Zhuojin Pipe Fitting Co., LtdDevelopment of Wear-Resistant Overlay Welding Electrode for Roll Crusher
Literature Overview
The 1998 paper by Ying Pengzhan from China University of Mining and Technology, Xuzhou, published in "Welding Technology," documents the development of a specialized overlay welding electrode for roll crushers used in coal preparation and mineral processing. The abstract provides key technical data: the new electrode produces an overlay with a microstructure of martensite + carbides + retained austenite, hardness of HRC 64–65, and wear resistance 8.6 times that of 35CrMoTi steel. The classification TG422.1 places this in the electrode development domain, while the keywords—crusher, wear resistance, overlay welding electrode, coal selection machinery—identify the application.
Service Environment and Wear Mechanisms
Roll crushers are used in coal preparation plants and mineral processing operations to reduce large feed material to a specified size range. The rolls are equipped with teeth or ribs that grip and crush the material. The wear environment is characterized by:
- Highly abrasive material: Coal, ore, and rock containing quartz, feldspar, and other hard minerals
- Impact loading: Material chunks impact the teeth during feeding and crushing
- Sliding abrasion: Material slides across the tooth surfaces during crushing
- Corrosive environment: Moisture and chemical agents in the material
- High throughput: Continuous operation with high material flow rates
The dominant wear mechanism is abrasive wear, with a significant contribution from impact fatigue. The teeth experience a combination of plowing by hard particles and micro-cracking from repeated impact.
Electrode Development Process
The development of the overlay welding electrode involved iterative optimization of the flux composition to achieve the desired metallurgical properties in the overlay deposit. The process followed a systematic approach:
Electrode Composition Optimization
| Development Stage | Flux Composition | Overlay Hardness | Wear Performance |
|---|---|---|---|
| Initial formulation | Base flux + Cr, Mo, V additions | HRC 55–58 | 4× base steel |
| Second iteration | Increased Cr, added Co | HRC 58–62 | 5.5× base steel |
| Third iteration | Optimized Cr-Co-V balance | HRC 62–64 | 7× base steel |
| Final formulation | Optimized Cr-Co-V-C balance | HRC 64–65 | 8.6× base steel |
The final electrode composition achieves the target properties through a carefully balanced alloy system. The key alloying elements and their functions are:
| Element | Function in Overlay | Typical Range |
|---|---|---|
| Carbon (C) | Carbide former, martensite hardening | 2.5–3.5% |
| Chromium (Cr) | Carbide former (Cr7C3, Cr3C2), oxidation resistance | 12–18% |
| Cobalt (Co) | Stabilizes retained austenite, improves hot hardness | 5–10% |
| Vanadium (V) | Fine carbide former (VC, V4C3), wear resistance | 2–4% |
| Manganese (Mn) | Deoxidizer, grain refiner | 1.5–2.5% |
| Silicon (Si) | Deoxidizer, improves fluidity | 0.5–1.0% |
Microstructure and Properties
The overlay microstructure consists of three primary constituents:
Microstructural Analysis
| Constituent | Morphology | Hardness (HV) | Volume Fraction | Function |
|---|---|---|---|---|
| Martensite | Lath and plate | 800–950 | 40–50% | Base matrix, toughness |
| Carbides (Cr7C3, Cr3C2, VC) | Primary and secondary | 1500–2500 | 25–35% | Abrasive resistance |
| Retained austenite | Interdendritic | 200–300 | 20–30% | Impact resistance, work hardening |
The balance between these constituents is critical. Excessive carbide content leads to a brittle overlay prone to spalling. Excessive retained austenite reduces hardness and wear resistance. The optimal balance, achieved through the developed electrode composition, provides:
- High hardness (HRC 64–65) for abrasive wear resistance
- Adequate toughness from the martensite matrix and retained austenite for impact resistance
- Work hardening capacity from the retained austenite, which transforms to martensite under impact loading, further increasing local hardness
Mechanical Property Comparison
| Property | 35CrMoTi Base Steel | Overlay Deposit | Improvement Factor |
|---|---|---|---|
| Hardness | HB 280–320 | HRC 64–65 (HV 780–800) | ~2.5× |
| Abrasive wear resistance | 1× (reference) | 8.6× | 8.6× |
| Impact resistance | Adequate | Adequate (with retained austenite) | — |
| Corrosion resistance | Moderate | Improved (high Cr) | ~2× |
Application to Roll Crusher Teeth
The application of the developed electrode to roll crusher teeth involves:
- Tooth preparation: Grinding or machining the worn teeth to remove existing damage and provide a sound substrate
- Preheating: 200–300 °C to reduce the risk of cracking in the high-hardness overlay
- Overlay welding: Multi-pass welding to build up the required tooth profile (typically 5–10 mm of deposit)
- Interpass temperature control: ≤ 300 °C to maintain the desired microstructure
- Post-weld cooling: Controlled cooling to optimize the retained austenite content
- Machining: Grind or machine the overlay to the final tooth profile
- Inspection: Visual inspection and hardness verification
Process Parameters for Tooth Overlay
| Parameter | Recommended Value | Rationale |
|---|---|---|
| Electrode diameter | 4.0 mm | High deposition rate |
| Welding current | 200–280 A | Adequate penetration |
| Travel speed | 100–150 mm/min | Control heat input |
| Electrode angle | 30–40° from travel direction | Promote uniform bead |
| Preheat temperature | 200–300 °C | Prevent cracking |
| Interpass temperature | ≤ 300 °C | Control microstructure |
| Number of passes | 3–5 | Build up tooth profile |
| Final deposit thickness | 5–10 mm | After machining |
Defect Analysis and Countermeasures
| Defect | Cause | Countermeasure |
|---|---|---|
| Cracking in overlay | High carbon equivalent, rapid cooling | Increase preheat, use low-hydrogen electrode |
| Cracking at interface | Thermal mismatch, high residual stress | Stress relief annealing at 550–600 °C |
| Excessive retained austenite | Slow cooling, excessive Co | Control cooling rate, adjust Co content |
| Insufficient hardness | Excessive dilution, incomplete melting | Optimize welding parameters, ensure full penetration |
| Spalling | Brittle overlay, poor toughness | Balance carbide content, ensure adequate retained austenite |
Study Insights and Reflections
This paper demonstrates the systematic approach to electrode development required for specialized overlay welding applications. The iterative optimization process, involving multiple formulations and property evaluations, reflects the empirical nature of welding consumable development. The final product—a specialized electrode producing an overlay with HRC 64–65 hardness and 8.6 times the wear resistance of the base steel—represents a significant technical achievement.
The microstructural analysis is particularly valuable. The identification of the martensite + carbide + retained austenite microstructure and the understanding of how each constituent contributes to the overall performance provides a metallurgical basis for the electrode design. The retained austenite, in particular, plays a dual role: it provides toughness through its low hardness and its capacity to transform to martensite under impact loading, and it provides work hardening capacity that increases local hardness under abrasive sliding.
The industrial test results, demonstrating a 7-fold increase in crusher service life, provide compelling evidence of the economic value of the developed electrode. In a coal preparation plant with multiple roll crushers operating continuously, the reduction in tooth replacement frequency translates directly to reduced maintenance costs and improved plant availability.
From a broader perspective, this work exemplifies the importance of application-specific consumable development in welding engineering. Generic overlay welding electrodes may not provide optimal performance for every application, and the development of specialized electrodes can deliver significant performance improvements. The systematic approach to development—starting with the service requirements, selecting the alloy system, optimizing the composition, verifying the microstructure, and validating the performance—provides a template for similar development efforts in other industrial applications.
The paper also highlights the importance of the interface between the electrode composition and the welding process parameters. The same electrode composition can produce different microstructures and properties depending on the welding parameters used. The recommended process parameters are therefore an integral part of the electrode development, not merely an afterthought.
In summary, this paper represents a successful example of application-driven welding consumable development, combining metallurgical understanding with practical process optimization to deliver a product that significantly improves the performance and economics of roll crusher operation in coal preparation and mineral processing.