Overlay Welding Repair of Hot Rolling Plate Coil Pickup Roller

Literature Overview

This paper by Sui Xiangrong and colleagues from the Welding Research Institute of China Metallurgical Group Corporation (Mechanical Engineering Materials, 2008, Vol. 32, No. 6, pp. 62–65) addresses a practical industrial maintenance challenge: the overlay welding repair of pickup rollers in hot strip mills. Pickup rollers are critical components in the hot rolling line that grip and transport the hot steel coil between rolling stands, subjecting them to extreme temperatures (up to 900–1100°C), heavy mechanical loads, and abrasive contact with the hot strip surface.

Consumable Selection and Process Parameters

The study evaluated two flux-cored wire (FCW) consumables for automatic submerged arc overlay welding (SAW):

Microstructural Comparison

Both YJ254-S and YJ245-S produce martensitic overlay microstructures with carbide precipitates, but the key differences lie in:

1. Carbide morphology and distribution — YJ245-S produces finer and more uniformly distributed carbides, contributing to improved wear resistance.
2. Matrix microstructure — The martensite in YJ245-S may contain a higher volume fraction of retained austenite, which provides toughness while maintaining hardness through strain-induced martensite transformation during service.
3. Grain refinement — The flux composition in YJ245-S may promote grain refinement in the overlay, reducing the effective grain size and improving both hardness and toughness.

Engineering Application Results

The practical application results are compelling:

The 20–50% extension in service life represents a significant economic benefit, considering that pickup roller replacement requires mill shutdown and substantial labor costs.

Process Optimization Considerations

For overlay welding repair of hot rolling mill components, the following process parameters must be carefully controlled:

1. Preheating temperature — Pickup rollers made of high-strength steel (typically 42CrMo or similar) require preheating to 200–300°C to prevent cold cracking in the HAZ and reduce residual stress.
2. Interpass temperature — Must be maintained between 150–250°C to control martensite transformation kinetics and prevent excessive hardness in the HAZ.
3. Post-weld stress relief — At 550–600°C for 2–4 hours, to relieve residual stresses that could cause overlay cracking during service.
4. Overlay thickness — Typically 3–5 mm for pickup rollers, providing sufficient wear reserve while minimizing heat input and distortion.

Key Reflections

The selection between YJ254-S and YJ245-S illustrates a fundamental principle in overlay consumable selection: the optimal choice is not the one with the highest hardness but the one that provides the best balance of hardness, toughness, and wear resistance for the specific service conditions. YJ245-S's superior performance likely stems from a more favorable combination of microstructural features rather than simply higher hardness.

The hot rolling mill environment imposes unique challenges — thermal cycling from hot strip contact, mechanical impact from coil handling, and abrasive wear from scale and oxide particles. The overlay must resist all three degradation mechanisms simultaneously, which is why high-Cr martensitic overlays with controlled carbide morphology are preferred over simpler high-carbon systems.

Study Insights

This case study demonstrates the economic value of overlay welding repair in heavy industry. The 20–50% extension in pickup roller service life translates directly into reduced mill downtime, lower spare parts inventory, and improved overall equipment effectiveness (OEE). For pipe and fitting manufacturers that operate hot rolling or forming equipment, similar overlay repair strategies can be applied to critical wear components such as mandrels, forming dies, and transfer rollers.

The key lesson is that consumable selection should be based on comprehensive performance evaluation — including field trial data — rather than solely on laboratory hardness measurements. The YJ245-S consumable's superior field performance, despite potentially similar hardness values to YJ254-S, underscores the importance of wear mechanism-specific testing in overlay consumable qualification.