Cladding Repair of Hot Rolling Transfer Roller Guides

Literature Overview

This study addresses the practical challenge of restoring worn hot rolling transfer roller guides through cladding repair, a critical maintenance activity in steel mills where roller guides are subjected to severe abrasive wear from hot steel slabs and billets. The roller guides must withstand temperatures up to 900°C during transfer, resist abrasion from rough steel surfaces, and maintain dimensional accuracy for proper slab alignment. The work presents the repair methodology, material selection, and performance validation of the cladding restoration process.

Failure Analysis and Material Selection

The original roller guides were made of low-alloy steel (Q345 equivalent) and experienced wear rates of 0.3-0.5 mm per month under normal operating conditions. The wear mechanism was identified as adhesive-abrasive wear, with the hot steel surface causing material transfer and plowing. The decision to use cladding repair rather than replacement was driven by cost considerations, as the roller guides are large components (typically 200-400 mm diameter, 600-1200 mm length) with significant material and fabrication costs.

The cladding material selected was a high-chromium white iron alloy (Cr15 equivalent) applied by flux-cored arc welding (FCAW) with a composite wire containing 12-14% Cr, 3-5% Mo, and 2.5-3.5% C. The high carbon and chromium content ensures the formation of hard carbides (Cr7C3, Fe3C) that provide exceptional wear resistance.

Repair Process Optimization

The repair process involved several critical steps to ensure proper adhesion and minimize residual stresses:

The critical process parameter was the heat input control. The first pass used a current of 180-200 A with a travel speed of 8-10 cm/min to achieve adequate fusion with the base metal while limiting dilution. Subsequent passes used progressively higher currents (250-320 A) with slower travel speeds (5-7 cm/min) to build up the required thickness efficiently.

The interpass temperature was maintained below 300°C to prevent excessive softening of the previously deposited layers. The total cladding thickness was typically 8-12 mm, providing sufficient material for multiple regrinding operations during service.

Performance Validation

The repaired roller guides were subjected to rigorous qualification testing before returning to service:

• Dimensional inspection: diameter tolerance ±0.5 mm, runout <0.3 mm
• Hardness verification: 550-650 HV30 across the cladding surface
• Magnetic particle testing (MT): no indications of cracks or inclusions
• Wear testing: laboratory pin-on-disk test confirmed 8-10x improvement over base metal
• Field performance: monitored wear rate of 0.06-0.09 mm/month over 12 months of service

The study also addressed the issue of thermal distortion during repair. Large roller guides are prone to warping during welding, which affects the concentricity and alignment. The use of symmetric welding sequences (opposite sides welded alternately) and controlled heat input minimized distortion to acceptable levels (<0.5 mm TIR).

Study Insights and Reflections

This case study demonstrates the economic and technical viability of cladding repair for large, expensive components in steel mill applications. The key insight is that the success of cladding repair depends not only on the selection of appropriate cladding material but also on careful process planning, including preheat, interpass temperature control, and post-weld stress relief. In my experience with hot rolling mill maintenance, the most common failure mode of repaired roller guides is not wear but rather spalling due to excessive residual stresses or inadequate adhesion at the fusion line. The stress relief treatment at 550°C is therefore not optional but essential for long-term service reliability. The study provides a practical framework that can be adapted for similar cladding repair applications across the steel industry.