Research Progress of Cold Rolling Support Roll Cladding Technology

Literature Overview

The study note titled "Research Progress of Cold Rolling Support Roll Cladding Technology" provides a comprehensive review of the cladding technologies used to extend the service life of cold rolling support rolls. Support rolls are the critical components of cold rolling mills that provide the necessary backing force to the work rolls during the rolling process. They are subjected to extremely high contact stresses, severe abrasive wear, and thermal cycling, which can lead to surface degradation and roll failure. The cladding of support rolls is a cost-effective method to extend their service life and reduce the frequency of roll replacement. This literature systematically covers the current state of support roll cladding technology, including the materials used, the welding processes, the quality control methods, and the challenges encountered in industrial practice.

Core Technical Points on Support Roll Cladding Materials

The literature reviews several families of cladding materials used for cold rolling support rolls. The first family is the high-chromium cast iron type, which includes materials such as Cr15, Cr20, and Cr26, which offer excellent abrasion resistance but limited toughness. The second family is the martensitic stainless steel type, which includes materials such as 410, 420, and 440C, which offer a good balance of hardness and toughness. The third family is the austenitic stainless steel type, which includes materials such as 310 and 316, which offer excellent corrosion resistance but lower hardness. The fourth family is the nickel-based superalloy type, which includes materials such as Inconel 625 and Hastelloy C276, which offer excellent resistance to thermal fatigue and corrosion but are expensive.

The literature emphasizes that the selection of cladding material must be driven by the specific operating conditions of the support roll. For rolls used in the roughing stands, where the contact stress is highest, high-chromium cast iron or martensitic stainless steel is preferred. For rolls used in the finishing stands, where the surface quality of the strip is critical, austenitic stainless steel or nickel-based superalloy is preferred.

Weld Overlay Process Analysis

The literature reviews several welding processes applicable to support roll cladding, including submerged arc welding (SAW), gas metal arc welding (GMAW), plasma transferred arc welding (PTA), and laser cladding. Each process presents distinct advantages and limitations in terms of dilution control, deposition efficiency, residual stress, and surface finish.

Submerged arc welding is the most widely used process for support roll cladding because of its high deposition rate and low dilution rate. However, it is limited to cylindrical surfaces and produces a rough surface that requires subsequent machining. Gas metal arc welding offers better flexibility for complex geometries and moderate dilution control, but the deposition rate is significantly lower. PTA powder cladding provides excellent compositional control and low dilution, making it ideal for high-performance alloys, though it requires specialized equipment. Laser cladding offers the lowest dilution and highest surface quality but is limited by the size of the treated area and the cost of equipment.

The process parameters discussed in the literature include heat input control, preheating temperature, interpass temperature, and post-weld heat treatment. For support roll cladding, a preheating temperature of 150–250°C is typically required to prevent cracking in the dilution zone. The interpass temperature must be maintained below 200°C to avoid over-tempering of the base material. Post-weld stress relief at 550–650°C for 2–4 hours is recommended to reduce residual stresses without significantly reducing the hardness of the cladding layer.

Common Defects and Countermeasures

The literature identifies several common defects encountered in support roll cladding, including surface cracks, undercuts, porosity, and spalling of the cladding layer. Surface cracks are primarily caused by excessive thermal gradients, high carbon equivalent of the base material, and insufficient preheating. Countermeasures include increasing the preheat temperature, reducing the heat input per pass, and using a multi-layer welding strategy with a compatible transition layer. Undercuts occur when the welding current is too high or the travel speed is too fast, and they can be mitigated by optimizing the welding parameters and using a proper backing material. Porosity is often caused by moisture in the flux or contamination of the welding wire, and it can be prevented through proper flux storage and shielding gas purity control. Spalling of the cladding layer is the most critical defect, as it leads to catastrophic roll failure. It is primarily caused by excessive residual stress at the cladding-substrate interface and poor metallurgical bonding. The literature recommends using a graded layer structure, where a low-carbon transition layer is deposited first, followed by the hardfacing alloy, to reduce the thermal mismatch between the two materials.

Integration with Engineering Practice

In engineering practice, the cladding of cold rolling support rolls typically follows a standardized procedure that begins with surface preparation of the roll. The surface must be cleaned of oil, rust, and scale, and the area to be clad must be machined to provide a sound bonding surface. The roll is then preheated uniformly using induction heating or gas heating. The cladding is applied in multiple passes, with the first pass serving as a transition layer and subsequent passes building up the required thickness. After cladding, the surface is machined to the final geometry, and the roll undergoes a final stress relief treatment.

The literature emphasizes the importance of quality control throughout the process. Visual inspection is performed after each pass to detect undercuts and surface cracks. Magnetic particle testing (MT) is used to detect subsurface cracks in the cladding layer and the heat-affected zone. Hardness testing is performed on the cross-section of the cladding layer to verify the hardness profile and ensure adequate dilution control. The bond strength between the cladding layer and the substrate can be evaluated through a tensile bond test or a shear test.

Study Insights and Reflections

The most significant insight gained from this literature is the concept of the graded cladding structure for support rolls. Traditional single-material cladding often fails because of the large mismatch between the thermal expansion coefficient of the hardfacing alloy and the base material. By introducing a transition layer with intermediate properties, the thermal stress at the interface is significantly reduced, and the service life of the roll is extended by a factor of 2 to 4. Another important insight is the recognition that the welding process must be selected based on the geometry of the roll surface. For cylindrical surfaces, SAW is the most economical choice, while for complex geometries, GMAW or laser cladding is more appropriate. The literature also highlights the importance of post-weld heat treatment in reducing residual stresses, which is often overlooked in practice but is critical for preventing delayed cracking.

Reference Value and Outlook

This literature provides a solid foundation for engineers working on cold rolling support roll maintenance and refurbishment. The systematic approach to material selection, process parameter optimization, and defect prevention can be directly applied to industrial settings. The future direction of this field lies in the development of functionally graded materials and the use of advanced welding technologies such as cold metal transfer (CMT) and wire arc additive manufacturing (WAAM) for roll cladding. These technologies offer better control over the microstructure and residual stress of the cladding layer, and they have the potential to further extend the service life of cold rolling support rolls. The literature also points toward the use of computational modeling to predict the residual stress distribution and crack initiation sites in clad rolls, which would enable more rational design of the cladding structure. Overall, this literature is a valuable resource for any engineer involved in roll maintenance and surface engineering, and its principles can be extended to other tribologically demanding applications.