Inconel® Alloy 625™ is a nickel chromium molybdenum alloy with high strength at elevated temperatures, combined with outstanding corrosion resistance. It has the best all-round combination of strength, high temperatures and corrosion resistance of the Inconel family of alloys. It is pre-qualified for use in pressure vessels up to 815°C. Inconel 625LCF is a special quality of the alloy for use in bellows.

Chemical Composition

ASTM B446 – Bar

Specified Minimum Mechanical Properties

ASTM B446 – Bar

Grade 1 – Annealed at 870°C minimum

Grade 2 – Solution Annealed at 1090°C (min), with or without stabilise anneal at 980°C (min) for sensitisation resistance.

Typical Applications for Inconel Alloy

Chemical plant, bellows, submerged marine components, weld overlays, power station scrubber systems, general corrosion applications for aggressive environments, combustion and ducting systems, fuel nozzles, after burners, aerospace components.

Description

Inconel 625 is a nickel chromium molybdenum solid solution strengthened high strength alloy, which retains strength to high temperatures. It is used from cryogenic temperatures to 980°C. Fatigue strength is outstanding, particularly as the bellows grade, Inconel 625LCF, where carbon, silicon and nitrogen are controlled to low levels. The alloys have good oxidation resistance and resist corrosion by many corrosive media. When exposed to high temperatures for long periods, Inconel 625 will age harden due to the niobium, titanium and aluminium additions. When aged there is an increase in strength and some loss of ductility and toughness.

Availability of Inconel

Austral Wright Metals can supply Inconel 625 as plate, sheet and strip, rod and bar, seamless and welded tube and pipe, welding fittings, forgings and forging billet. Inconel 625LCF is available as annealed sheet and strip from 0.13 mm to 2.54 mm thick, up to 1219 mm wide.

High temperature tensile properties of annealed Inconel® Alloy 625™ sheet.		Low cycle fatigue strength of Inconel® Alloy 625™ and Inconel® 625LCF™ at 480 – 650°C.

Pressure Vessels

AS1210 prequalifies Inconel 625 up to 625°C as flat products, and 650°C as bar and forgings. ASME Boiler & Pressure Vessel Code, Section VIII (Code Case 1409-5) allows annealed material to be used to 650°C, solution treated to 815°C.

Corrosion Resistance of Inconel

Inconel 625 has corrosion resistance to many environments. In mild environments such as atmosphere, fresh water and sea water, neutral salts and alkaline media there is almost no attack. In more aggressive media nickel and chromium resist oxidising attack, while nickel and molybdenum resist reducing environments. Molybdenum provides exceptional resistance to pitting and crevice corrosion, and niobium stabilises against sensitisation and intergranular corrosion. The nickel content makes Inconel 625 essentially free from chloride ion stress corrosion cracking. Inconel 625 also has excellent corrosion fatigue properties. Please consult Austral Wright Metals for specific advice on using Inconel metal for your application.

Corrosion Rates (mm/year) in a Municipal Waste Incinerator

at 650-700°C after 2050 hours and 6750 hours

Equivalent Specifications

Fabrication

Inconel 625 was developed for hot strength, so resists hot working. It is ductile and can be readily hot worked with high forces. The alloy can also be cold formed with heavy forces. Intermediate annealing may be needed.

Machinability

Inconel 625 is difficult to machine (class D-2). Heavy machines, sharp tools, slow speeds and deep uninterrupted cuts to remove the work hardened layer are needed.

Weldability

Inconel 625 is readily welded by GMAW (MIG), GTAW (TIG), SMAW (manual) and SAW processes. Preheat, post heat and post weld heat treatment are not required. The area around the weld must be clean to prevent contamination of the weld pool. Argon shielding gas is used.

Heat Treatment

Inconel 625 is annealed at 925–1040°C, cooling rate not critical. Solution anneal at 1090–1200°C. Stress relief, if required, is at 590–760°C, or up to 870°C for complete relief.

Physical Constants and Thermal Properties

Inconel 625 and 625LCF, Annealed

ASTM Product Specifications

Note: The Element Niobium is called Columbium in USA