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

Literature Overview

This paper by Sun Dale, Li Xiaobing, Yao Lisong, and Liu Chengmin (2008), published in the Journal of Northeastern University (Natural Science), presents the development of surfacing materials and welding processes for large slab continuous casting rolls. The research was conducted jointly by Northeastern University and Baosteel Research Institute, funded by the National Natural Science Foundation (50674022) and Baosteel's major research project (ZA9815). This work represents a significant industrial application of welding technology in metallurgical equipment, where the continuous casting roll surface must withstand extreme thermal cycling, mechanical loading, and chemical attack from molten steel.

Service Conditions and Failure Modes of Continuous Casting Rolls

Continuous casting rolls operate under uniquely severe conditions that distinguish them from conventional wear applications:

Service Parameter	Typical Value	Impact on Surface
Molten steel temperature	1450-1550°C	Extreme thermal load on roll surface
Thermal cycling frequency	1-5 cycles/hour	Thermal fatigue cracking
Contact pressure	2-5 MPa	Mechanical fatigue and indentation
Cooling water temperature	50-90°C	Thermal shock on water-cooled surface
Slag and scale attack	Continuous	Chemical corrosion and erosion

The primary failure modes identified include:

Thermal fatigue cracking: Repeated heating and cooling causes cyclic tensile and compressive stresses that initiate and propagate surface cracks.
Mechanical wear: Contact with solidifying steel shell and scale causes abrasive and adhesive wear.
Cold cracking: Residual stresses from welding combined with low-temperature conditions can cause delayed cracking in high-strength surfacing layers.
Scale adhesion and spalling: Scale formation on the roll surface can create stress concentrations and lead to surface spalling.

Surfacing Material Development

The research builds upon the well-established 1Cr13NiMo surfacing material system, which provides a good base of hardness, thermal stability, and cold cracking resistance. The key innovation involves the addition of functional alloying elements to further enhance performance:

Element	Function	Effect on Properties
1Cr13NiMo (base)	Base alloy system	Good cold cracking resistance, moderate hardness
Additional functional elements	Enhanced thermal fatigue resistance	Improved thermal shock performance
Optimized composition	Refined microstructure	Better strength-toughness balance

The developed surfacing welding strip and matching sintered flux represent a complete process package designed for submerged arc surfacing of continuous casting rolls. The matching flux composition is critical for controlling solidification behavior, deoxidation, and slag properties to achieve the desired microstructure in the deposited metal.

Process Parameter Optimization

Two critical process parameters were systematically investigated:

Interpass Temperature

The interpass temperature during multi-pass surfacing directly affects:

Low interpass temperature (<150°C): Promotes finer grain structure and higher hardness but increases residual stress and cold cracking risk.
Optimal interpass temperature: Balances microstructure refinement with stress relief through controlled reheating of previous passes.
High interpass temperature (>300°C): Reduces residual stress but coarsens microstructure and may reduce hardness below required levels.

Post-Weld Heat Treatment Temperature

The post-weld heat treatment serves to:

Relieve residual stresses that could cause delayed cracking or dimensional instability.
Temper the martensitic structure to optimize the strength-toughness balance.
Refine precipitate distribution for improved thermal fatigue resistance.

The study demonstrates that a reasonable combination of interpass temperature and post-weld heat treatment temperature yields the optimal microstructure and mechanical properties, with the new surfacing material exhibiting significantly improved thermal and cold fatigue performance compared to imported materials.

Performance Comparison and Engineering Validation

The developed surfacing material demonstrates clear advantages over imported alternatives:

Performance Criterion	New Material	Imported Material	Improvement
Microstructure	Optimized martensite + precipitates	Standard martensite	Finer, more uniform
Strength	Higher yield strength	Baseline	Improved
Thermal fatigue life	Extended	Baseline	Significantly improved
Cold fatigue resistance	Enhanced	Baseline	Improved
Overall roll life	Superior	Baseline	Extended service interval

The validation through actual continuous casting operation demonstrates that the new surfacing material achieves longer roll life than equivalent imported products, providing significant economic benefits through reduced replacement frequency and improved production continuity.

Engineering Practice Integration

For practical implementation in steel mill operations, the following considerations are essential:

Surface preparation: The roll surface must be thoroughly cleaned and ground before surfacing to ensure proper bonding and prevent contamination.
Multi-pass strategy: Typically 2-4 passes are applied to achieve the required surfacing thickness (usually 3-8 mm), with interpass temperature monitoring at each pass.
Welding sequence: A systematic welding sequence should be employed to minimize distortion and residual stress, typically using a balanced back-and-forth pattern.
Post-weld inspection: NDT examination (MT or PT) of the surfacing layer is recommended to detect surface cracks or lack of fusion before returning the roll to service.
Condition monitoring: During operation, regular inspection of the surfacing layer condition allows prediction of remaining service life and planned replacement scheduling.

Study Insights and Reflections

This work exemplifies the successful integration of fundamental materials research with industrial application requirements. The collaboration between an academic institution (Northeastern University) and an industrial research organization (Baosteel Research Institute) enabled the development of a surfacing solution that directly addresses the specific failure modes encountered in continuous casting operations.

The approach of building upon the proven 1Cr13NiMo base system while adding targeted functional elements represents a pragmatic engineering philosophy—incremental improvement of a known-good system rather than radical redesign. This approach minimizes qualification risk while achieving measurable performance gains.

The emphasis on both thermal fatigue and cold fatigue performance is particularly noteworthy, as these are the primary life-limiting factors for continuous casting roll surfacing layers. Many surfacing materials achieve high hardness but fail prematurely due to thermal fatigue cracking, and this work directly addresses that limitation through microstructural optimization and process parameter control.

For the broader welding engineering community, this study demonstrates the importance of understanding the complete service environment—not just the primary wear mechanism—when developing surfacing solutions for critical industrial equipment. The continuous casting roll application requires simultaneous resistance to thermal cycling, mechanical loading, chemical attack, and cold cracking, and only a holistic approach to material and process design can address all these requirements simultaneously.

The successful demonstration of superior performance compared to imported materials also highlights the growing capability of domestic Chinese welding technology to compete at the highest levels of industrial application, reducing dependence on foreign materials for critical metallurgical equipment components.