CLADDING TECHNOLOGY SHANXI CO., LTDWeld Overlay Repair of Slab Continuous Casting Machine Roll
Literature Overview
The study by Shan Lianying, published in 1998 in the journal "China Metallurgy," addresses the practical application of weld overlay technology for repairing rolls used in slab continuous casting machines at Anyang Iron and Steel (Group) Company Sanbo Company. Slab continuous casting machines are critical components in modern steel production, and the rolls that guide and support the solidifying slab operate under extreme conditions involving high temperatures, mechanical loads, and thermal cycling. The frequent failure of these rolls due to surface damage, cracking, and wear has been a persistent challenge for steel mills seeking to maximize production efficiency and minimize downtime.
Core Technical Content
The author investigated a systematic approach to repairing damaged slab casting machine rolls using weld overlay technology. The rolls in question were typically made of medium-carbon steel or low-alloy steel, with surface damage ranging from minor wear and scratches to deeper cracks and spalling. The repair process involved the removal of the damaged surface layer, surface preparation, and multi-pass weld overlay using appropriate consumables to restore the roll to serviceable condition.
The key technical challenges addressed in this study included:
- Managing the thermal stresses generated during welding on a cylindrical component with a relatively thin wall
- Selecting appropriate welding consumables that provide adequate wear resistance and thermal stability
- Controlling the residual stress distribution to prevent cracking during cooling
- Ensuring dimensional accuracy and surface finish suitable for casting machine operation
Process Parameters and Technical Approach
| Parameter | Value | Rationale |
|---|---|---|
| Base material | 45 steel or 50Mn | Typical roll material for casting machines |
| Preheating temperature | 200–300 °C | Reduce thermal gradient and prevent cracking |
| Overlay consumable | High-carbon cast iron or modified austenitic stainless steel | Provide wear resistance and thermal stability |
| Overlay thickness | 5–10 mm | Balance wear life and cost |
| Number of passes | 2–3 | Ensure complete fusion and uniform microstructure |
| Welding process | Submerged arc welding (SAW) or gas metal arc welding (GMAW) | High deposition rate and good fusion |
| Post-weld treatment | Stress relief at 550–650 °C for 2–4 hours | Reduce residual stresses |
| Surface finish | Grinding to Ra 1.6–3.2 μm | Meet casting machine requirements |
Defect Analysis and Quality Control
The study identified several common defects encountered during the repair process and proposed countermeasures:
- Surface cracking: Caused by high carbon equivalent and hydrogen embrittlement. Countermeasures included preheating, low-hydrogen consumables, and post-weld stress relief.
- Undercut: Resulting from excessive welding current or speed. Controlled by optimizing the welding parameters and using proper travel techniques.
- Porosity: Due to inadequate shielding or surface contamination. Prevented by thorough surface preparation and increased shielding gas flow.
- Dimensional deviation: Caused by thermal distortion during welding. Minimized by using multi-pass welding with balanced heat input and post-weld machining.
Service Performance and Economic Analysis
The repaired rolls demonstrated satisfactory service performance in the casting machine, with the following results:
- Service life: 60 to 80 percent of new rolls, depending on the severity of the original damage
- Repair cost: 10,000 to 20,000 RMB per roll, compared to 60,000 to 100,000 RMB for new rolls
- Repair time: 8 to 16 hours, compared to 3 to 6 weeks for new roll manufacturing and delivery
- Cost savings: 70 to 85 percent reduction in roll replacement costs
The economic analysis clearly demonstrated the viability of weld overlay repair as a cost-effective alternative to roll replacement, particularly for mills with limited capital budgets or those operating in regions where new roll supply is constrained.
Engineering Practice Recommendations
Based on the study findings, the following recommendations were made for the practical implementation of roll repair programs:
- Establish a repair criteria: Define the maximum acceptable damage depth and extent for repair eligibility. Rolls with damage exceeding 20 percent of the wall thickness or with deep cracks extending into the core should be retired rather than repaired.
- Implement a repair tracking system: Maintain records of all repairs performed on each roll, including the date, extent of damage, repair method, and service life after repair. This data can be used to optimize repair schedules and predict roll retirement.
- Train and certify repair personnel: Ensure that all welders performing roll repairs are properly trained and certified in the specific welding processes and consumables used. Regular qualification testing should be conducted to maintain welder competence.
- Standardize the repair process: Develop and document standard operating procedures for roll repair, including preheating, welding parameters, post-weld treatment, and inspection requirements. This ensures consistency and quality across all repairs.
- Conduct regular inspections: Implement a schedule of regular inspections of repaired rolls during service to detect any early signs of failure, such as cracking, spalling, or excessive wear.
Study Reflections
This 1998 study by Shan Lianying represents an important contribution to the practical application of weld overlay repair technology in the Chinese steel industry. The study's focus on economic analysis and practical implementation provides valuable guidance for mills considering the adoption of roll repair programs. The findings on service life and cost savings are particularly relevant for mills operating under financial constraints or those seeking to reduce their environmental footprint by extending the life of existing components. The study also highlights the importance of proper process control and quality assurance in ensuring the reliability of repaired rolls, a point that is often overlooked in practical operations. The work serves as a foundation for subsequent research and development in roll repair technology, and its principles remain applicable to modern casting machine roll repair programs.
Summary of Key Insights Across All Five Studies
The five studies collectively address critical aspects of weld overlay technology, from practical repair applications to advanced microstructural control techniques. The common thread running through all five studies is the importance of understanding and controlling the interaction between the welding process, the resulting microstructure, and the service performance of the overlay layer. Whether the application is roll repair in hot rolling mills, cavitation corrosion resistance improvement, electromagnetic microstructure control, carbon migration management, or casting machine roll repair, the fundamental principles of thermal management, consumable selection, and quality control remain central to achieving reliable and durable results. These studies collectively demonstrate that weld overlay technology is a versatile and cost-effective solution for extending the life of industrial components, provided that the process is carefully designed, executed, and controlled. The continued development and refinement of weld overlay techniques, including emerging approaches such as pulsed magnetic field treatment and TIG surface remelting, promise to further expand the capabilities and applications of this important technology in the years to come.