Stainless steel must not rust?
When brown rust spots (spots) appear on the surface of stainless steel, people are greatly surprised, thinking that stainless steel will not rust, and if it gets rusty, it is not stainless steel. In fact, this is a one-sided misconception about the lack of understanding of stainless steel. Stainless steel also can get rusty under certain conditions.
Stainless steel has the ability to resist atmospheric oxidation, that is, stainless, and also has the ability to resist corrosion in media containing acids, alkalis, and salts, that is, corrosion resistance. But the size of its resistance to corrosion with the chemical composition of its steel itself, mutual state, working conditions and surrounding medium type and change. Like 304 steel pipes, in the atmosphere of dry cleansing, absolute good resistant to corrosion ability is arranged, but it is moved on to riviera, in containing the sea fog of a large amount of salts, and will soon get rusty. Therefore, not any kind of stainless steel can resist corrosion and rust at any time.
Stainless steel relies on a layer of extremely thin, firm and dense stable chromium-rich oxide film (protective film) formed on its surface to prevent oxygen atoms from continuing to infiltrate and oxidize, thereby obtaining the ability to resist corrosion. Once there is some reason, this film is continuously damaged, and the oxygen atoms in the air or liquid will continuously infiltrate or the iron atoms in the metal will continuously separate out to form loose iron oxide, and the metal surface will be continuously damaged rust.
What kind of stainless steel is not easy to rust?
The main factors affecting the corrosion of stainless steel are the following three points.
1) The content of alloying elements
Generally speaking, steel with a chromium content of 10.5% 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 should be 8-10%, and the content of chromium should reach 18-20%. Such stainless steel will not rust under normal circumstances.
2) The smelting process of the production enterprise
The smelting process of the production enterprise will also affect the corrosion resistance of stainless steel. Large stainless steel factories with good smelting technology, advanced equipment, and advanced technology can guarantee the control of alloy elements, the removal of impurities, and the control of billet cooling temperature. Therefore, the product quality is stable and reliable, with good internal quality and 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.
3) External environment
A dry and well-ventilated environment is not easy to rust. The air humidity is high, the continuous rainy weather, or the environmental area with high pH in the air is easy to rust. 304 stainless steel, if the surrounding environment is too bad, it will rust.
Can you judge stainless steel with a magnet?
Many people go to buy stainless steel or stainless steel products, and they bring a small magnet with them. When they look at the goods, they think that the ones that cannot be sucked are good stainless steel. There will be no rust without magnetism. In fact, this is a wrong understanding.
Whether the stainless steel belt is magnetic or not is determined by the organizational structure. During the solidification process, due to the different solidification temperatures, stainless steel with different organizational structures such as "ferrite", "austenite" and "martensite" will be formed. Among them, "ferrite" Body" and "martensitic" stainless steels are magnetic. The "austenitic" stainless steel has good comprehensive mechanical properties, process performance and weldability, but only in terms of corrosion resistance, the magnetic "ferritic" stainless steel is stronger than the "austenitic" stainless steel.
The so-called 200 series and 300 series stainless steels with high manganese content and low nickel content currently 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 slightly magnetic, so it is a misunderstanding and unscientific to judge the quality of stainless steel with or without magnetism.
