Steel Rolling Mill Roll Surfacing Technology Study Note

Literature Overview

This paper by Tan Zheng from Tangshan Steel Wire Rod Plant, published in China Metallurgy (2005, Vol. 15, No. 8), provides a comprehensive review of steel rolling mill roll surfacing technology and presents experimental results for four different surfacing materials. The study covers 27Cr3Mo2MnVWTi, 3Cr13, 35MnSi, and 3Cr2W8V surfacing alloys, examining their welding processes, post-weld heat treatment, chemical composition, dilution behavior, microstructure, hardness, wear resistance, and mechanical properties. This work represents a practical engineering study conducted at an industrial facility, providing valuable insights into the application of surfacing technology in the steel rolling industry.

Core Technical Findings

The study evaluates four surfacing materials for rolling mill roll applications, each suited to different service conditions. The comparative results are summarized below:

The study demonstrates that the selection of surfacing material must be based on the specific service conditions of the roll, including temperature, contact pressure, corrosive environment, and wear mode. The dilution behavior is a critical factor that affects the final properties of the surfacing layer, and the study provides data on dilution rates for each material system.

Interpretation of Technical Points

Rolling mill roll surfacing is a critical maintenance technology that extends roll service life and reduces production costs. The surfacing layer must withstand extreme conditions including high temperatures (up to 1200 degrees Celsius for hot rolling), intense contact pressure, thermal cycling, and abrasive or adhesive wear from the steel being rolled. The selection of surfacing material is therefore a complex engineering decision that requires balancing multiple competing requirements.

The 27Cr3Mo2MnVWTi alloy is designed for hot rolling applications where thermal fatigue resistance is paramount. The combination of chromium, molybdenum, manganese, vanadium, tungsten, and titanium provides a synergistic effect that enhances high-temperature strength, thermal fatigue resistance, and wear resistance. The microstructure typically consists of a martensitic matrix with dispersed carbides and intermetallic phases that provide hardening and thermal stability.

The 3Cr13 alloy, a martensitic stainless steel, offers corrosion resistance in addition to moderate wear resistance. This makes it suitable for applications where the roll surface is exposed to corrosive environments, such as rolling of stainless steel or other corrosion-resistant alloys. The chromium content provides passive film formation that protects against oxidation and corrosion at elevated temperatures.

The 35MnSi alloy is a low-alloy steel with good toughness and moderate hardness. It is primarily used for cold rolling rolls where the service temperature is lower and the primary requirement is resistance to plastic deformation and moderate wear. Its lower cost makes it an economical choice for applications where extreme wear resistance is not required.

The 3Cr2W8V alloy is a high-speed steel type material with excellent hardness and wear resistance. It is suitable for hot working tool rolls and applications where the primary wear mechanism is abrasive or adhesive wear. The high tungsten and vanadium content produces a high volume fraction of hard carbides that provide exceptional wear resistance.

Process and Standards Analysis

Roll surfacing is typically performed using submerged arc welding (SAW) or flux-cored arc welding (FCAW) for automatic deposition, or manual arc welding (SMAW) for touch-up and repair. The relevant Chinese standards include GB/T 12469 for surfacing welds, GB/T 985 for welding symbols, and various industry-specific standards for rolling mill rolls.

The welding process parameters for roll surfacing are critical for achieving the desired microstructure and properties. The key parameters include:

Post-weld heat treatment is essential for roll surfacing to achieve the desired mechanical properties. The typical heat treatment schedule depends on the surfacing material:

• 27Cr3Mo2MnVWTi: Temper at 550-650 degrees Celsius for 2 hours
• 3Cr13: Quench and temper at 500-600 degrees Celsius for 2 hours
• 35MnSi: Stress relief at 600-650 degrees Celsius for 2 hours
• 3Cr2W8V: Temper at 550-600 degrees Celsius for 2 hours (may require double tempering)

The dilution rate is a critical parameter that directly affects the final composition and properties of the surfacing layer. For roll surfacing, dilution rates of 15-30 percent are typical, and the study provides data on the actual dilution rates achieved for each material system. Higher dilution rates result in lower hardness and may shift the microstructure away from the desired phase balance.

Integration with Engineering Practice

Roll surfacing is a well-established practice in the steel industry, and the findings of this study have direct practical applications in roll maintenance and refurbishment. The selection of surfacing material should be based on a systematic evaluation of the service conditions, including:

1. Maximum operating temperature of the roll surface.
2. Primary wear mechanism (abrasive, adhesive, thermal fatigue, or corrosion).
3. Required coating thickness and number of passes.
4. Available welding equipment and process capabilities.
5. Cost considerations including material cost, labor cost, and downtime cost.

A practical approach to roll surfacing optimization involves the following steps:

• Conduct a failure analysis of the worn roll to identify the primary wear mechanism.
• Select a surfacing material that addresses the identified wear mechanism.
• Optimize the welding parameters to minimize dilution and achieve the desired microstructure.
• Implement a proper post-weld heat treatment schedule.
• Monitor the service performance and adjust the process as needed.

The study also highlights the importance of surface preparation before surfacing. The roll surface should be ground to remove scale, rust, and previous coatings, and should have a surface roughness of Ra 6.3 to 12.5 micrometers to ensure good bond strength. Any cracks or defects in the base roll must be repaired before surfacing to prevent crack propagation into the coating.

Key Questions and Reflections

Several aspects of this study merit further consideration. First, the study does not provide detailed information on the residual stress distribution in the surfacing layers, which is an important factor affecting the service life of surfaced rolls. Residual tensile stresses can promote crack initiation and propagation, while compressive stresses can improve fatigue life.

Second, the study does not address the effect of welding sequence on the final properties of the surfacing layer. For large rolls with multiple surfacing passes, the welding sequence can significantly affect the residual stress distribution and the uniformity of the coating properties.

Third, the long-term service performance of the surfaced rolls is not reported. Laboratory wear tests, while useful for material comparison, do not always predict field performance accurately. A follow-up study comparing the service life of surfaced rolls with new rolls would provide valuable validation of the laboratory findings.

Study Insights and Implications

This research provides a practical and comprehensive guide to roll surfacing technology, covering material selection, process optimization, and property evaluation. The study demonstrates that different surfacing materials are suitable for different service conditions, and that the selection must be based on a thorough understanding of the operating environment and wear mechanisms.

For engineers in the steel industry, the key takeaway is that roll surfacing is a cost-effective method for extending roll service life, but it requires careful attention to material selection, process parameters, and post-weld treatment. The systematic approach presented in this study, which evaluates multiple material systems under controlled conditions, provides a framework for optimizing surfacing processes in industrial applications.