Filler metal for nickel alloy welding (for example ERNiCrMo-3 for UNS N06625 base metal, or ERNiCrMo-4 for UNS N10276) is selected from the AWS A5.14 classification and matched to the base metal by UNS number — not by trade name, and not by "what worked on the last job". Because nickel alloy weld metal is more viscous than stainless steel weld metal, it is also far less forgiving of contamination: the same technique that produces a sound 316L weld will produce porosity in a 625 weld if the consumable has absorbed moisture.
This guide sets out how the classification works, which filler matches which base metal, how to weld dissimilar joints, and the two consumable-handling rules that decide whether the weld passes radiography. For how the filler fits into a complete piping package, see How Do You Match Pipe, Fittings, Flanges and Filler Metal?.
What does the AWS classification code tell you?
The AWS A5.14 designation is a chemistry code. Read it in three parts — the prefix says it is a nickel-alloy filler, the following letters give the principal alloying elements in descending order, and the suffix is a sequential identifier for variants:
| Classification | Principal elements | Nominal chemistry (wt%) | Matches base metal |
|---|---|---|---|
| ERNi-1 | Ni | Ti 2.5–3.5, Ni balance | Nickel 200 / 201 (N02200 / N02201) |
| ERNiCu-7 | Ni-Cu | Cu 65–70, Ni balance | Monel 400 / K-500 (N04400 / N05500) |
| ERNiCr-3 | Ni-Cr | Cr 18–22, Nb+Ta 2.0–3.0 | Inconel 600 / 601, Incoloy 800 / 800H |
| ERNiFeCr-1 | Ni-Fe-Cr | Cr 19.5–23.5, Fe 22 min, Mo 2.5–3.5 | Incoloy 825 (N08825) |
| ERNiCrMo-3 | Ni-Cr-Mo | Cr 20–23, Mo 8–10, Nb+Ta 3.15–4.15 | Inconel 625 (N06625), 718 (N07718) |
| ERNiCrMo-4 | Ni-Cr-Mo | Cr 14.5–16.5, Mo 15–17, W 3–4.5 | Hastelloy C-276 (N10276) |
| ERNiCrMo-10 | Ni-Cr-Mo | Cr 20–22.5, Mo 13–15, W 2.5–3.5 | Hastelloy C-22 (N06022), C-2000 |
| ERNiCrMo-14 | Ni-Cr-Mo | Cr 20–22.5, Mo 15–17, W 3–4.5 | Hastelloy C-2000, high-Mo superalloys |
Two entries on that table decide most real jobs. **ERNiCrMo-3 is not a substitute for ERNiCrMo-4.** The molybdenum content differs by roughly a factor of two (8–10% against 15–17%), and molybdenum is what gives the weld metal its resistance to reducing acids and to pitting in chloride service. A C-276 vessel welded with 625 filler has a weld root that is materially less corrosion resistant than the plate either side of it, even though every certificate in the document package is genuine.
**ERNiCrMo-3 is, however, the correct choice for 625 and for most dissimilar joints**, because its higher niobium content gives it crack resistance that the high-molybdenum grades lack when diluted by stainless or carbon steel.
Which filler metal matches which base metal?
Match by UNS number first, then check the service:
| Base metal | UNS | Primary filler | Alternative |
|---|---|---|---|
| Nickel 200 / 201 | N02200 / N02201 | ERNi-1 | ERNiCr-3 for elevated temperature |
| Monel 400 | N04400 | ERNiCu-7 | ERNiCr-3 for dissimilar joints to steel |
| Monel K-500 | N05500 | ERNiCu-7 | — |
| Inconel 600 / 601 | N06600 / N06601 | ERNiCr-3 | ERNiCrMo-3 where more corrosion resistance is needed |
| Inconel 625 | N06625 | ERNiCrMo-3 | ERNiCrMo-4 for severe reducing acid |
| Inconel 718 | N07718 | ERNiFeCr-2 (718 filler) | ERNiCrMo-3 for non-ageing joints |
| Incoloy 800 / 800H / 800HT | N08800 / N08810 / N08811 | ERNiCr-3 | ERNiCrCoMo-1 for high creep service |
| Incoloy 825 | N08825 | ERNiFeCr-1 | ERNiCrMo-3 |
| Hastelloy C-276 | N10276 | ERNiCrMo-4 | — |
| Hastelloy C-22 / C-2000 | N06022 / N06200 | ERNiCrMo-10 / ERNiCrMo-14 | — |
| Hastelloy B-2 / B-3 | N10665 / N10675 | ERNiMo-2 / ERNiMo-7 | — |
| Hastelloy X | N06002 | ERNiCrMo-3 or ERNiCrCoMo-1 | — |
For age-hardenable grades such as 718 and X-750, the filler metal matters to the post-weld heat treatment as well: ERNiFeCr-2 is formulated so that the weld responds to the same ageing treatment as the base metal, and substituting 625 filler leaves an unaged, weaker weld that cannot be recovered by re-ageing.
How do you handle dissimilar metal joints?
Dissimilar joints are where filler selection has the largest consequence, because dilution from both sides changes the weld chemistry and the thermal expansion mismatch drives residual stress:
- 1. **Nickel alloy to stainless steel** — use ERNiCrMo-3 (625 filler) for 625, C-276 or 825 joined to 304/316L. The niobium stabilises the weld against the dilution and prevents the fissuring that occurs when a fully austenitic stainless filler is used against a nickel base metal.
- 2. **Nickel alloy to carbon steel** — use ERNiCr-3 for 600/800 families and ERNiCrMo-3 for the C-family. For sour service, the welded joint must still satisfy NACE MR0175 hardness limits; see our sour service alloy guide.
- 3. **Dissimilar joints in high-temperature service** — where the joint operates above roughly 425 °C, the difference in coefficient of thermal expansion between the nickel alloy and the carbon steel becomes the controlling design condition, and a transition piece or a graded joint is normally required rather than a direct weld.
- 4. **Never use a stainless filler on a nickel base metal** unless the design specifically calls for it. ER308L on 625 produces a weld with lower molybdenum and a different solidification mode, and the resulting joint will not meet the corrosion assumption of the design.
Which process and shielding gas should be used?
Nickel alloys are welded with the same processes as stainless steel, with two adjustments: lower heat input and stricter shielding.
| Process | Typical application | Shielding / electrode | Key parameter |
|---|---|---|---|
| GTAW (TIG) | Root passes, thin wall, critical joints | 100% argon, or argon + 2–5% H₂ for austenitic grades only | DCEN; do not use hydrogen additions on the Ni-Mo grades |
| SMAW (MMA) | Fill and cap, site work | Basic coated electrodes, e.g. ENiCrMo-4 | Electrodes must be dry; re-dry per manufacturer instructions after opening |
| GMAW (MIG) | Production fill passes | Argon-rich mixtures; pulsed transfer preferred | Short-circuit transfer is not recommended — lack of fusion |
| SAW (submerged arc) | Heavy-wall plate and pipe | Neutral or slightly basic flux | Not used on Ni-Mo grades where flux interaction is a risk |
The single most useful technique change relative to stainless steel is to **weld with a slightly longer arc, a lower current and a faster travel speed**, and to use a smaller electrode relative to the joint thickness. Nickel alloy weld metal is sluggish; a wide, slow weave puddle traps oxide and produces lack of fusion at the sidewalls.
What causes porosity and cracking, and how is it prevented?
Almost all defects in nickel alloy welding trace back to contamination rather than to the welder:
| Defect | Root cause | Prevention |
|---|---|---|
| Porosity (uniform) | Moisture absorbed by the electrode or filler wire | Re-dry SMAW electrodes; store bare wire in heated cabinets; wipe rods with acetone before use |
| Porosity (isolated) | Sulphur or oil on the base metal or on the filler | Degrease with acetone; remove all marking crayon and adhesive tape; do not use sulphur-bearing layout ink |
| Arc wander / poor wetting | Magnetic or contaminated surface, or oxidised filler | Clean to bright metal; use a longer arc; check the earth connection |
| Microfissuring in the HAZ | High heat input on a precipitation-strengthened or Ni-Mo grade | Reduce heat input and interpass temperature; use the matching filler |
| Loss of corrosion resistance in the weld | Wrong filler for the base metal (625 filler on C-276) | Match filler to UNS and to the service medium |
| Cracked root on thick sections | Restraint plus low-ductility weld metal | Pre-place the joint carefully; sequence the passes; use ERNiCrMo-3 for its crack resistance |
The sulphur point deserves emphasis. Nickel alloys form a low-melting nickel-sulphide eutectic, so a sulphur-bearing marker pen, a contaminated grinding wheel that previously touched carbon steel, or oil from a thread-cutting operation is enough to crack a weld that is otherwise perfect. Keep a dedicated set of stainless-only tools for nickel alloy work.
How should filler metal be specified and certified?
A welding consumable line item needs the classification, the diameter, the quantity and the certification, and for critical service it should also state the packaging:
- **Classification**, e.g. AWS A5.14 ERNiCrMo-3, plus the UNS of the matching base metal for confirmation.
- **Diameter**, e.g. 2.4 mm for GTAW root passes, 3.2 mm or 4.0 mm for fill and cap.
- **Form**, coated electrode to AWS A5.11 (ENiCrMo-4 for C-276) or bare rod to AWS A5.14.
- **Certification**, EN 10204 3.1 with the heat number traceable to the chemistry.
- **Packaging**, hermetically sealed tubes for bare wire where the joint is radiographed, and vacuum-sealed packs for electrodes.
Request the ferrite content only where a ferrite-bearing filler is used; the specification limits for that are set by the base metal standard, not by the filler standard. For grain size control in the base metal, ASTM E112 is the reference method.
Filler metal and matched welding consumables from Hangbo Alloy
Hangbo Alloy supplies nickel alloy base metal and the matched welding consumables in the same UNS grade families — Inconel 600/601/625/718, Incoloy 800/825, Hastelloy C-276/C-22, Monel 400/K-500 and Nickel 200/201 — with EN 10204 3.1 certification on both the base metal and the filler, and third-party inspection available on request. Because the pipe, the fittings and the consumable come from the same traceability chain, the weld procedure qualification has one document set rather than three.
Tell us the base metal UNS number and the service medium and we will confirm the filler classification, the diameter and the test package before the order ships.
Frequently asked questions
Can I weld Inconel 625 with 316L filler?
You can produce a weld, but you should not use it in corrosion service. ER316L diluted with 625 base metal produces a weld with a molybdenum content between the two and an austenitic-ferritic solidification mode that is prone to fissuring. Where a joint must be made and 625 filler is unavailable, use ERNiCr-3 rather than a stainless consumable.
Is ERNiCrMo-3 the same as Inconel 625 filler?
Yes — ERNiCrMo-3 is the AWS A5.14 classification for the filler metal whose chemistry matches Inconel 625 (UNS N06625). "Inconel" is a trademark of Special Metals Corporation, so a certificate will normally show the AWS classification and the UNS number rather than the trade name.
Why does my nickel alloy weld keep showing porosity?
In the great majority of cases the filler metal has absorbed moisture, or the joint surface carries sulphur contamination. Dry the electrodes per the manufacturer's schedule (typically 250–300 °C for one hour), store bare wire in a heated cabinet, degrease the joint with acetone, and keep grinding wheels and brushes dedicated to nickel alloys. Technique changes alone rarely fix porosity in nickel alloys.
Do I need to post-weld heat treat a nickel alloy joint?
Only where the base metal is precipitation-hardenable (718, X-750, A286) or where the service is in a chloride or polythionic environment and residual stress must be relieved. The solid-solution alloys — 625, C-276, 825, Monel 400 — are normally left as-welded, because the solution-annealing temperature would be needed to change the microstructure and that is impractical on a completed fabrication. See Inconel 718 Heat Treatment for the age-hardenable case.