CLADDING TECHNOLOGY SHANXI CO., LTDDevelopment of Fluxes for Submerged Arc Welding Wear-Resistant Cladding Layers
Literature Overview and Research Background
This study addresses the development of specialized fluxes for submerged arc welding (SAW) of high wear-resistant cladding layers, a critical technology in heavy industry where components such as mining equipment, cement mill liners, and material handling surfaces suffer severe abrasive and impact wear. The research focuses on formulating flux compositions that, when combined with appropriate wire electrodes, produce cladding deposits with hardness exceeding 50 HRC while maintaining adequate toughness to resist cracking under operational stress. The study is significant because flux composition in SAW directly controls dilution rate, carbon pickup, alloy recovery, and the resulting microstructure of the overlay layer.
Core Technical Approach
The research employs a systematic approach to flux formulation, varying the proportions of iron oxide, manganese oxide, calcium fluoride, silica, and alloying additions to optimize deposit properties. The flux acts not only as a protective medium but also as a dilution control agent and alloy source. Key design parameters include:
| Parameter | Typical Range | Target Value |
|---|---|---|
| Dilution rate | 10-35% | 15-20% |
| Carbon pickup | 0.3-0.8% | 0.5-0.6% |
| Manganese recovery | 60-85% | 75-80% |
| Deposit hardness | 45-60 HRC | 52-58 HRC |
| Crack sensitivity index | <0.3 | <0.2 |
The researchers conducted a series of single-pass and multi-pass SAW trials using H08Mn2SiA wire electrode with the developed fluxes, depositing on Q235 carbon steel substrates. The welding parameters were maintained at 300-400 A, 30-36 V, and travel speed of 200-300 mm/min, with flux coverage density of 5-8 kg/m².
Microstructure Analysis and Property Evaluation
Metallographic examination revealed that the optimized flux produced a microstructure consisting of martensite and retained austenite with dispersed carbide particles. The carbides formed primarily as M₇C₃ type chromium carbides, which provide excellent wear resistance through their high hardness and resistance to deformation. The retained austenite fraction, controlled by the alloying balance in the flux, provided beneficial toughness without significantly reducing hardness.
Hardness measurements showed a gradient from approximately 500 HV in the cladding layer to 200 HV in the base metal, with a distinct transition zone of 1-2 mm thickness. The dilution rate was successfully controlled at 15-18% for single-pass deposits and 20-25% for multi-pass builds, demonstrating the flux's effectiveness as a dilution barrier.
Engineering Practice Considerations
From an engineering application perspective, several practical issues emerged from the study that deserve attention in production environments:
- Flux storage and handling: The developed flux requires moisture control below 0.5% water content, necessitating oven drying at 250°C for 2 hours prior to use in humid environments.
- Spatter rate: The flux formulation achieved a spatter rate below 3%, which is critical for reducing wire consumption and improving productivity.
- Slag detachability: The slag was found to be easily removed at room temperature, reducing post-welding labor costs.
- Arc stability: The arc was stable across the tested current range, with minimal arc wandering observed.
However, the study noted that the cladding layer exhibited moderate susceptibility to hydrogen cracking when deposited on high-carbon substrates without preheating. A preheat temperature of 150-200°C is recommended for substrates with carbon equivalent exceeding 0.4%.
Defect Analysis and Countermeasures
The following defects were identified during trial welding and their root causes analyzed:
| Defect Type | Root Cause | Countermeasure |
|---|---|---|
| Surface porosity | Excessive moisture in flux | Strict drying protocol; sealed storage |
| Undercut | Excessive current density | Reduce current by 10-15%; increase travel speed |
| Cracking in transition zone | High dilution and carbon concentration | Increase flux coverage; use intermediate layer |
| Hardness variation | Inconsistent wire feed speed | Calibrate equipment; monitor voltage stability |
Study Insights and Implications
The most valuable insight from this literature is the recognition that flux composition optimization must be considered holistically, balancing dilution control, alloy recovery, and microstructure refinement simultaneously. The researchers demonstrated that adding 3-5% of a specific alloying oxide to the flux base composition significantly improved the carbide morphology, transitioning from coarse primary carbides to a finer, more uniformly distributed carbide network. This finding has direct implications for improving the fatigue resistance of cladding layers in cyclic loading applications, which is particularly relevant for pressure vessel components subjected to thermal cycling.
The study also highlights an important principle in SAW cladding: the flux serves as a tunable dilution barrier, and its composition can be adjusted to compensate for variations in substrate composition and wire alloy content. This flexibility is particularly valuable in repair welding scenarios where substrate material may vary. Future work should investigate the long-term wear performance of these cladding layers under actual service conditions, including thermal fatigue cycling and erosion-corrosion synergy.