What kinds of stainless steel are there?

Usually, according to the metallographic organization, the ordinary stainless steel is divided into three categories: austenitic stainless steel, iron type stainless steel, Martensite type stainless steel. On the basis of these three basic metallographic structures, duplex steels, precipitate hardened stainless steels and high alloy steels with less than 50% iron content are derived for specific needs and purposes.

1. Austenitic stainless steel. The matrix is stainless steel with face-centered cubic crystal structure austenite structure (CY phase), non-magnetic, mainly through cold processing to strengthen (and may lead to a certain degree of magnetism). The American Iron and Steel Institute uses 200 and 300 series numbers, such as 304.

2, iron type stainless steel. The matrix is a stainless steel with ferrite structure (a phase) dominated by body centered cubic crystal structure. It is magnetic and generally cannot be hardened by heat treatment, but it can be slightly strengthened by cold working. The American Iron and Steel Institute is 430 and 446.

3, Martensite stainless steel. The matrix of martensitic structure (body centered cubic or cubic), magnetic, through heat treatment can adjust its mechanical properties of stainless steel. American Iron and Steel Institute numbers 410, 420 and 440. Martensite has austenitic structure at high temperature, which is able to change to martensite (i.e. hardened) when cooled to room temperature at an appropriate rate.

4, austenitic ferrite (duplex) stainless steel. The matrix has both austenite and ferrite phase structure, and the content of the less phase matrix is generally more than 15%, which is magnetic and can be strengthened by cold working. 329 is a typical duplex stainless steel. Compared with austenitic stainless steel, duplex steel has higher strength, higher resistance to intergranular corrosion, chloride stress corrosion and spot corrosion.

5, precipitation hardening stainless steel. Stainless steel whose substrate is austenitic or martensitic and can be hardened by precipitation hardening. The American Iron and Steel Institute uses 600 series numbers such as 630, or 17-4pH.

Generally speaking, in addition to alloy, the corrosion resistance of austenitic stainless steel is relatively excellent, in the environment of low corrosion, ferritic stainless steel can be used, in mildly corrosive environment, if the material is required to have high strength or high hardness, martensitic stainless steel and precipitated hardened stainless steel can be used.

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