What are the classifications of stainless steel?
1. Austenitic stainless steel
Austenitic stainless steel refers to stainless steel having an austenite structure at normal temperature. When the steel contains about 18% Cr, Ni 8% to 25%, and C about 0.1%, it has a stable austenite structure. Austenitic chromium-nickel stainless steel includes the famous 18Cr-8Ni steel and high Cr-Ni series steel which is added with elements of Cr and Ni and added with elements such as Mo, Cu, Si, Nb and Ti. Austenitic stainless steel is non-magnetic and has high toughness and plasticity, but its strength is low. It is impossible to strengthen it by phase transformation. It can only be strengthened by cold working. If it is added with elements such as S, Ca, Se, Te, it has good Easy machinability.
2. Ferritic stainless steel
Ferritic stainless steel (400 series) contains 15% to 30% chromium and has a body-centered cubic crystal structure. These steels generally do not contain nickel, and sometimes contain a small amount of elements such as Mo, Ti, Nb, etc. These steels have the characteristics of large thermal conductivity, small expansion coefficient, good oxidation resistance, excellent resistance to stress corrosion, etc. Parts that are corroded by water vapor, water, and oxidizing acids. The price of ferritic stainless steel is not only relatively low and stable, but also has many unique features and advantages. It has been proven that ferritic stainless steel is extremely rare in many applications where austenitic stainless steel (300 series) was originally considered to be used. Excellent alternative material, ferritic stainless steel does not contain nickel, the main elements are chromium (>10%) and iron, chromium is a particularly corrosion-resistant element of stainless steel, and its price is relatively stable.
3. Duplex stainless steel
Duplex Stainless Steel (DSS) refers to about 50% of ferrite and austenite, and generally requires less than 30% of stainless steel. In the case of a lower C content, the Cr content is between 18% and 28%, and the Ni content is between 3% and 10%. Some steels also contain alloying elements such as Mo, Cu, Nb, Ti, and N.
This type of steel combines the characteristics of austenitic and ferritic stainless steel. Compared with ferrite, it has higher plasticity, toughness, no room temperature brittleness, resistance to intergranular corrosion and weldability, and iron retention. The 475 ° C brittleness and high thermal conductivity of the stainless steel are characterized by superplasticity. Compared with austenitic stainless steel, it has high strength and resistance to intergranular corrosion and chloride stress corrosion. Duplex stainless steel has excellent pitting resistance and is also a nickel-saving stainless steel.
4. Precipitation hardening stainless steel
Precipitation hardening stainless steel refers to the addition of different types and quantities of strengthening elements to the chemical composition of stainless steel. Different types and quantities of carbides, nitrides, carbonitrides and intermetallic compounds are precipitated by precipitation hardening. A type of high-strength stainless steel that not only increases the strength of steel but also maintains sufficient toughness, referred to as PH steel.
5. Martensitic stainless steel
High strength, but poor plasticity and weldability. The commonly used grades of martensitic stainless steels are 1Cr13, 3Cr13, etc., because of the high carbon content, they have high strength, hardness and wear resistance, but the corrosion resistance is slightly poor, which is used for high mechanical properties and corrosion resistance. General parts are required, such as springs, steam turbine blades, hydraulic valve valves, etc. This type of steel is used after quenching and tempering. Annealing and annealing are required after stamping.
