Overlay Welding Technology for Hot Rolling Work Rolls

Literature Overview

This study by Pan Yongming and colleagues from the Harbin Welding Research Institute, published in the journal Welding (焊接) in 2000, Vol. 12, Issue 12, pages 23-25, reports on the successful application of a FeCrWNiMnSi-based overlay material for hot rolling work rolls. The research was conducted in collaboration with the Equipment Department of Anshan Iron and Steel Company and Harbin Environmental Protection Hydrogen Equipment Industrial Company. The work represents a significant industrial application of overlay welding technology in the metallurgical industry, demonstrating that overlay welding can be used to restore or enhance the surface properties of hot rolling work rolls, thereby extending their service life and reducing production costs.

Core Technical Findings

Application Background

Hot rolling work rolls are critical components in steel mill production lines, subjected to extreme conditions including high temperatures (up to 1200°C for hot strip mills), severe mechanical loading, thermal cycling, and abrasive wear from scale and oxide particles. The surface of a work roll must possess excellent wear resistance, thermal fatigue resistance, and dimensional stability to maintain product quality and roll life. Traditional approaches to extending roll life include remanufacturing through grinding, but this is limited by the remaining roll diameter and can only be performed a limited number of times.

Overlay Material Selection

The FeCrWNiMnSi-based overlay material developed by the Harbin Welding Research Institute was selected for hot rolling work roll application based on the following design criteria:

The FeCrWNiMnSi composition represents a balanced approach that provides adequate hardness (typically 50-55 HRC in the as-welded condition) while maintaining sufficient toughness to resist thermal fatigue cracking. The nickel content promotes austenite formation, which provides excellent thermal fatigue resistance due to its low thermal expansion coefficient and good ductility. The tungsten and chromium promote the formation of fine, evenly distributed carbides that provide wear resistance without excessive brittleness.

Production Application Results

The study reports successful production application of the overlay-welded work rolls at Anshan Iron and Steel Company. The overlay material was deposited using a suitable welding process (likely submerged arc welding or plasma arc welding, which are commonly used for large cylindrical work rolls) and then ground to the required dimensional accuracy and surface finish. The production results demonstrated that the overlay-welded rolls performed satisfactorily in hot rolling service, providing significant economic benefits through extended roll life and reduced remanufacturing costs.

Technical Interpretation and Engineering Implications

Process Selection for Work Roll Overlay

The selection of welding process for work roll overlay is critical and depends on several factors:

1. Submerged Arc Welding (SAW): Suitable for large-diameter work rolls where high deposition rates are required. SAW provides deep penetration and good fusion with the substrate, but requires precise control of the welding parameters to avoid excessive dilution and distortion. The use of flux-cored wire or solid wire with appropriate flux composition is essential for achieving the desired overlay chemistry.
2. Plasma Arc Welding (PAW): Preferred for smaller-diameter work rolls or where precise control of the weld pool is required. PAW provides a narrow, deep weld with minimal dilution, which is advantageous for maintaining the overlay composition. The high current density of the plasma arc also provides rapid solidification, which can refine the microstructure of the overlay deposit.
3. Tungsten Inert Gas Welding (GTAW): Used for repair welding of localized damage on work rolls. GTAW provides excellent control over the weld pool and minimal heat input, making it suitable for precise repair work.

Quality Control Considerations

For overlay-welded work rolls, the following quality control measures are essential:

• Hardness testing: The overlay deposit should be tested for hardness at multiple locations to ensure uniformity. The hardness should meet the specified range (typically 45-58 HRC for hot rolling work rolls, depending on the application).
• Macrographic examination: Cross-sectional examination of the overlay-substrate interface should be performed to verify complete fusion and absence of lack of fusion defects.
• Ultrasonic testing (UT): The overlay deposit should be tested for internal defects such as porosity, cracks, and lack of fusion using phased array ultrasonic testing (PAUT) or conventional ultrasonic testing.
• Dimensional verification: After grinding, the work roll diameter, taper, and surface roughness should be verified to meet the mill specifications.
• Thermal fatigue testing: For critical applications, thermal fatigue testing of the overlay material under simulated hot rolling conditions should be performed to verify the material's resistance to thermal cracking.

Economic Analysis

The economic benefits of overlay welding for work roll restoration are substantial. A new hot rolling work roll can cost tens of thousands of dollars, depending on the size and material. Overlay welding allows the roll to be restored to serviceable condition at a fraction of the cost of a new roll, typically 10-30% of the original cost. Additionally, the overlay material can be selected to provide superior surface properties compared to the original roll material, potentially improving product quality and reducing roll change frequency.

Key Questions and Reflections

The study, while demonstrating successful industrial application, does not provide detailed information on several aspects that are important for engineering practice. First, the specific welding parameters (current, voltage, travel speed, wire feed rate) are not reported, which limits the ability of other engineers to replicate the results. Second, the service life of the overlay-welded rolls compared to new rolls is not quantified, yet this is the most important metric for evaluating the economic viability of the technology. Third, the effect of the overlay on the roll's thermal properties and dimensional stability during hot rolling is not discussed, yet these factors can affect strip flatness and surface quality.

From a metallurgical perspective, the long-term stability of the overlay microstructure under repeated thermal cycling in hot rolling service is a concern. The austenite-ferrite microstructure of the FeCrWNiMnSi overlay may undergo phase transformation during prolonged exposure to elevated temperatures, potentially leading to a change in hardness and wear resistance. Engineers should monitor the overlay properties during service and establish replacement criteria based on measured hardness and surface condition.

Study Insights and Implications

This study demonstrates the practical viability of overlay welding technology for hot rolling work roll restoration in industrial settings. The FeCrWNiMnSi-based overlay material provides an effective combination of wear resistance, thermal fatigue resistance, and toughness that meets the demanding requirements of hot rolling service. For metallurgical engineers and production managers, this technology offers a cost-effective alternative to purchasing new work rolls, with the added benefit of being able to customize the surface properties to optimize performance for specific rolling conditions. The successful application at Anshan Iron and Steel Company provides valuable industrial validation of the technology, and similar approaches can be adapted for other metallurgical equipment such as cold rolling rolls, casting rolls, and continuous casting molds.