why the performance of duplex stainless steel is so well?
The corrosion resistance of stainless steel is generally proportional to the ratio of chromium content. The chromium content of Cr≥12% will form a very thin and fine oxide film-passivation
film on the surface of stainless steel to protect the stainless steel from oxidation or corrosion by the medium.
Duplex stainless steels typically have a chromium content between 18% and 28%, so duplex stainless steels have excellent corrosion resistance.
Duplex Stainless Steel (DSS) means that ferrite and austenite each account for 50%, and some steels also contain alloying elements such as Mo, Cu, Nb, Ti, and N.
Classification of duplex stainless steel
Low alloy type, representing the grade UNS S32304 (23Cr-4Ni-0.1N), steel does not contain molybdenum, PREN value is 24-25,
can be used instead of AISI304 or 316 in terms of stress corrosion resistance.
Medium alloy type, the representative grade is UNS S31803 (22Cr-5Ni-3Mo-0.15N), PREN value is 32-33, and its corrosion
resistance is between AISI 316L and 6% Mo+N austenitic stainless steel.
High alloy type, generally containing 25% Cr, also containing molybdenum and nitrogen, and some also containing copper and tungsten,
standard grade UNSS32550 (25Cr-6Ni-3Mo-2Cu-0.2N), PREN value 38-39, this kind of steel The corrosion resistance of the duplex stainless steel is higher than 22% Cr.
Super duplex stainless steel with high molybdenum and nitrogen, standard grade UNS S32750 (25Cr-7Ni-3.7Mo-0.3N), some also contain tungsten and copper,
PREN value greater than 40, suitable for harsh media conditions, with Super austenitic stainless steel
The performance and advantages of duplex stainless steel compared to austenite and ferrite, where is the advantage, please see our next article.