PUSHING THE DETECTION LIMIT OF LIGHT ELEMENTS IN STEEL USING EPMA SOFT X-RAY EMISSION SPECTROMETER

摘要

New steel grades are developed with increasingly complex microstructures which call for improved microanalytical techniques with enhanced sensitivity and spatial resolution. Electron probe microanalysers (EPMA) have been used extensively in steel research to characterise the distribution of alloying elements at the microscale [1-4]. However, spatially resolved detection and quantification of light alloying elements in steel remain a challenge. With recent progress of X-ray sensitive spectrometers, collection of low energy X-rays, so called "soft" X-rays, is now possible with energy resolution of 0.3 eV using the soft X-ray emission spectrometer (SXES) [5]. Owing to the varied line spacing grating, soft X-rays in the range of 50 to 210 eV can be detected for light elements with concentrations below 0.01 mass%. In this work, we report on the characterisation of micro-features in steel for different case studies using the SXES detector installed on an EPMA featuring a field emission gun. Quantitative mapping is performed upon calibration of each element of interest using reference standards. Figures 1a and 1b show a typical mapping of N element in nitrided steel sample and the corresponding soft X-ray spectrum measured by SXES, respectively. Figure la shows the presence of elongated N-rich precipitates in the Fe matrix. The local concentration of N atoms is 0.054 mass% within the squared area and is in good agreement with the average bulk value of 0.08 mass%. The presented methodology is suitable for applications in characterisation of steel materials and processes and defectology.