Arc Overlay Welding Repair Process for 2010 Rolling Mill Rolls

Literature Overview

This study by Gong Shuili, Zhang Jianxun, Yu Qin, and Yin Litao, published in the journal Welding in 1999, addresses the arc overlay welding repair of 2010-type rolling mill rolls. The authors are affiliated with the Welding Research Institute of the School of Mechanical Engineering at Xi'an Jiaotong University, the Northwest Institute for Nuclear Technology, and the Jinan Gas Company. Rolling mill rolls are critical components in steel production, and their surface integrity directly affects product quality and production efficiency. The 2010 designation refers to a specific roll material grade used in hot rolling mills, and the repair of worn or damaged rolls through overlay welding is a cost-effective alternative to full roll replacement.

Core Technical Content

Challenges of Rolling Mill Roll Repair

Rolling mill rolls operate under extreme conditions involving high temperatures (up to 1200°C in hot rolling), severe mechanical contact with steel slabs, and continuous cyclic loading. The surface of the roll is subject to:

• Abrasive wear from iron oxide scale and refractory particles in the mill environment.
• Thermal fatigue from repeated heating and cooling during the rolling cycle.
• Contact fatigue from the high contact pressures between the roll and the workpiece.
• Chemical interaction with the hot steel surface, including diffusion of carbon and alloying elements.

Repairing these rolls through overlay welding is challenging because the weld deposit must match or exceed the performance of the original roll surface while maintaining compatibility with the roll core material. The repair process must also minimize residual stresses to prevent cracking during subsequent heat treatment or in-service operation.

Selection of Welding Process and Consumables

The study evaluates multiple arc welding processes for roll repair, including:

• Submerged arc welding (SAW): Suitable for large-area repair of roll surfaces with high deposition rates. Multiple passes are typically required to build up the repair layer to the specified thickness.
• Gas metal arc welding (GMAW): More flexible for irregular damage patterns and smaller repair areas. Lower deposition rates but better control over bead profile.
• Electroslag welding (ESW): Used for deep repair of roll cores or severe material loss. Provides excellent penetration and low dilution.

The selection of welding consumables is critical. For 2010 roll material, the overlay alloy must provide adequate hardness, wear resistance, and thermal stability. Common choices include:

Multi-Layer Repair Strategy

The repair of rolling mill rolls typically involves a multi-layer approach:

1. Undercut repair: Any undercut or material loss at the roll surface is first repaired with a compatible filler metal to restore the base geometry.
2. Transition layer: A layer of intermediate composition is deposited to bridge the metallurgical mismatch between the base roll material and the final overlay alloy. This layer reduces residual stresses and prevents cracking at the interface.
3. Overlay layer: The final wear-resistant layer is deposited using the selected hardfacing alloy. Multiple passes may be applied to achieve the required thickness and hardness profile.

Process Parameters and Quality Control

Critical Welding Parameters

The following parameters are critical to the success of the repair:

• Preheating temperature: Typically 200–350°C for 2010 roll material to reduce cooling rates and minimize residual stresses.
• Interpass temperature: Maintained between 150–250°C to prevent excessive thermal cycling and cracking.
• Travel speed: Optimized to achieve adequate penetration without excessive heat input. Typical range: 200–400 mm/min for SAW, 100–200 mm/min for GMAW.
• Heat input: Controlled to minimize dilution and residual stresses. Typical range: 0.5–1.5 kJ/mm for multi-pass repair.
• Post-weld heat treatment: Stress relief at 550–650°C for 2–4 hours to reduce residual stresses and stabilize the microstructure.

Quality Inspection Requirements

The repaired roll must undergo rigorous inspection before returning to service:

• Visual examination (VT): Check for surface defects, undercut, porosity, and incomplete fusion at the repair interface.
• Magnetic particle testing (MT): Detect surface and near-surface cracks in the repair layer and heat-affected zone.
• Ultrasonic testing (UT): Evaluate the bond strength between the repair layer and the base material.
• Hardness testing: Verify that the overlay layer meets the specified hardness range and that the hardness gradient at the interface is gradual.
• Dimensional check: Ensure the roll geometry, including diameter, roundness, and surface finish, meets specifications.

Engineering Practice and Case Studies

Case Study: Hot Rolling Mill Roll Repair

A typical case involves the repair of a 2010-type work roll in a hot strip mill. The roll exhibited surface cracking and material loss of approximately 3–5 mm depth due to thermal fatigue and abrasion. The repair procedure was as follows:

1. Surface preparation: The damaged area was ground smooth to expose sound material. The repair area was cleaned of scale, oxide, and contaminants.
2. Preheating: The roll was preheated to 300°C using induction heating.
3. Undercut repair: The material loss was filled with a low-carbon martensitic filler metal using GMAW to restore the base geometry.
4. Transition layer: A layer of Cr-Mo bearing steel type filler metal was deposited using SAW to create a metallurgical bridge.
5. Overlay layer: Two passes of high-carbon martensitic hardfacing alloy were applied using SAW to achieve a final thickness of 4–6 mm.
6. Post-weld heat treatment: The roll was stress-relieved at 600°C for 3 hours.
7. Inspection and finishing: The repaired surface was inspected by MT and UT, then ground to the required surface finish and dimensional tolerances.

Performance Evaluation

The repaired roll was returned to service and monitored for a period of six months. The results showed:

• No cracking or spalling of the repair layer during service.
• Hardness of the overlay layer maintained at 550–620 HV, within the specified range.
• Wear rate of the repaired area was comparable to the original roll surface.
• The repair extended the service life of the roll by an estimated 18–24 months, representing significant cost savings compared to full roll replacement.

Key Technical Points and FMEA Analysis

Failure Mode and Effects Analysis

Process Optimization Using PDCA Cycle

The repair process can be continuously improved using the PDCA (Plan-Do-Check-Act) framework:

• Plan: Define repair specifications, select consumables, establish welding parameters based on qualification tests.
• Do: Execute the repair procedure with strict adherence to the qualified parameters.
• Check: Inspect the repair through VT, MT, UT, and hardness testing. Evaluate performance during service.
• Act: Analyze inspection results and service performance. Update the repair procedure, consumable selection, or welding parameters based on findings.

Study Insights and Implications

The study by Gong et al. demonstrates that arc overlay welding is a viable and cost-effective method for repairing damaged rolling mill rolls. The key to success lies in careful selection of welding consumables, optimization of welding parameters, and rigorous quality control. The multi-layer repair strategy, with a transition layer to bridge metallurgical mismatches, is a critical technique that should be adopted in all roll repair operations.

One important insight from this study is the emphasis on post-weld heat treatment. The residual stresses induced during overlay welding can be significant, and without proper stress relief, the repaired roll may crack during subsequent heat treatment or in-service operation. The stress relief temperature and duration must be carefully controlled to avoid softening the overlay layer while effectively reducing residual stresses.

The economic benefits of roll repair through overlay welding are substantial. A single roll replacement can cost tens of thousands of dollars, while the repair cost is typically 10–20% of the replacement cost. Furthermore, the repair process significantly reduces downtime compared to the lead time for ordering and installing a new roll. This makes overlay welding repair an attractive option for mills seeking to optimize production efficiency and reduce operating costs.

The study also highlights the importance of operator skill and process discipline in achieving consistent repair quality. Arc overlay welding of rolls requires experienced welders who understand the metallurgical implications of their parameter selections. Training and certification programs for welders performing roll repairs are essential to ensure consistent quality.

Reference Value and Outlook

The work by Gong et al. provides a practical guide for the repair of rolling mill rolls through arc overlay welding. The techniques described, including multi-layer repair strategies, consumable selection criteria, and quality control procedures, are directly applicable to current industry practice. Future developments in roll repair technology may include the use of advanced hardfacing alloys with improved thermal fatigue resistance, automated welding systems for consistent parameter control, and in-situ monitoring techniques for real-time quality assessment.

The integration of overlay welding repair with predictive maintenance strategies represents a promising direction for future research. By monitoring roll wear and damage through sensor-based condition monitoring systems, mills can schedule repairs proactively, optimizing both roll life and production scheduling. The techniques described in this study provide the metallurgical foundation for such integrated approaches.

In conclusion, arc overlay welding repair of 2010 rolling mill rolls is a mature and effective technology that continues to play a vital role in the steel industry. The study by Gong et al. contributes valuable practical knowledge to this field, and its findings remain highly relevant to current engineering practice.