CLADDING TECHNOLOGY SHANXI CO., LTDThermal Protection Effect of FB Resin on Tungsten Carbide Particles During Flux-Cored Wire Wear-Resistant Cladding
Literature Overview
This paper, published in the Journal of Naval University of Engineering in 2012 by Li Lianjie and Gui Chibin from the Department of Naval Architecture and Ocean Engineering at the Naval University of Engineering, investigates the role of FB (flux binder) resin in preserving tungsten carbide (WC) particles during flux-cored wire (FCW) wear-resistant cladding operations. The study addresses a critical practical problem in naval and industrial wear-resistant coating applications, where the extreme thermal exposure during arc welding can cause significant degradation of WC particles through oxidation, dissolution, and agglomeration. The authors examine how the resin binder system in flux-cored wires provides a thermal barrier that protects WC reinforcement particles from the molten pool environment, thereby maintaining the microstructural integrity and wear resistance of the final cladding deposit.
Core Technical Analysis
The fundamental challenge in WC-reinforced flux-cored wire cladding lies in the incompatibility between the melting characteristics of the steel matrix and the high-melting-point ceramic reinforcement. Tungsten carbide has a melting point exceeding 2,800 degrees Celsius, but at welding arc temperatures (typically 6,000 to 12,000 degrees Celsius in the arc zone and 1,500 to 2,200 degrees Celsius in the molten pool), WC particles are susceptible to severe chemical attack. The primary degradation mechanisms include:
- Oxidation of WC to form WO3 and CO, which reduces the effective WC content in the deposit.
- Dissolution of tungsten and carbon into the molten steel matrix, forming Fe3W3C, Fe2W4C, and other iron tungsten carbides.
- Agglomeration and coarsening of WC particles due to prolonged exposure to the liquid steel.
- Formation of brittle intermetallic phases at the WC-steel interface that can act as crack initiation sites.
The FB resin system studied in this paper functions as a multifunctional binder that simultaneously provides mechanical integrity to the flux cored wire during handling and storage, and acts as a thermal and chemical barrier during welding. The resin decomposes at controlled temperatures, releasing protective gases and forming a refractory layer around WC particles before they are exposed to the full thermal severity of the arc.
Key Process Parameters
| Parameter | Typical Range | Effect on WC Retention |
|---|---|---|
| Welding current | 180-280 A | Higher current increases WC degradation |
| Travel speed | 150-350 mm/min | Faster speed reduces heat input and preserves WC |
| Wire feed speed | 4.5-7.5 m/min | Must be synchronized with travel speed |
| Arc voltage | 22-30 V | Lower voltage favors better WC protection |
| Preheat temperature | 50-150 degrees C | Moderate preheat reduces thermal gradient |
| Interpass temperature | 80-200 degrees C | Must be controlled to limit thermal cycles |
| Flux composition | SiO2-CaO-Al2O3-CaF2 | Basic fluxes provide better thermal insulation |
| WC particle size | 5-50 micrometers | Optimal range balances reinforcement and retention |
| WC content in wire | 20-40 wt% | Higher content requires more effective protection |
Microstructural Observations
The study reveals that without adequate resin protection, the as-welded cladding microstructure shows extensive WC degradation, with the original angular WC particles transformed into rounded, partially dissolved remnants surrounded by iron tungsten carbide phases. In contrast, with effective FB resin protection, the WC particles retain their original morphology and chemical composition, with minimal interfacial reaction. The microhardness of well-protected WC particles remains in the range of 2,200 to 2,600 HV, while degraded particles show hardness reductions of 30 to 50 percent.
Engineering Practice Implications
For naval applications, where wear-resistant cladding is used on propeller blades, hull plating in high-abrasion zones, and submarine components exposed to marine debris, the integrity of WC particles directly correlates with service life. The FB resin system enables the use of flux-cored wire cladding as an alternative to more expensive processes such as plasma transferred arc (PTA) cladding or hardfacing with gas-shielded methods. The cost advantage of FCW cladding is significant, with wire costs typically 40 to 60 percent lower than PTA consumables, and the process is more easily mechanized for large-area naval applications.
However, engineers must be aware that the thermal protection provided by the resin is only effective within a specific process window. Excessive welding heat input, regardless of resin quality, will ultimately overwhelm the protective mechanism. The study recommends a maximum linear heat input of 18 kJ/mm for WC-containing flux-cored wires, compared to the typical 25 to 35 kJ/mm range for standard structural flux-cored welding.
Common Defects and Countermeasures
| Defect | Root Cause | Countermeasure |
|---|---|---|
| WC particle dissolution | Excessive heat input | Reduce current, increase travel speed |
| Cracking at WC interface | Thermal stress from WC-steel mismatch | Use compatible filler with lower CTE |
| Porosity | Gas evolution from resin decomposition | Ensure proper flux coverage and shielding |
| Uneven WC distribution | Wire manufacturing inconsistency | Source control and incoming inspection |
| Incomplete fusion | Insufficient preheat on base metal | Increase preheat to 100-150 degrees C |
Study Insights
This research contributes meaningfully to the understanding of how consumable design can compensate for process limitations in wear-resistant cladding. The FB resin is not merely a mechanical binder but a functional engineering component that actively participates in the metallurgical outcome of the weld. This perspective is important for engineers who tend to focus on welding parameters while neglecting consumable chemistry. The study also highlights the importance of naval engineering applications driving fundamental research in cladding technology, as the demanding service conditions of marine environments require wear-resistant coatings with superior performance margins compared to industrial applications.
The practical recommendation is that any specification for WC-reinforced cladding must explicitly address the consumable system, not just the welding procedure parameters. A welding procedure specification (WPS) that omits consumable requirements for hardfacing applications is incomplete and may lead to unacceptable field performance.