Overlay Welding Process and Application Scheme for Cold Continuous Rolling Mill Backup Rolls

Literature Overview

The 2021 study by Zhang Yuntao, Geng Bo, Wang Jixiang, and Jiang Bo from Hesteel Group Handan Steel Company addresses the overlay welding process development and application scheme for cold continuous rolling mill (CCR) backup rolls. Backup rolls in cold rolling mills are subjected to extreme contact pressures, cyclic loading, and abrasive wear, making overlay welding a critical technology for extending roll life and maintaining rolling quality. This study represents a practical engineering approach to optimizing overlay welding for heavy industrial applications.

Core Technical Content

Service Conditions and Failure Modes

Cold continuous rolling mill backup rolls operate under demanding conditions:

• Contact pressure: 1000-2000 MPa at the roll bite
• Rolling speed: 50-200 m/min
• Roll diameter: 600-900 mm
• Roll length: 1500-2500 mm
• Service temperature: Ambient to 150°C
• Cycle life: 50,000-200,000 passes before regrinding

The primary failure modes include:

• Abrasive wear: Progressive material removal at the roll surface
• Roll chatter: Surface undulation due to dynamic instability
• Roll flatness deviation: Loss of geometric accuracy due to asymmetric wear
• Surface cracking: Fatigue cracks initiated by contact stress

Overlay Welding Process Development

The study developed a comprehensive overlay welding process for backup roll surface renewal:

Process Selection: Submerged arc welding (SAW) was selected as the primary process due to:

• High deposition rate (5-8 kg/h)
• Low dilution (5-10%)
• Excellent surface quality
• Suitability for large-scale industrial application

Consumable Selection: The overlay alloy was designed as a medium-carbon martensitic steel with the following characteristics:

• Carbon content: 0.5-0.8% for high hardness
• Chromium: 4-6% for hardenability and wear resistance
• Molybdenum: 0.8-1.5% for temper resistance
• Vanadium: 0.1-0.3% for carbide dispersion

Welding Parameters:

Multi-Pass Overlay Strategy

The overlay was applied in a multi-pass strategy to achieve the required thickness (typically 8-15 mm) with controlled microstructure:

1. First pass: Establishes the base layer with good fusion to the substrate
2. Intermediate passes: Build up thickness with consistent microstructure
3. Final pass: Surface pass with optimized composition for wear resistance

The total overlay thickness was designed to be 1.5-2 times the expected wear depth, providing adequate material for multiple regrinding cycles during the roll's service life.

Post-Weld Heat Treatment

The overlay was followed by a controlled heat treatment cycle:

• Tempering at 500-550°C for 2-4 hours: Achieves hardness of 45-50 HRC while maintaining adequate toughness
• Cooling rate: Controlled furnace cooling to minimize residual stresses
• Final hardness: 45-50 HRC in the overlay, 35-40 HRC in the substrate

Application Scheme and Engineering Practice

Roll Management Strategy

The study proposed a comprehensive roll management strategy incorporating overlay welding:

Roll Life Cycle:

1. New roll manufacturing: Core roll with base hardness 35-40 HRC
2. First overlay: After initial wear, apply 8-12 mm overlay
3. Service use: Multiple regrinding cycles during service
4. Second overlay: When regrinding limit is reached, apply additional overlay
5. Retirement: When total overlay thickness exceeds design limit

Regrinding Interval: Typically 50,000-100,000 passes, depending on wear rate and rolling conditions

Quality Control Protocol

The overlay welding process was supported by a rigorous quality control protocol:

Performance Results

The study reported the following performance improvements:

• Roll life extension: 2-3 times compared to non-overlaid rolls
• Surface quality: Maintained within tolerance for multiple regrinding cycles
• Roll flatness: Stable over the service life
• Cost reduction: 30-40% reduction in roll replacement costs
• Product quality: Improved strip flatness and surface finish

Key Questions and Reflections

The study raises important questions about the long-term reliability of overlay-welded backup rolls. While the short-term performance is excellent, the long-term behavior under cyclic contact loading requires ongoing monitoring. The interface between the overlay and substrate is a potential weak point, particularly under thermal cycling and high contact pressure.

Another reflection is the scalability of the overlay welding process for industrial applications. The process was developed for a specific roll size and service condition, and adaptation to different roll geometries and service conditions requires careful process optimization. The study provides a framework for this adaptation, but each application requires individual qualification.

Study Insights and Implications

This study demonstrates the practical value of overlay welding technology in extending the service life of critical industrial components. The development of a systematic overlay welding process, combined with a comprehensive roll management strategy, provides a cost-effective solution for maintaining rolling mill productivity. The work highlights the importance of integrating process development, quality control, and application management in a holistic approach to component life extension. For engineers working with heavy industrial components, the key takeaway is that overlay welding is not merely a surface treatment but a comprehensive engineering solution that requires careful process design, quality control, and lifecycle management.