Special Metal Welding: Choosing The Right Filler Metal
Jul 22, 2026
Introduction
Welding specialty metals - nickel alloys, heat-resistant steels, and corrosion-resistant grades - presents challenges far beyond those of standard carbon steel welding. The wrong filler metal can lead to premature corrosion failure, hot cracking, embrittlement, or catastrophic weld failure in service. For engineers and procurement professionals working with nickel-based alloys (Inconel, Hastelloy, Monel), heat-resistant steels (310S, 330), and dissimilar metal combinations, selecting the correct filler metal is a critical design decision.
This guide provides a systematic approach to filler metal selection for specialty alloys, covering AWS classifications, chemical composition matching, dissimilar weld considerations, and common pitfalls.
Product Overview
Filler metals for specialty alloy welding are classified under AWS A5.14 (nickel and nickel-alloy bare electrodes and rods) and AWS A5.11 (nickel and nickel-alloy covered electrodes). The most commonly used classifications include:
Nickel-Copper Series:
- ERNiCu-7 (Monel 190): For welding Monel 400 and overlay on steel
Nickel-Chromium-Iron Series:
- ERNiCr-3 (Inconel 82): The most versatile nickel filler; used for Inconel 600, 601, dissimilar welds between stainless and carbon steel
- ERNiCrFe-13 (Inconel 52MSS): Advanced filler for nuclear applications with improved DDC resistance
Nickel-Chromium-Molybdenum Series:
- ERNiCrMo-3 (Inconel 112): For welding Inconel 625, Hastelloy C-type, and overlay cladding
- ERNiCrMo-4 (Hastelloy C-276): For welding Hastelloy C-276 and C-4
- ERNiCrMo-10 (Hastelloy C-22): For welding Hastelloy C-22 and dissimilar corrosion-resistant overlays
- ERNiCrMo-14 (Hastelloy 686): Ultra-corrosion-resistant filler for severe environments
Nickel-Molybdenum Series:
- ERNiMo-7 (Hastelloy B-2): For welding Hastelloy B-2 in hydrochloric acid service
Comparison Table
Filler metal chemical composition:
| Element | ERNiCr-3 (82) | ERNiCrMo-3 (625) | ERNiCrMo-4 (C-276) | ERNiCrMo-10 (C-22) | ERNiCu-7 (Monel) |
|---|---|---|---|---|---|
| Ni | ≥ 67.0 | ≥ 58.0 | Bal. | Bal. | 62.0–69.0 |
| Cr | 18.0–22.0 | 20.0–23.0 | 14.5–16.5 | 20.0–22.5 | - |
| Mo | - | 8.0–10.0 | 15.0–17.0 | 12.5–14.5 | - |
| Fe | ≤ 3.0 | ≤ 5.0 | 4.0–7.0 | 2.0–6.0 | ≤ 2.5 |
| W | - | - | 3.0–4.5 | 2.5–3.5 | - |
| Cu | ≤ 0.50 | ≤ 0.50 | - | - | Bal. |
| C | ≤ 0.10 | ≤ 0.10 | ≤ 0.02 | ≤ 0.015 | ≤ 0.15 |
| Si | ≤ 0.50 | ≤ 0.50 | ≤ 0.08 | ≤ 0.08 | ≤ 1.25 |
| Mn | 2.5–3.5 | ≤ 0.50 | ≤ 1.0 | ≤ 0.5 | ≤ 4.0 |
All-weld metal mechanical properties:
| Property | ERNiCr-3 | ERNiCrMo-3 | ERNiCrMo-4 | ERNiCrMo-10 | ERNiCu-7 |
|---|---|---|---|---|---|
| Tensile Strength (MPa) | 550–650 | 760–860 | 690–790 | 690–790 | 480–580 |
| Yield Strength (MPa) | 250–350 | 350–450 | 280–380 | 350–450 | 250–350 |
| Elongation (%) | 35–45 | 30–40 | 35–45 | 35–45 | 30–40 |
| Impact at -196°C (J) | 50–70 | 60–80 | 60–80 | 60–80 | 30–50 |
| Max Service Temp (°C) | 980 | 815 | 1040 | 1040 | 480 |
Base metal to filler metal selection guide:
| Base Metal | Recommended Filler | AWS Class | Alternative |
|---|---|---|---|
| Inconel 600 | ERNiCr-3 | AWS A5.14 | ERNiCrFe-13 |
| Inconel 601 | ERNiCr-3 | AWS A5.14 | ERNiCrMo-3 |
| Inconel 625 | ERNiCrMo-3 | AWS A5.14 | ERNiCrMo-10 |
| Inconel 718 | ERNiFeCr-2 | AWS A5.14 | (precipitation-hardened) |
| Hastelloy C-276 | ERNiCrMo-4 | AWS A5.14 | ERNiCrMo-14 |
| Hastelloy C-22 | ERNiCrMo-10 | AWS A5.14 | ERNiCrMo-4 |
| Hastelloy B-2 | ERNiMo-7 | AWS A5.14 | - |
| Monel 400 | ERNiCu-7 | AWS A5.14 | ERNiCr-3 (dissimilar) |
| Nickel 200/201 | ERNi-1 | AWS A5.14 | ERNiCr-3 |
| 310S to 310S | ER310 | AWS A5.9 | ER312 |
| 310S to Carbon Steel | ERNiCr-3 | AWS A5.14 | ER309 |
| Stainless to Carbon Steel | ERNiCr-3 | AWS A5.14 | ER309L |
| Hastelloy to Stainless | ERNiCrMo-3 | AWS A5.14 | ERNiCrMo-4 |
Performance Analysis
Dilution and Alloy Matching
The fundamental principle of filler metal selection is ensuring the weld deposit, after dilution with the base metal, retains sufficient alloying elements to resist the service environment. A typical weld has 20–40% dilution from the base metal. For highly alloyed materials like Hastelloy C-276, using a matching filler (ERNiCrMo-4) ensures the weld deposit maintains the same corrosion resistance as the base metal. Using ERNiCrMo-3 (Inconel 625) for C-276 welds would result in lower molybdenum and no tungsten in the weld deposit, reducing pitting resistance.
Hot Cracking Prevention
Nickel-based alloys are particularly susceptible to hot cracking (solidification cracking) due to their wide solidification temperature range. Key preventive measures:
- Low heat input: Maintain 0.8–1.5 kJ/mm for GTAW, 1.0–2.0 kJ/mm for GMAW
- Interpass temperature control: Keep below 150°C for most nickel alloys, below 100°C for Hastelloy grades
- Bead shape: Use convex beads; avoid concave beads and wide flat beads that concentrate stress at the toes
- Stringer beads preferred over weave: Limit weave to 2.5× electrode diameter
- Cleanliness: Remove all oils, grease, oxides, and sulfur-containing marking materials before welding
Ductility Dip Cracking (DDC)
DDC is a metallurgical cracking phenomenon that occurs in the 650–1200°C temperature range during welding of high-nickel alloys. It is particularly problematic in ERNiCr-3 (Inconel 82) and ERNiCrFe-7 (Inconel 52) welds. Modern filler metals like ERNiCrFe-13 (Inconel 52MSS) contain controlled additions of Nb (2.0–2.5%) and Mo (3.0–4.0%) that dramatically improve DDC resistance.
Dissimilar Weld Considerations
When welding dissimilar metals (e.g., stainless steel to carbon steel, or nickel alloy to stainless steel), the filler metal must accommodate the differing thermal expansion coefficients, melting temperatures, and metallurgical compatibility. ERNiCr-3 is the preferred filler for most dissimilar welds because:
- Its high nickel content accommodates dilution from both austenitic stainless and ferritic base metals
- The 2.5–3.5% manganese provides good deoxidation and wetting
- It produces a fully austenitic weld deposit with excellent ductility
- It resists carbon migration across the weld interface at elevated temperatures
Post-Weld Heat Treatment (PWHT)
Most solid-solution nickel alloys (Inconel 600, 625, Hastelloy C-276, C-22) do not require PWHT after welding. However, stress relief may be specified for:
- Service environments causing stress corrosion cracking (caustic solutions, polythionic acid)
- Severe restraint conditions requiring dimensional stability
- Dissimilar welds where differential expansion could cause fatigue
When PWHT is required, typical parameters are 650–870°C for 1–2 hours, followed by controlled cooling. Never PWHT Hastelloy C-276 in the 540–870°C range where carbide precipitation occurs - this can destroy the alloy's corrosion resistance.
Application Guide
| Application | Base Metal | Filler Metal | Key Considerations |
|---|---|---|---|
| Pressure vessel cladding | Carbon steel + Inconel 625 overlay | ERNiCrMo-3 | Dilution control <10%; 2-layer minimum |
| FGD scrubber welds | Hastelloy C-276 | ERNiCrMo-4 | Matching filler; no PWHT; low heat input |
| Furnace tube welds | 310S stainless | ER310 or ERNiCr-3 | ERNiCr-3 for 310S-to-carbon steel |
| Heat exchanger tube-to-tubesheet | Inconel 600 to carbon steel | ERNiCr-3 | Dissimilar weld; high-temperature service |
| Chemical reactor lining | C-22 clad on steel | ERNiCrMo-10 | Corrosion overlay; 3-layer recommended |
| Offshore piping | Duplex 2205 to carbon steel | ERNiCrMo-3 | Superduplex alternative: ER2594 |
| Nuclear vessel welds | Inconel 690 to carbon steel | ERNiCrFe-13 | DDC-resistant; stringent NDE required |
| Aerospace components | Inconel 718 | ERNiFeCr-2 | Precipitation-hardened; requires aging |
| Marine components | Monel 400 to steel | ERNiCu-7 | Good strength; Cu migration control |
FAQ
Q1: Can I use ERNiCrMo-3 (Inconel 625 filler) for welding Hastelloy C-276?
It is possible but not ideal. ERNiCrMo-3 has lower molybdenum (8–10% vs. 15–17% in ERNiCrMo-4) and no tungsten. The resulting weld deposit will have reduced pitting resistance and lower crevice corrosion resistance compared to the C-276 base metal. For critical service in aggressive chloride environments, always use the matching ERNiCrMo-4 filler. For moderate corrosion environments, ERNiCrMo-3 may be acceptable as a cost-saving alternative.
Q2: What is the difference between ERNiCr-3 and ERNiCrMo-3?
ERNiCr-3 (Inconel 82) is a Ni-Cr-Fe filler with no molybdenum, designed primarily for Inconel 600/601 welds and dissimilar metal joints. ERNiCrMo-3 (Inconel 112) contains 8–10% molybdenum, which provides pitting resistance equivalent to PREN >40. ERNiCr-3 is used for high-temperature and dissimilar applications; ERNiCrMo-3 is used for corrosion-resistant applications matching Inconel 625.
Q3: How do I prevent hot cracking in nickel alloy welds?
Three critical measures: (1) Use low heat input (0.8–1.5 kJ/mm GTAW) to narrow the solidification range; (2) Maintain convex bead profiles with stringer or slight weave technique - avoid wide flat or concave beads; (3) Keep interpass temperature below 150°C and ensure thorough cleaning of all surface contaminants before welding.
Q4: Why can't I use stainless steel filler (ER308/ER316) for nickel alloy welds?
Stainless steel fillers contain 20–30% less nickel than nickel-alloy fillers. When diluted by a nickel-alloy base metal, the resulting weld deposit will have insufficient nickel and chromium to maintain corrosion or heat resistance. Additionally, the ferrite content in stainless fillers can form brittle intermetallic phases when mixed with high-nickel base metals, causing embrittlement and cracking.
Q5: What filler should I use for welding Hastelloy C-276 to 316L stainless steel?
ERNiCrMo-4 (matching C-276 filler) is the preferred choice. It ensures the weld deposit maintains the corrosion resistance of the more noble alloy (C-276). Alternatively, ERNiCrMo-10 (C-22 filler) can be used for even broader corrosion resistance. Never use ER316L or ER309L for this joint - the weld will be the weak link in corrosion performance.
Conclusion
Selecting the right filler metal for specialty alloy welding requires careful consideration of base metal composition, service environment, dilution effects, and cracking susceptibility. The general rule is to use a matching or overmatching filler metal - one whose alloy content equals or exceeds that of the base metal in the critical elements (Cr, Mo, W for corrosion; Ni, Cr, Fe for high-temperature strength).
For dissimilar welds, ERNiCr-3 remains the most versatile filler due to its ability to accommodate dilution from both nickel and iron-based base metals while maintaining a fully austenitic, crack-resistant deposit. For critical corrosion applications, always match the filler to the more noble base metal and verify weld deposit chemistry through PMI (positive material identification).
Proper welding procedure - low heat input, interpass control, cleanliness, and bead shape management - is equally important as filler selection. Even the best filler metal will fail if the welding parameters promote hot cracking or excessive dilution. For more on welding specific nickel alloys, see our guide on welding Hastelloy.
