CLADDING TECHNOLOGY SHANXI CO., LTDApplication of Diamond and Cemented Carbide Composite Overlay on Steel-Toothed Drill Bit Tooth Surface Strengthening
Literature Overview
This 2007 study published in China Mining Magazine investigates the application of diamond and cemented carbide composite overlay technology for strengthening the tooth surfaces of steel-toothed drill bits. Conducted at Southwest Petroleum University under the Ministry of Education Doctoral Point Fund (project 20050615003) and the Petroleum Science and Technology Innovation Fund, the research addresses a significant industrial problem: the rapid wear and failure of drill bit teeth during drilling operations.
Steel-toothed drill bits are extensively used in coal mining, metalliferous ore drilling, and oil well drilling operations. The tooth surface is subjected to severe abrasive wear, impact loading, and thermal cycling during drilling. Traditional surface hardening methods provide limited improvement, making composite overlay technology an attractive solution.
Core Technical Content
Wear Mechanisms in Drilling Operations
The wear of drill bit teeth occurs through multiple simultaneous mechanisms:
| Wear Mechanism | Dominant Condition | Wear Rate | Primary Damage Mode |
|---|---|---|---|
| Abrasive wear | Hard rock formation | High | Grooving and material removal |
| Adhesive wear | Soft-to-hard transition | Moderate | Material transfer and smearing |
| Impact wear | Hard rock impact | Moderate | Microcracking and spalling |
| Thermal fatigue | Continuous friction | Low to moderate | Surface cracking and flaking |
| Corrosive wear | Water-based mud | Low | Surface degradation |
Composite Overlay Design
The overlay system combines diamond particles with cemented carbide matrix to achieve complementary properties:
- Diamond phase: Provides extreme hardness (HV 8000-10000), excellent thermal conductivity, and low coefficient of friction. Diamond particles are typically 50-200 micrometers in size for surface overlay applications.
- Cemented carbide matrix: WC-Co or WC-Co-Cr cemented carbide provides toughness, thermal stability, and bonding capability with the steel substrate. Typical composition is 94 percent WC and 6 percent Co by weight.
- Interface design: The bonding between diamond and cemented carbide is critical. Direct bonding requires intermediate layers (Cr, TiC, or Ni) to prevent chemical reaction and improve adhesion.
Overlay Process Parameters
| Process Parameter | Typical Range | Optimization Target |
|---|---|---|
| Overlay thickness | 1-3 mm | Balance between wear resistance and bonding strength |
| Diamond particle size | 50-200 um | Larger particles for abrasive wear, smaller for impact resistance |
| Diamond volume fraction | 20-40% | Higher fraction increases hardness but reduces toughness |
| Heat input | 0.5-1.2 kJ/mm | Low heat input to minimize substrate dilution |
| Preheat temperature | 150-250 degrees C | Reduce thermal stress and improve bonding |
| Interpass temperature | Below 200 degrees C | Prevent carbide decomposition and diamond graphitization |
Microstructural Analysis
The overlay microstructure reveals several important features:
- Diamond distribution: Uniform distribution requires careful mixing and appropriate powder metallurgy techniques. Segregation of diamond particles reduces the effectiveness of the composite.
- Matrix bonding: The cemented carbide matrix must maintain its microstructure (WC particles in Co binder) through the welding thermal cycle. Excessive heat input can dissolve WC particles or cause cobalt oxidation.
- Interface integrity: The substrate-overlay interface should show no cracks, voids, or unmelted regions. Good metallurgical bonding requires adequate heat input without excessive dilution.
- Residual stress: Compressive residual stress at the surface is beneficial for fatigue resistance. Post-overlay grinding or peening can introduce beneficial compressive stress.
Performance Evaluation
Wear Testing Results
| Test Condition | Overlay Wear Rate | Bare Steel Wear Rate | Wear Resistance Improvement |
|---|---|---|---|
| Pin-on-disk (SiC paper) | 0.02-0.05 mm3/Nm | 0.5-1.0 mm3/Nm | 10-50 times |
| Rock abrasion (quartz sand) | 0.05-0.15 mm3/Nm | 1.0-2.0 mm3/Nm | 10-30 times |
| Impact abrasion (rock chips) | 0.1-0.3 mm3/Nm | 2.0-4.0 mm3/Nm | 10-20 times |
| High-temperature wear (400 degrees C) | 0.08-0.20 mm3/Nm | 1.5-3.0 mm3/Nm | 8-20 times |
Field Application Performance
Field trials in actual drilling operations typically show:
- Drill bit life extension: 2-5 times improvement over conventional hardfacing or heat treatment
- Cost reduction: Despite higher initial overlay cost, the extended service life reduces overall drilling costs by 30-50 percent
- Production improvement: Reduced bit changes increase drilling efficiency by 15-30 percent
- Reliability: Consistent performance across different geological formations
Engineering Practice Integration
Application Scenarios
| Application | Rock Type | Recommended Overlay | Expected Life Improvement |
|---|---|---|---|
| Coal seam drilling | Soft to medium coal | Diamond-cemented carbide (low diamond fraction) | 2-3 times |
| Metalliferous ore drilling | Medium to hard ore | Diamond-cemented carbide (medium diamond fraction) | 3-5 times |
| Oil well drilling | Hard formations | Diamond-cemented carbide (high diamond fraction) | 3-5 times |
| TBM cutting tools | Hard rock | Diamond-cemented carbide (high diamond fraction) | 4-6 times |
Process Optimization
- Powder preparation: Diamond particles should be cleaned and activated to improve bonding. Surface treatment with Cr or Ti compounds enhances adhesion to the cemented carbide matrix.
- Welding sequence: Multi-pass overlay with graded diamond content (lower at interface, higher at surface) optimizes bonding and wear resistance.
- Post-weld treatment: Light grinding removes surface defects and introduces compressive residual stress. Avoid excessive grinding that removes the diamond-rich surface layer.
- Quality control: Ultrasonic testing verifies overlay thickness and bonding quality. Hardness testing confirms diamond distribution and matrix integrity.
Key Questions and Reflections
The study raises several important considerations:
- Diamond graphitization: At temperatures above 600 degrees Celsius in the presence of iron, diamond can convert to graphite. How does the welding thermal cycle affect diamond stability?
- Thermal conductivity mismatch: Diamond has very high thermal conductivity compared to steel and cemented carbide. Does this create thermal stress during service?
- Cost-benefit analysis: Diamond is expensive. At what wear rate threshold does the composite overlay become economically justified?
- Scalability: Can the technology be applied to large-diameter drill bits and TBM cutters without loss of performance?
Study Insights and Outlook
This research demonstrates the significant potential of diamond-cemented carbide composite overlay for drill bit strengthening. The key insight is that combining the extreme hardness of diamond with the toughness of cemented carbide creates a synergistic effect that outperforms either material alone. Engineers should consider this technology for high-wear applications where conventional hardfacing provides insufficient protection. Future development should focus on improving diamond retention at elevated temperatures, optimizing particle size distribution for specific drilling conditions, and developing cost-effective large-scale application methods. The technology represents a significant advancement in surface engineering for drilling operations.