CLADDING TECHNOLOGY SHANXI CO., LTDPowder-Feeding Submerged Arc Weld Overlay Process
Literature Overview
This 1998 publication in Welding by researchers from Beijing Petrochemical College and the Harbin Welding Research Institute presents a novel approach to submerged arc weld overlay using powder feeding instead of conventional solid wire. The submerged arc welding (SAW) process has long been recognized as the preferred method for heavy overlay applications due to its high deposition rate, deep penetration, and excellent process stability. However, traditional SAW overlay using solid wire is limited by the wire diameter (typically 3.2–5.0 mm) and the resulting single-pass deposition geometry. The introduction of powder feeding offers a fundamentally different approach, enabling higher deposition rates, more flexible composition control, and improved overlay quality.
Process Description
The powder-feeding submerged arc weld overlay process (also known as powder-fed SAW or submerged arc powder welding) involves the simultaneous feeding of a solid flux and a welding powder into the arc zone, with the arc struck between an electrode (typically a copper contact tube) and the workpiece. The powder serves as the consumable filler metal, while the flux provides shielding, alloying, and slag formation.
Process Configuration
| Component | Specification |
|---|---|
| Electrode | Non-consumable copper contact tube (diameter 20–30 mm) |
| Powder | Spherical or irregular granular alloy powder (0.1–0.5 mm particle size) |
| Flux | Granular flux (0.3–1.0 mm particle size) |
| Powder feeding rate | 5–15 kg/h |
| Flux feeding rate | 3–8 kg/h |
| Current | 400–1200 A |
| Voltage | 25–40 V |
| Travel speed | 100–500 mm/min |
| Shielding gas (optional) | Argon or CO₂ for enhanced shielding |
Advantages of Powder-Feeding SAW Overlay
High Deposition Rate
The powder-feeding process achieves deposition rates of 10–25 kg/h, significantly exceeding the 5–10 kg/h achievable with solid wire SAW. This is attributed to:
- Higher arc energy density: The powder particles are pre-melted by the arc, creating a more concentrated energy input.
- Multiple melt pools: Individual powder particles create localized melt pools that merge to form a continuous overlay bead.
- Reduced dilution: The powder is deposited directly into the melt pool, minimizing mixing with the base metal.
Composition Flexibility
Powder feeding allows for:
- Multi-powder blending: Different powder compositions can be blended to achieve specific alloy compositions.
- Hardmetal powder incorporation: Carbide particles (WC, Cr₃C₂, TiC) can be incorporated into the powder feed to produce composite overlay layers.
- Gradient composition: The powder feed rate and composition can be varied along the travel direction to create gradient overlay layers.
Improved Overlay Quality
| Quality Parameter | Powder-Feeding SAW | Solid Wire SAW |
|---|---|---|
| Dilution rate | 5–10% | 10–20% |
| Porosity tendency | Low (spherical powder) | Moderate |
| Hardness uniformity | Excellent | Good |
| Surface finish | Smooth, uniform | Moderate |
| Layer thickness per pass | 3–8 mm | 2–5 mm |
| Cracking susceptibility | Low | Moderate |
Process Control Challenges
Powder Flow Uniformity
The consistent feeding of powder into the arc zone is critical for process stability. Challenges include:
- Powder bridging: Cohesive powders can bridge in the feeder hopper, causing intermittent feeding.
- Particle size distribution: Wide particle size distributions lead to inconsistent melting behavior.
- Moisture sensitivity: Some powders (particularly aluminum-containing alloys) are moisture-sensitive and require dry conditions.
Flux Management
The flux must be properly managed to ensure:
- Adequate shielding: Sufficient flux coverage to prevent atmospheric contamination
- Proper slag formation: Appropriate slag viscosity for easy removal
- Alloying control: Flux composition affects the final overlay composition
Thermal Management
The high deposition rate of powder-feeding SAW results in significant heat input, which must be managed to:
- Prevent excessive HAZ softening
- Control residual stress levels
- Maintain overlay layer microstructure
Applications
The powder-feeding SAW overlay process is particularly suited to:
- Heavy overlay of large components: Pressure vessel heads, heat exchanger tubesheets, and pipe elbows
- Composite overlay layers: Incorporating hardmetal carbides for wear resistance
- Repair of worn equipment: Mining equipment, cement kiln components, and power plant components
- Corrosion-resistant linings: Nickel-based alloy overlays for chemical processing equipment
Engineering Practice Considerations
From a practical standpoint, the powder-feeding SAW overlay process requires:
- Dedicated equipment: Powder feeders, flux feeders, and appropriate power sources are required
- Powder handling infrastructure: Dry storage, powder blending, and waste powder recovery systems
- Process monitoring: Real-time monitoring of powder feed rate, flux feed rate, current, voltage, and travel speed
- Quality control: Metallographic examination of overlay layer composition, hardness, and microstructure
Process Qualification
The qualification of powder-feeding SAW overlay procedures requires:
- WPS/PQR development: Following ASME Section IX or NB/T 47014 with appropriate modifications for powder feeding
- Mechanical testing: Hardness, tensile strength, impact toughness, and bond strength testing
- Non-destructive testing: UT, MT, PT, and RT for defect detection
- Corrosion testing: For corrosion-resistant overlay applications
Study Insights
The powder-feeding SAW overlay process represents a significant advancement in overlay welding technology, offering capabilities that are not achievable with conventional solid wire SAW. The process is particularly valuable for applications requiring high deposition rates, precise composition control, or composite overlay layers. However, the process also introduces additional complexity in terms of powder handling, process control, and quality assurance.
The work by these authors is notable for its systematic approach to process development and characterization. The emphasis on powder flow uniformity and flux management highlights the practical challenges that must be addressed for reliable industrial implementation. For engineers evaluating overlay process options, the powder-feeding SAW process should be considered when high deposition rates, composition flexibility, or composite overlay layers are required. The process represents a bridge between traditional welding and advanced thermal spray technologies, offering a unique combination of weld strength and deposition efficiency.