Development of Surfacing Materials and Processes for Long-Life Continuous Casting Rolls

Literature Overview and Research Significance

This study by Sun Dale, Li Xiaobing, Yao Lisong, and Liu Chengmin, conducted at Northeastern University and Baosteel Research Institute, was supported by the National Natural Science Foundation of China (Grant No. 50674022) and a major Baosteel research project (ZA9815). Published in the Journal of Northeastern University (Natural Science Edition) in 2008, this research addresses a critical industrial challenge: extending the service life of continuous casting (CC) rolls through advanced surfacing materials and optimized welding processes.

Core Technical Content and Industrial Context

Continuous casting rolls are critical components in steel production, directly contacting molten steel at temperatures exceeding 1400°C while subjected to intense thermal cycling, mechanical loading, and chemical attack from slag and inclusions. The typical service life of uncoated or conventionally coated rolls is limited to 500-1500 heats, with each heat representing the casting of a single strand. The economic impact of frequent roll replacement is substantial, affecting both production costs and throughput.

The research focuses on developing specialized surfacing materials and welding procedures that can withstand the extreme conditions of CC roll service. The primary failure modes include thermal fatigue cracking, spalling, surface wear, and corrosion from slag attack. The surfacing solution must address all these failure mechanisms simultaneously, requiring a carefully designed multi-phase microstructure with appropriate hardness, toughness, and thermal stability.

Surfacing Material Development and Composition Design

The developed surfacing materials incorporate several key design principles: high chromium content (20-30 wt%) for oxidation resistance and hard carbide formation, controlled carbon content (2-4 wt%) for carbide precipitation, and strategic addition of alloying elements (Mo, W, V, Nb) for high-temperature strength and thermal stability. The resulting overlay materials are designed to form a complex microstructure containing M7C3, M23C6, and MX-type carbides in a martensitic or austenitic matrix.

The microstructural design aims to create a gradient of properties from the substrate interface to the surface. Near the interface, the material must have adequate toughness to resist thermal fatigue cracking. At the surface, maximum hardness and wear resistance are required. This gradient is achieved through multi-layer deposition with varying compositions or through controlled solidification of a single alloy with appropriate cooling rates.

Process Development and Welding Procedure Optimization

The surfacing process for CC rolls typically employs submerged arc welding (SAW) or plasma transferred arc welding (PTA), depending on the roll geometry and production requirements. SAW offers high deposition rates suitable for large surface areas, while PTA provides better control over microstructure and lower dilution. The process parameters are carefully optimized to minimize residual stresses, prevent cracking, and achieve uniform overlay thickness.

Preheating to 200-300°C is typically required to reduce thermal gradients and prevent cold cracking. Post-weld heat treatment may be applied to relieve residual stresses and stabilize the microstructure. The interpass temperature is maintained between 150-250°C to prevent excessive thermal cycling that could initiate thermal fatigue cracks.

Performance Evaluation and Industrial Results

The developed surfacing materials and processes have demonstrated significant improvements in CC roll service life. In industrial trials at Baosteel, the enhanced surfacing system extended roll life from 800 heats to 3200 heats, representing a fourfold improvement. The premium alloy system achieved even greater improvement, extending life to 4000-5000 heats in some applications.

The failure analysis of failed rolls revealed that the primary failure mode shifted from surface spalling and thermal cracking to subsurface cracking at the overlay-substrate interface, indicating that the surfacing material itself was performing adequately but the bond quality needed further optimization. This finding guided subsequent research into improving interface bonding through better transition layer design and residual stress management.

Engineering Practice and Implementation Challenges

Implementing advanced surfacing materials and processes in industrial settings requires careful consideration of several practical factors. The consistency of powder or wire composition is critical, as variations in chemistry can lead to inconsistent performance. Process monitoring systems must be in place to ensure parameter control throughout the surfacing operation. Training of welding personnel is essential, as the advanced materials require skilled operators to achieve optimal results.

The economic analysis must consider not only the cost of materials and processing but also the productivity gains from extended roll life. Reduced roll change frequency means less downtime, higher production rates, and improved steel quality due to more stable casting conditions. The total cost of ownership approach typically demonstrates favorable economics for advanced surfacing systems despite higher initial material costs.

Key Reflections and Study Insights

This research represents a successful example of academic-industrial collaboration addressing a real production challenge. The systematic approach to material development, process optimization, and performance evaluation provides a model for similar industrial applications. The findings emphasize that extending component life requires not only superior materials but also careful process control and quality assurance. For the broader metallurgical and welding communities, this work demonstrates the potential of advanced surfacing technologies to significantly improve the economics and efficiency of heavy industrial processes. The continued development of CC roll surfacing technology remains an active research area, with ongoing efforts to push service life beyond 5000 heats through further material and process innovations.