Selection of Cladding Materials and Microstructure Performance of Cladding Layers for Hot Rolling Rolls

Literature Overview

This 2001 study by Hong Yongchang from the School of Metallurgy and Materials, Anhui University of Technology, addresses the critical engineering challenge of selecting appropriate weld overlay materials for hot rolling mill rolls and characterizing the resulting cladding layer microstructure and mechanical properties. Hot rolling rolls operate under extreme conditions—high temperatures exceeding 900 °C, severe mechanical contact stress from the workpiece, thermal cycling, and abrasive wear from iron scale and oxide inclusions. The cladding layer serves as the functional interface that determines roll life, surface quality of the rolled product, and overall production efficiency. The research was published in the Journal of Anhui University of Technology (Natural Science Edition) and represents early systematic work in the Chinese metallurgical research community on roll cladding technology.

Core Technical Content and Material Selection Criteria

The fundamental requirement for hot rolling roll cladding materials is a balance between hardness, thermal stability, abrasion resistance, and resistance to thermal cracking during the rolling process. The study examines several material systems commonly employed in the industry at that time.

The study emphasizes that material selection must be driven by the specific rolling application—hot slabbing, hot strip, hot wire, or rebar rolling each impose different thermal and mechanical demands. For slabbing mills where impact loads dominate, toughness and thermal shock resistance take precedence over hardness. For finishing mills where surface finish of the product is critical, thermal fatigue resistance and dimensional stability become the governing criteria.

Microstructure Analysis and Performance Characteristics

The cladding layer microstructure is governed by the solidification behavior during the welding process and the subsequent cooling conditions. The study examines several key microstructural features that directly influence service performance.

Solidification Microstructure

The solidification structure of the cladding layer typically consists of columnar dendrites growing from the fusion boundary. In high-carbon and high-alloy systems, the interdendritic regions are enriched in alloying elements and carbon, leading to the formation of:

• Ledeburite (Fe3C + austenite) decomposing into pearlite and cementite upon cooling
• Complex carbides including M7C3, M23C6, M6C, and MC-type carbides
• Retained austenite in high-alloy systems, which provides toughness but may transform upon heating during service

Phase Transformation and Heat Treatment Effects

The cooling rate after cladding significantly influences the microstructure. Rapid cooling produces martensite and bainite, while slower cooling allows pearlitic or ferritic transformations. The study highlights that the thermal cycling inherent in rolling service causes repeated austenitization and transformation of the cladding layer, which can lead to:

• Grain coarsening at elevated temperatures
• Carbide coarsening and spheroidization
• Tempering of martensite reducing hardness
• Possible phase transformations in metastable systems

Mechanical Properties and Wear Behavior

Hardness retention at elevated temperatures is the single most important property for hot roll cladding. The study reports typical hardness retention characteristics at 600 °C and 800 °C for different material systems. High-speed steel and carbide-containing alloys maintain 70-85% of room-temperature hardness at 600 °C, while high-carbon steels drop to 50-60% and austenitic stainless steels remain relatively stable but at lower absolute hardness levels.

Engineering Practice Implications

From a practical standpoint, this research underscores several critical points for engineers involved in roll cladding programs. First, the selection of cladding material must be matched to the specific rolling mill application rather than applied generically. Second, the welding process parameters—particularly heat input and cooling rate—must be controlled to achieve the desired microstructure in the cladding layer. Third, post-weld heat treatment may be necessary to optimize the balance between hardness and toughness.

The study also highlights the importance of understanding the interaction between the cladding layer and the roll body material. A proper metallurgical bond requires compatibility between the two materials, and the transition zone must be free of cracks, porosity, and excessive dilution. In practice, this means that the preheating temperature, interpass temperature, and cooling rate must be carefully controlled based on the specific material combination.

Key Reflections and Study Insights

Reviewing this work more than two decades later, several observations emerge. The fundamental principles of material selection remain valid—hardness, thermal stability, and toughness must be balanced according to application requirements. However, contemporary practices have evolved significantly in terms of available materials, welding processes, and quality control methods. The emergence of advanced consumables with tailored microstructures, hot-wire TIG cladding for precise control of dilution and microstructure, and laser cladding for localized repair have expanded the engineering options considerably.

The study's emphasis on microstructure-property relationships remains foundational. Understanding how solidification conditions, cooling rates, and thermal cycling affect the cladding layer microstructure is essential for predicting service life and identifying failure mechanisms. In modern practice, techniques such as differential scanning calorimetry, dilatometry, and high-temperature hardness testing provide more detailed characterization than was available in 2001, but the underlying metallurgical principles described in this work continue to guide material selection and process development.

One area where this research is particularly relevant today is in the context of sustainability and roll life extension. As steel mills seek to reduce energy consumption and improve productivity, maximizing roll life through optimized cladding programs becomes increasingly important. The systematic approach to material selection and microstructure control advocated in this study provides a sound foundation for modern cladding engineering programs.

In conclusion, this study by Hong Yongchang represents an important contribution to the understanding of hot rolling roll cladding technology, establishing fundamental principles for material selection, microstructure control, and performance optimization that remain relevant in contemporary engineering practice. The systematic approach to correlating cladding material chemistry, processing conditions, microstructure, and service performance provides a valuable framework for engineers developing and optimizing roll cladding programs in modern steel mills.