DUPLEX & SUPER DUPLEX STEEL

Duplex alloys were originally created to combat corrosion problems caused by chloride-bearing cooling waters and other aggressive chemical process fluids.

Called Duplex because of its mixed microstructure with about equal proportions of ferrite and austenite, duplex stainless steels are a family of grades, which range in corrosion performance depending on their alloy content. The chemical composition based on high contents of Cr and Mo, improves intergranular and pitting corrosion resistance, respectively. Additions of nitrogen can promote structural hardening by interstitial solid solution mechanism, which raises the yield strength and ultimate strength values without impairing toughness. Moreover, the two-phase microstructure guarantees higher resistance to pitting and stress corrosion cracking in comparison with conventional stainless steels.

Available forms are Duplex & Super Duplex Steel Seamless Pipe, Duplex & Super Duplex Steel Welded Pipe,Duplex & Super Duplex Steel Seamless Tube,Duplex & Super Duplex Steel Welded Tube,Duplex & Super Duplex Steel Round Bars,Duplex & Super Duplex Steel Welded Wire,Duplex & Super Duplex Steel Sheet,Duplex & Super Duplex Steel Plate,Duplex & Super Duplex Steel Forgings,Duplex & Super Duplex Steel Pipe Fittings and ,Duplex & Super Duplex Steel Flanges

The various Alloys

The development of the Duplex stainless steels has continued, graded for their corrosion performance depending on their alloy content. Today, modern duplex stainless steel can be divided into four groups:

Composition of Duplex Stainless Steels :

The table lists the duplex stainless steels covered in ASTM specifications for plate, sheet, and bar products.

UNS Typeb C Mn P S Si Cr Ni Mo N Cu
S31200 0.030 2.00 0.045 0.030 1.00 24.0-26.0 5.5-6.5 1.20-2.00 0.14-0.20
S31260 0.03 1.00 0.030 0.030 0.75 24.0-26.0 5.5-7.5 2.5-3.5 0.10-0.20 0.20-0.80
S31803 0.030 2.00 0.030 0.020 1.00 21.0-23.0 4.5-6.5 2.5-3.5 0.08-0.20
S32001 0.030 4.0-6.0 0.040 0.030 1.00 22.0-23.0 1.00-3.00 0.60 0.05-0.17 1.00
S32205 2205 0.030 2.00 0.030 0.020 1.00 19.5-21.5 4.5-6.5 0.14-0.20
S32304 2304 0.030 2.50 2.50 0.030 1.00 21.5-24.5 3.0-5.5 0.05-0.60 0.05-0.20 0.05-0.60
S32520 0.030 1.50 0.035 0.035 0.80 24.0-26.0 5.5-8.0 3.0-4.0 0.20-0.35 0.50-2.00
S32550 255 0.04 1.50 0.040 0.030 1.00 24.0-27.0 4.5-6.5 2.9-3.9 0.10-0.25 1.5-2.5
S32750 2507 0.030 1.20 0.035 0.020 0.80 24.0-26.0 6.0-8.0 3.0-5.0 0.24-0.32 0.50
S32760 0.030 1.00 0.030 0.010 1.00 24.0-26.0 6.0-8.0 3.0-4.0 0.20-0.30 0.50-1.00
S32900 329 d 0.06 1.00 0.040 0.030 0.75 23.0-28.0 2.5-5.0 1.0-2.0
S32950 0.03 2.00 0.035

BENEFITS

  • High strength
  • High resistance to pitting, crevice corrosion resistance
  • High resistance to stress corrosion cracking, corrosion fatigue and erosion
  • Good sulfide stress corrosion resistance
  • Low thermal expansion and higher heat conductivity than austenitic steels
  • Good workability and weldability.
  • High energy absorption.