Selection and Testing of Cladding Materials for Steel Mill Rolls

Literature Overview

This 2004 paper by Liu Huilin, Zheng Boping, Liao Zhi, and Cheng Xiaojun from Liangang Electromechanical Co., Ltd., published in Mining and Metallurgical Engineering, presents a comprehensive study on the selection and qualification testing of cladding materials for steel mill rolls. Steel rolls are among the most heavily loaded components in steel production, subjected to extreme combinations of compressive contact stress, abrasive wear from scale and oxide removal, thermal fatigue from repeated heating and cooling, and impact loading during rolling operations.

The research addresses the practical challenge of matching cladding material properties to specific roll service conditions — hot strip mill rolls, cold strip mill rolls, roughing mill rolls, and finishing mill rolls all experience fundamentally different loading conditions that demand different material solutions.

Cladding Material Classification and Properties

The authors evaluate three primary categories of cladding materials for steel mill roll applications:

Material Category	Typical Composition	Hardness (HV)	Abrasion Resistance	Thermal Shock Resistance	Typical Application
High-speed steel type	W6Mo5Cr4V2	850-950	Excellent	Good	Hot finishing rolls
Cemented carbide type	WC-Co (10-15% Co)	1200-1500	Excellent	Poor	Cold work rolls
High-chromium cast iron	Cr15-Cr25	700-850	Good	Excellent	Roughing mill rolls
Nickel-based hardfacing	Ni-15Cr-6B	600-700	Good	Excellent	Hot roughing rolls
Hardfacing with WC	Fe-5Cr-15WC	900-1100	Excellent	Moderate	Cold finishing rolls

Selection Criteria Framework

The paper proposes a systematic selection framework based on the following parameters:

Contact stress: Hot rolling contact stresses reach 2000-3500 MPa, requiring materials with high yield strength and work-hardening capacity.
Abrasive particles: Scale removal generates abrasive particles (Fe2O3, Fe3O4) with hardness 1000-1500 HV, demanding carbide-rich cladding compositions.
Thermal cycling: Temperature fluctuations of 100-200°C per rolling pass require excellent thermal fatigue resistance.
Roll diameter and speed: Larger rolls at higher speeds generate more severe impact loading, requiring tougher materials.

Testing Methodology and Results

The research employed a combination of laboratory testing and field trial evaluation to qualify cladding materials:

Laboratory Tests:

Dry sliding wear test against Fe2O3 abrasive slurry at 200°C and 500°C
Thermal fatigue test with 1000 cycles of 100°C-800°C heating and cooling
Hardness mapping at multiple depths (0.5, 1.0, 1.5, 2.0 mm)
Metallographic examination for carbide distribution and size

Field Trial Results (Hot Strip Mill Finishing Roll):

Cladding Material	Roll Life (Passes)	Surface Quality	Cost per Ton Steel
Base material (only)	8,500	Poor (galling)	Baseline
HSS hardfacing	22,000	Good	+15%
High-Cr cast iron	18,500	Good	+12%
Ni-based + WC	28,500	Excellent	+22%
Laser-clad WC-Co	35,000	Excellent	+35%

The field trial data clearly demonstrates that the Ni-based hardfacing with WC particles (Fe-5Cr-15WC composition) provides the best balance of roll life improvement and cost effectiveness, achieving 3.3 times the life of uncladded rolls at only 22% additional cost.

Welding Process Considerations

The paper emphasizes that the welding process used to apply the cladding is as critical as the cladding material itself. For steel mill roll applications, the following processes are recommended:

Flame hardfacing (oxy-fuel): Suitable for large-diameter rolls (D > 500 mm) with thick cladding (3-5 mm). Low heat input minimizes distortion but produces lower hardness (HV 600-700).
Submerged arc welding (SAW): Best for medium-thickness cladding (2-4 mm) with good productivity. Requires backing ring and careful flux selection.
Plasma transferred arc (PTA) welding: Optimal for precise cladding thickness control (0.5-2 mm) with excellent dilution control. Preferred for high-alloy hardfacing materials.
Laser cladding: Highest dilution control (<5%) but limited to thin cladding (<1 mm). Best suited for repair of worn rolls rather than new fabrication.

The base roll material (typically 42CrMo or 50MnCrNi3) must be preheated to 250-350°C before cladding to prevent cold cracking. Post-weld stress relief at 550-600°C for 2 hours is mandatory for rolls exceeding 300 mm in diameter.

Study Insights and Engineering Recommendations

This paper provides valuable guidance for steel plant engineers responsible for roll maintenance and life extension programs. The key insight is that cladding material selection must be driven by a quantitative understanding of service conditions rather than generic material recommendations. A high-speed steel roll in a hot roughing mill may experience fundamentally different degradation mechanisms than the same material in a finishing mill position.

The economic analysis presented in the paper is particularly instructive — while laser cladding with WC-Co provides the longest roll life (35,000 passes), the 35% cost premium may not be justified for high-volume production where roll changes are scheduled every 10,000-15,000 passes. The Ni-based + WC composition at 22% premium offering 3.3 times base life represents the optimal economic choice for most hot rolling applications.

For cold rolling applications where surface finish quality is paramount, the authors recommend laser cladding with fine-grained WC-Co compositions that produce surface roughness below Ra 0.2 μm after machining. The extremely low dilution achievable with laser cladding ensures that the cladding chemistry remains unaffected by the base roll material, providing consistent performance across multiple re-cladding cycles.