CLADDING TECHNOLOGY SHANXI CO., LTDMicrostructure and Properties of Flux-Cored Wire Overlay Hardfacing
Literature Overview
Published in 2009 in Hot Working Technology, this study by Ma Chao, Li Ainong, Xie Bing, and Wang Huachang from the School of Materials Science and Engineering at Wuhan University of Technology investigates the microstructural evolution and mechanical performance of hardfacing overlay layers deposited using flux-cored arc welding (FCAW) with flux-cored wire consumables. The research addresses a practical industrial need: the development of cost-effective, high-productivity hardfacing processes for components subjected to severe abrasive wear in mining, construction, and material handling equipment.
Core Technical Content
The study systematically examines how the self-shielded and gas-shielded flux-cored wire composition and welding parameters influence the overlay layer microstructure, hardness distribution, and wear resistance. Flux-cored wire overlay welding (FCAW overlay) offers distinct advantages over solid wire processes: higher deposition rates, better dilution control, and the ability to deposit layers with tailored microstructures through flux chemistry optimization.
Microstructural Analysis
The overlay microstructure typically consists of a matrix of tempered martensite or bainite with dispersed carbide particles. The flux composition plays a critical role in determining:
- Carbide type and morphology (Cr₇C₃, Cr₃C₂, Mo₂C, WC)
- Matrix hardness and toughness balance
- Crack resistance of the overlay layer
- Surface quality and spatter characteristics
Hardness Distribution
The hardness profile across the overlay thickness reveals characteristic zoning:
| Zone | Typical Hardness (HV) | Microstructure |
|---|---|---|
| Surface zone (0-0.5 mm) | 550-700 | Fine tempered martensite + fine carbides |
| Intermediate zone (0.5-2 mm) | 450-600 | Tempered martensite + coarse carbides |
| Base dilution zone (2-3 mm) | 300-400 | Mixed structure with base alloying |
| Base metal | 200-300 | Original base microstructure |
Wear Resistance Testing
Abrasive wear tests (dry sand-rubber wheel or pin-on-disk) demonstrate that the wear resistance correlates strongly with carbide volume fraction and carbide hardness relative to the matrix. Optimal wear performance requires a synergistic relationship where the matrix retains sufficient toughness to support the hard carbides without cracking.
Process Parameters and Their Effects
The study identifies the following critical process variables:
- Wire feed speed: Higher speeds increase deposition rate but may reduce penetration and increase dilution
- Travel speed: Affects heat input and thus grain size and phase composition
- Voltage: Controls arc stability and bead profile
- Flux composition: Silicon and manganese content in the flux directly affects alloying of the overlay
A typical process window for FCAW hardfacing with a 1.2 mm flux-cored wire is:
| Parameter | Range | Optimal |
|---|---|---|
| Voltage (V) | 24-32 | 27-29 |
| Wire feed speed (m/min) | 5-8 | 6-7 |
| Travel speed (cm/min) | 10-20 | 15 |
| Heat input (kJ/mm) | 1.5-3.5 | 2.0-2.5 |
| Preheat temperature | 100-200 °C | 150 °C |
Engineering Practice Integration
In practical applications, FCAW overlay hardfacing is particularly valuable for:
- Large surface areas: The high deposition rate (2-3 times that of solid wire GMAW) makes it economical for covering extensive wear surfaces on excavator buckets, conveyor rollers, and mill liners.
- Field repair: Self-shielded flux-cored wires eliminate the need for external shielding gas, enabling repair in remote locations.
- Multi-layer applications: The process readily supports multi-pass deposition with different wire compositions to achieve graded properties through the overlay thickness.
The main challenges in industrial implementation include managing hydrogen-induced cracking in thick overlays (requiring interpass temperature control of 100-200 °C), controlling spatter (which can be 5-10% of deposited metal), and ensuring adequate bond strength to the base material (particularly important for high-strength steels with carbon equivalents above 0.45%).
Key Technical Insights
The research confirms that the optimal balance between hardness and toughness in FCAW overlay layers is achieved through:
- A flux with moderate silicon content (1.0-1.5 wt%) to promote graphitization and reduce carbide brittleness
- Wire composition with chromium content of 10-15% combined with molybdenum 2-4% for balanced carbide formation
- Controlled cooling rates through appropriate interpass temperature management
- Avoidance of excessive dilution (target < 15% base metal dilution in the first pass)
Study Conclusions and Implications
The study demonstrates that flux-cored wire overlay welding can produce hardfacing layers with hardness exceeding 600 HV and wear resistance 3-5 times that of unclad carbon steel, while maintaining sufficient toughness to resist spalling under impact loading. The process offers a compelling alternative to solid wire hardfacing for applications requiring high productivity and good all-position weldability, particularly in the heavy equipment and mining sectors where component downtime directly impacts operational economics.