What Is the ISO Code for nickel alloy UNS N06625?
nickel alloy UNS N06625 is designated ISO NW6625. The same alloy is known as UNS N06625 in the unified numbering system and W.Nr. 2.4856 in the German Werkstoff system, and it is listed in NACE MR-01-75 for service in sour, sulfide-containing environments. All three designations refer to the same nickel-chromium-molybdenum-niobium composition.
Composition and Properties
nickel alloy UNS N06625 is a nickel-chromium alloy with molybdenum and niobium additions. It is popular for its high strength, excellent machinability including joining, and excellent corrosion resistance, and its service temperatures range from cryogenic to 1800 °F (982 °C). Strength is derived from the hardening effects of molybdenum and niobium on the nickel-chromium matrix, so precipitation hardening is not required. This combination of elements also provides excellent resistance to a wide range of exceptionally severe corrosive environments and to the effects of elevated temperatures such as oxidation and carburization.
Product Forms and Specification Map
The alloy is produced as tube, pipe, sheet, strip, plate, round bar, flat bar, forgings, hexagonal bar, wire and extrusions. For bars and forgings the governing documents include ASTM B 446 and ASME SB-446, ASTM B 564 and ASME SB-564, AMS 5666, AMS 5837 for wire, ISO 9723, ISO 9724 and ISO 9725, VdTÜV 499, BS 3076NA21, EN 10095, DIN 17752, DIN 17753, DIN 17754 and ASME Code Case 1935. For plate, sheet and strip the governing documents include ASTM B 443 and ASME SB-443, AMS 5599, AMS 5869 and MAM 5599, ISO 6208, VdTÜV 499, BS 3072NA21, EN 10095 and DIN 17750. For pipes and tubes the governing documents include ASTM B 444, ASTM B 829, ASME SB-444 and ASME SB-829 for seamless products; ASTM B 704, ASTM B 751, ASME SB-704 and ASME SB-751 for welded pipe; ASTM B 705, ASTM B 775, ASME SB-705 and ASME SB-775 for welded pipe, plus ISO 6207, AMS 5581, VdTÜV 499, BS 3074NA21 and DIN 17751. Fittings are covered by ASTM B 366 and ASME SB-366, and DIN 17744 defines the chemical composition of all product forms.
Why the Designation Matters
Specifying the correct designation matters because material bought to the wrong specification may not meet the chemistry, mechanical properties or testing required for the application. UNS N06625, W.Nr. 2.4856 and ISO NW6625 all identify the same nominal composition, but the product form determines which ASTM, ASME, AMS, ISO or DIN standard applies, and purchasers should state both the alloy designation and the product specification on the purchase order.
Selection Guidance
nickel alloy UNS N06625 is chosen when a single material must combine high strength with broad corrosion resistance over a very wide temperature range, from cryogenic piping to 982 °C oxidizing service. It is used in chemical and pollution-control equipment, marine hardware, nuclear reactors, thrust-reverser assemblies, fuel nozzles and afterburner components. For service where the temperature is more extreme or the strength requirement is higher, other grades such as 718 or X may be more appropriate.
Frequently Asked Questions
Is ISO NW6625 the same as UNS N06625? Yes. ISO NW6625, UNS N06625 and W.Nr. 2.4856 are different numbering systems for the same nominal nickel-chromium alloy composition.
Which ASTM standard covers nickel alloy UNS N06625 plate? ASTM B 443 covers plate, sheet and strip, with the ASME counterpart ASME SB-443; bars are covered by ASTM B 446 and forgings by ASTM B 564.
Does nickel alloy UNS N06625 require precipitation hardening? No. Its strength comes from solid-solution hardening by molybdenum and niobium, so it is used in the annealed condition without an aging treatment.
What is the maximum service temperature of nickel alloy UNS N06625? The alloy serves from cryogenic temperatures to about 1800 °F (982 °C) in oxidizing service, though long-term load-bearing applications are typically limited to lower temperatures.
Is nickel alloy UNS N06625 approved for sour service? Yes, it is listed in NACE MR-01-75 and is widely used in oil and gas service where sulfide stress cracking resistance is required.
What filler metal is used to weld nickel alloy UNS N06625? Matching-composition fillers such as ERNiCrMo-3 (AWS A5.14) are typically used to maintain corrosion resistance and strength in the weld metal.
