Application of Hardfaced Work Rolls on 4200 Hot Rolling Mill

Literature Overview

This technical paper by Wang Zhenyu from Wuyang Steel Company, published in Special Steel in 1993 (Vol. 14, No. 4, pp. 41-42), reports on the application of hardfaced work rolls on a 4200 hot rolling mill. The study addresses the critical challenge of work roll wear and failure in hot rolling operations, where work rolls are subjected to extreme thermal and mechanical loading. The paper provides practical insights into the benefits and challenges of hardfacing work rolls as a strategy for reducing roll consumption and improving cost efficiency in hot strip production.

Technical Background

Work rolls are among the most critical and most rapidly consumed components in a hot rolling mill. During hot rolling, the work roll surface is in direct contact with hot steel slabs at temperatures ranging from 900°C to 1200°C, while simultaneously bearing extremely high contact pressures that can exceed 1000 MPa. The combination of thermal loading, mechanical loading, and chemical interaction with the steel surface creates a uniquely severe operating environment that challenges even the most advanced roll materials.

The primary failure modes of work rolls in hot rolling include:

• Thermal cracking: Initiated by thermal fatigue at the roll surface due to repeated heating and cooling during rolling.
• Roll spalling: Surface layer detachment caused by thermal fatigue and mechanical fatigue.
• Abrasive wear: Gradual material removal from the roll surface due to contact with the hot steel and oxide scale.
• Roll burn: Severe localized heating and material transfer between the roll and the strip.
• Roll chipping: Mechanical fracture of the roll surface under high contact pressure.

Hardfacing Technology for Work Rolls

Hardfacing of work rolls involves depositing a wear-resistant layer on the roll surface to extend service life and improve performance. The hardfacing alloy must be selected to provide:

• High hardness at operating temperature
• Excellent thermal fatigue resistance
• Good resistance to spalling and chipping
• Adequate toughness to resist crack propagation
• Compatibility with the roll core material

Common Hardfacing Alloys for Work Rolls

Hardfacing Process Selection

The selection of the hardfacing process for work rolls is critical and depends on the roll geometry, production volume, and performance requirements:

• Submerged arc welding (SAW): Suitable for large diameter rolls, provides high deposition rates and good penetration.
• Plasma arc hardfacing: Offers precise heat input control and good bead formation, suitable for smaller diameter rolls.
• Electroslag welding (ESW): Used for thick deposits on large rolls, provides excellent metallurgical quality.
• Flame spraying / Thermal spraying: Used for thinner coatings, offers rapid application but limited thickness.
• Laser cladding: Provides precise control and minimal dilution, but limited to smaller areas.

Application on 4200 Mill

The 4200 hot rolling mill refers to a mill with 4200 mm roll diameter or a specific mill designation. The application of hardfaced work rolls on this mill involved several key considerations:

Roll Preparation

• Thorough cleaning and preparation of the roll surface to ensure good adhesion of the hardfacing layer.
• Inspection of the roll core for any defects that could compromise the hardfacing integrity.
• Measurement of the roll diameter and out-of-roundness to determine the required hardfacing thickness.

Hardfacing Procedure

• Selection of the appropriate hardfacing alloy based on the rolling conditions and product requirements.
• Optimization of welding parameters (current, voltage, travel speed, wire feed rate) for the roll geometry.
• Implementation of a systematic welding sequence to ensure uniform hardfacing coverage.
• Control of interpass temperature to minimize thermal stress and cracking.

Post-Hardfacing Treatment

• Stress relief annealing to reduce residual stresses in the hardfacing layer and the roll core.
• Grinding and finishing of the hardfaced surface to achieve the required surface roughness and dimensional accuracy.
• Non-destructive testing (MT, UT) to detect any subsurface defects or cracks.

Performance Results

The hardfaced work rolls demonstrated significant performance improvements compared to conventional work rolls:

• Extended service life between regrinding intervals
• Reduced frequency of roll change-outs
• Improved strip surface quality
• Reduced roll consumption cost
• Enhanced mill productivity

The specific performance improvements varied depending on the product being rolled, the rolling conditions, and the hardfacing alloy used. However, the general trend of improved performance was consistent across different applications.

Comparative Analysis with Industry Practice

The paper notes that major Chinese steel enterprises including Anshan Steel (Angang) and Taiyuan Steel (TISCO) had also adopted hardfaced work rolls, indicating a broader industry trend toward this technology. The adoption of hardfacing technology for work rolls represents a shift from a reactive approach (replacing failed rolls) to a proactive approach (preventing failure through surface engineering).

Study Insights and Implications

This study provides practical evidence that hardfacing technology can significantly improve the performance and economics of hot rolling operations. The application of hardfaced work rolls on the 4200 mill demonstrates that this technology is not limited to laboratory or pilot-scale applications but can be successfully implemented in large-scale industrial production.

For engineers involved in roll selection and maintenance, this study reinforces the importance of surface engineering as a tool for extending component life and reducing operational costs. The key to successful hardfacing of work rolls lies in the careful selection of the hardfacing alloy, the optimization of the hardfacing process, and the implementation of rigorous quality control measures. The integration of hardfacing technology into the roll management program requires a systematic approach that considers the entire roll lifecycle, from core selection and hardfacing through to regrinding and retirement.

The broader implications of this study extend beyond work rolls to other components in the steel processing industry that are subjected to severe wear and thermal loading. Components such as guide rolls, backup rolls, and finishing mill rolls can all benefit from hardfacing technology, and the principles established in this study are directly applicable to these applications. The successful industrial deployment of hardfaced work rolls validates the technology and provides a foundation for further development and optimization in this important area of surface engineering.