Speaker
Description
The control of recrystallization in ferritic stainless steels is critical for tailoring grain size and optimizing toughness, specially for high thickness grades. While the role of niobium (Nb) in delaying recrystallization is well established in austenitic systems, primarily for carbon steels which are usually hot rolled in austenite, its effect in ferritic stainless steels, which can be rolled in high temperature ferrite, is less discussed. In this work, we investigated the influence of Nb additions on the microstructural evolution of two Nb-alloyed high-chromium ferritic stainless steels, rolled in a laboratory-scale mill at temperatures between 800 °C and 1000 °C. Electron Backscatter Diffraction (EBSD) was used to quantify recrystallization, texture development and other microstructure characteristics. Our results confirms the strong effect of the Nb in solid solution (solute drag) on delaying recrystallization for the high Nb-grade. We believe that the strong segregation of Nb atoms to dislocations at elevated temperatures creates a substantial drag force, inhibiting boundary migration, ultimately affecting recrystallization. The project team managed to use these effects to improve the quality of such hot bands, as when subjected to subsequent heat treatment, these deformed microstructures produced finer grain sizes than fully recrystallized hot bands.
These findings underscore the critical role of solute drag in ferritic systems and provide insights for designing thermomechanical processing routes to achieve superior toughness in high thicknesses Nb-bearing ferritic stainless steels