The so-called duplex stainless steel has a half ferrite phase and half austenite phase in its solid quenching structure. Generally, the minimum phase content may reach 30%.

Due to the characteristics of two-phase structure, DSS has the advantages of both ferritic stainless steel and austenitic stainless steel by correctly controlling the chemical composition and heat treatment process.

Compared with austenitic stainless steel, duplex stainless steel has the following advantages:

(1) The yield strength is more than twice as high as that of ordinary austenitic stainless steel, and it has sufficient plastic toughness for forming. The wall thickness of tanks or pressure vessels made of duplex stainless steel is 30-50% less than that of common austenite, which is conducive to reducing costs.(2) It has excellent resistance to stress corrosion cracking. Even the duplex stainless steel with the lowest alloy content has higher resistance to stress corrosion cracking than the austenitic stainless steel, especially in the environment containing chloride ions. Stress corrosion is an outstanding problem that ordinary austenitic stainless steel is difficult to solve.

(3) The 2205 duplex stainless steel, which is widely used in many media, has better corrosion resistance than the ordinary 316L austenitic stainless steel, while the super duplex stainless steel has extremely high corrosion resistance. In some media, such as acetic acid and formic acid, it can even replace the high alloy austenitic stainless steel, or even the corrosion resistant alloy.

(4) It has good local corrosion resistance. Compared with austenitic stainless steel with the same alloy content, its wear resistance corrosion and fatigue corrosion performance are better than austenitic stainless steel.

(5) The linear expansion coefficient is lower than that of austenitic stainless steel and close to that of carbon steel. It is suitable for connecting with carbon steel and has important engineering significance, such as producing composite plates or linings.

(6) No matter under dynamic or static load conditions, it has higher energy absorption capacity than austenitic stainless steel, which has obvious advantages and practical application value for structural members to cope with sudden accidents such as collision and explosion.

Compared with austenitic stainless steel, the disadvantages of duplex stainless steel are as follows:

(1) The universality and versatility of application are not as good as those of austenitic stainless steel, for example, the service temperature must be controlled below 250 ℃.

(2) Its plasticity and toughness are lower than those of austenitic stainless steel, and its cold and hot working processes and formability are inferior to those of austenitic stainless steel.

(3) Due to the existence of medium temperature brittle zone, it is necessary to strictly control the process system of heat treatment and welding to avoid the appearance of harmful phases and damage the performance.

Compared with ferritic stainless steel, duplex stainless steel has the following advantages:

(1) The comprehensive mechanical properties are better than ferritic stainless steel, especially the plasticity and toughness, which are not as sensitive to brittleness as ferritic stainless steel.

(2) In addition to stress corrosion resistance, other local corrosion resistance properties are better than ferritic stainless steel.

(3) The cold processing property and cold forming property are far superior to ferritic stainless steel.

(4) The welding performance is also much better than that of ferritic stainless steel. Generally, preheating is not required before welding and heat treatment is not required after welding.

(5) The application range is wider than that of ferritic stainless steel.

Compared with ferritic stainless steel, the disadvantages of duplex stainless steel are as follows:

The alloy element content is high and the price is relatively high. Generally, the ferrite does not contain nickel.

To sum up, we can generally see the general picture of the service performance and process performance of DSS. With its superior mechanical and corrosion resistance, it has won the favor of users, and has become an excellent corrosion resistant engineering material that saves both weight and investment.