CLADDING TECHNOLOGY SHANXI CO., LTDApplication of Special Wear Resistant Material Overlay Welding Processes
Literature Overview and Industrial Context
This 2003 publication by Fan Jiangsui from Guangzhou Residential Construction Development Company focuses on the practical application of special wear-resistant material overlay welding processes in construction machinery. The study is notable for its emphasis on real-world industrial implementation rather than purely laboratory-based research. Construction machinery components such as bucket teeth, auger flights, conveyor rollers, and mixing paddles are subjected to severe abrasive wear from contact with soil, rock, and aggregate materials. The overlay welding of specialized wear-resistant materials to these components significantly extends service life and reduces replacement costs.
Classification of Wear Mechanisms and Material Selection
The study provides a systematic classification of wear mechanisms encountered in construction machinery and correlates them with appropriate overlay material selections. This classification approach is fundamental to rational overlay welding practice.
| Wear Mechanism | Typical Application | Recommended Overlay Material | Hardness (HRC) | Key Alloying Elements |
|---|---|---|---|---|
| Abrasive (hard) | Rock buckets, crushers | High-carbon martensite | 55-65 | C 2-3%, Cr 5-8% |
| Abrasive (soft) | Soil buckets, conveyors | Carbide composite | 45-55 | C 1-2%, Cr 8-12% |
| Adhesive | Mixing paddles, augers | High-chromium cast iron | 50-60 | Cr 20-30% |
| Erosive | Pump impellers, valves | Ni-Cr-Mo alloy | 40-50 | Ni 20-30%, Cr 10-15% |
| Corrosive-abrasive | Slurry handling | Duplex stainless | 35-45 | Cr 22-25%, Mo 3-5% |
The selection of overlay material must consider not only the hardness requirement but also the toughness requirements of the application. A very hard overlay material may be prone to spalling or chipping under impact loading, which is common in construction machinery service. The study emphasizes the importance of matching the overlay material toughness to the expected impact energy in service.
Overlay Welding Process Selection
The study evaluated several overlay welding processes for construction machinery applications, considering factors such as productivity, equipment requirements, field applicability, and cost-effectiveness.
| Process | Productivity | Equipment Cost | Field Applicability | Typical Overlay Thickness |
|---|---|---|---|---|
| SMAW (shielded metal arc) | Low | Low | Excellent | 2-5mm |
| SAW (submerged arc) | High | Moderate | Poor | 3-8mm |
| FCAW (flux-cored arc) | High | Moderate | Good | 2-6mm |
| GMAW (gas metal arc) | Moderate | Moderate | Good | 1-4mm |
| Oxy-fuel | Moderate | Low | Excellent | 1-3mm |
| PTA (plasma transfer arc) | High | High | Poor | 1-5mm |
For field repair of construction machinery, SMAW and FCAW were identified as the most practical processes due to their portability and equipment simplicity. For manufacturing and large-scale repair operations, SAW and PTA provide superior productivity and consistent overlay quality.
Key Process Parameters for Wear-Resistant Overlay Welding
The study documented optimized process parameters for the most commonly used processes:
- SMAW: Current 150-250A (depending on electrode diameter), DCEN polarity for high-alloy electrodes, short arc length (1-2mm), weaving pattern for uniform coverage.
- FCAW: Current 200-350A, wire feed speed 3-6m/min, travel speed 150-300mm/min, shielding gas CO2 or Ar+CO2 mixture.
- SAW: Current 400-700A, voltage 25-35V, travel speed 200-400mm/min, flux covered wire with wire diameter 1.6-3.2mm.
Common Defects and Countermeasures
The study documented several common defects encountered in wear-resistant overlay welding and their root causes:
- Cracking: High-carbon and high-alloy overlay materials are prone to hot cracking due to the formation of low-melting-point phases at grain boundaries. Countermeasures include preheating to 150-250°C, controlling interpass temperature below 200°C, and using electrodes with controlled sulfur and phosphorus content.
- Porosity: Gas porosity is common in high-alloy overlay welds due to the formation of oxides and nitrides in the molten pool. Countermeasures include thorough surface cleaning, proper flux coverage for SAW, and adequate shielding gas coverage for GMAW/FCAW.
- Spalling and delamination: Excessive hardness combined with inadequate toughness leads to overlay layer spalling under impact loading. Countermeasures include proper material selection for the service conditions, ensuring adequate overlay thickness, and avoiding single-pass thick deposits.
- Excessive dilution: Inadequate process control leads to excessive base metal dilution, reducing the effectiveness of the overlay layer. Countermeasures include proper parameter optimization, use of multiple thin passes, and verification of dilution through hardness profiling.
Study Insights and Practical Recommendations
This publication provides valuable practical guidance for the application of overlay welding technology in construction machinery maintenance. The systematic approach to material selection based on wear mechanism classification is directly applicable to real-world engineering decisions. The emphasis on process selection based on application context (field repair vs. manufacturing) reflects a mature understanding of the economic and practical constraints that influence welding process choices. The documented defect analysis and countermeasures provide a practical troubleshooting guide for field welders and quality inspectors. The study reinforces the principle that overlay welding success depends not only on material selection but also on proper process control, surface preparation, and post-weld inspection.