CLADDING TECHNOLOGY SHANXI CO., LTDDevelopment of High Wear-Resistant Flux-Cored Cladding Wire
Literature Overview
Flux-cored arc welding (FCAW) has become an increasingly popular cladding method due to its high deposition rates, good arc stability, and ability to deposit thick overlay layers in a single pass. However, conventional flux-cored wires often lack the wear resistance required for severe service conditions. This study focuses on the development of a high wear-resistant flux-cored cladding wire designed for applications such as mining equipment, cement mill liners, conveyor rollers, and other components subjected to severe abrasive wear.
Requirements for High Wear-Resistant Cladding Wire
The development of a high wear-resistant flux-cored wire requires meeting several simultaneous requirements:
| Requirement | Specification | Rationale |
|---|---|---|
| Hardness (as-welded) | 50–58 HRC | Abrasive wear resistance |
| Hardness (after 600°C temper) | 45–52 HRC | Thermal stability |
| Toughness | >20 J (Charpy V-notch) | Impact resistance |
| Dilution resistance | Low dilution rate (<15%) | Maintain overlay properties |
| Weldability | No cracks, no porosity | Production reliability |
| Deposition rate | >5 kg/h | Productivity |
| Fume level | Low | Operator health and safety |
| Cost | Competitive with solid wire | Economic viability |
Wire Design Philosophy
The high wear-resistant flux-cored wire is designed with a composite structure consisting of a steel sheath and a flux core containing alloying elements and wear-enhancing particles. The design philosophy is based on the following principles:
Sheath Design
The sheath is made of low-carbon steel with controlled composition to ensure good weldability and low dilution. The sheath composition is designed to minimize the dilution of base metal into the overlay while providing adequate mechanical strength for wire handling and feeding.
| Sheath Element | Content (%) | Function |
|---|---|---|
| C | 0.08–0.15 | Low carbon for weldability |
| Mn | 1.2–1.8 | Deoxidation, strength |
| Si | 0.3–0.6 | Deoxidation |
| Cr | 0.5–1.0 | Mild corrosion resistance |
| Balance | Fe | Base matrix |
Core Flux Design
The core flux contains the alloying elements that provide wear resistance to the overlay. The flux composition is designed to:
- Alloy the weld metal with carbide-forming elements (C, Cr, Mo, V, W).
- Deoxidize the weld pool to prevent porosity and inclusions.
- Stabilize the arc for consistent welding performance.
- Control the solidification structure to promote fine carbide distribution.
The core flux composition includes:
| Flux Component | Content (%) | Function |
|---|---|---|
| Cr2O3 | 15–20 | Chromium source, oxidation resistance |
| Fe2O3 | 10–15 | Iron source, arc stabilization |
| SiO2 | 5–8 | Deoxidation, slag formation |
| CaF2 | 8–12 | Arc stabilization, desulfurization |
| TiO2 | 5–8 | Arc stabilization, slag viscosity |
| C (as graphite) | 2–4 | Carbon source for carbide formation |
| MoO3 | 3–5 | Molybdenum source, wear resistance |
| V2O5 | 1–3 | Vanadium source, carbide formation |
| B4C | 2–3 | Boron carbide, extreme hardness |
| Graphite + CaCO3 | Balance | Fluxing, gas shielding |
Microstructure and Hardness
The microstructure of the overlay deposited from the developed wire consists of a martensitic matrix with uniformly distributed hard carbides. The carbides are primarily Cr7C3, Mo2C, and VC, with minor B4C particles from the added boron carbide. The hardness is achieved through a combination of:
- Solid solution strengthening from Cr, Mo, and V in the martensitic matrix.
- Carbide dispersion strengthening from fine, uniformly distributed carbides.
- Transformation toughening from retained austenite in some compositions.
| Microstructural Feature | Description | Contribution to Hardness |
|---|---|---|
| Martensitic matrix | Fine, lenticular martensite | Base hardness 45–50 HRC |
| Cr7C3 carbides | 1–3 μm, dispersed | +3–5 HRC |
| Mo2C carbides | 0.5–2 μm, dispersed | +2–3 HRC |
| VC carbides | 0.3–1 μm, dispersed | +2–3 HRC |
| B4C particles | 5–20 μm, irregular | Local hardness >2000 HV |
| Retained austenite | 5–15% | Toughness, transformation toughening |
Weldability and Process Parameters
The developed flux-cored wire is designed for use with both short-circuit and spray transfer modes of FCAW. The following table presents typical welding parameters:
| Parameter | Short-Circuit Mode | Spray Transfer Mode |
|---|---|---|
| Wire diameter | 1.2 mm | 1.2 mm or 1.6 mm |
| Current | 120–200 A | 250–400 A |
| Voltage | 18–24 V | 28–36 V |
| Travel speed | 200–400 mm/min | 300–600 mm/min |
| Deposition rate | 2–4 kg/h | 5–8 kg/h |
| Heat input | 0.5–1.5 kJ/mm | 1.0–2.5 kJ/mm |
| Shielding gas | None (self-shielded) | Ar/CO2 mixtures |
| Wire feed speed | 2–4 m/min | 4–8 m/min |
The wire is designed to be self-shielded, meaning it does not require external shielding gas. This is achieved through the CaF2 and CaCO3 in the core flux, which generate CO2 and other shielding gases during welding. However, for critical applications, external shielding gas can be used to further reduce porosity and improve weld quality.
Performance Testing
The developed wire was subjected to comprehensive performance testing:
| Test | Method | Result |
|---|---|---|
| Hardness (as-welded) | Rockwell C | 52–56 HRC |
| Hardness (after 600°C, 2h) | Rockwell C | 48–52 HRC |
| Wear resistance | Sand rub test (ASTM G65) | 3–5× improvement over base steel |
| Impact toughness | Charpy V-notch, -40°C | 15–25 J |
| Crack sensitivity | Small iron test (SIT) | No cracks |
| Dilution rate | OES analysis | 10–18% |
| Fume level | Mass concentration | <5 mg/m³ |
| Porosity | Visual + radiographic | <1% volume fraction |
The wear resistance improvement of 3–5× over base steel is attributed to the high hardness and the presence of hard carbides that resist abrasive wear through micro-cutting and ploughing mechanisms.
Comparison with Conventional Cladding Wires
The developed high wear-resistant flux-cored wire is compared with conventional flux-cored and solid wire cladding consumables:
| Property | Conventional FCAW Wire | Solid Wire (GTAW) | Developed High Wear Wire |
|---|---|---|---|
| Hardness (as-welded) | 35–42 HRC | 45–50 HRC | 52–56 HRC |
| Hardness (600°C tempered) | 30–35 HRC | 40–45 HRC | 48–52 HRC |
| Deposition rate (kg/h) | 3–5 | 1–2 | 5–8 |
| Dilution rate (%) | 15–25 | 10–20 | 10–18 |
| Crack sensitivity | Moderate | Low | Low |
| Cost per kg | Moderate | High | Moderate |
| External gas required | Yes | Yes | No (self-shielded) |
The developed wire offers superior hardness and wear resistance compared to conventional FCAW wires, while maintaining a higher deposition rate than solid wire processes. The self-shielded characteristic eliminates the need for external shielding gas, reducing equipment costs and improving field applicability.
Defect Analysis and Countermeasures
During the development process, several defects were encountered and addressed:
| Defect | Root Cause | Countermeasure |
|---|---|---|
| Surface cracking | High carbon and low toughness | Add retained austenite stabilizers (Mn, Ni) |
| Porosity | Incomplete deoxidation | Increase Al and Ti deoxidizer content |
| Hot cracking | High sulfur and phosphorus | Use low-S, low-P sheath steel |
| Uneven hardness | Segregation of alloying elements | Optimize flux composition for uniform distribution |
| Excessive spatter | High voltage and current | Optimize wire geometry and flux composition |
| Poor arc stability | Inconsistent flux packing | Improve flux compaction and wire drawing process |
Engineering Applications
The developed high wear-resistant flux-cored wire has been successfully applied to the following engineering components:
- Mining equipment: Bucket teeth, conveyor rollers, and scraper chains in coal and ore mining operations.
- Cement industry: Mill liners, grinding balls, and kiln wear plates.
- Agricultural machinery: Plowshares, harrow teeth, and tiller blades.
- Construction equipment: Bucket edges, blade edges, and hydraulic cylinder rods.
- Power generation: Coal handling equipment, ash conveyor systems, and boiler wear plates.
In a case study at a cement plant, the developed wire was used to clad the mill liners of a ball mill. The original liners, made of high-manganese steel, required replacement every 6 months. After cladding with the developed wire, the service life was extended to 18 months, representing a 3× improvement in service life and a significant reduction in maintenance costs.
Study Insights and Implications
This study demonstrates that the development of specialized flux-cored cladding wires can significantly improve the wear resistance of cladding overlays while maintaining good weldability and productivity. The key insight is that the core flux composition plays a critical role in determining the overlay properties, and careful optimization of the flux composition is essential for achieving the desired hardness, toughness, and wear resistance.
The self-shielded characteristic of the developed wire is particularly valuable for field applications where external shielding gas is not available. This expands the applicability of flux-cored cladding to remote locations and on-site repair operations.
From a manufacturing perspective, the production of high-quality flux-cored wires requires precise control of the flux composition, uniform flux packing, and consistent wire drawing. Any variation in the flux composition or packing density can lead to inconsistent weld properties and defects. Therefore, strict process control and quality assurance are essential for reliable production.
In conclusion, the development of high wear-resistant flux-cored cladding wire represents a significant advancement in cladding technology, providing a practical solution for severe wear applications where high hardness, good toughness, and high productivity are required simultaneously. The wire's self-shielded characteristic and competitive cost make it an attractive alternative to solid wire processes and conventional FCAW consumables.