Zhuojin Pipe Fitting Co., LtdOverlay Welding Technology for Rolls of Double-Roll Reversible Rolling Mills
Literature Overview
The paper by Gan Meijun from Ningbo Institute of Metallurgy, published in Shanghai Metals in 2001 (Vol. 23, No. 1, pp. 39-41), presents a comprehensive study of the overlay welding technology for the wear-resistant layer on rolls of a double-roll reversible rolling mill. The specific application involves rolls of diameter 360 mm and length 760 mm used in a reversible hot rolling mill. The study covers material selection, flux selection, welding parameter determination, and quality inspection of the overlay weld.
Core Technical Methodology
Process Parameters and Results
| Parameter | Value/Description |
|---|---|
| Roll dimensions | φ360 mm × 760 mm |
| Rolling mill type | Double-roll reversible hot rolling mill |
| Overlay hardness | HRC 47 |
| Roll life improvement | Increased by approximately 1 fold |
| Key aspects | Material selection, flux selection, welding parameters, quality inspection |
The study addresses the full scope of overlay welding technology for rolling mill rolls, which is a critical maintenance operation in steel processing plants. Rolling mill rolls are subjected to extreme conditions including high temperatures, heavy mechanical loads, thermal cycling, and abrasive contact with hot steel slabs. The overlay welding layer must provide wear resistance while maintaining adequate toughness to prevent catastrophic failure.
Material and Flux Selection
The selection of overlay welding materials and flux is a critical aspect of this technology. The overlay material must be compatible with the roll base material, provide adequate hardness and wear resistance, and resist spalling during service. The flux plays a crucial role in protecting the molten weld pool from atmospheric contamination, modifying the weld metal composition, and controlling the cooling rate.
Interpretation of Technical Points
The achievement of HRC 47 hardness in the overlay layer represents a careful balance between wear resistance and toughness. In hot rolling applications, excessively hard overlay layers may be prone to thermal fatigue cracking, while overly soft layers would wear prematurely. The HRC 47 level is typical for hot rolling mill roll overlays, providing adequate resistance to wear while maintaining sufficient ductility to withstand thermal and mechanical stresses.
The doubling of roll life is a significant economic benefit, as roll changes are one of the most costly maintenance operations in a steel mill. Each roll change requires significant downtime, labor, and material costs. The overlay welding technology effectively extends the service interval between roll changes, improving overall mill productivity.
From a 5W2H analysis: What (overlay welding of roll wear layer), Where (double-roll reversible hot rolling mill), When (during planned maintenance), Who (welding technicians and engineers), Why (to extend roll life and reduce costs), How (through optimized material, flux, and parameter selection), and How much (HRC 47 hardness, 1-fold life improvement).
Engineering Practice Integration
In steel mill operations, roll maintenance is a recurring and critical activity. The overlay welding process must be carefully controlled to ensure consistent quality across multiple passes and multiple rolls. Key process considerations include:
- Preheating to reduce residual stress and prevent cracking
- Interpass temperature control to maintain proper microstructure
- Weld sequence planning to minimize distortion
- Post-weld stress relief to reduce residual stresses
- Surface finishing to achieve required dimensional tolerances
In terms of FMEA, the primary failure modes for roll overlays include: spalling due to thermal fatigue, cracking at the overlay/base metal interface, delamination of the overlay layer, and premature wear. Each of these failure modes requires specific process controls and quality inspection procedures to prevent.
The quality inspection of the overlay weld is essential and typically includes visual inspection, dimensional measurement, hardness testing, and possibly non-destructive testing such as ultrasonic testing or magnetic particle inspection. The inspection criteria must be clearly defined and consistently applied to ensure uniform quality across all rolls.
Study Insights and Implications
This work represents practical industrial welding engineering at its best—addressing a real production problem with a technically sound and economically viable solution. The systematic approach to material selection, process parameter optimization, and quality control provides a template for similar overlay welding applications in other industrial settings.
A reflective consideration is that the study focuses on the process and results but does not extensively discuss the metallurgical aspects of the overlay layer, such as microstructure, phase composition, and dilution. Understanding these aspects is important for predicting long-term performance and optimizing the process for different operating conditions.
The principles documented here are applicable to a wide range of rolling mill applications, including cold rolling, strip mills, and plate mills. The specific parameters will vary depending on the operating conditions, but the systematic approach to process development and quality control remains the same.
This research demonstrates the significant economic impact of welding technology in heavy industry and provides a valuable reference for engineers involved in rolling mill maintenance and optimization.