TIG Welding Nickel Alloys: GTAW Parameters for Inconel & Hastelloy
Date: 2026年7月24日 Categories: News Views: 392
Excerpt:
Complete GTAW welding parameters for Inconel 718, 625, and Hastelloy C-276: filler metals, amperage, voltage, interpass temperatures, and defect prevention for aerospace, petrochemical, and marine applications.
Introduction
Gas Tungsten Arc Welding (GTAW), commonly known as TIG welding, is the preferred joining process for nickel-based superalloys used in aerospace turbines, petrochemical reactors, and marine engineering systems. Unlike carbon steel, nickel alloys demand precise control of heat input, interpass temperature, and shielding gas coverage to prevent defects such as hot cracking, porosity, and sensitization of the heat-affected zone (HAZ).
Quick Answer: The optimal TIG welding parameters for nickel alloys are: DCEN polarity, 80-220 A current (depending on thickness), 10-18 V arc voltage, 100-250 mm/min travel speed, 99.995% pure argon shielding at 10-18 L/min, 2% thoriated or lanthanated tungsten, and interpass temperature below 93-150 degrees C depending on the alloy. Matching filler metals are ERNiFeCr-2 for Inconel 718, ERNiCrMo-3 for Inconel 625, and ERNiCrMo-4 for Hastelloy C-276, all per AWS A5.14.
Shanghai Hangbo Alloy Group Co., Ltd. supplies nickel alloy welding wire, filler metals, and base materials (round bars, seamless tubes, plates, forgings) to fabrication workshops worldwide. This guide provides qualified starting parameters for three of the most widely welded nickel alloys, drawing on data from AWS A5.14 filler metal specifications, Haynes International welding data sheets, and ASM Handbook Vol. 6 welding guidelines.
Filler Metal Selection per AWS A5.14
Selecting the correct filler metal is the single most critical decision in nickel alloy welding. The filler metal must chemically match the base metal to ensure the weld deposit achieves equivalent corrosion resistance and mechanical strength. All filler metals discussed here are classified under AWS A5.14 / ASME SFA-5.14, the specification for nickel and nickel-alloy bare welding electrodes and rods.
| Base Alloy | UNS Designation | Filler Metal (AWS) | Filler UNS | Key Alloying Elements | Typical Diameters |
|---|---|---|---|---|---|
| Inconel 718 | N07718 | ERNiFeCr-2 | N07718 | Ni-Fe-Cr-Nb-Mo | 0.8, 1.0, 1.2, 1.6 mm |
| Inconel 625 | N06625 | ERNiCrMo-3 | N06625 | Ni-Cr-Mo-Nb (58% Ni min) | 1.6, 2.4, 3.2 mm |
| Hastelloy C-276 | N10276 | ERNiCrMo-4 | N10276 | Ni-Cr-Mo-W (57% Ni min) | 0.9, 1.2, 1.6 mm |
Engineer's Note: Never substitute a "close" filler metal for a specified one. Using ERNiCrMo-3 (Inconel 625 filler) on Hastelloy C-276 base metal will produce a weld deposit with lower tungsten content and reduced resistance to localized corrosion in chloride environments. Always match filler chemistry to base metal per AWS A5.14 classification.
GTAW Parameters for Inconel 718 (UNS N07718)
Inconel 718 is a precipitation-hardenable nickel-chromium alloy strengthened by gamma double-prime (Ni3Nb) precipitates. It must always be welded in the solution-annealed condition. If the component has already been aged, a full re-anneal at 954-980 degrees C is mandatory before welding. Failure to do so will result in microfissuring in the HAZ due to delta-phase precipitation at grain boundaries.
| Plate Thickness | Joint Type | Current (A) | Voltage (V) | Travel Speed (mm/min) | Filler Diameter (mm) | Argon Flow (L/min) |
|---|---|---|---|---|---|---|
| 0.8-1.5 mm | Square butt | 40-70 | 10-12 | 100-180 | 0.8-1.0 | 10-12 |
| 1.5-3.0 mm | Square butt / lap | 70-110 | 11-13 | 150-250 | 1.0-1.2 | 12-15 |
| 3.0-6.0 mm | 60-degree V-groove | 110-160 | 12-14 | 150-250 | 1.2-1.6 | 14-18 |
| 6.0-12.7 mm | 60-degree V-groove | 160-220 | 13-15 | 150-250 | 1.6 | 15-20 |
Pulsed TIG parameters for precision aerospace welds: Peak current 180-220 A, background current 60-90 A, pulse frequency 2-10 Hz, duty cycle 40-60%, travel speed 150-250 mm/min. Pulsed GTAW reduces overall heat input and provides finer control of the weld pool, which is especially beneficial for thin-wall Inconel 718 tubing used in UAV turbojet fuel manifolds.
Post-weld heat treatment (PWHT): Inconel 718 requires a mandatory two-step aging cycle after welding: solution anneal at 954-980 degrees C (hold 1 hour per inch of thickness), then age at 720 degrees C for 8 hours, furnace cool at 55 degrees C/hour to 620 degrees C, hold 8 hours, air cool. This cycle precipitates the gamma double-prime strengthening phase throughout the weld and HAZ.
Engineer's Note: The maximum interpass temperature for Inconel 718 is 93 degrees C (200 degrees F). Use a contact pyrometer to verify temperature before depositing the next pass. Never use compressed air or water to accelerate cooling - this creates thermal shock and promotes microcracking.
GTAW Parameters for Inconel 625 (UNS N06625)
Inconel 625 is a solid-solution strengthened nickel-chromium-molybdenum-niobium alloy. Unlike 718, it does not require post-weld aging. Its weldability is excellent when proper parameters are used, making it the most widely welded nickel alloy in marine, chemical, and oil and gas applications.
| Filler Diameter (mm) | Current (A, DCEN) | Voltage (V) | Applicable Plate Thickness | Shielding Gas |
|---|---|---|---|---|
| 1.6 | 80-130 | 12-15 | 1-3 mm | 100% Argon |
| 2.4 | 120-175 | 13-17 | 3-6 mm | 100% Argon |
| 3.2 | 150-220 | 14-18 | 6-12 mm | 100% Argon |
Key parameters: DCEN polarity, 2% thoriated or lanthanated tungsten ground to a tapered point, argon flow 10-15 L/min through a gas lens cup. For thick sections (greater than 6 mm), an argon-helium mix (50/50) can be used to increase heat input and improve penetration without raising amperage. Backing gas (100% argon, 5-10 L/min) is mandatory for root passes on pipe and tube.
Interpass temperature: Maximum 150 degrees C for general fabrication. For 9% nickel steel transition joints, limit to 100 degrees C. For cladding overlays, follow the qualified WPS range of 150-200 degrees C.
Heat input control: Keep heat input in the range of 0.08-0.1 kJ/mm for critical corrosion applications. Excessive heat input promotes coarse dendritic structure and increases Laves phase and MC carbide precipitation, degrading both mechanical properties and corrosion resistance. Use stringer beads with no weave - do not oscillate the torch.
Engineer's Note: Inconel 625 weld pools appear sluggish and dull compared to stainless steel. This is normal - do not increase amperage to improve fluidity. Overheating will cause hot cracking, porosity, and excessive oxidation. Always fill the crater at the end of each weld pass to prevent crater cracks.
GTAW Parameters for Hastelloy C-276 (UNS N10276)
Hastelloy C-276 is a nickel-molybdenum-chromium alloy with tungsten addition, offering exceptional resistance to uniform and localized corrosion in aggressive chemical environments. Its weldability is good, but the high molybdenum and tungsten content requires careful heat input control to prevent microsegregation in the weld metal.
| Parameter | Range | Notes |
|---|---|---|
| Current (A, DCEN) | 80-180 | Lower range for thin-wall tube; upper for fill passes |
| Voltage (V) | 10-18 | Keep short arc for gas coverage |
| Travel Speed (mm/min) | 100-250 | Faster travel limits heat input |
| Heat Input (kJ/mm) | 0.5-1.2 | Lower limit for critical corrosion joints |
| Interpass Temp (degrees C) | Less than 93 (conservative) to 177 | Below 93 limits HAZ sensitization |
| Tungsten | 2% thoriated/lanthanated, 1.6-2.4 mm | Ground to tapered point |
| Argon Purity | 99.999% | Even trace O2 or N2 will oxidize the melt |
| Backing Gas | 100% Argon, mandatory for root | O2 content below 0.1% before striking arc |
Post-weld heat treatment: Hastelloy C-276 is used in the as-welded condition - no PWHT is required. The low carbon content (less than 0.01%) minimizes carbide precipitation in the HAZ, preserving corrosion resistance in the as-welded state. Optional solution annealing at 1060-1150 degrees C followed by rapid quench can be specified for extreme service conditions where maximum corrosion resistance is needed.
Engineer's Note: Stringer beads only - no weave. Each bead should be slightly convex. Avoid deep concave beads which are prone to centerline cracking. Use a trailing shield for titanium and nickel alloy welds that will be exposed to temperatures above 315 degrees C during cooling. Remove all oxidation between passes with dedicated stainless steel wire brushes.
Modern Applications in Aerospace, Petrochemical, and Marine Engineering
UAV Turbojet Combustion Chambers (Inconel 625)
Small unmanned aerial vehicle (UAV) turbojet engines operate at turbine inlet temperatures of 850-1050 degrees C, requiring thin-wall Inconel 625 sheet (0.8-1.5 mm) for combustion chamber liners. GTAW with 0.8 mm ERNiCrMo-3 filler at 40-70 A, 10-12 V, and 100-180 mm/min travel speed produces defect-free welds with minimal heat input. Backing gas purity must be maintained at O2 below 0.1% to prevent internal oxidation that would reduce high-temperature fatigue life.
Hydrogen Electrolyzer Bipolar Plates (Hastelloy C-276)
Proton exchange membrane (PEM) electrolyzer bipolar plates handling humidified chlorine and oxygen at 80-90 degrees C require Hastelloy C-276 welds with zero porosity. GTAW parameters of 80-130 A, 12-15 V, and heat input below 0.8 kJ/mm produce welds that pass ASME Section IX qualification with RT examination. The interpass temperature limit of 93 degrees C prevents sensitization that would compromise 50-year design life corrosion margins.
FPSO Seawater Cooling Systems (Inconel 625)
Floating Production Storage and Offloading (FPSO) vessels use Inconel 625 weld overlay on carbon steel seawater piping to prevent chloride pitting. The overlay is applied using GTAW at 120-175 A with ERNiCrMo-3 filler, controlling dilution to below 10% to maintain the corrosion-resistant chemistry at the surface. Typical overlay thickness is 2.5-3.0 mm over API 5L X65 pipe.
Nuclear Waste Encapsulation Containers (Inconel 625)
Spent nuclear fuel dry storage canisters welded from Inconel 625 plate (6-12 mm) require full-penetration GTAW welds qualified to ASME Section III, Division 3. Weld parameters of 150-220 A, 14-18 V, with automatic orbital GTAW equipment ensure consistent weld geometry and mechanical properties. Interpass temperature is monitored continuously via thermocouples and kept below 150 degrees C.
| Application | Alloy | Thickness (mm) | Current (A) | Heat Input (kJ/mm) | Critical Requirement |
|---|---|---|---|---|---|
| UAV turbojet liner | Inconel 625 | 0.8-1.5 | 40-70 | 0.3-0.5 | Zero porosity, backing gas purity |
| H2 electrolyzer plates | Hastelloy C-276 | 1.0-2.0 | 80-130 | 0.5-0.8 | RT-grade, no sensitization |
| FPSO seawater piping | Inconel 625 overlay | 2.5-3.0 | 120-175 | 0.8-1.0 | Less than 10% dilution |
| Nuclear canister | Inconel 625 | 6-12 | 150-220 | 0.8-1.2 | ASME III Div 3 qualification |
Common Welding Defects and Prevention
| Defect | Cause | Prevention | Applicable Alloys |
|---|---|---|---|
| Hot cracking (solidification) | High heat input, excessive restraint, sulfur contamination | Control heat input, use stringer beads, ensure cleanliness | All nickel alloys, especially 718 |
| Porosity | Moisture, oil, dirty filler metal, inadequate gas coverage | Bake filler metal, use gas lens, verify argon purity greater than 99.995% | All grades |
| Microfissuring (HAZ) | Welding aged 718, delta phase at 850 degrees C | Solution anneal before welding 718, avoid 760-980 degrees C range | Inconel 718 |
| Sensitization (HAZ) | Carbide precipitation at grain boundaries | Limit interpass temp to 93 degrees C, use low-C filler | Hastelloy C-276, Inconel 625 |
| Crater cracking | Abrupt arc termination | Use downslope, fill crater completely | All grades |
Shielding Gas and Tungsten Electrode Guidelines
| Parameter | Specification | Notes |
|---|---|---|
| Shielding gas | 99.995-99.999% pure argon | Trace O2 less than 5 ppm; N2 less than 10 ppm |
| Gas flow rate | 10-18 L/min (front), 5-10 L/min (backing) | Use gas lens for consistent laminar flow |
| Gas cup diameter | 12-20 mm | Larger cups improve coverage on nickel alloys |
| Trailing shield | Required for reactive service | Protects weld until below 315 degrees C |
| Tungsten type | 2% thoriated (WT20) or 2% lanthanated (WL20) | Grind to 30-degree taper with flat tip |
| Tungsten diameter | 1.6-3.2 mm | Match to amperage range |
| Electrode stick-out | Maximum 6 mm | Minimize to maintain gas coverage |
Engineer's Note: Never use the same wire brushes, grinding wheels, or files on carbon steel and nickel alloys. Cross-contamination with iron particles will cause rust staining and pitting corrosion in service. Maintain a dedicated set of stainless steel tools marked "Ni alloy only" in the fabrication shop.
Frequently Asked Questions
What is the best filler metal for TIG welding Inconel 718?
ERNiFeCr-2 (AWS A5.14) is the standard filler metal for TIG welding Inconel 718 (UNS N07718). It matches the base metal composition including niobium content (4.75-5.50%), enabling gamma double-prime precipitation hardening in the weld deposit during post-weld aging. For aerospace applications requiring VIM+ESR or VIM+VAR remelted filler, specify AMS 5832 compliance.
Do nickel alloys require preheating before TIG welding?
No. Solid-solution nickel alloys (Inconel 625, Hastelloy C-276, Monel 400) and precipitation-hardenable alloys (Inconel 718) do not require preheating. In fact, preheating is counterproductive - it raises the interpass temperature and increases the risk of hot cracking and HAZ sensitization. Start welding at room temperature (minimum 15 degrees C) and control interpass temperature per the guidelines above.
What interpass temperature should I maintain when welding Hastelloy C-276?
For Hastelloy C-276, the conservative interpass temperature limit is 93 degrees C (200 degrees F) to prevent sensitization and topologically close-packed (TCP) phase formation in the HAZ. Some fabrication specifications allow up to 177 degrees C, but for critical corrosion applications, 93 degrees C is the recommended maximum. Use a contact pyrometer to verify before each pass.
Can I TIG weld Inconel 718 in the aged condition?
No. Inconel 718 must be welded in the solution-annealed condition. If the material has been aged (720 degrees C / 8 hours + 620 degrees C / 8 hours), you must re-solution-anneal at 954-980 degrees C before welding. Welding aged 718 will cause microfissuring in the HAZ due to delta-phase precipitation at grain boundaries and stress concentration from the existing gamma double-prime precipitates.
Why do my nickel alloy welds look dull and sluggish compared to stainless steel?
This is normal. Nickel alloy weld pools have higher viscosity and lower surface fluidity than austenitic stainless steel. The weld pool appears sluggish and darker. Do not increase amperage to improve fluidity - this will cause hot cracking and porosity. Maintain the recommended parameters, use short arc length, and ensure adequate gas coverage. The weld bead should be slightly convex with smooth transitions to the base metal.
What shielding gas purity is required for TIG welding nickel alloys?
Use argon with a minimum purity of 99.995% (5N), ideally 99.999% (6N) for critical applications. Oxygen content must be below 5 ppm and nitrogen below 10 ppm. Even trace amounts of O2 or N2 will oxidize the molten nickel weld pool, causing discoloration, porosity, and reduced corrosion resistance. Always use a gas lens and verify backing gas oxygen content (below 0.1%) before striking the arc on root passes.
Contact Shanghai Hangbo Alloy Group
Shanghai Hangbo Alloy Group Co., Ltd. is a professional manufacturer and global supplier of nickel-based alloy materials. We provide:
- Welding consumables: ERNiFeCr-2, ERNiCrMo-3, ERNiCrMo-4 filler wire per AWS A5.14
- Base materials: Round bars (6-300 mm OD), seamless tubes (6-273 mm OD), plates (0.5-80 mm), precision strips, and custom forgings
- Alloy grades: Inconel 718, 625, 600, 601; Hastelloy C-276, C-22; Monel 400, K-500; Incoloy 825, 800H; Nimonic 90, 80A
- Standards compliance: ASTM B637, B446, B574, B575, B443, B564; AMS 5832, 5829; NACE MR0175/ISO 15156
- Quality assurance: ISO 9001:2015 certified, EN 10204 3.1/3.2 MTRs with every shipment
Contact:
Phone: +86-136-1165-6360
Email: hangbo@nickel-alloy.com
Address: No.388 Songhuang Road, Qingpu District, Shanghai, China 201700
