A New Cladding Process for Continuous Casting Rolls

Literature Overview and Process Description

Continuous casting rolls are critical components in steel and aluminum production, subjected to extreme thermal cycling, mechanical abrasion, and chemical attack from molten metal and slag. Traditional repair and cladding methods often result in excessive downtime, poor metallurgical bonding, or overlay layers that spall prematurely under thermal shock. This study introduces an innovative cladding process for continuous casting rolls that combines hot-wire gas tungsten arc welding (HWTIG) with controlled interpass temperature management and a specialized consumable alloy composition to achieve superior thermal fatigue resistance and extended service life.

The new process addresses three fundamental challenges: achieving strong metallurgical bonding to the hardened roll substrate, minimizing dilution from the base metal into the overlay, and ensuring uniform overlay quality on the cylindrical roll surface. The process utilizes a proprietary wire electrode with enhanced chromium and niobium content, applied through a multi-pass HWTIG technique with interpass temperature maintained between 200°C and 300°C.

Process Parameters and Technical Advantages

The following table presents the key process parameters of the new cladding technique compared with conventional SAW and oxy-fuel overlay methods.

The HWTIG process achieves higher deposition rates than conventional TIG while maintaining lower heat input than SAW, resulting in a more favorable balance between productivity and metallurgical quality.

Metallurgical Analysis and Microstructure Evolution

Metallographic examination of the overlay/base metal interface reveals a well-bonded, crack-free transition zone with minimal dilution. The microstructure of the overlay layer consists of fine dendritic primary Cr23C6 carbides embedded in an austenitic matrix with retained delta ferrite (3-8%), providing excellent thermal fatigue resistance and wear resistance simultaneously.

The controlled interpass temperature of 200-300°C is critical to the process success. This temperature range promotes:

• Controlled grain growth at the weld interface without excessive coarsening
• Adequate plastic deformation of previously deposited layers to relieve residual stresses
• Prevention of hydrogen-induced cracking in the heat-affected zone of the hardened roll substrate
• Formation of a fine-grained heat-affected zone (HAZ) with minimal softening

The dilution rate of 5-12% is significantly lower than conventional methods, ensuring that the overlay composition remains within the designed thermodynamic window for optimal thermal fatigue performance. The niobium addition in the consumable wire promotes the formation of NbC carbides that pin grain boundaries and inhibit intergranular crack propagation during thermal cycling.

Engineering Practice and Implementation Considerations

For successful implementation of this process in industrial settings, several factors must be addressed:

• Roll surface preparation requires grinding to a roughness of Ra 12-20 μm followed by ultrasonic cleaning to remove contaminants and ensure reliable arc initiation.
• The roll should be preheated uniformly to 250-350°C using induction heating to reduce thermal gradients and minimize the risk of HAZ cracking in the hardened substrate.
• Wire feed speed should be synchronized with travel speed to maintain consistent bead profile; a wire-to-travel ratio of 1:1.2 to 1:1.5 provides optimal penetration and bead geometry.
• Argon shielding gas flow rate should be maintained at 15-20 L/min with a trailing shield to prevent oxidation of the hot overlay surface.
• Post-weld machining should be performed at a controlled depth of 0.5-1.0 mm per pass to achieve the required surface finish for casting applications.

Study Insights and Reflections

This new cladding process represents a significant advancement in continuous casting roll repair technology. The combination of HWTIG deposition with controlled interpass temperature management addresses the fundamental trade-off between productivity and metallurgical quality that has long plagued roll cladding operations. The reduced dilution rate achieved through the lower heat input of HWTIG is particularly significant, as it ensures that the overlay composition remains effective throughout the full thickness of the deposited layer.

The thermal fatigue life improvement of approximately 150-300% compared to conventional methods translates directly into extended roll service intervals and reduced production downtime. For a typical continuous caster producing 200,000 tons per year, even a modest extension of roll life from 30,000 to 50,000 thermal cycles represents substantial economic benefit.

The study also highlights the importance of consumable alloy design in cladding applications. The specific Cr-Nb combination in the proprietary wire electrode demonstrates that targeted microalloy additions can dramatically improve overlay performance without requiring exotic base materials. This approach offers a practical pathway for optimizing cladding performance through consumable engineering rather than process complexity alone.

The key lesson for engineers is that process innovation in cladding technology often comes from optimizing multiple parameters simultaneously rather than improving any single variable. The success of this new process depends on the synergistic interaction between wire composition, heat input, interpass temperature, and surface preparation, and achieving optimal results requires careful control of all these factors in concert.