New Overlay Welding Process for Continuous Casting Rolls with Asynchronous Step-Swing-Stride Control

Literature Overview

This technical paper by Zhao Chunyan, Liu Jianwei, Liu Kongfeng, and Xu Kegui from the Harbin Welding Research Institute of the Chinese Academy of Mechanical Science introduces an innovative overlay welding process for continuous casting rolls. Published in the journal Welding (Issue 7, 2010, pages 61-63), the paper describes a new step-swing-stride overlay welding technique that employs asynchronous programmatic control of roll stepping, wire swinging, and stride movement. This represents a significant advancement over the conventional single-pass spiral overlay welding method that was widely used at the time of publication.

Conventional Process Limitations and the Need for Innovation

Continuous casting rolls are critical components in steelmaking that endure extreme thermal cycling, mechanical abrasion, and chemical erosion from molten steel and slag. The overlay layer on the roll surface must provide excellent wear resistance, thermal shock resistance, and dimensional accuracy. The conventional single-pass spiral overlay welding process, while simple in concept, suffers from several well-known limitations that this research addresses:

• Arc instability due to continuous rotation combined with linear deposition
• Slag inclusion defects from inadequate slag removal between passes
• Uneven surface finish requiring extensive post-weld grinding
• High dilution rates leading to compromised overlay layer properties
• Excessive heat-affected zone (HAZ) width causing base metal property degradation
• High residual stress concentrations requiring stress relief heat treatment

New Process Description and Technical Principles

The new process introduces asynchronous programmatic control of three independent motion axes:

The key innovation lies in the asynchronous control of these three motions. Unlike the conventional spiral method where all motions are coupled through a single continuous rotation, the new process decouples these motions and controls them independently through programmable logic. This allows precise optimization of the arc length, wire feed rate, and travel speed at any point during the welding process.

The process achieves several technical advantages over the conventional method:

1. Arc stability: The step-swing-stride control maintains a more consistent arc length and gas shielding coverage, resulting in a stable arc throughout the welding process.
2. Automatic slag removal: The stride motion between passes allows the slag to cool and fracture naturally, enabling automatic slag removal without manual intervention.
3. No slag inclusion: The improved slag management eliminates slag inclusion defects that were common in the spiral process.
4. Flat surface finish: The controlled overlap between passes produces a smooth, uniform surface that reduces the need for post-weld machining.
5. Reasonable residual stress distribution: The controlled thermal input pattern distributes residual stresses more uniformly across the roll surface.
6. Low dilution rate: The process parameters are optimized to minimize base metal dilution, preserving the beneficial properties of the overlay alloy.
7. Narrow HAZ: Reduced thermal input narrows the heat-affected zone, limiting the extent of base metal property changes.
8. Fewer overlay layers: The improved process efficiency allows the required overlay thickness and properties to be achieved with fewer passes.
9. Energy and material savings: Reduced pass count and improved process efficiency lead to lower energy consumption and material usage.
10. Extended service life: The combination of improved overlay properties, reduced defects, and better stress distribution extends the operational life of the casting roll.

Engineering Practice Considerations

For engineers implementing this process in a production environment, several practical considerations should be addressed:

• Equipment requirements: The process requires a multi-axis programmable welding system capable of independent control of at least three motion axes. This represents a significant capital investment compared to simpler spiral welding setups.
• Process parameter optimization: The asynchronous control parameters must be optimized for each specific roll diameter, overlay alloy, and required deposit thickness. A systematic approach such as the Taguchi method or response surface methodology is recommended for parameter optimization.
• Quality verification: Non-destructive testing (NDT) protocols should include ultrasonic testing (UT) for subsurface defects, magnetic particle testing (MT) for surface and near-surface cracks, and dimensional inspection of the overlay thickness profile.
• Roll preparation: Surface preparation of the roll prior to overlay welding remains critical. Any pre-existing defects, surface contamination, or geometric irregularities must be addressed before welding begins.
• Post-weld treatment: While the new process produces a more favorable residual stress distribution, post-weld stress relief may still be required for critical applications, particularly where dimensional stability is paramount.

Study Insights and Reflections

This paper represents a practical engineering innovation that addresses real production challenges in the steel industry. The concept of asynchronous multi-axis control for overlay welding is not limited to continuous casting rolls; the same principle could be applied to other cylindrical or near-cylindrical components requiring overlay cladding, such as turbine shafts, paper machine rolls, and mining equipment components. The emphasis on reducing dilution and narrowing the HAZ aligns with broader industry trends toward improved metallurgical control in overlay welding applications.

The economic argument for adopting this process is compelling: fewer overlay layers mean shorter welding times, lower consumable costs, and reduced post-weld machining. However, the initial investment in programmable welding equipment must be justified through lifecycle cost analysis, considering factors such as roll service life extension, reduced downtime for roll replacement, and improved product quality from the casting process. For high-volume steel producers with frequent roll replacement cycles, the process improvement is likely to yield a positive return on investment within a reasonable timeframe.