CLADDING TECHNOLOGY SHANXI CO., LTDApplication of Fe-05 Wear-Resistant Overlay Alloy on Induced Draft Fans
Literature Overview and Context
The paper under review addresses the practical application of an Fe-05 wear-resistant weld overlay alloy on induced draft (ID) fans in power generation and cement production environments. Induced draft fans operate under extremely harsh conditions characterized by high-velocity flue gas streams carrying abrasive particulates such as fly ash, dust, and corrosive compounds. The base fan components, typically fabricated from carbon steel or low-alloy steel, suffer from rapid erosion-corrosion degradation, leading to frequent unscheduled shutdowns and high maintenance costs. The Fe-05 alloy is designed specifically to address this dual challenge of mechanical abrasion and chemical corrosion through a carefully engineered composition that balances hardness, toughness, and corrosion resistance.
Key Technical Content
The Fe-05 alloy belongs to the iron-based wear-resistant overlay family and typically contains elevated levels of chromium (approximately 10-14 wt%), molybdenum (1-2 wt%), and strategic additions of carbon and alloying elements to promote the formation of hard carbide phases within a matrix that retains sufficient ductility. The overlay process employed in the referenced application is predominantly submerged arc welding (SAW) or gas metal arc welding (GMAW), both of which offer high deposition rates suitable for large fan shroud and blade surfaces.
| Parameter | Typical Specification |
|---|---|
| Base material | Q235 or 16Mn carbon steel |
| Overlay alloy | Fe-05 (Cr ~12%, Mo ~1.5%, C ~2.0%) |
| Overlay thickness | 2.0-4.0 mm |
| Hardness of overlay | 45-55 HRC |
| Deposition rate (SAW) | 3.0-5.0 kg/h |
| Heat input | 20-35 kJ/mm |
| Preheat temperature | 100-150°C |
| Post-weld inspection | MT/PT of overlay surface |
Process Analysis and Engineering Considerations
The critical challenge in overlaying ID fan components lies in managing the thermal cycle imposed on the relatively thin fan shell and blade sections. Excessive heat input can cause warping and distortion of the fan geometry, which directly impacts aerodynamic performance and vibration characteristics. The recommended approach involves multi-pass welding with controlled interpass temperature below 200°C, alternating welding sequences to distribute thermal stress symmetrically, and the use of backing plates or temporary fixtures to minimize out-of-plane distortion.
The dilution rate between the Fe-05 overlay and the carbon steel base is a critical factor. High dilution (above 30%) reduces the hardness and corrosion resistance of the final overlay layer. The paper emphasizes the importance of achieving dilution below 20% through the use of a proper welding sequence that starts with a transition layer of lower-alloy consumable before applying the final Fe-05 overlay. This staged approach ensures metallurgical compatibility while maintaining the desired surface properties.
A significant finding from the literature is the importance of surface preparation prior to overlay application. The existing corroded and eroded surface of the fan must be thoroughly cleaned by grinding or shot blasting to a minimum Sa 2.5 cleanliness level. Residual corrosion products act as contaminants that can promote cracking and reduce bond strength. The bond strength between the overlay and base material, as verified by shear or peel testing, should exceed 200 MPa to ensure reliable service life.
Defect Analysis and Countermeasures
Common defects encountered during Fe-05 overlay welding on fan components include:
| Defect Type | Root Cause | Countermeasure |
|---|---|---|
| Surface cracking | Excessive carbon equivalent of base; high heat input | Preheat to 150°C; reduce heat input; control interpass temperature |
| Undercut | Excessive travel speed; improper gun angle | Optimize welding parameters; use proper electrode stickout |
| Excessive dilution | Too many passes; high heat input | Use transition layer; reduce number of passes; lower current |
| Warping | Asymmetric thermal input | Symmetric welding sequence; use clamping fixtures |
| Poor bond strength | Surface contamination; insufficient preheat | Strict surface cleaning; controlled preheat |
Study Insights and Practical Implications
From a practical standpoint, the application of Fe-05 overlay on ID fans represents a cost-effective maintenance strategy that can extend component service life by 3-5 times compared to bare carbon steel. The economic analysis presented in the literature demonstrates that the total cost of ownership, including overlay application, inspection, and labor, remains significantly lower than periodic fan replacement. However, the long-term success of this approach depends heavily on proper process control, skilled welder certification under NB/T 47014 or equivalent procedures, and rigorous post-weld inspection protocols.
The study also highlights an important operational consideration: the overlay thickness must be sufficient to withstand the expected erosion rate over the planned maintenance interval, but not so thick as to alter the aerodynamic profile of the fan blades. A thickness of 2.5-3.0 mm is generally considered optimal for most ID fan applications, providing adequate protection while maintaining acceptable aerodynamic efficiency.
In summary, the Fe-05 overlay alloy offers a proven and economically viable solution for extending the service life of induced draft fan components in abrasive and corrosive environments, provided that the welding procedure is carefully designed and executed with attention to thermal management, dilution control, and surface preparation.