CLADDING TECHNOLOGY SHANXI CO., LTDDevelopment of SJ403 Wear-Resistant Overlay Sintering Flux
Background and Technical Context
The 1994 research by He Shaoqing, Zhang Youhong, Yang Hui, Hu Chengfu, and Liu Hongbin from the Jinzhou Welding Rod Factory addressed the development of SJ403, a specialized sintered flux for wear-resistant overlay welding applications. Sintered fluxes play a critical role in shielded metal arc welding (SMAW) and flux-cored arc welding (FCAW) processes, providing arc stability, slag protection, deoxidation, and alloying. For wear-resistant overlay applications, the flux must be designed to promote the formation of hard, wear-resistant microstructures while maintaining weldability and producing a slag that is easy to remove.
Flux Design Principles for Wear-Resistant Overlays
The design of SJ403 was guided by the following principles:
- Arc stability — The flux must produce a stable, concentrated arc with minimal spatter, ensuring consistent weld bead geometry and dilution control.
- Slag protection — The slag must have adequate coverage to prevent atmospheric contamination, particularly oxygen and nitrogen absorption, which would degrade the mechanical properties of the overlay.
- Deoxidation — The flux must provide sufficient deoxidizers (Mn, Si, Al) to prevent oxide inclusion formation in the weld metal.
- Alloying — The flux composition must contribute appropriate alloying elements (Cr, Mo, V, B) to the weld metal to achieve the desired hardness and wear resistance.
- Slag removability — The slag must be easily removed from the weld bead to facilitate multi-pass welding and post-weld machining.
- Crack resistance — The flux must minimize the hydrogen content in the slag to prevent hydrogen-induced cracking in the overlay and base metal.
SJ403 Flux Composition and Properties
| Component | Content (wt%) | Function |
|---|---|---|
| CaF2 | 15–20 | Arc stabilizer, slag fluidity, hydrogen reduction |
| CaO | 20–25 | Basicity control, slag viscosity |
| SiO2 | 15–20 | Slag former, deoxidation |
| MnO | 8–12 | Deoxidizer, alloying (Mn contributes to hardness) |
| Al2O3 | 5–8 | Slag viscosity modifier, arc stability |
| TiO2 | 3–5 | Slag fluidity, wetting improvement |
| B2O3 | 1–3 | Boride formation promotion, hardness enhancement |
| Cr2O3 | 2–5 | Chromium alloying, carbide formation |
| V2O5 | 1–3 | Vanadium alloying, hard carbide formation |
| MoO3 | 1–2 | Molybdenum alloying, secondary hardening |
| Total moisture | < 0.5 | Hydrogen control, crack prevention |
The flux was sintered at 1100–1200 °C for 2–4 hours to achieve the desired pellet density and strength. The sintering temperature and time were critical: too low a temperature produced weak pellets that disintegrated during welding, while too high a temperature caused excessive sintering that reduced slag fluidity.
Microstructural Effects of SJ403 Flux
The SJ403 flux was designed to produce overlay deposits with the following microstructural characteristics:
- Matrix: Tempered martensite with high hardness (55–62 HRC after tempering)
- Carbides: Dispersed M7C3, M23C6, and VC carbides providing abrasion resistance
- Borides: Fine Fe2B and FeB particles contributing to solid solution strengthening
- Grain structure: Fine-grained due to the flux's influence on solidification nucleation
The flux composition was optimized to control the dilution rate and ensure that the final weld metal composition met the wear resistance specification. The chromium and vanadium oxides in the flux were reduced during welding to contribute Cr and V to the weld metal, while the B2O3 was partially reduced to introduce boron for boride formation.
Welding Performance and Testing
The SJ403 flux was evaluated in conjunction with appropriate core wires (high-carbon high-chromium alloy wires) in SMAW and FCAW processes. The following table summarizes the key performance parameters:
| Test Parameter | Result | Acceptance Criteria |
|---|---|---|
| Arc stability | Stable, no arc wandering | Stable arc throughout weld length |
| Spatter rate | < 5% | < 10% |
| Slag coverage | Complete, uniform | No bare weld metal exposed |
| Slag removability | Easy, single strike | Slag detaches in one piece |
| Hydrogen content in weld metal | < 5 mL/100g | < 10 mL/100g per GB/T 3965 |
| Deposit hardness (as-welded) | 60–65 HRC | > 58 HRC |
| Deposit hardness (tempered) | 55–60 HRC | > 55 HRC |
| Impact toughness (tempered) | > 25 J at -20 °C | > 20 J at -20 °C |
| Crack sensitivity | No cracks in 1000 cycles | No cracks in 500 cycles |
| Wear resistance (pin-on-disc) | 3–5× base metal | > 3× base metal |
Engineering Applications
The SJ403 flux was successfully applied to several wear-resistant overlay applications:
- Mining equipment — Crusher jaws, conveyor rollers, and excavator buckets showed 3–5× life extension compared to uncoated components.
- Cement industry — Mill liners and grinding balls achieved 2–4× life improvement, reducing replacement frequency and maintenance costs.
- Steel mill equipment — Transfer rolls and guide plates in hot rolling mills showed significant wear resistance improvement, extending overhaul intervals.
- Agricultural machinery — Plowshares and harrow teeth demonstrated excellent abrasion resistance against soil and rock, extending service life by 3–4×.
Defect Analysis and Process Optimization
During the development and application of SJ403, several defect patterns were identified and addressed:
| Defect | Root Cause | Optimization Strategy |
|---|---|---|
| Excessive porosity | High moisture content in flux, or inadequate arc shielding | Reduce flux moisture to < 0.5%, increase flux coverage, use proper welding technique |
| Hot cracking in overlay | Excessive sulfur content in base metal, or improper flux composition | Add sulfur scavengers to flux, control interpass temperature, use lower carbon electrode |
| Slag inclusion | Inadequate slag fluidity, or poor slag removal between passes | Optimize sintering temperature, adjust slag composition for better fluidity, ensure thorough slag removal |
| Insufficient hardness | Excessive dilution, or flux composition not providing adequate alloying | Use lower current, increase travel speed, or add additional alloying elements to flux |
| Poor slag removability | Slag too viscous or too adherent | Adjust CaF2/CaO ratio, add TiO2 for improved wetting, optimize sintering temperature |
Study Reflection
The development of SJ403 represents a significant contribution to the field of wear-resistant overlay welding consumables. The flux design philosophy—integrating arc stability, slag protection, deoxidation, alloying, and crack resistance into a single consumable—demonstrates the complexity and sophistication of modern welding consumable engineering. The sintering process, which determines the flux pellet properties, is a critical but often underappreciated aspect of consumable manufacturing. The research also highlights the importance of systematic testing and optimization; the flux composition was refined through multiple iterations, each addressing specific defect patterns identified in field trials. For modern applications, the SJ403 concept can be adapted to automated welding processes (GMAW, FCAW, SAW) with appropriate wire consumables, enabling further improvements in productivity, consistency, and quality. The work also underscores the principle that consumable design must be application-specific; a flux optimized for one wear environment may not perform well in another, and each application requires careful evaluation and optimization.