Classification, type and chemical composition of stainless steel

Stainless steel is divided into martensite and austenite, ferrite and duplex.

1. Martensitic chromium stainless steel is mainly low-carbon or high-carbon steel with chromium content in the range of 11.5%-18%. Designations 403, 410, 414, 416, 416 (Se), 420, 431, 440A, 440B and 440C, the corrosion resistance of these steels comes from “chromium”. The martensitic stainless steels widely used in various countries are as follows:
1. Low and medium carbon 13% Cr steel
2. High carbon 18% Cr steel
3. Low-carbon nickel-containing (about 2%) 17% Cr steel.

2. Austenitic stainless steel has stable austenite structure when Cr contains about 18%, Ni 8%~10%, and C about 0.1%. Non-magnetic and has high toughness and plasticity, but the strength is low, it is impossible to strengthen it by phase transformation, it can only be strengthened by cold working.

3. Ferritic stainless steel has a chromium content of 11% to 30%, and has a body-centered cubic crystal structure. Generally does not contain nickel, sometimes contains a small amount of Mo, Ti, Nb and other elements, large thermal conductivity, small expansion coefficient, good oxidation resistance, excellent stress corrosion resistance and other characteristics, mostly used in the manufacture of atmospheric resistance, water vapor, water and oxidation Acid corrosion parts. Poor plasticity, plasticity and corrosion resistance after welding are significantly reduced.

4. Austenitic-ferrite duplex stainless steel is a stainless steel with austenite and ferrite structure each accounting for about half. Containing C is low, Cr content is 18%~28%, Ni content is 3%~10%. Some steels also contain alloying elements such as Mo, Cu, Si, Nb, Ti, and N. This type of steel has the characteristics of austenitic and ferritic stainless steel. Compared with ferrite, it has higher plasticity and toughness, no room temperature brittleness, and has significantly improved intergranular corrosion resistance and welding performance, while maintaining iron. The 475°C brittleness and high thermal conductivity of plain stainless steel are characterized by superplasticity. Compared with austenitic stainless steel, the strength is high and the resistance to intergranular corrosion and chloride stress corrosion is significantly improved. Duplex stainless steel has excellent pitting corrosion resistance and is also a nickel-saving stainless steel.