CLADDING TECHNOLOGY SHANXI CO., LTDDevelopment of Cemented Carbide Composite Cladding Welding Electrodes
Literature Overview and Background
The research conducted by Zou Xumei in 1990 for Zigong Cemented Carbide Plant represents a significant milestone in the development of specialized cladding welding consumables. This work addressed the critical need for durable surface hardening solutions in industrial applications where wear resistance and toughness must coexist. The cemented carbide composite cladding electrode technology sought to combine the exceptional hardness of cemented carbide (typically WC-Co based) with the ductility of a metallic bonding layer, creating a multi-layered system that could withstand severe abrasion while resisting spalling and cracking under impact loading.
Core Technical Principles
The fundamental challenge in cemented carbide cladding lies in the metallurgical incompatibility between the hard ceramic-like carbide particles and the molten weld metal. Cemented carbide particles, typically composed of tungsten carbide (WC) with cobalt binder, exhibit a coefficient of thermal expansion significantly different from that of common steel substrates. This mismatch, combined with the high melting point of WC (approximately 2870°C) compared to the molten pool temperature (approximately 1600–1800°C), creates substantial thermal stresses during solidification. The composite electrode design incorporates a graded transition layer between the base metal and the carbide-rich surface, effectively managing residual stresses and preventing interfacial delamination.
The electrode composition typically includes a metallic binder matrix containing iron, nickel, or cobalt, with embedded cemented carbide particles of controlled size distribution. The particle size, generally ranging from 10 to 100 micrometers, directly influences the final hardness and toughness balance of the cladding layer. Smaller particles yield higher hardness but lower impact resistance, while larger particles provide better toughness at the expense of surface hardness.
Key Process Parameters and Metallurgical Considerations
The following table summarizes the critical process parameters identified in this research:
| Parameter | Typical Range | Influence on Performance |
|---|---|---|
| Welding current | 80–150 A | Controls dilution rate and carbide particle retention |
| Arc voltage | 18–25 V | Affects penetration depth and layer composition |
| Travel speed | 50–150 mm/min | Determines deposit thickness per pass |
| Preheat temperature | 150–300°C | Reduces thermal stress and hydrogen-induced cracking |
| Interpass temperature | 150–250°C | Controls cooling rate and microstructure refinement |
| Number of passes | 2–4 | Builds up required thickness with graded composition |
| Carbide particle size | 10–100 μm | Governs hardness-toughness balance |
| Dilution rate | 15–35% | Critical for maintaining carbide integrity |
Microstructural Analysis and Performance Characteristics
Metallographic examination of the cladding layer reveals a three-zone microstructure: a base metal heat-affected zone (HAZ), a transition zone with mixed composition, and a surface zone rich in cemented carbide particles. The transition zone is particularly important as it serves as a stress-relief region that prevents crack propagation from the surface into the base metal.
The hardness of the final cladding layer typically reaches HV 1000–1500, depending on the carbide content and particle distribution. This represents a substantial improvement over conventional hardfacing alloys such as cobalt-based Stellite alloys, which typically achieve HV 400–600. However, the trade-off is reduced impact toughness, making this technology suitable primarily for abrasive wear applications rather than impact-abrasion combined service conditions.
Engineering Practice and Application Scenarios
This electrode technology found primary application in mining equipment, cement industry components, and agricultural machinery where severe abrasive wear is the dominant failure mechanism. The field deployment experience demonstrated that the composite cladding layer could extend component service life by 3 to 5 times compared to uncladded components or those repaired with conventional hardfacing materials.
Common defects encountered during application include:
| Defect Type | Root Cause | Countermeasure |
|---|---|---|
| Surface cracking | Excessive thermal stress from high current | Reduce current, increase preheat |
| Particle agglomeration | Inadequate mixing in electrode coating | Improved manufacturing process |
| Poor bond strength | Base metal contamination or insufficient penetration | Surface preparation, proper current selection |
| Spalling | High dilution rate destroying carbide integrity | Optimize travel speed and current |
| Porosity | Hydrogen absorption from moisture | Electrode baking before use |
Study Insights and Reflections
The significance of this 1990 research cannot be overstated in the context of Chinese industrial development at that time. The domestic development of specialized welding consumables reduced reliance on imported products and enabled local manufacturers to address wear problems with economically viable solutions. The composite electrode approach demonstrated that combining advanced materials science with practical welding engineering could yield transformative results for industrial maintenance and component life extension.
From a metallurgical perspective, this work highlighted the importance of understanding particle-matrix interactions in weld deposits. The retention of cemented carbide particles during solidification, without excessive dissolution or coarsening, requires careful control of cooling rates and thermal cycles. This understanding has since been incorporated into more advanced cladding technologies, including plasma transferred arc (PTA) cladding and laser cladding processes that offer even better control over particle distribution.
The research also underscored the practical challenge of balancing hardness with toughness in hardfacing applications. While HV 1000+ hardness provides exceptional abrasion resistance, the accompanying brittleness necessitates careful application to components not subjected to significant impact loading. Engineers must always evaluate the full service environment, including thermal cycling, chemical exposure, and mechanical loading conditions, before selecting this technology for a specific application.