Overview of Metallurgical Roll Cladding Technology

Literature Background and Scope

The paper authored by Shen Fenggang and Liu Jingfeng from the Welding Research Institute of China Metallurgical Engineering Corporation Building Research Institute was published in China Surface Engineering in 2006. It provides a comprehensive review of the metallurgical roll cladding technology, which is critical for extending the service life of rolls used in hot and cold rolling mills. Metallurgical rolls are subjected to extreme thermal cycling, mechanical loading, and chemical attack from scale, oxide, and lubricants. The cladding layer must provide wear resistance, thermal fatigue resistance, and chemical stability while maintaining adequate bonding strength with the roll substrate.

This review covers the principal cladding processes applicable to roll surfaces, including submerged arc welding (SAW), gas metal arc welding (GMAW), electroslag welding (ESW), plasma transferred arc (PTA) cladding, and laser cladding. Each process is evaluated in terms of dilution rate, deposition rate, residual stress, and metallurgical compatibility with typical roll substrates such as high-carbon chrome steel (e.g., AISI H11, H13) and low-carbon steel cores.

Core Technical Points

Cladding Process Selection Matrix

Material Selection for Cladding Layers

The review highlights that the selection of cladding material is governed by the service environment. For hot strip mills, materials with high thermal fatigue resistance such as CoCr alloy (Stellite 6), NiCrMo alloy, and high-chromium cast iron are preferred. For cold strip mills, where abrasive wear dominates, materials such as high-carbon high-chromium steel (Cr12MoV), tungsten carbide-filled alloys, and martensitic stainless steels are recommended. The dilution effect from the substrate is a critical concern; high dilution can significantly alter the microstructure and reduce the hardness and wear resistance of the as-deposited layer.

Process Parameters and Defect Control

The paper discusses the typical process parameter windows for each method. For GMAW cladding on rolls, a wire diameter of 1.2 mm, current of 180-220 A, voltage of 24-28 V, and travel speed of 8-12 mm/min are typical. The preheating temperature is generally maintained at 200-400 °C for high-carbon steel substrates to reduce residual stress and prevent cracking. Post-weld heat treatment at 600-700 °C for 2-4 hours is recommended to relieve residual stresses and improve the toughness of the cladding layer.

Common defects identified include:

Engineering Practice Insights

In practice, the selection of cladding process for metallurgical rolls must consider not only the metallurgical requirements but also the geometric constraints of the roll. For large-diameter rolls (diameter > 500 mm), electroslag welding and submerged arc welding are preferred due to their high deposition rates. For small-diameter precision rolls (diameter < 200 mm), laser cladding or PTA cladding is more suitable because of the low dilution and precise heat input control.

The dilution effect remains the most challenging issue in roll cladding. For a two-pass GMAW cladding with 1.2 mm wire on a high-carbon steel roll, the dilution in the first pass can reach 40-50%, while the second pass dilution drops to 15-25%. To achieve a final cladding layer with less than 20% dilution, at least three passes are typically required. This multi-pass approach, however, increases the thermal cycle and may cause interpass cracking if not properly controlled.

The paper also discusses the importance of surface preparation. The roll surface must be ground to remove scale, oxide, and decarburized layers. The grinding depth should be at least 1-2 mm to ensure a clean, oxide-free substrate. Failure to adequately prepare the surface can lead to poor bonding and premature delamination during service.

Key Reflections

One of the most valuable contributions of this review is the systematic comparison of cladding processes for different roll geometries and service conditions. The emphasis on dilution control as the primary factor governing cladding quality is well-founded. In engineering practice, the dilution rate must be measured by chemical analysis of the interface region, and the results must be correlated with hardness and wear test data to validate the process selection.

The review also highlights the importance of post-weld heat treatment. Without proper stress relief, the residual stresses in the cladding layer can reach 200-400 MPa, which can cause cracking during subsequent machining or during thermal cycling in service. The recommended stress relief temperature of 600-700 °C must be carefully controlled to avoid tempering the hard carbides in the cladding layer.

Summary

This review provides a solid foundation for understanding the metallurgical roll cladding technology landscape. The systematic evaluation of processes, materials, and process parameters serves as a practical reference for engineers selecting cladding solutions for specific roll applications. The emphasis on dilution control, surface preparation, and post-weld heat treatment reflects the practical challenges that must be addressed in industrial implementation. The insights gained from this review are directly applicable to the design and qualification of cladding processes for metallurgical rolls in hot and cold rolling mills.