Research on Wear-Resistant Cladding Electrodes for Hot Rolling Rolls

Literature Overview

The 1997 study by Ying Pengzhan, Ge Changlu, and Cai Yingjun from China University of Mining and Technology represents an early but significant contribution to the field of hot rolling roll hardfacing. Published in the journal Hot Working Technology, this research addresses the critical challenge of roll surface degradation in continuous hot strip and bar mills, where rolls are subjected to extreme thermal cycling, mechanical abrasion, and chemical attack from scale and lubricants. The authors developed a series of specialized cladding electrodes designed specifically for the demanding service conditions of hot rolling applications, representing a systematic approach to extending roll life through metallurgical optimization.

Core Technical Approach

The research adopted a multi-parameter optimization methodology to develop electrodes suitable for hot rolling roll restoration and hardfacing. The key design philosophy centered on achieving a composite microstructure that balances hardness, toughness, and thermal stability — three properties that are often in direct conflict in hardfacing alloys.

The electrode compositions were developed around several fundamental alloying strategies:

• High-carbon martensitic systems: Based on Cr12-type or Cr13-type steels with carbon content ranging from 1.8% to 3.5%, producing primary carbides (M₇C₃ or M₃C) in a tempered martensitic matrix.
• High-chromium cast iron systems: With 25–35% Cr content, forming extensive M₇C₃ carbide networks that provide exceptional abrasive wear resistance.
• Nickel-based systems: Ni-Cr-B-Si type alloys offering thermal stability above 500°C, suitable for the hottest zones of the roll barrel.

Key Technical Parameters

Microstructural Analysis and Dilution Control

The authors emphasized that dilution from the base steel substrate is the single most critical factor governing the final overlay properties. In hot rolling roll applications, the base material is typically a forged alloy steel (e.g., 4Cr5MoSiV or 30CrNiMo7) with hardness around 250–300 HV. Excessive dilution reduces the overlay hardness by 100–200 HV, directly compromising wear life.

The study identified several strategies to minimize dilution:

1. Flux composition optimization: Using fluxes with high SiO₂ and Al₂O₃ content to promote slag coverage and reduce base metal involvement.
2. Electrode core design: Incorporating alloy powders or chips directly into the electrode core to compensate for dilution losses.
3. Multi-pass welding sequences: Applying the first pass with lower current to establish a thin, low-dilution layer, followed by subsequent passes with higher current for productivity.

The microstructural evolution in the overlay layer was characterized by the presence of:

• Primary M₇C₃ carbides (Cr₇C₃) appearing as elongated plates or vermicular networks
• Secondary M₂₃C₆ carbides precipitating from the martensitic matrix during cooling
• Retained austenite (up to 15–25%) stabilized by high carbon and alloy content, which transforms during service thermal cycling

Engineering Practice Implications

From a practical standpoint, this research addresses a real industrial pain point. In a typical 2000 mm wide hot strip mill, roll barrel diameter is approximately 700–800 mm, and the roll surface undergoes continuous scale removal at temperatures between 900–1200°C. The wear mechanism is predominantly abrasive, with oxide scale particles acting as third-body abrasives. The cladding electrode must therefore provide:

• Surface hardness exceeding 550 HV to resist abrasive wear
• Thermal stability maintaining hardness above 500°C
• Sufficient toughness to resist thermal crack initiation and propagation
• Good metallurgical bond strength to the roll core material (typically >30 MPa)

The electrode design philosophy described in this paper aligns with modern practices where hot rolling rolls are periodically reground and recladded. A typical maintenance cycle involves grinding 0.5–1.0 mm off the worn surface, followed by applying 2–3 mm of overlay material in 2–3 passes, then regrounding to the required surface finish (Ra < 1.6 μm).

Study Insights and Reflections

Reading this paper nearly three decades later, one appreciates both its contributions and its limitations. The research was conducted during a period when computational metallurgy and advanced characterization techniques were not widely available, so the optimization relied heavily on empirical approaches and systematic trial-and-error experimentation. Nevertheless, the fundamental metallurgical understanding — the relationship between carbon and chromium content, carbide morphology, and wear resistance — remains valid and continues to inform modern electrode development.

One notable insight is the recognition that the optimal cladding composition is not a single universal solution but depends on the specific service zone of the roll. The crown region of a work roll experiences the highest temperatures and scale contact, requiring Ni-based or high-Cr cast iron overlays, while the backup roll surface primarily needs thermal shock resistance, achievable with martensitic Cr12-type overlays. This zonal approach to cladding material selection is still standard practice today.

The research also highlights an often-overlooked aspect: the importance of welding procedure control. Even with an optimally designed electrode, poor welding technique — excessive heat input, inadequate interpass temperature control, or improper joint preparation — can completely negate the benefits of the alloy design. The authors' emphasis on welding parameter standardization foreshadows the modern emphasis on welding procedure qualification and control.

Summary

This 1997 study represents a foundational contribution to the field of hot rolling roll hardfacing, establishing systematic approaches to electrode composition design, dilution control, and welding parameter optimization. The research demonstrates that achieving the required combination of hardness, thermal stability, and toughness for hot rolling service requires careful balance of carbon, chromium, and molybdenum content, coupled with rigorous control of welding heat input and interpass temperatures. The multi-pass welding strategy with progressive current adjustment, the use of alloy-rich electrode cores to compensate for dilution, and the zonal material selection philosophy all remain directly applicable to modern roll maintenance practices. For engineers involved in roll restoration and hardfacing today, this paper provides valuable historical context and fundamental metallurgical principles that continue to underpin contemporary practice.