Duplex Stainless Steel refers to stainless steel with ferrite and austenite each accounting for about 50%. Generally, the content of less phases needs to be at least 30%. In the case of low C content, the Cr content is 18% to 28%, and the Ni content is 3% to 10%. Some steels also contain alloying elements such as Mo, Cu, Nb, Ti, and N.
Duplex stainless steel VS austenitic & ferritic stainless steel
Due to the characteristics of the two-phase structure, through the correct control of the chemical composition and heat treatment process, the duplex stainless steel has the advantages of both ferritic stainless steel and austenitic stainless steel.
Compared with austenitic stainless steel, the advantages of duplex stainless steel are as follows:
1.The yield strength is more than twice that of ordinary austenitic stainless steel, and it has sufficient plastic toughness for forming. The wall thickness of storage tanks or pressure vessels made of duplex stainless steel is 30-50% less than that of commonly used austenite, which is beneficial to reduce 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 austenitic stainless steel, especially in an environment containing chloride ions. Stress corrosion is a prominent problem that is difficult to solve for ordinary austenitic stainless steel.
3.The corrosion resistance of 2205 duplex stainless steel, which is most commonly used in many media, is better than ordinary 316L austenitic stainless steel, while super duplex stainless steel has extremely high corrosion resistance. In some media, such as acetic acid, Formic acid can even replace high-alloy austenitic stainless steel and even corrosion-resistant alloys.
4.It has good local corrosion resistance. Compared with austenitic stainless steel with the same alloy content, its wear corrosion resistance and fatigue corrosion resistance are better than austenitic stainless steel.
5.The coefficient of linear expansion is lower than that of austenitic stainless steel, which is close to that of carbon steel. It is suitable for connection with carbon steel and has important engineering significance, such as the production of composite plates or linings. (6) No matter under dynamic load or static load, it has higher energy absorption capacity than austenitic stainless steel, which is suitable for structural parts to cope with sudden accidents such as collision and explosion. Duplex stainless steel has obvious advantages and has practical application value.
Compared with austenitic stainless steel, the disadvantages of duplex stainless steel are as follows:
1.The universality and versatility of the application are not as good as the austenitic stainless steel, for example, the use temperature must be controlled below 250 degrees Celsius.
2.Its plastic toughness is lower than that of austenitic stainless steel, and its cold and hot processing technology and forming performance are not as good as austenitic stainless steel.
3. There is a medium temperature brittle zone, and the process system of heat treatment and welding needs to be strictly controlled to avoid the appearance of harmful phases and damage performance.
Compared with ferritic stainless steel, the advantages of duplex stainless steel are as follows:
1.The comprehensive mechanical properties are better than ferritic stainless steel, especially the plastic toughness, which is not as sensitive to brittleness as ferritic stainless steel.
2.Except for stress corrosion resistance, other local corrosion resistance is better than ferritic stainless steel.
3. Cold working process performance and cold forming performance are far better than 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 after welding.
5. The application range is wider than ferritic stainless steel.
Compared with ferritic stainless steel, the disadvantages of duplex stainless steel are as follows:
The content of alloying elements is high and the price is relatively high. Generally, ferrite does not contain nickel.