According to its structure, stainless steel can be divided into austenitic stainless steel, ferritic stainless steel, duplex stainless steel, martensitic stainless steel and precipitation hardening stainless steel. The comparison of main service characteristics of various types of stainless steel is shown in table 2-5-6. See table 2-5-7 for the characteristics and uses of the main brands of stainless steel in China; See table 2-5-8 for the characteristics and uses of the main brands of Japanese JIS standards.

1、 Austenitic stainless steel

Austenitic stainless steel is an important type of stainless steel, and its output and consumption account for 70% of the total stainless steel. According to the alloying method, austenitic stainless steel can be divided into chromium nickel steel and iron chromium manganese steel. The former takes nickel as austenitizing element and is the main body of austenitic steel; The latter is a nickel saving steel with manganese and nitrogen instead of expensive nickel.

Generally speaking, austenitic steel has good corrosion resistance and good comprehensive mechanical and process properties, but its strength and hardness are low.

2、 Ferritic stainless steel

Ferritic stainless steel contains 11% - 30% chromium and basically no nickel. It is a nickel saving steel. In service, the microstructure is mainly ferrite.

Ferritic stainless steel has high strength and low cold work hardening tendency. It has excellent local corrosion resistance such as chloride stress corrosion, pitting corrosion and crevice corrosion, but it is sensitive to intergranular corrosion and poor low-temperature toughness.

3、 Duplex stainless steel

It is generally believed that austenitic + ferritic duplex stainless steel can be called if there is more than 15% ferrite on austenitic matrix or more than 15% austenite on ferritic matrix.

Duplex stainless steel has the advantages of both austenitic steel and ferritic steel.

4、 Martensitic stainless steel

Martensitic stainless steel is a kind of steel whose properties can be adjusted by heat treatment, and its strength and hardness are high.

5、 Precipitation hardening stainless steel

Precipitation hardening stainless steel is a kind of steel in which carbides are precipitated by heat treatment, so as to improve the strength.