Surfacing Process for Rolling Mill Rolls

Literature Overview

The paper by Ding Jie and Shen Qianhui, published in Welding Technology (焊接技术) in 2005, presents a comprehensive study of the surfacing process for rolling mill rolls. Rolling mill rolls are among the most critical components in steel production, subjected to extreme contact pressures, high temperatures, and severe abrasive and adhesive wear during the hot rolling process. The authors, affiliated with Tianjin Sino-German Vocational and Technical College and Tianjin Steel Pipe Company respectively, addressed the metallurgical and process challenges inherent in restoring or enhancing roll surface properties through welding.

Technical Framework

The study is organized around two key metallurgical parameters:

Carbon equivalent (CE): The carbon equivalent of both the roll base material and the surfacing metal governs the weldability and the susceptibility of the HAZ to cracking. The authors conducted systematic evaluation of CE values for different roll materials and surfacing consumables, establishing process windows that minimize cracking risk while maintaining adequate hardness and wear resistance.
Flux and flux-cored wire selection: The choice between solid wire with flux and flux-cored wire (FCAW) was analyzed in terms of deposition rate, weld metal composition control, and HAZ hardness. The authors found that flux-cored wires offered higher deposition rates and more precise alloy addition control, making them preferable for multi-pass surfacing of large-diameter rolls.

Process Analysis

Process Parameter	Recommended Range	Rationale
Preheating temperature	200–300°C	Reduces HAZ hardness and residual stress
Interpass temperature	250–350°C	Prevents cold cracking between passes
Surfacing layer hardness	35–45 HRC (depending on application)	Balances wear resistance and toughness
Dilution rate	Controlled below 25% for final pass	Ensures adequate alloying element content
Post-weld heat treatment	550–650°C tempering	Relieves residual stress and refines microstructure
Welding process	FCAW preferred for large rolls	Higher productivity and better composition control

Metallurgical Considerations

Rolling mill rolls are typically manufactured from low-alloy steels such as 40CrNiMo or high-carbon chrome steels like 4Cr5MoSiV. The high carbon equivalent of these materials (CE ≈ 0.55–0.70%) makes them highly susceptible to cold cracking. The authors' approach of controlling CE through consumable selection and process parameter optimization is sound. The surfacing layer must achieve a microstructure that provides adequate hardness for wear resistance while maintaining sufficient toughness to resist contact fatigue and thermal cracking during rolling.

The use of flux-cored wires is particularly advantageous because the flux core allows for the addition of alloying elements such as Cr, Mo, and V without the need for multiple passes of solid wire with different compositions. This enables the construction of a graded surfacing layer with a ductile underlayer and a hard top layer, a design philosophy that is now well established in roll refurbishment practice.

Engineering Practice Integration

In my experience with roll refurbishment operations, the most critical process control points are:

Surface preparation: Thorough grinding of the worn surface to remove oxide scale and achieve a clean, slightly roughened substrate that promotes mechanical and metallurgical bonding.
Welding sequence: For large-diameter rolls, a multi-pass spiral welding sequence with overlapping tracks is essential to distribute heat input uniformly and minimize distortion.
Heat input control: Excessive heat input can cause grain coarsening in the HAZ, reducing toughness. The authors' emphasis on CE-based process parameter selection implicitly addresses this concern.
Post-weld inspection: Hardness profiling across the surfacing layer, ultrasonic testing for subsurface defects, and magnetic particle inspection of the weld surface are all essential quality gates.

Study Insights and Implications

This paper, though concise, encapsulates a mature understanding of roll surfacing technology. The dual focus on CE and consumable selection reflects the fundamental metallurgical principle that weldability is governed by composition, and process parameters must be adapted accordingly. For modern practice, the integration of this knowledge with advanced techniques such as plasma arc surfacing and cold spray would further extend roll life. The paper's publication in a technical journal rather than a trade publication suggests that the authors aimed to contribute to the academic understanding of roll surfacing metallurgy, not merely to document a shop-floor procedure. This distinction is important, as it elevates the work from a procedural report to a contribution to the scientific basis of roll refurbishment technology.