Classification Of Duplex Stainless Steel According To PRE Value

PRE (ie Cr%+3.3×(Mo+1/2W)%+16×N%) value in steel.

1. Low-alloy dual-phase steel: Representative grade: UNS S32304 (23Cr-4Ni-0.1N), no molybdenum in the steel, pitting corrosion resistance equivalent, PRE value 24-25, can replace AISI304 in stress corrosion resistance ( 0Cr18Ni9) or 316L (00Cr17Ni12Mo2).

2. Medium alloy type dual-phase steel: Representative grade: UNS S31803 (22Cr-5Ni-3Mo-0.15N), PRE value is 32-33, its corrosion resistance is between AISI316L (00Cr17Ni12Mo2) and 6%Mo+N Austria between tensite stainless steels.

3. High-alloy duplex steel: This type of duplex stainless steel contains up to 25% chromium, and it appeared first in the duplex stainless steel series, such as 329 in the United States, and then developed in major industrial countries, with many grades and applications. very broad. The early development of low-carbon and molybdenum-free Cr25Ni5 type duplex steel, such as IN-744 (0Cr26Ni6Ti), 2323 (0Cr26Ni5), etc., then developed a number of 1% ~ 3% Mo high chromium duplex stainless steel, improve The corrosion resistance of steel has been improved, the scope of use has been expanded, and it has been included in standards successively, such as 329J1 (0Cr25Ni5Mo2), DIN1.4582 (0Cr25Ni7Mo1.5), etc. However, due to the increase in the amount of ferrite near the weld after welding, it may even be possible Becoming a single-phase structure deteriorates the performance of the steel, thus limiting its use; in order to solve this problem, ultra-low carbon nitrogen-containing duplex stainless steels with more suitable two-phase ratios have been developed since the 1970s. In addition to molybdenum, some The grades also incorporate elements such as copper and tungsten to further improve corrosion resistance. Such as NTK R-4 (00Cr25Ni5Mo2N), DP3 (00Cr25Ni7Mo3WCuN) and so on.

4. Super dual-phase steel: refers to the dual-phase steel with PREN>40, containing 25% Cr and high molybdenum (>3.5%) and high nitrogen (0.22% ~ 0.30%), the main grades are UNS S32550 (UR52N+), S32750 (SAF 2507) and S32760 (Zeron 100) were developed by companies such as CLI in France, SANDVIK in Sweden and MATER+PLATT in the United Kingdom. Their deformed materials came out in about 1990 and 1991, and entered the market in recent years. The composition of these three steels is similar, the difference lies in the content of tungsten and copper.