CLADDING TECHNOLOGY SHANXI CO., LTDStudy Note on Tungsten Carbide Hardfacing of Hammer Crusher Hammer Heads
Literature Overview
The literature under review, authored by Li Shuping, Tang Qingchun, Huang Shuhao, and Liu Yetong (2009), addresses the hardfacing of tungsten carbide (WC) onto hammer crusher hammer heads used in mineral processing and crushing operations. Hammer heads are subjected to extreme abrasion and impact during the crushing of hard ores, making them one of the most wear-critical components in a hammer crusher. The original carbon steel hammer heads suffer from rapid wear, necessitating frequent replacement and causing significant downtime. The authors propose a tungsten carbide-based hardfacing approach to dramatically extend service life.
Core Technical Approach
The fundamental challenge in hardfacing hammer heads with tungsten carbide lies in the metallurgical incompatibility between the WC particles and the steel matrix. Tungsten carbide is extremely hard (Vickers hardness above 2000 HV) but inherently brittle, and its high melting point (2870 °C) makes conventional fusion welding difficult. The authors describe a weld overlay process that embeds WC particles into a metallic binder matrix during deposition.
The process involves the following key steps:
- Surface preparation of the hammer head, including cleaning of oxide scale, rust, and contaminants.
- Application of a transition layer to improve bonding between the base steel and the hardfacing alloy.
- Multi-pass hardfacing deposition with controlled heat input to embed WC particles while avoiding excessive melting and decomposition of the carbide.
- Post-weld heat treatment, typically involving tempering to relieve residual stresses and optimize the microstructure.
Key Process Parameters
| Parameter | Typical Range | Rationale |
|---|---|---|
| Heat input | Low to moderate (1.0–2.5 kJ/mm) | Prevent WC decomposition and grain coarsening |
| Preheating temperature | 200–300 °C | Reduce cooling rate, minimize cracking |
| Interpass temperature | 150–250 °C | Control thermal cycling |
| Number of passes | 3–5 | Achieve adequate overlay thickness (3–5 mm) |
| Post-weld tempering | 550–650 °C, 2 h | Relieve residual stress, stabilize carbide |
Microstructure and Wear Mechanism Analysis
The hardfacing microstructure typically consists of WC particles dispersed in a martensitic or austenitic binder matrix. The binder alloy composition is critical: a high-carbon, high-chromium composition promotes the formation of hard carbides (Cr7C3, Fe3C) in addition to the retained WC particles, creating a synergistic wear-resistant microstructure.
The primary wear mechanism in hammer crusher service is abrasive wear, supplemented by impact fatigue. The WC particles act as hard abrasion-resistant phases that resist material removal by hard particles in the ore. The binder matrix provides the necessary toughness to absorb impact energy and prevent catastrophic brittle fracture of the overlay.
Common Defects and Countermeasures
| Defect Type | Root Cause | Countermeasure |
|---|---|---|
| Cracking (longitudinal) | Excessive cooling rate, high residual stress | Preheat, reduce heat input, tempering |
| WC decomposition | Overheating during deposition | Reduce arc voltage, increase travel speed |
| Poor bonding | Contamination, insufficient fusion | Thorough surface preparation, adequate heat input |
| Spalling/delamination | Thermal mismatch, high residual stress | Post-weld stress relief, graded transition layer |
Engineering Practice Insights
From a practical standpoint, the success of WC hardfacing on hammer heads depends heavily on the geometric design of the hammer head and the welding position. Hammer heads are typically curved, and the welder must maintain consistent arc parameters across varying positions. The use of automated or semi-automated welding equipment significantly improves consistency and productivity.
The service life improvement achieved by WC hardfacing is typically 3–5 times that of unhardfaced hammer heads, depending on the ore hardness and crusher operating conditions. However, the hardfacing must be designed to accommodate the impact loading: excessive overlay thickness can lead to spalling under repeated impact, while too thin a layer provides insufficient wear reserve.
The economic evaluation must balance the upfront cost of hardfacing consumables and labor against the reduced frequency of hammer head replacement and the associated downtime costs. In many mining operations, the ROI is achieved within the first replacement cycle.
Study Reflections and Implications
This literature highlights a classic engineering trade-off between hardness and toughness in wear-resistant overlay design. The tungsten carbide hardfacing approach is particularly effective for abrasive wear scenarios, but it must be carefully engineered to avoid introducing brittleness that compromises impact resistance. The transition layer concept deserves special attention, as it addresses the metallurgical compatibility issue between the base steel and the hardfacing alloy.
For practitioners, the key takeaway is that hardfacing is not merely a surface treatment but a structural modification that must be designed in conjunction with the component's loading conditions. The geometry, welding sequence, and post-weld treatment all play critical roles in achieving the desired balance of wear resistance and durability.