Corrosion Resistant Alloys

NAS 74N (UNS S32750)

- Super Duplex Stainless Steel

NAS74N is a super duplex stainless steel with pitting resistance equivalent (PRE*) number higher than 40, whichprovides not only excellent corrosion resistance but also excellent strength properties. In particular, NAS74N has superior localized corrosion resistance compared with UNS S32205(NAS329J3L, SUS329J3L), and UNS S32506 (NAS64, SUS329J4L). Therefore, NAS74N is used for those applications under severe environments such as chemical plants and desalination plants. Nippon Yakin supplies NAS74N in the form of plate, sheet and strip.

*PRE=%Cr+3.3X%Mo+16X%N

Products & Materials

NAS 74N Spec Sheet (PDF 278KB)

  • Nippon Yakin GradeNAS 74N
  • UNSS32750
  • EN / DIN1.4410
  • JIS
  • Chemical Composition25Cr-7Ni-3.8Mo-0.27N
Metal working in progress

Coil

Sheet

Plate

Workability Attention should be paid for the strength behavior of NAS74N which abruptly increases below 1000℃ in spite of the lower strength than Type 304 at high temperatures. Solution annealing should be carried out after hot working. Attention has to be also paid for the behavior of cold workability because of the higher proof stress along with the lower elongation than Type 304.
Weldability Conventional welding processes including GTAW (TIG), GMAW (MIG/MA) can be used. Use of filler metals for UNS S32750 is recommended. Neither preheating nor post-weld heat treatment is necessary. Interpass temperature should be no more than 100℃ in order to prevent precipitation of intermetallic compounds of σ phases that result in brittleness.
Heat Treatment Solution annealing of NAS74N should be performed at the temperature range from 1025 to 1125℃. This should be followed by quick quench dipping into water or other alternative ways to according to ASTM A480/A480M leading to prevent brittleness by 475℃ brittleness and σ phases.
Pickling A mixture of nitric and fluoric acids is applied for pickling. In addition, due to its higher corrosion resistance, immersion into fused salt bath before pickling is significantly effective to take scale off. And further occasion shot blasting before pickling is extremely effective.
Applications Chemical plant, Chemical tanker, Seawater desalination system, Seawater pump
Certification It is possible to manufacture UNS S32750 in accordance with the NORSOK standard below. The thickness is up to 40mm.
  • NORSOK M-650
  • NORSOK M-630 MDS D55

Corrosion Resistant Alloys