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Invar 36 welding wire is a specialized filler material used primarily for welding Invar 36 (UNS K93600), a nickel-iron alloy known for its extremely low coefficient of thermal expansion. This property makes the welding process highly sensitive, as maintaining thermal stability is critical for dimensional accuracy in precision applications such as aerospace tooling, cryogenic assemblies, and electronic components. The right welding wire ensures strong, crack-free joints that retain the low-expansion characteristics of the base material.
Composition of Invar 36 Welding Wire
The chemical composition of Invar 36 welding wire is nearly identical to the base metal to ensure compatibility and consistent thermal expansion behavior:
| Element | Typical Content (%) |
|---|---|
| Nickel (Ni) | 35.0 – 37.0 |
| Iron (Fe) | Balance |
| Carbon (C) | ≤ 0.05 |
| Silicon (Si) | ≤ 0.35 |
| Manganese (Mn) | ≤ 0.60 |
| Sulfur (S) | ≤ 0.02 |
| Phosphorus (P) | ≤ 0.02 |
Available Specifications and Standards
Invar 36 welding wire is manufactured under strict specifications to meet high-performance standards:
| Specification | Description |
|---|---|
| UNS | K93600 |
| AWS | A5.14 ERNiFeCr-1 (common substitute) |
| ISO | 18274 (NiFe alloy wire category) |
| Form | Spools, straight lengths, TIG/MIG formats |
Welding Methods Compatible with Invar 36 Wire
Invar 36 welding wire can be used with several welding methods, each suitable for specific project requirements:
| Welding Method | Details |
|---|---|
| TIG (GTAW) | Preferred for precise, low-heat applications; minimal distortion |
| MIG (GMAW) | Used for higher productivity welds on thicker sections |
| Plasma Arc Welding | High precision; used in aerospace applications |
Key Welding Considerations
To preserve the properties of Invar 36 during welding, several precautions must be taken:
| Factor | Best Practice |
|---|---|
| Heat Input | Use low heat to reduce thermal distortion |
| Preheating | Typically not required |
| Interpass Temperature | Keep below 150°C |
| Post-Weld Heat Treatment | Usually avoided unless stress relief is needed |
| Shielding Gas | Use pure argon or argon-helium mixtures |
Applications of Invar 36 Welding Wire
Invar 36 welding wire is critical in applications where thermal expansion must be tightly controlled:
| Industry | Application |
|---|---|
| Aerospace | Tooling, satellite structures, avionics |
| Cryogenics | Liquid nitrogen tanks, low-temp piping |
| Optics | Mounts, fixtures, interferometer frames |
| Scientific Equipment | Measuring instruments, calibration fixtures |
Product Forms and Sizes
Invar 36 welding wire is available in a range of diameters for different welding techniques:
| Diameter (mm) | Typical Use |
|---|---|
| 0.8 | Thin sheet TIG welding |
| 1.0 | General-purpose TIG/MIG |
| 1.2 | Heavy section MIG |
| 2.0 | Manual arc or heavy-duty TIG |
Related Questions
What shielding gas should be used with Invar 36 welding wire?
Pure argon or argon-helium mixtures are commonly used as shielding gases when welding Invar 36 to maintain weld purity and reduce oxidation.
Can Invar 36 be welded to stainless steel?
Yes, but it requires a suitable dissimilar metal welding technique and possibly a different filler wire like ERNiCr-3 to ensure strong joint performance and minimize cracking.
Is Invar 36 difficult to weld?
Yes, Invar 36 is sensitive to welding heat. Its low thermal expansion means heat can cause distortion and microstructural changes, so controlled welding techniques and low heat input are necessary.