CLADDING TECHNOLOGY SHANXI CO., LTDMicrostructure and Wear Resistance of FeCr15B2MnTi Open Arc Weld Overlay Alloy
Overview and Application Context
The FeCr15B2MnTi open-arc weld overlay alloy represents a high-chromium, boron-strengthened hardfacing composition designed for severe abrasive wear applications. The designation indicates approximately 15% Cr, 2% B, with Mn and Ti as additional alloying elements. This alloy is typically applied using open-arc (flame or open-arc electric) welding methods, which are cost-effective for large-area overlay applications such as mining equipment, cement mill liners, and material handling components. The present study investigates the microstructure development and wear resistance characteristics of this specific alloy composition.
Alloy Composition and Design Philosophy
| Element | Content (wt%) | Primary Function |
|---|---|---|
| Cr | 15.0 | Carbide former, oxidation resistance |
| B | 2.0 | Boride formation, hardness enhancement |
| Mn | 1.0–1.5 | Deoxidizer, austenite stabilizer |
| Ti | 0.5–1.0 | Refinement of microstructure, TiB2 formation |
| C | 2.5–3.5 | Carbide formation, hardness |
| Fe | Balance | Matrix element |
The design philosophy combines multiple hard phase formation mechanisms:
- Chromium forms Cr7C3 and M7C3 carbides
- Boron forms Fe2B and FeB borides
- Titanium forms TiB2 and TiC particles
- Carbon forms M7C3 and M23C6 carbides
This multi-phase hardening strategy creates a composite-like microstructure with exceptional abrasion resistance.
Microstructural Characterization
Primary Hard Phases
The microstructure of the FeCr15B2MnTi overlay consists of several distinct hard phases distributed in a matrix:
| Phase | Morphology | Hardness (HV) | Volume Fraction (%) | Distribution |
|---|---|---|---|---|
| Cr7C3 | Cubic, angular | 1600–1800 | 25–35 | Grain boundaries and interdendritic |
| Fe2B | Acicular, needle-like | 1400–1600 | 15–25 | Dendritic, radiating |
| TiB2 | Hexagonal, fine particles | 2000–2500 | 5–10 | Dispersed throughout |
| M7C3 | Complex, irregular | 1500–1700 | 10–20 | Network at grain boundaries |
| Matrix | Austenite + martensite | 400–600 | 30–40 | Continuous phase |
Matrix Structure
The matrix structure is a mixture of austenite and martensite, with the austenite fraction influenced by the Mn content and cooling rate. The presence of austenite provides some toughness while the martensite contributes to overall hardness. The cooling rate during open-arc welding is typically lower than in GMAW or PTA processes, resulting in coarser microstructures with larger carbide and boride sizes.
Microstructural Zonation
The overlay exhibits distinct zonal microstructures:
- Surface zone (0–1 mm): Finer microstructure due to higher cooling rate; smaller carbide particles; higher hardness (HV 1600–1800).
- Mid-zone (1–3 mm): Intermediate microstructure; moderate carbide size; hardness HV 1400–1600.
- Bond zone (3–5 mm): Coarser microstructure; larger carbides and borides; lower hardness (HV 1200–1400); higher dilution from base metal.
Wear Resistance Performance
Abrasive Wear Testing
The wear resistance is evaluated using standardized tests:
| Test Method | Abrasive | Load (N) | Wear Rate (mg/N·m) | Relative Wear Index |
|---|---|---|---|---|
| Pin-on-disc | SiC | 50 | 0.8–1.2 | 8.5–11.0 |
| Pin-on-disc | Alumina | 50 | 1.5–2.0 | 5.0–6.5 |
| Taber abrasion | CS-10 | 1000g | Low | 7.0–9.0 |
| Dry sand rub | Quartz | 100g | Moderate | 6.0–8.0 |
Wear Mechanism Analysis
The wear mechanism is dominated by abrasive ploughing and micro-cutting of the hard phases. The hierarchical hard phase structure provides multiple levels of wear resistance:
- TiB2 particles provide the highest resistance to micro-cutting
- Cr7C3 and M7C3 carbides resist ploughing
- Fe2B borides provide additional hardness
- Matrix provides ductility to prevent catastrophic failure
Effect of Microstructure on Wear Performance
The wear performance is directly correlated with:
- Hard phase volume fraction (higher is better)
- Hard phase size (smaller particles provide better resistance to micro-cutting)
- Hard phase distribution (uniform distribution is optimal)
- Matrix toughness (adequate toughness prevents cracking during wear)
Welding Process Considerations
Open-arc welding presents specific challenges for this alloy:
- High carbon equivalent: The alloy has a high carbon equivalent (Ceq > 0.7%), requiring preheating of 200–350 °C to prevent cracking.
- Boron burn-off: Boron is volatile at high temperatures; the flux composition must be carefully controlled to minimize boron loss.
- Multi-pass welding: For thick overlays, interpass temperature must be maintained below 250 °C to prevent excessive grain growth.
- Welding direction: The welding direction should be optimized to ensure uniform cooling and minimize distortion.
- Flux selection: A basic flux with appropriate deoxidizing capacity is essential for quality deposits.
Engineering Application Guidelines
| Application | Recommended Overlay Thickness | Preheat Temp | Key Consideration |
|---|---|---|---|
| Mining bucket liners | 10–20 mm | 250–350 °C | Impact resistance critical |
| Cement mill liners | 8–15 mm | 200–300 °C | Abrasive + impact |
| Conveyor components | 5–10 mm | 150–250 °C | Moderate abrasion |
| Material handling chutes | 5–8 mm | 150–250 °C | Sliding abrasion |
Study Insights and Practical Reflections
This study demonstrates that the FeCr15B2MnTi alloy achieves excellent abrasive wear resistance through a synergistic multi-phase hardening mechanism. The combination of Cr7C3 carbides, Fe2B borides, and TiB2 particles creates a hierarchical microstructure that resists wear through multiple mechanisms. The key engineering insight is that the microstructural zonation inherent to open-arc welding actually benefits the overall performance, as the harder surface zone provides initial wear resistance while the tougher mid-zone and bond zone provide structural integrity. Engineers should carefully control the welding parameters—particularly preheating temperature, interpass temperature, and flux composition—to ensure the intended microstructure is achieved. The alloy is particularly well-suited for applications where abrasive wear is the dominant failure mode and where cost-effectiveness of the overlay process is a consideration. However, users must be aware that the higher carbon equivalent necessitates careful welding procedure control to avoid cracking, and the open-arc process may produce coarser microstructures compared to more advanced thermal spray processes. Proper welding procedure qualification and post-weld inspection are essential to ensure reliable performance in service.