CLADDING TECHNOLOGY SHANXI CO., LTDStudy Note on Research and Development of Wear-Resistant Overlay Welding Electrodes for Hot Rolling Rolls
Literature Overview
The paper by Ying Pengzhan, Ge Changlu, and Cai Yingjun from China University of Mining and Technology, published in 1997 in the journal "Hot Working Technology," presents research on the development of specialized overlay welding electrodes for hot rolling mill rolls. Hot rolling mills represent one of the most demanding industrial applications for wear-resistant overlay welding, where roll surfaces are subjected to extreme temperatures, mechanical contact stresses, and abrasive wear from hot steel strips.
Service Environment and Wear Mechanisms
Hot rolling rolls operate under uniquely harsh conditions that create complex, multi-mechanism wear:
| Wear Mechanism | Dominant Condition | Typical Contribution |
|---|---|---|
| Abrasive wear | Hard scale and inclusions in steel strip | 40-60% |
| Oxidative wear | High temperature oxidation at 800-1200°C | 20-30% |
| Adhesive wear | Metal-to-metal contact at strip-roll interface | 10-20% |
| Fatigue wear | Cyclic contact stress from rolling | 5-15% |
| Thermal fatigue | Repeated heating and cooling cycles | 5-10% |
The operating environment presents several critical challenges:
- Roll surface temperature reaching 800-1200°C during hot rolling operations
- Contact pressures of 1500-2500 MPa between roll and strip
- Continuous exposure to iron oxide scale and rolling mill scales
- Thermal cycling between operating temperature and water cooling
- Chemical interaction between roll surface and hot steel strip
Electrode Design Philosophy
The research approach to developing overlay electrodes for hot rolling rolls requires a fundamentally different philosophy compared to cold wear applications. The electrode composition must balance:
- High-temperature hardness retention: The overlay must maintain adequate hardness at 600-900°C, requiring materials with strong temperature-hardness retention characteristics.
- Oxidation resistance: Formation of a protective oxide layer at elevated temperatures is essential for long-term service.
- Thermal shock resistance: The overlay must withstand rapid temperature changes without cracking or spalling.
- Anti-adhesion properties: The overlay surface must resist bonding with hot steel strip to prevent material transfer and surface degradation.
Composition Development and Optimization
Based on the research findings, the following composition strategies were evaluated:
Option A: High-Chromium Martensitic System
- Chromium: 12-18 wt% for oxidation resistance and martensite formation
- Carbon: 0.8-1.2 wt% for carbide precipitation strengthening
- Molybdenum: 3-5 wt% for high-temperature strength and carbide stability
- Vanadium: 1-2 wt% for fine carbide dispersion
- Expected hardness: 50-55 HRC at room temperature, 40-45 HRC at 800°C
Option B: High-Nickel Austenitic System
- Nickel: 10-15 wt% for austenite stabilization
- Chromium: 8-12 wt% for oxidation resistance
- Carbon: 0.3-0.6 wt% for carbide precipitation
- Manganese: 4-6 wt% for austenite formation
- Expected hardness: 35-42 HRC at room temperature, good thermal shock resistance
Option C: Boron-Reinforced System
- Iron-boron base with controlled boride formation
- Chromium: 10-15 wt% for oxidation resistance
- Carbon: 1.5-2.5 wt% for additional carbide formation
- Boron: 0.5-1.0 wt% for boride phase formation
- Expected hardness: 55-60 HRC at room temperature, moderate high-temperature performance
Process Parameters for Hot Rolling Roll Overlay
The welding procedure for hot rolling roll overlay application requires careful control:
| Parameter | Specification | Rationale |
|---|---|---|
| Preheat temperature | 300-400°C | Reduce thermal gradient, prevent cracking |
| Welding current | 220-300 A (SMAW) | Adequate penetration without excessive dilution |
| Travel speed | 40-60 mm/min | Controlled heat input for desired microstructure |
| Electrode angle | 15-25° from vertical | Optimize arc force and bead profile |
| Pass thickness | 3-5 mm per pass | Maintain adequate fusion without excessive cooling |
| Total overlay thickness | 8-15 mm | Balance protection depth with cost |
| Interpass temperature | 300-400°C | Maintain thermal continuity |
Performance Evaluation Results
The developed electrodes demonstrated the following performance in laboratory and field testing:
| Performance Indicator | Developed Electrode | Conventional Electrode | Improvement |
|---|---|---|---|
| Room temperature hardness | 52-58 HRC | 38-45 HRC | 40-60% |
| 800°C hardness | 40-45 HRC | 25-30 HRC | 50-65% |
| Abrasive wear rate | 0.03-0.05 mm³/N·m | 0.12-0.18 mm³/N·m | 60-75% reduction |
| Thermal fatigue cycles | 5000+ | 1500-2000 | 2.5-3x improvement |
| Service life extension | 3-5x | Baseline | Significant |
| Crack resistance | Crack-free | Some cracking | Superior |
Engineering Implementation Considerations
For successful field implementation of hot rolling roll overlay welding, the following considerations are essential:
- Roll preparation: The roll surface must be thoroughly cleaned and prepared to ensure proper fusion. Any existing oxide scale, rust, or contamination must be removed by grinding or shot blasting.
- Thermal management: Due to the large mass of hot rolling rolls, preheating and interpass temperature control require significant energy input. Induction heating or oxy-fuel preheating is typically employed.
- Dilution control: The large thermal mass of the roll creates significant dilution in the first pass. Multi-pass welding with composition-optimized first-pass electrodes is recommended.
- Post-weld treatment: Stress relief at 600-650°C for 2-4 hours is recommended to reduce residual stresses that could cause overlay cracking during thermal cycling in service.
- Inspection requirements: Visual inspection, magnetic particle inspection (MT), and ultrasonic testing (UT) should be performed to ensure overlay quality and detect any defects before returning the roll to service.
Study Insights and Practical Implications
This 1997 research by Ying Pengzhan and colleagues represents important work in the development of specialized welding consumables for the steel industry. The systematic approach to understanding wear mechanisms, composition optimization, and process parameter development established a methodology that remains relevant for contemporary hot rolling roll maintenance. The emphasis on high-temperature properties rather than room temperature hardness reflects a mature understanding of the actual service conditions. For today's engineers, this work provides valuable guidance on approaching overlay welding for hot work applications, where the selection criteria differ significantly from cold wear applications. The research also highlights the importance of considering the entire lifecycle of the component, from welding procedure development through field application and performance monitoring, in the development of successful overlay welding solutions for critical industrial equipment.