AL-6XN

AL-6XN

AL-6XN super-austenitic stainless steel (UNS N08367)

  • 6.3% molybdenum
  • Over 25 years of proven seawater service
  • Practical immunity to chloride stress cracking
  • 50% stronger than stainless
  • ASME coverage up to 800°F
  • Easily welded
  • Available in ALL product forms

AL-6XN® alloy (UNS N08367) is a low carbon, high purity, nitrogen-bearing "super-austenitic" stainless alloy. The AL6XN alloy was designed to be a seawater resistant material and has since been demonstrated to be resistant to a broad range of very corrosive environments. The high strength and corrosion resistance of the AL6XN alloy make it a better choice than the conventional duplex stainless steels and a cost effective alternative to more expensive nickel-base alloys where excellent formability, weldability, strength and corrosion resistance are essential.

Performance Profile

The levels of chromium, molybdenum and nitrogen in AL-6XN all serve to provide resistance to acidic oxidizing chloride solutions previously achieved only by the nickel base alloys. High nickel (24%) and molybdenum (6.3%) contents make AL-6XN a solution to chloride ion stress corrosion cracking. Because of its nitrogen content, AL-6XN has greater tensile strength than common austenitic stainlesses, while retaining high ductility and impact strength. The ASME allowable stresses for AL-6XN are up to 75% higher than for 316L stainless, and more than twice those for the copper-nickel alloys.

Chemistry

 CrNiMoCNMnSiPSCuFe
MIN 20.00 23.50 6.00 -- 0.18 -- -- -- -- --  
MAX 22.00 25.50 7.00 0.03 0.25 2.00 1.00 0.04 0.03 0.75 Balance

Specifications

ASME B-31.1 Case 155-1, ASME SA 182, ASME SA 240, ASME SA 249, ASME SA 312, ASME SA 479, ASME SB 276, ASME SB 366, ASME SB 462, ASME SB 564, ASME SB 675, ASME SB 688, ASME SB 691, ASME SB-366 Code Case N-438-3
ASTM A 182, ASTM A 240, ASTM A 249, ASTM A 312, ASTM A 479, ASTM B 366, ASTM B 462, ASTM B 472, ASTM B 564, ASTM B 675, ASTM B 676, ASTM B 688, ASTM B 691, ASTM B 804
UNS N08367

Inventory

AL-6XN Billet, AL-6XN Concentric Reducers, AL-6XN Fittings, AL-6XN Forged Billet, AL-6XN Forgings, AL-6XN Pipe, AL-6XN Plate, AL-6XN Round Bar, AL-6XN Sheet, AL-6XN Stub Ends, AL-6XN Tees, AL-6XN Welding Products

Common Trade Names

AL6XN, UNS N08367

Features

  • Excellent resistance to pitting and crevice corrosion in chloride solutions
  • Practical immunity to stress corrosion cracking in NaCl environments
  • High strength and toughness

Applications

  • AL-6XN FGD Scrubbers FGD Scrubbers
  • AL-6XN Reverse Osmosis Reverse Osmosis
  • AL-6XN Distillation Column Distillation Columns
  • AL-6XN Offshore Oil & Gas Offshore Oil and Gas
  • AL-6XN Heat Exchanger Heat Exchangers

Physical Properties

Density: 0.291 lb/in 3
Melting Point: 2410-2540°F
Electrical Resistivity: 535 Ohm-circ mil/ft

Temperature, °F 70 200 300 400 600 700 800
Coefficient* of Thermal Expansion, in/in°F x 10 -6 - 7.9 8.3 8.4 8.6 8.7 8.8
Thermal Conductivity
Btu • ft/ft2 • hr • °F
6.7 7.5 8.1 8.7 10.0 10.6 11.2
Modulus of Elasticity, Dynamic psi x 10 6 28.3 27.4 - 26.1 24.8 - 23.4

* 70°F to indicated temperature.

Mechanical Properties

Minimum Specified Properties, ASME SB-688 Plate

Ultimate Tensile Strength, ksi 95
0.2% Yield Strength, ksi 45
Elongation 30
Hardness MAX, HRC 30.5

Typical Tensile Properties, Plate

Temperature, °F -450 -320 70 200 400 600 800 1000
Ultimate Tensile Strength, ksi 218.0 196.0 108.0 99.9 90.3 86.0 87.0 83.6
0.2% Yield Strength, ksi 142.0 107.0 53.0 49.4 40.4 36.3 36.0 34.0
Elongation, % 36 49 47 47 46 47 48 50
Charpy Impact V-notch, ft-lbs 322* 85 140 -- -- -- -- --

*KIC Fracture Toughness

ASME Maximum Allowable Stresses, Section VIII, Division 1, ksi

200°F 400°F 600°F 800°F
AL-6XN Alloy 27.1 24.6 23.3 22.6
316L 20.0 19.3 17.0 15.9
Alloy 400 18.7 18.7 18.7 15.0

Fabrication

The low carbon and high nitrogen contents in AL-6XN alloy (UNS N08367) minimize the precipitation of carbides and secondary phases that can occur during welding. Therefore as-welded assemblies can be placed in service, provided a suitable over-matched filler metal, such as alloy 625 is used. AL6XN alloy can be welded in the field using procedures similar to those used with other austenitic stainless steels.

Rolled Alloys AL-6XN (UNS N08367) Fabrication Guide gives welding parameters, welding joint designs, machining, bending and forming data.

Corrosion Resistance

AL-6XN has excellent corrosion resistance in high chloride environments as well as many acids. Below is a quick summary of the critical pitting and crevice corrosion resistance compared to many other alloys. AL-6XN has improved properties over stainless steels and all duplex grades. The practical immunity to chloride stress corrosion cracking has pushed AL-6XN (UNS N08367) into many seawater applications including seawater reverse osmosis. The resistance to acid and chloride environments is proven by over 20 years of service in the flue gas desulfurization process at coal fired electric power plants.

Alloy% MoCCCT, °FCPT, °FPREN
316L 2.1 < 28 68 24
2205 3.1 68 120 35
904L 4.4 75 130 36
ZERON 100 3.5 108 180 41
AL-6XN 6.3 110 172 44
625 9.0 113 - 51

* CCCT - 10% FeCl3 6H20, per ASTM G 48 Practice B, CPT - 1 M NaCl, per ASTM G 150, PREN = Cr + 3.3 Mo + 16N