CLADDING TECHNOLOGY SHANXI CO., LTDPre-Placed Additional Filler Metal Plate Submerged Arc Cladding
Literature Overview
This study note examines an innovative submerged arc cladding technique that employs pre-placed additional filler metal plates as a means of achieving high-quality overlay deposits with reduced dilution and improved metallurgical compatibility. This method represents a departure from conventional submerged arc welding (SAW) cladding, where the overlay material is supplied solely through the welding wire or flux. By pre-placing additional filler metal plates at the weld interface, the technique ensures a higher alloy content in the overlay and better control over the dilution ratio between the base metal and the overlay material.
Core Technical Content
The pre-placed filler metal plate technique involves positioning a strip or plate of the desired overlay alloy material on the substrate surface before the submerged arc welding operation begins. As the arc melts the substrate and the pre-placed plate simultaneously, the resulting weld pool achieves a composition that is determined by the relative melting rates of the substrate and the filler plate. This approach effectively decouples the overlay composition from the wire composition, providing greater flexibility in material selection and process design.
Process Configuration and Parameters
The process configuration involves the following key elements:
- Substrate preparation: The substrate surface is ground smooth and cleaned to remove oxide scale and contamination
- Filler plate placement: The filler metal plate is positioned on the substrate with precise alignment to ensure uniform coverage
- Welding consumables: A low-alloy or carbon steel wire is used as the primary heat source and minor filler
- Flux system: A specialized flux is employed to provide adequate shielding, slag coverage, and potential alloying contribution
- Welding parameters: Current, voltage, travel speed, and arc length are optimized to control the melting ratio
| Parameter | Typical Value | Function |
|---|---|---|
| Welding current | 500–800 A | Adequate melting of filler plate and substrate |
| Arc voltage | 30–45 V | Control arc stability and penetration |
| Travel speed | 200–400 mm/min | Balance deposition rate and dilution |
| Filler plate thickness | 3–6 mm | Provide sufficient alloy reservoir |
| Wire diameter | 3.2–5.0 mm | Match current capacity and heat input |
| Flux coverage | Full arc and weld pool | Shielding and slag formation |
Dilution Control and Microstructure
The primary advantage of the pre-placed filler plate technique is the ability to precisely control the dilution ratio between the substrate and the overlay material. By adjusting the filler plate thickness, composition, and welding parameters, the dilution can be maintained within a narrow range that ensures the desired overlay properties.
The microstructure of the overlay deposit is characterized by:
- A columnar grain structure in the fusion zone adjacent to the substrate
- An equiaxed grain structure in the upper portion of the deposit
- A transition zone where the composition gradient from substrate to overlay is visible
- Possible intermetallic phases at the interface depending on the material combination
The dilution ratio is typically expressed as the weight percentage of base metal in the overlay deposit. For high-alloy overlay applications, dilution ratios below 30% are generally required to ensure that the overlay retains its intended corrosion resistance or wear resistance properties. The pre-placed filler plate technique can achieve dilution ratios as low as 10–15%, compared to 30–50% for conventional wire-only SAW cladding.
Engineering Practice Applications
This technique is particularly advantageous for applications requiring thick overlay deposits with high alloy content, such as:
- Nickel-based alloy cladding on carbon steel pressure vessels for hydrogen service
- Copper-nickel alloy cladding on steel substrates for marine applications
- Titanium alloy cladding on steel substrates for chemical processing equipment
- High-chromium cast iron cladding on steel substrates for wear-resistant surfaces
In pressure vessel fabrication, the pre-placed filler plate technique is often used for the final overlay pass on clad-plate vessels to ensure that the surface layer achieves the required alloy composition. The technique is also employed in the repair of worn or corroded components where the base metal has been significantly depleted and a substantial build-up of alloy material is required.
Quality Control and Inspection
The quality of the pre-placed filler plate cladding is evaluated through the following inspection methods:
| Inspection Method | Purpose | Acceptance Criteria |
|---|---|---|
| Visual examination | Surface quality, undercut, porosity | No visible defects exceeding 2 mm |
| Ultrasonic testing | Bond strength, internal defects | No indications exceeding 20% DAC |
| Magnetic particle testing | Surface and near-surface cracks | No linear indications |
| Chemical analysis | Dilution ratio, composition verification | Within ±2% of specified composition |
| Hardness testing | Uniformity of overlay properties | Within specified range per material spec |
| Macroscopic examination | Interface quality, dilution assessment | No cracks or voids at interface |
Study Insights and Reflections
The pre-placed filler metal plate technique represents a significant advancement in submerged arc cladding technology, addressing the fundamental limitation of dilution control in conventional wire-only processes. By providing a reservoir of high-alloy material directly at the weld interface, the technique ensures that the overlay composition is dominated by the filler plate material rather than the substrate material.
The key insight from this literature is that the pre-placed filler plate technique requires careful process design to ensure uniform melting of the filler plate across the entire weld width. If the filler plate melts unevenly, localized variations in dilution can occur, leading to compositional and property gradients within the overlay deposit. Process optimization must therefore focus on achieving uniform arc energy distribution and consistent filler plate melting throughout the welding operation.
This technique also highlights the importance of filler plate quality and placement precision. The filler plate must be free of defects, have uniform thickness, and be placed with precise alignment to ensure consistent overlay properties. Any deviation in filler plate quality or placement can result in localized dilution variations that compromise the performance of the overlay deposit.