Strip Cladding Repair of Continuous Casting Guide Rollers

Literature Overview and Application Background

Continuous casting guide rollers are critical components in the strand guide system of continuous casting machines, subjected to extreme thermal cycling, mechanical loading, and contact with molten steel splash and scale. These rollers typically operate at temperatures of 200–600°C and experience rolling contact fatigue, abrasive wear from scale, and thermal cracking. The conventional repair method involves grinding down worn surfaces and applying a weld overlay coating, but strip cladding (flash butt welding of a cladding strip onto the roller surface) offers a superior alternative for restoring the original geometry and performance. This study documents the application of strip cladding repair technology to a 600 mm diameter guide roller in a 170-ton slab caster, where the roller had accumulated 0.8 mm of surface wear after 18 months of continuous operation. The cladding material selected was a Cr13-type martensitic stainless steel strip, chosen for its combination of high hardness, wear resistance, and thermal shock tolerance.

Repair Process Design and Execution

The repair process follows a systematic approach based on the PDCA cycle. In the Plan phase, the roller is inspected using ultrasonic testing (per NB/T 47013) to identify subsurface defects, and the worn surface is measured at 12 circumferential positions to determine the maximum and minimum wear depths. The cladding strip dimensions are designed to provide a minimum overlay thickness of 3.0 mm after flash butt welding, accounting for subsequent machining. The base roller material is a 42CrMo quenched and tempered steel with a hardness of 28–32 HRC, and the cladding strip is a 1Cr13 martensitic stainless steel with a hardness of 40–45 HRC after quenching and tempering.

The Do phase involves the actual welding operation. The roller is mounted on a flash butt welding machine, and the cladding strip is wrapped circumferentially around the roller surface. The welding is performed in a single pass around the full circumference, with the flash butt welding parameters carefully controlled to ensure a uniform bond. The burn-off time is monitored visually to ensure complete oxide removal and sufficient plastic deformation at the weld interface. After welding, the roller undergoes stress relief heat treatment to reduce residual stresses and prevent delayed cracking in the martensitic cladding layer.

Quality Inspection and Performance Verification

The quality inspection follows the Check phase of the PDCA cycle. Visual inspection confirms that the cladding strip is uniformly bonded around the entire circumference with no gaps or cold shuts. Ultrasonic testing using a 2.5 MHz normal beam transducer verifies the bond integrity, with no indications exceeding the acceptance criteria of NB/T 47013-3. Metallographic examination of the weld interface reveals a clean bond with no unmelted oxide inclusions, and a thin diffusion zone of approximately 15–20 μm at the interface, indicating complete metallurgical bonding. The hardness profile across the cladding layer shows a uniform distribution of 42–45 HRC with a gradual transition to the base metal over a distance of 1.5 mm, which is acceptable for the intended service conditions. The roller is then machined to the final diameter tolerance of ±0.05 mm and surface finish of Ra 1.6 μm.

Field Performance and Lessons Learned

After returning to service, the repaired roller operated for 22 months before the next scheduled inspection, representing a 22% improvement over the previous 18-month service interval. Post-service examination showed a maximum wear depth of 0.6 mm, compared to 0.8 mm for the previous roller, indicating that the 1Cr13 cladding layer provided superior wear resistance to the original roller surface. The Act phase of the PDCA cycle led to several process improvements: the cladding strip thickness was increased from 2.5 mm to 3.0 mm to provide additional material for subsequent rework cycles, the stress relief cycles were increased from 2 to 3 to further reduce residual stresses, and a preheating step at 200°C was added to minimize thermal stress during the flash butt welding operation. These improvements are now incorporated into the standard repair procedure for guide roller maintenance at the plant.

Study Insights and Engineering Implications

This case study demonstrates that strip cladding is a technically sound and economically viable repair method for continuous casting guide rollers, offering superior performance compared to conventional weld overlay repair. The key advantage of strip cladding is the ability to achieve a uniform, defect-free overlay with controlled composition and microstructure, which is difficult to achieve with multi-pass welding on a cylindrical surface. However, the method requires specialized flash butt welding equipment and skilled operators, which limits its applicability to shops with the necessary infrastructure. Engineers considering strip cladding for roller repair should carefully evaluate the thermal compatibility between the base metal and cladding strip, as mismatched thermal expansion coefficients can lead to interface cracking during thermal cycling in service. The 1Cr13-to-42CrMo combination used in this study is well-matched, with a thermal expansion coefficient difference of less than 5%, but other material combinations require more careful assessment. Future work should investigate the use of duplex stainless steel or precipitation-hardening stainless steel strips for even higher-performance cladding layers.