Band Electrode Overlay Repair of Continuous Casting Guide Rollers

Literature Overview

This paper by Zhang Xiangfu, published in Welding Technology (2007, Vol. 36, No. 2, pp. 71-72), presents a practical engineering solution for the repair of worn continuous casting guide rollers using band electrode overlay welding technology. The paper analyzes the working environment and failure mechanisms of guide rollers, then describes the development and application of a repair methodology using 0Cr13NiMoN overlay metal with carbon-nitrogen strengthening technology.

Core Technical Content

Continuous casting guide rollers operate in extremely demanding conditions. They must withstand:

Mechanical loading: Contact pressure from the molten or semi-solid steel billet, typically 10-30 MPa depending on the caster design and steel grade.
Thermal cycling: Temperature gradients from ambient to 1000°C+ at the contact surface, with rapid cooling between passes.
Abrasive wear: Contact with scale, oxide inclusions, and refractory particles.
Erosive wear: Impact from scale fragments and water spray impingement.
Thermal fatigue: Repeated heating and cooling cycles causing surface cracking.

Failure Mechanisms of Guide Rollers

Failure Mode	Mechanism	Typical Location
Abrasive wear	Sliding contact with scale and oxide	Roller surface
Erosive wear	Particle impact from water spray and scale	Roller surface near water entry
Thermal fatigue	Cyclic thermal stress causing surface cracking	Roller surface
Spalling	Accumulated thermal fatigue leading to material loss	Roller surface
Bearing damage	Misalignment and overloading	Roller bearing seats
Base metal cracking	Thermal fatigue and stress concentration	Roller core

Repair Technology and Process

The repair methodology described in the paper employs several innovative techniques:

Band Electrode Longitudinal Overlay Welding

Band electrode (strip electrode) welding provides several advantages over traditional stick electrode welding for roller repair:

High deposition rate: Band electrodes deposit material at rates 3-5 times higher than equivalent stick electrodes, reducing repair time significantly.
Consistent weld geometry: The uniform cross-section of band electrodes produces consistent weld bead profiles, which is critical for maintaining roller surface geometry.
Reduced dilution: The controlled heat input and shielding of band electrode welding minimize base metal dilution, ensuring the overlay properties are maintained.
Lower hydrogen content: The shielding gas protection reduces hydrogen pickup, minimizing the risk of hydrogen-induced cracking.

Edge Overlap Welding Method

The edge overlap technique is used to ensure complete coverage and avoid edge defects. By overlapping each subsequent pass by a specified amount (typically 30-50% of the bead width), the following benefits are achieved:

Complete coverage without gaps or undercut at bead boundaries
Uniform weld metal composition across the surface
Improved surface finish and geometry accuracy
Reduced risk of lack of fusion between adjacent beads

Carbon-Nitrogen Strengthening Technology

The auxiliary carbon-nitrogen strengthening technology involves adding carbon and nitrogen to the weld pool to form fine nitride and carbide precipitates. This technique:

Increases surface hardness beyond what the base alloy composition alone would achieve
Forms fine, dispersed strengthening phases (such as CrN, Cr2N, and various carbides)
Improves wear resistance without significantly reducing toughness
Allows the use of a moderately alloyed base composition that is less prone to cracking

Overlay Material: 0Cr13NiMoN

Property	Typical Value
Composition (wt%)	C: 0.05-0.15, Cr: 12-14, Ni: 1.5-2.5, Mo: 0.8-1.2, N: 0.15-0.30
Hardness (as-welded)	35-45 HRC
Hardness (after C-N strengthening)	45-55 HRC
Microstructure	Martensite with fine nitride/carbide precipitates
Dilution tolerance	Moderate (maintains properties at 10-20% dilution)

Engineering Practice Integration

The repair procedure should follow a systematic approach:

Surface preparation: Remove worn material by grinding to expose sound base metal. Ensure adequate root preparation for the first overlay pass.
Preheating: Apply moderate preheat (150-250°C) to reduce thermal stress and minimize the risk of cold cracking in the base metal.
Overlay welding: Apply the band electrode overlay in multiple passes, maintaining consistent travel speed, torch angle, and overlap.
Post-weld treatment: Depending on the required properties, apply stress relief or tempering treatment.
Surface finishing: Grind or polish the surface to restore the original roller geometry and surface finish.
Inspection: Perform visual inspection, dimensional verification, and hardness testing to confirm repair quality.

Key Questions and Reflections

The paper demonstrates the practical value of combining multiple welding technologies to achieve a superior repair outcome. The integration of band electrode welding for efficiency, edge overlap for quality, and carbon-nitrogen strengthening for enhanced properties represents a sophisticated approach to overlay repair. However, several questions remain for further investigation:

What is the long-term field performance of the repaired rollers compared to new rollers?
How does the repair affect the thermal fatigue resistance of the roller surface?
What are the economic benefits in terms of cost reduction and downtime minimization?

Study Insights and Implications

This paper provides a practical, field-proven methodology for extending the service life of continuous casting guide rollers. The approach is particularly valuable in steel mills where continuous casting operations run 24/7 and any unplanned downtime is extremely costly. The use of band electrode welding technology significantly reduces repair time compared to conventional methods, while the carbon-nitrogen strengthening technology provides enhanced wear resistance that may match or exceed the original roller performance. This study exemplifies how welding technology innovation can directly contribute to improved industrial productivity and reduced maintenance costs.