Knowledge of stainless steel
Stainless Steel (Stainless Steel) is the abbreviation of stainless acid-resistant steel, resistant to air, steam, water and other weak corrosive media or stainless steel; The steel that is resistant to chemical corrosion media (acid, alkali, salt and other chemical etching) is called resistant steel. Due to the difference in the chemical composition of the two, the former is not necessarily resistant to chemical medium corrosion, while the latter is generally stainless. The corrosion resistance of stainless steel depends on the alloying elements contained in the steel.
Usually divided by metallographic organization:
Generally, according to the metallographic organization, the ordinary stainless steel is divided into three categories: Austenitic stainless steel, ferritic stainless steel, martensitic stainless steel. On the basis of these three basic metallographic structures, for specific needs and purposes, and derived from the duplex steel, precipitation hardening stainless steel and iron content of less than 50% of the high alloy steel.
1, Austenitic stainless steel
The matrix is mainly stainless steel with a face-centered cubic crystal structure of austenitic structure (CY phase), non-magnetic, mainly through cold working to strengthen it (and may result in a certain magnetic). The American Iron and Steel Institute uses 200 and 300 series numbers, such as 304.
2, iron type stainless steel
The matrix is dominated by ferrite structure (phase a) of body-centered cubic crystal structure, magnetic, generally can not be hardened by heat treatment, but cold working can make it slightly strengthened stainless steel. The American Iron and Steel Institute is marked 430 and 446.
3. Martensitic stainless steel
The matrix is martensitic structure (body-centered cubic or cubic), magnetic stainless steel, its mechanical properties can be adjusted by heat treatment. The American Iron and Steel Institute uses numbers 410, 420, and 440. Martensite has an austenitic structure at high temperatures, and when cooled to room temperature at an appropriate rate, the austenitic structure is able to convert to martensite (i.e., hardened).
4, austenitic ferritic (duplex) stainless steel
The matrix has both austenitic and ferritic two-phase structure, of which the content of the less phase matrix is generally greater than 15%, is magnetic, and can be strengthened by cold working stainless steel, 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 point corrosion.
5, precipitation hardening stainless steel
Stainless steel whose matrix is austenitic or martensitic and can be hardened by precipitation hardening. The American Iron and Steel Institute uses 600 series numbers, such as 630, which is 17-4PH.
In general, in addition to alloys, the corrosion resistance of austenitic stainless steel is relatively excellent, in a less corrosive environment, ferritic stainless steel can be used, in a mildly corrosive environment, if the material is required to have high strength or high hardness, martensitic stainless steel and precipitation hardened stainless steel can be used.
