Due to the characteristics of the two-phase structure, through the correct control of the chemical composition and heat treatment process, DSS combines the advantages of 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 double that of ordinary austenitic stainless steel, and it has sufficient plastic toughness for forming. The wall thickness of the storage tank or pressure vessel made of duplex stainless steel is 30-50% less than that of commonly used 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 austenitic stainless steel, especially in the environment containing chloride ions. Stress corrosion is a prominent problem that ordinary austenitic stainless steel is difficult to solve.
(3) The corrosion resistance of 2205 duplex stainless steel, which is the most common application in many media, is superior to 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 or even corrosion-resistant alloys.
(4) It has good local corrosion resistance. Compared with austenitic stainless steel with equivalent alloy content, its wear resistance and fatigue corrosion resistance are superior to austenitic stainless steel.
(5) The coefficient of linear expansion is lower than that of austenitic stainless steel, close to carbon steel, suitable for connection with carbon steel, and has important engineering significance, such as the production of composite panels or lining.
(6) No matter under dynamic or static load conditions, it has a higher energy absorption capacity than austenitic stainless steel. This has obvious advantages for structural parts to deal with unexpected accidents such as collisions and explosions, and has practical application value .
Compared with austenitic stainless steel, the weakness of duplex stainless steel is as follows:
(1) The universality and versatility of the application are not as good as austenitic stainless steel, for example, its 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 impair performance.
Compared with ferritic stainless steel, the advantages of duplex stainless steel are as follows:
(1) The overall mechanical properties are better than ferritic stainless steels, especially the plastic toughness, which is not as sensitive to brittleness as ferritic stainless steels.
(2) In addition to stress corrosion resistance, other local corrosion resistance is better than ferritic stainless steel.
(3) The cold working process performance and cold forming performance are far superior to ferritic stainless steel.
(4) Welding performance is also far superior to ferritic stainless steel. Generally, preheating is not required before welding, and no heat treatment is required after welding.
(5) The application range is wider than ferritic stainless steel.
Compared with ferritic stainless steel, the weakness of duplex stainless steel is as follows:
The alloy element content is high, the price is relatively high, the general ferrite does not contain nickel.
In summary, it can be summarized the overview of the performance and process performance of DSS. It has won the favor of users with its superior mechanical and corrosion resistance comprehensive performance, and has become an excellent resistance to both weight and investment. Erosion of engineering materials.
The austenite type is non-magnetic or weakly magnetic, and martensite or ferrite is magnetic.
The most commonly used stainless steel for decorative tube sheets is austenitic 304 material, which is generally non-magnetic or weak-magnetic, but the magnetic composition may fluctuate due to smelting or the processing state may be different, but this may not be considered as Counterfeit or unqualified, what is the reason?
As mentioned above, austenite is non-magnetic or weakly magnetic, and martensite or ferrite is magnetic. Due to segregation of components during smelting or improper heat treatment, it will cause a small amount of martensite or ferrite in austenitic 304 stainless steel. Body organization. In this way, 304 stainless steel will have a weak magnetic.
In addition, after cold working of 304 stainless steel, the structure will also be transformed into martensite. The greater the degree of cold working deformation, the more martensite transformation, the greater the magnetic properties of steel. Like a batch of steel belts, Φ76 tubes are produced without obvious magnetic induction, and Φ9.5 tubes are produced. Due to the large bending deformation, the magnetic sense is more obvious. The deformation of the square rectangular tube is larger than that of the round tube, especially the corner part, the deformation is more intense and the magnetic is more obvious.
To completely eliminate the magnetic properties of 304 steel caused by the above reasons, the stable austenite structure can be restored by high-temperature solution treatment to eliminate the magnetic properties.