High nitrogen Super-Austenitic Stainless Steel for Heavy Thickness Components in Oil and Gas

摘要

Though highly alloyed stainless steels or corrosion resistant nickel based alloys are widely used for many applications involving corrosion issues, their use remain mostly limited to relatively small wall thickness components. The manufacture of large wall thickness forgings is difficult as the highly corrosion resistant alloys (super-duplex stainless steels, 6Mo super-austenitic stainless steels, Ni-Cr-Mo or Ni-Cr-Mo-W alloys) cannot be made from large size ingots without significant segregation of the alloying elements. Segregations cannot be always removed with the thermo-mechanical processing of ingots and intermetallic phases remain in the final product impairing the mechanical properties and/or the corrosion resistance. This paper presents the UNS S31266 super-austenitic steel grade specially designed for improved microstructural stability and for improved mechanical properties compared to most of commercially available austenitic stainless steels and annealed corrosion resistant nickel based alloys. A specific focus is on powder metallurgal production and subsequent hot isostatic pressing (hipping) of large wall thickness components for this super-austenitic stainless steel.