CLADDING TECHNOLOGY SHANXI CO., LTDEffect of Shielding Gas on Microstructure and Properties of Tungsten Carbide Flux-Cored Wire Overlay Layer
Literature Overview
This study note examines a 2017 publication by Yuan Xiaobo and colleagues from Shenyang University of Technology and Guangdong Institute of Materials, published in the Journal of Welding. The research investigates the influence of shielding gas composition on the microstructure, hardness, and wear resistance of tungsten carbide (WC) flux-cored wire overlay layers. This work is supported by multiple Guangdong Provincial International Science and Technology Cooperation Projects and represents a systematic investigation into one of the most critical process variables in FCAW hardfacing applications.
Core Technical Content
Tungsten carbide flux-cored wire overlay welding is widely used for repairing and protecting components subjected to severe abrasive wear, such as mining equipment, cement mill liners, and hydraulic excavator buckets. The WC particles in the overlay provide exceptional hardness (HRC 60-70), but their distribution, retention, and bonding with the matrix are critically dependent on the shielding gas atmosphere during welding.
The research compared three shielding gas compositions:
| Shielding Gas Composition | Ar + CO2 (80/20) | Ar + CO2 (70/30) | Pure Argon |
|---|---|---|---|
| Hardness (HV) | 1350-1420 | 1280-1350 | 1400-1480 |
| WC retention rate | 72-78% | 65-72% | 78-85% |
| Dilution rate | 18-22% | 20-25% | 15-20% |
| Crack susceptibility | Low | Moderate | Low |
| Deposition efficiency | High | High | Moderate |
| Cost per meter | Medium | Low | High |
Microstructural Analysis and Gas Mechanism
The shielding gas composition affects the overlay microstructure through multiple mechanisms:
- Carbon activity control: CO2 is a reactive gas that increases carbon activity in the arc plasma, promoting carburization of the molten pool. This can lead to excessive carbon content, increased retained austenite, and reduced WC particle retention due to carbide dissolution.
- Thermal input modification: CO2 increases arc voltage and heat input compared to pure argon, which affects the cooling rate and consequently the phase transformation behavior in the solidified overlay.
- WC particle dissolution: Higher CO2 content accelerates the dissolution of WC particles in the molten pool, reducing the effective hardening phase content and lowering the final hardness of the overlay layer.
- Oxide inclusion formation: Reactive gases promote oxide formation at the WC-particle/matrix interface, which can either improve bonding (if controlled) or create weak interfaces (if excessive).
The optimal gas composition balances these competing effects. Pure argon provides the best WC retention and hardness but at higher cost and with lower deposition efficiency. The 80/20 Ar/CO2 mixture offers a practical compromise for industrial applications where cost and productivity are important considerations.
Process Parameters and Their Interaction with Shielding Gas
The interaction between shielding gas composition and other welding parameters is critical for achieving optimal overlay properties:
| Parameter | Optimal with Pure Ar | Optimal with Ar/CO2 80/20 |
|---|---|---|
| Current (A) | 180-220 | 200-250 |
| Voltage (V) | 24-28 | 28-32 |
| Travel speed (mm/min) | 150-200 | 180-250 |
| Wire feed speed (m/min) | 4-6 | 5-7 |
| Number of passes | 2-3 | 2-3 |
| Interpass temperature | <150°C | <150°C |
Wear Testing Results and Engineering Implications
Abrasive wear testing (ASTM G65 dry sand-rubber wheel test) demonstrated that overlays produced with pure argon shielding exhibited 15-20% better wear resistance compared to those produced with 80/20 Ar/CO2. The improved wear performance correlated directly with higher WC particle retention rates and more uniform carbide distribution throughout the overlay cross-section.
However, the economic analysis revealed that pure argon shielding increases gas cost by approximately 3-4 times compared to Ar/CO2 mixtures. For high-volume industrial applications, the 80/20 mixture provides acceptable performance at significantly lower cost, making it the preferred choice for most production environments.
Study Insights and Recommendations
This research provides valuable quantitative data for shielding gas selection in WC FCAW overlay applications. The key takeaway is that shielding gas composition is not merely a secondary parameter but a primary factor governing overlay quality. Engineers should conduct gas-specific qualification testing for each production environment, as ambient conditions, wind exposure, and component geometry all affect the effective shielding atmosphere.
For future practice, the development of flux-cored wires with enhanced WC particle bonding strength—through surface treatment or matrix composition modification—could reduce the sensitivity to shielding gas composition, potentially enabling the use of lower-cost gas mixtures without significant performance degradation. This represents an important direction for reducing the total cost of ownership in industrial overlay welding operations.