Views: 0 Author: Site Editor Publish Time: 2022-08-17 Origin: Site
Stainless steel refers to the steel resistant to weak corrosive media such as air, steam and water and chemical corrosive media such as acid, alkali and salt, also known as stainless and acid resistant steel. The corrosion resistance of stainless steel depends on the alloy elements contained in the steel.
Generally, according to the metallographic structure, ordinary stainless steel is divided into three categories: austenitic stainless steel, ferritic stainless steel and martensitic stainless steel. On the basis of these three basic metallographic structures, dual phase steel, precipitation hardening stainless steel and high alloy steel with iron content less than 50% have been derived for specific needs and purposes.
1.Austenitic stainless steel. Stainless steel whose matrix is mainly austenite structure (CY phase) with face centered cubic crystal structure and is non-magnetic. It is mainly strengthened (and may cause certain magnetism) by cold processing. The American Iron and Steel Association is indicated by 200 and 300 series numbers, such as 304.
2. Ferritic stainless steel. The matrix is mainly ferrite structure (phase a) with 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 Association designates 430 and 446.
3. Martensitic stainless steel. Stainless steel whose matrix is martensitic structure (body centered cubic or cubic), magnetic and whose mechanical properties can be adjusted by heat treatment. The American Iron and Steel Association is numbered 410, 420 and 440. Martensite has austenite structure at high temperature. When it is cooled to room temperature at an appropriate speed, the austenite structure can be transformed into martensite (i.e., hardened).
4. AUSTENITIC FERRITIC (duplex) stainless steel. The matrix has both austenitic and ferritic two-phase structures. The content of less phase matrix is generally more than 15%. It is a magnetic stainless steel that can be strengthened by cold processing. 329 is a typical dual phase stainless steel. Compared with austenitic stainless steel, the dual phase steel has higher strength, better resistance to intergranular corrosion, chloride stress corrosion and pitting corrosion.
5. Precipitation hardening stainless steel. Stainless steel whose matrix is austenite or martensite and can be hardened by precipitation hardening treatment. American Iron and Steel Association is indicated by 600 series numbers, such as 630, i.e. 17-4PH.
Generally speaking, in addition to alloys, austenitic stainless steel has excellent corrosion resistance. In the environment with low corrosion, ferritic stainless steel can be used. In the environment with mild corrosion, if the material is required to have high strength or high hardness, martensitic stainless steel and precipitation hardening stainless steel can be used.
