Zhuojin Pipe Fitting Co., LtdApplication of Overlay Welding Technology on Backup Rolls in Hot Strip Continuous Rolling Mills
Literature Overview
This 1993 paper by Lu Daocheng, Wu Gang, Lin Youzuo, and Lin Zhong, published in Shanghai Metals, documents the pioneering application of overlay welding technology for the refurbishment and reuse of backup rolls in hot strip continuous rolling mills at Shanghai No.1 Steel Plant. The study addresses a critical industrial challenge: backup rolls in hot rolling mills are subjected to extreme thermal and mechanical loads, leading to surface degradation, work hardening, and eventual failure. Rather than scrapping these expensive large-diameter rolls, the authors investigated overlay welding as a cost-effective restoration method, working in collaboration with Shanghai Stellite Company for the supply of specialized welding consumables.
Core Technical Content
The research focused on selecting appropriate overlay welding materials and establishing repeatable welding procedures capable of restoring the functional surface properties of backup rolls. The backup rolls in hot strip mills typically experience temperatures exceeding 900°C during operation, combined with high compressive contact stresses from the work rolls and strip. This creates a demanding service environment requiring overlay materials with excellent thermal stability, resistance to thermal fatigue, and adequate hardness retention at elevated temperatures.
Overlay Material Selection
The material selection process considered several critical factors including thermal conductivity matching, coefficient of thermal expansion compatibility, and resistance to thermal cracking during both the welding process and subsequent service. Stellite-type alloys were evaluated for their proven track record in high-temperature applications, while iron-based and nickel-based hardfacing alloys were also considered for specific performance requirements.
| Parameter | Typical Requirement | Selected Material Characteristic |
|---|---|---|
| Operating temperature | 800-950°C | Retained hardness at elevated temperature |
| Contact stress | 2000-3500 MPa | Adequate compressive strength |
| Thermal cycles | Continuous | Resistance to thermal fatigue cracking |
| Hardness at room temperature | 35-50 HRC | Wear resistance against steel strip |
| Dilution resistance | High | Self-fluxing or low-dilution process |
Welding Process Parameters
The overlay welding was performed using submerged arc welding (SAW) and/or gas-shielded metal arc welding (GMAW) processes, selected for their ability to deposit thick layers with controlled dilution. Key process parameters included:
- Preheating temperature of 200-300°C to reduce residual stress and prevent cracking in the base metal heat-affected zone
- Interpass temperature control maintained between 150-250°C to manage thermal gradients
- Multiple pass deposition to achieve required overlay thickness (typically 6-12 mm)
- Controlled welding speed to balance deposition rate with penetration control
- Post-weld heat treatment to relieve residual stresses and optimize microstructure
Engineering Practice and Economic Analysis
The economic evaluation demonstrated significant cost savings compared to the procurement of new backup rolls. A single backup roll in a modern hot strip mill can weigh several tons and cost substantial capital investment. Through overlay welding restoration, the service life could be extended by multiple cycles, with each restoration cycle representing a fraction of the original roll cost.
The study also highlighted practical challenges encountered during implementation:
- Surface preparation of the worn roll required careful grinding to remove severely degraded material while maintaining dimensional accuracy
- Geometric tolerances after welding required post-weld machining to restore the roll profile to specified roundness and diameter tolerances
- Quality control included hardness testing, ultrasonic examination for internal defects, and dimensional verification after machining
Key Insights and Reflections
This early work represents an important milestone in the industrial application of overlay welding for heavy equipment restoration. The approach demonstrated that proper material selection combined with disciplined process control could effectively restore worn components to functional condition. The methodology established in this study remains relevant to modern practices, where overlay welding continues to be the preferred method for refurbishing rolling mill rolls, forming rolls, and other critical components in the steel industry. The emphasis on economic analysis alongside technical performance is particularly valuable, as it provides the business justification necessary for adopting new technologies in production environments.