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Stainless steel characteristics

Air, steam, water resistance and other weak corrosive media and acids, alkalis, salts and other chemical erosion corrosion of steel. Also known as stainless and acid-resistant steels. In practice, often weak corrosion-resistant steel known as stainless steel, corrosion and chemical resistance of steel known as acid-resistant steel. Because of the differences in chemical composition, the former is not necessarily resistant to chemical corrosion, while the latter generally has no rust. Depends on the corrosion resistance of stainless steel contains alloying elements in steel. Chromium is a basic element made of corrosion-resistant stainless steel, when the chromium in steel capacity of about 1.2%, chrome with oxygen in the corrosive medium, on a steel surface to form a thin layer of oxide film (film), prevents the matrix further corrosion of steel. Besides chromium, a frequently used alloying elements are nickel, molybdenum, copper, titanium, niobium, nitrogen, to meet various applications requirements on structure and properties of stainless steel.

Stainless steel classifications
Stainless steel usually in the matrix are divided into:
? Ferritic stainless steel. Chromium-containing 12%~30%. Its corrosion resistance, toughness and weldability of chromium content increases, resistance to chloride stress corrosion performance superior to other types of stainless steel.
? Austenitic stainless steel. Chromium is greater than 18%, also contains about 8% of nickel, titanium, molybdenum and a small amount of nitrogen and other elements. Good performance can be corrosion resistance to a variety of media.
? Austenitic-ferritic duplex stainless steel. Both austenitic and ferritic stainless steel advantages, and Super plasticity.
? Martensite stainless steel. High strength, ductility and weldability is inferior.
⒌ precipitation hardened stainless steel. Has has very good formability, good weldability, can be used as ultra high-strength materials in nuclear industry, aviation and aerospace industries.

Classified according to the composition of Cr (SUS400), Cr-Ni (SUS300), Cr-Mn-Ni (SUS200) and precipitation hardening lines (SUS600).
Stainless steel corrosion causes
All metals react with atmospheric oxygen, the oxide film formed on the surface. Unfortunately, in the continuation of iron oxide is formed on oxidation of ordinary carbon steel, corrosion continued to expand, eventually forming holes. You can use paint or oxidation of metal (for example, zinc, chromium and nickel) plating to ensure the surface of carbon steel, but as you know it, this protection is only a film. If the protective layer is damaged, the following steel begins to rust.
Corrosion resistance of stainless steel depends on chrome, but because chrome is one of steel, so protection is not the same.
Chrome add up to 10. 5%, significantly increased resistance to atmospheric corrosion of steel, but higher chromium content, although you may still increase corrosion resistance, but not obvious. Because when alloyed with chromium on steel, changed into similar to the type of surface oxide formed on the surface of pure chromium metal oxides. This tight adhesion of chromium-rich oxide surface, preventing further oxidation. This oxide layer can be extremely thin, natural sheen on the surface of steel can be seen through it, made of stainless steel with special surface. And if the damaged surface, exposed steel surfaces and the atmospheric response to repair itself, forms the “passivation”, continues to play a protective role.

Therefore, all stainless steels have a common characteristic of chrome content in 10. More than 5%.
Application and construction related to the area of steel is usually only six. They both contain 17~22% chromium, better steel contains nickel. Add Mo can be further improved atmospheric corrosion, in particular atmospheric corrosion resistance to chloride.

Source: http://www.steel-tubes.com/

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