CLADDING TECHNOLOGY SHANXI CO., LTDDevelopment and Application of Continuous Casting Weld Overlay Clad Rolls at Panzhihua Steel
Literature Overview
The research by Li Dadong, Lin Jiandong, Sun Jingming, Xu Zichao, Li Zaiyou, Liu Weizhong, Yao Chengbao, and Qiu Daorong (1999) documents the development and industrial application of continuous casting weld overlay clad rolls at Panzhihua Steel Group. This study represents a pioneering effort in the application of weld overlay technology to continuous casting equipment, specifically targeting the improvement of roll surface performance in the steelmaking process. The work was conducted collaboratively by the Panzhihua Steel Research Institute, Panzhihua Steel Machinery Manufacturing Company, Panzhihua Steel Titanium Extraction Steelmaking Plant, and Panzhihua Steel Mechanical Management Department, reflecting a comprehensive approach to technology development and industrial implementation.
Core Technical Points
Continuous casting rolls are critical components in steelmaking that are subjected to severe thermal and mechanical loading during the casting process. The roll surface experiences temperatures up to 1200-1500 °C, intense thermal cycling, and contact with molten steel. Traditional chrome-plated or hardfacing rolls suffer from limited service life, frequent replacement, and production downtime. The weld overlay clad roll technology offers a significant improvement by depositing a wear-resistant and thermally stable overlay layer on the roll surface during the continuous casting process itself.
| Parameter | Specification |
|---|---|
| Roll material | 20CrMnTi or similar low-carbon steel |
| Overlay material | Ni-based or Cr-based hardfacing alloy |
| Overlay thickness | 2-5 mm |
| Welding process | Electroslag welding (ESW) or submerged arc welding (SAW) |
| Roll diameter | 300-800 mm (depending on application) |
| Roll length | 1000-3000 mm |
| Service life improvement | 3-5× compared to chrome-plated rolls |
| Thermal stability | Up to 1200 °C |
| Wear resistance | 3-5× improved |
Process Development and Technical Challenges
The development of continuous casting weld overlay clad rolls presented several technical challenges that required innovative solutions:
- Thermal management: The roll core and overlay layer have different thermal expansion coefficients, which can lead to thermal stresses and potential cracking during the casting process. The solution involved careful selection of overlay materials with compatible thermal expansion coefficients and the use of transition layers.
- Bond strength: The bond between the overlay layer and the roll core must withstand the severe mechanical and thermal loading during casting. The study employed electroslag welding (ESW) for thick overlay deposition, which provides excellent penetration and strong bonding.
- Surface quality: The overlay surface must be smooth and uniform to ensure proper contact with the steel slab and to minimize surface defects. The study developed post-weld machining and grinding procedures to achieve the required surface finish.
- Scale-up: The transition from laboratory-scale trials to full-scale industrial production required careful process optimization and quality control.
Metallurgical Analysis and Performance
The metallurgical analysis of the weld overlay clad rolls revealed the following characteristics:
| Zone | Microstructure | Hardness (HV) | Key Elements |
|---|---|---|---|
| Overlay surface | Austenite + carbides | 500-600 | Ni, Cr, Mo |
| Overlay mid-layer | Ferrite + austenite | 350-450 | Ni, Cr, Mo, Fe |
| Transition zone | Mixed structure | 250-350 | Fe, Ni, Cr |
| Roll core | Ferrite + pearlite | 150-200 | Fe, C, Mn, Cr |
The overlay layer composition was optimized to provide a balance between wear resistance, thermal stability, and thermal fatigue resistance. The use of Ni-based alloys (such as Stellite-type) provided excellent performance in high-temperature wear applications, while Cr-based alloys offered better thermal stability at lower cost.
Industrial Application Results
The industrial application of the continuous casting weld overlay clad rolls at Panzhihua Steel demonstrated significant improvements:
| Metric | Chrome-Plated Roll | Weld Overlay Clad Roll | Improvement |
|---|---|---|---|
| Service life (hours) | 200-300 | 800-1200 | 3-4× |
| Replacement frequency | Every 2-3 days | Every 10-14 days | 4-5× reduction |
| Production downtime | High | Low | Significant reduction |
| Surface quality | Good | Excellent | Improved |
| Cost per hour of service | Higher | Lower | 40-50% reduction |
The study reports that the weld overlay clad rolls achieved a service life of 800-1200 hours, compared to 200-300 hours for traditional chrome-plated rolls. This represents a 3-5× improvement in service life, translating to significant cost savings and reduced production downtime.
Quality Control and Inspection
The quality control program for the continuous casting weld overlay clad rolls included:
- Visual inspection: Checking for surface defects, porosity, and uneven overlay.
- Magnetic particle testing (MT): Detecting surface and near-surface cracks.
- Ultrasonic testing (UT): Verifying bond strength and detecting subsurface defects.
- Hardness testing: Measuring the hardness profile across the overlay layer.
- Wear testing: Evaluating wear resistance under simulated casting conditions.
- Thermal cycling test: Verifying thermal fatigue resistance under repeated heating and cooling.
Engineering Practice Integration
The findings of this study have been widely applied in the steel industry for:
- Continuous casting strand guides and rolls
- Rolling mill work rolls
- Hot strip mill backup rolls
- Blast furnace tuyere components
The technology has also been adapted for other severe-wear applications in the mining, cement, and power generation industries. The key to successful implementation is the careful selection of overlay materials, optimization of welding parameters, and establishment of a comprehensive quality control program.
Key Questions and Reflections
A critical question raised by this research is the long-term reliability of the weld overlay clad rolls under extended service conditions. While the initial performance is excellent, the repeated thermal cycling and mechanical loading can lead to progressive degradation of the overlay layer. The study suggests that regular inspection and monitoring of the overlay condition should be incorporated into the maintenance program.
Another important consideration is the environmental impact of the welding process. The use of fluxes and shielding gases in electroslag welding and submerged arc welding can have environmental implications, and the study recommends the use of low-fume fluxes and proper ventilation systems.
Study Insights and Implications
This research represents a significant advancement in the application of weld overlay technology to continuous casting equipment. The findings demonstrate that weld overlay clad rolls offer a substantial improvement in service life, cost-effectiveness, and production reliability compared to traditional chrome-plated rolls. The systematic approach of combining metallurgical analysis, process optimization, and industrial validation provides a robust framework for the development and implementation of advanced roll technologies. Engineers working on roll technology and severe-wear applications should pay close attention to the material selection, process parameters, and quality control aspects highlighted in this study to ensure optimal performance and reliability.