Surfacing Technology for 750mm Slab Mill Rolls Technical Summary

Literature Overview

This 1990 paper published in Shandong Metallurgy (Vol. 12, No. 3, pp. 51-54) presents a comprehensive summary of the surfacing (overlay welding) technology applied to the rolls of a 750 mm slab mill. The classification numbers TG333.17 and TG455 confirm the work sits at the intersection of rolling technology and welding. During the early 1990s in China, the heavy plate and slab mills were undergoing modernization, and roll life was a critical bottleneck in production economics. The authors document their systematic approach to restoring and improving the working surfaces of mill rolls through surfacing, which was a practical and cost-effective alternative to full roll replacement.

Core Technical Content

The paper addresses the fundamental challenge of roll surfacing: achieving a durable, wear-resistant overlay on a large cylindrical substrate while maintaining dimensional accuracy and metallurgical soundness. The key issues investigated include the selection of surfacing materials compatible with the roll core steel, the welding process parameters that minimize residual stress and distortion, and the post-weld heat treatment requirements to ensure long-term service reliability.

The authors emphasize that the 750 mm slab mill operates under extreme conditions involving high contact pressure, abrasive wear from scale and oxide particles, and cyclic thermal loading. The surfacing layer must therefore possess high hardness, good hot hardness, and resistance to thermal fatigue cracking. The substrate material, typically a low-carbon or low-alloy steel roll core, must be preheated adequately to prevent cold cracking in the weld metal and heat-affected zone.

Process Parameter	Typical Range	Rationale
Preheat Temperature	250-400°C	Reduce HAZ hardness, prevent cold cracking
Interpass Temperature	200-350°C	Control thermal cycling, limit residual stress
Surfacing Layers	2-4 passes	Build up required thickness, improve metallurgical transition
Welding Process	SMAW or SAW	Suitable for large cylindrical surfaces, good deposition rate
Post-Weld Heat Treatment	550-650°C stress relief	Reduce residual stresses, stabilize microstructure

Key Technical Points and Engineering Practice

The paper highlights several critical observations that remain relevant to modern roll maintenance practice. First, the selection of surfacing electrode composition is decisive: the alloying elements (Cr, Mo, V, W) must be balanced to provide wear resistance without introducing excessive brittleness or susceptibility to thermal cracking. Second, the welding sequence must be carefully planned to minimize cumulative distortion on the large-diameter roll surface. The authors describe a symmetrical welding pattern that progresses around the roll circumference, ensuring that thermal expansion is distributed evenly.

Third, the paper stresses the importance of non-destructive testing (NDT) after surfacing completion. Visual inspection, magnetic particle testing (MT), and in some cases ultrasonic testing (UT) are employed to detect surface cracks, lack of fusion, and porosity. Any detected defects must be ground out and re-welded before the roll enters service. The acceptance criteria are stringent because a single undetected crack in the surfacing layer can propagate rapidly under the cyclic loading of the slab mill, leading to catastrophic roll failure.

Study Insights and Implications

Reading this paper with the benefit of decades of subsequent experience, one can appreciate both the practical wisdom and the limitations of the era. The paper reflects a period when welding technology was still evolving rapidly in Chinese heavy industry, and systematic process optimization was just beginning to be applied to roll maintenance. The emphasis on empirical parameter selection, guided by field trial results, was appropriate for the time but would today be supplemented by finite element simulation of residual stress and distortion.

The core lesson remains valid: roll surfacing is not merely a matter of depositing hard material on a surface. It requires an integrated approach that considers metallurgical compatibility, thermal management, geometric control, and quality assurance. For engineers working in modern rolling mill maintenance, this paper serves as a valuable historical reference that illustrates the foundational principles still governing today's practices. The transition from manual SMAW to mechanized surfacing systems, and from empirical to simulation-based process design, has been the trajectory of progress since 1990, but the underlying metallurgical and mechanical considerations have not changed.