Study Note on Weld Overlay Repair of Rolling Mill Guide Plate Heads

Literature Overview and Technical Background

This 1994 publication from the Steel Research Institute of Maanshan Steel Company, authored by Wan Weiguo, documents the weld overlay repair of rolling mill guide plate heads—critical components that direct and align the steel strip as it passes through the rolling mill. Guide plate heads are subject to continuous contact with hot steel strip (typically 800–1100 °C for hot rolling) and experience severe abrasive wear, thermal fatigue, and impact loading. When the guide surface becomes worn or damaged, the strip alignment is compromised, leading to edge defects, increased rolling resistance, and potential production stoppages.

The technical challenge of repairing guide plate heads lies in the combination of materials involved: the guide plate body is typically made from carbon steel or low-alloy steel, while the guide surface must be overlaid with a hard, heat-resistant alloy capable of withstanding repeated thermal cycling and abrasive contact with hot steel. The repair must restore the precise geometry of the guide surface, which directly affects strip quality and rolling accuracy.

Repair Process and Material Selection

The repair methodology employed a combination of GTAW (gas tungsten arc welding) and plasma transferred arc (PTA) welding, with careful selection of filler materials based on the operating conditions:

The layered approach addresses the metallurgical challenges of dissimilar metal welding: the Ni-Fe transition layer provides good wetting and bonding to the steel base, the Cr-based intermediate layer provides thermal shock resistance and moderate hardness, and the Ni-based surface layer provides the required hardness (HV 400–500) and heat resistance for contact with hot steel strip.

Process Parameters and Heat Input Control

The heat input was carefully controlled to prevent excessive dilution of the overlay layers, which would reduce the hardness and wear resistance of the surface. For the GTAW passes, a heat input of 0.5–2.0 kJ/mm was used, with the lower values applied to the transition layer to minimize dilution of the Ni-Fe alloy into the carbon steel base. The PTA surface pass used slightly higher heat input to ensure good fusion with the intermediate layer while maintaining the alloy composition of the surface.

Defect Analysis and Countermeasures

The most common defect encountered was surface cracking in the overlay layer, particularly in the Ni-based surface layer. This was attributed to the high cooling rate and thermal stress generated during welding. The countermeasure was to reduce the heat input for the final PTA pass and apply a post-weld annealing treatment at 800–900 °C for 1–2 hours to relieve residual stresses and promote grain refinement.

Engineering Practice and Maintenance Strategy

The repair of rolling mill guide plate heads is typically performed during scheduled maintenance intervals, which provides an opportunity for comprehensive inspection and assessment before repair. The recommended maintenance strategy includes:

1. Regular inspection: Visual inspection of the guide surface every 1–3 months, with detailed measurement of wear depth every 6 months.
2. Wear limit: When the guide surface wear exceeds 2–3 mm or when the surface profile deviates from the original geometry by more than 0.5 mm, repair is recommended.
3. Pre-repair assessment: Ultrasonic testing of the guide plate body to check for subsurface cracks or delamination before applying overlay.
4. Post-repair verification: Hardness testing, dimensional measurement, and surface profile verification after repair and machining.

The economic analysis showed that weld overlay repair extended the service life of guide plate heads by 2–3 times compared to simple grinding and resurfacing, while being significantly less expensive than replacement with new guide plates.

Study Insights and Reflections

This industrial repair study from Maanshan Steel provides valuable practical insights into the repair of critical rolling mill components. The layered overlay approach—using different alloy compositions for transition, intermediate, and surface layers—demonstrates a sophisticated understanding of metallurgical compatibility and functional requirements. The emphasis on heat input control and post-weld treatment reflects the practical experience gained from addressing the specific challenges of repairing components that operate under extreme thermal and mechanical conditions. For maintenance engineers in steel mills and other heavy industries, this work provides a proven methodology for extending component life through skilled weld overlay repair, reducing both material costs and production downtime. The systematic defect analysis and countermeasure approach also serves as a model for quality improvement in industrial repair operations.

In conclusion, these five studies collectively represent a comprehensive body of knowledge spanning copper alloy overlay on cast iron, stainless steel and Ni-based overlay on high-pressure valve bodies, carbide valve seat repair, proactive overlay of rolling mill frames, and guide plate head repair. Together, they illustrate the breadth of weld overlay applications in pressure equipment manufacturing and heavy industrial maintenance, from precision valve sealing surfaces to massive structural components. The common thread across all applications is the critical importance of interface metallurgy, heat input control, and systematic quality assurance in achieving reliable and durable overlay welds. These foundational studies, dating from 1989 to 2000, continue to provide valuable engineering guidance for practitioners working in valve manufacturing, pressure vessel fabrication, and heavy industrial maintenance today.