CLADDING TECHNOLOGY SHANXI CO., LTDOverlay Welding Technology for Rolls of Double-Roll Reversible Rolling Mills
Literature Overview
The paper by Gan Meijun from the Ningbo Institute of Metallurgy, published in the journal Shanghai Metals in 2001, addresses a critical industrial problem: the restoration and surface hardening of rolls used in double-roll reversible rolling mills. These heavy-duty rolls operate under extreme conditions of high contact stress, thermal cycling, and abrasive wear, making them among the most demanding components in continuous metal-forming production lines. The study reports on the application of overlay welding (hardfacing) to extend roll service life and maintain dimensional accuracy without requiring full roll replacement.
Core Technical Content
Double-roll reversible rolling mills are commonly employed in medium-to-heavy plate and strip production where the direction of roll rotation is periodically reversed to compensate for asymmetry. The roll surface is subjected to alternating compressive and shear stresses, with peak contact pressures often exceeding 2000 MPa during heavy rolling operations. The original roll material, typically medium-carbon or low-alloy forged steel (such as 45 steel or 50CrNiMo), provides adequate core toughness but insufficient surface hardness and wear resistance for extended service.
The overlay welding approach described in this study involves the application of a hardfacing layer onto the roll surface using arc welding processes. The key objectives are:
- Achieve surface hardness in the range of 55–62 HRC to resist abrasive and adhesive wear
- Maintain adequate dilution control to prevent excessive softening of the hardfacing alloy
- Ensure sound bonding between the overlay layer and the base roll material
- Preserve the roll's cylindrical geometry and dimensional tolerances for subsequent grinding
Process Parameters and Material Selection
Based on the engineering context described in the literature, the following process considerations are central to successful roll overlay welding:
| Parameter | Typical Range | Rationale |
|---|---|---|
| Base material | 45 steel, 50CrNiMo | Core toughness requirement |
| Hardfacing alloy | Cr-Cr2C, Cr-V, or Ni-based | Wear resistance |
| Welding process | Multi-layer SAW or GMAW | High deposition rate |
| Preheating temperature | 200–300 °C | Reduce residual stress, prevent cracking |
| Interpass temperature | ≤300 °C | Control microstructure coarsening |
| Post-weld treatment | Stress-relief annealing at 550–600 °C | Reduce residual stress |
| Final surface hardness | 55–62 HRC | Wear resistance target |
| Overlay layer thickness | 8–15 mm | Balance wear life vs. cost |
Process Analysis and Defect Prevention
The challenge in overlay welding of large-diameter rolls lies in managing thermal distortion and residual stresses. Because the roll is a massive cylindrical body with high thermal mass, the welding heat input creates steep thermal gradients that can lead to:
- Cracking in the overlay layer – particularly with high-carbon Cr-Cr2C hardfacing alloys where carbon segregation and carbide network formation promote hot cracking
- Delamination at the bond line – caused by hydrogen-induced cracking or poor fusion due to inadequate preheating
- Geometric distortion – ovality development along the roll axis that compromises rolling quality
The study emphasizes the importance of multi-pass welding with controlled layer thickness (typically 3–5 mm per pass) and the use of backing plates or support rings to prevent weld sagging on horizontal rolls. The welding sequence must follow a symmetrical pattern around the roll circumference to minimize ovalization.
Engineering Practice Implications
From a practical standpoint, this work is highly relevant to steel mills and non-ferrous rolling operations where roll replacement represents a significant cost and production downtime. The overlay welding approach allows for:
- Hot-standby roll rotation – multiple rolls can be maintained with overlay layers, rotating between service, grinding, and re-overlay cycles
- In-situ repair – worn or damaged rolls can be restored on-site without shipping to a specialized grinding facility
- Surface property upgrading – new hardfacing compositions can be applied to address specific wear mechanisms encountered during production
The economic analysis implicit in this work suggests that overlay welding can extend roll life by 2–3 times compared to unclad rolls, with a cost per ton of rolled product that is significantly lower than periodic roll replacement.
Key Questions and Reflections
Several questions arise from studying this work:
- How does the thermal fatigue resistance of the overlay layer compare to that of induction-hardened or plasma-nitrided surfaces under cyclic thermal loading?
- What is the long-term behavior of the bond interface after extended service, particularly regarding spalling or delamination under impact loading?
- Can the overlay welding process be optimized for thinner layers (3–5 mm) with higher hardness to reduce material consumption while maintaining adequate wear life?
The 2001 publication date places this work at a time when Chinese steel industry was rapidly expanding, and the demand for reliable roll maintenance technology was acute. The practical orientation of this study reflects the engineering culture of that era – focused on solving immediate production problems with proven welding technology rather than pursuing exotic surface engineering approaches.
Summary
This literature provides a solid foundation for understanding the application of overlay welding in heavy industrial roll restoration. The core insight is that careful control of welding parameters, particularly preheat and interpass temperatures, combined with appropriate hardfacing alloy selection, can significantly extend roll service life while maintaining dimensional accuracy. For engineers involved in rolling mill maintenance, this work serves as a practical reference for developing overlay welding procedures that balance wear resistance, processability, and economic viability in demanding production environments.