Stainless steel is the abbreviation of stainless acid-resistant steel. It is a type of steel that can withstand weak corrosive media such as air, steam, and water or has stainless properties, such as 201 stainless steel (1Cr17Mn6Ni5N); and steel that is resistant to chemical corrosion media (acids, alkalis, salts, etc.) is called acid-resistant steel, such as 304 stainless steel (06Cr19Ni10) and 316 stainless steel (0Cr17Ni12Mo2). Due to the difference in chemical composition between the two, their corrosion resistance is different. Ordinary stainless steel such as 201 stainless steel is generally not resistant to chemical corrosion, while 304, 316 and other 3 series stainless steels are resistant to chemical corrosion.
Common marking methods in the market include chemical formula (06Cr19Ni10) and SUS (SUS304), among which 06Cr19Ni10 generally indicates national standard production, 304 generally indicates American ASTM standard production, and SUS indicates Japanese standard production.
Common Testing Methods For Stainless Steel:
In fact, stainless steel is not completely rust-free, but it has better corrosion resistance than ordinary steel. Even if they are both stainless steel, there is a big difference in corrosion resistance, such as 2 series stainless steel and 3 series stainless steel. Sometimes it is difficult to distinguish whether the material we get is 2 series or 3 series before it has been tested in the environment for a long time.
There are many detection methods on the market, among which there are two relatively simple methods.
The 2 series represented by 201 contains higher carbon and manganese, and the surface will be darker even if polished. It will be bright black;
The 201 material is relatively hard, and the sparks will be more and larger when cutting; on the other hand, the 3 series represented by 304 will be brighter, and the texture is relatively soft, and the cutting sparks will be much smaller.
Application Areas Of 304 And 316 Stainless Steel:
Stainless steel is closely related to our lives. 201 and 304 stainless steel are used more, and 316 stainless steel is of higher quality. Both 304 and 316 are stainless acid-resistant steels. Both are sanitary stainless steels and are suitable for use in coastal areas. However, when the chlorine content in the use environment is relatively high, it is recommended to use 316, because the corrosion resistance of 304 is mainly due to the chromium oxide layer on the surface, that is, the passivation layer. When the chlorine content in the environment is relatively high, it will corrode the chromium oxide layer, thereby achieving the purpose of corroding the matrix. However, 316 stainless steel contains molybdenum, and the addition of molybdenum makes it form a special corrosion-resistant structure.
Both 304 and 316 are sanitary stainless steels, and there is no obvious difference in daily use. However, in special occasions, such as when there are strict requirements for thermal expansion, high-temperature precision parts should still choose 316 material. After all, 316 basically does not have thermal expansion and contraction.
Why Does Intergranular Corrosion Occur?
201, 304, and 316 are all austenitic stainless steels. They are said to be non-magnetic, and some are weakly magnetic because of the segregation of components during smelting or improper heat treatment, which leads to a small amount of martensite or ferrite in austenite. The corrosion resistance of austenitic stainless steel comes from the chromium oxide protective layer formed on the metal surface. When the material temperature is heated to 450-900 degrees, the structure changes, and chromium carbide will form along the edge of the crystal instead of a chromium oxide protective layer, which reduces the corrosion resistance. This is also called "intergranular corrosion". As a result, 304L and 316L stainless steels appeared. Both of them have less intergranular corrosion due to their low carbon content. It should be noted that higher intergranular corrosion sensitivity does not mean that non-low carbon content is more susceptible to corrosion. In a high-chlorine environment, this sensitivity is also higher. Henan Jinbailai Co., Ltd. specializes in providing various specifications of stainless steel pipes, plates, etc., which can be rolled and cut to size, and customized. Welcome to consult.
