CLADDING TECHNOLOGY SHANXI CO., LTDWeld Overlay Technology for Hot Rolling Support Rolls
Technical Context and Industrial Significance
The 2009 research by Lin Jiandong from the Panzhihua Steel Research Institute addresses one of the most demanding applications of overlay welding in heavy industry: the restoration and enhancement of hot rolling support rolls. Support rolls in hot strip mills operate under extreme combined loading conditions, including contact stress from the work roll, thermal cycling from molten steel contact (up to 1200°C), and mechanical fatigue from repeated rolling cycles. The overlay welding of wear-resistant and heat-resistant alloys onto the roll surface is a critical maintenance technology that directly impacts mill availability, product quality, and operational costs. This study is particularly significant given that Panzhihua Steel is a major integrated steel producer in southwestern China, and the research reflects genuine industrial problem-solving rather than purely academic inquiry.
Overlay Process Selection and Material System
The study examines the application of hardfacing and wear-resistant overlay alloys on support roll surfaces using submerged arc welding (SAW) and plasma transferred arc (PTA) techniques. The selection of overlay material is governed by the specific service conditions:
| Overlay Material System | Typical Application | Key Properties | Process |
|---|---|---|---|
| High-Cr cast iron (Cr20-Cr30) | Work roll surface | High hardness, thermal shock resistance | SAW |
| Hardfacing alloy (Co-based or Ni-based) | Support roll bearing raceway | High wear resistance, low friction | PTA |
| Austenitic stainless steel (304/321) | General support roll body | Corrosion resistance, toughness | SAW |
| High-alloy steel (Cr-Mo-V) | Support roll body reinforcement | High strength, fatigue resistance | SAW |
The PTA process is preferred for the bearing raceway application due to its ability to produce a thin, dense, and well-bonded overlay layer with minimal dilution from the base material. The SAW process is more economical for large-area body reinforcement where deposition rate and cost efficiency are paramount.
Key Technical Challenges and Solutions
The primary challenges in support roll overlay welding include:
- Thermal distortion control: Support rolls are large cylindrical components (typically 1000–1500 mm diameter and 3000–6000 mm length) with tight dimensional tolerances. The heat input from overlay welding can cause significant barrel distortion and out-of-roundness. The study recommends using a multi-pass, multi-start technique with controlled interpass temperature (below 150°C) and possibly post-weld stress-relief annealing at 550–650°C.
- Bond strength and spallation resistance: The overlay layer must resist spallation under cyclic contact loading. This requires careful control of the weld metal composition to ensure adequate toughness and a gradual hardness gradient from the base material to the overlay surface.
- Surface quality: The overlay surface must be machined to a specified roughness (typically Ra 1.6–3.2 μm) to ensure proper lubrication and contact with the work roll. Excessive porosity, inclusions, or lack of fusion in the overlay layer can lead to surface defects in the rolled product.
- Residual stress management: The high residual stresses from overlay welding can initiate surface cracking under thermal cycling. The study suggests using a back-step welding sequence and post-weld vibration stress relief to mitigate this risk.
Engineering Practice and Maintenance Strategy
From an engineering perspective, the study provides a practical framework for support roll overlay maintenance. The recommended procedure involves grinding the existing surface to remove damaged material, cleaning and preheating the roll to 200–300°C, applying a transition pass of low-dilution alloy, followed by the main overlay passes, and finally machining to final dimensions. The overlay thickness is typically 3–5 mm for body reinforcement and 1–2 mm for bearing raceway applications. The total maintenance cycle time for a single roll is approximately 8–16 hours depending on the extent of damage and the number of passes required.
The study also highlights the importance of quality control through ultrasonic testing (UT) of the overlay layer for lack of fusion and internal defects, and hardness profiling to verify the hardness gradient. The economic analysis demonstrates that overlay welding restoration is significantly more cost-effective than roll replacement, with typical savings of 60–70% per maintenance cycle.
This research exemplifies how overlay welding technology can extend the service life of critical industrial components and improve overall production efficiency in the steel industry.