Current Status of Continuous Casting Roll Surfacing Technology

Literature Overview

This paper by Yang Zhengyong from Baosteel Equipment Maintenance Company, published in the journal Welding in 2006 (No. 10, pp. 57–59), provides an overview of the current status of surfacing technology for continuous casting rolls in steel enterprises. The paper addresses the importance of continuous casting rolls in steel production, the challenges associated with their wear and repair, and the various surfacing techniques employed to extend roll life and improve production efficiency. While the paper is relatively concise, it captures the state of practice at a critical time in the development of Chinese steel industry capabilities.

Core Technical Points

Role of Continuous Casting Rolls

Continuous casting rolls are critical components in the continuous casting process, where molten steel is cast into semi-finished products (slabs, billets, or blooms) through a series of water-cooled rolls. The rolls are subjected to severe operating conditions:

These conditions result in multiple failure modes including thermal fatigue cracking, abrasive wear, adhesive wear, oxidation, and thermal shock damage. Surfacing is employed to restore worn roll surfaces and to provide enhanced wear and thermal fatigue resistance.

Surfacing Techniques

The paper reviews several surfacing techniques applicable to continuous casting rolls:

1. Submerged arc welding (SAW): High deposition rate, suitable for thick repair layers, requires flux and wire feeding equipment.
2. Shielded metal arc welding (SMAW): Portable, suitable for field repairs, lower deposition rate, higher operator skill dependency.
3. Gas metal arc welding (GMAW): Good deposition rate, versatile, suitable for automated applications.
4. Flux cored arc welding (FCAW): High deposition rate, good mechanical properties, suitable for automated applications.
5. Plasma arc welding (PAW): High energy density, deep penetration, suitable for precise repairs.
6. Thermal spraying: Suitable for surface modification, lower bond strength compared to fusion welding.

Surfacing Materials

The selection of surfacing materials depends on the specific application and failure mode:

• High-carbon chromium steels (e.g., AISI 52100, GCr15): For bearing-type applications requiring high hardness and wear resistance.
• High-manganese steels (e.g., AISI ADI, Hadfield steel): For applications involving impact and abrasion, utilizing the work-hardening capability.
• Nickel-based alloys (e.g., Alloy 625, Alloy 718): For high-temperature applications requiring oxidation and corrosion resistance.
• Cobalt-based alloys (e.g., Stellite 6): For severe wear conditions requiring high hardness and temperature stability.
• Cast iron (e.g., high-chromium iron): For cost-effective applications where high hardness is required.

Quality Considerations

Key quality considerations for continuous casting roll surfacing include:

1. Bond strength: The interface between the surfacing layer and the roll substrate must have adequate bond strength to withstand operating loads.
2. Crack resistance: The surfacing layer must resist thermal fatigue cracking under cyclic thermal loading.
3. Hardness uniformity: Hardness variations within the surfacing layer can lead to uneven wear and premature failure.
4. Surface finish: The surface finish of the surfacing layer affects the quality of the cast product and the roll's contact with the casting.
5. Thermal conductivity: The surfacing layer must maintain adequate thermal conductivity to facilitate heat dissipation from the roll surface.

Engineering Practice Implications

Roll Maintenance Strategy

A comprehensive roll maintenance strategy should include:

1. Regular inspection: Visual and dimensional inspection at planned intervals to detect early signs of wear and damage.
2. Surface profiling: Measurement of roll surface profile to assess wear patterns and determine when repair is required.
3. Surfacing repair: Application of appropriate surfacing material and technique to restore roll surface and provide enhanced protection.
4. Grinding and finishing: Post-surfacing grinding to achieve the required surface finish and dimensional accuracy.
5. Performance monitoring: Tracking of roll life and production metrics to evaluate the effectiveness of the maintenance strategy.

Process Optimization

For optimal surfacing performance on continuous casting rolls, the following process parameters should be optimized:

• Preheat temperature: Adequate preheat is required to reduce thermal gradients and minimize cracking risk, typically 150–300°C depending on the base material and surfacing material.
• Interpass temperature: Controlled interpass temperature prevents excessive cooling between passes and maintains adequate ductility in the deposited metal.
• Welding sequence: The welding sequence should be designed to minimize distortion and residual stress, often using a symmetric pattern for multi-pass repairs.
• Post-weld heat treatment: PWHT may be required to relieve residual stresses and improve the microstructure of the surfacing layer, particularly for thick repair layers.
• Surface preparation: Thorough cleaning and preparation of the repair area is essential for achieving adequate bond strength and minimizing defects.

Defect Analysis and Prevention

Common defects in continuous casting roll surfacing layers include:

• Cracking: Thermal fatigue cracks and solidification cracks can occur due to thermal cycling, high restraint, or inappropriate material selection.
• Spalling: Delamination of the surfacing layer from the substrate due to inadequate bond strength or excessive thermal cycling.
• Uneven wear: Non-uniform wear patterns due to variations in surfacing layer properties or roll alignment.
• Pitting: Localized corrosion or erosion damage at the roll surface.
• Hardness variation: Inconsistent hardness within the surfacing layer due to variations in welding parameters or material composition.

Study Insights and Reflections

This paper, while published in 2006, captures an important period in the development of Chinese steel industry capabilities. The continuous casting process has become the dominant method for steel production, and the reliability and efficiency of casting rolls are critical to production performance. The evolution of surfacing technology for casting rolls has been driven by the need to increase roll life, reduce maintenance costs, and improve the quality of cast products.

One significant trend in the development of casting roll technology is the shift from simple surfacing repair to more sophisticated surface engineering approaches. This includes the use of gradient layers, multi-layer surfacing with tailored properties, and the integration of surface modification techniques such as laser cladding and thermal spraying. These advanced approaches offer improved performance but require more sophisticated equipment and expertise.

Another important consideration is the integration of surfacing technology with overall roll management strategies. Modern steel plants increasingly employ predictive maintenance approaches based on condition monitoring and data analysis, which can optimize the timing and extent of roll repairs. This requires close collaboration between production, maintenance, and metallurgy teams to develop and implement effective strategies.

The paper also highlights the importance of standardization and qualification in surfacing applications. The development of appropriate welding procedure specifications, qualification testing, and quality control procedures is essential to ensure consistent and reliable surfacing performance. Standards such as ASME Section IX, AWS D10.9, and various national standards provide frameworks for procedure qualification and quality control.

In conclusion, the continuous development and refinement of surfacing technology for continuous casting rolls remains a critical area of research and practice in the steel industry. Advances in materials, processes, and monitoring technologies continue to improve roll life and production efficiency, contributing to the overall competitiveness of steel producers.