How to avoid composition segregation between the working layer and core of the mill roll?
Controlling the microstructural uniformity in centrifugal casting of mill roll is a core challenge for enhancing mill roll performance. Under centrifugal force, high-density elements (e.g., W, Mo) in alloys like high-speed steel tend to accumulate in the outer working layer, while low-density elements (e.g., V, C) migrate toward the core, causing composition segregation. This segregation not only leads to inconsistent properties in the working layer but also increases the risk of thermal fatigue cracks and other failures of mill roll.
To suppress segregation, multi-dimensional process optimization is required:
Alloy composition design: Adding niobium (Nb) to form composite carbides with densities close to the molten steel (e.g., W-V-Mo-Nb-based carbides) ,which can significantly reduce vanadium (V) segregation,but it necessitate synergistic regulation with other elements.
Process parameter optimization: Reducing the mold rotation speed (e.g., controlling below 950 r/min) weakens element migration driven by centrifugal force. Meanwhile, using chill coatings or water-cooling systems to increase solidification speed shortens the element diffusion time window. Studies show that the chill layer of mill roll exhibits significantly reduced segregation due to rapid solidification.
Pouring system improvement: Mill rolls use a specialized bottom-pouring ladle to create pre-stirred vortices and utilize siphon effects can re-homogenize light and heavy elements during pouring. For example, in copper-aluminum alloy casting, optimizing ladle dimensions (e.g., Dā=1.3Dā) and nozzle diameter (d=0.07Dā) effectively suppresses specific gravity segregation.