W-Concentration 3D Mapping in SKH51 Steel by Dual-Energy K-Absorption Edge Subtraction Imaging

Abstract

Three-dimensional W-concentration mapping is attempted in a high speed tool steel, SKH51 by applying K-absorption edge subtraction imaging utilizing high energy X-ray in synchrotron radiation facility. Effect of a sample-to-detector distance on spatial resolution had already been reported in high-energy X-ray microtomography. Therefore, effect of the sample-to-detector distance on W-concentration obtained by the Kabsorption edge subtraction imaging has been assessed in this study. A fine CT image was obtained in 65 mm sample-to-detector distance with the influence of both scattering and diffraction on spatial resolution. Although image quality depended on sample-to-detector distance, the distance did not affect Wconcentration measured by the absorption edge subtraction imaging so much, because the effect is limited on object interface. The average W-concentration in whole specimen was consistent with the chemical composition in the SKH51 steel. The maximum W-concentration also agreed with the SEM-EDS result. It was not easy to assess W-concentration on a carbide particle by means of segmentation based on a linear absorption coefficient. The average W-concentration at an aggregated particle, which looks a large coarse particle in CT image, corresponded to the average W-concentration that was estimated based on SEM-EDS. Therefore, it was concluded that W-concentration obtained by K-absorption edge subtraction imaging was accurate. Three-dimensional W-concentration mapping was available in steels by dual-energy K-absorption edge subtraction imaging utilizing high energy X-ray.