CLADDING TECHNOLOGY SHANXI CO., LTDTungsten Carbide Cladding Process for Hammer Blades of Feed Grinders
Literature Overview
This study, published in 2010 in the journal "Grain and Feed Industry" by researchers from the School of Mechanical Engineering at Beijing Technology and Business University, addresses a critical industrial problem: the rapid abrasive wear of hammer blades used in feed grinding mills. Feed grinders operate under severe impact-abrasion conditions where hammer blades are subjected to high-frequency collisions with grain particles, leading to shortened service life and frequent replacement. The authors investigate tungsten carbide (WC) hardfacing cladding as a solution to extend blade life through the application of a high-hardness, wear-resistant overlay layer.
Core Technical Content
The fundamental approach involves depositing a tungsten carbide-based hardfacing alloy onto the working surface of steel hammer blades using arc welding overlay techniques. The key technical challenge lies in balancing three competing requirements: sufficient hardness for abrasion resistance, adequate toughness to resist impact fracture during grinding operation, and reliable metallurgical bonding between the WC-rich overlay and the base steel substrate.
Material System and Composition Design
The WC-based cladding alloy typically contains 60–80 wt% WC particles in a cobalt or nickel-based binder matrix. The cobalt binder is preferred for high-temperature applications due to its superior thermal stability, while nickel binders offer better room-temperature toughness. The particle size distribution of WC (typically 15–45 μm) significantly influences both the hardness and the crack resistance of the deposited layer.
| Parameter | Typical Range | Influence |
|---|---|---|
| WC content | 60–80 wt% | Higher content increases hardness but reduces toughness |
| WC particle size | 15–45 μm | Finer particles improve toughness; coarser particles increase hardness |
| Binder matrix | Co-based or Ni-based | Co offers better high-T stability; Ni offers better room-T toughness |
| Overlay hardness | 1200–1800 HV | Target range for abrasive wear resistance |
| Overlay thickness | 2–4 mm | Sufficient to resist wear but not excessive to avoid spalling |
| Bond strength | >15 MPa | Ensures reliable adhesion during impact service |
Process Parameters and Technique Selection
The welding process commonly employed for this application is manual metal arc welding (SMAW) or submerged arc welding (SAW) using specialized hardfacing electrodes or flux-cored wires. Process parameters are carefully controlled to prevent excessive dilution of the WC particles by the base metal, which would reduce the effective hardness of the overlay.
| Process Parameter | Recommended Value | Rationale |
|---|---|---|
| Arc voltage | 22–28 V | Lower voltage reduces dilution |
| Welding current | 180–260 A | Moderate current to control heat input |
| Travel speed | 3–6 mm/s | Slower speed increases deposit volume but raises dilution |
| Preheat temperature | 150–250 °C | Reduces residual stress and cracking tendency |
| Interpass temperature | <300 °C | Prevents excessive grain growth and cracking |
| Post-weld treatment | Stress relief at 500–600 °C | Eliminates residual stresses |
Microstructure and Performance Characteristics
The as-deposited microstructure consists of undissolved WC particles dispersed in a matrix of Co or Ni solid solution with possible formation of Co₃W or Ni₃W intermetallics at the particle-matrix interface. The hardness of the overlay is primarily determined by the volume fraction of retained WC particles and the hardness of the binder matrix.
Key performance indicators include:
- Dry sliding wear life improvement of 5–8 times compared to uncladded blades
- Impact fatigue life improvement of 3–5 times under typical grinding conditions
- Surface roughness Ra of 1.6–3.2 μm after grinding preparation
Defect Analysis and Countermeasures
| Defect Type | Root Cause | Countermeasure |
|---|---|---|
| Cracking in overlay | High thermal stress from Co-binder CTE mismatch | Reduce welding current; increase preheat; apply multiple thin passes |
| Excessive dilution | Too high heat input or too fast travel speed | Lower current; increase travel speed; use shorter arc length |
| Porosity | Incomplete melting of WC particles | Ensure proper electrode drying; increase current slightly |
| Spalling | Poor bond strength at interface | Improve surface preparation; use compatible filler metal |
| Soft spots | Localized dilution or incomplete WC melting | Use multiple passes with cross-hatching pattern |
Engineering Practice Insights
From an engineering practice perspective, the most critical lesson from this work is that hardfacing for impact-abrasion applications requires a fundamentally different approach than for pure abrasive wear. Hammer blades in feed grinders experience both severe abrasion and repeated impact loading, meaning that maximum hardness alone is insufficient. The optimal design must achieve a balance where the overlay hardness exceeds approximately 1000 HV while maintaining adequate fracture toughness to prevent catastrophic brittle failure.
The practical implementation typically involves a two-layer strategy: a first layer of compatible transition alloy (such as a Ni-Cr-based alloy) to ensure metallurgical compatibility and bonding strength, followed by the WC-hardfacing layer for wear resistance. This approach has been validated in field applications at multiple feed processing facilities where hammer blade life was extended from approximately 40 hours to 200–300 hours of continuous operation.
Study Insights and Reflections
This literature represents a practical, application-driven approach to solving a common industrial wear problem. The study highlights an important principle in hardfacing engineering: the selection of overlay material and process parameters must be guided by the specific wear mechanism (abrasion, impact, erosion, or combinations thereof) rather than simply maximizing a single property such as hardness. The WC-Co system remains one of the most reliable and widely used hardfacing solutions for feed processing equipment, and the process development described in this work provides a solid foundation for further optimization through modern techniques such as plasma transferred arc (PTA) or laser cladding, which offer even lower dilution and more precise compositional control.