Chemical composition

Nickel includes cobalt where stated in the standard. Footnotes as given in each ASTM specification.

Molybdenum (8–10%) and niobium (about 3.5%) stiffen the nickel-chromium matrix and provide resistance to pitting and crevice corrosion; the high chromium resists oxidising media. The mill test certificate shows the actual analysis for each heat.

Mechanical properties

Values for Grade 1 annealed material; size limits and Grade 2 (solution annealed) properties as given in each standard.

Grade 1 (annealed) material is used up to about 595 °C, where its higher room-temperature strength is valuable. Grade 2 (solution annealed) is used above that temperature, where creep and rupture strength matter.

Equivalent grades and physical properties

Equivalent designations are similar but not identical; order to the standard you need.

Typical values from recognised industry references, for guidance only; they are not specification limits.

See the full grade equivalent chart for other grades.

Corrosion and heat resistance

Inconel 625 has a pitting resistance equivalent number of about 50, so it resists pitting and crevice corrosion in seawater and brines, including warm seawater where stainless steels fail. Its high nickel makes it practically immune to chloride stress corrosion cracking. It resists mineral acids such as nitric, phosphoric and dilute sulphuric and hydrochloric acid, mixed acids, and sour oil and gas environments. At high temperatures it resists oxidation and carburisation, and its strength and fatigue resistance make it useful in thermal cycling.

Long exposure between about 600 °C and 850 °C can reduce ductility through precipitation, which is considered in the design of high-temperature equipment.

Inconel 625 products we supply

• Inconel 625 pipes and tubes – seamless to ASTM B444, welded to B704 and B705.
• Plates and sheets – ASTM B443.
• Inconel 625 round bars – ASTM B446, AMS 5666.
• Flanges and forged fittings – ASTM B564.
• Butt-weld fittings – ASTM B366 WPNCMC.
• Fasteners and wire – from B446 bar; welding wire ERNiCrMo-3.

All Inconel alloys are on the Inconel page.

Comparable alloys

Inconel 600 has no molybdenum or niobium; it is used mainly for high-temperature oxidation resistance and in caustic and chloride-stress-cracking service, but is far less resistant to pitting than 625. Hastelloy C276 has more molybdenum and tungsten and is preferred in strongly reducing acids such as hydrochloric acid and in wet chlorine, while 625 is stronger and better in oxidising media. Super duplex stainless steels are lower-cost alternatives for seawater at moderate temperatures, and Incoloy 825 for milder acid service.

Typical applications of Inconel 625

Inconel 625 is used for seawater piping, heat exchangers and risers offshore, subsea components and bolting, sour-gas flowlines and as corrosion-resistant overlay and cladding inside carbon steel pipes and vessels, flue-gas desulphurisation and scrubbers, chemical process equipment, aircraft exhaust ducting and engine thrust-reverser parts, expansion bellows, nuclear and power plant components, and marine propeller blades and cable sheathing.

Fabrication

Inconel 625 is readily welded by TIG, MIG and manual arc processes using matching ERNiCrMo-3 filler, which is also widely used for dissimilar welds and weld overlay. It forms well cold, although it is strong and work-hardens, so more force is needed than for stainless steel. Machining needs rigid set-ups, sharp carbide tools, low speeds and plenty of coolant. No post-weld heat treatment is normally needed for corrosion resistance.