Zhuojin Pipe Fitting Co., LtdWear-Resistant Overlay Welding Repair Process for Cold Rolling Rolls
Literature Overview
Yu Chengkui and Yang Zhenlin (Wuhan University of Technology and Tianjin Quality and Technical Supervision Bureau, 2006) presented a practical study on the overlay welding repair of Cr3-type cold rolling work rolls. Published in Welding Technology (Vol. 35, No. 3, pp. 27–28), this paper focuses on the local overlay repair of worn cold rolling rolls, examining welding parameters, microstructure, and wear performance. While relatively concise, the study provides valuable engineering insights into the repair of high-performance cold rolling rolls, which are critical assets in steel mills.
Core Technical Approach
Cold rolling work rolls are subject to extreme conditions: high contact stresses, sliding contact with the steel strip, and often the presence of lubricants and cooling fluids. The Cr3-type cold rolling roll is typically made from a high-chromium cast iron or a steel with substantial chromium content, providing inherent wear resistance through the formation of hard carbides. When localized wear occurs—such as roll crown deviation, surface scoring, or localized material loss—the roll can be restored through overlay welding rather than complete replacement, offering significant cost savings.
The authors investigated two different overlay welding processes and optimized the welding parameters for each. The key considerations included:
- Welding heat input control: Cold rolling rolls require low heat input to minimize the HAZ and avoid distortion of the roll barrel, which would affect roll flatness and strip gauge accuracy.
- Welding material selection: The overlay material must match or exceed the hardness and wear resistance of the base roll material while maintaining good weldability.
- Layer thickness and geometry: The overlay must be thick enough to provide wear life but thin enough to avoid excessive heat accumulation.
Process Parameters and Performance Evaluation
The study compared two overlay welding processes and evaluated the resulting overlay performance through wear tests and metallographic examination. The following table summarizes the key process and performance parameters:
| Parameter | Process Variant 1 | Process Variant 2 | Engineering Rationale |
|---|---|---|---|
| Welding process | Lower heat input | Higher heat input | Trade-off between HAZ and deposition rate |
| Preheat temperature | Low or none | Moderate | Cold rolling rolls resist cracking but HAZ softening is a concern |
| Interpass temperature | Strictly controlled | Less restrictive | Prevents cumulative heat buildup |
| Overlay hardness | Higher | Lower | Inverse relationship with heat input |
| Wear resistance | Superior | Moderate | Harder overlay resists abrasive wear better |
| Microstructure | Fine-grained, high carbide density | Coarser, moderate carbide density | Heat input controls solidification rate |
The wear tests demonstrated that the lower-heat-input process produced overlays with superior wear resistance, consistent with the expectation that lower heat input results in finer microstructures and higher carbide density. The metallographic examination confirmed that the overlay microstructure in the lower-heat-input variant featured a high density of hard carbide phases (Cr₇C₃, Cr₂₃C₆) dispersed in a tough matrix, providing excellent abrasion resistance.
Engineering Practice Implications
For steel mill maintenance engineers, this study offers several practical takeaways:
- Local repair is economically viable: Overlay welding repair of cold rolling rolls can extend roll life significantly, reducing the frequency of roll replacement and associated downtime. However, the repair must be performed with precision to maintain roll geometry and surface finish.
- Heat input is the critical parameter: Lower heat input processes (such as GTAW or low-current GMAW) should be preferred for cold rolling roll repair, despite potentially lower deposition rates, because they minimize HAZ softening and distortion.
- Post-weld machining is essential: After overlay welding, the roll surface must be ground to restore the original surface profile and finish. The overlay thickness should be designed to allow for adequate grinding stock while maintaining sufficient wear-resistant material.
- Process consistency is paramount: Cold rolling roll repair requires strict process control, including consistent travel speed, torch angle, and interpass temperature monitoring, to ensure uniform overlay properties across the repaired zone.
Study Insights and Reflections
This study, though concise, captures the essence of practical overlay welding engineering: the optimization of process parameters to balance competing requirements such as deposition rate, heat input, microstructure, and geometry control. The case of cold rolling roll repair is particularly instructive because it involves a high-precision component where even minor distortions can lead to product quality issues. The findings reinforce the principle that in overlay welding repair, the process must be tailored to the specific application requirements rather than following generic welding procedures. For engineers involved in rolling mill maintenance, this work provides a foundation for developing site-specific repair procedures that can be validated through trial repairs and wear life tracking. The emphasis on heat input control also has broader applicability to other precision component repairs, such as turbine blades, bearing surfaces, and hydraulic cylinder bores.