Description
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
| 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 | – |
Physical Properties
| 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 |
General Data
| Standard | Alloy 20 |
| UNS | N08020 |
| WERKSTOFF NR. | 2.4660 |
| EN | NiCr20CuMo |
| BS | |
| AFNOR | Z2NCUD31-20AZ |
| JIS |
Standards Specifications
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 |
Forms of Supply
Pipe and tubing, fittings and flanges, washers.
Corrosion Resistance
The following is the data on the corrosion rate of the alloy in the presence of an aqueous medium in my (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
Heat Treatment
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.
Weldability
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.
Machining
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.
Applications
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.
Possible Grade and Alternatives
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 |
