Can Inconel 718 be welded?
Yes. 718 is the most weldable superalloy: TIG or EB weld it solution annealed with 718 filler, then re-solution and age. The risks are strain-age cracking and Laves phase in the weld.
Inconel 718 was designed to be weldable. Its hardening phase (gamma double prime, Ni3Nb) precipitates slowly, so the weld and heat-affected zone do not age and crack during welding the way faster-aging alloys such as Waspaloy or Rene 41 do. TIG (GTAW) is the standard for most job-shop work, electron beam and laser for thin, precise or deep joints, and resistance welding for sheet. The matching filler is ERNiFeCr-2 (AWS A5.14), sold as Inconel 718 filler metal or AMS 5832 wire. Where the joint does not need base-metal strength, ERNiCr-3 (Inconel 82 type) gives a more ductile, crack-resistant weld at about half the aged strength.
Weld in the solution-annealed condition, and heat treat afterward. The standard sequence is: anneal at 955-980 °C (1750-1800 °F), weld, re-solution anneal at the same temperature to relieve welding stress and homogenise the weld, then the double age (720 °C / 1325 °F 8 h, furnace cool to 620 °C / 1150 °F, hold to 18 h total). That gives a joint at 90% or better of base-metal strength. Welding an aged part and re-aging without a solution anneal is done for repairs, but the heat-affected zone will be overaged and weaker. Welding in the aged condition also raises the risk of strain-age cracking: the high residual stress from welding plus the contraction of the precipitates during the first age can crack the heat-affected zone. The solution anneal before aging is the protection against it.
Two weld-metal issues need control. Niobium segregates into the last liquid to freeze and forms Laves phase, a brittle intermetallic, in the weld centreline; low heat input, small beads and a fast cooling rate keep it fine and dispersed. Microfissuring in the heat-affected zone of thick, heavily restrained joints is reduced with low heat input and a fine-grained base metal (specify the grain size on the cert for critical weldments). Cleanliness is as important as on titanium: degrease, remove oxide by grinding or pickling, and keep sulfur (cutting oil, marking crayons) off the joint, because sulfur embrittles nickel alloys. Argon back-purge is needed on tube and full-penetration welds. AWS D17.1 (aerospace) or ASME IX governs qualification.
Welding for Inconel 718 parts: where to send them
What to specify
- Base metal: Inconel 718 solution annealed per AMS 5662 (bar), AMS 5596 (sheet) or AMS 5597, with a fine grain size (ASTM 5 or finer) for critical weldments
- Filler: ERNiFeCr-2 / AMS 5832 (matching 718) for heat-treated joints; ERNiCr-3 only for joints that will stay soft, and state which
- Weld sequence: weld annealed, re-solution anneal at 955-980 °C, then double age per AMS 5662 / AMS 2774; state if a repair on aged material is permitted and how
- Welding to AWS D17.1 (Class A for rotating or pressure parts) or ASME IX, with a weld map and interpass temperature limit (about 120 °C / 250 °F)
- Low heat input and stringer beads; argon back-purge on tube and full-penetration welds
- Cleaning: solvent degrease, mechanical or chemical oxide removal, no sulfur-bearing lubricants or markers on the joint
- Inspection: dye penetrant on all welds, radiography or ultrasonic on Class A, and a hardness or tensile coupon after aging
Pitfalls
- Welding an aged part and aging again without a solution anneal; strain-age cracking or a weak heat-affected zone
- High heat input and large weld pools that segregate niobium into brittle Laves phase along the centreline
- Sulfur from cutting oil or marking crayons embrittling the heat-affected zone
- Coarse-grained base metal on a thick restrained joint, giving heat-affected-zone microfissures
- Assuming 718 welds like stainless in the shop; it needs the heat-treat sequence and aerospace-level cleanliness
- Air-furnace heat treatment leaving heavy oxide that must be blasted or pickled before the next operation
Frequently asked questions
- What filler is used to weld Inconel 718?
- Matching 718 filler, ERNiFeCr-2 to AWS A5.14 (AMS 5832 wire), when the weld will be solution annealed and aged. ERNiCr-3 (Inconel 82 type) is used for a softer, more ductile joint that will not be aged.
- Should Inconel 718 be welded before or after heat treatment?
- Before. Weld in the solution-annealed condition, then re-anneal and double age. Welding after aging invites strain-age cracking and leaves a weaker heat-affected zone unless the whole part is re-solution treated.
- What is strain-age cracking in Inconel 718?
- Cracking in the heat-affected zone when high welding residual stress combines with the contraction of precipitates forming during the first age. 718 is less prone than most superalloys because it ages slowly; a solution anneal before aging removes the residual stress and prevents it.
