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Austenitic SS Alloy 20

Austenitic SS Alloy 20

ALLOY 20 | N08020 | 2.4660 | NICR20CUMO | Z2NCUD31-20AZ

Alloy 20, also known as Carpenter 20 is an austenitic nickel-iron-chromium alloy and has an excellent resistance to acid attack, especially sulfuric acid. It also shows fine resistance in phosphorous acid, nitric acid and chloride environments.

Unlike other metals, alloy 20 has a pre-eminent resistance to chloride stress corrosion cracking, resistance to pitting and crevice corrosion.

The corrosion rate of the alloy in the presence of various concentrations of sulfuric acid is completely off the charts, varying from 4 to 30 mils per year. (thousands of an inch per year)

The alloy also has stabilization against sensitization and resultant intergranular corrosion. Hence, under appropriate media and proper temperatures, the alloy exceptionally retains its austenitic phase and the granular structure without much stress.

The applications are limited to 1000 °F as per ASME. The alloy has a composition which makes it debatable to be called as a stainless steel or nickel alloy, either way it serves its purpose and is considered great for corrosion resistance. The alloy is chosen over Stainless Steel 316L many times for resistance to stress corrosion cracking. With a composition of 33% Nickel, the alloy has immunity to chloride stress corrosion cracking. Alloy 20 also has restricted amount of carbon; hence brittleness is avoided. With columbium stabilization, the welded fabrications can be used in corrosive atmospheres without post weld heat treatments (the presence of columbium in the alloy tends to minimize the precipitation of carbides in the heat affected zone, so the material may be used in the "as welded" condition).

TIG (Tungsten Inert Gas), MIG (Metal Inert Gas) and SAW (Submerged Arc Welding) are used with the help of appropriate filler metal, depending upon welding to be done with similar or dissimilar higher alloys. On conducting charpy v- notch test, the material could absorb 200 ft-lbs of energy. The Alloy 20 can be formed either by hot working or cold working processes. Using traditional methods, and then heat treating for strength and annealing for stress removal.

  • Chemical properties
  • Physical properties
  • General data
  • Standards Specifications
  • Forms of Supply
  • Corrosion Resistance
  • Heat Treatment
  • Weldability
  • Machining
  • Applications
  • Possible grade alternatives
Grade   Ni C Cr Mn Si P Mo S Fe Cu NB TA
Alloy 20 Min. 32.00 - 19.0 - - - 2.00 - 29.85 3.00 8Xc-1.00
Max. 38.00 0.07 21.0 2.00 1.00 0.045 3.00 0.035 - 4.00 -
Density 8.05 g/cm3/0.292 lb/in.3
Melting Point 1443 °C (2430 °F)
Specific Heat 0.12 Btu/lb•°F
Thermal Conductivity @ 212°F 12.3 W/mK 90.8 Btu•in./ft2•h•°F
Elastic Modulus 28.0 X 103 ksi
Electrical Resistivity 651 ohm-cir mil/ft
Annealing 1725°F and 1850°F
Poisson Ratio 0.31
Standard Alloy 20
UNS N08020
WERKSTOFF NR. 2.4660
EN NiCr20CuMo
BS  
AFNOR Z2NCUD31-20AZ
JIS  
Pipes & Tubes
Summary Standards
Standard Specification for Welded UNS N08020, N08024, and N08026 Alloy Pipe ASTM B464
Standard Specification for Welded UNS N08020, N08024, and N08026 Alloy Tubes ASTM B468
Standard Specification for Electric Fusion Welded Nickel and Nickel Alloy Pipe ASTM B474
Specification for Forged or Rolled UNS N06030,N06022,N06035,N06200,N06059,N06686,N08020,N08024,N08026,N08367,N10276,N10665, N10675,N10629, N08031,N06045, N06025, & R20033 Alloy Pipe Flanges, Forged Fitting, & Valves & Parts for Corrosive ASTM B462
Standard Specification for Seamless UNS N08020, UNS N08026, and UNS N08024 Nickel-Alloy Pipe and Tube ASTM B729
Standard Specification for Seamless Ferritic and Austenitic Alloy-Steel Boiler, Superheater, and Heat-Exchanger Tubes ASTM A213
Standard Specification for Seamless, Welded, and Heavily Cold Worked Austenitic Stainless Steel Pipes ASTM A312
Standard Specification for Electric-Fusion-Welded Austenitic Chromium-Nickel Stainless Steel Pipe for High-Temperature Service and General Applications ASTM A358
Fittings & Flanges
Summary Standards
Standard Specification for Factory-Made Wrought Nickel and Nickel Alloy Fittings ASTM B366
Standard Specification for Forged or Rolled Alloy and Stainless Steel Pipe Flanges, Forged Fittings, and Valves and Parts for High-Temperature Service ASTM A182
Standard Specification for Wrought Austenitic Stainless Steel Piping Fittings ASTM A403

Pipe and tubing, fittings and flanges, washers.

The following is the data of corrosion rate of the alloy in the presence of aqueous medium in mpy (mils per year).
10% H2SO4 (Sulfuric Acid) - 13.2 mpy
70% H2SO4 @ 167°F (Sulfuric Acid) - 5 mpy
10% H3NO3S (Sulfamic Acid) - 9.6 mpy
1% HCl (Hydrochloric Acid) - 39.6 mpy
45% CH2O2 (Formic Acid) - 8.4 mpy
20% H3PO3 (Phosphoric Acid) - 0.2 mpy
10% C2H2O4 (Oxalic Acid) - 31.2 mpy
50% NaOH (Sodium Hydroxide) - 7.2 mpy

Hot forged material to be heat treated between 2100°F and 2250°F ensuring proper temperature control followed be annealing the material between 1725°F and 1850°F for 30 minutes followed by water quench.

Welding of the alloy is commonly performed by TIG, MIG and SAW with either matching filler metal ER320LR for TIG and MIG and E320LR for SAW for similar metals, and AWS ERNiCrMo-3 used for TIG and MIG, ENiCrMo-3 for SAW for dissimilar or higher alloys such as 316, alloy 22.

Due to columbium stabilization, the welded metal can directly be used without post weld heat treatment.

With normal processing speeds and processes that are used in grades 316 and 317, super quality and fine finishing with Alloy 20 can be obtained.

Equipment for the manufacture of synthetic rubber, plastics, organic and heavy chemicals, pharmaceuticals, solvents and explosives, pickling equipment, process piping, mixing tanks, Bubble caps, food and dye production.

Grade SS 316
Grade   Ni C Cr Mn Si P Mo S N
316 Min. 10.0 - 16.0 - - 0 2.00 - -
Max. 14.0 0.08 18.0 2.00 0.75 0.045 3.00 0.03 0.10
Grade Ti 6-4
Grade   C N2 O2 AL V H2-Sheet H-2 Bar H-2 Billet Fe Ti
Ti 6-4 Min. - - - 5.56 3.5 - - - - Bal.
Max. 0.08 0.25 0.20 6.76 4.5 0.015 0.0125 0.01 0.25 -
Grade Hastelloy C276
Grade   Ni C Co Mn Si Cr W S V Fe P MO
Hastelloy C276 Min Bal(50.99) - - - - 14.5 3.0 - - 4.0 - 15.0
Max - 0.010 2.5 1.00 0.08 16.5 4.5 - 0.35 7.0 0.04 17.0

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