Why does stainless steel rust?

1、 What is stainless steel?

Stainless steel is a kind of steel. Steel refers to the steel containing less than 2% carbon (c), and more than 2% iron. Alloy elements such as chromium (CR), nickel (Ni), manganese (MN), silicon (SI), titanium (TI) and molybdenum (MO) are added to the steel in the smelting process to improve the performance of the steel and make the steel have corrosion resistance (i.e. no rust), which is what we often call stainless steel. For example, our stainless steel products: banjos, swivel house end joint, house clamps , exhaust manifold, etc.

2、 Why does stainless steel rust?

Stainless steel has the ability to resist atmospheric oxidation – rust resistance, and also has the ability to resist corrosion in the medium containing acid, alkali and salt, that is, corrosion resistance. However, the corrosion resistance of the steel varies with its chemical composition, mutual state, service condition and environmental medium type.

Stainless steel is a very thin, solid and fine stable chromium rich oxide film (protective film) formed on its surface to prevent oxygen atoms from continuing to penetrate and oxidize, and obtain corrosion resistance. Once the film is continuously damaged for some reason, the oxygen atoms in the air or liquid will continuously infiltrate or the iron atoms in the metal will continuously separate out, forming loose iron oxide, and the metal surface will be continuously corroded. There are many forms of damage to this surface facial mask, and the following are common in daily life:

1. Dust containing other metal elements or attachments of dissimilar metal particles are stored on the surface of stainless steel. In the humid air, the condensate between the attachments and stainless steel connects them into a micro cell, causing electrochemical reaction and damaging the protective film, which is called electrochemical corrosion.

2. Organic juices (such as melons and vegetables, noodle soup and phlegm) adhere to the surface of stainless steel. In the presence of water and oxygen, they form organic acids, which will corrode the metal surface for a long time.

3. The surface of stainless steel is adhered with acid, alkali and salt substances (such as alkali water and lime water spray test for wall decoration) to cause local corrosion. 4. In the polluted air (the atmosphere containing a large amount of sulfide, oxide and hydrogen oxide), when encountering condensed water, sulfuric acid, nitric acid and acetic acid liquid points will be formed, causing chemical corrosion.

3、 How to deal with rust spots on stainless steel?

a) Chemical method:

Use pickling paste or spray to assist the rusted parts to re passivate and form chromium oxide film to restore the corrosion resistance. After pickling, it is very important to wash with clean water properly to remove all pollutants and acid residues. After all treatment, use polishing equipment to polish again and seal with polishing wax. For those with slight rust spots locally, the 1:1 mixture of gasoline and engine oil can be used to wipe off the rust spots with a clean rag.

b) Mechanical method:

Blast cleaning, shot blasting with glass or ceramic particles, annihilation, brushing and polishing. It is possible to wipe off the contamination caused by the previously removed materials, polishing materials or annihilation materials by mechanical methods. All kinds of pollution, especially foreign iron particles, may become a source of corrosion, especially in humid environment. Therefore, the mechanically cleaned surface should preferably be formally cleaned under dry conditions. The mechanical method can only clean the surface, and cannot change the corrosion resistance of the material itself. Therefore, it is recommended to re polish with polishing equipment after mechanical cleaning and seal with polishing wax.