CLADDING TECHNOLOGY SHANXI CO., LTDTIG Welding of Pure Nickel to 304 Austenitic Stainless Steel: Process, Microstructure, and Properties
Literature Overview
This 2014 publication in Electric Welder journal by Zhao Hulin, Wang Xijing, Shen Liang, and Wang Jiang from Lanzhou University of Technology and Jinchuan Group Nickel and Cobalt Research Institute provides a comprehensive study of TIG welding between pure nickel (Ni) and 304 austenitic stainless steel. This dissimilar metal welding topic is highly relevant to cladding applications where nickel-based overlays are deposited on stainless steel substrates for enhanced corrosion resistance in aggressive environments.
Core Technical Content
Dissimilar Metal Welding Challenges
The Ni/304SS joint presents several metallurgical challenges:
- Thermal expansion mismatch: Pure nickel (13.2 × 10⁻⁶/K) and 304SS (17.3 × 10⁻⁶/K) generate significant thermal stresses during cooling.
- Solidification cracking susceptibility: The wide solidification range of nickel-based weld metals creates hot cracking tendencies.
- Microstructural complexity: Multiple phases form at the interface including Ni₃Fe, Ni(Fe,Cr), and austenite/ferrite mixtures.
- Dilution effects: Carbon steel and stainless steel dilution into the nickel weld metal alters composition and properties.
Welding Process Parameters
| Parameter | Optimized Value | Effect on Joint Quality |
|---|---|---|
| Welding current | 120–180 A | Penetration and dilution control |
| Welding speed | 200–400 mm/min | Heat input management |
| Shielding gas | 100% Argon or 95% Ar/5% He | Arc stability and penetration |
| Filler wire | Ni-201 or Ni-2200 | Composition compatibility |
| Preheat | 150–300°C | Reduce cracking susceptibility |
| Interpass temperature | < 300°C | Control microstructure evolution |
Microstructural Analysis
Metallographic examination of the weld joint revealed distinct zones:
- Base metal zones: Pure nickel (equiaxed grains) and 304SS (austenitic structure with some delta ferrite)
- Heat-affected zones: Grain growth in nickel side; precipitation of carbides and intermetallics in SS side
- Weld metal: Complex microstructure with austenite, delta ferrite, and intermetallic phases (Ni₃Fe, Ni₇Fe₃)
- Interface zone: Transition region with progressive compositional changes and mixed phases
The presence of brittle intermetallic compounds at the Ni/SS interface was identified as a potential weakness, particularly under thermal cycling conditions.
Mechanical Properties
| Test Method | Weld Joint | Base Metal (Ni) | Base Metal (304SS) |
|---|---|---|---|
| Tensile strength (MPa) | 520–650 | 420–500 | 550–650 |
| Elongation (%) | 18–25 | 35–45 | 35–45 |
| Hardness (HV) | 180–220 | 130–160 | 180–220 |
| Impact energy (J) | 45–65 | 80–120 | 60–90 |
The weld joint properties were generally lower than both base metals due to the formation of brittle intermetallic phases and the dilution effects.
Integration with Engineering Practice
For nickel-based cladding applications on stainless steel substrates, this research provides critical insights:
- Filler metal selection: Ni-201 (Ni-Cu alloy) or Ni-2200 (Ni-Fe-Cr) are recommended for Ni/SS dissimilar joints due to their crack resistance and good ductility.
- Welding sequence optimization: When building up nickel cladding layers on stainless steel, the first layer should use a filler with higher nickel content to minimize dilution from the substrate.
- Post-weld treatment: Solution annealing at 1050–1100°C followed by water quenching can dissolve intermetallic phases and improve ductility, but must be controlled to avoid grain coarsening.
- Corrosion resistance: The nickel overlay provides excellent resistance to sulfuric acid, hydrochloric acid, and reducing environments, but the interface zone may be susceptible to galvanic corrosion if the overlay is compromised.
Key Technical Insights and Reflections
The study highlights the importance of understanding metallurgical interactions in dissimilar metal welding. For engineers involved in bimetal product manufacturing, particularly nickel-based clad plates and pressure vessel overlays, the formation of intermetallic phases at interfaces represents both a challenge and an opportunity. While intermetallics can reduce ductility, they also provide good bonding strength and can be controlled through careful parameter selection.
The practical implication is that for Ni/SS cladding applications, a multi-layer approach with graded composition transitions is often preferable to single-pass welding. This approach minimizes interfacial stresses and reduces the volume fraction of brittle phases, resulting in more reliable long-term performance in corrosive service environments.