Stainless steel
Stainless and acid-resistant steel is referred to as stainless steel. It is composed of two parts: stainless steel and acid-resistant steel. In short, the steel that can resist atmospheric corrosion is called stainless steel, and the steel that can resist chemical medium corrosion is called acid-resistant steel. Stainless steel is a high-alloy steel with more than 60% iron as the matrix and alloying elements such as chromium, nickel, and molybdenum added.
When the chromium content in the steel exceeds 12%, the steel is not easy to corrode and rust in the air and dilute nitric acid. The reason is that chromium can form a very tight chromium oxide film on the steel surface, which effectively protects the steel from corrosion. The chromium content in stainless steel generally exceeds 14%, but stainless steel is not absolutely free of rust. In coastal areas or some places with severe air pollution, when the chloride ion content in the air is large, there may be some rust spots on the surface of stainless steel exposed to the atmosphere, but these rust spots are limited to the surface and will not erode the internal matrix of the stainless steel.
Generally speaking, steel containing more than 12% Wcr has the characteristics of stainless steel. Stainless steel can be divided into five categories according to the microstructure after heat treatment: ferritic stainless steel, martensitic stainless steel, and austenitic stainless steel. , Austenitic-ferritic stainless steel and precipitation carbide stainless steel.
Stainless steel is usually divided into:
1. Ferritic stainless steel. Chromium 12% to 30%. Its corrosion resistance, toughness and weldability increase with the increase of chromium content, and its resistance to chloride stress corrosion is better than other types of stainless steel.
2. Austenitic stainless steel. It contains more than 18% chromium, about 8% nickel and a small amount of molybdenum, titanium, nitrogen and other elements. It has good comprehensive performance and is resistant to corrosion by various media.
3. Austenitic-ferritic duplex stainless steel. It has the advantages of both austenitic and ferritic stainless steels, and has superplasticity.
4. Martensitic stainless steel. High strength, but poor plasticity and weldability.
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