appear on the surface of stainless steel, people are surprised: Why does stainless steel also rust? In fact, this is a one-sided wrong view due to lack of understanding of stainless steel. Stainless steel can also rust under certain conditions. Stainless steel refers to alloy steel containing more than 12% chromium. There are many varieties. Most of them are low-priced stainless steel that does not contain nickel. The most commonly used stainless steel in industry is 1Cr18NT, which contains 18% chromium and 9% nickel. It is easy to passivate. , good corrosion resistance.

Stainless steel has a certain ability to resist atmospheric corrosion and also has the ability to resist corrosion in media containing acids, alkalis, and salts. However, its corrosion resistance changes with the chemical composition of the material itself, processing status, usage conditions and environmental factors. For example, 304 steel pipe has excellent corrosion resistance in a dry and clean atmosphere. However, if it is used in coastal areas, it will quickly rust in the sea fog containing a large amount of salt.

Stainless steel relies on the formation of an extremely thin, strong and fine chromium-containing oxide film on its surface to prevent the continued penetration and oxidation of oxygen atoms, thereby obtaining the ability to prevent rust. Once this film is damaged for some reason, oxygen atoms in the air or liquid will continue to separate out, forming loose iron oxide, and the metal surface will rust. Common ones in daily life include the following:

1. Dust mixed with other metal elements or attachments of heterogeneous metal particles accumulate on the surface of stainless steel. In humid air, micro-batteries are formed, triggering electrochemical reactions and causing electrochemical corrosion.

2. The surface of stainless steel contains acid, alkali and salt substances, causing local corrosion.

3. Organic juice adheres to the surface of stainless steel. In the presence of water and oxygen, organic acids are formed and corrode the metal surface.

4. There are a large amount of sulfur dioxide, carbon dioxide, oxidizing gas and other gases in the air, which will form acid through condensed water, causing chemical corrosion.

In order to ensure that the metal surface is permanently bright and will not be rusted, the decorative stainless steel surface must be cleaned and scrubbed frequently to remove attachments and eliminate external factors that cause corrosion.