CLADDING TECHNOLOGY SHANXI CO., LTDResearch Progress on TIG Cladding Technology A Study Note
Literature Overview and Scope
This study note reflects on the comprehensive review of TIG (Gas Tungsten Arc Welding) cladding technology, which has emerged as one of the most versatile and widely adopted methods for producing bimetallic surfaces in pressure vessel fabrication, heat exchanger manufacturing, and corrosion-resistant component production. The reviewed literature covers the evolution of TIG cladding from manual single-pass applications to multi-pass automated systems, including hot-wire TIG (HWTIG) and cold-wire TIG (CWTIG) variants. The scope encompasses process fundamentals, parameter optimization, microstructural control, and quality assurance practices relevant to standards such as ASME IX, NB/T 47014, and ASTM A263.
Core Technical Principles and Process Windows
TIG cladding operates on the principle of arc melting of a filler wire onto a prepared base metal substrate, with the molten pool being controlled by inert gas shielding (typically argon or helium-argon mixtures). The fundamental process parameters include arc current, voltage, travel speed, wire feed rate, torch angle, and shielding gas flow rate. For conventional TIG cladding, typical current densities range from 8 to 20 A/mm² depending on the filler material and joint configuration. The following table summarizes representative process windows for common cladding applications:
| Parameter | Conventional TIG | Hot-Wire TIG (HWTIG) | Cold-Wire TIG (CWTIG) |
|---|---|---|---|
| Arc Current | 60–200 A | 60–150 A | 60–150 A |
| Travel Speed | 20–80 mm/min | 80–300 mm/min | 80–300 mm/min |
| Wire Feed Rate | 0 (manual) | 5–20 m/min | 5–20 m/min |
| Deposition Rate | 0.5–2 kg/h | 5–15 kg/h | 3–10 kg/h |
| Dilution Ratio | 15–40% | 5–20% | 10–25% |
| Shielding Gas | Ar / Ar-He | Ar / Ar-He | Ar / Ar-He |
The dilution ratio, defined as the percentage of base metal dissolved into the cladding layer, is a critical quality indicator. For corrosion-resistant overlays such as 316L stainless steel on carbon steel, dilution must typically be controlled below 20% to maintain acceptable corrosion resistance. HWTIG achieves lower dilution by preheating the filler wire to 200–600°C, which increases the wire feed contribution to the molten pool without raising the arc power proportionally.
Microstructural Evolution and Bond Quality
The dilution ratio directly governs the microstructure at the cladding-base metal interface. In stainless steel cladding on low-carbon steel, a martensitic transition zone often forms at the interface when dilution exceeds 25%, leading to reduced corrosion resistance and potential cracking susceptibility. The reviewed studies emphasize that interfacial microstructure can be optimized through controlled preheating of the base metal (typically 100–200°C for stainless steel overlays), reduced interpass temperature (below 150°C for austenitic stainless steel), and multi-pass strategies with thin individual pass thicknesses of 1.5–2.5 mm.
Bond strength testing, conducted per ASTM A263 Section 7 or equivalent national standards, typically requires a minimum shear strength of 100 MPa for stainless steel cladding on carbon steel. The bond strength is influenced by the cleanliness of the base metal surface, the wetting behavior of the molten pool, and the absence of oxide inclusions at the interface. Surface preparation methods such as machining, grinding, and acid pickling are essential to remove surface contamination and ensure metallurgical bonding.
Common Defects and Countermeasures
The literature identifies several recurring defects in TIG cladding operations, each with distinct root causes and corrective actions:
| Defect Type | Root Cause | Detection Method | Countermeasure |
|---|---|---|---|
| Cracking | High dilution, hydrogen embrittlement, low ductility of overlay | Visual, MT, PT | Reduce dilution, preheat base, control interpass temperature |
| Porosity | Contaminated wire or base surface, inadequate shielding | RT, UT | Improve surface cleanliness, increase gas flow, use dry wire |
| Lack of Fusion | Low heat input, excessive travel speed | UT, MT | Increase current, reduce travel speed, optimize torch angle |
| Excessive Dilution | High arc power, thin pass thickness, high travel speed | Metallographic, chemical analysis | Reduce current, increase wire feed, use HWTIG |
| Spatter | Excessive current, contaminated shielding gas | Visual | Reduce current, verify gas purity, improve gas nozzle design |
Integration with Engineering Practice
In pressure vessel fabrication, TIG cladding is frequently applied to hydrogenation reactors, acid service vessels, and heat exchanger tubesheets where the base material provides mechanical strength while the overlay provides corrosion resistance. For example, in a hydrogenation reactor lined with 316L stainless steel, the TIG cladding process must comply with NB/T 47014 qualification requirements, including welder performance qualification with minimum 3 passes and a minimum total thickness of 3 mm. The interpass temperature control is particularly critical for austenitic stainless steel overlays, where exceeding 250°C can lead to sensitization and intergranular corrosion susceptibility.
The application of PDCA (Plan-Do-Check-Act) methodology in TIG cladding quality management is recommended for production environments. The Plan phase involves WPS development and welder qualification; the Do phase covers actual cladding execution with real-time parameter monitoring; the Check phase includes NDT (MT, PT, UT) and bond strength verification; and the Act phase encompasses corrective actions based on defect analysis and process improvement.
Key Reflections and Study Insights
The most significant insight from this literature review is the recognition that TIG cladding quality is not solely determined by welding parameters but is fundamentally governed by the interplay between thermal input, dilution control, and microstructural evolution at the interface. The transition from manual to automated TIG systems has improved consistency and reproducibility, but the underlying metallurgical principles remain unchanged. Engineers must maintain a deep understanding of solidification behavior, phase transformation, and interfacial bonding mechanisms to effectively troubleshoot production issues. Furthermore, the emergence of hybrid techniques such as HWTIG and CWTIG has expanded the process envelope, enabling higher deposition rates while maintaining low dilution, which is particularly valuable for thick cladding applications on large pressure vessels.
Summary
TIG cladding technology has matured into a highly reliable method for producing corrosion-resistant and wear-resistant overlays on pressure vessels and bimetallic products. The key to successful application lies in rigorous process parameter control, thorough surface preparation, and systematic quality verification. Engineers should continue to pursue process optimization through numerical simulation, experimental validation, and adherence to established standards to ensure the long-term performance and safety of cladded components in demanding industrial environments.