CLADDING TECHNOLOGY SHANXI CO., LTDNew Cladding Process for Continuous Casting Rolls A Literature Study Note
Literature Overview
This 2010 publication from the Harbin Welding Research Institute of the Chinese Academy of Mechanical Sciences, authored by Zhao Chunyan, Liu Jianwei, Liu Kongfeng, and Xu Kegui, addresses a critical industrial challenge in the steelmaking sector: the development of a novel weld overlay process specifically designed for continuous casting rolls. Continuous casting rolls are subjected to extreme thermal cycling, mechanical loading, and chemical attack from molten steel during the casting process, making their surface integrity a decisive factor in product quality and roll service life. The conventional overlay approaches at that time were often limited by issues such as insufficient bonding strength, poor thermal fatigue resistance, and high dilution rates from the base metal into the overlay layer.
Core Technical Approach
The study introduces a modified cladding process that integrates preheating strategy optimization, multi-pass welding sequence control, and post-weld thermal management to achieve superior metallurgical bonding between the cast steel roll substrate and the overlay alloy. The key innovation lies in the selection of a tailored filler metal system and the process parameter window that minimizes interfacial defects while maximizing hardness and wear resistance in the overlay layer.
The process parameters investigated typically involve the following ranges:
| Parameter | Typical Range | Purpose |
|---|---|---|
| Preheat temperature | 250-350°C | Reduce thermal gradient, prevent cold cracking |
| Interpass temperature | 150-250°C | Control cooling rate, avoid excessive hardness |
| Welding current | 350-500 A (SAW) | Ensure adequate penetration and dilution control |
| Travel speed | 300-500 mm/min | Balance deposition rate and heat input |
| Number of overlay passes | 3-5 | Achieve target thickness with controlled dilution |
| Post-weld heat treatment | 550-650°C for 2-4 h | Stress relief and microstructure homogenization |
The process utilizes submerged arc welding (SAW) as the primary cladding method due to its high deposition efficiency, deep penetration characteristics, and excellent shielding against atmospheric contamination. The multi-pass strategy ensures that the dilution ratio from the base metal into the final overlay layer remains below the critical threshold—typically 20-25%—which is essential for preserving the alloying effects of the overlay material.
Metallurgical Analysis and Microstructural Evolution
The microstructural evolution in the overlay layer and the heat-affected zone (HAZ) is a central focus of the study. In the overlay zone, the microstructure typically consists of a mixture of martensite, bainite, and carbide phases, depending on the cooling rate and alloy composition. The HAZ adjacent to the base metal exhibits a transformed region where the original austenite grains are refined due to the thermal cycling of the welding process.
The interfacial bonding between the base metal and the overlay layer is evaluated through microhardness profiling across the weld cross-section. A smooth transition in hardness from the base metal (typically 200-250 HV) to the overlay layer (typically 450-550 HV) indicates good metallurgical bonding without the presence of interfacial cracks or lack-of-fusion defects. The study emphasizes that the interpass temperature control is the most critical variable affecting this transition, as excessive interpass temperatures lead to grain coarsening in the HAZ and increased dilution.
Defect Analysis and Countermeasures
Based on the engineering experience reflected in this literature, the following common defects and their countermeasures are summarized:
| Defect Type | Root Cause | Countermeasure |
|---|---|---|
| Interfacial cracking | Excessive thermal gradient, high carbon equivalent of base metal | Increase preheat temperature, reduce cooling rate with back-gassing |
| Lack of fusion at interface | Insufficient penetration, surface contamination | Increase current, ensure proper surface preparation (grind to bare metal) |
| Overlay spalling | Poor bonding strength, residual stress | Optimize post-weld heat treatment, reduce welding stress with proper backing |
| Excessive dilution | Too few passes, high travel speed | Increase number of passes, reduce travel speed, use appropriate wire diameter |
| Porosity in overlay | Contamination, flux moisture | Use low-hydrogen flux, proper flux storage and pre-drying |
Engineering Practice Integration
In continuous casting operations, the roll surface must withstand repeated thermal shock cycles at temperatures approaching 1500°C during steel casting, followed by rapid water cooling. The overlay layer must therefore exhibit excellent thermal fatigue resistance, high hardness for wear protection, and sufficient toughness to resist crack propagation. The study demonstrates that the optimized process achieves a service life improvement of approximately 30-50% compared to conventional overlay methods, which is a significant economic benefit given the high cost of roll replacement and the production downtime associated with roll changes.
The practical implementation of this process requires careful attention to the following engineering considerations: the roll surface must be machined to a uniform geometry prior to cladding to ensure consistent weld geometry; the cladding should be applied to a minimum thickness of 3-5 mm to ensure adequate remaining thickness after surface resurfacing during the roll's service life; and the final overlay surface should be ground and polished to a surface roughness of Ra 0.8-1.6 μm to minimize surface-initiated crack formation during thermal cycling.
Key Questions and Reflections
Several important questions arise from this study that warrant further investigation. First, the long-term thermal fatigue behavior of the overlay layer under actual continuous casting conditions—where the thermal cycling frequency can exceed 100,000 cycles over the roll's service life—remains an area requiring more comprehensive testing. Second, the interaction between the overlay microstructure and the base metal's carbon equivalent under repeated thermal cycling could lead to progressive degradation at the interface, a phenomenon that is difficult to simulate in laboratory conditions.
Additionally, the study raises the question of whether the process can be adapted for different roll materials, such as those used for casting non-ferrous alloys or specialty steels, where the thermal expansion coefficient mismatch between the base and overlay could be more severe. The economic viability of the process also depends on the availability of the specific filler metal and flux systems, which may be limited in certain regions.
Study Insights and Implications
This literature represents an important contribution to the field of industrial cladding technology, particularly for the steelmaking industry where roll availability directly impacts production continuity. The systematic approach to process optimization—combining preheat control, multi-pass strategy, and post-weld heat treatment—provides a replicable framework that can be adapted to other cladding applications involving cast iron or cast steel substrates.
The broader implication is that process innovation in cladding technology is not limited to the development of new filler materials but also encompasses the intelligent design of process parameters and sequences. This study exemplifies how a deep understanding of the metallurgical mechanisms governing interfacial bonding, combined with practical engineering constraints, can lead to meaningful improvements in component service life. For engineers working in related fields, the key takeaway is that the optimization of thermal management—both during welding and post-weld—is often more impactful than the selection of a marginally different filler alloy.