Today, let's take a look together at "Introduction to Stainless Steel Classification and Application

The types of stainless steel are classified according to their composition into the Cr series (400 series), the Cr-Ni series (300 series), the Cr-Mn-Ni series (200 series), and the precipitation hardening series (600 series). 

I. Classification of stainless steel by microstructure:

1) Ferritic stainless steel (numbers in the 400 series): Ferritic stainless steel not only has good corrosion resistance but also has the greatest characteristics of excellent oxidation resistance, excellent stress resistance, and good thermal conductivity and very small expansion coefficient. However, ferritic stainless steel has poor plasticity, so this type of stainless steel material is mainly used to manufacture corrosion-resistant components.

2) Austenitic stainless steel (200, 300 series): Stainless steel with austenitic structure at room temperature, containing 8% to 10% Ni, about 18% Cr, and about 0.1% C, and a small amount of molybdenum, titanium, nitrogen, etc. It has good comprehensive performance and can resist corrosion by various media. 201, 202, 301, 304, 316, 309, 321, etc. are all austenitic stainless steel.

3) Austenitic-ferritic duplex stainless steel is a type of stainless steel with equal proportions of austenitic and ferritic structures inside. It has the characteristics of both austenitic and ferritic stainless steel materials, and compared with ferritic stainless steel, it has better plasticity, higher toughness, and better thermal conductivity and smaller expansion coefficient.

4) Martensitic stainless steel (part of the 400 series): Stainless steel that can adjust its mechanical properties through heat treatment. This type of steel has a higher hardness after quenching and different strength and toughness combinations at different tempering temperatures. The standard martensitic stainless steel types are: 403, 410, 414, 416, 416(Se), 420, 431, 440A, 440B, and 440C.

5) Precipitation hardening stainless steel: Precipitation hardening stainless steel refers to stainless steel with different types and quantities of strengthening elements added on the basis of the chemical composition of stainless steel, through the precipitation hardening process, different types and quantities of carbides, nitrides, carbide-nitrides, and intermetallic compounds are precipitated, which not only increases the strength of the steel but also maintains sufficient toughness. Precipitation hardening stainless steel can be classified into three types according to its microstructure: martensitic type, semi-austenitic type, and austenitic type. 

II. Relationship between Chemical Composition and Stainless Steel Properties

1. Carbon (C): Can increase hardness and strength. Excessive content will reduce its ductility and corrosion resistance.

2. Chromium (Cr): Can enhance corrosion resistance and oxidation resistance, refine grain size, increase strength, hardness and wear resistance.

3. Nickel (Ni): Can increase high-temperature strength and corrosion resistance, and reduce the rate of cold work hardening.

4. Molybdenum (Mo): Increases strength and has excellent corrosion resistance to oxides and seawater.

5. Copper (Cu): Facilitates cold processing and reduces magnetism.