CLADDING TECHNOLOGY SHANXI CO., LTDTungsten Carbide Cladding on Hammer Crusher Hammer Heads - Study Reflection
Literature Overview and Context
Hammer crusher hammer heads are subjected to severe abrasion and impact during material crushing operations in mining and cement industries. The base material, typically low-carbon steel or medium-carbon steel, cannot withstand the abrasive wear conditions encountered in service. The literature under study addresses the application of tungsten carbide (WC) particle-reinforced composite overlay welding on hammer heads, aiming to extend service life significantly. This topic sits at the intersection of hardfacing metallurgy, particle reinforcement technology, and practical field application, making it highly relevant to engineers working in surface engineering and wear-resistant component fabrication.
The core challenge in WC composite cladding lies in achieving strong bonding between the tungsten carbide particles and the metallic matrix while maintaining sufficient toughness to resist impact fracture. The study examines various overlay methods including submerged arc welding (SAW) with flux-cored wire, gas metal arc welding (GMAW), and plasma transferred arc (PTA) welding, evaluating their respective merits in terms of dilution control, particle retention, and microstructure quality.
Core Technical Points and Process Parameters
The selection of tungsten carbide particle size, shape, and concentration is critical to the final wear resistance performance. The literature highlights several key parameters that govern the quality of the overlay layer:
| Parameter | Typical Range | Recommended Value | Rationale |
|---|---|---|---|
| WC particle size | 10-100 μm | 20-50 μm | Balances wear resistance and toughness |
| WC concentration (wt%) | 30-70% | 40-55% | Higher content risks brittleness and poor bonding |
| Preheat temperature | 200-400 °C | 300 °C | Prevents cracking in base material |
| Interpass temperature | 150-300 °C | 200 °C | Controls cooling rate and residual stress |
| Overlay thickness | 3-8 mm | 5-6 mm | Sufficient for service life without excessive cost |
| Post-weld heat treatment | 500-700 °C | 600 °C, 2h | Relieves residual stress and improves toughness |
The dilution rate between the base metal and the overlay layer is another critical factor. In SAW overlay using flux-cored wire, the dilution rate typically ranges from 15% to 35%, which can significantly alter the composition and hardness profile of the final overlay. The study recommends using a two-pass approach where the first pass acts as a transition layer to reduce dilution effects in the subsequent wear-resistant overlay pass.
The bonding mechanism between WC particles and the metallic matrix involves both mechanical interlocking and metallurgical bonding. During welding, the high temperature causes partial melting of the WC particles at the interface, forming a carbide-steel composite structure. However, excessive heat input can lead to complete dissolution of WC particles, resulting in loss of reinforcing effect and formation of soft phases. The optimal heat input window for WC composite cladding is approximately 10-15 kJ/mm, which provides sufficient melting of particle surfaces while preserving the bulk integrity of the carbide particles.
Microstructure Analysis and Performance Evaluation
The microstructure of the WC composite overlay layer consists of three distinct regions: the dilution zone near the interface, the transition zone with partially dissolved carbide particles, and the surface zone with intact WC particles embedded in a hardened martensitic matrix. The hardness distribution across the overlay thickness typically shows a gradient from 600-700 HV at the surface to 400-500 HV near the interface, with the base metal remaining at approximately 200 HV.
The wear resistance of the overlay layer is evaluated using pin-on-disk tribological testing under dry sliding conditions. The wear rate of the WC composite overlay is typically 0.5-2.0 × 10⁻³ mm³/(N·m), compared to 10-20 × 10⁻³ mm³/(N·m) for the unclad base material, representing a 5-10 fold improvement in wear life. The impact resistance is assessed through Charpy V-notch testing, with values of 15-25 J/cm² for the overlay layer, which is acceptable for hammer crusher applications where impact energy is moderate.
A critical finding from the literature is the formation of iron carbides (Fe₃C and M₇C₃) at the WC-steel interface during welding. These iron carbides can actually contribute positively to wear resistance by providing additional hard phases, but their excessive formation can compromise toughness. The balance between WC particle retention and iron carbide formation is governed by the cooling rate and heat input, with slower cooling rates favoring more complete iron carbide formation.
Common Defects and Countermeasures
| Defect Type | Root Cause | Countermeasure |
|---|---|---|
| Cracking at interface | Excessive dilution, high carbon equivalent | Preheat to 300°C, use low-carbon transition layer |
| WC particle dissolution | Excessive heat input | Reduce current, increase travel speed |
| Porosity | Flux contamination, inadequate shielding | Use dry flux, ensure proper gas flow rate |
| Poor bonding | Insufficient base metal preparation | Grinding to bare metal, degreasing |
| Overlay spalling | High residual stress, improper PWHT | Implement proper post-weld heat treatment |
The most common failure mode observed in field applications is spalling of the overlay layer from the base material, which is primarily attributed to high residual stresses developed during welding. The residual stress in the overlay layer can reach 400-600 MPa, which exceeds the yield strength of the overlay material. Implementing a proper post-weld heat treatment cycle at 600°C for 2 hours effectively reduces residual stresses to below 200 MPa, significantly improving the service life of the cladded hammer heads.
Engineering Practice and Field Application
In practical applications at cement plants and mining operations, the cladded hammer heads have demonstrated service life improvements of 3-5 times compared to unclad components. The typical service life of an unclad hammer head in limestone crushing is approximately 800-1200 hours, while the WC composite cladded version achieves 3000-5000 hours before replacement is required. This translates to significant cost savings in terms of downtime, replacement material, and labor.
The welding procedure qualification follows NB/T 47014 and ASME IX requirements, with the qualification coupon undergoing mechanical testing including tensile testing, bend testing, and hardness profiling across the overlay thickness. The minimum acceptable hardness at the surface is 600 HV, and the hardness must remain above 500 HV at a depth of 2 mm from the surface to ensure adequate wear protection.
The process parameters for GMAW overlay using flux-cored wire with WC particles typically involve a current range of 250-350 A, voltage of 28-35 V, and travel speed of 200-300 mm/min. The wire diameter of 1.6 mm is most commonly used, with a stick-out length of 15-20 mm to ensure stable arc and proper melting of the flux core containing WC particles.
Study Insights and Engineering Implications
The study of tungsten carbide composite cladding on hammer crusher hammer heads reveals several important engineering principles. First, the optimal WC particle size is not simply the finest available but rather a balanced value that provides sufficient hardness while maintaining adequate toughness and bonding strength. Second, the dilution rate must be carefully controlled through proper base metal preparation and welding parameter selection, as excessive dilution can compromise the wear resistance benefits of the overlay.
From a quality control perspective, the implementation of a systematic inspection protocol is essential. This includes visual inspection of the overlay surface for uniformity, hardness testing at multiple depths to verify the gradient profile, and magnetic particle inspection to detect any surface or near-surface cracks. The acceptance criteria should specify a maximum allowable hardness variation of ±50 HV across the overlay surface and a minimum bond strength of 15 MPa in a bond strength test.
The economic analysis presented in the literature demonstrates that despite the additional cost of the cladding process (approximately 30-50% increase in component cost), the extended service life and reduced downtime result in a net cost reduction of 40-60% over the component lifecycle. This makes the technology highly attractive for applications where hammer head replacement is frequent and downtime is costly.
In conclusion, the tungsten carbide composite cladding technology for hammer crusher hammer heads represents a mature and effective solution for extending component life in abrasive service conditions. The key to successful implementation lies in proper selection of WC particle specifications, careful control of welding parameters to minimize dilution and particle dissolution, and rigorous quality control procedures to ensure consistent overlay quality. Engineers should pay particular attention to the interplay between heat input, cooling rate, and particle behavior, as these factors collectively determine the final performance of the cladded component.