CLADDING TECHNOLOGY SHANXI CO., LTDDevelopment of High Wear-Resistant Overlay Flux-Cored Wire
Literature Overview
This research focuses on the development and characterization of a high wear-resistant flux-cored welding wire (FCW) for overlay applications in severe abrasion environments. Flux-cored arc welding (FCAW) offers significant advantages over solid wire processes for hardfacing applications due to higher deposition rates, deeper penetration, and the ability to alloy the weld metal through the flux core. The study addresses compositional design, flux formulation, mechanical properties, and wear performance of the developed consumable.
Compositional Design Strategy
The high wear-resistant overlay FCW was designed based on the principle of carbide hardening combined with matrix toughening. The wire composition targets a balance between hardness (for abrasion resistance) and toughness (to prevent spalling under impact loading).
| Component | Wire Core (wt%) | Flux Addition (wt%) | Final Overlay (wt%) |
|---|---|---|---|
| C | 1.8–2.2 | 0.3–0.5 | 2.0–2.5 |
| Cr | 18–22 | 2–4 | 20–26 |
| Mo | 2.5–3.5 | 0.5–1.0 | 3.0–4.5 |
| V | 1.0–1.8 | 0.2–0.4 | 1.2–2.0 |
| Mn | 1.2–1.8 | 0.3–0.6 | 1.5–2.2 |
| Si | 0.3–0.6 | 0.1–0.2 | 0.4–0.8 |
The flux core composition includes deoxidizers (FeSi, FeMn), alloying agents (FeCr, FeMo, FeV), arc stabilizers (CaCO₃, MgCO₃, Na₂CO₃), and gas-forming agents (TiO₂, SiO₂). The flux also serves to protect the weld pool from atmospheric contamination and to refine the weld microstructure through controlled slag composition.
Microstructural Development and Hardenability
The overlay deposit microstructure consists of:
- Primary carbides: Cr₇C₃ and Cr₂₃C₆ particles with sizes ranging from 5–15 μm, dispersed throughout the matrix.
- Secondary carbides: (Cr,Mo,V)₂C and (Cr,V)C particles in the 1–3 μm range, providing additional hardening.
- Matrix: Mixture of martensite and retained austenite, with the austenite content controlled at 8–15% to provide impact toughness.
- Intermetallic phases: Small quantities of sigma phase (Cr₂₅C₆) at grain boundaries when cooling rates are below 10 °C/s.
The hardenability of the overlay alloy is achieved through the high carbon and alloy content, which lowers the Ms (martensite start) temperature to approximately 180–220 °C. This ensures that the overlay transforms to martensite during normal air cooling after welding, achieving hardness values of 55–62 HRC without requiring post-weld heat treatment.
Wear Performance Testing
The wear resistance of the developed FCW overlay was evaluated using standardized testing methods:
| Test Method | Test Conditions | Wear Rate (mm³/N·m) | Comparison to Base Metal |
|---|---|---|---|
| ASTM G65 pin-on-disk | SiC paper, 50 N load | 4.2 × 10⁻⁷ | 1/12 of base metal |
| Dry sand-rubber wheel | 220# silica sand, 30 N | 2.8 × 10⁻⁷ | 1/15 of base metal |
| Rock abrasion (ASTM G98) | 40-60 mesh garnet, 30 N | 0.0032 cm³/g | 1/10 of base metal |
| Three-body abrasion | Sand slurry, 50 N | 1.5 × 10⁻⁷ | 1/18 of base metal |
The excellent wear resistance is attributed to the high volume fraction of hard carbide particles (approximately 30–35%) combined with the hard martensitic matrix. The carbide particles act as load-bearing elements that resist penetration by abrasive asperities, while the matrix provides the necessary toughness to prevent inter-carbide fracture.
Process Parameters and Welding Performance
The FCAW process parameters for optimal overlay performance include:
| Parameter | Range | Notes |
|---|---|---|
| Voltage | 28–34 V | Higher voltage increases spray transfer stability |
| Current | 250–380 A | Current density affects dilution rate |
| Travel speed | 300–500 mm/min | Slower speed increases dilution and carbide coarsening |
| Wire feed speed | 4.5–7.0 m/min | Must be synchronized with travel speed |
| Shielding gas | CO₂ or Ar + 20% CO₂ | Pure CO₂ gives deeper penetration |
| Nozzle diameter | 16–20 mm | Adequate gas coverage required |
| Stick-out length | 15–25 mm | Affects arc stability and heat input |
Dilution rate is a critical parameter for overlay applications. For the developed FCW, dilution typically ranges from 25–40% depending on base metal thickness and welding parameters. Higher dilution reduces overlay hardness and carbide content, so multi-pass welding with thin layers is recommended to maintain overlay properties throughout the deposit thickness.
Defect Analysis and Countermeasures
| Defect Type | Root Cause | Countermeasure |
|---|---|---|
| Porosity | Inadequate gas shielding, flux moisture | Ensure proper nozzle alignment; bake flux if needed |
| Undercut | Excessive travel speed or current | Reduce travel speed; adjust current to match voltage |
| Cracking | High dilution, rapid cooling | Use preheat; reduce heat input; control interpass temp |
| Incomplete fusion | Low current, excessive travel speed | Increase current; reduce travel speed; improve fit-up |
| Excessive spatter | Excessive voltage or arc length | Reduce voltage; maintain proper stick-out |
Engineering Practice Integration
The developed high wear-resistant overlay FCW is particularly suitable for applications including:
- Mining equipment: Crusher hammers, conveyor rollers, and bucket teeth subjected to severe abrasion by ore and rock.
- Cement industry: Kiln liners, mill liners, and preheater components exposed to abrasive cement clinker.
- Power generation: Coal mill rollers, fan blades, and boiler tubes in ash-laden environments.
- Construction equipment: Excavator bucket teeth, grader blades, and bulldozer shoes.
From a production standpoint, the FCAW process offers deposition rates of 6–10 kg/h compared to 1.5–3 kg/h for SMAW, making it significantly more economical for large-scale overlay operations. However, the wire must be stored in controlled humidity environments (relative humidity below 60%) to prevent flux degradation and porosity formation.
Study Insights and Implications
The development of high wear-resistant overlay FCW represents a significant advancement in hardfacing technology, combining the high productivity of flux-cored processes with the exceptional wear resistance of high-alloy hardfacing compositions. The key insight from this research is that the flux core serves not merely as a carrier for alloying elements but as an active participant in microstructural development. The slag composition influences grain growth, carbide precipitation, and residual stress development in the overlay deposit. This holistic understanding of the flux-metal interaction is essential for consumable development and should guide future research into advanced flux formulations. The practical implications extend to welding procedure qualification, where the dilution rate and resulting overlay properties must be verified through systematic testing rather than assumed from consumable specifications alone.