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, so the product quality is stable and reliable, the internal quality is good, and it is not easy to rust. On the contrary, some small steel mills have backward equipment and backward technology. During the smelting process, impurities cannot be removed, and the products produced will inevitably 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.

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.

Is good stainless steel. Without magnetism, it will not rust. In fact, this is a wrong understanding. The fact that the stainless steel strip does not have magnetism is determined by its structure. During the solidification process of molten steel, "ferrite" will be formed due to different solidification temperatures.

"Austenitic" and "martensite" stainless steels with different structures, among which "ferritic" and "martensitic" stainless steels are all magnetic. "Austenitic" stainless steel has good comprehensive mechanical properties and process performance and weldability, but only in terms of corrosion resistance, magnetic "ferritic" stainless steel is stronger than "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 far 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.

Why does stainless steel rust?

When brown rust spots (spots) appear on the surface of stainless steel, people are greatly surprised: "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. For example, 304 material has absolutely excellent corrosion resistance in a dry and clean atmosphere, but if it is moved to a coastal area, it will rust quickly in the sea fog containing a lot of salt. Therefore, not any kind of stainless steel can resist corrosion and rust at any time.

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 penetrate and continue to oxidize, and to obtain corrosion resistance. Once for some reason, the film is constantly damaged, the oxygen atoms in the air or liquid will continue to penetrate 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. There are many forms of damage to this surface film, the most common in daily life are the following:

1. The surface of the stainless steel accumulates dust containing other metal elements or the attachments of dissimilar metal particles. In the humid air, the condensed water between the attachments and the stainless steel connects the two into a micro-battery, which triggers an electrochemical reaction. , the protective film is damaged, called electrochemical corrosion.

2. Organic juices (such as melons, vegetables, noodle soup, sputum, etc.) adhere to the surface of stainless steel. In the presence of water and oxygen, organic acids are formed, and organic acids are formed to corrode the metal surface for a long time.

3. The surface of stainless steel adheres to contain acids, alkalis and salts (such as alkali water and lime water spraying for decoration of walls), causing local corrosion.

4. In polluted air (atmosphere containing a large amount of sulfide, oxide and hydrogen oxide), when it encounters condensed water, it will form liquid spots of sulfuric acid, nitric acid and acetic acid, causing chemical corrosion.

The above conditions can cause damage to the protective film on the stainless steel surface and cause corrosion. Therefore, to ensure that the metal surface is permanently bright and does not get rusted, we recommend:

① The surface of decorative stainless steel must be cleaned and scrubbed frequently to remove attachments and eliminate external factors that cause rust.

② There are stainless steels made of 201 and 202 materials on the market that are easy to rust in coastal areas, and are suitable for use in environments without industrial pollution and air corrosion.

③ In seaside areas, use 304 stainless steel, which can resist seawater corrosion.

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 part 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 rinse properly with clean 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 preferably 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.