CLADDING TECHNOLOGY SHANXI CO., LTDDevelopment of Sintered Flux for Roll Cladding Weld Overlay
Literature Overview and Research Background
Roll cladding is a critical technology in the rolling mill industry where work rolls and backup rolls are subjected to extreme abrasion, thermal fatigue, and mechanical loading during hot or cold rolling operations. The selection of cladding consumables, particularly flux systems in submerged arc welding (SAW) and electroslag welding (ESW), directly governs the microstructure, hardness profile, and service life of the overlay layer. The reviewed literature focuses on the design and development of a sintered flux specifically formulated for roll cladding applications, addressing the persistent challenges of poor metallurgical bonding, excessive dilution from the base steel, and inconsistent hardness distribution in conventional cladding consumables.
The research team identified that traditional rolled fluxes often suffer from insufficient deoxidation capability, leading to oxide inclusions in the weld metal, and inadequate alloying efficiency due to poor flux chemistry. The sintered flux under investigation was designed with a controlled particle size distribution, enhanced basicity index, and optimized alloy addition ratios to achieve superior metallurgical quality in the cladding layer.
Core Technical Points and Flux Design Principles
The sintered flux composition was engineered around several key design parameters that significantly influence weld metal properties. The basicity index (BI) was maintained between 1.8 and 2.2, which provides adequate slag viscosity for proper arc stability while ensuring sufficient deoxidation through the addition of SiO2 and CaF2. The particle size distribution was controlled within the range of 0.5 to 3.0 mm, which is critical for maintaining a uniform arc coverage and preventing flux segregation during welding.
| Parameter | Target Range | Rationale |
|---|---|---|
| Basicity Index (BI) | 1.8 - 2.2 | Balances slag fluidity and deoxidation |
| Particle Size | 0.5 - 3.0 mm | Ensures uniform arc coverage |
| SiO2 Content | 35 - 42% | Promotes deoxidation and slag formation |
| CaF2 Content | 12 - 18% | Refines grain structure, reduces cracking |
| MnO Content | 8 - 14% | Alloying element for weld metal |
| Si Content | 2 - 5% | Deoxidizer and alloying addition |
| C Content | 0.3 - 0.8% | Carbon source for carbide formation in overlay |
The flux formulation incorporated specific alloying additions including Cr2O3, MoO3, and WC to promote the formation of hard carbide phases in the cladding layer. The sintering temperature was optimized at 950 to 1050 degrees Celsius, which ensures adequate particle bonding without excessive sintering that would reduce flux permeability and arc stability. The moisture content of the sintered flux was maintained below 0.5%, which is essential for preventing hydrogen-induced cracking in the weld metal, particularly when cladding high-carbon or high-alloy steels on carbon steel substrates.
Microstructural Analysis and Performance Evaluation
Metallographic examination of the cladding layer produced with the developed sintered flux revealed a predominantly martensitic matrix with dispersed carbide particles. The carbide phase consisted primarily of M7C3 and M23C6 type carbides, which provided excellent wear resistance through their high hardness (approximately 1800 to 2200 HV) and thermal stability. The grain size in the cladding layer was refined to less than 10 micrometers due to the CaF2 addition in the flux, which promoted heterogeneous nucleation during solidification.
Dilution from the base steel was measured at approximately 8 to 12 percent, which is within the acceptable range for roll cladding applications. The hardness profile across the cladding layer showed a uniform distribution of 55 to 62 HRC, with a gradual transition to the base steel hardness. This uniformity was attributed to the consistent alloying efficiency of the sintered flux, which maintained stable chemical composition in the weld metal across multiple welding passes.
Wear testing using a pin-on-disk tribometer demonstrated that the cladding layer produced with the sintered flux exhibited 35 to 45 percent improvement in wear resistance compared to cladding layers produced with conventional rolled flux. The improvement was primarily attributed to the higher volume fraction of hard carbide phases and the finer grain structure achieved through the optimized flux chemistry.
Engineering Practice Implications and Process Recommendations
From an engineering practice perspective, the development of this sintered flux addresses several critical process challenges encountered in roll cladding operations. The improved arc stability reduces the risk of undercuts and porosity, which are common defects in roll cladding due to the high welding speeds typically employed in production environments. The controlled moisture content minimizes the risk of hydrogen-induced cracking, which is particularly important when cladding high-alloy overlay materials on low-alloy steel substrates that are susceptible to delayed cracking.
The flux preheating requirement was determined to be 150 to 200 degrees Celsius for 2 hours, which ensures that any residual moisture is eliminated before welding. This preheating step is particularly critical in humid environments where flux moisture pickup can occur rapidly. The recommended welding parameters for the developed flux include a current range of 500 to 800 amperes, an arc voltage of 28 to 36 volts, and a travel speed of 150 to 250 mm/min, depending on the cladding thickness required.
Quality control procedures should include routine moisture testing of the flux before each production shift, visual inspection of the cladding surface for porosity or undercut, and periodic hardness profiling to verify that the overlay properties remain within specification. Non-destructive testing using magnetic particle inspection (MT) should be performed on the cladding surface to detect any surface cracks or lack of fusion defects, particularly at the bond line between the cladding layer and the base steel.
Study Insights and Concluding Remarks
The development of a purpose-designed sintered flux for roll cladding represents a significant advancement in consumable technology that directly addresses the practical challenges faced in industrial roll refurbishment operations. The key insight from this literature is that flux chemistry is not merely a supporting element in the welding process but a primary determinant of overlay layer quality, service life, and overall cost-effectiveness. The optimized basicity index, controlled particle size distribution, and strategic alloy additions collectively enable the production of cladding layers with superior wear resistance, uniform hardness, and reduced defect rates.
For engineering teams involved in roll cladding operations, the adoption of such purpose-designed fluxes should be accompanied by systematic process qualification in accordance with NB/T 47014 or equivalent standards, ensuring that the flux is qualified for the specific base material and welding procedure in use. The long-term benefits include reduced downtime for roll refurbishment, extended roll life, and lower overall production costs. Future work should focus on further optimizing the flux for specific service environments such as hot strip mill applications where thermal fatigue resistance is paramount, and on developing flux formulations that are compatible with automated cladding equipment for improved production efficiency.