Short-Process Cladding Repair of Rolling Mills

Literature Overview

The 2010 publication in Electric Welder addresses the repair of rolling mills (rolling mill rolls) using a short-process cladding approach. Rolling mill rolls are subjected to extreme conditions during operation, including high contact pressure, elevated temperatures, abrasive contact with hot metal, and thermal cycling. These conditions lead to surface wear, thermal cracking, and spalling of the roll surface, necessitating periodic repair or replacement. The short-process cladding approach aims to minimize repair time while restoring the functional surface properties of the roll, thereby reducing production downtime and extending roll service life.

Core Technical Approach

The short-process cladding repair of rolling mills typically involves a combination of surface preparation, cladding deposition, and post-weld treatment, all designed to be completed within a minimal time window. The process flow is streamlined to reduce the number of intermediate steps, inspection points, and thermal cycles. Key elements of the short-process approach include the use of high-deposition-rate welding methods, optimized preheat and interpass temperature control, and efficient post-weld heat treatment or stress relief procedures.

Typical Process Flow for Short-Process Cladding Repair

Step	Description	Time Estimate
1. Surface inspection	UT/MT for cracks and subsurface defects	1–2 hours
2. Surface preparation	Grinding to remove damaged layer, cleaning	2–4 hours
3. Preheating	Controlled heating to reduce cracking risk	1–2 hours
4. Cladding deposition	Multi-pass welding with high-deposition-rate method	4–8 hours
5. Stress relief	Post-weld heat treatment to reduce residual stress	2–4 hours
6. Post-weld inspection	Hardness, MT, dimensional check	1–2 hours
Total		11–22 hours

The literature emphasizes the use of submerged arc welding (SAW) or flux-cored arc welding (FCAW) for the cladding deposition step, as these methods offer high deposition rates (up to 10–15 kg/h for SAW) while maintaining good arc stability and slag protection. For the cladding layer material, hardfacing alloys with appropriate hardness (typically 45–60 HRC) and wear resistance are selected based on the rolling mill application — hot rolling, cold rolling, or strip finishing.

Material Selection and Performance

The selection of cladding material for rolling mill roll repair is critical and depends on the specific service conditions. For hot rolling applications, where the roll surface is exposed to temperatures up to 1200°C and contact with hot steel, the cladding material must have excellent thermal fatigue resistance and spalling resistance. Typical materials include high-alloy chromium-molybdenum steels (e.g., Stellite-type alloys) or nickel-based superalloys. For cold rolling applications, where the primary concern is surface hardness and dimensional accuracy, hardfacing alloys with high carbon and chromium content are preferred.

Common Cladding Materials for Rolling Mill Rolls

Material Type	Typical Composition	Hardness (HRC)	Application
High-Cr-Mo steel	12% Cr, 2% Mo, 0.5% C	45–55	Hot rolling
Stellite 6	60% Cr, 15% Co, 5% Mo, 1% C	40–50	Hot rolling, high temperature
Ni-based hardfacing	60% Ni, 15% Cr, 5% Mo	45–55	General wear
High-C hardfacing	3% C, 10% Cr, 5% W	55–65	Cold rolling, strip finishing

Process Optimization and Quality Control

The short-process approach requires careful optimization of welding parameters to ensure that the reduced number of process steps does not compromise the quality of the repair. The interpass temperature must be maintained within a narrow window — high enough to prevent cracking but low enough to avoid excessive grain growth in the cladding layer. The literature recommends an interpass temperature of 150–250°C for most rolling mill roll repairs, with the exact value depending on the base material and the specific cladding alloy used.

Post-weld stress relief is a critical step that cannot be omitted even in a short-process approach. Residual stresses from welding can lead to delayed cracking, distortion, and premature failure of the repaired roll. A stress relief treatment at 550–650°C for 1–2 hours is typically sufficient to reduce residual stresses to acceptable levels without affecting the hardness of the cladding layer.

Defect Prevention Strategy

Defect	Prevention Measure
Thermal cracking	Adequate preheat, controlled interpass temperature
Spalling	Proper cladding material selection, stress relief
Poor bond strength	Thorough surface preparation, adequate bonding pass
Hardness variation	Uniform heat input, consistent travel speed
Distortion	Symmetric cladding pattern, low heat input per pass

Study Insights and Implications

The short-process cladding repair approach for rolling mills represents a practical engineering solution to the challenge of minimizing downtime while maintaining repair quality. The key insight from this literature is that process efficiency and quality are not mutually exclusive — by carefully optimizing each step of the repair process, it is possible to achieve both. Engineers should note that the short-process approach is particularly well-suited for rolling mill rolls because the geometry is relatively simple (cylindrical), the repair areas are well-defined, and the service conditions are predictable. For more complex geometries or unpredictable service conditions, a more conservative and thorough repair approach may be warranted. The literature also highlights the importance of having a well-defined inspection and acceptance criteria, as the reduced number of process steps means that any defect introduced early in the process may not be caught until after the repair is complete.