Analysis of microscopy techniques to measure segregation in continuous-cast steel slabs

Abstract

The accurate characterisation of centreline segregation requires precise measurements of composition variations over large length scales (10 ${}^{-1}$ $m$ ) across the centreline of the cast product, while having high resolution, sufficient to quantify the significant composition variations between dendrites due to microsegregation at very small length scales (10 ${}^{-5}m$ ). This study investigates the potential of a novel microscopy technique, named Synchrotron Micro X-ray Flurorescence (SMXRF), to generate large-scale high-resolution segregation maps from a steel sample taken from a thin slab caster. Two methods, Point Analysis and Regression Analysis, are proposed for SMXRF data calibration. By comparing with the traditional Laser-Induced Breakdown Spectroscopy (LIBS), and Electron Probe Micro Analyser (EPMA) techniques, we show that SMXRF is successful in quantitative characterisation of centreline segregation. Over large areas (e.g. 12 $\times$ 16 ${\mathrm{mm}}^2$ ) and at high resolution (10-50 $\mu m$ pixel size) various techniques yield comparable outcomes in terms of composition maps and solute profiles. The findings also highlight the importance of both high spatial resolution and large field of view to have a quantitative, accurate, and efficient measurement tool to investigate segregation phenomena.

Keywords: EPMA; LIBS; SMXRF; centreline segregation; continuous casting.