Zhuojin Pipe Fitting Co., LtdWear-Resistant Overlay Welding Process for Excavator Bucket Teeth
Literature Overview
The paper by Ge Changlu and Ye Rongchang (1996), published in Metal Mine, provides a comprehensive overview of wear-resistant overlay welding processes for excavator bucket teeth, shovel buckets, and loader teeth. Although published in the mid-1990s, the fundamental metallurgical principles and process selection criteria remain highly relevant to modern heavy equipment manufacturing. The authors systematically present welding consumables, process parameters, and service performance data for different operating conditions, making this a valuable reference for engineers involved in wear-resistant cladding applications.
Operating Conditions and Wear Mechanisms
Excavator bucket teeth experience complex loading conditions that combine impact, abrasion, and adhesive wear. The selection of overlay material and process must be matched to the specific service environment:
| Operating Condition | Dominant Wear Mechanism | Recommended Overlay Material | Typical Hardness (HRC) |
|---|---|---|---|
| Hard rock excavation | Abrasion + impact | High-carbon martensite (Cr12MoV-type) | 50-55 |
| Soil and gravel | Abrasion | Medium-carbon alloy steel | 40-48 |
| Coal mining | Abrasion + corrosion | Medium-carbon alloy with Mo | 42-50 |
| Hard clay | Abrasion | High-carbon alloy steel | 45-52 |
The authors emphasize that there is no universal overlay material; the selection must be based on a careful analysis of the wear mechanism, impact energy, and environmental conditions.
Welding Process Selection and Parameters
The primary process used for bucket tooth overlay welding is SMAW (shielded metal arc welding) due to its portability and suitability for field repair. The following process parameters were identified as critical:
- Welding current: 180-260 A for electrodes of E5015-type classification, depending on electrode diameter (3.2-4.0 mm).
- Arc length: Maintained at 1.0-1.5 times the electrode diameter to ensure stable arc and consistent penetration.
- Welding position: Predominantly flat and horizontal positions for bucket teeth; vertical and overhead positions require reduced current by 10-20%.
- Preheating: Generally not required for low-carbon steel base metals, but recommended at 150-200°C for high-carbon or alloyed substrates to reduce hydrogen-induced cracking.
The authors also discuss the use of multi-layer welds for thick overlay requirements, where the first layer provides dilution control and subsequent layers build up the desired hard microstructure. The interpass temperature should be maintained below 200°C to ensure proper hardening response in the martensitic overlay.
Microstructure and Hardness Control
The wear resistance of the overlay is directly related to its microstructure. For high-carbon martensitic overlays, the target microstructure consists of:
- Primary carbides (Cr7C3, Fe3C) providing abrasion resistance
- Martensite matrix providing hardness and strength
- Retained austenite (controlled below 15%) providing toughness against impact
The hardness profile typically shows a gradient from the surface (highest hardness, ~55 HRC) to the fusion zone (lowest hardness, ~35 HRC). This gradient is beneficial as it provides a tough transition to the base metal. However, excessive retained austenite (>20%) can lead to soft spots and premature wear.
Engineering Practice and Field Performance
The authors report field data showing that properly designed overlay welds can extend the service life of bucket teeth by 2-3 times compared to bare steel teeth. The key to success is not only material selection but also proper surface preparation, including grinding of the base metal to remove rust and scale, and ensuring good edge preparation for weld attachment.
A critical practical observation is that the overlay must be designed with adequate thickness to prevent breakthrough by the base metal during service. The recommended minimum overlay thickness is 3-5 mm for standard applications, increasing to 6-8 mm for severe impact conditions. Thinner overlays may initially show good hardness but fail prematurely due to substrate breakthrough.
Study Insights and Reflections
This paper, despite its age, provides a solid foundation for understanding the relationship between wear mechanism, material selection, and process parameters. The systematic approach to matching overlay materials to operating conditions is directly applicable to modern applications such as overlay welding of mining equipment, cement mill liners, and even pipe fittings in abrasive slurry service. The emphasis on hardness gradients and retained austenite control reflects an understanding of welding metallurgy that remains current. One area where modern practice has evolved is the use of hardfacing consumables with more controlled compositions and the application of automated GMAW and SAW processes for thicker overlays, which offer better consistency and productivity than manual SMAW.