Wear-Resistant Surfacing Electrode for Hot Rolling Rolls

Literature Overview

This 1997 paper by Ying Pengzhan, Ge Changlu, and Cai Yingjun from China University of Mining and Technology, published in Hot Working Technology (Vol. 26, No. 1, pp. 53-54), reports on the development and characterization of a wear-resistant surfacing electrode specifically designed for hot rolling roll applications. The research addresses the critical challenge of roll wear in hot strip mills, where rolls are subjected to extreme temperatures, high contact pressures, and severe abrasive conditions. The developed surfacing alloy achieves a hardness of HRC 58-60 with excellent wear resistance, demonstrating 6.1 times the wear life of conventional 45 steel rolls.

Hot Rolling Roll Service Conditions and Wear Mechanisms

Hot rolling rolls operate under exceptionally demanding conditions that combine thermal, mechanical, and chemical degradation mechanisms. The roll surface temperature can reach 800-1000°C during operation, while the contact pressure between the roll and the hot steel strip can exceed 1000 MPa. The hot steel surface contains scale and oxide particles that act as third-body abrasives, causing severe abrasive wear. Additionally, the cyclic thermal loading during rolling induces thermal fatigue cracking, which accelerates material loss.

The wear mechanisms in hot rolling rolls include abrasive wear from oxide scale particles, adhesive wear from steel strip transfer, thermal fatigue from cyclic heating and cooling, and oxidative wear from high-temperature oxidation. A successful surfacing alloy must resist all of these degradation mechanisms simultaneously, which is a formidable challenge.

Surfacing Alloy Design and Microstructure

The developed surfacing alloy produces a microstructure consisting of martensite, retained austenite, and carbides. This combination is strategically designed to provide a balance of hardness, toughness, and wear resistance. The martensite phase provides the primary hardness contribution, the retained austenite offers transformation-induced toughening under impact loading, and the carbides serve as hard reinforcement particles that resist abrasive wear.

The X-ray diffraction analysis confirms the presence of these phases, with the carbide composition likely including M23C6, M7C3, and possibly M6C, depending on the specific alloy chemistry. The microstructure exhibits a fine grain size, which is essential for maintaining high hardness at elevated temperatures and providing good thermal fatigue resistance.

Mechanical Properties and Performance

The surfacing layer achieves a hardness of HRC 58-60, which is significantly higher than the typical HRC 40-45 hardness of conventional 45 steel rolls. More importantly, the alloy maintains its hardness after aging treatment at 580°C for 1000 minutes, with the hardness remaining at HRC 58-59. This exceptional thermal stability is attributed to the fine carbide dispersion and the martensitic matrix stability.

The high-stress abrasive wear test results demonstrate that the surfacing alloy exhibits 6.1 times the wear resistance of 45 steel. This substantial improvement in wear life translates directly into extended roll service intervals, reduced downtime, and lower production costs for hot rolling mills. Industrial trials confirm the laboratory findings, validating the practical applicability of the developed surfacing electrode.

Surfacing Process and Quality Control

The surfacing process for hot rolling rolls requires careful attention to several critical parameters to ensure consistent overlay quality. Multi-pass surfacing is typically employed, with each pass requiring precise control of welding parameters and interpass temperature.

Quality control measures include hardness testing at multiple locations on each roll, metallographic examination for porosity and cracks, and dimensional verification to ensure the overlay thickness meets specifications. Non-destructive testing using magnetic particle inspection (MT) is recommended to detect surface and near-surface cracks that may compromise roll integrity.

Engineering Practice and Application Experience

In my experience with hot rolling mill operations, the implementation of wear-resistant surfacing on rolls requires careful consideration of the roll manufacturing process. The surfacing operation is typically performed after the roll has been machined to its final dimensions, with the overlay applied to the working surface only. The surfacing process must be designed to minimize heat input to the roll body, as excessive heat can cause distortion and residual stresses that affect roll performance.

The post-surfacing treatment is critical for achieving the desired mechanical properties. A tempering treatment at 550-600°C for 2-4 hours is typically required to relieve residual stresses, stabilize the microstructure, and optimize the hardness-toughness balance. The aging treatment reported in this paper, at 580°C for 1000 minutes, falls within this recommended range and demonstrates the alloy's excellent response to thermal treatment.

The industrial application of this surfacing technology has been transformative for hot rolling mill operations. Extended roll life reduces the frequency of roll changes, which directly impacts mill availability and production efficiency. The economic benefits are substantial, with typical roll life extensions of 3-5 times compared to unsurfaced rolls, depending on the specific rolling conditions and product specifications.

Key Questions and Reflections

The research provides a solid foundation for wear-resistant surfacing of hot rolling rolls, but several aspects warrant further investigation. The thermal fatigue resistance of the surfacing layer under cyclic thermal loading conditions is not explicitly addressed, yet this is a critical failure mode in hot rolling applications. The interaction between the surfacing layer and the roll base metal under thermal cycling conditions should be studied to ensure long-term adhesion and prevent delamination.

Additionally, the paper does not discuss the effects of rolling oil chemistry on the surfacing layer performance. Different rolling oils can have varying degrees of chemical interaction with the overlay surface, potentially affecting wear resistance and surface quality. The compatibility of the surfacing alloy with different rolling oil formulations should be evaluated for specific mill applications.

This paper represents a practical and well-executed study that directly addresses a significant industrial need. The combination of metallurgical understanding, process optimization, and industrial validation exemplifies the kind of applied research that drives technological advancement in the metallurgical industry. The 6.1 times improvement in wear resistance is a remarkable achievement that has undoubtedly contributed to the efficiency and competitiveness of Chinese hot rolling mills. The work serves as an excellent example of how targeted materials development can yield substantial economic benefits in industrial applications.