Duplex Stainless Steel (Duplex Stainless Steel) and ordinary stainless steel (such as austenitic stainless steel, ferritic stainless steel, etc.) have some significant differences in composition, structure, performance and so on. Here are the main differences:

1. Structure composition
Duplex stainless steel: As the name suggests, the microstructure of duplex stainless steel is composed of two phases: ** austenite ** and ** ferrite **, and the usual ratio is 50% austenite and 50% ferrite. This structure gives it excellent strength, corrosion resistance and crack resistance.
Ordinary stainless steel:
Austenitic stainless steel (such as 304, 316) is mainly composed of austenitic structure, has good toughness and corrosion resistance, but the strength is low.
Ferritic stainless steel (such as 430) is mainly composed of ferritic, has high corrosion resistance and good oxidation resistance, but poor toughness, easy to embrittlement.

2. Mechanical properties
Duplex stainless steel: Due to the combination of ferritic and austenitic phases, duplex stainless steel usually has higher tensile strength and yield strength, which is higher than austenitic stainless steel and can usually withstand greater loads.
Ordinary stainless steel: Austenitic stainless steel has a lower strength, and although it has better ductility and toughness, it may not be as good as duplex stainless steel in applications with high strength requirements. The strength of ferritic stainless steel is higher than that of austenite, but it is relatively brittle.

3. Corrosion resistance
Duplex stainless steel: has excellent corrosion resistance, especially to pitting and stress corrosion cracking (SCC) caused by chloride. Duplex stainless steel is particularly outstanding in Marine and chemical environments.
Ordinary stainless steel:
Austenitic stainless steel: has good corrosion resistance, but stress corrosion problems may occur in high temperature and high chlorine environments.
Ferritic stainless steel: poor corrosion resistance, especially in chlorine-containing environments, prone to pitting.

4. Weldability
Duplex stainless steel: The weldability of duplex stainless steel is more complex, and special attention needs to be paid to controlling the heat input when welding to avoid producing too much single-phase structure (such as complete ferrite or complete austenite), which may affect the performance. High-quality welding requires the use of appropriate welding materials and control processes.
Ordinary stainless steel: Austenitic stainless steel usually has good weldability, easy welding, and good strength after welding. The weldability of ferritic stainless steel is poor and cracks are easy to occur.

5. Application field
Duplex stainless steel: Because of its superior strength and corrosion resistance, it is widely used in the fields of chemical industry, Marine engineering, oil and gas, paper making and sewage treatment. Especially suitable for high corrosive environment and high strength requirements.
Ordinary stainless steel: Austenitic stainless steel is widely used in: kitchen equipment, food industry, chemical equipment, etc., because of its good formability and corrosion resistance. Ferritic stainless steel is mainly used in: automobile exhaust system, home equipment, etc. **

6. Cost
Duplex stainless steel: Duplex stainless steel is usually more expensive due to its complex production process and special alloy composition.
Ordinary stainless steel: The cost of austenitic and ferritic stainless steel is relatively low, especially austenitic stainless steel.

In SUMMARY:
The biggest advantage of duplex stainless steel is that it combines the advantages of austenite and ferrite to provide higher strength and better corrosion resistance, which is especially suitable for applications in extreme environments. Ordinary stainless steel has more choice and flexibility in price, processing technology and performance, and is suitable for general industrial use.