Superaustenitic stainless steel has the same structure as the common austenitic alloys, but they have enhanced levels of elements such as chromium, nickel, molybdenum, copper, and nitrogen, which give them superior strength and corrosion resistance.
Superaustenitic stainless steel alloys are characterized by their high nickel and molybdenum contents plus nitrogen. The most common of the alloys are 904L, AL-6XN, 254 SMO, 25-6MO and 1925 hMO.Superaustenitic metal designed to resistcrevice corrosion, pitting, chloride-induced corrosion, and stress corrosion cracking. It can also withstand alkaline and salt solutions, protecting against metallic contami- nation of product and preventing rapid degradation of the fluid transfer system.
These superaustenitic stainless steel alloys have a face-centered cubic crystal structure similar to other austenitic stainless steel and are non-magnetic and their magnetic permeability remains low even after severe cold forming. The nitrogen addition provides the alloy with improved resistance to pitting and crevice corrosion, a greater resistance to localized corrosion in oxidizing chlorides and reducing solutions plus higher strength. Nitrogen also helps to significantly reduce the potential formation of harmful secondary phases during welding.
| Superaustenitic Stainless Steel | ||||||||
| Alloy (UNS Designation) | End Use | Composition nominal wt% | Specifications | Density lb/in3 (g/cm3) | Tensile Strength ksi. (MPa) | 0.2%Yield Strength ksi. (MPa) | Elong- ation % | Hardness |
| N08020 | Flue gas scrubbers, Sulphuric acid tanks and racks, Process piping, Heat exchangers, Manufacture of solvents/explosives/plastics/synthetic fibers/organic chemicals/pharmaceuticals | C 0.07 max, Mn 2.0 max, P 0.045 max, S 0.035 max, Si 1.0 max, Cr 19.0-21.0, Ni 32.0-38.0, Mo 2.0-3.0, Cu 3.0-4.0, Cb+Ta (8xC)min-1.0 max, Fe balance | ASTM B-463 ASME SB-463 | 0.292 (8.09) | 80 min (550 min) | 35 min (240 min) | 30 min | 95RockwellB max |
| S34565 | Desalination, seawater piping, offshore oil production, pollution control (FGD) | C 0.03 max, Mn 5.0-7.0, P 0.03 max, S 0.01 max, Si 1.0 max, Cr 23.0-25.0, Ni 16.0-18.0, Mo 4.0-5.0, N 0.4-0.6, Cb 0.1 max, Fe balance | ASTM A 240 ASME SA-240 | 0.29 (8.03) | 115 min (795 min) | 60 min (415 min) | 35 min | 100 Rockwell B max |
| 904L / N08904 | High efficiency furnace vent pipe, pulp & paper processing equipment, welding electrodes and fittings. | C 0.02 max, Mn 2.0 max, P 0.045 max, S 0.035 max, Si 1.0 max, Cr 19.0-23.0, Ni 23.0-28.0, Mo 4.0-5.0, N 0.1 max, Cu 1.0-2.0, Fe Balance | ASTM A-240 ASME SB-625 | 0.287 (7.95) | 71 min (490 min) | 31 min (220 min) | 35 min | 90 Rockwell B max |
| N08367 | Desalination, seawater piping and critical components on offshore oil platforms | C 0.030 max, Mn 2.0 max, P 0.040 max, S 0.030 max, Si 1.0 max, Cr 20.0-22.0, Ni 23.5-25.5, Mo 6.0-7.0, N 0.18-0.25, Cu 0.75 max, Fe Balance (PREN 50.0 min) | ASTM A 240, ASTM B 688 ASME SA-240, ASME SB-688 | 0.291 (8.06) | 100 min (Sheet) / 95 min (Plate) (690 min / 655 min) | 45 min (310 min) | 30 min | 100 Rockwell B max |
| N08367 | Desalination, seawater piping and critical components on offshore oil platforms. | C 0.030 max, Mn 2.0 max, P 0.040 max, S 0.030 max, Si 1.0 max, Cr 20.0-22.0, Ni 23.5-25.5, Mo 6.0-7.0, N 0.18-0.25, Cu 0.75 max, Fe Balance | ASTM A 240, ASTM B 688 ASME SA-240, ASME SB-688 | 0.291 (8.06) | 100 min (sheet) / 95 min (plate) (690 min / 655 min) | 45 min (310 min) | 30 min | 100 Rockwell B max |
| JS700? N08700 | Wet scrubbers in municipal incinerators, wet-process phosphoric acid plants, chlorine dioxide pulp bleaching | C 0.04 max, Mn 2.0 max, P 0.04 max, S 0.03 max, Si 1.0 max, Cr 19.0-23.0, Ni 24.0-26.0, Mo 4.3-5.0, Cu 0.5, Cb (8xC)min-0.4 max, Fe Balance | ASTM A240 ASTM B599 | 0.287 (7.95) | 80 min (550 min) | 35 min (240 min) | 30 min | 90 Rockwell B max |
