Initial Exploration of Rolling Mill Roll Surfacing Process

Literature Overview

The paper by Zhang Wen, published in Special Steel Technology (Vol. 6, No. 1, 1999), provides an early-stage investigation into the surfacing process for rolling mill rolls. Rolling mill rolls are among the most heavily loaded components in steel production, subjected to extreme compressive, bending, and contact stresses, as well as thermal cycling, abrasion from scale, and corrosion from lubricants and coolant. Surfacing is a well-established method for restoring worn rolls or applying wear-resistant surfaces to new rolls, but the process parameters and control strategies are highly specific to the roll application.

Core Technical Content

Surfacing Requirements for Rolling Mill Rolls

Rolling mill rolls face unique challenges that distinguish them from other surfacing applications:

Extremely high contact stresses (Hertzian contact pressures can exceed 3 GPa)
Thermal cycling between ambient temperature and hot rolling temperatures (up to 1200 °C for hot strip mills)
Abrasive wear from oxide scale and iron particles
Corrosive attack from rolling lubricants and coolant
Vibration and dynamic loading during operation
Cyclic plastic deformation at the roll surface

The surfacing layer must therefore possess a combination of high hardness, high toughness, thermal fatigue resistance, and good adhesion to the roll substrate.

Process Parameter Control

The paper emphasizes the importance of controlling process parameters and strict operational procedures to achieve satisfactory surfacing results. While the paper is brief and does not provide extensive quantitative data, the following process aspects are identified as critical:

Process Aspect	Importance	Typical Control Measure
Preheat Temperature	Prevent cold cracking, reduce residual stress	Based on roll material and thickness
Interpass Temperature	Control thermal cycle, prevent cracking	Maintained within specified range
Welding Current and Voltage	Control heat input, penetration, dilution	Optimized for bead profile and bonding
Travel Speed	Control bead width and height	Adjusted for desired deposition rate
Electrode/Powder Selection	Match required surface properties	Based on service conditions
Layer Thickness	Balance wear resistance and toughness	Typically 3-10 mm for roll surfacing

Post-Weld Processing

The paper mentions post-weld machining and heat treatment as integral parts of the surfacing process. After surfacing, the roll surface must be ground or turned to achieve the precise diameter and surface finish required for the rolling process. The grinding process itself can introduce residual stresses and microstructural changes at the surface, which must be considered in the overall process design.

Post-weld heat treatment is typically performed to:

Relieve residual stresses from the welding process
Temper any martensitic phases in the deposited metal
Stabilize the microstructure against thermal cycling during service
Improve the toughness of the surfacing layer

Surfacing Material Selection

The selection of surfacing material depends on the specific rolling application:

For hot strip mill rolls: materials with excellent thermal fatigue resistance and scale spalling resistance are required, such as high-speed steel or cobalt-based alloys.
For cold roll mill rolls: materials with high hardness and wear resistance are preferred, such as chromium-carbide hardfacing alloys.
For slab mill rolls: materials with a balance of hardness and toughness are needed to resist both abrasion and impact.

Key Questions and Reflections

The paper, being an early-stage exploration, does not provide extensive quantitative data on the performance of the surfacing layers. This limits its direct applicability to current engineering practice, but the fundamental principles it outlines remain valid.

One critical question is the long-term performance of the surfacing layer under the extreme conditions of rolling mill operation. The thermal fatigue behavior of the surfacing layer, particularly at the interface with the substrate, is a major concern. Thermal cycling can cause spalling of the surfacing layer if the bond strength is insufficient or if the thermal expansion mismatch is not properly managed.

Another consideration is the effect of surfacing on the roll's fatigue life. While the surfacing layer improves wear resistance, it may introduce stress concentrations at the layer boundary that could initiate fatigue cracks. The transition zone between the surfacing layer and the substrate must be carefully designed to minimize these stress concentrations.

The paper also raises the question of process repeatability and quality consistency. In a production environment, surfacing must be performed consistently across multiple rolls and multiple passes. This requires rigorous process control, operator training, and quality assurance procedures.

Study Insights and Reference Value

This paper serves as an early reference point for the development of rolling mill roll surfacing technology. While it is brief and lacks the depth of more recent publications, it establishes the fundamental framework for process development and parameter control.

The emphasis on process parameter control and strict operational procedures is a timeless principle in surfacing technology. The paper reinforces the idea that even well-designed surfacing materials will fail if the welding process is not properly controlled. Engineers should view this paper as a foundational reference and supplement it with more recent literature on roll surfacing materials, processes, and performance data.

The paper's focus on post-weld machining and heat treatment highlights an often-overlooked aspect of surfacing technology. The final surface quality of a roll is determined not just by the surfacing process but also by the subsequent machining and heat treatment operations. Engineers must consider the entire process chain when designing a surfacing solution for rolling mill rolls.