Do you want to know how to see mill rolls’ roll wear?

Abstract: 

Hot-rolled mill rolls operate under extreme conditions—including high temperatures of 600–1,000 °C, contact stresses in the order of GPa, and rapid cooling and heating—making wear inevitable. According to a classic review by Spuzic et al. (1994) published in Wear, roll wear is primarily classified into six mechanisms:

In actual rolling operations, these six wear mechanisms never occur in isolation; rather, they are coupled and mutually reinforcing. Abrasive wear is the most common form of chronic wear; fatigue wear and thermal cracking are the primary causes of unplanned downtime; and due to these coupled effects, the actual service life of rolling rolls is often shorter than predicted by models based on a single mechanism.

Quick On-Site Identification: Examine the roll surface characteristics—parallel scratches → abrasive wear; metal adhesion → adhesive wear; spalling pits → fatigue wear; hairline cracks → thermal cracking; oxide scaling → corrosive wear; multiple combinations → coupled damage.

Keywords: Hot rolling rolls; wear mechanisms; abrasive wear; fatigue wear; thermal cracking; coupled damage

Introduction

In hot rolling mills, rolls are the core consumable components. Whether producing rebar, structural sections, or flat products, rolls are in direct contact with red-hot steel billets, enduring extreme loads. The surface condition of rolls directly determines product dimensional accuracy and surface quality. Understanding roll wear mechanisms is the theoretical foundation for optimizing rolling processes and extending roll service life.

But not all wear is the same. Different wear mechanisms produce different surface features, require different countermeasures, and ultimately determine how long a roll can stay on the mill.

This article systematically reviews six major roll wear mechanisms based on the classic review published in Wear (Spuzic et al., 1994) and related research (Colás et al., 1999), providing a comprehensive reference framework for roll material development, process optimization, and on-site maintenance.

Service Conditions and Wear Characteristics of Rolling Mill Rolls

During hot rolling, rolls operate under extremely harsh conditions:

Under these multi-factor coupled conditions, roll surface material gradually degrades due to the combined effects of mechanical, thermal, and chemical actions. Wear is inevitable, but the dominant mechanisms and control strategies vary for different types of wear.

Six Major Wear Mechanisms

1. Abrasive Wear

Mechanism Description:

Abrasive wear is one of the most common forms of roll wear in hot rolling. During heating and rolling, iron oxide scale (mainly FeO, Fe₃O₄, and Fe₂O₃) forms on the steel billet surface. These oxide particles are significantly harder than the roll matrix metal. Under high pressure, these hard particles are pressed into the roll surface, creating a micro-cutting effect during relative sliding, gradually removing roll surface material.

Typical Morphological Features:

The roll surface exhibits fine scratches and grooves parallel to the rolling direction. Microscopic observation reveals carbides protruding above the matrix surface, with the surrounding matrix preferentially worn, forming a “relief” structure. As wear progresses, carbide particles fracture or detach entirely, accelerating surface roughening.

Key Influencing Factors:

Scale thickness, positively correlated with heating temperature and holding time

Rolling speed, affecting scale fracture and removal efficiency

Roll matrix hardness and carbide content, determining abrasive wear resistance

2. Adhesive Wear

Mechanism Description:

Adhesive wear occurs when two metal surfaces — the roll and the workpiece — achieve atomic-level contact under high temperature and high pressure, forming localized “cold welds.” These welds are then forcibly sheared apart during relative sliding, causing material transfer from one surface to the other. Under hot rolling conditions, contact zone temperatures exceed 1000°C, and fresh metal surfaces are continuously exposed, providing ideal conditions for atomic diffusion and bonding.

Typical Conditions and Morphology:

High-strength steels and stainless steels are particularly prone to adhesive wear. The roll surface shows irregularly distributed metal deposits (pick-up), leaving rough tear pits after detachment. Microstructural examination reveals transferred layers and mechanically mixed layers.

Key Influencing Factors:

Contact temperature and pressure

Affinity (mutual solubility) between workpiece and roll materials

Lubrication conditions and interface oxide film status

3. Fatigue Wear

Mechanism Description:

Fatigue wear results from cumulative damage under cyclic contact stress. Each revolution of the roll subjects the surface material to one complete loading-unloading cycle. Taking a finishing work roll in a 1580 hot strip mill as an example, contact cycles can reach tens of thousands within a single rolling campaign. Under repeated stress, micro-cracks initiate within the material, progressively propagate to critical dimensions, and ultimately cause spalling.

Crack Initiation and Propagation Characteristics:

Research indicates that fatigue cracks preferentially initiate at the interface between primary carbides and the matrix. The morphology, size, and distribution of carbides have a decisive influence on fatigue life. Carbides distributed in a network or chain pattern provide continuous paths for crack propagation, accelerating failure. Spalling pits show fatigue striations and secondary cracks at the bottom.

Key Influencing Factors:

Contact stress amplitude and distribution

Carbide morphology and matrix interface bonding strength

Material toughness and residual stress state

4. Thermal Cracking

Mechanism Description:

Thermal cracking is caused by cyclic thermal stresses resulting from roll surface temperature fluctuations. When in contact with the workpiece, the roll surface temperature rises sharply; when sprayed with cooling water, it cools rapidly. This repeated thermal expansion and contraction generates cyclic thermal stresses in the surface layer. When thermal stress exceeds the material’s high-temperature yield strength or critical thermal shock resistance, surface cracks initiate.

Crack Morphology and Propagation:

Thermal cracks typically appear in a network pattern (heat checking), initially confined to the surface layer at shallow depths. As rolling continues, cracks propagate along grain boundaries or carbide networks toward deeper regions, eventually interconnecting with other cracks, leading to large-scale material spalling or serving as initiation sites for fatigue cracks.

Key Influencing Factors:

Cooling water flow rate, temperature, and distribution uniformity.

Roll material thermal conductivity and thermal expansion coefficient.

High-temperature strength and thermal shock resistance.

Carbide morphology influences thermal crack resistance.

5. Corrosive Wear

Mechanism Description:

Corrosive wear results from the synergy between high-temperature oxidation and mechanical wear. In the hot rolling environment, the roll surface contacts high-temperature water vapor and oxidizing atmospheres, undergoing oxidation reactions to form oxide films. XRD analysis shows that the oxide layer on hot rolling work rolls mainly consists of Fe₂O₃ (hematite) and Fe₃O₄ (magnetite). The oxide film is then removed by mechanical contact, exposing fresh metal that oxidizes again, creating a cyclic process of “oxidation-wear-reoxidation.”

Micro-Mechanisms:

The integrity of the oxide film and its adhesion to the matrix determine the rate of corrosive wear. Dense, well-adhered oxide films provide protection; loose oxide films accelerate wear. Grain boundaries and carbide interfaces are preferential oxidation paths, weakening overall material performance.

Key Influencing Factors:

Roll surface temperature and oxidizing atmosphere.

Oxide film growth rate and adhesion.

Roll material oxidation resistance.

6. Mechanical-Thermal Coupled Damage

Coupling Mechanism Analysis:

In actual rolling processes, the five wear mechanisms described above never occur in isolation — they interact and reinforce each other through multiple pathways:

The distribution of internal stresses along the roll radius is non-uniform — circumferential, axial, and longitudinal stresses exhibit different variation patterns at different depths. This complex stress field further complicates coupled damage.

Engineering Significance of Coupling Effects:

Coupled interactions mean that actual roll service life is often shorter than predictions based on single-mechanism models. Understanding the interactions between various mechanisms is the theoretical prerequisite for developing systematic protection strategies.

Summary and Comparison of Wear Mechanisms

How to Identify Wear Patterns on Site

For mill engineers and operators, being able to visually identify the dominant wear mechanism on a used roll is the first step toward improving roll performance. Here is a quick field identification guide:

Conclusion

Hot rolling roll wear is a complex process involving the coupling of mechanical, thermal, and chemical factors. The five basic mechanisms — abrasive wear, adhesive wear, fatigue wear, thermal cracking, and corrosive wear — interact through multiple pathways, collectively determining roll service life and surface quality.

Understanding these wear mechanisms enables:

At the material design stage — Optimize chemical composition and heat treatment based on dominant wear mechanisms

At the operation stage — Slow down wear progression through process parameter adjustment and cooling optimization

At the maintenance stage — Accurately diagnose failure causes based on wear characteristics, and develop rational regrinding and replacement strategies

As the steel industry continues to raise requirements for product quality and cost control, in-depth research on roll wear mechanisms remains a critical topic in materials science and rolling technology.

This article is based on the classic review by Spuzic et al. (1994) published in Wear, and subsequent research by Colás et al. (1999).