CLADDING TECHNOLOGY SHANXI CO., LTDDevelopment of Composite Hardfacing Electrodes with Cemented Carbide Reinforcement
Literature Overview
This 1990 publication by Zou Xumei from the Zigong Cemented Carbide Plant addresses the development of composite hardfacing welding electrodes that incorporate cemented carbide particles into the electrode coating or consumable insert. The work was driven by industrial demand for wear-resistant overlay coatings on equipment subjected to severe abrasive conditions, particularly in mining, cement, and chemical processing sectors. The technical approach represents an early Chinese effort to bridge the gap between conventional hardfacing consumables and the superior abrasion resistance offered by tungsten carbide-based cemented carbides.
Core Technical Approach
The fundamental concept involves embedding or incorporating cemented carbide (WC-Co) particles directly into the electrode structure, creating a composite consumable where the welding arc melts both the base electrode material and the embedded carbide particles simultaneously. This produces a weld overlay deposit containing dispersed WC particles in a hardfacing matrix, combining the toughness of a metallic binder phase with the extreme hardness of the carbide reinforcement.
The development process would have involved several critical technical challenges:
| Parameter | Target / Requirement | Engineering Rationale |
|---|---|---|
| WC particle size | 5–50 μm typical range | Smaller particles provide better dispersion; larger particles risk cracking |
| WC-Co binder ratio | 5–10% Co typical | Controls WC particle bonding to matrix during melting |
| Electrode coating composition | Ni-Cr or Fe-Cr-C type | Must be compatible with WC during arc melting |
| Hardness of deposit | ≥ HRC 65 (target) | Required for severe abrasive wear applications |
| Bond strength to base | ≥ 25 MPa | Prevents spalling under impact loading |
| Cracking tendency | Minimize | WC is brittle; thermal cycling causes microcracking |
Key Technical Points and Process Analysis
Electrode Design Considerations
The composite electrode design must account for the fact that cemented carbide has a melting point far exceeding that of the electrode core material. WC melts at approximately 2870°C, while the steel electrode core melts at roughly 1500°C. In practice, during arc welding, the WC particles do not fully melt but rather undergo partial dissolution and diffusion into the molten weld pool. This partial dissolution is actually beneficial because it preserves the hardness of the carbide phase while allowing sufficient wetting and bonding to the matrix.
The electrode geometry is critical. A common approach involves placing a strip of cemented carbide powder compacted with a metallic binder at the tip of the electrode, or embedding WC particles within the flux coating. The coating must be formulated to provide adequate arc stability, slag protection, and deoxidation while not interfering with the carbide particle retention in the deposit.
Metallurgical Challenges
The primary metallurgical concern is the formation of brittle intermetallic compounds at the interface between the WC particles and the molten matrix. During solidification, the WC particles can react with the molten iron or nickel matrix to form Fe₃W or Ni₃W intermetallics, which are extremely brittle and detrimental to the mechanical properties of the overlay. To mitigate this, the electrode composition is carefully designed with controlled carbon and chromium levels, and the cooling rate is managed through interpass temperature control during multi-pass welding.
Hardness and Wear Performance
The resulting overlay deposit achieves hardness values typically in the range of 800–1200 HV, significantly exceeding conventional hardfacing deposits (which typically achieve 500–700 HV). The wear resistance improvement is attributed to the ploughing and micro-cutting mechanism resistance provided by the hard WC particles dispersed in the tougher matrix. However, the trade-off is reduced impact toughness, which must be evaluated for each specific application.
Engineering Practice Implications
In practical application, these composite electrodes are particularly suitable for components subjected to dry sliding abrasion with hard abrasive particles, such as crusher components, sand pump impellers, and conveyor rollers. The repair procedure typically involves:
- Surface preparation by grinding or machining to remove existing worn material and expose sound base metal
- Preheating to 250–350°C to reduce thermal stress and minimize cracking risk
- Multi-pass welding with controlled interpass temperature below 300°C
- Post-weld stress relief at 400–450°C for 1–2 hours (avoiding temperatures above 500°C which can cause WC decomposition)
The cost-benefit analysis must consider that while the electrode itself is more expensive than conventional hardfacing electrodes, the extended service life of the repaired component often justifies the additional consumable cost.
Study Insights and Reflections
This 1990 publication represents an important early effort in Chinese welding consumable technology development. The approach of incorporating cemented carbide into hardfacing electrodes was relatively novel at the time and demonstrated the innovation capability of specialized Chinese manufacturing enterprises. From a modern perspective, the technology has been largely superseded by plasma transferred arc (PTA) cladding with WC-Co powder and laser cladding with carbide-containing alloys, which offer superior control over particle distribution and deposit microstructure. However, the fundamental metallurgical principles remain valid, and the electrode-based approach retains value for field repair situations where portable equipment is preferred over stationary plasma or laser systems.
The key insight from this work is that the composite approach—combining a tough metallic matrix with hard ceramic reinforcement—remains the most effective strategy for achieving high abrasion resistance in weld overlays. This principle continues to guide modern overlay technology development, whether the reinforcement is WC, Cr₃C₂, or other hard carbides, and whether the delivery method is arc welding, plasma, or laser.