1. What is stainless steel?
Stainless steel is a type of steel. Steel refers to steel containing less than 2% of carbon (C), and more than 2% is iron. The addition of chromium (Cr), nickel (Ni), manganese (Mn), silicon (Si), titanium (Ti), molybdenum (Mo) and other alloying elements during the smelting process improves the performance of the steel and makes the steel more resistant to corrosion. (that is, not rusted) is what we often call stainless steel.
2. Why does stainless steel have different steel grades?
In the smelting process of stainless steel, due to the different varieties of alloying elements added, the amount of addition of different varieties is different. Their characteristics are also different. In order to distinguish them, they are crowned with different steel grades. The following is a table of "alloying elements" content of different steel grades of common decorative stainless steels for reference only:
Steel grade Carbon (C) Silicon (Si) Manganese (Mn) Phosphorus (P) Sulfur (S) Chromium (Cr) Nickel (Ni) Molybdenum (Mo) Copper (Cu)
304 ≤0.08 ≤1.00 ≤2.00 ≤0.045 ≤0.03 18-20 8-10
301 ≤0.15 ≤1.00 ≤2.00 ≤0.045 ≤0.03 16-18 6-8
202 ≤0.15 ≤1.00 7.5-10 ≤0.05 ≤0.03 17-19 4-6
201 ≤0.15 ≤1.00 5.5-7.5 ≤0.05 ≤0.03 16-18 3.5-5.5
3. What kind of stainless steel is not easy to rust?
There are three main factors that affect stainless steel corrosion:
One: the content of alloying elements, generally speaking, the content of chromium is 10.5%, the steel is not easy to rust. The higher the content of chromium and nickel, the better the corrosion resistance. For example, the content of nickel in 304 material is 8-10%, and the content of chromium is 18-20%. Such stainless steel will not rust under normal circumstances.
Second: the smelting process of the manufacturer will also affect the corrosion resistance of stainless steel. A large stainless steel plant with good smelting technology, advanced equipment and advanced technology can ensure the control of alloying elements, the removal of impurities, and the control of the cooling temperature of the billet. Therefore, the product quality is stable and reliable, the internal quality is good, and it is not easy to rust.
Third: the external environment, the climate is dry and ventilated, and the environment is not easy to rust. The air humidity is high, continuous rainy weather, or environmental areas with high pH in the air are prone to rust. 304 stainless steel, if the surrounding environment is too bad, it will rust.
Fourth, stainless steel is without magnetism, is it good stainless steel without magnetism? If the microstrip is magnetic, is it not 304?
Many customers go to the market to buy stainless steel and bring a small magnet with them. Without magnetism, it will not rust. In fact, this is a wrong understanding. Whether the stainless steel strip does not have magnetism is determined by its structure. During the solidification process of molten steel, due to the different solidification temperatures, stainless steel with different structures such as "ferrite", "austenite" and "martensite" will be formed. Among them, "ferrite". Both "solid" and "martensitic" stainless steels are magnetic. The "austenitic" stainless steel has good comprehensive mechanical properties and process performance, and the weldability is good, but only in terms of corrosion resistance, the magnetic "ferritic" stainless steel is stronger than the "austenitic" stainless steel. At present, the so-called 200 series and 300 series stainless steels with high manganese content and low nickel content in the market are not magnetic, but their performance is very different from that of 304 with high nickel content. On the contrary, 304 has been stretched, annealed, polished, cast, etc. Process treatment will also be microstrip magnetic, so it is a misunderstanding and unscientific to judge the quality of stainless steel by using stainless steel strip without magnetism.
5. Why does stainless steel rust?
When brown rust spots (spots) appear on the surface of stainless steel, people are amazed: "Stainless steel will not rust, and if it rusts, it is not stainless steel, and there may be a problem with the steel." In fact, this is a one-sided misconception about the lack of understanding of stainless steel. Stainless steel can also rust under certain conditions.
Stainless steel has the ability to resist atmospheric oxidation, that is, rust resistance, and also has the ability to resist corrosion in media containing acids, alkalis and salts, that is, corrosion resistance. However, the size of its corrosion resistance is changed with the chemical composition of the steel itself, the mutual state, the conditions of use and the type of environmental media. Stainless steel is a very thin, firm and stable chromium-rich oxide film (protective film) formed on its surface to prevent oxygen atoms from continuing to infiltrate and continue to oxidize, so as to obtain the ability to resist corrosion. Once the film is damaged continuously for some reason, the oxygen atoms in the air or liquid will continue to infiltrate or the iron atoms in the metal will continue to separate out, forming loose iron oxide, and the metal surface will be constantly exposed to Rust.
6. How to deal with rust spots on stainless steel?
a) Chemical method:
Use pickling paste or spray to assist the re-passivation of the rusted parts to form a chromium oxide film to restore the corrosion resistance. After pickling, in order to remove all contaminants and acid residues, it is very important to properly rinse with water. After all treatment, re-polish with polishing equipment, and seal with polishing wax. For local slight rust spots, you can also use a 1:1 mixture of gasoline and engine oil to wipe off the rust spots with a clean rag.
b) Mechanical methods:
Sandblast cleaning, blast cleaning with glass or ceramic particles, annihilation, brushing and polishing. It is possible to mechanically wipe away contamination from previously removed material, polishing material, or submerged material. All kinds of contamination, especially foreign iron particles, can be a source of corrosion, especially in humid environments. Therefore, mechanically cleaned surfaces should only be properly cleaned in dry conditions. The use of mechanical methods 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. Just wipe off the rust with a clean rag.
b) Mechanical methods:
Sandblast cleaning, blast cleaning with glass or ceramic particles, annihilation, brushing and polishing. It is possible to mechanically wipe away contamination from previously removed material, polishing material, or submerged material. All kinds of contamination, especially foreign iron particles, can be a source of corrosion, especially in humid environments. Therefore, mechanically cleaned surfaces should only be properly cleaned in dry conditions. The use of mechanical methods 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.
