CLADDING TECHNOLOGY SHANXI CO., LTDLow-Dilution Overlay Welding Technology for Clad Wear-Resistant Thin Plates
Literature Overview
Published in 1997 in the journal Welding (焊接), this paper by Zhao Kun, Cheng Zhiguo, Bai Fuping from the Harbin Welding Research Institute and Zi Zhuanghui from the Heilongjiang Provincial Labor Bureau Boiler and Pressure Vessel Technical Inspection Institute, addresses a specialized but critically important problem in clad plate manufacturing: achieving low dilution overlay welding on thin-section wear-resistant plates. Thin clad plates present unique challenges because the limited base metal thickness restricts the allowable heat input, while the requirement for a high-performance overlay layer demands sufficient deposition to ensure the desired composition and properties. The authors investigated process parameters and techniques to minimize base metal dilution while maintaining adequate bond strength and overlay integrity.
Core Technical Content
The Dilution Problem in Thin Plate Cladding
In clad plate manufacturing, dilution—the mixing of base metal into the overlay weld metal—is a primary concern because it degrades the chemical composition and mechanical properties of the overlay layer. For wear-resistant applications, dilution introduces softer base metal into the overlay, reducing hardness and wear resistance. In thin plate applications, the problem is compounded because:
- The base plate thickness limits the number of overlay passes that can be applied without excessive heat accumulation.
- The first overlay layer inevitably has higher dilution than subsequent layers.
- Excessive heat input risks burning through the thin base plate or causing unacceptable distortion.
| Plate Configuration | Base Plate | Overlay Layer | Typical Thickness |
|---|---|---|---|
| Carbon steel / hardfacing | Q235 or 16Mn | High-C martensitic or carbide alloy | 3-6 mm base + 2-5 mm overlay |
| Low-alloy steel / stainless | 16Mn or 15CrMo | 304 or 316 stainless | 4-8 mm base + 2-4 mm overlay |
| Carbon steel / nickel alloy | Q235 | Inconel or Monel type | 5-10 mm base + 2-3 mm overlay |
Low-Dilution Process Strategies
The authors proposed several strategies to achieve low dilution in thin plate overlay welding:
- Surfacing layer technique: Depositing an intermediate surfacing layer with a composition close to the final overlay material before applying the production overlay layers. This ensures that subsequent passes experience minimal dilution from the base metal.
- Low-heat-input welding processes: Utilizing processes such as gas tungsten arc welding (GTAW/TIG) or plasma transferred arc (PTA) welding, which offer concentrated heat sources and reduced base metal melting per unit of deposited metal.
- Multi-pass thin bead strategy: Applying multiple thin weld beads rather than fewer wide ones, which reduces the heat input per unit length and limits the depth of base metal melting in each pass.
- Submerged arc welding with low-current parameters: For higher deposition rates, SAW with reduced current and increased travel speed can be used to limit dilution while maintaining productivity.
- Flux-cored wire with self-shielded flux: FCAW can provide higher deposition rates than GTAW while maintaining reasonable dilution levels when appropriate wire compositions are selected.
Typical Process Parameters
| Process | Current (A) | Voltage (V) | Travel Speed (mm/min) | Heat Input (kJ/mm) | Expected Dilution (%) |
|---|---|---|---|---|---|
| GTAW/TIG | 120-180 | 14-18 | 150-300 | 0.4-0.8 | 10-25% |
| PTA | 200-300 | 20-28 | 100-200 | 0.6-1.2 | 5-15% |
| SAW (low) | 300-400 | 28-34 | 300-500 | 1.0-1.8 | 15-30% |
| FCAW | 200-300 | 22-28 | 200-400 | 0.8-1.5 | 15-30% |
Quality Control Requirements
The paper emphasizes the importance of rigorous quality control for low-dilution clad plates:
- Chemical analysis: Spectroscopic analysis of the overlay layer to verify dilution levels are within acceptable limits (typically < 30% for wear-resistant applications, < 20% for corrosion-resistant applications).
- Hardness mapping: Vickers or Rockwell hardness tests across the overlay thickness to identify the dilution gradient and confirm uniform hardness in the working surface.
- Bond strength testing: Shear or tensile tests at the overlay-base metal interface to verify adequate metallurgical bonding.
- Non-destructive examination: Magnetic particle testing (MT) or ultrasonic testing (UT) to detect cracks, lack of fusion, or other discontinuities.
- Metallographic examination: Cross-sectional microstructural analysis to evaluate the dilution zone, grain structure, and any phase transformations at the interface.
Integration with Engineering Practice
The work described in this paper is particularly relevant to the manufacturing of thin clad plates used in pressure vessels, heat exchangers, and other equipment where the clad layer provides corrosion or wear resistance while the base plate provides mechanical strength. The low-dilution requirement is especially critical for nickel-based alloy overlays on carbon steel, where even moderate dilution can significantly reduce the corrosion resistance of the overlay layer.
In modern practice, the principles described in this 1997 paper have been extended through the use of automated PTA systems, laser cladding, and hot-wire TIG processes, all of which offer improved dilution control compared to the manual and semi-automated processes studied by the authors. However, the fundamental challenge—balancing dilution control against deposition rate and productivity—remains central to cladding engineering.
Study Reflections
This paper represents an important contribution to the understanding of dilution control in thin-section cladding applications. The systematic investigation of process parameters and their effect on dilution levels provides a valuable reference for engineers designing cladding processes for thin plates. The collaboration between the Harbin Welding Research Institute and the pressure vessel inspection authority also underscores the connection between welding research and equipment safety, reminding us that cladding quality directly impacts the integrity and service life of pressure-containing equipment. The engineering lessons from this work—particularly regarding surfacing layers, low-heat-input processes, and multi-pass strategies—remain applicable in contemporary cladding practice.